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1. Bent Singlet Cyclobutylcarbene: Computed Geometry, Properties, and Product Selectivity of a NonclassicalCarbene

By Rosenberg, Murray G.; Brinker, Udo H.From Journal of Organic Chemistry (2019), 84(18), 11873-11884. Language: English, Database: CAPLUS,DOI:10.1021/acs.joc.9b01732

Ab initio computations of cyclobutylcarbene (c-C4H7CH) wereperformed using the UMP4(fc)/6-311++G(2df,2p)//UMP2(full)/6-311++G(d,p) theor. model. The carbene's most striking featureis its :CH-group. It is markedly bent toward the elongated C1'-C2' bond in the singlet ground-state but not in the triplet state,which is at least 1.1 kcal/mol higher in energy. Nonclassical3C2E bonding among the C1, C1', and C2' atoms is prominentin the HOMO-1. The electron-donating ability of thenonbonding HOMO is thereby enhanced. The intensifiednucleophilicity of the singlet carbene is manifested inquantifiable ways. For example, its hard and soft acid andbase (HSAB) hardness, HSAB abs. electronegativity, and gas-phase proton affinity rival those of ylide-stabilized N-heterocyclic carbenes. It is computed to act as a nucleophiletoward alkenes with higher HSAB hardness values. Transitionstates from singlet cyclobutylcarbene to bicyclo[2.1.0]pentane,cyclopentene, and methylenecyclobutane were computed andconfirmed by intrinsic reaction coordinate calcns. Activationenergies depend on the singlet's conformation with regard to c-C4H7 ring-puckering, :CH-group rotation, and :CH-groupbending. The singlet's bent :CH-group favorsbicyclo[2.1.0]pentane and cyclopentene formation.

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2. Competitive Nitrogen versus Carbon Tunneling

By Nunes, Claudio M.; Eckhardt, Andre K.; Reva, Igor; Fausto, Rui; Schreiner, Peter R.From Journal of the American Chemical Society (2019), 141(36), 14340-14348. Language: English, Database:CAPLUS, DOI:10.1021/jacs.9b06869

Quantum mech. tunneling (QMT) of heavy atoms like carbon ornitrogen has been considered very unlikely for the longest time,but recent evidence suggests that heavy-atom QMT does occurmore frequently than typically assumed. Here we demonstratethat carbon vs nitrogen heavy-atom QMT can even becompetitive leading to two different products originating fromthe same starting material. Amino-substituted benzazirine wasgenerated in solid argon (3-18 K) and found to decayspontaneously in the dark, with a half-life of 210 min, to p-aminophenylnitrene and amino-substituted ketenimine. Thereaction rate is independent of the cryogenic temp., incontradiction to the rules inferred from classical transition statetheory. Quantum chem. computations confirm the existence oftwo competitive carbon vs nitrogen QMT reaction pathways.This discovery emphasizes the quantum nature of atoms andmols., thereby enabling a much higher level of control and adeeper understanding of the factors that govern chem.reactivity.

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3. Chemical speciation of aqueous hydrogen fluoride at various temperatures from 298.15 K to 353.15 K

By El Guendouzi, Mohamed; Faridi, Jamal; Khamar, LhachmiFrom Fluid Phase Equilibria (2019), 499, 112244. Language: English, Database: CAPLUS,DOI:10.1016/j.fluid.2019.112244

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The chem. speciation of aq. hydrofluoric acid solns. was investigated at various temps. The exptl. results and calcns.were carried out to study a qual. and quant. speciation of the system HF-H2O. Literature review of thermodn. andspeciation studies of aq. hydrogen fluoride were reported and revealed some deficiencies at various temps. The dissocn.of HF in the aq. soln. is not complete, which exhibits a concn.-dependent stoichiometric coeff. and directly influences thethermodn. properties. Neglecting this concn. dependence leads to erroneous osmotic coeffs. for solns. of weakelectrolytes. The water activities of the HF-H2O system were measured within the molality range from 0.10 mol kg-1 to6.00 mol kg-1 at different temps. from 298.15 K to 353.15 K using the hygrometric method. From these measurements,on the basis of the fluorine 19F NMR and the chem. equil., the qual. and quant. speciation aq. hydrofluoric acid solns.were performed resp. The deployed approach was developed based on ion interaction model to describe the behavior ofHF aq. solns., considering a polyelectrolyte system HF - H - F - HF2 - H2F3 - H2O. The calcd. species HF(aq), H+, F-, HF2- and H2F3 -were detd. at various temps. From the complementary techniques and the developed model, the resultsreflect the present species and allow describing the behavior of hydrofluoric acid aq. solns.~0 Citings

4. Pathways for O2 Electroreduction over Substitutional FeN4, HOFeN4, and OFeN4 in Graphene Bulk Sites:Critical Evaluation of Overpotential Predictions Using LGER and CHE Models

By Anderson, Alfred B.; Holby, Edward F.From Journal of Physical Chemistry C (2019), 123(30), 18398-18409. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpcc.9b03703

We performed quantum chem. calcns. using the plane-wavebasis set d. functional theory with the PBE-GGA exchange-correlation functional for three sites present substitutionally ingraphite basal planes, elucidating their possible activity towardelectrochem. redn. of O2 to water. Using results of the linearGibbs energy relationship (LGER) and computational hydrogenelectrode (CHE) models, we calcd. the activity descriptors. TheCHE-based predictions of three of the std. reversible potentialsduring the four-electron oxygen redn. reaction to water in bulksoln. are accurate within around 0.1 V when bond zero-pointvibrational energies are subtracted from the bond calcd.strengths. However, the error for OOH(aq) redn. to O(aq) +H2O(aq) is large (-0.96 V) and is caused by the large calcd. O-OH bond strength. With zero-point energies not subtractedfrom the calcd. bond strengths, errors in potentials for formingH-O bonds in bulk soln. increase, but the error in the reversiblepotential for the overall four-electron redn. is small. Usingsubstitutional FeN4 sites in graphene, we calcd. reversiblepotentials for the steps in six redn. mechanisms, includingforming OH bonded to a neighboring C site. We show how theLGER and CHE models are related and critically evaluate thequality of the predictions based on errors in the bond strengthcalcns. We conclude that the HO-FeN4 site has the lowestoverpotential and is stable at relevant potentials.

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5. Quantum proton tunneling in multi-electron/-proton transfer electrode processes

By Sakaushi, KenFrom Faraday Discussions (2019), Ahead of Print. Language: English, Database: CAPLUS, DOI:10.1039/c9fd00032a

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Quantum proton tunneling (QPT) in two representative multi-electron/-proton transfer electrode processes, i.e. hydrogenevolution reaction (HER) and oxygen redn. reaction (ORR), was investigated using polycryst. platinum (pcPt) and gold(pcAu) electrodes at 298 K (K). To observe quantum effects in the electrode processes, the hydrogen/deuterium kineticisotope effect const. ratio (≈KH/D) was measured in various conditions. For the HER in both acidic and alk. conditions,results show that the pcPt exhibits a negligible or weak QPT evident by the small value of KH/D (1 < KH/D < 3), whichindicates that the semiclassical transition state theory (SC-TST) scheme dominates the rate-detg. step (RDS). For pcAuin an alk. condition, the KH/D was a small value of ca. 1 at a low η region around 0.2 V. However, at a high η region >0.6V, a high KH/D (>13) was obtained. These results suggest a transition of the electrode process from SC-TST to a fullQTP in the RDS on increasing the overpotential. For ORR with pcPt, KH/D higher than the theor. max. in SC-TST wasobsd. in the alk. condition at a low overpotential region. A primitive but robust theor. anal. suggests that the QPTgoverns the rate-detg. step of ORR in this condition. However, this full QPT path transits to the classical in a higheroverpotential region. Therefore, contrary to the HER on pcAu in alk., the electrode process shows a transition from a fullQPT to SC-TST on increasing the overpotential. No QPT in ORR on a pcPt electrode was obsd. in an acidic condition.This report describes that the QPT in surface electrochem. systems is strongly affected by the choice of system.Although several systems show a clear manifestation of QPT in the electrode processes and also primitive interpretationscan be made of these observations, deriving a fine mol.-level picture of the results including several complicated effectsremains challenging. However, the observations suggest that selection of a full QPT path might be affected strongly bydifferent microscopic proton transfer mechanisms, i.e. proton transfer from hydronium ion or water mols.~0 Citings

6. Enhanced reactivity of flourine with para-hydrogen in cold interstellar clouds by resonance-induced quantumtunnelling

By Yang, Tiangang; Huang, Long; Xiao, Chunlei; Chen, Jun; Wang, Tao; Dai, Dongxu; Lique, Francois; Alexander,Millard H.; Sun, Zhigang; Zhang, Dong H.; et alFrom Nature Chemistry (2019), 11(8), 744-749. Language: English, Database: CAPLUS, DOI:10.1038/s41557-019-0280-3

Chem. reactions are important in the evolution of low-temp. interstellar clouds, where the quantum tunnelling effectbecomes significant. The F + para-H2 → HF + H reaction, which has a significant barrier of 1.8 kcal mol-1, is animportant source of HF in interstellar clouds; however, the dynamics of this quantum-tunnelling-induced reactivity at lowtemp. is unknown. Here, we show that this quantum tunnelling is caused by a post-barrier resonance state. Quantum-state-resolved crossed-beam scattering measurements reveal that this resonance state has a collision energy of ∼5 meVand a lifetime of ∼80 fs, which are in excellent agreement with a recent anion photoelectron spectroscopic study.Accurate quantum reactive scattering calcns. on the new iCSZ-LWAL potential energy surfaces provides a detailedexplanation of the exptl. results. The reaction rate for this system was also theor. detd. accurately at temps. as low as 1K.~0 Citings

7. A new class of reaction path based potential energy surfaces enabling accurate black box chemical rateconstant calculations

By Steffen, JulienFrom Journal of Chemical Physics (2019), 150(15), 154105/1-154105/22. Language: English, Database: CAPLUS,DOI:10.1063/1.5092589

A new method for constructing a full-dimensional potential energy surface representation in black-box fashion for anarbitrary reaction is presented. With limited knowledge of the system and with a limited no. of ref.-level data points, it ispossible to calc. reaction rate consts. with high quality. Building on our recently published application of Grimme'squantum-mech. derived force field (QMDFF) and its empirical valence bond extension EVB-QMDFF to rate const.calcns., an improved EVB coupling method with local corrections was developed in order to avoid spurious problems forcertain systems and hence to achieve an even wider range of applicability. A given reaction path (RP) is modeled as aparametric curve via cubic spline interpolation; regions offside this path are then extrapolated with quadratic Taylorseries, and regions around the transition state are cor. by introduction of direct ref. interpolation; the method is namedtransition region cor. RP-EVB-QMDFF (TREQ). To verify the quality of TREQ, six reactions were chosen for which full-dimensional anal. potential surfaces are available in the literature. Chem. reaction rates were calcd. with ring polymermol. dynamics on the ref. surfaces as well as on the TREQ surfaces resulting in excellent agreement. (c) 2019 AmericanInstitute of Physics.~0 Citings

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8. DNA-binding affinity, cytotoxicity, apoptosis, cell cycle inhibition and molecular docking studies of a newstilbene derivative

By Mehdipour, Maryam; Dehghan, Gholamreza; Yekta, Reza; Hanifeh Ahagh, Mina; Mahdavi, Majid; Ghasemi, Zarrin;Fathi, ZahraFrom Nucleosides, Nucleotides & Nucleic Acids (2019), 38(2), 101-118. Language: English, Database: CAPLUS,DOI:10.1080/15257770.2018.1498517

Stilbene derivs. have been found to possess promising anticancer activities against human cancer cell lines in vitro. Inthe present study, the authors have investigated cytotoxic, apoptosis induction and DNA binding activity of new stilbenederiv., (E)-1-(4-Chlorophenyl)-4,5-diphenyl-2-[4-(4-methoxystyryl)phenyl]-1H-imidazol (STIM) on K562 chronic myeloidleukemia cell line. Via MTT assay STIM demonstrated cytotoxic activity against K562 cell line with IC50 value of 150 µM.Apoptosis, as the mechanism of cell death, was evaluated by morphol. study and flow cytometric anal. In vitro DNAbinding property of STIM has been studied by vital spectroscopic techniques, which indicated that STIM interact withctDNA through groove binding mode and binding const. (Kb) was estd. to be 6.9 × 104 M-1. Docking studies revealedthat hydrophobic is the most important interaction in STIM-DNA complex, and that the ligand (STIM) interacts with DNAvia groove binding mode and the binding energy was calcd. as -13.37 kcal/mol. Taken together, the present studysuggests that STIM exhibits anticancer effect on K562 cell line through the induction of apoptosis as well as cell cyclearrest at Sub-G1 phase and also can bind to double helix DNA in vitro.~0 Citings

9. Macroscopic quantum escape of Bose-Einstein condensates: Analysis of experimentally realizable quasi-one-dimensional traps

By Alcala, Diego A.; Urban, Gregor; Weidemuller, Matthias; Carr, Lincoln D.From Physical Review A (2018), 98(2), 023619. Language: English, Database: CAPLUS,DOI:10.1103/physreva.98.023619

The variational JWKB method is used to det. exptl. accessible macroscopic quantum tunneling regimes of quasiboundBose-Einstein condensates in two quasi-one-dimensional trap configurations. The potentials can be created by magneticand optical traps: a sym. trap from two offset Gaussian barriers and a tilt trap from a linear gradient and Gaussian barrier.Scaling laws in barrier parameters, ranging from inverse polynomial to square root times exponential, are calcd. andused to elucidate different dynamical regimes, such as when classical oscillations dominate tunneling rates in the sym.trap. The sym. trap is found to be versatile, with tunneling times at and below 1 s, able to hold 103-104 atoms, andrealizable for atoms ranging from rubidium to lithium, with unadjusted scattering lengths. The tilt trap producessubsecond tunneling times, is able to hold a few hundred atoms of lighter elements such as lithium, and requires the useof Feshbach resonance to reduce scattering lengths. To explore a large parameter space, an extended Gaussianvariational ansatz is used, which can approx. large traps with Thomas-Fermi profiles. Nonlinear interactions in theGross-Pitaevskii equation are shown to produce addnl. effective mean-field barriers, affecting scaling laws.~0 Citings

10. Theoretical insight into the photophysical properties of long-lifetime Ir(III) and Rh(III) complexes for two-photon photodynamic therapy

By Yin, Xue; Lai, Xiao-Yong; Wang, Xin; Liu, Ying-TaoFrom Physical Chemistry Chemical Physics (2019), 21(16), 8394-8401. Language: English, Database: CAPLUS,DOI:10.1039/c9cp00512a

Two-photon photodynamic therapy (TP-PDT) plays crucial roles in curing tumors because it involves deep penetration ofdrugs into the tissue and has minimal damage to the surrounding cells. Our theor. study was aimed at providing freshinsights into photosensitizers, such as [Ir(Nˆ C)2(Nˆ N)]+ (Nˆ C = 2-phenylpyridine, Nˆ N = bis-benzimidazole) and [Rh(Nˆ

C)2(Nˆ N)]+, to treat cancer via the TP-PDT route. To better understand the properties of the complexes [Ir(Nˆ C)2(Nˆ N)]+and [Rh(Nˆ C)2(Nˆ N)]+, the one-photon and two-photon absorption electronic spectra, energy gap (∆ES-T), strength oftwo-photon absorption cross-section (δ), spin-orbit matrix element (❬S1|HˆSO|Tj❭), and phosphorescence lifetimes (τ) werecalcd. by DFT and TD-DFT. The calcn. results suggested that both complexes met the criteria (i.e. an efficient ISCprocess, enough energy to produce 1O2 and phototherapeutic window of the absorption wavelength) of photosensitizers;importantly, the designed complex [Rh(Nˆ C)2(Nˆ N)]+ had better performance than [Ir(Nˆ C)2(Nˆ N)]+, esp. in the long-lived triplet excited state. It is expected that our research can make quite a few contributions to the development ofphotosensitizers and establish some guidelines for expts. based on TP-PDT.~0 Citings

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11. Tunneling by 16 Carbons: Planar Bond Shifting in [16]Annulene

By Michel, Cameron S.; Lampkin, Philip P.; Shezaf, Jonathan Z.; Moll, Joseph F.; Castro, Claire; Karney, William L.From Journal of the American Chemical Society (2019), 141(13), 5286-5293. Language: English, Database: CAPLUS,DOI:10.1021/jacs.8b13131

Midsized annulenes are known to undergo rapid π-bondshifting. Given that heavy-atom tunneling plays a role in planarbond shifting of cyclobutadiene, we computationally exploredthe contribution of heavy-atom tunneling to planar π-bondshifting in the major (CTCTCTCT, 5a) and minor (CTCTTCTT,6a) known isomers of [16]annulene. UM06-2X/cc-pVDZcalcns. yield bond-shifting barriers of ca. 10 kcal/mol. Theresults also reveal extremely narrow barrier widths, suggestinga high probability of tunneling for these bond-shifting reactions.Rate consts. were calcd. using canonical variational transitionstate theory (CVT) as well as with small curvature tunneling(SCT) contributions, via direct dynamics. For the major isomer5a, the computed SCT rate const. for bond shifting at 80 K is0.16 s-1, corresponding to a half-life of 4.3 s, and indicating thatbond shifting is rapid at cryogenic temps. despite a 10 kcal/molbarrier. This contrasts with the CVT rate const. of 8.0 × 10-15 s-1 at 80 K. The minor isomer 6a is predicted to undergo rapidbond shifting via tunneling even at 10 K. For both isomers,bond shifting is predicted to be much faster than competingconformation change despite lower barriers for the latterprocess. The preference for bond shifting represents cases oftunneling control in which the preferred reaction is dominatedby heavy-atom motions. At all temps. below -50 °C, tunnelingis predicted to dominate the bond shifting process for both 5aand 6a. Thus, [16]annulene is predicted to be an example oftunneling by 16 carbons. Bond shifting in both isomers ispredicted to be rapid at temps. accessible by soln.-phase NMRspectroscopy, and an expt. is proposed to verify thesepredictions.

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12. Real-Space Observation of Quantum Tunneling by a Carbon Atom: Flipping Reaction of Formaldehyde onCu(110)

By Lin, Chenfang; Durant, Emile; Persson, Mats; Rossi, Mariana; Kumagai, TakashiFrom Journal of Physical Chemistry Letters (2019), 10(3), 645-649. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpclett.8b03806

We present a direct observation of carbon-atom tunneling inthe flipping reaction of formaldehyde between its two mirror-reflected states on a Cu(110) surface using low-temp. scanningtunneling microscopy (STM). The flipping reaction wasmonitored in real time, and the reaction rate was found to betemp. independent below 10 K. This indicates that this reactionis governed by quantum mech. tunneling, albeit involving asubstantial motion of the carbon atom (∼1 Å). In addn.,deuteration of the formaldehyde mol. resulted in a significantkinetic isotope effect (RCH2O/RCD2O ≈ 10). The adsorptionstructure, reaction pathway, and tunneling probability wereexamd. by d. functional theory calcns., which corroborate theexptl. observations.

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13. Studies on lysozyme modifications induced by substituted p-benzoquinones

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By Kim, Jisook; Thomas, Charles A.; Ewald, Jacob M.; Kurien, Neethu M.; Booker, Mary E.; Greve, Hendrik J.; Albu,Titus V.From Bioorganic Chemistry (2019), 85, 386-398. Language: English, Database: CAPLUS,DOI:10.1016/j.bioorg.2019.01.018

Protein misfolding can facilitate a protein damaging process and makes it susceptible to a series of events such asunfolding, adduct formation, oligomerization, or aggregation. Loss of a protein's native structure may result in its biol.malfunction and/or cellular toxicity that could cause assocd. diseases. Several factors were identified for causingstructural changes of a protein, however quinone-induced protein modifications received very little attention whether foramyloidal or non-amyloidal proteins. In this paper, we report our investigation on lysozyme modifications upon treatmentwith selected benzoquinones (BQs), utilizing fluorescence spectroscopy including anisotropy detn., UV-Vis spectroscopy,and SDS-PAGE. Lysozyme was reacted with substituted BQs in order to examine substituent effects on proteinmodifications. In addn., we evaluated lysozyme modifications induced by 1,4-benzoquinone in concn.-, pH-, temp.-, andtime-dependent studies. Our study shows that all BQs can readily modify lysozyme in a complex manner through adductformation, oligomerization, polymeric aggregation, and/or fibrillization. Electrochem. properties of selected BQs weremonitored using cyclic voltammetry in phosphate buffered aq. soln., and it was found that quinone redn. potentialscorrelate well with their reactivity trend toward lysozyme.~0 Citings

14. On the Theory of Electrolytic Dissociation, the Greenhouse Effect, and Activation Energy in(Electro)Catalysis: A Tribute to Svante Augustus Arrhenius

By Masa, Justus; Barwe, Stefan; Andronescu, Corina; Schuhmann, WolfgangFrom Chemistry - A European Journal (2019), 25(1), 158-166. Language: English, Database: CAPLUS,DOI:10.1002/chem.201805264

A biog. for Svante Augustus Arrhenius, born Feb. 19, 1859 in Balingsta forsamling, Sweden, and died Oct. 2, 1927 inStockholm, Sweden, is presented. Arrheius received the Nobel Prize for Chem. in 1903 "in recognition of theextraordinary services he rendered to the advancement of chem. by his electrolytic theory of dissocn.". Arrhenius was aphysicist, and he received his PhD from the University of Uppsala, where he later became a professor for phys. chem.,the first in the country for this subject. He was offered several positions as professor abroad, but decided to remain inSweden and to build a Nobel Institute for phys. chem. using the Nobel funds. He remained director of the Institute untilhis death. There are powerful lessons to take from Svante August Arrhenius' journey leading to a Nobel laureate asthere are from his tremendous contributions to chem. and science in general, including climate science, immunochem.and cosmol. The theory of electrolytic dissocn. for which Arrhenius received the 1903 Nobel Prize in Chem. has had aprofound impact on our understanding of the chem. of solns., chem. reactivity, mechanisms underlying chem.transformations as well as physiol. processes. As a tribute to Arrhenius, we present a brief historical perspective andpresent status of the theory of electrolytic dissocn., its relevance and role to the development of electrochem., as well assome perspectives on the possible role of the theory to future advancements in electroanal., electrocatalysis andelectrochem. energy storage. The review briefly highlights Arrhenius' contribution to climate science owing to his studieson the potential effects of increased anthropogenic CO2 emissions on the global climate. These studies were far aheadof their time and revealed a daunting global dilemma, global warming, that we are faced with today. Efforts to abate orreverse CO2 accumulation constitute one of the most pressing scientific problems of our time, "man's urgent strive tosave self from the adverse effects of his self-orchestrated change on the climate". Finally, we review the application ofthe Arrhenius equation that correlates reaction rate consts. (k) and temp. (T); k=Ae(-Ea/RT), in detg. reaction barriers incatalysis with a particular focus on recent modifications of the equation to account for reactions exhibiting non-linearArrhenius behavior with concave curvature due to prevalence of quantum mech. tunneling, as well as infrequentconvexity of Arrhenius plots due to decrease of the microcanonical rate coeff. with energy as obsd. for some enzymecatalyzed reactions.~0 Citings

15. Recent advances in energy chemistry of precious-metal-free catalysts for oxygen electrocatalysis

By Wang, Bin; Cui, Xiaoyang; Huang, Jia-Qi; Cao, Rui; Zhang, QiangFrom Chinese Chemical Letters (2018), 29(12), 1757-1767. Language: English, Database: CAPLUS,DOI:10.1016/j.cclet.2018.11.021

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A review. The oxygen evolution reaction (OER) and oxygen redn. reaction (ORR) are coupled with various sustainableenergy systems and are significant for the future energy scenario. Both of them suffer from sluggish kinetics, which callsfor cost-effective and high-performance electrocatalysts to promote. The oxygen electrolysis of OER and ORR isheterogeneous reaction, which involves reactant and electron transfer, and a serial of complicate surface reactions. Bothintrinsic catalyst activity and extrinsic physicochem. characters play a vital role in overall electrocatalytic reactivity.Herein, recent advances in rational design and effective construction of precious-metal-free materials are reviewed forOER and ORR, resp., in the respects of electronic structure regulation, nanostructure tailor, and freestanding electrodefabrication. The reaction mechanism of OER and ORR are also updated. This review provides emerging energy chem.concepts and materials chem. strategies of electrocatalysts for OER and ORR, which is also enlightening for otherenergy conversion devices with targeted optimization.~4 Citings

16. Dynamic electrochemical impedance study of methanol oxidation at Pt at elevated temperatures

By Holm, Thomas; Dahlstroem, Per Kristian; Sunde, Svein; Seland, Frode; Harrington, David A.From Electrochimica Acta (2019), 295, 139-147. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2018.10.071

The methanol oxidn. reaction (MOR) is studied at temps. up to 140 °C by a combination of cyclic voltammetry,chronoamperometry, and dynamic electrochem. impedance spectroscopy (dEIS). A mechanistic anal. of the reaction isdone based on the Tafel relation, the calcd. activation energy, and the fitting of dEIS data. At the fuel cell relevantpotentials, 0-0.80 V vs RHE, the MOR mechanism is similar at all temps. The rate-detg. step is the adsorption of waterat low overpotentials (< 0.50 V vs RHE), a combination of the methanol adsorption reaction and the surface reactionbetween adsorbed CO and OH at intermediate potentials (0.50-0.65 V vs RHE), and the methanol adsorption reaction athigh potentials (> 0.65 V vs RHE). The shoulder on the oxidn. peak at 0.60-0.65 V vs RHE corresponds well with wherethe CO coverage approaches zero.~10 Citings

17. First-principles view on photoelectrochemistry: water-splitting as case study

By Hellman, Anders; Wang, BaochangFrom Inorganics (2017), 5(2), 37/1-37/27. Language: English, Database: CAPLUS, DOI:10.3390/inorganics5020037

Photoelectrochem. is truly an interdisciplinary field; a natural nexus between chem. and physics. In short,photoelectrochem. can be divided into three sub-processes, namely (i) the creation of electron-hole pairs by lightabsorption; (ii) sepn./transport on the charge carriers and finally (iii) the water splitting reaction. The challenge is tounderstand all three processes on a microscopic scale and, perhaps even more importantly, how to combine theprocesses in an optimal way. This review will highlight some first-principles insights to the above sub-processes, inparticular as they occur using metal oxides. Based on these insights, challenges and future directions of first-principlesmethods in the field of photoelectrochem. will be discussed.~5 Citings

18. DFT studies on quantum mechanical tunneling in tautomerization of three-membered rings

By Jana, Kalyanashis; Ganguly, BishwajitFrom Physical Chemistry Chemical Physics (2018), 20(44), 28049-28058. Language: English, Database: CAPLUS,DOI:10.1039/c8cp03963a

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We have examd. keto-enol and amino-imino tautomerization in a set of three-membered ring systems (1-5) in theabsence and presence of water mols. Aromaticity governs the keto-enol and amino-imino tautomerization processes in(1-5), which lead to the formation of enol and imine derivs. The possibility of quantum mech. tunneling (QMT) has notbeen reported in the tautomerization processes of three-membered ring systems. M062X/6-311+G(d,p) level of theoryQMT calcns. reveal that tunneling is not possible in the water unassisted processes because of very high free energyactivation barriers. The activation free energy barriers for the amino-imino tautomerization of 5, aziridine-2,3-diimine, andone water assisted, 5-W, are 58.1 kcal mol-1 and 14.8 kcal mol-1, resp. and the lowest among the 3-membered ringsexamd. The classical over the barrier rate const. (kCVT) obtained by QMT calcn. for 5-W → 5-W-P is 10.6 s-1 at 273 K.Inclusion of small curvature tunneling (SCT) enhances the classical over the barrier rate const. by 15.1 times at 273 K,i.e., kCVT+SCT is 160 s-1 and reveals nonclassical behavior for the tautomerization of 5-W. A higher kinetic isotope effectin the tautomerization process of 4-W and 5-W also indicates a pronounced contribution of tunneling toward thetautomerization process. The two-water assisted tautomerization of 3 has the highest activation free energy barrier in theseries indicating a nonclassical contribution to 3-2W→3-2W-P. These results suggest that the tautomerization processesof 1-5 are exptl. feasible by tunneling and aromaticity.~0 Citings

19. Macroscopic quantum escape of Bose-Einstein condensates: analysis of experimentally realizable quasi-one-dimensional traps

By Alcala, Diego A.; Urban, Gregor; Weidemueller, Matthias; Carr, Lincoln D.From arXiv.org, e-Print Archive, Condensed Matter (2018), 1-12. Language: English, Database: CAPLUS

The variational-JWKB method is used to det. exptl. accessible macroscopic quantum tunneling regimes of quasi-boundBose-Einstein condensates in two quasi one-dimensional trap configurations. The potentials can be created by magneticand optical traps; a sym. trap from two o set Gaussian barriers and a tilt trap from a linear gradient and Gaussian barrier.Scaling laws in barrier parameters, ranging from inverse polynomial to square root times exponential, are calcd. andused to elucidate different dynamical regimes, such as when classical oscillations dominate tunneling rates in the sym.trap. The sym. trap is found to be versatile, with tunneling times at and below one second, able to hold 103 to 104 atoms,and realizable for atoms ranging from rubidium to lithium, with unadjusted scattering lengths. The tilt trap produces sub-second tunneling times, is able to hold a few hundred atoms of lighter elements like lithium, and requiring the use ofFeshbach resonance to reduce scattering lengths. To explore a large parameter space, an extended Gaussianvariational ansatz is used, which can approx. large traps with Thomas-Fermi profiles. Nonlinear interactions in theGross-Pitaevskii equation are shown to produce addnl. effective mean-field barriers, a ecting scaling laws.~0 Citings

20. Tuning the Spin, Aromaticity, and Quantum Tunneling in Computationally Designed Fulvalenes

By Solel, Ephrath; Kozuch, SebastianFrom Journal of Organic Chemistry (2018), 83(18), 10826-10834. Language: English, Database: CAPLUS,DOI:10.1021/acs.joc.8b01541

Pentafulvalene is a sym. unsatd. hydrocarbon built from twofive-membered rings connected by an exocyclic double bond,where each ring is one electron short of being a 6π-electronarom. system. Here, we show computationally that byselectively introducing electron withdrawing and donatingsubstituents, we can design pentafulvalene derivs. that exhibittunable aromaticity properties. Pentafulvalene can be shapedinto a species with connected arom.-antiarom. rings, which canalso achieve π-bond shifting by carbon tunneling. We proposean NMR technique that can exptl. prove such tunnelingmechanism. In addn., we devised a doubly arom. fulvaleneinvolving both Huckel and Baird aromaticities. These resultscan open possibilities to create novel mols. in terms of spinstate, aromaticity, and reactivity by quantum tunneling.

~3 Citings

21. Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

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By Wentrup, CurtFrom Angewandte Chemie, International Edition (2018), 57(36), 11508-11521. Language: English, Database:CAPLUS, DOI:10.1002/anie.201804863

A review. Carbenes and nitrenes can exist in both singlet and triplet states, sometimes equally stable andinterconverting either thermally or photochem. Many carbene and nitrene reactions proceed via tunneling at low temps.Numerous singlet and triplet states have been characterized spectroscopically, and a detailed understanding of thechem. and phys. properties of carbenes and nitrenes is emerging. There has been significant progress in the directobservation of carbenes, nitrenes, and many other reactive intermediates in recent years through the application ofmatrix photolysis and flash vacuum pyrolysis linked with matrix isolation at cryogenic temps. Authors understanding ofsinglet and triplet states has improved through the interplay of spectroscopy and computations. Bistable carbenes andnitrenes as well as many examples of tunneling have been discovered and numerous rearrangements andfragmentations have been documented. The correlation of the zero-field splitting parameter D with calcd. spin densitieson nitrenes and carbenes is discussed. This Minireview gives an overview of some of these developments.~12 Citings

22. Electronic structure calculations on electrolyte-electrode interfaces: Successes and limitations

By Jinnouchi, Ryosuke; Kodama, Kensaku; Morimoto, YuFrom Current Opinion in Electrochemistry (2018), 8, 103-109. Language: English, Database: CAPLUS,DOI:10.1016/j.coelec.2018.03.024

D. functional theory calcns. on electrolyte-electrode interfaces are briefly reviewed in this article. The calcn. methods areroughly categorized into two types: calcns. on elec. neutral surfaces and electrified surfaces. The former methods havebeen successfully applied to reproduce obsd. trends in catalytic activities and to design new materials. The methods,however, cannot evaluate any electrochem. properties originated from surface electrifications. By this reason, severaltheor. methods on electrified interfaces have been proposed. The methods can provide properties originated fromcharge transfers, such as electrosorption valency values, symmetry factors and potential-dependent spectroscopies,within self-consistent manners. Many limitations, however, still exist, and further studies are necessary particularly oneffects of dynamical at. motions on free energies.~4 Citings

23. Reaction Mechanism for Oxygen Reduction on Platinum: Existence of a Fast Initial Chemical Step and aSoluble Species Different from H2O2

By Gomez-Marin, Ana; Feliu, Juan; Edson, TicianelliFrom ACS Catalysis (2018), 8(9), 7931-7943. Language: English, Database: CAPLUS, DOI:10.1021/acscatal.8b01291

The oxygen redn. reaction (ORR) on platinum in perchloric acidis studied under transient conditions at stationary andnonstationary electrodes. Only under these conditions, thepresence of a fast initial chem. step in the mechanism, givingrise to a sol., short-lived intermediate proposed to be the HO2*radical, is revealed by comparing exptl. and calcd. curves bynumerical simulations of simple reaction schemes. Theformation of this species and the existence of a zero-currentcycle involving it would be the main reasons for the lack ofredn. currents at potentials higher than the ORR reaction onset.Addnl., regardless of the exact subsequent steps after the initialchem. reaction, if HO2* is generated it would disproportionateto hydrogen peroxide, which implies that both species would bealways produced during the ORR on Pt. The presence of HO2*and H2O2 would profoundly affect the durability of Pt-basedcatalysts and should be taken into account in the design ofmaterials for fuel cell cathodes.

~2 Citings

24. Ring-polymer molecular dynamics study on rate coefficients of hydrogen abstraction of methane: A reduced-dimensional model

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By Meng, QingyongFrom Chemical Physics Letters (2018), 706, 383-387. Language: English, Database: CAPLUS,DOI:10.1016/j.cplett.2018.06.042

To enhance computational efficiency of ring-polymer mol. dynamics (RPMD), reduced-dimensional models are proposedfor X + YCZ3→ XY + CZ3. In these models, bond parameters of CZ3 are fixed keeping the C3v symmetry. These modelsare denoted by r-RPMD, t-RPMD, p-RPMD, i-RPMD, and irc-RPMD. Extensive RPMD calcns. in both full- and reduced-dimensional fashions are performed for H + CH4. The computational efficiency of the reduced-dimensional calcn. isfound to be enhanced by a factor of roughly 3.5, which is close to 4 (factor for 12D → 3D). Good agreements betweenirc-RPMD and previous results are found.~2 Citings

25. Hydrolysis reaction promotes changes in coordination mode of Ru(II)/acylthiourea organometalliccomplexes with cytotoxicity against human lung tumor cell lines

By Cunha, Beatriz N.; Colina-Vegas, Legna; Plutin, Ana M.; Silveira, Rafael G.; Honorato, Joao; Oliveira, Katia M.;Cominetti, Marcia R.; Ferreira, Antonio G.; Castellano, Eduardo E.; Batista, Alzir A.From Journal of Inorganic Biochemistry (2018), 186, 147-156. Language: English, Database: CAPLUS,DOI:10.1016/j.jinorgbio.2018.06.007

In this study, Ru(II)-arene complexes with acylthiourea ligands of the type [Ru(η6-p-cymene)(PPh3)(T)Cl]PF6 (1-5) and[Ru(η6-p-cymene)(PPh3)(T)]PF6 (1a, 4a), where PPh3 = triphenylphosphine and T = N-acyl-N'(monosubstituted)thiourea,were synthesized and characterized, and their cytotoxic properties were also evaluated. Compds. 1a and 4a wereobtained from the hydrolysis reaction of 1 and 4. All complexes showed unusual coordination modes for acylthiourealigands, which are coordinated in a monodentate fashion (S) in 1-5, while they found to be bidentate (S,N), in 1a and 4a.To the best of the authors' knowledge, 1a and 4a are the first crystallog. reported ruthenium compds. with acylthioureacoordinated via S and N(amide) atoms. The cytotoxicity of the compds. was evaluated in human lung cells, A549 andMRC-5. The IC50 values ranging from 0.25 to 0.61 µM after 48 h incubation in lung cancer cells indicate that thecompds. showed high cytotoxicity with values significantly lower than the ref. drug, cisplatin (11.84 µM). Interactionstudies were carried out using human serum albumin (HSA) and DNA. All complexes showed similar cytotoxic activity,however complex 1a, which is the hydrolysis product of 1, presented the highest activity and selectivity among all sevencompds. synthesized here. Complexes 1 and 1a inhibited the colony formation decreasing the colony size and inducingmorphol. changes in A549 cells. These complexes induced apoptosis cell death and promoted cell cycle arrest in theSub-G1 phase with a decrease in the cell no. at the S phase.~5 Citings

26. Application of Q2MM to predictions in stereoselective synthesis

By Rosales, Anthony R.; Quinn, Taylor R.; Wahlers, Jessica; Tomberg, Anna; Zhang, Xin; Helquist, Paul; Wiest, Olaf;Norrby, Per-OlaFrom Chemical Communications (Cambridge, United Kingdom) (2018), 54(60), 8294-8311. Language: English,Database: CAPLUS, DOI:10.1039/C8CC03695K

A review on the basic ideas behind Q2MM (Quantum-Guided Mol. Mechanics) capable of deriving TSFFs (transitionstate force fields) that allow the fast and accurate predictions of stereoselectivity for a wide range of catalyticenantioselective reactions.~1 Citing

27. Concepts and computational methods for the electrochemical interface and applications: Past, present, andfuture

By Anderson, Alfred B.From Current Opinion in Electrochemistry (2017), 1(1), 27-33. Language: English, Database: CAPLUS,DOI:10.1016/j.coelec.2016.12.010

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In the nearly 100 years since Faraday published his paper "On Elec. Decompn." in 1834, little was learned about theelectrode-electrolyte interface. The useful Nernst equation and Tafel relationships were developed in 1889 and 1905,resp., and it was not until the Schrodinger equation was discovered that the groundwork was laid for Gurney's 1931formulation of a model for electron transfer at the electrochem. interface. Yet things developed slowly until Marcusdeveloped his theory in the 1950s. Applications and generalizations of Gurney's formalism were held back by theabsence of powerful computers. This current opinion piece traces through the development of computational models forproperties of the electrochem. interface beginning in the 1980s with semiempirical theories that to some extent mimickedGurney's formalism, and culminating with recent codes that include all the significant interactions that det. electrontransfer reversible potentials and activation energies and their dependencies on the electrode potential. Some theoriesdeveloped along the way that have restrictions but are still useful are included in the discussion. The writer believesconditions are now set for major advancements in understanding and technol. using modern theory in combination withexptl. techniques.~5 Citings

28. Porous Pt3Ni with enhanced activity and durability towards oxygen reduction reaction

By Mi, Shuying; Cheng, Na; Jiang, Hao; Li, Chunzhong; Jiang, HaiboFrom RSC Advances (2018), 8(28), 15344-15351. Language: English, Database: CAPLUS,DOI:10.1039/C8RA02219D

The size of nanocrystals (NCs) is regarded as one of the vital factors detg. their electrochem. performance. To achievehigh electrochem. activity and durability at the same time still remains a big challenge. This work has demonstrated thesuccessful synthesis of Pt3Ni nanocrystals of large size with porous characteristics (PNC-Pt3Ni). The mass and specificactivity of the as-prepd. catalyst are 6 and 6.6 times more than those of com. Pt/C at 0.9 V vs. the reversible hydrogenelectrode (RHE), resp. More importantly, PNC-Pt3Ni prevails against a durability test (23.7% loss of mass activity after10 000 potential cycling) with little change to the porous morphol. under harsh exptl. conditions. D. functional theorycalcns. show a much lower activation energy for PNC-Pt3Ni during the process of dissocn. of the oxygen mol. adsorbedon the surface of the catalyst, which may account for the improvement in the catalytic activity. The lower seriesresistance for PNC-Pt3Ni is also verified by electrochem. impedance spectroscopy (EIS) data, resulting from fewer grainboundaries for nanocrystals with large sizes. This exciting work contributes a new strategy for the optimization ofelectrochem. performance and durability.~0 Citings

29. Solvent-Dependent Hemilability of (2-Diphenylphosphino)Phenol in a Ru(II) para-Cymene System

By Biancalana, Lorenzo; Ciancaleoni, Gianluca; Zacchini, Stefano; Monti, Andrea; Marchetti, Fabio; Pampaloni, GuidoFrom Organometallics (2018), 37(9), 1381-1391. Language: English, Database: CAPLUS,DOI:10.1021/acs.organomet.8b00071

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The addn. of Ph2P(2-C6H4OH) to [(η6-p-cymene)RuCl(µ-Cl)]2gave three distinct products, depending on the exptl.conditions. The previously reported [(η6-p-cymene)RuClκ2P,O-PPh2(2-C6H4O)], 1, was obtained in 90%yield using MeOH as the solvent, in the presence of a base(Et3N). Conversely, [(η6-p-cymene)RuClκ2P,O-PPh2(2-C6H4OH)]Cl, [2]Cl, was afforded (88% yield) in MeOH withoutusing the base. However, [(η6-p-cymene)RuCl2κP-PPh2(2-C6H4OH)], 3, was the major species in chlorinated solvents.Compds. 1, [2]Cl, and 3 were characterized by anal. andspectroscopic (IR, NMR) methods. The x-ray structures of [2]+and 3 were detd., with the latter forming H bond dimeric units inthe solid state. The dissoln. of [2]Cl into deuterated solvents,except MeOH, led to rapid equilibration between [2]Cl and 3,revealing the hemilabile behavior of the phosphino-phenolligand. According to Pulsed-Field Gradient Spin Echo (PGSE)-NMR and DFT studies, the dimeric nature of 3 persists in soln.;thus, the H-bonding properties of MeOH are crucial to stabilize[2]Cl with respect to 3, with the latter being 3.4 kcal mol-1 morestable than the former in the gas phase. Compd. 1 underwentelectrophilic addns. by HCl, HBF4, and MeCOCl to give, resp.,[2]Cl (the reverse process being viable with Et3N), [2]BF4, andthe ester [(η6-p-cymene)RuCl2κP-PPh2(2-C6H4OCOMe)], 5.The reaction of 1 with AgNO3 afforded the nitrate complex [(η6-p-cymene)Ru(NO3)κ2P,O-PPh2(2-C6H4O)], 4. [2]BF4, 4, and5 were isolated in the solid state in good to high yields andcharacterized by elemental anal. and IR and NMRspectroscopy.

~1 Citing

30. Oxygen reduction reaction on Pt(1 1 1), Pt(2 2 1), and Ni/Au1Pt3(2 2 1) surfaces: Probing scalingrelationships of reaction energetics and interfacial composition

By Wang, Hao; An, Wei; Liu, Xiaoyang; Heath Turner, C.From Chemical Engineering Science (2018), 184, 239-250. Language: English, Database: CAPLUS,DOI:10.1016/j.ces.2018.03.054

We investigate the oxygen redn. reaction (ORR) on Pt(1 1 1), Pt(2 2 1), and Ni/Au1Pt3(2 2 1) surfaces using periodic d.functional theory (DFT) calcns. augmented with kinetic Monte Carlo (KMC) simulations. In the DFT calcns., both auniform elec. field and an implicit solvent were employed to quantify the changes in the ORR energetics. Based on theDFT values and the reaction mechanism of ORR, KMC simulations were performed to predict the current densities andthe surface populations as a function of the electrode potential on the different catalyst surfaces. These results werecompared to an ORR model with energetics approximated using scaling relationships. The two approaches for obtainingenergetic parameters yield different KMC-predicted polarization curves. An anal. of the surface species concns. on Pt(11 1), Pt(2 2 1), and Ni/Au1Pt3(2 2 1) indicates dramatic concn. variations at different potentials. Direct neighbor-neighborinteractions on the surface were also tested, but they were found to only moderately influence the surface speciesconcns., and they led to imperceptible changes in the predicted current densities. Overall, we predict that an alloysurface of Ni/Au1Pt3(2 2 1) can significantly shift the onset potential of the polarization curve to higher potentials,providing guidance for future electrocatalyst design.~2 Citings

31. Crossed Molecular Beam Study of H+CH4 and H+CD4 Reactions: Vibrationally Excited CH3/CD3 ProductChannels

By Chen, Wen-tao; Yu, Sheng-rui; Yuan, Dao-fu; Xie, Ting; Yang, Jia-yue; Wang, Si-wen; Luo, Chang; Tan, Yu-xin;Miao, Yue; Zhang, Wei-qing; et alFrom Chinese Journal of Chemical Physics (2017), 30(6), 609-613. Language: English, Database: CAPLUS,DOI:10.1063/1674-0068/30/cjcp1711215

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We study the H+CH4/CD4→H2/HD+CH3/CD3 reactions using the time sliced velocity map ion imaging technique. Ionimages of the CH3/CD3 products were measured by the (2+1) resonance enhanced multi-photon ionization (REMPI)detection method. Besides the CH3/CD3 products in the ground state, ion images of the vibrationally excited CH3/CD3products were also obsd. at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of theproducts CH3/CD3 in vibrationally excited states gradually vary from backward scattering to sideways scattering as thecollision energy increases. Compared to the CH3/CD3 products in the ground state, the CH3/CD3 products invibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a moreimportant role in the vibrationally excited product channels. (c) 2017 American Institute of Physics.~1 Citing

32. N-type B-S co-doping and S doping in diamond from first principles

By Tang, Lin; Yue, Ruifeng; Wang, YanFrom Carbon (2018), 130, 458-465. Language: English, Database: CAPLUS, DOI:10.1016/j.carbon.2018.01.028

The S-doped diamond and B-S co-doped diamond at different concns. were investigated by the d. functional theory(DFT) to explore the possibility to achieve effective and shallow donors in diamond. We found for the first time that theValence Band max. (VBM) and the Intermediate Band (IB) min. of B-S co-doped diamond are located at the same κ-pointΓ, which is quite different from the indirect energy gap of S-doped diamond and pure diamond. Although the simulatedionization energy of B-S defect is deeper than that of S defect, the impurities formation energy is much lower than that ofS defect. It suggests that the introduction of B help improve the soly. of S in diamond. Besides, the electron effectivemass of IB of B-S co-doped diamond is much smaller than that of the S-doped diamond, which may lead to cond.promotion for diamond. Comparison of the d. of states in both cases, it is found that the S-3p states are responsible forconduction band, as well as the B-2p states of B-S co-doped diamond have a little contribution to its conduction band. Itcan conclude that with the assistance of B, S is a suitable shallow donor impurity in diamond.~2 Citings

33. Atom Transfer Radical Addition Catalyzed by Ruthenium-Arene Complexes Bearing a Hybrid Phosphine-Diene Ligand

By Chotard, Florian; Malacea-Kabbara, Raluca; Balan, Cedric; Bodio, Ewen; Picquet, Michel; Richard, Philippe; Ponce-Vargas, Miguel; Fleurat-Lessard, Paul; Le Gendre, PierreFrom Organometallics (2018), 37(5), 812-820. Language: English, Database: CAPLUS,DOI:10.1021/acs.organomet.7b00851

The synthesis and the characterization of arene Ru complexesbearing either (3,5-cycloheptadienyl)diphenylphosphine or(cycloheptyl)diphenylphosphine are reported. Upon irradn. orheating, all these complexes lose their arene ligand but thenbehave differently depending on the nature of the phosphineligand. (Cycloheptadienyl)phosphine complexes[(C7H9)Ph2RuCl2(η6-cymene)] (1) and [(C7H9)Ph2RuCl2(η6-BzOEt)] (3) give a cationic dinuclear Ru complex [Ru2(µ-Cl)3((η4-3,5-cycloheptadienyl)PPh2-κP)2][Cl] (5) for which thetwo Ru atoms are bridged by three chlorido ligands and flankedby two tridentate (cycloheptadienyl)phosphines.(Cycloheptyl)diphenylphosphine complexes[(C7H13)Ph2RuCl2(η6-cymene)] (2) and [(C7H13)Ph2RuCl2(η6-BzOEt)] (4) undergo arene exchange when toluene was usedas solvent or degrade in CH2Cl2. ATRA catalytic trialsconducted in parallel with these complexes using CCl4 andstyrene as std. substrates, highlighted the deep impact of thedienyl moiety on the results. In smooth conditions (UV irradn.or moderate heating), only (cycloheptyl)phosphine derivs. giveKharasch adduct in satisfactory yields. Their performance wasconsiderably improved by combining irradn. and heating. Athigher temp., the cationic dinuclear complex 5 revealed asactive and robust, giving turnover nos. as high as 9700 whentetradecene and CCl4 were used as substrates.

~4 Citings

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34. Heavy Atom Secondary Kinetic Isotope Effect on H-Tunneling

By Eckhardt, Andre K.; Gerbig, Dennis; Schreiner, Peter R.From Journal of Physical Chemistry A (2018), 122(5), 1488-1495. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpca.7b12118

Although frequently employed, heavy atom kinetic isotopeeffects (KIE) have not been reported for quantum mech.tunneling reactions. Here we examine the secondary KIEthrough 13C-substitution of the carbene atom inmethylhydroxycarbene (H3C-C-OH) in its [1,2]H-tunneling shiftreaction to acetaldehyde (H3C-CHO). Our study employsmatrix-isolation IR spectroscopy in various inert gases andquantum chem. computations. Depending on the choice of thematrix host gas, the KIE varies within a range of 1.0 in xenon to1.4 in neon. A KIE of 1.1 was computed using the Wentzel-Kramers-Brillouin (WKB) CVT/SCT, and instanton approachesfor the gas phase at the B3LYP/cc-pVTZ level of theory.Computations with explicit consideration of the noble gasenvironment indicate that the surrounding atoms influence thetunneling reaction barrier height and width. The tunneling half-lives computed with the WKB approach are in good agreementwith the exptl. results in the different noble gases.

~5 Citings

35. 1H, 13C, and 15N NMR conformational characterization of a series of 2-acetylthiazolethiosemicarbazonecompounds

By Carroll, William R.; Gardner, Dylan M.; Melton, Elizabeth R.; Murphy, Shana T.; Buckner, Arielle K.; Fulmer,Madison S.; Qualls, William G.; Lisic, Edward C.From Journal of Molecular Structure (2018), 1157, 8-13. Language: English, Database: CAPLUS,DOI:10.1016/j.molstruc.2017.11.061

A series of new 2-acetylthiazolethiosemicarbazone mols. belonging to a family of pharmaceutically relevant mols. wassynthesized and characterized. These mols. showed atropisomeric properties and occupied two distinct conformationsat room temp. Each of these configurations was characterized by NMR and identified as both internally hydrogenbonded and non-hydrogen bonded forms. The knowledge of these two forms and their identities may be of use to thoseseeking to employ this family of mols. in a pharmaceutical context.~3 Citings

36. Quantum fluctuations of a fullerene cage modulate its internal magnetic environment

By Kawatsu, Tsutomu; Tachikawa, MasanoriFrom Physical Chemistry Chemical Physics (2018), 20(3), 1673-1684. Language: English, Database: CAPLUS,DOI:10.1039/C7CP06401B

To investigate the effect of quantum fluctuations on the magnetic environment inside a C60 fullerene cage, we havecalcd. the nuclear magnetic shielding const. of protons in H2@C60 and HD@C60 systems by on-the-fly ab initio pathintegral simulation, including both thermal and nuclear quantum effects. The most dominant upfield from an isolatedhydrogen mol. occurs due to the diamagnetic current of the C60 cage, which is partly canceled by the paramagneticcurrent, where the paramagnetic contribution is enlarged by the zero-point vibrational fluctuation of the C60 carbonbackbone structure via a widely distributed HOMO-LUMO gap. This quantum modulation mechanism of the nuclearmagnetic shielding const. is newly proposed. Because this quantum effect is independent of the difference between H2and HD, the H2/HD isotope shift occurs in spite of the C60 cage. The nuclear magnetic consts. computed for H2@C60and HD@C60 are 32.047 and 32.081 ppm, resp., which are in reasonable agreement with the corresponding values of32.19 and 32.23 ppm estd. from the exptl. values of the chem. shifts.~3 Citings

37. Computational Chemistry: The Fate of Current Methods and Future Challenges

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By Grimme, Stefan; Schreiner, Peter R.From Angewandte Chemie, International Edition (2018), 57(16), 4170-4176. Language: English, Database: CAPLUS,DOI:10.1002/anie.201709943

In this essay, we attempt to make predictions about the fate and development of the computational mol. sciences. Ofcourse, it is not the first time that the future challenges for computational org. chem. and biochem. are considered; thesewere outlined in complementary contexts recently. In this article, the authors take a somewhat different perspective andemphasize the changes expected for chem. that are triggered by the rapid developments and increasingly strongerinfluences from theory, algorithms, and data-driven technologies. The authors of this essay are about the same age andhave a general overview of a period of about 25 years during which they have actively contributed to the field ofcomputational chem. Hence, it appears sensible to make predictions extending 25 years into the future, roughly to theyear 2043 (when both authors will long be retired).~22 Citings

38. Dioxygen in Polyoxometalate Mediated Reactions

By Weinstock, Ira A.; Schreiber, Roy E.; Neumann, RonnyFrom Chemical Reviews (Washington, DC, United States) (2018), 118(5), 2680-2717. Language: English, Database:CAPLUS, DOI:10.1021/acs.chemrev.7b00444

A review. The authors consider the use of mol. oxygen inreactions mediated by polyoxometalates. Polyoxometalatesare anionic metal oxide clusters of a variety of structures thatare sol. in liq. phases and therefore amenable to homogeneouscatalytic transformations. Often, they are active for electrontransfer oxidns. of a myriad of substrates and upon redn. canbe reoxidized by mol. oxygen. For example, thephosphovanadomolybdate, H5PV2Mo10O40, can oxidize Pd(0)thereby enabling aerobic reactions catalyzed by Pd andH5PV2Mo10O40. In a similar vein, polyoxometalates canstabilize metal nanoparticles, leading to addnl. transformations.Furthermore, electron transfer oxidn. of other substrates suchas halides and sulfur-contg. compds. is possible. Moreuniquely, H5PV2Mo10O40 and its analogs can mediate electrontransfer-oxygen transfer reactions where oxygen atoms aretransferred from the polyoxometalate to the substrate. Thisunique property has enabled correspondingly uniquetransformations involving carbon-carbon, carbon-hydrogen, andcarbon-metal bond activation. The pathway for the reoxidn. ofvanadomolybdates with O2 appears to be an inner-spherereaction, but the oxidn. of one-electron reducedpolyoxotungstates has been shown through intensive researchto be an outer-sphere reaction. Beyond electron transfer andelectron transfer-oxygen transfer aerobic transformations, therea few examples of apparent dioxygenase activity where bothoxygen atoms are donated to a substrate.

~46 Citings

39. Variational transition state theory: theoretical framework and recent developments

By Bao, Junwei Lucas; Truhlar, Donald G.From Chemical Society Reviews (2017), 46(24), 7548-7596. Language: English, Database: CAPLUS,DOI:10.1039/C7CS00602K

This article reviews the fundamentals of variational transition state theory (VTST), its recent theor. development, andsome modern applications. The theor. methods reviewed here include multidimensional quantum mech. tunneling,multistructural VTST (MS-VTST), multi-path VTST (MP-VTST), both reaction-path VTST (RP-VTST) and variablereaction coordinate VTST (VRC-VTST), system-specific quantum Rice-Ramsperger-Kassel theory (SS-QRRK) forpredicting pressure-dependent rate consts., and VTST in the solid phase, liq. phase, and enzymes. We also providesome perspectives regarding the general applicability of VTST.~38 Citings

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40. Tuning the cytotoxicity of ruthenium(II) para-cymene complexes by mono-substitution at atriphenylphosphine/phenoxydiphenylphosphine ligand

By Biancalana, Lorenzo; Zacchini, Stefano; Ferri, Nicola; Lupo, Maria Giovanna; Pampaloni, Guido; Marchetti, FabioFrom Dalton Transactions (2017), 46(47), 16589-16604. Language: English, Database: CAPLUS,DOI:10.1039/C7DT03385K

[RuCl2(η6-p-cymene)(κP-Ph2PR)] [R = 4-C6H4OSiMe2 tBu, 1; R = 4-C6H4Br, 2; R = OC(:O)CHCl2, 3; R = OPh, 4; R =O(2-C6H4SiMe2 tBu), 5] and [Ru(C2O4)(η6-p-cymene)κP-Ph2PO(2-C6H4(SiMe2 tBu))], 6, were obtained in 83-98% yieldfrom Ru(II) arene precursors by three different synthetic strategies. The unprecedented phosphine Ph2P(O(2-C6H4SiMe2tBu)) was synthesized in 86% yield from 2-C6H4Br(OSiMe2 tBu) and Ph2PCl, via intramol. O to C 1,3-migration of the silylgroup (retro-Brook rearrangement). All the complexes were fully characterized by anal. and spectroscopic methods, andby single crystal x-ray diffraction in the cases of 3, 4, 5 and 6. Complexes 1-6 and the model compds. [RuCl2(η6-p-cymene)(κP-PPh3)] (Ru-PPh3) and [Ru(C2O4)(η6-p-cymene)(κP-PPh3)] (Ru-PPh3-O) underwent slow degrdn. in CHCl3solns. upon air contact; the mixed valence complex [(η6-p-cymene)Ru(µ-Cl)3RuCl2(κP-PPh3)], 7, was isolated from asoln. of Ru-PPh3 in CHCl3, and x-ray identified. The antiproliferative activity of 1-6 and Ru-PPh3, Ru-PPh3-O and[RuCl2(η6-p-cymene)(κP-PTA)] (RAPTA-C) was assessed towards the triple-neg. breast cancer cell line MDA-MB-231,the ovarian carcinoma cell line A2780 and human skin fibroblasts (HSF). Complexes 1, 2, 5 and 6 displayed IC50 valuessignificantly lower than that of cisplatin, with 2 providing a more potent cytotoxic effect on MDA-MB-231 and A2780cancer cells compared to the noncancerous cell line (HSF). The stability of all complexes in DMSO/water soln. waselucidated by NMR and cond. measurements, and in particular 35Cl NMR spectroscopy was helpful to check the possiblechloride dissocn. The stability studies suggest that the cytotoxic activity in vitro of the compds. is mainly ascribable toRu(II) species still bound to the P ligand.~16 Citings

41. Fast Heavy-Atom Tunneling in Trifluoroacetyl Nitrene

By Wu, Zhuang; Feng, Ruijuan; Li, Hongmin; Xu, Jian; Deng, Guohai; Abe, Manabu; Begue, Didier; Liu, Kun; Zeng,XiaoqingFrom Angewandte Chemie, International Edition (2017), 56(49), 15672-15676. Language: English, Database:CAPLUS, DOI:10.1002/anie.201710307

Chem. reactions involving quantum mech. tunneling (QMT) increasingly attract the attention of scientists. In contrast tothe hydrogen-tunneling as frequently obsd. in chem. and biol., tunneling solely by heavy atoms is rare. Herein, we reportheavy-atom tunneling in trifluoroacetyl nitrene, CF3C(O)N. The carbonyl nitrene CF3C(O)N in the triplet ground state wasgenerated in cryogenic matrixes by laser (193 or 266 nm) photolysis of CF3C(O)N3 and characterized by IR and EPRspectroscopy. In contrast to the theor. predicted activation barriers (>10 kcal mol-1), CF3C(O)N undergoes rapidrearrangement into CF3NCO with half-life times of less than 10 min and unprecedentedly large 14N/15N kinetic isotopeeffects (1.18-1.33) in solid Ar, Ne, and N2 matrixes even at 2.8 K. The tunneling disappearance of CF3C(O)N becomesmuch slower in the chem. active toluene and in 2-methyltetrahydrofuran at 5 K.~8 Citings

42. The inhibition of hydrogen peroxide reduction at low potentials on Pt(111): Hydrogen adsorption orinterfacial charge?

By Briega-Martos, Valentin; Herrero, Enrique; Feliu, Juan M.From Electrochemistry Communications (2017), 85, 32-35. Language: English, Database: CAPLUS,DOI:10.1016/j.elecom.2017.10.016

The hydrogen peroxide redn. reaction (HPRR) on Pt(111) has been studied for the first time in acid to neutral pH valuesin the absence of anion specific adsorption using the HMRDE configuration. The onset for the redn. is ca. 0.95 V (RHE)for the Pt(111), irresp. of the pH value. At more neg. potential values, the redn. is inhibited. It has been found that thediminution of the activity on Pt(111) occurs at the same potential value in the SHE scale for the different pH values. Thisindicates that this deactivation is not dependent on the hydrogen adsorption process, as has been previously suggested.However, it appears to be related to the interface water reorganization and the potential of zero free charge of the metalsurface. In addn., studies in alk. conditions suggest that the presence of adsorbed OH species promotes the totalconversion of hydrogen peroxide to water.~5 Citings

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43. Photochemistry of 2-Formylphenylnitrene: A Doorway to Heavy-Atom Tunneling of a Benzazirine to a CyclicKetenimine

By Nunes, Claudio M.; Reva, Igor; Kozuch, Sebastian; McMahon, Robert J.; Fausto, RuiFrom Journal of the American Chemical Society (2017), 139(48), 17649-17659. Language: English, Database:CAPLUS, DOI:10.1021/jacs.7b10495

The slippery potential energy surface of aryl nitrenes hasrevealed unexpected and fascinating reactions. To exploresuch a challenging surface, one powerful approach is to use acombination of a cryogenic matrix environment and a tunablenarrowband radiation source. In this way, we discovered theheavy-atom tunneling reaction involving spontaneous ringexpansion of a fused-ring benzazirine into a seven-memberedring cyclic ketenimine. The benzazirine was generated in situby the photochem. of protium and deuterated triplet 2-formylphenylnitrene isolated in an argon matrix. The ring-expansion reaction takes place at 10 K with a rate const. of∼7.4 × 10-7 s-1, despite an estd. activation barrier of 7.5 kcalmol-1. Moreover, it shows only a marginal increase in the rateupon increase of the abs. temp. by a factor of 2. Computedrate consts. with and without tunneling confirm that the reactioncan only occur by a tunneling process from the ground state atcryogenic conditions. It was also found that the ring-expansionreaction rate is more than 1 order of magnitude faster when thesample is exposed to broadband IR radiation.

~8 Citings

44. Computational Prediction of Excited-State Carbon Tunneling in the Two Steps of Triplet Zimmerman Di-π-Methane Rearrangement

By Li, Xin; Liao, Tao; Chung, Lung WaFrom Journal of the American Chemical Society (2017), 139(46), 16438-16441. Language: English, Database:CAPLUS, DOI:10.1021/jacs.7b07539

The photoinduced Zimmerman di-π-methane (DPM)rearrangement of polycyclic mols. to form synthetically usefulcyclopropane derivs. was found exptl. to proceed in a tripletexcited state. We have applied state-of-the-art quantum mech.methods, including M06-2X, DLPNO-CCSD(T) and variationaltransition-state theory with multidimensional tunnelingcorrections, to an investigation of the reaction rates of the twosteps in the triplet DPM rearrangement of dibenzobarrelene,benzobarrelene and barrelene. This study predicts a highprobability of carbon tunneling in regions around the twoconsecutive transition states at 200-300 K, and anenhancement in the rates by 104-276/35-67% with carbontunneling at 200/300 K. The Arrhenius plots of the rate consts.were found to be curved at low temps. Moreover, thecomputed 12C/13C kinetic isotope effects were affectedsignificantly by carbon tunneling and temp. Our predictions ofelectronically excited-state carbon tunneling and twoconsecutive carbon tunneling are unprecedented. Heavy-atomtunneling in some photoinduced reactions with reactiveintermediates and narrow barriers can be potentially obsd. atrelatively low temp. in expts.

~6 Citings

45. Theoretical approaches for dynamical ordering of biomolecular systems

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By Okumura, Hisashi; Higashi, Masahiro; Yoshida, Yuichiro; Sato, Hirofumi; Akiyama, RyoFrom Biochimica et Biophysica Acta, General Subjects (2018), 1862(2), 212-228. Language: English, Database:CAPLUS, DOI:10.1016/j.bbagen.2017.10.001

A review. Living systems are characterized by the dynamic assembly and disassembly of biomols. The dynamicalordering mechanism of these biomols. has been investigated both exptl. and theor. The main theor. approaches includequantum mech. (QM) calcn., all-atom (AA) modeling, and coarse-grained (CG) modeling. The selected approachdepends on the size of the target system (which differs among electrons, atoms, mols., and mol. assemblies). Thesehierarchal approaches can be combined with mol. dynamics (MD) simulation and/or integral equation theories for liqs.,which cover all size hierarchies. We review the framework of quantum mech./mol. mech. (QM/MM) calcns., AA MDsimulations, CG modeling, and integral equation theories. Applications of these methods to the dynamical ordering ofbiomol. systems are also exemplified. The QM/MM calcn. enables the study of chem. reactions. The AA MD simulation,which omits the QM calcn., can follow longer time-scale phenomena. By reducing the no. of degrees of freedom and thecomputational cost, CG modeling can follow much longer time-scale phenomena than AA modeling. Integral equationtheories for liqs. elucidate the liq. structure, for example, whether the liq. follows a radial distribution function. Thesetheor. approaches can analyze the dynamic behaviors of biomol. systems. They also provide useful tools for exploringthe dynamic ordering systems of biomols., such as self-assembly. This article is part of a Special Issue entitled "Biophys.Exploration of Dynamical Ordering of Biomol. Systems" edited by Dr. Koichi Kato.~2 Citings

46. Heavy-Atom Tunneling Calculations in Thirteen Organic Reactions: Tunneling Contributions are Substantial,and Bell's Formula Closely Approximates Multidimensional Tunneling at ≥250 K

By Doubleday, Charles; Armas, Randy; Walker, Dana; Cosgriff, Christopher V.; Greer, Edyta M.From Angewandte Chemie, International Edition (2017), 56(42), 13099-13102. Language: English, Database:CAPLUS, DOI:10.1002/anie.201708489

Multidimensional tunneling calcns. are carried out for 13 reactions, to test the scope of heavy-atom tunneling in org.chem., and to check the accuracy of one-dimensional tunneling models. The reactions include pericyclic,cycloaromatization, radical cyclization and ring opening, and SN 2. When compared at the temps. that give the sameeffective rate const. of 3x10-5 s-1, tunneling accounts for 25-95 % of the rate in 8 of the 13 reactions. Values oftransmission coeffs. predicted by Bell's formula, κBell , agree well with multidimensional tunneling (canonical variationaltransition state theory with small curvature tunneling), κSCT. Mean unsigned deviations of κBell vs. κSCT are 0.08, 0.04,0.02 at 250, 300 and 400 K. This suggests that κBell is a useful first choice for predicting transmission coeffs. in heavy-atom tunnelling.~6 Citings

47. Accurate potential energy surfaces for hydrogen abstraction reactions: A benchmark study on the XYG3doubly hybrid density functional

By Chen, Jun; Su, Neil Qiang; Xu, Xin; Zhang, Dong H.From Journal of Computational Chemistry (2017), 38(27), 2326-2334. Language: English, Database: CAPLUS,DOI:10.1002/jcc.24886

The potential energy surface (PES) for the H + CH4 system has been constructed with the recently developed XYG3doubly hybrid functional, while those with the std. B3LYP hybrid functional, and the Moller-Plesset perturbation theory upto the second order (MP2) are also presented for comparison. Quantum dynamics studies demonstrated thatsatisfactory results on the reaction probabilities and the rate coeffs. can be obtained on top of the XYG3-PES, ascompared to the results based on the highly accurate, yet expensive, CCSD(T)-PES (Li et al., J. Chem. Phys. 2015, 142,204302). Further investigation suggested that the XYG3 functional is useful in providing accurate rate coeffs. for somelarger systems involving H atom abstractions. © 2017 Wiley Periodicals, Inc.~1 Citing

48. The Cope Rearrangement of 1,5-Dimethylsemibullvalene-2(4)-d1: Experimental Evidence for Heavy-AtomTunneling

By Schleif, Tim; Mieres-Perez, Joel; Henkel, Stefan; Ertelt, Melanie; Borden, Weston Thatcher; Sander, WolframFrom Angewandte Chemie, International Edition (2017), 56(36), 10746-10749. Language: English, Database:CAPLUS, DOI:10.1002/anie.201704787

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As an exptl. test of the theor. prediction that heavy-atom tunneling is involved in the degenerate Cope rearrangement ofsemibullvalenes at cryogenic temps., monodeuterated 1,5-dimethylsemibullvalene isotopomers were prepd. andinvestigated by IR spectroscopy using the matrix isolation technique. As predicted, the less thermodynamically stableisotopomer rearranges at cryogenic temps. in the dark to the more stable one, while broadband IR irradn. above 2000cm-1 results in an equilibration of the isotopomeric ratio. Since this reaction proceeds with a rate const. in the order of10-4 s-1 despite an exptl. barrier of Ea = 4.8 kcal mol-1 and with only a shallow temp. dependence, the results areinterpreted in terms of heavy-atom tunneling.~7 Citings

49. Perovskite electrocatalysts for the oxygen reduction reaction in alkaline media

By Risch, MarcelFrom Catalysts (2017), 7(5), 154/1-154/31. Language: English, Database: CAPLUS, DOI:10.3390/catal7050154

Oxygen redn. is considered a key reaction for electrochem. energy conversion but slow kinetics hamper application infuel cells and metal-air batteries. In this review, the prospect of perovskite oxides for the oxygen redn. reaction (ORR) inalk. media is reviewed with respect to fundamental insight into activity and possible mechanisms. For gaining theseinsights, special emphasis is placed on highly cryst. perovskite films that have only recently become available forelectrochem. interrogation. The prospects for applications are evaluated based on recent progress in the synthesis ofperovskite nanoparticles. The review concludes with the current understanding of oxygen redn. on perovskite oxides anda perspective on opportunities for future fundamental and applied research.~8 Citings

50. Isotope-Controlled Selectivity by Quantum Tunneling: Hydrogen Migration versus Ring Expansion inCyclopropylmethylcarbenes

By Nandi, Ashim; Gerbig, Dennis; Schreiner, Peter R.; Borden, Weston Thatcher; Kozuch, SebastianFrom Journal of the American Chemical Society (2017), 139(27), 9097-9099. Language: English, Database: CAPLUS,DOI:10.1021/jacs.7b04593

Using the tunneling-controlled reactivity ofcyclopropylmethylcarbene, we demonstrate the viability ofisotope-controlled selectivity (ICS), a novel control element ofchem. reactivity where a mol. system with two conceivableproducts of tunneling exclusively produces one or the other,depending only on isotopic compn. Our multidimensionalsmall-curvature tunneling (SCT) computations indicate that,under cryogenic conditions, 1-methoxycyclopropylmethylcarbene shows rapid H-migration to1-methoxy-1-vinylcyclopropane, whereas deuterium-substituted1-methoxycyclopropyl-d3-methylcarbene undergoes ringexpansion to 1-d3-methylcyclobutene. This predicted changein reactivity constitutes the first example of a kinetic isotopeeffect that discriminates between the formation of two products.

~6 Citings

51. Electrocatalytic C-H/N-H Coupling of 2'-Aminoacetophenones for the Synthesis of Isatins

By Qian, Peng; Su, Ji-Hu; Wang, Yukang; Bi, Meixiang; Zha, Zhenggen; Wang, ZhiyongFrom Journal of Organic Chemistry (2017), 82(12), 6434-6440. Language: English, Database: CAPLUS,DOI:10.1021/acs.joc.7b00635

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2'-Aminoacetophenones undergo a C(sp3)-H oxidn. followed byintramol. C-N bond formation by virtue of a simple electrochem.oxidn. in the presence of n-Bu4NI, providing various isatins withmoderate to good yields. The reaction intermediates weredetected, and a radical-based pathway was proposed.

~40 Citings

52. Spectroscopic Studies of How Moisture Enhances CO Oxidation over Au/BN at Ambient Temperature

By Tran-Thuy, Tuyet-Mai; Chen, Chin-Chih; Lin, Shawn D.From ACS Catalysis (2017), 7(7), 4304-4312. Language: English, Database: CAPLUS, DOI:10.1021/acscatal.7b01374

Gold catalysts readily catalyze CO oxidn. at subambient temp.,wherein moisture can influence the activity, typically with avolcano-shaped dependence. In this study, we examinemoisture-enhanced CO oxidn. over Au/BN. The room-temp.CO oxidn. activity of Au/BN increases quickly with increasingmoisture content up to 100% relative humidity (RH). In situdiffuse reflectance IR Fourier transform spectroscopy (DRIFTS)and in situ UV-vis diffuse reflectance spectroscopy (UV-vis-DRS) demonstrate that mainly metallic gold is present on the h-BN support. Surface intermediates are found when moisture isfed together with CO and O2, attributable to *CO(H2O)n and*OOH, resp. These surface intermediates are reactive whencounter-reactant is purged. Injection of isotope-labeled H2 18Odemonstrates that OH from H2O takes part in the process ofCO2 formation. The results of this study provide directevidence showing moisture-enhanced CO adsorption,moisture-enhanced O2 adsorption, and their activation that canpossibly lead to promotion of CO oxidn. over the Au/BNcatalyst.

~6 Citings

53. Cheap but accurate calculation of chemical reaction rate constants from ab initio data, via system-specific,black-box force fields

By Steffen, Julien; Hartke, BerndFrom Journal of Chemical Physics (2017), 147(16), 161701/1-161701/11. Language: English, Database: CAPLUS,DOI:10.1063/1.4979712

Building on the recently published quantum-mech. derived force field (QMDFF) and its empirical valence bond extension,EVB-QMDFF, it is now possible to generate a reliable potential energy surface for any given elementary reaction step inan essentially black box manner. This requires a limited and pre-defined set of ref. data near the reaction path andgenerates an accurate approxn. of the ref. potential energy surface, on and off the reaction path. This intermediaterepresentation can be used to generate reaction rate data, with far better accuracy and reliability than with traditionalapproaches based on transition state theory (TST) or variational extensions thereof (VTST), even if those includesophisticated tunneling corrections. However, the addnl. expense at the ref. level remains very modest. Wedemonstrate all this for three arbitrarily chosen example reactions. (c) 2017 American Institute of Physics.~2 Citings

54. Analysis of Hydrogen Atom Abstraction from Ethylbenzene by an FeVO(TAML) Complex

By Shen, Longzhu Q.; Kundu, Soumen; Collins, Terrence J.; Bominaar, Emile L.From Inorganic Chemistry (2017), 56(8), 4347-4356. Language: English, Database: CAPLUS,DOI:10.1021/acs.inorgchem.6b02796

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It was shown previously that the rate of hydrogen atomabstraction, k, from ethylbenzene (EB) by TAML complex[FeV(O)B*]- (1) in acetonitrile exhibits a large kinetic isotopeeffect (KIE ∼ 26) in the exptl. range 233-243 K. Theextrapolated tangents of ln(k/T) vs. T-1 plots for EB-d10 and EBgave a large, neg. intercept difference, Int(EB) - Int(EB-d10) = -34.5 J mol-1 K-1 for T-1 → 0, which is exclusively due to anisotopic mass effect on tunneling. A decompn. of the apparentactivation barrier in terms of electronic, ZPE, thermal enthalpic,tunneling, and entropic contributions is presented. Tunnelingcorrections to ∆H and ∆S are large. The DFT prediction, usingfunctional B3LYP and basis set 6-311G, for the electroniccontribution is significantly smaller than suggested by expt.However, the agreement improves after correction for the basisset superposition error in the interaction between EB and 1.The kinetic model employed was used to predict rate consts.outside the exptl. temp. range, which enabled us to comparethe reactivity of 1 with those of other hydrogen abstractingcomplexes.

~3 Citings

55. Hydrogen Tunneling above Room Temperature Evidenced by Infrared Ion Spectroscopy

By Schaefer, Mathias; Peckelsen, Katrin; Paul, Mathias; Martens, Jonathan; Oomens, Jos; Berden, Giel; Berkessel,Albrecht; Meijer, Anthony J. H. M.From Journal of the American Chemical Society (2017), 139(16), 5779-5786. Language: English, Database: CAPLUS,DOI:10.1021/jacs.6b10348

While hydrogen tunneling at elevated temps. has, for instance,often been postulated in biochem. processes, spectroscopicproof is thus far limited to cryogenic conditions, under whichthermal reactivity is negligible. We report spectroscopicevidence for H-tunneling in the gas phase at temps. around320-350 K obsd. in the isomerization reaction of ahydroxycarbene into an aldehyde. The charge-tagged carbenewas generated in situ in a tandem mass spectrometer bydecarboxylation of oxo[4-(trimethylammonio)phenyl]acetic acidupon collision induced dissocn. All ion structures involved arecharacterized by IR ion spectroscopy and quantum chem.calcns. The charge-tagged phenylhydroxycarbene undergoesa 1,2-H-shift to the corresponding aldehyde with an half-life ofabout 10 s, evidenced by isomer-selective two-color (IR-IR)spectroscopy. In contrast, the deuterated (OD) carbene analogshowed much reduced 1,2-D-shift reactivity with an estd. half-life of at least 200 s under the exptl. conditions, and providesclear evidence for hydrogen atom tunneling in the H-isotopologue. This is the first spectroscopic confirmation ofhydrogen atom tunneling governing 1,2-H-shift reactions atnoncryogenic temps., which is of broad significance for a rangeof (bio)chem. processes, including enzymic transformationsand organocatalysis.

~3 Citings

56. Dynamical barrier and isotope effects in the simplest substitution reaction via Walden inversion mechanism

By Zhao, Zhiqiang; Zhang, Zhaojun; Liu, Shu; Zhang, Dong H.From Nature Communications (2017), 8, 14506pp.. Language: English, Database: CAPLUS,DOI:10.1038/ncomms14506

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Reactions occurring at a carbon atom through the Walden inversion mechanism are one of the most important and usefulclasses of reactions in chem. Here we report an accurate theor. study of the simplest reaction of that type: the H+CH4substitution reaction and its isotope analogs. It is found that the reaction threshold vs. collision energy is considerablyhigher than the barrier height. The reaction exhibits a strong normal secondary isotope effect on the cross-sectionsmeasured above the reaction threshold, and a small but reverse secondary kinetic isotope effect at room temp. Detailedanal. reveals that the reaction proceeds along a path with a higher barrier height instead of the min.-energy path becausethe umbrella angle of the non-reacting Me group cannot change synchronously with the other reaction coordinates duringthe reaction due to insufficient energy transfer from the translational motion to the umbrella mode.~5 Citings

57. Effect of B-S co-doping on large diamonds synthesis under high pressure and high temperature

By Zhang, He; Li, Shangsheng; Li, Guanghui; Su, Taichao; Hu, Meihua; Ma, Hongan; Jia, Xiaopeng; Li, YongFrom International Journal of Refractory Metals & Hard Materials (2017), 66, 26-30. Language: English, Database:CAPLUS, DOI:10.1016/j.ijrmhm.2017.02.002

Large single-crystal diamonds with n-type semiconductor were synthesized from S/B-S co-doping FeNiCo-C systemunder high pressure and high temp. (HPHT) in this paper. It was found that the slight variation of the additive S contenthad not made obvious change for the color of diamonds synthesized from FeNiCo-C system. The B-S co-dopingsamples became more transparent and yellow than the samples added alone by S. The anal. of XPS spectra andFourier transform IR (FTIR) spectroscopy showed the presence of B and S in the obtained diamonds. The elec.properties of large diamond crystals were tested by Van der Pauw method with a four-point probe. The highest value ofthe hall mobility was 628.726 cm2/vs. And the lowest value of the resistivity was 9.33 × 105 Ω·cm with boron additive of0.8 wt.% and sulfur of 2 wt.% doping to diamond which was confirmed as n-type. This work indicated that B-S co-dopingto synthesize diamond crystals was a trend to promote the elec. properties of large diamond crystals.~1 Citing

58. A simple method to approximate electrode potential-dependent activation energies using density functionaltheory

By Akhade, Sneha A.; Bernstein, Nicole J.; Esopi, Monica R.; Regula, Michael J.; Janik, Michael J.From Catalysis Today (2017), 288, 63-73. Language: English, Database: CAPLUS, DOI:10.1016/j.cattod.2017.01.050

D. functional theory (DFT) examn. of electrocatalytic mechanisms are useful in fuel cell/electrolysis development, but thecalcn. of potential-dependent activation barriers for elementary steps involving electron and ion transfer remainschallenging. A simple and transferable DFT approach to est. these const. potential barriers for inner sphere electrochem.reactions is presented. The challenge of finding the transition state for an electrochem. reaction step (A* + H+ + e- →AH*, where * denotes surface-adsorbed species) is met by using an equiv. analogous nonelectrochem. reaction (A* + H*

→ AH*). The transition state of the nonelectrochem. step is referenced to an equil. potential (U0), at which the analogousnonelectrochem. state µ(H*) is in equil. with its equiv. electrochem. state µ(H+ + e-), allowing for the barrier to bereferenced to the chem. potential of the ion in the bulk electrolyte. The potential-dependence is incorporated byextrapolating the activation energy using Marcus theory. The 1st elementary step of CO2 electroredn. to COOH* wasused as a detailed example case for illustrating the method. Addnl. elementary redn. reactions involving C-H, O-H andN-H bond formations are included to demonstrate the transferability of the method. The method is simple and easy toimplement to approx. potential-dependent activation energies at the computational cost of a singly hydrogenation barriercalcn. and can aid in the development of more active and selective catalysts for electrochem. reactions.~12 Citings

59. Appearance of New Oscillation (Named Oscillation H) Induced by Na2SO4 and K2SO4 in Electroreduction ofH2O2 on Platinum

By Mukouyama, Yoshiharu; Kawasaki, Hirokazu; Hara, Daisuke; Yamada, Yuri; Nakanishi, ShujiFrom Journal of the Electrochemical Society (2017), 164(2), H1-H10. Language: English, Database: CAPLUS,DOI:10.1149/2.0011702jes

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The redn. of H2O2 on Pt electrodes in H2SO4 solns. shows a various types of electrochem. oscillations, namedsequentially from A to G, as is reported previously. This paper shows that salts such as Na2SO4 and K2SO4, which areoften used as supporting electrolytes for electrochem. reactions, cause significant effects on the H2O2 redn. A newpotential oscillation, named oscillations H, appears in the H2O2-H2SO4-Pt system when Na2SO4 or K2SO4 is added to thesolns. Oscillation H is induced by the cations originating from the salts, Na+ and K+, though they do not react on Ptelectrode. In the presence of Na+ or K+, the local pH at the electrode surface becomes basic, and consequently theoxidn. of HO2 -, formed via a dissocn. of H2O2 (H2O2 → HO2 - + H+), occurs on the electrode surface. O bubbles due tothe HO2 - oxidn. evolve from the electrode synchronously with the potential oscillation. Detailed studies, includingelectrochem. impedance measurements and numerical simulation, reveal that oscillation H can be explained by aninterplay of the HO2 - oxidn. and an autocatalytic effect involved in the H2O2 redn.~2 Citings

60. Syntheses, characterization and catalytic activities of half-sandwich ruthenium complexes with naphthalene-based Schiff base ligands

By Jia, Wei-Guo; Wang, Zhi-Bao; Zhi, Xue-Ting; Han, Jia-Qin; Sun, YingFrom Journal of Coordination Chemistry (2017), 70(5), 848-858. Language: English, Database: CAPLUS,DOI:10.1080/00958972.2017.1284322

Four ruthenium(II) p-cymene complexes with naphthalene-based Schiff base ligands [Ru(p-cymene)LCl] have beensynthesized and characterized. The half-sandwich ruthenium complexes were characterized by 1H and 13C NMRspectra, elemental analyses, and IR spectrometry. The mol. structures were confirmed by single-crystal X-ray diffraction.Furthermore, these half-sandwich ruthenium complexes are highly active catalysts for the hydrogenation of nitroarenes toanilines using NaBH4 as the reducing agent in ethanol at room temp.~7 Citings

61. Hyaluronic acid modification of RNase A and its intracellular delivery using lipid-like nanoparticles

By Wang, Xiaoying; Li, Yamin; Li, Quanshun; Neufeld, Caleb I.; Pouli, Dimitra; Sun, Shuo; Yang, Liu; Deng, Pu; Wang,Ming; Georgakoudi, Irene; et alFrom Journal of Controlled Release (2017), 263, 39-45. Language: English, Database: CAPLUS,DOI:10.1016/j.jconrel.2017.01.037

Developing safe and effective nanosystems to deliver active and therapeutic proteins to targeted cells and organs is animportant tool for many biomedical applications. We present here a simple and efficient strategy for this purpose:delivering hyaluronic acid (HA)-modified RNase A (RNase A-HA) in nanocomplex with cationic lipid-like mols. (lipidoids)to cancer cells, resulting in targeted inhibition of cancer proliferation. The chem. conjugation of RNase A with HA bothincreased the supramol. interaction with carrier lipidoids, promoting protein encapsulation efficacy, and facilitated cancercell targeting via interaction with overexpressed CD44. Through confocal laser scanning microscopy and flow cytometryanal., we demonstrated that protein/lipidoid nanoparticles could facilely enter cells with high CD44 expression, and inhibitcell proliferation in a dose-dependent manner.~16 Citings

62. Nonempirically tuning range-separated functionals for dipole polarizabilities of nanostructures containinghydrogen bonds

By Alipour, Mojtaba; Fallahzadeh, ParisaFrom Theoretical Chemistry Accounts (2017), 136(2), 1-8. Language: English, Database: CAPLUS,DOI:10.1007/s00214-016-2046-y

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Owing to the fact that the conventional d. functional theory (DFT) approxns. cannot accurately interpret some of theground and excited state properties, optimally tuned range-sepd. (OT-RS) d. functionals have been developed andsuccessfully applied to several problems over the last years. In this work, the accountability of OT-RS DFT approxns. isput into broader perspective for optical properties of hydrogen-bonded systems. More specifically, besides analyzing theperformance of std. long-range cor. (LC) functionals, the two new nonempirically OT-RS functionals are presented fordipole polarizabilities of hydrogen-bonded nanoclusters. The performance of the proposed OT-RS d. functionals incomparison with other LC functionals is assessed in detail for isotropic and anisotropic polarizabilities of variousnanoclusters of H2O, NH3, HF, and binary mixts. of HF-H2O. From the obtained results, the novel OT-RS functionals areshown to be accurate for the calcns. of dipole polarizabilities of the hydrogen-bonded systems. On the whole, our studyextends the applicability of OT-RS d. functionals for modeling the elec. response properties of hydrogen-bondednanoclusters.~1 Citing

63. Mechanism and kinetics of the electrocatalytic reaction responsible for the high cost of hydrogen fuel cells

By Cheng, Tao; Goddard, William A.; An, Qi; Xiao, Hai; Merinov, Boris; Morozov, SergeyFrom Physical Chemistry Chemical Physics (2017), 19(4), 2666-2673. Language: English, Database: CAPLUS,DOI:10.1039/C6CP08055C

The sluggish O redn. reaction (ORR) is a major impediment to the economic use of H fuel cells in transportation. Theauthors report the full ORR reaction mechanism for Pt(111) based on Quantum Mechanics (QM) based Reactivemetadynamics (RµD) simulations including explicit H2O to obtain free energy reaction barriers at 298 K. The lowestenergy pathway for 4 e- H2O formation is: 1st, *OOH formation; 2nd, *OOH redn. to H2O and O*; 3rd, O* hydrolysis usingsurface H2O to produce 2 *OH and finally *OH hydration to H2O. H2O formation is the rate-detg. step (RDS) for potentials>0.87 V, the normal operating range. Considering the Eley-Rideal (ER) mechanism involving protons from the solvent,the authors predict the free energy reaction barrier at 298 K for H2O formation to be 0.25 eV for an external potentialbelow U = 0.87 V and 0.41 eV at U = 1.23 V, in good agreement with exptl. values of 0.22 eV and 0.44 eV, resp. Withthe mechanism now fully understood, the authors can use this now validated methodol. to examine the changes uponalloying and surface modifications to increase the rate by reducing the barrier for H2O formation.~11 Citings

64. Method for studying high temperature aqueous electrochemical systems: Methanol and glycerol oxidation

By Holm, Thomas; Dahlstroem, Per Kristian; Burheim, Odne S.; Sunde, Svein; Harrington, David A.; Seland, FrodeFrom Electrochimica Acta (2016), 222, 1792-1799. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2016.11.130

A method for high purity aq. electrochem. expts. at temps. above the normal b.p. of water and at temps. up to 140 °C isdescribed. A three-electrode cell in a self-pressurized glass autoclave is heated in an oil bath. Slow ramping of thetemp. allows efficient acquisition of kinetic parameters such as activation energies, oxidn. onset potentials and Tafelslopes by using cyclic voltammetry. The oxidn. of two org. alcs. with different volatilities, methanol (high volatility) andglycerol (low volatility), are studied to demonstrate the capabilities of the method. Methanol oxidn. on platinum is foundto have a similar mechanism at all temps., with either dissociative adsorption of water or dissociative adsorption ofmethanol as the rate-detg. step. In the case of glycerol oxidn. on platinum, the mechanism changes at 110 °C. At lowtemps. dissociative adsorption of water or dissociative adsorption of glycerol is suggested to be the rate-detg. step. Athigher temps., a significant decrease in onset potential was obsd. and the glycerol is suggested to selectively oxidize toglyceraldehyde or dihydroxyacetone, with dissociative glycerol adsorption as the rate-detg. step.~5 Citings

65. Influence of artificially aged gas diffusion layers on the water management of polymer electrolyte membranefuel cells analyzed with in-operando synchrotron imaging

By Arlt, Tobias; Klages, Merle; Messerschmidt, Matthias; Scholta, Joachim; Manke, IngoFrom Energy (Oxford, United Kingdom) (2017), 118, 502-511. Language: English, Database: CAPLUS,DOI:10.1016/j.energy.2016.10.061

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The influence of artificial ageing of gas diffusion layers (GDLs) on the cell performance was investigated using highresoln. synchrotron radiog. State-of-the-art GDLs of the type SIGRACET SGL 25BC were aged for 0 h, 16 h and 24 h ina hydrogen peroxide soln. before they were assembled in the fuel cells. In-operando radiog. measurements werecombined with voltage and contact angle measurements. Correlations between applied ageing conditions, GDL watersatn. and cell performance were revealed. Hereby, all cell operating conditions were tested several times to est. thereproducibility of in-operando radiog. fuel cell measurements. Water films at the GDL-membrane and at the GDL-flowfield interfaces were found and attributed to MPL cracks and large pores in the GDL structure. The combination of thesecracks and pores are assumed to play a crucial role for blocked gas paths, leading to an undersupply with reactants andan increased humidification of the membrane. It is shown that water agglomerations directly impact the membraneresistance. We assume that the hydrophobicity of the fibers inside the GDL is more important for the cell performancethan water agglomerations at the membrane-GDL interface.~13 Citings

66. A comparative DFT study of oxygen reduction reaction on mononuclear and binuclear cobalt and ironphthalocyanines

By Chen, Xin; Li, Mengke; Yu, Zongxue; Ke, QiangFrom Russian Journal of Physical Chemistry A (2016), 90(12), 2413-2417. Language: English, Database: CAPLUS,DOI:10.1134/S0036024416120323

The oxygen redn. reaction (ORR) catalyzed by mononuclear and planar binuclear cobalt (CoPc) and iron phthalocyanine(FePc) catalysts is investigated in detail by d. functional theory (DFT) methods. The calcn. results indicate that the ORRactivity of Fe-based Pcs is much higher than that of Co-based Pcs, which is due to the fact that the former could catalyze4e- ORRs, while the latter could catalyze only 2e- ORRs from O2 to H2O2. The original high activities of Fe-based Pcscould be attributed to their high energy level of the HOMO (HOMO), which could lead to the stronger adsorption energybetween catalysts and ORR species. Nevertheless, the HOMO of Co-based Pcs is the ring orbital, not the 3d Co orbital,thereby inhibiting the electron transfer from metal to adsorbates. Furthermore, compared with mononuclear FePc, theplanar binuclear FePc has more stable structure in acidic medium and more suitable adsorption energy of ORR species,making it a promising non-precious electrocatalyst for ORR.~5 Citings

67. The electronic structure of alloxan monohydrate. Spectroscopic and density functional synergic approach

By Elroby, Shaaban A.; Aziz, Saadullah G.; Hilal, Rifaat H.From Journal of Molecular Structure (2017), 1130, 487-496. Language: English, Database: CAPLUS,DOI:10.1016/j.molstruc.2016.10.069

Quant. interpretation and assignments of the electronic absorption spectra, vibrational and 1- and two-dimensional NMRspectra of alloxan, are detailed. A synergic anal. based on DFT and TD-DFT calcns. and the exptl. findings areperformed. Attempt is made to relate these spectral findings to the electronic structure of alloxan. The computedelectronic spectrum predicted three well defined bands. Natural transition orbital anal. indicate an intramol. chargetransfer from npπ orbital of the water oxygen atom resulting in the short wavelength nπ* at ∼200 nm. Also, UV-photoabsorption cross section for alloxan and its monohydrate are simulated. The spectrum, composed of 10 excitedstates, was simulated with the nuclear ensemble approxn., sampling a Wigner distribution with 300 points. The FTIRspectrum of alloxan, measured in the solid state as KBr pellets is reported and is computed at the DFT/B3LYP/6-311++G** level of theory. All obsd. vibrations are assigned. The 600 MHz 1- and two-dimensional COSY, 1H NMRspectra of alloxan, measured in DMSO, are reported and analyzed and computed theor. using the GIAO method.Hydrogen-bond interactions are responsible for remarkable downfield shift of 1H NMR peaks for alloxan.~0 Citings

68. 1,2-Shift of Element-Centered Groups (RnE) in Carbenoid Anions [RnECF2CFCl]- and its Relevance forNucleophilic Vinylic Substitution: a DFT Study

By Sazonov, Petr K.; Gloriozov, Igor P.; Oprunenko, Yuri F.; Beletskaya, Irina P.From ChemistrySelect (2016), 1(12), 3384-3396. Language: English, Database: CAPLUS,DOI:10.1002/slct.201600649

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The 1,2-shift of β-substituent to the carbenic or carbenoid center is one of the primary reaction pathways for theseintermediates. In the present work the 1,2-shift of various element-centered groups in carbenoid anions [RnECF2CFCl]-(E = C, N, Si, Ge, Sn, P, As, Sb, S, Se, Te, R=Me) is for the first time examd. with the help of d. functional theory calcns.The calcns. were performed on the models of free carbenoid anions [RnECF2CFCl]- and their Na+ and [NMe4]+ salts. Inall cases the 1,2-shift of the RnE-groups formed by the elements of the third and subsequent periods was calcd. to bemuch more facile than for carbon-centered groups. Calcd. ∆G‡ are as low as 4-6 kcal/mol for the 5-th period Me3Sn- andMe2Sb groups. An even more facile 1,2-shift precludes the existence of the corresponding β-element substitutedcarbenes. Periodicity trends, correlation anal. and NBO anal. of the transition state structures were used to discriminatebetween different intrinsic mechanisms. In free carbenoid anions the main mechanisms of 1,2-shift of RnE-groups are:(a) electrophilic shift of R3E- (E = Si, Ge, Sn) and Ph-groups; (b) nucleophilic shift of RS- group (c) dyotropic-typepathway for RS-, RSe-, RO-, R2N and R3C- groups. In carbenoid ion pairs: (a) nucleophilic shift of RnE- (E = Si, Ge, Sn,P, As, Sb) and Re(CO)5- groups; (b) nucleophilic substitution involving the lone pair of RS-, RSe- and R2N- groups.~1 Citing

69. Evidence of a Nitrene Tunneling Reaction: Spontaneous Rearrangement of 2-Formyl Phenylnitrene to anImino Ketene in Low-Temperature Matrixes

By Nunes, Claudio M.; Knezz, Stephanie N.; Reva, Igor; Fausto, Rui; McMahon, Robert J.From Journal of the American Chemical Society (2016), 138(47), 15287-15290. Language: English, Database:CAPLUS, DOI:10.1021/jacs.6b07368

Triplet 2-formyl phenylnitrene was generated by photolysis of 2-formyl phenylazide isolated in Ar, Kr, and Xe matrixes andcharacterized by IR, UV-visible, and EPR spectroscopies.Upon generation at 10 K, the triplet nitrene spontaneouslyrearranges in the dark to singlet 6-imino-2,4-cyclohexadien-1-ketene on the time scale of several hours. The intramol. [1,4] Hatom shift from the nitrene to the imino ketene occurs bytunneling, on the triplet manifold, followed by intersystemcrossing. This case constitutes the first direct evidence of atunneling reaction involving a nitrene.

~11 Citings

70. Quantum Scattering Calculations of Transport Properties for the H-N2 and H-CH4 Collision Pairs

By Dagdigian, Paul J.From Journal of Physical Chemistry A (2016), 120(40), 7793-7799. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpca.6b08232

Transport properties for collisions of hydrogen atoms with mol.nitrogen and methane were calcd. through close-couplingquantum scattering calcns. For these calcns., potential energysurfaces for the interaction of H atoms with these mols., withtheir geometries fixed at the resp. equil. structures, wereobtained with a coupled cluster method that included single,double, and (perturbatively) triple excitations [RCCSD(T)]. Thecomputed transport properties for H-N2 were found to besimilar in magnitude to those computed in a previous study butsignificantly different from those obtained through theconventional approach that employs isotropic Lennard-Jones(LJ) (12-6) potentials. The differences in the transportproperties for H-CH4 computed in this work and those estd.with isotropic LJ potentials are somewhat smaller.

~1 Citing

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71. Conformer-specific hydrogen atom tunnelling in trifluoromethylhydroxycarbene

By Mardyukov, Artur; Quanz, Henrik; Schreiner, Peter R.From Nature Chemistry (2017), 9(1), 71-76. Language: English, Database: CAPLUS, DOI:10.1038/nchem.2609

Conformational control of org. reactions is at the heart of the biomol. sciences. To achieve a particular reactivity, one ofmany conformers may be selected, for instance, by a (bio)catalyst, as the geometrically most suited and appropriatelyreactive species. The equilibration of energetically close-lying conformers is typically assumed to be facile and lessenergetically taxing than the reaction under consideration itself: this is termed the 'Curtin-Hammett principle'. Here, weshow that the trans conformer of trifluoromethylhydroxycarbene preferentially rearranges through a facile quantum-mech.hydrogen tunnelling pathway, while its cis conformer is entirely unreactive. Hence, this presents the first example of aconformer-specific hydrogen tunnelling reaction. The Curtin-Hammett principle is not applicable, due to the high barrierbetween the two conformers.~16 Citings

72. Potential energy surfaces from high fidelity fitting of ab initio points: the permutation invariant polynomial -neural network approach

By Jiang, Bin; Li, Jun; Guo, HuaFrom International Reviews in Physical Chemistry (2016), 35(3), 479-506. Language: English, Database: CAPLUS,DOI:10.1080/0144235X.2016.1200347

With advances in ab initio theory, it is now possible to calc. electronic energies within chem. (<1 kcal/mol) accuracy.However, it is still challenging to represent faithfully a large no. of ab initio points with a multidimensional anal. functionover a large configuration space, which is needed for accurate dynamical studies. In this Review, we discuss our recentwork on a new potential-fitting approach based on artificial neural networks, which are ultra-flexible in representing anymultidimensional real functions. A unique feature of our neural network approach is how the symmetries, particularlythose assocd. with the exchange of identical atoms in the system, are enforced. To this end, symmetry functions in theform of symmetrised monomials that satisfy a particular type of symmetry possessed by the system are used in the inputlayer of the neural network. This approach is rigorous, accurate, and efficient. It is also simple to implement, requiringno modification of the neural network routines. Its applications to the construction of multi-dimensional potential energysurfaces in many gas phase and gas-surface systems as surveyed here.~107 Citings

73. Theoretical modeling of polymer electrolyte membranes

By Zhou, Su; Pei, Fenglai; De Lile, JeffreyEdited By:Fang, JianhuaFrom Electrochemical Polymer Electrolyte Membranes (2015), 539-621. Language: English, Database: CAPLUS,DOI:10.1201/b18369-13

A review. This chapter will focus on the modeling of membrane electrode assemble and its polymer electrolytemembrane. As an extension, application of membranes in other cases will be recommended, such as in lithium battery,vanadium redox flow battery (VRFB), chlor-alkali electrolysis, water electrolysis, and solar cell. Finally, several typicalexamples will be given, including Pt and Pt alloy simulation with d. functional theory (DFT), water formation and Ptadsorption on carbon reactive force field simulation, and coarse-grained simulations.~0 Citings

74. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension

By Greene, Samuel M.; Shan, Xiao; Clary, David C.From Journal of Chemical Physics (2016), 144(24), 244116/1-244116/14. Language: English, Database: CAPLUS,DOI:10.1063/1.4954840

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Semiclassical Transition State Theory (SCTST), a method for calcg. rate consts. of chem. reactions, offers gains incomputational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST,reaction probabilities are calcd. from third and fourth potential derivs. along all vibrational degrees of freedom. However,the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to largersystems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivs. along thereaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivs. are obtained fromnumerical ab initio Hessian matrix calcns. at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied toimprove the accuracy of these derivs. Reaction barriers are calcd. at the CCSD(T)/cc-pVTZ level. Results from FDSCTST agree with results from previous theor. and exptl. studies when Richardson extrapolation is applied. Results fromour implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calcns. in addn. to those forconventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency ofthe 1-D method suggest its potential as a means of approximating rate consts. for systems too large for existing quantumscattering methods. (c) 2016 American Institute of Physics.~7 Citings

75. How theory and simulation can drive fuel cell electrocatalysis

By Eslamibidgoli, Mohammad J.; Huang, Jun; Kadyk, Thomas; Malek, Ali; Eikerling, MichaelFrom Nano Energy (2016), 29, 334-361. Language: English, Database: CAPLUS, DOI:10.1016/j.nanoen.2016.06.004

Over the last decade, theory and modeling have become essential tools to navigate the parameter space that governsactivity and stability of electrocatalyst systems for polymer electrolyte fuel cells. This perspective covers essentialphenomena from at. scale to nanoscale and discusses the impact of the key parameters at play. It is centered aroundthe development of first-principles electrochem. methods as a foremost goal in the field. The general modelingframework entails at its core a self-consistency problem that must be solved to relate the metal phase potential todescriptors of catalyst activity and stability. D. functional theory has captured a central role in this rapidly evolving field.The article puts more than usual emphasis on aspects of the multifaceted challenges in fuel cell electrocatalysis that atpresent lie beyond the capabilities of d. functional theory; they include metal charging and solvent effects. Following thegeneral discussion of the theor.-computational framework, an approach for "deciphering" the oxygen redn. reaction isdemonstrated; it reconciles reaction pathways and free energy profiles obtained from d. functional theory simulations withkinetic modeling of surface reactions and effective kinetic parameters. Another section dwells on the importance of metalcharging phenomena that are esp. important for the catalytic function of nanoporous media. The penultimate sectionexposes the ambivalent role of Pt oxide formation in modulating catalytic properties for the oxygen redn. reaction as wellas for catalyst corrosion.~27 Citings

76. Ethanol Electro-oxidation on Palladium Revisited Using Polarization Modulation Infrared ReflectionAbsorption Spectroscopy (PM-IRRAS) and Density Functional Theory (DFT): Why Is It Difficult To Break the C-CBond?

By Monyoncho, Evans A.; Steinmann, Stephan N.; Michel, Carine; Baranova, Elena A.; Woo, Tom K.; Sautet, PhilippeFrom ACS Catalysis (2016), 6(8), 4894-4906. Language: English, Database: CAPLUS, DOI:10.1021/acscatal.6b00289

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Insights into the ethanol electro-oxidn. reaction mechanism onpalladium in alk. media are presented combining polarizationmodulation IR reflection absorption spectroscopy (PM-IRRAS)and d. functional theory (DFT) calcns. The synergy betweenPM-IRRAS and DFT calcns. helps to explain why the C-C bondis not broken during ethanol electro-oxidn., and the reactionstops at acetate. Coupling chronoamperometry (CA) with insitu PM-IRRAS enables us to simultaneously identify ethanolelectro-oxidn. products on the catalyst surface and in the bulksoln. We show that, at lower potential, it is possible to breakthe C-C bond on Pd/C in alk. media to form CO2. However, theselectivity is poor, because of competition with the formation ofacetate and other side products, which gets worse at higherpotentials. DFT computations complete the picture using thecomputational hydrogen electrode approach. Thecomputations highlight the pivotal role of the CH3COintermediate that can either undergo a C-C bond scissionyielding CO and then CO2 or that can be oxidized towardCH3COO-. The latter is a dead end in the reaction schemetoward CO2 prodn., since it cannot be easily oxidized norbroken into C1 fragments. However, CH3CO is not the mostfavored intermediate formed from ethanol electro-oxidn. on Pd,hence limiting the prodn. of CO2.

~33 Citings

77. Two-Dimensional Group IV Monochalcogenides: Anode Materials for Li-Ion Batteries

By Karmakar, Sharmistha; Chowdhury, Chandra; Datta, AyanFrom Journal of Physical Chemistry C (2016), 120(27), 14522-14530. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpcc.6b04152

The selection of a suitable electrode material is a fundamentalstep in the development of Li-ion batteries (LIBs) to achieveenhanced performance. In the present study, the feasibility isexplored of monolayers of phosphorene analogs, namely,group IV monochalcogenides (SiS, SiSe, GeS, GeSe, SnS, andSnSe), to serve as anode materials in LIBs by d. functionaltheory (DFT). The exploratory study indicates that lithium bindsefficiently to these monolayers, with Li@SiS and Li@SiSeshowing appreciable stability comparable to that ofphosphorene. The zero-point-energy-cor. min.-energy pathway(MEP) for Li diffusion demonstrates high anisotropy for bothSiS and SiSe, with a low diffusion barrier of ∼0.15 eV along thezigzag direction. Inclusion of corrections due to quantumeffects such as the zero-point energy (ZPE) and quantummech. tunneling (QMT) increases the diffusion rates by 6-10%at room temp. and results in increasingly significantcontributions as the temp. is reduced (40-55% increment at T =100 K). The calcd. theor. capacities for SiS and SiSe are 445.7and 250.44 mA h g-1, resp., which are well above those ofexisting com. available anode materials. Both SiS and SiSepreserve their structural integrity upon lithiation, justifying theirrole as host materials for lithium. A semiconductor → metallictransition is obsd. upon full lithiation for both materials. All ofthese exceptional properties, including low diffusion barrier,moderate to high specific capacity, low open-circuit voltage(OCV), small vol. change, and good elec. cond., suggest thatmonolayer SiS and SiSe could serve as promising electrodematerials in LIBs.

~38 Citings

78. The synthesis of "BCN" diamond materials with different B/N additives under high pressure and hightemperature

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By Sun, Shishuai; Cui, Wen; Jia, Xiaopeng; Ma, Hong-an; Lv, JiangFrom International Journal of Refractory Metals & Hard Materials (2016), 59, 56-60. Language: English, Database:CAPLUS, DOI:10.1016/j.ijrmhm.2016.05.013

The diamond crystals co-doped with B and N atoms were prepd. under high pressure and high temp. (HPHT) tosynthesize "BCN" diamond material. The two kinds of "BCN" diamond materials with different additives have beensynthesized, corresponding to the h-BN, NaN3 and B powder systems, resp. The results showed that the synthesized"BCN" diamonds from h-BN additive are strip-shaped diamonds. However, when the boron and nitrogen sources fromNaN3 and B powder additives were used, the synthesized "BCN" diamonds had traditional hex-octahedron shapes withnon-uniform colors. The results of FTIR and XPS showed that there is stronger B-N bonding in the "BCN" diamondsobtained from Fe-Ni-C-h-BN system than the Fe-Ni-C-NaN3-B system under the synthesis conditions used in theseexpts. The changes of the crystn. medium caused by the different B and N source additives resulted in the differenceboth of synthesis conditions and characteristics of the synthesized "BCN" diamond crystals, leading to the results of ourobservation.~0 Citings

79. Tunnelling in carbonic acid

By Wagner, J. Philipp; Reisenauer, Hans Peter; Hirvonen, Viivi; Wu, Chia-Hua; Tyberg, Joseph L.; Allen, Wesley D.;Schreiner, Peter R.From Chemical Communications (Cambridge, United Kingdom) (2016), 52(50), 7858-7861. Language: English,Database: CAPLUS, DOI:10.1039/C6CC01756H

The cis,trans-conformer of carbonic acid (H2CO3), generated by near-IR radiation, undergoes an unreported quantummech. tunnelling rotamerization with half-lives in cryogenic matrixes of 4-20 h, depending on temp. and host material.First-principles quantum chem. at high levels of theory gives a tunnelling half-life of about 1 h, quite near those measuredfor the fastest rotamerizations.~13 Citings

80. Modeling the oscillative behavior and carbon monoxide removal by current pulsing technique in H2/COmixtures for Pt catalyst layer

By Ozdemir, Mehmet Ozan; Pasaogullari, UgurFrom International Journal of Hydrogen Energy (2016), 41(25), 10854-10869. Language: English, Database: CAPLUS,DOI:10.1016/j.ijhydene.2016.05.055

The main objectives of this study are to investigate the carbon monoxide (CO) poisoning and a mitigation method of high-level CO in a platinum (Pt) catalyst layer using hydrogen (H2)/CO mixt. as the inlet fuel. Two sep. levels of poisoning,1000 and 10,000 ppm CO at the anode fuel, are considered and investigated in detail. For this purpose, a one-dimensional transient model is developed including the diffusion of hydrogen and carbon monoxide, the conservation ofadsorbed species, and ionic and electronic charges. As a result of CO poisoning, oscillations in overpotential andcoverage of adsorbed species are obsd. for 1000 ppm CO level, while the similar situation is not detected for 10,000 ppmCO. Hence, the behavior of oscillations throughout the catalyst layer thickness, and the reasons are explored for thelower concn. case. For 10,000 ppm CO, a mitigation technique, in which c.d. is pulsed from 0.1 to 2.5 A/cm2 for a periodof time, is performed in order to remove the adsorbed CO from the Pt sites. It is concluded that up to 92% of COcoverage within the catalyst layer can be removed, and 70% of the catalyst layer length is detd. to be completely CO-freefollowing the application of current pulsing.~6 Citings

81. Theoretical Modeling and Facile Synthesis of Highly Active Boron-Doped Palladium Catalyst for the OxygenReduction Reaction

By Doan, Tat Thang Vo; Wang, Jingbo; Poon, Kee Chun; Tan, Desmond C. L.; Khezri, Bahareh; Webster, Richard D.;Su, Haibin; Sato, HirotakaFrom Angewandte Chemie, International Edition (2016), 55(24), 6842-6847. Language: English, Database: CAPLUS,DOI:10.1002/anie.201601727

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A highly active alternative to Pt electrocatalysts for the O redn. reaction (ORR), which is the cathode-electrode reaction offuel cells, is sought for higher fuel-cell performance. The theor. modeling reveals that B-doped Pd (Pd-B) weakens theabsorption of ORR intermediates with nearly optimal binding energy by lowering the barrier assocd. with O2 dissocn.,suggesting Pd-B should be highly active for ORR. In fact, Pd-B, facile synthesized by an electroless deposition process,exhibits 2.2 times and 8.8 times higher specific activity and 14 times and 35 times less costly than com. pure Pd and Ptcatalysts, resp. Another computational result is that the surface core level of Pd is neg. shifted by B doping, as confirmedby XPS, and implies that filling the d. of states related to the anti-bonding of O to Pd surfaces with excess electrons fromB doping, weakens the O bonding to Pd and boosts the catalytic activity.~13 Citings

82. Atom Tunneling in Chemistry

By Meisner, Jan; Kaestner, JohannesFrom Angewandte Chemie, International Edition (2016), 55(18), 5400-5413. Language: English, Database: CAPLUS,DOI:10.1002/anie.201511028

A review. Quantum mech. tunneling of atoms is increasingly found to play an important role in many chem.transformations. Exptl., atom tunneling can be indirectly detected by temp.-independent rate consts. at low temp. or byenhanced kinetic isotope effects. In contrast, the influence of tunneling on the reaction rates can be monitored directlythrough computational investigations. The tunnel effect, for example, changes reaction paths and branching ratios,enables chem. reactions in an astrochem. environment that would be impossible by thermal transition, and influencesbiochem. processes.~61 Citings

83. Tuning selectivity of electrochemical reactions by atomically dispersed platinum catalyst

By Choi, Chang Hyuck; Kim, Minho; Kwon, Han Chang; Cho, Sung June; Yun, Seongho; Kim, Hee-Tak; Mayrhofer,Karl J. J.; Kim, Hyungjun; Choi, MinkeeFrom Nature Communications (2016), 7, 10922. Language: English, Database: CAPLUS, DOI:10.1038/ncomms10922

Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (orsingle site) metal centers, but its realization remains challenging so far, because carbon, as the most widely usedelectrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon,simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (i.e., highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form ofhighly dispersed species including site isolated atoms. In the oxygen redn. reaction, this catalyst does not follow aconventional four-electron pathway producing H2O, but selectively produces H2O2 even over extended times withoutsignificant degrdn. of the activity. Thus, this approach constitutes a potentially promising route for producing importantfine chem. H2O2, and also offers opportunities for tuning the selectivity of other electrochem. reactions on various metalcatalysts.~136 Citings

84. Harvest and utilization of chemical energy in wastes by microbial fuel cells

By Sun, Min; Zhai, Lin-Feng; Li, Wen-Wei; Yu, Han-QingFrom Chemical Society Reviews (2016), 45(10), 2847-2870. Language: English, Database: CAPLUS,DOI:10.1039/C5CS00903K

Org. wastes are now increasingly viewed as a resource of energy that can be harvested by suitable biotechnologies.One promising technol. is microbial fuel cells (MFC), which can generate electricity from the degrdn. of org. pollutants.While the environmental benefits of MFC in waste treatment have been recognized, their potential as an energy produceris not fully understood. Although progresses in material and engineering have greatly improved the power output fromMFC, how to efficiently utilize the MFC's energy in real-world scenario remains a challenge. In this review, fundamentalunderstandings on the energy-generating capacity of MFC from real waste treatment are provided and the challengesand opportunities are discussed. The limiting factors restricting the energy output and impairing the long-term reliabilityof MFC are also analyzed. Several energy storage and in situ utilization strategies for the management of MFC's energyare proposed, and future research needs for real-world application of this approach are explored.~63 Citings

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85. Assessing a First-Principles Model of an Electrochemical Interface by Comparison with Experiment

By Steinmann, Stephan N.; Sautet, PhilippeFrom Journal of Physical Chemistry C (2016), 120(10), 5619-5623. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpcc.6b01938

Electrified interfaces are central for electrocatalysis, batteries,and mol. electronics. Exptl. characterization of these complexinterfaces with at. resoln. is highly challenging. First-principlesmodeling could provide a link between the measurablequantities and an at. scale understanding. However, suchsimulations are far from straightforward. Although approachesthat include the effect of the potential and the electrolyte havebeen proposed, detailed validation has been scarce and"indirect" since atomically resolved exptl. studies of systemsthat can be convincingly simulated are scarce. We introducehere the adsorption of pyridine on Au(111) as a convenient andrelevant model: the adsorption mode of pyridine switches as afunction of the electrochem. potential. We demonstrate that theprimitive surface charging model gives qual. correct results at alow complexity. For quant. agreement, however, the modelneeds to include a more realistic description of the elec. doublelayer. Approximating the latter through the linearized Poisson-Boltzmann equation leads to a quant. improvement, loweringthe error in the transition potential from 1 V to an acceptable0.3 V. Hence, we demonstrate the qual. usefulness of thesurface charging method and the excellent agreement that canbe obtained by slightly more sophisticated electrolyte models.

~28 Citings

86. An investigation of one- versus two-dimensional semiclassical transition state theory for H atom abstractionand exchange reactions

By Greene, Samuel M.; Shan, Xiao; Clary, David C.From Journal of Chemical Physics (2016), 144(8), 084113/1-084113/13. Language: English, Database: CAPLUS,DOI:10.1063/1.4942161

We investigate which terms in Reduced-Dimensionality Semiclassical Transition State Theory (RD SCTST) contributemost significantly in rate const. calcns. of hydrogen extn. and exchange reactions of hydrocarbons. We also investigatethe importance of deep tunneling corrections to the theory. In addn., we introduce a novel formulation of the theory inJacobi coordinates. For the reactions of H atoms with methane, ethane, and cyclopropane, we find that a one-dimensional (1-D) version of the theory without deep tunneling corrections compares well with 2-D SCTST results andaccurate quantum scattering results. For the "heavy-light-heavy" H atom exchange reaction between CH3 and CH4,deep tunneling corrections are needed to yield 1-D results that compare well with 2-D results. The finding that accuraterate consts. can be obtained from derivs. of the potential along only one dimension further validates RD SCTST as acomputationally efficient yet accurate rate const. theory. (c) 2016 American Institute of Physics.~7 Citings

87. Interaction of p-benzoquinone with hemoglobin in smoker's blood causes alteration of structure and loss ofoxygen binding capacity

By Ghosh, Arunava; Banerjee, Santanu; Mitra, Amrita; Muralidharan, Monita; Roy, Bappaditya; Banerjee, Rajat;Mandal, Amit Kumar; Chatterjee, Indu B.From Toxicology Reports (2016), 3, 295-305. Language: English, Database: CAPLUS,DOI:10.1016/j.toxrep.2016.02.001

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Cigarette smoke (CS) is an important source of morbidity and early mortality worldwide. Besides causing various life-threatening diseases, CS is also known to cause hypoxia. Chronic hypoxia would induce early aging and prematuredeath. Continuation of smoking during pregnancy is a known risk for the unborn child. Although carbon monoxide (CO)is considered to be a cause of hypoxia, the effect of other component(s) of CS on hypoxia is not known. Here we showby immunoblots and mass spectra analyses that in smoker's blood p-benzoquinone (p-BQ) derived from CS formscovalent adducts with cysteine 93 residues in both the β chains of Hb (Hb) producing Hb-p-BQ adducts. UV-vis spectraand CD spectra analyses show that upon complexation with p-BQ the structure of Hb is altered. Compared tononsmoker's Hb, the content of α-helix decreased significantly in smoker's Hb (p = 0.0224). p-BQ also inducesaggregation of smoker's Hb as demonstrated by SDS-PAGE, dynamic light scattering and at. force microscopy.Alteration of Hb structure in smoker's blood is accompanied by reduced oxygen binding capacity. Our results provide thefirst proof that p-BQ is a cause of hypoxia in smokers. We also show that although both p-BQ and CO are responsiblefor causing hypoxia in smokers, exposure to CO further affects the function over and above that produced by Hb-p-BQadduct.~3 Citings

88. Manganese Compounds as Water-Oxidizing Catalysts: From the Natural Water-Oxidizing Complex toNanosized Manganese Oxide Structures

By Najafpour, Mohammad Mahdi; Renger, Gernot; Holynska, Malgorzata; Moghaddam, Atefeh Nemati; Aro, Eva-Mari;Carpentier, Robert; Nishihara, Hiroshi; Eaton-Rye, Julian J.; Shen, Jian-Ren; Allakhverdiev, Suleyman I.From Chemical Reviews (Washington, DC, United States) (2016), 116(5), 2886-2936. Language: English, Database:CAPLUS, DOI:10.1021/acs.chemrev.5b00340

All cyanobacteria, algae, and plants use a similar water-oxidizing catalyst for water oxidn. This catalyst is housed inPhotosystem II, a membrane-protein complex that functions asa light-driven water oxidase in oxygenic photosynthesis. Wateroxidn. is also an important reaction in artificial photosynthesisbecause it has the potential to provide cheap electrons fromwater for hydrogen prodn. or for the redn. of carbon dioxide onan industrial scale. The water-oxidizing complex ofPhotosystem II is a Mn-Ca cluster that oxidizes water with alow overpotential and high turnover frequency no. of up to 25-90 mols. of O2 released per s. In this Review, we discuss theat. structure of the Mn-Ca cluster of the Photosystem II water-oxidizing complex from the viewpoint that the underlyingmechanism can be informative when designing artificial water-oxidizing catalysts. This is followed by consideration offunctional Mn-based model complexes for water oxidn. and theissue of Mn complexes decompg. to Mn oxide. We thenprovide a detailed assessment of the chem. of Mn oxides byconsidering how their bulk and nanoscale properties contributeto their effectiveness as water-oxidizing catalysts.

~211 Citings

89. Predicting Reaction Mechanisms and Potentials in Acid and Base from Self-Consistent Quantum Theory:H(ads) and OH(ads) Deposition on the Pt(111) Electrode

By Zhao, Meng; Anderson, Alfred B.From Journal of Physical Chemistry Letters (2016), 7(4), 711-714. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpclett.5b02826

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It has been shown recently that when reactants and productsare well modeled within a comprehensive self-consistent theoryfor the electrochem. interface, accurate predictions are possiblefor reversible potentials, Urev, in acid electrolyte for reactionssuch as redn. of H+(aq) to form under potential depositedH(ads) and oxidn. of an OH bond of H2O(ads) to depositOH(ads). Predictions are based on calcd. Gibbs energies forthe reactant and product being equal at the reversible potential,which is the potential at the crossing point for reaction andproduct Gibbs energies, plotted as functions of electrodepotential. In this Letter, it is demonstrated that the samecapability holds for these reactions in basic electrolyte. Thisdemonstration opens up the opportunity for predictions ofreversible potentials and mechanisms for other electrocatalyticreactions in base.

~4 Citings

90. Photodegradation of malachite green dye catalyzed by Keggin-type polyoxometalates under visible-lightirradiation: Transition metal substituted effects

By Liu, Chun-Guang; Zheng, Ting; Liu, Shuang; Zhang, Han-YuFrom Journal of Molecular Structure (2016), 1110, 44-52. Language: English, Database: CAPLUS,DOI:10.1016/j.molstruc.2016.01.015

Keggin-type polyoxometalates (POMs) (NH4)3[PW12O40] and its mono-transition-metal-substituted species(NH4)5[PW11O39MII(H2O)] (M = Mn, Fe, Co, Ni, Cu, Zn) were synthesized and used as photocatalyst to activate O2 forthe degrdn. of dye mol. under visible-light irradn. Because of the strong adsorption on the surface of POM catalyst,malachite green (MG) mol. was employed as a mol. probe to test their photocatalytic activity. The photodegrdn. studyshows that introduction of transition metal ion increases the degrdn. of MG in the following order: Mn < Fe < Co <[PW12O40]3- < Ni < Cu < Zn, which indicates that the photocatalytic activity of these POMs is sensitive to the transitionmetal substituted effects. Electronic structure anal. based on the d. functional theory calcns. shows that a moderatedecrease of oxidizing ability of POM catalyst may improve the photocatalytic activity in the degrdn. of dye mol. undervisible-light irradn. Meanwhile, intermediate products about the photocatalytic oxidn. of MG mol. were proposed from gaschromatograph mass spectrometer anal.~19 Citings

91. Thermal and kinetic studies of the polynuclear coordination compound obtained through the reaction of 1,3-propanediol with Ni(NO3)2 · 6 H2O

By Niculescu, Mircea; Magda, Angela; Jurca, Marius; Costea, Liviu; Pode, VasileFrom Revista de Chimie (Bucharest, Romania) (2015), 66(8), 1217-1221. Language: English, Database: CAPLUS

Our paper presents the exptl. results of the thermal anal. of Ni(ll)-polynuclear coordination compd. having as ligand 3-hydroxypropionate anion (L), which is oxidn. product of 1,3-propanediol. The reaction between 1,3-propanediol andNi(NO3)2 × 6H2O occurs, under specific working conditions, with the oxidn. of 1,3-propanediol to the 3-hydroxypropronate anion (HO-CH2-CH2-COO). The thermal properties of the synthesized polynuclear coordinationcompd. have been investigated by TG, DTG and DTA. The kinetic anal. of the nonisothermal data has been carried outthrough the isoconversional method. The simple oxide obtained through thermolysis was characterized by IR, X-rayspectroscopy, SEM (SEM) and elemental anal.~1 Citing

92. Role of Heavy Atom Tunneling in Myers-Saito Cyclization of Cyclic Enyne-Cumulene Systems

By Karmakar, Sharmistha; Datta, AyanFrom Journal of Physical Chemistry B (2016), 120(5), 945-950. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpcb.5b12465

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Direct dynamics calcn. using canonical variational transitionstate theory (CVT) inclusive of small curvature tunneling (SCT)reveals heavy atom tunneling in Myers-Saito cyclization of 10-and 9-membered cyclic enyne-cumulene systems like 1,6-didehydro[10]annulene and deriv. of neocarzinostatin, resp.The pure d. functional theory functional, BLYP at a 6-31+G(d,p) basis set reproduce the obsd. reaction energies andbarriers within 1.0 kcal/mol. The calcd. rate consts. ofcyclization inclusive of heavy atom tunneling (kCVT+SCT = 3.26 ×10-4 s-1 at 222 K; t1/2 = 35 min) are in excellent agreement withexpts. (t1/2 ∼ 21-31 min). Both primary and secondary kineticisotope effect (KIE) become enhanced significantly uponinclusion of quantum mech. tunneling. An Arrhenius plot of KIEshows measurable curvature at the exptl. temp. of 222 K. Thetranslation vector for the cyclization reactions in the transition-states (TS) show significant motion of primary and secondarycarbon atoms explaining the origin of large KIE.

~11 Citings

93. Reactions that involve tunneling by carbon and the role that calculations have played in their study

By Borden, Weston ThatcherFrom Wiley Interdisciplinary Reviews: Computational Molecular Science (2016), 6(1), 20-46. Language: English,Database: CAPLUS, DOI:10.1002/wcms.1235

Chem. reactions can proceed either by passage of the reactants over the reaction barrier or by tunneling through thebarrier. During the past 40 years, it has become clear that tunneling, not only by hydrogen but also by carbon, can occur,provided that the reaction barrier is narrow and that tunneling occurs at energies that are not too far below the top of thebarrier. This review discusses those reactions in which tunneling by carbon has been predicted to occur by calcns.and/or been found to occur by expts. WIREs Comput Mol Sci 2016, 6:20-46. doi: 10.1002/wcms.1235 For furtherresources related to this article, please visit the .~22 Citings

94. Synthesis of LaF3 nanosheets with high fluorine mobility investigated by NMR relaxometry and diffusometry

By Gulina, L. B.; Schafer, M.; Privalov, A. F.; Tolstoy, V. P.; Murin, I. V.From Journal of Chemical Physics (2015), 143(23), 234702/1-234702/7. Language: English, Database: CAPLUS,DOI:10.1063/1.4937415

Ionically conducting lanthanum fluoride (LaF3), displaying a nanoscopic lamellar structure, has been synthesized at thesurface of an aq. soln. of LaCl3 and HF. The structure and the chem. compn. of the conductor have been analyzed bySEM, electron probe microanal., X-ray powder diffraction, FTIR, and 19F magic angle spinning NMR spectroscopy. Thefluorine dynamics have been studied by NMR diffusometry and relaxometry in a temp. range from room temp. up to 875K. The fluorine self-diffusion coeff. of the nanostructured LaF3 is about two orders of magnitude larger than that of bulkLaF3. This material is highly promising for many typical applications of fluorine ionic systems. (c) 2015 AmericanInstitute of Physics.~5 Citings

95. Submolecular regulation of cell transformation by deuterium depleting water exchange reactions in thetricarboxylic acid substrate cycle

By Boros, Laszlo G.; D'Agostino, Dominic P.; Katz, Howard E.; Roth, Justine P.; Meuillet, Emmanuelle J.; Somlyai,GaborFrom Medical Hypotheses (2016), 87, 69-74. Language: English, Database: CAPLUS,DOI:10.1016/j.mehy.2015.11.016

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The naturally occurring isotope of hydrogen (1H), deuterium (2H), could have an important biol. role. Deuterium depletedwater delays tumor progression in mice, dogs, cats and humans. Hydratase enzymes of the tricarboxylic acid (TCA)cycle control cell growth and deplete deuterium from redox cofactors, fatty acids and DNA, which undergo hydride ionand hydrogen atom transfer reactions. A model is proposed that emphasizes the terminal complex of mitochondrialelectron transport chain reducing mol. oxygen to deuterium depleted water (DDW); this affects gluconeogenesis as wellas fatty acid oxidn. In the former, the DDW is thought to diminish the deuteration of sugar-phosphates in the DNAbackbone, helping to preserve stability of hydrogen bond networks, possibly protecting against aneuploidy and resistingstrand breaks, occurring upon exposure to radiation and certain anticancer chemotherapeutics. DDW is proposed hereto link cancer prevention and treatment using natural ketogenic diets, low deuterium drinking water, as well as DDWprodn. as the mitochondrial downstream mechanism of targeted anti-cancer drugs such as Avastin and Glivec. The roleof 2H in biol. is a potential missing link to the elusive cancer puzzle seemingly correlated with cancer epidemiol. inwestern populations as a result of excessive 2H loading from processed carbohydrate intake in place of natural fatconsumption.~8 Citings

96. Modeling of electron transfer across electrochemical interfaces: State-of-the art and challenges for quantumand computational chemistry

By Nazmutdinov, Renat R.; Bronshtein, Michael D.; Zinkicheva, Tamara T.; Glukhov, Dmitrii V.From International Journal of Quantum Chemistry (2016), 116(3), 189-201. Language: English, Database: CAPLUS,DOI:10.1002/qua.25035

State-of-the-art in the area of quantum-chem. modeling of electron transfer (ET) processes at metal electrode/electrolytesoln. interfaces is reviewed. Emphasis is put on key quantities which control the ET rate (activation energy, transmissioncoeff., and work terms). Orbital overlap effect in electrocatalysis is thoroughly discussed. The advantages anddrawbacks of cluster and periodical slab models for a metal electrode when describing redox processes are analyzed aswell. It is stressed that reliable quant. estns. of the rate consts. of interfacial charge transfer reactions are hardlypossible, while predictions of qual. interesting effects are more valuable. © 2015 Wiley Periodicals, Inc.~16 Citings

97. Mode specific dynamics of the H2 + CH3 → H + CH4 reaction studied using quasi-classical trajectory andeight-dimensional quantum dynamics methods

By Wang, Yan; Li, Jun; Chen, Liuyang; Lu, Yunpeng; Yang, Minghui; Guo, HuaFrom Journal of Chemical Physics (2015), 143(15), 154307/1-154307/7. Language: English, Database: CAPLUS,DOI:10.1063/1.4933240

An eight-dimensional quantum dynamical model is proposed and applied to the title reaction. The reaction probabilitiesand integral cross sections have been detd. for both the ground and excited vibrational states of the two reactants. Theresults indicate that the H2 stretching and CH3 umbrella modes, along with the translational energy, strongly promote thereactivity, while the CH3 sym. stretching mode has a negligible effect. The obsd. mode specificity is confirmed by full-dimensional quasi-classical trajectory calcns. The mode specificity can be interpreted by the recently proposed suddenvector projection model, which attributes the enhancement effects of the reactant modes to their strong couplings withthe reaction coordinate at the transition state. (c) 2015 American Institute of Physics.~5 Citings

98. Physical Organic Chemistry - A Personal Perspective

By Sander, WolframFrom Israel Journal of Chemistry (2016), 56(1), 62-65. Language: English, Database: CAPLUS,DOI:10.1002/ijch.201500047

A review. Phys. org. chem. plays a unifying role in chem. by combining a large variety of exptl. and theor. techniques tocreate simplified, intuitively understandable concepts of chem. processes. The concept of "antiaromaticity" is used todemonstrate how complex expts. may result in general models that allow chemists to predict the chem. and phys.properties of difficult to access mols. and even of transition states. Cyclooctatetraene and the fluorenyl cation are usedas examples to illustrate some working methods of phys. org. chem.~1 Citing

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99. Infrared laser Stark spectroscopy of hydroxymethoxycarbene in 4He nanodroplets

By Broderick, Bernadette M.; Moradi, Christopher P.; Douberly, Gary E.From Chemical Physics Letters (2015), 639, 99-104. Language: English, Database: CAPLUS,DOI:10.1016/j.cplett.2015.09.001

Hydroxymethoxycarbene, MeO(HO)C:, was produced via pyrolysis of monomethyl oxalate and subsequently isolated in4He nanodroplets. IR laser spectroscopy reveals two rotationally resolved a,b-hybrid bands in the OH-stretch region,which are assigned to trans,trans- and cis,trans-rotamers. Stark spectroscopy of the trans,trans-OH stretch bandprovides the a-axis inertial component of the dipole moment, µa = 0.62(7) D. The computed equil. dipole moment agreeswell with the expectation value detd. from expt., consistent with a semi-rigid MeO(HO)C: backbone computed via apotential energy scan at the B3LYP/cc-pVTZ level of theory, which reveals substantial conformer interconversion barriersof ≈17 kcal/mol.~0 Citings

100. DFT calculations on electro-oxidations and dissolutions of Pt and Pt-Au nanoparticles

By Jinnouchi, Ryosuke; Suzuki, Kensaku Kodama Takahisa; Morimoto, YuFrom Catalysis Today (2016), 262, 100-109. Language: English, Database: CAPLUS,DOI:10.1016/j.cattod.2015.08.020

DFT calcns. were carried out on electro-oxidns. and dissolns. of pure Pt and Pt-Au nanoparticles. Calcns. indicated thatelectro-oxidns. are initiated by OH adsorbate formations at (1 0 0)-edges of the pure Pt nanoparticle of 260 atoms at 0.5V (RHE). The formed OH adsorbates are replaced by O adsorbates at 0.75 V, and the formed O adsorbates aggregateat (1 1 0)-edges of the nanoparticle to form 1-dimensional PtO2 chains. Further increase in the electrode potentialcauses gradual increases in O adsorbates at the facets of the nanoparticle, and the formed O atoms start sinking into thesubsurfaces to form α-PtO2 monolayers at 1.18 V. Calcns. indicated that the edges of the pure Pt nanoparticle werecovered too strongly with the O adsorbates at 0.9 V to allow for adsorptions of oxygen mols. at those surface sites. Ptatoms located at the edges were, therefore, judged to be inactive for oxygen redn. reaction (ORR). The Pt atoms locatedat the edges were also shown to be easily dissolved into the solns. because they do not have strong binding energieswith the particle. Further calcns. on the Pt-Au nanoparticle indicated that the corrosive Pt dissolns. can be suppressedby substitutional introductions of Au atoms at the edges of the nanoparticle without lowering ORR activity.~9 Citings

101. Electrochemical Formation of Reactive Oxygen Species at Pt (111)-A Density Functional Theory Study

By Eslamibidgoli, Mohammad J.; Eikerling, Michael H.From ACS Catalysis (2015), 5(10), 6090-6098. Language: English, Database: CAPLUS,DOI:10.1021/acscatal.5b01154

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D. functional theory was used to investigate the influence of thePt adsorption state on the formation of hydrogen peroxide(H2O2) and hydroxyl radical (.bul.OH) as two important reactiveoxygen species. We generated the free energy diagrams ofredn. sequences involving O2 and H2O2 as reactants andH2O2, .bul.OH, or H2O as products. The Pt (111)-waterinterface was considered in three adsorption states that areencountered in different regions of the electrode potential: anadsorption state with a monolayer of hydrogen (low electrodepotential), a clean surface (intermediate potential), and anadsorption state with 1/3 of a monolayer of oxygen (highpotential). Results reveal a strong impact of surface waterinteractions on the pathways of water oxidn. and oxygen redn.reactions. In agreement with exptl. results reported in theliterature, we found that the oxygen redn. pathway is highlysensitive to the hydrogen coverage. Coverage by onemonolayer hydrogen renders the surface highly hydrophobic,thereby suppressing its activity for the oxygen redn. Therefore,for high hydrogen coverage, the formation of H2O2 by a two-electron pathway becomes a preferred path. We discussresults in the context of radical-initiated chem. degrdn. ofpolymer electrolyte membranes in polymer electrolyte fuel cells.

~14 Citings

102. Insights Gained by Modeling the Kinetics of Archetypal Hydrogen Atom Transfer Reactions: NH3 + ·H H2N·+ H2 and CH4 + ·H H3C· + H2

By Zavitsas, Andreas A.From International Journal of Chemical Kinetics (2015), 47(10), 638-657. Language: English, Database: CAPLUS,DOI:10.1002/kin.20937

Exptl. measurements of the kinetics of the title reactions extend to temp. ranges of 1360 K for the ammonia-hydrogenreaction and of 1602 K for the methane-hydrogen reaction. Curved plots of ln(k) vs. 1/T are obtained. Many theor.calcns. modeling these reactions routinely use tunneling corrections to match expt. The steepness and curvatures of theplots are modeled successfully in this work and are shown to be caused solely by changes in the bond dissocn. energiesof the bonds involved in the reactions without invoking tunneling or any other adjustable parameters. The conclusion thattunneling does not contribute significantly to the rates in the temp. range of the measurements is in stark contrast withthose theor. calcns. invoking large tunneling factors in the exptl. temp. range. Support for the conclusion is provided bytheor. calcns. of harmonic quantum transition state theory implementing instanton theory. There is direct exptl. evidencethat significant tunneling occurs in some H atom transfers, as with isotopomers of H2 + ·H and other H transfers at verylow temps. However, there is no direct exptl. evidence of significant tunneling contributions to the rates of the titlereactions in the temp. range of the measurements. Insights are gained into what specific forces must be overcome bythe enthalpy of activation for reaction to occur.~0 Citings

103. Characterization of the 1,1-HCl Elimination Reaction of Vibrationally Excited CD3CHFCl Molecules andAssignment of Threshold Energies for 1,1-HCl and 1,2-DCl plus 1,1-HF and 1,2-DF Elimination Reactions

By Brown, Timothy M.; Nestler, Matthew J.; Rossabi, Samuel M.; Heard, George L.; Setser, D. W.; Holmes, Bert E.From Journal of Physical Chemistry A (2015), 119(36), 9441-9451. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpca.5b06638

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Vibrationally excited CD3CHFCl mols. with 96 kcal mol-1 ofenergy were generated by the recombination of CD3 andCHFCl radicals in a room-temp. bath gas. The four competingunimol. decompn. reactions, namely, 1,1-HCl and 1,2-DClelimination and 1,1-HF and 1,2-DF elimination, were obsd., andthe individual rate consts. were measured. The productbranching fractions are 0.60, 0.27, 0.09, and 0.04 for 1,2-DCl,1,1-HCl, 1,2-DF, and 1,1-HF elimination, resp. Electronicstructure calcns. were used to define models of the fourtransition states. The statistical rate consts. calcd. from thesemodels were compared to the exptl. rate consts. The assignedthreshold energies with ±2 kcal mol-1 uncertainty are 60, 72,65, and 74 kcal mol-1 for the 1,2-DCl, 1,1-HCl, 1,2-DF, and 1,1-HF reactions, resp. The loose structure of the 1,1-HX transitionstates, which is exemplified by the order of magnitude largerpre-exponential factor relative to the 1,2-HX eliminationreactions, compensates for the high threshold energy; thus, the1,1-HX elimination reaction rates can compete with the 1,2-HXelimination reactions for high levels of vibrational excitation inCD3CHFCl. The 1,1-HCl and 1,1-HF reactions are obsd. viathe CD2=CDF and CD2=CDCl products formed fromisomerization of the CD3CF and CD3CCl carbenes. These D-atom migration reactions are discussed, and the possibility oftunneling is evaluated. The transition states developed fromthe 1,1-HCl and 1,1-HF reactions of CD3CHFCl are comparedto models for the HCl and HF elimination reactions of CHF2Cl,CHFCl2, and CH2FCl.

~5 Citings

104. Metal Free Azide-Alkyne Click Reaction: Role of Substituents and Heavy Atom Tunneling

By Karmakar, Sharmistha; Datta, AyanFrom Journal of Physical Chemistry B (2015), 119(35), 11540-11547. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpcb.5b05758

Metal free click reactions provide an excellent noninvasive toolto modify and understand the processes in biol. systems.Release of ring strain in cyclooctynes on reaction with azideson the formation of triazoles results in small activation energiesfor various intermol. Huisgen reactions (1-9). Substitution ofdifluoro groups at the α, α' position of the cyclooctyne ringenhances the rates of cycloaddns. by 10 and 20 times for Meazide and benzyl azide resp. at room temp. The computed rateenhancement on difluoro substitution using direct dynamicalcalcns. using the canonical variational transition state theory(CVT/CAG) with small curvature tunneling (SCT) correctionsare in excellent agreement with the exptl. results. For theintramol. click reaction (10) notwithstanding its much higheractivation energy, quantum mech. tunneling (QMT) enhancesthe rate of cycloaddn. significantly and increases the N14/N15

primary kinetic isotope effect at 298 K. QMT is shown to berather efficient in 10 due to a thin barrier of ∼2.4 Å. Thepresent study shows that tunneling effects can be significant forintramol. click reactions.

~10 Citings

105. Effect of temperature on the oxygen reduction reaction kinetic at nitrogen-doped carbon nanotubes for fuelcell cathode

By Wong, W. Y.; Daud, W. R. W.; Mohamad, A. B.; Loh, K. S.From International Journal of Hydrogen Energy (2015), 40(35), 11444-11450. Language: English, Database: CAPLUS,DOI:10.1016/j.ijhydene.2015.06.006

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One of the tech. challenges in commercializing proton exchange membrane fuel cell (PEMFC) technol. in this century isrelated to cost redn. of the fuel cell components esp. the cost of the electrochem. catalysts, which are normally noblemetals such as Pt. N doped C nanotubes (NCNT) made by doping N as an n-type dopant in C nanotubes, possesscatalytic activity towards O redn. reaction (ORR). Functionally modified NCNT can become a cheaper alternativeelectrochem. catalyst that is as good as the noble metals such as Pt. Since the efficiency of the fuel cell is dependent oncell temps., this study looks at the effects of the temps. towards ORR at 298-343 K in 0.5 M H2SO4 on the metal-freeNCNT using a thin-film rotating-ring disk electrode (RRDE). The NCNT catalysts were synthesized via CVD withethylenediamine and Fe phthalocyanine and post-treatment process was carried out prior to the anal. The optimum ORRactivity in NCNT was achieved at 50°, beyond which, the ORR activity decreased. To increase ORR activity beyond thistemp., the NCNT should be modified by compositing it with other metal or nonmetal to improve its activity at higher temp.~12 Citings

106. Modeling the HCOOH/CO2 Electrocatalytic Reaction: When Details Are Key

By Steinmann, Stephan N.; Michel, Carine; Schwiedernoch, Renate; Filhol, Jean-Sebastien; Sautet, PhilippeFrom ChemPhysChem (2015), 16(11), 2307-2311. Language: English, Database: CAPLUS,DOI:10.1002/cphc.201500187

The authors' 1st principles simulations of the electrooxidn. of formic acid over Ni identify the reorientation of the formateintermediate and the desorption of CO2 as the rate-limiting steps. Although they are not assocd. with an electrontransfer, these barriers are strongly modified when the electrochem. potential is explicitly accounted for and whenmodeling the influence of the solvent. Hence, such a level of modeling is key to understand the kinetic limitations thatpenalize the reaction.~19 Citings

107. Using Implicit Solvent in Ab Initio Electrochemical Modeling: Investigating Li+/Li Electrochemistry at aLi/Solvent Interface

By Lespes, Nicolas; Filhol, Jean-SebastienFrom Journal of Chemical Theory and Computation (2015), 11(7), 3375-3382. Language: English, Database: CAPLUS,DOI:10.1021/acs.jctc.5b00170

This paper focuses on the use of implicit solvent inelectrochem. d. functional theory (DFT) calcns. We investigateboth the necessity and limits of an implicit solvent polarizablecontinuum model (PCM). In order to recover the properelectrochem. behavior of the surface and, in particular, a properpotential scale, the solvent model is detd. to be mandatory: inthe limit of a high dielec. const., the surface capacitancebecomes independent of the interslab space used in the modeland, therefore, the electrochem. properties become intrinsic ofthe interface structure. We show that the computed surfacecapacitance is not only dependent on the implicit solvent dielec.const., but also on the solvent cavity parameter that should beprecisely tuned. This model is then applied to the Li/electrolyteinterface in order to check its ability to compute thermodn.equil. properties. The use of a purely implicit solvent approachallows the recovery of a more reasonable equil. potential for theLi+/Li redox pair, compared to vacuum approaches, but apotential that it is still off by 1.5 V. Then, the inclusion ofexplicit solvent mols. improves the description of the solvent-Li+chem. bond in the first solvation shell and allows recovery ofthe exptl. value within 100 mV. Finally, we show that the redoxactive center involves the first solvation shell of Li+ , suggestinga particular pathway for the obsd. solvent dissocn. in Li-ionbatteries.

~15 Citings

108. On the tunneling instability of a hypercoordinated carbocation

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By Kozuch, SebastianFrom Physical Chemistry Chemical Physics (2015), 17(26), 16688-16691. Language: English, Database: CAPLUS,DOI:10.1039/C5CP02080H

C(CH3)5 +, a pentacoordinate carbocation, was recently described as a "fleeting" mol., i.e., stable only at low temps.Herein it is shown using theor. methods that, owing to carbon tunneling, the mol. is not persistent even at 0 K. Onepossible way to lengthen its lifespan is by deuterium substitution, in spite of the fact that no bond to hydrogen is broken.~4 Citings

109. A permutationally invariant full-dimensional ab initio potential energy surface for the abstraction andexchange channels of the H + CH4 system

By Li, Jun; Chen, Jun; Zhao, Zhiqiang; Xie, Daiqian; Zhang, Dong H.; Guo, HuaFrom Journal of Chemical Physics (2015), 142(20), 204302/1-204302/6. Language: English, Database: CAPLUS,DOI:10.1063/1.4921412

We report a permutationally invariant global potential energy surface (PES) for the H + CH4 system based on ∼63 000data points calcd. at a high ab initio level (UCCSD(T)-F12a/AVTZ) using the recently proposed permutation invariantpolynomial-neural network method. The small fitting error (5.1 meV) indicates a faithful representation of the ab initiopoints over a large configuration space. The rate coeffs. calcd. on the PES using tunneling cor. transition-state theoryand quasi-classical trajectory are found to agree well with the available exptl. and previous quantum dynamical results.The calcd. total reaction probabilities (Jtot = 0) including the abstraction and exchange channels using the new potentialby a reduced dimensional quantum dynamic method are essentially the same as those on the Xu-Chen-Zhang PES[Chin. J. Chem. Phys. 27, 373 (2014)]. (c) 2015 American Institute of Physics.~23 Citings

110. Role of oxygen-containing species at Pt(111) on the oxygen reduction reaction in acid media

By Gomez-Marin, Ana M.; Feliu, Juan M.From Journal of Solid State Electrochemistry (2015), 19(9), 2831-2841. Language: English, Database: CAPLUS,DOI:10.1007/s10008-015-2850-7

The oxygen redn. reaction (ORR) is one of the fundamental reactions in electrochem. and has been widely studied, butthe mechanistic details of ORR still remain elusive. In this work, the role of electrochem. oxygenated species, such asadsorbed hydroxide, OHads, adsorbed oxygen, Oads, and Pt(111) oxide, PtO, in the ORR dynamics is studied byemploying electrochem. techniques, i.e., combining rotating disk mass-transport control with potential sweep rateperturbation. In this framework, a redn. peak at 0.85 V, EORR, is detected. This peak shows a different electrochem.dynamics than that of Pt(111) oxides. The data anal. suggests that neither OHads nor Oads are the main bottleneck in themechanism. Instead, results support the redn. of a sol. intermediate species as the rate detg. step in the mechanism.On the other hand, PtO species, which are generated at relatively high potentials and are responsible of surfacedisordering, strongly inhibit the ORR as long as they are adsorbed in the electrode surface.~10 Citings

111. Reactive intermediates in 4He nanodroplets: Infrared laser Stark spectroscopy of dihydroxycarbene

By Broderick, Bernadette M.; McCaslin, Laura; Moradi, Christopher P.; Stanton, John F.; Douberly, Gary E.From Journal of Chemical Physics (2015), 142(14), 144309/1-144309/7. Language: English, Database: CAPLUS,DOI:10.1063/1.4917421

Singlet dihydroxycarbene (HOCOH) is produced via pyrolytic decompn. of oxalic acid, captured by helium nanodroplets,and probed with IR laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to eithertrans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical wts., and comparisons toelectronic structure theory calcns. Stark spectroscopy provides the inertial components of the permanent elec. dipolemoments for these rotamers. The dipole components for trans,trans- and trans,cis-rotamers are (µa, µb) = (0.00, 0.68(6))and (1.63(3), 1.50(5)), resp. The IR spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent witha previously proposed pyrolytic decompn. mechanism of oxalic acid and computations of HOCOH torsionalinterconversion and tautomerization barriers. (c) 2015 American Institute of Physics.~0 Citings

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112. Characterization of the 1,1-HF Elimination Reaction from the Competition between the 1,1-HF and 1,2-DFUnimolecular Elimination Reactions of CD3CD2CHF2

By Wormack, Leah N.; McGreal, Meghan E.; McClintock, Corey E.; Heard, George L.; Setser, D. W.; Holmes, Bert E.From Journal of Physical Chemistry A (2015), 119(17), 3887-3896. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpca.5b01129

The recombination of CHF2 and C2D5 radicals was used toproduce CD3CD2CHF2* mols. with 96 kcal mol-1 of vibrationalenergy in a room temp. bath gas. The formation ofCD3CD=CHF and CD3CD=CDF was used to identify the 1,2-DF and 1,1-HF unimol. elimination channels; CD3CD=CDF isformed by isomerization of the singlet-state CD3CD2CFcarbene. The total unimol. rate const. is 1.6 × 106 s-1, and thebranching ratio for 1,1-HF elimination is 0.25. Thresholdenergies of 64 ± 2 and 73 ± 2 kcal mol-1 were assigned to the1,2-DF and 1,1-HF reaction channels. The E and Z isomers of1-fluoropropene were obsd. for each reaction; approx. 30% ofthe CD3CD=CDF mols. derived from 1,1-HF eliminationretained enough energy to undergo cis-trans isomerization.Electronic structure calcns. with d.-functional theory were usedto characterize the transition-state structures and the H atommigration barrier for CD3CD2CF. Adjustment of the rate consts.to account for kinetic-isotope effects suggest that the branchingratio would be 0.20 for 1,1-HF elimination from C2H5CHF2.The results from an earlier study of CD3CHF2 and CH3CHF2are also reinterpreted to assign a threshold energy of 74 kcalmol-1 for the 1,1-HF elimination reaction. Because CHF2CHF2*is generated in the photolysis system, the 1,1-and 1,2-HF-elimination reactions of CHF2CHF2* are discussed. The 1,1-HF channel was identified by trapping the CF2HCF carbenewith cis-butene-2.

~6 Citings

113. Direct dynamics study of the N(4S) + CH3(2A2'') reaction

By Chiba, Sachie; Honda, Tomohiro; Kondo, Manami; Takayanagi, ToshiyukiFrom Computational & Theoretical Chemistry (2015), 1061, 46-51. Language: English, Database: CAPLUS,DOI:10.1016/j.comptc.2015.03.015

Direct dynamics simulations were performed to understand the mechanisms of the N(4S) + CH3 reaction on both thetriplet and singlet potential energy surfaces using the B3LYP/6-31(d, p) method with modified hybrid parameters for theexchange-correlation functional. The hybrid parameters were detd. so as that the stationary-point energy levels on thepotential energy surfaces reproduce those obtained at the CASPT2 results. The trajectories starting from the N(4S) +CH3 reactants on the triplet potential surface mostly lead to the H + H2CN products via the CH3N intermediate. Therelative translation energy distribution of this channel shows that the reaction dynamics is nonstatistical. The trajectorieson the singlet potential energy surface were also propagated from the CH2=NH intermediate structure. We found thatabout 10% of the reactive trajectories showed 'roaming dynamics,' which lead to the H2 + HCN/HNC products throughintramol. hydrogen abstraction.~0 Citings

114. Determination of Spin Inversion Probability, H-Tunneling Correction, and Regioselectivity in the Two-StateReactivity of Nonheme Iron(IV)-Oxo Complexes

By Kwon, Yoon Hye; Mai, Binh Khanh; Lee, Yong-Min; Dhuri, Sunder N.; Mandal, Debasish; Cho, Kyung-Bin; Kim,Yongho; Shaik, Sason; Nam, WonwooFrom Journal of Physical Chemistry Letters (2015), 6(8), 1472-1476. Language: English, Database: CAPLUS,DOI:10.1021/acs.jpclett.5b00527

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We show by expts. that nonheme FeIVO species react withcyclohexene to yield selective hydrogen atom transfer (HAT)reactions with virtually no C=C epoxidn. Straightforward DFTcalcns. reveal, however, that C=C epoxidn. on the S = 2 statepossesses a low-energy barrier and should contributesubstantially to the oxidn. of cyclohexene by the nonhemeFeIVO species. By modeling the selectivity of this two-sitereactivity, we show that an interplay of tunneling and spininversion probability (SIP) reverses the apparent barriers andprefers exclusive S = 1 HAT over mixed HAT and C=Cepoxidn. on S = 2. The model enables us to derive a SIP valueby combining exptl. and theor. results.

~30 Citings

115. Antibacterial action of doped CoFe2O4 nanocrystals on multidrug resistant bacterial strains

By Velho-Pereira, S.; Noronha, A.; Mathias, A.; Zakane, R.; Naik, V.; Naik, P.; Salker, A. V.; Naik, S. R.From Materials Science & Engineering, C: Materials for Biological Applications (2015), 52, 282-287. Language:English, Database: CAPLUS, DOI:10.1016/j.msec.2015.03.046

The bactericidal effect of pristine and doped cobalt ferrite nanoparticles has been evaluated against multiple drugresistant clin. strains by assessing the no. of colony-forming units (CFU). Monophasic polycryst. ferrites have beenprepd. by the malate-glycolate sol-gel autocombustion method as confirmed by the X-ray diffraction study. Variouschanges occurring during the preparative stages have been demonstrated using TG-DTA anal. which is wellcomplemented by the FTIR spectroscopy. The antibacterial studies carried out demonstrate a bactericidal effect of thenanoparticles wherein the no. of CFU has been found to decrease with doping. Cellular distortions have been revealedthrough SEM. Variation in the no. of CFU with dopant type is also reported herein.~9 Citings

116. A DFT study of oxygen reduction reaction mechanism over O-doped graphene-supported Pt4, Pt3Fe andPt3V alloy catalysts

By Jin, Nian; Han, Jinyu; Wang, Hua; Zhu, Xinli; Ge, QingfengFrom International Journal of Hydrogen Energy (2015), 40(15), 5126-5134. Language: English, Database: CAPLUS,DOI:10.1016/j.ijhydene.2015.02.101

D. functional theory calcns. were performed to investigate the pathways of the oxygen redn. reaction over the Pt4 andPt3M (M = Fe, V) clusters supported on the O-doped graphene substrate. The results show that the defect sites resultingfrom oxygen doping become the anchor sites for metal clusters. Our results also showed that O2 adsorbs as a di-oxygenspecies on the supported Pt4 and Pt3Fe clusters, but dissocs. spontaneously on supported Pt3V. The di-oxygen speciesdissocs. into co-adsorbed HO* and O* upon redn. on both supported Pt4 and Pt3Fe and no stable HOO* intermediateswere isolated. On supported Pt4, further redn. via both HO* + HO* and H2O* + O* routes is possible, with reactionfavoring the HO* + HO* route energetically. On supported Pt3Fe, the HO* + HO* and H2O* + O* routes are competitive.On supported Pt3V, the redn. reaction is likely to proceed exclusively through the HO* + HO* route as no stable co-adsorbed H2O and O* state was isolated. The results were discussed in the context of the exptl. obsd. enhancement ofORR reactivity on the graphene supported Pt3Cr and Pt3Co nanocatalysts.~16 Citings

117. Biological implications of 2-chlorocyclohexa-2,5-diene-1,4-dione toward ribonuclease A

By Vaughn, Albert R.; Redman, Caitlin B.; Kang, Sophia M.; Kim, JisookFrom Advances in Bioscience and Biotechnology (2013), 4(1), 22-28. Language: English, Database: CAPLUS,DOI:10.4236/abb.2013.41004

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2-Chlorocyclohexa-2,5-diene-1,4-dione (CBQ) or 2-chloro1,4-benzquinone is one of the common metabolites ofpolycyclic arom. hydrocarbons generated through industrial processes. This report describes the biol. effects of CBQtoward RNase A (RNase). We also investigated the inhibition of RNase modifications and the reactivity of CBQ towardselected amino acids. The study was carried out by incubating RNase or amino acids with CBQ in a concn.- and a time-dependent manner at 37°C and pH 7.0. SDS-PAGE results showed oligomerization as well as polymeric aggregation ofRNase when incubated with CBQ as early as in 10 min. CBQ-induced RNase modifications were inhibited in thepresence of NADH or ascorbic acid. CBQ reactivity toward selected amino acids was also evaluated by detg. thesecond-order rate consts. for the reactions of CBQ with selected amino acids. It was found that the reactivity towardCBQ decreased in the order of lysine > threonine > serine >> aspartate > cysteine.~4 Citings

118. H + H2 quantum dynamics using potential energy surfaces based on the XYG3 type of doubly hybriddensity functionals: Validation of the density functionals

By Su, Neil Qiang; Chen, Jun; Sun, Zhigang; Zhang, Dong H.; Xu, XinFrom Journal of Chemical Physics (2015), 142(8), 084107/1-084107/9. Language: English, Database: CAPLUS,DOI:10.1063/1.4913196

The potential energy surfaces for the H + H2 exchange reaction are detd., using the std. Becke-3_parameter-Lee-Yang-Parr (B3LYP) hybrid exchange-correlation functional and the recently developed XYG3 type (xDH) doubly hybridfunctionals. Quantum dynamical results calcd. on these d. functional theory surfaces revealed that the accuracy for thesurfaces from the xDH functionals is quite satisfactory as compared to the benchmark Boothroyd-Keogh-Martin-Peterson-2 surface, whereas B3LYP is wholly inadequate in describing this simplest reaction despite the fact that it hasbeen widely used to study reactions in complex systems. It is shown that further improvements can be achieved if thexDH functional parameters are fine-tuned to be reaction specific. (c) 2015 American Institute of Physics.~0 Citings

119. A comparison study on ribonuclease A modifications induced by substituted p-benzoquinones

By Kim, Jisook; Albu, Titus V.; Vaughn, Albert R.; Kang, Sophia M.; Carver, Ethan A.; Stickle, Dawn M.From Bioorganic Chemistry (2015), 59, 106-116. Language: English, Database: CAPLUS,DOI:10.1016/j.bioorg.2015.02.004

In this paper, we present our investigation on RNase A (RNase) modifications induced by 1,4-benzoquinone (PBQ), 2-methyl-1,4-benzoquinone (MBQ), and 2-chloro-1,4-benzoquinone (CBQ). The goal of the study was to evaluatequinone-induced protein modifications as well as substituent effects, utilizing several techniques such as SDS-PAGE,fluorescence spectroscopy, microscopy, and LC-ESI+-QTOF-MS. SDS-PAGE expts. revealed that all quinones modifyRNase through oligomerization as well as polymeric aggregation; with CBQ functioning as the most efficient quinonewhile MBQ was least efficient. The fluorescence emission was found to be less intense and the anisotropy values werefound to be slightly higher for the modified RNase compared to the unmodified RNase. UV-Vis spectroscopy indicatedthat all three quinones formed adducts in which they were covalently linked to RNase. Confocal imaging anal. showedthat the presence of CBQ resulted in massive RNase aggregation, while PBQ-treated RNase formed much smalleraggregates. MBQ-treated RNase exhibited microg. features that closely resembled those of the unmodified RNase. LC-ESI+-QTOF-MS studies indicated the nature of PBQ- and CBQ-induced RNase modifications are complex mainly due tosimultaneously occurrence of both adduct formation and oligomerization. Kinetic studies on quinone reactivity towardlysine revealed the rank order of CBQ > PBQ » MBQ, based on the second-order rate consts. We also utilized SEM inorder to investigate the effect of modified RNase on the biomineralization of salts.~2 Citings

120. Recent advancements in Pt and Pt-free catalysts for oxygen reduction reaction

By Nie, Yao; Li, Li; Wei, ZidongFrom Chemical Society Reviews (2015), 44(8), 2168-2201. Language: English, Database: CAPLUS,DOI:10.1039/C4CS00484A

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Developing highly efficient catalysts for the oxygen redn. reaction (ORR) is key to the fabrication of com. viable fuel celldevices and metal-air batteries for future energy applications. Herein, we review the most recent advances in thedevelopment of Pt-based and Pt-free materials in the field of fuel cell ORR catalysis. This review covers catalyst materialselection, design, synthesis, and characterization, as well as the theor. understanding of the catalysis process andmechanisms. The integration of these catalysts into fuel cell operations and the resulting performance/durability are alsodiscussed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.~810 Citings

121. Computational Organic Chemistry: Bridging Theory and Experiment in Establishing the Mechanisms ofChemical Reactions

By Cheng, Gui-Juan; Zhang, Xinhao; Chung, Lung Wa; Xu, Liping; Wu, Yun-DongFrom Journal of the American Chemical Society (2015), 137(5), 1706-1725. Language: English, Database: CAPLUS,DOI:10.1021/ja5112749

A review. Understanding the mechanisms of chem. reactions,esp. catalysis, has been an important and active area ofcomputational org. chem., and close collaborations betweenexperimentalists and theorists represent a growing trend. ThisPerspective provides examples of such productivecollaborations. The understanding of various reactionmechanisms and the insight gained from these studies areemphasized. The applications of various exptl. techniques inelucidation of reaction details as well as the development ofvarious computational techniques to meet the demand ofemerging synthetic methods, e.g., C-H activation,organocatalysis, and single electron transfer, are presentedalong with some conventional developments of mechanisticaspects. Examples of applications are selected to demonstratethe advantages and limitations of these techniques. Somechallenges in the mechanistic studies and predictions ofreactions are also analyzed.

~139 Citings

122. O2 Dissociation on M@Pt Core-Shell Particles for 3d, 4d, and 5d Transition Metals

By Jennings, Paul C.; Aleksandrov, Hristiyan A.; Neyman, Konstantin M.; Johnston, Roy L.From Journal of Physical Chemistry C (2015), 119(20), 11031-11041. Language: English, Database: CAPLUS,DOI:10.1021/jp511598e

D. functional theory calcns. are performed to investigateoxygen dissocn. on 38-atom truncated octahedron platinum-based particles. This study progresses our previous work,where it was shown that flexibility of the outer Pt shell played acrucial role in facilitating fast oxygen dissocn. In this study, theeffect of forming M@Pt (M core, Pt shell) particles for a rangeof metal cores (M = 3d, 4d, and 5d transition metals) isconsidered, with respect to O2 dissocn. on the Pt(111) facets.We show that forming M@Pt particles with late transition metalcores results in favorable shell flexibility for very low O2dissocn. barriers. Conversely, alloying with early transitionmetals results in a more rigid Pt shell because of dominant M-Pt interactions, which prevent lowering of the dissocn. barriers.

~26 Citings

123. Membrane degradation in PEM water electrolyzer: Numerical modeling and experimental evidence of theinfluence of temperature and current density

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By Chandesris, M.; Medeau, V.; Guillet, N.; Chelghoum, S.; Thoby, D.; Fouda-Onana, F.From International Journal of Hydrogen Energy (2015), 40(3), 1353-1366. Language: English, Database: CAPLUS,DOI:10.1016/j.ijhydene.2014.11.111

A 1-dimensional polymer electrolyte membrane H2O electrolyzer (PEMWE) model that incorporates chem. degrdn. of themembrane is developed to study the influence of temp. and c.d. on the membrane degrdn. In the 1-dimensionalperformance model, electronic and ionic transports through the different cell components are considered together withthe electrochem. behavior of the anodic and cathodic catalyst layers. The membrane degrdn. model describes the Ocross-over from the anode to the cathode side, the formation of H peroxide at the cathode side together with thesubsequent formation of radicals via Fenton reactions involving metal-ion impurities and the membrane degrdn. Thedevelopment of the model is supported by specific single cell expts. to both validate the different modeling assumptionsand det. some of the phys. parameters involved in the performance and degrdn. models. The single-cell degrdn. testsconfirm that most of the membrane degrdn. occurs at the cathode side and also show the strong influence of the temp.on the degrdn. rate. The effect of the c.d. on the degrdn. rate is more complex and presents a max. at quite low c.d.This phenomena, obsd. in the expts., is well captured by the model. The model is then used to study the time evolutionof the membrane thickness. The coupling between the performance and the chem. degrdn. models allows to capture theacceleration of membrane thinning.~37 Citings

124. Interplay between Reaction Mechanism and Hydroxyl Species for Water Formation on Pt(111)

By Ferreira de Morais, Rodrigo; Franco, Alejandro A.; Sautet, Philippe; Loffreda, DavidFrom ACS Catalysis (2015), 5(2), 1068-1077. Language: English, Database: CAPLUS, DOI:10.1021/cs5012525

Predicting the reaction mechanism of H2O and H2O2 formationon a Pt catalyst is a crucial step toward the understanding ofthe corresponding selectivity in polymer electrolyte membranefuel cells. In this perspective, the environment of the catalyticactive site should play an important role; however, its explicitdescription at the at. scale is an ongoing challenge for theor.approaches. The authors propose to model 3 effects of theenvironment: surface hydroxyl coverage, temp., and reactantpressure. A detailed study of the reaction mechanism of H2Oand H2O2 formation on a Pt surface is reported from d.functional theory (DFT) calcns. and Gibbs free energydiagrams. In std. conditions of reaction (1 atm and 353 K), theselectivity toward H2O and H2O2 depends on the competitionbetween 2 reaction paths (mol. O direct dissocn. andhydrogenation), which can be tuned by the partial coverage ofOH intermediate. At a low coverage of 1/12 ML, the catalystactivity is expected to be low due to a preferential but activateddirect O dissocn. When the OH partial coverage increases, thehydroperoxyl route becomes favorable, hence leading tohydroxyl and H2O by the nonactivated OOH dismutation. Thedirect O dissocn. and the whole reaction mechanism aresensitive to the hydroxyl partial coverage. The gas/metalmodel opens the way to new elementary mechanisms in thepresence of aq. electrolyte and elec. field that would explainhow H2O can be produced at the beginning of the reaction (atlow coverage).

~11 Citings

125. Mechanisms for Ethanol Electrooxidation on Pt(111) and Adsorption Bond Strengths Defining an IdealCatalyst

By Asiri, Haleema Aied; Anderson, Alfred B.From Journal of the Electrochemical Society (2015), 162(1), F115-F122. Language: English, Database: CAPLUS,DOI:10.1149/2.0781501jes

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EtOH electrooxidn. on the Pt(111) electrode was studied with computational theory. Using a solvation model and amodified Poison-Boltzmann theory for electrolyte polarization, std. reversible potentials for forming 17 reactionintermediates in soln. were calcd. with d. functional theory. Reversible potentials for adsorbed intermediates were thendetd. by inputting calcd. adsorption energies into a linear Gibbs energy relation. A path to CO2 was found where surfacepotentials were low and close to the calcd. 0.004 V reversible potential for the 12 electron oxidn. of EtOH. An exceptionwas the 0.49 V potential for forming the OH(ads) from H2O(l), this being required for oxidn. of CO(ads) and RH(ads)intermediates. The surface potentials show that acetyl, OCCH3(ads) forms at small pos. potentials and decomps. toCH(ads), CH3(ads), and CO(ads), which poison the surface at these potentials. Energy losses due to nonelectrontransfer reaction steps are small and cause a small shift in the reversible potential for the 12 electron oxidn. Values foradsorption bond strengths over a perfect catalyst were detd. On an ideal catalyst most intermediates will adsorb moreweakly and OH more strongly than on Pt(111).~18 Citings

126. Oxygen reduction reaction on neighboring Fe-N4 and quaternary-N sites of pyrolized Fe/N/C catalyst

By Saputro, Adhitya G.; Kasai, HideakiFrom Physical Chemistry Chemical Physics (2015), 17(5), 3059-3071. Language: English, Database: CAPLUS,DOI:10.1039/C4CP04811C

We study the interaction between the TM-Nx and metal-free active sites of a pyrolized TM/N/C catalyst and its effect ontheir ORR activities. We particularly choose a Fe-N4-edge-graphene and a quaternary-N-doped zigzag edge asrepresentatives of TM-Nx and the metal-free active sites, resp. We find that the interaction of the Fe-N4 and quaternary-N-doped sites at the zigzag edge of graphene enhances the ORR free energy profile at the quaternary-N-doped site.However, the ORR free energy profile at the Fe-N4 site is not affected by this interaction.~23 Citings

127. Tunneling Isomerization of Small Carboxylic Acids and Their Complexes in Solid Matrixes: A ComputationalInsight

By Tsuge, Masashi; Khriachtchev, LeonidFrom Journal of Physical Chemistry A (2015), 119(11), 2628-2635. Language: English, Database: CAPLUS,DOI:10.1021/jp509692b

We have studied hydrogen-atom tunneling in the cis-to-transconformational change of some carboxylic acid monomers andformic acid (FA) complexes and dimers at the MP2(full) andCCSD(T) levels of theory within the Wentzel-Kramers-Brillouinapproxn. The barrier for the min. energy path, where the OHbond length and the COH bending angle are optimized, isfound to be a good approxn. for providing the highest barriertransparency. The matrix effect on the transmission coeffs. ofcis-FA monomer, trans-cis FA dimer (tc1), and cis-acetic acidmonomer are modeled by the polarizable continuum model(PCM) at the MP2(full) level of theory in different environments.For the cis-FA monomer and trans-cis FA dimer (tc1), thecalcd. transmission coeffs. agree with the exptl. lifetimes obsd.in noble-gas solids. However, this method cannot reproducethe exptl. results obtained for cis-acetic acid. Moreover, thelong lifetime of cis-FA and cis-acetic acid in the N2 environmentcannot be reproduced either, which is most probably due tospecific interactions that are not included in the PCM. Thecalcn. for cis-HCOOD shows a strong decrease of the barriertransparency compared to that for cis-HCOOH, which isconsistent with the expts. In general, good agreement is obsd.between the calcd. barrier transparency (including PCM) andexptl. tunneling rate. However, some exceptions are found,which shows that addnl. factors influence the tunneling rate.

~22 Citings

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128. Tafel Kinetics of Electrocatalytic Reactions: From Experiment to First-Principles

By Fang, Ya-Hui; Liu, Zhi-PanFrom ACS Catalysis (2014), 4(12), 4364-4376. Language: English, Database: CAPLUS, DOI:10.1021/cs501312v

The Tafel equation is of fundamental importance inelectrochem. kinetics, formulating a quant. relation between thecurrent and the applied electrochem. potential. The recentyears have seen the rapid expansion and development in theapplication of 1st-principles d. functional theory (DFT)simulation on electrocatalytic reactions that occur at the solid-liq. interface. This article reviews the current theor. methodsfor electrochem. modeling, in particular, those for the directcomputation of Tafel kinetics of electrocatalytic reactions onsurfaces based on DFT calcns. Representative reactions,namely, H evolution and O evolution reactions, are selected toillustrate how the theor. methods are applied to compute quant.the kinetics of multiple-step electrochem. reactions. Theauthors summarize in detail the computation procedure basedon the 1st-principles periodic continuum solvation method forobtaining the charge transfer coeff. (CTC) and deducing thepotential-dependent reaction rate. The theor. results on theTafel kinetics of electrochem. reactions are generalized anddiscussed.

~62 Citings

129. Effects of reagent rotational excitation on the H + CHD3 → H2 + CD3 reaction: A seven dimensional time-dependent wave packet study

By Zhang, Zhaojun; Zhang, Dong H.From Journal of Chemical Physics (2014), 141(14), 144309/1-144309/8. Language: English, Database: CAPLUS,DOI:10.1063/1.4897308

Seven-dimensional time-dependent wave packet calcns. have been carried out for the title reaction to obtain reactionprobabilities and cross sections for CHD3 in J0 = 1, 2 rotationally excited initial states with k0 = 0 - J0 (the projection ofCHD3 rotational angular momentum on its C3 axis). Under the centrifugal sudden (CS) approxn., the initial states withthe projection of the total angular momentum on the body fixed axis (K0) equal to k0 are found to be much more reactive,indicating strong dependence of reactivity on the orientation of the reagent CHD3 with respect to the relative velocitybetween the reagents H and CHD3. However, at the coupled-channel (CC) level this dependence becomes muchweaker although in general the K0 specified cross sections for the K0 = k0 initial states remain primary to the overall crosssections, implying the Coriolis coupling is important to the dynamics of the reaction. The calcd. CS and CC integral crosssections obtained after K0 averaging for the J0 = 1, 2 initial states with all different k0 are essentially identical to thecorresponding CS and CC results for the J0 = 0 initial state, meaning that the initial rotational excitation of CHD3 up to J0= 2, regardless of its initial k0, does not have any effect on the total cross sections for the title reaction, and the errorsintroduced by the CS approxn. on integral cross sections for the rotationally excited J0 = 1, 2 initial states are the sameas those for the J0 = 0 initial state. (c) 2014 American Institute of Physics.~25 Citings

130. First Principles Calculation Study on Surfaces and Water Interfaces of Boron-Doped Diamond

By Futera, Zdenek; Watanabe, Takeshi; Einaga, Yasuaki; Tateyama, YoshitakaFrom Journal of Physical Chemistry C (2014), 118(38), 22040-22052. Language: English, Database: CAPLUS,DOI:10.1021/jp506046m

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The authors studied H2O interfaces of B-doped diamond (BDD)terminated by H, O, and hydroxyl groups by using d. functionaltheory (DFT)-based mol. dynamics to elucidate theelectrochem. behaviors of the as-grown and oxidized BDDelectrodes. The reversible outer-sphere electron transfer onthe as-grown electrode and the irreversibility on the oxidizedelectrode, obsd. in the expt., are well explained by the BDDband position and subsurface band bending, which depend onthe termination and interfacial dipoles. The reductive characterof the H-terminated BDD is found, while the interface coveredby the carbonyl O is clearly oxidative. The redox character ofthe hydroxyl termination depends on the lateral H bondingnetwork among the termination groups and is rather oxidativeat the H2O interface. The authors also examd. the preferenceof the B position in the diamond and the stability of B pairs andclusters. Probably the wide distribution of the single B dopantsis crucial to the BDD cond., against the tendency of clustering.These results give novel atomistic aspects of the terminationand the B doping effects on the BDD electrodes, which isuseful for further exploration of the efficient electrochem.applications of BDD.

~9 Citings

131. Global Potential Energy Surface for the H + CH4 ↔ H2 + CH3 Reaction using Neural Networks

By Xu, Xin; Chen, Jun; Zhang, Dong H.From Chinese Journal of Chemical Physics (2014), 27(4), 373-379. Language: English, Database: CAPLUS,DOI:10.1063/1674-0068/27/04/373-379

A global potential energy surface (PES) for the H + CH4 ↔ H2 + CH3 reaction has been constructed using the neuralnetworks method based on 47783 high level ab initio geometry points. Extensive quasi-classical trajectories andquantum scattering calcns. were carried out to check the convergence of the PES. This PES, fully converged withrespect to the fitting procedure and the no. of ab initio points, has a very small fitting error, and was much faster onevaluation than the modified Shepard interpolating PES, representing the best available PES for this benchmark polyat.system.~27 Citings

132. Reactions of Atomic Hydrogen with Formic Acid and Carbon Monoxide in Solid Parahydrogen II: DeuteratedReaction Studies

By Wonderly, William R.; Anderson, David T.From Journal of Physical Chemistry A (2014), 118(36), 7653-7662. Language: English, Database: CAPLUS,DOI:10.1021/jp502469p

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It is difficult to det. whether the measured rate const. forreaction of at. hydrogen with formic acid reported in Part 1reflects the H atom quantum diffusion rate or the rate const. forthe tunneling reaction step. In Part 2 of this series, we presentkinetic studies of the postphotolysis H atom reactions withdeuterated formic acid (DCOOD) to address this ambiguity.Short duration 193 nm in situ photolysis of DCOOD trapped insolid parahydrogen results in partial depletion of the DCOODprecursor and photoprodn. of primarily CO, CO2, DOCO, HCOand mobile H atoms. At 1.9 K we observe post-irradn. growthin the concns. of DOCO and HCO that can be explained by Hatom tunneling reactions with DCOOD and CO, resp.Conducting expts. with different deuterium isotopomers offormic acid (DCOOD, DCOOH, HCOOD and HCOOH) providesstrong circumstantial evidence the reaction involves H atomabstraction from the alkyl group of formic acid. Further, theanomalous temp. dependence measured for the H + HCOOHreaction in Part 1 is also obsd. for the analogous reactions withdeuterated formic acid. The rate consts. extd. for H atomreactions with DCOOD and HCOOH are equiv. to within exptl.uncertainty. This lack of a kinetic isotope effect in themeasured rate const. is interpreted as evidence the reactionsare diffusion limited; the measured rate const. reflects the Hatom diffusion rate and not the tunneling reaction rate.Whether or not H atom reactions with chem. species in solidparahydrogen are diffusion limited is one of the outstandingquestions in this field, and this work makes significant stridestoward showing the reaction kinetics with formic acid arediffusion limited.

~10 Citings

133. Biological implications of benzoquinones

By Kim, JisookEdited By:Price, Ervin R.; Johnson, Smith CFrom Quinones (2013), 57-84. Language: English, Database: CAPLUS

A review. Benzoquinones (BQs) represent the simplest form of quinones, contg. two carbonyl groups on a six-membered ring. They are ubiquitously found in diverse organisms as free quinones, protein cofactors, or an integral partof the mitochondrial electron transport chain (ETC). In addn., many BQs are identified as environmental toxinsgenerated from industrial processes as the metabolites of polycyclic arom. hydrocarbons, contributing tobioaccumulation. To date, animal and epidemiol. studies revealed that the quinone derivs. of benzene metabolitesserves as a source of inducing abnormal cell behavior, leading to cancer or triggering immune response. Whetheroccurring endogenously in living organisms or exogenously in the environment, there is a universal understanding on therole of BQs as potential toxins, except some limited cases like protein-bound BQs or electron carriers in the ETC.Studies done at a mol.-level approach revealed that BQs exhibit both genotoxicity and non-genotoxicity/epigenetictoxicity, targeting both cellular DNA and proteins. The mechanism of their action is thought to occur via the combinationof oxidative damage intervened by redox-cycling, adduct formation with DNA and proteins, and proteincrosslinking/protein conformation change.~0 Citings

134. A Quantum Mechanical "Jack in the Box": Rapid Rearrangement of a Tetrahedryl-Tetrahedrane via HeavyAtom Tunneling

By Kozuch, SebastianFrom Organic Letters (2014), 16(16), 4102-4105. Language: English, Database: CAPLUS, DOI:10.1021/ol5017977

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A bridged tetrahedryl-tetrahedrane ("TT") was, theor.,recognized as the holder of the chem. record for the shortest C-C single bond in a stable mol. However, owing to its strainednature, this mol. is prone to rearrange to a carbene via ringcontraction. Although TT was predicted to be stable torearrangement at very low temps., our calcns. find that, due tocarbon quantum mech. tunneling, even at 0 K it willimmediately rearrange, with a half-life of only 4 ms. TTprovides an excellent example of why tunneling effect shouldbe considered in the stability anal. of a theor. conceived mol.,even at cryogenic temps.

~9 Citings

135. Photoelectrochemical water splitting: a first principles approach

By Hellman, AndersFrom RSC Energy and Environment Series (2013), 9(Photoelectrochemical Water Splitting), 266-288. Language:English, Database: CAPLUS

This paper discusses on photoelectrochem. water splitting by first principles approach.~1 Citing

136. Computational and 13C Investigations of the Diazadienes and Oxazadienes Formed via the Rearrangementof Methylenecyclopropyl Hydrazones and Oximes

By Chen, Bo; Scott, Mark E.; Adams, Bruce A.; Hrovat, David A.; Borden, Weston Thatcher; Lautens, MarkFrom Organic Letters (2014), 16(15), 3930-3933. Language: English, Database: CAPLUS, DOI:10.1021/ol501710m

Computational and further exptl. investigations of the previouslyreported diazadienes, obtained via the rearrangement ofmethylenecyclopropyl hydrazone 1 are reported. Calcns. at theCCSD(T)/cc-pVTZ//B3LYP/6-31G(d) level of theory indicatethat the initially reported product 3 would, if formed, undergorapid electrocyclic ring opening and, hence, would be unstableunder the reaction conditions. Based on this computationalprediction, further anal. of the 13C NMR spectrum, previouslyattributed to 3, led to the revision of structure 3 to that of its N-tosylaminopyrrole constitutional isomer 11. Similarly, structure8, formed in the rearrangement of oxime 6, was revised to thatof N-hydroxypyrrole 12.

~7 Citings

137. Valence Bond-Based Hybrid Quantum Mechanics Molecular Mechanics Approaches and Proper Inclusion ofthe Effect of the Surroundings

By Shurki, Avital; Sharir-Ivry, AvitalFrom Israel Journal of Chemistry (2014), 54(8-9), 1189-1204. Language: English, Database: CAPLUS,DOI:10.1002/ijch.201400038

A review. The pioneering development of multiscale models for complex chem. systems by Karplus, Levitt, and Warshel,including the hybrid quantum mechanics mol. mechanics (QM/MM) approach and its application to enzymes, establisheda new field in chem. that allows the modeling of reactivity within complex chem. systems. Inspired by the potential ofsuch methods, many groups developed different QM/MM variants. Valence bond (VB) theory, which always was and stillis an important conceptual tool for chemists, is well suited to deal with problems of chem. reactivity. Hence, here wereview VB-based QM/MM methods, including the early semi-empirical methods that utilize VB concepts and more recentab initio VB-based QM/MM methods. Special emphasis is given to the different ways to include effects of thesurroundings on the solute. It is shown that within the VB framework, simple mech. embedding for each diabatic state,followed by mixing of the states, accounts for most of these effects.

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~2 Citings

138. DFT studies of oxygen dissociation on the 116-atom platinum truncated octahedron particle

By Jennings, Paul C.; Aleksandrov, Hristiyan A.; Neyman, Konstantin M.; Johnston, Roy L.From Physical Chemistry Chemical Physics (2014), 16(48), 26539-26545. Language: English, Database: CAPLUS,DOI:10.1039/C4CP02147A

D. functional theory calcns. are performed to investigate oxygen dissocn. on 116-atom truncated octahedron platinumparticles. This work builds on results presented previously [Jennings et al., Nanoscale, 2014, 6, 1153], where it wasshown that shell flexibility played an important role in facilitating fast oxygen dissocn. In this study, through investigationof the larger particle size, it is shown that oxygen dissocn. on the (111) facet of pure platinum species is still aided byshell flexibility at larger sizes. Only the hollow sites close to the edges of the (111) facet mediate oxygen dissocn.;oxygen is bound too weakly at other hollow sites for dissocn. to occur. Further studies are performed on the (100) facet,which is larger for the Pt116 particle than for either the Pt38 or Pt79 ones. Much higher dissocn. barriers are found on the(100) facet compared to the (111) facet, where the bridge sites are favorable for oxygen dissocn.~15 Citings

139. Novel Recipe for Double-Hybrid Density Functional Computations of Linear and Nonlinear Polarizabilities ofMolecules and Nanoclusters

By Alipour, MojtabaFrom Journal of Physical Chemistry A (2014), 118(28), 5333-5342. Language: English, Database: CAPLUS,DOI:10.1021/jp503959w

Double-hybrid (DH) d. functionals are now among the mostapplied methods for quantum chem. calcns. within d. functionaltheory (DFT). In this work, a new DH d. functional is developedfor linear and nonlinear optical properties of mols. andhydrogen-bonded nanoclusters. The proposed functional,denominated as PBEDH-P (-P stands for polarizability), isbased on Perdew-Burke-Ernzerhof (PBE) exchange andcorrelation functionals and includes 68% Hartree-Fockexchange and 31% correlation from second-order Moller-Plesset perturbation theory (MP2). From the obtained results,PBEDH-P is shown to be accurate for the calcns. ofhyperpolarizability, isotropic and anisotropic polarizabilities, anddipole moment of mols. and hydrogen-bonded nanoclusters ofH2O (neutral, protonated, and deprotonated), NH3, HF, andbinary mixts. of HF-H2O. This novel DH functional not onlyreveals a considerable improvement in comparison to therecently proposed parameter-free and parametrized DHs butalso seems to be superior to the MP2 method in some cases.Moreover, we find that using only contributions of electron pairswith opposite spin for the perturbative part within scaledopposite-spin scheme does not represent a great improvementover PBEDH-P. On the whole, our study nominates PBEDH-Pas a promising model for the calcns. of elec. responseproperties, where the DH d. functionals again come into playand further evidence of the quality of these approxns. arehighlighted.

~14 Citings

140. Reaction Path Following with Sparse Interpolation

By Nance, James; Jakubikova, Elena; Kelley, C. T.From Journal of Chemical Theory and Computation (2014), 10(8), 2942-2949. Language: English, Database: CAPLUS,DOI:10.1021/ct5004669

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Computing the potential energy of an N-atom mol. is anexpensive optimization process of 3N - 6 mol. coordinates, sofollowing reaction pathways as a function of all 3N - 6coordinates is unfeasible for large mols. In this paper, wepresent a method that isolates d < 3N - 6 mol. coordinates andcontinuously follows reaction paths on d-dimensional potentialenergy surfaces approximated by a Smolyak's sparse gridinterpolation algorithm. Compared to dense grids, sparse gridsefficiently improve the ratio of invested storage and computingtime to approxn. accuracy and thus allow one to increase theno. of coordinates d in mol. reaction path following simulations.Furthermore, evaluation of the interpolant is much lessexpensive than the evaluation of the actual energy function, soour technique offers a computationally efficient way to simulatereaction paths on ground and excited state potential energysurfaces. To demonstrate the capabilities of our method, wepresent simulation results for the isomerization of 2-butene withtwo, three, and six degrees of freedom.

~3 Citings

141. n-type doping of diamond semiconductor

By Yan, Cuixia; Dai, Ying; Huang, BaibiaoFrom Advances in Materials Science Research (2012), 14, 57-83. Language: English, Database: CAPLUS

A review. Great efforts were made both theor. and exptl. to achieve available n-type diamond materials during the pastyears. In this review, recent investigations about the effects of the impurities on the n-type electronic properties ofdiamond materials are looked back. Topics covered include electronic properties of diamond, types, doping methods,the influences of various donor impurities and two dopants codoping on n-type electronic properties of diamond. Inaddn., the influences of hydrogen and vacancy defects on donor impurities are also discussed in detail. Finally, anotherpossible approach to achieve n-type diamond materials by the cond. type transition from p-type to n-type throughdeuteration is introduced. Various attempted explains for the conversion mechanism from p-type to n-type cond. arereviewed. The paper provides a relatively complete picture of doping n-type diamond and necessary information of n-type diamond investigation, which is helpful for those who are starting to work in the field of n-type diamond materials.~0 Citings

142. Heavy atom tunneling in the automerization of pentalene and other antiaromatic systems

By Kozuch, SebastianFrom RSC Advances (2014), 4(41), 21650-21656. Language: English, Database: CAPLUS,DOI:10.1039/C4RA02191F

Cyclobutadiene is a well-known system that can automerize (i.e. undergo a π bond-shifting) by a heavy atom tunnelingmechanism. To understand the rules that allow this process, a theor. study has been carried out on the contribution oftunneling to the automerization reactions of several other mols. with antiarom. π systems i.e. pentalene, heptalene,acepentalene, and substituted pentalenes. The calcns. find that automerization of mols. such as pentalene, which haveplanar structures, are most likely to proceed by rapid carbon tunneling from the lowest vibrational state, since such mols.have relatively low activation energy and narrow barriers. However, if a mol. is not planar (thus formally 'non-arom.')and/or requires large geometry changes in order to reach the automerization transition state, then the tunneling will bestrongly hindered. In some cases, such as heptalene and tri-tert-butylpentalene, the rearrangement of the reactantrequires a modest amt. of thermal energy, which can be followed by the π bond-shifting through a tunneling mechanism('thermally activated tunneling').~14 Citings

143. Novel Coupled Structures of FeWO4/TiO2 and FeWO4/TiO2/CdS Designed for Highly Efficient Visible-LightPhotocatalysis

By Bera, Sandipan; Rawal, Sher Bahadur; Kim, Hark Jin; Lee, Wan InFrom ACS Applied Materials & Interfaces (2014), 6(12), 9654-9663. Language: English, Database: CAPLUS,DOI:10.1021/am502079x

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A quadrilateral disk-shaped FeWO4 nanocrystal (NC) with anav. size of ∼35 nm was prepd. via hydrothermal reaction. Theobtained dark brown FeWO4 NC with a bandgap (Eg) of 1.98eV was then coupled with TiO2 to form FeWO4/TiO2composites. The valence band (VB) of FeWO4 (+2.8 eV vsNHE) was more pos. than that of TiO2 (+2.7 eV); thus thissystem could be classified as a type-B heterojunction. Undervisible-light irradn., 5/95 FeWO4/TiO2 (by wt %) exhibitedremarkable photocatalytic activity: the amt. of CO2 evolvedfrom gaseous 2-propanol (IP) and the decompn. rate of aq.salicylic acid (SA) were, resp., 1.7 and 2.5 times greater thanthose of typical nitrogen-doped TiO2 (N-TiO2). This uniquecatalytic property was deduced to arise from theintersemiconductor hole transfer between the VBs of FeWO4and TiO2. Herein, several exptl. evidence were also providedto confirm the hole-transfer mechanism. To further enhancethe catalytic efficiency, double-heterojunctionedFeWO4/TiO2/CdS composites were prepd. by loading CdSquantum dots (QDs) onto the FeWO4/TiO2 surface.Surprisingly, the catalytic activity for evolving CO2 from IP was2.6 times greater than that of bare FeWO4/TiO2 and 4.4 timesgreater than that of N-TiO2, suggesting that both holes andelectrons were essential species in decompg. org. compds.

~33 Citings

144. Quantum Mechanical Fragment Methods Based on Partitioning Atoms or Partitioning Coordinates

By Wang, Bo; Yang, Ke R.; Xu, Xuefei; Isegawa, Miho; Leverentz, Hannah R.; Truhlar, Donald G.From Accounts of Chemical Research (2014), 47(9), 2731-2738. Language: English, Database: CAPLUS,DOI:10.1021/ar500068a

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A review. The development of more efficient and moreaccurate ways to represent reactive potential energy surfacesis a requirement for extending the simulation of large systemsto more complex systems, longer-time dynamical processes,and more complete statistical mech. sampling. One way totreat large systems is by direct dynamics fragment methods.Another way is by fitting system-specific analytic potentialenergy functions with methods adapted to large systems. Herewe consider both approaches. First we consider threefragment methods that allow a given monomer to appear inmore than one fragment. The first two approaches are theelectrostatically embedded many-body (EE-MB) expansion andthe electrostatically embedded many-body expansion of thecorrelation energy (EE-MB-CE), which we have shown to yieldquite accurate results even when one restricts the calcns. toinclude only electrostatically embedded dimers. The thirdfragment method is the electrostatically embedded mol.tailoring approach (EE-MTA), which is more flexible than EE-MB and EE-MB-CE. We show that electrostatic embeddinggreatly improves the accuracy of these approaches comparedwith the original unembedded approaches. Quantum mech.fragment methods share with combined quantum mech./mol.mech. (QM/MM) methods the need to treat a quantum mech.fragment in the presence of the rest of the system, which isesp. challenging for those parts of the rest of the system thatare close to the boundary of the quantum mech. fragment.This is a delicate matter even for fragments that are notcovalently bonded to the rest of the system, but it becomeseven more difficult when the boundary of the quantum mech.fragment cuts a bond. We have developed a suite of methodsfor more realistically treating interactions across suchboundaries. These methods include redistributing andbalancing the external partial at. charges and the use of tunedfluorine atoms for capping dangling bonds, and we have shownthat they can greatly improve the accuracy. Finally we presenta new approach that goes beyond QM/MM by combining theconvenience of mol. mechanics with the accuracy of fitting apotential function to electronic structure calcns. on a specificsystem. To make the latter practical for systems with a largeno. of degrees of freedom, we developed a method tointerpolate between local internal-coordinate fits to the potentialenergy. A key issue for the application to large systems is thatrather than assigning the atoms or monomers to fragments, weassign the internal coordinates to reaction, secondary, andtertiary sets. Thus, we make a partition in coordinate spacerather than atom space. Fits to the local dependence of thepotential energy on tertiary coordinates are arrayed along apreselected reaction coordinate at a sequence of geometriescalled anchor points; the potential energy function is called ananchor points reactive potential. Electrostatically embeddedfragment methods and the anchor points reactive potential,because they are based on treating an entire system byquantum mech. electronic structure methods but are affordablefor large and complex systems, have the potential to open newareas for accurate simulations where combined QM/MMmethods are inadequate.

~12 Citings

145. Reversible potentials for steps in methanol and formic acid oxidation to CO2; adsorption energies ofintermediates on the ideal electrocatalyst for methanol oxidation and CO2 reduction

By Anderson, Alfred B.; Asiri, Haleema AiedFrom Physical Chemistry Chemical Physics (2014), 16(22), 10587-10599. Language: English, Database: CAPLUS,DOI:10.1039/C3CP54837F

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Quantum chem. theory was used to identify the reasons for Pt's limitations as an electrocatalyst for oxidizing MeOH atfuel cell anodes. The linear Gibbs energy relation (LGER) method is employed to predict reversible potentials forreaction steps for intermediates on the electrode surface. In this procedure, std. reversible potentials are calcd. for thereactions in bulk soln. phase and then they are perturbed using calcd. adsorption bond strengths to the electrodesurface, yielding the equil. potentials for each electron transfer step for adsorbed intermediates. Adsorption properties ofideal electrocatalysts for the MeOH oxidn. are found by imposing the condition that the reversible potential of eachelectron transfer step is that for the overall reaction. The adsorption bond strengths that provide the ideal properties alsoapply to formic acid oxidn. and CO2 redn. It is instructive to think of the ideal electrocatalyst as a lens that focusses thereversible potentials for the n individual electron transfer steps to the reversible potential for the n-electron process. Theideal catalyst will adsorb many intermediates, including HOOC, CO, OCH, HOC, HOCH, HOCH2, and OCH3 moreweakly than Pt, and OOCH and OH more strongly. For example, for one possible pathway it is necessary to weakenadsorption bond strengths for HOCH2, HOCH, OCH, HOOC by ∼0.5 eV, weaken adsorption CO by ∼1.1 eV andstrengthen OH adsorption by ∼0.6 eV. These results imply a need for developing new multi-component catalysts.~14 Citings

146. Oxygen reduction reaction at Pt single crystals: a critical overview

By Gomez-Marin, Ana Ma.; Rizo, Ruben; Feliu, Juan M.From Catalysis Science & Technology (2014), 4(6), 1685-1698. Language: English, Database: CAPLUS,DOI:10.1039/c3cy01049j

A review. O redn. reaction (ORR) dynamics at Pt single crystal surfaces is reviewed, and exptl. results in acid and alk.solns. are discussed in the framework of theor. studies. Special emphasis is devoted to point out the role of the surfacecharge, H2O structure and adsorbed O contg. species. Addnl., discussion about the possible relevance of H2O2 as anintermediate species is also included. The ORR is a complex process affected by many different factors and so neithersurface charge nor O-contg. species coverage alone are a detg. factor of the electrode activity. Instead, adlayerstructures and the relation between adsorbed H2O, H2Oads, H2O dissocn. products, OHads or Oads, and PtO oxidespecies coverage affect the whole energetics of the adsorption processes and may det. the surface reactivity. Finally, ifH2O2 is an intermediate product in the ORR mechanism, it would be crucial to find a suitable catalyst able to effectivelyreduce H2O2 at high potentials and inhibit its oxidn.~60 Citings

147. Molecularly imprinted polypyrrole based impedimentric sensor for theophylline determination

By Ratautaite, Vilma; Janssens, Stoffel D.; Haenen, Ken; Nesladek, Milos; Ramanaviciene, Almira; Baleviciute, Ieva;Ramanavicius, ArunasFrom Electrochimica Acta (2014), 130, 361-367. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2014.03.035

Developed was a impedimetric sensor based on oxygen-terminated boron-doped nanocryst. diamond (B:NCD:O)modified with theophylline-imprinted polypyrrole is described. H2O2-induced chem. formation of polypyrrole molecularlyimprinted by theophylline was applied for the modification of conducting silicon substrate covered by B:NCD:O film. Non-imprinted polypyrrole layer was formed on similar substrate to prove efficiency of imprinted polypyrrole. Electrochem.impedance spectroscopy was applied for the evaluation of analyte-induced changes in electrochem.capacitance/resistance. The impact of polymn. duration on the capacitance of impedimetric sensor was estd. A differentimpedance behavior was obsd. at different ratio of polymd. monomer and template mol. in the polymn. media. Theinfluence of ethanol as additive to polymn. media on registered changes in capacitance/resistance was evaluated.Degrdn. of sensor stored in buffer soln. was evaluated.~30 Citings

148. Temperature response and durability characterization of an optical fiber sensor for the detection ofhydrogen peroxide

By Botero-Cadavid, Juan F.; Wild, Peter; Djilali, NedFrom Electrochimica Acta (2014), 129, 416-424. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2014.02.088

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H2O2 is a precursor to damage mechanisms in numerous applications; its monitoring is important and challenging. Theeffect of temp. on the performance and durability of a recently developed optical fiber sensors sensitive to the presenceof H2O2 in low concns. was studied. The sensors are fabricated by immobilizing Prussian blue within a multilayer ofelectrostatically self-assembled polyelectrolytes. The sensing principle of this optical electrode relies on the change inthe intensity of the reflected light when Prussian white is oxidized back to the blue state due to the presence of H2O2.The amplitude of the intensity of the reflected light is found to vary with temp. in a quadratic fashion, but the characteristicresponse time which correlates with concn. remains const. Thus the sensing device retains its abilities to det. andquantify the concn. of H2O2 in a liq. soln. Addnl., the degrdn. of these fiber sensors when subjected to high temp. wasexamd. Four optical fiber sensing devices were subjected to different testing conditions and a characterization protocolthat included: measurement of the intensity of the cyanide stretch (2150 cm-1) via Raman micro spectroscopy; imagingwith SEM; and measurement of the presence of Fe ions using energy dispersive x-ray spectroscopy. The results show agradual degrdn. of the sensing device as a result of progressive desorption of the polyelectrolyte multilayer structure thatleads to leaching of the Prussian reagent. This degrdn. mechanism does not compromise the functionality of the devicewhich is found sufficiently robust for multiple tests at high temp. The simplicity of this sensing system combined with itsrelative robustness and reusability make it a good a good candidate for minimally intrusive and localized monitoring ofH2O2 formation in operating PEMFCs.~4 Citings

149. The reactivity game: theoretical predictions for heavy atom tunneling in adamantyl and related carbenes

By Kozuch, S.From Physical Chemistry Chemical Physics (2014), 16(17), 7718-7727. Language: English, Database: CAPLUS,DOI:10.1039/C4CP00115J

The possibility of carbon atom tunneling at cryogenic temps. for carbene-based ring expansion of adamantane analogscalls for a delicate balance of reactivity to exptl. detect the transpiring reaction. An overly reactive carbene willprecipitously decay; an excessively stable carbene will not tunnel. Nevertheless, the factors that affect the quantum-mech. tunneling (QMT) reactivity - mass, barrier height and width - are strikingly different from the classical "over thebarrier" thermal mechanism. Herein, comparisons with exptl. values and predictions on measurable rate consts. fornovel carbene systems are presented by way of small curvature tunneling (SCT) computations. Adamantane,noradamantane and bisnoradamantane have a significantly different C-C bond strain and reactivity, which can bemodulated by tinkering with the carbene substituent atom (H, Cl or F) to obtain an observable lifetime of the reactant.The influence of barrier heights and widths, kinetic isotope effects (KIEs), the detection of the tunneling-detg. atoms(TDA) and the comparisons with hydrogen-based reactions are discussed with the objective of finding the phys. limits forQMT.~17 Citings

150. Some reflections on the understanding of the oxygen reduction reaction at Pt(111)

By Gomez-Marin, Ana M.; Rizo, Ruben; Feliu, Juan M.From Beilstein Journal of Nanotechnology (2013), 4, 956-967, 12 pp.. Language: English, Database: CAPLUS,DOI:10.3762/bjnano.4.108

A review. The oxygen redn. reaction (ORR) is a pivotal process in electrochem. Unfortunately, after decades ofintensive research, a fundamental knowledge about its reaction mechanism is still lacking. In this paper, a global andcrit. view on the most important exptl. and theor. results regarding the ORR on Pt(111) and its vicinal surfaces, in bothacidic and alk. media, is taken. Phenomena such as the ORR surface structure sensitivity and the lack of a redn. currentat high potentials are discussed in the light of the surface oxidn. and disordering processes and the possible relevance ofthe hydrogen peroxide redn. and oxidn. reactions in the ORR mechanism. The necessity to build precise and realisticreaction models, which are deducted from reliable exptl. results that need to be carefully taken under strict workingconditions is shown. Therefore, progress in the understanding of this important reaction on a mol. level, and the choiceof the right approach for the design of the electrocatalysts for fuel-cell cathodes is only possible through a cooperativeapproach between theory and expts.~16 Citings

151. Variation in the magnetic moment of Indium doped Ce0.1Y2.9Fe5O12 garnet relative to the site inversion

By Naik, S. R.; Salker, A. V.From Journal of Alloys and Compounds (2014), 600, 137-145. Language: English, Database: CAPLUS,DOI:10.1016/j.jallcom.2014.02.101

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Prominent changes in magnetic moment was obsd. for In3+ doped cubic garnet ferrites prepd. by the modified sol-gelauto combustion method. Systematic studies on the structure and magnetic properties were carried out. The malateglycolate precursor proves to be efficient in the synthesis of the garnet system. X-ray Diffraction technique was used toconfirm the phase formation and purity. Morphol. of the compds. was detd. with the help of SEM proving the particles tobe submicron in size. XPS and Raman spectroscopy were used to confirm the desired valence states and monophasicformation of the compds. Selective occupation of the tetrahedral over octahedral sites by In3+ ions for the 1st dopedcompd. was proved with the help of Mossbauer spectroscopy. Influence of site selectivity of In3+ ions on the resultantmagnetic properties were studied by vibrating sample magnetometer. Magnetic moment with respect to the Zero FieldCooling and Field Cooling is also measured. Selective occupation of the tetrahedral sites by the In3+ ions with initialdoping and its effect on the overall magnetic properties is a significant finding of this study.~10 Citings

152. Reaction mechanisms of CO2 electrochemical reduction on Cu(1 1 1) determined with density functionaltheory

By Nie, Xiaowa; Luo, Wenjia; Janik, Michael J.; Asthagiri, AravindFrom Journal of Catalysis (2014), 312, 108-122. Language: English, Database: CAPLUS,DOI:10.1016/j.jcat.2014.01.013

D. functional theory (DFT) was used to det. the potential-dependent reaction free energies and activation barriers forseveral reaction paths of CO2 (CO2) electrochem. redn. on the Cu(1 1 1) surface. The role of water solvation on CO2redn. paths was explored by evaluating H2O-assisted surface hydrogenation and proton (H) shuttling with varioussolvation models. Electrochem. OH bond formation reactions occur through H2O-assisted H-shuttling, whereas CH bondformation occurs with negligible H2O involvement via direct reaction with adsorbed H* on the Cu(1 1 1) surface. TheDFT-computed kinetic path shows that the exptl. obsd. prodn. of methane and ethylene on Cu(1 1 1) catalysts occursthrough the redn. of CO (CO*) to a hydroxymethylidyne (COH*) intermediate. Methane is produced from the redn. of theCOH* to C* and then sequential hydrogenation. Ethylene prodn. shares the COH* path with methane prodn., where themethane to ethylene selectivity depends on CH* 2 and H* coverages. The reported potential-dependent activationbarriers provide kinetics consistent with obsd. exptl. redn. overpotentials and selectivity to methane and ethylene overMeOH for the electroredn. of CO2 on Cu catalysts.~131 Citings

153. Dedication to the honor of professor eugen segal on the occasion of his 80th birthday

By Budrugeac, Petru; Carp, OanaFrom Revue Roumaine de Chimie (2013), 58(4-5), 297-326. Language: English, Database: CAPLUS

~0 Citings

154. Velocity Map Imaging Study of the Reaction Dynamics of the H + CH4 → H2 + CH3 Reaction: The IsotopeEffects

By Pan, Huilin; Yang, Jiayue; Shuai, Quan; Zhang, Dong; Zhang, Weiqing; Wu, Guorong; Dai, Dongxu; Jiang, Bo;Zhang, Donghui; Yang, XuemingFrom Journal of Physical Chemistry A (2014), 118(13), 2426-2430. Language: English, Database: CAPLUS,DOI:10.1021/jp501681h

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Following our previous study on the H + CD4 → HD + CD3reaction, the reaction of H + CH4 → H2 + CH3 at collisionenergies ranging from 0.72 to 1.99 eV is studied using crossed-beam and time-sliced velocity map ion imaging techniques.The product angular and translational energy distributions atfour different collision energies were derived from themeasured images. The excitation function was also measuredfrom these images together with a careful calibration of the Hatom beam intensities at different collision energies. All ofthese results are compared with those of the H + CD4 reactionto investigate the isotope effects. The isotope effects are allobsd. in the product angular distributions, the translationalenergy distributions, and the excitation function and furtherconfirm the reaction mechanism proposed in the previous studyon the H + CD4 reaction.

~8 Citings

155. Heavy-Atom Tunneling in the Ring Opening of a Strained Cyclopropene at Very Low Temperatures

By Ertelt, Melanie; Hrovat, David A.; Borden, Weston Thatcher; Sander, WolframFrom Chemistry - A European Journal (2014), 20(16), 4713-4720. Language: English, Database: CAPLUS,DOI:10.1002/chem.201303792

The highly strained 1H-bicyclo[3.1.0]-hexa-3,5-dien-2-one 1 is metastable, and rearranges to 4-oxacyclohexa-2,5-dienylidene 2 in inert gas matrixes (neon, argon, krypton, xenon, and nitrogen) at temps. as low as 3 K. The kinetics forthis rearrangement show pronounced matrix effects, but in a given matrix, the reaction rate is independent of temp.between 3 and 20 K. This temp. independence means that the activation energy is zero in this temp. range, indicatingthat the reaction proceeds through quantum mech. tunneling from the lowest vibrational level of the reactant. At temps.above 20 K, the rate increases, resulting in curved Arrhenius plots that are also indicative of thermally activatedtunneling. These exptl. findings are supported by calcns. performed at the CASSCF and CASPT2 levels by using thesmall-curvature tunneling (SCT) approxn.~17 Citings

156. Potential energy surface fitting by a statistically localized, permutationally invariant, local interpolatingmoving least squares method for the many-body potential: Method and application to N4

By Bender, Jason D.; Doraiswamy, Sriram; Truhlar, Donald G.; Candler, Graham V.From Journal of Chemical Physics (2014), 140(5), 054302/1-054302/16. Language: English, Database: CAPLUS,DOI:10.1063/1.4862157

Fitting potential energy surfaces to analytic forms is an important first step for efficient mol. dynamics simulations. Here,we present an improved version of the local interpolating moving least squares method (L-IMLS) for such fitting. Ourmethod has three key improvements. First, pairwise interactions are modeled sep. from many-body interactions.Second, permutational invariance is incorporated in the basis functions, using permutationally invariant polynomials inMorse variables, and in the wt. functions. Third, computational cost is reduced by statistical localization, in which westatistically correlate the cutoff radius with data point d. We motivate our discussion in this paper with a review of globaland local least-squares-based fitting methods in one dimension. Then, we develop our method in six dimensions, andwe note that it allows the analytic evaluation of gradients, a feature that is important for mol. dynamics. The approach,which we call statistically localized, permutationally invariant, local interpolating moving least squares fitting of the many-body potential (SL-PI-L-IMLS-MP, or, more simply, L-IMLS-G2), is used to fit a potential energy surface to an electronicstructure dataset for N4. We discuss its performance on the dataset and give directions for further research, includingapplications to trajectory calcns. (c) 2014 American Institute of Physics.~11 Citings

157. Apparatus and mechanism of photosynthetic water splitting as nature's blueprint for efficient solar energyexploitation

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By Renger, GernotEdited By:Razeghifard, RezaFrom Natural and Artificial Photosynthesis (2013), 65-119. Language: English, Database: CAPLUS,DOI:10.1002/9781118659892.ch3

A review. This article describes the principles of solar energy exploitation by water splitting, with special emphasis on theperformance of this process in oxygen evolving photosynthetic organisms. This fascinating unique device offers anexcellent blueprint in stimulating considerations on the development of artificial systems for large-scale and efficient useof solar radiation as a free energy source. The most delicate part of the overall process is the oxidn. of two water mols.leading to oxygen formation and H+ release. The problems of this reaction and how it is performed in the multimericphotosystem II (PSII) core complex of the photosynthetic app. were focused.~1 Citing

158. Tunneling in the reactions of carbenes and oxacarbenes

By Gerbig, Dennis; Schreiner, Peter R.From Wiley Series on Reactive Intermediates in Chemistry and Biology (2014), 7(Contemporary Carbene Chemistry),193-215. Language: English, Database: CAPLUS

A review. Tunneling is a common phenomenon in the physics of fundamental particles, for example, for electrons in(semi)conducting materials. Yet, examples of comparable importance of tunneling in chem. transformations are stilllimited. In chem. kinetics, tunneling of entire atoms is generally evaluated only as a quantum mech. correction to the rateconsts. derived from various classical or semiclassical approaches. A reaction mechanism that only becomes feasibledue to the existence of quantum mech. tunneling was not known until the advent of hydroxycarbenes, which occupy aconsiderable part of this review.~2 Citings

159. Constant-Charge Reaction Theory for Potential-Dependent Reaction Kinetics at the Solid-Liquid Interface

By Fang, Ya-Hui; Wei, Guang-Feng; Liu, Zhi-PanFrom Journal of Physical Chemistry C (2014), 118(7), 3629-3635. Language: English, Database: CAPLUS,DOI:10.1021/jp411531f

To understand the potential-dependent kinetics of reactions atthe solid-liq. interface, we derive a const.-charge reactiontheory for understanding the coupled charge transfer during thechem. bond making/breaking. The charge transfer coeff. (CTC)for reactions at the solid-liq. interface is shown to be linearlyproportional to the electrochem. potential change from theinitial state to the transition state as well the interfacedifferential capacitance at the const.-charge model, and can befurther related to the net dipole change normal to the surfaceduring the reaction. Using the const.-charge theory, the CTCcan be explicitly calcd. on the basis of the first principlescalcns. without the need to assume the redox behavior of theelementary reactions and thus provide a unique possibility toevaluate and compare the magnitude of CTC for differentreactions across different surfaces. By examg. a series ofinterface reactions and comparing the calcd. CTC values, wepropose simple rules to understand and predict the chargetransfer coeff. of three classes of the interface elementaryreactions. The role of surface dipole, solvation, and mol.adsorption strength on the CTC can now be clarified from firstprinciples calcns.

~11 Citings

160. Role of Quantum Mechanical Tunneling on the γ-Effect of Silicon on Carbenes in 3-Trimethylsilylcyclobutylidene

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By Karmakar, Sharmistha; Datta, AyanFrom Journal of Physical Chemistry B (2014), 118(9), 2553-2558. Language: English, Database: CAPLUS,DOI:10.1021/jp4116029

Quantum mech. tunneling (QMT) is increasingly being realizedas an important phenomenon that can enhance the rate ofreactions even at room temp. Recently, the ability of atrimethylsilane (TMS) group to activate 1,3-H shift to a carbenefrom a γ-position was demonstrated. Direct dynamical calcns.(using canonical varitational transition state theory) inclusive ofsmall curvature tunneling (CVT-SCT) show that QMT plays adecisive role in such 1,3-H migration in both the presence andabsence of TMS. The presence of a TMS group reduces theactivation energy of 1,3-H shift reaction via 1,3-equatorialinteraction of the TMS group with the carbene. Tunnelingacross the smaller barrier enhances the overall forward rate ofthe reaction. The Arrhenius plot for the reaction showssubstantial curvature in comparison to the CVT mechanism atroom temp. Arrhenius plots for the kinetic isotope effects(KIEs) for the γ-deuterated and per deuterated 3-trimethylsilylcyclobutylidene also show strong deviations fromthe classical over the barrier mechanism. The magnitude ofthe KIE is suggestive of QMT from the vibrational excited statesof the carbenes.

~12 Citings

161. Anchor Points Reactive Potential for Bond-Breaking Reactions

By Yang, Ke R.; Xu, Xuefei; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2014), 10(3), 924-933. Language: English, Database: CAPLUS,DOI:10.1021/ct401074s

We present a new method for fitting potential energy surfacesin mol.-mechanics-like internal coordinates based on data fromelectronic structure calcns. The method should be applicableto chem. reactions involving either bond dissocn. orisomerization and is illustrated here for bond dissocn., inparticular the breaking of an O-H bond in methanol and thebreaking of an N-H bond in dimethylamine. As compared topreviously available systematic methods for fitting globalpotential energy surfaces, it extends the max. size of thesystem than can be treated by at least an order of magnitude.

~9 Citings

162. Effect of Er doping on the structural and magnetic properties of cobalt-ferrite

By Prathapani, Sateesh; Vinitha, M.; Jayaraman, T. V.; Das, D.From Journal of Applied Physics (Melville, NY, United States) (2014), 115(17), 17A502/1-17A502/3. Language:English, Database: CAPLUS, DOI:10.1063/1.4854915

Nanocryst. particulates of Er doped Co ferrites CoFe2-xErxO4 (0 ≤ x ≤ 0.04), were synthesized, using sol-gel assistedautocombustion method. Co-, Fe-, and Er- nitrates were the oxidizers, and malic acid served as a fuel and chelatingagent. Calcination (400-600° for 4 h) of the precursor powders was followed by sintering (1000° for 4 h) and structuraland magnetic characterization. X-ray diffraction confirmed the formation of single phase of spinel for the compns. x = 0,0.01, and 0.02; and for higher compns. an addnl. orthoferrite phase formed along with the spinel phase. Latticeparameter of the doped Co-ferrites was higher than that of pure CoFe2O4. The obsd. red shift in the doped Co-ferritesindicates the presence of induced strain in the CoFe2O4 matrix due to large size of the Er+3 compared to Fe+3. Greaterthan 2-fold increase in coercivity (∼66 kA/m for x = 0.02) was obsd. in doped Co-ferrites compared to CoFe2O4 (∼29kA/m). (c) 2014 American Institute of Physics.

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~6 Citings

163. Chemical Kinetics and Mechanisms of Complex Systems: A Perspective on Recent Theoretical Advances

By Klippenstein, Stephen J.; Pande, Vijay S.; Truhlar, Donald G.From Journal of the American Chemical Society (2014), 136(2), 528-546. Language: English, Database: CAPLUS,DOI:10.1021/ja408723a

A review. An overview of the current status of the theory ofchem. kinetics and mechanisms for complex processes ispresented. The authors attempt to assess the status of thefield for reactions in the gas phase, at gas-solid interfaces, inliq. solns., in enzymes, and for protein folding. Some unifyingconcepts such as potential energy surfaces, free energy,master equations, and reaction coordinates occur in more thanone area. The authors hope this Perspective will be useful forhighlighting recent advances and for identifying important areasfor future research.

~99 Citings

164. Combined first-principles molecular dynamics/density functional theory study of ammonia electrooxidationon Pt(100) electrode

By Skachkov, Dmitry; Venkateswara Rao, Chitturi; Ishikawa, YasuyukiFrom Journal of Physical Chemistry C (2013), 117(48), 25451-25466. Language: English, Database: CAPLUS,DOI:10.1021/jp4048874

A combined first-principles mol. dynamics/d. functional theorystudy of the electrooxidn. of ammonia is conducted to gain anat.-level understanding of the electrocatalytic processes at thePt(100)/alk. soln. interface and to probe the mechanistic detailsof ammonia electrooxidn. on the metal surface. A systematicstudy of adsorption and relative stability of ammonia and theintermediate species on the Pt(100) surface as a function ofpotential is carried out and activation energy profiles for themechanistic steps in the ammonia oxidn. are presented. Thereaction mechanism is potential dependent: the modeling studysupports the Oswin and Salomon's mechanism for moderatesurface potentials (≥+0.5 V vs RHE), and the Gerischer andMaurer's mechanism for lower potentials (<+0.5 V vs RHE).The high electrocatalytic activity of Pt(100) is ascribed to thefacile dimerization of bridging nitrogen atoms to form mol.nitrogen, whereas low activity of Pt(111) and Pt(110) is imputedto the nitrogen atoms that are strongly bound at hollow sitesand poisoning the surface.

~28 Citings

165. Calculations on Tunneling in the Reactions of Noradamantyl Carbenes

By Kozuch, Sebastian; Zhang, Xue; Hrovat, David A.; Borden, Weston ThatcherFrom Journal of the American Chemical Society (2013), 135(46), 17274-17277. Language: English, Database:CAPLUS, DOI:10.1021/ja409176u

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Noradamantylchlorocarbene was found exptl. to undergo ringexpansion to 2-chloro-adamantene at cryogenic temps. Therate const., calcd. with inclusion of small-curvature tunneling, iswithin a factor of 2 of the rate const. measured at 9 K in anitrogen matrix. Calcns. predict that nor-adamantyl-fluoro-carbene will not be found to rearrange under these conditions.The rate const. for carbon tunneling in the ring expansion ofnor-adamantyl-methyl-carbene (1d) to 2-methyladamantene atT 10 K is lower by >8 orders of magnitude than the rate const.for formation of 3-vinylnoradamantane from 1d by hydrogenmigration.

~24 Citings

166. DFT calculations on H, OH and O adsorbate formations on Pt(111) and Pt(332) electrodes

By Jinnouchi, Ryosuke; Kodama, Kensaku; Morimoto, YuFrom Journal of Electroanalytical Chemistry (2014), 716, 31-44. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2013.09.031

D. functional theory combined with a modified Poisson-Boltzmann theory (DFT-MPB) is applied to H, OH and Oadsorbate formations on electrified Pt(111) and Pt(332) surfaces in an acid aq. soln. In this method, the chem. bondsbetween adsorbates and electrodes are quant. described by the DFT, and solvation and elec. field effects by the elec.double layer are described by combining explicit H2O adlayer models and modeled continuum electrolyte. H, OH and Oare bound less strongly to (110)-step on Pt(332) than to terrace on Pt(111) in the elec. double layer while the trend isopposite in vacuum. The trend in the elec. double layer is consistent with the authors' exptl.-obtained cyclicvoltammograms, in which H and (hydr)oxides are formed less easily (at lower and higher potentials, resp.) on Pt(332)than on Pt(111). The small binding energies in the modeled elec. double layer mainly stem from destabilizations ofadsorbates by the presence of strongly adsorbed H2O mols. forming 1-dimensional H-bond networks on the step. Othereffects also contribute to the destabilizations: the strain on the Pt(332) terrace, the confinement by the Pt atoms near thestep and the H2O orientation changes by the formations of adsorbates.~45 Citings

167. Mechanism of oxygen reduction reaction catalyzed by Fe(Co)-Nx/C

By Chen, Xin; Li, Fan; Zhang, Nanlin; An, Li; Xia, DingguoFrom Physical Chemistry Chemical Physics (2013), 15(44), 19330-19336. Language: English, Database: CAPLUS,DOI:10.1039/c3cp52802b

Fe(Co)-Nx/C is an important candidate catalyst for the next generation p exchange membrane fuel cells (PEMFC), butthe relation between the structure and the O redn. activity is still unclear. The different active site structures of Fe(Co)-Nx/C are explored and the O redn. catalytic mechanisms are studied by d. functional theory (DFT). Different kinds of Me-Nx/C motifs, including the edge site around the graphene sheet and the internal site in the graphene sheet (as well as inthe graphyne sheet), are constructed and studied. The calcd. results suggest that for the edge active sites, high O2adsorption strength may result in direct oxidn. of metal ions thus losing their catalytic activity. The internal active sitesare stable in acidic soln. and display catalytic ability of O redn. The catalytic activity of the internal site is affected by 3factors: the kind of internal metal ion, the bonded N or C atoms with metal ions and the size of the graphene sheet.~34 Citings

168. Surface Processes on Interstellar Amorphous Solid Water: Adsorption, Diffusion, Tunneling Reactions, andNuclear-Spin Conversion

By Hama, Tetsuya; Watanabe, NaokiFrom Chemical Reviews (Washington, DC, United States) (2013), 113(12), 8783-8839. Language: English, Database:CAPLUS, DOI:10.1021/cr4000978

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A review.

~91 Citings

169. Electrocatalytic Dechlorination of Atrazine Using Binuclear Iron Phthalocyanine as Electrocatalysts

By Chen, Xin; Hu, Xiaoming; An, Li; Zhang, Nanlin; Xia, Dingguo; Zuo, Xia; Wang, XiayanFrom Electrocatalysis (2014), 5(1), 68-74. Language: English, Database: CAPLUS, DOI:10.1007/s12678-013-0164-z

The electrochem. redn. approach has been suggested as a promising method for detoxification of chlorine-contg. arom.hydrocarbons. In this study, the electrocatalytic dechlorination of atrazine was studied by a non-noble catalyst, binucleariron phthalocyanine coated onto multi-walled carbon nanotubes (bi-FePc/MWNT). Both exptl. and theor. results indicatethat dechlorination of atrazine occurs rapidly on bi-FePc/MWNT electrode. The reaction depends on the adsorption ofthe chlorinated org. compd. on the electrode surface and the reaction rate with hydroxy. By liq. chromatog.-tandem massspectrometer technique, the dechlorination product of atrazine can be assigned to 2-hydroxy-4-ethylamino-6-isopropylamino-1,3,5-triazine, which could be disposed by more convenient and economic biodegrdn. method.~16 Citings

170. N-type doping of diamond semiconductor

By Yan, Cuixia; Dai, Ying; Huang, BaibiaoFrom Materials Science Research Journal (2012), 6(3-4), 275-301. Language: English, Database: CAPLUS

A review. Great efforts have been made both theor. and exptl. to achieve available n-type diamond materials during thepast years. In this review, recent investigations about the effects of the impurities on the n-type electronic properties ofdiamond materials are looked back. Topics covered include electronic properties of diamond, types, doping methods,the influences of various donor impurities and two dopants codoping on n-type electronic properties of diamond. Inaddn., the influences of hydrogen and vacancy defects on donor impurities are also discussed in detail. Finally, anotherpossible approach to achieve n-type diamond materials by the cond. type transition from p-type to n-type throughdeuteration is introduced. Various attempted explains for the conversion mechanism from p-type to n-type cond. arereviewed. The paper provides a relatively complete picture of doping n-type diamond and necessary information of n-type diamond investigation, which is helpful for those who are starting to work in the field of n-type diamond materials.~0 Citings

171. Functionalization of Monolayer h-BN by a Metal Support for the Oxygen Reduction Reaction

By Lyalin, Andrey; Nakayama, Akira; Uosaki, Kohei; Taketsugu, TetsuyaFrom Journal of Physical Chemistry C (2013), 117(41), 21359-21370. Language: English, Database: CAPLUS,DOI:10.1021/jp406751n

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The catalytic activity for the O redn. reaction (ORR) of ahexagonal B nitride (h-BN) monolayer supported on a Ni(111)surface was studied theor. using d.-functional theory. TheNi(111) support can critically change the chem. and phys.properties of defect-free monolayer h-BN, considerablypromoting the adsorption of O2, OOH, OH, and O species, andtherefore, inert defect-free monolayer h-BN can befunctionalized by the metal support and become catalyticallyactive for the ORR. Although simple potential-dependentmodeling of the energetics of the ORR on h-BN/Ni(111)indicates the limitation of the ORR process due to the largeoverpotential, the authors' calcns. demonstrate the ability tofunctionalize inert materials for the ORR and open new ways todesign effective Pt-free catalysts for fuel-cell technol.

~62 Citings

172. Reaction dynamics of CH3 + HBr → CH4 Br at 150-1000 K

By Ree, Jongbaik; Kim, Yoo Hang; Shin, Hyung KyuFrom Bulletin of the Korean Chemical Society (2013), 34(8), 2473-2479. Language: English, Database: CAPLUS,DOI:10.5012/bkcs.2013.34.8.2473

The kinetics of the radical-polar mol. reaction CH3 + HBr → CH4 + Br has been studied at temps. between 150 and 1000K using classical dynamics procedures. Potential energy surfaces constructed using anal. forms of inter- and intramol.interaction energies show a shallow well and barrier in the entrance channel, which affect the collision dynamics at lowtemps. Different collision models are used to distinguish the reaction occurring at low- and high-temp. regions. Thereaction proceeds rapidly via a complex-mode mechanism below room temp. showing strong neg. temp. dependence,where the effects of mol. attraction, H-atom tunneling and recrossing of collision complexes are found to be important.The temp. dependence of the rate const. between 400 and 1000 K is pos., the values increasing in accordance with theincrease of the mean speed of collision. The rate const. varies from 7.6 × 10-12 at 150 K to 3.7 × 10-12 at 1000 K via amin. value of 2.5 × 10-12 cm3 mol.-1 s-1 at 400 K.~7 Citings

173. Development of open-boundary cluster model approach for electrochemical systems and its application toAg+ adsorption on Au(111) and Ag(111) electrodes

By Iida, Kenji; Yasuike, Tomokazu; Nobusada, KatsuyukiFrom Journal of Chemical Physics (2013), 139(10), 104101/1-104101/7. Language: English, Database: CAPLUS,DOI:10.1063/1.4820360

The authors present a theor. method to study electrochem. processes from a finite-temp. d. functional theory (FT-DFT)approach combined with the authors' recently developed open-boundary cluster model (OCM). A semi-infinite electrodeis well mimicked by a finite-sized simple cluster with an open quantum boundary condition rationalized by OCM. Anequil. state between adsorbates and an electrode is described by the grand canonical formulation of FT-DFT. Theseimplements allow the authors to calc. electronic properties of an adsorbate and electrode system at a const. chem.potential µ, i.e., electrode potential. A solvation effect is approximated by a conductor-like polarized continuum model.The method is applied to the electrochem. processes of Ag+ adsorption on Au(111) and Ag(111). The present const. µapproach proved essential to electrochem. systems, demonstrating that the method qual. reproduces the exptl. evidencethat Ag+ adsorbs more on the Au electrode than the Ag one, while the conventional quantum chem. approach with aconst. no. of electrons incorrectly gives exactly the opposite result. (c) 2013 American Institute of Physics.~2 Citings

174. AM1 Specific Reaction Parameters for Reactions of Hydroxide Ion with Halomethanes in ComplexEnvironments: Development and Testing

By Liang, Shuai; Roitberg, Adrian E.From Journal of Chemical Theory and Computation (2013), 9(10), 4470-4480. Language: English, Database: CAPLUS,DOI:10.1021/ct400471m

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A specific reaction parameters (SRP) approach is used toreparameterize the semiempirical AM1 method to representtwo SN2 reactions of OH- with halomethanes (CH3F andCH3Cl). The objective is to develop SRP models that are ableto accurately reproduce ab initio potential energy surfaces butwith a redn. of several orders of magnitude in computationalcost. The developed models, labeled AM1-SRP, have beentested in gas and aq. phases. The results show that the AM1-SRP models are able to predict a min. reaction path in closeagreement with high level ab initio calcns. in gas phase. AQM/MM simulation method with the solutes represented by theAM1-SRP models is used to compute the free energy profilesof the reactions in aq. phase. The AM1-SRP models predictreaction free energies and free energy barriers in goodagreement with exptl. values. The current study indicates thatsemiempirical models may be improved to accuratelyreproduce an ab initio min. reaction path at a considerablylower cost. The SRP approach is expected to be useful in longtime scale mol. dynamics simulations where it is veryexpensive to use ab initio methods, specially in condensedphases.

~10 Citings

175. Importance of catalyst stability vis-a-vis hydrogen peroxide formation rates in PEM fuel cell electrodes

By Sethuraman, Vijay A.; Weidner, John W.; Haug, Andrew T.; Pemberton, Marianne; Protsailo, Lesia V.From arXiv.org, e-Print Archive, Condensed Matter (2013), 1-38, arXiv:1308.4042v1 [cond-mat.mtrl-sci]. Language:English, Database: CAPLUS

The role of catalyst stability on the adverse effects of hydrogen peroxide (H2O2) formation rates in a proton exchangemembrane fuel cell (PEMFC) is investigated for Pt, Pt binary (PtX, X = Co, Ru, Rh, V, Ni) and ternary (PtCoX, X = Ir, Rh)catalysts. The selectivity of these catalysts towards H2O2 formation in the oxygen redn. reaction (ORR) was measuredon a rotating ring disk electrode. These measured values were used in conjunction with local oxygen and proton concns.to est. local H2O2 formation rates in a PEMFC anode and cathode. The effect of H2O2 formation rates on the most activeand durable of these catalysts (PtCo and PtIrCo) on Nafion membrane durability was studied using a single-sidedmembrane electrode assembly (MEA) with a built-in ref. electrode. Fluoride ion concn. in the effluent water was used asan indicator of the membrane degrdn. rate. PtIrCo had the least fluorine emission rate (FER) followed by PtCo/KB andPt/KB. Though PtCo and PtIrCo show higher selectivity for H2O2 formation than unalloyed Pt, they did not contribute tomembrane degrdn. This result is explained in terms of catalyst stability as measured in potential cycling tests in liq.electrolyte as well as in a functional PEM fuel cell.~0 Citings

176. CO Oxidation on Supported Single Pt Atoms: Experimental and ab Initio Density Functional Studies of COInteraction with Pt Atom on θ-Al2O3(010) Surface

By Moses-DeBusk, Melanie; Yoon, Mina; Allard, Lawrence F.; Mullins, David R.; Wu, Zili; Yang, Xiaofan; Veith,Gabriel; Stocks, G. Malcolm; Narula, Chaitanya K.From Journal of the American Chemical Society (2013), 135(34), 12634-12645. Language: English, Database:CAPLUS, DOI:10.1021/ja401847c

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Although there are only a few known examples of supportedsingle-atom catalysts, they are unique because they bridge thegap between homogeneous and heterogeneous catalysis.Here, we report the CO oxidn. activity of monodisperse singlePt atoms supported on an inert substrate, θ-alumina (Al2O3), inthe presence of stoichiometric oxygen. Since CO oxidn. onsingle Pt atoms cannot occur via a conventional Langmuir-Hinshelwood scheme (L-H scheme) which requires at least onePt-Pt bond, we carried out a first-principles d. functional theor.study of a proposed pathway which is a variation on theconventional L-H scheme and inspired by the organometallicchem. of platinum. We find that a single supported Pt atomprefers to bond to O2 over CO. CO then bonds with theoxygenated Pt atom and forms a carbonate which dissocs. toliberate CO2, leaving an oxygen atom on Pt. Subsequentreaction with another CO mol. regenerates the single-atomcatalyst. The energetics of the proposed mechanism suggeststhat the single Pt atoms will get covered with CO3 unless thetemp. is raised to eliminate CO2. We find evidence for CO3coverage at room temp. supporting the proposed mechanism inan in situ diffuse reflectance IR study of CO adsorption on thecatalyst's supported single atoms. Thus, our results clearlyshow that supported Pt single atoms are catalytically active andthat this catalytic activity can occur without involving thesubstrate. Characterization by electron microscopy and X-rayabsorption studies of the monodisperse Pt/θ-Al2O3 are alsopresented.

~226 Citings

177. 3d transition metal impurities in diamond: electronic properties and chemical trends

By Assali, L. V. C.; Machado, W. V. M.; Justo, J. F.From arXiv.org, e-Print Archive, Condensed Matter (2013), 1-19, arXiv:1307.3278v1 [cond-mat.mtrl-sci]. Language:English, Database: CAPLUS

First principles calcns. have been used to investigate the trends on the properties of isolated 3d transition metalimpurities (from Sc to Cu) in diamond. Those impurities have small formation energies in the substitutional or doublesemi-vacancy sites, and large energies in the interstitial one. Going from Sc to Cu, the 3d-related energy levels in thebandgap move from the top of the bandgap toward the valence band in all three sites. Trends in electronic propertiesand transition energies of the impurities, in the substitutional or interstitial sites, are well described by a simplemicroscopic model considering the electronic occupation of the 3d-related levels. On the other hand, for the impurities inthe double semi-vacancy site, there is a weak interaction between the divacancy- and the 3d-related orbitals, resulting invacancy- and 3d-related levels in the materials bandgap.~0 Citings

178. Electrocatalysis and pH (a review)

By Tarasevich, M. R.; Korchagin, O. V.From Russian Journal of Electrochemistry (2013), 49(7), 600-618. Language: English, Database: CAPLUS,DOI:10.1134/S102319351307015X

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A review. The factors detg. pH effects on principal catalytic reactions in low-temp. fuel cells (oxygen redn., hydrogenoxidn., and primary alcs. oxidn.) were analyzed. The decreasing of hydrogen oxidn. rate when passing from acidicelectrolytes to basic ones was shown to be due to the electrode surface blocking by oxygen-contg. species and changesin the adsorbed hydrogen energy state. In the case of oxygen redn., the key factors detg. the process' kinetics andmechanism are: the O2 adsorption energy, the adsorbed mol. protonation, and the oxygen reaction thermodn. Theprocess' high selectivity in acidic electrolytes at platinum electrodes is caused by rather high Pt-O2 bond energy and itsprotonation. The passing from acidic electrolytes to basic ones involves a decrease in the oxygen adsorption energy,both at platinum and nonplatinum catalysts, hence, in the selectivity of the oxygen-to-water redn. reaction. The increasein the methanol and ethanol oxidn. rate in basic media, as compared with acidic ones, is due to changes in the reactingspecies' structure (because of the alc. mols. dissocn.) on the one hand, and active OHads species inflow to the reactionzone, on the other hand. In the case of ethanol, the above-listed factors det. the process' increased selectivity withrespect to CO2 at higher pHs. Based on the survey and valuation, priority guidelines in the electrocatalysis of com.important reactions are formulated, in particular, concepts of electrocatalysis at nonplatinum electrode materials that arestable in basic electrolytes, and approaches to the practical control of the rate and selectivity of oxygen redn. and primaryalcs. oxidn. over wide pH range.~28 Citings

179. Correct Interpretation of How Tunneling Proceeds at Low Temperatures in the Proton Transfer ReactionsInvolving Thiotropolone: A Comment

By Fernandez-Ramos, AntonioFrom Angewandte Chemie, International Edition (2013), 52(32), 8204-8205. Language: English, Database: CAPLUS,DOI:10.1002/anie.201303206

A polemic. The author claims that the canonical variational transition-state theory calcns. with small-curvature tunnelingcorrections (CVT/SCT) of Jose and Data on the intramol. proton transfer processes in thiotropolone and tropolone areincorrect, and that the conclusions derived from those calcns. are erroneous. A correct interpretation of tunneling effectsis given.~7 Citings

180. Roadmap to spline-fitting potentials in high dimensions

By Patricio, M.; Santos, J. L.; Patricio, F.; Varandas, A. J. C.From Journal of Mathematical Chemistry (2013), 51(7), 1729-1746. Language: English, Database: CAPLUS,DOI:10.1007/s10910-013-0173-4

The use of the theory of splines to approx. the potential energy surface in mol. dynamics is examd. It is envisaged thatsuch an approxn. should be able to accurately capture the potentials' behavior and be computationally cost effective,both for one-dimensional and n-dimensional problems with n arbitrary. In this regard, the problem of dimensionality ispinpointed, with shape-preserving splines emerging as a viable alternative for fitting surfaces in multidimensional spaces.An algorithm is also presented to allow the use of non-uniform meshes with high accuracy fitting and less interpolationpoints.~10 Citings

181. Methane hydrates and their HF doped analogues

By Mondal, Sukanta; Giri, Santanab; Chattaraj, Pratim KumarFrom Chemical Physics Letters (2013), 578, 110-114. Language: English, Database: CAPLUS,DOI:10.1016/j.cplett.2013.06.017

A computational study is carried out to simulate methane hydrates as well as to know the effect of HF doping on theirstability and structure. By using ab initio mol. dynamics simulation interaction of methane with HF doped clathratehydrates is studied. The total energy profiles present insights into the stability and structure of methane hydrates. TheHF doping increases the stability of the methane hydrates without any distortion of the cage when methane isencapsulated in 512 cages.~3 Citings

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182. Aryl Nitrene Rearrangements: Spectroscopic Observation of a Benzazirine and Its Ring Expansion to aKetenimine by Heavy-Atom Tunneling

By Inui, Hiroshi; Sawada, Kazuhiro; Oishi, Shigero; Ushida, Kiminori; McMahon, Robert J.From Journal of the American Chemical Society (2013), 135(28), 10246-10249. Language: English, Database:CAPLUS, DOI:10.1021/ja404172s

In the photodecompns. of 4-methoxyphenyl azide (1) and 4-methylthiophenyl azide (5) in argon matrixes at cryogenictemps., benzazirine intermediates were identified on the basisof IR spectra. As expected, the benzazirines photochem.rearranged to the corresponding ketenimines and tripletnitrenes. Interestingly, with the methylthio substituent, therearrangement of benzazirine 8 to ketenimine 7 occurred at1.49 × 10-5 s-1 even in the dark at 10 K, despite a computedactivation barrier of 3.4 kcal mol-1. Because this rate is 1057

times higher than that calcd. for passing over the barrier andbecause it shows no temp. dependence, the rearrangementmechanism is interpreted in terms of heavy-atom tunneling.

~25 Citings

183. Computational Evidence for Heavy-Atom Tunneling in the Bergman Cyclization of a 10-Membered-RingEnediyne

By Greer, Edyta M.; Cosgriff, Christopher V.; Doubleday, CharlesFrom Journal of the American Chemical Society (2013), 135(28), 10194-10197. Language: English, Database:CAPLUS, DOI:10.1021/ja402445a

DFT and CASSCF calcns. for the cyclization of (3Z)-cyclodec-3-en-1,5-diyne were carried out to investigate heavy-atomtunneling. At 37 °C, tunneling was computed to enhance therate by 38-40% over the transition-state theory rate. Intramol.12C/13C kinetic isotope effects were predicted to be substantial,with a steep temp. dependence. These results are discussedin relation to recent exptl. findings that show heavy-atomtunneling at moderate temps. The calcns. point to thepossibility of a simple computational test for the likelihood ofheavy-atom tunneling using std. quantum-chem. information.

~17 Citings

184. Design of visible-light photocatalysts by coupling of narrow bandgap semiconductors and TiO2: effect oftheir relative energy band positions on the photocatalytic efficiency

By Rawal, Sher Bahadur; Bera, Sandipan; Lee, Daeki; Jang, Du-Jeon; Lee, Wan InFrom Catalysis Science & Technology (2013), 3(7), 1822-1830. Language: English, Database: CAPLUS,DOI:10.1039/c3cy00004d

According to relative energy band positions between TiO2 and visible-light-absorbing semiconductors, three differenttypes of heterojunction were designed, and their visible-light photocatalytic efficiencies were analyzed. In Type-Aheterojunction, the conduction band (CB) level of sensitizer is positioned at a more neg. side than that of TiO2, whereasin Type-B system its valence band (VB) level is more pos. than that of TiO2 and in Type-C system the sensitizer energylevel is located between the CB and VB of TiO2. In evolving CO2 from gaseous 2-propanol (IP) under visible-light irradn.,the Type-B systems such as FeTiO3/TiO2, Ag3PO4/TiO2, W18O49/TiO2, and Sb-doped SnO2 (ATO)/TiO2 demonstratednoticeably higher photocatalytic efficiency than the Type-A such as CdS/TiO2 and CdSe/TiO2, while the Type-C such asNiTiO3/TiO2, CoTiO3/TiO2, and Fe2O3/TiO2 did not show any appreciable improvement. Remarkably high visible-lightphotocatalytic activity of Type-B heterojunction structures could be explained by inter-semiconductor hole-transfermechanism between the VB of the sensitizer and that of TiO2. The evidence for the hole-transport between sensitizerand TiO2 was also obtained by monitoring the hole-scavenging reactions with iodide (I-) and 1,4-terephthalic acid (TA).~95 Citings

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185. Concerted hydrogen atom and electron transfer mechanism for catalysis by lysine-specific demethylase

By Yu, Tao; Higashi, Masahiro; Cembran, Alessandro; Gao, Jiali; Truhlar, Donald G.From Journal of Physical Chemistry B (2013), 117(28), 8422-8429. Language: English, Database: CAPLUS,DOI:10.1021/jp404292t

The free energy profile for the postulated hydride transferreaction mechanism for the catalysis of protein Lysdemethylation by lysine-specific demethylase LSD1 was calcd.The potential energy surface was obtained by using combinedelectrostatically embedded multiconfiguration mol. mechanics(EE-MCMM) and single-configuration mol. mechanics (MM).The authors employed a const. valence bond coupling term toobtain anal. energies and gradients of the EE-MCMMsubsystem, which contained 45 quantum mechanics (QM)atoms and which was parametrized with DFT calcns.employing specific reaction parameters obtained by matchinghigh-level wave function calcns. In the MM region, the authorsemployed the Amber ff03 and TIP3P force fields. The freeenergy of activation at 300 K was calcd. by mol. dynamics (MD)umbrella sampling on a system with 102,090 atoms as themax. of the free energy profile along the reaction coordinate asobtained by the weighted histogram anal. method with 17umbrella sampling windows. This yielded a free energy ofactivation of only 10 kcal/mol, showing that the previouslypostulated direct hydride transfer reaction mechanism isplausible, although the authors found that it was betterinterpreted as a concerted transfer of a H atom and anelectron.

~10 Citings

186. Theoretical analysis on the kinetic isotope effects of bimolecular nucleophilic substitution (SN2) reactionsand their temperature dependence

By Tsai, Wan-Chen; Hu, Wei-PingFrom Molecules (2013), 18, 4816-4843. Language: English, Database: CAPLUS, DOI:10.3390/molecules18044816

Factors affecting the kinetic isotope effects (KIEs) of the gas-phase SN2 reactions and their temp. dependence havebeen analyzed using the ion-mol. collision theory and the transition state theory (TST). The quantum-mech. tunnelingeffects were also considered using the canonical variational theory with small curvature tunneling (CVT/SCT). We havebenchmarked a few ab initio and d. functional theory (DFT) methods for their performance in predicting the deuteriumKIEs against eleven exptl. values. The results showed that the MP2/aug-cc-pVDZ method gave the most accurateprediction overall. The slight inverse deuterium KIEs usually obsd. for the gas-phase SN2 reactions at room temp. weredue to the balance of the normal rotational contribution and the significant inverse vibrational contribution. Since thevibrational contribution is a sensitive function of temp. while the rotation contribution is temp. independent, the KIEs arethus also temp. dependent. For SN2 reactions with appreciable barrier heights, the tunneling effects were predicted tocontribute significantly both to the rate consts. and to the carbon-13 and carbon-14 KIEs, which suggested importantcarbon atom tunneling at and below room temp.~5 Citings

187. Possibility of Having HF-Doped Hydrogen Hydrates

By Mondal, Sukanta; Giri, Santanab; Chattaraj, Pratim K.From Journal of Physical Chemistry C (2013), 117(22), 11625-11634. Language: English, Database: CAPLUS,DOI:10.1021/jp401342r

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A multiscale computational work is assessed to envisage theeffect of HF doping on the stability, structure, and reactivity ofclathrate hydrates. Interaction of mol. hydrogen with HF-dopedclathrate hydrates is studied through ab initio mol. dynamicssimulation with the aid of conceptual d. functional theory. Theviability of hydrogen encapsulation in HF-doped clathratehydrates is justified in terms of the assocd. interaction energy,reaction enthalpy, hardness, and electrophilicity values. Calcd.thermodn. parameters are well-correlated with the max.hardness principle and min. electrophilicity principle for allcases. It is obsd. that HF doping significantly increases thestability of the studied clathrate hydrates and it also enhancesthe binding energy and reaction enthalpy for the encapsulationof hydrogen mols.

~8 Citings

188. New Insights into the Oxygen Reduction Reaction Mechanism on Pt (111): A Detailed Electrochemical Study

By Gomez-Marin, Ana M.; Feliu, Juan M.From ChemSusChem (2013), 6(6), 1091-1100. Language: English, Database: CAPLUS, DOI:10.1002/cssc.201200847

The O redn. reaction (ORR) is undoubtedly the most important fuel-cell cathodic reaction. A detailed electrochem. anal.of the ORR on Pt (111) in nonadsorbing electrolytes was performed, which included the high-potential region Eup=1.15 Vwhile ensuring the electrode surface structure stability. Probably the redn. of a sol. intermediate species formed duringthe ORR is the rate-detg. step in the whole reaction mechanism. This species does not undergo any other electrochem.reaction at E>0.9 V and may accumulate close to the electrode surface. Together with dissolved O2, this intermediatemay modify the oxide-growth dynamics on Pt (111). Hence, both species interact with the electrode surface throughcomplex catalytic networks. Under certain exptl. conditions, oxygenated species from the oxidn. of Pt (111) mayenhance the overall ORR current. These results propose an alternative to explain the current state of the art for thisfundamental process.~34 Citings

189. STEREODYNAMICS STUDY OF THE ABSTRACTION REACTION H + CD4 → HD + CD3

By Cheng, Dahai; Yang, Tiangang; Chen, MaoduFrom Journal of Theoretical & Computational Chemistry (2013), 12(2), 1250109/1-1250109/9. Language: English,Database: CAPLUS, DOI:10.1142/S021963361250109X

A new London-Eyring-Polanyi-Sato (LEPS) potential energy surface (PES) is employed in this work to study the stereoproperties for the abstraction reaction of hydrogen with methane at its rovibrationally ground state using thequasiclassical trajectory method (QCT). A quasi-triat. approxn. is used to treat the CD3 group of CD4 as a pseudoatom.The calcd. excitation function of the title reaction can give a good agreement to most exptl. and theor. data at collisionenergies (Ec = 1.5 ~ 2.5 eV). Further study of the product HD in reaction H + CD4(v = 0, j = 0) → HD + CD3 and D +CH4(v = 0, j = 0) → HD + CH3 shows the dependence of the product rotational polarization on collision energies andmass factor, but P(θr) is not sensitive to both the collision energies and the mass factor.~1 Citing

190. Classical dynamics of chemical reactions in a quantum spirit

By Bonnet, LaurentFrom International Reviews in Physical Chemistry (2013), 32(2), 171-228. Language: English, Database: CAPLUS,DOI:10.1080/0144235X.2012.752905

A review. Mol. beam expts. provide fascinating data on how atoms move in the course of chem. reactions. In order totheor. reproduce these data at relatively low computational cost and to interpret them, nuclei are often treated asclassical particles, even though we have known for about a century that, in the range of energies usually available tochem. systems, their motion is best described by the laws of quantum mechanics. Nevertheless, over the last decadethis approxn. has been shown to work unexpectedly well, provided that a few constraints are introduced into the calcns.in order to take into account the quantisation of product internal motions. Why this is so and the nature of the previousconstraints are the central issues of this review article.

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~57 Citings

191. Chain length dependence of polyol synthesis of zinc ferrite nanoparticles: why is diethylene glycol sodifferent?

By Rishikeshi, Supriya N.; Joshi, Satyawati S.; Temgire, Mayur K.; Bellare, Jayesh R.From Dalton Transactions (2013), 42(15), 5430-5438. Language: English, Database: CAPLUS,DOI:10.1039/c2dt32026f

Superparamagnetic ZnFe2O4 nanoparticles with size range of 28-38 nm were synthesized by polyol process based onuse of varying chain length glycols as solvent. The authors have offered, for the first time, the plausible mechanismbehind in situ formation of zinc ferric oxalate hydroxide hydrate [Fe2Zn(C2O4)2(OH)3]+·4H2O complex from diethylene andpolyethylene glycol. The authors are also reporting, the magnetic properties of above complexes. The authors found aferromagnetic ordering in precursor complex compds. The intermediate hydrocarbon chain between the oxalato bridgedmetal cations plays a crucial role in obtaining anomalous magnetic behavior. ZnFe2O4 nanoparticles obtained afterannealing the DEGylated precursor complex (precursor complex formed in diethylene glycol) showed the highestsuperparamagnetic (SPM) behavior (22.4 emu g-1) among others. The reasons for anomalous SPM behavior ofZnFe2O4 nanoparticles are explained on the basis of the degree of inversion of the spinel structure, high surface-to-vol.ratio, which causes non-collinear spin arrangement in a surface layer and higher oxygen concn. on the surface of deadorg. layer, which increases the unpaired valence electrons leading to uncompensated surface spins.~19 Citings

192. Rate coefficients and kinetic isotope effects of the X + CH4 → CH3 + HX (X = H, D, Mu) reactions from ringpolymer molecular dynamics

By Li, Yongle; Suleimanov, Yury V.; Li, Jun; Green, William H.; Guo, HuaFrom Journal of Chemical Physics (2013), 138(9), 094307/1-094307/9. Language: English, Database: CAPLUS,DOI:10.1063/1.4793394

The thermal rate coeffs. and kinetic isotope effects have been calcd. using ring polymer mol. dynamics (RPMD) for theprototypical reactions between methane and several hydrogen isotopes (H, D, and Mu). The excellent agreement withthe theor. rate coeffs. of the H + CH4 reaction obtained previously from a multi-configuration time-dependent Hartreecalcn. on the same potential energy surface provides strong evidence for the accuracy of the RPMD approach. Thesequantum mech. rate coeffs. are also in good agreement with the results obtained previously using the transition-statetheory with semiclassical tunneling corrections for the H/D + CH4 reactions. However, it is shown that the RPMD ratecoeffs. for the ultralight Mu reaction with CH4 are significantly smaller than the exptl. data, presumably suggestinginaccuracies in the potential energy surface and/or exptl. errors. Significant discrepancies between the RPMD andtransition-state theory results have also been found for this challenging system. (c) 2013 American Institute of Physics.~31 Citings

193. Ab initio based potential energy surface and kinetics study of the OH + NH3 hydrogen abstraction reaction

By Monge-Palacios, M.; Rangel, C.; Espinosa-Garcia, J.From Journal of Chemical Physics (2013), 138(8), 084305/1-084305/14. Language: English, Database: CAPLUS,DOI:10.1063/1.4792719

A full-dimensional anal. potential energy surface (PES) for the OH + NH3 → H2O + NH2 gas-phase reaction wasdeveloped based exclusively on high-level ab initio calcns. This reaction presents a very complicated shape with wellsalong the reaction path. Using a wide spectrum of properties of the reactive system (equil. geometries, vibrationalfrequencies, and relative energies of the stationary points, topol. of the reaction path, and points on the reaction swath)as ref., the resulting anal. PES reproduces reasonably well the input ab initio information obtained at the coupled-clustersingle double triple (CCSD(T)) = FULL/aug-cc-pVTZ//CCSD(T) = FC/cc-pVTZ single point level, which represents asevere test of the new surface. As a first application, on this anal. PES we perform an extensive kinetics study usingvariational transition-state theory with semiclassical transmission coeffs. over a wide temp. range, 200-2000 K. Theforward rate consts. reproduce the exptl. measurements, while the reverse ones are slightly underestimated. However,the detailed anal. of the exptl. equil. consts. (from which the reverse rate consts. are obtained) permits us to concludethat the exptl. reverse rate consts. must be re-evaluated. Another severe test of the new surface is the anal. of thekinetic isotope effects (KIEs), which were not included in the fitting procedure. The KIEs reproduce the values obtainedfrom ab initio calcns. in the common temp. range, although unfortunately no exptl. information is available forcomparison. (c) 2013 American Institute of Physics.

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~5 Citings

194. Electrocatalysis

By Jacob, TimoEdited By:Beller, Matthias; Renken, Albert; van Santen, RutgerFrom Catalysis (2012), 201-215. Language: English, Database: CAPLUS

A review. Discussed are the concepts detg. electrochem. interfaces. First each species was characterized by discussingthe electrochem. potential, which is followed by a detailed description of the electrochem. double layer. Finally, thededuced concepts will be applied to the oxygen redn. reaction (ORR) at a Pt electrode, which can be considered as oneof the most fundamental reactions in electrochem.~0 Citings

195. Chemistry computationally and experimentally: how will computational organic chemistry impact organictheories, mechanisms, and synthesis in the twenty-first century?

By Yu, Zhi-Xiang; Liang, YongEdited By:Ding, Kuiling; Dai, Li-XinFrom Organic Chemistry (2012), 561-601. Language: English, Database: CAPLUS,DOI:10.1002/9783527664801.ch15

A review. Computational org. chem. [1, 2], sometimes also called theor. org. chem., has been revolutionizing org. chem.since its origin in the 1920s when the Schrodinger equation was first developed. Computational org. chem. impacted org.chem. in the last century, mainly on understandings of chem. reactivities and the reaction mechanisms, and thedevelopment of theories and concepts, which are still widely used today in both chem. and biochem.~2 Citings

196. Modelling electrified interfaces in quantum chemistry: constant charge vs. constant potential

By Benedikt, Udo; Schneider, Wolfgang B.; Auer, Alexander A.From Physical Chemistry Chemical Physics (2013), 15(8), 2712-2724. Language: English, Database: CAPLUS,DOI:10.1039/c2cp42675g

The proper description of electrified metal/soln. interfaces, as they occur in electrochem. systems, is a key component forsimulating the unique features of electrocatalytic reactions using electronic structure calcns. While in std. solid state(plane wave, periodic boundary conditions) d. functional theory (DFT) calcns. several models for describing electrochem.environments exist, for cluster models in a quantum chem. approach (AO basis, finite system) this is not straightforward.In this work, two different approaches for the theor. description of electrified interfaces of nanoparticles, the const. chargeand the const. potential model, are discussed. Different schemes for describing electrochem. reactions includingsolvation models are tested for a consistent description of the electrochem. potential and the local chem. behavior forfinite structures. The different schemes and models are investigated for the oxygen redn. reaction (ORR) on ahemispherical cuboctahedral platinum nanoparticle.~16 Citings

197. Recent progress in nitrogen-doped carbon and its composites as electrocatalysts for fuel cell applications

By Wong, W. Y.; Daud, W. R. W.; Mohamad, A. B.; Kadhum, A. A. H.; Loh, K. S.; Majlan, E. H.From International Journal of Hydrogen Energy (2013), 38(22), 9370-9386. Language: English, Database: CAPLUS,DOI:10.1016/j.ijhydene.2012.12.095

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A review. The emergence of fuel cell technol. has created a new tool for the generation of clean, high efficiencyalternative energy for humans. The research and development of new catalysts to replace the expensive and rareplatinum (Pt) to reduce the overall cost of fuel cells is ongoing in this area. Nitrogen-doped carbon and its compositespossess great potential for fuel cell catalyst applications esp. at the oxygen redn. cathode. It is proposed that thereaction mechanisms of nitrogen-doped carbon catalysts for oxygen redn. involve adsorption of oxygen at the partiallypolarized carbon atoms adjacent to the nitrogen dopants, different from the mechanism at platinum catalysts, whichutilize d-bands filling at oxygen adsorption sites. Nitrogen doping in both carbon nanostructures and its composites withactive metals or ceramics are reviewed. Nitrogen-doped carbon without composite metals, displays high catalytic activityin alk. fuel cells and exhibits significant activity in proton exchange membrane fuel cells and direct methanol fuel cells.Pt-based catalysts with nitrogen-doped carbon supports show enhanced catalytic activity towards oxygen redn.,attributed to the enhanced anchoring of Pt to the support that results in better dispersion and stability of the electrodes.For nitrogen-doped carbon composites with non-noble metals (Fe, Co, etc), enhanced activity is seen in both protonexchange and alk. fuel cells. There are many ongoing debates about the nature of nitrogen-carbon bond in catalysis.Pyrrole- and pyridinic-type nitrogen generally considered to be responsible for the catalytic sites in acidic and alk. media,resp. In recent years, significant efforts have been made towards increasing the stability of nitrogen-doped carboncatalysts in acidic media through the formation of composites with ceramic or metal oxide materials. This article reviewsthe progress in the area of this new class of catalysts and their composites for greater enhancement of oxygen redn.activity and stability in various fuel cell applications.~105 Citings

198. Tunneling control of chemical reactions: C-H insertion versus H-tunneling in tert-butylhydroxycarbene

By Ley, David; Gerbig, Dennis; Schreiner, Peter R.From Chemical Science (2013), 4(2), 677-684. Language: English, Database: CAPLUS, DOI:10.1039/C2SC21555A

Elusive tert-butylhydroxycarbene was generated in the gas phase via high-vacuum flash pyrolysis of tert-butylglyoxylicacid at 960 °C. The pyrolysis products were subsequently matrix isolated in solid Ar at 11 K and characterized by meansof IR spectroscopy. While still being exposed to the harsh pyrolysis conditions, the hydroxycarbene undergoes CH-insertion to dimethylcyclopropanol, as well as a CC-insertion to novel methylbutenol, with activation barriers of 23.8 and31.0 kcal mol-1, resp. Once embedded in the cold Ar matrix, the carbene transforms to its isomer pivaldehyde not onlyby photolysis, but it also cuts through the barrier of 27.3 kcal mol-1 by quantum mech. tunneling. The temp. independenthalf-life is measured as 1.7 h; the tunneling pathway was entirely blocked upon O-deuteration. The exptl. half-life of tert-butylhydroxycarbene was verified by tunneling computations applying the Wentzel-Kramers-Brillouin formalism on themin. energy path evaluated at the computationally feasible M06-2X/6-311++G(d,p) level of theory. Our exptl. findings aresupported by relative energy computations at the CCSD(T)/cc-pVDZ level of theory.~22 Citings

199. A six-dimensional state-to-state quantum dynamics study of the H + CH4 → H2 + CH3 reaction (J = 0)

By Liu, Shu; Chen, Jun; Zhang, Zhaojun; Zhang, Dong H.From Journal of Chemical Physics (2013), 138(1), 011101/1-011101/4. Language: English, Database: CAPLUS,DOI:10.1063/1.4774116

We report a quantum state-to-state reaction dynamics study for the title reaction. The calcn. was based on an approxn.that we introduced to the eight-dimensional model for the X + YCZ3 → XY + CZ3 type of reactions that restricts the non-reacting CZ3 group in C3V symmetry proposed by , by assuming that the CZ3 group can rotate freely with respect to itsC3V symmetry axis. With the CH bond length in group fixed at its equil. distance, the degree of freedom included in thecalcn. was reduced to six. Our calcn. shows that the six-dimensional treatment can produce reaction probabilitiesessentially indistinguishable from the seven-dimensional (with CH bond length fixed in the original eight-dimensionalmodel) results. The product vibrational/rotational state distributions and product energy partitioning information arepresented for ground initial rovibrational state with the total angular momentum J = 0. (c) 2013 American Institute ofPhysics.~25 Citings

200. Role of conformational structures and torsional anharmonicity in controlling chemical reaction rates andrelative yields: butanal + HO2 reactions

By Zheng, Jingjing; Seal, Prasenjit; Truhlar, Donald G.From Chemical Science (2013), 4(1), 200-212. Language: English, Database: CAPLUS, DOI:10.1039/C2SC21090H

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Aldehyde-radical reactions are important in atm. and combustion chem., and the reactions studied here also serve moregenerally to illustrate a fundamental aspect of chem. kinetics that has been relatively unexplored from a quant. point ofview, in particular the roles of multiple structures and torsional anharmonicity in detg. the rate consts. and branchingratios (product yields). We consider hydrogen abstraction from four carbon sites of butanal (carbonyl-C, α-C, β-C and γ-C) by hydroperoxyl radical. We employed multi-structural variational transition state theory for studying the first threechannels; this uses a multi-faceted dividing surface and allows us to include the contributions of multiple structures ofboth reacting species and transition states. Multi-configurational Shepard interpolation (MCSI) was used to obtain thegeometries and energies of the potential energy surface along the min.-energy paths, with gradients and Hessians calcd.by the M08-HX/maug-cc-pVTZ method. We find the nos. of structures obtained for the transition states are 46, 60, 72and 76, resp. for the H abstraction at the carbonyl C, the α position, the β position and the γ position. Our results showthat neglecting the factors arising from multiple structures and torsional anharmonicity would lead to errors at 300, 1000and 2400 K of factors of 8, 11 and 10 for abstraction at the carbonyl-O, 2, 11 and 25 at the α-C position, 2, 23 and 47 atthe β-C position, and 0.6, 8 and 18 at the γ-C position. The errors would be even larger at high temp. for the reverse ofthe H abstraction at the β-C. Relative yields are changed as much as a factor of 7.0 at 200 K, a factor of 5.0 at 298 K,and a factor of 3.7 in the other direction at 2400 K. The strong dependence of the product ratios on the multi-structuralanharmonicity factors shows that such factors play an important role in controlling branching ratios in reactionmechanism networks.~24 Citings

201. Theoretical study on the gas-phase SN2 reaction of microhydrated fluoride with methyl fluoride

By Chen, Jien-Lian; Hu, Wei-PingFrom Journal of the Chinese Chemical Society (Weinheim, Germany) (2012), 59(11), 1401-1408. Language: English,Database: CAPLUS, DOI:10.1002/jccs.201200128

The rate consts. for the gas-phase SN2 reaction of F- (H2O) with CH3F have been calcd. using the dual-level variationaltransition state theory including multidimensional tunneling from 50 to 500 K. Tunneling was found to dominate thereaction below 200 K. The deuterium, 13C, and 14C kinetic isotope effects (KIEs) and solvent (D2O) isotope effects(SKIEs) were also calcd. in the same temp. range. The results indicated that the deuterium and heavy watersubstitutions resulted in inverse KIEs (0.6∼0.8) while the 13C and 14C substitutions resulted in normal KIEs (1.0∼1.2) atroom temp. The calcd. carbon KIEs increased significantly below 80 K due to the differences in the magnitude of thetunneling effects for different isotopic substitutions.~5 Citings

202. Protein dynamics and enzyme catalysis: the ghost in the machine?

By Glowacki, David R.; Harvey, Jeremy N.; Mulholland, Adrian J.From Biochemical Society Symposia (2012), 79(Frontiers in Biological Catalysis), 43-55. Language: English,Database: CAPLUS

A review. One of the most controversial questions in enzymol. today is whether protein dynamics are significant inenzyme catalysis. Particular issue in these debates is the unusual temp.-dependence of some kinetic isotope effects forenzyme-catalyzed reactions. In the present paper, the authors review the authors' recent model that is capable ofreproducing intriguing temp.-dependences of enzyme reactions involving significant quantum tunneling. This modelrelies on treating multiple conformations of the enzyme-substrate complex. The results show that direct 'driving' motionsof proteins are not necessary to explain exptl. observations, and show that enzyme reactivity can be understood andaccounted for in the framework of transition state theory.~1 Citing

203. Biofuel Combustion. Energetics and Kinetics of Hydrogen Abstraction from Carbon-1 in n-Butanol by theHydroperoxyl Radical Calculated by Coupled Cluster and Density Functional Theories and MultistructuralVariational Transition-State Theory with Multidimensional Tunneling

By Alecu, I. M.; Zheng, Jingjing; Papajak, Ewa; Yu, Tao; Truhlar, Donald G.From Journal of Physical Chemistry A (2012), 116(50), 12206-12213. Language: English, Database: CAPLUS,DOI:10.1021/jp308460y

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Multistructural canonical variational transition-state theory withsmall-curvature multidimensional tunneling (MS-CVT/SCT) isemployed to calc. thermal rate consts. for hydrogen-atomabstraction from carbon-1 of n-butanol by the hydroperoxylradical over the temp. range 250-2000 K. The M08-SO hybridmeta-GGA d. functional was validated against CCSD(T)-F12aexplicitly correlated wave function calcns. with the jul-cc-pVTZbasis set. It was then used to compute the properties of allstationary points and the energies and Hessians of a fewnonstationary points along the reaction path, which were thenused to generate a potential energy surface by themulticonfiguration Shepard interpolation (MCSI) method. Theinternal rotations in the transition state for this reaction (likethose in the reactant alc.) are strongly coupled to each otherand generate multiple stable conformations, which makeimportant contributions to the partition functions. It is shownthat neglecting to account for the multiple-structure effects andtorsional potential anharmonicity effects that arise from thetorsional modes would lead to order-of-magnitude errors in thecalcd. rate consts. at temps. of interest in combustion.

~24 Citings

204. Visible-Light Photocatalytic Properties of W18O49/TiO2 and WO3/TiO2 Heterocomposites

By Rawal, Sher Bahadur; Bera, Sandipan; Lee, Wan InFrom Catalysis Letters (2012), 142(12), 1482-1488. Language: English, Database: CAPLUS, DOI:10.1007/s10562-012-0924-z

Abstr.: Dark blue W18O49 nanorod (NR) with ∼50 nm length and ∼4 nm width was synthesized by thermally inducedcrystal growth process. Pale yellow WO3 NR with the same dimension was also prepd. by post-annealing the as-prepd.W18O49 NR at 400 °C in air. The W18O49/TiO2 and WO3/TiO2 nanocomposites were then formed by coupling thecorresponding NRs and TiO2 by sol-gel process. Under visible-light irradn. (λ ≥ 422 nm), the W18O49/TiO2 showed aremarkably high photocatalytic activity in removing gaseous 2-propanol (IP) and in evolving CO2. Its efficiency (6.9 ppmCO2 in 2 h) was more than twice that of the WO3/TiO2, which seems to be caused by a profound visible-light absorbanceof W18O49 NR.~21 Citings

205. Multistructural Variational Transition State Theory: Kinetics of the Hydrogen Abstraction from Carbon-2 of2-Methyl-1-propanol by Hydroperoxyl Radical Including All Structures and Torsional Anharmonicity

By Xu, Xuefei; Yu, Tao; Papajak, Ewa; Truhlar, Donald G.From Journal of Physical Chemistry A (2012), 116(43), 10480-10487. Language: English, Database: CAPLUS,DOI:10.1021/jp307504p

The authors calcd. the forward and reverse rate consts. of thehydrogen abstraction reaction from carbon-2 of 2-methyl-1-propanol by hydroperoxyl radical over the temp. range 250-2400 K by using multistructural canonical variational transitionstate theory (MS-CVT) including both multiple-structure andtorsional potential anharmonicity effects by the multistructuraltorsional anharmonicity (MS-T) method. In these calcns.,multidimensional tunneling (MT) probabilities used to computethe tunneling transmission coeffs. were evaluated by the small-curvature tunneling (SCT) approxn. Comparison with the rateconsts. obtained by the single-structural harmonic oscillator(SS-HO) approxn. shows that multistructural anharmonicityincreases the forward rate consts. for all temps., but thereverse rate consts. are reduced for temps. <430 K andincreased for higher temps. The neglect of multistructuraltorsional anharmonicity would lead to errors of factors of 1.5,8.8, and 13 at 300, 1000, and 2400 K, resp., for the forwardreaction, and would lead to errors of factors of 0.76, 3.0, and6.0, resp., at these temps. for the reverse reaction.

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~13 Citings

206. Multi-path variational transition state theory for chemical reaction rates of complex polyatomic species:ethanol + OH reactions

By Zheng, Jingjing; Truhlar, Donald G.From Faraday Discussions (2012), 157(Molecular Reaction Dynamics in Gases, Liquids and Interfaces), 59-88.Language: English, Database: CAPLUS, DOI:10.1039/c2fd20012k

Complex mols. often have many structures (conformations) of the reactants and the transition states, and thesestructures may be connected by coupled-mode torsions and pseudorotations; some but not all structures may havehydrogen bonds in the transition state or reagents. A quant. theory of the reaction rates of complex mols. must takeaccount of these structures, their coupled-mode nature, their qual. different character, and the possibility of mergingreaction paths at high temp. We have recently developed a coupled-mode theory called multi-structural variationaltransition state theory (MS-VTST) and an extension, called multi-path variational transition state theory (MP-VTST), thatincludes a treatment of the differences in the multi-dimensional tunneling paths and their contributions to the reactionrate. The MP-VTST method was presented for unimol. reactions in the original paper and has now been extended tobimol. reactions. The MS-VTST and MP-VTST formulations of variational transition state theory include multi-facetedconfiguration-space dividing surfaces to define the variational transition state. They occupy an intermediate positionbetween single-conformation variational transition state theory (VTST), which has been used successfully for small mols.,and ensemble-averaged variational transition state theory (EA-VTST), which has been used successfully for enzymekinetics. The theories are illustrated and compared here by application to three thermal rate consts. for reactions ofethanol with hydroxyl radical-reactions with 4, 6, and 14 saddle points.~65 Citings

207. Tunneling Governs Intramolecular Proton Transfer in Thiotropolone at Room Temperature

By Jose, Deepthi; Datta, AyanFrom Angewandte Chemie, International Edition (2012), 51(37), 9389-9392, S9389/1-S9389/13. Language: English,Database: CAPLUS, DOI:10.1002/anie.201203355

Calcns. of proton tunneling in thiotropolone using canonical variational transition state theory with the small-curvaturetunneling approxn. from the lowest vibrational level across a narrow and small barrier accounts for the temp.independence of the tautomerism reaction across a rise in reaction temp. of 190 K.~14 Citings

208. Theoretical analysis of the effect of particle size and support on the kinetics of oxygen reduction reactionon platinum nanoparticles

By Viswanathan, Venkatasubramanian; Wang, Frank Yi-FeiFrom Nanoscale (2012), 4(16), 5110-5117. Language: English, Database: CAPLUS, DOI:10.1039/c2nr30572k

Performed a first-principles based computational anal. of the effect of particle size and support material on theelectrocatalytic activity of Pt nanoparticles. Using a mechanism for oxygen redn. that accounts for elec. field effects andstabilization from the water layer on the (111) and (100) facets, it is shown that the model used agrees well with linearsweep voltammetry and rotating ring disk electrode expts. The per-site activity of the nanoparticle sats. for particles >5nm and it is shown that the optimal particle size is in the range of 2.5-3.5 nm, which agrees well with recent exptl. work.The effect of support material was examd. and shown that the perimeter sites on the metal-support interface areimportant in detg. the overall activity of the nanoparticles. Also simple geometric ests. were developed for the activitywhich can be used for detg. the activity of other particle shapes and sizes.~20 Citings

209. Alignment of electronic energy levels at electrochemical interfaces

By Cheng, Jun; Sprik, MichielFrom Physical Chemistry Chemical Physics (2012), 14(32), 11245-11267. Language: English, Database: CAPLUS,DOI:10.1039/c2cp41652b

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The position of electronic energy levels in a phase depends on the surface potentials at its boundaries. Bringing twophases in contact at an interface will alter the surface potentials shifting the energy levels relative to each other. Calcg.such shifts for electrochem. interfaces requires a combination of methods from computational surface science and phys.chem. The problem is closely related to the computation of potentials of electrochem. inactive electrodes. These so-called ideally polarizable interfaces are impossible to cross for electrons. In this perspective the authors review two d.functional theory based methods that were developed for this purpose, the work function method and the H insertionmethod. The key expressions of the two methods are derived from the formal theory of abs. electrode potentials. As anillustration of the work function method the authors review the computation of the potential of zero charge of the Pt(111)-H2O interface as recently published by a no. of groups. The example of the H insertion method is from the authors' ownwork on the rutile TiO2(110)-H2O interface at the point of zero proton charge. The calcns. are summarized in leveldiagrams aligning the electronic energy levels of the solid electrode (Fermi level of the metal, valence band max. andconduction band min. of the semiconductor) to the band edges of liq. H2O and the std. potential for the redn. of thehydroxyl radical. All potentials are calcd. at the same level of d. functional theory using the std. H electrode as commonenergy ref. Comparison to expt. identifies the treatment of the valence band of H2O as a potentially dangerous source oferror for application to electrocatalysis and photocatalysis.~126 Citings

210. Tunneling Rearrangement of 1-Azulenylcarbene

By Henkel, Stefan; Huynh, Y-am; Neuhaus, Patrik; Winkler, Michael; Sander, WolframFrom Journal of the American Chemical Society (2012), 134(32), 13204-13207. Language: English, Database:CAPLUS, DOI:10.1021/ja3050376

1-Azulenylcarbene was synthesized by photolysis of 1-azulenyldiazomethane in argon or neon matrixes at 3-10 K.The highly polar singlet carbene is only metastable andundergoes a tunneling rearrangement to 8-methylene-bicyclo[5.3.0]deca-1,3,5,6,9-pentaene. After substitution of the4 and 8 positions with deuterium, the rearrangement iscompletely inhibited. This indicates a very large kinetic isotopeeffect, as expected for a tunneling reaction.

~13 Citings

211. Modeling of the symmetry factor of electrochemical proton discharge via the Volmer reaction

By Bjorketun, Maarten E.; Tripkovic, Vladimir; Skulason, Egill; Rossmeisl, JanFrom Catalysis Today (2013), 202, 168-174. Language: English, Database: CAPLUS,DOI:10.1016/j.cattod.2012.05.044

A scheme for evaluating symmetry factors of elementary electrode reactions using a d. functional theory (DFT) basedmodel of the electrochem. double layer is presented. As an illustration, the symmetry factor is detd. for H adsorption viathe electrochem. Volmer reaction. The DFT results are compared with predictions of an anal. single electron transfermodel with quadratic reactant and product free energy surfaces. The anal. model, fed with input parameters calcd. byDFT, is shown to give symmetry factors in reasonable agreement with those of the full-scale DFT model. Probably qual.ests. of symmetry factors can should be obtained at a moderate cost by combining comparatively cheap DFT calcns. withreasonably sophisticated anal. models.~8 Citings

212. An ab initio study of surface electrochemical disproportionation: The case of a water monolayer adsorbedon a Pd(1 1 1) surface

By Filhol, Jean-Sebastien; Doublet, Marie-LiesseFrom Catalysis Today (2013), 202, 87-97. Language: English, Database: CAPLUS, DOI:10.1016/j.cattod.2012.04.023

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The authors present a theor. study of the structural response of model H2O monolayers on a Pd(1 1 1) surface uponvarious electrochem. conditions. Whereas the H2O mols. pointing toward the vacuum are mostly electrochem. inactive,those lying parallel to the surface undergo an oxidative adsorption under oxidizing conditions, and those pointing towardthe surface show a reductive adsorption under reducing conditions. The oxidative adsorption results from the interactionof the H2O 1b1 orbital with the metal surface dz2 band which becomes bonding only under oxidative conditions. Thereductive adsorption arises from the interaction of the H2O 4a1-2b2 orbitals with the dz2 band of the Pd surface. Thiselectronic anal. of electrochem. effects is further validated using the Fukui function assocd. with the H2O monolayers.The Fukui function is a powerful tool for studying electrochem. effects as it is directly linked with the electrochem. bondreorganization and other parameters like the surface capacitance. The electrochem. stability diagram for these H2Omonolayers is computed using a new correction for the DFT electrochem. calcns. and compared to previous results. Thephase transformation from a pos. charge H-up to a neg. charged H-down phase is here confirmed with, however, apotential shifted up to 4.5 V compared to the authors' previous report (4.3 V). The neutral phase is found to consist in apos. charged H-up phase and a neg. charged H-down phase. This phenomenon is confirmed by large super-cell calcns.with different ratio of H-up and H-down phases. The stability of the mixed charged phases is then rationalized in terms ofan electrochem. disproportionation whose origin and consequences are further discussed in regards to the resultspreviously obtained from the ice rules.~33 Citings

213. Enhancement in the magnetic moment with Cr3+ doping and its effect on the magneto-structural propertiesof Ce0.1Y2.9Fe5O12

By Naik, S. R.; Salker, A. V.From Physical Chemistry Chemical Physics (2012), 14(28), 10032-10040. Language: English, Database: CAPLUS,DOI:10.1039/c2cp41155e

A change in the overall magnetic moment of Cr3+ doped cubic garnet ferrites prepd. by the modified sol-gel autocombustion method was investigated. A systematic crystal field theory (CFT) approach is utilized towards understandingthis variation in the overall magnetic moment. The malate glycolate precursor obtained in the sol-gel autocombustionmethod proves to be efficient in the monophasic prepn. of the garnet system. X-ray diffraction (XRD) confirms the phaseformation and purity. XPS and Raman spectroscopy have been utilized to confirm the valence states of the elementsand monophasic formation of the compds. A change in the magnetic hyperfine field with doping is revealed byMossbauer spectroscopy. A vibrating sample magnetometer (VSM) was employed to probe the change in the magneticproperties with the change in the compn. and temp. The decrease in the magnitude of the antiferromagnetic interactionat a and d sites, with the inclusion of Cr3+ at the a site and a contribution of L-S coupling from the Cr3+ ions towards anincrease in the resultant magnetic moment, is the significant finding of this investigation.~15 Citings

214. Photosynthetic water splitting: apparatus and mechanism

By Renger, GernotFrom Advances in Photosynthesis and Respiration (2012), 34(Photosynthesis), 359-414. Language: English,Database: CAPLUS, DOI:10.1007/978-94-007-1579-0_17

A review. This chapter reviews our current knowledge on the reactions leading to light-induced water splitting into mol.oxygen and hydrogen, bound in the form of plastoquinol. This process takes place in the multimeric protein complex ofPhotosystem II (PS II). After a brief description of the basic principles of biol. solar energy exploitation throughphotosynthesis, general features of the kinetics, energetics and the structural array and nature of the cofactors of PS IIare presented. The overall reaction pattern of the water:plastoquinone oxidoreductase comprises three types ofsequences: (a) light-induced charge sepn. leading to the "stabilized" radical pair P680+·Q-· A; (b) oxidative water splittinginto mol. oxygen and four protons released into the lumen, driven by P680+· as oxidant and with tyrosine YZ involved asintermediate, and (c) two-step redn. of plastoquinone to quinol under uptake of two protons from the cytoplasm/stroma bythe use of Q-· A as reductant. Evidence is presented that within the (Chl a)4 PheOx (x = 0, 1 or 2) unit, which constitutesthe photoactive pigment P680, the lowest singlet exciton state predominantly located on Chl aD1 acts as electron donorfor the primary charge sepn. and that the exceptionally high redn. potential of P680 mainly originates from a specifichydrophobic protein microenvironment. The key step of oxidative water splitting is the 0-0 bond formation which isshown to occur most likely at the level of a binuclearly complexed peroxide. It is emphasized that the protein matrixplays a key role in tuning the energetics and kinetics. Examples are presented for effects of protein relaxation andflexibility on the reaction pattern of PS II.~25 Citings

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215. A DFT-Based Analysis of the Gold-Catalyzed Cycloisomerization of 1-Siloxy 1,5-Enynes to Cyclohexadienes

By Soriano, Elena; Marco-Contelles, JoseFrom Journal of Organic Chemistry (2012), 77(14), 6231-6238. Language: English, Database: CAPLUS,DOI:10.1021/jo301057j

The authors present a deep theor. study on the intriguing andunexpected gold-catalyzed cycloisomerization of siloxy enynesto cyclohexadienes. To this end, the authors have evaluatedthe electronic and steric properties for three types of alkynylsubstituents along the reaction paths and the implications onthe evolution through divergent, competitive pathways. For analkynyl -OR substituent, the results strongly suggest apolarization of the π electrons along the delocalized C2-C1-Osystem in the key cyclopropyl-carbene intermediate, which isenhanced by the bulkiness of the R group. The resultsreproduce the exptl. observations in excellent agreement andprovide interesting and useful clues for predicting the effects ofthe alkynyl substituent on the nature of the key intermediateand, hence, on the reactivity mode and selectivity.

~13 Citings

216. A comparative DFT study of the catalytic activity of MnO2 (2 1 1) and (2-2-1) surfaces for an oxygenreduction reaction

By Li, Li; Wei, Zidong; Chen, Siguo; Qi, Xueqiang; Ding, Wei; Xia, Meirong; Li, Rong; Xiong, Kun; Deng, Zihua; Gao,YuanyuanFrom Chemical Physics Letters (2012), 539-540, 89-93. Language: English, Database: CAPLUS,DOI:10.1016/j.cplett.2012.04.055

The catalytic activity of β-MnO2 with high-index (2 1 1) and (2-2-1) surfaces for oxygen redn. (ORR) were studied using d.functional theory (DFT). MnO2 (2-2-1) has a higher HOMO energy level and a higher elec. cond. than MnO2 (2 1 1).Thus, MnO2 (2-2-1) surface is more beneficial for electron transfer between the O2 and the catalyst. The calcn. of theadsorption energies shows that the MnO2 (2 1 1) surface has a stronger interaction with the intermediate OH of the ORRthan the MnO2 (2-2-1) surface. Therefore, the activity of MnO2 (2 1 1) is inferior to that of MnO2 (2-2-1) for ORRcatalysis.~12 Citings

217. Proton exchange in acid-base complexes induced by reaction coordinates with heavy atom motions

By Alavi, Saman; Taghikhani, MahdiFrom Chemical Physics (2012), 402, 105-112. Language: English, Database: CAPLUS,DOI:10.1016/j.chemphys.2012.05.004

We extend previous work on nitric acid-ammonia and nitric acid-alkylamine complexes to illustrate that proton exchangereaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strongacid-strong base complexes. The complexes studied involve the biol. and atmospherically relevant glycine, formic,acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of theimaginary frequencies assocd. with the proton exchange transition states are <400 cm-1. This contrasts with widelystudied proton exchange reactions between sym. carboxylic acid dimers or asym. DNA base pair and their analogswhere the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for thetransition states are >1100 cm-1. Calcns. on complexes of these acids with water are performed for comparison.Variations of normal vibration modes along the reaction coordinate in the complexes are described.~1 Citing

218. Accuracy of low-level surface in hierarchical construction of potential energy surface

By Wang, Chun-rui; Zhang, Dong H.From Chinese Journal of Chemical Physics (2012), 25(2), 186-190. Language: English, Database: CAPLUS,DOI:10.1088/1674-0068/25/02/186-190

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The effects of low-level PES on the overall accuracy of the final surface constructed by using hierarchical constructionwere investigated with the constructions of a no. of global surfaces for the H3 system at UHF (UMP2, DFT-B3LYP,UCCSD(T))/vtz, and UCCSD(T)/avqz levels of theory. The total reaction probabilities for the H + H2 reaction calcd. onthese surfaces revealed that the accuracy of UCCSD(T)/avqz surface is very close to the well-known BKMP2 surface,while the UCCSD(T)/vtz PES has a slightly higher barrier. In contrast, the low-level theories (UHF, UMP2, DFT-B3LYP)with vtz basis set can only provide a qual. description of this simplest reaction despite the fact that they are widely usedto study reactions in complex systems. On the other hand, although these theories are not accurate on describing thereaction, they can be used to provide the low-level PESs for hierarchical construction of the UCCSD(T)/avqz PES withthe no. of UCCSD(T)/avqz energies substantially reduced.~1 Citing

219. Mechanism of light induced water splitting in Photosystem II of oxygen evolving photosynthetic organisms

By Renger, GernotFrom Biochimica et Biophysica Acta, Bioenergetics (2012), 1817(8), 1164-1176. Language: English, Database:CAPLUS, DOI:10.1016/j.bbabio.2012.02.005

The reactions of light induced oxidative water splitting were analyzed within the framework of the empirical rate const.-distance relationship of non-adiabatic electron transfer in biol. systems. Comparison of these results with exptl. dataleads to the following conclusions: (1) The oxidn. of tyrosine Yz by the cation radical P680+· in systems with an intactwater oxidizing complex (WOC) is kinetically limited by the non-adiabatic electron transfer step and the extent of thisreaction is thermodynamically detd. by relaxation processes in the environment including rearrangements of hydrogenbond network(s). In marked contrast, all Yz ox induced oxidn. steps in the WOC up to redox state S3 are kineticallylimited by trigger reactions which are slower by orders of magnitude than the rates calcd. for non-adiabatic electrontransfer. (3) The overall rate of the triggered reaction sequence of Yz ox redn. by the WOC in redox state S3 eventuallyleading to formation and release of O2 is kinetically limited by an uphill electron transfer step. Alternative models arediscussed for this reaction. The protein matrix of the WOC and bound water mols. provide an optimized dynamiclandscape of hydrogen bonded protons for catalyzing oxidative water splitting energetically driven by light inducedformation of the cation radical P680+·. In this way the PS II core acts as a mol. machine formed during a longevolutionary process. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: fromNatural to Artificial.~82 Citings

220. Protein dynamics and enzyme catalysis: the ghost in the machine?

By Glowacki, David R.; Harvey, Jeremy N.; Mulholland, Adrian J.From Biochemical Society Transactions (2012), 40(3), 515-521. Language: English, Database: CAPLUS,DOI:10.1042/BST20120047

A review. One of the most controversial questions in enzymol. today is whether protein dynamics are significant inenzyme catalysis. A particular issue in these debates is the unusual temp.-dependence of some kinetic isotope effectsfor enzyme-catalyzed reactions. In the present paper, we review our recent model that is capable of reproducingintriguing temp.-dependences of enzyme reactions involving significant quantum tunnelling. This model relies on treatingmultiple conformations of the enzyme-substrate complex. The results show that direct driving' motions of proteins arenot necessary to explain exptl. observations, and show that enzyme reactivity can be understood and accounted for inthe framework of transition state theory.~9 Citings

221. Density Functional Theory Study of the Oxygen Reduction Reaction on a Cobalt-Polypyrrole CompositeCatalyst

By Chen, Xin; Li, Fan; Wang, Xiayan; Sun, Shaorui; Xia, DingguoFrom Journal of Physical Chemistry C (2012), 116(23), 12553-12558. Language: English, Database: CAPLUS,DOI:10.1021/jp300638e

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A theor. study of the O redn. mechanism catalyzed by Co-polypyrrole was studied in detail by d. functional theory methodusing the BLYP/DZP basis set. The calcns. suggest that theCo-polypyrrole has a Pt-like catalytic behavior based on theadsorption energetics of the reaction intermediates. The di-Co-polypyrrole catalyst exhibits a higher catalytic activity than thatof mono-Co-polypyrrole, due to the fact that the PPy chains indi-Co-polypyrrole have a regular structure.

~26 Citings

222. Infrared Characterization of the HCOOH···CO2 Complexes in Solid Argon: Stabilization of the Higher-EnergyConformer of Formic Acid

By Tsuge, Masashi; Marushkevich, Kseniya; Rasanen, Markku; Khriachtchev, LeonidFrom Journal of Physical Chemistry A (2012), 116(22), 5305-5311. Language: English, Database: CAPLUS,DOI:10.1021/jp302911p

The complexes of formic acid (HCOOH, FA) with CO2 arestudied by IR spectroscopy in an Ar matrix. Two trans-FA···CO2 and 1 cis-FA···CO2 complexes are exptl. identifiedwhile the calcns. at the MP2(full)/6-311++G(2d,2p) level oftheory predict 1 more min. for the cis-FA···CO2 complex. Thecomplex of the higher-energy conformer cis-FA with CO2 isprepd. by vibrational excitation of the ground-state trans-FAconformer combined with thermal annealing. The lifetime ofthe cis-FA···CO2 complex in an Ar matrix at 10 K is 2 orders ofmagnitude longer than that of the cis-FA monomer. This bigdifference is explained by the computational results which showa higher stabilization barrier for the complex. The solvationeffects in solid Ar are theor. estd. and their contribution to thestabilization barriers of the higher-energy species is discussed.The relative barrier transmissions for H tunneling in the cis-FA···CO2 complex and cis-FA monomer are in good agreementwith the exptl. decay rates.

~15 Citings

223. Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

By Stephens, Ifan E. L.; Bondarenko, Alexander S.; Gronbjerg, Ulrik; Rossmeisl, Jan; Chorkendorff, IbFrom Energy & Environmental Science (2012), 5(5), 6744-6762. Language: English, Database: CAPLUS,DOI:10.1039/c2ee03590a

A review. The high cost of low temp. fuel cells is to a large part dictated by the high loading of Pt required to catalyze theoxygen redn. reaction (ORR). Arguably the most viable route to decrease the Pt loading, and to hence commercializethese devices, is to improve the ORR activity of Pt by alloying it with other metals. In this perspective paper we providean overview of the fundamentals underlying the redn. of oxygen on platinum and its alloys. We also report the ORRactivity of Pt5La for the first time, which shows a 3.5- to 4.5-fold improvement in activity over Pt in the range 0.9 to 0.87 V,resp. We employ angle resolved XPS and d. functional theory calcns. to understand the activity of Pt5La.~562 Citings

224. Tunnelling control of chemical reactions - the organic chemist's perspective

By Ley, David; Gerbig, Dennis; Schreiner, Peter R.From Organic & Biomolecular Chemistry (2012), 10(19), 3781-3790. Language: English, Database: CAPLUS,DOI:10.1039/c2ob07170c

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A review. Even though quantum mech. tunnelling was appearing recurrently mostly in theor. studies that emphasize itsdecisive role for many chem. reactions, it still appears suspicious to most org. chemists. Recent expts. in combinationwith powerful computational approaches, however, demonstrated that tunnelling must be included to fully understandchem. reactivity. Here the authors provide an overview of the importance of tunnelling in org. chem. reactions.~85 Citings

225. Isotope Effects and Heavy-Atom Tunneling in the Roush Allylboration of Aldehydes

By Vetticatt, Mathew J.; Singleton, Daniel A.From Organic Letters (2012), 14(9), 2370-2373. Language: English, Database: CAPLUS, DOI:10.1021/ol300789a

Intermol. 13C kinetic isotope effects (KIEs) for the Roushallylboration of p-anisaldehyde were detd. using a novelapproach. The exptl. 13C KIEs fit qual. with the expected rate-limiting cyclic transition state, but they are far higher than theor.predictions based on conventional transition state theory. Thisdiscrepancy is attributed to a substantial contribution of heavy-atom tunneling to the reaction, and this is supported bymultidimensional tunneling calcns. that reproduce the obsd.KIEs.

~16 Citings

226. Oxygen reduction reaction on cobalt-(6)pyrrole cluster: density functional theory study

By Saputro, Adhitya G.; Rusydi, Febdian; Kasai, Hideaki; Dipojono, Hermawan K.From Journal of the Physical Society of Japan (2012), 81(3), 034703/1-034703/5. Language: English, Database:CAPLUS, DOI:10.1143/JPSJ.81.034703

We investigate the potential energy surface profile for various water formation reaction schemes on an unsupportedcobalt-(6)pyrrole [Co-(6)Ppy] cluster in the vacuum state by d. functional theory (DFT) calcns. We find that in the Co-(6)Ppy cluster, the formation of H2O2 is energetically not favorable. Instead of forming H2O2ad, the HO2ad + H reactionforms 2OHad or Oad + H2O immediately. The adsorption of H2O2 on the Co-(6)Ppy cluster is possible only if the H2O2mol. comes from or forms outside of the cluster. The formation of two OH mols. instead of H2O2 on the Co-(6)Ppy clustersuggests that the oxygen redn. reaction (ORR) mechanism on the unsupported Co-(6)Ppy cluster in the vacuum stateprefers the direct four-electron redn. to water.~0 Citings

227. Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene

By Pharr, Caroline R.; Kopff, Laura A.; Bennett, Brian; Reid, Scott A.; McMahon, Robert J.From Journal of the American Chemical Society (2012), 134(14), 6443-6454. Language: English, Database: CAPLUS,DOI:10.1021/ja300927d

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Photolysis (λ > 543 nm) of 3-thienyldiazomethane (1), matrixisolated in Ar or N2 at 10 K, yields triplet 3-thienylcarbene (13)and α-thial-methylenecyclopropene (9). Carbene 13 wascharacterized by IR, UV/visible, and EPR spectroscopy. Theconformational isomers of 3-thienylcarbene (s-E and s-Z)exhibit an unusually large difference in zero-field splittingparameters in the triplet EPR spectrum (|D/hcl = 0.508 cm-1,|E/hcl = 0.0554 cm-1; |D/hcl = 0.579 cm-1, |E/hcl = 0.0315 cm-1).Natural Bond Orbital (NBO) calcns. reveal substantiallydiffering spin densities in the 3-thienyl ring at the positionsadjacent to the carbene center, which is one factor contributingto the large difference in D values. NBO calcns. also reveal astabilizing interaction between the sp orbital of the carbenecarbon in the s-Z rotamer of 13 and the antibonding σ orbitalbetween sulfur and the neighboring carbon-an interaction thatis not obsd. in the s-E rotamer of 13. In contrast to the EPRspectra, the electronic absorption spectra of the rotamers oftriplet 3-thienylcarbene (13) are indistinguishable under exptl.conditions. The carbene exhibits a weak electronic absorptionin the visible spectrum (λmax = 467 nm) that is characteristic oftriplet arylcarbenes. Although studies of 2-thienyldiazomethane(2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4)provided further insight into the photochem. interconversionsamong C5H4S or C5H4O isomers, these studies did not lead tothe spectroscopic detection of the corresponding tripletcarbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), resp.).

~10 Citings

228. Hydrogen tunnelling influences the isomerization of some small radicals of interstellar importance. Atheoretical investigation

By Wang, Tianfang; Bowie, John H.From Organic & Biomolecular Chemistry (2012), 10(16), 3219-3228. Language: English, Database: CAPLUS,DOI:10.1039/c2ob07102a

Hydrogen atom isomerizations within five radical systems (i.e., CH3√NH/√CH2NH; CH3O√/√CH2OH; √CH2SH/CH3S√;CH3CO2√/√CH2CO2H; and HOCH2CH2O√/HO√CHCH2OH) were studied via quantum-mech. hydrogen tunnelling throughreaction barriers. The reaction rates including hydrogen tunnelling effects were calcd. for these gas phase reactions at300-0 K using Wenzel-Kramers-Brillouin (WKB) and Eckart methods. The Eckart method is unsatisfactory for the lasttwo systems listed above, because it significantly underestimates the width of the reaction barriers for theinterconversions. The calcns. at all-electron CCSD(T)/CBS level of theory indicate that the barriers for all reactions(forward and reverse) are >100 kJ mol-1, meaning that the chem. reactivity of the reactants is limited in the absence ofhydrogen tunnelling. Hydrogen tunnelling, in some cases, enhance rates of reaction by >100 orders of magnitude at lowtemp., and around 2 orders of magnitude at room temp., compared to results obtained from canonical variationaltransition state theory. Tunnelling cor. reaction rates suggest that some of these isomerization reactions may occur ininterstellar media.~7 Citings

229. Atom Tunneling in Organic Transformations

By Patureau, Frederic W.From Angewandte Chemie, International Edition (2012), 51(20), 4784-4786. Language: English, Database: CAPLUS,DOI:10.1002/anie.201200991

A review.~6 Citings

230. QCT and QM calculations of the Cl(2P) + NH3 reaction: influence of the reactant well on the dynamics

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By Monge-Palacios, M.; Yang, M.; Espinosa-Garcia, J.From Physical Chemistry Chemical Physics (2012), 14(14), 4824-4834. Language: English, Database: CAPLUS,DOI:10.1039/c2cp00008c

A detailed dynamics study, using both quasi-classical trajectory (QCT) and reduced-dimensional quantum mech. (QM)calcns., was carried out to understand the reactivity and mechanism of the Cl(2P) + NH3 = HCl + NH2 gas-phasereaction, which evolves through deep wells in the entry and exit channels. The calcns. were performed on an anal.potential energy surface recently developed by our group, PES-2010, together with a simplified model surface, mod-PES,in which the reactant well is removed to analyze its influence. The main finding was that the QCT and QM methods showa change of the reaction probability with collision energy, suggesting a change of the at.-level mechanism of reaction withenergy. This change disappeared when the mod-PES was used, showing that the behavior at low energies is a directconsequence of the existence of the reactant well. Anal. of the trajectories showed that different mechanisms operatedepending on the collision energy. Thus, while at high energies (Ecoll > 5 kcal mol-1) practically all trajectories are direct,at low energies (Ecoll < 3 kcal mol-1) the trajectories are indirect, i.e., with the mediation of a trapping complex in the entryand/or the exit wells. The reactant complex allows repeated encounters between the reactants, increasing the reactionprobability at low energies. The differential cross section results reinforce this change of mechanism, showing also theinfluence of the reactant well on this reaction. Thus, the PES-2010 surface yields a forward-backward symmetry in thescattering, while when the reactant well is removed with the mod-PES the shape is more isotropic.~9 Citings

231. Multi-structural variational transition state theory: kinetics of the 1,5-hydrogen shift isomerization of the 1-butoxyl radical including all structures and torsional anharmonicity

By Xu, Xuefei; Papajak, Ewa; Zheng, Jingjing; Truhlar, Donald G.From Physical Chemistry Chemical Physics (2012), 14(12), 4204-4216. Language: English, Database: CAPLUS,DOI:10.1039/c2cp23692c

We investigate the statistical thermodn. and kinetics of the 1,5-hydrogen shift isomerization reaction of the 1-butoxylradical and its reverse isomerization. The partition functions and thermodn. functions (entropy, enthalpy, heat capacity,and Gibbs free energy) are calcd. using the multi-structural torsional (MS-T) anharmonicity method including allstructures for three species (reactant, product, and transition state) involved in the reaction. The calcd. thermodn.quantities have been compared to those estd. by the empirical group additivity (GA) method. The kinetics of the unimol.isomerization reaction was investigated using multi-structural canonical variational transition state theory (MS-CVT)including both multiple-structure and torsional (MS-T) anharmonicity effects. In these calcns., multidimensional tunneling(MT) probabilities were evaluated by the small-curvature tunneling (SCT) approxn. and compared to results obtained withthe zero-curvature tunneling (ZCT) approxn. The high-pressure-limit rate consts. for both the forward and reversereactions are reported as calcd. by MS-CVT/MT, where MT can be ZCT or SCT. Comparison with the rate consts.obtained by the single-structural harmonic oscillator (SS-HO) approxn. shows the importance of anharmonicity in the rateconsts. of these reactions, and the effect of multi-structural anharmonicity is found to be very large. Whereas thetunneling effect increases the rate consts., the MS-T anharmonicity decreases them at all temps. The two effectscounteract each other at temps. 385 K and 264 K for forward and reverse reactions, resp., and tunneling dominates atlower temps. while MS-T anharmonicity has a larger effect at higher temps. The multi-structural torsional anharmonicityeffect reduces the final reverse reaction rate consts. by a much larger factor than it does to the forward ones as a resultof the existence of more low-energy structures of the product 4-hydroxy-1-Bu radical than the reactant 1-butoxyl radical.As a consequence there is also a very large effect on the equil. const. The neglect of multi-structural anharmonicity willlead to large errors in the estn. of reverse reaction rate consts.~21 Citings

232. Nature of the Selenium Submonolayer Effect on the Oxygen Electroreduction Reaction Activity of Ru(0001)

By Stolbov, SergeyFrom Journal of Physical Chemistry C (2012), 116(12), 7173-7179. Language: English, Database: CAPLUS,DOI:10.1021/jp2072952

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I present here results of 1st principles studies of the adsorptionenergetics of the intermediates of the O electroredn. reaction(ORR) on a Se-modified Ru(0001) surface. The calcns. wereperformed for 1/3 and 2/3 monolayer coverage of Se, as wellas for clean Ru(0001) as a ref. The binding energies of O andOH on Ru(0001) decrease significantly with the presence ofSe, and this effect increases with the Se coverage. The Sesurface modification is found not to change the Ru local d. ofelectronic states noticeably. However, Se atoms acceptelectronic charge from the surface and thus become neg.charged. As a result, they repeal electrostatically the adsorbedneg. charged O and OH intermediates and in this way reducetheir binding energies. This effect provides an alternative wayof tuning the reactivity of the catalyst surfaces. Since for theRu case redn. of the O and OH binding energies makes ORRenergetically favorable, Se modification dramatically improvesthe ORR rate on Ru. Adsorption of O2 and coadsorption of theORR intermediates and H2O also were studied. The effect ofcoadsorption on the binding energies of O and OH arediscussed.

~10 Citings

233. Metal-assisted Lossen Rearrangement

By Jasikova, Lucie; Hanikyrova, Eva; Skriba, Anton; Jasik, Juraj; Roithova, JanaFrom Journal of Organic Chemistry (2012), 77(6), 2829-2836. Language: English, Database: CAPLUS,DOI:10.1021/jo300031f

A new reaction mechanism for the Lossen rearrangement ofhydroxamic acids catalyzed by basic salts is presented. It isshown that the rearrangement proceeds in metal complexes ofdeprotonated hydroxamic acids. The deprotonation can occureither at the oxygen atom (obsd. for the zinc complexes) or atthe nitrogen atom (obsd. for the potassium complexes). Bothanionic forms are characterized by IR multiphoton dissocn.spectroscopy. The rearrangements proceed from the reactiveN-deprotonated metal hydroxamates and lead to metalcarbamates. The mechanism is elucidated by computationalchem., mass-spectrometric studies, and preparative expts.

~20 Citings

234. Calculation of kinetic data using computational methods

By Cossio, Fernando P.Edited By:DaCosta, Herbert; Fan, MaohongFrom Rate Constant Calculation for Thermal Reactions (2012), 33-65. Language: English, Database: CAPLUS,DOI:10.1002/9781118166123.ch2

A review. The authors discuss computational methods in which transformations involving medium-size mols. in soln. areinvolved.~2 Citings

235. FTIR and thermal studies on gel grown neodymium tartrate crystals

By Patil, H. M.; Sawant, D. K.; Bhavsar, D. S.; Patil, J. H.; Girase, K. D.From Journal of Thermal Analysis and Calorimetry (2012), 107(3), 1031-1037. Language: English, Database:CAPLUS, DOI:10.1007/s10973-011-1599-1

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The growth of Nd tartrate crystals was achieved in silica gel by single diffusion method. Optimum conditions wereestablished for the growth of good quality crystals. FTIR spectroscopic study indicates H2O mols. and tartrate ligandsand suggests that tartrate ions are doubly ionized. The thermal behavior of the material was studied using TG, DTA,deriv. TG (DTG) and DSC. TGA support the suggested chem. formula of the grown crystal to be Nd2(C4H4O6)3·7H2O,and the presence of seven H2O mols. as H2O of hydration. The material is thermally stable up 45° beyond which itdecomps. through many stages till the formation of Nd oxide (Nd2O3) at 995°. The decompn. pattern is reported to betypical of a hydrated metal tartrate.~7 Citings

236. Growth and thermal behavior of mixed crystals of calcium cadmium tartrate in silica gels

By Sawant, D. K.; Patil, H. M.; Bhavsar, D. S.; Patil, J. H.; Girase, K. D.From Journal of Thermal Analysis and Calorimetry (2012), 107(3), 1047-1053. Language: English, Database:CAPLUS, DOI:10.1007/s10973-011-1600-z

In this study, calcium cadmium tartrate single crystals were grown in silica gel at ambient temp. Effects of variousparameters like gel pH, gel aging, gel d., and concn. of reactants on the growth of these crystals were studied. Crystalshaving different morphologies and habits were obtained. Transparent, diamond-like pyramidal-shaped crystals ofcalcium cadmium tartrate were obtained. Some of the crystals obtained were faint yellowish, with some milky whitecrystals being attached to them due to fast growth rate; faces are well developed and polished. The grown crystals werecharacterized by thermoanalytic techniques (TG, DTA, and DTG), and powder X-ray diffraction (XRD). The crystalsystem is confirmed to be orthorhombic having lattice parameters a = 7.9411 Å, b = 7.0396 Å, and c = 6.7271 Å as detd.by powder XRD anal. TG, DTA, and DTG analyses show a remarkable thermal stability. The results of theseobservations are described and discussed.~1 Citing

237. Photosynthetic O2 evolution

By Messinger, Johannes; Noguchi, Takumi; Yano, JunkoFrom RSC Energy and Environment Series (2012), 5(Molecular Solar Fuels), 163-207. Language: English, Database:CAPLUS

A review on the structure of the water-oxidizing complex in photosystem II and the mechanism of photosynthetic water-splitting, as well as the concepts that may be important for developing manmade systems for converting solar energy intofuels.~32 Citings

238. First principles study of sulfuric acid anion adsorption on a Pt(111) electrode

By Jinnouchi, Ryosuke; Hatanaka, Tatsuya; Morimoto, Yu; Osawa, MasatoshiFrom Physical Chemistry Chemical Physics (2012), 14(9), 3208-3218. Language: English, Database: CAPLUS,DOI:10.1039/c2cp23172g

A first principles theory combined with a continuum electrolyte theory is applied to adsorption of sulfuric acid anions onPt(111) in 0.1 M H2SO4 soln. The theor. free energy diagram indicates that sulfuric acid anions adsorb as bisulfate in thepotential range of 0.41 < U ≤ 0.48 V (RHE) and as sulfate in 0.48 V (RHE) < U. This diagram also indicates that sulfateinhibits formations of surface oxide and hydroxide. Charge anal. shows that the total charge transferred for the formationof the full coverage sulfate adlayer is 90 µC cm-2, and that the electrosorption valency value is -0.45 to -0.95 in 0.41 < U≤ 0.48 V (RHE) and -1.75 to -1.85 in U > 0.48 V (RHE) in good agreement with expts. reported in the literature. Vibrationanal. indicates that the vibration frequencies obsd. exptl. at 1250 and 950 cm-1 can be assigned, resp., to the S-O(uncoordinated) and sym. S-O stretching modes for sulfate, and that the higher frequency mode has a larger potential-dependence (58 cm-1 V-1) than the lower one.~37 Citings

239. Taking Ockham's razor to enzyme dynamics and catalysis

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By Glowacki, David R.; Harvey, Jeremy N.; Mulholland, Adrian J.From Nature Chemistry (2012), 4(3), 169-176. Language: English, Database: CAPLUS, DOI:10.1038/nchem.1244

A review. The role of protein dynamics in enzyme catalysis is a matter of intense current debate. Enzyme-catalyzedreactions that involve significant quantum tunneling can give rise to exptl. kinetic isotope effects with complex temp.dependences, and it has been suggested that std. statistical rate theories, such as transition-state theory, are inadequatefor their explanation. Here, the authors have introduced aspects of transition-state theory relevant to the study ofenzyme reactivity, taking cues from chem. kinetics and dynamics studies of small mols. in the gas phase and in soln.,where breakdowns of statistical theories have received significant attention and their origins are relatively betterunderstood. The authors discuss recent theor. approaches to understanding enzyme activity and then show how exptl.observations for a no. of enzymes may be reproduced using a transition-state theory framework with phys. reasonableparameters. Essential to this simple model is the inclusion of multiple conformations with different reactivity.~147 Citings

240. Block-Localized Wavefunction (BLW) Based Two-State Approach for Charge Transfers between PhenylRings

By Mo, Yirong; Song, Lingchun; Lin, Yuchun; Liu, Minghong; Cao, Zexing; Wu, WeiFrom Journal of Chemical Theory and Computation (2012), 8(3), 800-805. Language: English, Database: CAPLUS,DOI:10.1021/ct2008318

The block-localized wave function (BLW) method is the simplest and most efficient variant of ab initio valence bond (VB)theory which defines electron-localized resonance states following the conventional VB concepts. Here, a BLW-basedtwo-state approach is proposed to probe the charge/hole transfer reactions within the Marcus-Hush model. With thisapproach, both the electronic coupling and reorganization energies can be derived at the ab initio level. Pilot applicationsto the electron/hole transfers between two Ph rings are presented. Good exponential correlation between the electroniccoupling energy and the donor-acceptor distance is shown, whereas the inner-sphere reorganization shows littlegeometric dependency. Computations also support the assumption in Marcus theory that the thermal electron transferbarrier (∆G*), which is a sum of the reaction barrier (∆Ea) for electron/hole transfer and the coupling energy (VAB), is aquarter of the reorganization energy (λ).~17 Citings

241. The resting-state of the Pt-black electrode in acid solution and the structure of the adsorption layer.Coulometric and electrochemical quartz crystal microbalance measurements

By Bucur, R. V.From Electrochimica Acta (2012), 62, 354-361. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2011.12.057

The properties of Pt-electrodes in 1 M HClO4 soln., in air, were studied both in the resting-state and mild oxidn.conditions, within the potential range of 1000 mV and 1600 mV. Cyclic voltammetry (CV) and cathodic strippingvoltammetry (CSV) were used for coulometric detn. of the amt. of O-contg. species adsorbed on the electrode surfaceduring the oxidn.-redn. reactions. Simultaneously, the mass of the adsorption layer was measured in situ, with theelectrochem. quartz crystal microbalance (EQCM). The surface of the Pt-black electrode in the resting-state is coveredwith OH*-species (apparently a ML), which are spontaneously generated by immersion in the aq. soln. without anypolarization potential. The surface of the Pt smooth electrode is covered uppermost by a sub-monolayer of O, in similarconditions. The resting-state of the Pt-black electrode was characterized by a reproducible value of the rest potential, E r= 1040 ± 5 mV (av. of 10 samples) and a redn. peak in CV mode at E'p = 791 ± 7 mV (av. of 10 samples). In anodicpolarization conditions, PtOH* is oxidized to PtO*, in CV mode, and to Pt(O2)*, in the potentiostatic mode. The redn. peakof PtO* in CV mode is E''p = 694 ± 9 mV (av. of 10 samples), indicating a stronger bond to the surface of the electrode.The yielding of Pt(O2)* is not fast enough to accommodate the increase of the oxidn. potential by finite sweep rate of theCV mode at 10 mV s-1. Therefore this oxidn. level could not be achieved in CV mode. The prolonged oxidn. in thepotentiostatic mode results in the coverage of the surface of Pt-black electrode with a monolayer of (O2)*-species.~3 Citings

242. Directly Measured Activation Parameters for the Ring Expansions of Cyclopropylhalocarbenes

By Shen, Yong-miao; Moss, Robert A.; Krogh-Jespersen, KarstenFrom Organic Letters (2012), 14(3), 910-913. Language: English, Database: CAPLUS, DOI:10.1021/ol203426e

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Activation parameters have been redetd. for the ringexpansions of cyclopropylchlorocarbene andcyclopropylfluorocarbene; agreement between the exptl. andcomputed activation parameters has been significantlyimproved.

~3 Citings

243. Simulating Linear Sweep Voltammetry from First-Principles: Application to Electrochemical Oxidation ofWater on Pt(111) and Pt3Ni(111)

By Viswanathan, Venkatasubramanian; Hansen, Heine Anton; Rossmeisl, Jan; Jaramillo, Thomas Francisco; Pitsch,Heinz; Noerskov, Jens K.From Journal of Physical Chemistry C (2012), 116(7), 4698-4704. Language: English, Database: CAPLUS,DOI:10.1021/jp210802q

Cyclic voltammetry is a fundamental exptl. method forcharacterizing adsorbates on electrochem. surfaces. Theauthors present a model for the electrochem. solid-liq.interface, and the authors simulate the linear sweepvoltammogram of the electrochem. oxidn. of H2O on Pt(111)and Pt3Ni(111), based on kinetic and thermodn. parameterscomputed by D. Functional Theory (DFT) and the dynamics ofthe system solved through Monte Carlo-based methods. Themodel predicts onset of OH and O formation in goodagreement with voltammetric and ex situ XPS expts.

~53 Citings

244. Change in the magnetostructural properties of rare earth doped cobalt ferrites relative to the magneticanisotropy

By Naik, S. R.; Salker, A. V.From Journal of Materials Chemistry (2012), 22(6), 2740-2750. Language: English, Database: CAPLUS,DOI:10.1039/C2JM15228B

The superparamagnetic properties of the doped cobalt ferrite nanocrystals were demonstrated. The significance of thesol-gel autocombustion method in yielding the as obtained doped Co ferrite oxide powder in the nano-range was verywell complemented with structural, dimensional and morphol. anal. techniques such as x-ray diffraction (XRD), TEM,particle size anal., and SEM. The lattice strain and lattice parameters were calcd. by making use of the Williamson-Hallextrapolation. The valence states of the metal ions and single phase formation of the polycryst. oxides were confirmedwith the help of XPS and Raman Spectroscopy. The magnetic measurements M-H and M-T were carried outdemonstrating a change in the magnetic moment and a superparamagnetic-ferrimagnetic transition in the ferrite system.The influence of the distribution of the metal ions in the crystal lattice and the dimensions of the ferrite oxides on theresultant magnetic properties was demonstrated. The contribution of the spin-orbit coupling generating from the Co2+

ions in the octahedral lattice towards higher magnetic anisotropy and hence the magnetic properties is investigated. Theresults provide an insight into the inter-relationship of the particle dimension, the spin-orbit coupling and the resultingsuperparamagnetic property.~101 Citings

245. Mechanisms of the Oxygen Reduction Reaction on Defective Graphene-Supported Pt Nanoparticles fromFirst-Principles

By Lim, Dong-Hee; Wilcox, JenniferFrom Journal of Physical Chemistry C (2012), 116(5), 3653-3660. Language: English, Database: CAPLUS,DOI:10.1021/jp210796e

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The mechanisms of the O redn. reaction (ORR) on defectivegraphene-supported Pt13 nanoparticles were studied tounderstand the effect of defective graphene support on theORR and predict details of ORR pathways. The authorsemployed d. functional theory (DFT) predictions using theprojector-augmented wave (PAW) method within thegeneralized gradient approxn. (GGA). Free energy diagramsfor the ORR over supported and unsupported Pt13nanoparticles were constructed to provide the stability ofpossible intermediates in the electrochem. reaction pathways.The defective graphene support may provide a balance in thebinding of ORR intermediates on Pt13 nanoparticles by tuningthe relatively high reactivity of free Pt13 nanoparticles that bindthe ORR intermediates too strongly subsequently leading toslow kinetics. The defective graphene support lowers not onlythe activation energy for O2 dissocn. from 0.37 to 0.16 eV, butalso the energy barrier of the rate-limiting step by reducing thestability of HO* species. The authors predict the ORRmechanisms via direct four-electron and series two-electronpathways. An activation free energy (0.16 eV) for O2 dissocn.from adsorbed O2 * at a bridge site on the supported Pt13nanoparticle into O* + O* species (i.e., the direct pathway) islower than the free energy barrier (0.29 eV) for the formation ofHOO* species from adsorbed O2 * at the corresponding atopsite, indicating that the direct pathway may be preferred as theinitial step of the ORR mechanism. Also, charge is transferredfrom the Pt13 nanoparticle to both defective graphene and theORR intermediate species.

~192 Citings

246. Through the wall: Tunneling control of chemical reactions

By Ley, David; Gerbig, Dennis; Schreiner, Peter R.From Nachrichten aus der Chemie (2011), 59(12), 1139-1141. Language: German, Database: CAPLUS

A review. Because of the tunneling phenomenon quantum-mech. particles can penetrate certain potential barriers. Thiscircumstance has consequences for our rather classically shaped understanding of chemoselectivity, since chem.systems are not always confined by potential barriers.~1 Citing

247. Kinetics of the Hydrogen Abstraction from Carbon-3 of 1-Butanol by Hydroperoxyl Radical: Multi-StructuralVariational Transition-State Calculations of a Reaction with 262 Conformations of the Transition State

By Seal, Prasenjit; Papajak, Ewa; Truhlar, Donald G.From Journal of Physical Chemistry Letters (2012), 3(2), 264-271. Language: English, Database: CAPLUS,DOI:10.1021/jz201546e

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We estd. rate consts. for the hydrogen abstraction from carbon-3 of 1-butanol by hydroperoxyl radical, a critically importantreaction in the combustion of biofuel. We employed therecently developed multi-structural variational transition-statetheory (MS-VTST), which utilizes a multifaceted dividingsurface that allows us to include the contributions of multiplestructures for reacting species and transition states. First,multiconfigurational Shepard interpolation-based on mol.-mechanics-guided interpolation of electronic-structure Hessiandata obtained by the M08 HX/jun-cc-pVTZ electronic modelchem.-was used to obtain the portion of the potential energysurface needed for single-structure variational transition-statetheory rate consts. including multidimensional tunneling; then,the M08-HX/MG3S electronic model chem. was used to calc.multi-structural torsional anharmonicity factors to complete theMS-VTST rate const. calcns. The lowest-energy structures ofthe transition state have strongly bent hydrogen bonds. Ourresults indicate that neglect of multi-structural anharmonicitywould lead to errors of factors of 0.3, 46, and 171 at 200, 1000,and 2400 K for this reaction.

~42 Citings

248. Insights into electrocatalysis

By Anderson, Alfred B.From Physical Chemistry Chemical Physics (2012), 14(4), 1330-1338. Language: English, Database: CAPLUS,DOI:10.1039/C2CP23616H

When std. reversible potentials for bulk soln. reactions, U0, are known, the reversible potentials when the reactant andproduct are adsorbed on an electrocatalyst surface, Urevsurf, are given in terms of these potentials and the adsorptionGibbs energy bond strengths:When the ∆adsG (Ox) and ∆adsG (Red) values are known at potential Urevsurf, thisequation is exact. When the overpotential for a multi-electron transfer reaction is minimal, each electron transfer takesplace at the std. reversible potential for the overall reaction. In the case of O2 redn. to water via the intermediate stepOOH(aq) O(aq) + OH(aq), or via O2(g) 2O(aq), the resp. endergonic O-O dissocn. Gibbs energies are shown to be2.52 eV and 4.76 eV. When the oxygen product and water reactant adsorb weakly, as on platinum, the adsorption Gibbsenergies, ∆adsG, for O, OH, and OOH intermediates can be uniquely predicted using these data. All of the above dependexclusively on exptl. detd. data. Reversible potentials have been calcd. for oxygen redn. steps on the platinumelectrocatalyst surface using Interface 1.0, a comprehensive computational code for the potential dependence of theelectrochem. interface. Using these results as benchmarks, is found to be accurate to around 0.1 V when the ∆adsG arevalues calcd. for the potentials of zero charge, instead of 1.229 V, which is a significant simplification. The variation in∆adsG values between the calcd. potentials of zero charge and 1.229 V are found to be 0.2 eV V-1 or less. Prior work,using internal adsorption energies calcd. at the potential of zero charge in place of Gibbs energies in was found to beaccurate to within about 0.2 V. On platinum ∆adsG of the reaction OOH(ads) O(ads) + OH(ads) is calcd. at the potentialof zero charge for the reactant and product to be about 1.2 eV exergonic under Langmuir conditions, and this Gibbsenergy loss reduces the 1.229 V four-electron reversible potential on the platinum surface to an effective reversiblepotential of about 0.93 V for this mechanism on platinum. The effective reversible potential is a consequence ofefficiency loss, not kinetics. Based on these values, the onset potential for four-electron oxygen redn. will be less than orequal to the effective reversible potential and on pure Pt(111) it appears to be equal to it.~64 Citings

249. Multipath Variational Transition State Theory: Rate Constant of the 1,4-Hydrogen Shift Isomerization of the2-Cyclohexylethyl Radical

By Yu, Tao; Zheng, Jingjing; Truhlar, Donald G.From Journal of Physical Chemistry A (2012), 116(1), 297-308. Language: English, Database: CAPLUS,DOI:10.1021/jp209146b

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The authors propose a new formulation of variational transitionstate theory called multipath variational transition state theory(MP-VTST). A new formulation is employed to calc. theforward and reverse thermal rate const. of the 1,4-hydrogenshift isomerization of the 2-cyclohexylethyl radical in the gasphase. First, the authors find and optimize all the local-min.-energy structures of the reaction, product, and transition state.Then, for the lowest-energy transition state structures, thereaction path is calcd. by using multiconfiguration Shepardinterpolation (MSCI) method to represent the potential energysurface, and, from this representation, also the ground-statevibrationally adiabatic potential energy curve, the reaction-pathcurvature vector, and the generalized free energy of activationprofile are calcd. With this information, the path-averagedgeneralized transmission coeffs. ❬γ❭ are evaluated. Then,thermal rate const. contg. the multiple-structure anharmonicityand torsional anharmonicity effects is calcd. usingmultistructural transition state theory (MS-TST). The final MP-VTST thermal rate const. is obtained by multiplying kMS-T MS-TST by ❬γ❭. In these calcns., the M06 d. functional is utilized tocompute the energy, gradient, and Hessian at the Shepardpoints, and the M06-2X d. functional is used to obtain thestructures (conformers) of the reactant, product, and the saddlepoint for computing the multistructural anharmonicity factors.

~41 Citings

250. Dynamical tunneling and control

By Keshavamurthy, SrihariEdited By:Keshavamurthy, Srihari; Schlagheck, PeterFrom Dynamical Tunneling (2011), 225-255. Language: English, Database: CAPLUS, DOI:10.1201/b10712-11

A review presents two examples of dynamical tunneling and control. It also discusses Davis-Heller system.~0 Citings

251. First principles based mean field model for oxygen reduction reaction

By Jinnouchi, Ryosuke; Kodama, Kensaku; Hatanaka, Tatsuya; Morimoto, YuFrom Physical Chemistry Chemical Physics (2011), 13(47), 21070-21083. Language: English, Database: CAPLUS,DOI:10.1039/c1cp21349k

A first principles-based mean field model was developed for the oxygen redn. reaction (ORR) taking account of thecoverage- and material-dependent reversible potentials of the elementary steps. This model was applied to thesimulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O2 atms. The results areconsistent with those shown by past exptl. and theor. studies on surface coverages under Ar atm., the shape of thecurrent-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggeststhat the oxygen associative pathway including HO2(ads) formation is the main pathway on Pt(111), and that the ratedetg. step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloysand core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partialpressure of O2(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces theapparent reaction order with respect to the partial pressure to less than unity. This model shows details on how thereaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated.~53 Citings

252. A multiscale theoretical methodology for the calculation of electrochemical observables from ab initio data:Application to the oxygen reduction reaction in a Pt(1 1 1)-based polymer electrolyte membrane fuel cell

By Ferreira de Morais, Rodrigo; Sautet, Philippe; Loffreda, David; Franco, Alejandro A.From Electrochimica Acta (2011), 56(28), 10842-10856. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2011.05.109

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The authors present a multiscale theor. methodol. that scales up ab initio calcd. data into elementary kinetic models tosimulate Polymer Electrolyte Membrane Fuel Cells (PEMFC) transient operation. Detailed D. Functional Theory (DFT)calcns. were performed on a model Pt(1 1 1) surface to det. the elementary kinetic rates of the O Redn. Reaction (ORR)mechanism at a Pt-based PEMFC cathode. These parameters include the effect of surface coverage on the activationbarriers and are implemented into a Mean Field model describing the behavior of the elec. field and charge distribution atthe nanoscale interfacial vicinity to the catalyst, which is in turn coupled with microscale and mesoscale level modelsdescribing the charge and reactants and H2O transport phenomena across the cell. The impact of two possible ORRmechanisms on the simulated i-V curves was studied: a 1st route connected with the dissociative adsorption of O2 onPt(1 1 1), a 2nd route related to the formation and the transformation of OOH surface species. The similarities anddifferences of the assocd. calcd. i-V responses for each of these routes and the consequences on the interpretation ofelectrochem. observables at the cell level are discussed.~14 Citings

253. Electrochemistry of diamond

By Pleskov, YuriEdited By:Brillas, Enric; Martinez-Huitle, Carlos AlbertoFrom Synthetic Diamond Films (2011), 79-108. Language: English, Database: CAPLUS

A review. An overview is presented of the principal electrochem. properties of CVD-diamond, with emphasis on thesemiconductor and structural effects.~5 Citings

254. 3d transition metal impurities in diamond: Electronic properties and chemical trends

By Assali, L. V. C.; Machado, W. V. M.; Justo, J. F.From Physical Review B: Condensed Matter and Materials Physics (2011), 84(15), 155205/1-155205/7. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.84.155205

First principles calcns. have been used to investigate the trends on the properties of isolated 3d transition metalimpurities (from Sc to Cu) in diamond. Those impurities have small formation energies in the substitutional or doublesemivacancy sites and large energies in the interstitial site. Going from Sc to Cu, the 3d-related energy levels in theband gap move from the top of the band gap toward the valence band in all three sites. Trends in electronic propertiesand transition energies of the impurities, in the substitutional or interstitial sites, are well described by a simplemicroscopic model considering the electronic occupation of the 3d-related levels. On the other hand, for the impurities inthe double semivacancy site, there is a weak interaction between the divacancy- and the 3d-related orbitals, resulting invacancy- and 3d-related levels in the materials band gap.~7 Citings

255. Constructing potential energy surfaces for polyatomic systems: recent progress and new problems

By Espinosa-Garcia, J.; Monge-Palacios, M.; Corchado, J. C.From Advances in Physical Chemistry (2012), 164752, 19 pp.. Language: English, Database: CAPLUS,DOI:10.1155/2012/164752

A review. Different methods of constructing potential energy surfaces in polyat. systems are reviewed, with the emphasisput on fitting, interpolation, and anal. (defined by functional forms) approaches, based on quantum chem. electronicstructure calcns. The different approaches are reviewed first, followed by a comparison using the benchmark H + CH4and the H + NH3gas-phase hydrogen abstraction reactions. Different kinetics and dynamics properties are analyzed forthese reactions and compared with the available exptl. data, which permits one to est. the advantages anddisadvantages of each method. Finally, we analyze different problems with increasing difficulty in the potential energyconstruction: spin-orbit coupling, mol. size, and more complicated reactions with several maxima and min., which test thesoundness and general applicability of each method. We conclude that, although the field of small systems, typicallyatom-diatom, is mature, there still remains much work to be done in the field of polyat. systems.~6 Citings

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256. Se-modified Ru nanoparticles as ORR catalysts - Part 1: Synthesis and analysis by RRDE and in PEFCs

By Johnston, Christina M.; Cao, Dianxue; Choi, Jong-Ho; Babu, Panakkattu K.; Garzon, Fernando; Zelenay, PiotrFrom Journal of Electroanalytical Chemistry (2011), 662(1), 257-266. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2011.07.015

We report a new method of prepn. of a methanol-tolerant Se/Ru cathode catalyst for the direct methanol fuel cell (DMFC), whereby selenium is deposited on ruthenium nanoparticles by H2-redn. of SeO2 in aq. soln. at room temp. Theobtained Se/Ru(aq.) was studied by electrochem. measurements and tested as a cathode catalyst in H2-air and directmethanol fuel cells. The new catalyst formulation (Se/Ru(aq.)) is shown to be superior to Se/Ru synthesized fromxylenes solvent and to Ru black by RRDE measurements, in terms of both activity and selectivity for complete oxygenredn. to water. Although Ru black is less active, the Tafel slopes and activation energies of Se/Ru catalysts andreduced-Ru black are similar, implying similar ORR mechanisms. In H2-air fuel cell tests, Se/Ru(aq.) was more activethan Se/Ru(xyl) at all voltages. Compared to Ru black, Se/Ru(aq.) was superior at low current densities, but Ru blackslightly exceeded the performance of Se/Ru at high current densities. To explain the RRDE and fuel cell observations,the two roles of Se as an inhibitor of Ru oxidn. and as a site-blocker are discussed.~10 Citings

257. Multi-structural variational transition state theory. Kinetics of the 1,4-hydrogen shift isomerization of thepentyl radical with torsional anharmonicity

By Yu, Tao; Zheng, Jingjing; Truhlar, Donald G.From Chemical Science (2011), 2(11), 2199-2213. Language: English, Database: CAPLUS, DOI:10.1039/c1sc00225b

We present a new formulation of variational transition state theory (VTST) called multi-structural VTST (MS-VTST) andthe use of this to calc. the rate const. for the 1,4-hydrogen shift isomerization reaction of 1-pentyl radical and that for thereverse reaction. MS-VTST uses a multi-faceted dividing surface and provides a convenient way to include thecontributions of many structures (typically conformers) of the reactant and the transition state in rate const. calcns. Inthis particular application, we also account for the torsional anharmonicity. We used the multi-configuration Shepardinterpolation method to efficiently generate a semi-global portion of the potential energy surface from a small no. of high-level electronic structure calcns. using the M06 d. functional in order to compute the energies and Hessians of Shepardpoints along a reaction path. The M06-2X d. functional was used to calc. the multi-structural anharmonicity effect,including all of the structures of the reactant, product and transition state. To predict the thermal rate const., VTSTcalcns. were performed to obtain the canonical variational rate const. over the temp. range 200-2000 K A transmissioncoeff. is calcd. by the multidimensional small-curvature tunneling (SCT) approxn. The final MS-CVT/SCT thermal rateconst. was detd. by combining a reaction rate calcn. in the single-structural harmonic oscillator approxn. (includingtunneling) with the multi-structural anharmonicity torsional factor. The calcd. forward rate const. agrees very well withexptl.-based evaluations of the high-pressure limit for the temp. range 300-1300 K, although it is a factor of 2.5-3.0 lowerthan the single-structural harmonic oscillator approxn. over this temp. range. We anticipate that MS-VTST will begenerally useful for calcg. the reaction rates of complex mols. with multiple torsions.~74 Citings

258. Theoretical Prediction on the Thermal Stability of Cyclic Ozone and Strong Oxygen Tunneling

By Chen, Jien-Lian; Hu, Wei-PingFrom Journal of the American Chemical Society (2011), 133(40), 16045-16053. Language: English, Database:CAPLUS, DOI:10.1021/ja203428x

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Dual-level dynamics calcn. with variational transition statetheory including multidimensional tunneling has beenperformed on the isomerization reaction of cyclic ozone →normal (open) ozone, which was believed to be the stability-detg. reaction of the elusive cyclic ozone mol. under thermalcondition. The high-level potential energy surface data wereobtained from the calcn. using the MRCISD+Q theory with theaug-cc-pVQZ basis set, while the low-level reaction pathinformation was obtained using the hybrid d. functional theoryB3LYP with the cc-pVTZ basis set. The calcd. results showedvery significant tunneling effects below 300 K (a factor of ∼200at 300 K and over 107 at 200 K). Because of the strongtunneling effects and the potential energy surface crossing ofthe 1A1 and 1A2 states, the isomerization reactions were foundto be significantly faster than previously believed. The half-lifeof the cyclic ozone was estd. only ∼10 s at 200 K and ∼70 sbelow 100 K, which might partly explain the unsuccessfulattempts for its exptl. identification. The kinetic isotope effects(KIEs) for various 18O substitution reactions were also calcd. asa function of temp. and were as high as 10 at very low temp.Because of the large KIEs, the exptl. identification of the cyclic18O3 seems more promising.

~17 Citings

259. Density functional theory-based electrochemical models for the oxygen reduction reaction: Comparison ofmodeling approaches for electric field and solvent effects

By Yeh, Kuan-Yu; Janik, Michael J.From Journal of Computational Chemistry (2011), 32(16), 3399-3408. Language: English, Database: CAPLUS,DOI:10.1002/jcc.21919

D. functional theory (DFT) based electrochem. models are applied to systematically examine the effect of solvent, localelec. field, and electrode potential on O redn. reaction (ORR) kinetics. Specifically, the key elementary reaction steps ofO2 dissocn., O2 protonation, and redn. of a hydroxyl adsorbate to H2O over the Pt(111) surface were considered. Thelocal elec. field has slight influence on reaction energetics at the vacuum interface. Solvent mols. stabilize surfaceadsorbates, assisting O redn. A collective solvation-potential coupled effect is identified by including long range solvent-solvent interactions in the DFT model. The dominant path of the ORR reaction varies with electrode potential and amongthe modeling approaches considered. The potential dependent reaction path detd. from the solvated model qual. agreeswith expt. ORR kinetics. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011.~35 Citings

260. First-principles based microkinetic modeling of borohydride oxidation on a Au(1 1 1) electrode

By Rostamikia, Gholamreza; Mendoza, Alfonso J.; Hickner, Michael A.; Janik, Michael J.From Journal of Power Sources (2011), 196(22), 9228-9237. Language: English, Database: CAPLUS,DOI:10.1016/j.jpowsour.2011.07.042

Borohydride oxidn. electrokinetics over the Au(1 1 1) surface are simulated using first-principles detd. elementary rateconsts. and a microkinetic model. A method to approx. the potential dependent elementary step activation barriersbased on d. functional theory calcns. is developed and applied to the min. energy path for borohydride oxidn. Activationbarriers of the equiv. non-electrochem. reactions are calcd. and made potential dependent using the Butler-Volmerequation. The kinetic controlled region of the borohydride oxidn. reaction linear sweep voltammogram over the Au(1 1 1)surface is simulated. The simulation results suggest that B-H bond contg. species are stable surface intermediates atpotentials where an oxidn. current is obsd. The predicted rate is most sensitive to the symmetry factor and the BH2OHdissocn. barrier. Surface-enhanced Raman spectroscopy confirms the presence of BH3 as a stable intermediate.~59 Citings

261. Mechanism of Oxygen Electro-Reduction on Au-Modified Pt: Minimizing O Coverage and Pt Site Exposuretoward Highly Stable and Active Cathode

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By Fang, Ya-Hui; Liu, Zhi-PanFrom Journal of Physical Chemistry C (2011), 115(35), 17508-17515. Language: English, Database: CAPLUS,DOI:10.1021/jp205376b

To catalyze O redn. reaction (ORR) under electrochem.conditions approaching its thermodn. limit, i.e., 1.23 V vs.normal H electrode, was consistently pursued by chemists.Metal electrodes, even noble metals, undergo severe corrosionat the high potential, accompanied with the rapid decrease inactivity. A comprehensive understanding of both the stabilityand the catalytic activity of the Pt surface is urgently called fortoward the rational design of a new ORR catalyst. This work,by using chem. inert Au as a modifier to the Pt surface, studiedthe stability and the activity of a set of Au/Pt composites using1st-principles-based theor. methods designed for the modelingof solid/liq. electrocatalysis. By computing the surface phasediagram and the corrosion thermodn., the presence of Au canremarkably reduce the in situ O atom coverage to be below acrit. local 0.5 monolayer (ML) and thus protect the neighboringPt sites from corrosion. The AuPt surface alloy with a very lowamt. of Au dispersing in the Pt surface layer is sufficient tostabilize the whole catalyst surface. With the calcd. ORRprofiles, ORR activity in AuPt surface alloys is not sensitive tothe Au concn., and a good activity is maintained with the Auconcn. up to 7/8 ML. Fundamentally, this is because the min.active site of ORR requires only two neighboring Pt atoms (withan OOH pathway), and the majority of surface Pt sites on purePt are in fact nonactive spectators that are terminated by Oatoms at the working potentials. The key factors controlling theORR activity and surface stability are therefore unified as themin. O coverage and the min. exposure of Pt (active) sites.The theory presented here suggests that the structuralengineering to sep. active sites (e.g., two Pt atoms) by inertelements (e.g., Au) is an effective approach for yielding astable, active, and economic catalyst. Exptl. observations onAu/Pt composite catalysts are discussed in the context ofcurrent findings, focusing on the thermodn. tendency for AuPtsurface alloy formation.

~17 Citings

262. Nature of selenium sub-monolayer effect on the oxygen electro-reduction reaction activity of Ru(0001)

By Stolbov, SergeyFrom arXiv.org, e-Print Archive, Physics (2011), 1-18, arXiv:1108.0118v1 [physics.chem-ph]. Language: English,Database: CAPLUS

I present here the results of the first principles studies of the adsorption energetics of the intermediates of the oxygenelectro-redn. reaction (ORR) on the Se modified Ru(0001) surface. The calcns. were performed for the 1/3 ML and 1/6ML coverage of Se, as well as for the clean Ru(0001) as a ref. The binding energies of O and OH on Ru(0001) are foundto decrease significantly upon the presence of the Se and this effect to be increasing with the Se coverage. The Sesurface modification is found not to change Ru LDOS noticeably. However, Se atoms accept electronic charge from thesurface and thus become neg. charged. As a result, they repeal electrostatically the adsorbed neg. charged O and OHintermediates, and this way reduce their binding energies. This effect provide an alternative way of tuning reactivity ofthe catalyst surfaces. Since for the Ru case, redn. of the O and OH binding energies makes ORR energeticallyfavorable, Se modification dramatically improve the ORR rate on Ru. Adsorption of O2 and co-adsorption of the ORRintermediates and water have also been studied. The effect of the co-adsorption on the binding energies of O and OHare discussed.~0 Citings

263. Empirical valence bond models for reactive potential energy surfaces: A parallel multilevel genetic programapproach

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By Bellucci, Michael A.; Coker, David F.From Journal of Chemical Physics (2011), 135(4), 044115/1-044115/17. Language: English, Database: CAPLUS,DOI:10.1063/1.3610907

We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevelgenetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space andparameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronicstructure calcns. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of geneticprogramming on two different levels. The lower level genetic programs are used to optimize coevolving populations inparallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lowerlevel genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutationsthat most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy andefficiency. The algorithm's accuracy and efficiency is tested against a std. parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model forproton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent. (c) 2011 American Institute of Physics.~3 Citings

264. Effects of reagent vibrational excitation on the dynamics of the H + CHD3 → H2 + CD3 reaction: A seven-dimensional time-dependent wave packet study

By Zhou, Yong; Wang, Chunrui; Zhang, Dong H.From Journal of Chemical Physics (2011), 135(2), 024313/1-024313/9. Language: English, Database: CAPLUS,DOI:10.1063/1.3609923

Seven-dimensional time-dependent wave packet calcns. were carried out to study the title reaction on the potentialenergy surface constructed recently by the group. Total reaction probabilities and integral cross sections were calcd. fora no. of initial vibration states. The fundamental C-H stretching excitation can promote the reaction dramatically. At E =1.53 eV, it enhances the integral cross section by a factor of 13.2, which is in good agreement with the quasiclassicaltrajectory result on the ZBB1 potential energy surface, but larger than that on the EG-2002 potential energy surface. Thethermal rate consts. were obtained for the title reaction by taking into account the contributions from all relevant initialvibration states. The ground initial state has a dominant contribution to the thermal rate const. at low temp. region. Asthe temp. increases, the relative contribution to the thermal rate const. from the ground initial state decreases quickly,and those from the stretching and bending excited states increases substantially. It is estd. that the C-H stretching modecontributes ∼40% of the thermal rate const. at T = 1000 K despite the fact that the overall population for stretchingexcited states is tiny. (c) 2011 American Institute of Physics.~31 Citings

265. Review on the properties of nano-/ microstructures in the catalyst layer of PEMFC

By Yu, Xiao; Yuan, Jinliang; Sunden, BengtFrom Journal of Fuel Cell Science and Technology (2011), 8(3), 34001/1-34001/13. Language: English, Database:CAPLUS, DOI:10.1115/1.4003170

A review. The catalyst layer (CL) of a proton exchange membrane fuel cell involves various particles and pores thatspan a wide range of length scales, from several nanometers to a few microns. The success of the CL design dependsdecisively on understanding the detailed structure in microscale or even in nanoscale. In this paper, the properties ofnano-/microstructures are outlined, and the phys. and chem. processes are analyzed on the Pt surfaces. A softwarepackage of automatic simulation environment is developed and applied to investigate the electronic structure of the Pt-Hsystem. Then, the H2 dissociative adsorption process is obtained using the nudged elastic band approach. Themodeling of the nanocomposites in the CLs is a multiscale problem. The nanoscale models are used for investigatingthe structural evolution and the interactions between Pt/C particles and polymer components; while the microscalesimulations, which aim to bridge mol. methods and continuum methods, are extended to describe the morphol. ofheterogeneous materials and rationalize their effective properties beyond length- and time-scale limitations of theatomistic simulations. However, there are still some major challenges and limitations in these modeling and simulations.The multiscale modeling should be developed to demonstrate the usefulness for engineering design with thelongstanding goal of predicting particle-structure-property.~0 Citings

266. Toward a computational tool predicting the stereochemical outcome of asymmetric reactions: Developmentof the molecular mechanics-based program ACE and application to asymmetric epoxidation reactions

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By Weill, Nathanael; Corbeil, Christopher R.; De Schutter, Joris W.; Moitessier, NicolasFrom Journal of Computational Chemistry (2011), 32(13), 2878-2889. Language: English, Database: CAPLUS,DOI:10.1002/jcc.21869

The development and application of ACE, a program that predicts the stereochem. outcome of asym. reactions ispresented. As major implementations, ACE includes a genetic algorithm to carry out an efficient global conformationalsearch combined with a conjugate gradient minimization routine for local optimization and a corner flap algorithm tosearch ring conformations. Further improvements have been made that enable ACE to generate Boltzmann populationsof conformations, to investigate highly asynchronous reactions, to compute fluctuating partial at. charges and solvationenergy and to automatically construct reactants and products from libraries of catalysts and substrates. Validation onpreviously investigated reactions (asym. Diels-Alder cycloaddns. and organocatalyzed aldol reactions) followed byapplication to a no. of alkene epoxidn. reactions and a comparative study of DFT-derived and ACE-derived predictionsdemonstrate the accuracy and usefulness of ACE in the context of asym. catalyst design. © 2011 Wiley Periodicals, Inc.J Comput Chem, 2011.~21 Citings

267. Computational study on OH radical reaction with CHF2CHFCHF2(HFC-245ea) between 200 and 400 K

By Ali, Mohamad Akbar; Rajakumar, B.From International Journal of Chemical Kinetics (2011), 43(8), 418-430. Language: English, Database: CAPLUS,DOI:10.1002/kin.20569

The rate coeffs. of the CHF2CHFCHF2 (HFC-245ea) + OH reaction were computed using G3B3 theory in the temp.range 200 and 400 K. Geometries were optimized for all reactants, transition states, and products at the B3LYP level oftheory using 6-31G* and 6-311++G** basis sets. Three rotamers (R1, R2, and R3) of CHF2CHFCHF2 were identifiedusing a potential energy surface scan. Thirteen independent transition states were identified and confirmed by intrinsicreaction coordinate calcns. The kinetic parameters due to all different transition states are presented in this paper. Allthe three rotamers were taken into account in computing the rate coeffs. Throughout the temp. range of this study,rotamer R3 contributes significantly (more than 90%), whereas the other two rotamers R1 and R2 contribute less to thetotal rate coeff. The rate coeffs. for the title reaction were computed to be k = (1.86 ± 0.17) × 10-13 exp[-(748±26)/T]cm3mol.-1s-1 and (1.25 ± 0.23) × 10-13 exp[-(587±50)/T] cm3mol.-1 s-1 with Wigner's and Eckart's unsym. tunnelingmethods, resp., and they are in reasonable agreement with the exptl. measured ones. © 2011 Wiley Periodicals, Inc. IntJ Chem Kinet 43: 418-430, 2011.~12 Citings

268. Fast and reliable location of stationary points in a reaction path

By Cantillo, David; Avalos, Martin; Babiano, Reyes; Cintas, Pedro; Jimenez, Jose L.; Palacios, Juan C.From Journal of Physical Organic Chemistry (2012), 25(1), 77-82. Language: English, Database: CAPLUS,DOI:10.1002/poc.1877

This manuscript describes an easy, accurate, and expeditious methodol. to locate all the stationary points in commonorg. reactions. The protocol is based on the anal. of potential energy surfaces (PES) by fitting the calcd. data to a math.function. The method has been tested in several org. reactions, esp. cycloaddns. In all cases, we succeeded in locatingthe bond parameters for the existing saddle points and intermediates, which were further corroborated by conventionalgeometry optimizations of the corresponding stationary points. Thus, the concerted or stepwise character of a typicalcycloaddn. can easily be predicted. It should be emphasized that this protocol is not intended to replace the currentcomputational methodol. to construct a PES, which is otherwise a long and rather tedious procedure, usually applied tovery discrete mol. system. We prove instead that the present surrogate represents a valuable shortcut to identifystationary points at a given level of theory, which is in turn both reproducible and accurate and should be of interest to alarge readership of practitioners engaged in mechanistic studies, who often fear quantum computational methods.Copyright © 2011 John Wiley & Sons, Ltd.~2 Citings

269. Hydronium adsorption on OOH precovered Pt(111) surface: effects of electrode potential

By Son, Do Ngoc; Cong, Bach Thanh; Kasai, HideakiFrom Journal of Nanoscience and Nanotechnology (2011), 11(4), 2983-2989. Language: English, Database: CAPLUS,DOI:10.1166/jnn.2011.3903

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Using the DFT-based total energy calcns., the hydronium adsorption on the OOH precovered Pt(111) surface wasstudied. The electrode potential was modeled by varying the electron affinity of the redn. center [OOH + H3O(H2O)]+.Two possible structures of this redn. center on the Pt surface are HOOH + 2H2O and 2(OH) + 2H2O. Evidently, thedissocn. of HOOH into 2(OH) can be accomplished by changing the electrode potential to the higher value by 0.16 V.The activation energy for the dissocn. is ≈0.1 eV. The optimized structures are also obtained.~4 Citings

270. Light- and Heavy-Atom Tunneling in Rearrangement Reactions of Cyclopropylcarbenes

By Gerbig, Dennis; Ley, David; Schreiner, Peter R.From Organic Letters (2011), 13(13), 3526-3529. Language: English, Database: CAPLUS, DOI:10.1021/ol2013457

The authors studied both light- and heavy-atom tunneling in therearrangements of cyclopropylcarbenes using canonicalvariational transition state theory with multidimensionaltunneling corrections canonical variational canonical variational(CVT/MT) and the Wentzel-Kramers-Brillouin (WKB) formalism.Halo- and hydroxy-substituted cyclopropylcarbenes were foundnot to undergo carbon tunneling owing to wide reactionbarriers. However, while carbon tunneling plays a major role inthe ring expansion of parent cyclopropylcarbene yieldingcyclobutene, cyclopropylmethylcarbene is prone to undergohydrogen tunneling to give cyclopropylmethylene.

~34 Citings

271. Light-induced oxidative water splitting in photosynthesis: Energetics, kinetics and mechanism

By Renger, GernotFrom Journal of Photochemistry and Photobiology, B: Biology (2011), 104(1-2), 35-43. Language: English, Database:CAPLUS, DOI:10.1016/j.jphotobiol.2011.01.023

A review. The essential steps of photosynthetic water splitting take place in Photosystem II (PS II) and comprise threedifferent reaction sequences: (i) light induced formation of the radical pair P680+· QA-·, (ii) P680+· driven oxidative watersplitting into O2 and four protons, and (iii) two step plastoquinone redn. to plastoquinol by QA-·. This mini-review brieflysummarizes our state of knowledge on energetics, kinetics and mechanism of oxidative water splitting. Essentialfeatures of the two types of reactions involved are described: (a) P680+· redn. by the redox active tyrosine Yz and (b)sequence of oxidn. steps induced by Yzox in the water-oxidizing complex (WOC). The rate of the former reaction islimited by the non-adiabatic electron transfer (NET) step and the multi-phase kinetics shown to originate from a sequenceof relaxation processes. In marked contrast, the rate of the stepwise oxidn. by Yzox of the WOC up to the redox level S3is not limited by NET but by trigger reactions which probably comprise proton shifts and/or conformational changes. Theoverall rate of the final reaction sequence leading to formation and release of O2 is assumed to be limited by the electrontransfer step from the S3 state of WOC to Yzox due to involvement of an endergonic redox equil. Currently discussedcontroversial ideas on possible pathways are briefly outlined. Several crucial points of the mechanism of oxidative watersplitting, like O-O bond formation, role of local proton shift(s), details of hydrogen bonding, are still not clarified andremain a challenging topic of future research.~55 Citings

272. Towards active and stable oxygen reduction cathodes: a density functional theory survey on Pt2M skinalloys

By Wei, Guang-Feng; Liu, Zhi-PanFrom Energy & Environmental Science (2011), 4(4), 1268-1272. Language: English, Database: CAPLUS,DOI:10.1039/c0ee00762e

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Pt metal, when used as a cathode for oxygen redn. (O2 + 4H+ + 4e- → 2H2O), suffers from high overpotential andcatalyst corrosion. Here, first-principles based theor. methods for electrochem. systems are utilized to identify the crit.factors affecting cathode performance. By analyzing a large set of Pt alloys, we show that alloys are in general lessstable than Pt at the same O coverage under electrochem. conditions, and that maintaining a zero O coverage at theworking potentials (e.g. 0.9 V) is key to achieve both high activity and stability. Two quantities, i.e. the surface corrosionenergy and the free energy barrier to OOH dissocn., are found to be the main descriptors for the stability and activity. APt2Mo skin alloy is discovered to be a good candidate for an oxygen redn. cathode. The theor. framework provides anew route for the rational design of oxygen redn. catalysts.~21 Citings

273. Charge transport in organic semiconductors: a multiscale modeling

By Martinelli, Nicolas; Olivier, Yoann; Muccioli, Luca; Minoia, Andrea; Brocorens, Patrick; Delgado, Mari-Carmen Ruiz;Zannoni, Claudio; Beljonne, David; Lazzaroni, Roberto; Bredas, Jean-Luc; et alEdited By:Samori, Paolo; Cacialli, FrancoFrom Functional Supramolecular Architectures (2011), 1, 3-37. Language: English, Database: CAPLUS

A review on some recent works showing the benefit of coupling force field and quantum chem. calcns. to shed light onthe transport properties of org. semiconductors. The selected studies focus on org. conjugated materials widelyinvestigated at the exptl. level to ease comparison between exptl. and theor. data and aim at demonstrating that themodeling tools can be applied to both small mols. and polymer chains.~5 Citings

274. Synthesis and characterization of new hydroxycarboxylate compounds obtained in the redox reactionbetween Fe(NO3)3 and diol

By Stefanescu, O.; Vlase, T.; Vlase, G.; Doca, N.; Stefanescu, M.From Thermochimica Acta (2011), 519(1-2), 22-27. Language: English, Database: CAPLUS,DOI:10.1016/j.tca.2011.02.024

The paper presents exptl. studies and structural studies of two new Fe(III) hydroxycarboxylate coordination compds. Thehomopolynuclear complex combinations of Fe(III) glyoxylate and succinate type were obtained in the redox reactionbetween Fe(NO3)3 and diols (1,2-ethanediol and 1,4-butanediol). The synthesized coordination compds. and theproducts formed during their thermal conversion were characterized by thermal anal. (in air and nitrogen), FTIR and UV-visible spectrometry, Mossbauer spectrometry, electron microscopy and XRD. By thermal decompn. of the complexcombinations, at 300°, the well crystd. pure phase γ-Fe2O3 as nanoparticles were formed.~9 Citings

275. An ab initio study of electrochemical vs. electromechanical properties: the case of CO adsorbed on aPt(111) surface

By Mamatkulov, M.; Filhol, J.-S.From Physical Chemistry Chemical Physics (2011), 13(17), 7675-7684. Language: English, Database: CAPLUS,DOI:10.1039/c0cp01444c

The authors have studied electrochem. vibrational and energy properties of CO/Pt(111) in the framework of periodic d.functional theory (DFT) calcns. The authors used a modified version of the previously developed Filhol-Neurock methodto correct the unphys. contributions arising from homogeneous background countercharge in the case of thick metallicslabs. The stability of different CO adsorption sites on Pt(111) (Top, Bridge, Hcp, Fcc) was studied at const. elec. field.The energies are dominated by the surface dipole interaction with the external elec. field: a strong pos. elec. field favorsthe surfaces with the lower dipole moment (that correspond to the ones with the lower coordination). The Stark tuningslope of the CO stretching frequency for a Top site was calcd. for different surface coverages in very good agreementwith both exptl. and other theor. results. Finally, the authors have performed an anal. of the origin of Stark shifts showingthat the total Stark effect can be split into two competing components. The 1st one corresponds to the direct effect ofcharging on the C-O chem. bond: it is referred as an electrochem. effect. The 2nd is the consequence of the surfacedipole interaction with the applied elec. field that modifies the C-O distance, inducing a change of the C-O force const.because of C-O bond anharmonicity: it is referred as the electromech. effect. In the CO/Pt(111) case, the dominantcontribution is electromech. The electrochem. contribution is very small because the electronic system involved in thesurface charging is mostly nonbonding as analyzed by looking at the surface Fukui function.

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~48 Citings

276. Recent trends and developments in polymer electrolyte membrane fuel cell modelling

By Shah, A. A.; Luo, K. H.; Ralph, T. R.; Walsh, F. C.From Electrochimica Acta (2011), 56(11), 3731-3757. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2010.10.046

A review. Modeling and simulation are well-established tools for studying the phys. processes inside a polymerelectrolyte membrane (PEM) fuel cell. The early literature paid great attention to steady-state transport phenomena inthe main components, which continues to be a focus of ongoing activities. There is, however, a growing interest inmodeling other aspects of fuel cell operation, such as transient performance and degrdn. phenomena. There also was agrowth in the no. of mol. and pore-level studies of transport phenomena in fuel cell components, enabled bydevelopments in simulation techniques and enhancements in computer hardware. Such approaches are capable ofrepresenting important small-scale phenomena more faithfully than traditional macroscopic models. This reviewsummarizes recent activity in PEM fuel cell modeling, with a focus on detailed phys. models, and considers its potentialsignificance. An industrial perspective is also provided, highlighting the current use of modeling in the test and designcycles, and outlining future requirements.~53 Citings

277. The empirical valence bond model: theory and applications

By Kamerlin, Shina C. L.; Warshel, AriehFrom Wiley Interdisciplinary Reviews: Computational Molecular Science (2011), 1(1), 30-45. Language: English,Database: CAPLUS, DOI:10.1002/wcms.10

A review. Recent years have seen an explosion in computer power, allowing for the examn. of ever more challengingproblems. For instance, a recent simulation study, which was the first of its kind, was able to actually explore thedynamical nature of enzyme catalysis on a millisecond timescale, something that as recently as a year or two ago wouldhave been considered impossible. However, the questions that need addressing are nevertheless very complex, andexptl. approaches can unfortunately often be inconclusive in answering them. Therefore, it is essential to have anapproach that is both reliable and able to capture complex systems in order to resolve long-standing controversies[particularly with regards to questions such as the origin of enzyme catalysis, where the relevant energy contributionscannot be sepd. without some computational models]. Herein, we will present the empirical valence bond (EVB)approach, which, at present, is arguably the most powerful tool for examg. chem. reactivity in the condensed phase. Wewill illustrate the effectiveness of the EVB method when evaluating, for instance, catalytic effects and demonstrate that itis currently the optimal tool for elucidating challenging problems such as understanding the catalytic power of enzymes.Finally, the increasing appreciation of this approach can maybe best illustrated not only by its proliferation but also byattempts to capture its basic chem. under a different name, as will be discussed in this work.~91 Citings

278. With a Little Help from My Friends: Forty Years of Fruitful Chemical Collaborations

By Borden, Weston ThatcherFrom Journal of Organic Chemistry (2011), 76(9), 2943-2964. Language: English, Database: CAPLUS,DOI:10.1021/jo200213x

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A review. Over the past 40 years, much of the author'sresearch, both computational and exptl., has involvedcollaborations. This review describes some of the author'scollaborative research in eight different areas of org. and theor.chem.: hydrocarbons contg. unsaturatively, 1,3-bridgedcyclobutane rings, the use of orbital topol. for predicting theground states of diradicals, violations of Hund's rule, the chem.of phenylnitrenes, tunneling by carbon in org. reactions, theCope rearrangement and the effect of substituents on it,pyramidalized alkenes, dehydrocubanes, cubyl cation, andoctanitrocubane, and the effects of geminal fluorine substitutionat C-2 of 1,3-diradicals. Highlighted in this review are thesynergism between calcns. and expts. in the author's researchand the many different roles that serendipity has played in thecollaborations that are described herein. Publications of theauthor, based on collaborations, B3LYP/6-31G* energies ofisodesmic reactions involving bicyclo[2.1.1]hex-2-ene, 2,3-dimethylenebicyclo[2.1.1]hexane, 1,2-dimethylenecyclopentane, cyclopentene,benzobicyclo[2.1.1]hex-2-ene, and benzocyclopentene,optimized geometries, energies, and vibrational frequencies forthese mols., and a brief description of a CI approach tounderstanding symmetry breaking in TMM, are given in SI.

~11 Citings

279. Controlled Oxide Removal and Surface Morphology on InSb(100) Using Gas Phase HF/H2O

By Lie, Fee Li; Muscat, Anthony J.From Journal of Physical Chemistry C (2011), 115(15), 7440-7449. Language: English, Database: CAPLUS,DOI:10.1021/jp110151y

The native oxide removal, surface termination, compn., andmorphol. of InSb(100) surfaces etched in gas phase HF/H2Omixts. at a total pressure of 100 Torr and 29 °C wereinvestigated using quant. XPS, at. force microscopy (AFM), andSEM as a function of the HF to water partial pressure ratio.Gas phase HF/H2O etching preferentially removed antimonyoxide and left a residue that was indium fluoride rich. Waterplayed a crit. role in the process by directly participating in theetching reaction and promoting the desorption of fluorideetching products. The lowest HF to H2O ratio studied was 0.3,and this mixt. removed over 90% of the native oxide, producinga smooth surface that consisted of an Sb-terminated substrate,an elemental Sb layer (2 Å), and an indium fluoride-richoverlayer (< 10 Å). Excess elemental Sb was only obsd. at lowoxygen coverages, suggesting that its formation was abyproduct of HF preferentially reacting with In atoms from thesubstrate. Moderate HF to H2O ratios of 0.8-1.2 removed theoxide and yielded the same surface compn. as the lowest ratio;yet, oblate spheroid islands were produced on the surface withheights of 4-60 nm and composed of indium fluoride that hadagglomerated due to the surface energy of the underlyingelemental Sb layer. These islands covered about 10% of thesurface area and were imaged using AFM and SEM. Thehighest HF to H2O ratio studied was 2.3, and this mixt.removed about 70% of the native oxide. The surface wassmooth and terminated with Sb covered by a ∼ 27 Å thickindium fluoride-rich overlayer. The accumulation of indiumfluoride on the surface at high HF to H2O ratios must havecreated a barrier for transport of the etchants to the surface.Control of both the compn. and the morphol. of the InSb(100)surface was possible with gas phase HF, providing moreprocess latitude than obsd. with liq. phase HF etching, whichwas used as a baseline.

~9 Citings

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280. Reaction of 5-nitrosobarbituric acids with thiosemicarbazide

By Yavolovskii, A. A.; Rakipov, I. M.; Kamalov, G. L.From Russian Journal of General Chemistry (2011), 81(2), 447-448. Language: English, Database: CAPLUS,DOI:10.1134/S1070363211020356

The reaction of 5-nitrosobarbituric acids with thiosemicarbazide in acidic medium gave 2-[1-R-2,4,6-trioxo-tetrahydropyrimidine-5(6H)-ylidene]thiosemicarbazones. The structure and tautomerism of thiosemicarbazones weredetd. by the NMR spectroscopy.~1 Citing

281. Computational chemistry tools for the study of environmental chemistry problems

By Ventura, Oscar N.; Segovia, Marc E.; Badenes, Maria Paula; Kieninger, Martina; Bottinelli, Fiorentina; Irving,KennethEdited By:Paz, Jose Luis; Hernandez, Antonio JFrom New Developments in Quantum Chemistry (2009), 109-164. Language: English, Database: CAPLUS

A review on set of cases in which the use of modern computational chem. affords data which is either exptl. unavailableor of doubtful precision, such as in the field of environmental chem. problems.~1 Citing

282. Effect of contaminants on polymer electrolyte membrane fuel cells

By Zamel, Nada; Li, XianguoFrom Progress in Energy and Combustion Science (2011), 37(3), 292-329. Language: English, Database: CAPLUS,DOI:10.1016/j.pecs.2010.06.003

A review. Increasing demand for energy, energy security and the need to minimize the impact on the environmentrelated to energy are the major drivers for the research and development of alternative energy technologies. Polymerelectrolyte membrane (PEM) fuel cells are a promising alternative technol. However, their performance, in other wordsefficiency, can be hindered severely by the presence of contaminants. Impurities in the oxidant and fuel feeds act asbarriers to the oxygen redn. and hydrogen oxidn. These impurities arise from the use of atm. air as the oxidant andhydrogen from reformate as the fuel. The electrolyte membrane can be attacked by ions originating from the cellcomponents. These ions decrease the mech. and chem. stability of the membrane resulting in the decrease of protoncond. and reactant crossover. Due to the severity of these poisoning phenomena, much work has been dedicated tounderstanding their chem. kinetics, their effects and mitigation methods. This paper provides a comprehensive review ofthe exptl., anal. and numerical work devoted to understanding the contamination of the cathode, electrolyte membraneand anode. A summary of future directions and research topics is also given.~82 Citings

283. The reduction of dioxygen by Keggin heteropolytungstates

By Snir, Ophir; Wang, Yifeng; Weinstock, Ira A.From Israel Journal of Chemistry (2011), 51(2), 247-258. Language: English, Database: CAPLUS,DOI:10.1002/ijch.201100026

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A review. Reversible redox chemistries are an inherent feature of numerous metal oxide cluster anions (POMs).Moreover, as discrete mol. structures with well-defined and controllable soln. chemistries, POMs can be deployed asphysicochem. probes for studying inorg. reaction mechanisms. In the past decade, we have used an iso-structural seriesof α-Keggin heteropolytungstate cluster anions to systematically investigate a no. of fundamental topics, includingelectron transfer to O2. The iso-structural series of cluster anions was obtained by varying the heteroatom, Xn+, in theplenary, Td-symmetry α-Keggin ion, Xn+W12O40 (8-n)-, from Al3+ to Si4+ to P5+. This results in a stepwise and linearmodulation of ion charge and redn. potential, whose concerted effects on reaction rates can be used to better understandelectron-transfer processes. Starting from the acquisition of activation parameters assocd. with electron self-exchangebetween the POMs themselves, the studies discussed in this review provide a detailed account of electron transfer fromreduced α-Keggin heteropolytungstate anions to O2, culminating in the recent discovery of a fundamentally newmechanism for electron transfer to O2 in water.~4 Citings

284. Methodology for the Development of Thermodynamic Models Describing Substances That Exhibit ComplexAssociation Interactions

By Baburao, Barath; Visco, Donald P.From Journal of Chemical & Engineering Data (2011), 56(4), 1506-1525. Language: English, Database: CAPLUS,DOI:10.1021/je1011955

This work describes a methodol. for the development of a thermodn. model describing the substances that show strongself- and cross-assocn. interactions. The methodol. is fundamentally based on the chem. theory of assocn. interactions.The system used as a case study in this work is a binary mixt. contg. hydrogen fluoride and water (HF + H2O). Earlierstudies have failed to provide a reasonable description of this binary mixt. because of the complex assocn. interactionsbetween these compds., which were not adequately modeled. In this work, the phase behavior of this mixt. isunderstood by exploring these complex assocn. interactions. Pure HF was modeled using 14 different assocn. schemesthat allow the formations of different phys. meaningful oligomers with different distribution schemes (1-2, 1-6, 1-2-6, etc.),where the 1-2 scheme allows the formation of monomers and dimers and likewise. The parameters for these purecomponent schemes were obtained by correlating the phase coexistence properties of pure HF and were also used topredict several other pure component properties (∆Hvap, CP, Cv, Z, etc.). The dominance of these assocn. patterns andtheir distribution were understood on the basis of their predictive ability. The pure component assocn. schemes thatwere developed for HF and water were extended to the binary mixt. The phase coexistence properties were correlatedusing different assocn. patterns for the pure components with and without considerations for the strong assocn. betweenthem. The significance of these self- and cross-assocn. patterns are studied and understood on the basis of thecorrelative and the predictive ability of the assocn. schemes. The effect of including the cross-assocs. that are mostlikely to be formed in this mixt., from a mol. level hybrid meta-d. functional theory study, is also discussed. The methodol.described in this work can be utilized to understand and predict the bulk-phase thermodn. properties of substances thatshow complex assocn. interactions at a mol. level.~1 Citing

285. Experimental and theoretical study of the 2-Alkoxyethylidene rearrangement

By Graves, Kimberly S.; Thamattoor, Dasan M.; Rablen, Paul R.From Journal of Organic Chemistry (2011), 76(6), 1584-1591. Language: English, Database: CAPLUS,DOI:10.1021/jo1020536

The rearrangement of 2-ethoxyethylidene, generatedphotochem. from a nonnitrogenous precursor, leads to Et vinylether. Although this product could result, in principle, from a1,2-hydrogen shift and/or a 1,2-ethoxy shift in the carbene, adeuterium labeling study indicates an essentially exclusivepreference for hydrogen migration. The exptl. results are inagreement with CCSD and W1BD calcns. for the simpler 2-methoxyethylidene system that show a prohibitively largebarrier for the methoxy shift and a negligible barrier for thehydride shift.

~15 Citings

286. Ab initio potential energy surface and quantum dynamics for the H + CH4 → H2 + CH3 reaction

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By Zhou, Yong; Fu, Bina; Wang, Chunrui; Collins, Michael A.; Zhang, Dong H.From Journal of Chemical Physics (2011), 134(6), 064323/1-064323/8. Language: English, Database: CAPLUS,DOI:10.1063/1.3552088

A new full-dimensional potential energy surface for the title reaction has been constructed using the modified Shepardinterpolation scheme. Energies and derivs. were calcd. using the UCCSD(T) method with aug-cc-pVTZ and 6-311++G(3df,2pd) basis sets, resp. A total no. of 30 000 data points were selected from a huge no. of mol. configurationssampled by trajectory method. Quantum dynamical calcns. showed that the potential energy surface is well convergedfor the no. of data points for collision energy up to 2.5 eV. Total reaction probabilities and integral cross sections werecalcd. on the present surface, as well as on the ZBB3 and EG-2008 surfaces for the title reaction. Satisfactoryagreements were achieved between the present and the ZBB3 potential energy surfaces, indicating we are approachingthe final stage to obtain a global potential energy surface of quant. accuracy for this benchmark polyat. system. Ourcalcns. also showed that the EG-2008 surface is less accurate than the present and ZBB3 surfaces, particularly in highenergy region. (c) 2011 American Institute of Physics.~35 Citings

287. Mechanism of an enhanced oxygen reduction reaction at platinum-based electrocatalysts: identificationand quantification of oxygen species adsorbed on electrodes by X-ray photoelectron spectroscopy

By Wakisaka, Mitsuru; Watanabe, Masahiro; Uchida, HiroyukiEdited By:Wieckowski, Andrzej; Norskov, Jens KFrom Fuel Cell Science (2010), 147-168. Language: English, Database: CAPLUS, DOI:10.1002/9780470630693.ch4

In this chapter, a novel XPS study of the enhanced ORR mechanism of Pt-based alloy electrodes is presented. Themethodol. employed for the identification and quantification of O-contg. species adsorbed on the Pt-based electrodes byXPS is described. The assignments of O species are extensively discussed by using a well-defined Pt(111) single-crystal electrode. Four types of O species were distinguished, with binding energies at 529.6, 530.5, 531.1, and 532.6eV; the 1st two were assigned to adsorbed at. O and hydroxyl, while the latter two were assigned to the bilayer H2Omols. The coverage of each O species was found to vary with the electrode potential and strongly depend on the Ptelectrode types. The coverages of O species in O2-satd. soln. also differ from those in N2-purged soln. Specifically, thecoverage of at. O increased in the potential region where ORR took place. As compared to pure Pt, the enhanced ORRmechanism at the Pt-based alloy electrodes is discussed, from the coverage changes of at. O during ORR as well asapparent rate consts. for the ORR evaluated by hydrodynamic voltammograms using channel flow double electrodes.~9 Citings

288. Bimolecular reaction rates from ring polymer molecular dynamics: Application to H + CH4→ H2 + CH3

By Suleimanov, Yury V.; Collepardo-Guevara, Rosana; Manolopoulos, David E.From Journal of Chemical Physics (2011), 134(4), 044131/1-044131/10. Language: English, Database: CAPLUS,DOI:10.1063/1.3533275

In a recent paper, we have developed an efficient implementation of the ring polymer mol. dynamics (RPMD) method forcalcg. bimol. chem. reaction rates in the gas phase, and illustrated it with applications to some benchmark atom-diatomreactions. In this paper, we show that the same methodol. can readily be used to treat more complex polyat. reactions intheir full dimensionality, such as the hydrogen abstraction reaction from methane, H + CH2 → H2 + CH3. The presentcalcns. were carried out using a modified and recalibrated version of the Jordan-Gilbert potential energy surface. Thethermal rate coeffs. obtained between 200 and 2000 K are presented and compared with previous results for the samepotential energy surface. Throughout the temp. range that is available for comparison, the RPMD approxn. gives betteragreement with accurate quantum mech. (multiconfigurational time-dependent Hartree) calcns. than do either thecentroid d. version of quantum transition state theory (QTST) or the quantum instanton (QI) model. The RPMD ratecoeffs. are within a factor of 2 of the exact quantum mech. rate coeffs. at temps. in the deep tunneling regime. Theseresults indicate that our previous assessment of the accuracy of the RPMD approxn. for atom-diatom reactions remainsvalid for more complex polyat. reactions. They also suggest that the sensitivity of the QTST and QI rate coeffs. to thechoice of the transition state dividing surface becomes more of an issue as the dimensionality of the reaction increases.(c) 2011 American Institute of Physics.~55 Citings

289. Theoretical Study on Dissolution and Reprecipitation Mechanism of Pt Complex in Pt Electrocatalyst

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By Ishimoto, Takayoshi; Ogura, Teppei; Umeda, Minoru; Koyama, MichihisaFrom Journal of Physical Chemistry C (2011), 115(7), 3136-3142. Language: English, Database: CAPLUS,DOI:10.1021/jp1075274

We systematically analyzed the formation energy and solvationfree energy of four- and six-coordinate Pt(II) and Pt(IV)complexes with three types of ligands (H2O, OH-, and HSO4 -)in concd. sulfuric acid to rationalize the Pt electrocatalystdegrdn. and dissoln. mechanisms as a model for a polymerelectrolyte fuel cell. Because the formation energy andsolvation free energy of Pt(IV) complexes are larger than thoseof Pt(II) complexes, the Pt(IV) complexes are more probable asthe dissolved Pt species than Pt(II). The local relaxationsabout at. charges and geometry by the substitution of OH- orHSO4 - for H2O are one of the factors influencing the stability ofdissolved Pt complex. We predict the [Pt(H2O)2(OH)4] and[Pt(OH)4]2- are important complexes for desorption from the Ptsurface based on the desorption energy anal. of Pt complexfrom the Pt surface. The [Pt(H2O)4]2+ complex, which isformed by a redn. reaction from Pt(IV) and a proton addn.reaction, shows the possibility of the final form before repptn.on the Pt surface. We theor. estd. the Pt dissoln. and repptn.mechanisms from an atomistic view.

~8 Citings

290. Theories for predicting reversible potentials of reactions on electrode surfaces from internal and Gibbsenergies: applications to ORR

By Anderson, Alfred B.From ECS Transactions (2010), 28(19, Progress in Spectro-Electrochemistry and Surface Science of ElectrocatalyticalInterfaces), 1-17. Language: English, Database: CAPLUS, DOI:10.1149/1.3491360

A review. Charge self-consistent calcns. were found feasible they were used to develop ways to calc. reversiblepotentials and potential dependencies of electron transfer reactions for adsorbed mols. Here, emphasizing O2 redn., isan overview of these quantum electrochem. developments at Case University is presented.~5 Citings

291. Computational simulations on the oxygen reduction reaction in electrochemical systems

By Keith, John A.; Jacob, TimoFrom Modern Aspects of Electrochemistry (2010), 50(Theory and Experiment in Electrocatalysis), 89-132. Language:English, Database: CAPLUS, DOI:10.1007/978-1-4419-5594-4_3

A review of electrochem. redn. of oxygen and its theor. and exptl. data is given. The reaction mechanism on platinumand carbon and bimetallic surfaces and alloys is described. The theor. studies are reviewed. The simulations ofbimetallic alloys surface are discussed. The catalytic behavior of electrode system is analyzed. An importance of theoxygen redn. due to applications in fuel cells is pointed out.~6 Citings

292. Mechanism and Tafel lines of electro-oxidation of water to oxygen on RuO2(110)

By Fang, Ya-Hui; Liu, Zhi-PanFrom Journal of the American Chemical Society (2010), 132(51), 18214-18222. Language: English, Database:CAPLUS, DOI:10.1021/ja1069272

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How to efficiently oxidize H2O to O2 (H2O → 1/2O2 + 2H+ + 2e-)is a great challenge for electrochem./photo water splittingowing to the high overpotential and catalyst corrosion. Hereextensive periodic first-principles calcns. integrated withmodified-Poisson-Boltzmann electrostatics are utilized to revealthe phys. origin of the high overpotential of the electrocatalyticoxygen evolution reaction (OER) on RuO2(110). By detg. thesurface phase diagram, exploring the possible reactionchannels, and computing the Tafel lines, we are able toelucidate some long-standing puzzles on the OER kinetics fromthe at. level. We show that OER occurs directly on an O-terminated surface phase above 1.58 V vs. NHE, but indirectlyon a OH/O mixed phase below 1.58 V by converting first theOH/O mixed phase to the O-terminated phase locally. Therate-detg. step of OER involves an unusual water oxidn.reaction following a Eley-Rideal-like mechanism, where a watermol. from soln. breaks its OH bond over surface Os withconcurrent new O-OH bond formation. The free energy barrieris 0.74 eV at 1.58 V, and it decreases linearly with the increaseof potential above 1.58 V (a slope of 0.56). In contrast, thetraditionally regarded surface oxygen coupling reaction with aLangmuir-Hinshelwood mechanism is energetically lessfavored and its barrier is weakly affected by the potential.Fundamentally, we show that the empirical linearbarrier∼potential relation is caused by the linear structuralresponse of the solvated transition state to the change ofpotential. Finally, the general strategy for finding better OERanode is also presented.

~238 Citings

293. Theoretical Studies of Potential-Dependent and Competing Mechanisms of the Electrocatalytic OxygenReduction Reaction on Pt(111)

By Keith, John A.; Jacob, TimoFrom Angewandte Chemie, International Edition (2010), 49(49), 9521-9525. Language: English, Database: CAPLUS,DOI:10.1002/anie.201004794

The first principle mechanistic study of the electrochem. oxygen redn.. mechanism on Pt(111) electrodes is reported.Authors bench-marked quantum mechanics calcns. to exptl. data and reported a multi-pathway mechanism which issensitive to reaction conditions and specifically to the applied potential. A simple anal. based on calc. rate consts.remarkably reproduces exptl. known factors concerning the electrocatalytic oxygen redn., indicating the controversial at.-scale mechanism for the reaction.~133 Citings

294. Electron flux during pericyclic reactions in the tunneling limit: Quantum simulation for cyclooctatetraene

By Hege, Hans-Christian; Manz, Joern; Marquardt, Falko; Paulus, Beate; Schild, AxelFrom Chemical Physics (2010), 376(1-3), 46-55. Language: English, Database: CAPLUS,DOI:10.1016/j.chemphys.2010.07.033

Pericyclic rearrangement of cyclooctatetraene proceeds from equiv. sets of two reactants to two products. In the ideallimit of coherent tunneling, these reactants and products may tunnel to each other by ring inversions and by double bondshifting (DBS). We derive simple cosinusoidal or sinusoidal time evolutions of the bond-to-bond electron fluxes andyields during DBS, for the tunneling scenario. These overall yields and fluxes may be decompd. into variouscontributions for electrons in so called pericyclic, other valence, and core orbitals. Pericyclic orbitals are defined as thesubset of valence orbitals which describe the changes of Lewis structures during the pericyclic reaction. The quantumdynamical results are compared with the traditional scheme of fluxes of electrons in pericyclic orbitals, as provided byarrows in Lewis structures.~27 Citings

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295. Back to the Coordination Modes of the Thiosemicarbazonate Chain: new Insights from Diorganolead(IV)and Lead(II) Derivatives of Isatin-3-thiosemicarbazone

By Casas, Jose S.; Casanova, Noelia; Garcia-Tasende, Maria S.; Sanchez, Agustin; Sordo, Jose; Touceda, Angeles;Vazquez, SauloFrom European Journal of Inorganic Chemistry (2010), (31), 4992-5004. Language: English, Database: CAPLUS,DOI:10.1002/ejic.201000669

The syntheses and characterizations of the new heteroleptic complexes [PbPh2(OAc)(N2-L1)]·MeOH·EtOH,[PbPh2(OAc)(N3-L2)]·H2O, [Pb(OAc)(N2-L1)], [Pb(OAc)(N3-L1)]·3H2O and [Pb(OAc)(N2-L2)] HL1 = isatin-3-thiosemicarbazone, HL2 = isatin-3-(N1-methylthiosemicarbazone); N2-Lx = thiosemicarbazonate bound through O,S andthe hydrazinic [N(2)] nitrogen atom; N3-Lx = thiosemicarbazonate bound through the O,S and the iminic [N(3)] nitrogenatom are described. The single-crystal x-ray structures of HL2, [PbPh2(OAc)(N2-L1)]·MeOH·EtOH, [PbPh2(OAc)(N3-L2)]·H2O, [Pb(OAc)(N2-L1)] and [Pb(OAc)(N3-L1)]·3H2O have been solved. The organometallic compds.[PbPh2(OAc)(N2-L1)]·MeOH·EtOH and [PbPh2(OAc)(N3-L2)]·H2O have a roughly similar distorted bipyramidal pentagonalstereochem., with apical Ph groups and both the O,Nx,S-coordinated Lx- and the anisobidentate AcO- ligands in theequatorial plane. In [PbPh2(OAc)(N2-L1)]·MeOH·EtOH, the (N2-L1)- ligand forms a four- and a six-membered chelate ringwith the metal, whereas in [PbPh2(OAc)(N3-L2)]·H2O the two chelate rings formed by (N3-L2)- are five-membered. ThePbII complexes, [Pb(OAc)(N2-L1)] and [Pb(OAc)(N3-L1)], which were isolated from the same soln., are linkage isomers.These compds. have a rather irregular stereochem. that suggests the presence of a stereochem. active lone electronpair; in [Pb(OAc)(N2-L1)] the (L1)- ligand is O,N2,S-coordinated and in [Pb(OAc)(N3-L1)] this ligand is O,N3,S-coordinated.Analyses of all these systems in soln. by 1H and 13C NMR spectroscopy showed that during synthesis the kineticallycontrolled O,N2,S isomer formed first due to the rigidity of the ligand. If the compd. remains in soln., slow partialevolution to the O,N3,S isomer occurs. DFT calcns. predict that [Pb(OAc)(N3-L1)] is slightly more stable than[Pb(OAc)(N2-L1)] both in the gas phase and in DMSO soln. The calcns. also modeled structures for the two isomersclose to those obtained by x-ray diffraction studies.~3 Citings

296. Dissociation Dynamics of Isotopologs of CH5 Studied by Charge Exchange of CH5+ with Cs andQuasiclassical Trajectory Calculations

By Mann, Jennifer E.; Xie, Zhen; Savee, John D.; Bowman, Joel M.; Continetti, Robert E.From Journal of Physical Chemistry A (2010), 114(43), 11408-11416. Language: English, Database: CAPLUS,DOI:10.1021/jp105119v

The product branching fractions and dissocn. dynamics for thedissocn. of CH5, CH2D3, CHD4, and CD5 have been exptl.measured following charge exchange of the parent cations withCs. These results are compared with quasiclassical trajectorycalcns. run on an ab initio potential energy surface for CH5. Inall cases it is found that dissocn. channels involving theejection of a single atom (H or D) are dominant. Thestatistically weighted branching fractions show that in the mixedisotopologs, ejection of a hydrogen atom is favored over adeuterium atom. The results are consistent with the fluxionalnature of CH5 + isotopologs - no evidence was found forquantum localization upon deuteration in the comparison of theexptl. and theor. branching fractions, possibly as a result of thevibrational temp. of the cations (estd. to be as high as 1660 Kfor high frequency modes). This comparison of expt. andtheory provides a test of the CH5 potential energy surface athigh levels of excitation.

~5 Citings

297. Pyrolytical characterization of transition metal complexes of cobalt, nickel, copper and zinc withethylenediamine-N,N'-diacetate

By Rehman, S.; Arshad, M.; Masud, K.; Afzal, R.; Salma, U.From Journal of Thermal Analysis and Calorimetry (2010), 102(2), 715-722. Language: English, Database: CAPLUS,DOI:10.1007/s10973-009-0184-3

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Octahedral complexes, [M(EDDA)(H2O)2]·H2O (where, M+2 = Co(II), Cu(II), Ni(II) and Zn(II); EDDA, ethylenediamine-N,N'-diacetate), were prepd. and studied by TG and DTA. Their compns. were studied by elemental anal. to ensure theirpurity and structural elucidation was based on spectral and magnetic properties. Thermal decompn. of these distortedoctahedral complexes, [Ni(EDDA)(H2O)2], [Co(EDDA)(H2O)2]·H2O, [Cu(EDDA)(H2O)2]·H2O and [Zn(EDDA)(H2O)2]·H2Ocame of in one, two, three and four steps, resp., upon heating to 800°, with the loss of org. and inorg. fragments. Liganddecompd. in three steps. The thermal degrdn. of all the complexes in static air atm. started at temps. lower than thoseobsd. for the free ligand degrdn. (Ni-complex being the only exception). The compn. of intermediates formed duringdegrdn. was confirmed by microanal. and IR spectroscopy. The residues corresponded to metal oxide except for Ni(II)and Zn(II) complexes. Thermal stability of the complexes increased in the following sequence: Cu(II)∼Co(II)<Zn(II)<Ni(II).~8 Citings

298. First Principles Calculations on Site-Dependent Dissolution Potentials of Supported and Unsupported PtParticles

By Jinnouchi, Ryosuke; Toyoda, Eishiro; Hatanaka, Tatsuya; Morimoto, YuFrom Journal of Physical Chemistry C (2010), 114(41), 17557-17568. Language: English, Database: CAPLUS,DOI:10.1021/jp106593d

Site-dependent redox potentials of the Pt dissoln. reaction, Pt→ Pt2+(aq) + 2e-, from Pt particles with and without carbonsupports were calcd. by a first principles method. The calcn.result showed a clear site-dependence in which the redoxpotentials for the Pt atoms at edges are lower than those for Ptatoms at flat surfaces. This site-dependence is roughlycorrelated with the d-band center of the dissolving Pt atom, andPt atoms with higher d-band centers dissolve more easily to thesoln. The effects of perfect and defected graphenes on theredox potential are less than 0.1 V. For the platinum atomattaching to the carbons, a slightly neg. effect (lowering theredox potential) is obtained, because the bond strengthbetween Pt particles and carbons is enhanced by the defectcreation after the dissoln. reaction.

~44 Citings

299. Atomistic modeling in study of polymer electrolyte fuel cells - a review

By Zhou, Xiangyang; Zhou, Juanjuan; Yin, YijinFrom Modern Aspects of Electrochemistry (2010), 49(Modeling and Diagnostics of Polymer Electrolyte Fuel Cells),307-380. Language: English, Database: CAPLUS, DOI:10.1007/978-0-387-98068-3_9

A review on the recent developments in atomistic modeling of polymer electrolyte fuel cells. It emphasizes on thecomparison of the methods presented in the review, like ab initio mol. dynamic, mol. dynamic, kinetic Monte Carlo, andcontinuum method.~0 Citings

300. Tunnelling in the O + CO reaction

By Goumans, T. P. M.; Andersson, StefanFrom Monthly Notices of the Royal Astronomical Society (2010), 406(4), 2213-2217. Language: English, Database:CAPLUS, DOI:10.1111/j.1365-2966.2010.16836.x

The importance of tunnelling in the formation of CO2 from O(3P) + CO at very low temps. is studied with harmonicquantum transition state theory. To optimize the quantum transition state, we have used both fitted potential energysurfaces and direct dynamics, where forces and energies are calcd. by a quantum chem. code on the fly as they areneeded. While tunnelling does increase the classical reaction rate for the O(3P) + CO addn. reaction at very low temps.,the onset of tunnelling is at too low temps. for the reaction to significantly contribute to the formation of interstellar CO2.Instead, it is more likely that an oxygen atom impinging on an interstellar ice would form a loosely bound complex withadsorbed CO, which may subsequently react with a hydrogen atom to ultimately yield CO2.~42 Citings

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301. Theoretical investigations of the oxygen reduction reaction on Pt(111)

By Keith, John A.; Jerkiewicz, Gregory; Jacob, TimoFrom ChemPhysChem (2010), 11(13), 2779-2794. Language: English, Database: CAPLUS,DOI:10.1002/cphc.201000286

A review. Computational modeling can provide important insights into chem. reactions in both applied and fundamentalfields of research. One of the most crit. processes needed in practical renewable energy sources is the oxygen redn.reaction (ORR). Besides being the key process in combustion and corrosion, the ORR has an elusive mechanism thatmay proceed in a no. of complicated reaction steps in electrochem. fuel cells. Indeed, the mechanism of the ORR onhighly studied Pt(111) electrodes was the subject of interest and debate for decades. Herein, first the theory behindthese types of simulations are outlineed and then is shown how to use these quantum mech. approaches and approxns.to create a realistic model. After reviewing the performance of these methods in studying the binding of mol. oxygen toPt(111), the authors' own results are outlined elucidating the ORR and its dependence on environmental parameters,such as solvent, thermodn. energies, and the presence of an external electrode potential. This approach can, inprinciple, be applied to other equally complicated investigations of other surfaces or electrochem. reactions.~125 Citings

302. Mechanism and Activity of Photocatalytic Oxygen Evolution on Titania Anatase in Aqueous Surroundings

By Li, Ye-Fei; Liu, Zhi-Pan; Liu, LuLu; Gao, WeiguoFrom Journal of the American Chemical Society (2010), 132(37), 13008-13015. Language: English, Database:CAPLUS, DOI:10.1021/ja105340b

Due to its high overpotential and low efficiency, the conversionof water to O2 using solar energy remains a bottleneck forphotocatalytic water splitting. Here the microscopicmechanisms of the oxygen evolution reaction (OER) ondifferently structured anatase surfaces in aq. surroundings,namely, (101), (001), and (102), are detd. and comparedsystematically by combining first-principles d. functional theorycalcns. and a parallel periodic continuum solvation model. Theauthors show that OER involves the sequential removal ofprotons from surface oxidative species, forming surface peroxoand superoxo intermediates. The initiating step, the first protonremoval, dictates the high overpotential. Only at anoverpotential of 0.7 V (1.93 V vs SHE) does this rate-controllingstep become surmountable at room temp.: the free energychange of the step is 0.69, 0.63, and 0.61 eV for (101), (102),and (001) surfaces, resp. Therefore the authors conclude that(i) OER is not sensitive to the local surface structure of anataseand (ii) visible light (<∼590 nm) is, in principle, capable ofdriving the photocatalytic OER on anatase kinetically. By co-doping high-valent elements into the anatase subsurface, theauthors demonstrate that the high overpotential of the OER canbe significantly reduced, with extra occupied levels above thevalence band.

~199 Citings

303. Solvation and Zero-Point-Energy Effects on OH(ads) Reduction on Pt(111) Electrodes

By Anderson, Alfred B.; Uddin, Jamal; Jinnouchi, RyoskeFrom Journal of Physical Chemistry C (2010), 114(35), 14946-14952. Language: English, Database: CAPLUS,DOI:10.1021/jp1041734

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The linear Gibbs energy relation (LGER) is a theor. model inwhich one adds to the known bulk soln.-phase reversiblepotential for a reaction involving electron transfer the internalenergy change, divided by nF, when the reactants andproducts are adsorbed, where n is the no. of electronstransferred and F is the Faraday const. This yields predictionsof the reversible potentials for the same reactions but with thereactants and products in adsorbed states on the electrodesurface. The LGER theory was used in previous studies whereDe bond strengths, measured from the bottom of the Born-Oppenheimer potential at equil., were used rather than the Dovalues, which include zero-point vibrational energies. Here,when zero-point energies are included, the result is to increasethe reversible potential for OH(ads) redn. to H2O(ads) onPt(111) electrodes, an important fuel-cell cathode reaction, by0.05 V. The effects of solvation also are small, decreasing theLGER prediction by 0.09 V. These results were calcd. by usinga self-consistent theory incorporating two-dimensional slab-band d. functional calcns. with the solvation handled by amodified Poisson-Boltzmann theory and a dielec.-continuummodel. The net result is to decrease the LGER prediction of0.86 V for the reaction with H bonding of the reactant andproduct to adsorbed H2O to 0.82 V, which is a close match withthe exptl. value of ∼0.77 V. These findings explain theusefulness of the LGER theory for rapid screening of fuel-cellelectrocatalysts.

~16 Citings

304. Experimental Evidence for Heavy-Atom Tunneling in the Ring-Opening of Cyclopropylcarbinyl Radical fromIntramolecular 12C/13C Kinetic Isotope Effects

By Gonzalez-James, Ollie M.; Zhang, Xue; Datta, Ayan; Hrovat, David A.; Borden, Weston Thatcher; Singleton, DanielA.From Journal of the American Chemical Society (2010), 132(36), 12548-12549. Language: English, Database:CAPLUS, DOI:10.1021/ja1055593

The intramol. 13C kinetic isotope effects for the ring-opening ofcyclopropylcarbinyl radical were detd. over a broad temp.range. The obsd. isotope effects are unprecedentedly large,ranging from 1.062 at 80 °C to 1.163 at -100 °C. Semiclassicalcalcns. employing canonical variational transition-state theorydrastically underpredict the obsd. isotope effects, but thepredicted isotope effects including tunneling by a small-curvature tunneling model match well with expt. These resultsand a curvature in the Arrhenius plot of the isotope effectssupport the recently predicted importance of heavy-atomtunneling in cyclopropylcarbinyl ring-opening.

~47 Citings

305. Molecules with labile bonds: selected annulenes and bridged homotropilidenes

By Williams, Richard V.Edited By:Dodziuk, HelenaFrom Strained Hydrocarbons (2009), 399-424. Language: English, Database: CAPLUS,DOI:10.1002/9783527627134.ch8

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A review. The complex properties of cyclobutadiene and cyclooctatetraene are now well understood. Enticing newresults resurrect old questions about the annulenes: Where does natural bond alternation begin and just how (anti)arom.are they The location of Mobius transition states for annulene isomerization nicely addresses the long-standing andvexing question of why these formal cis-trans isomerizations are so facile. The cyclophanediene dihydropyrene equil. isnow better understood and predictions regarding substituent effects on the barrier to this electrocyclization are beingtested exptl. Many barbaralanes and semibullvalenes with miniscule exptl. barriers to their Cope rearrangement are nowknown. The thermochromism and solvatochromism of these bridged homotropilidenes has been thoroughly investigatedand even a semibullvalene solvate with a homoarom. ground state found. Again, through calcns., several ground statebishomoarom. semibullvalenes have been identified. Now all that remains is the synthesis and exptl. verification of thefirst neutral bishomoarom.!~7 Citings

306. Proton Transfer Studied Using a Combined Ab Initio Reactive Potential Energy Surface with Quantum PathIntegral Methodology

By Wong, Kim F.; Sonnenberg, Jason L.; Paesani, Francesco; Yamamoto, Takeshi; Vanicek, Jiri; Zhang, Wei;Schlegel, H. Bernhard; Case, David A.; Cheatham, Thomas E., III; Miller, William H.; et alFrom Journal of Chemical Theory and Computation (2010), 6(9), 2566-2580. Language: English, Database: CAPLUS,DOI:10.1021/ct900579k

The rates of intramol. proton transfer are calcd. on a full-dimensional reactive electronic potential energy surface thatincorporates high-level ab initio calcns. along the reaction path and by using classical transition state theory, path-integralquantum transition state theory, and the quantum instanton approach. The specific example problem studied ismalonaldehyde. Ests. of the kinetic isotope effect using the latter two methods are found to be in reasonable agreementwith each other. Improvements and extensions of this practical, yet chem. accurate framework for the calcns. ofquantized, reactive dynamics are also discussed.~43 Citings

307. Concerted Proton-Electron Transfer to Dioxygen in Water

By Snir, Ophir; Wang, Yifeng; Tuckerman, Mark E.; Geletii, Yurii V.; Weinstock, Ira A.From Journal of the American Chemical Society (2010), 132(33), 11678-11691. Language: English, Database:CAPLUS, DOI:10.1021/ja104392k

Concerted proton-electron transfer (CPET) is documented forthe homogeneous redn. of O2 to HO2 · in water by the one-electron-reduced heteropolytungstate anion, α-PW12O40 4-

(11e). At 0.01-0.3 M H+, O2 redn. occurs via outer-sphereelectron transfer followed by proton transfer (ETPT, with rateconst. kET). Between 0.30 and 1.9 M H+, rates increaselinearly with [H+] due to a parallel CPET pathway in which H+ isnow a reactant: (1/2)kobs = kET + kCPET[H+] (kET = 1.2 M-1/s-1;kCPET = 0.8 M-2/s-1). Control expts. rule out preassocn.between H+ and 11e. Anal. of plausible rate expressions showsthat the first-order dependence on [H+] is uniquely consistentwith multisite CPET, and a deuterium kinetic isotope effect of1.7 is obsd. Redns. of O2 by α-SiW12O40 5- confirm theor.predictions that CPET decreases in significance as ETbecomes less endergonic. Marcus anal., including the temp.dependence of ∆G°, gives reorganization energies, λET = 41.5kcal/mol-1 and λCPET = 52.4 kcal/mol-1. At 1.5 M H+, ∼75% ofthe (11e,O2) encounter pairs form within 6 Å of H+ ions. Thisvalue (6 ± 1 Å) is the "reaction distance" for proton diffusionand probably close to that for CPET. Even so, the 70-200 pslifetimes of the (11e,O2) pairs provide addnl. time for H+ todiffuse closer to O2. CPET is first-order in [H+] because ke for"cage escape" from (11e,O2) pairs is much larger than kCPET,such that the rate expression for CPET becomes -(1/2)d[11e]/dt= (kd/ke)kCPET[11e][O2][H+], where kd is the rate const. for(11e,O2) pair formation. Overall, the findings suggest that theemergence of CPET, with hydronium ion as the proton donor,may prove a general feature of sufficiently endergonic redns. ofdioxygen by otherwise "outer-sphere" complexes (or electrodereactions) at sufficiently low pH values in water.

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~27 Citings

308. Depression of reactivity by the collision energy in the single barrier H + CD4 → HD + CD3 reaction

By Zhang, Weiqing; Zhou, Yong; Wu, Guorong; Lu, Yunpeng; Pan, Huilin; Fu, Bina; Shuai, Quan; Liu, Lan; Liu, Shu;Zhang, Liling; et alFrom Proceedings of the National Academy of Sciences of the United States of America (2010), 107(29), 12782-12785, S12782/1-S12782/5. Language: English, Database: CAPLUS, DOI:10.1073/pnas.1006910107

Crossed mol. beam expts. and accurate quantum scattering calcns. have been carried out for the polyat. H + CD4 → HD+ CD3 reaction. Unprecedented agreement has been achieved between theory and expts. on the energy dependence ofthe integral cross section in a wide collision energy region that first rises and then falls considerably as the collisionenergy increases far over the reaction barrier for this simple hydrogen abstraction reaction. Detailed theor. anal. showsthat at collision energies far above the barrier the incoming H-atom moves so quickly that the heavier D-atom on CD4cannot concertedly follow it to form the HD product, resulting in the decline of reactivity with the increase of collisionenergy. We propose that this is also the very mechanism, operating in many abstraction reactions, which causes thedifferential cross section in the backward direction to decrease substantially or even vanish at collision energies farabove the barrier height.~33 Citings

309. Kinetics of hydrogen-transfer isomerizations of butoxyl radicals

By Zheng, Jingjing; Truhlar, Donald G.From Physical Chemistry Chemical Physics (2010), 12(28), 7782-7793. Language: English, Database: CAPLUS,DOI:10.1039/b927504e

Five isomerization reactions involving intramol. hydrogen-transfer in butoxyl radicals have been studied using variationaltransition state theory with small curvature tunneling. A set of best ests. of barrier heights and reaction energies forthese five reactions was obtained by using coupled cluster theory including single and double excitations with a quasi-perturbative treatment of connected triple excitations and a basis set extrapolated to the complete basis set limit pluscore-valence correlation contributions and scalar relativistic corrections. This work predicts high-pressure limiting rateconsts. of these five reactions over the temp. range 200-2500 K and clarifies the available exptl. data from indirectmeasurements. This study shows the importance of performing rate calcns. with proper accounting for tunneling andtorsional anharmonicity. The authors also proposed two new models for use in fitting rate consts. over wide ranges oftemp.~116 Citings

310. Tunneling in enzymatic and nonenzymatic hydrogen transfer reactions

By Truhlar, Donald G.From Journal of Physical Organic Chemistry (2010), 23(7), 660-676. Language: English, Database: CAPLUS,DOI:10.1002/poc.1676

A review. This paper is an opportunity for the author to respond to an invitation to share his viewpoint by writing anopinion piece on proton tunneling, esp. from the point of view of whether it has a greater importance in enzymic reactionsthan in other reactions. The paper begins with a discussion of the emergence of a conceptual framework for includingtunneling in reaction rate calcns.; the framework is general enough to include not only transfer of protons but alsotransfer of H atoms and hydride ions and their isotopes, and not only enzymically catalyzed reactions but alsononenzymic reactions. The author then discusses special issues that arise when the reaction rate under consideration isfor an enzyme-catalyzed reaction. The emphasis is on phys. considerations in reaction rate calcns., not on system-specific comparison of results for different modes of reaction. It is argued that enzymic and nonenzymic reactions maybe treated within the same basic framework except that ensemble averaging, which is not usually required for gas-phasereactions, is essential for treating enzyme reactions. Enzymes explicitly discussed include methylamine dehydrogenase,arom. amine dehydrogenase, Escherichia coli dihydrofolate reductase, hyperthermophilic dihydrofolate reductase, liveralc. dehydrogenase, methylmalonyl-CoA mutase, soybean lipoxygenase, copper amine oxidase, pentaerythritoltetranitrate reductase, morphinone reductase, enolase, xylose isomerase, and 4-oxalocrotonate tautomerase.~70 Citings

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311. Oxygen reduction reaction of PEMFC cathode by molecular simulations

By Liu, Chuang; Wu, Yuhou; Sun, Hong; Tang, YulanFrom Advanced Materials Research (Zuerich, Switzerland) (2010), 105-106(Chinese Ceramics Communications), 698-700. Language: English, Database: CAPLUS, DOI:10.4028/www.scientific.net/AMR.105-106.698

Cathode catalyst layer plays an important role in PEMFC. Electrochem. reaction in cathode catalyst layer is a controlprocess for the performance in PEMFC. In this paper, oxygen redn. reaction (ORR) is studied by mol. simulations basedon a series pathway which consist of four steps. We calcd. the free energy of four steps resp. by mol. simulations.Comparing free energy of our steps, we found that the fourth step can release more energy than the other steps. At thesame time, we found that the energy released in ORR is decreased with the increase of temp. The process of the firststep in the series pathway release less energy than that of other steps. The results are very helpful for optimization ofconstruction in the cathode and improving performance of PEM fuel cell.~0 Citings

312. Cathode contamination modeling in fuel cells

By Shi, Zheng; Song, Datong; Li, Hui; Zhang, Jianlu; Liu, Zhong-Sheng; Zhang, JiujunEdited By:Li, HuiFrom Proton Exchange Membrane Fuel Cells (2010), 179-207. Language: English, Database: CAPLUS

A review on cathode contamination modeling, particularly kinetic modeling. It discusses cathode oxygen redn.mechanisms and oxygen redn. kinetic models. It presents the application of a cathode contamination model to feedstream toluene contamination, and discusses the effects of toluene contamination on fuel cell performance. It concludeswith a summary of cathode contamination research.~0 Citings

313. Density functional theory applied to electrocatalysis

By Venkatachalam, S.; Jacob, T.Edited By:Vielstich, Wolf; Yokokawa, Harumi; Gasteiger, Hubert AFrom Handbook of Fuel Cells (2009), 5, 133-151. Language: English, Database: CAPLUS,DOI:10.1002/9780470974001.f500008

This study performed periodic d. functional theory (DFT) calcns. and thermodn. considerations to evaluate thecorresponding (a, T, ∆ϕ) surface phase diagram for Pt(111) in contact with an aq. electrolyte. The DFT calcns. ondifferent reaction pathways for the oxygen redn. reaction (ORR) were also described. It was obsd. that while below 0.95V no stable and ordered oxygen overlayer formed, between 0.95 and 1.20 V the well-known p(2 x 2)-O becomesthermodynamically stable. Further increased of the electrode potentials then led to a surface oxide or even PtO2 bulkoxide. In the ORR, two major pathways can be distinguished, first was the O2 dissocn. pathway that involves thedissocn. of dioxygen as one of the first reaction steps to generate two oxygen atoms on the surface, which then can reactwith adsorbed H atoms to form water. The second pathway was the OOH/H2O2-formation pathway, in which the O2 mol.is not dissocd. directly but reacts with hydrogen to OOH or H2O2, which then dissocs. Between the two main reactionmechanisms, it was found that when performing std. DFT calcns. in gas phase only, H2O2 formation was preferred, butwhen including environmental effects (i.e., water solvation), the overall kinetics was modified, leading to almost the samepreference for the O2 dissocn. and the OOH-formation mechanisms, but blocking of the hydrogen peroxide pathway.~3 Citings

314. Six-dimensional dynamics study of reactive and non reactive scattering of H2 from Cu(111) using achemically accurate potential energy surface

By Diaz, C.; Olsen, R. A.; Auerbach, D. J.; Kroes, G. J.From Physical Chemistry Chemical Physics (2010), 12(24), 6499-6519. Language: English, Database: CAPLUS,DOI:10.1039/c001956a

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The authors have studied the interaction of H2 on Cu(111) using quasi-classical and quantum dynamics, and a chem.accurate six-dimensional potential energy surface (PES). The PES was computed using the specific reaction parameter(SRP) approach to d. functional theory (DFT), in an implementation adapted to mols. interacting with metal surfaces. Toperform this study the authors have applied the Born-Oppenheimer static surface (BOSS) approxn., i.e., the authors usedboth the Born-Oppenheimer (BO) and the static surface (SS) approxns. The theor. approach accurately describes expts.on dissociative adsorption, the effect of mol. vibrational and rotational motion on dissociative (associative) adsorption(desorption), and rotational excitation upon scattering. More specifically, dynamics calcns. on reactive scattering of H2reproduce reaction probabilities measured in mol. beam expts., effective barrier heights describing the dependence ofreaction on the initial rovibrational state, and data on rotationally inelastic scattering with chem. accuracy (i.e., within 1kcal mol-1 ≈ 4.2 kJ mol-1). These processes are not affected much by surface motion, either because they weremeasured using a low surface temp., Ts, or because the computed observable is independent of Ts. However, toaccount for the dependence of mol. orientation on a reaction the inclusion of surface motion is required. Also vibrationalexcitation is poorly described within the BOSS approxn., suggesting a breakdown of this approxn.~65 Citings

315. Improved Non-Pt Alloys for the Oxygen Reduction Reaction at Fuel Cell Cathodes Predicted from QuantumMechanics

By Yu, Ted H.; Sha, Yao; Merinov, Boris V.; Goddard, William A., IIIFrom Journal of Physical Chemistry C (2010), 114(26), 11527-11533. Language: English, Database: CAPLUS,DOI:10.1021/jp1024735

Based on studies on Pt3Co and Pt3Ni, the authors developedthe hypothesis that improved alloy catalysts for the O redn.reaction (ORR) at fuel cell cathodes should have a surfacelayer that is noble (e.g., Pt, Pd, or Rh) while the 2nd layershould have ∼50% electropos. metal to decrease the crit.barriers for ORR. The authors then used quantum mechanics(QM) to examine 80 binary alloys Y3X, where Y = Pt, Pd, Rh,and X is any of the 3 rows of transition metals (columns 3-11).This study identified that for Pd3X, good segregating alloysinclude X = Re (best), W, Os, Mo, Ru, Ir, Tc, Rh, Co, Ta, Nb,and Ni. Of these the authors selected Pd3W as particularlypromising since it is known exptl. to form an ordered alloy andhas a desirable d-band center. The authors then examd. thecrit. barriers for various steps of the ORR with Pd3W andcompared them to the analogous barriers for Pt, Pt3Co, andPd. Probably Pd3W will exhibit ORR properties improved overpure Pd and close to that of pure Pt. The cost of Pd3W is ∼6times less than pure Pt, suggesting that Pd3W catalysts mightlead to decreases in catalyst cost, while maintainingperformance.

~35 Citings

316. In0.53Ga0.47As(1 0 0) native oxide removal by liquid and gas phase HF/H2O chemistries

By Lie, F. L.; Rachmady, W.; Muscat, A. J.From Microelectronic Engineering (2010), 87(9), 1656-1660. Language: English, Database: CAPLUS,DOI:10.1016/j.mee.2009.12.070

The native oxide removal, surface termination, and stoichiometry of InGaAs(1 0 0) surfaces using liq. and gas phaseHF/H2O etching were studied using XPS. Oxide removal in liq. phase HF stopped at the As layer, producing eitherelemental or H-terminated As. The surface oxidized upon air exposure, forming a 4.8 Å As2O3 layer on an As richInGaAs sub-surface (17% In, 16% Ga, 66% As). A sub atm. gas phase HF/H2O process (100 Torr, 29 °C, 0.5 min)completely removed As2O3 and produced mainly In and Ga fluorides, since As fluoride is volatile at these exptl.conditions. Once enough F accumulated on the surface, the water sticking probability decreased and the etchingreaction proceeded at a much lower rate. The highest oxide removal (4.2 Å residual oxide) was achieved after 5 min ofetching. As2O3 and As2O5 were completely removed and considerably more InF3 and GaF3 were produced. Thesurface contained a group III-fluoride rich overlayer (34% In, 36% Ga) on a slightly As rich bulk (21% In, 21% Ga, and58% As). The As rich InGaAs sub-surface produced with both liq. and the longer gas phase HF treatments is intrinsic toHF-InGaAs chem., although the oxide removal mechanism is likely different.~12 Citings

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317. Phenylhydroxycarbene

By Gerbig, Dennis; Reisenauer, Hans Peter; Wu, Chia-Hua; Ley, David; Allen, Wesley D.; Schreiner, Peter R.From Journal of the American Chemical Society (2010), 132(21), 7273-7275. Language: English, Database: CAPLUS,DOI:10.1021/ja9107885

Phenylhydroxycarbene (Ph-C-OH, 1), the parent of allarylhydroxycarbenes, was generated by high-vacuum flashpyrolysis of phenylglyoxylic acid at 600 °C andspectroscopically characterized (IR, UV-vis) via immediatematrix isolation in solid Ar at 11 K. The identity of 1 wasunequivocally confirmed by the precise agreement between theobsd. IR bands and (unscaled) anharmonic vibrationalfrequencies computed from a CCSD(T)/cc-pVDZ quartic forcefield. The UV-vis spectrum of 1 displays a broad band withmax. absorption at 500 ± 25 nm (2.5 ± 0.1 eV) that extends to∼640 nm (1.9 eV), in full accord with combined CCSD(T)/cc-pVQZ and EOM-CCSD/cc-pVTZ computations that yield a gas-phase vertical (adiabatic) excitation energy of 2.7 (1.9) eV.Unlike singlet phenylchlorocarbene, 1 does not undergophotochem. ring expansion. Instead, 1 exhibits quantum-mech.hydrogen tunneling to benzaldehyde underneath a formidablebarrier of 28.8 kcal mol-1, even at cryogenic temps. Theremarkable hydrogen tunneling mechanism is supported by thetemp. insensitivity of the obsd. half-life (2.5 h) andsubstantiated by a comparable theor. half-life (3.3 h) detd. fromhigh-level barrier penetration integrals computed along theintrinsic reaction path. As expected, deuteration turns off thetunneling mechanism, so d-1 is stable under otherwise identicalconditions.

~40 Citings

318. Catalytic pyrolysis of CHF3 over activated carbon and activated carbon supported potassium catalyst

By Han, Wenfeng; Kennedy, Eric M.; Liu, Huazhang; Li, Ying; Adesina, Adesoji A.; Mackie, John C.; Dlugogorski,Bogdan Z.From Journal of Fluorine Chemistry (2010), 131(6), 698-703. Language: English, Database: CAPLUS,DOI:10.1016/j.jfluchem.2010.03.002

The catalytic activity of activated carbon (AC) and activated carbon supported potassium for the decompn. of CHF3 wasinvestigated at temps. between 873 and 1173 K and at a space velocity of 4300 h-1. It is found that activated carbonsupported potassium shows high and relatively stable activity during the pyrolysis of CHF3 under the conditions studied.Compared with the gas phase reaction, the conversion of CHF3 increases by up to 10 times between 873 and 1123 K,with the major products being C2F4 and C3F6. Selectivities as high as 55% to C2F4 and 35% to C3F6 are achieved underoptimum conditions. The main byproduct HF readily reacts with K2O in the catalyst, converting the catalyst from K2O/ACinto KF/AC. Selectivity to the major products remains relatively const. following this transformation.~11 Citings

319. Effect of Nanoporous Structure on Enhanced Electrochemical Reaction

By Han, Ji-Hyung; Lee, Eonji; Park, Sejin; Chang, Rakwoo; Chung, Taek DongFrom Journal of Physical Chemistry C (2010), 114(21), 9546-9553. Language: English, Database: CAPLUS,DOI:10.1021/jp909382b

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Geometric factors affecting the enhanced electrocatalysis onnanoporous Pt (L2-ePt) were examd. by electrochem. methodsand computer simulations. The exptl. results revealed that theelectrochem. enhancement of O2 and H2O2 does not comeonly from expansion of the active surface area (so-calledroughness factor, fR) of L2-ePt. The presence of extracontribution was verified by the fact that significantenhancement in electrocatalytic reactions remained even afterthe effect of the fR was eliminated from the electrochem. redoxbehavior of O2 and H2O2 on L2-ePt electrodes. Not only thevoltammetric observation but also potentiometric pH responsesof L2-ePt suggested unique nanoporous effects other than thesurface enlargement in regard to heterogeneous electrochem.reactions. L2-ePt showed near Nernstian behavior, fasterresponse time, and less hysteresis even if the real surface areawas smaller than that of flat Pt. Increased residence time nearthe electrode surface due to extremely confined space ofnanoporous structure is proposed as possible origins andexamd. by the Monte Carlo simulations of simple modelelectrodes. The theor. approaches indicated that longresidence time of reactant at electrode surface by confinementeffect of the nanoporous environment well accounted for theexptl. results.

~45 Citings

320. Inelastic collisions and chemical reactions of molecules at ultracold temperatures

By Quemener, Goulven; Balakrishnan, Naduvalath; Dalgarno, AlexanderEdited By:Krems, Roman V.; Stwalley, William C.; Friedrich, BretislavFrom Cold Molecules (2009), 69-124. Language: English, Database: CAPLUS

A review on the recent progress in characterizing mol. processes and chem. reactions at cold and ultracold temps., withparticular emphasis on theor. developments in quantum-dynamics simulations of atom-mol. collision systems over thelast 10 years. Topics discussed include inelastic atom-mol. collisions, chem. reactions at ultracold temps., and inelasticmol.-mol. collisions.~18 Citings

321. Theoretical studies on the electronic structures and spectra of single silicon-doped SWCNTs

By Gao, Peng; Yu, Yingying; Ni, Zhangqin; Teng, QiwenFrom Central European Journal of Chemistry (2010), 8(3), 587-593. Language: English, Database: CAPLUS,DOI:10.2478/s11532-010-0018-y

The equil. geometries and electronic structures of a series of SWCNTs doped with a silicon atom were studied by usingd. function theory (DFT). The most stable doping site of silicon predicted at B3LYP/6-31G(d,p) level was located nearthe boundary of the SWCNTs. The energy gaps of (3,3) C48, (3,3) C60 and (3,3) C72 were resp. decreased by 0.43, 0.25and 0.14 eV after doping. Based on the B3LYP/6-31G(d) optimized geometries, the electronic spectra of the dopedSWCNTs were computed using the INDO/CIS method. The first UV absorption at 973.9 nm of (5,5)-Si(L) (C59Si)compared with that at 937.5 nm of (5,5) (C60) was red-shifted. The 13C NMR spectra and nuclear independent chem.shifts (NICS) of the doped SWCNTs were investigated at B3LYP/6-31G(d) level. The chem. shift at 119.4 of the carbonatom bonded with the silicon atom in (3,3)-Si(L) (C59Si) in comparison with that at 144.1 of the same carbon atom in (3,3)(C60) moved upfield. The tendency of the aromaticity (NICS = -0.1) for (3,3)-Si(H) (C47Si) with respect to that of the anti-aromaticity (NICS = 6.0) for (3,3) (C48) was predicted.~3 Citings

322. Kinetics of OH radical reaction with CF3CHFCH2F (HFC-245eb) between 200 and 400K: G3MP2, G3B3 andtransition state theory calculations

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By Ali, Mohamad Akbar; Rajakumar, B.From Journal of Molecular Structure: THEOCHEM (2010), 949(1-3), 73-81. Language: English, Database: CAPLUS,DOI:10.1016/j.theochem.2010.03.006

The rate coeffs. of hydroxyl radical (OH) reaction with CF3CHFCH2F (HFC-245eb) were computed using G3MP2 andG3B3 theories between 200 and 400 K. Nine different transition states were identified for the title reaction and confirmedby intrinsic reaction coordinate (IRC) calcns. The contributions of all the individual hydrogen atoms in different rotamersfor the title reaction were computed and compared with the results obtained by exptl. methods and structure activityrelations (SAR). The rate coeffs. for the title reaction were computed to be k = (1.57 ± 0.14) × 10-13 exp[-(690 ± 26)/T]cm3 mol.-1 s-1at G3MP2, and k = (0.97 ± 0.13) × 10-13 exp[-(513 ± 39)/T] cm3 mol.-1 s-1 at G3B3 theories. Theor. calcd.rate coeffs. are in good agreement with the exptl. results. The tropospheric lifetime of CF3CHFCH2F because of itsreaction with OH radicals are computed to be 2.52 and 2.14 years at G3MP2 and G3B3 level of theories, resp.~10 Citings

323. Comparison of the Oxygen Reduction Reaction between NaOH and KOH Solutions on a Pt Electrode: TheElectrolyte-Dependent Effect

By Jin, Wei; Du, Hao; Zheng, Shili; Xu, Hongbin; Zhang, YiFrom Journal of Physical Chemistry B (2010), 114(19), 6542-6548. Language: English, Database: CAPLUS,DOI:10.1021/jp102367u

The oxygen redn. reaction (ORR) on a polycryst. Pt surfacewas studied using cyclic voltammetry techniques, and theinfluence of reaction media on the ORR was examd. bycomparing the ORR in NaOH and KOH solns. with concn.ranging from 0.5 to 14 M at 298 K. In NaOH and KOH solns.,the ORR, a quasi-reversible diffusion-controlled reaction, islargely dependent on the electrolyte conditions, and KOHsolns. are superior to NaOH solns. for the ORR process in boththermodn. and kinetic consideration. As the alk. concn.increases, the ORR performance frustrates, and theprotonation of superoxide is suppressed; thus, the ORR shiftsfrom a 2e redn. pathway to a 1e redn. pathway in both solns.

~88 Citings

324. Theoretical study of the competitive decomposition and isomerization of 1-hexyl radical

By Wang, Feng; Cao, Dong-Bo; Liu, Gang; Ren, Jie; Li, Yong-WangFrom Theoretical Chemistry Accounts (2010), 126(1-2), 87-98. Language: English, Database: CAPLUS,DOI:10.1007/s00214-009-0685-y

The ground-state potential energy surface of the 1-hexyl system, including the main decompn. and isomerizationprocesses, was calcd. with the MPW1K, BB1K, MPWB1K, MPW1B95, BMK, M05-2X and CBS-QB3 methods. Thermalrate coeffs. of different reaction channels and branching ratios were then calcd. using the master equation formulation at250-2,500 K. The results clearly point out that the 1,5 H atom transfer reaction of 1-hexyl radical with exothermicityproceeds through the lowest reaction barrier, whereas the decompn. processes are thermodynamically unfavorable withlarge endothermicity. The temp. effect is important on the relative importance of different reactions in the 1-hexyl system.In the low-temp. range of 250-900 K, isomerization reactions, esp. 1,5 H atom transfer reaction of 1-hexyl radical, aredominating and responsible for over 82.17% of all the reactions, due to their smaller reaction barriers than those of thedecompn. reactions. Also, an equil. process involving the isomeric forms of the hexyl radicals appearing at relative lowtemp. was validated theor. However, isomerization and decompn. processes are kinetically competitive andsimultaneously important under normal pyrolysis conditions.~15 Citings

325. Formation of β-Ruthenium-Substituted Enones from Propargyl Alcohols

By Casey, Charles P.; Jiao, Xiangdong; Guzei, Ilia. A.From Organometallics (2010), 29(21), 4829-4836. Language: English, Database: CAPLUS, DOI:10.1021/om100012j

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The reaction of the dienone ruthenium dicarbonyl dimer [2,5-Ph-3,4-Tol(η5-C4CO)]Ru(CO)22 (7) with propargyl alc. at roomtemp. gave a high yield of β-ruthenium-enal (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2(CH≡CHCHO) (8E), which wascharacterized spectroscopically and by x-ray crystallog.Reaction of 7 with pent-2-yn-1-ol led to the kinetic formation ofthe E-isomer (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2[CEt≡CHCHO] (10E-Et), which isomerized toan equil. mixt. of Z- and E-isomers upon heating. The intramol.nature of the 1,2-hydrogen shifts involved in these reactionswas established by the absence of crossover products in thereaction of 7 with a mixt. of PhC≡CCH2OH and PhC≡CCD2OH.A primary deuterium isotope effect (kH/kD ≈ 11) was seen onthe product-forming step in the reaction of 7 withPhC≡CCHDOH. The reaction of PhC≡CCH3 with 7 producedthe alkyne complex [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η2-PhC≡CCH3) (14). The key step in the mechanism of thereaction of 7 with propargyl alcs. is proposed to be an in-plane1,2-hydrogen migration to an electrophilic carbon of acomplexed alkyne.

~4 Citings

326. The effect of platinum in a Nafion membrane on the durability of the membrane under fuel cell conditions

By Zhao, D.; Yi, B. L.; Zhang, H. M.; Liu, MeilinFrom Journal of Power Sources (2010), 195(15), 4606-4612. Language: English, Database: CAPLUS,DOI:10.1016/j.jpowsour.2010.02.043

The effect of platinum on free radical generation and membrane degrdn. in proton exchange membrane (PEM) fuel cellsis investigated using three typical cell configurations. Examns. of the fluoride emission rates (FERs) under differenttesting conditions indicate that platinum deposited in the membrane plays an important role as a catalytic center for theformation of H2O2 and HO· free radicals, leading to PEM degrdn. The chem. durability of the membranes is tested inaccelerated Fenton tests. It confirms the formation of free radicals in the presence of platinum in the decompn. of H2O2by colorimetric method with DMSO as the trapping agent. In addn., structural and morphol. changes of the membranesare characterized using FT-IR spectroscopy and SEM.~34 Citings

327. Exploring matrix isolated carbenes and bis-carbenes with electronic spectroscopy as a guide

By Sheridan, Robert S.From Journal of Physical Organic Chemistry (2010), 23(4), 326-332. Language: English, Database: CAPLUS,DOI:10.1002/poc.1649

A review. Singlet carbenes exhibit very informative electronic spectra, which vary as a sensitive function of substituentsand geometries. In particular, the lowest energy σ-p type excitations for singlet carbenes range broadly from the shortwavelength UV to the near IR. Substituent effects on the energy of this key electronic transition can be rationalized byvery simple orbital mixing arguments, and parallel similar influences on singlet-triplet energies. Besides providingvaluable electronic information on singlet carbenes and bis-carbenes which were studied by low temp. matrix isolationmethods, UV/visible spectroscopy has often guided studies of conformation-dependent photochem. of these species.Insights learned from exptl. and calcd. UV/visible spectra of a broad range of matrix isolated singlet carbenes and bis-carbenes are described. Copyright © 2010 John Wiley and Sons, Ltd.~6 Citings

328. Electrochemical reactions at the electrode/solution interface: Theory and applications to water electrolysisand oxygen reduction

By Fang, Ya Hui; Liu, Zhi PanFrom Science China: Chemistry (2010), 53(3), 543-552. Language: English, Database: CAPLUS,DOI:10.1007/s11426-010-0047-6

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A review. Theor. simulations on complex electrochem. processes have been developed on the basis of theunderstanding in electrochem., which has benefited from quantum mechanics calcns. This article reviews the recentprogress on the theory and applications in electrocatalysis. Two representative reactions, namely water electrolysis andoxygen redn., are selected to illustrate how the theor. methods are applied to electrocatalytic reactions. The microscopicnature of these electrochem. reactions under the applied potentials is described and the understanding of the reactions issummarized. The thermodn. and kinetics of the electrochem. reactions affected by the interplay of the electrochem.potential, the bonding strength and the local surface structure are addressed at the at. level.~11 Citings

329. Symmetry and Fourier analysis of the ab initio-determined torsional variation of structural and Hessian-related quantities for application to vibration-torsion-rotation interactions in CH3OH

By Xu, Li-Hong; Hougen, J. T.; Fisher, J. M.; Lees, R. M.From Journal of Molecular Spectroscopy (2010), 260(2), 88-104. Language: English, Database: CAPLUS,DOI:10.1016/j.jms.2010.01.001

The aim of the present paper is to investigate the use of quantum chem. calcns. to obtain the torsional dependence ofvarious structural and vibrational-force-field-related quantities that could help in estg. the vibration-torsion-rotationinteraction terms needed to treat perturbations obsd. in the spectra of methanol-like mols. We begin by using theGaussian suite of programs to det. the steepest-descent path from a stationary point at the top of the internal rotationpotential barrier in methanol to the equil. structure at the bottom of the barrier. This procedure requires detg. the gradient V of the potential (as calcd. in mass-weighted Cartesian coordinates) along the internal rotation path. In addn., we usethe Gaussian suite to calc. the Hessian V along this path and to generate from these second derivs. the 3N - 7 small-amplitude vibrational frequencies and the 3N Cartesian vibrational displacements for each of these vibrations. We thensymmetrize the internal coordinates used in presenting the structures, gradients, Hessians and vibrational displacementsalong the path to take into account the periodic variation of the behavior of the three Me hydrogen atoms Hi as they passin turn through the Cs-plane of the HOC frame. The symmetrized linear combinations of the CHi stretches, of the OCHibends, and of the HOCHi dihedral angles of the Me group depend on the internal rotation angle γ and they are detd. byconsidering coordinate transformations from the G6 permutation-inversion group appropriate for internally rotatingmethanol. This symmetrization procedure permits us to explore the feasibility of expressing the structures, gradients,Hessians, and vibrational displacement vectors along the internal rotation path as short Fourier series in γ, which is oneof the main goals of this paper. In summary, we find that the symmetrized structures, gradients, and Hessians, as wellas nine of the 11 projected vibrational frequencies and the vibrational displacement vectors for the three vibrationsoccurring primarily in the HOC frame can be expressed by short Fourier series expansions to their precision in theGaussian output, and that these series involve only sin 3nγ or only cos 3nγ terms, as required by G6 symmetryconsiderations. A preliminary discussion is given of why short Fourier expansions fail for the projected frequencies of thetwo Me asym. stretches, and for the vibrational displacement vectors of the Me group vibrational modes. Looking moreclosely at the symmetrized and projected 3N × 3N Hessian, we find algebraically that only elements in the (3N - 7) × (3N- 7) small-amplitude-vibrational block of the Hessian are useful for spectroscopic problems. Non-zero elements in therest of the 3N × 3N symmetrized and projected Hessian cannot be converted into quantities needed for perturbationstudies.~11 Citings

330. Quantum effects in biological systems

By Sarovar, MohanFrom Proceedings of SPIE (2010), 7561(Optical Biopsy VII), 75610D/1-75610D/9. Language: English, Database:CAPLUS, DOI:10.1117/12.841015

A review. Identification of non-trivial quantum mech. effects in the functioning of biol. systems has been a long-standingand elusive goal in the fields of physics, chem. and biol. Recent progress in control and measurement technologies, esp.in the optical spectroscopy domain, have made possible the identification of such effects. In particular, electroniccoherence was recently shown to survive for relatively long times in photosynthetic light harvesting complexes despitethe effects of noisy biomol. environments. Motivated by this exptl. discovery, several recent studies have combinedtechniques from quantum information, quantum dynamical theory and chem. physics to characterize the extent andnature of quantum dynamics in light harvesting structures. I will review these results and summarize our understandingof the subtle quantum effects in photosynthetic complexes. Then I will outline the remarkable properties of lightharvesting complexes that allow quantum effects to be significant at dynamically relevant timescales, despite thedecohering biomol. environment. Finally, I will conclude by discussing the implications of quantum effects in lightharvesting complexes, and in biol. systems in general.~0 Citings

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331. Synthesis, structure and thermal behavior of oxalato-bridged Rb+ and H3O+ extended frameworks withdifferent dimensionalities

By Kherfi, Hamza; Hamadene, Malika; Guehria-Laidoudi, Achoura; Dahaoui, Slimane; Lecomte, ClaudeFrom Materials (2010), 3, 1281-1301. Language: English, Database: CAPLUS, DOI:10.3390/ma3021281

Correlative studies of three oxalato-bridged polymers, obtained under hydrothermal conditions for the two isostructuralcompds. Rb(HC2O4)(H2C2O4)(H2O)2∞ 1 (I) and H3O(HC2O4)(H2C2O4).2H2O∞ 1, (II) and by conventional syntheticmethod for Rb(HC2O4)∞ 3 (III) allowed the identification of H-bond patterns and structural dimensionality. Ferroicdomain structures are confirmed by elec. measurements performed on III. Although II resembles one oxalic acidsesquihydrate, its structure detn. doesn't display any kind of disorder and leads to recognition of a supramol. networkidentical to hybrid s-block series, where moreover, unusual H3O+ and NH4 + similarity is brought out. Thermal behaviorsshow that 1D frameworks with extended H-bonds, whether with or without a metal center, have the same stability.Inversely, despite the dimensionalities, the same metallic intermediate and final compds. are obtained for the two Rb+

ferroic materials.~3 Citings

332. Gradient-based multiconfiguration Shepard interpolation for generating potential energy surfaces forpolyatomic reactions

By Tishchenko, Oksana; Truhlar, Donald G.From Journal of Chemical Physics (2010), 132(8), 084109/1-084109/6. Language: English, Database: CAPLUS,DOI:10.1063/1.3310296

This paper describes and illustrates a way to construct multidimensional representations of reactive potential energysurfaces (PESs) by a multiconfiguration Shepard interpolation (MCSI) method based only on gradient information, i.e.,without using any Hessian information from electronic structure calcns. MCSI, which is called multiconfiguration mol.mechanics (MCMM) in previous articles, is a semiautomated method designed for constructing full-dimensional PESs forsubsequent dynamics calcns. (classical trajectories, full quantum dynamics, or variational transition state theory withmultidimensional tunneling). The MCSI method is based on Shepard interpolation of Taylor series expansions of thecoupling term of a 2 × 2 electronically diabatic Hamiltonian matrix with the diagonal elements representing nonreactiveanal. PESs for reactants and products. In contrast to the previously developed method, these expansions are truncatedin the present version at the first order, and, therefore, no input of electronic structure Hessians is required. Theaccuracy of the interpolated energies is evaluated for two test reactions, namely, the reaction OH + H2 → H2O + H andthe hydrogen atom abstraction from a model of α-tocopherol by Me radical. The latter reaction involves 38 atoms and a108-dimensional PES. The mean unsigned errors averaged over a wide range of representative nuclear configurations(corresponding to an energy range of 19.5 kcal/mol in the former case and 32 kcal/mol in the latter) are found to be within1 kcal/mol for both reactions, based on 13 gradients in one case and 11 in the other. The gradient-based MCMM methodcan be applied for efficient representations of multidimensional PESs in cases where anal. electronic structure Hessiansare too expensive or unavailable, and it provides new opportunities to employ high-level electronic structure calcns. fordynamics at an affordable cost. (c) 2010 American Institute of Physics.~10 Citings

333. Electrochemical Hydrogen Oxidation on Pt(110): A Combined Direct Molecular Dynamics/DensityFunctional Theory Study

By Santana, Juan A.; Mateo, Juan J.; Ishikawa, YasuyukiFrom Journal of Physical Chemistry C (2010), 114(11), 4995-5002. Language: English, Database: CAPLUS,DOI:10.1021/jp909834q

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A 1st-principles direct mol. dynamics and d. functional theorystudy of the electrooxidn. of mol. hydrogen at the Pt(110)/H2Ointerface was conducted to gain an at.-level understanding ofthe electrocatalytic processes and of adsorbed reactionintermediates. The H2 electrooxidn. follows the Tafel-Volmermechanism - a homolytic H-H bond cleavage and formation ofadsorbed terminal H atoms atop the topmost Pt, followed byoxidn. of the adsorbed reaction intermediates. Potential-dependent activation energies computed for the H redoxreactions were employed to predict the Tafel plot for Helectrooxidn. The theor. predicted Tafel plot is in very goodagreement with expt. in support of the Tafel-Volmer mechanismfor the Pt(110) surface.

~28 Citings

334. Canonical Variational Transition-State Theory Study of the CF3CHFCH2F + OH Reaction

By Gonzalez-Lafont, Angels; Lluch, Jose M.; Varela-Alvarez, Adrian; Sordo, Jose A.From Journal of Physical Chemistry A (2010), 114(8), 2768-2777. Language: English, Database: CAPLUS,DOI:10.1021/jp909675u

Variational transition-state theory rate consts. withmultidimensional tunneling contributions using the smallcurvature method have been calcd. for the CF3CHFCH2F(HFC-245eb) + OH reaction over a temp. range from 200 to800 K. The mPW1B95-41.0 hybrid functional, parametrized byAlbu and Swaminathan to generate theor. rate consts. nearlyidentical to the exptl. values for the CH3F + OH reaction, hasbeen used in conjunction with the 6-31+G(d,p) basis set toexplore the potential energy surface of the title reaction. Thefunctional provides results within the limits of chem. accuracy,supporting the conclusions about transferability of a previousstudy on the CF3CH2CH3 + OH reaction. Fourteen differentreaction channels have been explored, all of them withsignificant contributions to the global rate consts.

~2 Citings

335. Unearthing the unconventional

By Carpenter, Barry K.From Nature Chemistry (2010), 2(2), 80-82. Language: English, Database: CAPLUS, DOI:10.1038/nchem.531

A review. Quantum tunnelling can at times be the cause of kinetic isotope effects, and in these cases conventionalwisdom has been that mols. with isotopes of larger mass will react more slowly. New calcns., however, predict thatsometimes the reverse should be true.~3 Citings

336. Application of density functional theory to CO tolerance in fuel cells: a brief review

By Stolbov, Sergey; Ortigoza, Marisol Alcantara; Rahman, Talat S.From Journal of Physics: Condensed Matter (2009), 21(47), 474226/1-474226/9. Language: English, Database:CAPLUS, DOI:10.1088/0953-8984/21/47/474226

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A review. The large-scale application of fuel cells in a H economy is possible only with a decrease in the cost andimprovement of the electrocatalytic properties of the electrodes. This can be achieved through rational design of newmaterials, which requires an understanding of the microscopic mechanisms underlying electrocatalysis. The authorsreview briefly some applications of d. functional theory (DFT) to this problem, with particular ref. to the obsd. high COtolerance of Pt-Ru-based anodes. These DFT-based calcns. trace the changes in the surface electronic structure andthe energy landscape induced by formation of Pt islets on facets of Ru nanoparticles which lead to the preferred diffusionof CO from Pt sites to Ru, where it exhibits a high rate of reaction with hydroxyls, which are generally present. Theauthors also consider the energetics of stabilization of the Pt islets on the Ru nanoparticles.~1 Citing

337. Inelastic collisions and chemical reactions of molecules at ultracold temperatures

By Quemener, Goulven; Balakrishnan, Naduvalath; Dalgarno, AlexanderFrom arXiv.org, e-Print Archive, Physics (2010), 1-28, arXiv:1001.1713v1 [physics.chem-ph]. Language: English,Database: CAPLUS

A review. This paper summarizes the recent theor. works on inelastic collisions and chem. reactions at cold andultracold temps. involving neutral or ionic systems of atoms and mols. Tables of zero-temp. rate consts. of various mols.are provided.~0 Citings

338. The EVB as a quantitative tool for formulating simulations and analyzing biological and chemical reactions

By Kamerlin, Shina C. L.; Warshel, AriehFrom Faraday Discussions (2010), 145, 71-106. Language: English, Database: CAPLUS, DOI:10.1039/B907354J

Recent years have seen dramatic improvements in computer power, allowing ever more challenging problems to beapproached. In light of this, it is imperative to have a quant. model for examg. chem. reactivity, both in the condensedphase and in soln., as well as to accurately quantify phys. org. chem. (particularly as exptl. approaches can often beinconclusive). Similarly, computational approaches allow for great progress in studying enzyme catalysis, as they allowfor the sepn. of the relevant energy contributions to catalysis. Due to the complexity of the problems that needaddressing, there is a need for an approach that can combine reliability with an ability to capture complex systems inorder to resolve long-standing controversies in a unique way. Herein, we will demonstrate that the empirical valencebond (EVB) approach provides a powerful way to connect the classical concepts of phys. org. chem. to the actualenergies of enzymic reactions by means of computation. Addnl., we will discuss the proliferation of this approach, aswell as attempts to capture its basic chem. and repackage it under different names. We believe that the EVB approach isthe most powerful tool that is currently available for studies of chem. processes in the condensed phase in general andenzymes in particular, particularly when trying to explore the different proposals about the origin of the catalytic power ofenzymes.~63 Citings

339. Rate coefficients for the reaction of OH with CF3CH2CH3 (HFC-263fb) between 200 and 400 K: Ab initio,DFT, and transition state theory calculations

By Ali, Mohamad Akbar; Rajakumar, B.From Journal of Computational Chemistry (2010), 31(3), 500-509. Language: English, Database: CAPLUS,DOI:10.1002/jcc.21336

Rate coeffs. for the reaction of the hydroxyl radical with CF3CH2CH3 (HFC-263fb) were computed using ab initiomethods, viz. MP2, G3MP2, and G3B3 theories between 200 and 400 K Structures of the reactants in the ground state(GS) and transition state (TS) were optimized at MP2(FULL)/6-31G*, MP2(FULL)/6-311+ +G**, and B3LYP/6-31G* levelof theories. Seven TSs were identified for the title reaction in the above theories. However, five out of seven TSs aresym. distinct. The kinetic parameters due to these five different TSs are presented in this manuscript. Intrinsic reactioncoordinate (IRC) calcns. were performed to confirm the existence of transition states. The contributions of all theindividual hydrogens in the substrate for the reaction are estd. and compared with the results obtained using StructureAdditivity Relationships. The rate coeffs. for the title reaction were computed to be k = (7.96 ± 0.93) × 10-13 exp [-(2245± 30)/T] cm3 mol.-1 s-1 at MP2, k = (9.50 ± 0.93) × 10-13 exp [-(1162 ± 30)/T] cm3 mol.-1 s-1 at G3MP2, and k = (7.01 ±0.88) × 10-13 exp [-(753 ± 35)/T] cm3 mol.-1 s-1at G3B3 theories. The theor. computed rate coeffs. are in excellentagreement with the exptl. detd. ones. The OH-driven atm. lifetimes of this compd. are computed to be 132, 2.2, and 0.7years at, MP2, G3MP2, and G3B3 level of theories, resp. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010.

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~10 Citings

340. Muonium as a model for interstitial hydrogen in the semiconducting and semimetallic elements

By Cox, S. F. J.From Reports on Progress in Physics (2009), 72(11), 116501/1-116501/130. Language: English, Database: CAPLUS,DOI:10.1088/0034-4885/72/11/116501

A review. Although the interstitial hydrogen atom would seem to be one of the simplest defect centers in any lattice, itssolid state chem. is in fact unknown in many materials, not least amongst the elements. In semiconductors, therealization that hydrogen can profoundly influence electronic properties even as a trace impurity has prompted its studyby all available means-but still only in the functionally important or potentially important materials-for the elements, Si, Geand diamond. Even here, it was not studies of hydrogen itself but of its pseudo-isotope, muonium, that first provided themuch needed microscopic pictures of crystallog. site and local electronic structure-now comprehensively confirmed by abinitio computation and such data as exists for monat., interstitial hydrogen centers in Si. Muonium can be formed in avariety of neutral paramagnetic states when pos. muons are implanted into non-metals. The simple trapped atom iscommonly only metastable. It coexists with or reacts to give defect centers with the unpaired electron in somewhat moreextended orbitals. Indications of complete delocalization into effective mass states are discussed for B, α-Sn, Bi andeven Ge, but otherwise all the muonium centers seen in the elemental semiconductors are deep and relatively compact.These are revealed, distinguished and characterized by µSR spectroscopy-muon spin rotation and resonance informingon sites and spin-d. distributions, muon spin relaxation on motional dynamics and charge-state transitions. This Reportdocuments the progress of µSR studies for all the semiconductors and semimetals of the p-block elements, Groups III-VIof the Periodic Table. The striking spectra and originally unanticipated results for Group IV are for the most part wellknown but deserve summarizing and updating; the sheer diversity of muonium states found is still remarkable, esp. incarbon allotropes. The interplay of crystallog. site and charge state in Si and Ge at high temps., or under illumination,reflects the capture and loss of charge carriers that should model the elec. activity of monat. hydrogen but still challengestheor. descriptions. Spin-flip scattering of conduction electrons by the paramagnetic centers is revealed in heavily dopedn-type material, as well as some modification of the local electronic structures. The corresponding spectroscopy for thesolid elements of Groups III, V and VI is rather less well known and is reviewed here for the first time; a good deal ofpreviously unpublished data is also included. Theor. expectations and computational modeling are sparse, here. Recentresults for B suggest a relatively shallow center with mol. character; P and As show deeper quasi-at. states, but still withsubstantial overlap of spin d. onto surrounding host atoms. Particular attention is paid to the chalcogens. Muoniumcenters in Te show charge-state transitions already around room temp.; the identification of those in S and Se has beencomplicated by unusual spin dynamics of a different character, here attributed to spin-orbit coupling and interstitialreorientation. In the metals and semimetals, muonium is not formed as a paramagnetic center. Here the implantedmuons mimic interstitial protons and interest shifts to a variety of other topics, including aspects of charge screening (α-Sn, Sb, Bi), site preference and quantum mobility (Al, β-Sn, Pb). The post-transition metals receive only a brief mention,by way of contrast with the nonmetals. Systematic studies of local susceptibility via measurements of muon Knight shiftsextends in favorable cases to revealing the elusive high-field Condon domains (Al, Sn, Pb, Bi). Some new information isavailable on the superconducting phases. Appendices include a derivation of the spin Hamiltonian for paramagneticmuonium centers or mol. radicals having varying admixts. of orbital angular momentum, including the extreme case oforbital degeneracy, and examine the consequences of significant spin-orbit coupling for µSR spectroscopy and muonspin relaxation. This is the framework for the tentative assignments made here for the muonium defect centers formed insulfur and selenium, namely diat. species resembling the chalcogen monohydrides. Equally, it provides guidelines foreventual solid-state detection of OMu-the elusive muoniated hydroxyl radical.~4 Citings

341. Structure and vibrational spectra of H+(HF)n (n=2-9) clusters: An ab initio study

By Sophy, K. B.; Kuo, Jer-LaiFrom Journal of Chemical Physics (2009), 131(22), 224307/1-224307/8. Language: English, Database: CAPLUS,DOI:10.1063/1.3268502

The morphol. development of the hydrogen bond network in the protonated hydrogen fluoride clusters, H+(HF)n (n=2-9),is investigated in detail by ab initio methods. We find a dominance of the linear morphol., which is energetically wellsepd. from the other min. energy morphologies of the clusters. The geometry for these clusters shows a pattern due tothe cooperativity effect prevalent in the hydrogen bonds, as a result of the difference in electronegativities of hydrogenand fluorine atom in the HF mol. The variations in the covalent HF and hydrogen bond distances in the clusters are inturn reflected in the vibrational spectra. Distinct HF stretching modes for the linear and ring with tail structures wereidentified. We have discussed the signature peaks for the two possible ion-core morphologies present in the clusters.The highly corrosive nature of HF makes it difficult to study using expts. We, thus, believe that our structure andvibrational spectra calcns. would be useful in understanding the key features in these systems. (c) 2009 AmericanInstitute of Physics.

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~1 Citing

342. Selenium: A Nonprecious Metal Cathode Catalyst for Oxygen Reduction

By Kurak, Kiera A.; Anderson, Alfred B.From Journal of the Electrochemical Society (2010), 157(1), B173-B179. Language: English, Database: CAPLUS,DOI:10.1149/1.3258662

From voltammetric studies, trigonal phase Se (t-Se) nanotubes, which are bundles of hexagonally packed helical chainsof Se atoms, were shown by others to be stable in acid and have a double-layer region extending from -0.2 (std.hydrogen electrode) to 0.75 V. This is broader than the ∼0.4 to ∼0.7 V double layer for Pt and presents a potential rangethat might allow oxygen redn. activity. This paper presents theor. predictions of oxygen redn. mechanisms on t-Se.Adsorption energies from Gaussian cluster hybrid d. functional and Vienna ab initio simulation program d. functionalcalcns. are used in the linear Gibbs energy relation to predict the reversible potentials for the 1-electron redn. stepsduring the 4-electron redn. of O2 to H2O, which ideally occurs at 1.229 V. Adsorption energies for redn. intermediatesare calcd. using single-chain models. Calcd. reversible potentials for the 4 redn. steps lead to the prediction that the stepwith the highest overpotential is the reductive elimination of OH(ads) to form H2O and occurs at ∼0.8 V. The overallbehavior predicted for t-Se is similar to that of Pt, and probably t-Se is worthy of trials as a potential oxygen cathodeelectrocatalyst.~9 Citings

343. Oxygen reduction on Pt(111) cathode of fuel cells

By Son, Do Ngoc; Nakanishi, Hiroshi; David, Melanie Yadao; Kasai, HideakiFrom Journal of the Physical Society of Japan (2009), 78(11), 114601/1-114601/10. Language: English, Database:CAPLUS, DOI:10.1143/JPSJ.78.114601

We investigate the oxygen redn. reaction on Pt(111) surface in the presence of hydronium ion. The oxygen redn.reaction is proposed to proceed by two adsorption pathways. One is by the dissociative adsorption that forms adsorbedoxygen atoms Oad on the surface ("ad" means in the adsorbed state on the surface), followed by a reductive transition inthe presence of hydronium ion that converts Oad into the adsorbed hydroxyl (OH)ad. In this pathway, the first electron istransferred after dissocn. of O2. The other is through the mol. adsorption on the surface, followed by a reductiveadsorption in the presence of hydronium ion in which first electron is transferred after the O2 adsorption to form theadsorbed end-on intermediate OadOH before continuing the reaction with another hydronium ion to form the adsorbedhydroxyl (OH)ad. In both cases, the reaction is completed by the reductive desorption of (OH)ad in the presence ofhydronium ion to form water mols. In this work, we focus our study on the reductive transition in the first pathway and thereductive adsorption in the second pathway. Through adiabatic potential energy for the proton motion from hydroniumion to the Pt surface, the isolated state of H3O+ from the Pt surface is detd., which is then used as the initial state forstudying the potential energy of hydronium motion. In addn., the optimized structures for the reaction intermediates arealso obtained. Comparing the results of non-hydrated and hydrated H3O+, we find that increasing the no. of water mols.stabilizes the (OH)ad in the reductive transition and the OadOH in the reductive adsorption. Moreover, water mols.generate the activation barrier for the OadOH intermediate formation in the reductive adsorption.~4 Citings

344. Membrane degradation mechanisms and accelerated durability testing of proton exchange membrane fuelcells

By Fenton, James M.; Rodgers, Marianne P.; Slattery, Darlene K.; Huang, Xinyu; Mittal, Vishal O.; Bonville, LeonardJ.; Kunz, H. RussellFrom ECS Transactions (2009), 25(1, Proton Exchange Membrane Fuel Cells 9), 233-247. Language: English,Database: CAPLUS, DOI:10.1149/1.3210575

Mol. H2 and O2 reacting on the surface of Pt catalyst to form the membrane degrading species is the dominatingmembrane degrdn. mechanism in PEMFCs; not the formation of active oxygen species from H2O2 decompn. or the directformation of active oxygen species in the oxygen redn. reaction. The source of H2 or O2 is from the reactant crossoverthrough the membrane. The reaction mechanism is chem. in nature and depends upon the catalyst surface propertiesand the relative concns. of H2 and O2 at the catalyst. The membrane degrdn. rate also depends on the residence time ofthe species in the membrane and the vol. of the membrane. The sulfonic acid groups in the Nafion side chain are key tothe mechanism by which the radical species attack the polymer.

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~12 Citings

345. Kinetic Monte Carlo Simulations of Solid Oxide Fuel Cell

By Pornprasertsuk, Rojana; Holme, Tim; Prinz, Friedrich B.From Journal of the Electrochemical Society (2009), 156(12), B1406-B1416. Language: English, Database: CAPLUS,DOI:10.1149/1.3232209

The kinetic Monte Carlo technique was employed to simulate an entire solid oxide fuel cell during operation to gaininsight into the electrode kinetics and rate-limiting steps in the intermediate temp. range. By combining the quantumsimulation studies of oxide ion migration in the fuel cell electrolyte with the exptl. studies of the cathode and anodereaction rates, a complete solid oxide fuel cell can be modeled. To study the effect of triple phase boundaries and thesize of the catalyst, simulations were performed for different sizes of Pt clusters on the electrolyte surface. The resultsconfirm that the charge-transfer reaction rates depend on the catalyst size. The fuel cell with smaller catalyst particlesproduces higher power d. as expected. The reaction rates of each process were recorded as a function of time. Theoverpotentials were subsequently detd. as a function of catalyst size. The results show that oxygen adsorption is theslowest step on the cathode, while water formation is the slowest step on the anode. The methodol. can be used tooptimize the catalyst size on both electrodes to reduce the activation loss in intermediate-temp. solid oxide fuel cells.~7 Citings

346. Electronic structure models of oxygen adsorption at the solvated, electrified Pt(111) interface

By Yeh, Kuan-Yu; Wasileski, Sally A.; Janik, Michael J.From Physical Chemistry Chemical Physics (2009), 11(43), 10108-10117. Language: English, Database: CAPLUS,DOI:10.1039/b909233a

The adsorption of mol. oxygen is the 1st step in the oxygen redn. reaction. Influences of interfacial water structure andelectrode potential on oxygen adsorption to the Pt(111) surface were evaluated using d. functional theory. Twoapproaches were used to model the electrification of the interface, an applied homogeneous elec. field and the double-ref. method of Filhol, Taylor, and Neurock. The free energy change for mol. oxygen replacement of water at the surfaceshows qual. different trends between the two models. The inclusion of solvation effects and direct control of theelectrode potential offered by the double-ref. method indicated that O2 replacement of water is favorable at all potentialsstudied, and O2 binding becomes more favorable with increasing potential. This trend is contrary to that obsd. using anexternal elec. field model to represent the electrochem. double layer, and arises due to the compounded effect ofpotential on water-surface, oxygen-surface, and water-mol. oxygen interactions. Oxygen replacement of adsorbed waterdoes not limit the overall oxygen redn. reaction rate at a proton-exchange membrane fuel cell cathode. The impacts ofaspects of model construction (no. of water layers, water d.) and variation of electrode potential on the O2-Pt(111)interaction are described.~22 Citings

347. Efficient Approach to Reactive Molecular Dynamics with Accurate Forces

By Higashi, Masahiro; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2009), 5(11), 2925-2929. Language: English, Database: CAPLUS,DOI:10.1021/ct900301d

D. functional theory is a powerful and efficient method for calcg. potential energy surfaces for chem. reactions, but itsapplication to complex systems, such as reactions in enzymes, is often prohibitively expensive, even when high-leveltheory is applied only to a primary subsystem, such as an active site, and when the remaining system is treated by mol.mechanics. Here we show how the combination of multiconfiguration mol. mechanics with charge response kernels canspeed up such calcns. by three or more orders of magnitude. The resulting method, called electrostatically embeddedmulticonfiguration mol. mechanics, is illustrated by calcg. the free energy of activation profile for the dehalogenation of1,2-dichloroethane by haloalkane dehalogenase. This shows how hybrid d. functionals or other high-level electronicstructure methods can now be used efficiently in simulations that require extensive sampling, such as for calcg. freeenergy profiles along a high-barrier reaction coordinate.~15 Citings

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348. P-doped diamond grown on (110)-textured microcrystalline diamond. Growth, characterization and devices

By Haenen, Ken; Lazea, Andrada; Barjon, Julien; D'Haen, Jan; Habka, Nada; Teraji, Tokuyuki; Koizumi, Satoshi;Mortet, VincentFrom Journal of Physics: Condensed Matter (2009), 21(36), 364204/1-364204/10. Language: English, Database:CAPLUS, DOI:10.1088/0953-8984/21/36/364204

The formation and properties of (110)-textured P-doped microcryst. CVD diamond were studied. Based on severalmicroscopy techniques, with a special emphasis on electron backscattered diffraction, a detailed detn. of the grainorientations with respect to the ext. [110] axis is given. The different orientations present in the film, in combination withlow phosphine concns. in the gas phase, lead to a variation in P incorporation that can vary over 3 orders of magnitude,as detd. with cathodoluminescence mapping. The role of the surface morphol. in the observation of these largeincorporation differences is explained. Hall measurements confirm that the films are n-type conductive with a thermalactivation energy of 0.56 eV. Based on B-doped substrates, pn junctions were created, showing a rectification ratio ofnearly 104 at ±25 V.~4 Citings

349. On the Impact of Steric and Electronic Properties of Ligands on Gold(I)-Catalyzed Cycloaddition Reactions

By Benitez, Diego; Tkatchouk, Ekaterina; Gonzalez, Ana Z.; Goddard, William A., III; Toste, F. DeanFrom Organic Letters (2009), 11(21), 4798-4801. Language: English, Database: CAPLUS, DOI:10.1021/ol9018002

It is shown that [4 + 3] and [4 + 2] cycloaddn. pathways areaccessible in the Au(I) catalysis of allene-dienes. Seven-membered ring gold-stabilized carbenes, originating from the [4+ 3] cycloaddn. process, are unstable and can rearrange via a1,2-H or a 1,2-alkyl shift to yield six- and seven-memberedproducts. Both steric and electronic properties of the AuL+

catalyst affect the electronic structure of the intermediate gold-stabilized carbene and its subsequent reactivity.

~119 Citings

350. Activation Energies of the Electrooxidation of Formic Acid on Pt(100)

By Angelucci, Camilo A.; Varela, Hamilton; Herrero, Enrique; Feliu, Juan M.From Journal of Physical Chemistry C (2009), 113(43), 18835-18841. Language: English, Database: CAPLUS,DOI:10.1021/jp907723k

The electrooxidn. of small org. mols. on Pt surfaces usually involves different structure-dependent steps that includeadsorption and desorption of various species and multiple reaction pathways. Because temp. plays a decisive role oneach individual step, understanding its global influence on the reaction mechanism is often a difficult task, esp. when thesystem is studied under far from equil. conditions in the presence of kinetic instabilities. Aiming at contributing to unravelthis problem, herein, the authors report an exptl. study of the role played by temp. on the electrooxidn. of formic acid on aPt(100) electrode. The system was studied under both close and far from equil. conditions, and apparent activationenergies were estd. using different strategies. Overall, comparable activation energies were estd. under oscillatory andquasi-stationary conditions, at high potentials. At low potentials, the poisoning process assocd. with the formic aciddehydration step presented a negligible dependence with temp. and, therefore, zero activation energy. From the exptl.findings, probably formic acid dehydration is the main, but maybe not the unique, step that differentiates the temp.dependence of the oscillatory electrooxidn. of formic acid on Pt(100) with that on polycryst. Pt.~29 Citings

351. Dissecting Competitive Mechanisms: Thionation vs. Cycloaddition in the Reaction of Thioisomunchnoneswith Isothiocyanates under Microwave Irradiation

By Cantillo, David; Avalos, Martin; Babiano, Reyes; Cintas, Pedro; Jimenez, Jose L.; Light, Mark E.; Palacios, Juan C.From Journal of Organic Chemistry (2009), 74(20), 7644-7650. Language: English, Database: CAPLUS,DOI:10.1021/jo900960a

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This paper documents in detail the reaction of 1,3-thiazolium-4-olates (thioisomunchnones) with aryl isothiocyanates. Havingdemonstrated with a chiral model that thionation occurs underthese conditions to provide 1,3-thiazolium-4-thiolates and thatthis process is actually a stepwise domino reaction, we extendthis study to monocyclic thioisomunchnones. Herein,competition between thionation and 1,3-dipolar cycloaddn.takes place. The process is synthetically disappointing at roomtemp. requiring prolonged reaction times for completion. Theprotocol has been subsequently investigated by using bothmicrowave dielec. heating and conventional thermal heating (oilbath) in DMF at 100 °C with an accurate internal reaction temp.measurement. Although a slight acceleration was obsd. forreactions conducted under microwave irradn., for most casesthe obsd. yields and chemoselectivities were quite similar.Thus one can conclude that, within exptl. errors, the reactivity isnot related to nonthermal effects in agreement with recentreassessments on this subject, particularly by Kappe andassocs. The whole reaction system, which includes numerousheavy atoms, can be computationally modeled with a hybridONIOM[B3LYP/6-31G(d):PM3] level. This reproduces wellexptl. results and suggests a sequential mechanism. To furthercorroborate the nonconcertedness, the potential energy surface(PES) has been constructed for simplified models, locating thecorresponding stationary points. In doing so, we introduce forthe first time a useful and convenient math. protocol to locatethe stationary points along a reaction path. The protocol isquite simple and should convince many org. chemists thatcertain daunting theor. treatments can be made easy.

~9 Citings

352. Exploring 1,2-Hydrogen Shift in Silicon Nanoparticles: Reaction Kinetics from Quantum ChemicalCalculations and Derivation of Transition State Group Additivity Database

By Adamczyk, Andrew J.; Reyniers, Marie-Francoise; Marin, Guy B.; Broadbelt, Linda J.From Journal of Physical Chemistry A (2009), 113(41), 10933-10946. Language: English, Database: CAPLUS,DOI:10.1021/jp9062516

Accurate rate coeffs. for 35 1,2-hydrogen shift reactions for hydrides contg. up to 10 silicon atoms have been calcd. usingG3//B3LYP. The overall reactions exhibit two distinct barriers. Overcoming the first barrier results in the formation of ahydrogen-bridged intermediate species from a substituted silylene and is characterized by a low activation energy.Passing over the second barrier converts this stable intermediate into the double-bonded silene. Values for the singleevent Arrhenius pre-exponential factor, A, and the activation energy, Ea, were calcd. from the G3//B3LYP rate coeffs.,and a group additivity scheme was developed to predict A and Ea. The values predicted by group additivity are moreaccurate than structure/reactivity relationships currently used in the literature, which rely on a representative A value andthe Evans-Polanyi correlation to predict Ea. The structural factors that have the most pronounced effect on A and Eawere considered, and the presence of rings was shown to influence these values strongly.~19 Citings

353. Materials science of hydrogen/oxygen fuel cell catalysis

By Erlebacher, J.From Solid State Physics (2009), 61, 77-141. Language: English, Database: CAPLUS

A review on the physics of the catalytic reactions in the acidic hydrogen/oxygen fuel cell using Pt-based catalysts. Thethermodn. and chem. of the H2/O2 fuel cell are discussed, followed by a microstructural description of state-of-the-artproton exchange membrane (PEM) fuel cells. The hydrogen oxidn. reaction at the anode, which involves the dissocn. ofhydrogen into protons and electrons is then discussed. This discussion involves reactant transport into and out of thecatalyst layer, poisoning of the catalyst by fuel impurities, and strategies to improve all of these issues. Oxygen redn. atthe cathode is then considered, as well as how advanced computational methods, particularly d. functional theory (DFT)methods, are producing predictions/calcns. that are driving exptl. discovery of new materials. Some key areas wheresurface physics can offer solns. to crucial catalyst design problems are identified.

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~9 Citings

354. How Potentials of Zero Charge and Potentials for Water Oxidation to OH(ads) on Pt(111) Electrodes VaryWith Coverage

By Tian, Feng; Jinnouchi, Ryosuke; Anderson, Alfred B.From Journal of Physical Chemistry C (2009), 113(40), 17484-17492. Language: English, Database: CAPLUS,DOI:10.1021/jp905377d

Self-consistent potential-dependent quantum chem. calcns. onthe formation of OH(ads) from H2O(ads) oxidn. on the Pt(111)surface in acidic soln. were performed using a unified theory forthe electrochem. interface. The potentials of zero charge(PZC) are relatively insensitive to H2O(ads) coverage and,when adsorbed OH is present, are very sensitive to theOH(ads)/H2O(ads) ratio. The PZC generally increases as thedegree of oxidn. of the surface is increased by higher OH(ads)coverage. Std. reversible potentials for the formation of 1/6monolayer (ML) OH(ads) from oxidn. of H2O(ads) for initial H2Ocoverage values of 1/6, 1/3, 1/2, and 2/3 ML were calcd. andare resp. 0.71, 0.59, 0.65, and 0.63 V on the SHE scale.These calcd. reversible potentials agree well with exptl.measurements of onset potentials for H2O oxidn., but it isargued using exptl. measurements of the groups of Orts andWatanabe that the 0.59 V value corresponds to the room temp.interface. The reversible potentials for oxidizing the last 1/6 MLof H2O(ads) at 1/3, 1/2, and 2/3 ML initial H2O coverage areresp. 1.25, 1.29, and 1.21 V. The high reversible potentials areattributed to the loss of stabilizations from H bonding whenH2O(ads) is oxidized to OH(ads) and suggest that highcoverage for OH(ads) beyond 1/3 ML can exist only at highelectrode potentials. However, the exptl. results of Watanabeand the preliminary theor. studies show that the OH(ads) isoxidized to O(ads) at ∼0.8 V, well before such high potentialsare reached.

~40 Citings

355. Model thermodynamics and the role of free-carrier energy at high temperatures. Nitrogen and boron pairingin diamond

By MacLeod, R. M.; Murray, S. W.; Goss, J. P.; Briddon, P. R.; Eyre, R. J.From Physical Review B: Condensed Matter and Materials Physics (2009), 80(5), 054106/1-054106/7. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.80.054106

The role of configurational, vibrational, and elec. terms in the temp.-dependent binding energy of impurity pairs at hightemps. is considered by use of the example of B and N in diamond. To calc. the free binding energy, we have developeda formalism for quantification of the free carrier contribution to the free binding energy. For doping concns. of 1018 cm-3,N2 is favored over isolated substitutional N for temps. 2600 K, and boron favors the isolated substitutional form above∼750 K. Comparing with typical exptl. conditions for growth or heat treatment, we show that the calcns. account for thedifferent behavior obsd. for B and N. For B, the electronic contribution is large at low concns. at the temp. at which Bs isable to migrate and cannot be neglected.~1 Citing

356. Quasiclassical trajectory study of H+SiH4 reactions in full-dimensionality reveals atomic-level mechanisms

By Cao, Jianwei; Zhang, Zhijun; Zhang, Chunfang; Liu, Kun; Wang, Manhui; Bian, WenshengFrom Proceedings of the National Academy of Sciences of the United States of America (2009), 106(32), 13180-13185, S13180/1-S13180/17. Language: English, Database: CAPLUS, DOI:10.1073/pnas.0903934106

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This work elucidates new at.-level mechanisms that may be common in a range of chem. reactions, and our findings areimportant for the understanding of the nature of polyat. abstraction and exchange reactions. A global 12-dimensional abinitio potential energy surface (PES), which describes both H+SiH4 abstraction and exchange reactions is constructed,based on the modified Shepard interpolation method and UCCSD(T)/cc-pVQZ energy calcns. at 4,015 geometries. ThisPES has a classical barrier height of 5.35 kcal/mol for abstraction (our best est. is 5.35 ± 0.15 kcal/mol from extensive abinitio calcns.), and an exothermicity of - 13.12 kcal/mol, in excellent agreement with expt. Quasiclassical trajectorycalcns. on this new PES reveal interesting features of detailed dynamical quantities and underlying new mechanisms.Our calcd. product angular distributions for exchange are in the forward hemisphere with a tail sideways, and areattributed to the combination of three mechanisms: inversion, torsion-tilt, and side-inversion. With increase of collisionenergy our calcd. angular distributions for abstraction first peak at backward scattering and then shift toward smallerscattering angles, which is explained by a competition between rebound and stripping mechanisms; here stripping isseen at much lower energies, but is conceptually similar to what was obsd. in the reaction of H+CD4 by Zare andcoworkers. Each of these at.-level mechanisms is confirmed by direct examn. of trajectories, and two of them (torsion-tiltand side-inversion) are proposed and designated in this work.~13 Citings

357. Structural analysis of HS(CD2)12(O-CH2-CH2)6OCH3 ,monolayers on gold by means of polarizationmodulation infrared reflection absorption spectroscopy. Progress of the reaction with bromine.

By Brand, Izabella; Nullmeier, Martina; Kluener, Thorsten; Jogireddy, Rajamalleswaramma; Christoffers, Jens;Wittstock, GuntherFrom Langmuir (2010), 26(1), 362-370. Language: English, Database: CAPLUS, DOI:10.1021/la9020993

A self-assembled monolayer (SAM) on gold was formed with specifically perdeuterated hexaethylene glycol-terminatedalkanethiol HS(CD2)12(O-CH2-CH2)6OMe (D-OEG). The structure of the d-alkane and the oligoethylene glycol (OEG)parts of the mol. in a SAM was studied by polarization modulation IR reflection absorption spectroscopy. The D-OEGmonolayers are highly ordered and exist in a cryst. phase. The d-alkane chain adopts an all-trans conformation. Both,the d-alkane chain and long axis of the OEG part make an angle of 26.0° ± 1.5° with respect to the surface normal, avalue characteristic for the tilt of solid n-alkane thiols in the SAMs on Au. The positions of νas(COC) and CH2 waggingand rocking modes indicate a helical arrangement of the OEG chains. The D-OEG SAMs were exposed to 25 µM Br2 intwo ways: (i) by immersion into the Br2 soln. and (ii) in the galvanic cell Au|D-OEG SAM|25 µM Br2 + 0.1M Na2SO4|| 50µM KBr + 0.1M Na2SO4|Au. In the galvanic cell, the oxidant (Br2) is scavenged by a heterogeneous electron transferreaction, slowing the reaction of D-OEG with Br2. The slow progress of the reaction with Br2 allowed one to drawconclusions about mol. rearrangements taking place during this reaction. The reaction with Br2 starts on boundariesand/or defects present in the SAM. First, at the defect place, the α-C atom of the OEG chain reacts with Br2 and theOEG part of the mol. is removed from the monolayer. In consequence an increase in disorder in the OEG part of theSAM is obsd. The same mechanism of the reaction with Br2 is applied for the d-dodecane alkanethiol part of the mol.This reaction is slow, thus the order and the tilt of the hydrocarbon chain changes only a little during the reaction time.~12 Citings

358. Hydrogen abstraction from CF3CF2CFH2 and CF3CFHCF2H by OH radicals and Cl atoms: theoreticalenthalpies and rate constants

By Gao, Hong; Wang, Ying; Wang, Qin; Liu, Jing-Yao; Sun, Chia-ChungFrom Theoretical Chemistry Accounts (2009), 124(1-2), 59-70. Language: English, Database: CAPLUS,DOI:10.1007/s00214-009-0581-5

The hydrogen abstraction reactions of CF3CF2CFH2 and CF3CFHCF2H with OH radicals and Cl atoms have beenstudied theor. by a dual-level direct dynamics method. Two stable conformers of CF3CF2CFH2 with C s and C 1symmetries and all possible abstraction channels for each reaction are all taken into consideration. Optimizedgeometries and frequencies of all the stationary points and extra points along min.-energy path (MEP) have beencomputed at the BB1K/6-31+G(d, p) level of theory. To refine the energy profile of each reaction channel, single pointenergy calcns. have been performed by the BMC-CCSD method. The rate consts. are evaluated by canonical variationaltransition state theory (CVT) with the small-curvature tunneling correction method (SCT) over a wide temp. range of 200-1,000 K. The detailed branching ratios of four reactions are discussed. The good agreement found between our theor.rate consts. and the available exptl. data suggests that the present approach could provide a reliable prediction for theCF3CFHCF2H + Cl reaction about which there is little exptl. information. The kinetic calcns. show that the SCT effectplays an important role in all channels. In addn., in order to further reveal the thermodn. properties, the enthalpies offormation of the reactants (CF3CF2CFH2 and CF3CFHCF2H) and the product radicals (CF3CF2CFH, CF3CFCF2H, andCF3CFHCF2) are evaluated by applying isodesmic reactions at both BMC-CCSD//BB1K/6-31+G(d, p) and MC-QCISD//BB1K/6-31+G(d, p) levels of theory.~3 Citings

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359. Synthesis, structural characterization and thermal analysis of the cobalt(II) oxalate obtained through thereaction of 1,2-ethanediol with Co(NO3)2·6H2O

By Birzescu, M.; Niculescu, M.; Dumitru, Raluca; Carp, Oana; Segal, E.From Journal of Thermal Analysis and Calorimetry (2009), 96(3), 979-986. Language: English, Database: CAPLUS,DOI:10.1007/s10973-009-0054-z

The homopolynuclear coordination compd. [CoL·2.5H2O]n with L = C2O4 2- was synthesized by a new unconventionalmethod. It consists of a redox reaction between 1,2-ethanediol and cobalt nitrate in presence of nitric acid. Thecoordination compd. was characterized by chem. anal., electronic and vibrational spectra, and thermal anal. In thecoordination compd. the Co(II) ion exists in a high spin octahedral configuration and oxalate anion acts as double-bridgeligand, tetradentate, similar as in CoC2O4·2H2O obtained by the classical method. Nonstoichiometric oxide, Co3O4+0.25with deficit in cobalt and normal spinel Co3O4 were identified as thermal decompn. intermediates. As final product ofdecompn., the oxide CoO was obtained.~21 Citings

360. Protonation of O2 adsorbed on a Pt3 island supported on transition metal surfaces

By Sotelo, Juan C.; Seminario, Jorge M.From Journal of Chemical Physics (2009), 131(4), 044709/1-044709/11. Language: English, Database: CAPLUS,DOI:10.1063/1.3179690

The redn. in oxygen on bimetallic tips XSPt3 (XS=Co3, Ni3, Pt6, Co3Pt3) in aq. acid medium is studied. It is found that alocally neutral neighborhood of an active site in the bimetallic tip as well as adduct hydration assist in the protonation. Itis concluded that metallic tips of Pt, Co3Pt, and Co are comparable in performance for the oxygen redn. reaction. For anadduct, the larger the bonding energy of the Pt3-island to the (XS) substrate, the more charged the oxygen mol. becomesfor different levels of protonation. Furthermore, if a hydroxyl OOH group is formed as a result of protonation, theinteraction of the cation with O2 decreases with increasing level of hydration. (c) 2009 American Institute of Physics.~0 Citings

361. Synthesis, characterization and theoretical calculations of 5-methoxyisatin-3-thiosemicarbazone derivatives

By Kandemirli, Fatma; Arslan, Taner; Koksoy, Baybars; Yilmaz, MehmetFrom Journal of the Chemical Society of Pakistan (2009), 31(3), 498-504. Language: English, Database: CAPLUS

In this study, new 5-methoxyisatin-3-(N-phenyl)thiosemicarbazone (3a),5-methoxyisatin-3-(N-benzyl) thiosemicarbazone(3b) and 5-methoxyisatin-3-(N-(4-chlorophenyl))thiosemicarbazone (3c) were synthesized and characterized byelemental anal., IR spectra, mass spectra, 1H-NMR and 13C-NMR spectra. The reaction mechanism and quantum-chem. calcns. were done for the 5-methoxyisatin-3-(N-phenyl)thiosemicarbazone (3a).~6 Citings

362. DFT study of halogen impurity in diamond

By Yan, Cui Xia; Dai, Ying; Huang, Bai BiaoFrom Journal of Physics D: Applied Physics (2009), 42(14), 145407/1-145407/6. Language: English, Database:CAPLUS, DOI:10.1088/0022-3727/42/14/145407

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A first-principles study has been carried out to evaluate the electronic properties of diamond doped with halogen X (= F,Cl, Br, I) based on d. functional theory (DFT). Our work shows that doping becomes more difficult in the order F < Cl <Br < I for either substitutional or interstitial doping into diamond. Substitutional doping is energetically more favorableowing to smaller formation energy than the interstitial doping. The calcd. results show that the F defect accepts electronsand acts as acceptor in diamond. However, the dopant Cl/Br/I donates electrons to diamond lattice, which indicates thatCl/Br/I may serve as a donor in diamond. It is found that substitutional I is a good choice for achieving n-type diamondmaterial among the donors. Further calcns. examine the influence of H atom on the electronic properties of diamonddoped with donor dopant Cl/Br/I and show that H atom incorporation makes Fermi level EF shift towards the valenceband (VB) and the activation energy of the donor Cl/Br/I increases. Therefore, halogen impurities doping into diamondshould be carried out under H-poor environments. In addn., Xs (X = Cl, Br, I) prefers to bind to vacancy defects to form aXs-V complex, which is no longer a shallow donor.~2 Citings

363. Co(II)-Ni(II) heteropolynuclear coordination compound obtained through the reaction of 1,2-propanediolwith metallic nitrates as precursor for mixed oxide of spinel type NiCo2O4

By Niculescu, M.; Birzescu, M.; Dumitru, Raluca; Sisu, E.; Budrugeac, P.From Thermochimica Acta (2009), 493(1-2), 1-5. Language: English, Database: CAPLUS,DOI:10.1016/j.tca.2008.03.011

The authors present the exptl. results of the thermal anal. of heteropolynuclear coordination compd.[Co2NiL3(OH)3(H2O)3]n, where L is lactate anion, obtained by a new method, through the reaction of 1,2-propanediol withM(NO3)2·6H2O (M: Co, Ni). The reaction between 1,2-propanediol and M(NO3)2·6H2O (M: Co, Ni) occurs with the oxidn.of 1,2-propanediol to the lactate anion (L), coordinated to M(II). The thermal properties of the synthesized polynuclearcoordination compd., [Co2NiL3(OH)3(H2O)3]n, were studied by TG, DTG and DTA. The mixed oxide of spinel type,NiCo2O4, purified with NiO, obtained by thermal decompn. of heteropolynuclear coordination compd. was characterizedby IR spectroscopy, x-ray powder diffraction (XRD) and elemental anal.~12 Citings

364. Direct Dynamics Study of Hydrogen-Transfer Isomerization of 1-Pentyl and 1-Hexyl Radicals

By Zheng, Jingjing; Truhlar, Donald G.From Journal of Physical Chemistry A (2009), 113(43), 11919-11925. Language: English, Database: CAPLUS,DOI:10.1021/jp903345x

The rate consts. of three intramol. hydrogen-transfer isomerization reactions, namely, 1-4 isomerization of the 1-pentylradical and 1-4 and 1-5 isomerizations of the 1-hexyl radical, are calcd. using variational transition state theory withmultidimensional tunneling, in particular by using canonical variational theory (CVT, which is the version of variationaltransition state theory in which the transition state dividing surface is optimized for a canonical ensemble) with small-curvature tunneling (SCT) for the transmission coeff. The required potential energy surfaces were obtained implicitly bydirect dynamics employing interpolated variational transition state theory with mapping (IVTST-M) and variationaltransition state theory with interpolated single-point energies (VTST-ISPE). Single-level direct dynamics calcns. wereperformed for all of the reactions by IVTST-M using M06-2X/MG3S or M08-HX/cc-pVTZ+ potential energy surfaces orboth. The stationary points of 1-4 isomerization of 1-pentyl and the stationary points for the forward reactions of 1-4 and1-5 isomerizations of 1-hexyl were also optimized by BMC-CCSD, and for all three reactions we also performed dual-level direct dynamics calcns. using VTST-ISPE in which MCG3-MPW single-point energies served as the higher level.The calcd. MCG3-MPW//M06-2X/MG3S rate consts. agree well with exptl. values for 1-4 isomerization of the 1-pentylradical at high temp., and this validates the accuracy of this theor. method for 1-4 isomerization. The MCG3-MPW//M06-2X/MG3S method was therefore used to make a reliable prediction for the rata consts. of 1-4 isomerization of the 1-hexylradical for which a direct exptl. measurement is not available. The calcd. CVT/SCT/M08-HX/cc-pVTZ+ rate consts.agree well with exptl. values for 1-5 isomerization of the 1-hexyl radical, and they show that the tunneling effect for thesereactions was underestimated in previous work.~30 Citings

365. On Unjustifiably Misrepresenting the EVB Approach While Simultaneously Adopting It

By Kamerlin, Shina C. L.; Cao, Jie; Rosta, Edina; Warshel, AriehFrom Journal of Physical Chemistry B (2009), 113(31), 10905-10915. Language: English, Database: CAPLUS,DOI:10.1021/jp901709f

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In recent years, the EVB has become a widely used tool in the QM/MM modeling of reactions in condensed phases andin biol. systems, with ever increasing popularity. However, despite the fact that its power and validity have beenrepeatedly established since 1980, a recent work has strongly criticized this approach, while not discussing the fact thatone of the authors is effectively using it himself for both gas-phase and soln. studies. Here, we have responded to themost serious unjustified assertions of that paper, covering both the more problematic aspects of that work and the morecomplex scientific aspects. Addnl., we have demonstrated that the poor EVB results shown in Valero et al. which wherepresented as verification of the unreliability of the EVB model were in fact obtained by the use of incorrect parameters,without comparing to the correct surface obtained by our program.~21 Citings

366. EPR spectroscopic investigation of radical-induced degradation of partially fluorinated aromatic modelcompounds for fuel cell membranes

By Schoenberger, Frank; Kerres, Jochen; Dilger, Herbert; Roduner, EmilFrom Physical Chemistry Chemical Physics (2009), 11(27), 5782-5795. Language: English, Database: CAPLUS,DOI:10.1039/b817070c

EPR spectroscopic investigations of reactions between monomeric model compds. representing typical structuralmoieties of poly(aryl) ionomers and photochem. generated hydroxyl radicals are reported. Deoxygenated solns. of themodel compds. (in a water/methanol mixt.) contg. hydrogen peroxide at defined pH values were exposed to UV light inthe flow cell within the cavity of an EPR spectrometer. Spectra were analyzed by computer simulation and the formedradicals were assigned by comparing their g-factors and hyperfine coupling consts. (hfccs) with those from the literatureand from d. functional theory (DFT) calcns. The relevance for polymer electrolyte membrane fuel cells (PEMFCs) andalk.-anion exchange membrane fuel cells (AAEMFCs) is discussed.~3 Citings

367. Importance of catalyst stability vis-a-vis hydrogen peroxide formation rates in PEM fuel cell electrodes

By Sethuraman, Vijay A.; Weidner, John W.; Haug, Andrew T.; Pemberton, Marianne; Protsailo, Lesia V.From Electrochimica Acta (2009), 54(23), 5571-5582. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2009.04.062

The role of catalyst stability on the adverse effects of H2O2 formation rates in a p exchange membrane fuel cell (PEMFC)was studied for Pt, Pt binary (PtX, X = Co, Ru, Rh, V, Ni) and ternary (PtCoX, X = Ir, Rh) catalysts supported on KetjenBlack (KB) C. The selectivity of these catalysts towards H2O2 formation in the O redn. reaction (ORR) was measured ona rotating ring disk electrode. These measured values were used in conjunction with local O and p concns. to est. localH2O2 formation rates in a PEMFC anode and cathode. The effect of H2O2 formation rates on the most active anddurable of these catalysts (PtCo and PtIrCo) on Nafion membrane durability was studied using a single-sided membraneelectrode assembly (MEA) with a built-in ref. electrode. F- concn. in the effluent H2O was used as an indicator of themembrane degrdn. rate. PtIrCo had the least F emission rate followed by PtCo/KB and Pt/KB. Though PtCo and PtIrCoshow higher selectivity for H2O2 formation than unalloyed Pt, they did not contribute to membrane degrdn. This result isexplained in terms of catalyst stability as measured in potential cycling tests in liq. electrolyte as well as in a functionalPEM fuel cell.~42 Citings

368. Structure Prediction of Bis(amino acidato)copper(II) Complexes with a New Force Field for MolecularModeling

By Sabolovic, Jasmina; Gomzi, VjeranFrom Journal of Chemical Theory and Computation (2009), 5(7), 1940-1954. Language: English, Database: CAPLUS,DOI:10.1021/ct9000203

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This article presents a new force field whose parameterization was based on exptl. crystal data and quantum chem.obtained vacuum structures of a series of copper(II) complexes with aliph. α-amino acids and their N-alkyl derivs., alongwith the SPC/E water model. The ability of the new force field to reproduce and predict the structural properties of thecopper(II) complexes in the gas phase, in simulated cryst. surroundings, and solvated in water is examd. Mol. dynamics(MD) simulations with the new force field yielded time-av. structural coordinates of bis(glycinato)copper(II) [the only oneof 25 modeled bis(amino acidato)copper(II) systems with published exptl. structural data in aq. soln. at room temp.] withinthe exptl. error values. The study of the cis-trans isomerization of bis(glycinato)copper(II) in aq. medium at 300 K usingthe quantum chem. polarized continuum model revealed a small energy difference (5 kJ mol-1) between the solvated cisand trans min., in line with the MD energy estns. The new force field proved promising in predicting the assocn. of thecomplexes in aq. soln. and formation of a nucleus of crystn.~17 Citings

369. Key role of work hardening in superconductivity/superfluidity, heat conductivity and ultimate strainincrease, evolution, cancer, aging and other phase transitions

By Kisel, V. P.From arXiv.org, e-Print Archive, Physics (2009), 1-15, arXiv:0905.4428v1 [physics.gen-ph]. Language: English,Database: CAPLUS

A review. The shear/laminar flow of liqs./gas/plasma/biol. cells (BC), etc. is equiv. to dislocation-like shear of solids. Theturbulent flow is the next stage of deformation/multiplication of dislocation-like defects and their ordering in sub-grainsand grain-boundaries, then grains slip-rotation in the direction approx. perpendicular to the shear flow. Phase transitionsare governed by unified deformation hardening/softening under hydrostatic pressure, particle irradn. and impurity(isotope) chem. pressure, hard confining conditions and cooling, etc. thus changing elec., magnetic, ferroelec., thermal,optical properties. Dislocation-like work hardening, DWH, is detd. by nonmonotonous properties of dislocation doubleedge-cross-jog slip, and ultra-strong DWH gives the lowest drag for any dislocation-like plasticity at phase transitions.This provides the same micromechanisms of the ultimate stage of conventional deformation (superfluidity) of ordinaryliqs., i.e., H2O, kerosine and glycerin, liq. and solid He, quasi-particle condensates. The key role of DWH is confirmed forsupercond., integer and fractional quantum Hall effects and the enhancement of ultimate strain and diffusion underdeformation down to nanostructures, etc. Phase transformations in biol. cells (explosive events of diversity andpopulation of species and diseases - for example, locust and plaque bacteria, evolution, aging and cancer, bursts in thedevelopment of human intellectual possibilities languages, culture, arts and sciences, history, etc.) depend on the samedeformation effects in biol. evolution.~0 Citings

370. Quantum Tunneling in Testosterone 6β-Hydroxylation by Cytochrome P450: Reaction DynamicsCalculations Employing Multiconfiguration Molecular-Mechanical Potential Energy Surfaces

By Zhang, Yan; Lin, HaiFrom Journal of Physical Chemistry A (2009), 113(43), 11501-11508. Language: English, Database: CAPLUS,DOI:10.1021/jp901850c

Testosterone hydroxylation is a prototypical reaction of human cytochrome P 450 3A4, which metabolizes about 50% oforal drugs on the market. Reaction dynamics calcns. were carried out for the testosterone 6β-hydrogen abstraction andthe 6β-d1-testosterone 6β-deuterium abstraction employing a model that consists of the substrate and the active oxidantcompd. I. The calcns. were performed at the level of canonical variational transition state theory with multidimensionaltunneling and were based on a semiglobal full-dimensional potential energy surface generated by the multiconfigurationmol. mechanics technique. The tunneling coeffs. were found to be around 3, indicating substantial contributions byquantum tunneling. However, the tunneling made only modest contributions to the kinetic isotope effects. The kineticisotope effects were computed to be about 2 in the doublet spin state and about 5 in the quartet spin state.~9 Citings

371. Conformational Switching Induced by Near-Infrared Laser Irradiation

By Sharma, Archna; Reva, Igor; Fausto, RuiFrom Journal of the American Chemical Society (2009), 131(25), 8752-8753. Language: English, Database: CAPLUS,DOI:10.1021/ja903211f

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This work describes a mol. system where it is possible toeffectively control the interconversion between two differentstable conformational states, using selective narrow-band near-IR irradn. Monomers of hydroxyacetone (HA) isolated in lowtemp. argon matrixes at 15 K exist exclusively in theconformational ground state Cc. Narrow-band near-IRvibrational excitation of the first OH stretching overtone of theCc form resulted in conformational isomerization. Thephotoproduct was identified as the higher energy Tt conformerof HA, and it was found to be stable at 15 K. The reverseisomerization, converting Tt into Cc, could also be induced bylaser excitation of the first OH stretching overtone of the Ttform. The interpretation of the exptl. observations wassupported by anharmonic and harmonic calcns. of thevibrational spectra and barriers to intramol. rotation.

~42 Citings

372. Non-Hermitian Multiconfiguration Molecular Mechanics

By Tishchenko, Oksana; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2009), 5(6), 1454-1461. Language: English, Database: CAPLUS,DOI:10.1021/ct900077g

We present a new version of the multiconfiguration mol. mechanics (MCMM) algorithm for fitting potential energysurfaces of complex reactive systems. The main improvement consists in allowing the valence bond CI matrix to be non-Hermitian, which broadens the range of geometries over which the potential energy surface can be fit accurately. Asecond improvement is that the new algorithm has simpler gradients and Hessians and executes faster. Theperformance of the new algorithm is evaluated using the example of two model reactions.~12 Citings

373. Visualizing Chemical Reactions and Crossover Processes in a Fuel Cell Inserted in the ESR Resonator:Detection by Spin Trapping of Oxygen Radicals, Nafion-Derived Fragments, and Hydrogen and Deuterium Atoms

By Danilczuk, Marek; Coms, Frank D.; Schlick, ShulamithFrom Journal of Physical Chemistry B (2009), 113(23), 8031-8042. Language: English, Database: CAPLUS,DOI:10.1021/jp901597f

Exptl. results obtained in situ with a fuel cell (FC) inserted in the resonator of an ESR spectrometer are presented. Thisset-up enabled observation of the sep. processes at anode and cathode sides and monitoring of the formation of HO· andHOO· radicals, H· and D· radicals and atoms as well as radical fragments derived from the Nafion membrane. Thepresence of the radicals was detd. by spin-trapping ESR with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap.The in situ FC was operated at 300 K with a membrane-electrode assembly (MEA) based on Nafion 117 and Pt ascatalyst, at closed- and open-circuit voltage (CCV and OCV) conditions. Expts. with H2 and D2 at the anode and O2 atthe cathode were performed. The DMPO/OH adduct was detected only at the cathode for CCV operation, suggestinggeneration of hydroxyl radicals from H2O2 formed electrochem. via the 2-electron redn. of O. The DMPO/OOH adduct,detected in this study for the 1st time in a FC, appeared at the cathode and anode for OCV operation, and at the cathodeafter CCV FC operation of ≥2 h. These results were interpreted in terms of electrochem. generation of HOO· at thecathode, HO· + H2O2 → H2O + HOO·, and its chem. generation at the anode from H atoms and crossover O, H· + O2 →HOO·. DMPO/H and DMPO/D adducts were detected at the anode and cathode sides, for CCV and OCV operation, H·

and D· are aggressive radicals that remove F from the tertiary C in the polymer membrane chain, leading to chainfragmentation. C-centered radical (CCR) adducts were detected at the cathode after CCV FC operation and weak CCRsignals were also detected at the anode. CCRs can originate only from the Nafion membranes and their presenceindicates membrane fragmentation. This study demonstrated that FC operation involves processes such as gascrossover, reactions at the catalyst surface and possible attack of the membrane by reactive H· or D· that do not occur inex situ expts. in the lab., thus implying different mechanistic pathways in the 2 types of expts.~88 Citings

374. The hydrogen abstraction reaction H + CH4. II. Theoretical investigation of the kinetics and dynamics

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By Espinosa-Garcia, J.; Nyman, G.; Corchado, J. C.From Journal of Chemical Physics (2009), 130(18), 184315/1-184315/9. Language: English, Database: CAPLUS,DOI:10.1063/1.3132594

On a new potential energy surface (PES-2008) developed by our group (preceding paper), we performed an extensivekinetics study using variational transition-state theory with semiclassical transmission coeffs. over a wide temp. range of250-2000 K and a dynamics study using quasiclassical trajectory (QCT) and quantum-mech. (QM) calcns. at collisionenergies between 0.7 and 2.0 eV for the title reaction and isotopically substituted versions. Kinetically, the H + CH4forward and reverse thermal rate consts. reproduce the available exptl. data, with a small curvature of the Arrhenius plotindicating the role of tunneling in this hydrogen abstraction reaction. Five sets of kinetic isotope effects are also calcd. Ingeneral, they reproduce the exptl. information. Dynamically, we focused on the H + CD4 reaction because there aremore exptl. studies for comparison. Most of the available energy appears as product translational energy (55%-68%),with the HD product being vibrationally cold (v'= 0,1) in agreement with expt., although rotationally hotter than expt. Thereaction cross section is practically negligible at 0.7 eV and still small at 1.5 eV, reproducing the exptl. evidence, althoughour values are smaller. The product angular distribution is analyzed using QCT and QM methods. While at low energies(0.7 eV) both the QCT and the QM calcns. yield forward scattered CD3 product, i.e., a rebound mechanism, at highenergy (1.2 eV) only the QM calcns. reproduce the expt. The agreement with this wide variety of kinetic and dynamicexptl. data (always qual. and in some cases quant.) shows the capacity of the PES-2008 surface to describe the reactionsystem. (c) 2009 American Institute of Physics.~8 Citings

375. The hydrogen abstraction reaction H + CH4. I. New analytical potential energy surface based on fitting to abinitio calculations

By Corchado, Jose C.; Bravo, Jose L.; Espinosa-Garcia, JoaquinFrom Journal of Chemical Physics (2009), 130(18), 184314/1-184314/10. Language: English, Database: CAPLUS,DOI:10.1063/1.3132223

A new anal. potential energy surface is presented for the reaction of hydrogen abstraction from methane by a hydrogenatom. It is based on an anal. expression proposed by , and its fittable parameters were obtained by a multibeginningoptimization procedure to reproduce high-level ab initio electronic structure calcns. obtained at the CCSD(T)/cc-pVTZlevel. The ab initio information employed in the fit includes properties (equil. geometries, relative energies, andvibrational frequencies) of the reactants, products, saddle point, points on the reaction path, and points on the reactionswath. No exptl. information is used. By comparison with the ref. results we show that the resulting surface reproduceswell not only the ab initio data used in the fitting but also other thermochem. and kinetic results computed at the same abinitio level, such as equil. consts., rate consts., and kinetic isotope effects, which were not used in the fit. In this way weshow that the new potential energy surface is correctly fitted and almost as accurate as the CCSD(T)/cc-pVTZ method indescribing the kinetics of the reaction. We analyze the limitations of the functional form and the fitting method employed,and suggest some solns. to their drawbacks. In a forthcoming communication, we test the quality of the new surface bycomparing its results with exptl. values. (c) 2009 American Institute of Physics.~22 Citings

376. Tunnelling does not contribute significantly to enzyme catalysis, but studying temperature dependence ofisotope effects is useful

By Liu, Hanbin; Warshel, AriehEdited By:Allemann, Rudolf K.; Scrutton, Nigel SFrom Quantum Tunnelling in Enzyme-Catalysed Reactions (2009), 242-267. Language: English, Database: CAPLUS,DOI:10.1039/9781847559975-00242

A review. The authors summarize the results from studies of the temp. dependence of the kinetic isotope effect indifferent mutants of dihydrofolate reductase and lipoxygenase and discuss the conclusion that emerge from thesestudies.~4 Citings

377. Kinetic isotope effects from hybrid classical and quantum path integral computations

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By Gao, Jiali; Wong, Kin-Yiu; Major, Dan T.; Cembran, Alessandro; Song, Lingchun; Lin, Yen-Lin; Fan, Yao; Ma,ShuhuaEdited By:Allemann, Rudolf K.; Scrutton, Nigel SFrom Quantum Tunnelling in Enzyme-Catalysed Reactions (2009), 105-131. Language: English, Database: CAPLUS,DOI:10.1039/9781847559975-00105

A review. The authors summarize the theor. background, the representation of the potential-energy surface, and theintegrated path integral-free energy perturbation and umbrella sampling method computational details. The paperconcludes with highlights of the main findings.~4 Citings

378. DFT study of difference caused by catalyst supports in Pt and Pd catalysis of oxygen reduction reaction

By Li, Li; Wei, Zi Dong; Zhang, Yi; Qi, Xue Qiang; Xia, Mei Rong; Zhang, Jie; Shao, Zhi Gang; Sun, Cai XinFrom Science in China, Series B: Chemistry (2009), 52(5), 571-578. Language: English, Database: CAPLUS,DOI:10.1007/s11426-009-0006-2

Based on an exptl. phenomenon that catalytic activity of Pt and Pd for oxygen redn. reaction (ORR) changes withcatalyst supports from C to TiO2, d. function theory (DFT) was used to elucidate the cause behind the difference incatalysis caused by catalyst supports. First, factors closely assocd. with the first electron transfer of the ORR wereassessed in the light of quantum chem. Then intermediate (at. oxygen, O) adsorption strength on the catalyst surfacewas calcd. In terms of min. energy difference, the best orbital symmetry match, and the max. orbital overlap, TiO2 doesbring about a very pos. effect on catalysts Pd/TiO2 for the first electron transfer of the ORR. Esp., TiO2 remarkablyexpands the space size of Pd/TiO2 HOMO orbital and improves orbital overlap of Pd/TiO2 HOMO and O2 LUMO. Theanal. of deformation d. and partial d. of states shows that the strong interaction between Pt and Ti leads to a strongadsorption of intermediate O on Pt/TiO2, but the strong interaction between Pd and surface O causes pos. net charge ofPd and a weak adsorption of intermediate O on Pd/TiO2. Thus, the ORR can proceed more smoothly on Pd/TiO2 thanPt/TiO2 in every respect of max. orbital overlap and rate delay by intermediate O. The research also discloses thatseveral factors lead to less activity of TiO2-supported Pt and Pd catalysts than the C-supported ones for the ORR. Thesefactors include the poor dispersion of Pt and Pd particles on TiO2, poor elec. conduction of TiO2 carrier itself, and biggerenergy difference between HOMO of TiO2-carried metallic catalysts and LUMO of O2 mol. due to electrons deeplyembedded in the semiconductor TiO2 carrier.~9 Citings

379. Surface Phase Diagram and Oxygen Coupling Kinetics on Flat and Stepped Pt Surfaces underElectrochemical Potentials

By Fang, Ya-Hui; Liu, Zhi-PanFrom Journal of Physical Chemistry C (2009), 113(22), 9765-9772. Language: English, Database: CAPLUS,DOI:10.1021/jp901091a

Electrochem. reactions catalyzed by metal electrode, despite their huge importance in industry, are not well understoodat the at. level. In relevance to H2O electrolysis, the oxygen coupling reaction on Pt metal surfaces is systematicallystudied in this work by combining periodic d. functional theory calcns. with a new theor. approach to mimic theelectrochem. environment. In the approach, the surface is explicitly polarized by adding/subtracting charges and thecounter charges are placed as Gaussian-distributed plane charges in a vacuum. With this method, the surface phasediagrams for both the closed-packed Pt(111) and stepped Pt(211) are detd., which demonstrates that stepped surfacesites can better accumulate oxidative species and thus reach to a higher local oxygen coverage compared to Pt(111) at agiven potential. The H2O environment is proved to affect the phase diagram marginally. By fully exploring the possibleoxygen coupling channels on Pt surfaces, the oxygen coupling reaction is kinetically difficult on metallic Pt surfaces <1.4V. There is no facile O coupling channels on Pt(111), as the barriers are ≥1 eV. Although an O + OH → OOH reactioncan eventually occur at the stepped sites with an increase of local O coverage and the calcd. barrier is <0.7 eV at 1.4 V(normal H electrode), at such high potentials the (111) surface can already undergo surface oxidn. due to the penetrationof oxygen into sublayers. The theory thus indicates that oxygen evolution on Pt anode occurs on Pt surface oxides asdictated by thermodn. and also demonstrates that the local surface structure and coverage can be more important inaffecting the barrier of surface reactions than the elec. fields.~53 Citings

380. Application of QM/MM Methods in Theoretical Studies of Enzyme Catalysis

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By Wang, Xi-Jun; Dai, Cong-Ying; Zhang, Yuan-Li; Wei, Dong-QingFrom AIP Conference Proceedings (2009), 1102(Theory and Applications of Computational Chemistry), 114-121.Language: English, Database: CAPLUS, DOI:10.1063/1.3108362

The QM/MM methods enjoy considerable attention recently due to their successful application on various complexsystems. This paper gives brief introduction of the development of QM/MM methods. Then we focus our attention to themost recent applications in studies of enzyme catalysis. (c) 2009 American Institute of Physics.~0 Citings

381. Nitrogen-Treated Graphite and Oxygen Electroreduction on Pyridinic Edge Sites

By Kurak, Kiera A.; Anderson, Alfred. B.From Journal of Physical Chemistry C (2009), 113(16), 6730-6734. Language: English, Database: CAPLUS,DOI:10.1021/jp811518e

From literature reports, some N-treated graphite electrodes catalyze the 4-electron electroredn. of O2 to H2O in acid.The linear Gibbs energy relation is used to predict the reversible potentials for forming intermediates during O2 redn. inacid over graphene doped with 2 N atoms substituting for adjacent edge CH groups. This procedure, generally accuratewithin ∼0.2 V, is useful for estg. overpotentials for electrode surface catalyzed reactions. Using bond strengths fromVASP (Vienna ab initio Software Package) slab-band d. functional calcns., it is predicted that one of the edge N has Hbonded to it at potentials of ∼1.70 V and below. In the 1st redn. step, the OOH that forms then dissocs. on the edge intoO that bonds strongly to N with OH weakly assocd. with it. The calcd. reversible potential is ∼0.89 V. The OH isproposed to abstr. H from an edge NH, forming H2O. The H is then replaced in a redn. reaction. The reversible potentialfor reducing the O(ads) to OH(ads) on the edge with is ∼-0.60 V, well neg. of the potential range of interest for oxygenredn., which means this edge structure will be stable at the potentials of interest. The edge has an unpaired electron andOOH bonds to the C atom bridging ON···NH with a strength corresponding to a reversible potential of ∼0.73 V. Thismeans that the 2-electron redn. product, H2O2, can form at a potential close to the ∼0.695 V std. reversible potential.The absence of any apparent pathway for the direct 4-electron redn. suggests that (i) some other catalytic site structureinvolving substituent N is involved or (ii) the peroxide pathway is being followed with O2 and H2O generation when peroxyintermediates disproportionate or (iii) impurity transition metals are contributing to direct 4-electron redn.~142 Citings

382. Distributed Gaussian Valence Bond Surface Derived from Ab Initio Calculations

By Sonnenberg, Jason L.; Wong, Kim F.; Voth, Gregory A.; Schlegel, H. BernhardFrom Journal of Chemical Theory and Computation (2009), 5(4), 949-961. Language: English, Database: CAPLUS,DOI:10.1021/ct800477y

The exptl. and computational results for the tautomerization reaction of 2-pyridone are reviewed. G3, G4, CBS-APNO,and W1 model chemistries are used to generate state-of-the-art reaction energetics for the tautomerization reaction withand without catalytic water mols. in both the gas and aq. phases. Reactive, electronic potential energy surfaces for usein mol. dynamics simulations were generated for these reactions following a recently improved empirical valence bondformulation. The form of mol. mechanics potentials needed for a satisfactory fit is also discussed.~25 Citings

383. Carbenes: Synthesis, properties, and organometallic chemistry

By de Fremont, Pierre; Marion, Nicolas; Nolan, Steven P.From Coordination Chemistry Reviews (2009), 253(7+8), 862-892. Language: English, Database: CAPLUS,DOI:10.1016/j.ccr.2008.05.018

A review. Carbenes, thought of only as transient species for a long time, have become ubiquitous in organometallicchem. Their interaction with a metal center, which allows for their classification as a function of the nature of thecarbene-metal bond, has inspired the studies of many research groups in every area of chem., from phys. chem. to org.synthesis. In this Review, the authors intend to give a general overview of carbenes in a broad sense, discussing singletand triplet carbenes with all variations within these families. More precisely, the authors describe here, for Fischer- andSchrock-type carbenes, N-heterocyclic carbenes and non-stabilized ones, the different synthetic routes to both theimmediate precursors of carbenes and their metal complexes. Addnl., their steric and electronic properties are discussedin the light of both exptl. and theor. studies.

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~501 Citings

384. Molecular modelling for transition metal complexes: Dealing with d-electron effects

By Deeth, Robert J.; Anastasi, Anna; Diedrich, Christian; Randell, KrisFrom Coordination Chemistry Reviews (2009), 253(5+6), 795-816. Language: English, Database: CAPLUS,DOI:10.1016/j.ccr.2008.06.018

A review. The development and application of mol. mechanics methods which include an explicit treatment of d-electroneffects are reviewed. The origins of the authors' ligand field mol. mechanics (LFMM) method are traced from Hitchman'ssimple expression for predicting the M-L bond length change accompanying a d-d transition through to the generalimplementation of LFMM within the mol. operating environment, including anal. energy gradients, explicit M-L π-bondingand d-s mixing effects, plus a term for handling different spin states. The LFMM applications cover simple coordinationcomplexes of Cu(II) where a single parameter set treats multiple coordination nos.; the treatment of the complete Jahn-Teller effect in six-coordinate d9 Cu(II) complexes including elongated and compressed structures and the interveningbarrier height; the parameterization of Co(III) and Ni(II) species to enable both high- and low-spin complexes to betreated with a single parameter set; the unusual and highly distorted Type 1 center in blue copper' enzymes; anddinuclear species contg. the [Cu2O2]2+ moiety found in Type 3 copper enzymes and the important Cu-O π-bondingeffects. The LFMM has also spawned two approaches, the ligand field extension of the sum of interactions betweenfragments ab initio (SIBFA) model and an extension to the general utility lattice program (GULP). The former wasapplied to some simple Cu(II) species while the latter was applied to d4 Mn(III)-oxides. Both are limited to σ effects only.In addn., the related effective crystal field model of Tschougreeff is discussed and compared with the LFMM approach.Providing one is prepd. to develop the necessary parameters, the LFMM and related approaches are capable ofdelivering DFT-quality results but up to four orders of magnitude faster.~93 Citings

385. Pressure effect on Hg-12(n-1)n superconductors and Casimir effect in nanometer scale

By Orlando, M. T. D.; Belich, H.; Alves, L. J.; Passamai, J. L., Jr.; Pires, J. M.; Santos, E. M.; Rodrigues, V. A.; Costa-Soares, T.From Journal of Physics A: Mathematical and Theoretical (2009), 42(2), 025502/1-025502/7. Language: English,Database: CAPLUS, DOI:10.1088/1751-8113/42/2/025502

A description is presented for the Tc pressure-dependent behavior of Hg-12(n-1)n superconductors that takes intoaccount the Casimir effect by considering the CuO2 conducting layers to act as plasma sheets. The Casimir energyarises from the parallel plasma sheets (Cu-O planes) whenever these are sepd. by distances on the nanometer scale.The Tc pressure dependence in Hg-12(n-1)n superconductors can be described by a pressure-induced charge transfertogether with intrinsic terms that are assocd. with the Casimir energy. For Hg-12(n-1)n samples with optimum oxygencontent, the charge transfer term vanishes, leaving an explicit expression for the intrinsic term. By picking up realisticparameters and inserting them in the expression for the Tc pressure dependence, we have a good agreement with exptl.intrinsic term data obsd. in the mercury family Hg-12(n-1)n superconductors.~3 Citings

386. Historical overview and fundamental aspects of molecular catalysts for energy conversion

By Okada, T.; Abe, T.; Kaneko, M.From Springer Series in Materials Science (2009), 111(Molecular Catalysts for Energy Conversion), 1-36. Language:English, Database: CAPLUS

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A review. In this chapter we focus on the historical background of the electrocatalysts esp. of mol. catalysts that areconsidered as key technol. for energy conversion systems. The energy conversion is a basic process with whichhumans can utilize natural energy by converting into useful forms of energy such as heat, electricity, or other secondaryenergies. The most important process to be established in this century will be the usage of renewable energy, which hasleast impact on the global environment. The central technologies for this process will be solar cells, photosynthesis, andfuel cells. Hydrogen energy society would be the most probable choice interconnecting these technologies, and towardthis goal the establishment of efficient catalysts is indispensable. The designing of mol. catalysts is an important issuefor solving the energy conversion yields and efficiency. Through biomimetic approaches many good candidates ofcatalysts for energy conversion have been studied. Porphyrins from cytochrome analogs have been studied since late1960s as oxygen redn. center or oxygen carrier with variety of modifications. Also redn. of H+ is part of an artificialphotosynthesis, and many supra-mol. and hybrid complexes are studied since 1970s. The chapter starts with the historyand design concepts of oxygen redn. catalysts and fuel oxidn. catalysts in fuel cells, to cope with the control of multi-electron transfer reactions. The state-of-the-art mol. catalysts are characterized as metal-nitrogen ligand complex ormetal-nitrogen-oxygen conjugates on carbon support. Photochem. redn. of H+ is reviewed which is coupled to wateroxidn., where historically metallophthalocyanines or polypyridyl complexes are studied intensively since mid-1980s.Charge sepn. antenna chlorophylls are models of dye-sensitizers for photoreductive H2 evolution, and these areincorporated in Graetzel cell for electrochem. solar cells. Design and application of mol. catalysts for these cells arereviewed.~5 Citings

387. Effect of excess hydrogen on the electronic properties of passivated diamond

By Yan, C. X.; Dai, Y.; Long, R.; Jiang, H.; Huang, B. B.; Zhang, R. Q.; Zhang, W. J.; Bello, I.From Journal of Physics and Chemistry of Solids (2009), 70(2), 307-311. Language: English, Database: CAPLUS,DOI:10.1016/j.jpcs.2008.10.026

Recently, Yan et al. reported a theor. approach to overcome the n-type doping problem of diamond by passivating the Bacceptor and the redn. of ionization energy of dopants. Using the proposed approach, the authors have systemicallystudied the effect of excess H atoms on the electronic properties of a passivated system [diamond doped with (B+H)complex] based on the variation of Fermi level from 1st-principle calcns. The excess H atom is responsible for n-typebehavior when all valence electrons of substitutional B atom participate in the hybridization between substitutional B andH atoms. On the contrary, when part of valence electrons of the substitutional B atom participates in the hybridization, Hatoms make the passivated system show p-type or insulator behavior. Further the excess H atoms are more apt to makethe passivated system show p-type rather than n-type behavior under the same conditions. It leads to a much morecomprehensive understanding of the interaction between the excess H atoms and the passivated system compared withthat of Yan et al. The results may be useful to provide guidance for exptl. work on obtaining n-type diamond in the future.~3 Citings

388. Valence-Bond Order (VBO): A New Approach to Modeling Reactive Potential Energy Surfaces for ComplexSystems, Materials, and Nanoparticles

By Zhao, Meiyu; Iron, Mark A.; Staszewski, Przemyslaw; Schultz, Nathan E.; Valero, Rosendo; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2009), 5(3), 594-604. Language: English, Database: CAPLUS,DOI:10.1021/ct8004535

The extension of mol. mechanics to reactive systems, metals, and covalently bonded clusters with variable coordinationnos. requires new functional forms beyond those popular for org. chem. and biomols. Here we present a new scheme forreactive mol. mechanics, which is denoted as the valence-bond order model, for approximating reactive potential energysurfaces in large mols., clusters, nanoparticles, solids, and other condensed-phase materials, esp. those contg. metals.The model is motivated by a moment approxn. to tight binding MO theory, and we test how well one can approx. potentialenergy surfaces with a very simple functional form involving only interat. distances with no explicit dependence on bondangles or dihedral angles. For large systems the computational requirements scale linearly with system size, and nodiagonalizations or iterations are required; thus the method is well suited to large-scale simulations. The method isillustrated here by developing a force field for particles and solids composed of aluminum and hydrogen. The parameterswere optimized against both interaction energies and relative interaction energies. The method performs well for purealuminum clusters, nanoparticles, and bulk lattices and reasonably well for pure hydrogen clusters; the mean unsignederror per atom for the aluminum-hydrogen clusters is 0.1 eV/atom.~8 Citings

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389. Shallow donors in diamond: Be and Mg

By Yan, C. X.; Dai, Y.; Huang, B. B.; Long, R.; Guo, M.From Computational Materials Science (2009), 44(4), 1286-1290. Language: English, Database: CAPLUS,DOI:10.1016/j.commatsci.2008.08.017

The electronic properties of the impurities Be, Mg and the hydrogen complexes Be-H, Mg-H in diamond have beeninvestigated by first-principle calcns. It is found that the interstitial Be- or Mg- doped diamond are of n-type metal cond.character. Even at low impurity concn. the doped diamond also appears n-type behavior. The further results indicatethat the interstitial Be or Mg doping diamond should be synthesized at H-poor conditions to obtain the n-type materialbecause most of hydrogen atom may result in interstitial Be- and Mg- doped diamond p-type semiconductor or insulator.The substitutional Be and Mg show acceptor behaviors and may compensate other interstitial donors in -diamond. Ourresults are very helpful to the research of n-type doping in diamond for the future exptl. work.~3 Citings

390. Parameter Dependence in the Local Reaction Center Model for the Electrochemical Interface

By Zhang, Tianhou; Anderson, Alfred B.From Journal of Physical Chemistry C (2009), 113(8), 3197-3202. Language: English, Database: CAPLUS,DOI:10.1021/jp808948v

A systematic study of OH redn. to H2O in acid electrolyte on Pt and the reverse reaction was carried out in the localreaction center model approach using B3LYP and MP2 calcns. and basis sets with and without diffuse functions. Thecalcd. electrode-potential-dependent electron transfer activation energy curves have the same general shapes and arerobust toward shifts on the potential scale caused by changing the elec. field at the reaction center. This opens thepossibility of fixing a set of calcd. activation energy curves to a single datum known from expt. and then makingpredictions at other potentials.~12 Citings

391. Efficient global representations of potential energy functions: Trajectory calculations of bimolecular gas-phase reactions by multiconfiguration molecular mechanics

By Tishchenko, Oksana; Truhlar, Donald G.From Journal of Chemical Physics (2009), 130(2), 024105/1-024105/15. Language: English, Database: CAPLUS,DOI:10.1063/1.3042145

Multiconfiguration mol. mechanics (MCMM) was previously applied to calc. potential energies, gradients, and Hessiansalong a reaction path and in the large-curvature tunneling swath, and it was shown that one could calc. variationaltransition state theory rate consts. with optimized multidimensional tunneling without requiring more than a few electronicstructure Hessians. It was also used for mol. dynamics simulations of liq.-phase potentials of mean force as functions ofa reaction coordinate. In the present article we present some improvements to the formalism and also show that withthese improvements we can use the method for the harder problem of trajectory calcns. on gas-phase bimol. reactivecollisions. In particular, we apply the MCMM algorithm to the model reaction OH + H2 → H2O + H, for which weconstruct the global full-dimensional interpolated potential energy surfaces with various nos. of electronic structureHessians and various mol. mechanics force fields, and we assess the quality of these fits by quasiclassical trajectorycalcns. We demonstrate that chem. accuracy (1-2 kcal/mol) can be reached for a MCMM potential in dynamicallyimportant regions with a fairly small no. of electronic structure Hessians. We also discuss the origins of the errors in theinterpolated energies and a possible way to improve the accuracy. (c) 2009 American Institute of Physics.~2 Citings

392. Modeling electrocatalytic reaction systems from first principles

By Wasileski, Sally A.; Taylor, Christopher D.; Neurock, MatthewFrom Topics in Applied Physics (2009), 113(Device and Materials Modeling in PEM Fuel Cells), 551-574. Language:English, Database: CAPLUS, DOI:10.1007/978-0-387-78691-9_21

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A review. A survey dealing with the some of the advances in the development and application of ab initio methodstoward understanding the intrinsic reactivity of the metal and the influence of the reactive site and its environment,focussed on: (a) the chem. of the aq.-phase on transition metal surfaces and its influence on the kinetics and thermodn.within example reaction mechanisms, and (b) computational models of the electrode interface that are able to account fora referenced and tunable surface potential and the role of the surface potential in controlling electrocatalytic reactions,discussed in detail for an example reaction of importance to fuel cell electrocatalysis: methanol dehydrogenation overplatinum(111) interfaces.~10 Citings

393. Multi-scale modeling of CO oxidation on Pt-based electrocatalysts

By Saravanan, Chandra; Markovic, N. M.; Head-Gordon, M.; Ross, P. N.From Topics in Applied Physics (2009), 113(Device and Materials Modeling in PEM Fuel Cells), 533-549. Language:English, Database: CAPLUS, DOI:10.1007/978-0-387-78691-9_20

A review. A survey is given dealing with a hierarchical computational approach to describe macroscopic catalyticprocesses in fuel cells with the help of d. functional theory calcns. to obtain an atomistic view of reactions on Pt-based (Ptand PtRu) surfaces, followed by quantum chem. calcns. to develop a consistent coarse-grained lattice model, and kineticMonte Carlo simulations to study complex multi-step reaction kinetics on the electrode surfaces at much larger length-scales and time-scales compared to atomistic dimensions.~0 Citings

394. Reactivity of bimetallic nanoclusters toward the oxygen reduction in acid medium

By Balbuena, Perla B.; Wang, Yixuan; Lamas, Eduardo J.; Calvo, Sergio R.; Agapito, Luis A.; Seminario, Jorge M.From Topics in Applied Physics (2009), 113(Device and Materials Modeling in PEM Fuel Cells), 509-532. Language:English, Database: CAPLUS, DOI:10.1007/978-0-387-78691-9_19

A review. A survey is given dealing with the oxygen redn. mechanism on Pt(111) surfaces based on the Car-Parrinellomol. dynamics (CPMD) simulations, with emphasis on the effects of degree of proton solvation, proximity proton-mol.oxygen, and surface charge on the first step of the reaction, in relation to the catalyst/hydrated membrane interfacialstructure. The effect, that alloy catalyst ensembles may have on the first redn. step based on the d. functional theory(DFT) calcns. and other theor. and exptl. results is analyzed, the subsequent electron redn. steps, emphasizing thedifferences between the adsorption of intermediates, such as O, OH, and water, and the prodn., adsorption, and dissocn.of hydrogen peroxide, on Pt and Pt-alloy surfaces and clusters is discussed also the current status and perspectives forthe design of more efficient and less costly fuel cell electrocatalysts.~3 Citings

395. Double role of water in the fuel cell oxygen reduction reaction

By Ogasawara, H.; Naslund, L.-A.; MacNaughton, J. B.; Anniyev, T.; Nilsson, A.From ECS Transactions (2008), 16(2), 1385-1394. Language: English, Database: CAPLUS, DOI:10.1149/1.2981979

H2O is present during the normal operating condition of polymer electrolyte membrane fuel cells (PEMFCs) and theauthors have, through model expts. on a Pt surface using XPS, studied its role in 2 different stages in the O redn.reaction (ORR). The activation of O to the adsorbed at. phase occurs readily in the dry region, but not in the humidregion process. In this case, H2O is acting to inhibit the active sites on the catalyst. On the contrary, H2O is found topromote the redn. of adsorbed at. O in the formation of a H2O-hydroxyl surface complex.~10 Citings

396. Electron paramagnetic resonance of sulfur at a split-vacancy site in diamond

By Baker, J. M.; van Wyk, J. A.; Goss, J. P.; Briddon, P. R.From Physical Review B: Condensed Matter and Materials Physics (2008), 78(23), 235203/1-235203/9. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.78.235203

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In natural diamonds a sulfur-related paramagnetic center labeled W31 has been previously tentatively assigned to aninterstitial sulfur species in a pos. charge state. However, we show by combining an assessment of available exptl. dataand d.-functional simulations that the hyperfine tensors can be attributed to a defect made up from sulfur at the center ofa divacancy, the so-called split vacancy, in the neg. charge state. These acceptors are highly likely to be formed in S-implanted material and are a likely cause for high resistivity in material implanted with sulfur in the attempt to produce n-type conduction.~1 Citing

397. A general model for air-side proton exchange membrane fuel cell contamination

By Shi, Zheng; Song, Datong; Li, Hui; Fatih, Khalid; Tang, Yanghua; Zhang, Jianlu; Wang, Zhenwei; Wu, Shaohong;Liu, Zhong-Sheng; Wang, Haijiang; et alFrom Journal of Power Sources (2009), 186(2), 435-445. Language: English, Database: CAPLUS,DOI:10.1016/j.jpowsour.2008.10.029

This paper presents a general model for air-side feed stream contamination that has the capability of simulating bothtransient and steady-state performance of a PEM fuel cell in the presence of air-side feed stream impurities. The modelis developed based on the O redn. reaction mechanism, contaminant surface adsorption/desorption, and electrochem.reaction kinetics. The model is then applied to the study of air-side toluene contamination. Exptl. data for toluenecontamination at 4 current densities (0.2, 0.5, 0.75 and 1.0 A cm-2) and 3 contamination levels (1, 5 and 10 ppm) wereused to validate the model. It is expected that, with parameter adjustment, this model can also be used to predictperformance degrdn. caused by other air impurities such as N oxides (NOx) and S oxides (SOx).~14 Citings

398. Progress in Ab Initio QM/MM Free-Energy Simulations of Electrostatic Energies in Proteins: AcceleratedQM/MM Studies of pKa, Redox Reactions and Solvation Free Energies

By Kamerlin, Shina C. L.; Haranczyk, Maciej; Warshel, AriehFrom Journal of Physical Chemistry B (2009), 113(5), 1253-1272. Language: English, Database: CAPLUS,DOI:10.1021/jp8071712

A review. Hybrid quantum mech./mol. mech. (QM/MM) approaches have been used to provide a general scheme forchem. reactions in proteins. However, such approaches still present a major challenge to computational chemists, notonly because of the need for very large computer time in order to evaluate the QM energy but also because of the needfor proper computational sampling. This review focuses on the sampling issue in QM/MM evaluations of electrostaticenergies in proteins. We chose this example since electrostatic energies play a major role in controlling the function ofproteins and are key to the structure-function correlation of biol. mols. Thus, the correct treatment of electrostatics isessential for the accurate simulation of biol. systems. Although we will be presenting different types of QM/MM calcns. ofelectrostatic energies (and related properties) here, our focus will be on pKa calcns. This reflects the fact that pKa's ofionizable groups in proteins provide one of the most direct benchmarks for the accuracy of electrostatic models ofmacromols. While pKa calcns. by semimacroscopic models have given reasonable results in many cases, existingattempts to perform pKa calcns. using QM/MM-FEP have led to discrepancies between calcd. and exptl. values. In thiswork, we accelerate our QM/MM calcns. using an updated mean charge distribution and a classical ref. potential. Weexamine both a surface residue (Asp3) of the bovine pancreatic trypsin inhibitor and a residue buried in a hydrophobicpocket (Lys102) of the T4-lysozyme mutant. We demonstrate that, by using this approach, we are able to reproduce therelevant side chain pKa's with an accuracy of 3 kcal/mol. This is well within the 7 kcal/mol energy difference obsd. instudies of enzymic catalysis, and is thus sufficient accuracy to det. the main contributions to the catalytic energies ofenzymes. We also provide an overall perspective of the potential of QM/MM calcns. in general evaluations ofelectrostatic free energies, pointing out that our approach should provide a very powerful and accurate tool to predict theelectrostatics of not only soln. but also enzymic reactions, as well as the solvation free energies of even larger systems,such as nucleic acid bases incorporated into DNA.~193 Citings

399. First-Principles Analysis of the Initial Electroreduction Steps of Oxygen over Pt(111)

By Janik, Michael J.; Taylor, Christopher D.; Neurock, MatthewFrom Journal of the Electrochemical Society (2009), 156(1), B126-B135. Language: English, Database: CAPLUS,DOI:10.1149/1.3008005

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The sluggish kinetics assocd. with the oxygen redn. reaction (ORR) at the proton exchange membrane fuel cell cathodeleads to high overpotentials and limits fuel cell performance. Although significant progress was made in 1st-principlesmodeling of the ORR, the complexity of the electrified aq./metal interface has limited advances in the use of theory toelucidate the influence of electrode potential on the mechanism and kinetics. The 1st redn. step of adsorbed mol.oxygen was speculated to be the rate-detg. step in the ORR. Periodic d. functional theor. calcns. are carried out with thedouble-ref. method developed by J.S. Filhol and M, Neurock (2006) to det. the potential dependence of the reactionenergy and activation barrier for the redn. of O2 to OOH on the fully hydrated Pt(111) surface. This method allows fortuning the electrode potential with a slab representation of the electrode surface. Electron transfer is found to precedethe protonation of the adsorbed O2 mol., occurring with the proton formally residing as an H3O+ species connected to theadsorbed O2 mol. by H bonding through 2 addnl. H2O mols. The importance of the periodic representation of the metalelectronic structure and the inclusion of extended solvation in considering the elementary kinetics is discussed.~144 Citings

400. Quasi-classical trajectory calculations in asymmetrically substituted polyatomic systems of the type A +CX3Y → products: the H + CH3Cl hydrogen abstraction reaction channel

By Rangel, Cipriano; Corchado, Jose C.; Espinosa-Garcia, JoaquinFrom Physical Chemistry Chemical Physics (2008), 10(45), 6776-6786. Language: English, Database: CAPLUS,DOI:10.1039/b809999e

A state-to-state dynamics study was performed for the first time for asym. substituted reactions of the type H + CX3Y →products, and was applied to the H + CH3Cl gas-phase hydrogen abstraction reaction, analyzing the influence of CH3Clreactant vibrational stretching and bending excitations. Quasi-classical trajectory calcns. were performed on an anal.potential energy surface constructed previously by our group. The strong coupling between different vibrational modes inthe entry channel makes the reaction non-adiabatic and the reactant vibrational excitation increases the reactivity of thevibrational ground-state by factors of ≈ 2-3 depending on the excited mode. While the H2 and CH2Cl products appearwith similar moderate amts. of internal energy, about 25% of the total available energy, most of this energy appears astranslational energy, and the reactant vibrational excitation has little influence. The two products appear vibrationallycold, and in the case of the H2 product, also rotationally cold. The product angular distribution is predominantlysideways-backward, the sideways component increasing with the vibrational excitation of the H2 product. The reactantvibrational excitations have little effect on this behavior. Finally, comparison with theor. results for the analog H + CH4reaction shows that the dynamic behavior of the two reactions is similar, with the chlorine substituent effect being smallor negligible.~2 Citings

401. Modeling the electrified solid-liquid interface

By Rossmeisl, Jan; Skulason, Egill; Bjoerketun, Marten E.; Tripkovic, Vladimir; Norskov, Jens K.From Chemical Physics Letters (2008), 466(1-3), 68-71. Language: English, Database: CAPLUS,DOI:10.1016/j.cplett.2008.10.024

A detailed atomistic model based on d. functional theory calcns. is presented of the charged solid-electrolyte interface.Having protons solvated in a H2O bilayer outside a Pt(111) slab with excess electrons, the interface capacitance is welldescribed and the work function can be related directly to the potential scale of the normal hydrogen electrode. Alsofinite-size effects in common periodic slab-type calcns. can be avoided in calcns. of activation energies and reactionenergies for charge transfer reactions, where the authors use the Heyrovsky reaction for hydrogen oxidn. over a Pt(111)electrode as an example.~180 Citings

402. Regioselectivity preference of testosterone hydroxylation by cytochrome P450 3A4

By Zhang, Yan; Morisetti, Phani; Kim, Jeffery; Smith, Lynelle; Lin, HaiFrom Theoretical Chemistry Accounts (2008), 121(5-6), 313-319. Language: English, Database: CAPLUS,DOI:10.1007/s00214-008-0480-1

Theor. studies are presented into the exptl. obsd. regioselectivity difference of testosterone hydroxylation by cytochromeP 450 3A4 at the 1β, 2β, 6β, and 15β positions. Such regioselectivity is investigated by d. functional theory calcns. on amodel system. The barrier heights of hydrogen abstraction, which are cor. by zero-point vibrational energies, arecomputed to be about 10.1, 13.6, 14.4, and 16.2 kcal/mol for the 6β-, 2β-, 15β-, and 1β-positions, resp. The calcd.barriers suggest the regioselectivity preference of 6β » 2β >15β >1β, which is in good agreement with exptl. findings.

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~11 Citings

403. Thermal decomposition of metal complexes of type MLX2 (M = Co(II), Cu(II), Zn(II), and Cd(II); L = DIE; X =NO3-) by TG-DTA-DTG techniques in air atmosphere

By Arshad, Muhammad; Saeed-ur-Rehman; Qureshi, Ammad Hussain; Masud, Khalid; Arif, Muhammad; Saeed,Aamer; Ahmed, RiazFrom Turkish Journal of Chemistry (2008), 32(5), 593-604. Language: English, Database: CAPLUS

The nitrate complexes of transition metals with 1,2-bis(imidazolyl)ethane (DIE), M(DIE)(NO3)2, where M = Co(II), Cu(II),Zn(II), and Cd(II), were synthesized. The compns. of metal complexes and ligand were studied by elemental anal. toensure their purity and the structure elucidations were based on cond. measurements, room temp. magnetic momentstudies, 1H NMR, and electronic and IR spectra. The thermal behavior of these complexes possessing distortedtetrahedral geometry and their ligand was studied by thermoanal. techniques in static air atm. to det. their mode ofdecompn. and thermal stability. All these complexes and ligand show 2-step wt. loss upon heating to 740°, withsimultaneous loss of inorg. and org. fragments exhibiting almost the same mode of decompn. pattern. The residue afterheating >640° corresponded to metal oxide. There was no residue in the case of ligand. The compn. of intermediateand end products formed during degrdn. was confirmed by microanal. and IR spectroscopy. It follows from the resultsthat the thermal stability of the complexes increases in the following sequence: Co(II) < Cu(II) < Zn(II) < Cd(II).~7 Citings

404. Experimental and Theoretical Study of the Carbon-13 and Deuterium Kinetic Isotope Effects in the Cl andOH Reactions of CH3F

By Marinkovic, Marina; Gruber-Stadler, Margret; Nicovich, J. Michael; Soller, Raenell; Mulhauser, Max; Wine, Paul H.;Bache-Andreassen, Lihn; Nielsen, Claus J.From Journal of Physical Chemistry A (2008), 112(48), 12416-12429. Language: English, Database: CAPLUS,DOI:10.1021/jp807609d

A laser flash photolysis-resonance fluorescence technique has been employed to det. abs. rate coeffs. for the CH3F + Clreaction in N2 bath gas in the temp. range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to amodified Arrhenius expression k(T) = 1.14 × 10-12 × (T/298)2.26 exp-313/T. The OH and Cl reaction rates of 13CH3Fand CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 ± 2 K and 1013 ± 10 hPa inpurified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data fromthe HITRAN database and measured IR spectra as refs. The relative reaction rates defined by α = klight/kheavy were detd.to be kOH+CH3F/kOH+CD3F = 4.067 ± 0.018, kOH+CH3F/kOH+13CH3F = 1.067 ± 0.006, kCl+CH3F/kCl+CD3F = 5.11 ± 0.07, andkCl+CH3F/kCl+13CH3F = 1.016 ± 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions ofCH3F have been further investigated by quantum chem. methods and variational transition state theory.~8 Citings

405. Copper(II) oxalate obtained through the reaction of 1,2-ethanediol with Cu(NO3)2·3H2O. Structuralinvestigations and thermal analysis

By Birzescu, M.; Niculescu, M.; Dumitru, Raluca; Budrugeac, P.; Segal, E.From Journal of Thermal Analysis and Calorimetry (2008), 94(1), 297-303. Language: English, Database: CAPLUS,DOI:10.1007/s10973-007-8599-1

The paper presents the exptl. results of the structural studies and thermal anal. of copper(II) oxalate, a polynuclearcoordination compd., obtained by a new method, through the reaction of 1,2-ethanediol with Cu(NO3)2·3H2O. Thereaction between 1,2-ethanediol and Cu(NO3)2·3H2O occurs, under some working conditions, with the oxidn. of 1,2-ethanediol to the oxalate anion (L). The synthesized polynuclear coordination compd., [CuL·0.3H2O]n, was characterizedby chem. anal., electronic and vibrational spectra and thermal anal. The thermal properties of the polynuclearcoordination compd. were studied by TG, DTG and DSC. The obtained decompn. product is CuO. Powder XRD, IRspectroscopy and TEM were used to characterize the compn., the cryst. structure and the surface morphol. of the copperoxide obtained through thermolysis. The thermal conversion product, copper(II) oxide, has a microporous structure witha large specific area.~22 Citings

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406. Theoretical Study of Early Steps in Corrosion of Pt and Pt/Co Alloy Electrodes

By Tian, Feng; Anderson, Alfred B.From Journal of Physical Chemistry C (2008), 112(47), 18566-18571. Language: English, Database: CAPLUS,DOI:10.1021/jp807094m

Theor. studies of Pt and PtCo alloy electrode dissolns. in PEMFCs were made using adsorption energies from VASPslab band calcns. on the metal surfaces in a linear Gibbs energy relation. The reversible potential for Co-OH formationfrom oxidn. of H2O on the Pt3Co(111) surface is 0.50 V, which is significantly lower than the calcd. 0.70 V reversiblepotential for Pt-OH formation on the Pt(111) surface. Co(OH)2 formation from oxidn. of H2O on the Pt3Co(111) surfacewas calcd. to take place at a lower potential than Pt(OH)2 formation on the Pt(111) surface, with the resp. reversiblepotentials 0.58 and 1.92 V. These results for what may be the initial steps of anodic dissoln. indicate that Co will dissolveat lower potential than Pt in the alloy surface and leave behind a Pt surface skin when the potential is >∼0.50 V. Thereversible potential for OH formation on a step of edge atom on Pt(111) surface from oxidn. of H2O is 0.60 V, which is0.10 V lower than reversible potential on the terrace sites, which implies that edge atoms are removed 1st. The final stepof dissoln. is believed to be the hydrolysis of the Pt2+ hydroxide, which considering the small equil. const. reported byPourbaix, should proceed slowly.~17 Citings

407. Theoretical models for doping diamond for semiconductor applications

By Goss, J. P.; Eyre, R. J.; Briddon, P. R.From Physica Status Solidi B: Basic Solid State Physics (2008), 245(9), 1679-1700. Language: English, Database:CAPLUS, DOI:10.1002/pssb.200744115

A review. Diamond is a material with superlative properties in terms of carrier mobilities and device characteristics forhigh power electronics applications. Although p-type diamond is routinely available using boron, n-type material viaimpurity doping during the growth of diamond has historically been limited in success, partly because nitrogen is a hyper-deep donor, but compounded by the compact lattice leading to low solubilities for alternative species. Implantationdoping is often hampered by persistent residual damage leading to significant levels of compensation and the formationof dopant complexes with lattice vacancies. Expt. has been augmented by the application of quantum-chem. methods toassess the likely properties should specific impurities or impurity complexes be realisable in real materials. The reviewoutlines many of the doping strategies explored for diamond, including simple impurity doping and co-doping.~17 Citings

408. Development of a Finite-Temperature Density Functional Approach to Electrochemical Reactions

By Shiratori, Kazuya; Nobusada, KatsuyukiFrom Journal of Physical Chemistry A (2008), 112(42), 10681-10688. Language: English, Database: CAPLUS,DOI:10.1021/jp803923f

The authors present a computational method to calc. the electronic states of a mol. in an electrochem. environment. Themethod is based on the recently developed finite-temp. d. functional theory approach to calc. the electronic structures ata const. chem. potential. A solvent effect is treated at the level of the extended self-consistent reaction field model,which allows considering a nonequil. solvation effect. An exchange-correlation functional with a long-range correction isemployed in this calcn., because the functional is adjusted so that the deriv. discontinuity of energy with respect to a no.of electrons could be satisfied. The deriv. discontinuity condition plays a crucial role in an electrochem. system. Thecomputational results are presented for a reaction of NO+ + e- NO in chem. equil. Owing to the improvement in thesolvation effect and the exchange-correlation functional, the calcd. activation free energy is in good agreement with exptl.results.~10 Citings

409. VB/MM-The Validity of the Underlying Approximations

By Sharir-Ivry, Avital; Shurki, AvitalFrom Journal of Physical Chemistry B (2008), 112(39), 12491-12497. Language: English, Database: CAPLUS,DOI:10.1021/jp802667y

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Two recently developed methods VB/MM and d. embedded VB/MM (DE-VB/MM) are compared, and their resp.approxns. are examd. The two methods combine valence-bond (VB) calcns. with mol. mechanics (MM) and aim to allowVB anal. of reactions in large biol. environments. Furthermore, the two methods utilize two major approxns.-regardingboth the overlap and the reduced resonance integral between the various VB configurations. The difference between thetwo methods, however, is that VB/MM employs these approxns. for the overall interaction of the reacting fragments withtheir surrounding, whereas DE-VB/MM employs the approxns. only with regards to the van der Waals (VdW) interactionswhereas the electrostatic interactions are calcd. rigorously at the quantum level. The approxns. that lay the grounds forthe two methods involve the assumption that the overlap between the VB configurations and the resp. reducedresonance integral are both invariant to the environment. Similar approxns. are utilized in several other VB-basedQM/MM methods. However, although extensively used, these approxns. were never rigorously proved. Here, thedevelopment is exploited of the DE-VB/MM method to numerically examine the approxns. by calcg. the accurate as wellas the approximated values of overlap and reduced resonance integral for systems where the environment involves onlyelectrostatic interactions. The quality of the approxns. is examd. together with their effect on the abs. energies, the wavefunction, and the overall energetics. Three test cases are chosen, the dissocn. of CH3F and LiF and the identity SN2reaction. It is shown that the approxns. are usually good with the exception of cases where extreme changes areexpected in the wave function. Furthermore, the impact of the approxns. on the overall wave function and the overallenergetics is found to be quite small. It is concluded that VB/MM, where the approxns. are used more extensively, canserve as the first method of choice.~7 Citings

410. Theoretical study of migration processes in bulk diamond

By Butorac, B.; Mainwood, A.From Diamond and Related Materials (2008), 17(7-10), 1225-1228. Language: English, Database: CAPLUS,DOI:10.1016/j.diamond.2008.03.038

A large no. of complex defects are seen in natural and synthetic diamonds, but it is not known whether they form duringgrowth or as a result of later processes. An understanding of diffusion profiles of the dopant impurities is crucial fordesign of electronic devices. We present here theor. work on migration processes for several complexes including N, Hand vacancies in diamond, to find out how they form. First-principles d. functional calcns. have been performed to studystructural properties and the activation energies for migration of these defects. Migration paths were derived byconstructing a set of several intermediate structures between two energy min. by linear interpolation. The effect of temp.on calcd. barriers is described by including vibrational energy and entropy. It was found that the energy barrier formigration of interstitial hydrogen between two bond-centered positions is 2.8 eV. Also, hydrogen is readily trapped byboth vacancies and by the N-V complex. Energies liberated in these reactions are 5.5 eV and 5.8 eV resp.~6 Citings

411. Electrocatalyst theories based on local reaction center models, linear Gibbs energy relationships, and nowthe full Gibbs energies

By Anderson, Alfred B.From Preprints of Symposia - American Chemical Society, Division of Fuel Chemistry (2008), 53(2), 709-710.Language: English, Database: CAPLUS

It was demonstrated that free energy corrections, solvation, and surface charging contributions were all significant to theaccurate detn. of reversible potentials for the forming of intermediates on electrocatalyst surfaces. The effect of surfacecharging was relatively small, but it helped to understand the quant. successes of former studies.~0 Citings

412. Electrochemistry on the computer: Understanding how to tailor the metal overlayers for the oxygenreduction reaction

By Rossmeisl, J.; Norskov, J. K.From Surface Science (2008), 602(14), 2337-2338. Language: English, Database: CAPLUS,DOI:10.1016/j.susc.2008.05.015

~21 Citings

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413. Ligand Field Stabilization and Activation Energies Revisited: Molecular Modeling of the Thermodynamicand Kinetic Properties of Divalent, First-Row Aqua Complexes

By Deeth, Robert J.; Randell, KrisFrom Inorganic Chemistry (2008), 47(16), 7377-7388. Language: English, Database: CAPLUS, DOI:10.1021/ic800628j

Ligand Field Mol. Mechanics (LFMM) parameters have beendeveloped for the hexaaqua complexes of the divalent first rowmetals V2+ through to Zn2+. The LFMM parameters provide anexplicit description of the d electron stabilization energies andare tuned to reproduce both the exptl. structures and therelative energetics of the hexaaqua complexes in aq. soln. plusJohnson and Nelson's data (Inorg. Chem., 1995, 34, 5666-5671) for hypothetical complexes from which the ligand fieldstabilization energy has been removed. The LFMM calcns.automatically reveal the typical, strong Jahn-Teller distortionsof the d4 Cr(II) and d9 Cu(II) species plus the structurallysmaller, but still energetically significant, distortions of the d6

Fe(II) and d7 Co(II) complexes. The latter are largely mediatedvia M-O π interactions which are explicitly treated in the LFMMmethod via the Angular Overlap Model eπ parameter whichtreats the π interactions perpendicular to the ligand plane.Without further parameter modification, we then predict approx.reaction barriers for both associative and dissociative ligandexchange based on simplified model pathways. Thecorrelation between computed barrier heights and exptl.exchange rate consts. is generally excellent with the slowestreactions (involving V and Ni) having the largest barriers whilethe fastest reactions (Cu and Cr) have near zero barriers. Inagreement with expt., the LFMM model further confirms thatk(V) < k(Ni) and k(Co) < k(Fe) which contrasts with theclassical crystal field activation energy anal. of Basolo andPearson which predicts k(V) = k(Ni) and the reverse order ofreactivity for Fe and Co species. LFMM further predicts amechanistic changeover from an associatively activatedprocess at Mn to dissociatively activated exchange for Fe, Co,and Ni which is consistent with exptl. activation vols. andpreviously published high level quantum chem. calcns.

~22 Citings

414. A hierarchical construction scheme for accurate potential energy surface generation: An application to theF+H2 reaction

By Fu, Bina; Xu, Xin; Zhang, Dong H.From Journal of Chemical Physics (2008), 129(1), 011103/1-011103/4. Language: English, Database: CAPLUS,DOI:10.1063/1.2955729

We present a hierarchical construction scheme for accurate ab initio potential energy surface generation. The scheme isbased on the observation that when mol. configuration changes, the variation in the potential energy difference betweendifferent ab initio methods is much smaller than the variation for potential energy itself. This means that it is easier tonumerically represent energy difference to achieve a desired accuracy. Because the computational cost for ab initiocalcns. increases very rapidly with the accuracy, one can gain substantial saving in computational time by constructing ahigh accurate potential energy surface as a sum of a low accurate surface based on extensive ab initio data points andan energy difference surface for high and low accuracy ab initio methods based on much fewer data points. The newscheme was applied to construct an accurate ground potential energy surface for the FH2 system using the coupled-cluster method and a very large basis set. The constructed potential energy surface is found to be more accurate ondescribing the resonance states in the FH2 and FHD systems than the existing surfaces. (c) 2008 American Institute ofPhysics.~12 Citings

415. Electronic structure calculations of liquid-solid interfaces. Combination of density functional theory andmodified Poisson-Boltzmann theory

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By Jinnouchi, Ryosuke; Anderson, Alfred B.From Physical Review B: Condensed Matter and Materials Physics (2008), 77(24), 245417/1-245417/18. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.77.245417

A robust and efficient computational method for electronic structure calcns. of liq.-solid interfaces is presented. Thetheory employs the d. functional theory and a modified Poisson-Boltzmann theory, combining them through a smoothdielec. model function. The free energy, including electrostatic and nonelectrostatic interactions between solutes and thesolvation medium, is formulated, and its first derivs. with at. positions are presented. This methodol. is applied to 2different topics; one is the potential of zero charge (PZC) of Pt(111), and the other is a poisoning of active sites for the O-redn. reaction (ORR) by interfacial water mols. on Pt(111). The results of the first topic show that induced chargeredistributions caused by the adsorption of water mols. form a surface dipole moment that dominates the exptl. obsd.neg. shift in the PZC when Pt is immersed in an aq. electrolyte. The results of the second topic show the possibility of adecrease in the surface coverage of the first reaction precursor to the ORR due to site blocking by the adsorbed watermols.~55 Citings

416. Special catalytic systems: electrocatalysis: fundamental of electrocatalysis

By Krischer, Katharina; Savinova, Elena R.Edited By:Ertl, GerhardFrom Handbook of Heterogeneous Catalysis (2nd Edition) (2008), 4, 1873-1905. Language: English, Database:CAPLUS

A review. A survey dealing with some fundamental principles of electrocatalysis and discussing the electrocatalyticreactions that occur at hydrogen and oxygen electrodes in detail. Emphasis was put on those properties of theelectrochem. environment that introduce a qual. difference to heterogeneous reactions and also on the theor. foundationof phenomenol. approaches that are used in practice to judge the quality of an electrocatalytic material. The applicationof these methods was demonstrated and at the same time the large variety of exptl. methods was exemplified that areavailable to study the solid/liq. interface and the diversity of catalyst forms (ranging from single crystals to supportednanoparticles) and materials that may be used followed by parallels between heterogeneous catalysis andelectrocatalysis.~6 Citings

417. Some observations on the oxygen reduction reaction (ORR) at platinum catalysts based on post year 2000reports

By Gottesfeld, ShimshonFrom ECS Transactions (2008), 6(25, Electrochemistry of Novel Electrode Materials for Energy Conversion andStorage), 51-67. Language: English, Database: CAPLUS, DOI:10.1149/1.2943224

A review. This paper examines theor. and exptl. ORR work performed post year 2000, with the targets of reviewing newinsights and new advances and addressing remaining apparent disagreements on proper reading and interpretation ofnew theor. and exptl. ORR results. It is argued that the description of the ORR rate at a Pt, or Pt alloy catalyst in a fuelcell cathode, has to be relevant to the actual nature of the catalyst surface in the fuel cell-relevant potential range, i.e., aPt surface with potential dependent coverage by chemisorbed oxygen which blocks metal sites required for the ORR. Away to achieve this goal, is to express the pre-exponential factor in the rate expression in terms of the cathode potentialvs. E0 Pt-OH2/ Pt-OH, while the exponential factor remains a function of over-potential vs. E0 H2O/O2. It is further suggested,that the surface couple Pt-OH2 / Pt-OH, can be described as "redox mediator" for the ORR process at a Pt catalyst with apartially oxidized surface and, consequently, "ignition" of the ORR process at Pt may critically depend on the p.d. E- E0

Pt-OH2/Pt-OH.~24 Citings

418. A first-principles study of molecular oxygen dissociation at an electrode surface: a comparison of potentialvariation and coadsorption effects

By Wasileski, Sally A.; Janik, Michael J.From Physical Chemistry Chemical Physics (2008), 10(25), 3613-3627. Language: English, Database: CAPLUS,DOI:10.1039/b803157f

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Influences of coadsorbed Na and H2O, aq. solvent, and electrode potential on the kinetics of O2 dissocn. over Pt(111)are systematically studied using d. functional theory models of vacuum and electrochem. interfaces. Na coadsorptionalters the electronic states of Pt to stabilize the reactant (O2 *), transition, and (2O*) states by facilitating electron donationto oxygen, causing a more exothermic reaction energy (-0.84 eV for Na and O2, -0.81 eV for isolated O2) and a decreasein dissocn. barrier (0.39 eV for Na and O2, 0.57 eV for isolated O2). Solvation decreases the reaction energy (-0.67 eV)due to enhanced H bond stabilization of O2 * compared to 2O*. The influence of Na is less pronounced at the solvatedinterface (barrier decreases by only 0.11 eV) because H2O screens Na charge-donation. In the electrochem. modelsystem, the dissocn. energy becomes more exothermic and the barrier decreases toward more pos. potentials.Potential-dependent behavior results from changes in interfacial dipole moment and polarizability between O2 *, thedissocn. transition state, and 2O*; each are influenced by changes in adsorption and hydrogen bonding. Coadsorption ofNa in the solvated system dampens the dipole moment change between O2 * and 2O* and significantly increases thepolarizability at the dissocn. transition state and for 2O*; the combination causes little change in the reaction energy butreduces the activation barrier by 0.08 eV at 0 V vs. normal hydrogen electrode. The potential-dependent behaviorcontrasts that detd. at a const. surface charge or from an applied elec. field, illustrating the importance of considering theelectrochem. potential at the fully-solvated interface in detg. reaction energetics, even for nonredox reactions.~47 Citings

419. First-Principles Analysis of Oxygen-Containing Adsorbates Formed from the Electrochemical Discharge ofWater on Pt(111)

By Rai, V.; Aryanpour, M.; Pitsch, H.From Journal of Physical Chemistry C (2008), 112(26), 9760-9768. Language: English, Database: CAPLUS,DOI:10.1021/jp710811s

A combination of d. functional theory (DFT) calcns. and dynamic Monte Carlo (DMC) simulations was employed to studythe process of oxygen-contg. adsorbates formed from the electrochem. discharge of H2O on Pt(111) in acidicenvironment. Potential-dependent activation energy and rate coeffs., as input for DMC simulations, were obtained for theelectrochem. reactions and for use in DFT calcns. From DMC simulations, OHads is the dominant adsorbate between0.5-0.8 V, but >0.8 V OHads and Oads coexist. Ordered structures are found for OHads at 0.8 V and for Oads at 0.9 V.These results agree well with cyclic voltammetry and electrochem.-XPS measurements.~39 Citings

420. Thermal analysis of the cobalt(II) oxalate obtained through the reaction of 1,2-ethanediol withCo(NO3)2·6H2O

By Avram, Livia; Dumitru, RalucaFrom Annals of West University of Timisoara, Series of Chemistry (2007), 16(4), 7-10. Language: English, Database:CAPLUS

The paper presents the exptl. results of the thermal anal. of cobalt(II) oxalate, a homopolynuclear coordination compd.,obtained by a new method, through the reaction of 1,2-ethanediol with Co(NO3)2·6H2O. The reaction between 1,2-ethanediol and Co(NO3)2·6H2O occurs, under specific working conditions, with the oxidn. of 1,2-ethanediol to the oxalateanion (L). The thermal behavior of the synthesized homopolynuclear coordination compd., [CoL·2.5H2O]n, has beeninvestigated by non isothermal method (TG, DTG and DTA) under dynamic atm. aer and nitrogen. Cobalt oxide obtainedby thermal decompn. of this coordinative compd. was characterized by IR spectroscopy and x-ray diffraction (XRD).~1 Citing

421. Combined Electrostatically Embedded Multiconfiguration Molecular Mechanics and Molecular MechanicalMethod: Application to Molecular Dynamics Simulation of a Chemical Reaction in Aqueous Solution with HybridDensity Functional Theory

By Higashi, Masahiro; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2008), 4(7), 1032-1039. Language: English, Database: CAPLUS,DOI:10.1021/ct8000816

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We here combine the electrostatically embedded multiconfiguration mol. mechanics (EE-MCMM) method for generatingglobal potential energy surfaces in the presence of an electrostatic potential with mol. mechanics (MM). The resultingEE-MCMM/MM method is illustrated by applying it to carry out a mol. dynamics simulation for the sym. bimol. reaction Cl-+ CH3Cl' → ClCH3 + Cl'- in aq. soln. with hybrid d. functional theory as the quantum mech. level. The potential of meanforce is calcd., and the free energy barrier is found to be 25.3 kcal/mol, which is in good agreement with previous work.The advantage of the combined EE-MCMM and MM method is that the no. of quantum mech. calcns. required for theactive subsystem is very small compared to straight direct dynamics.~27 Citings

422. Theoretical study of the dynamics of the H + CH4 and H + C2H6 reactions using a specific-reaction-parameter semiempirical Hamiltonian

By Layfield, Joshua P.; Owens, Matthew D.; Troya, DiegoFrom Journal of Chemical Physics (2008), 128(19), 194302/1-194302/12. Language: English, Database: CAPLUS,DOI:10.1063/1.2918358

We present a theor. study of the reactions of hydrogen atoms with methane and ethane mols. and isotopomers. High-accuracy electronic-structure calcns. have been carried out to characterize representative regions of the potential-energysurface (PES) of various reaction pathways, including H abstraction and H exchange. These ab initio calcns. have beensubsequently employed to derive an improved set of parameters for the modified sym.-orthogonalized INDO (MSINDO)semiempirical Hamiltonian, which are specific to the H+alkane family of reactions. The specific-reaction-parameter(SRP) Hamiltonian has then been used to perform a quasiclassical-trajectory study of both the H + CH4 and H + C2H6reactions. The calcd. values of dynamics properties of the H + CH4 H2 + CH3 reaction and isotopologues, including alkylproduct speed distributions, diat. product internal-state distributions, and cross sections, are generally in good agreementwith expt. and with the results provided by the ZBB3 PES. The results of trajectories propagated with the SRPHamiltonian for the H+C2H6 H2 + C2H5 reaction also agree with expt. The level of agreement between the results calcd.with the SRP Hamiltonian and expt. in both the H + methane and H + ethane reactions indicates that semiempiricalHamiltonians can be improved for not only a specific reaction but also a family of reactions. (c) 2008 American Instituteof Physics.~9 Citings

423. Aqueous and Surface Redox Potentials from Self-Consistently Determined Gibbs Energies

By Jinnouchi, Ryosuke; Anderson, Alfred B.From Journal of Physical Chemistry C (2008), 112(24), 8747-8750. Language: English, Database: CAPLUS,DOI:10.1021/jp802627s

A self-consistent band theory was developed for electrochem.interfaces. The surface potential is adjustable by addingsurface charge, and a counter charge distribution in the doublelayer is detd. self-consistently using a modified Poisson-Boltzmann theory within a dielec. continuum model. Theauthors demonstrate a theory to predict, to useful accuracy, thereversible potentials for 34 acid or base aq. phase reactionsand 4 reactions that are key to understanding electrocatalysisby Pt in oxygen cathodes in fuel cells. The authors believe thistheory will find many applications.

~83 Citings

424. Mechanism of Molecular Oxygen Reduction at the Cathode of a PEM Fuel Cell: Non-ElectrochemicalReactions on Catalytic Pt Particles

By Walch, Stephen; Dhanda, Abhishek; Aryanpour, Masoud; Pitsch, HeinzFrom Journal of Physical Chemistry C (2008), 112(22), 8464-8475. Language: English, Database: CAPLUS,DOI:10.1021/jp7114127

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Various catalytic reactions in proton exchange membrane (PEM) fuel cells are discussed, and the effects of differentsteps, parallel pathways, and side reactions are analyzed for the oxygen redn. reaction mechanism. A suitablemechanism table is formulated for the prominent pathway of oxygen redn. reaction. The kinetics of the proposednonelectrochem. reactions on platinum surfaces are then studied using the B3LYP d. functional theory with the Wadt andHay relativistic effective core potentials and basis sets augmented with a 4f function on Pt. The reactions considered areO2(ads) ↔ O(ads) + O(ads) (1), O2H(ads) ↔ O(ads) + OH(ads) (2), H2O(ads) ↔ H(ads) + OH(ads) (3), OH(ads) + OH(ads) ↔ O(ads) +H2O(ads) (4), and OH(ads) + O(ads) ↔ O(ads) + OH(ads) (5). Calibration calcns. are carried out for reaction 1 on a single Ptatom using the CASSCF/MRCI method with a cc-pVDZ/relativistic effective core potential basis set for Pt and the aug-cc-pVDZ basis set for O. Comparison with B3LYP d. functional theory calcns. shows that the latter method overestimatesbinding energies by more than a factor of 2, but the barrier heights with respect to reactants are accurate. This result isconsistent with calcns. for the outer min. for mol. oxygen on Pt(111), where the computed binding energy is about afactor of 2 larger than what is found from expts. We find that, while a Pt2 cluster gives qual. correct results, the resultsare strongly influenced by cluster size effects, and inclusion of nearest neighbor atoms in at least the top and secondlayers is necessary for accurate energetics. The rates computed within the conventional transition state theory plus aWigner est. for tunneling using barriers obtained from the largest clusters show that the second, fourth, and fifth reactionsare most important on the surface of catalytic Pt particles. Solvation effects were investigated using a model consistingof cyclic (H2O)n structures and were found to be small.~38 Citings

425. Electrochemical kinetics and X-ray absorption spectroscopy investigations of select chalcogenideelectrocatalysts for oxygen reduction reaction applications

By Ziegelbauer, Joseph M.; Murthi, Vivek S.; O'Laoire, Cormac; Gulla, Andrea F.; Mukerjee, SanjeevFrom Electrochimica Acta (2008), 53(17), 5587-5596. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2008.02.091

Transition metal-based chalcogenide electrocatalysts exhibit a promising level of performance for O redn. reactionapplications while offering significant economic benefits over the state of the art Pt/C systems. The most active materialsare based on RuxSey clusters, but the toxicity of Se will most likely limit their embrace by the marketplace. S-basedanalogs do not suffer from toxicity issues, but suffer from substantially less activity and stability than their Se brethren.The structure/property relations that result in these properties are not understood due to ambiguities regarding thespecific morphologies of RuxSy-based chalcogenides. To clarify these properties, an electrochem. kinetics study wasinterpreted in light of extensive x-ray diffraction, SEM, and in situ x-ray absorption spectroscopy evaluations. Theperformance characteristics of ternary MxRuySz/C (M = Mo, Rh, or Re) chalcogenide electrocatalysts synthesized by thenow-std. low-temp. nonaq. (NA) route are compared to com. available (De Nora) Rh- and Ru-based systems.Interpretation of performance differences is made in regards to bulk and surface properties of these systems. Inparticular, the overall trends of the measured activation energies in respect to increasing overpotential and the grossenergy values can be explained in regards to these differences.~33 Citings

426. Electrical and photoelectrical characterization of undoped and S-doped nanocrystalline diamond films

By Kulkarni, P.; Porter, L. M.; Koeck, F. A. M.; Tang, Y.-J.; Nemanich, R. J.From Journal of Applied Physics (2008), 103(8), 084905/1-084905/8. Language: English, Database: CAPLUS,DOI:10.1063/1.2908884

Nanocryst. diamond (NCD) films are being intensively researched for a variety of potential applications, such as opticalwindows, electrochem. electrodes, and electron emitting surfaces for field emission displays. Zr, Ti, Cu, and Pt onintrinsic and lightly S-doped (n-type) NCD films were elec. and photoelec. characterized. Intrinsic and S-doped NCDfilms were synthesized on 1 in. diam. quartz and Si substrates by microwave plasma assisted CVD. All metals showedlinear (Ohmic) current-voltage characteristics in the as-deposited state. The Schottky barrier heights (ΦB) at the metal-film interface were investigated using x-ray and UV photoelectron spectroscopies. The undoped NCD films exhibited aneg. electron affinity and a band gap of 5.0±0.4 eV. The ΦB were calcd. based on this band gap measurement and theconsistent indication from Hall measurements that the films are n-type. The ΦB values were calcd. from shifts in thecore-level (C1s) peaks immediately obtained before and after in situ, successive metal depositions. The ΦB values forZr, Ti, and Pt on undoped films were calcd. to be 3.3, 3.2, and 3.7 eV, resp. The S-doped films also showed increasingΦB with metal work functions: 3.0, 3.1, and 3.4 eV for Zr, Ti, and Pt, resp. In general accordance with the barrier heighttrends, the specific contact resistivity (ρc) values increased with the metal work functions for both undoped and S-dopedfilms. For the undoped films ρc increased from 3 × 10-5 Ω cm2 for Zr to 6.4 × 10-3 Ω cm2 for Pt. The ρc values for the S-doped films were approx. two orders of magnitude lower than those for the undoped films: 3.5 × 10-7-4.5 × 10-5 Ω cm2 forZr and Pt, resp. The Hall-effect measurements indicated that the av. sheet resistivity and carrier concn. values were 0.16and 3.5 × 1018 cm-3 for the undoped films and 0.15 Ω cm and 4.9 × 1019 cm-3 for the S-doped films. (c) 2008 AmericanInstitute of Physics.

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~2 Citings

427. Catalytic aspects of oxygen reduction in metal corrosion

By Szabo, S.; Bakos, I.From Corrosion Reviews (2008), 26(1), 51-71. Language: English, Database: CAPLUS, DOI:10.1515/corrrev.2008.51

The most important cathodic process of metal corrosion is oxygen redn. This process, however, is a complicatedmultistep catalytic process. A well known catalytic oxygen activator is the acidic Fe3+/Fe2+ redox system. In the case ofrusting iron the Fe2+ ion contg. lepidocrocite is the catalytic activator of oxygen. There are many metal complexescapable of oxygen activation. They can help increasing metal corrosion rate.~3 Citings

428. Effect of Co doping on catalytic activity of small Pt clusters

By Kumar, T. J. Dhilip; Zhou, Chenggang; Cheng, Hansong; Forrey, Robert C.; Balakrishnan, N.From Journal of Chemical Physics (2008), 128(12), 124704/1-124704/11. Language: English, Database: CAPLUS,DOI:10.1063/1.2839437

Pt is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no Pt content is oneof the grand challenges in fuel cell research. The electronic structures of Pt4 and Pt3Co clusters and the adsorption ofH2, O2, and CO mols. on the 2 clusters were studied using DFT. H2 undergoes dissociative chemisorption on thetetrahedral clusters in head-on and side-on approaches to Pt centers. O2 dissocn. occurs primarily in 3- and 4-centercoordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O2 is higher for the Co-dopedcluster. For CO, the Pt-atop orientation is preferred for both Pt4 and Pt3Co tetrahedral clusters. Adsorption of CO mol.on tetrahedral Pt3Co for side-on approach leads to isomerization to planar rhombus geometry. An anal. of Hirshfeldcharge distribution shows that the clusters become more polarized after adsorption of the mols. (c) 2008 AmericanInstitute of Physics.~3 Citings

429. Bound substitutional impurity pairs in diamond: a density functional study

By Goss, J. P.; Eyre, R. J.; Briddon, P. R.From Journal of Physics: Condensed Matter (2008), 20(8), 085217/1-085217/9. Language: English, Database:CAPLUS, DOI:10.1088/0953-8984/20/8/085217

Substitutional nitrogen and boron are known to form nearest-neighbor pairs in diamond, leading to donor and acceptorlevels deep within the band-gap relative to the isolated counterparts. For n-type doping, even isolated nitrogen donorspossess very deep levels, and thus larger impurities are used. With species such as phosphorus and sulfur, elasticrepulsion might be expected to prevent donor aggregation seen for the smaller dopant species. However, we show fromd. functional simulations that large impurities can form addnl. chem. interactions when in close proximity, rendering themenergetically bound. These direct, localized interactions produce localized elec. levels deep in the band-gap, renderingthem inactive for elec. conduction, and possibly optically active. As a consequence, pairing of P, S and other species inheavily doped and/or high-temp. annealed material would impact upon elec. activation of dopants.~0 Citings

430. Calculating Reaction Rates with Partial Hessians: Validation of the Mobile Block Hessian Approach

By Ghysels, A.; Van Speybroeck, V.; Verstraelen, T.; Van Neck, D.; Waroquier, M.From Journal of Chemical Theory and Computation (2008), 4(4), 614-625. Language: English, Database: CAPLUS,DOI:10.1021/ct7002836

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In an earlier paper, the authors have developed a new method, the mobile block Hessian (MBH), to accurately calc.vibrational modes for partially optimized mol. structures. The proposed procedure remedies the artifact of imaginaryfrequencies, occurring in std. frequency calcns., when parts of the mol. system are optimized at different levels of theory.Frequencies are an essential ingredient in predicting reaction rate coeffs. due to their input in the vibrational partitionfunctions. The question arises whether the MBH method is able to describe the chem. reaction kinetics in an accurateway in large mol. systems where a full quantum chem. treatment at a reasonably high level of theory is unfeasible due tocomputational constraints. In this work, such a validation is tested in depth. The MBH method opens a lot ofperspectives in predicting accurate kinetic parameters in chem. reactions where the std. full Hessian procedure fails.~30 Citings

431. Hybrid quantum and classical methods for computing kinetic isotope effects of chemical reactions insolutions and in enzymes

By Gao, Jiali; Major, Dan T.; Fan, Yao; Lin, Yen-lin; Ma, Shuhua; Wong, Kin-YiuFrom Methods in Molecular Biology (Totowa, NJ, United States) (2008), 443(Molecular Modeling of Proteins), 37-62.Language: English, Database: CAPLUS

A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects areemphasized: 1) combined quantum mech. and mol. mech. methods are used to represent the potential energy surfacefor modeling bond forming and breaking processes, 2) instantaneous normal mode analyses are used to incorporatequantum vibrational free energies to the classical potential of mean force, and 3) multidimensional tunneling methods areused to est. quantum effects on the reaction coordinate motion. Centroid path integral simulations are described to makequantum corrections to the classical potential of mean force. In this method, the nuclear quantum vibrational andtunneling contributions are not separable. An integrated centroid path integral-free energy perturbation and umbrellasampling (PI-FEP/UM) method along with a bisection sampling procedure was summarized, which provides an accurate,easily convergent method for computing kinetic isotope effects for chem. reactions in soln. and in enzymes. In theensemble-averaged variational transition state theory with multidimensional tunneling (EA-VTST/MT), these threeaspects of quantum mech. effects can be individually treated, providing useful insights into the mechanism of enzymicreactions. These methods are illustrated by applications to a model process in the gas phase, the decarboxylationreaction of N-Me picolinate in water, and the proton abstraction and reprotonation process catalyzed by alanineracemase. These examples show that the incorporation of quantum mech. effects is essential for enzyme kineticssimulations.~4 Citings

432. Why did nature choose manganese to make oxygen?

By Armstrong, Fraser A.From Philosophical Transactions of the Royal Society, B: Biological Sciences (2008), 363(1494), 1263-1270.Language: English, Database: CAPLUS, DOI:10.1098/rstb.2007.2223

A review. This paper discusses the suitability of manganese for its function in catalyzing the formation of mol. oxygenfrom water. Manganese is an abundant element. In terms of its inherent properties, Mn has a particularly rich redoxchem. compared with other d-block elements, with several oxidizing states accessible. The most stable-state Mn2+

behaves like a Group 2 element-it is mobile, weakly complexing, easily taken up by cells and redox-inactive in simple aq.media. Only in the presence of suitable ligands does Mn2+ become oxidized, so it provides an uncomplicated buildingunit for the oxygen-evolving center (OEC). The intermediate oxidn. states Mn(III) and Mn(IV) are strongly complexed byO2- and form robust mixed-valence poly-oxo clusters in which the Mn(IV)/Mn(III) ratio can be elevated, one electron at atime, accumulating oxidizing potential and capacity. The OEC is a Mn4CaOx cluster that undergoes sequential oxidns. byP680+ at potentials above 1 V, ultimately to a super-oxidized level that includes one Mn(V) or a Mn(IV)-oxyl radical. Thelatter is powerfully oxidizing and provides the crucial 'power stroke' necessary to generate an O-O bond. This leaves acenter still rich in Mn(IV), ensuring a rapid follow-through to O2.~88 Citings

433. Formation of CO2 on a carbonaceous surface: a quantum chemical study

By Goumans, T. P. M.; Uppal, Madeeha A.; Brown, Wendy A.From Monthly Notices of the Royal Astronomical Society (2008), 384(3), 1158-1164. Language: English, Database:CAPLUS, DOI:10.1111/j.1365-2966.2007.12788.x

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The formation of CO2 in the gas phase and on a polyarom. hydrocarbon surface (coronene) via three possible pathwaysis investigated with d. functional theory. Calcns. show that the coronene surface catalyzes the formation of CO2 onmodel grain surfaces. The addn. of 3O to CO is activated by 2530 K in the gas phase. This barrier is lowered by 253 Kfor the Eley-Rideal mechanism and 952 K for the hot-atom mechanism on the surface of coronene. Alternative pathwaysfor the formation of CO2 are the addn. of 3O to the HCO radical, followed by dissocn. of the HCO2 intermediate. The O +HCO addn. is barrierless in the gas phase and on the surface and is more than sufficiently exothermic to subsequentlycleave the H-C bond. The third mechanism, OH + CO addn. followed by H removal from the energized HOCOintermediate, has a gas-phase exit barrier that is 1160 K lower than the entrance barrier. On the coronene surface,however, both barriers are almost equal. Because the HOCO intermediate can also be stabilized by energy dissipationto the surface, it is anticipated that for the surface reaction the adsorbed HOCO could be a long-lived intermediate. Inthis case, the stabilized HOCO intermediate could react, in a barrierless manner, with a hydrogen atom to form H2 +CO2, HCO2H, or H2O + CO.~48 Citings

434. Transport effects in the oxygen reduction reaction on nanostructured, planar glassy carbon supportedPt/GC model electrodes

By Schneider, A.; Colmenares, L.; Seidel, Y. E.; Jusys, Z.; Wickman, B.; Kasemo, B.; Behm, R. J.From Physical Chemistry Chemical Physics (2008), 10(14), 1931-1943. Language: English, Database: CAPLUS,DOI:10.1039/b719775f

The role of transport and re-adsorption processes on the oxygen redn. reaction (ORR), and in particular on its selectivitywas studied using nanostructured model electrodes consisting of arrays of Pt nanostructures of well-defined size andsepn. on a planar glassy C (GC) substrate. The electrochem. measurements were performed under controlled transportconditions in a double-disk electrode thin-layer flow-cell configuration; the model electrodes were fabricated by colloidallithog. techniques, yielding Pt nanostructures of well defined and controlled size and d. (diam.: 140 or 85 nm, height: 20or 10 nm, sepn.: from 1-2 to >10 diams.). The nanostructured model electrodes were characterized by SEM andelectrochem. probing of the active surface area (via the hydrogen adsorption charge). The electrocatalyticmeasurements revealed a pronounced variation of the H2O2 yield, which increases by up to 2 orders of magnitude withincreasing sepn. and decreasing size of the Pt nanostructures. Similar, though less pronounced effects were obsd. uponvarying the electrolyte flow and thus the mass transport characteristics. These effects are discussed in a reaction modelwhich includes (i) direct redn. to H2O on the Pt surface and (ii) addnl. H2O2 formation and desorption on both Pt and Csurfaces and subsequent partial re-adsorption and further redn. of the H2O2 mols. on the Pt surface.~109 Citings

435. Electrostatically Embedded Multiconfiguration Molecular Mechanics Based on the Combined DensityFunctional and Molecular Mechanical Method

By Higashi, Masahiro; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2008), 4(5), 790-803. Language: English, Database: CAPLUS,DOI:10.1021/ct800004y

We present a new method for generating global or semiglobal potential energy surfaces in the presence of anelectrostatic potential; the new method can be used to model chem. reactions in soln. or in an enzyme, nanocavity, orother chem. environment. The method extends the multiconfiguration mol. mechanics method so that the energydepends on the electrostatic potential at each at. center. The charge distribution of the system can also be calcd. Weillustrate the method by applying it to the sym. bimol. reaction Cl- + CH3Cl' → ClCH3 + Cl'- in aq. soln., where thepotential energy information is obtained by the combined d. functional and mol. mech. method, i.e., by the combinedquantum mech. and mol. mech. method (QM/MM) with the QM level being d. functional theory. It is found that we candescribe a semiglobal potential energy surface in aq. soln. with electronic structure information obtained entirely in thegas phase, including the linear and quadratic responses to variations in the electrostatic potential distribution. Thesemiglobal potential energy surface calcd. by the present method is in good agreement with that calcd. directly withoutany fitting.~50 Citings

436. Reinforced Membrane Durability in Proton Exchange Membrane Fuel Cell Stacks for AutomotiveApplications

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By Ralph, T. R.; Barnwell, D. E.; Bouwman, P. J.; Hodgkinson, A. J.; Petch, M. I.; Pollington, M.From Journal of the Electrochemical Society (2008), 155(4), B411-B422. Language: English, Database: CAPLUS,DOI:10.1149/1.2838163

A key requirement for automotive proton exchange membrane fuel cell stacks is improved performance and durability.High-performance can be delivered using perfluorosulfonic acid (PFSA) membranes that are thin (30 µm) and have lowequiv. wt. (920). Initial durability in a single cell confirmed edge protection films prevent premature membrane electrodeassembly (MEA) failure. This allowed the true MEA durability to be assessed in 30-cell stacks. Based on phys. leaktests and open-circuit voltage (OCV) decay rates a Johnson Matthey Fuel Cells (JMFC) reinforced membrane provided a6-fold improvement in durability compared to com. available nonreinforced membranes. The improved durability isascribed to increased dimensional stability during hydration/dehydration and an improved resistance to tear propagation.The com. membranes fail mech., accelerated by chem. attack of the ionomer. The reinforced membrane is mech. robustand fails due to removal of the PFSA ionomer from the reinforcement by chem. attack. Accelerated OCV hold tests withhydrocarbon membranes confirmed the chem. attack was from the radicals generated by H2 and O2 gas crossoverthrough the membrane. Adding a H2O2 decompn. catalyst to the JMFC reinforced membrane significantly extended themembrane lifetime at OCV, suggesting H2O2 was the major source of the damaging radicals. The automotive durabilitytarget of 5500 h should be achievable using the JMFC reinforced membrane contg. the H2O2 decompn. catalyst.~18 Citings

437. Characterization of Ligand Effects on Water Activation in Triarylphosphine-Stabilized Pt NanoparticleCatalysts by X-ray Absorption Spectroscopy

By Gatewood, Daniel S.; Schull, Terence L.; Baturina, Olga; Pietron, Jeremy J.; Garsany, Yannick; Swider-Lyons,Karen E.; Ramaker, David E.From Journal of Physical Chemistry C (2008), 112(13), 4961-4970. Language: English, Database: CAPLUS,DOI:10.1021/jp709588c

The synthesis, prepn., and electrochem. characterization of triphenylphosphinetriphosphonic acid (TPPTP) stabilized Ptparticles were reported previously with the observation that the TPPTP ligands increase the specific activity of Pt for theoxygen redn. reaction (ORR). The ORR activity of the Pt/TPPTP electrocatalyst is probed by analyzing H2O activationwith Pt L3-edge x-ray absorption spectroscopy and the EXAFS and Delta XANES anal. techniques. The results arecompared with that for similarly prepd. Pt/C and Pt stabilized by an oxidized TPPTP ligand (Pt/ox-TPPTP). The Ptparticles in the Pt/TPPTP catalyst at 0.54 V (RHE) are complexed via the P (i.e., Pt-P<tp) with ∼0.3 ML of TPPTP.Approx. 1/2 of this converts to a Pt-O-P<tp linkage at 1.0 V; these species exist on the surface along with a dramaticallyreduced OH coverage. The redn. in OH coverage enhances the surface-specific (ORR) rate relative to the same-sizedPt particles on C. The Pt/ox-TPPTP catalysts are linked via a 3-fold coordinated Pt≡O-P<tp, which severely blocks sitesand makes the electrocatalysts almost inactive to H2O activation and the ORR. The relative importance of site blocking,hydrophobic effects, and electronic effects are discussed with hydrophobic effects believed to dominate in the Pt/TPPTPcatalyst and site blocking in the Pt/ox-TPPTP catalyst.~24 Citings

438. Microsolvation of Hydrogen Sulfide: Exploration of H2S·(H2O)n and SH-·H3O+·(H2O)n-1 (n = 5-7) ClusterStructures on Ab Initio Potential Energy Surfaces by the Scaled Hypersphere Search Method

By Maeda, Satoshi; Ohno, KoichiFrom Journal of Physical Chemistry A (2008), 112(13), 2962-2968. Language: English, Database: CAPLUS,DOI:10.1021/jp710494n

The scaled hypersphere search method was applied to ab initio potential energy surfaces of the H2S·(H2O)n/SH-

·H3O+·(H2O)n-1 system with n = 5-7. Local min. databases including 121, 326, and 553 structures for n = 5-7, resp., wereobtained based on calcns. at the MP2/6-311++G(3df,2p)//B3LYP/6-31+G** level. In these small cluster sizes, the SH-

·H3O+·(H2O)n-1 type is still unstable relative to the H2S·(H2O)n type, and the global min. for H2S·(H2O)n are very similar tothose of pure water clusters of (H2O)n+1. Thermodn. simulations based on the present databases showed a structuretransition from the well-mixed (H2O)n+1-like global min. at low temps. to unmixed complexes between H2S and (H2O)n athigh temps.~24 Citings

439. Shape-controlled fabrication of platinum electrocatalyst by pulse electrodeposition

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By Ye, Feng; Chen, Ling; Li, Jingjing; Li, Jianling; Wang, XindongFrom Electrochemistry Communications (2008), 10(3), 476-479. Language: English, Database: CAPLUS,DOI:10.1016/j.elecom.2008.01.011

Platinum catalysts were pulse electrodeposited on carbon black/Nafion substrates in solns. with or without shape-controlagents such as polyethylene glycol (PEG-10000) or lead (II) acetate (LA). The SEM and electrochem. measurementsshowed that the morphol., microstructure and electrocatalytic activities of the platinum deposits changed by usingdifferent additives. The morphol. of Pt evolved from spherical clusters to clump-like crystal aggregations and elongatedleaf-like flake clusters by using PEG-10000 and LA, resp. For the Pt catalyst deposited by introducing PEG-10000, itsactive surface area and electrocatalytic activities towards methanol electro-oxidn. and oxygen electro-redn. wereremarkably improved. The possible mechanism for the change of the morphol. has been preliminarily discussed.~33 Citings

440. Photosynthetic water splitting

By Messinger, Johannes; Renger, GernotFrom Comprehensive Series in Photochemical & Photobiological Sciences (2008), 9(Primary Processes ofPhotosynthesis, Part 2), 291-349. Language: English, Database: CAPLUS

A review. This chapter reviews our current state of knowledge on the structure and functional pattern of the wateroxidizing complex (WOC) in photosynthesis. The reactions leading to oxidative water splitting into mol. oxygen and fourprotons take place at a multimeric metal center, the Mn4OxCa cluster (x symbolizes the no. of oxobridges). The overallprocess consists of a reaction sequence of four oxidn. steps (Kok cycle), which is energetically driven by the stronglyoxidizing cation radical P680+· with tyrosine YZ acting as intermediary redox carrier. The energetics and kinetics of thesereactions are described. Based on the Kok-scheme as a fingerprint for the interpretation of spectroscopic data,information is obtained on the electronic configuration and nuclear geometry of the different redox states Si, in particularon the valence states and the distances between the metal centers. Furthermore, the exchange kinetics of substratewater in the Si states are presented. The transitions S0 → S1 and S1 → S2 are shown to be metal-centered redox steps,while S2 → S3 is favored to be a ligand-centered reaction. The redox states S3 and/or S3YZ OX could comprise redoxisomerism and tautomerism equil. Finally, we attempt to cast our current knowledge about photosynthetic water splittinginto a mechanism.~55 Citings

441. Theoretical rate constants and kinetic isotope effects in the reaction of methane with H, D, T, and Mu atoms

By Espinosa-Garcia, J.From Physical Chemistry Chemical Physics (2008), 10(9), 1277-1284. Language: English, Database: CAPLUS,DOI:10.1039/b714489j

The rate consts. and kinetic isotope effects of the reaction of methane with four isotopes of hydrogen, protium (H),deuterium (D), tritium (T), and muonium (Mu), were studied using variational transition state theory with multidimensionaltunneling on an anal. potential energy surface, PES-2002, previously constructed by our group. For the four isotopes,our kinetics results agree reasonably with available exptl. measurements, improving previous theor. results that useddifferent potential energy surfaces and/or theor. approaches. In the comparison of the reactivity between protium andmuonium, which is the most severe test of the surface and theor. method due to the large mass difference between thetwo isotopes, some sources of discrepancy between theory and expt. were analyzed. These were the zero-point energy,tunneling effect, and the role of the reactivity from methane excited vibrational states.~19 Citings

442. Density Embedded VB/MM: A Hybrid ab Initio VB/MM with Electrostatic Embedding

By Sharir-Ivry, Avital; Crown, Hadar A.; Wu, Wei; Shurki, AvitalFrom Journal of Physical Chemistry A (2008), 112(11), 2489-2496. Language: English, Database: CAPLUS,DOI:10.1021/jp710395b

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A hybrid QM/MM method that combines ab initio valence-bond (VB) with mol. mechanics (MM) is presented. Themethod utilizes the ab initio VB approach to describe the reactive fragments and MM to describe the environment thusallows VB calcns. of reactions in large biol. systems. The method, termed d. embedded VB/MM (DE-VB/MM), is anextension of the recently developed VB/MM method. It involves calcn. of the electrostatic interaction between thereactive fragments and their environment using the electrostatic embedding scheme. Namely, the electrostaticinteractions are represented as one-electron integrals in the ab initio VB Hamiltonian, hence taking into account the wavefunction polarization of the reactive fragments due to the environment. Moreover, the assumptions that were utilized inan earlier version of the method, VB/MM, to formulate the electrostatic interactions effect on the off-diagonal matrixelements are no longer required in the DE-VB/MM methodol. Using DE-VB/MM, one can calc., in addn. to the adiabaticground state reaction profile, the energy of the diabatic VB configurations as well as the VB state correlation diagram forthe reaction. The abilities of the method are exemplified on the identity SN2 reaction of a chloride anion with Me chloridein aq. soln. Both the VB configurations diagram and the state correlation diagram are presented. The results are shownto be in very good agreement with both exptl. and other computational data, suggesting that DE-VB/MM is a propermethod for application to different reactivity problems in biol. systems.~15 Citings

443. MPSA effects on copper electrodeposition investigated by molecular dynamics simulations

By Guymon, Clint G.; Harb, John N.; Rowley, Richard L.; Wheeler, Dean R.From Journal of Chemical Physics (2008), 128(4), 044717/1-044717/12. Language: English, Database: CAPLUS,DOI:10.1063/1.2824928

In superconformal filling of Cu-chip interconnects, org. additives are used to fill high-aspect-ratio trenches or vias fromthe bottom up. The authors report on the development of intermol. potentials and use mol. dynamics simulations toprovide insight into the mol. function of an org. additive (3-mercaptopropanesulfonic acid or MPSA) important insuperconformal electrodeposition. The authors also study how the presence of NaCl affects the surface adsorption andsurface action of MPSA as well as the charge distribution in the system. NaCl addn. decreases the adsorption strengthof MPSA at a simulated Cu surface and attenuates the Cu-ion assocn. with MPSA. The model also was used to simulateinduced-charge effects and adsorption on a nonplanar electrode surface. (c) 2008 American Institute of Physics.~2 Citings

444. An algorithm for mass matrix calculation of internally constrained molecular geometries

By Aryanpour, Masoud; Dhanda, Abhishek; Pitsch, HeinzFrom Journal of Chemical Physics (2008), 128(4), 044113/1-044113/8. Language: English, Database: CAPLUS,DOI:10.1063/1.2827489

Dynamic models for mol. systems require the detn. of corresponding mass matrix. For constrained geometries, thesecomputations are often not trivial but need special considerations. Here, assembling the mass matrix of internallyconstrained mol. structures is formulated as an optimization problem. Anal. expressions are derived for the soln. of thedifferent possible cases depending on the rank of the constraint matrix. Geometrical interpretations are further used toenhance the soln. concept. As an application, we evaluate the mass matrix for a constrained mol. undergoing anelectron-transfer reaction. The preexponential factor for this reaction is computed based on the harmonic model. (c)2008 American Institute of Physics.~0 Citings

445. Hydrogen peroxide formation rates in a PEMFC anode and cathode. Effect of humidity and temperature

By Sethuraman, Vijay A.; Weidner, John W.; Haug, Andrew T.; Motupally, Sathya; Protsailo, Lesia V.From Journal of the Electrochemical Society (2007), 155(1), B50-B57. Language: English, Database: CAPLUS,DOI:10.1149/1.2801980

Hydrogen peroxide formation rates in a proton exchange membrane fuel cell (PEMFC) anode and cathode were estd. asa function of humidity and temp. by studying the oxygen redn. reaction on a rotating ring-disk electrode. Fuel cellconditions were replicated by depositing a film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temp.,dissolved O2 concn., and the acidity levels in HClO4. The HClO4 acidity was correlated to ionomer water activity andhence fuel cell humidity. The H2O2 formation rates showed a linear dependence on oxygen concn. and squaredependence on water activity. The H2O2 selectivity in oxygen redn. reaction was independent of oxygen concn. butincreased with the decrease in water activity (i.e., decreased humidity). Potential dependent activation energy for theH2O2 formation reaction was estd. from data obtained at different temps.

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~89 Citings

446. The Carbene Reactivity Surface: A Classification

By Mieusset, Jean-Luc; Brinker, Udo H.From Journal of Organic Chemistry (2008), 73(4), 1553-1558. Language: English, Database: CAPLUS,DOI:10.1021/jo7026118

A new two-dimensional classification of singlet carbenes basedon the difference in reactivity of their insertion reactions into theC-H bonds of acetonitrile and isobutane is presented. Thisclassification combines the stability and the philicity of divalentspecies. Until now all of the exptl. based philicity scales arebased on the addn. to alkenes. Also, a new terminol. fordescribing the reactivity of carbenes is introduced. Among thealkyl carbenes, acetyl carbene (2) and cyclopentadienylideneare shown as highly reactive electrophilic carbenes, whereasthe other alkylidenes and alkenylidenes studied are all lessactive than 2 and more nucleophilic. The stabilized-nucleophilic bicyclo[2.1.1]hex-2-en-5-ylidene (13) possesses astability similar to that of cyclic alkyl amino carbene (CAAC) Iand aminophosphoniocarbene, Me2(Me3P)C:. Stronghydrogen bridging is found between a C-H bond of acetonitrileand the nucleophilic carbenes 13 and II.

~36 Citings

447. Empirical valence bond models for reactive potential energy surfaces. II. Intramolecular proton transfer inpyridone and the Claisen reaction of allyl vinyl ether

By Sonnenberg, Jason L.; Schlegel, H. BernhardFrom Molecular Physics (2007), 105(19-22), 2719-2729. Language: English, Database: CAPLUS,DOI:10.1080/00268970701622277

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Empirical valence bond (EVB) surfaces have been constructed for 2-pyridone-2-hydroxypyridine proton transfer and forthe Claisen rearrangement of allyl vinyl ether at the MP2/6-311 + G(d,p) level of theory. A distributed Gaussian approachis used to approx. the interaction matrix elements. Parameters for the distributed Gaussians are detd. by fitting toenergy, gradient and Hessian data obtained from ab initio electronic structure calcns. at one to nine points along thereaction path. An efficient DIIS (direct inversion of iterative subspace) method is used to solve the fitting equations.Criteria for choosing internal coordinates for the representation of the potential energy surfaces and for the interactionmatrix element are discussed. Practical techniques for detg. the placement and exponents of the Gaussians aredescribed. With one set of s-, p- and d-type Gaussians at the transition state, the error in the energy along the reactionpath is less than 10 kJ mol-1 for pyridone tautomerization. Five sets of Gaussians reduces the error to less than 5 kJmol-1 and seven Gaussians drops the error below 1 kJ mol-1. The Claisen rearrangement is more challenging andrequires seven Gaussians to achieve an error of less than 4 kJ mol-1 for energies along the reaction path.~9 Citings

448. A mechanistic approach to elucidate ethanol electro-oxidation

By Tapan, Niyazi AlperFrom Turkish Journal of Chemistry (2007), 31(5), 427-443. Language: English, Database: CAPLUS

In order to elucidate the mechanism of ethanol oxidn., a simple cylindrical diffusion-surface reaction was developed on aplatinum disk electrode. An ethanol electro-oxidn. mechanism was proposed, in which electrochem. reactions proceedwithout adsorption of any electro-oxidn. products (C2 type) on the surface. After the simulation of the proposedmechanism, it was seen that the model can explain ethanol electro-oxidn. behavior without any surface CO formation.The simulation of the mechanism indicated that the formation of acetaldehyde through the oxidn. of bulk ethanol is therate detg. step between 0.6 and 0.75 V vs. RHE, the formation of surface acetate through bulk ethanol becomes the ratedetg. step. According to the proposed oxidn. model, around 0.7 V vs. RHE, acetaldehyde coverage becomes the majorsurface species, and acetate formation starts around 0.7 V vs. RHE. Surface species profiles of the proposed modelshow that C2 type species play an important role in ethanol electro-oxidn.~7 Citings

449. Canonical Variational Transition-State Theory Study of the CF3CH2CH3 + OH Reaction

By Gonzalez-Lafont, Angels; Lluch, Jose M.; Varela-Alvarez, Adrian; Sordo, Jose A.From Journal of Physical Chemistry B (2008), 112(2), 328-335. Language: English, Database: CAPLUS,DOI:10.1021/jp075298v

Variational transition-state theory rate consts. with multidimensional tunneling contributions using the small curvaturemethod have been calcd. for the CF3CH2CH3 (HFC-263fb) + OH reaction over a temp. range from 200 to 373 K. ThemPW1B95-41.0 hybrid functional, parametrized by Albu and Swaminathan to generate theor. rate consts. nearly identicalto the exptl. values for the CH3F + OH reaction, has been used in conjunction with the 6-31+G** basis set to explore thepotential energy surface of the title reaction. The good agreement found between theor. predictions and the exptl. dataavailable suggests that the present approach is an excellent option to obtain high-quality results at low computationalcost for direct dynamics studies of hydrogen abstraction reactions from complex hydrofluorocarbons. The reliability ofthe structure activity relationship used to est. rate const. values for OH reactions with hydrofluorocarbons is alsodiscussed in detail.~17 Citings

450. Double-trap kinetic equation for the oxygen reduction reaction on Pt(111) in acidic media

By Wang, Jia X.; Zhang, Junliang; Adzic, Radoslav R.From Journal of Physical Chemistry A (2007), 111(49), 12702-12710. Language: English, Database: CAPLUS,DOI:10.1021/jp076104e

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The authors derived an intrinsic kinetic equation for the 4-electron oxygen redn. reaction (ORR) in acidic media usingfree energies of activation and adsorption as the kinetic parameters. The kinetic model consists of 4 essentialelementary reactions: a dissociative adsorption (DA) and a reductive adsorption (RA), which yield 2 reactionintermediates, O and OH; a reductive transition (RT) from O to OH; and a reductive desorption (RD) of OH. Analyticexpressions were found for the O and OH adsorption isotherms by solving the steady-state rate equations. For the ORRon Pt(111) in 0.1M HClO4 soln., the authors analyzed the measured polarization curves, thereby deducing activation freeenergies that are consistent with the values from theor. calcns. The reductive adsorption (∆G*0 RA = 0.46 eV) is not therate-detg. step (RDS) for the ORR on Pt because dissociative adsorption (∆G*0 DA = 0.26 eV) offers a more favorablepathway at high potentials. It, however, generates strongly adsorbed O. The high activation barriers for the O to OHtransition (∆G*0 RT = 0.50 eV) and OH desorption (∆G*0 RD = 0.45 eV) cause a large potential loss for the desorption-limited ORR. As the OH coverage increases to a const. value with decreasing potential, the Tafel slope increases to thevalue detd. by a sym. electron-transfer coeff. The authors discuss the role of adsorption isotherm in kinetic anal. and, viaactivity-and-barrier plots, illustrate why the RDS may vary with reaction conditions or may not exist. Recognizing suchfeatures of electrocatalytic reactions can facilitate reaching the long-standing goal of quant. descriptions and predictionsof electrocatalysts' activities.~125 Citings

451. Coherent proton tunneling in hydrogen bonds of isolated molecules: malonaldehyde and tropolone

By Redington, Richard L.Edited By:Hynes, James TFrom Hydrogen-Transfer Reactions (2007), 1, 3-31. Language: English, Database: CAPLUS,DOI:10.1002/9783527611546.ch1

A review.~11 Citings

452. Variational transition state theory in the treatment of hydrogen transfer reactions

By Truhlar, Donald G.; Garrett, Bruce C.Edited By:Hynes, James TFrom Hydrogen-Transfer Reactions (2007), 2, 833-874. Language: English, Database: CAPLUS,DOI:10.1002/9783527611546.ch27

A review on variational transition state theory, with a focus on how quantum mech. effects are incorporated. Examples ofH-transfer reactions are given to illustrate the concepts and to highlight special considerations or procedures required indifferent cases. The examples span the range from simple gas-phase hydrogen atom transfer reactions (triat. to polyat.systems), to solid-state and liq.-phase reactions, including complex reactions in biomol. enzyme systems.~12 Citings

453. ESR methods for assessing the stability of polymer membranes used in fuel cells

By Roduner, Emil; Schlick, ShulamithEdited By:Schlick, ShulamithFrom Advanced ESR Methods in Polymer Research (2006), 197-228. Language: English, Database: CAPLUS,DOI:10.1002/047005350X.ch8

This review describes the reactions that occur in fuel cell environment, asseses various methods used to produce O-centered radicals that decrease the membrane stability, and summerizes progress made in the detection (directly byESR or via spin trapping) of O radicals and membrane-derived fragments.~16 Citings

454. Molecular rearrangements: part 2

By Coxon, J. M.From Organic Reaction Mechanisms (2007), 499-560. Language: English, Database: CAPLUS

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A review.~0 Citings

455. Carbenes and nitrenes

By Christlieb, M.; Hodgson, D. M.; Gras, E.From Organic Reaction Mechanisms (2007), 161-191. Language: English, Database: CAPLUS

A book. Topics include structure and reactivity, generation, addn., metal-bound carbenes, insertion and abstraction,rearrangement, nitrenes, nucleophiles and electrophiles, silylenes and germylenes, four-electron boron.~0 Citings

456. An efficient synthesis of fluorocyclopentenes using fluoroalkylidenecarbenes

By Guan, Tong; Takemura, Kohei; Senboku, Hisanori; Yoshida, Masanori; Hara, ShojiFrom Tetrahedron Letters (2008), 49(1), 76-79. Language: English, Database: CAPLUS,DOI:10.1016/j.tetlet.2007.11.019

An efficient synthesis of fluorocyclopentenes, e.g. I, is described. By treatment of (2-fluoroalkenyl)iodonium salts withpotassium tert-butoxide, (α-fluoroalkylidene)carbenes were generated efficiently to give fluorocyclopentenes via 1,5-C-Hinsertion. Fluorocyclopentenes having a functionality, such as chlorine, acetoxy, or ketone, and a spirofluorocyclopentene were synthesized in good yields.

~3 Citings

457. Molecular rearrangements: part 2

By Brandi, A.; Gensini, M.; Pisaneschi, F.From Organic Reaction Mechanisms (2006), 515-580. Language: English, Database: CAPLUS

A review.~0 Citings

458. Advances in the development of methods for the application of carbenes and nitrenes in organic synthesis

By Hodgson, D. M.; Christlieb, M.; Gras, E.From Organic Reaction Mechanisms (2006), 169-194. Language: English, Database: CAPLUS

A book. Advances in the development of methods for the application of carbenes and nitrenes in org. synthesis werediscussed. Topics included structure and reactivity, generation of carbenes, etc., addn. and fragmentation reactions,rearrangement reactions, nitrenes, nucleophiles and electrophiles, silylene derivs. and germylene derivs. Org. reactionmechanisms.~0 Citings

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459. Photosystem II: Structure and mechanism of the water:plastoquinone oxidoreductase

By Kern, Jan; Renger, GernotFrom Photosynthesis Research (2007), 94(2-3), 183-202. Language: English, Database: CAPLUS,DOI:10.1007/s11120-007-9201-1

A review. This mini-review briefly summarizes our current knowledge on the reaction pattern of light-driven watersplitting and the structure of Photosystem II that acts as a water:plastoquinone oxidoreductase. The overall processcomprises three types of reaction sequences: (a) light-induced charge sepn. leading to formation of the radical ion pairP680+.bul.Q-.bul. A; (b) redn. of plastoquinone to plastoquinol at the QB site via a two-step reaction sequence with Q-.bul. Aas reductant and (c) oxidative water splitting into O2 and four protons at a manganese-contg. catalytic site via a four-stepsequence driven by P680+.bul. as oxidant and a redox active tyrosine YZ acting as mediator. Based on recent progress inX-ray diffraction crystallog. structure anal. the array of the cofactors within the protein matrix is discussed in relation tothe functional pattern. Special emphasis is paid on the structure of the catalytic sites of PQH2 formation (QB-site) andoxidative water splitting (Mn4OxCa cluster). The energetics and kinetics of the reactions taking place at these sites arepresented only in a very concise manner with ref. to recent up-to-date reviews. It is illustrated that several questions onthe mechanism of oxidative water splitting and the structure of the catalytic sites are far from being satisfactorilyanswered.~109 Citings

460. Exploring haem-based alternatives for oxygen reduction catalysis in fuel cells-a status report of our firstprinciples calculations

By Dy, E. S.; Roman, T. A.; Kubota, Y.; Miyamoto, K.; Kasai, H.From Journal of Physics: Condensed Matter (2007), 19(44), 445010/1-445010/12. Language: English, Database:CAPLUS, DOI:10.1088/0953-8984/19/44/445010

For hydrogen fuel cells to become com. viable, an alternative catalyst to platinum surfaces that is both efficient andaffordable must be discovered. Haem and haem derivs. as potentials substitutes are considered. The authors discussthe oxygen redn. reaction on both the platinum surface and on haem. The authors then introduce the suggestions basedon d.-functional studies on how to improve haem's oxygen-redn. capabilities, which can be summarized as follows:inducing the singlet state, inducing side-on interaction, mimicking cytochrome c oxidase by adding a copper-imidazolecomplex, using platinum deposited on tin porphyrin instead of haem, and using oxomolybdenum porphyrin instead ofhaem. The authors shall focus on the last three methods because of their exptl. practicability.~2 Citings

461. Can we predict the location of impurities in diamond nanoparticles?

By Barnard, A. S.; Sternberg, M.From Diamond and Related Materials (2007), 16(12), 2078-2082. Language: English, Database: CAPLUS,DOI:10.1016/j.diamond.2007.05.011

Although most com. nanodiamonds contain impurities, it is still largely unknown whether a given species will be locatedwithin the core or at the surface of the nanocrystals. This question is significant, since in the former case a suitable atommay act as a dopant, but in the latter case it will merely be an adsorbate. Presented here are d. functional tight-bindingsimulations examg. the potential energy surface of substitutional nitrogen and boron in diamond nanocrystals, directlycomparing results for a no. of crystallog. inequivalent sites. The results predict that both nitrogen and boron aremetastable within the core of bucky-diamond and nanodiamond, and are therefore unlikely to be stable as dopants withinthese nanoparticles.~36 Citings

462. Hybrid density functional theory with a specific reaction parameter: hydrogen abstraction reaction ofdifluoromethane by the hydroxyl radical

By Albu, Titus V.; Swaminathan, SaravananFrom Journal of Molecular Modeling (2007), 13(11), 1109-1121. Language: English, Database: CAPLUS,DOI:10.1007/s00894-007-0235-2

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Accurate potential energy surfaces for the OH+CH2F2 → H2O+CHF2 reaction are constructed using hybrid and hybridmeta d. functional theory methods (mPW1PW91, B1B95, and mPW1B95) with specific reaction parameters inconjunction with the 6-31+G(d,p) basis set. The accuracy of a surface is examd. by comparing the calcd. rate consts.with the exptl. ones. The rate consts. are calcd. over the temp. range 200-1,500 K using variational transition statetheory with multidimensional tunneling contributions. The hybrid d. functional theory methods with specific-reaction-parameter Hartree-Fock exchange contributions (39.2-41.0% for mPW1PW91, 41.0-42.2% for B1B95, and 44.9-46.3%for mPW1B95, resp.) provide accurate rate consts. over an extended temp. range. The classical barrier height for thehydrogen abstraction reaction on these potential energy surfaces is 5.0-5.3 kcal mol-1, and the best est. value is 5.14kcal mol-1.~1 Citing

463. Computational Chemistry of Polyatomic Reaction Kinetics and Dynamics: The Quest for an Accurate CH5Potential Energy Surface

By Albu, Titus V.; Espinosa-Garcia, Joaquin; Truhlar, Donald G.From Chemical Reviews (Washington, DC, United States) (2007), 107(11), 5101-5132. Language: English, Database:CAPLUS, DOI:10.1021/cr078026x

A review. Over more than six decades, the H + CH4 reaction and its isotopic variants have represented a target againstwhich to test kinetics and dynamics theories and potential energy surfaces for polyat. reactions. This comprehensivereview concerns the development of a multidimensional potential energy surface for the CH5 system and how dynamicscalcns. on the various approx. surfaces, that have been developed, compare with exptl. detd. kinetic and dynamicparameters.~51 Citings

464. Multicoefficient Gaussian-3 Calculation of the Rate Constant for the OH + CH4 Reaction and Its 12C/13CKinetic Isotope Effect with Emphasis on the Effects of Coordinate System and Torsional Treatment

By Ellingson, Benjamin A.; Pu, Jingzhi; Lin, Hai; Zhao, Yan; Truhlar, Donald G.From Journal of Physical Chemistry A (2007), 111(45), 11706-11717. Language: English, Database: CAPLUS,DOI:10.1021/jp072843j

Rate consts. and 12C/13C kinetic isotope effects are calcd. by direct dynamics for the OH + CH4 → H2O + CH3 reaction.The electronic structure calcns. required to generate the implicit potential energy surface were carried out by the high-level multicoefficient Gaussian-3/version-3 (MCG3) method and compared to two other multilevel methods, MC3BB andMC3MPW, and three d. functional methods, M06-2X, BB1K, and MPW1K. The rate consts. and 12C/13C kinetic isotopeeffects are shown to depend strongly on the coordinate system used to calc. the frequencies as well as on the methodused to account for the torsional anharmonicity of the lowest-frequency vibrational mode of the generalized transitionstates.~21 Citings

465. A theoretical investigation on the isomerism and the NMR properties of thiosemicarbazones

By Nuwan De Silva, N. W. S. V.; Albu, Titus V.From Central European Journal of Chemistry (2007), 5(2), 396-419. Language: English, Database: CAPLUS,DOI:10.2478/s11532-007-0012-1

Hybrid d. functional theory calcns. at the mPW1PW91/6-31+G(d,p) level of theory have been used to investigate theoptimized structures and other mol. properties of five different series of thiosemicarbazones. The investigated compds.were obtained from acenaphthenequinone, isatin and its derivs., and alloxan. The focus of the study is the isomerismand the NMR characterization of these thiosemicarbazones. It was found that only one isomer is expected forthiosemicarbazones and methylthiosemicarbazones, while for dimethylthiosemicarbazones, two isomers are possible.All investigated thiosemicarbazones exhibit a hydrazinic proton that is highly deshielded and resonates far downfield inthe proton NMR spectra. This proton is a part of a characteristic six-membered ring, and its NMR properties are a resultof its strong, intermol. hydrogen bond. The relationships between the calcd. 1H and 13C NMR chem. shifts and variousgeometric parameters are reported.~3 Citings

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466. Dielectric and thermal behaviour of holmium tartrate trihydrate crystals

By Want, B.; Ahmad, F.; Kotru, P. N.From Crystal Research and Technology (2007), 42(8), 822-828. Language: English, Database: CAPLUS,DOI:10.1002/crat.200710912

Measurements on dielec. const. of Ho tartrate trihydrate crystals at frequencies of the applied a.c. in the range 1 kHz to 1MHz and at temp. in the range 30-330° are reported. The dielec. const. ε' increases with temp. at all frequencies, attainsa peak near 250°, and then decreases as the temp. goes beyond 250°. The anomalous dielec. behavior at near about250° is attributed to be as a result of crystallog./polymorphic phase transition brought about in the material. The resultson the dielec. behavior of the material are supplemented by results of thermal anal. viz., TG and DTA.Thermogravimetric and differential thermal analytic techniques were used to study thermal behavior of the material. Thematerial is thermally stable ≤220° beyond which it decomps. through three stages till the formation of holmium oxide at1200°. The non-isothermal kinetic parameters e.g., activation energy and the frequency factor were evaluated for 1st 2stages of thermal decompn. by the integral method of Coats and Redfern.~5 Citings

467. Nanotechnology for fuel cell applications

By Mainardi, D. S.; Mahalik, N. P.Edited By:Mahalik, Nitaigour PremchandFrom Micromanufacturing and Nanotechnology (2006), 425-440. Language: English, Database: CAPLUS,DOI:10.1007/3-540-29339-6_18

A review. The current state of fuel cell technol. is presented, and the application of nanoparticles for the construction ofanode and cathode catalysts is discussed. The electrochem. processes on a fuel cell anode are outlined, and the exptl.experiences with carbon nanotubes as catalyst supports are described. It was demonstrated that Pt nanoparticlessupported on carbon nanotubes exhibited a higher electrocatalytic activity towards the redn. of O2 than Pt nanoparticlessupported on carbon black.~2 Citings

468. Simulation of the Oxygen Reduction Reaction at an RDE in 0.5 M H2SO4 Including an AdsorptionMechanism

By Dong, Q.; Santhanagopalan, S.; White, R. E.From Journal of the Electrochemical Society (2007), 154(9), A888-A899. Language: English, Database: CAPLUS,DOI:10.1149/1.2756994

Oxygen redn. on the surface of a rotating disk electrode (RDE) in 0.5M H2SO4 is simulated by including mass transfer,adsorption, and charge transfer. A generalized model for the adsorption and reaction of several species is introduced.The oxygen redn. reaction is simulated as a limiting case where oxygen is the only species adsorbed, and oxygen redn.is the only reaction that takes place on the surface of the electrode. The model is based on the Nernst-Planck equationsfor mass transfer and the Butler-Volmer equation for electrochem. kinetics. The simulated polarization curves capturethe change in the Tafel slopes, which are obsd. exptl. but cannot be explained by the normal 4-electron-transfermechanism. The adsorption model is compared with the 4-electron-transfer model by fitting exptl. data to both modelsusing a nonlinear parameter estn. technique. The effects of changes in some important kinetic parameters aredemonstrated.~14 Citings

469. Oxidative photosynthetic water splitting: Energetics, kinetics and mechanism

By Renger, GernotFrom Photosynthesis Research (2007), 92(3), 407-425. Language: English, Database: CAPLUS, DOI:10.1007/s11120-007-9185-x

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A review on current knowledge on oxidative water splitting in photosynthesis. Based on the extended Kok model (Kok,Forbush, McGloin (1970) Photochem Photobiol 11:457-476) as a framework, the energetics and kinetics of two differenttypes of reactions comprising the overall process are discussed: (i) P680+.bul. redn. by the redox active tyrosine YZ ofpolypeptide D1 and (ii) Yox z induced oxidn. of the four step sequence in the water oxidizing complex (WOC) leading tothe formation of mol. oxygen. The mode of coupling between electron transport (ET) and proton transfer (PT) is of keymechanistic relevance for the redox turnover of YZ and the reactions within the WOC. The peculiar energetics of theoxidn. steps in the WOC assure that redox state S1 is thermodynamically most stable. This is a general feature in alloxygen evolving photosynthetic organisms and assumed to be of physiol. relevance. The reaction coordinate ofoxidative water splitting is discussed on the basis of the available information about the Gibbs energy differencesbetween the individual redox states Si+1 and Si and the data reported for the activation energies of the individual oxidn.steps in the WOC. Finally, an attempt is made to cast our current state of knowledge into a mechanism of oxidativewater splitting with special emphasis on the formation of the essential O-O bond and on the active role of the protein intuning the local proton activity that depends on time and redox state Si. The O-O linkage is assumed to take place at thelevel of a complexed peroxide.~68 Citings

470. Direct molecular dynamics and density-functional theoretical study of the electrochemical hydrogenoxidation reaction and underpotential deposition of H on Pt(111)

By Ishikawa, Yasuyuki; Mateo, Juan J.; Tryk, Donald A.; Cabrera, Carlos R.From Journal of Electroanalytical Chemistry (2007), 607(1-2), 37-46. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2006.10.011

A combined direct mol. dynamics/d.-functional theor. study of the electrooxidn. of hydrogen at the Pt(111)/H2O interfacewas carried out to provide insights into the reaction mechanism. The H2 oxidn. proceeds via the Heyrovsky process - aheterolytic bond breaking brought about by the impinging hydrogen mol. striking the metal surface. The products are ahydrated H+ ion and a strongly adsorbed H atom lying nearly flat in a bridging position on the Pt(111) surface. Thebridging H interacts only weakly with the aq. phase of the metal/soln. interface and imparts unique electronic andvibrational properties characteristic of underpotentially deposited H. Potential-dependent activation energies for thehydrogen redox reactions were evaluated.~47 Citings

471. Requirements for the generalization of the ab initio two-state model for external electric field inducedelectron transfer at electrodes

By Migani, Annapaola; Illas, FrancescFrom Journal of Electroanalytical Chemistry (2007), 607(1-2), 25-36. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2006.09.013

This work reports a careful systematic anal. of the validity of the ab initio 2-state model for electron transfer betweenhalides and various transition metal single crystal electrodes induced by an external elec. field. The surfaces arerepresented by cluster models and the electron transfer is modeled by compact ab initio wave functions, which are alinear combination of donor-acceptor valence bond structures (DA and D+A-) written in an appropriate orbital basis. The2-state model is able to successfully describe the ET for all those adsorbate/surface systems that feature a sufficientlylarge vertical equil. distance (orbitals well localized on the fragments and valence bond structures properly defined), andexhibit at least a partially ionic character. The former condition occurs always when the solvent is explicitly taken intoaccount, whereas the latter is fulfilled when not complete charge transfer occurs upon chemisorption.~1 Citing

472. Block-Localized Wavefunction (BLW) Method at the Density Functional Theory (DFT) Level

By Mo, Yirong; Song, Lingchun; Lin, YuchunFrom Journal of Physical Chemistry A (2007), 111(34), 8291-8301. Language: English, Database: CAPLUS,DOI:10.1021/jp0724065

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The block-localized wavefunction (BLW) approach is an ab initio valence bond (VB) method incorporating the efficiencyof MO theory. It can generate the wavefunction for a resonance structure or diabatic state self-consistently bypartitioning the overall electrons and primitive orbitals into several subgroups and expanding each block-localized MO inonly one subspace. Although block-localized MOs in the same subspace are constrained to be orthogonal (a feature ofMO theory), orbitals between different subspaces are generally nonorthogonal (a feature of VB theory). The BLWmethod is particularly useful in the quantification of the electron delocalization (resonance) effect within a mol. and thecharge-transfer effect between mols. The authors extend the BLW method to the d. functional theory (DFT) level andimplement the BLW-DFT method to the quantum mech. software GAMESS. Test applications to the π conjugation in theplanar allyl radical and ions with the basis sets of 6-31G(d), 6-31+G(d), 6-311+G(d,p), and cc-pVTZ show that the basisset dependency is insignificant. The BLW-DFT method can also be used to elucidate the nature of intermol. interactions.Examples of π-cation interactions and solute-solvent interactions will be presented and discussed. By expressing eachdiabatic state with one BLW, the BLW method can be further used to study chem. reactions and electron-transferprocesses whose potential energy surfaces are typically described by two or more diabatic states.~173 Citings

473. Two-state model based on the block-localized wave function method

By Mo, YirongFrom Journal of Chemical Physics (2007), 126(22), 224104/1-224104/9. Language: English, Database: CAPLUS,DOI:10.1063/1.2746026

The block-localized wave function (BLW) method is a variant of ab initio valence bond method but retains the efficiencyof MO methods. It can derive the wave function for a diabatic (resonance) state self-consistently and is available at theHartree-Fock (HF) and d. functional theory (DFT) levels. In this work we present a two-state model based on the BLWmethod. Although numerous empirical and semiempirical two-state models, such as the Marcus-Hush two-state model,have been proposed to describe a chem. reaction process, the advantage of this BLW-based two-state model is that noempirical parameter is required. Important quantities such as the electronic coupling energy, structural wts. of twodiabatic states, and excitation energy can be uniquely derived from the energies of two diabatic states and the adiabaticstate at the same HF or DFT level. Two simple examples of formamide and thioformamide in the gas phase and aq.soln. are presented and discussed. The solvation of formamide and thioformamide was studied with the combined abinitio quantum mech. and mol. mech. Monte Carlo simulations, together with the BLW-DFT calcns. and analyses. Due tothe favorable solute-solvent electrostatic interaction, the contribution of the ionic resonance structure to the ground stateof formamide and thioformamide significantly increases, and for thioformamide the ionic form is even more stable thanthe covalent form. Thus, thioformamide in aq. soln. is essentially ionic rather than covalent. Although our two-statemodel in general underestimates the electronic excitation energies, it can predict relative solvatochromic shifts well. Forinstance, the intense ππ* transition for formamide upon solvation undergoes a red shift of 0.3 eV, compared with theexptl. data (0.40-0.5 eV).~3 Citings

474. Vibrational modes in partially optimized molecular systems

By Ghysels, A.; Van Neck, D.; Van Speybroeck, V.; Verstraelen, T.; Waroquier, M.From Journal of Chemical Physics (2007), 126(22), 224102/1-224102/13. Language: English, Database: CAPLUS,DOI:10.1063/1.2737444

The authors develop a method to accurately calc. localized vibrational modes for partially optimized mol. structures or forstructures contg. link atoms. The method avoids artificially introduced imaginary frequencies and keeps track of theinvariance under global translations and rotations. Only a subblock of the Hessian matrix has to be constructed anddiagonalized, leading to a serious redn. of the computational time for the frequency anal. The mobile block Hessianapproach (MBH) proposed in this work can be regarded as an extension of the partial Hessian vibrational anal. approachproposed by Head [Int. J. Quantum Chem. 65, 827(1997)]. Instead of giving the nonoptimized region of the system aninfinite mass, it is allowed to move as a rigid body with respect to the optimized region of the system. The MBHapproach is then extended to the case where several parts of the mol. can move as independent multiple rigid blocks incombination with single atoms. The merits of both models are extensively tested on EtOH and di-n-octyl-ether.~20 Citings

475. Membrane degradation mechanisms in PEMFCs

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By Mittal, Vishal O.; Kunz, H. Russell; Fenton, James M.From ECS Transactions (2006), 3(1, Proton Exchange Membrane Fuel Cells 6), 507-517. Language: English,Database: CAPLUS, DOI:10.1149/1.2356172

Based on exptl. findings it is suggested that formation of active oxygen species from H2O2 decompn. or the directformation of active oxygen species in the oxygen redn. reaction are not the dominating membrane degrdn. mechanismsin polymer electrolyte membrane fuel cells (PEMFCs), instead it is the mol. H2 and O2 that react on the surface of the Ptcatalyst to form the membrane degrading species. The source of H2 or O2 is from reactant crossover through themembrane. The reaction mechanism is chem. in nature and depends upon the catalyst surface properties and therelative concns. of H2 and O2 at the catalyst. The membrane degrdn. rate also depends on the residence time of thespecies in the membrane and the vol. of the membrane. The sulfonic acid groups in the Nafion side chain are key to themechanism by which the radical species attack the polymer.~7 Citings

476. A model for the electroreduction of molecular oxygen

By Mustain, William E.; Prakash, JaiFrom Journal of the Electrochemical Society (2007), 154(7), A668-A676. Language: English, Database: CAPLUS,DOI:10.1149/1.2735915

The kinetics of the oxygen redn. reaction (ORR) was studied by decompg. the polarization curves obtained using apolycryst. Pt rotating disk electrode in an aq. H2SO4 electrolyte. The ORR model that is presented is novel in itsexpression of the pre-exponential factor in the traditional Butler-Volmer equation. It is postulated that this term can bedescribed as an intrinsic kinetic frequency factor multiplied by probability functions that describe the kinetic behaviorbased on spatial, energetic, and electron-transfer effects. Literature values are taken for the oxygen-binding energy tocalc. the adsorption equil. behavior and both the activation energy and electron tunneling are used to quantify the kineticprobability functions. The frequency factors were calcd. as 2.0 s-1 for the 4-electron redn. and 1.3 × 102 s-1 for the 2-electron redn. The model appears to simulate important features of the ORR, including the magnitude of the obsd.current and the activation overpotential, though slight deviations in the potential persist. Results of the model are used todiscuss the potential to describe tailor-made catalysts for the ORR.~14 Citings

477. Membrane Degradation Mechanisms in PEMFCs

By Mittal, Vishal O.; Kunz, H. Russell; Fenton, James M.From Journal of the Electrochemical Society (2007), 154(7), B652-B656. Language: English, Database: CAPLUS,DOI:10.1149/1.2734869

Nafion membrane degrdn. was studied in a polymer electrolyte membrane fuel cell (PEMFC) under accelerated agingconditions. Fuel cell effluent H2O was analyzed to det. the fluoride emission rate. Formation of active O species fromH2O2 decompn. or the direct formation of active O species in the O redn. reaction are not the dominating membranedegrdn. mechanisms in PEMFCs. Instead, membrane degrdn. occurs because mol. H2 and O2 react on the surface ofthe Pt catalyst to form membrane-degrading species. The source of H2 or O2 is from reactant crossover through themembrane. The reaction mechanism is chem. and depends upon the catalyst surface properties and the relative concns.of H2 and O2 at the catalyst. The membrane degrdn. rate also depends on the residence time of active O species in themembrane and vol. of the membrane. The sulfonic acid groups in the Nafion side chain are key to the mechanism bywhich radical species attack the polymer.~128 Citings

478. Absorption of Atomic Oxygen into Subsurfaces of Pt(100) and Pt(111): Density Functional Theory Study

By Gu, Zhihui; Balbuena, Perla B.From Journal of Physical Chemistry C (2007), 111(27), 9877-9883. Language: English, Database: CAPLUS,DOI:10.1021/jp0711693

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D. functional theory is used to examine binding energies and the most stable sites of at. oxygen adsorbed on Pt(111) andPt(100) surfaces as a function of surface coverage, as well as to evaluate the absorption energies and the energeticallymost favorable sites of at. oxygen located in the subsurface, as a function of subsurface coverage. Based on theabsorption energies, it is found that the tetrahedral site underneath the hcp hollow site is energetically the most favorablesite to absorb at. oxygen in the subsurface of Pt(111), and the tetrahedral site underneath the bridge site is thecorresponding energetically most favorable subsurface site in Pt(100) cells. Min. energy paths identified for the diffusionof low-coverage adsorbed at. oxygen into the subsurface sites for Pt(111) and Pt(100) cells indicate the existence of highkinetic barriers to such diffusion.~74 Citings

479. Reaction pattern and mechanism of light induced oxidative water splitting in photosynthesis

By Renger, Gernot; Kuehn, PhilippFrom Biochimica et Biophysica Acta, Bioenergetics (2007), 1767(6), 458-471. Language: English, Database: CAPLUS,DOI:10.1016/j.bbabio.2006.12.004

This mini review is an attempt to briefly summarize our current knowledge on light driven oxidative water splitting inphotosynthesis. The reaction leading to mol. oxygen and four protons via photosynthesis comprises thermodn. andkinetic constraints that require a balanced fine tuning of the reaction coordinates. The mode of coupling betweenelectron (ET) and proton transfer (PT) reactions is shown to be of key mechanistic relevance for the redox turnover of YZand the reactions within the WOC. The WOC is characterized by peculiar energetics of its oxidn. steps in the WOC. Inall oxygen evolving photosynthetic organisms the redox state S1 is thermodynamically most stable and therefore thisgeneral feature is assumed to be of physiol. relevance. Available information on the Gibbs energy differences betweenthe individual redox states Si+1 and Si and on the activation energies of their oxidative transitions are used to construct ageneral reaction coordinate of oxidative water splitting in photosystem II (PS II). Finally, an attempt is presented to castour current state of knowledge into a mechanism of oxidative water splitting with special emphasis on the formation of theessential O-O bond and the active role of the protein environment in tuning the local proton activity that depends on timeand redox state Si. The O-O linkage is assumed to take place within a multistate equil. at the redox level of S3,comprising both redox isomerism and proton tautomerism. It is proposed that one state, S3(P), attains an electronicconfiguration and nuclear geometry that corresponds with a hydrogen bonded peroxide which acts as the entatic state forthe generation of complexed mol. oxygen through S3(P) oxidn. by Yox Z.~20 Citings

480. Kinetics and mechanism for the oxygen reduction reaction on polycrystalline cobalt-palladiumelectrocatalysts in acid media

By Mustain, William E.; Prakash, JaiFrom Journal of Power Sources (2007), 170(1), 28-37. Language: English, Database: CAPLUS,DOI:10.1016/j.jpowsour.2007.04.005

Cobalt-palladium (CoPdx) bimetallic electrocatalysts of various compns. were prepd. and their phys. and electrochem.properties were examd. The nominal compn. of the polycryst. electrocatalysts was estd. by energy dispersive X-ray anal.(EDX) and the lattice parameters were evaluated using X-ray diffraction (XRD). Electrocatalytic activity of the CoPdxelectrodes for the oxygen redn. reaction was compared using cyclic voltammograms obtained in oxygen satd., 0.5 MH2SO4. CoPd3 was identified as having the highest activity, showing peak currents comparable to a polycryst. Ptelectrode under identical exptl. conditions. The rotating disk electrode technique was used to collect kinetic data for theoxygen redn. on CoPd3 and the activity of the binary electrocatalysts was evaluated. Kinetic and mechanistic aspects ofthe oxygen redn. reaction on CoPd3 are discussed and specific ways in which the surface structures may be involved areproposed.~94 Citings

481. Hydrogen Oxidation and Evolution on Platinum Electrodes in Base: Theoretical Study

By Zhang, Tianhou; Anderson, Alfred B.From Journal of Physical Chemistry C (2007), 111(24), 8644-8648. Language: English, Database: CAPLUS,DOI:10.1021/jp070125r

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Electrode potential dependent activation energies for electron transfer were calcd. for the hydrogen evolution andhydrogen oxidn. reactions on Pt in base using the local reaction center model and constrained variation theory.Comparison is made with previous calcns. for these reactions in acid using the same approach and with exptl. literatureresults for acid and base. The results of the calcns. are consistent with the Tafel-Volmer mechanism for H2 oxidn. and amixt. of Tafel-Volmer and Heyrovsky-Volmer mechanism for H2 evolution in basic electrolyte on Pt surfaces.~20 Citings

482. Proton transfer to oxygen adsorbed on Pt: how to initiate oxygen reduction reaction

By Tsuda, Muneyuki; Kasai, HideakiFrom Journal of the Physical Society of Japan (2007), 76(2), 024801/1-024801/4. Language: English, Database:CAPLUS, DOI:10.1143/JPSJ.76.024801

The authors study the proton transfer to oxygen adsorbed on a Pt catalyst using ab initio d. functional calcns. The protontends to preferentially migrate to O2 as compared to O because the HOMO level of the Pt-O2 system is higher than thatof the Pt-O system. Probably the oxygen redn. reaction (ORR) on Pt tends to initiate from the prodn. of a hydroperoxo (-OOH) species.~1 Citing

483. Quantum mechanical tunneling in organic reactive intermediates

By Sheridan, Robert S.Edited By:Platz, Matthew S.; Moss, Robert A.; Jones, Maitland, JrFrom Reviews of Reactive Intermediate Chemistry (2007), 415-463. Language: English, Database: CAPLUS,DOI:10.1002/9780470120828.ch10


484. Thermal behaviour of some Al(III)-Mg(II) polynuclear coordination compounds with polycarboxylic acidanions as ligands, precursors of aluminates

By Carp, O.; Patron, L.; Mindru, I.; Suciu, C.From Journal of Thermal Analysis and Calorimetry (2007), 88(1), 77-81. Language: English, Database: CAPLUS,DOI:10.1007/s10973-006-8081-5

A TG, DTG and DTA study of three polynuclear coordination compds., contg. Al(III)-Mg(II),(NH4)4[Al2Mg(C4O5H4)4(OH)4].bul.2H2O, (NH4)4[MgAl2(C4H4O6)4(OH)4].bul.3H2O and(NH4)2[Al2Mg(C6O7H11)5(OH)5].bul.3H2O, is reported together with the assocd. thermal decompn. mechanismrationalized in terms of intermediate products. As decompn. end-product, Mg-Al spinel was obtained. The values ofMgAl2O4 mean crystallite size depend on the anionic ligand contained by the precursor compd., varying in the order:malate (143 Å) contained by the precursor compd., varying in the order: malate (143 Å) < gluconate (165 Å) < tartarate(180 Å).~2 Citings

485. Global Potential Energy Surfaces with Correct Permutation Symmetry by Multiconfiguration MolecularMechanics

By Tishchenko, Oksana; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2007), 3(3), 938-948. Language: English, Database: CAPLUS,DOI:10.1021/ct600315h

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In the framework of the previously developed multiconfiguration mol. mechanics (MCMM) method, we present a newalgorithm for constructing global potential energy surfaces that are invariant with respect to the exchange of identicalnuclei. We illustrate the new algorithm by its application to the HOH'' + H' → OH + H'H'', OH' + HH'', OH'' + HH', HOH' +H'', and H''OH' + H reactions. As part of the MCMM methodol., the new scheme can be used to generatemultidimensional global PESs for both small and large systems where a few reaction pathways need to be treated assym. equiv.~13 Citings

486. Computing tunneling paths with the Hamilton-Jacobi equation and the fast marching method

By Dey, Bijoy K.; Ayers, Paul W.From Molecular Physics (2007), 105(1), 71-83. Language: English, Database: CAPLUS,DOI:10.1080/00268970601131999

We present a new method for computing the most probable tunneling paths based on the min. imaginary action principle.Unlike many conventional methods, the paths are calcd. without resorting to an optimization (minimization) scheme.Instead, a fast marching method coupled with a back-propagation scheme is used to efficiently compute the tunnelingpaths. The fast marching method solves a Hamilton-Jacobi equation for the imaginary action on a discrete grid wherethe action value at an initial point (usually the reactant state configuration) is known in the beginning. Subsequently, aback-propagation scheme uses a steepest descent method on the imaginary action surface to compute a pathconnecting an arbitrary point on the potential energy surface (usually a state in the product valley) to the initial state. Theproposed method is demonstrated for the tunneling paths of two different systems: a model 2D potential surface and thecollinear A + B-A → A-B + A reaction. Unlike existing methods, where the tunneling path is based on a presumedreaction coordinate and a correction is made with respect to the reaction coordinate within an 'adiabatic' approxn., theproposed method is very general and makes no assumptions about the relationship between the reaction coordinate andtunneling path.~15 Citings

487. Why is there such a small overpotential for O2 electro reduction by copper laccase?

By Schweiger, Hannes; Vayner, Ellen; Anderson, Alfred B.From Proceedings - Electrochemical Society (2006), 2005-11(Electrocatalysis), 213-221. Language: English,Database: CAPLUS

Quantum chem. predictions are made of the reversible potentials for the intermediates formed during the 4-electron redn.of O2 by Cu laccase, using 3 loosely assocd. partially ligated CuI centers as models for the active site. Two mechanismswere studied, the Pt surface mechanism in acid electrolyte and the proposed laccase mechanism for basic electrolyte.Both are found viable and the CuII-OH redn. step has the lowest potential and so is responsible for the predictedoverpotential, which is less than for Pt electrodes, but more than in the natural laccase. Adding more ligands would beexpected to reduce the predicted overpotential to the very small measured value by reducing O and OH bond strengthsto the active site.~0 Citings

488. Theory for the potential shift for OHads formation on the Pt-skin on Pt3Cr(111) in acid

By Roques, Jerome; Anderson, Alfred B.From Proceedings - Electrochemical Society (2005), 2003-30(Fundamental Understanding of Electrode Processes),330-359. Language: English, Database: CAPLUS

The authors present results of a periodic spin-d.-functional theory study of the electronic structure and the localadsorption properties of the annealed Pt3Cr alloy surface in comparison with the Pt(111) surface. Each is modeled as afour-layer slab where the two topmost layers and the adsorbates are allowed to relax. The annealed alloy has Ptsegregated to the surface and is modeled by a Pt(111) monolayer covering the Pt3Cr(111) L12 face bulk phase alloy.The authors have calcd. OH and H2O structures and adsorption energies at low coverage. The top adsorption sites werepredicted to be most stable for these adsorbates on both surfaces, but adsorption energies for both decrease on the Pt-skin, with a larger decrease for OH. An empirical model based on reaction energy calcns. in acid was used to est. thereversible potential of OHads formation from H2Oads on the Pt-skin and on Pt(111) in acid. A pos. shift (∆Uo = 0.11 V) ispredicted for the surface of the Pt-skin relative to Pt(111). This result is in qual. agreement with the 40-60 mV redn. inoverpotential obsd. exptl. for O redn. on the Pt3Cr alloy compared to Pt surfaces, which is attributed to OHads being asurface poison.

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489. One dimensional diffusion-controlled kinetic model for oxygen reduction

By Mustain, William; Prakash, JaiFrom Proceedings - Electrochemical Society (2005), 2003-30(Fundamental Understanding of Electrode Processes),71-90. Language: English, Database: CAPLUS

A one-dimensional, diffusion-controlled model has been developed to describe oxygen redn. behavior on a rotating diskelectrode in acidic media. The proposed model introduces novel expressions for both the electrochem. and adsorptiverate consts. These functions have the form of a product of an ideal rate const. and a series of probability functions thatdescribe the deviation from ideality of the true rate const. caused by steric hindrance, energy deficiency and electronicinteraction/exchange. Rotating ring-disk electrode data is used to divulge the kinetic behavior of oxygen on platinum.Also, adsorption parameters are detd. by numerical parameter estn. of exptl. data on a rotating disk electrode. Thispaper lays the theor. framework for the proposed model as well as describing the methods by which all parameters willbe detd. A future paper will consider data from a library of disk electrode materials. This will allow all electrochem. andadsorptive parameters to be accurately calcd. Finally, the predictive abilities of the proposed model will be tested.~0 Citings

490. Oxygen electroreduction on carbon materials

By Tryk, Donald A.; Cabrera, Carlos R.; Fujishima, Akira; Spataru, NicolaeFrom Proceedings - Electrochemical Society (2005), 2003-30(Fundamental Understanding of Electrode Processes),45-57. Language: English, Database: CAPLUS

Previous work showed that O redn. on various types of C, graphite and diamond surfaces proceeds via an overall two-electron pathway to produce H2O2 in aq. soln. In general, the rate-detg. process is the 1st electron transfer, to producethe superoxide radical anion. On polycryst. B-doped diamond (BDD) electrodes, this process is extremely inhibited,occurring at more neg. potentials than it does on the basal plane of highly ordered pyrolytic graphite (HOPG) in alk. aq.soln. This is most likely due to the near-absence of catalytic C-O functional groups on the BDD surface. On this surfacein acid soln., O2 redn. occurs at almost precisely the same potential (vs. a pH-insensitive electrode), demonstrating thatthe reaction is essentially pH-insensitive. Probably this is due to the fact that the principal chem. reaction that follows thegeneration of superoxide is the reaction of the latter with H2O itself. On glassy C (GC), there are both electrocatalyticand nonelectrocatalytic pathways. For the latter, the electrochem. and chem. parameters are similar to those for BDD,except that the electron transfer (ET) rate const. is about three orders of magnitude larger, which shifts the voltammetricpeak by ∼0.39 V pos. Probably even though this process are not electrocatalytic in a redox-mediation sense, it still relieson the presence of O-contg. surface groups, which facilitate the ET. The 2nd pathway, in contrast, is electrocatalytic inthe redox-mediation sense, and it relies on the presence of singly reduced quinones, i.e., radical anions, on the GCsurface. On BDD, depending on the quality of the sample, small amts. of graphitic impurities can exist, whose surfacescan be oxidized to produce quinone-like functional groups, and these can support a small amt. of catalyzed O redn., atpotentials significantly pos. of the main O redn. process in both alk. and acid soln.~11 Citings

491. Electrode potential-dependent stages in OHads formation on the Pt3Cr alloy (111) surface

By Roques, Jerome; Anderson, Alfred B.From Proceedings - Electrochemical Society (2005), 2003-30(Fundamental Understanding of Electrode Processes),10-44. Language: English, Database: CAPLUS

Results of a periodic spin-d.-functional theory study of the electronic structure and the local adsorption properties of themixed Pt3Cr(111) alloy surface are presented. A slab composed of four-atom-layers is used to model the (111) surfaceof the L12 bulk phase with the two topmost layers and adsorbed species allowed to relax. Adsorption energies of OHand H2O have been calcd. as functions of initial OH coverage. Using these energies in an empirical model based on thereaction energy calcns. for acid electrolyte, we have estd. the reversible potential shift of OHads formation from H2Oads onthe Pt3Cr(111) alloy relative to Pt(111) surface. For the first 1/4 ML coverage H2O and OH are more stable on the Crsites and a neg. shift of 0.55 V is calcd. The shifts for the next 1/4 monolayer instalment, forming OHads on Pt is alsoneg., - 0.15 V. Shifts for going to 3/4 and 1 ML OHads coverage are both pos. Hydrogen bonding between adsorbedmols. plays a role at higher coverage. O2 adsorption is studied on the 1/2 ML OHads covered surface and it is found tobond more weakly than H2O, suggesting that if the sputtered alloy surface is active toward O2 redn., as the sputteredPt3Co and Pt3Ni surfaces are, Pt islands may be responsible.

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492. Variational transition state theory with multidimensional tunneling

By Fernandez-Ramos, Antonio; Ellingson, Benjamin A.; Garrett, Bruce C.; Truhlar, Donald G.From Reviews in Computational Chemistry (2007), 23, 125-232. Language: English, Database: CAPLUS,DOI:10.1002/9780470116449.ch3

A review. The following topics are discussed: VTST for gas-phase reactions; practical methods for quantized VTSTcalcns.; quantum effects on reaction coordinate motion; building potential energy surfaces from electronic structurecalcns.; reactions in liqs.; ensemble-averaged VTST;.~173 Citings

493. Hybrid density functional theory with a specific reaction parameter: Hydrogen abstraction reaction oftrifluoromethane by the hydroxyl radical

By Albu, Titus V.; Swaminathan, SaravananFrom Theoretical Chemistry Accounts (2007), 117(3), 383-395. Language: English, Database: CAPLUS,DOI:10.1007/s00214-006-0166-5

Potential energy surfaces are developed and tested for the OH + CHF3 → H2O + CF3 reaction. The objective is to obtainsurfaces that give calcd. rate consts. comparable to the exptl. ones. The potential energy surfaces are constructed usinghybrid and hybrid meta d. functional theory methods (mPW1PW91, B1B95, and mPW1B95) with specific reactionparameters in conjunction with the 6-31+ G(d,p) basis set. The rate consts. are calcd. over the temp. range 200-1,500 Kusing variational transition state theory with multidimensional tunneling contributions. The hybrid d. functional theorymethods with specific-reaction-parameter Hartree-Fock exchange contributions (32.8-34.8% for mPW1PW91, 34.2-36.0% for B1B95, and 37.8-39.7% for mPW1B95, resp.) provide accurate rate consts. over an extended temp. range.The classical barrier height for the hydrogen abstraction reaction is 6.5-6.9 kcal/mol on these potential energy surfaces,and the best est. value is 6.77 kcal/mol.~7 Citings

494. Mapping the location and configuration of nitrogen in diamond nanoparticles

By Barnard, Amanda S.; Sternberg, MichaelFrom Nanotechnology (2007), 18(2), 025702/1-025702/11. Language: English, Database: CAPLUS,DOI:10.1088/0957-4484/18/2/025702

Understanding how impurities such as nitrogen are included in diamond nanoparticles is expected to be important for usein future nanodevices, such as qubits for quantum computing. Most com. diamond nanoparticles contain approx. 2-3%nitrogen, but it is difficult to det. exptl. whether it is located within the core or at the surface of the nanoparticles.Presented here are d. functional tight-binding simulations examg. the configuration and potential energy surface ofsubstitutional nitrogen in diamond nanoparticles, directly comparing results of different sizes, shapes and surface chem.The results predict that nitrogen is metastable within the core of both hydrogenated and dehydrogenated particles, butthat the binding energy, coordination and preferred location is dependent upon the structure of the nanoparticle as awhole.~4 Citings

495. Thermoanalytical (TG-DTA-DTG) investigations of uranium (VI) and thorium (IV) complexes of o-hydroxyN,N'-dimethylbenzylamine in static air atmosphere

By Khan, S.; Anwar, C. J.; Arshad, M.; Masud, K.From Radiochimica Acta (2006), 94(12), 853-858. Language: English, Database: CAPLUS,DOI:10.1524/ract.2006.94.12.853

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Differential thermal and thermogravimetric analyses of actinide metal o-hydroxy N,N'-dimethylbenzylamine complexes ofthe formulas, [LMO2X2], [LMO2SO4] and [LTh(NO3)4], where M = U, L = o-C6H4OHCH2N(CH3)2 and X = Cl2, NO3 - havebeen carried out to explore their degrdn. patterns. The evolved products were identified on the basis of loss in wt. on TGcoupled with DTA curves. The thermal decompn. of these complexes occurred with the loss of inorg. and org. fragmentsand exhibited almost similar mode of degrdn. with minor differences. The compn. of the intermediates formed duringdegrdn. was confirmed by microanal. and IR spectroscopy. The residues, after heating above 545 °C, corresponded tometal oxides. Degrdn. mechanisms of these complexes have also been proposed.~4 Citings

496. Heats of Formation of Diphosphene, Phosphinophosphinidene, Diphosphine, and Their Methyl Derivatives,and Mechanism of the Borane-Assisted Hydrogen Release

By Matus, Myrna H.; Nguyen, Minh Tho; Dixon, David A.From Journal of Physical Chemistry A (2007), 111(9), 1726-1736. Language: English, Database: CAPLUS,DOI:10.1021/jp067892v

The heats of formation of diphosphene (cis- and trans-P2H2), phopshinophosphinidene (singlet and triplet H2PP), anddiphosphine (P2H4), as well as those of the P2H and P2H3 radicals resulting from PH bond cleavages, have been calcd.by using high-level ab initio electronic structure theory. Energies were calcd. using coupled-cluster theory with aperturbative treatment for triple excitations (CCSD(T)) and employing augmented correlation consistent basis sets withaddnl. tight d-functions on P (aug-cc-pV(n + d)Z) up to quadruple- or quintuple-ζ, to perform a complete basis setextrapolation for the energy. Geometries and vibrational frequencies were detd. with the CCSD(T) method. Core-valence and scalar relativistic corrections were included, as well as scaled zero-point energies. We find the followingheats of formation (kcal/mol) at 298 [0] K: ∆H°f(P2H) = 53.4 [54.4]; ∆H°f(cis-P2H2) = 32.0 [33.9]; ∆H°f(trans-P2H2) = 28.7[30.6]; ∆H°f(H2PP) = 53.7 [55.6]; ∆H°f(3H2PP) = 56.5 [58.3]; ∆H°f(P2H3) = 32.3 [34.8]; ∆H°f(P2H4) = 5.7 [9.1] (expt., 5.0 ±1.0 at 298 K); and ∆H°f(CH3PH2) = -5.0 [-1.4]. We est. these values to have an accuracy of ±1.0 kcal/mol. In contrast toearlier results, we found a singlet ground state for phosphinophosphinidene (H2PP) with a singlet-triplet energy gap of2.8 kcal/mol. We calcd. the heats of formation of the methylated derivs. CH3PPH, CH3HPPH2, CH3PPCH3, CH3HPP,(CH3)2PP, (CH3)2PPH2, and CH3HPPHCH3 by using isodesmic reactions at the MP2/CBS level. The calcd. results forthe hydrogenation reactions RPPR + H2 → RHPPHR and R2PP + H2 → R2PPH2 show that substitution of an org.substituent for H improves the energetics, suggesting that secondary diphosphines and diphosphenes are potentialcandidates for use in a chem. hydrogen storage system. A comparison with the nitrogen analogs is given. Themechanism for H2-generation from diphosphine without and with BH3 as a catalyst was examd. Including tunnelingcorrections, the rate const. for the catalyzed reaction is 4.5 × 1015 times faster than the uncatalyzed result starting fromsepd. catalyst and PH2PH2.~31 Citings

497. Hydrogen evolution on diamond electrodes by the Volmer-Heyrovsky mechanism. Prediction of reversiblepotentials and activation energies

By Cai, Yu; Anderson, Alfred B.; Angus, John C.; Kostadinov, Lubomir N.From Journal of the Electrochemical Society (2007), 154(2), F36-F43. Language: English, Database: CAPLUS,DOI:10.1149/1.2403044

H evolution on (111) diamond electrode surfaces was studied by hybrid d. functional theory with cluster models. Thereductive hydronium ion discharge in the Volmer-Heyrovsky (V-H) mechanism to form H2 is activated when there waseither a bond-inserted interstitial H defect or a substitutional B defect in the near subsurface region. Activation energiesfor the Heyrovsky reaction were calcd. for the doped and undoped surfaces as functions of electrode potential, rangingbetween 0 and -3.2 V, using a constrained variation theory. Weakly adsorbed H assocd. with near subsurfacesubstitutional B defects catalyze the H evolution activity that was obsd. for B-doped diamond electrodes. Following theelectron transfer, the authors found no barrier for forming H2, irresp. of whether the defect was H or B. A barrier wasfound for H evolution on defect-free diamond. Calcd. activation energies for the Volmer reaction step were lower than forthe Heyrovsky step, which indicates the Heyrovsky step is rate limiting. An important conclusion from this work is thatthe B doping of diamond not only provides cond., but, the authors propose, also gives rise to a weakly bonded H thatparticipates in the V-H mechanism of H evolution.~17 Citings

498. Performance of hybrid density functional theory methods toward oxygen electroreduction over platinum

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By Albu, Titus V.; Mikel, Sean E.From Electrochimica Acta (2007), 52(9), 3149-3159. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2006.09.057

The performance of a large no. of hybrid d. functional theory methods is evaluated toward calcg. potential-dependentactivation energies for uncatalyzed and Pt-catalyzed oxygen redn. and hydroperoxyl oxidn. This reaction is the 1st stepand the rate-detg. step in the electrochem. oxygen redn., which is the cathodic process in electrolyte-based fuel cells.Special focus is put on detg. methods that allow results comparable to those previously calcd. using MP2 method withthe 6-31G(d,p) basis set for oxygen and hydrogen and the LANL2DZ basis set for Pt. This level of theory was shown toreproduce well, within the model used here, key features of exptl. data. Hybrid d. functional theory methods with small(<30%) Hartree-Fock exchange contributions give less accurate results mainly due to underestimated calcd. activationenergies while methods with higher (around 50%) Hartree-Fock exchange contributions give results closer to the targetones. New hybrid d. functional theory methods with specific reaction parameters that give superior results are proposed.The best overall performance is found for the method denoted as B1B95-50 in which the Hartree-Fock exchangecontribution is half. This method is computationally affordable and offers promise as a reliable method in applications tolarger systems.~6 Citings

499. QM/MM: what have we learned, where are we, and where do we go from here?

By Lin, Hai; Truhlar, Donald G.From Theoretical Chemistry Accounts (2007), 117(2), 185-199. Language: English, Database: CAPLUS,DOI:10.1007/s00214-006-0143-z

A review of the current status of the most popular methods for combined quantum mech./mol. mech. (QM/MM) calcns.,including their advantages and disadvantages. There is a special emphasis on very general link-atom methods andvarious ways to treat the charge near the boundary. Mech. and elec. embedding are contrasted. We consider methodsapplicable to gas-phase org. chem., liq.-phase org. and organometallic chem., biochem., and solid-state chem. Then wereview some recent tests of QM/MM methods and summarize what we learn about QM/MM from these studies. We alsodiscuss some available software. Finally, we present a few comments about future directions of research in this excitingarea, where we focus on more intimate blends of QM with MM.~664 Citings

500. Rotating disk electrode study of supported and unsupported catalysts for PEMFC application

By Dundar, F.; Smirnova, A.; Dong, X.; Ata, A.; Sammes, N.From Journal of Fuel Cell Science and Technology (2006), 3(4), 428-433. Language: English, Database: CAPLUS,DOI:10.1115/1.2349524

The electrochem. study of different supported and unsupported Pt-based catalysts used in polymer electrolyte fuel cells(PEMFCs) has been made by means of thin film rotating disk electrode (RDE) method. The comparison of electrochem.surface area (ESA) was made using cyclic voltammetry measurements in H2SO4 or HClO4 at room temp. and scanningrates of 20 and 100 mV/s. Oxygen redn. activity for aerogel-supported and carbon-supported Pt catalysts was evaluatedat various rotation speeds in the range of 0-2500 rpm and compared to the catalytic activity of unsupported Pt-blackcatalyst. The calcd. values of Levich const. for the oxygen redn. reaction (ORR) indicate dependence on the appliedvoltage and either 4 or 2-4 electron transfer mechanism. The hydrogen peroxide byproduct formation was detd. with arotating ring disk electrode (RRDE) and was obsd. to take place mostly at voltages below 0.6 V due to the limitationsfrom mass transport effects. The results obtained at different Pt loadings in the range of 10-46.5 wt % Pt demonstratedthat XC-72 and aerogel-based catalysts are foreseen to have higher ESA in comparison to other tested supported andunsupported com. available catalysts.~13 Citings

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501. Valence bond theory for chemical dynamics

By Truhlar, Donald G.From Journal of Computational Chemistry (2007), 28(1), 73-86. Language: English, Database: CAPLUS,DOI:10.1002/jcc.20529

A review. This essay provides a perspective on several issues in valence bond theory: the phys. significance ofsemilocal bonding orbitals, the capability of valence bond concepts to explain systems with multireferences character, theuse of valence bond theory to provide anal. representations of potential energy surfaces for chem. dynamics by themethod of semiempirical valence bond potential energy surfaces (an early example of specific reaction parameters), bymulticonfiguration mol. mechanics, by the combined valence bond-mol. mechanics method, and by the use of valencebond states as coupled diabatic states for describing electronically nonadiabatic processes (photochem.). The essayincludes both ab initio and semiempirical approaches.~58 Citings

502. Molecular Mechanism for H2 Release from BH3NH3, Including the Catalytic Role of the Lewis Acid BH3

By Nguyen, Minh Tho; Nguyen, Vinh Son; Matus, Myrna H.; Gopakumar, G.; Dixon, David A.From Journal of Physical Chemistry A (2007), 111(4), 679-690. Language: English, Database: CAPLUS,DOI:10.1021/jp066175y

Electronic structure calcns. using various methods, up to the coupled-cluster CCSD(T) level, in conjunction with the aug-cc-pVnZ basis sets with n = D, T, and Q, extrapolated to the complete basis set limit, show that BH3 can act as anefficient bifunctional acid-base catalyst in the H2 elimination reactions of XHnYHn systems (X, Y = C, B, N). Such acatalyst is needed as the generation of H2 from isoelectronic ethane and borane amine compds. proceeds with an energybarrier much higher than that of the X-Y bond energy. The asymptotic energy barrier for H2 release is decreased from36.4 kcal/mol in BH3NH3 to 6.0 kcal/mol with the presence of BH3 relative to the mol. asymptote. The NH3 mol. can alsoparticipate in a similar catalytic process but induces a smaller redn. of the energy barrier. The kinetics of theseprocesses was analyzed by both transition-state and RRKM theory. The catalytic effect of BH3 was also probed by ananal. of the electronic densities of the transition structures using the atom-in-mol. (AIM) and electron localization function(ELF) approaches.~142 Citings

503. Atomic nanodesign

By Rieth, Michael; Schommers, WolframEdited By:Rieth, Michael; Schommers, WolframFrom Handbook of Theoretical and Computational Nanotechnology (2006), 1, 15-102. Language: English, Database:CAPLUS

A review on methods which are adequate for the theor. treatment of nanosystems, focusing on the mol. dynamicsmethod. The structure and dynamics of the atoms that form nanosystems are discussed, along with models andmethods for the description of interaction potentials, some principal points in connection with the Monte Carlo method,soln. of Schrodinger's equation for an electron in an interaction potential of general shape, methods of quantum chem.,types of interactions in condensed matter physics, detn. of pair potentials in metals, sensitivity of system propertiesagainst potential variations, and design of nanosystems.~3 Citings

504. CoPdx oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells

By Mustain, William E.; Kepler, Keith; Prakash, JaiFrom Electrochimica Acta (2006), 52(5), 2102-2108. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2006.08.020

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The electrochem. activity of C-supported Co-Pd alloy electrocatalysts of various compns. were studied for the oxygenredn. reaction in a 5 cm2 single cell polymer electrolyte membrane fuel cell. The polarization expts. were conducted atvarious temps. between 30 and 60° and the redn. performance compared with data from a com. Pt catalyst underidentical conditions. Study of the catalytic activity of the CoPdx PEMFC system with varying compn. reveals that anominal Co-Pd at. ratio of 1:3, CoPd3, exhibits the best performance of all studied catalysts, exhibiting a catalytic activitycomparable to the com. Pt catalyst. The ORR on CoPd3 has a low activation energy, 52 kJ/mol, and a Tafel slope of ∼60mV/decade, indicating that the rate-detg. step is a chem. step following the 1st electron transfer step and may involve thebreaking of the oxygen bond. The CoPd3 catalyst also exhibits excellent chem. stability, with the open circuit cell voltagedecreasing by only 3% and the obsd. current decreasing by only 10% at 0.8 V over 25 h. The CoPd3 catalyst alsoexhibits superior tolerance to MeOH crossover poisoning than Pt.~67 Citings

505. Reduction of O2 to Superoxide Anion (O2.bul.-) in Water by Heteropolytungstate Cluster-Anions

By Geletii, Yurii V.; Hill, Craig L.; Atalla, Rajai H.; Weinstock, Ira A.From Journal of the American Chemical Society (2006), 128(51), 17033-17042. Language: English, Database:CAPLUS, DOI:10.1021/ja064244g

Fundamental information concerning the mechanism ofelectron transfer from reduced heteropolytungstates (POMred)to O2, and the effect of donor-ion charge on redn. of O2 tosuperoxide anion (O2 .bul.-), is obtained using an isostructuralseries of 1e--reduced donors: α-Xn+W12O40 (9-n)-, Xn+ = Al3+,Si4+, P5+. For all three, a single rate expression is obsd.: -d[POMred]/dt = 2k12[POMred][O2], where k12 is for the rate-limiting electron transfer from POMred to O2. At pH 2 (175 mMionic strength), k12 increases from 1.4 ± 0.2 to 8.5 ± 1 to 24 ± 2M-1s-1 as Xn+ is varied from P5+ (3red) to Si4+ (2red) to Al3+

(1red). Variable-pH data (for 1red) and solvent-kinetic isotope(KIE = kH/kD) data (all three ions) indicate that protonatedsuperoxide (HO2·) is formed in two steps-electron transfer,followed by proton transfer (ET-PT mechanism)-rather than viasimultaneous proton-coupled electron transfer (PCET).Support for an outersphere mechanism is provided byagreement between exptl. k12 values and those calcd. usingthe Marcus cross relation. Further evidence is provided by thesmall variation in k12 obsd. when Xn+ is changed from P5+ toSi4+ to Al3+, and the driving force for formation of O2 .bul.- (aq),which increases as cluster-anion charge becomes more neg.,increases by nearly +0.4 V (a decrease of >9 kcal mol-1 in∆G°). The weak dependence of k12 on POM redn. potentialsreflects the outersphere ET-PT mechanism: as the anionsbecome more neg. charged, the "successor-complex" ion pairsare subject to larger anion-anion repulsions, in the order [(3ox 3-

)(O2 .bul.-)]4- < [(2ox 4-)(O2 .bul.-)]5- < [(1ox 5-)(O2 .bul.-)]6-. Thisreveals an inherent limitation to the use of heteropolytungstatecharge and redn. potential to control rates of electron transferto O2 under turnover conditions in catalysis.

~40 Citings

506. The origin of shallow n-type conductivity in boron-doped diamond with H or S co-doping. Density functionaltheory study

By Cai, Yu; Zhang, Tianhou; Anderson, Alfred B.; Angus, John C.; Kostadinov, Lubomir N.; Albu, Titus V.From Diamond and Related Materials (2006), 15(11-12), 1868-1877. Language: English, Database: CAPLUS,DOI:10.1016/j.diamond.2006.08.029

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The ionization potentials and the electron affinities of doped diamond were calcd. using B3LYP hybrid d. functional theoryand nanocryst. cluster models, while taking into account the quantum confinement of the charge carriers. In many casesdonor and acceptor levels were created in the middle of the gap between the conduction and valence bands. A possibleexplanation for the n-type behavior created by co-doping diamond films with B and S is given in terms of thermallyactivated electron donation from an SVS (V is vacancy) donor to a BB acceptor band. Both lie deep in the band gap. Itis proposed that electrons in the BB acceptor band are mobile charge carriers. It is also proposed that the conversion ofB-doped diamond from p-type cond., with hole charge carriers in the top of the valence band, to n-type cond., followingtreatment in a D plasma, may arise from formation of interstitial H donor levels and BnHm acceptor levels that create anacceptor band in which electrons are mobile. Again, both are deep in the band gap of pure diamond. In a prior attemptto explain this n-type behavior, BHn defects with unrelaxed structures were proposed to be shallow donors to thediamond conduction band. This paper shows that these defects become deep donors when their structures areoptimized. Finally, defects created from vacancies with 1-4 H in them are shown to be deep donors to the diamondconduction band.~17 Citings

507. Optimizing the Performance of the Multiconfiguration Molecular Mechanics Method

By Tishchenko, Oksana; Truhlar, Donald G.From Journal of Physical Chemistry A (2006), 110(50), 13530-13536. Language: English, Database: CAPLUS,DOI:10.1021/jp0640833

Multiconfiguration mol. mechanics (MCMM) is a general algorithm for constructing potential energy surfaces for reactivesystems. This paper illustrates how the performance of the MCMM method can be improved by adopting improved mol.mechanics parameters. We carry out calcns. of reaction rate consts. using variational transition state theory withoptimized multidimensional tunneling on the MCMM PESs for three hydrogen transfer reactions, and we compare theresults to direct dynamics. We find that the MCMM method with as little as one electronic structure Hessian can describethe dynamically important regions of the ground-electronic state PES, including the corner-cutting-tunneling region of thereaction swath, with practical accuracy.~23 Citings

508. Modeling the Kinetics of Bimolecular Reactions

By Fernandez-Ramos, Antonio; Miller, James A.; Klippenstein, Stephen J.; Truhlar, Donald G.From Chemical Reviews (Washington, DC, United States) (2006), 106(11), 4518-4584. Language: English, Database:CAPLUS, DOI:10.1021/cr050205w

A review. Theor. and computational modeling of bimol. reactions involving thermodn., kinetics, and energy transfer thatcan be used for gas-phase thermal reactions, gas-phase microcanonical and state-selected reactions, and condensed-phase chem. reactions are reviewed.~336 Citings

509. Rearrangements of cyclobutanes

By Tanko, J. M.Edited By:Rappoport, Zvi; Liebman, Joel FFrom Chemistry of Cyclobutanes (2005), 1, 497-519. Language: English, Database: CAPLUS,DOI:10.1002/0470864028.ch11

A review.~2 Citings

510. Antiaromaticity and aromaticity in carbocyclic four-membered rings

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By Eckert-Maksic, M.; Maksic, Z. B.Edited By:Rappoport, Zvi; Liebman, Joel FFrom Chemistry of Cyclobutanes (2005), 1, 17-81. Language: English, Database: CAPLUS,DOI:10.1002/0470864028.ch2

A review.~4 Citings

511. Unusual origins of isotope effects in enzyme-catalysed reactions

By Northrop, Dexter B.From Philosophical Transactions of the Royal Society, B: Biological Sciences (2006), 361(1472), 1341-1349.Language: English, Database: CAPLUS, DOI:10.1098/rstb.2006.1875

High hydrostatic pressure is a neglected tool for probing the origins of isotope effects. In chem. reactions, normalprimary deuterium isotope effects (DIEs) arising solely from differences in zero point energies are unaffected bypressure; but some anomalous isotope effects in which hydrogen tunneling is suspected are partially suppressed. Insome enzymic reactions, high pressure completely suppresses the DIE. The authors have now measured the effects ofhigh pressure on the parallel 13C heavy atom isotope effect of yeast alc. dehydrogenase and found that it is alsosuppressed by high pressure and, similarly, suppressed in its entirety. Moreover, the vol. changes assocd. with thesuppression of both deuterium and heavy atom isotope effects are virtually identical. The equivalent decrease inactivation vols. for hydride transfer, when one mass unit is added to the carbon end of a scissile C-H bond as when onemass unit is added to the hydrogen end, suggests a common origin. Given that carbon is highly unlikely to undergotunneling, it follows that hydrogen is not doing so either. The origin of these isotope effects must lie elsewhere. Theauthors offer protein domain motions as a possibility.~21 Citings

512. Characterization and theory of electrocatalysts based on scanning electrochemical microscopy screeningmethods

By Fernandez, Jose L.; White, J. Michael; Sun, Yangming; Tang, Wenjie; Henkelman, Graeme; Bard, Allen J.From Langmuir (2006), 22(25), 10426-10431. Language: English, Database: CAPLUS, DOI:10.1021/la061164h

A strategy for finding new electrocatalysts for the oxygen redn.reaction (ORR) in acidic solns. is outlined and illustrated withresults for Pd-Co catalysts. This is based on establishingguidelines for selecting test systems, rapid prepn. of arrays,and rapid screening by scanning electrochem. microscopy.Promising candidates are further tested as supportedelectrocatalysts by larger scale electrochem. methods and infuel cells, with optimization of the compn. and structure. Thosethat emerge are characterized by a variety of methods,including x-ray diffraction, SEM, and x-ray photoemissionspectroscopy. Finally, d. functional theory is used for detailedcalcns. of oxygen adsorption and dissocn. on the material andprovides better guidelines for further testing.

~60 Citings

513. The microwave spectrum of a two-top peptide mimetic: The N-acetyl alanine methyl ester molecule

By Plusquellic, David F.; Kleiner, Isabelle; Demaison, Jean; Suenram, Richard D.; Lavrich, Richard J.; Lovas, Frank J.;Fraser, Gerald T.; Ilyushin, Vadim V.From Journal of Chemical Physics (2006), 125(10), 104312/1-104312/13. Language: English, Database: CAPLUS,DOI:10.1063/1.2348871

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The rotational spectrum of N-acetyl alanine Me ester, a deriv. of the biomimetic, N-acetyl alanine N'-Me amide or alaninedipeptide, has been measured using a mini Fourier transform spectrometer between 9 and 25 GHz as part of a projectundertaken to det. the conformational structures of various peptide mimetics from the torsion-rotation parameters of low-barrier Me tops. Torsion-rotation splittings from two of the three Me tops capping the acetyl end of the -NH-C(=O)- andthe methoxy end of -C(=O)-O- groups account for most of the obsd. lines. In addn. to the AA state, two E states havebeen assigned and include an AE state having a torsional barrier of 396.45(7) cm-1 (methoxy rotor) and an EA statehaving a barrier of 64.96(4) cm-1 (acetyl rotor). The obsd. torsional barriers and rotational consts. of alanine dipeptideand its Me ester are compared with predictions from Moller-Plesset second-order perturbation theory (MP2) and d.functional theory (DFT) in an effort to explore systematic errors at the two levels of theory. After accounting for zero-point energy differences, the torsional barriers at the MP2/cc-pVTZ level are in excellent agreement with expt. for theacetyl and methoxy groups while DFT predictions range from 8% to 80% too high or low. DFT is found to consistentlyoverestimate the overall mol. size while MP2 methods give structures that are undersized. Structural discrepancies ofsimilar magnitude are evident in previous DFT results of cryst. peptides.~4 Citings

514. MnO2-Pt/C composite electrodes for preventing voltage reversal effects with polymer electrolyte membranefuel cells

By Wei, Z. D.; Ji, M. B.; Hong, Y.; Sun, C. X.; Chan, S. H.; Shen, P. K.From Journal of Power Sources (2006), 160(1), 246-251. Language: English, Database: CAPLUS,DOI:10.1016/j.jpowsour.2006.01.028

H2O is produced at the cathode of p-exchange membrane fuel cells (PEMFCs). If H2O is not removed effectively, itwould accumulate at the cathode and cause electrode flooding. The consequence is O starvation, thus increasing theconcn. overpotential of the cathode. In the worst scenarios, a p redn. reaction (PRR), instead of the O redn. reaction(ORR), may occur at the cathode. Not only will this cause a cathode potential drop, but the output voltage of a single cellwould likely be reversed due to O starvation. This phenomenon is termed the voltage reversal effect (VRE). To studyand resolve the VRE problem, a MnO2-Pt/C composite electrode was used to replace the conventional Pt/C electrode.Probably the electrochem. redn. of MnO2 in the composite electrode has almost the same Nernstian potential as theORR, which would serve as a substitute for the ORR in the case of O starvation. Thus, the voltage reversal effectcaused by PRR can be avoided. Two environments, N2- and O2-satd. H2SO4, were adopted to simulate 2 cases, i.e., O2starvation and O2 rich. MnO2-Pt/C can prevent the voltage reversal effect to a certain extent. In a N2-satd. 1 M H2SO4soln., the c.d. of the Pt/C electrode made of 0.6 mg Pt/cm2 was ∼0, while for the MnO2-Pt/C composite electrode made of0.4 mg Pt/cm2 and 0.8 mg MnO2/cm2, it was ≤10 mA/cm2. Though the current generated on the MnO2-Pt/C compositeelectrode in the case of O starvation is not as great as that in the case when O rich, it might be high enough for somecases, such as powering a radio, hearing-aid and so like miniature devices. In an O2-satd. 1 M H2SO4, the presence ofMnO2 in a MnO2-Pt/C composite electrode primarily plays a catalytic role in the ORR. It enhances the catalytic behaviorof Pt for the ORR. The impedance spectra of MnO2-Pt/C and Pt/C electrodes were carried out for the 2 gases in bubbledelectrolyte, which further confirmed that MnO2 in the composite electrode does substitute for O as an electron-acceptor inthe case of O starvation. The discharged MnO2 can then be restored to its initial state, regardless of whether it is in Orich or starved conditions.~15 Citings

515. Quantum chemical modelling of the rate determining step for oxygen reduction on quinones

By Johnsson Wass, J. R. Tobias; Ahlberg, Elisabet; Panas, Itai; Schiffrin, David J.From Physical Chemistry Chemical Physics (2006), 8(36), 4189-4199. Language: English, Database: CAPLUS,DOI:10.1039/b606671b

Two inner-sphere electrocatalytic channels for quinone-mediated redn. of mol. oxygen to form hydrogen peroxide wereaddressed by d. functional theory. Each of the channels comprises an initial rate detg. chem. step and a subsequentelectrochem. redn. step by which peroxide is produced. The redn. mechanism was detd. for 9,10-anthraquinone and9,10-phenanthrenequinone and the quantum chem. results are compared with exptl. results. Two distinctly differentstructures were detd. for the crit. chem. step depending on whether the catalytic site is present as HQ· or Q·-. While asuperoxo species is formed on HQ·, a van der Waals (vdW) type compd. is formed on Q·-. The Gibbs energy ofactivation for the semiquinone/oxygen reaction is largely detd. by the entropy term. The results explain the exptl. obsd.pH dependence of the O2 redn. rate on quinone functionalized electrodes.~7 Citings

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516. Conformational Product Control in the Low-Temperature Photochemistry of Cyclopropylcarbenes

By Zuev, Peter S.; Sheridan, Robert S.; Sauers, Ronald R.; Moss, Robert A.; Chu, GaoshengFrom Organic Letters (2006), 8(21), 4963-4966. Language: English, Database: CAPLUS, DOI:10.1021/ol0620601

Different conformers of two fused-ringcyclopropylchlorocarbenes are shown to undergo distinct,wavelength-selectable, photochem. in low-temp. matrixes.Conformers with H and Cl syn give ring expansionpredominantly, whereas those with H and Cl anti mainlyfragment.

~4 Citings

517. Theoretical study of H2O dissociation and CO oxidation on Pt2Mo(111)

By Wang, J. G.; Hammer, B.From Journal of Catalysis (2006), 243(1), 192-198. Language: English, Database: CAPLUS,DOI:10.1016/j.jcat.2006.07.009

DFT was used to study the adsorption and catalytic oxidn. of CO by H2O on a fully H2O-covered Pt2Mo(111) surface.Surface H2O was modeled by a double H2O bilayer. The calcns. quantify the role of the proposed mechanisms of theCO-tolerant behavior of Pt-based anode materials for low-temp. fuel cells. The Pt2Mo surface is more CO-tolerant thanthe pure Pt surface for 2 reasons. The ligand effect, in which the CO coverage is lowered through decreased bindingenergy at the Pt sites of the alloyed surface, is supported by calcd. CO binding energies of 0.3-0.4 eV on the H2O-covered alloy surface vs. much higher binding energies (0.8-1.2 eV) on the H2O-covered Pt surface. The bifunctionalmechanism in which H2O dissocs. into OH, which in turn oxidizes adsorbed CO into CO2, is also evident from the calcns.Although the dissocn. of H2O on Pt(111) is a highly endothermic reaction (∆E ∼ 0.5-0.6 eV), it becomes almost a thermo-neutral reaction on Pt2Mo(111), because the Mo sites bind the OH groups more strongly. The oxidn. of the adsorbed COis calcd. to proceed via formation of an adsorbed COOH intermediate. Depending on the initial CO adsorption site, theCOOH formation energy is ≥0.18 eV, meaning that CO oxidn. should be possible at moderate overpotentials. In terms ofthe H2O dissocn. step, the Pt2Mo(111) alloy surface is superior to similar PtNi and PtRu alloy surfaces.~28 Citings

518. Effect of Catalyst Properties on Membrane Degradation Rate and the Underlying Degradation Mechanism inPEMFCs

By Mittal, Vishal O.; Kunz, H. Russell; Fenton, James M.From Journal of the Electrochemical Society (2006), 153(9), A1755-A1759. Language: English, Database: CAPLUS,DOI:10.1149/1.2219708

Nafion membrane degrdn. was studied in a polymer electrolyte membrane fuel cell (PEMFC) under accelerated decayconditions. Fluoride emission rate (FER) detd. by fuel cell effluent water anal. was used to quantify the membranedegrdn. Membrane degrdn. is most likely caused either directly or indirectly by the species formed as a result of the H2and O2 reaction on the catalyst. To further understand the mechanism, the effects of the catalyst location, type, itsinteraction with O2 and H2O, and cell c.d. on the FER were studied and their implications on the underlying membranedegrdn. mechanism are discussed.~100 Citings

519. Automerization reaction of cyclobutadiene and its barrier height: An ab initio benchmark multireferenceaverage-quadratic coupled cluster study

By Eckert-Maksic, Mirjana; Vazdar, Mario; Barbatti, Mario; Lischka, Hans; Maksic, Zvonimir B.From Journal of Chemical Physics (2006), 125(6), 064310/1-064310/9. Language: English, Database: CAPLUS,DOI:10.1063/1.2222366

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The problem of the double bond flipping interconversion of the two equiv. ground state structures of cyclobutadiene(CBD) is addressed at the multireference av.-quadratic coupled cluster level of theory, which is capable of optimizing thestructural parameters of the ground, transition, and excited states on an equal footing. The barrier height involving boththe electronic and zero-point vibrational energy contributions is 6.3 kcal mol-1, which is higher than the best earlier theor.est. of 4.0 kcal mol-1. This result is confirmed by including into the ref. space the orbitals of the CC σ bonds beyond thestd. π orbital space. It places the present value into the middle of the range of the measured data (1.6-10 kcal mol-1). Anadiabatic singlet-triplet energy gap of 7.4 kcal mol-1 between the transition state 1Btg and the first triplet 3A2g state isobtained. A low barrier height for the CBD automerization and a small ∆E(3A2g,1B1g) gap bear some relevance on thehighly pronounced reactivity of CBD, which is briefly discussed.~16 Citings

520. X-Ray Absorption Spectroscopy Studies of Water Activation on an RhxSy Electrocatalyst for OxygenReduction Reaction Applications

By Ziegelbauer, J. M.; Gatewood, D.; Gulla, A. F.; Ramaker, D. E.; Mukerjee, S.From Electrochemical and Solid-State Letters (2006), 9(9), A430-A434. Language: English, Database: CAPLUS,DOI:10.1149/1.2218304

The prototype chalcogenide electrocatalyst RhxSy was probed in situ via a synchrotron-based X-ray absorption near-edge structure (XANES) technique to elucidate specific sites and modes of water activation during oxygen redn. reaction.X-ray diffraction revealed a mixt. of phases (Rh2S3, Rh3S4, and Rh17S15). Theor. generated XANES on a variety ofgeometries of O(H) adsorption on the predominant Rh3S4 phase were compared to the exptl. data. We show for the firsttime that the electrocatalyst first adsorbs O(H) in a onefold configuration at lower potentials and n-fold at potentialsgreater than 0.80 V. This expectedly has important consequences for oxygen redn. reaction on alternative chalcogenidematerials.~26 Citings

521. Importance of long-range interactions in chemical reactions at cold and ultracold temperatures

By Weck, Philippe F.; Balakrishnan, N.From International Reviews in Physical Chemistry (2006), 25(3), 283-311. Language: English, Database: CAPLUS,DOI:10.1080/01442350600791894

A review of the recent progress achieved in the theor. description of chem. reactions at low temps. In particular, wediscuss the crucial role played by the van der Waals interaction potential in quantum-mech. scattering calcns. of atom-diatom collisions in the cold and ultracold regimes, where abstraction reactions proceed by tunnelling. The importance ofzero-energy resonances in enhancing the reactivity in the zero-temp. limit is assessed. The impact of Feshbachresonances assocd. with the decay of metastable states of van der Waals complexes on reactive scattering is addressedthrough a series of examples. Finally, we discuss the sensitivity of the reaction dynamics to the topol. of the van derWaals well.~87 Citings

522. Multiconfiguration Molecular Mechanics Based on Combined Quantum Mechanical and MolecularMechanical Calculations

By Lin, Hai; Zhao, Yan; Tishchenko, Oksana; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2006), 2(5), 1237-1254. Language: English, Database: CAPLUS,DOI:10.1021/ct600171u

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The multiconfiguration mol. mechanics (MCMM) method is a general algorithm for generating potential energy surfacesfor chem. reactions by fitting high-level electronic structure data with the help of mol. mech. (MM) potentials. It waspreviously developed as an extension of std. MM to reactive systems by inclusion of multidimensional resonanceinteractions between MM configurations corresponding to specific valence bonding patterns, with the resonance matrixelement obtained from quantum mech. (QM) electronic structure calcns. In particular, the resonance matrix element isobtained by multidimensional interpolation employing a finite no. of geometries at which electronic-structure calcns. of theenergy, gradient, and Hessian are carried out. In this paper, we present a strategy for combining MCMM with hybridquantum mech. mol. mech. (QM/MM) methods. In the new scheme, electronic-structure information for obtaining theresonance integral is obtained by means of hybrid QM/MM calcns. instead of fully QM calcns. As such, the new strategycan be applied to the studies of very large reactive systems. The new MCMM scheme is tested for two hydrogen-transfer reactions. Very encouraging convergence is obtained for rate consts. including tunneling, suggesting that thenew MCMM method, called QM/MM-MCMM, is a very general, stable, and efficient procedure for generating potentialenergy surfaces for large reactive systems. The results are found to converge well with respect to the no. of Hessians.The results are also compared to calcns. in which the resonance integral data are obtained by pure QM, and thisillustrates the sensitivity of reaction rate calcns. to the treatment of the QM-MM border. For the smaller of the twosystems, comparison is also made to direct dynamics calcns. in which the potential energies are computed quantummech. on the fly.~33 Citings

523. Adsorption and Dissociation of H2O2 on Pt and Pt-Alloy Clusters and Surfaces

By Balbuena, Perla B.; Calvo, Sergio R.; Lamas, Eduardo J.; Salazar, Pablo F.; Seminario, Jorge M.From Journal of Physical Chemistry B (2006), 110(35), 17452-17459. Language: English, Database: CAPLUS,DOI:10.1021/jp063027z

The adsorption of H2O2 on Pt and Pt-M alloys, where M is Cr, Co, or Ni, is studied using d. functional theory. Bindingenergies calcd. with a hybrid DFT functional (B3PW91) are at -0.71 to -0.88 eV for H2O2 adsorbed with one of theoxygen atoms on top Pt positions of Pt3, Pt2M, and PtM2, and enhanced values at -0.81 to -1.09 eV are found on top Niand Co sites of the Pt2M clusters. Adsorption on top sites of Pt10 yields a weaker binding of -0.48 eV, whereas onperiodic Pt(111) and Pt3Co(111) surfaces, H2O2 generally dissocs. into 2 OH radicals. However, attempts to attach H2O2on bridge sites cause spontaneous dissocn. of H2O2 into 2 adsorbed OH radicals, suggesting that stable adsorptions onbridge sites are not possible for any of the clusters or extended surfaces that are being studied. Also the H2O-H2O2interaction reduces the strength of the adsorption of H2O2 on these clusters and surfaces.~62 Citings

524. Valence Bond - Rebirth of the Phoenix or Relic from the Stone Age

By Shurki, AvitalFrom Theoretical Chemistry Accounts (2006), 116(1-3), 253-261. Language: English, Database: CAPLUS,DOI:10.1007/s00214-005-0071-3

A review. The valence bond (VB) method has enjoyed its prime time during the early stages in the field of quantumchem. After the advent of MO methods VB lost its popularity but continued to be improved and refined by a smallcommunity of scientists who appreciated its power of revealing insight into the origins of chem. reactivity. This reviewsummarizes the developments of the VB theory in the past few decades by focusing on two major areas of research:Studies of the reactivity of small chem. systems and discovering the origins of enzyme catalysis. In both cases theunique capabilities of VB that facilitated discoveries of new concepts in an elegant and seemingly effortless way arediscussed. It is suggested that owing to the success of these discoveries VB methodol. is once again steadily gainingmomentum. It is believed that VB concepts will play a major role in the future of theor. chem.~8 Citings

525. Ab initio electronic structure theory as an aid to understanding excited state hydrogen transfer in moderateto large systems

By Webb, Simon P.From Theoretical Chemistry Accounts (2006), 116(1-3), 355-372. Language: English, Database: CAPLUS,DOI:10.1007/s00214-005-0011-2

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Hypocrellin and hypericin are naturally occurring polycyclic perylene quinones, and they have both been found to exhibitphotoactivated antiviral and anticancer activity. One mode of action proposed involves excited-state hydrogen transfer.Consequently these compds. have been widely studied using spectroscopic methods, and are found to both absorb andemit in the visible region. Recently an analog dihydroxy perylene quinone was synthesized in order to examine itsantiviral activity in relation to the naturally occurring compds. Its UV-visible absorption and emission spectra are quitedifferent to those of hypocrellin and hypericin, with very weak absorption and no visibility of emission at all. The ab initoexcited-state methods, CI singles (CIS), state-averaged complete active space SCF (SA-CASSCF), and SA-multireference perturbation theory (SA-MRMP2) are used to examine the origin of this different absorption and emissionbehavior. Owing to the size of these systems (between 24 and 40 heavy atoms) extensive use of parallel processoralgorithms was made, esp. a parallel AO-based CIS energy and gradient code developed at the ABCC. Theperformance of these methods, and possible, as well as future directions and prospects are discussed.~6 Citings

526. Multidimensional tunneling, recrossing, and the transmission coefficient for enzymatic reactions

By Pu, Jingzhi; Gao, Jiali; Truhlar, Donald G.From Chemical Reviews (Washington, DC, United States) (2006), 106(8), 3140-3169. Language: English, Database:CAPLUS, DOI:10.1021/cr050308e

A review on the reaction rate of enzyme-catalyzed reactions, with emphasis on the effects of multidimensional tunneling,recrossing, and the transmission coeff. The application of transition state theory (TST) to enzyme reactions is discussed,together with studies on quantum mech. tunneling effects in enzymes and non-statistical dynamical effects in enzymereactions, exptl. manifestations of hydrogen tunneling in enzymes, isotope effects on Arrhenius pre-exponential factors,temp. dependence of kinetic isotope effects (KIEs), conceptual models that explain the magnitudes of the measured KIEsand their temp. dependence, quant. computational methods used to elucidate the role of quantum mech. tunneling andrecrossing in enzyme catalysis, and estn. of recrossing transmission coeffs. for enzymic reactions.~248 Citings

527. Dissolution of Oxygen Reduction Electrocatalysts in an Acidic Environment: Density Functional TheoryStudy

By Gu, Zhihui; Balbuena, Perla B.From Journal of Physical Chemistry A (2006), 110(32), 9783-9787. Language: English, Database: CAPLUS,DOI:10.1021/jp063447o

DFT is employed to det. the reaction thermodn. of a group ofchem. and electrochem. reactions chosen to study the dissoln.of metal atoms from oxygen redn. reaction catalysts in an acidmedium. Once a set of thermodynamically allowed reactions isestablished, those reactions are selected to study the relativestabilities of Pt atoms and of other transition metal atoms (Ir,Pd, Rh, Ni, and Co) toward the dissoln. reactions. The dissoln.reactions that are found thermodynamically favorable areelectrochem. and involve adsorbed oxygenated compds. thatare intermediate species of the oxygen redn. reaction. Ir is themost stable among the various pure metals in comparison toPt. Most of the metals alloyed with Pt cause a decrease of thePt stability against dissoln., except for Ni, which does not affectit. However, the influence of Pt on the stability of the 2nd metalin the alloy follows the same trend as in pure metal catalysts,with Ir being the most stable. When both atoms in a PtM alloyare involved in dissoln. reactions, alloyed Ir is also found morestable than Pt in a given dissoln. reaction, and the samebehavior is found in alloyed Co for most of the reactionsstudied.

~52 Citings

528. Hybrid density functional theory investigation of the hydrogen abstraction reaction of fluoromethane by thehydroxyl radical

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By Mikel, Sean E.; Albu, Titus V.From Journal of Undergraduate Chemistry Research (2006), 5(2), 75-81. Language: English, Database: CAPLUS

A no. of hybrid d. functional theory methods have been used to calc. energetic and geometric parameters for thehydrogen abstraction reaction of fluoromethane by the hydroxyl radical, an important atm. reaction. The results showthat some of the theor. methods investigated here give calcd. classical barrier heights for the abstraction reaction that arevery small while other methods overestimate the recommended value. The detg. factor is the contribution of the Hartree-Fock exchange. We propose three new hybrid d. functional theory methods that give classical barrier heights in therange of the best est. proposed in the literature of 2.8-3.1 kcal/mol.~3 Citings

529. Quantum Tunneling in the Midrange Vibrational Fundamentals of Tropolone

By Redington, Richard L.; Redington, Theresa E.; Sams, Robert L.From Journal of Physical Chemistry A (2006), 110(31), 9633-9642. Language: English, Database: CAPLUS,DOI:10.1021/jp062068s

The Fourier transform IR spectrum of tropolone(OH) vapor in the 1175-1700 cm-1 region is reported at 0.0025 and 0.10cm-1 spectral resolns. The 12 vibrational fundamentals in this region of rapidly rising vibrational state d. are dominatedby mixts. of the CC, CO, CCH, and COH internal coordinates. Ests. based on the measurement of sharp Q branchpeaks are reported for 11 of the spectral doublet component sepns. DSν = |∆ν ± ∆0|. ∆0 = 0.974 Cm-1 is the known zero-point splitting, and three a1 modes show tunneling splittings ∆ν ≈ ∆0, four b2 modes show splittings ∆ν ≈ 0.90∆0, and theremaining four modes show splittings ∆νv falling 5-14% from ∆0. Significantly, the splitting for the nominal COH bendingmode ν8 (a1) is small, i.e., 10% from ∆0. Many of the vibrational excited states demonstrate strong anharmonic behavior,but there are only mild perturbations on the tautomerization mechanism driving ∆0. The data suggest, esp. for the higherfrequency a1 fundamentals, the onset of selective intramol. vibrational energy redistribution processes that are fast onthe time scale of the tautomerization process. These appear to delocalize and smooth out the topog. modifications of thezero-point potential energy surface that are anticipated to follow absorption of the νν photon. Further, the spectra showthe propensity for the ∆ν splittings of b2 and other complex vibrations to be damped relative to ∆0.~7 Citings

530. Kinetics of electrochemical O2 reduction on Pt

By Zhdanov, Vladimir P.; Kasemo, BengtFrom Electrochemistry Communications (2006), 8(7), 1132-1136. Language: English, Database: CAPLUS,DOI:10.1016/j.elecom.2006.05.003

The kinetics of O2 redn. on Pt (with NAFION as electrolyte) is 1st order in O2 in a wide range of reaction conditions.Recent DFT calcns. indicate that during this reaction the at.-O coverage may be appreciable. To adjust these twofindings, the authors analyze the reaction kinetics corresponding to the dissociative and associative mechanisms withparticipation of at. O. If the reaction steps are described by using the Langmuir equations, the kinetics are predicted tobe 1st order only in the situations when the O coverage is low. With O-O lateral interactions, the model based on theassociative mechanism is able to predict the 1st-order kinetics in a wide range of pressure even if the O coverage isappreciable.~30 Citings

531. Adiabatic approximations to internal rotation

By Allen, Wesley D.; Bodi, Andras; Szalay, Viktor; Csaszar, Attila G.From Journal of Chemical Physics (2006), 124(22), 224310/1-224310/9. Language: English, Database: CAPLUS,DOI:10.1063/1.2207614

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A no. of subtle and confusing issues are addressed concerning large amplitude motion (LAM) coordinates (χ) for internalmol. motions, using the Me rotation in acetaldehyde (CH3CHO) as a model problem. If the LAM coordinate is chosen tobe one of the H-C-C-O dihedral angles ρ1, ρ2, or ρ3, it lacks the required 2π/3 periodicity, and its use is thus undesirable.An excellent local internal coordinate for this model problem is τ3=1/3(ρ1+ρ2+ρ3-2π). A similarly good but nonlocalcoordinate for the adiabatic approxn. of internal rotation is provided by the intrinsic reaction coordinate s. Comparison ofthe mass-independent V0(τ3) and the mass-dependent V0(s) internal rotation curves shows that the two are virtuallyidentical for the parent isotopolog of acetaldehyde. A unified internal coordinate projection scheme for detg.complementary vibrational frequencies and subsequently VZPVE(χ) along a path for LAM has been formulated, whereVZPVE(χ) is the zero-point vibrational energy correction to the internal rotation curve. In addn. to its simplicity, theprojection scheme developed for a distinguished reaction path generated by constrained optimizations is appealingbecause the vibrational frequencies along the LAM path are invariant to chem. meaningful choices of the internalcoordinates for the complementary modes.~4 Citings

532. Hybrid density functional theory study of fragment ions generated during mass spectrometry of 1,3-dioxanederivatives

By Albu, Titus V.From Rapid Communications in Mass Spectrometry (2006), 20(12), 1871-1876. Language: English, Database:CAPLUS, DOI:10.1002/rcm.2530

It was recently reported that the cis,cis and trans,trans diastereoisomers of four 2(r)-R-2,4(R),6(S)-trimethyl-1,3-dioxanederivs. show distinct electron ionization mass spectra. As a possible explanation for this finding, probably the ionsgenerated during the mass spectrometry of these compds. could follow different fragmentation patterns that initiate fromdifferent ion conformations. Hybrid d. functional theory methods were used to study the conformational preference ofthree ions involved in the mass spectrometry of some 1,3-dioxane derivs. There is indeed more than one stable ionconformation for each of the studied ions. Energy profiles along the torsional coordinates connecting the conformers arepresented, and factors influencing the relative stability of ion conformations are discussed.~0 Citings

533. Thermal properties of solid coordination compounds. IV. Some applications in materials science

By Carp, Oana; Patron, Luminita; Segal, EugenFrom Revue Roumaine de Chimie (2006), 51(1), 5-12. Language: English, Database: CAPLUS

A review. The main applications of thermal reactions of solid coordination compds. in the field of materials science,namely generation of tailor-made materials with specific phys. or chem. properties, are crit. reviewed. The synthesis ofmixed oxides with various structures (spinel, garnet, hexagonal, perovskite) represents definitely the main application inthis field. The syntheses of sulfides, metals, nitrides, composite materials, and new complexes (which cannot besynthesized in aq. solns.) are also reviewed.~7 Citings

534. Theoretical insights into the structure and reactivity of the aqueous/metal interface

By Taylor, Christopher D.; Neurock, MatthewFrom Current Opinion in Solid State & Materials Science (2006), 9(1-2), 49-65. Language: English, Database:CAPLUS, DOI:10.1016/j.cossms.2006.03.007

A review describing recent developments in the theor. description of mol. and at. interactions occurring at the interfacebetween an aq. soln. and a metal surface. The effect of solvent upon reaction kinetics and thermodn. is the result ofsteric, as well as electrostatic participation. The authors describe theor. developments in the description of isolated, film,cluster and condensed phase models of water mols. on metal surfaces, electron and ion transfer between adsorbed andsoln. particles and the metal surface, chem. transformations of water on metal surfaces, and theor. studies of catalyticand electrocatalytic processes at the metal/water interface.~84 Citings

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535. Surface conductivity of undoped, hydrogen-terminated diamond

By Chakrapani, Vidhya; Anderson, Alfred B.; Angus, John C.From AIChE Annual Meeting, Conference Proceedings, Cincinnati, OH, United States, Oct. 30-Nov. 4, 2005 (2005),395c/1-395c/10. Language: English, Database: CAPLUS

A unique feature of H-terminated diamond is its surface cond. Although its origin is not fully understood, the proposedelectrochem. transfer-doping model is gaining acceptance. A p-type accumulation layer forms in the diamond when theFermi level of the diamond is higher than the chem. potential, µe, of electrons in an adsorbed H2O layer on the diamondsurface. The chem. potential of electrons in the H2O film is most likely fixed by the O redox couple. The cond. increasesupon exposure to acidic vapors and decreases when exposed to basic vapors, which lower and raise µe resp. Addn. ofH2O2, an intermediate in the electrochem. redn. of O, increases the effect. Increasing the surface work function byfluorinating or oxidizing the diamond eliminates the surface cond. Measurements of cond. in air and in vacuum weremade as a function of temp. and are consistent with the electrochem. transfer-doping model. This effect may not beunique to diamond, but may also be responsible for obsd. cond. in semiconducting C nanotubes. The results, in general,support the electrochem. transfer-doping model; however, some uncertainty remains in the nature of the electrochem.couple. Full understanding of the effect may enable a new class of sensors.~0 Citings

536. Hybrid Density Functional Theory with Specific Reaction Parameter: Hydrogen Abstraction Reaction ofFluoromethane by the Hydroxyl Radical

By Albu, Titus V.; Swaminathan, SaravananFrom Journal of Physical Chemistry A (2006), 110(24), 7663-7671. Language: English, Database: CAPLUS,DOI:10.1021/jp0615454

Three potential energy surfaces with specific reaction parameters are developed and tested for the OH + CH3F → H2O +CH2F reaction. The goal of this work is to det. surfaces that provide calcd. reaction rate consts. that are comparable tothe exptl. data. The potential energy surfaces are constructed using hybrid and hybrid meta d. functional theorymethods, and the levels of electronic structure theory used in this study are mPW1PW91, B1B95, and mPW1B95 inconjunction with the 6-31+G(d,p) basis set. The reaction rate consts. are calcd. over the range 200-1500 K usingvariational transition state theory with multidimensional tunneling contributions. New specific-reaction-parameterHartree-Fock contributions are detd., and the hybrid d. functional theory methods with these new contributions (35.5 ±1.2% for mPW1PW91, 36.6 ± 1.2% for B1B95, and 40.7 ± 1.2% for mPW1B95, resp.) reproduce accurate rate consts.over an extended temp. range. On these potential energy surfaces, the classical barrier height for the hydrogenabstraction reaction is detd. to be 3.4-3.8 kcal/mol, with a best est. value of 3.6 kcal/mol.~12 Citings

537. First principles reaction modeling of the electrochemical interface: Consideration and calculation of atunable surface potential from atomic and electronic structure

By Taylor, Christopher D.; Wasileski, Sally A.; Filhol, Jean-Sebastien; Neurock, MatthewFrom Physical Review B: Condensed Matter and Materials Physics (2006), 73(16), 165402/1-165402/16. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.73.165402

A method for calcg. and subsequently tuning the electrochem. potential of a half cell using periodic plane-wave d.functional theory and a homogeneous counter-charge is presented and evaluated by comparison to simulations whichexplicitly model the counter charge by a plane of ions. The method involves the establishment of 2 ref. potentials, onerelated to the potential of the free electron in vacuo, and the other related to the potential of H2O species far from theelectrode. The surface potential can be specifically adjusted by the explicit introduction of excess or deficit surfacecharges in the simulation cell and the application of periodic boundary conditions. The authors demonstrate the absenceof field emission from the electrode over the range of realistic electrochem. potentials covered and confirm that themethod can explicitly det. reaction energies and adsorption geometries as a function of electrochem. potential. Thislatter point is most useful as it asserts the viability of this method to model electrochem. and electrocatalytic systems ofacademic as well as applied interest. The authors present 2 case studies. The 1st examines the changes in thestructure of H2O at the metal interface as a function of potential over Cu(111). At cathodic potential, the authors observethe repulsion of H2O from the interface and the rotation of the H2O dipole toward the interface. The 2nd study follows theinitial pathways for the electrocatalytic activation of MeOH over Pt(111) and the corresponding potential dependentreaction energetics for these paths. Changes in the electrochem. potential can significantly alter the reaction energeticsas well as the overall reaction selectivity. While the case studies presented herein described equil. geometries (i.e., theideal forms at zero kelvin), the method is also suitable for application to ensembles of thermally activated systems.~54 Citings

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538. Thermal investigations of nickel-zinc ferrites formation from malate coordination compounds

By Carp, Oana; Patron, Luminita; Pascu, G.; Mindru, Ioana; Stanica, N.From Journal of Thermal Analysis and Calorimetry (2006), 84(2), 391-394. Language: English, Database: CAPLUS,DOI:10.1007/s10973-005-6920-4

Nickel-zinc ferrites have been synthesized via thermal decompn. of polynuclear coordination compds. contg. as ligandthe anion of malic acid, namely (NH4)[Fe2NixZn1-x(C4H4O5)(OH)3]·nH2O (x = 0.25, 0.5 and 0.75, n = 3 and 5). Acomparison between the thermal behavior of the studied polynuclear coordination compds. is inferred. Fe2NixZn1-xO4 (n= 0.25, 0.5 and 0.75) ferrites with mean particle sizes of 65-85 Å and free from other phases are formed after a heatingtreatment of only 1 h at 500°C.~9 Citings

539. Empirical Valence-Bond Models for Reactive Potential Energy Surfaces Using Distributed Gaussians

By Schlegel, H. Bernhard; Sonnenberg, Jason L.From Journal of Chemical Theory and Computation (2006), 2(4), 905-911. Language: English, Database: CAPLUS,DOI:10.1021/ct600084p

A new method for constructing empirical valence bond potential energy surfaces for reactions is presented. Building onthe generalized Gaussian approach of Chang-Miller, V12 2(q) is represented by a Gaussian times a polynomial at thetransition state and generalized to handle any no. of data points on the potential energy surface. The method is appliedto two model surfaces and the HCN isomerization reaction. The applications demonstrate that the present methodovercomes the divergence problems encountered in some other approaches. The use of Cartesian vs. internal orredundant internal coordinates is discussed.~43 Citings

540. Variational transition-state theory and multidimensional tunneling for simple and complex reactions in thegas phase, solids, liquids, and enzymes

By Truhlar, Donald G.Edited By:Kohen, Amnon; Limbach, Hans-HeinrichFrom Isotope Effects in Chemistry and Biology (2006), 579-619. Language: English, Database: CAPLUS,DOI:10.1201/9781420028027.ch22

A review. The assumptions underlying the formalism available for practical calcns. of the rate consts. and kinetic isotopeeffects of complex systems are discussed, with special emphasis on conceptual and operational issues such as thequasiequil. approxn., the reaction coordinate, quantization of vibration, treatment of tunneling, coupling of a primarysystem to a bath, and the different ways of putting the components of the calcns. together for reactions in the gas phase,liqs., and in enzymes. Some calcns. of KIEs are also presented.~35 Citings

541. Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphitesurface. I. H-chemisorbed case

By Martinazzo, Rocco; Tantardini, Gian FrancoFrom Journal of Chemical Physics (2006), 124(12), 124702/1-124702/14. Language: English, Database: CAPLUS,DOI:10.1063/1.2177654

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Collision induced (CI) processes involving hydrogen atoms on a graphite surface are studied quantum mech. within therigid, flat surface approxn., using a time-dependent wave packet method. The Eley-Rideal (ER) reaction and collisioninduced desorption (CID) cross sections are obtained with the help of 2 propagations which use different sets ofcoordinates, a product and a reagent set. Several adsorbate-substrate initial states of the target H atom in thechemisorption well are considered, and CI processes are studied over a wide range of projectile energy. (i) the Eley-Rideal reaction is the major reactive outcome and (ii) CID cross sections do not exceed 4 Å2 and present dynamicthresholds for low values of the target vibrational quantum no. ER cross sections show oscillations at high energieswhich cannot be reproduced by classical and quasiclassical trajectory calcns. They are related to the vibrationalexcitation of the reaction products, which is a rather steep decreasing function of the collision energy. This behaviorcauses a selective population of the low-lying vibrational states and allows the quantization of the product mol. states tomanifest itself in a collisional observable. A peak structure in the CID cross section is also obsd. and is assigned to theselective population of metastable states of the transient mol. hydrogen.~5 Citings

542. Studies on thermal decomposition of uranium(VI) and thorium(IV) complexes of o-carboxy N,N'-dimethylbenzylamine by thermoanalytical techniques in static air atmosphere

By Khan, Samina; Anwar, Chaudhary JamilFrom Radiochimica Acta (2006), 94(1), 23-28. Language: English, Database: CAPLUS, DOI:10.1524/ract.2006.94.1.23

The o-carboxy N-N'-dimethylbenzylamine uranium(VI) and thorium(IV) complexes, o-C6H4COOHCH2N(CH3)2UO2SO4 (I),o-C6H4COOHCH2N(CH3)2UO2(NO3)2 (II), o-C6H4COOHCH2N(CH3)2UO2Cl2 (III), and o-C6H4COOHCH2N(CH3)2Th(NO3)4 (IV) were prepd. and studied by means of thermoanal. techniques in static air atm. tounderstand their mode of decompn. and thermal stability. Their compns. were investigated by elemental anal. in order toensure their purity, and structure elucidations were based on proton NMR and IR spectra. Study of their thermaldecompn. showed that they pyrolyzed in stages: the degrdn. of square bipyramidal complexes (I and III) occurred in fourstages; hexagonal bipyramidal complex (II) also followed the same pattern. The decompn. of bicapped square antiprismcomplex (IV) proceeded in three steps. The thermal decompn. of these complexes occurred with the loss of inorg. andorg. fragments and exhibited almost the same mode of decompn. The compn. of the intermediate formed during degrdn.was confirmed by microanal. and IR spectroscopy. The residue after heating above 480 °C corresponded to metal oxide.It follows from the results that the thermal stability of the complexes increases in the following sequence: Complex II,Complex IV < Complex III < Complex I.~6 Citings

543. Flocculation-Induced Homolysis of Hydrogen Peroxide in Aqueous Colloid Solution of Titanium DioxideNanoparticles

By Du, Yikui; Rabani, JosephFrom Journal of Physical Chemistry B (2006), 110(12), 6123-6128. Language: English, Database: CAPLUS,DOI:10.1021/jp0567117

Thermal generation of oxygen and hydroxylated arom. compds. by hydrogen peroxide, catalyzed by flocculation oftitanium dioxide nanocrystallites aq. suspension upon addn. of hydrogen peroxide, is reported. The oxidn. involvescatalytic cleavage of a peroxide mol. followed by hydroxyl reaction with the org. solutes. The catalytic hydroxylation isassocd. with formation of TiO2-H2O2 aggregates, which occurs within a specific range of [TiO2]/[H2O2] ratio. Comparisonof the activation energy to literature values in the absence of nanoparticles indicates that flocculation induces an increaseof the rate without decreasing the activation energy. This is, to the best of our knowledge, a unique case of nanoparticlescatalysis driven by formation of a three-dimensional structure of the suspended particles.~10 Citings

544. Convergent Iterative Constrained Variation Algorithm for Calculation of Electron-Transfer Transition States

By Aryanpour, M.; Rai, V.; Pitsch, H.From Journal of the Electrochemical Society (2006), 153(3), E52-E57. Language: English, Database: CAPLUS,DOI:10.1149/1.2160449

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We present an efficient math. framework to det. the potential-dependent transition states of electron transfer reactions byquantum calcns. This approach makes it more feasible to study heterogeneous electron transfer processes with thetheory of local reaction center for electron transfer. It is shown that the new formulation regenerates previously publishedresults obtained by the constrained variation method. Our soln. algorithm replaces the constrained optimization problemdefined in a multidimensional space by a single equation in terms of only one variable that is solved for in each iteration.This method leads to fast convergence, reliability, and robustness of the located transition states for more complexsystems with a larger no. of degrees of freedom, esp. for smooth energy surfaces.~13 Citings

545. Effect of Pressure on a Heavy-Atom Isotope Effect of Yeast Alcohol Dehydrogenase

By Park, Hyun; Girdaukas, Gary G.; Northrop, Dexter B.From Journal of the American Chemical Society (2006), 128(6), 1868-1872. Language: English, Database: CAPLUS,DOI:10.1021/ja056525e

Hydrostatic pressure causes a monophasic decrease in the 13Cprimary isotope effect expressed on the oxidn. of benzyl alc. byyeast alc. dehydrogenase. The primary isotope effect wasmeasured by the competitive method, using whole-mol. massspectrometry. The effect is therefore an expression of isotopicdiscrimination on the kinetic parameter V/K, which measuressubstrate capture. Moderate pressure increases capture byactivating hydride transfer, the transition state of which musttherefore have a smaller vol. than the free alc. plus thecapturing form of enzyme [Cho, Y.-K.; Northrop, D. B. Biochem.1999, 38, 7470-7475]. The decrease in the 13C isotope effectwith increasing pressure means that the transition state forhydride transfer from the heavy atom must have an evensmaller vol., measured here to be 13 mL·mol-1. The pressuredata factor the kinetic isotope effect into a semiclassicalreactant-state component, with a null value of k12/k13 = 1, and atransition-state component of Q12/Q13 = 1.028 (borrowing Bell'snomenclature for hydrogen tunneling corrections). A similarexpt. involving a deuterium isotope effect previously returnedthe same vol. and null value, plus a pressure-sensitive isotopeeffect [Northrop, D. B.; Cho, Y.-K. Biochem. 2000, 39, 2406-2412]. Consistent with precedence in the chem. literature, thelatter suggested a possibility of hydrogen tunneling; however, itis unlikely that carbon can engage in significant tunneling atambient temp. The fact that the decrease in activation vols. forhydride transfer is equiv. when one mass unit is added to thecarbon end of a scissile C-H bond and when one mass unit isadded to the hydrogen end is significant and suggests acommon origin.

~16 Citings

546. Current status of ab initio quantum chemistry study for oxygen electroreduction on fuel cell catalysts

By Shi, Zheng; Zhang, Jiujun; Liu, Zhong-Sheng; Wang, Haijiang; Wilkinson, David P.From Electrochimica Acta (2006), 51(10), 1905-1916. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2005.07.006

A review. Recent progress in the ab initio quantum chem. study of cathode oxygen redn. on fuel cell catalysts isreviewed with emphasis on d. functional theory and ab initio mol. dynamics methods. The capabilities of these methodsare illustrated using examples of oxygen adsorption on transition metals and alloys, and the redn. mechanism. Ab initiostudies can calc. adsorption geometry, energy, the dissocn. energy barrier, reversible potential, activation energy, andpotential dependant properties for elementary electron transfer steps. Even though ab initio study in this field is still at anearly stage, it has already demonstrated its predictive ability in the trend of adsorption energy on transition metals andalloys, and illustrated its potential in identifying better electrocatalysts.~100 Citings

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547. Quantum Chemical Modeling of the Reduction of Quinones

By Johnsson Wass, J. R. Tobias; Ahlberg, Elisabet; Panas, Itai; Schiffrin, David J.From Journal of Physical Chemistry A (2006), 110(5), 2005-2020. Language: English, Database: CAPLUS,DOI:10.1021/jp055414z

A systematic study of the redox properties of six parent quinones has been carried out using quantum chem. methods.The redn. of the ortho (o-) and para (p-) isomers of benzoquinone and naphthoquinone, 9,10-anthraquinone and 9,10-phenanthrenequinone to the corresponding hydroquinones and semiquinone radicals was investigated at the B3LYP/6-311+G(d,p) level of theory. Thermodn. functions in the gas-phase were calcd. for all the redn. reactions. Gibbs energiesof reaction and std. potentials in water for the redns. were detd. using the IEF-PCM model and an empirical correction tothe calcns. based on the limited thermodn. data available for the quinones. Potentials were calcd. both for the directredn. to the quinols, and for the two-step redn. via the neutral semiquinones. The calcd. potentials for the 2e-, 2H+ redns.were found in good agreement with expt. and to display the same trends as gas-phase enthalpies and energies, i.e., tocorrelate with the no. of C:C double bonds, as well as on the relative position of the C:O groups. The small deviationsbetween expt. and theor. predicted std. potentials were found to originate from basis set incompleteness and theshortcomings in the B3LYP exchange correlation functional rather than the models used for the thermochem. calcns. ordescription of solvation. Accurate theor. shifts in std. potentials for the p-/o- pairs of Q ↔ HQ and HQ ↔ H2Q reactionsare presented and compared to expt. Reliable std. potentials and shifts for the neutral semiquinones are predicted forthe first time.~18 Citings

548. A molecular orbital analysis of Cu(I)-catalyzed cyclopropanation using diazoalkanes with CH3 and CF3substituents

By Howell, James A. S.From Dalton Transactions (2006), (4), 545-553. Language: English, Database: CAPLUS, DOI:10.1039/B510011A

The mechanism of cyclopropanation catalyzed by Cu(I) complexes has been investigated by calcn. using a series ofdiazoalkanes contg. inductive electron donating (methyl) and withdrawing (CF3) substituents and a range of metalfragments (Cu+, [(DAB)Cu]+, ClCu and (triflate)Cu). Copper-diazoalkane complexes exist as an equil. of C- and N-bonded isomers. Catalysis occurs through lowering of the activation energy for rate detg. C-N bond cleavage of the C-bonded isomer; this is most marked for (triflate)Cu. Direct reaction of the copper-carbene complex occurs to yield stablecupracyclobutanes in all but one case. Associative substitution of the cupracyclobutane by diazoalkane completes thecatalytic cycle.~7 Citings

549. O2 Reduction on Graphite and Nitrogen-Doped Graphite: Experiment and Theory

By Sidik, Reyimjan A.; Anderson, Alfred B.; Subramanian, Nalini P.; Kumaraguru, Swaminatha P.; Popov, Branko N.From Journal of Physical Chemistry B (2006), 110(4), 1787-1793. Language: English, Database: CAPLUS,DOI:10.1021/jp055150g

An exptl. and theor. study of electroredn. of O2 to H2O2 is presented. The exptl. measurements of nitrided Ketjenblackindicated an onset potential for redn. of ∼0.5 V (SHE) compared to the onset potential of 0.2 V obsd. for untreated C.Quantum calcns. on cluster models of nitrided and un-nitrided graphite sheets show that C radical sites formed adjacentto substitutional N in graphite are active for O2 electroredn. to H2O2 via and adsorbed OOH intermediate. The weakcatalytic effect of untreated C is attributed to weaker bonding of OOH to the H atom-terminated graphite edges.Substitutional N atoms that are far from graphite sheet edges will be active, and those that are close to the edges will beless active. Interference from electrochem. redn. of H atoms on the reactive sites is considered, and in the potentialrange of H2O2 formation the reactive sites are not blocked by adsorbed H atoms.~442 Citings

550. Effect of cobalt bis(dicarbollides) on electrochemical oxygen reduction on Pt electrode in methanol-acidsolution

By Shiroishi, Hidenobu; Ayato, Yusuke; Rais, Jiri; Kunimatsu, Keiji; Osawa, Masatoshi; Okada, TatsuhiroFrom Electrochimica Acta (2006), 51(7), 1225-1234. Language: English, Database: CAPLUS,DOI:10.1016/j.electacta.2005.06.017

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Electrochem. oxygen redn. on a Pt electrode was studied in MeOH-0.05 M H2SO4 aq. solns. in the presence of acids ofCo bis(dicarbollide) (H+B-, H+[(1,2-C2B9H11)2-3-Co](-)) or its hexachlorinated deriv. (H+BCl-, H+[(8,8',9,9',12,12'-Cl6(1,2-C2B9H8)2-3-Co)](-)). MeOH oxidn. was suppressed with H+BCl- significantly, and selective oxygen redn. was achieved ona Pt electrode. The efficiency of oxygen redn. to H2O, which depended on the electrode potential, was lower by 2% to20% than that without H+BCl-. The mechanism was studied by surface-enhanced IR absorption spectroscopy (SEIRAS).H+BCl- suppresses formation of both the catalytic poison, linear CO (ads.), from MeOH and the formate, the intermediateof the non-CO path of MeOH oxidn.~5 Citings

551. Co9S8 as a Catalyst for Electroreduction of O2: Quantum Chemistry Predictions

By Sidik, Reyimjan A.; Anderson, Alfred B.From Journal of Physical Chemistry B (2006), 110(2), 936-941. Language: English, Database: CAPLUS,DOI:10.1021/jp054487f

The slab band quantum computational approach in the Vienna ab initio simulation package (VASP) is used to calc. theadsorption energies of reactants, reaction intermediates, and products in O2 redn. and in H2O oxidn. in acid on 3crystallog. surfaces of pentlandite structure Co9S8. Reversible potentials for the reaction steps involving electron andproton transfer are detd. by using the energies in a linear Gibbs free energy relation. The partially OH-covered (202)surface is active toward O2 redn. and should have overpotential behavior similar to that obsd. for Pt electrodes. Onestructure in the predicted 4-electron redn. mechanism is novel:S2- provides an adsorption site for O following O-O bondscission, which, unlike the case of Pt electrodes, takes place prior to the 1st redn. step.~117 Citings

552. Electrochemical reduction of the O2 molecule to the O2- radical ion - A theoretical approach

By Ignaczak, Anna; Schmickler, Wolfgang; Bartenschlager, SonjaFrom Journal of Electroanalytical Chemistry (2006), 586(2), 297-307. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2005.09.020

Quantum effects in the kinetics of the reaction O2 + e → O2 - were evaluated theor. The spectral properties and thepotential energy curves of the oxygen mol. and the superoxide ion were obtained from quantum DFT calcns. at theG96PW91/6-311+G* level. From these curves, the vibrational eigenfunctions and eigenvalues of the reactant and theproduct were calcd. The corresponding nonadiabatic redn. rate was obtained from 1st-order perturbation theory. Thepartial contributions coming from the ground and excited states of both species are analyzed. The contribution of the O2- excited states to the rate is negligibly small for low overpotentials. Their participation rises when higher overpotentialsare applied.~16 Citings

553. Hybrid ab initio VB/MM Method - A Valence Bond Ride through Classical Landscapes

By Shurki, Avital; Crown, Hadar A.From Journal of Physical Chemistry B (2005), 109(49), 23638-23644. Language: English, Database: CAPLUS,DOI:10.1021/jp054913x

The development of a new hybrid (QM/MM) method, where the QM part is treated by ab initio valence bond (VB) theoryis presented. This VB/MM method has the advantages of empirical VB (EVB) methodol. but does not rely on empiricalparameterization for the quantum part. The method implements embedding of the quantum region of each diabatic statesep., by treating the electrostatic interactions between QM and MM regions classically. Addnl., it assumes that changesof the off diagonal matrix element due to different environments are such that the overall resonance integral does notchange. These assumptions are discussed in detail and the validity of the method is shown to be successful in threedifferent bond dissocn. processes, where bond dissocn. as well as solvation energies compare very well with the exptl.data.~28 Citings

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554. Why Is There Such a Small Overpotential for O2 Electroreduction by Copper Laccase?

By Schweiger, Hannes; Vayner, Ellen; Anderson, Alfred B.From Electrochemical and Solid-State Letters (2005), 8(11), A585-A587. Language: English, Database: CAPLUS,DOI:10.1149/1.2050547

Quantum chem. predictions are made of reversible potentials for intermediates formed during the four-electron redn. ofO2 by copper laccase, using three loosely assocd. partially ligated CuI centers as models for the active site. Twomechanisms are studied, the platinum surface mechanism in acid electrolyte, and the proposed laccase mechanism forbasic electrolyte. Both are found viable. The CuII-OH- redn. to H2O step has the lowest potential, making it responsiblefor the predicted low overpotential. Compared to laccase, the overpotential is somewhat high but completing the ligandcoordination would be expected to lead to smaller predicted overpotentials.~17 Citings

555. Dynamics of the Concerted Triple Proton Transfer in Cyclic Water Trimer Using the MulticonfigurationMolecular Mechanics Algorithm

By Kim, Yangsoo; Kim, YonghoFrom Journal of Physical Chemistry A (2006), 110(2), 600-608. Language: English, Database: CAPLUS,DOI:10.1021/jp0530193

Cyclic water clusters are important mol. species to understand the nature of hydrogen bonded networks. Theor. studiesfor the dynamics of triple proton transfer in the cyclic water trimer were performed. The potential energy surface (PES) oftriple proton transfer is generated by the multiconfiguration mol. mechanics (MCMM) algorithm. We have used theMP2/6-31G(d,p) level for high-level ab initio data (energies, gradients, and Hessians), which are used in the Shepardinterpolation. Eight high-level ref. points were added step by step, including two points for the crit. configurations of thelarge curvature tunneling paths. The more high-level points are used, the better the potential energy surfaces become.The rate const. and kinetic isotope effect (KIE) for the triple proton transfer at 300 K, which have been calcd. by thecanonical variational transition-state theory with microcanonical optimized multidimensional semiclassical tunnelingapproxn., are 1.6 × 10-3 s-1 and 230, resp. Tunneling is very important not only for the triple proton transfer but also forthe triple deuterium transfer. The MCMM results show good agreement with those from the direct ab initio dynamicscalcns.~9 Citings

556. Electrochemical effects on diamond surfaces: Wide potential window, reactivity, spectroscopy, dopinglevels and surface conductivity

By Martin, Heidi B.; Eaton, Sally C.; Landau, Uziel; Angus, John C.Edited By:Fujishima, AkiraFrom Diamond Electrochemistry (2005), 26-50. Language: English, Database: CAPLUS, DOI:10.1016/B978-044451908-5/50005-X

A review. Diamond is finding application as an electrode material because of its extremely wide potential window in aq.soln., low background currents, resistance to fouling, chem. stability in aggressive environments, lack of surface oxide,transparency, and relative ease of functionalization. These attributes make diamond esp. attractive for sensors, for thegeneration of highly reactive intermediates, for electrosynthesis, and for spectroscopic studies of surface processes.Also, the inter-relation between surface cond. and the chem. environment provides another means for the study ofdiamond and may serve as the basis for sensors.~2 Citings

557. Quantum Effects in an Exoergic, Barrierless Reaction at High Collision Energies

By Martinazzo, Rocco; Tantardini, Gian FrancoFrom Journal of Physical Chemistry A (2005), 109(42), 9379-9383. Language: English, Database: CAPLUS,DOI:10.1021/jp053820c

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The exoergic Eley-Rideal hydrogen recombination on graphitesurfaces is known to produce vibrationally hot product mols.Realistic quantum scattering calcns. at normal incidence over awide range of collision energies show that the degree ofvibrational excitation of the reaction product is a steepdecreasing function of the collision energy. This results inselective population of the lower-lying vibrational levels andgives rise to an oscillating structure in the total reaction cross-sections at high energies, which cannot be reproduced byclassical and quasi-classical trajectory calcns. An analogousquantum structure appears in the total collision-induceddesorption cross-sections and is assigned to selectivepopulation of the metastable states of the transient mol.hydrogen.

~21 Citings

558. Anharmonic spectra of methanol and silanol: A comparative study

By Partal Urena, F.; Lopez Gonzalez, J. J.; Marquez, F.From Journal of Molecular Spectroscopy (2005), 233(2), 203-209. Language: English, Database: CAPLUS,DOI:10.1016/j.jms.2005.07.001

Anharmonic vibrational spectra of methanol and silanol as well as of some of their deuterated isotopomers are analyzedusing the vibrational SCF approxn. cor. by second order perturbation theory (cc-VSCF). Exptl. frequencies in the case ofmethanol and its isotopomers are in general reproduced and anharmonic effects in their vibrational spectra are suitablyexplained. The similar species contg. Si, i.e., silanol, is very unstable. Exptl. data about its vibrational spectra are rare inthe literature and the only theor. data available come from the harmonic approach. Thus, to predict further anharmoniceffects in its vibrational spectra, we extend our results on methanol to the silanol mol.~2 Citings

559. Design of Oxygen Reduction Bimetallic Catalysts: Ab-Initio-Derived Thermodynamic Guidelines

By Wang, Yixuan; Balbuena, Perla B.From Journal of Physical Chemistry B (2005), 109(40), 18902-18906. Language: English, Database: CAPLUS,DOI:10.1021/jp0543779

The Gibbs free energies of key elementary steps for the electrocatalytic oxygen redn. reaction (ORR) are calcd. withB3LYP type of d. functional theory: O2 + M + H+ + e- (0 eV) → HOO-M (∆G1), HOO-M + M → HO-M + O-M (∆G2), O2 +2M + H+ + e- (0 eV) → O-M + HO-M (∆G3), and HO-M + O-M + 3H+ + 3e- (0 eV) → 2H2O + 2M (∆G4), where H+ ismodeled as H3 +O(H2O)3 and M stands for the adsorption site of a metal catalyst modeled by a single metal atom as wellas by an M3 cluster. Taking Pt as a ref., ∆G4 is plotted against ∆G1 for 17 metals from groups V to XII. No single metalhas both ∆G1 and ∆G4 more neg. than Pt, although some of them have either more neg. ∆G1 or more neg. ∆G4. Thisenables one to explain thermodynamically why no other single metal catalyzes the ORR as effectively as Pt does. Also,a thermodn. anal. reveals that the signs of ∆∆G (the difference between ∆G of other metals and ∆G of Pt) stronglycorrelate with the valence electronic structure of metals, i.e., ∆∆G1 < 0 and ∆∆G4 > 0 for metals M with vacant valence dorbitals, whereas ∆∆G1 > 0 and ∆∆G4 < 0 for metals M' with fully occupied valence d orbitals. Thus, a simple thermodn.rule for the design of bimetallic catalysts for the ORR is proposed: couple a metal M (∆∆G1 < 0) with a 2nd metal M'(∆∆G4 < 0) to form an alloy catalyst MM'3. The rationale behind this selection is based on M being more efficient for therate-detg. step, i.e., for the formation of the adsorbed species M-OOH, while M' can enhance the redns. of O and OH inthe last 3 electron-transfer steps.~143 Citings

560. Electric field induced electron transfer at the adsorbate-surface interface. Effect of the type of metal surface

By Migani, Annapaola; Sousa, Carmen; Sanz, Fausto; Illas, FrancescFrom Physical Chemistry Chemical Physics (2005), 7(18), 3353-3358. Language: English, Database: CAPLUS,DOI:10.1039/b505481h

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The ab initio two-state model for electron transfer induced by an external elec. field has been applied to the chlorideoxidn. on Cu, Rh, Pd, Ag, Pt and Au (001) surface models. The two electronic states involved in the model representphys. situations where the electron transferred from the chloride anion to the metal surface lies either on the halide or onthe metal substrate. The model assumes that electron transfer takes place when these two states become degenerateand this is achieved by applying an external elec. field. Two different situations representing either ultrahigh vacuum orelectrochem. conditions have been considered. For the former the present study shows that elec. field necessary toachieve degeneracy of the two electronic states is directly related to the metal surface work function whereas for thelatter, it is found to be rather insensitive to the metal surface.~6 Citings

561. A New Algorithm for Efficient Direct Dynamics Calculations of Large-Curvature Tunneling and ItsApplication to Radical Reactions with 9-15 Atoms

By Fernandez-Ramos, Antonio; Truhlar, Donald G.From Journal of Chemical Theory and Computation (2005), 1(6), 1063-1078. Language: English, Database: CAPLUS,DOI:10.1021/ct050153i

We present a new algorithm for carrying out large-curvature tunneling calcns. that account for extreme corner-cuttingtunneling in hydrogen atom, proton, and hydride transfer reactions. The algorithm is based on two-dimensionalinterpolation in a phys. motived set of variables that span the space of tunneling paths and tunneling energies. With thisnew algorithm, we are able to carry out d. functional theory direct dynamics calcns. of the rate consts., includingmultidimensional tunneling, for a set of hydrogen atom transfer reactions involving 9-15 atoms and up to 7 nonhydrogenicatoms. The reactions considered involve the abstraction of a hydrogen atom from hydrocarbons by a trifluoromethylradical, and in particular, we consider the reactions of CF3 with CH4, C2H6, and C3H8. We also calc. several kineticisotope effects. The electronic structure is treated by the MPWB1K/6-31+G(d,p) method, which is validated bycomparison to exptl. results and to CBS-Q, MCG3, and G3SX(MP3) calcns. for CF3 + CH4. Harmonic vibrationalfrequencies along the reaction path are calcd. in curvilinear coordinates with scaled frequencies, and anharmonicity isincluded in the lowest-frequency torsion.~24 Citings

562. Substitutional Nitrogen in Nanodiamond and Bucky-Diamond Particles

By Barnard, A. S.; Sternberg, M.From Journal of Physical Chemistry B (2005), 109(36), 17107-17112. Language: English, Database: CAPLUS,DOI:10.1021/jp0524126

The inclusion of dopants (such as N) in diamond nanoparticles is expected to be important for use in future nanodevices,such as qubits for quantum computing. Although most com. diamond nanoparticles contain a small fraction of N, it is stillunclear whether it is located within the core or at the surface of the nanoparticle. Presented here are d. functional tightbinding simulations examg. the configuration, potential energy surface, and electronic charge of substitutional N innanodiamond and bucky-diamond particles. The results predict that N probably is positioned at the surface of bothhydrogenated nanodiamond and (dehydrogenated) bucky-diamond, and that the coordination of the dopants within theparticles is dependent upon the surface structure.~62 Citings

563. Electroreduction Activity of Hydrogen Peroxide on Pt and Au Electrodes

By Li, Xiao; Heryadi, Dodi; Gewirth, Andrew A.From Langmuir (2005), 21(20), 9251-9259. Language: English, Database: CAPLUS, DOI:10.1021/la0508745

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H2O2 electroredn. on both catalytically active Pt and inactive Ausurfaces are studied by using both surface-enhanced Ramanspectroscopy (SERS) and d. functional theory (DFT) calcns.SERS measurements on Pt show Pt-OH at neg. potentials,which suggests that hydroxide is formed as an intermediateduring the electroredn. process. Addnl., the O-O stretch modeof H2O2 is obsd. on Pt, which shifts to lower energy as potentialis swept neg., indicating that the O-O bond is elongated. Forcomparison, there is no variation in the energy of the same O-O mode on Au surfaces, and there is no observation of Au-OH.DFT calcns. show that H2O2 adsorption on Pt(110) results inthe dissocn. of O-O bond and the formation of Pt-OH bond. OnAu, O-O bond elongation is calcd. to occur only on the (110)face. However, the magnitude of the elongation is muchsmaller than that found on Pt(110).

~47 Citings

564. Simulation and bonding of dopants in nanocrystalline diamond

By Barnard, A. S.; Russo, S. P.; Snook, I. K.From Journal of Nanoscience and Nanotechnology (2005), 5(9), 1395-1407. Language: English, Database: CAPLUS,DOI:10.1166/jnn.2005.306

A review. The doping of the wide-band gap semiconductor diamond has lead to the invention of many electronic andoptoelectronic devices. Impurities can be introduced into diamond during chem. vapor deposition or high pressure-hightemp. growth, resulting in materials with unusual phys. and chem. properties. For electronic applications one of the mainobjectives in the doping of diamond is the prodn. of p-type and n-type semiconductors materials; however, the study ofdopants in diamond nanoparticles is considered important for use in nanodevices, or as qubits for quantum computing.Such devices require that bonding of dopants in nanodiamond must be positioned substitutionally at a lattice site, andmust exhibit minimal or no possibility of diffusion to the nanocrystallite surface. In light of these requirements, a no. ofcomputational studies have been undertaken to examine the stability of various dopants in various forms of nanocryst.diamond. Presented here is a review of some such studies, undertaken using quantum mech. based simulationmethods, to provide an overview of the crystal stability of doped nanodiamond for use in diamondoid nanodevices.~8 Citings

565. Potential Energy Surface Profile of the Oxygen Reduction Reaction on a Pt Cluster: Adsorption andDecomposition of OOH and H2O2

By Wang, Yixuan; Balbuena, Perla B.From Journal of Chemical Theory and Computation (2005), 1(5), 935-943. Language: English, Database: CAPLUS,DOI:10.1021/ct0500794

Because of their essential roles on detg. pathways of the oxygen redn. reaction (ORR), the adsorption behavior anddecompn. of the radical OOH and hydrogen peroxide on Pt clusters (Ptn, n = 3, 6, and 10) are extensively investigatedusing d. functional theory. Two types of adsorption of the radical OOH on Pt clusters are found. One-end adsorbedhydrogen peroxide H2O2, arising from redn. of adsorbed OOH, is also located on Pt3, with an adsorption energy of -0.63eV, suggesting that the ORR may proceed via a series pathway generating H2O2 as an intermediate. However, sinceOOH readily decomps. on Pt3 into atop adsorbed at. oxygen and hydroxyl with an activation energy of only ∼0.25 eV, theOOR may take place preferentially via a direct pathway without H2O2 produced. A potential energy surface profile for theORR is proposed, and the adsorption properties of other involved oxide species are characterized.~50 Citings

566. Vacancy-impurity complexes and limitations for implantation doping of diamond

By Goss, J. P.; Briddon, P. R.; Rayson, M. J.; Sque, S. J.; Jones, R.From Physical Review B: Condensed Matter and Materials Physics (2005), 72(3), 035214/1-035214/11. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.72.035214

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Many candidates were proposed as shallow donors in diamond, but the small lattice const. means that manysubstitutional impurities generate large strains and thus yield low solubilities. Strained impurities favor complex formationwith other defects and, in particular, the lattice vacancy. We report the results of first-principles calcns. regarding thegeometry, electronic structure, and energetics of impurity-vacancy complexes in diamond and show that such complexesexplain the generally low doping efficiency for implanted material.~12 Citings

567. Pt3Cr(111) alloy effect on the reversible potential of OOH(ads) formation from O2(ads) relative to Pt(111)1

By Roques, Jerome; Anderson, Alfred B.From Journal of Fuel Cell Science and Technology (2005), 2(2), 86-93. Language: English, Database: CAPLUS,DOI:10.1115/1.1867972

A quantum mech. study of O2 and OOH adsorption on Pt(111) and on a Pt monolayer on Pt3Cr(111) is presented. Thecalcd. adsorption energies are used to predict the reversible potential for O2 redn. to OOH(ads) on these surfaces. Theresulting 0.43 V for Pt(111) and 0.49 V for the Pt skin on the Pt3Cr(111) are far from the 1.23 V reversible potential forthe four-electron redn. to water. However, OOH(ads) easily dissocs. over Ptn sites (n≥2) to OH(ads) and O(ads), thelatter forming with a redn. potential greater than 1.23 V and the resulting heat loss contributes to the overpotential in thefour-electron redn. process.~25 Citings

568. Potential shift for OH(ads) formation on the Pt skin on Pt3Co(111) electrodes in acid. Theory andexperiment

By Roques, Jerome; Anderson, Alfred B.; Murthi, Vivek S.; Mukerjee, SanjeevFrom Journal of the Electrochemical Society (2005), 152(6), E193-E199. Language: English, Database: CAPLUS,DOI:10.1149/1.1896328

This study combines theor. predictions and exptl. measurements to understand the beneficial effect of alloying Co into Ptfor electroredn. of O. C-supported Pt3Co catalyst particles were characterized by XRD and x-ray absorption near-edgestructure, which indicated a surface layer composed of Pt, called the Pt skin. Electrochem. measurements were made in1 M trifluoro methane sulfonic acid with a rotating ring disk setup. Cyclic voltammetry showed significantly less oxideformation in the >0.8 V range over the skin on the alloy compared to non-alloyed Pt. Tafel plots showed a 50-70 mVredn. in overpotential for O2 redn. over the Pt skin. The Vienna Ab Initio Simulation Program was used for calcg. H2Oand OH adsorption bond strengths on the Pt skin on Pt3Co(111) for comparison to prior work with the Pt(111) surface.Bond strength variations were used to est. the shift in reversible potential for OHads formation from H2Oads oxidn. A shiftof 80 mV was found, which indicates that an increase in the reversible potential for OHads formation correlates with adecrease in overpotential for O2 redn. over the Pt skin on Pt3Co nanoparticles.~52 Citings

569. Heavy atom tunneling in chemical reactions: study of H + LiF collisions

By Weck, P. F.; Balakrishnan, N.From Journal of Chemical Physics (2005), 122(23), 234310/1-234310/7. Language: English, Database: CAPLUS,DOI:10.1063/1.1930847

The H + LiF(X 1Σ+,υ = 0-2,j = 0) → HF(X 1Σ+,υ',j') + Li(2S) bimol. process is investigated by means of quantum scatteringcalcns. on the chem. accurate X 2A' LiHF potential energy surface of Aguado et al. [A. Aguado, M. Paniagua, C. Sanz,and J. Roncero, J. Chem. Phys. 119, 10088 (2003)]. Calcns. have been performed for zero total angular momentum fortranslational energies from 10-7 to 10-1 eV. Initial-state selected reaction probabilities and cross sections arecharacterized by resonances originating from the decay of metastable states of the H···F-Li and Li···F-H van der Waalscomplexes. Extensive assignment of the resonances has been carried out by performing quasibound states calcns. inthe entrance and exit channel wells. Chem. reactivity is found to be significantly enhanced by vibrational excitation at lowtemps., although reactivity appears much less favorable than nonreactive processes due to the inefficient tunneling of therelatively heavy fluorine atom strongly bound in van der Waals complexes.~3 Citings

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570. Secondary Alpha Isotope Effects on Deuterium Tunneling in Triplet o-Methylanthrones: ExtraordinarySensitivity to Barrier Width

By Campos, Luis M.; Warrier, Manoj V.; Peterfy, Krisztina; Houk, K. N.; Garcia-Garibay, Miguel A.From Journal of the American Chemical Society (2005), 127(29), 10178-10179. Language: English, Database:CAPLUS, DOI:10.1021/ja052487n

The rates of deuterium transfer in the photoenolization of triplet1,4-dimethyl-10H-anthracene-9-one (1) with varying degrees ofdeuterium label in their Me groups (1-d3, 1-d2, and 1-d) havebeen investigated as a function of temp. between 5 and 77 K.Measurable rate consts. in the case of 1-d3 and 1-d2 were usedto construct Arrhenius plots which illustrate the expectedcurvature and leveling off of rate const. vs. temp. Thedifference in tunneling rate consts. of 1-d3 and 1-d2 yields atunneling isotope effect, TIE = 2.4, which is attributed to thesecondary alpha isotopic substitution. D. functional theory(DFT, B3LYP/6-31G*) calcns. were carried out to obtainstructural and energetic information for the H(D) transfer alongthe triplet state zero-point energy levels. The temp.dependence of the rate consts. for each isotopologue wassimulated with a model that considers the frequency of the C-Dstretching mode and the quantum mech. permeability detd.from calcd. energy parameters. The model suggests that adifference in barrier width of only 0.015 Å between 1-d3 and 1-d2 leads to the obsd. 2-fold difference between tunneling rates.

~13 Citings

571. 18O effects on the infrared spectrum and skeletal tunneling of tropolone

By Redington, Richard L.; Redington, Theresa E.; Blake, Thomas A.; Sams, Robert L.; Johnson, Timothy J.From Journal of Chemical Physics (2005), 122(22), 224311/1-224311/12. Language: English, Database: CAPLUS,DOI:10.1063/1.1897367

IR-absorption profiles obsd. for vibrational transitions of gaseous tropolone often show sharp Q branch peaks, some ofthem ultranarrow spikes, indicative of the band origins for vibrational state-specific spectral tunneling doublets. O isotopeeffects for 2 CH wagging fundamentals, the COH torsion fundamental, and the skeletal contortion fundamental arereported. They allow considerations to be given: (1) O isotope effects on the vibrational frequencies and state-specifictunneling splittings; (2) the asymmetry offset of the potential-energy min. for 16O and 18O tropolone; and (3) addnl. detailsconcerning previously proposed high J rotation-contortion resonances in the contortional fundamental. The new resultshelp to characterize the skeletal contortion fundamental and support the joint participation of skeletal tunneling with Htunneling in the vibrational state-specific tautomerization processes of tropolone in its ground electronic state.~4 Citings

572. First-Principles Modeling of Dopants in C29 and C29H24 Nanodiamonds

By Barnard, A. S.; Russo, S. P.; Snook, I. K.From Journal of Physical Chemistry B (2005), 109(24), 11991-11995. Language: English, Database: CAPLUS,DOI:10.1021/jp051519q

Presented here is our continuing first-principles d. functional theory study of the structural stability of a select group ofdopants in diamond nanocrystals. On the basis of the work of others concerning dopants in diamond and endohedralatoms in fullerenes, the dopants selected for use here are oxygen, aluminum, silicon, phosphorus, and sulfur. Theseatoms were included substitutionally in the center of a 29-carbon-atom nanodiamond crystal, and each structure wasrelaxed using the Vienna Ab Initio Simulation Package. We describe the bonding and structure of the relaxed dopednanocrystals via examn. of the electron charge d. and point group symmetry. In combination with our previously reportedresults, it is anticipated that these results will assist in providing a better understanding of the mech. stability of dopednanodiamonds for use in diamond nanodevices.~9 Citings

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573. Advancements in the local reaction center electron transfer theory and the transition state structure in thefirst step of oxygen reduction over platinum

By Anderson, Alfred B.; Cai, Yu; Sidik, Reyimjan A.; Kang, Dae BokFrom Journal of Electroanalytical Chemistry (2005), 580(1), 17-22. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2005.03.009

This paper demonstrates the importance of calcg. both the redn. and oxidn. electrode potential-dependent activationenergy curves, Ea(U), and then evaluating the resp. derived Ea(U) curves from them when using constrained variationtheory for electron transfer to a local reaction center, an approach developed in this lab. A structure parameter averagingis introduced for calcg. improved results if the calcd. and derived results are not in satisfactory agreement. Thisaveraging technique is used to improve upon a previous study of the 1st step of O2 redn. to H2O2 or H2O when bondedto Pt and to show the role that twisting of Pt-O-O-H+ can play by increasing its electron affinity and lowering the activationenergy. By the same token, oxidn. of peroxide proceeds with a higher barrier when the mol. is allowed to be twisted,which is its stable structure.~40 Citings

574. Activation energies for the 1,2-carbon migration of ring-fused cyclopropylchlorocarbenes

By Chu, Gaosheng; Moss, Robert A.; Sauers, Ronald R.; Sheridan, Robert S.; Zuev, Peter S.From Tetrahedron Letters (2005), 46(23), 4137-4141. Language: English, Database: CAPLUS,DOI:10.1016/j.tetlet.2005.03.209

Fused-ring cyclopropylchlorocarbenes 2 and 3 ring expand to fused-ring chlorocyclobutenes 10 and 11, resp., withactivation energies of 3-4 kcal/mol and activation entropies of ∼-20 e.u. Carbon tunneling appears to be unimportant atlow temps.~6 Citings

575. Cobalt concentration effect in Pt1-xCox on the reversible potential for forming OHads from H2Oads in acidsolution

By Roques, Jerome; Anderson, Alfred B.From Surface Science (2005), 581(2-3), 105-117. Language: English, Database: CAPLUS,DOI:10.1016/j.susc.2005.02.035

The authors present results of a periodic spin-d.-functional theory study of the effect of the Co concn. in Ptx-1Coxsurfaces on the reversible potential for forming OH(ads) from H2O(ads). Adsorbed OH is recognized as a poison tooxygen cathodes that contributes to the high O2 redn. overpotential. Five surface compns. with a Co concn. of 0%, 25%,50%, 75% and 100% were studied, and these surfaces were covered with a monolayer Pt skin. The OH(ads) formationpotential depends significantly on the sub-surface compn. Alloying Pt with Co atoms led to an increasingly pos. shift ofthe reversible potential for forming OH(ads), as the amt. of Co is increased. Beyond 75% Co concn. the effect levels off.Exptl., the Pt3Co alloy was well studied and is believed to be covered by a Pt skin and the potential for OH(ads)formation on it, from H2O oxidn., is shifted pos. The present theor. results suggest that if Pt skins form on alloys moreconcd. in Co than Pt3Co, the pos. shift in the potential for OH(ads) formation will be greater and, on an oxygen cathode ina fuel cell, the overpotential for O2 redn. will be even less.~38 Citings

576. Calculating Reversible Potentials for Pt-H and Pt-OH Bond Formation in Basic Solutions

By Cai, Yu; Anderson, Alfred B.From Journal of Physical Chemistry B (2005), 109(15), 7557-7563. Language: English, Database: CAPLUS,DOI:10.1021/jp0458102

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Two redox reactions on Pt electrodes in base, the formation of underpotential deposited hydrogen, forming a Pt-H bond,and the electrooxidn. of H2O, forming a Pt-OH bond, were studied by 2 methods. The 1st applies a linear relationbetween reaction energy in soln. and std. reversible potential, an approach recently used in this lab. to predict theformation potential of the surface-bonded species. This method depends on the availability of accurate surfaceadsorption bond strengths from measurement or theory and can be applied in 2 formats, the empirical model and thelinear correlation model. The 2nd method treats the reaction within the so-called double-layer model where reactantsand products on the surface are well defined and are experiencing the influence of the electrolyte. When this approach isused, 2 coordination shells of hydrogen bonded H2O mols. are found necessary to sufficiently stabilize the hydroxide ionin this model, unlike acid for which past work showed only one shell around the hydronium ion is needed. The calcd.reversible potentials for both reactions by the empirical and linear correlation models are in good agreement with theexptl. onset potentials obsd. in cyclic voltammetry measurements for Pt(111) surface electrodes when empirical oraccurately calcd. H, OH, and H2O adsorption energies are used. The double layer models for these reactions also yieldsatisfactory results, and the models should be useful for studying electron-transfer reactions in base, as has alreadybeen done for forming Pt-H and Pt-OH in acid soln.~18 Citings

577. Heavy atom tunneling in chemical reactions: study of H + LiF collisions

By Weck, P. F.; Balakrishnan, N.From Los Alamos National Laboratory, Preprint Archive, Physics (2005), 1-19, arXiv:physics/0502145. Language:English, Database: CAPLUS

The H + LiF(X1Σ+,v = 0 - 2,j = 0) → HF(X1Σ+,v',j') + Li(2S) bimol. process is investigated by means of quantum scatteringcalcns. on the chem. accurate X 2A' LiHF potential energy surface of Aguado et al. Calcns. have been performed forzero total angular momentum for translational energies from 10-7 to 10-1 eV. Initial-state selected reaction probabilitiesand cross sections are characterized by resonances originating from the decay of metastable states of the H···F - Li andLi···F - H van der Waals complexes. Extensive assignment of the resonances has been carried out by performing quasi-bound states calcns. in the entrance and exit channel wells. Chem. reactivity is found to be significantly enhanced byvibrational excitation at low temps., although reactivity appears much less favorable than non-reactive processes due tothe inefficient tunneling of the relatively heavy fluorine atom strongly bound in van der Waals complexes.~1 Citing

578. Theoretical study of the adsorption and dissociation of oxygen on Pt(111) in the presence of homogeneouselectric fields

By Hyman, Matthew P.; Medlin, J. WillFrom Journal of Physical Chemistry B (2005), 109(13), 6304-6310. Language: English, Database: CAPLUS,DOI:10.1021/jp045155y

The effect of homogeneous elec. fields on the adsorption energies of at. and mol. O and the dissocn. activation energy ofmol. O on Pt(111) were studied by d. functional theory (DFT). Pos. elec. fields, corresponding to pos. charged surfaces,reduce the adsorption energies of the O species on Pt(111), whereas neg. fields increase the adsorption energies. Themagnitude of the energy change for a given field is primarily detd. by the static surface dipole moment induced byadsorption. On 10-atom Pt(111) clusters, the adsorption energy of at. O decreased by ca. 0.25 eV in the presence of a0.51 V/Å (0.01 au) elec. field. This energy change, however, is heavily dependent on the no. of atoms in the Pt(111)cluster, as the static dipole moment decreases with cluster size. Similar calcns. with periodic slab models revealed achange in energy smaller by roughly an order of magnitude relative to the 10-atom cluster results. Calcns. with adsorbedmol. O and its transition state for dissocn. showed similar behavior. Addnl., substrate relaxation in periodic slab modelslowers the static dipole moment and, therefore, the effect of elec. field on binding energy. The electrostatic effect of elec.fields at fuel cell cathodes may be sufficiently large to influence the O redn. reaction kinetics by increasing the activationenergy for dissocn.~84 Citings

579. Temperature Dependence of Oxygen Reduction Activity at Pt-Fe, Pt-Co, and Pt-Ni Alloy Electrodes

By Wakabayashi, Noriaki; Takeichi, Masayuki; Uchida, Hiroyuki; Watanabe, MasahiroFrom Journal of Physical Chemistry B (2005), 109(12), 5836-5841. Language: English, Database: CAPLUS,DOI:10.1021/jp046204+

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Oxygen redn. reaction (ORR) activity and H2O2 formation at Pt54Fe46, Pt68Co32, and Pt63Ni37 electrodes in 0.1M HClO4soln. at 20 to 90° were studied by using a channel flow double electrode method. At 20-50°, the apparent rate consts.kapp for ORR at these electrodes are 2.4-4.0 times larger than that at a pure Pt electrode, whereas their apparentactivation energies of 41 kJ mol-1 at -0.525 V vs. E° (0.760 V vs. RHE at 30°) were comparable to that at the Ptelectrode. H2O2 yield was ∼1.0% at Pt54Fe46 and ∼0.16% at Pt68Co32 and Pt63Ni37 between 0.3 and 1.0 V vs. RHE. Thekapp values at the alloy electrodes decreased with elevating temp. >60°, and settled to almost the same values at the Ptelectrode. The H2O2 prodn. was not detected at the alloy electrodes once heated at the high temp. in the soln., probablydue to the thickening of the Pt skin-layer by a considerable dissoln. of nonprecious metal components (Fe, Co, Ni) fromthe alloys.~152 Citings

580. Valence bond theory, its history, fundamentals, and applications: A primer

By Shaik, Sason; Hiberty, Philippe C.From Reviews in Computational Chemistry (2004), 20, 1-100. Language: English, Database: CAPLUS,DOI:10.1002/0471678856.ch1

A review. A book chapter in which fundamentals applications of Valence bond theory are discussed.~80 Citings

581. Temperature Dependence of Carbon-13 Kinetic Isotope Effects of Importance to Global Climate Change

By Lin, Hai; Zhao, Yan; Ellingson, Benjamin A.; Pu, Jingzhi; Truhlar, Donald G.From Journal of the American Chemical Society (2005), 127(9), 2830-2831. Language: English, Database: CAPLUS,DOI:10.1021/ja0434026

We report here a theor. study of the 13C kinetic isotope effect(KIE) and its temp. dependence for the reaction OH + CH4 →H2O + CH3, the major sink of atm. methane in the troposphere.The KIE values at various atmospherically significant temps.were detd. by direct dynamics using variational transition statetheory with multidimensional tunneling contributions(VTST/MT). The potential energy surfaces (PESs) weregenerated by hybrid d. functional theory, as well as by recentlydeveloped doubly hybrid d. functional theory methods.Comparisons of our calcd. KIEs with exptl. data and theor.values in the literature reveal the crit. contributions due tomultidimensional tunneling and torsion anharmonicity, as wellas the crit. issue of the choice of internal rotational axis.

~16 Citings

582. A Computational Study of the Effect of Bending on Secondary Kinetic Isotope Effects in SN2 TransitionStates

By Hasanayn, Faraj; Streitwieser, Andrew; Al-Rifai, RashaFrom Journal of the American Chemical Society (2005), 127(7), 2249-2255. Language: English, Database: CAPLUS,DOI:10.1021/ja0487978

Using conventional transition state theory, the secondarydeuterium kinetic isotope effect (KIE) in the inversion SN2reaction of CH3F and F- is calcd. to be small, 0.98 (T = 298 K).This is shown to be the result of a balance among opposingentropy and enthalpy terms. By contrast, KIE in the retentionSN2 mechanism is calcd. to be large (1.5). Accordingly, KIE isa potential observable for discriminating between the twomechanisms. Large KIE's are also found for the inversion andretention mechanisms of the ion pair reactions between CH3Fand LiF. All of the transition structures leading to large KIE'shave a bent FCF angle and an imaginary frequency that issensitive to deuterium labeling.

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~21 Citings

583. Copper ferrite prepared by the soft chemical method

By Gingasu, Dana; Patron, Luminita; Mindru, Ioana; Stanica, Nicolae; Balint, IoanFrom Revue Roumaine de Chimie (2004), 49(8), 669-674. Language: English, Database: CAPLUS

Copper ferrite, Fe2CuO4, was synthesized by the soft chem. method, via thermal decompn. of polynuclear coordinationcompd. precursors, contg. polyhydroxicarboxylic acid anionic ligands (malate, tartrate, gluconate). The polynuclearcoordination compd. precursors were characterized by chem. anal., IR and UV-visible spectra, magnetic measurementsand thermal anal. The tetragonal Fe2CuO4 obtained were characterized by XRD, IR spectra, magnetic measurements.The av. particle size of these ferrites ranged between 26-30 nm, proving the fine nature of the powders. The surfacearea of the copper ferrites varies between 60-68 m2/g.~8 Citings

584. Activation Energies for Oxygen Reduction on Platinum Alloys: Theory and Experiment

By Anderson, Alfred B.; Roques, Jerome; Mukerjee, Sanjeev; Murthi, Vivek S.; Markovic, Nenad M.; Stamenkovic,VojislavFrom Journal of Physical Chemistry B (2005), 109(3), 1198-1203. Language: English, Database: CAPLUS,DOI:10.1021/jp047468z

A combined theor. and exptl. anal. of the electrode potential dependencies of activation energies is presented for the 1ststep in oxygen redn. over Pt and Pt alloy catalysts in both polycryst. and C supported form. Tafel data for several of thecatalysts are used to predict potential-dependent activation energies for oxygen redn. over the 0.6-0.9 V range in strongand weak acid. Comparisons with the theor. curve show good agreement >0.8 V, suggesting a fairly const.preexponential factor. Arrhenius detns. of activation energies over the 0.7-0.9 V range yield little trend for weak acid,possibly because of the larger uncertainties in the Arrhenius fits, but the strong acid results have smaller uncertaintiesand for them the measured activation energies trend up with potential.~141 Citings

585. Chlorine isotope effects on chemical reactions

By Sicinska, D.; Rostkowski, M.; Paneth, P.From Current Organic Chemistry (2005), 9(1), 75-88. Language: English, Database: CAPLUS,DOI:10.2174/1385272053369295

A review. A crit. review of applications of chlorine kinetic isotope effects in studies of org. reactions mechanisms ispresented. Reports from the last five years are considered. During this time chlorine kinetic isotope effects were appliedmainly in studies of elimination reactions and nucleophilic substitution reactions. In several cases chem. models werealso used as models of the intrinsic kinetic isotope effects in several enzymic reactions. Both exptl. and theor.approaches were used.~8 Citings

586. Interaction of hydrogen with boron, phosphorus, and sulfur in diamond

By Lombardi, E. B.; Mainwood, Alison; Osuch, K.From Physical Review B: Condensed Matter and Materials Physics (2004), 70(20), 205201/1-205201/12. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.70.205201

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The prodn. of n-type doped diamond has proved very difficult. P, and possibly S, when in substitutional sites in thelattice, forms a donor which could be used in electronic devices. B, which is a relatively shallow acceptor, can bepassivated by H, and it is possible that some of the difficulties in producing elec. active donors could be due to theirpassivation by the H which is present during the chem. vapor deposition growth of diamond. We report ab initio modelingof these dopants and their complexes with H in diamond and show that it is energetically favorable for H to be trappedand to passivate B and P. S with one H atom produces shallow donor levels in the band gap of diamond with apreviously unconsidered configuration being the most stable and producing the shallowest level. We show that the S-Hpair is stable under conditions of limited H availability. It is energetically favorable for both P-H and P-H2 to dissoc.forming H2*. H diffusion in n-type P-doped diamond is inhibited by this formation of immobile H2*. This is in contrast toB-doped diamond, where we predict that H2* will dissoc. in the presence of substitutional B atoms, forming B-Hcomplexes. The recently obsd. shallow n-type cond. is unlikely to arise from B-D2 complexes, because these complexeswould dissoc. into B-D plus a distant D interstitial. They would induce deep levels in the band gap.~5 Citings

587. Multi-scale molecular modeling of chemical reactivity

By Santiso, Erik E.; Gubbins, Keith E.From Molecular Simulation (2004), 30(11-12), 699-748. Language: English, Database: CAPLUS,DOI:10.1080/08927020412331294878

A review of the most widely used methods to model chem. reactions, at both the electronic and atomistic levels. While,in principle, ab initio methods alone should provide the required prediction of reaction mechanisms, yields and rates, inpractice this can rarely be achieved due to the intensive nature of the computations and the poor scaling of thecomputational burden with the no. of electrons. In many applications a combination of ab initio and semi-classicalatomistic simulations will be needed. Specialized atomistic simulation methods are necessary, since the reactions arethemselves rare events, and the free energy landscape for the reaction is often rugged with many possible reactionpaths. We provide a survey of these methods, with comments on their applicability and a description of their strengthsand weaknesses.~51 Citings

588. Calculation of the Tafel Plot for H2 Oxidation on Pt(100) from Potential-Dependent Activation Energies

By Anderson, Alfred B.; Cai, YuFrom Journal of Physical Chemistry B (2004), 108(52), 19917-19920. Language: English, Database: CAPLUS,DOI:10.1021/jp046194c

Quantum mech. detd. electrode potential dependent activation energies for hydronium ion discharge over Pt-H(Heyrovsky reaction) and the reverse reaction were used to predict Tafel plots. The calcd. Tafel plot for H2 oxidn. issimilar in shape to an exptl. plot from the literature for a Pt(100) electrode and will overlap it when an appropriatepreexponential factor is chosen in the Arrhenius expression. This provides strong theor. support for the 1st electron-transfer step being rate limiting during H2 oxidn. over the potential range 0 to 0.15 V, and the 2nd electron-transfer stepbeing rate limiting during H2 evolution over this electrode. The exchange c.d. is detd. from the calcd. oxidn. and redn.currents and is found to overestimate expt. primarily because the predicted activation energy at the reversible potentialunderestimates the exptl. value. This study illustrates that curvature in nonlinear Tafel plots may stem from the potentialdependence of the activation energies or transfer coeffs. as well as diffusion and concn. gradient effects. The obsd. c.d.and its increase, leveling off, and then decrease at potentials greater than the activation energy-controlled region areattributed to removal of under potential deposited H, passing through the double layer region, and then site blocking byH2O and its oxidn. product OH(ads).~20 Citings

589. Ensemble-averaged variational transition state theory with optimized multidimensional tunneling forenzyme kinetics and other condensed-phase reactions

By Truhlar, Donald G.; Gao, Jiali; Garcia-Viloca, Mireia; Alhambra, Cristobal; Corchado, Jose; Sanchez, Maria Luz;Poulsen, Tina D.From International Journal of Quantum Chemistry (2004), 100(6), 1136-1152. Language: English, Database: CAPLUS,DOI:10.1002/qua.20205

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A review. This paper provides an overview of a new method developed to include quantum mech. effects and freeenergy sampling in calcns. of reaction rates in enzymes. The paper includes an overview of variational transition statetheory with optimized multidimensional tunneling for simple gas-phase reactions and then shows how this is extended toincorporate free energy effects and to include protein motions in the reaction coordinate by ensemble averaging. Finallywe summarize recent comparisons to expt. for primary and secondary kinetic isotope effects for proton and hydridetransfer reactions catalyzed by enzymes.~105 Citings

590. Ab Initio Calculations of Intermediates of Oxygen Reduction on Low-Index Platinum Surfaces

By Panchenko, A.; Koper, M. T. M.; Shubina, T. E.; Mitchell, S. J.; Roduner, E.From Journal of the Electrochemical Society (2004), 151(12), A2016-A2027. Language: English, Database: CAPLUS,DOI:10.1149/1.1809586

Properties of the oxygen mol., at. oxygen, and intermediate products of its redn., OH, OOH, H2O2 on (111), (100), and(110) Pt surfaces have been investigated using periodic d. functional theory. The Pt surfaces are modeled as four-layerslabs. Adsorption energies and geometries, as well as the charge-transfer properties are calcd. Computedcharacteristics of the adsorbed oxygen redn. intermediates supply known tendencies of the low index Pt surface activitiesunder different exptl. conditions. Elec. field dependencies of the properties of all species adsorbed on a Pt9(111) clusterhave been also studied. Lowering the field causes an increase of the O-O bond length of O2ads, attracting the mol. to thePt surface and increasing the charge transfer from Pt to 2π* orbitals of the oxygen mol. The weakening of the O-O bondis evidenced by a decrease of the O-O stretching frequency. The charge-transfer from the Pt9 cluster to the adsorbatesis obsd. for all species. In our calcns. hydrogen peroxide was unstable on all three low-index Pt surfaces and dissocd.into two hydroxyls or a water mol. and at. oxygen. The results of the calcns. are discussed in the context of themechanism of oxygen redn.~136 Citings

591. UPS of Boron-Sulfur Co-Doped, n-Type Diamond

By Vaddiraju, Sreeram; Eaton-Magana, Sally; Chaney, John A.; Sunkara, Mahendra K.From Electrochemical and Solid-State Letters (2004), 7(12), G331-G334. Language: English, Database: CAPLUS,DOI:10.1149/1.1817985

The band structure of n-type diamond samples co-doped with boron and sulfur was studied using UPS (UPS) and Mott-Schottky anal. The results show that the Fermi energy of the co-doped diamond is about 0.8-1.9 eV above the Fermilevel of boron-doped diamond. The electron affinities of the samples ranged from -0.7 to -1.4 eV as evidenced by UPS.These results provide support for the presence of an acceptor impurity band within the bandgap region of the co-dopeddiamond samples.~4 Citings

592. Electrode Potential-Dependent Stages in OHads Formation on the Pt3Cr Alloy (111) Surface

By Roques, Jerome; Anderson, Alfred B.From Journal of the Electrochemical Society (2004), 151(11), E340-E347. Language: English, Database: CAPLUS,DOI:10.1149/1.1805519

Results of a periodic spin-d.-functional theory study of the electronic structure and the local adsorption properties of thePt3Cr(111) alloy surface are presented. A slab composed of four-atom-layer is used to model the (111) surface of theL12 bulk phase with the two topmost layers and adsorbed species allowed to relax. Adsorption energies for OH and H2Ohave been calcd. as functions of initial OH coverage. Using these energies in a model based on reaction energies foracid electrolyte, we have calcd. reversible potential shifts, ∆U°, for OHads formation from H2Oads on different surface sitesof the Pt3Cr(111) alloy relative to the Pt(111) surface. For the first 0.25 monolayer (ML) coverage, H2O and OH are morestable on the Cr sites and a ∆U° = -0.55 V is calcd. For the next 0.25 ML instalment, forming OHads on Pt, ∆U° = -0.15 V.Shifts in U° for going to 0.75 and 1 ML OHads coverage are both pos. Hydrogen bonding between adsorbed mols. playsa role at higher coverage. O2 adsorption was studied on the 0.5 ML OHads covered surface and was found to bond moreweakly than H2O, allowing us to suggest that if the sputtered alloy surface is active toward O2 redn., as the sputteredPt3Co and Pt3Ni surfaces are, Pt islands may be responsible.~30 Citings

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593. Synthesis of spinelic oxides using polynuclear malates coordination compounds. Nickel ferrite

By Mindru, Ioana; Patron, Luminita; Carp, Oana; Marinescu, Gabriela; Pascu, Mirela; Pascu, Gabriel; Diamandescu,LucianFrom Revue Roumaine de Chimie (2004), 49(3-4), 235-245. Language: English, Database: CAPLUS

Ni ferrite was obtained by the thermal decompn. of three malates coordination compds.:[Fe2Ni(C4H4O5)2.5(OH)2]NO3·5H2O, [Fe2Ni(C4H8N2O3)4](NO3)8·24H2O and (NH4)[Fe2Ni(C4H4O5)3(OH)3]·3H2O. Thesolid state transformations were studied by TG/DTA anal., IR, x-ray diffraction, Mossbauer, magnetic and BET studies.The solid state mechanisms, as well as the characteristics of the final products are strongly influenced by the nature ofthe precursors, esp. by their homogeneity at at. scale and compn.~5 Citings

594. Consequences of structural and biophysical studies for the molecular mechanism of photosyntheticoxygen evolution: functional roles for calcium and bicarbonate

By Dasgupta, Jyotishman; van Willigen, Rogier T.; Dismukes, G. CharlesFrom Physical Chemistry Chemical Physics (2004), 6(20), 4793-4802. Language: English, Database: CAPLUS,DOI:10.1039/b408270b

A review. Possible chem. mechanisms for catalyzing O2 evolution from water in natural photosynthesis are summarized,based on the at. and electronic structures of the inorg. core as revealed by spectroscopic and X-ray diffraction expts. andinsights gained from inorg. complexes that achieve O-O bond formation. The thermodn. and kinetic requirements for thismulti-step reaction are reexamd., including the coupling of the individual electron-proton steps (PCET) and the O-O bondformation step. The four oxygen atoms at the corners of the proposed hetero-cubical Mn3CaO4 core (3 µ3-oxos and oneµ4-oxo) can be distinguished by the no. and types of chem. bonds to Ca2+ and Mn (geometries and orbital hybridization).Two of these µ3-oxos, postulated as substrates, are located at unique sites indicative of sp2 + pπ hybridized orbitals.Both proposed substrate oxos are strongly hydrogen-bonded to different protein carboxylate residues, which arepostulated as the initial proton transfer sites. Ca2+ is weakly bonded to these substrate oxos via non-directional ionicbonds that are postulated to provide stereochem. flexibility for the homolytic formation of the O-O bond. A previouslypostulated heterolytic pathway involving an electrophilic oxo and nucleophilic hydroxide species is reevaluated. Weextend this mechanism by postulating roles for (bi)carbonate either in proton transfer or delivering the nucleophile for O2formation.~50 Citings

595. Triplet carbenes

By Tomioka, HideoEdited By:Moss, Robert A.; Platz, Matthew S.; Jones, Maitland, JrFrom Reactive Intermediate Chemistry (2004), 375-461. Language: English, Database: CAPLUS


596. Singlet carbenes

By Jones, Maitland, Jr.; Moss, Robert A.Edited By:Moss, Robert A.; Platz, Matthew S.; Jones, Maitland, JrFrom Reactive Intermediate Chemistry (2004), 273-328. Language: English, Database: CAPLUS


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597. New hybrid method for reactive systems from integrating molecular orbital or molecular mechanicsmethods with analytical potential energy surfaces

By Espinosa-Garcia, Joaquin; Rangel, Cipriano; Navarrete, Marta; Corchado, Jose C.From Journal of Chemical Physics (2004), 121(11), 5098-5108. Language: English, Database: CAPLUS,DOI:10.1063/1.1784448

A computational approach to calcg. potential energy surfaces for reactive systems is presented and tested. This hybridapproach is based on integrated methods where calcns. for a small model system are performed by using anal. potentialenergy surfaces, and for the real system by using MO or mol. mechanics methods. The method is tested on a hydrogenabstraction reaction by using the variational transition-state theory with multidimensional tunneling corrections. Theagreement between the calcd. and exptl. information depends on the quality of the method chosen for the real system.When the real system is treated by accurate quantum mechanics methods, the rate consts. are in excellent agreementwith the exptl. measurements over a wide temp. range. When the real system is treated by mol. mechanics methods, theresults are still good, which is very encouraging since mol. mechanics itself is not at all capable of describing this reactivesystem. Since no exptl. information or addnl. fits are required to apply this method, it can be used to improve theaccuracy of MO methods or to extend the mol. mechanics method to treat any reactive system with the single constraintof the availability of an anal. potential energy surface that describes the model system.~2 Citings

598. Carbon Tunneling in the Ring Expansion of Noradamantylchlorocarbene

By Moss, Robert A.; Sauers, Ronald R.; Sheridan, Robert S.; Tian, Jingzhi; Zuev, Peter S.From Journal of the American Chemical Society (2004), 126(33), 10196-10197. Language: English, Database:CAPLUS, DOI:10.1021/ja0488939

Irradn. of 3-(3-noradamantyl)-3-chlorodiazirine produced thecorresponding noradamantylchlorocarbene, which could bedetected in soln. with laser flash photolysis via its pyridiniumylide, and in N2 or Ar matrixes at 9 K with IR and UV/visspectroscopy. At ambient temps., or on irradn. in the cryogenicmatrixes, the carbene rearranged to 2-chloro-1-adamantene,which could be trapped in soln. and which was characterizedby IR and UV/vis at low temps. In the dark at 9 K, the carbenealso slowly ring-expanded to the chloroadamantene, at a rateca. 10111 times faster than predicted by its B3LYP-calcd.activation barrier. It is proposed that the low-temp.rearrangement occurs through carbon quantum mech.tunneling.

~46 Citings

599. Platinum Monolayer Electrocatalysts for O2 Reduction: Pt Monolayer on Pd(111) and on Carbon-SupportedPd Nanoparticles

By Zhang, J.; Mo, Y.; Vukmirovic, M. B.; Klie, R.; Sasaki, K.; Adzic, R. R.From Journal of Physical Chemistry B (2004), 108(30), 10955-10964. Language: English, Database: CAPLUS,DOI:10.1021/jp0379953

The kinetics of oxygen redn. was studied in acid solns. on Pt monolayers deposited on a Pd(111) surface and on C-supported Pd nanoparticles using the rotating disk-ring electrode technique. These electrocatalysts were prepd. by anew method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially deposited Cumonolayer on a Pd substrate and characterized by scanning tunneling and transmission electron microscopies. Thekinetics of O2 redn. shows a significant enhancement at Pt monolayers on Pd(111) and Pd nanoparticle surfaces incomparison with the reaction on Pt(111) and Pt nanoparticles. The 4-electron redn., with a 1st-charge transfer-rate detg.step, is operative on both surfaces. The obsd. increase in the catalytic activity of Pt monolayer surfaces compared withPt bulk and nanoparticle electrodes may reflect decreased formation of PtOH. An enhanced at. scale surface roughnessand low coordination of some atoms may contribute to the obsd. activity. Placing a Pt monolayer on a suitable metalnanoparticle substrate is an attractive way of designing better O2 redn. electrocatalysts. Also, by using this method thePt content is reduced to very low levels. The Pt mass-specific activity of the Pt/Pd/C electrode is 5-8 times higher thanthat of the Pt/C electrocatalyst. The noble metal (Pt + Pd) mass-specific activity is 2 times higher than that of Pt/C.~531 Citings

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600. A New Interpretation of Chlorine Leaving Group Kinetic Isotope Effects; A Theoretical Approach

By Dybala-Defratyka, Agnieszka; Rostkowski, Michal; Matsson, Olle; Westaway, Kenneth C.; Paneth, PiotrFrom Journal of Organic Chemistry (2004), 69(15), 4900-4905. Language: English, Database: CAPLUS,DOI:10.1021/jo049327z

The chlorine leaving group kinetic isotope effects (KIEs) for theSN2 reactions between Me chloride and a wide range ofanionic, neutral, and radical anion nucleophiles were calcd. inthe gas phase and, in several cases, using a continuum solventmodel. In contrast to the expected linear dependence of thechlorine KIEs on the Cα-Cl bond order in the transition state,the KIEs fell in a very small range (1.0056-1.0091), eventhough the Cα-Cl transition state bond orders varied widelyfrom approx. 0.32 to 0.78, a range from reactant-like to veryproduct-like. This renders chlorine KIEs, and possibly otherleaving-group KIEs, less useful for studies of reactionmechanisms than commonly assumed. A partial explanationfor this unexpected relationship between the Cα-Cl transitionstate bond order and the magnitude of the chlorine KIE ispresented.

~25 Citings

601. Combining molecular dynamics and ab initio quantum-chemistry to describe electron transfer reactions inelectrochemical environments

By Dominguez-Ariza, David; Hartnig, Christoph; Sousa, Carmen; Illas, FrancescFrom Journal of Chemical Physics (2004), 121(2), 1066-1073. Language: English, Database: CAPLUS,DOI:10.1063/1.1760071

A theor. model is presented aimed to provide a detailed microscopic description of the electron transfer reaction in anelectrochem. environment. The present approach is based on the known 2 state model extended by the novelty that theenergy of the 2 states involved in the electron transfer reaction is computed quantum mech. as a function of the solventcoordinate, as defined in the Marcus theory, and of the intensity of an external elec. field. The solvent conformationsdefining the reaction coordinate are obtained from classical mol. dynamics and then transferred to the quantum mech.model. The overall approach was applied to the electron transfer between a chloride anion and a single crystal Cu(100)electrode. The solvent exerts a strong influence on the equil. geometry of the halide and hence on the relative energy ofthe 2 states involved in the electron transfer reaction. Finally, both solvent fluctuations and external field facilitate theelectron transfer although solvent effects have a stronger influence.~16 Citings

602. Oxygen Reduction Kinetics in Low and Medium Temperature Acid Environment: Correlation of WaterActivation and Surface Properties in Supported Pt and Pt Alloy Electrocatalysts

By Murthi, Vivek S.; Urian, R. Craig; Mukerjee, SanjeevFrom Journal of Physical Chemistry B (2004), 108(30), 11011-11023. Language: English, Database: CAPLUS,DOI:10.1021/jp048985k

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Kinetics of oxygen redn. reaction on supported Pt and several Pt alloy electrocatalysts (PtCo/C and PtFe/C) were studiedin terms of the effect of alloying on the initiation and extent of surface oxide formation (water activation: xH2O + Pt*(M) →(M)Pt-[OH]x + xH+ + xe-). For this, a systematic RRDE study was conducted in trifluoromethanesulfonic acid (TFMSA) asa function of concn. (in the range 1 to 6 M) which corresponds to a change in mole ratio of H2O/acid from 50:1 in 1 M to4:1 in 6 M TFMSA. This change in relative amt. of H2O in the various concns. can also be indirectly correlated to therelative humidity in an operating PEM fuel cell. The scope of this effort was (a) to confirm the shift and lowering of H2Oactivation on supported Pt alloy electrocatalysts relative to Pt at lower concns. (1 M); (b) to compare the inherent activityfor ORR on supported Pt and Pt alloy nanoparticles without the effect of oxide formation via activation of H2O, this wasenabled at higher concns. of TFMSA (6 M); (c) to relate the activation energy values at 1 M for Pt and Pt alloyelectrocatalysts for further insight into the nature of the rate-detg. step in the mechanism; and (d) to examine the relativeformation of peroxides via a parallel pathway for Pt and Pt alloy electrocatalysts in 1 and 6 M TFMSA. For fully hydratedsystems akin to 1 M concn. the alloys shift the formation and extent of H2O activation on the Pt alloy surfaces; this wascorrelated with in-situ XAS data (changes to Pt electronic states and short-range at. order) as well as via direct EXAFSprobe of the formation of oxygenated species >0.75 V (typical potential for initiation of surface oxides on Pt). Thelowering of oxide formation agrees well with the extent of enhancement of ORR activity. Activation energy detns. at 1 Mconcn. however revealed no difference between Pt and Pt alloys, indicating thereby that the rate-limiting step remainsunchanged. At lower H2O activity (6 M) with negligible H2O activation (and hence surface oxides), the Pt surfacepossesses a higher activity for ORR as compared to the alloys. The detn. of peroxide yield on the Pt surface showedthat there was variation both in terms of alloy formation as well as the H2O activity at the interface. All these results arediscussed in the context of a PEM fuel cell operating in the low to medium temp. range (70-120°) and humidity variation(100 to 10%).~252 Citings

603. Structural investigations and thermal analysis of the coordination compound obtained through the reactionof 1,3-propanediol with Co(NO3)2·6H2O

By Niculescu, Mircea; Vaszilcsin, Nicolae; Davidescu, Corneliu Mircea; Negrea, Petru; Birzescu, Mihail; Budrugeac,PetruFrom Revue Roumaine de Chimie (2003), 48(12), 997-1006. Language: English, Database: CAPLUS

The paper presents the exptl. results of the structural investigations and thermal anal. of a new cobalt(II)-polynuclearcoordination compd. having as ligand the 3-hydroxypropionate anion (L), which is the oxidn. product of 1,3-propanediol.The reaction between 1,3-propanediol and Co(NO3)2·6H2O occurs with the oxidn. of 1,3-propanediol to the 3-hydroxypropionate anion. The synthesized polynuclear coordination compd., [Co2(OH)2L2(H2O)2]n, was characterized bychem. anal., electronic and vibrational spectra and magnetic measurements. The thermal properties of the compd. havebeen investigated by TG, DTG and DTA. Cobalt oxide obtained through thermolysis was characterized by IR, X-rayspectroscopy and elemental anal.~13 Citings

604. Polynuclear complexes of chromium(III) and M(II) (M: Mn, Co, Ni, Zn) with thiourea

By Badea, Mihaela; Olar, Rodica; Marinescu, Dana; Cristurean, Elena; Brezeanu, MariaFrom Revue Roumaine de Chimie (2003), 48(12), 927-937. Language: English, Database: CAPLUS

Four polynuclear complexes contg. Cr(III) and M(II) (M = Mn, Co, Ni, Zn) [Cr2MnTu4(CH3COO)2(H2O)4](NO3)6,[Cr2MTu6(H2O)6](NO3)8 (M = Co, Zn) and [Cr2NiTu6(H2O)8](NO3)8 (Tu = thiourea) were synthesized and characterizedusing chem. and spectral methods. The results of the thermal anal. performed in static air atm. recommended thesecomplexes as precursors for mixed oxides and sulfides of the Cr2MX4 (X: O, S) type.~1 Citing

605. The Reversible Hydrogen Electrode: Potential-Dependent Activation Energies over Platinum from QuantumTheory

By Cai, Yu; Anderson, Alfred B.From Journal of Physical Chemistry B (2004), 108(28), 9829-9833. Language: English, Database: CAPLUS,DOI:10.1021/jp037126d

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Potential-dependent activation energies are calcd. quantum mech., using a local reaction center model, for the hydrogenredn.-oxidn. reaction over Pt by the Volmer-Heyrovsky mechanism, Pt-H + H+ + e-(U) ↔ Pt + H2 (i), modeled by Pt-H···H+(OH2)(OH2)2 + e-(U) ↔ Pt···H-H···OH2(OH2)2 (ii). A contribution from the electrolyte to the potential of the reactioncenters in ii is included in the ab initio Hamiltonian. The reversible potential predicted for i based on model ii is 0.04 V,close to the std. hydrogen electrode value of 0 V, and the predicted activation energy at the predicted reversible potentialis 0.076 eV, close to the literature value of 0.12 eV for the apparent activation energy. The theor. results validate thepossibility of the Volmer-Heyrovsky mechanism being followed on Pt.~44 Citings

606. Boron-hydrogen complexes in diamond

By Goss, J. P.; Briddon, P. R.; Sque, S. J.; Jones, R.From Physical Review B: Condensed Matter and Materials Physics (2004), 69(16), 165215/1-165215/8. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.69.165215

Boron in diamond traps hydrogen forming passive Bs-H pairs. Boron trapping two deuterium atoms has been speculatedas forming a shallow donor (0.23-0.34 eV below the conduction band). The authors present the results of first-principlescalcns. of boron complexes with 2-4 hydrogen atoms. The binding energy of the second and subsequent H atoms issmall, and none of the structures found are shallow donors. The authors also present the structure of interstitial boron,the boron-vacancy complex, and their interaction with hydrogen.~2 Citings

607. Computational atomic nanodesign

By Rieth, Michael; Schommers, WolframEdited By:Nalwa, Hari SinghFrom Encyclopedia of Nanoscience and Nanotechnology (2004), 2, 51-103. Language: English, Database: CAPLUS

A review. The following topic are discussed: quantum-theor. treatment of nanosystems, basic properties at thenanolevel, modeling of nanosystems, interaction potentials, mol. dynamics, Monte Carlo method.~0 Citings

608. Temperature dependence of the COads oxidation process on Pt(111), Pt(100), and Pt(110) electrodes

By Herrero, Enrique; Alvarez, Bernabe; Feliu, Juan M.; Blais, Sonia; Radovic-Hrapovic, Zorana; Jerkiewicz, GregoryFrom Journal of Electroanalytical Chemistry (2004), 567(1), 139-149. Language: English, Database: CAPLUS,DOI:10.1016/j.jelechem.2003.12.019

The influence of temp. variation on the COads oxidative desorption at Pt(111), Pt(100), and Pt(110) electrodes in 0.5MH2SO4 and 0.1M HClO4 solns. is examd. A distinct shift of the COads stripping peak towards less-pos. potentials is obsd.as the temp. is increased from 273 to 333 K. Despite the displacement of the desorption peak towards lower potentials,its c.d. and shape remain unaffected for the Pt(111) and Pt(100) electrodes, therefore indicating that the oxidn.mechanism for the COads is not influenced by the temp. variation in this particular range. However, the morphol. of thepeak on the Pt(110) electrode changes significantly with the temp., of the interaction with the oxide formation. Theactivation energies for the oxidn. processes in the 2 media were evaluated through the dependence of the peak potentialand the voltammetric current of the peak with the temp. The activation energy obtained in H2SO4 is ∼15-25 kJ mol-1higher than that in HClO4, highlighting the role of the anions in the oxidn. process.~65 Citings

609. Rate Constant Calculation for HArF → Ar + HF and HKrF → Kr + HF Reactions by Dual-Level VariationalTransition State Theory with Quantized Reactant State Tunneling

By Chen, Yung-Lung; Hu, Wei-PingFrom Journal of Physical Chemistry A (2004), 108(20), 4449-4454. Language: English, Database: CAPLUS,DOI:10.1021/jp049740a

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The rate consts. for the gas-phase dissocn. of HArF and HKrF through the bending coordinates have been calcd. usingthe dual-level variational transition state theory with quantized reactant state tunneling (QRST) from 20 to 600 K.Tunneling was found to dominate the reaction below 250 K, and the rate consts. were found to be approx. temp.independent below 100 K. The deuterium kinetic isotope effects (KIEs) were also calcd. in the same temp. range. Thecalcd. KIEs showed dramatic increases below 250 K due to the large differences in the hydrogen and deuteriumtunneling rates. Compared to the conventional tunneling method, the QRST predicts appreciably higher rate consts.below 50 K and makes the transition from the temp.-dependent domain to the temp.-independent domain more sharply.At the low-temp. asymptote, the QRST predicts 30% to 40% higher KIEs than the conventional tunneling method.~13 Citings

610. Efficient Molecular Mechanics for Chemical Reactions: Multiconfiguration Molecular Mechanics UsingPartial Electronic Structure Hessians

By Lin, Hai; Pu, Jingzhi; Albu, Titus V.; Truhlar, Donald G.From Journal of Physical Chemistry A (2004), 108(18), 4112-4124. Language: English, Database: CAPLUS,DOI:10.1021/jp049972+

Multiconfiguration mol. mechanics (MCMM) is a method for representing polyat. potential energy surfaces by combiningmol. mechanics potentials for the reactant and product wells with electronic structure data (energy, gradient, andHessian) at the saddle point and a small no. of nonstationary points. A general strategy for placement of thenonstationary points has been developed [Albu, T. V.; Corchado, J. C.; Truhlar, D. G. J. Phys. Chem. A 2001, 105, 8465]for fitting potential energy surfaces in the vicinity of the reaction path and in the reaction swath region and for calcg. rateconsts. for atom transfer reactions by variational transition state theory with multidimensional tunneling. We improve theefficiency of the MCMM method by using electronic structure calcns. only for certain crit. elements of the Hessians at thenonstationary points and by using interpolation for the other elements at the nonstationary points. We tested this newMCMM strategy for a diverse test suite of six reactions involving hydrogen-atom transfer. The new method yields quiteaccurate rate consts. as compared with the std. MCMM strategy employing full electronic structure Hessians and also ascompared with direct dynamics calcns. using an uninterpolated full potential energy surface at the same electronicstructure level. In comparison with the std. MCMM strategy, this new procedure reduces the computational effort assocd.with the nonstationary points by a factor of up to 3 for the test reactions and up to 11 for even larger reactive systems.~34 Citings

611. Oxygen Electroreduction on FeII and FeIII Coordinated to N4 Chelates. Reversible Potentials for theIntermediate Steps from Quantum Theory

By Anderson, Alfred B.; Sidik, Reyimjan A.From Journal of Physical Chemistry B (2004), 108(16), 5031-5035. Language: English, Database: CAPLUS,DOI:10.1021/jp037184z

From spin-unrestricted hybrid gradient-cor. Becke, Lee, Yang, and Parr B3LYP d. functional calcns. and the reaction sitemodels Fe(NH2)2(NH3)2 for FeII, and Fe(NH2)2(NH3)2OH for FeIII, FeII is predicted to be the active site for the 4-electronredn. of oxygen by heat-treated Fe macrocycles. It is favored over FeIII in the 1st step of the mechanism because of asite blocking effect: H2O bonds strongly to the FeIII site, blocking it against O2 adsorption, and it does not bond strongly toFeII. The stronger bonding of the product of the 1st redn. step, OOH, to FeII compared to FeIII also helps by contributingto a more pos. reversible potential for its formation over FeII. Subsequent redn. steps have high reversible potentialsover both centers, paralleling an earlier study of oxygen redn. over a single Pt site. However, the important differencecompared to Pt is the H-bonding interaction between (OHOH) bonded to FeII and a nitrogen lone-pair orbital in the N4chelate. This is in addn. to the O lone-pair donation bond to the FeII center and is proposed to prevent H2O2 from leavingas a 2-electron redn. product, as it was predicted to do over a single Pt site, and provides a path for redn. to H2O.~75 Citings

612. Roles of Proton and Electric Field in the Electroreduction of O2 on Pt(111) Surfaces: Results of an Ab-InitioMolecular Dynamics Study

By Wang, Yixuan; Balbuena, Perla B.From Journal of Physical Chemistry B (2004), 108(14), 4376-4384. Language: English, Database: CAPLUS,DOI:10.1021/jp037323c

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The electroredn. of O2 on the Pt(111) surface is studied with Car-Parrinello mol. dynamics simulations of O2/Pt(111), O2+ H+(H2O)3/Pt(111), and O2 + H+(H2O)3 + e-/ Pt(111). Starting from a parallel configuration where O2 is 3.0 Å over thePt(111) surface along a bridge site, stepwise adsorptions of 2 O atoms are obsd., leading to a 1-end chemisorptionprecursor (Pauling model of adsorption). The formation of the precursor has a very low barrier (0.08 eV), whereas noclear barrier was found for its decompn. Addn. of H+(H2O)3 induces rapid formation of the proton-transfer intermediateH+-O2···Pt(111), followed by an electron transfer from the Pt slab that yields a chemisorbed precursor H-O-O-Ptn, inwhich the hydroxyl end is considerably more sepd. than the oxygen end from the Pt(111) surface. Compared with the O2+ H+(H2O)3/Pt(111) system, the presence of an electron in O2 + H+(H2O)3 + e-/ Pt(111) greatly enhances the lifetime ofthe proton-transfer intermediate H+-O-O···Pt(111), and consequently it delays the subsequent electron transfer, whichyields the formation of the 1-end chemisorbed precursor H-O-O-Ptn. Evolutions of the Kohn-Sham energy for the last 2cases show that the formation of H-O-O-Ptn has a much higher activation barrier than its dissocn. (0.4 vs. 0.1 eV),indicating that the formation of chemisorbed H-O2 species is the rate-detg. step for the 1st electron transfer of theelectroredn. of O2.~83 Citings

613. α,ω-Diferrocenyl Cumulene Molecular Wires Studied by Density Functional Theory

By Bildstein, Benno; Loza, Olga; Chizhov, YuriFrom Organometallics (2004), 23(8), 1825-1835. Language: English, Database: CAPLUS, DOI:10.1021/om034234d

D. functional theory calcns. for neutral and oxidizeddiferrocenyldiphenylcumulenes, [Fc(Ph)Cn(Ph)Fc] with n = 2, 4,6, 8, were performed at the B3LYP/6-31G level without anyrestrictions in symmetry. Geometrically, of the four possiblediastereomeric structures of the neutral cumulenes, nopreferential conformation was revealed, and the calcd.structures reproduce the exptl. x-ray structural data quite well.The spin d. of all mono- and dications is located on the ironatoms, but not on the cumulene chain. Calcns. of the ionizationpotentials for monocations show a breakdown of Koopmans'theorem. A calibration procedure was proposed for evaluationof vertical ionization potentials, resulting in values with exptl.accuracy. UV-visible absorptions are assigned in terms of theirband max., transition energies, and bandwidths on the basis ofdeconvoluted exptl. spectra and on the basis of comparisonwith structurally related compds. Calcns. of the characteristichigh-frequency sym. vibrations of the cumulene chain show avery good match with exptl. Raman bands. Redox potentials insoln. are calcd. by a simplified model on the basis of empiricalfindings; the results reproduce the exptl. half-wave potentialsquite satisfactorily and allow an est. of an electrochem. decayslope and an effective conjugation limit in these cumulene mol.wires. The structural, chem., optical, electrochem., and MOproperties of 2-31 make ferrocenyl cumulenes very promisingmol. objects with great potential in mol.-scale electronics incomparison with pure org. mol. wires.

~18 Citings

614. Kinetic Analysis of Oxygen Reduction on Pt(111) in Acid Solutions: Intrinsic Kinetic Parameters and AnionAdsorption Effects

By Wang, J. X.; Markovic, N. M.; Adzic, R. R.From Journal of Physical Chemistry B (2004), 108(13), 4127-4133. Language: English, Database: CAPLUS,DOI:10.1021/jp037593v

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Oxygen redn. reaction (ORR) kinetics in acid solns. was studied by anal. of the polarization curves obtained by rotatingdisk electrode method for Pt(111) in HClO4 and H2SO4 solns. The model for ORR kinetic currents assumes that theintrinsic exchange current and Tafel slope are independent of anion adsorption. The site blocking and electronic effectsof adsorbed OH (in HClO4) and bisulfate (in H2SO4) were evaluated with the adsorption isotherms incorporated in themodel. The best fits yielded the intrinsic Tafel slope in the range from -118 to -130 mV/dec, supporting single electrontransfer in the rate-detg. step with the corresponding transfer coeffs. equal to 0.50 and 0.45, resp. In addn. to siteblocking, a neg. electronic effect on ORR kinetics was found for both OH and bisulfate with the effect of the latter beingmuch stronger. The deviation of the apparent Tafel slope in HClO4 from its intrinsic value can be fully accounted for bythe site blocking and electronic effects of adsorbed OH ions, which vary with coverage over the mixed kinetic-diffusioncontrolled region. For Pt nanoparticle catalysts, the apparent Tafel slope is similar to that for Pt(111) in HClO4 and thepos. potential shift is mainly due to the increase in apparent exchange current as effective surface area increases.~328 Citings

615. Theory for the Potential Shift for OHads Formation on the Pt Skin on Pt3Cr(111) in Acid

By Roques, Jerome; Anderson, Alfred B.From Journal of the Electrochemical Society (2004), 151(3), E85-E91. Language: English, Database: CAPLUS,DOI:10.1149/1.1645265

We present results of a periodic spin-d.-functional theory study of the electronic structure and the local adsorptionproperties of the annealed Pt3Cr alloy surface in comparison with the Pt(111) surface. Each is modeled as a four-layerslab where the two topmost layers and the adsorbates are allowed to relax. The annealed alloy has Pt segregated to thesurface and is modeled by a Pt(111) monolayer covering the Pt3Cr(111) L12 face bulk phase alloy. We have calcd. OHand H2O structures and adsorption energies at low coverage. The top adsorption sites are predicted to be the moststable for these adsorbates on both surfaces, but adsorption energies for both decrease on the Pt skin, with a largerdecrease for OH. An empirical model based on reaction energy calcns. in acid is used to est. the reversible potential ofOHads formation from H2Oads on the Pt skin and on Pt(111) in acid. A pos. shift (∆U° = 0.11 V) is predicted for thesurface of the Pt skin relative to Pt(111). This result is in qual. agreement with the 40-60 mV redn. in overpotential obsd.exptl. for oxygen redn. on the Pt3Cr alloy compared to Pt surfaces, which is attributed to OHads being a surface poison.~55 Citings

616. Bifunctional catalytic activity of manganese oxide toward O2 reduction: novel insight into the mechanism ofalkaline air electrode

By Ohsaka, Takeo; Mao, Lanqun; Arihara, Kazuki; Sotomura, TadashiFrom Electrochemistry Communications (2004), 6(3), 273-277. Language: English, Database: CAPLUS,DOI:10.1016/j.elecom.2004.01.007

The mechanism of electro-catalytic redn. of oxygen (O2) with manganese oxide was studied by cyclic voltammetry androtating ring-disc electrode voltammetry using MnOOH-modified glassy carbon (GC) electrodes in alk. media. The O2redn. at the MnOOH-modified GC electrodes was found to undergo an electrochem. process followed by sequentdisproportionations of the electrochem. redn. intermediates, i.e., superoxide anion (O.bul.- 2) and hydrogen peroxide (HO-

2, in 0.10 M KOH soln.). The manganese oxides, which are used as the electrocatalysts in the alk. air electrodes, werefirst found to possess an excellent catalytic activity not only for the disproportionation of the produced O.bul.- 2 into O2 andHO- 2 but also for that of the produced HO- 2 into O2 and OH-. Such bifunctional catalytic activities of MnOOH for thesequent disproportionations of O2 √- and HO2 -, combined with electrochem. redn. of O2 mediated by surface functionalgroups at carbon electrode surface, substantially effect a quasi-four-electron redn. of O2 at the MnOOH-based alk. airelectrodes.~83 Citings

617. Do heavy nuclei see light at the end of the tunnel?

By Berger, RobertFrom Angewandte Chemie, International Edition (2004), 43(4), 398-401. Language: English, Database: CAPLUS,DOI:10.1002/anie.200301675

A review/discussion of the tunneling study of P. Zuev et al. (2003). Low-temp. expts. and calcns. on the ring expansionof (1-methylcyclobutyl)fluorocarbene, which involves considerable movement of the heavy nuclei, indicate that tunnelingthrough the barrier is more favorable than the classical route over the "mountain pass".

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~5 Citings

618. Radical Clock Substrates, Their C-H Hydroxylation Mechanism by Cytochrome P450, and Other ReactivityPatterns: What Does Theory Reveal about the Clocks' Behavior?

By Kumar, Devesh; de Visser, Samueel P.; Sharma, Pankaz K.; Cohen, Shimrit; Shaik, SasonFrom Journal of the American Chemical Society (2004), 126(6), 1907-1920. Language: English, Database: CAPLUS,DOI:10.1021/ja039439s

There is an ongoing and tantalizing controversy regarding themechanism of a key process in nature, C-H hydroxylation, bythe enzyme cytochrome P 450 (Auclaire, K.; Hu, Z.; Little, D.M.; Ortiz de Montellano, P. R.; Groves, J. T. J. Am. Chem. Soc.2002, 124, 6020-6027; Newcomb, M.; Aebisher, D.; Shen, R.;Esala, R.; Chandrasena, P.; Hollenberg, P. F.; Coon, M. J. J.Am. Chem. Soc. 2003, 125, 6064-6065). To definitely resolvethis controversy, theory must first address the actual systemsthat have been used by expt., and that generated thecontroversy. This is done in the present paper, whichconstitutes the first extensive theor. study of such two exptl.systems, trans-2-phenylmethyl-cyclopropane (1) and trans-2-phenyl-iso-propylcyclopropane (4). The theor. study of thesesubstrates reveals that the only low energy pathway for C-Hhydroxylation is the two-state rebound mechanism describedoriginally for methane hydroxylation (Ogliaro, F.; Harris, N.;Cohen, S.; Filatov, M.; de Visser, S. P.; Shaik, S. J. Am. Chem.Soc. 2000, 122, 8977-8989). The paper shows that thescenario of a two-state rebound mechanism accommodatesmuch of the exptl. data. The computational results provide agood match to exptl. results concerning the very differentextents of rearrangement for 1 (20-30%) vs. 4 (virtually none),lead to product isotope effect for the reaction of 1, in thedirection of the exptl. result, and predict as well the obsd.metabolic switching from Me to Ph hydroxylation, which occursupon deuteration of the Me group. Furthermore, the studyreveals that an intimate ion pair species involving an alkylcarbocation derived from 4 gives no rearranged products, againin accord with expt. This coherent match between theory andexpt. cannot be merely accidental; it comes close to being aproof that the actual mechanism of C-H hydroxylation involvesthe two-state reactivity revealed by theory. Anal. of therearrangement modes of the carbocations derived from 1 and 4excludes the participation of free carbocations during thehydroxylation of these substrates. Finally, the mechanisticsignificance of product isotope effect (different isotope effectsfor the rearranged and unrearranged alc. products) is analyzed.It is shown to be a sensitive probe of two-state reactivity; thesize of the intrinsic product isotope effect and its directionreveal the structural differences of the hydrogen abstractiontransition states in the low-spin vs. high-spin reactionmanifolds.

~122 Citings

619. Co-doping of diamond with boron and sulfur

By Li, Rong-Bin; Hu, Xiao-Jun; Shen, He-Sheng; He, Xian-ChangFrom Journal of Materials Science (2004), 39(3), 1135-1137. Language: English, Database: CAPLUS

The effect of S doping and B/S co-doping on mutual diamond film incorporation is studied. Limited amts. of B facilitatethe incorporation of S atoms into diamond. The amt. of S atom incorporation into diamond is increased by 1.5 times dueto adding limited addns. of B atom. With increase of S-incorporation, the activation energy of cond. decreases from 0.52to 0.39 eV. The activated energy of 0.39 eV is estd. with S incorporation at levels of up to 0.15%. This suggests that theexistence of the C-S bond is responsible for the incorporation of S into the diamond lattice of CVD grown films.

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~6 Citings

620. Co-doping of diamond with boron and sulfur

By Eaton, Sally C.; Anderson, Alfred B.; Angus, John C.From NASA Conference Publication (2003), 2003-212319(Proceedings of the Seventh Applied DiamondConference/Third Frontier Carbon Technology Joint Conference, 2003), 527-532. Language: English, Database:CAPLUS

The characterization of diamond co-doped with boron and sulfur is reported. SIMS anal. show that the sulfur is concd. inthe near surface region, although increased concns. of sulfur above background levels appear in the bulk diamond aswell. Hall effect and thermoelec. power measurements indicate that the cond. is n-type in the surface region and can beeither n- or p-type in the bulk, depending on the degree of compensation with boron. The co-doped samples are notstable at elevated temps. and there is an irreversible loss of cond. when heated above 400 K in air. Electrochem.polarization of the n-type diamond showed blocking at anodic potentials up to +5 V vs. the SCE. Two types of p/njunctions using the n-type boron/sulfur co-doped diamond were made: one using boron-doped diamond as the p-typeside and the other using the p-type surface cond. induced by hydrogen termination. The turn-on voltage in both junctionswas approx. 0.5 V, which suggests that the Fermi level in the n-type diamond is low in the band gap. The n-type cond.likely arises from an impurity band. The nature of the centers giving rise to the cond. is not known.~0 Citings

621. Synthesis, Characterization and Thermal Decompositions. Studies of Some Malates CoordinationCompounds. I. Iron nickel compounds

By Carp, O.; Patron, L.; Mindru, I.; Marinescu, G.; Diamandescu, L.; Banuta, A.From Journal of Thermal Analysis and Calorimetry (2003), 74(3), 789-799. Language: English, Database: CAPLUS,DOI:10.1023/B:JTAN.0000011011.48105.34

The thermal behavior of [Fe2Ni(C4H4O5)2.5(OH)2]NO3·5H2O, [Fe2Ni(C4H8O3N2)4](NO3)8·24H2O and(NH4)[Fe2Ni(C4H4O5)3(OH)3]·3H2O was studied to evaluate their suitability as nickel ferrite precursors. For a completeand reliable assignment of the thermal transformations, the isolable solid intermediates and end products werecharacterized by IR, x-ray diffraction and Mossbauer studies. A decompn. scheme is proposed.~15 Citings

622. Variational transition state theory calculations for the rate constants of the hydrogen scrambling and thedissociation of BH5 using the multiconfiguration molecular mechanics algorithm

By Kim, Kyung Hyun; Kim, YonghoFrom Journal of Chemical Physics (2004), 120(2), 623-630. Language: English, Database: CAPLUS,DOI:10.1063/1.1630305

The BH5 mol. contains a weak two-electron-three-center bond and it requires extremely high level of theories to calc. theenergy and structure correctly. The potential energy of the hydrogen scrambling in BH5 has been generated by themulticonfiguration mol. mechanics algorithm with 15 high-level Shepard interpolation points, which would be practicallyimpossible to obtain otherwise. The high-level interpolation points were obtained from the multicoefficient correlatedquantum mech. methods. The more high-level points are used, the better the shape of the potential energy surface. Therate consts. are calcd. using the variational transition state theory including multidimensional tunneling approxn. Thepotential energy curve for the BH5 dissocn. has also been calcd., and the variational transition state was located to obtainthe dissocn. rate consts. Tunneling is very important in the scrambling, and there is large variational effect on thedissocn. The rate consts. for the scrambling and the dissocn. are 2.1 × 109 and 2.3 × 1012 s-1 at 300 K, resp., whichsuggests that the dissocn. is three orders of magnitude faster than the scrambling.~17 Citings

623. A Computational Investigation of the Reactions of Methylene, Chlorocarbene, and Dichlorocarbene withCyclopropane

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By Sevin, Fatma; McKee, Michael L.; Shevlin, Philip B.From Journal of Organic Chemistry (2004), 69(2), 382-386. Language: English, Database: CAPLUS,DOI:10.1021/jo0348928

The reactions of CH2, CHCl, and CCl2 with cyclopropane 1,have been examd. computationally. In all cases the lowestenergy reaction between the carbene and 1 is predicted to beC-H insertion. In the reaction of CH2 with 1, the transition statefor C-C insertion leading to cyclobutane is 1.7 kcal/mol higherin enthalpy than the transition state for C-H insertion at theG3B3 level. A pathway higher in energy than C-H insertion inthe reactions of CHCl and CCl2 with 1 involves two-bondcleavages generating ethylene along with chloro anddichloroethylene, resp.

~9 Citings

624. Soft chemical synthesis and characterisation of some substituted ferrites

By Olar, Rodica; Badea, Mihaela; Diamandescu, L.; Cristurean, Elena; Marinescu, Dana; Mihaila-Tarabasanu, Doina;Stanica, N.; Brezeanu, MariaFrom Journal of Alloys and Compounds (2004), 363(1-2), 257-262. Language: English, Database: CAPLUS,DOI:10.1016/S0925-8388(03)00452-3

Substituted ferrites with the chem. compn. MxFe1-xFe2O4·nH2O (M: Mn(II), x: 0.35, n: 0.4; M: Ni(II), x: 0.38, n: 1; M: Zn(II),x: 0.45, n: 0.35) were prepd. by a soft chem. method using as starting materials magnetite and suitable acetates. Thesecompds. were characterized by elemental chem. anal., thermal anal., IR spectroscopy, x-ray diffraction on powder, TEMstudies as well as Mossbauer spectroscopy and magnetic measurements at room temp. The x-ray diffraction studyindicates that the substituted ferrites adopt a cubic structure and the size of particles detd. from the diffraction peak isfairly close to that indicated for agglomerates by TEM. The magnetic methods agree to the substitution of Fe(II) in theoctahedral positions preserving the inverse spinel structure.~5 Citings

625. Asymmetric hydrous RuO2 ultracapacitors with self-charging capabilities

By Wartena, Ryan; Durdall, Jennifer; Swider-Lyons, Karen E.From Proceedings - Electrochemical Society (2003), 2002-26(Solid-State Ionic Devices III), 444-455. Language:English, Database: CAPLUS

Hydrous ruthenium oxide (RuO2·xH2O or RuOxHy) has a high specific capacitance, making it an attractive material forultracapacitor electrodes. Hydrous RuO2 ultracapacitors are usually fabricated with sym. pos. and neg. electrodes, whichcan hold a p.d. up to 1.4 V when fully charged. A disadvantage of the electrodes is that the high protonic and metalliccond. plus the catalytic nature of hydrous RuO2 makes self-discharge and potential recovery a significant problem inpractical applications. We demonstrate that the potential recovery and self-discharge phenomena in hydrous RuO2 andPt, resp., can be used as an asset for self-recharging in asym. systems. Asym. ultracapacitors are fabricated with pos.electrodes of hydrous RuO2 on Pt foil and neg. electrodes of Pt foil. After assembly, the cells have open circuit voltages(OCVs) of 0.2 to 0.7 V, which vary with the concns. of sulfuric acid in the electrolyte, the compn. of the electrodes and theno. of cycles performed. The cells are discharged from their OCV to 0 V in pulses of 4 to 400 µA/cm2 to yield meanpowers ranging from 0.28 µW/cm2 to 0.7 mW/cm2. While resting, the cells recharge to their original OCV in 30 to 240min due to self-discharge and potential recovery reactions. To date, these asym. cells have been operated for over 800h and more than 200 cycles. In the future, these self-recharging hydrous RuO2/Pt systems may be useful as powersources for autonomous microsystems.~0 Citings

626. Theory at the electrochemical interface: reversible potentials and potential-dependent activation energies

By Anderson, Alfred B.From Electrochimica Acta (2003), 48(25-26), 3743-3749. Language: English, Database: CAPLUS,DOI:10.1016/S0013-4686(03)00539-5

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A review. A bulk and double-layer model for calcg. reversible potentials is described, with examples related tofundamental reactions at anodes and cathodes in fuel cells, including H2O oxidn. to OH(ads) and oxygen redn. to H2O onPt. The double-layer model can be the basis for calcns. of electrode potential-dependent redox activation energies. Inthis approach, the reaction center is treated as an open system and the electron transfers between it and the surroundingelectrode when the reaction center's electron affinity (for redn.) or ionization potential (for oxidn.) matches the thermodn.work function of the electrode. For greater accuracy, the electrolyte contribution to the redox center's Hamiltonian can betaken into account in an approx. way as a Madelung sum over a lattice of av. ion positions. When this is done,reasonable values for activation energies and reversible potentials for elementary electrocatalytic fuel cell-relatedreactions are obtained. This theory should help identify improved fuel cell catalysts and it should find applications toother areas of electrochem. It can also be improved by extending it to give potential-dependent bond polarizations inadsorbed intermediates by incorporating charges on the electrode surface atoms and compensating charges in thedouble layer, though such calcns. are highly computationally demanding.~33 Citings

627. Reproducing kernel Hilbert space interpolation methods as a paradigm of high dimensional modelrepresentations: Application to multidimensional potential energy surface construction

By Ho, Tak-San; Rabitz, HerschelFrom Journal of Chemical Physics (2003), 119(13), 6433-6442. Language: English, Database: CAPLUS,DOI:10.1063/1.1603219

A generic high dimensional model representation (HDMR) method is presented for approximating multivariate functionsin terms of functions of fewer variables and for going beyond the tensor-product formulation. Within the framework ofreproducing kernel Hilbert space (RKHS) interpolation techniques, an HDMR is formulated for constructing globalpotential energy surfaces. The HDMR tools in conjunction with a successive multilevel decompn. technique provideefficient and accurate procedures for reducing a multidimensional interpolation problem to smaller, independentsubproblems. When compared to the conventional tensor-product approach, the RKHS-HDMR methods can accuratelyproduce smooth potential energy surfaces over dynamically relevant, nonrectangular regions using far fewer ab initiodata points. Numerical results are given for a reduced two-level RKHS-HDMR of the C(1D) + H2 reactive system. Theproposed RKHS-HDMR is intimately related to Gordon's blending-function methods for multivariate interpolation andapproxn. The general findings in the paper and the successful illustration provide a foundation for further applications ofthe techniques.~42 Citings

628. Electro-oxidation of CO on Pt-based electrodes simulated by electronic structure calculations

By Saravanan, Chandra; Dunietz, Barry D.; Markovic, Nenad M.; Somorjai, Gabor A.; Ross, Phil N.; Head-Gordon,MartinFrom Journal of Electroanalytical Chemistry (2003), 554-555, 459-465. Language: English, Database: CAPLUS,DOI:10.1016/S0022-0728(03)00414-5

CO electrooxidn. on Pt-based electrodes is simulated by d. functional calcns. on cluster models. A surface boundcomplex of CO with OH is identified as a crucial intermediate in the mechanism of CO oxidn. The complex under theinfluence of an appropriate potential and in the presence of H2O undergoes CO oxidn. The potential energy surface forthis reaction as a function of the potential of the electrode is presented, and the barrier for the reaction is shown to vanishabove a sufficiently pos. applied potential. The different major barriers for the process are highlighted by comparing themechanism on pure Pt to a Ru-Pt alloy.~15 Citings

629. Mechanism for the electrooxidation of carbon monoxide on platinum by H2O. Density functional theorycalculation

By Narayanasamy, Jayakumar; Anderson, Alfred B.From Journal of Electroanalytical Chemistry (2003), 554-555, 35-40. Language: English, Database: CAPLUS,DOI:10.1016/S0022-0728(03)00024-X

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A recent theor. study of the electrooxidn. of CO on Pt found a low energy pathway wherein CO(ads) and OH(ads) bondto form COOH(ads) which reacts with a 2nd OH(ads) to yield CO2 and H2O(ads) A. Anderson and N. Neshev (2002).The B3LYP hybrid d. functional theory is used to examine an alternative mechanism for COOH(ads) formation and itsdecompn. The direct attack of CO(ads) by H2O to form, by electrooxidn., COOH(ads)+H+(aq.) or by H2O(ads) to formCOOH(ads)+H(ads) have resp. activation energies of 1.7 eV at the calcd. reversible potential (0.7 V on the H scale) or1.2 eV. Both are higher than that obtained in the above-mentioned study. An activation energy of 0.7 eV calcd. for thedecompn. of COOH(ads) to CO2 and H(ads) is also greater than that obtained in the earlier study. From this, thereaction mechanism obtained in the earlier study is confirmed as the lowest energy pathway, and the alternativemechanisms explored in the present study are not the cause of the 0.3 V CO(ads) oxidn. prewave in acid electrolytes.The over-all conclusion is that the electrode potential-dependent rate-limiting step is the oxidn. of H2O to form theOH(ads) oxidant for CO(ads) removal and the prewave probably is due to the lower potentials of OH(ads) formation atstep and defect sites where OH adsorption is stronger than on terraces.~15 Citings

630. A Conversation on VB vs MO Theory: A Never-Ending Rivalry?

By Hoffmann, Roald; Shaik, Sason; Hiberty, Philippe C.From Accounts of Chemical Research (2003), 36(10), 750-756. Language: English, Database: CAPLUS,DOI:10.1021/ar030162a

Quantum mechanics has provided chem. with two general theories, valence bond (VB) theory and MO theory. The twotheories were developed at about the same time, but quickly diverged into rival schools that have competed, sometimesfervently, on charting the mental map and epistemol. of chem. Three practitioners of MO and VB theory talk - fighting alittle, trying to understand - of the past and present of these two approaches to describing bonding in mols.~89 Citings

631. Constrained Variation Calculations of Electron-Transfer Transition States Using the Lagrange Method

By Kostadinov, Lubomir N.; Anderson, Alfred B.From Electrochemical and Solid-State Letters (2003), 6(10), E30-E33. Language: English, Database: CAPLUS,DOI:10.1149/1.1607571

Recently, this lab. demonstrated that activation internal energies for those electron-transfer reactions that simultaneouslyinclude bond scission and bond formation can be calcd. to reasonable accuracy as functions of electrode potential.Using local reaction center models, the electron transfer is assumed to take place when, due to thermal fluctuations, itselectron affinity or ionization potential equals the thermodn. work function of the electrode for the desired potential, forredn. or oxidn. reactions, resp. Transition states for such reactions cannot be located by conventional means. Here isdemonstrated how they may be found using constrained variation theory.~18 Citings

632. Ab initio quantum-chemical calculations in electrochemistry

By Koper, Marc T. M.From Modern Aspects of Electrochemistry (2003), 36, 51-130. Language: English, Database: CAPLUS

A review. First, general aspects of quantum chem. and of electronic-structure calcns. are briefly illustrated using eitherwave-function-based methods or d.-functional-theory-based methods. The electronic-structure calcns. are combinedwith mol. dynamics resulting in the ab initio mol. dynamics or the so-called Carr-Parinello mol. dynamics. Then, specificapplications are discussed, mainly the adsorption of atoms and mols. on electrochem. surfaces. It is described, how theeffect of the electrode potential can be modeled in an ab initio calcn. The adsorption of halogens and halides on metalsurfaces is treated as well as the chemisorption of CO on metals and alloys. Next, the field-dependent chemisorptionand the interfacial Stark effect are addressed, esp. the potential-dependent adsorption of CO. Another topic treated isthe interaction of water and of its dissocn. products with metal surfaces. Finally, ab initio quantum-chem. methods andab initio mol. dynamics are applied for the modeling of electrochem. reactions.~23 Citings

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633. Ab initio modelling of boron and nitrogen in diamond nanowires

By Barnard, A. S.; Russo, S. P.; Snook, I. K.From Philosophical Magazine (2003), 83(19), 2301-2309. Language: English, Database: CAPLUS,DOI:10.1080/0141861031000104172

An anal. is presented of the bonding and structural properties of dehydrogenated and hydrogenated doped cylindricaldiamond nanowires calcd. using the Vienna Ab Initio Simulation Package, employing d. functional theory within thegeneralized-gradient approxn. The dopants studied here have been inserted substitutionally along the axis of an infiniteone-dimensional diamond nanowire and include the single-electron acceptor boron and the single-electron donornitrogen. The doped nanowires have then been re-relaxed, and properties compared with the undoped structures. Thestructural properties of relaxed nanowires considered here include an examn. bonding via the electron charge d., with theaim of providing a better understanding of the effects of dopants on the stability of diamond nanostructures andnanodevices.~10 Citings

634. Hydrogen atom pairs in diamond bulk and at the surface: hybrid density functional theory and clustermodels

By Anderson, Alfred B.; Kostadinov, Lubomir N.; Angus, John C.From Physical Review B: Condensed Matter and Materials Physics (2003), 67(23), 233402/1-233402/4. Language:English, Database: CAPLUS, DOI:10.1103/PhysRevB.67.233402

Hydrogen pair defects in bulk diamond and on the (111) surface have been investigated using hybrid d. functional theoryand cluster models, including relaxation of defect atoms. The H*2 defect, consisting of one hydrogen atom in a bondinserted (BI) site and the other in an adjacent "antibonding" site, is calcd. to be 2.65 eV more stable than two isolated BIhydrogen atoms, and 3.97 eV less stable than two gas phase hydrogen atoms. This is in general agreement with resultscalcd. by other methods that have been reported in the literature. However, when the "antibonding" hydrogen atom is onthe surface and the BI hydrogen is just beneath it, the energy with respect to two gas phase hydrogen atoms (hydrogenatoms are present in the reactor and are necessary for growth) is stable by 0.95 eV and it is stable by 7.57 eV relative totwo bulk BI hydrogens. The hydrogen atom bond to the surface has a strength of 3.89 eV. Such structures have notbeen reported previously and they may contribute to the excess hydrogen found at diamond surfaces and may provide aroute to H*2 formation in the bulk.~0 Citings

635. H + H2 quantum dynamics using potential energy surfaces from density functional theory

By Grant, David M.; Wilson, Philip J.; Tozer, David J.; Althorpe, Stuart C.From Chemical Physics Letters (2003), 375(1,2), 162-166. Language: English, Database: CAPLUS,DOI:10.1016/S0009-2614(03)00861-3

D. functional theory (DFT) potential energy surfaces are detd. for the collinear H + H2 reaction, using the std. B3LYP,B97-1, and B97-2 hybrid exchange-correlation energy functionals. The surfaces are used to calc. state-to-state reactionprobabilities. B3LYP is wholly inadequate, whereas B97-1 and B97-2 yield a realistic description of the reactiondynamics, reproducing the widths and spacings of the resonances. Further improvements in functional quality arerequired, particularly with regard to the height and width of the DFT barrier.~8 Citings

636. A potential energy surface construction scheme for accurate reaction rate calculations: General approachand a test for the H+CH4→H2+CH3 reaction

By Wu, Tao; Manthe, UweFrom Journal of Chemical Physics (2003), 119(1), 14-23. Language: English, Database: CAPLUS,DOI:10.1063/1.1577328

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An approach for the construction of accurate potential energy surfaces for reaction rate calcns. is presented. It employsShepard interpolation with ref. points randomly selected from range of geometries relevant for the reaction rate.Quantum dynamics calcns., which use the multiconfigurational time-dependent Hartree approach and flux correlationfunctions to obtain thermal rate consts., monitor the convergence of the potential energy surface with increasing no. ofref. points. As a test of the approach, the H+CH4→H2+CH3 reaction is studied and the analytic Jordan-Gilbert potentialenergy surface is reproduced by the interpolation scheme. About 40 ref. points are required in the interpolation to obtaina converged interpolated surface which reproduces the thermal rate consts. with errors smaller than 20%.~47 Citings

637. Calculating Reversible Potentials for Elementary Reactions in Acid and Base from Model Reaction Energies

By Narayanasamy, Jayakumar; Anderson, Alfred B.From Journal of Physical Chemistry B (2003), 107(28), 6898-6901. Language: English, Database: CAPLUS,DOI:10.1021/jp027706v

Reversible potentials, U°, were calcd. based on reactions energies, Er, for the intermediate steps in the outer-sphereoxygen redn. reactions to H2O. The working formula is U° = (-Er eV-1 + c) V, where U° is the reversible potential and theref. energy of the electron is -4.6 eV on the phys. (vacuum) or 0 V on the hydrogen scale. Results using a 6-31G** basisin the B3LYP hybrid d. functional theory are comparable to ab initio MP2 results obtained previously for acid soln. with c0.49 for the former and 0.50 for the latter. Both methods work for basic soln. but, unlike in acid, the c values aredifferent, 0.58 for B3LYP and 0.76 for MP2, reflecting differences in the 2 computational methods in treating anions.~13 Citings

638. Theory of hydrogen in diamond

By Goss, Jonathan P.From Journal of Physics: Condensed Matter (2003), 15(17), R551-R580. Language: English, Database: CAPLUS,DOI:10.1088/0953-8984/15/17/201

A review. Hydrogen is a ubiquitous impurity in diamond but in contrast to other group IV materials the microscopicstructure adopted in bulk material has largely remained elusive. It has therefore been the role of modeling to predict theproperties of H in bulk diamond, as well as the interactions with impurities and other defects. Presented here is anaccount of the current theor. understanding of hydrogen in diamond. Topics include theor. approaches, muonium andinterstitial hydrogen, di-hydrogen aggregates, hydrogenated lattice vacancies, complexes of hydrogen with impurities,and hydrogen and extended defects.~54 Citings

639. Iron, nickel and zinc malate coordination compounds. Synthesis, characterization, and thermal behavior

By Patron, L.; Carp, O.; Mindru, I.; Marinescu, G.; Segal, E.From Journal of Thermal Analysis and Calorimetry (2003), 72(1), 281-288. Language: English, Database: CAPLUS

The coordinations compds. (NH4)[Fe(C4H4O5)(OH)2]·0.5H2O, [Ni(C4H4O5)]·3H2O and [Zn(C4H4O5)]·5H2O weresynthesized by a pptn. method and characterized by chem. anal., spectral (IR, UV-visible) and magnetical studies. In therange 50-600° stepped thermal decompns. occur with formation of anhyd. malates, malonates, oxoacetates (Fe and Nicompds.) and hydroxocarbonate (Zn compd.) as intermediates obsd. by FTIR spectroscopy. α-Fe2O3, NiO and ZnOconstitute the final decompn. products.~27 Citings

640. Functional and structural analogs of the dioxygen reduction site in terminal oxidases

By Collman, James P.; Boulatov, Roman; Sunderland, Christopher J.Edited By:Kadish, Karl M.; Smith, Kevin M.; Guilard, RogerFrom Porphyrin Handbook (2003), 11, 1-49. Language: English, Database: CAPLUS, DOI:10.1016/B978-0-08-092385-7.50007-0

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A review discusses the design, synthesis and evaluation of functional and structural models of heme/copper terminaloxidases. Heme/copper terminal oxidases are a superfamily of multisubunit membrane enzymes catalyzing the redn. ofdioxygen to water as a means of clearing the electron transport system of electrons derived from oxidative catabolism.The structural and spectroscopic models of the heme/copper terminal oxidases include the oxo and hydroxo bridgedsystem, cyanide bridged system, carboxylate bridged system, and carbon monoxide adducts of (por)FeIICuI systems.~65 Citings

641. Peroxide Electroreduction on Bi-Modified Au Surfaces: Vibrational Spectroscopy and Density FunctionalCalculations

By Li, Xiao; Gewirth, Andrew A.From Journal of the American Chemical Society (2003), 125(23), 7086-7099. Language: English, Database: CAPLUS,DOI:10.1021/ja034125q

The mechanism of the electroredn. of peroxide on Bi-submonolayer-modified Au(111) surfaces is examd. using surface-enhanced Raman scattering (SERS) measurements along with detailed d. functional theory (DFT) calcns. Thespectroscopy shows Bi-OH and Bi-O species at potentials just pos. of that where peroxide is reduced. These speciesare not present in solns. absent of either peroxide or Bi. DFT calcns. show that peroxide is unstable relative to Bi-OHwhen Bi is present in the (2 × 2) configuration on Au(111) known from previous work to be catalytically active. Thespacing between Bi adatoms is such that peroxide assocn. with 2 Bi cannot occur without O-O bond cleavage. The fullBi monolayer is catalytically inactive and exhibits none of the Bi-OH or Bi-O signals seen for the active surface. Thecalcns. show that as the Bi coverage becomes greater and the Bi adatom spacing becomes smaller, peroxide can adsorbon Bi without O-O bond rupture. These results indicate an important role for M-OH species in peroxide electroredn.~54 Citings

642. Theoretical Calculation of Activation Energies for Pt + H+(aq.) + e-(U) ↔ Pt-H: Activation Energy-BasedSymmetry Factors in the Marcus Normal and Inverted Regions

By Anderson, Alfred B.; Sidik, Reyimjan A.; Narayanasamy, Jayakumar; Shiller, PaulFrom Journal of Physical Chemistry B (2003), 107(19), 4618-4623. Language: English, Database: CAPLUS,DOI:10.1021/jp0271099

The low coverage reversible potential for underpotential deposition of hydrogen on platinum in acid electrolyte is calcd.quantum mech. with 2 approaches, (i) one using the calcd. reaction energy for the overall reaction and an added const.and (ii) the other based on a model of the electrochem. interface. The former yields 0.40 V and the latter 0.48 V, bothclose to the obsd. value of ∼0.40 V. Electrode-potential-dependent activation energies are calcd. using the interfacemodel for the redn. of the hydronium ion to form the Pt-H bond and for the reverse oxidn. reaction over the -0.3 to 3.0 Vrange. To make this possible, the model explicitly excludes the hydrogen evolution reaction at the cathodic end and H2Ooxidn. at the anodic end of the potential range. Cathodic and anodic symmetry factors are detd. from the slopes of theactivation energy curves, which are used as models for the corresponding activation free energy curves. They areextended into the Marcus-inverted regions for oxidn. and redn. The symmetry factors add to 1.0 in the normal region andin the inverted regions and are not linear functions of the electrode potential.~25 Citings

643. The bioinorganic chemistry of iron in oxygenases and supramolecular assemblies

By Groves, John T.From Proceedings of the National Academy of Sciences of the United States of America (2003), 100(7), 3569-3574.Language: English, Database: CAPLUS, DOI:10.1073/pnas.0830019100

A review. The bioinorg. chem. of Fe is central to life processes. Organisms must recruit iron from their environment,control iron storage and trafficking within cells, assemble the complex, iron-contg. redox cofactors of metalloproteins, andmanage a myriad of biochem. transformations by those enzymes. The coordination chem. and the variable oxidn. statesof iron provide the essential mechanistic machinery of this metab. The current understanding of several aspects of thechem. of iron in biol. are discussed with an emphasis on the oxygen activation and transfer reactions mediated by hemeand nonheme iron proteins and the interactions of amphiphilic iron siderophores with lipid membranes.~254 Citings

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644. Transition from Hydrogen Atom to Hydride Abstraction by Mn4O4(O2PPh2)6 versus [Mn4O4(O2PPh2)6]+:O-H Bond Dissociation Energies and the Formation of Mn4O3(OH)(O2PPh2)6

By Carrell, Thomas G.; Bourles, Emilie; Lin, Matthew; Dismukes, G. CharlesFrom Inorganic Chemistry (2003), 42(9), 2849-2858. Language: English, Database: CAPLUS, DOI:10.1021/ic025977e

Synthesis, characterization, and reactions of the novel Mn-oxo cubane complex [Mn4O4(O2PPh2)6](ClO4), 1+(ClO4 -), aredescribed. Cation 1+ is composed of the [Mn4O4]7+ core surrounded by six bidentate phosphinate ligands. The proton-coupled electron transfer (pcet) reactions of phenothiazine (pzH), the cation radical (pzH.bul.+)(ClO4 -), and the neutralpz.bul. radical with 1+ are reported and compared to Mn4O4(O2PPh2)6 (1). Compd. 1+(ClO4 -) reacts with excess pzH viafour sequential redn. steps that transfer a total of five electrons and four protons to 1+. This reaction forms the doublydehydrated Mn cluster Mn4O2(O2PPh2)6 (2) and two H2O mols. derived from the corner O atoms. The 1st pcet stepforms the novel complex Mn4O3(OH)(O2PPh2)6 (1H) and 1 equiv of the pz+ cation by net hydride transfer from pzH.Spectroscopic characterization of isolated 1H is reported. Redn. of 1 by pzH or para-substituted phenols also produces1H via net H atom transfer. A lower limit to the homolytic bond dissocn. energy (BDE) (1H → 1 + H) is >94 kcal/molusing soln. phase BDEs for pzH and para-substituted phenols. The heterolytic BDE was estd. for the hydride transferreaction 1H → 1+ + H- (BDE ∼ 127 kcal/mol). These comparisons reveal the O-H bond in 1H to be among the strongestof any Mn-hydroxo complex measured thus far. In three successive H atom transfer steps, 1H abstrs. three H atomsfrom three pzH mols. to form complex 2. Complex 2 is identical to the pinned butterfly cluster produced by the reaction of1 with pzH (Ruettinger, W. F., et al., 2000). The Mn oxidn. states in 2 are formally Mn4(2II,2III), and no further redn.occurs in excess pzH. By contrast, outer-sphere electron-only reductants such as cobaltocene reduce both 1+ and 1 tothe all Mn(II) oxidn. level and cause cluster fragmentation. The reaction of pzH.bul.+ with 1+ produces 1H and the pz+

cation by net H atom transfer, and terminates at 1 equiv of pzH.bul.+ with no further reaction at excess. By contrast, pz.bul.

does not react with 1+ at all, indicating that redn. of 1+ by electron transfer to form pz+ does not occur without a proton(pcet to 1+ is thermodynamically required). Exptl. free energy changes account for these pcet reactions and the absenceof electron transfer for any of the phenothiazine series. H atom abstraction from substrates by 1 vs. hydride abstractionby 1+ illustrates the transition to two-electron 1-proton pcet chem. in the [Mn4O4]7+ core that is understood from freeenergy consideration. This transition provides a concrete example of the predicted lowest-energy pathway for the oxidn.of two H2O mols. to H2O2 as an intermediate within the photosynthetic H2O-oxidizing enzyme (vs. sequential 1-electron/proton steps). The implications for the mechanism of photosynthetic H2O splitting are discussed.~45 Citings

645. Ab initio modelling of B and N in diamond nanowires

By Barnard, A. S.; Russo, S. P.; Snook, I. K.From Chemistry Preprint Server, Physical Chemistry (2003), 1-19, CPS: physchem/0303005. Language: English,Database: CAPLUS

An anal. of the bonding and structural properties of dehydrogenated and hydrogenated doped cylindrical diamondnanowires calcd. using the Vienna Ab initio Simulation Package (VASP), employing D. Functional Theory (DFT) withinthe Generalized Gradient Approxn. (GGA), is presented. The dopants studied here have been inserted substitutionallyalong the axis of an infinite, one dimensional diamond nanowire, and include the single electron acceptor boron and thesingle electron donor nitrogen. The doped nanowires have then been re-relaxed, and properties compared to theundoped structures. Structural properties of relaxed nanowires considered here include an examn. bonding via theelectron charge d.; with the aim of providing a better understanding of the effects of dopants on the stability of diamondnanostructures and nanodevices.~0 Citings

646. Temperature dependence of the kinetic isotope effect and tunneling contribution in the innermolecularreaction of phenylcarbene inside a hemicarcerand

By Kemmis, Carly; Warmuth, RalfFrom Journal of Supramolecular Chemistry (2003), 1(4-6), 253-267. Language: English, Database: CAPLUS

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The mobility and kinetic isotope effect (KIE) for the inner phase acetal insertion of phenylcarbene 1 have been probedinside the partially deuterated hemicarcerand d40-5 and the parent 5. Hemicarcerand d40-5 has OCH2O spanners in itsupper and OCD2O spanners in its lower hemisphere. Phenylcarbene was generated photochem. from incarceratedphenyldiazirine 4. At low temp., hemicarceplex 54 shows carceroisomerism and different populations of carceroisomers.In the photolysis of d40-54, C-H bond insertion exceeded 50%, which supports that transient 1 is rotationally mobile withinits life-time. The KIE in the solid state increases with decreasing temp. The Arrhenius parameters AH/AD = 4.2 ± 0.3 andthe linearity of the Arrhenius plot of KIE suggests that both isotopes tunnel considerably over the whole exptl. temp.range (0-196°C). In soln., the KIE shows unusual temp. dependence. The KIEs are explained by postulating threereaction phases 5 with different C-H bond reactivity: (1) the reaction phase in soln. (2) The reaction phase in the solidstate and (3) the reaction phase in a frozen soln. The latter is characterized by partially inward rotated α-CH2 groups ofthe four O(CH2)4O bridges of 5.~3 Citings

647. Chemistry: Chemical reactions involving quantum tunneling

By McMahon, Robert J.From Science (Washington, DC, United States) (2003), 299(5608), 833-834. Language: English, Database: CAPLUS,DOI:10.1126/science.1080715

A review of the title subject. The characterization of the tunneling process in org. reactions, e.g., nonlinear Arrheniusbehavior, unusual isotope effects, and rate independence of temp. are discussed.~50 Citings

648. Carbon Tunneling from a Single Quantum State

By Zuev, Peter S.; Sheridan, Robert S.; Albu, Titus V.; Truhlar, Donald G.; Hrovat, David A.; Borden, Weston ThatcherFrom Science (Washington, DC, United States) (2003), 299(5608), 867-870. Language: English, Database: CAPLUS,DOI:10.1126/science.1079294

We obsd. ring expansion of 1-methylcyclobutylfluorocarbene at 8 K, a reaction that involves carbon tunneling. Themeasured rate consts. were 4.0 × 10-6 per s in nitrogen and 4 × 10-5 per s in argon. Calcns. indicated that at this temp.the reaction proceeds from a single quantum state of the reactant so that the computed rate const. has achieved a temp.-independent limit. According to calcns., the tunneling contribution to the rate is 152 orders of magnitude greater than thecontribution from passage over the barrier. We discuss environmental effects of the solid-state inert-gas matrix on thereaction rate.~128 Citings

649. Separation of quantum and classical behavior in proton transfer reactions: implications from studies ofsecondary kinetic isotope effects

By Iftimie, Radu; Schofield, JeremyFrom International Journal of Quantum Chemistry (2003), 91(3), 404-413. Language: English, Database: CAPLUS,DOI:10.1002/qua.10392

In this article the separability of the nuclear degrees of freedom system into mixed quantum and classical components isexamd. by looking at secondary kinetic isotope effects in a model proton transfer reaction. To explore this issue, thenature of secondary kinetic isotope effects is investigated by means of mol. mechanics and ab initio simulations of amodel system in which intramol. proton transfer occurs in a region whose chem. topol. is similar to that ofmalonaldehyde. Isotope effects are calcd. using importance sampling Monte Carlo techniques designed to improve thestatistical efficiency of ab initio simulations within the framework of quantum centroid transition state theory. The ab initioresults for kinetic isotope effects are contrasted with those obtained using two mol. mechanics potential energy functions.It is demonstrated that the calcd. isotope effects are extremely sensitive to subtle features of the potential energysurface, which suggests that information from ab initio structure and energy calcns. about configurations along thereaction path must be utilized in the construction of classical potentials to obtain accurate secondary kinetic isotope effectpredictions. It is also demonstrated that quantum nuclear degrees of freedom of all secondary atoms that movesignificantly as a chem. reaction proceeds should be treated explicitly, as even secondary heavy-atom tunneling effectscould be significant.~15 Citings

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650. Mapping the Potential Energy Surface of the Tolylcarbene Rearrangement in the Inner Phase of aHemicarcerand

By Kerdelhue, Jean-Luc; Langenwalter, Kevin J.; Warmuth, RalfFrom Journal of the American Chemical Society (2003), 125(4), 973-986. Language: English, Database: CAPLUS,DOI:10.1021/ja027831k

Photolysis of p-tolyldiazirine (6) in the inner phase of a hemicarcerand with four butane-1,4-dioxy linker groups (5) inC6D5CD3 at 77 K yields the 5-methylcycloheptatetraene hemicarceplex 5@3b in 41% together with innermol. reactionproducts resulting from an insertion of transient p-tolylcarbene (1b) into an acetal C-H or linker C-O bond of 5 and fromthe addn. of 1b to an aryl unit of 5. The yield of incarcerated 3b increased up to 67% if 6 is photolyzed inside ahemicarcerand with deuterated spanners and butane-1,4-dioxy linker groups (d48-5). Hemicarceplex 5@3b is not formedif the photolysis is carried out in CDCl3. Incarcerated 3b is stable at room temp. in the absence of oxygen and ischaracterized by 1D and 2D NMR spectroscopy. In the presence of oxygen, 3b reacts quant. to yield toluene and CO2.Upon heating solns. of d48-5 3b in C6D5CD3, 3b rearranges to 1b and m-tolylcarbene (18). Both tolylcarbenesimmediately react with the surrounding host. From a product anal. and the measured rate consts. for the thermaldecompn. of d48-5@3b in the temp. range 70-102°C, the activation parameters for the 3b to 1b and 3b to 18rearrangements are calcd. (3b to 1b: ∆G373 = 27.3 ± 1.4 kcal/mol, ∆H373 = 26.4 ± 1.0 kcal/mol, T∆S373 = -0.9 ± 1.0kcal/mol; 3b to 18: ∆G373 = 27.8 ± 1.4 kcal/mol, ∆H373 = 19.7 ± 1.0 kcal/mol, T∆S373 = 8.1 ± 1.0 kcal/mol). Thesevalues are compared with those calcd. by Geise and Hadad at the B3LYP/6-311+G** level of theory (Geise, C. M.;Hadad, C. M. J. Org. Chem. 2002, 67, 2532-2540). The slightly higher inner phase activation free energy of the 3b to 18rearrangement is explained through steric constraints imposed by the surrounding hemicarcerand on the transition state.The enthalpy-entropy compensation obsd. for the 3b to 18 rearrangement is discussed and interpreted as a result of ahemicarcerand and solvent reorganization along the reaction coordinate. It is taken as indirect evidence for theintermediacy of 2-methylbicyclo[4.1.0]hepta-2,4,6-triene in the 3b to 18 rearrangement.~25 Citings

651. Kinetic isotope effects for concerted multiple proton transfer: A direct dynamics study of an active-sitemodel of carbonic anhydrase II

By Smedarchina, Zorka; Siebrand, Willem; Fernandez-Ramos, Antonio; Cui, QiangFrom Journal of the American Chemical Society (2003), 125(1), 243-251. Language: English, Database: CAPLUS,DOI:10.1021/ja0210594

The rate const. of the reaction catalyzed by the enzyme carbonic anhydrase II, which removes carbon dioxide from bodyfluids, is calcd. for a model of the active site. The rate-detg. step is proton transfer from a zinc-bound water mol. to ahistidine residue via a bridge of two or more water mols. The structure of the active site is known from x-ray studiesexcept for the no. and location of the water mols. Model calcns. are reported for a system of 58 atoms including a four-coordinated zinc ion connected to a methylimidazole mol. by a chain of two waters, constrained to reproduce the size ofthe active site. The structure and vibrational force field are calcd. by an approx. d. functional treatment of the proton-transfer step at the Self-Consistent-Charge D. Functional Tight Binding (SCC-DFTB) level. A single transition state isfound indicating concerted triple proton transfer. Direct-dynamics calcns. for proton and deuteron transfer andcombinations thereof, based on the Approx. Instanton Method and on Variational Transition State Theory with TunnelingCorrections, are in fair agreement and yield rates that are considerably higher and kinetic isotope effects (KIEs) that aresomewhat higher than expt. Classical rate consts. obtained from Transition State Theory are smaller than the quantumvalues but the corresponding KIEs are five times larger. For multiple proton transfer along water bridges classical KIEsare shown to be generally larger than quantum KIEs, which invalidates the std. to distinguish tunneling and over-barriertransfer. In the present case, a three-way comparison of classical and quantum results with the obsd. data is necessaryto conclude that proton transfer along the bridge proceeds by tunneling. The results suggest that the two-water bridge ispresent in low concns. but makes a substantial contribution to proton transport because of its high efficiency. Bridgingstructures contg. more water mols. may have lower energies but are expected to be less efficient. The obsd. exponentialdependence of the KIEs on the deuterium concn. in H2O/D2O mixts. implies concerted transfer and thus rules outsubstantial contributions from structures that lead to stepwise transfer via solvated hydronium ions, which presumablydominate proton transfer in less efficient carbonic anhydrase isoenzymes.~92 Citings

652. Oxygen reduction on a platinum cluster

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By Li, Tao; Balbuena, Perla B.From Chemical Physics Letters (2002), 367(3,4), 439-447. Language: English, Database: CAPLUS,DOI:10.1016/S0009-2614(02)01755-4

The reaction Pt5O2(ads)+H+(aq)+e- Pt5-OOH is analyzed on the basis of d. functional theory calcns. The electrontransfer process takes place gradually as the hydronium ion gets close to the adsorbed O. At a certain small Oads-H···Owater distance, the barrier for proton and electron transfer becomes negligible. The effect of an elec. field on thereaction is studied by charging the metal/adsorbate complex, and that of a solvation shell on the proton transfer processis explored by using the H3O+(H2O)2 ion cluster to model the hydrated proton.~37 Citings

653. Polynuclear coordination compounds as precursors for CuFe2O4

By Marinescu, Gabriela; Patron, Luminita; Carp, Oana; Diamandescu, Lucian; Stanica, Nicolae; Meghea, Aurelia;Brezeanu, Maria; Grenier, Jean-Claude; Etourneau, JeanFrom Journal of Materials Chemistry (2002), 12(12), 3458-3462. Language: English, Database: CAPLUS,DOI:10.1039/b206604c

The possibility of obtaining Cu ferrite through the thermal decompn. of the two polynuclear coordination compds.:(NH4)8[Fe2Cu(C2O4)8] (I) and [Fe2Cu(C2O4)2(OH)4]·4H2O (II) was considered. The polynuclear compds. werecharacterized by various phys. chem. techniques, e.g., IR, UV-visible, EPR, Mossbauer spectra, thermal anal. andmagnetic measurements. The final products obtained after thermal decompn. of the complex compds. were analyzed byx-ray diffraction. A mixt. of tetragonal CuFe2O4, α-Fe2O3 and CuO is generated from the thermolysis of compd. I, while aclean tetragonal CuFe2O4 with satn. magnetization of 26.89 emu g-1 was obtained from compd. II.~22 Citings

654. Breathing-orbital valence bond method - a modern valence bond method that includes dynamic correlation

By Hiberty, Philippe C.; Shaik, SasonFrom Theoretical Chemistry Accounts (2002), 108(5), 255-272. Language: English, Database: CAPLUS,DOI:10.1007/s00214-002-0364-8

This account describes the breathing-orbital valence bond (BOVB) method, a modern valence bond method thatincorporates differential dynamic correlation assocd. with the bond making and breaking of a chem. event. The methodaims to combine the properties of interpretability and compactness of the classical valence bond method with goodaccuracy of the energetics. The domain of applicability of the BOVB method is mainly for problems that requireinterpretation of an electronic wave function in terms of Lewis structures. The method generates all the covalent andionic Lewis structures that are relevant to the electronic state, and represents each of them by a single valence bondconfiguration state function. A balanced description of the different Lewis structures is then ensured by allowing eachconfiguration to have its specific set of orbitals during the optimization process. In this framework, the dynamiccorrelation assocd. with the breaking or forming of a bond is viewed as the instantaneous adaptation of the orbitals to theelectron fluctuation inherent to the bond; hence, the "breathing orbital" characterization. Applications of the BOVBmethod to a variety of problems are described, for example, two-electron bonds, odd-electron bonds, bonds to transitionmetals, resonance energies, and diabatic surfaces. In all these applications, the method is shown to provide bondingenergies that compare well to accurately calcd. or exptl. values, despite the extreme compactness of the wave functions.~111 Citings

655. A Quantum Chemical Model for Electric Field Induced Electron Transfer at Metal Electrodes. Application toHalide Oxidation on Cu(100)

By Dominguez-Ariza, David; Sousa, Carmen; Illas, FrancescFrom Journal of Physical Chemistry B (2002), 106(48), 12483-12490. Language: English, Database: CAPLUS,DOI:10.1021/jp020973g

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A model based on the use of ab initio quantum chem. explicitly correlated wave functions is proposed to study theelectronic transfer reaction between an adsorbate and a metallic electrode. In this model, the effects of the electrodepotential are simulated through the application of a uniform external elec. field. This field exerts an influence on therelative stability of the 2 electronic states that are mainly involved in the electron transfer. These electronic states havethe transferred electron localized either in the electrode or in the adsorbate. The model was applied to the electrontransfer between halides and a cluster model representation of the Cu(100) single-crystal electrode. A linear correlationbetween the elec. field intensity at which the 2 electronic states involved in the charge-transfer process becomedegenerate and the normal redn. electrode potential is found. The existence of this linear correlation indicates that theproposed model contains the essential physics governing the trend of halide oxidn. at a metal electrode.~6 Citings

656. A priori rate constants for kinetic modeling

By Sumathi, R.; Green, William H., Jr.From Theoretical Chemistry Accounts (2002), 108(4), 187-213. Language: English, Database: CAPLUS,DOI:10.1007/s00214-002-0368-4

The article describes the use of kinetic models of multicomponent reacting systems for the development of efficient andaccurate methods for estg. rate consts. It also presents new rate ests. for several types of reactions involving O andHO2, and highlights several tech. issues requiring further work by the theor. chem. community.~67 Citings

657. Valence Bond Modeling of Barriers in the Nonidentity Hydrogen Abstraction Reactions, X'.bul. + H-X → X'-H+ X.bul. (X' ≠ X = CH3, SiH3, GeH3, SnH3, PbH3)

By Song, Lingchun; Wu, Wei; Dong, Kunming; Hiberty, Philippe C.; Shaik, SasonFrom Journal of Physical Chemistry A (2002), 106(46), 11361-11370. Language: English, Database: CAPLUS,DOI:10.1021/jp026438y

Breathing orbital valence bond (BOVB) computations (Hiberty, P. C.; Humbel, S.; Byrman, C. P.; van Lenthe, J. H. J.Chem. Phys. 1994, 101, 5969) are used to obtain nonidentity barriers for hydrogen transfer reactions between X and X'groups, X ≠ X' = CH3, SiH3, GeH3, SnH3, PbH3. Modeling of these barriers by means of VB state correlation diagrams(Shaik, S.; Shurki, A. Angew. Chem., Int. Ed. Engl. 1999, 38, 586) leads to a simple expression for the barrier (eq 29) asan interplay of an intrinsic term and the reaction driving force. The equation predicts barrier heights that are compatiblewith the BOVB computed barrier heights. Its comparison with the Marcus equation shows similarities and differences.~34 Citings

658. Mechanism for the Electro-oxidation of Carbon Monoxide on Platinum, Including Electrode PotentialDependence

By Anderson, Alfred B.; Neshev, Nikolay M.From Journal of the Electrochemical Society (2002), 149(10), E383-E388. Language: English, Database: CAPLUS,DOI:10.1149/1.1506934

B3LYP hybrid d. functional calcns. show that CO and OH bonded to Pt2 react with a low activation energy (calcd. 0.44eV) to form -COOH bonded to a 1-fold site of Pt2. An OH bonded to the adjacent 1-fold site attracts the acid group by Hbonding and a low activation energy (calcd. 0.23 eV) separates this complex from CO2+H2O-Pt2. The similarity of thebond strengths between Pt2 and CO, OH, and H2O to measured chemisorption bond strengths from the literature makesthese results worth considering as a model for the electrooxidn. of CO(ads) by OH(ads) on Pt anodes. Calcns. ofactivation energies for the oxidative deprotonation of Pt2-COOH indicate that high activation energies are to be expectedfor the reaction -COOH(ads) + H2O → CO2 + H3O+(aq.) + e-(U) at the electrode potentials where CO(ads) is removed(∼0.6 V). Therefore, the formation of OH(ads) from oxidn. of H2O, shown in another study to have a low activationenergy and a reversible potential of ∼0.57 V, is the cause of the obsd. overpotential for the electrooxidn. of CO(ads).~51 Citings

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659. Molecular dynamics simulation of the first electron transfer step in the oxygen reduction reaction

By Hartnig, Christoph; Koper, Marc T. M.From Journal of Electroanalytical Chemistry (2002), 532(1-2), 165-170. Language: English, Database: CAPLUS,DOI:10.1016/S0022-0728(02)00970-1

We present a mol. dynamics simulation of solvent reorganization in the first electron transfer step in the oxygen redn.reaction, i.e. O2+e- O2 -, modeled as taking place in the outer Helmholtz plane. The first electron transfer step is usuallyconsidered the rate-detg. step from many exptl. studies. From our results, we conclude that solvent reorganization ratherthan inner-sphere reorganization provides the dominant contribution to the activation barrier, if no specific interaction ofO2 or O2 - with the electrode is included. The free energy surfaces for solvent reorganization are strongly non-linearowing to the effect of electrostriction, which is not incorporated in the classical Marcus electron transfer theory. In spiteof the non-sym. free energy barrier, the transfer coeff. at equil. is still close to 0.5, whereas it would be estd. to be muchlower from harmonic model considerations.~47 Citings

660. O2 reduction and CO oxidation at the Pt-electrolyte interface. The role of H2O and OH adsorption bondstrengths

By Anderson, Alfred B.From Electrochimica Acta (2002), 47(22-23), 3759-3763. Language: English, Database: CAPLUS,DOI:10.1016/S0013-4686(02)00346-8

The nature of surface sites on which OH(ads) forms in acid and basic electrolytes is discussed based on the anal. ofexptl. results in the literature and the results of quantum calcns. Theor. evidence is given for OH(ads) forming in acidsoln. on Pt surfaces by the reaction Pt-OH2···OH2(OH)2 ↔ Pt-OH···H+-OH2(OH2)2 + e-(U) (i)and an anal. of exptl. resultssuggests that in base it forms by the reaction Pt-OH2···OH-(HOH)2 ↔ Pt-OH···H-OH(HOH)2 + e-(U) (ii). The reversiblepotential for reaction (i) is 0.62 V, which is essentially the onset potential for OH(ads) formation in weak acid electrolytes.Probably OH(ads) forms at potentials as low as ∼0.17 V in weak basic electrolyte by reaction (ii) where H2O mols. bondby lone-pair donation to unblocked Ptδ+ sites of the hydrided electrode surface, and as the potential is increased to thedouble layer region, beginning at 0.4 V, H2O no longer bonds with the surface to participate in this reaction. Thisbehavior would explain the ∼0.3 V prewave in CO(ads) oxidn. by OH(ads). At the potential of zero charge, ∼0.6 V, H2Oagain adsorbs and the reaction resumes. It is concluded based on exptl. and theor. evidence that 4-electron O2 redn. onPt electrodes at low overpotentials requires a special site characterized by a relatively small ratio of OH to H2Oadsorption bond strengths and or a higher activation energy for OH(ads) formation by reaction (i), as well as a weakability to adsorb anions.~107 Citings

661. Polynuclear complex compounds as precursors for chromites

By Patron, Luminita; Carp, Oana; Pocol, Valerica; Modrogan, Elena; Barjega, Ruxandra; Segal, Eugen; Brezeanu,MariaFrom Revue Roumaine de Chimie (2002), 46(4), 277-282. Language: English, Database: CAPLUS

Polynuclear coordination compds., (NH4)2[Cr2MII(C4H4O5)4(OH)2]·2H2O and [Cr2MII(C6H11O7)4(C6H10O7)2]·2H2O (whereMII = CoII, CuII) were synthesized as precursors of chromites. These compds. were characterized by elemental chem.anal., vibrational and electronic spectral measurements, magnetic susceptibilities and thermal anal. CuCr2O4 andCoCr2O4 spinels were obtained from thermal decompns.~2 Citings

662. Density functional theory study of O2 electroreduction when bonded to a Pt dual site

By Sidik, Reyimjan A.; Anderson, Alfred B.From Journal of Electroanalytical Chemistry (2002), 528(1-2), 69-76. Language: English, Database: CAPLUS,DOI:10.1016/S0022-0728(02)00851-3

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The B3LYP hybrid d. functional theory (DFT) was used to study the four-electron redn. mechanism of oxygen on platinumin aq. acid electrolytes. The calcns. indicate that, (a) O2 bonded to a dual site on Pt2 does not dissoc. before the 1stelectron transfer and the product for this step, OOH, easily dissocs. with a small 0.06 eV activation barrier to formadsorbed O and OH; (b) the 1st electron transfer step has the highest activation barrier and hence it is rate detg., inagreement with the proposed kinetic model in the literature; (c) the elec. field of the reacting solvated hydronium ionsignificantly increases the electron affinities of the species being reduced, indicating that a proton is involved in the ratedetg. 1st, as well as in the subsequent steps of the redn.; (d) the symmetry factor β for the 1st step is 0.5 (or less) in thehigh over-potential region and ∼1.0 in the low overpotential region, in approx. agreement with Tafel plots in the literature;(e) the calcd. activation energy at 1.23 V (SHE) for the 1st step is 0.6 eV, close to the exptl. effective activation energyvalue of 0.44 eV on Pt(111) in H2SO4.~155 Citings

663. Mechanism for the electrooxidation of water to OH and O bonded to platinum: quantum chemical theory

By Anderson, Alfred B.; Neshev, Nikolay M.; Sidik, Reyimjan A.; Shiller, PaulFrom Electrochimica Acta (2002), 47(18), 2999-3008. Language: English, Database: CAPLUS, DOI:10.1016/S0013-4686(02)00203-7

Based on B3LYP hybrid d. functional calcns., it is concluded from activation and reaction energies that OH will not formon a Pt dimer by OH bond cleavage in :Neither will the hydroxyl bond dissoc. over the Pt :Recent exptl. measurementsfor Pt surfaces yield Pt-O and Pt-H bond strengths that lead to the same conclusion, and show that the Pt dimer is aworthwhile model for the above chem. on Pt surfaces. This means that the initial step in the electrochem. generation ofOH(ads) on Pt electrodes is not O-H bond cleavage in H2O over a dual Pt site as previously proposed. Bond strengthssimilar to Pt-O and Pt-H surface values are also calcd. for H2O, OH, and H bonded to a single Pt atom. This allows thecalcn. of potential-dependent activation energies for oxidative deprotonation of H2O and OH over a 1-fold surface sitemodeled by a single Pt atom by using an approach recently developed in this lab. Transition states are calcd. withrespect to H bonded precursors using the following optimized structure models. The activation energies for and , basedon ab initio MP2 theory, show that H2O(ads) and OH(ads) can oxidatively deprotonate with low activation energies at theresp. calcd. reversible potentials of ∼0.57 and ∼1.32 V, to yield OH(ads) and O(ads). The model is extended to includethe effect of the electrolyte ions on the potential at the reaction center i.e. by adding a Madelung potential to theHamiltonian. The results are consistent with the formation of the important OH(ads) oxidant on fuel cell anodes beingunder thermodn. control, with low activation barriers at the reversible potential.~74 Citings

664. Quantum mechanical methods for enzyme kinetics

By Gao, Jiali; Truhlar, Donald G.From Annual Review of Physical Chemistry (2002), 53, 467-505. Language: English, Database: CAPLUS,DOI:10.1146/annurev.physchem.53.091301.150114

A review. This review discusses methods for the incorporation of quantum mech. effects into enzyme kineticssimulations in which the enzyme is an explicit part of the model. We emphasize three aspects: (a) use of quantum mech.electronic structure methods such as MO theory and d. functional theory, usually in conjunction with mol. mechanics; (b)treating vibrational motions quantum mech., either in an instantaneous harmonic approxn., or by path integrals, or by athree-dimensional wave function coupled to classical nuclear motion; (c) incorporation of multidimensional tunnelingapproxns. into reaction rate calcns.~597 Citings

665. Dynamics of 1,2-Hydrogen Migration in Carbenes and Ring Expansion in Cyclopropylcarbenes

By Albu, Titus V.; Lynch, Benjamin J.; Truhlar, Donald G.; Goren, Alan C.; Hrovat, David A.; Borden, Weston Thatcher;Moss, Robert A.From Journal of Physical Chemistry A (2002), 106(21), 5323-5338. Language: English, Database: CAPLUS,DOI:10.1021/jp020544i

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Variational transition state theory with multidimensional tunneling contributions has been used to calc. the rate consts.,kinetic isotope effects, and activation energies for 1,2-shifts in methylchlorocarbene, benzylchlorocarbene,cyclopropylfluorocarbene, and cyclopropylchlorocarbene. Calcns. have been performed for the rearrangements both inthe gas phase and in various solvents. Including solvation effects reduces the calcd. activation barrier for each of thesereactions. The effects of quantum mech. tunneling are computed to be significant for the 1,2-hydrogen migrations and tobe bigger for hydrogen than for deuterium. Consequently, the deuterium kinetic isotope effects are predicted to berelatively large but to decrease with increasing temp. In contrast, tunneling is not calcd. to play a significant role in eitherof the halocyclopropylcarbene rearrangements, which both involve the 1,2-shift of a CH2 group. Thus, heavy-atomtunneling is apparently not responsible for the fact that the calcd. activation parameters are very different from expt. forcyclopropylfluorocarbene, with the exptl. activation enthalpy much smaller than the calcd. one and the exptl. activationentropy much more neg. than the computed value. Possible causes for the large differences between the calcd. andmeasured activation parameters are discussed.~42 Citings

666. Reply to Comment on Molecular Mechanics for Chemical Reactions

By Truhlar, Donald G.From Journal of Physical Chemistry A (2002), 106(19), 5048-5050. Language: English, Database: CAPLUS,DOI:10.1021/jp0143342

A polemic in answer to J. Florian (ibid., 2002, 106) concerning acronyms of various combined mol.-mechanics/valence-bond/MO methods.~22 Citings

667. Interpolated Algorithm for Large-Curvature Tunneling Calculations of Transmission Coefficients forVariational Transition State Theory Calculations of Reaction Rates

By Fernandez-Ramos, Antonio; Truhlar, Donald G.; Corchado, Jose C.; Espinosa-Garcia, JoaquinFrom Journal of Physical Chemistry A (2002), 106(19), 4957-4960. Language: English, Database: CAPLUS,DOI:10.1021/jp014204t

We present a new algorithm for carrying out large-curvature tunneling (LCT) calcns. The new algorithm, calledinterpolated LCT (or ILCT) is based on interpolation by splines under tension. It is tested on five hydrogen-atom transferreactions. We find that the cost of LCT calcns. can be reduced by more than an order of magnitude.~18 Citings

668. Comment on Molecular Mechanics for Chemical Reactions

By Florian, JanFrom Journal of Physical Chemistry A (2002), 106(19), 5046-5047. Language: English, Database: CAPLUS,DOI:10.1021/jp0135510

Clarification is given on nomenclature for empirical valence bond (EVB) method and other mol. mechanics (MM)methods.~22 Citings

669. Numerical solving of the vibrational time-independent Schrodinger equation in one and two dimensionsusing the variational method

By Stare, Jernej; Mavri, JanezFrom Computer Physics Communications (2002), 143(3), 222-240. Language: English, Database: CAPLUS,DOI:10.1016/S0010-4655(01)00457-X

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A program package for variational solving of the time-independent Schrodinger equation (SE) in one and two dimensionsis described. The first part of the program package includes the fitting program (FIT) with which the ab initio or DFTcalcd. points are fitted to a computationally inexpensive functional form. Proper fitting of the potential energy surface iscrucial for the quality of the results. The second part of the package consists of a program for variational solving of theSE (2DSCHRODINGER) using either a shifted Gaussian basis set or the rectangular basis set proposed by Balint-Kurtiand coworkers [J. Chem. Phys. 91 (1989) 3571]. The third part of the program package consists of the calcn. of theexpectation values, IR and Raman spectra (XPECT), and the visualization of results (PLOT). The program package isapplied to study a quantum harmonic oscillator and an intramol., strong hydrogen bond in picolinic acid N-oxide. For theformer system anal. solns. exist, while for the latter system a comparison with the exptl. data is made. The advantagesand disadvantages of the applied methods are discussed.~56 Citings

670. Structural investigations and thermal analysis of the complex compound obtained through the reaction of1,3-propanediol with Ni(NO3)2.6H2O

By Niculescu, M.; Vaszilcsin, N.; Budrugeac, P.From Studia Universitatis Babes-Bolyai, Chemia (1999), 44(1-2), 275-286. Language: English, Database: CAPLUS

The reaction between 1,3-propanediol and Ni(NO3)2.6H2O was studied. The product contained 2-hydroxypropionateanion (L) as ligand. [Ni2(OH)2L2(H2O)20.5H2O]n was studied by thermal anal., electronic and IR spectroscopy andmagnetic methods. Nickel oxide obtained by thermolysis of this coordinative compd. was characterized by IR and x-rayspectroscopy.~0 Citings

671. Thermal and structural investigation of the reaction between 1,2-propanediol and Co(NO3)2·6H2O

By Niculescu, M.; Vaszilcsin, N.; Birzescu, M.; Budrugeac, P.; Segal, E.From Journal of Thermal Analysis and Calorimetry (2001), 65(3), 881-889. Language: English, Database: CAPLUS

The results of a study concerning the reaction between 1,2-propanediol and Co(NO3)2·6H2O, leading to a complex contg.the lactate anion (L) as ligand are presented. The obtained solid homopolynuclear coordination compd.[Co2(OH)2L2(H2O)2·0.5H2O]n, was studied by thermal anal., electronic and IR spectroscopy and magnetic methods. Cooxide obtained by thermal decompn. of this coordinative compd. was characterized by IR and x-ray spectroscopy.~27 Citings

672. Studies of model dependence in an ab initio approach to uncatalyzed oxygen reduction and the calculationof transfer coefficients

By Albu, T. V.; Anderson, A. B.From Electrochimica Acta (2001), 46(19), 3001-3013. Language: English, Database: CAPLUS, DOI:10.1016/S0013-4686(01)00515-1

In a recent study [J. Am. Chem. Soc. 121 (1999) 11855], an ab initio approach to calc. potential dependent activationenergies was applied in studying the outer-sphere O2 redn. and H2O oxidn. The purpose of this paper is to examineinfluences of changes in the calculational methodol. and the reactant structural models. The first step in the overall four-electron redn. of O2 to water,O2(g)+H+(aq)+e-(U)[rlhar2]HOO(aq)is the focus of this work. U is the electrode potentialand H+(aq) is modeled by the [HOH2(OH2)2]+ cluster. For an electrode potential of 0.727 V on the hydrogen scale, thefindings of this study are: In addn. to the above, the transfer coeffs. in the Butler-Volmer equation relating c.d. tooverpotential are calcd. and discussed.~30 Citings

673. Spectral and thermal studies of some malonate complexes. A new synthetic route leading to spinel-typeoxides

By Mindru, Ioana; Patron, Luminita; Carp, Oana; Marinescu, Gabriela; Brezeanu, Maria; Segal, EugenFrom Revue Roumaine de Chimie (2001), 45(7-8), 601-608. Language: English, Database: CAPLUS

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The [Co(C3O4H2)(H2O)2.5]2, [Co(C3O4H2)(H2O)]2, (NH4)[Fe(C3O4H2)2(H2O)]2 and (NH4)2[Fe2Co(C3O4H2)2(OH)6(H2O)2]coordination compds. were synthesized and characterized by chem. anal., vibrational and electronic spectra and thermalanal. For the [Co(C3O4H2)(H2O)2.5]2 compd. a thermochromic phenomenon was identified. The values of thenonisothermal kinetic parameters for the dehydration step were detd. The final products resulted from the thermaldecompn. of the coordination compds. are spinel oxides: Co3O4, Fe3O4/γFe2O3 and CoFe2O4, resp.~6 Citings

674. Lanthanide ortho-ferrites obtained by nonconventional methods

By Plostinaru, Silvia; Patron, Luminita; Marinescu, GabrielaFrom Roumanian Chemical Quarterly Reviews (2001), 8(1), 3-8. Language: English, Database: CAPLUS

A review, with 30 refs., discusses nonconventional methods for the synthesis of lanthanide orthoferrites:, including thedecompn. of polynuclear complex compds.; the hydrolysis method; the decompn. of alkoxides and the autopropagationcombustion method. All these methods have a common feature, the synthesis of polynuclear complex compds. whosedecompn. either in the reaction medium, or in solid state, leads to orthoferrites. All oxides obtained were analyzed by x-ray diffraction and were characterized by physicochem. methods (electronic and IR, spectra and magneticmeasurements).~0 Citings

675. Thermal and structural investigation of the reaction between 1,2-propanediol and Ni(NO3)2·6H2O

By Niculescu, M.; Vaszilcsin, N.; Birzescu, M.; Budrugeac, P.; Segal, E.From Journal of Thermal Analysis and Calorimetry (2001), 63(1), 181-189. Language: English, Database: CAPLUS

The authors present the results of a study concerning the reaction between 1,2-propanediol and Ni(NO3)2·6H2O, leadingto a complex contg. as ligand the lactate anion (L), suggesting that the oxidn. of 1,2-propanediol occurs at the primaryhydroxyl group. The obtained solid homopolynuclear combination, [Ni2(OH)2L2(H2O)2·0.5H2O]n, was studied by thermalanal., electron and IR spectroscopy, and magnetic methods. Nickel oxide obtained by thermolysis of this complexcompd. was characterized by IR, x-ray spectroscopy and elemental anal. All the studies indicated that the complexcompd. was characterized by pseudooctahedral configuration of the Ni(II) ion. Thermal anal. of the homopolynuclearcomplex compd. enabled to prove the thermal decompn. mechanism.~16 Citings

676. Catalytic effect of platinum on oxygen reduction. An ab initio model including electrode potentialdependence

By Anderson, Alfred B.; Albu, Titus V.From Journal of the Electrochemical Society (2000), 147(11), 4229-4238. Language: English, Database: CAPLUS,DOI:10.1149/1.1394046

The effects of bonding to a platinum atom were calcd. for the redn. of oxygen to water. The electron-correlation cor. MP2method was used, and the electrode potential was modeled by variations in values for the electron affinities of thereaction centers. Potential-dependent transition state structures and activation energies are reported for the one-electronreactions. Lowest energy pathways are predicted. Pathways with high activation energies are excluded. Compared touncatalyzed outer-Helmholtz-plane values, bonding to the Pt has the effect of decreasing the calcd. high redn. activationenergies for O2 and H2O2. Bonding to Pt also decreases the HOO radical and increases the HO radical activationenergy values. The reverse reaction, oxidn. of H2O to O2, is also discussed in light of these results. The issues ofpotential-dependent double-layer potential drops and adsorbate bond polarizations are discussed, and it is pointed outthat the results of this study can be used to est. the effects of such potential drops.~159 Citings

677. Mechanisms of reactions in solution

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By Winterton, N.From Annual Reports on the Progress of Chemistry, Section A: Inorganic Chemistry (2000), 96, 557-623. Language:English, Database: CAPLUS, DOI:10.1039/b003776l

A review with 1196 refs. Inorg. reaction mechanism are crit. to our understanding of a range of biol., biomedical,environmental and industrial transformations as well as being of intrinsic interest. As previously, the survey of the 1999literature on this topic does not include studies of homogeneous catalysis, redox processes involving org. substrates,alkane oxidn., org. reactions of the p-block elements, fluxional, photochem., radiochem., solid state or heterogeneousprocesses unless they are of particular mechanistic importance, relevance or interest.~11 Citings

678. Thermal behaviour of some solid coordination compounds with malic acid as ligand

By Albu, T. V.; Mindru, I.; Patron, L.; Segal, E.; Brezeanu, M.From Thermochimica Acta (1999), 340-341, 235-240. Language: English, Database: CAPLUS, DOI:10.1016/S0040-6031(99)00268-3

The authors present the results concerning the synthesis and the characterization of some coordination compds. withmalic acid as ligand: Co(C4H4O5)·2H2O, [Fe2(C4H4O5)(OH)4]·4H2O and [Fe2Co(C4H4O5)2(OH)4]·6H2O. Theheterometallic compd. is a precursor of Co-ferrite. The values of the nonisothermal kinetic parameters for thedehydration reactions were detd. These values obtained by three integrals methods are in a satisfactory agreement.~11 Citings

679. Ab Initio Determination of Reversible Potentials and Activation Energies for Outer-Sphere OxygenReduction to Water and the Reverse Oxidation Reaction

By Anderson, Alfred B.; Albu, Titus V.From Journal of the American Chemical Society (1999), 121(50), 11855-11863. Language: English, Database:CAPLUS, DOI:10.1021/ja992735d

The outer-sphere redn. of oxygen to water according to O2(g) + 4H+(aq.) + 4e- → 2H2O(l) (1) and its reverse reaction areanalyzed using self-consistent ab initio MP2/6-31G** calcns. over the electrode potential range of U = 0-2 V (H+/H2).Activation energies are calcd. for each of the four 1-electron steps: O2 + H+ + e-(U) → HOO.bul. (2); HOO.bul. + H+ + e-(U)→ H2O2 (3); H2O2 + H+ + e-(U) → HO.bul. + H2O (4); and HO.bul. + H+ + e-(U) → H2O (5). In the calculational model H+ isa hydronium ion with two water mols. hydrogen bonded to it. The electrode potential U(V) is given by U/V = ϕ/eV -ϕH+/H2/eV (6) where ϕ and ϕH+/H2 are the thermodn. work functions of the electrode surface and of the std. hydrogenelectrode surface, resp. Electron transfer is assumed to occur when the electron affinity, EA, of the reaction complex isthe ionization potential, IP, of the electrode and there is an equil. so that ϕ = IP = EA. The electron transfers to anRO···H+···OH2(OH2) orbital that is H+···OH2 antibonding and RO···H+ bonding and this orbital is greatly stabilized by theelec. field due to the pos. charge. Over the potential range considered, activation energies for the redn. reactionsdecrease in the sequence (4) > (2) > (3) > (5). For the reverse reactions the activation energies decrease according to(5) > (4) ≈ (3) > (2). Calcd. reversible potentials, U°, as detd. simply from reaction energies for reactions 1, 4, 5, 2 + 3and reactions 4 + 5 differ from the measured values by a const.~143 Citings

680. Coulometric and thermogravimetric differentiations of water from organic groups on heating heterometallicalkoxides of glycerol

By Mendelovici, E.From Journal of Materials Science Letters (1999), 18(21), 1711-1712. Language: English, Database: CAPLUS

The thermal decompn. of Fe, Mn, and Co heterometallic alkoxides of glycerol was studied by using TG/DTG from roomtemp. to 1000° in flowing air and nitrogen. The water contents of the same samples were detd. by the coulometric KarlFischer titrn. method from room temp. to 270°. An Fe-Co sample was also followed using x-ray diffraction.~0 Citings

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681. Using quantum chemistry to determine electrochemical potential dependencies of adsorbate properties andredox activation energies

By Anderson, Alfred B.From Proceedings - Electrochemical Society (1999), 99-14(Tutorials in Electrochemical Engineering--MathematicalModeling), 1-7. Language: English, Database: CAPLUS

A review, with 23 refs. Two currently applicable approaches to detg. electrode potential dependencies of adsorbateproperties and redox reaction activation energies are outlined. The first, a semiempirical non-charge-self-consistentvalence band energy shift technique, focuses on potential-dependent bond polarizations in specifically adsorbed mols.Applications to the vibrational frequency of adsorbed CO, H2O decompn., and other reactions on electrodes show usefulpredictive and interpretive capabilities. The second is ab initio, and deals with the potential dependence of redoxreaction activation energies in the bulk soln. and also for adsorbed mols. In the latter case potential dependent surface-adsorbate bond polarizations are omitted. Calcd. activation energies and their potential dependencies for the outersphere four-electron redn. of O2 demonstrate promise for this model. Bonding of O2 to Pt is shown to have a catalyticeffect. For reactions in the double layer region, the effect of any known double layer potential drop can be included.Ways of adding potential-dependent bond polarizations are suggested.~0 Citings

682. Depression of reactivity by the collision energy in the single barrier H + CD4 -> HD + CD3 reaction

By Zhang Weiqing; Zhou Yong; Wu Guorong; Lu Yunpeng; Pan Huilin; Fu Bina; Shuai Quan; Liu Lan; Liu Shu; ZhangLiling; et alFrom Proceedings of the National Academy of Sciences of the United States of America (2010), 107(29), 12782-5,Language: English, Database: MEDLINE

Crossed molecular beam experiments and accurate quantum scattering calculations have been carried out for thepolyatomic H + CD(4) --> HD + CD(3) reaction. Unprecedented agreement has been achieved between theory andexperiments on the energy dependence of the integral cross section in a wide collision energy region that first risesand then falls considerably as the collision energy increases far over the reaction barrier for this simple hydrogenabstraction reaction. Detailed theoretical analysis shows that at collision energies far above the barrier the incomingH-atom moves so quickly that the heavier D-atom on CD(4) cannot concertedly follow it to form the HD product,resulting in the decline of reactivity with the increase of collision energy. We propose that this is also the verymechanism, operating in many abstraction reactions, which causes the differential cross section in the backwarddirection to decrease substantially or even vanish at collision energies far above the barrier height.

~0 Citings

683. Quasiclassical trajectory study of H+SiH4 reactions in full-dimensionality reveals atomic-level mechanisms

By Cao Jianwei; Zhang Zhijun; Zhang Chunfang; Liu Kun; Wang Manhui; Bian WenshengFrom Proceedings of the National Academy of Sciences of the United States of America (2009), 106(32), 13180-5,Language: English, Database: MEDLINE

This work elucidates new atomic-level mechanisms that may be common in a range of chemical reactions, and ourfindings are important for the understanding of the nature of polyatomic abstraction and exchange reactions. A global12-dimensional ab initio potential energy surface (PES), which describes both H+SiH(4) abstraction and exchangereactions is constructed, based on the modified Shepard interpolation method and UCCSD(T)/cc-pVQZ energycalculations at 4,015 geometries. This PES has a classical barrier height of 5.35 kcal/mol for abstraction (our bestestimate is 5.35 +/- 0.15 kcal/mol from extensive ab initio calculations), and an exothermicity of -13.12 kcal/mol, inexcellent agreement with experiment. Quasiclassical trajectory calculations on this new PES reveal interestingfeatures of detailed dynamical quantities and underlying new mechanisms. Our calculated product angulardistributions for exchange are in the forward hemisphere with a tail sideways, and are attributed to the combination ofthree mechanisms: inversion, torsion-tilt, and side-inversion. With increase of collision energy our calculated angulardistributions for abstraction first peak at backward scattering and then shift toward smaller scattering angles, which isexplained by a competition between rebound and stripping mechanisms; here stripping is seen at much lowerenergies, but is conceptually similar to what was observed in the reaction of H+CD(4) by Zare and coworkers [CamdenJP, et al. (2005) J Am Chem Soc 127:11898-11899]. Each of these atomic-level mechanisms is confirmed by directexamination of trajectories, and two of them (torsion-tilt and side-inversion) are proposed and designated in this work.

~1 Citing

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