research article biomimetic sulfide oxidation by the means...

Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 651274 7 pageshttpdxdoiorg1011552013651274

Research ArticleBiomimetic Sulfide Oxidation by the Means of ImmobilizedFe(III)-5101520-tetrakis(pentafluorophenyl)porphin underMild Experimental Conditions

Paolo Zucca12 Gianmarco Cocco2 Manuela Pintus2

Antonio Rescigno2 and Enrico Sanjust2

1 Consorzio UNO Universita Oristano 09170 Oristano Italy2 Unita di Chimica Biologica e Biotecnologie Biochimiche Dipartimento di Scienze Biomediche (DiSB) Universita di CagliariComplesso Universitario 09042 Monserrato Italy

Correspondence should be addressed to Enrico Sanjust sanjustunicait

Received 27 May 2013 Revised 16 September 2013 Accepted 16 September 2013

Academic Editor Theocharis C Stamatatos

Copyright copy 2013 Paolo Zucca et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

This paper describes the oxidation of inorganic sulfide to sulfate minimizing the formation of elemental sulfur The describedcatalytic reaction uses dilute hydrogen peroxide at nearly neutral pH values in the presence of a bioinspired heterogenized andcommercial ferriporphin A substantial increase of the percentage of sulfide converted to sulfate is obtained in comparison withthe yields obtained when working with hydrogen peroxide alone The biomimetic catalyst also proved to be a much more efficientcatalyst than horseradish peroxidase Accordingly it could be suitable for large-scale applications Further studies are in progressto drive sulfate yields up to nearly quantitative

1 Introduction

Recently emissions containing hydrogen sulfide (H2S) have

been a health and environmental issue since it is unfortu-nately a very toxic compound for many human tissues [1]produced by many human activities

Many chemical and physical methods have been pro-posed for its degradation [2ndash10] However they are usuallyfeatured by extreme operational conditions turning thewhole processes to be economically impacting

Also microbiological methods have been suggested showing however several problems concerning the long time ofreaction stability and compatibility of the rubbery mem-branes with the gas components [11 12]

Even an enzymatic alternative has been described [13ndash15] since organic sulfides (thioethers RndashSndashR1015840) can be selec-tively oxidized to the corresponding sulfoxides and sulfonesunder very mild conditions with the help for example ofBDS (biodesulfurization) [14 15] catalyzed by enzymes suchas oxygenases However the industrial applicability of enzy-matic BDS has not yet been obtained since the enzyme

sources are limited and the costs are too high [13] Not nec-essarily BDS leads to sulfur elimination from sulfur-contai-ning organic molecules In most cases thiols and thioethersrespectively change to sulfonic acid and sulfones An alterna-tive approach to eliminate thiols has been proposed involv-ing the combined action of mushroom tyrosinase air andsuitable catechols The o-quinones arising from the enzymeaction covalently bind thiols leading to odorless compounds[16]

Recently also metalloporphins have been suggested ascatalysts for removal of thioethers [13 17 18] These macro-cycles represent a very versatile class of redox catalysts beingable to oxidize different recalcitrant organic compoundsunder quite mild operational conditions [19ndash23]

However in order to achieve an inexpensive and feasibleprocess the immobilization of the catalysts should be per-formed in order to allow catalysts recovery proper ligandsupply and stabilization of the catalysts [24 25] In ourprevious studies we reported the immobilization of somemetalloporphins onto solid supports emulating the structureof cytochrome P-450 and ligninolytic peroxidases These

2 Journal of Chemistry

O

O

CH

NH

N

N

N

N

N

F F

F

F

F

R

R R

R

Fe+

R =

PVA

bead

Figure 1 Proposed structure of the catalytic adduct PP-PVAFeTFPP

catalytic adducts were able to oxidize both lignin modelcompounds (recently reviewed in [26]) and durable textiledyes [27ndash29]

In this paper we describe the immobilization of a com-mercially available Fe-porphin onto a solid support graftedwith pyridine residues (Figure 1 [30]) The ability of thisadduct to oxidize sulfide ion leading to sulfate has beenstudied focusing on the minimization of the amount ofelemental sulfur produced The catalytic conditions havebeen fully evaluated in the perspective of a mild and feasibleindustrial process Also a comparison with an enzymaticsystem has been performed

2 Experimental

All the reagents used were of the best grade available andwere used as purchased without further purification Fullyhydrolysed PVA Av MW 30000ndash50000 was from Aldrich(Milan Italy cat number 363138) Glutaraldehyde as a 50aqueous solution mainly containing oligomers in addition tothe monomeric aldehyde was from Fluka Milan Italy catnumber 49629

21 Preparation of FeTFPPPP-PVA Adduct The preparationFeTFPPPP-PVA adduct was performed as already described[30]

Briefly aminopropyl cross-linked PVA (AP-PVA) wasprepared by treating 500mL of a 10 wv PVA aqueous

solution with 5mL 4-aminobutyraldehyde diethyl acetal andpH was adjusted to sim2 with 6M HCl

Then 10mL of a 50 vv glutaraldehyde aqueous solutionwas added under stirring and the pH adjusted to sim1 with 6MHCl The obtained gel was kept at 90∘C for 1 h and finallyovernight at 25∘C The product was ground for 10min at16000 rpmwithUltra Turrax T25 Basic (IKATechnikMilanItaly) exhaustively washed with water 01M NaOH wateragain 2-propanol and finally carefully dried into a warmoven

Each gram of the AP-PVA powder was suspended inexcess water and treated with 01mL of 4-pyridinecarbo-xaldehyde The pH was adjusted to 5 with 01M acetic acidsodium acetate buffer and 05 g sodium cyanoborohydridewas added After 24 h the support was exhaustively washedwith 01M aqueous glycerol water 01MNaOH water againand 2-propanol The wet PP-PVA was then carefully driedovernight in a vacuum oven at 50∘C

Each gram of PP-PVA was treated with 20mg FeTFPPsolubilized in 10mL DMSOThe slurry was kept 24 h stirringin the dark (because of metalloporphin photosensitivity)and washed exhaustively at first with DMSO then with 2-propanol The adduct was finally dried at 50∘C in a vacuumoven

Bound metalloporphin was quantified by differencethrough spectrophotometric measurement (UltroSpec 2100pro Amersham Bioscience Milan Italy) at 411 nm (120576

411=

115000Mminus1 cmminus1 in DMSO) as already described [30]

22 Catalytic Assay A mixture containing 10mg of catalyst(corresponding to 067mg063 120583mol of ferriporphin) sus-pended in 1mL of 25mM buffer solution containing 10mMNaHS and 45mM aqueous H

2O2was kept stirring at 25∘C

in the dark Blank experiments were performed without onesubstrate or without catalyst In a series of experiments theconcentrations of the substrates were varied within a properrange

After prefixed periods of time aliquots of the reactionsolution (500120583L) were treated with 100 EU of purifiedcatalase for 301015840 at 25∘C and used for sulfide and sulfatequantification In order to test catalytic performance atvarious pHs some McIlvaine buffers were used pH 3 pH 4pH 5 pH 6 pH 7 and pH 8

23 Sulfide and Sulfate Determination Sulfide concentrationwas determined through photometric automatized cuvettetest LCK653 (Hack Lange Rheineck Switzerland) using DR2700 Portable Spectrophotometer (Hack Lange RheineckSwitzerland)

Sulfate was estimated after acidification of the samples(200120583L) with 50120583L 1M HCl To remove some colloidal sul-fur when necessary the acidified samples were centrifuged at12000timesg for 15min Sulfate analysis was performed throughphotometric automatized cuvette test LCK153 (Hack LangeRheineck Switzerland) based on a nephelometric measure

24 Enzymatic Comparison When horseradish peroxidase(HRP) was used up to 15 EU was present in a final volume

Journal of Chemistry 3

of 1mL of 25mM buffer (pH 5) NaHS 10mM and 88mMH2O2

3 Results and Discussion

In a previous paper we had fully characterized the adductPP-PVAFeTFPP and studied its catalytic activity on lignin-model compounds [30]

Under the described experimental conditions PP-PVAFeTFPP was also able to achieve more than 70 conversionof the sulfide in 24 h In the same time high amounts of sulfatewere produced in the presence of hydrogen peroxide andthe described heterogenized ferriporphin (more than 60 in24 h) Many combinations of different substrate concentra-tions (both peroxide and sulfide) catalyst and buffers weretested to optimize the oxidation of sulfide to sulfate withthe aim of minimizing the production of elemental colloidalsulfur whose removal is rather tedious

An outstanding well-known property of hydrogen sulfideand of its anions HSminusand S2minus in fact is the high tendencyto produce elemental sulfur upon mild oxidation A milkycolloidal turbidity arises in aqueous solutions hindering areliable analysis of residual sulfide unless such sulfur is notproperly removed Apart from the analytical concerns froma technological perspective the hardly recoverable colloidalsulfur is a drawback of any procedure involving hydrogensulfide oxidation

Elemental sulfur was not apparent during PP-PVAFeTFPP catalysis at neutral or alkaline pH values where itwas kept into the solution by residual sulfide as polysulfidesS119909

2minus These are readily decomposed upon acidification andthe arising sulfur was removed by centrifugation whenappropriate as noted above

On the contrary sulfate recovery would not be a problemeven at a plant scale as it could be precipitated as calciumsulfate (gypsum) dried and placed in landfill or eventuallyused as a soil improver in agriculture

When the reaction was studied within a range of severalhours careful comparison with proper blank samples wasnecessary to take into account the slow autoxidation ofsulfide in particular at alkaline pH values

The pH influence on the efficiency of sulfide removal wasstudied within the pH range 3ndash8 Figure 2 clearly shows thatthe optimal pH for sulfide oxidative removal is 5 although areasonable efficiencywas still observed at pH 8The efficiencydrop was higher on the acidic side of the studied range

Taking into the due account the main aim of this studynamely the complete oxidation of sulfide to sulfate thecorrect stoichiometric ratio (1 4 at least) between sulfide andhydrogen peroxidemust bemaintained Namely the reactionis as follows

H2S + 4H

2O2997888rarr SO

4

2minus+ 4H2O + 2H+ (1)

Otherwise oxidation will be incomplete and formation ofcolloidal sulfur andor polysulfides becomes more likelyFurthermore under such conditions the analytical determi-nation of reactants was quite uncertain

120

100

80

60

40

20

0

3 4 5 6 7 8

pH

Cata

lytic

activ

ity (

)

Figure 2 PP-PVAFeTFPP oxidizes hydrogen sulfide with a pH-dependent behavior 10mg of catalyst reacted in the presence of25mM buffer solution 10mM NaHS and 45mM H

2O2(1mL

final volume) at 25∘C for 24 h Results are expressed as sulfideconversion (ie sulfide removal regardless of the chemical natureof the oxidation product(s)) (119899 = 5)

Such a problem of incomplete oxidation simply doesnot exist in the case of thiols (mercaptans) that are easilyand cleanly oxidized to the corresponding sulfonic acids[31] Organic sulfides (thioethers) are converted to the cor-responding sulfones upon oxidation [32] also under met-alloporphin catalysis [33ndash36] Therefore clean oxidation ofhydrogen sulfide in water to sulfate under mild operativeconditions is a serious challenge However the ability ofconcentrate hydrogen peroxide to oxidize hydrogen sulfideat slightly alkaline pH is well known by far Anyway wehave faced the problem with the aid of a bioinspired catalystnamely an electron-deficient ferriporphin immobilized onto a suitable hydrophilic insoluble support (Figure 1) Thiswas found to be capable of promoting sulfide oxidation tosulfate under very low concentrations of hydrogen peroxideAs noted above many data exist relative to metalloporphin-catalyzed oxidation of sulfide to the corresponding sulfox-ides andor sulfones under proper experimental conditionsSomewhat surprisingly no data have been found in the liter-ature about hydrogen sulfide oxidation by metalloporphin-based catalysts under experimental conditions similar tothose effective in the case of organic sulfides The alreadynoted high tendency of H

2S to be oxidized with production

of colloidal elemental sulfur in particular under alkalineconditions is most probably the explanation of such a lack ofpublished studies A vast number of experimental trials werein fact necessary to find the optimal conditions to converthydrogen sulfide to sulfate taking into the due account thatan excessive peroxide concentration could oxidatively destroythe same catalyst A slight H

2S oxidation was seen also in the

blank experiments where the immobilized metalloporphinwas present and hydrogen peroxide was omitted from thereaction mixture This could be explained by means of ahypothetical redox reaction where the ferric porphin wasslowly reduced by H

2S to its ferrous counterpart This could


80

60

110 Blank792 704 44

40

20

0

Sulfa

te y

ield

24

h (

)

[H2O2] (mM)

Figure 3 Sulfate yields obtained under PP-PVA-FeTFPP catalysisAppropriate blank experiments were carried out in absence ofhydrogen peroxide (Blank bar in the figure) 10mg of catalyst reactedin the presence of 25mMbuffer solution pH5 10mMNaHS and theindicated H

2O2at 25∘C for 24 h (final volume 1mL) (119899 = 5)

Table 1Multicycle activity of the supportedmetalloporphine 10mgof catalyst reacted in the presence of 25mM buffer solution 10mMNaHS and 45mMH2O2 (1mL final volume) at 25∘C for 2 h (119899 = 3)

Cycle Residual activity1 1002 913 904 805 786 767 718 63

in turn react with molecular oxygen thus regenerating theferric catalyst and closing the catalytic cycle

Also hydrogen peroxide in the absence of the ferripor-phin catalyst could oxidize hydrogen sulfide However theyields of sulfate are sharply lower whereas more colloidalsulfur was formed All the sulfate yields upon catalyticoxidation compared to the described blank experiments aresummarized in Figure 3

PP-PVAFeTFPPwas also able to keep its catalytic activityafter several catalytic cycles The results summarized inTable 1 showed that over 60 of initial catalytic activity ismaintained after 8 catalytic cycles

The biomimetic oxidation of PP-PVAFeTFPP was alsocompared with enzymatic catalysis by the means of hors-eradish peroxidase (HRP) The results are summarized inFigure 4

HRP was not able to exceed 30 sulfide conversion evenat the highest concentration tested In the same conditionPP-PVAFeTFPP allowed a twofold higher conversion being

100

80

60

40

20

0

HRP (milli-EU)

19 9

19

90

190

370

740

1500

PP-P

VA

FeTF

PP

Sulfi

de co

nver

sion

in24

h (

)

Figure 4 Comparison between the biomimetic catalysis andhorseradish peroxidase (HRP) The indicated EU of HRP wasincubated in a final volume of 1mL of 25mM buffer pH 5 10mMNaHS and 88mMH

2O2 PP-PVAFeTFPP catalysis occurred in the

same conditions described in Figure 3 (119899 = 5)

therefore quite a more promising large-scale alternative forsulfide treatment

With respect to the possible oxidation mechanism(s)some different paths could be hypothesized (Figure 5) A pos-sibility is the ldquoclassicalrdquo peroxidase-like mechanism alreadyproposed for enzymatic sulfoxidation of thioethers [37] Inthis path theCompound I analogue Porph+∙Fe(IV)=Oextractsone electron fromH

2S orHSminus leading to radical speciesH

2S+∙

orHS∙ respectivelyThese could in turn react with the solventwater so triggering the further oxidation Alternatively theradical species arising from sulfide oxidation reacts withthe Compound II analogue PorphFe(IV)=O (oxygen reboundmechanism) The intervention of the solvent should be mostprobably ruled out by analogy to that found in thioethersulfoxidation by hydrogen peroxide in the presence of thesame ferriporphin described here [38] Instead the oxygenrebound mechanism should be the main path leading fromsulfide to sulfate under PP-PVAFeTFPP catalysis Thishypothesis is strengthened by the observation that thioethersare oxidized to their sulfoxide counterparts by horseradishand lignin peroxidases with incorporation of 18O in thearising sulfoxides when the oxygen donor is H

2

18O2 Any-

way the arising sulfoxides are formed with low yields owingto the low tendency of peroxidase to transfer their oxygenfrom the corresponding Compound I to the substrate [39] Aremarkable exception is that of chloroperoxidases that followa direct oxygen transfer mechanism [40] Not surprisinglythe peroxidase we have chosen (horseradish peroxidase) forthe reasons of the low costs related to a potential plantscale application was rather unsatisfactory also as a sulfideoxidation catalyst evenwhenused in high concentrations rel-ative to those of the sulfide substrate So we have concluded


Cpd II analogueO

N

N

N

O

PVA bead

PVA beadPVA bead

HS∙HS∙

HSminus

HSminus

H2O

Native state

[HSOminus]

[HSOminus]

H2O2

H2O2

H2O2

+ ∙

Cpd Ianalogue

(a)

(b)(c)

Fe(IV)

(IV)FeFe(III)

SO4

2minus

SO4

2minus

Figure 5 Proposed catalytic path for the immobilized metalloporphin Path (a) represents the direct oxygen transfer from compound Ianalogue to sulfide Paths (b) and (c) represent the rebound mechanism via compound II

that hydrogen sulfide removal by hydrogen peroxide throughperoxidase catalysis is not a feasible process

In the case of metalloporphin catalysis a direct transfer ofthe oxygen atom from theCompound I analogue to the sulfurin sulfide could be envisaged and has been discussed in theliteraturewith concerns to thioethers (path (a) of Figure 5 [3941]) However the prevailing view is a rebound mechanismfor these substrates [38] (paths (b) and (c) of Figure 5) Inthe case of (hydrogen) sulfide an electron transfer fromthe (hydrogen) sulfide to the Compound I analogue wouldbe immediately followed by an oxygen transfer from thearising Compound II analogue to the sulfide radical By thisway we suggest that an extremely reactive and transientsulfenic intermediate HSOH or HSOminus should arise quicklyevolving to more oxidized sulfur compounds and finally tosulfate most probably by the direct action of excess hydrogenperoxide possibly without any need of further metallopor-phin catalysis As a point of fact the alternative hypothesispostulating a direct oxygen transfer should anyway lead tothe same products

4 Conclusion

We have shown the ability of a commercial metalloporphinimmobilized on to a cross-linked functionalized hydrophilicpolymer to catalyze the hydrogen sulfide oxidation to sulfateunder very mild operative conditions and avoiding the for-mation of significant amount of elemental sulfurTherefore adiluted and nearly neutral hydrogen peroxide solution couldbe a tool to accomplish the oxidation in the presence of thedescribed heterogenized ferriporphin Biomimetic adductalso led to better catalytic performances than its enzymatic

counterpart PP-PVAFeTFPP could be therefore a feasiblealternative also in the large-scale process of H

2S removal

Abbreviations

PVA Poly(vinylalcohol)AP-PVA 3-Aminopropyl-functionalized PVA

cross-linked with glutaraldehydePP-PVA 41015840-Pyridylmethyl-3-aminopropyl-

functionalized PVA cross-linked withglutaraldehyde

FeTFPP 5101520-Tetrakis(pentafluorophenyl)porphin-iron(III) chloride

Conflict of Interests

The authors declare that they have no conflict of interests

Acknowledgments

This research was partly funded by Fondazione Banco diSardegna (Project Code 8612012) and Regione AutonomaSardegna (PO Sardegna FSE 2007ndash2013 LR72007 BandoGiovani Ricercatori Project CRP1 27 and PO Sardegna FSE2007ndash2013 LR72007 Ricerca di Base Bando 2008 ProjectCRP1 408)

References

[1] S Chou M Fay S Keith L Ingerman and L ChappellToxicological Profile for Hydrogen Sulfide US Department ofHealth and Human Services Atlanta Ga USA 2006


[2] T K Ghosh and E L Tollefson ldquoKinetic and reaction mecha-nism of hydrogen sulfide oxidation over activated carbon in thetemperature range of 125ndash200∘CrdquoCanadian Journal of ChemicalEngineering vol 64 no 6 pp 969ndash976 1986

[3] M Govindan S J Chung J W Jang and I S MoonldquoRemoval of hydrogen sulfide through an electrochemicallyassisted scrubbing process using an active Co(III) catalyst at lowtemperaturesrdquo Chemical Engineering Journal vol 209 no 1 pp601ndash606 2012

[4] J R Kastner and K C Das ldquoWet scrubber analysis of volatileorganic compound removal in the rendering industryrdquo Journalof the Air andWaste Management Association vol 52 no 4 pp459ndash469 2002

[5] E Y Lee N Y Lee K-S Cho and H W Ryu ldquoRemoval ofhydrogen sulfide by sulfate-resistant Acidithiobacillus thioox-idans AZ11rdquo Journal of Bioscience and Bioengineering vol 101no 4 pp 309ndash314 2006

[6] P Oyarzun F Arancibia C Canales and G E Aroca ldquoBiofil-tration of high concentration of hydrogen sulphide usingThiobacillus thioparusrdquo Process Biochemistry vol 39 no 2 pp165ndash170 2003

[7] A Primavera A Trovarelli P Andreussi and G DolcettildquoThe effect of water in the low-temperature catalytic oxidationof hydrogen sulfide to sulfur over activated carbonrdquo AppliedCatalysis A vol 173 no 2 pp 185ndash192 1998

[8] M Steijns and PMars ldquoThe role of sulfur trapped inmicroporesin the catalytic partial oxidation of hydrogen sulfide withoxygenrdquo Journal of Catalysis vol 35 no 1 pp 11ndash17 1974

[9] M Fortuny J A Baeza X Gamisans et al ldquoBiological sweeten-ing of energy gases mimics in biotrickling filtersrdquoChemospherevol 71 no 1 pp 10ndash17 2008

[10] Y Ma J Zhao and B Yang ldquoRemoval of H2S in waste gases byan activated carbon bioreactorrdquo International Biodeteriorationand Biodegradation vol 57 no 2 pp 93ndash98 2006

[11] A Makaruk M Miltner and M Harasek ldquoBiogas desulfuriza-tion and biogas upgrading using a hybrid membrane systemmdashmodeling studyrdquo Water Science and Technology vol 67 no 2pp 326ndash332 2013

[12] C Liu J Liu J Li et al ldquoRemoval of H2S by co-immobilizedbacteria and fungi biocatalysts in a bio-trickling filterrdquo ProcessSafety and Environmental Protection vol 91 no 1-2 pp 145ndash1522013

[13] X Zhou X Chen YWang and Y Jin ldquoBiomimetic oxidation ofsulfides based on Fe III porphyrin under the mild conditionsrdquoin Proceedings of the International Conference on BiomedicalEngineering and Biotechnology (ICBEB rsquo12) pp 101ndash103 2012

[14] T Ohshiro T Hirata and Y Izumi ldquoMicrobial desulfurizationof dibenzothiophene in the presence of hydrocarbonrdquo AppliedMicrobiology and Biotechnology vol 44 no 1-2 pp 249ndash2521995

[15] C Oldfield O Pogrebinsky J Simmonds E S Olson and CF Kulpa ldquoElucidation of the metabolic pathway for dibenzoth-iophene desulphurization by Rhodococcus sp strain IGTS8(ATCC 53968)rdquo Microbiology vol 143 no 9 pp 2961ndash29731997

[16] O Negishi and T Ozawa ldquoEffect of polyphenol oxidase ondeodorizationrdquo Bioscience Biotechnology and Biochemistry vol61 no 12 pp 2080ndash2084 1997

[17] S Zakavi A Abasi A R Pourali and S Talebzadeh ldquoMetallo-porphyrin-catalyzed chemoselective oxidation of sulfides withpolyvinylpyrrolidone-supported hydrogen peroxide a simple

catalytic system for selective oxidation of sulfides to sulfoxidesrdquoBulletin of the Korean Chemical Society vol 33 no 1 pp 35ndash382012

[18] X Zhou X Chen Y Jin and I E Marko ldquoEvidence of twokey intermediates contributing to the selectivity of P450-biomi-metic oxidation of sulfides to sulfoxides and sulfonesrdquo Chem-istry vol 7 no 10 pp 2253ndash2257 2012

[19] G Dıaz-Dıaz M C Blanco-Lopez M J Lobo-CastanonA J Miranda-Ordieres and P Tunon-Blanco ldquoHemo-acrylicpolymers as catalyst for the oxidative dehalogenation of 2 4 6-trichlorophenol Chloroperoxidasersquos mimic imprinting effectsrdquoJournal of Molecular Catalysis A vol 353 no 1 pp 117ndash121 2012

[20] B Fontaine A Nuzzo R Spaccini and A Piccolo ldquoDegrada-tion of 2 4-dichlorophenol and coupling into humic matter byoxidative biomimetic catalysis with iron-porphyrinrdquo Journal ofGeochemical Exploration vol 129 no 1 pp 28ndash33 2012

[21] A Nuzzo and A Piccolo ldquoEnhanced catechol oxidation byheterogeneous biomimetic catalysts immobilized on clay min-eralsrdquo Journal of Molecular Catalysis A vol 371 no 1 pp 8ndash142013

[22] Q Zhu Y Mizutani S Maeno and M Fukushima ldquoOxidativedebromination and degradation of tetrabromo-bisphenol A bya functionalized Silica-supported Iron (III)-tetrakis (p-sulfo-natophenyl) porphyrin catalystrdquo Molecules vol 18 no 5 pp5360ndash5372 2013

[23] P Zucca A Rescigno and E Sanjust ldquoLigninolytic peroxidase-like activity of a synthetic metalloporphine immobilized ontomercapto-grafted crosslinked PVA inspired by the active site ofcytochrome P450rdquo Chinese Journal of Catalysis vol 32 no 11pp 1663ndash1666 2011

[24] A M D Rocha Gonsalves and M M Pereira ldquoState of the artin the development of biomimetic oxidation catalystsrdquo Journalof Molecular Catalysis A vol 113 no 1-2 pp 209ndash221 1996

[25] P Zucca G Mocci A Rescigno and E Sanjust ldquo5101520-Tetrakis(4-sulfonato-phenyl)porphine-Mn(III) immobilizedon imidazole-activated silica as a novel lignin-peroxidase-likebiomimetic catalystrdquo Journal of Molecular Catalysis A vol 278no 1-2 pp 220ndash227 2007

[26] P ZuccaA RescignoAC Rinaldi andE Sanjust ldquoBiomimeticmetalloporphines and metalloporphyrins as potential tools fordelignification molecular mechanisms and application per-spectivesrdquo Journal of Molecular Catalysis A 2013

[27] P Zucca A Rescigno M Pintus A C Rinaldi and ESanjust ldquoDegradation of textile dyes using immobilized ligninperoxidase-like metalloporphines under mild experimentalconditionsrdquo Chemistry Central Journal vol 6 article 161 2012

[28] P Zucca C Vinci A Rescigno E Dumitriu and E San-just ldquoIs the bleaching of phenosafranine by hydrogen perox-ide oxidation catalyzed by silica-supported 5101520-tetrakis-(sulfonatophenyl)porphine-Mn(III) really biomimeticrdquo Jour-nal of Molecular Catalysis A vol 321 no 1-2 pp 27ndash33 2010

[29] P Zucca C Vinci F Sollai A Rescigno and E SanjustldquoDegradation of Alizarin Red S under mild experimental con-ditions by immobilized 5101520-tetrakis(4-sulfonatophenyl)porphine-Mn(III) as a biomimetic peroxidase-like catalystrdquoJournal of Molecular Catalysis A vol 288 no 1-2 pp 97ndash1022008

[30] P Zucca F Sollai A Garau A Rescigno and E SanjustldquoFe(III)-5101520-tetrakis(pentafluorophenyl)porphine supp-orted onpyridyl-functionalized crosslinked poly(vinyl alcohol)as a biomimetic versatile-peroxidase-like catalystrdquo Journal ofMolecular Catalysis A vol 306 no 1-2 pp 89ndash96 2009


[31] E Cano-Serrano JM Campos-Martin and J L G Fierro ldquoSul-fonic acid-functionalized silica through quantitative oxidationof thiol groupsrdquo Chemical Communications vol 9 no 2 pp246ndash247 2003

[32] M Kirihara A Itou T Noguchi and J Yamamoto ldquoTantalumcarbide or niobium carbide catalyzed oxidation of sulfideswith hydrogen peroxide Highly efficient and chemoselectivesyntheses of sulfoxides and sulfonesrdquo Synlett no 10 pp 1557ndash1561 2010

[33] E Baciocchi M F Gerini and A Lapi ldquoSynthesis of sulfox-ides by the hydrogen peroxide induced oxidation of sulfidescatalyzed by iron tetrakis(pentafluorophenyl)porphyrin scopeand chemoselectivityrdquo Journal of Organic Chemistry vol 69 no10 pp 3586ndash3589 2004

[34] M Moghadam S Tangestaninejad V Mirkhani I Mohamma-dpoor-Baltork and A A Abbasi-Larki ldquoBiomimetic oxidationof sulfides with sodium periodate catalyzed by polystyrene-bound manganese (III) tetrapyridylporphyrinrdquo Applied Catal-ysis A vol 349 no 1-2 pp 177ndash181 2008

[35] A Ghaemi S Rayati S Zakavi and N Safari ldquoHighly efficientoxidation of sulfides to sulfones with tetra-n-butylammoniumhydrogen monopersulfate catalyzed by 120573-tri- and tetra-bromi-nated meso-tetraphenylporphyrinatomanganese(III) acetaterdquoApplied Catalysis A vol 353 no 2 pp 154ndash159 2009

[36] A Rezaeifard M Jafarpour H Raissi E Ghiamati and ATootoonchi ldquoFactors affecting the reactivity and selectivity inthe oxidation of sulfides with tetra-n-butylammonium per-oxomonosulfate catalyzed by Mn(III) porphyrins significantnitrogen donor effectsrdquo Polyhedron vol 30 no 4 pp 592ndash5982011

[37] H B DunfordHeme Peroxidase JohnWiley amp Sons NewYorkNY USA 1999

[38] E Baciocchi M F Gerini O Lanzalunga A Lapi andM G LoPiparo ldquoMechanism of the oxidation of aromatic sulfides cata-lysed by a water soluble iron porphyrinrdquoOrganic and Biomolec-ular Chemistry vol 1 no 2 pp 422ndash426 2003

[39] Y Goto T Matsui S-I Ozaki Y Watanabe and S FukuzumildquoMechanisms of sulfoxidation catalyzed by high-valent inter-mediates of heme enzymes electron-transfer vs oxygen-tran-sfer mechanismrdquo Journal of the American Chemical Society vol121 no 41 pp 9497ndash9502 1999

[40] E Baciocchi O Lanzalunga S Malandrucco M Ioele and SSteenken ldquoOxidation of sulfides by peroxidases Involvement ofradical cations and the rate of the oxygen rebound steprdquo Journalof the American Chemical Society vol 118 no 37 pp 8973ndash89741996

[41] W Ando R Tajima and T Takata ldquoOxidation of sulfide withArIO catalyzed with TPPM(III)Clrdquo Tetrahedron Letters vol 23no 16 pp 1685ndash1688 1982

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CatalystsJournal of


O

O

CH

NH

N

N

N

N

N

F F

F

F

F

R

R R

R

Fe+

R =

PVA

bead

Figure 1 Proposed structure of the catalytic adduct PP-PVAFeTFPP

catalytic adducts were able to oxidize both lignin modelcompounds (recently reviewed in [26]) and durable textiledyes [27ndash29]

In this paper we describe the immobilization of a com-mercially available Fe-porphin onto a solid support graftedwith pyridine residues (Figure 1 [30]) The ability of thisadduct to oxidize sulfide ion leading to sulfate has beenstudied focusing on the minimization of the amount ofelemental sulfur produced The catalytic conditions havebeen fully evaluated in the perspective of a mild and feasibleindustrial process Also a comparison with an enzymaticsystem has been performed

2 Experimental

All the reagents used were of the best grade available andwere used as purchased without further purification Fullyhydrolysed PVA Av MW 30000ndash50000 was from Aldrich(Milan Italy cat number 363138) Glutaraldehyde as a 50aqueous solution mainly containing oligomers in addition tothe monomeric aldehyde was from Fluka Milan Italy catnumber 49629

21 Preparation of FeTFPPPP-PVA Adduct The preparationFeTFPPPP-PVA adduct was performed as already described[30]

Briefly aminopropyl cross-linked PVA (AP-PVA) wasprepared by treating 500mL of a 10 wv PVA aqueous

solution with 5mL 4-aminobutyraldehyde diethyl acetal andpH was adjusted to sim2 with 6M HCl

Then 10mL of a 50 vv glutaraldehyde aqueous solutionwas added under stirring and the pH adjusted to sim1 with 6MHCl The obtained gel was kept at 90∘C for 1 h and finallyovernight at 25∘C The product was ground for 10min at16000 rpmwithUltra Turrax T25 Basic (IKATechnikMilanItaly) exhaustively washed with water 01M NaOH wateragain 2-propanol and finally carefully dried into a warmoven

Each gram of the AP-PVA powder was suspended inexcess water and treated with 01mL of 4-pyridinecarbo-xaldehyde The pH was adjusted to 5 with 01M acetic acidsodium acetate buffer and 05 g sodium cyanoborohydridewas added After 24 h the support was exhaustively washedwith 01M aqueous glycerol water 01MNaOH water againand 2-propanol The wet PP-PVA was then carefully driedovernight in a vacuum oven at 50∘C

Each gram of PP-PVA was treated with 20mg FeTFPPsolubilized in 10mL DMSOThe slurry was kept 24 h stirringin the dark (because of metalloporphin photosensitivity)and washed exhaustively at first with DMSO then with 2-propanol The adduct was finally dried at 50∘C in a vacuumoven

Bound metalloporphin was quantified by differencethrough spectrophotometric measurement (UltroSpec 2100pro Amersham Bioscience Milan Italy) at 411 nm (120576

411=

115000Mminus1 cmminus1 in DMSO) as already described [30]

22 Catalytic Assay A mixture containing 10mg of catalyst(corresponding to 067mg063 120583mol of ferriporphin) sus-pended in 1mL of 25mM buffer solution containing 10mMNaHS and 45mM aqueous H

2O2was kept stirring at 25∘C

in the dark Blank experiments were performed without onesubstrate or without catalyst In a series of experiments theconcentrations of the substrates were varied within a properrange

After prefixed periods of time aliquots of the reactionsolution (500120583L) were treated with 100 EU of purifiedcatalase for 301015840 at 25∘C and used for sulfide and sulfatequantification In order to test catalytic performance atvarious pHs some McIlvaine buffers were used pH 3 pH 4pH 5 pH 6 pH 7 and pH 8

23 Sulfide and Sulfate Determination Sulfide concentrationwas determined through photometric automatized cuvettetest LCK653 (Hack Lange Rheineck Switzerland) using DR2700 Portable Spectrophotometer (Hack Lange RheineckSwitzerland)

Sulfate was estimated after acidification of the samples(200120583L) with 50120583L 1M HCl To remove some colloidal sul-fur when necessary the acidified samples were centrifuged at12000timesg for 15min Sulfate analysis was performed throughphotometric automatized cuvette test LCK153 (Hack LangeRheineck Switzerland) based on a nephelometric measure

24 Enzymatic Comparison When horseradish peroxidase(HRP) was used up to 15 EU was present in a final volume













H2S + 4H

2O2997888rarr SO

4

2minus+ 4H2O + 2H+ (1)


120

100

80

60

40

20

0

3 4 5 6 7 8

pH

Cata

lytic

activ

ity (

)


2O2(1mL









80

60

110 Blank792 704 44

40

20

0

Sulfa

te y

ield

24

h (

)

[H2O2] (mM)










100

80

60

40

20

0

HRP (milli-EU)

19 9

19

90

190

370

740

1500

PP-P

VA

FeTF

PP

Sulfi

de co

nver

sion

in24

h (

)







2S+∙


2

18O2 Any-



Cpd II analogueO

N

N

N

O

PVA bead

PVA beadPVA bead

HS∙HS∙

HSminus

HSminus

H2O

Native state

[HSOminus]

[HSOminus]

H2O2

H2O2

H2O2

+ ∙

Cpd Ianalogue

(a)

(b)(c)

Fe(IV)

(IV)FeFe(III)

SO4

2minus

SO4

2minus




4 Conclusion



2S removal

Abbreviations







Acknowledgments


References






















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of













H2S + 4H

2O2997888rarr SO

4

2minus+ 4H2O + 2H+ (1)


120

100

80

60

40

20

0

3 4 5 6 7 8

pH

Cata

lytic

activ

ity (

)


2O2(1mL









80

60

110 Blank792 704 44

40

20

0

Sulfa

te y

ield

24

h (

)

[H2O2] (mM)










100

80

60

40

20

0

HRP (milli-EU)

19 9

19

90

190

370

740

1500

PP-P

VA

FeTF

PP

Sulfi

de co

nver

sion

in24

h (

)







2S+∙


2

18O2 Any-



Cpd II analogueO

N

N

N

O

PVA bead

PVA beadPVA bead

HS∙HS∙

HSminus

HSminus

H2O

Native state

[HSOminus]

[HSOminus]

H2O2

H2O2

H2O2

+ ∙

Cpd Ianalogue

(a)

(b)(c)

Fe(IV)

(IV)FeFe(III)

SO4

2minus

SO4

2minus




4 Conclusion



2S removal

Abbreviations







Acknowledgments


References






















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


80

60

110 Blank792 704 44

40

20

0

Sulfa

te y

ield

24

h (

)

[H2O2] (mM)










100

80

60

40

20

0

HRP (milli-EU)

19 9

19

90

190

370

740

1500

PP-P

VA

FeTF

PP

Sulfi

de co

nver

sion

in24

h (

)







2S+∙


2

18O2 Any-



Cpd II analogueO

N

N

N

O

PVA bead

PVA beadPVA bead

HS∙HS∙

HSminus

HSminus

H2O

Native state

[HSOminus]

[HSOminus]

H2O2

H2O2

H2O2

+ ∙

Cpd Ianalogue

(a)

(b)(c)

Fe(IV)

(IV)FeFe(III)

SO4

2minus

SO4

2minus




4 Conclusion



2S removal

Abbreviations







Acknowledgments


References






















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Cpd II analogueO

N

N

N

O

PVA bead

PVA beadPVA bead

HS∙HS∙

HSminus

HSminus

H2O

Native state

[HSOminus]

[HSOminus]

H2O2

H2O2

H2O2

+ ∙

Cpd Ianalogue

(a)

(b)(c)

Fe(IV)

(IV)FeFe(III)

SO4

2minus

SO4

2minus




4 Conclusion



2S removal

Abbreviations







Acknowledgments


References






















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article biomimetic sulfide oxidation by the means...

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