-
CHAPTER I
General Introduction
The area of inorganic chemistry, which most widely developed in the last few
decades is mainly due to coordination chemistry and applies very particularly to the
coordination compounds of transition metals. The chemistry of coordination compounds
has always been a challenge to the inorganic chemists as it has more branches now-a-
days.
Coordination compounds play a very significant role in our lives, the study of
them has contributed to the highest degree of understanding the chemical bond in
inorganic chemistry. As a whole classical coordination chemistry deals with the
formation of adducts by metal in their higher oxidation states bonded to inorganic or
organic ions or molecules. Interest in both basic and hi-tech research with these materials
continues at a rapid pace.
Metals play a vital role in an immense number of extensively differing biological
processes. Some of these processes are quite specific in their metal ion requirements, in
that only certain metal ions in specified oxidation states can accomplish the necessary
catalytic structural requirement. Metal ion dependent processes are found through out the
life science and vary tremendously in their function and complexity.
It is now appreciated that metal ions control a vast range of processes in biology.
Many new and exciting developments in the field of biochemistry create interest out of
inorganic chemists to court in the new area called “Bioinorganic Chemistry”.
1
-
One of the principal themes of bioinorganic chemistry is the synthesis of metal
complexes that have the ability to mimic the functional properties of natural
metalloproteins [1,2]. Proteins, some vitamins and enzymes contain metal ions in their
structure involving macromolecular ligands. The chemistry of metal complexes with
multidentate ligands having delocalized π-orbitals, such as Schiff bases or porphyrins has
recently gained more attention because of their use as models in biological systems.
Schiff bases
The condensation of primary amines with aldehydes and ketones give imines.
Imines that contain an aryl group bound to the nitrogen or to the carbon atom are called
Schiff bases, since their synthesis was first reported by Schiff [3].
Schiff bases are capable of forming coordinate bonds with many of metal ions
through both azomethine group and phenolic group or via its azomethine or phenolic
groups [4-19]. A large number of Schiff bases and their complexes are significant interest
and attention because of their biological activity including anti-tumor, antibacterial,
fungicidal and anti-carcinogenic properties [7-12] and catalytic activity [12-19].
Naphthylideneimine Schiff base complexes (Figure 1.1) possessing luminescence
property, catalyze oxidation of primary and secondary alcohols into their corresponding
carbonyl compounds in the presence of N-methylmorpholine-N-oxide (NMO) as the
source of oxygen have been reported recently [14]. The formation of high valent RuIV= O
species as a catalytic intermediate is proposed for the catalytic process.
2
-
Figure 1.1 Structure of the bidentate Schiff bases.
L-Amino acid Schiff bases with N,O donor system have been reported by Taqui
Khan et al [20]. and are used as catalyst of enantio selective epoxide of 1,2-di hydro-
naphthalene. Nitro substituted benzaldehyde Schiff bases were used in organic catalytic
reactions [21]. Schiff bases of N-methyl and N-acetyl isatin derivatives with different
arylamines have been prepared and screened for anti convulsant activities [22].
Antibacterial screening of monobasic bidentate Schiff base complexes
(Figure 1.2) with N,O donor have been reported [23].
C N
H R
OH
OCH3
(R = -CH3, -C5H4N, -C6H12)
Figure 1.2 Structure of monobasic bidentate Schiff base complexes with N,O donor.
3
-
Schiff bases of ethylenediamine/triethylenetetramine (salen) with benzaldehyde/
cinnamic aldehyde/salicylaldehyde as corrosion inhibitors of zinc in sulphuric acid have
been reported by Desai et al [24].
Recent report says, Schiff bases (Figure 1.3) are also employed as fluorescent
indicators by spectrofluorimetric monitoring of small changes of pH [25].
Figure 1.3 Structure of fluorescent Schiff bases.
Transition Metal complexes
The phenomenon of complex formation is really a very general one, but is
especially noted among the transition metal ions. For bonding, the metal must posses
vacant orbitals and these orbitals symmetrically must be correct, sterically available and
4
-
of reasonably low energy. Since transition metal ions generally meet these requirements
best, it is not surprising that they form complexes readily.
The transition elements play vital role in coordination complexes mainly because
of the following characteristics [26-29]:
variable oxidation state (electron transfer properties),
coordination geometries (octahedral, tetrahedral, square planar, pyramidal, etc.),
spectral and magnetic features, ligand field effects, unpaired d-electrons,
formation of chelated complexes,
most M2+ and higher oxidation states are borderline or hard acids and generally
prefer borderline or hard base such as O and N-donor groups; lower oxidation states
e.g. Cu(I) are softer acid will bind the soft bases such as O2, CO, N2, and S. and
formation of polynuclear metal species e.g. dimers, tetramers with bridging.
Metal coordination complexes have a wide diversity of technological and
industrial applications ranging from catalysis to anticancer drugs [30].
Ruthenium complexes
Ruthenium Schiff base complexes, particularly those containing oxygen and
nitrogen as donor atoms were found to be very efficient catalysts in the oxidation of
alcohols and alkenes. Electron transfer reactions are fundamental and play important role
in chemical and biological processes. As the coordination environment around the central
metal ion directs properties of the complexes, complexation of ruthenium by ligands of
different types has been of significant importance.
5
-
Ruthenium(II) complexes
Ruthenium(II) compounds display long luminescence life time and are extremely
photo stable [31,32].
There is a continuing interest in the development of probes for nucleic acid
structure determination. In recent years, a number of metal chelates have been used as
DNA structural probes and as chemotherapeutic agents. In particular, ruthenium(II)
complexes of the type [Ru(LL)3]n+, where LL is a bidentate ligands of various nature,
have been extensively studied as probes for the determination of nucleic acid
structure.[33-38] The application of these complexes as DNA structural probes is due to
their water solubility, coordinatively saturated nature and substitution inertness.
Catlytic activity and antibacterial screening of Ru(II) Schiff base complexes of
the type [Ru(CO)(EPh3)(B)(L)] (E = P or As; B= PPh3, AsPh3, py or pip; L = Schiff
bases have been reported by Balasubramanian et al [39].
DNA binding and antibacterial screening of dehydroacetic acid complexes
(Figure 1.4 A&B) of Ru(II) and Ru(III) containing PPh3/AsPh3 have been recently
reported by Chitrapriya et al [40].
Figure 1.4(A) Structure of Ru(III) dehydroacetic acid complexes.
6
-
Figure 1.4(B) Structure of Ru(II) dehydroacetic acid complexes.
Recent studies indicate that ruthenium complexes (Figure 1.5) are promising
candidates for NLO materials because of their rich photochemical properties and varied
coordination form [41-46].
7
-
Figure 1.5 Structures of the ruthenium(II) complexes possess NLO property.
Ruthenium(II) complexes containing triphenylphosphine/triphenylarsine and tetra
dentate Schiff bases are found to be effective catalysts in the oxidation of primary and
secondary alcohols using N-methylmorpholine-N-oxide as oxidant [47]. The catalytic
activity of these triphenylarsine complexes have been compared with that of
triphenylphosphine complexes and with similar ruthenium(III) complexes.
Ruthenium(III) complexes
Prabhakaran et al [11] synthesized ruthenium(III) complexes (Figure 1.6)
containing tetradentate Schiff base to test its antibacterial activity.
Figure 1.6 Structure of tetradentate Schiff base ligand.
8
-
Ramesh et al [18] reported catalytic oxidation of primary alcohols by some of the
ruthenium(III) Schiff base complexes (Figure 1.7) was carried out in CH2Cl2 in the
presence of N-methylmorpholine-N-oxide.
Figure 1.7 Ruthenium(III) Schiff base complexes.
Kannan et al [48] synthesized a series of new ruthenium(III) Schiff base
complexes (Figure 1.8) incorporating triphenylphosphine/triphenylarsine and chloride/
bromide ligands, and have been reported as efficient catalyst for the oxidation of both
primary and secondary alcohols to the corresponding carbonyl compounds with excellent
yields in the presence of NMO. Further, the possible explanations for the mode of action
of these complexes against two different microbes S. aureus and E. coli are described.
Figure 1.8 Structure of Ru(III) Schiff base complexes.
9
-
Copper(II)/Cobalt(II)/Nickel(II) complexes
The transition metals especially first row transition metal ions are well known for
their ability to form wide range of coordination complexes in which octahedral,
tetrahedral, and square planar geometries predominate. Copper(II) is a typical transition
metal ion to form complexes, but less typical in its reluctance to take up a regular
octahedral (or) tetrahedral geometry. The magnitude of the splitting of the electronic
energy levels in copper(II) complexes tend to be larger than other first row transition
metals due to the presence of large Jahn-Teller distortion.
Copper is one of the essential trace elements present in living organisms. A
number of important redox enzymes like hemocyanins, superoxide dismutase, blue
copper proteins, etc., contains copper atoms bound to protein molecules.
Copper(II) complexes with amino acids are cited as having potent anti-
inflammatory and anti- ulcer activity [49]. Copper ions are found to present in the active
sties of large number of metalloproteins, which involved in important biological electron
transfer reactions as well as in the molecular oxygen redox reactions [50,51].
There has been a substantial interest in the rational design of novel transition metal
complexes, which bind and cleave duplex DNA with high sequence or structure
selectivity. The characterization of DNA recognition by small transition-metal complexes
has been substantially aided by the DNA cleavage chemistry that is associated with
redox-active or photoactivated metal complexes.
10
-
Non–covalent interactions between positively charged metallointercalators and
the base–pair stack of DNA has been an area of interest for some time. It is clear that a
number of factors affect both the sequence selectivity of intercalators binding to DNA
and the resulting twist angle, and therefore it is necessary to understand the structural
features of intercalators that control the specificity of their binding. This, inturn should
lead to the design of more specifically targeted intercalators.
The synthesis and investigation of synthetic reversible dioxygen carriers have
attracted substantial interest in recent years and their physico-chemical properties are
sufficiently favorable for application in industries and medicine [52,53]. Synthetic
oxygen carriers have been studied extensively over several decades for two main reasons
viz (i) to understand the mechanism of oxygen binding proteins and (ii) to design
complexes suitable for practical applications. Co(II) complexes of porphyrins, Schiff
bases and tetraaza systems (Figure 1.9(A-C) are usually studied as models for oxygen
carriers. Schiff bases used for the studies of oxygen carrying properties are generally
tetradentate, of which at least two of the ligating atoms should be nitrogen, with the
others being nitrogen, oxygen, sulphur (or) combination of the three.
Tian et al [54] reported the nuclease activity (DNA cleavage) of Cobalt(II)
complexes with pBR 322 DNA in the absence of any external agents.
11
-
(A)
(B)
(C)
Figure 1.9(A-C) Co(II) complexes of porphyrins, Schiff bases and tetraaza systems.
12
-
The intercalative DNA-Binding studies of a Nickel(II) coordination compound
Ni(bpy)2dppz2+ have been reported [55]. The calculated intrinsic binding constant for the
same is 1.5 × 104 M−1. These features are equivalent to those observed with
Ru(bpy)2dppz2+ and suggest that nickel complex binds by intercalation in a manner that
parallels Ru(bpy)2dppz2+ [56].
Square planar nickel(II) complexes were studied owing to their known catalytic
activity towards olefin epoxidation.
Biological studies
Nucleic acids viz. ribonucleic acid (RNA) and deoxyribonucleic acid (DNA),
contain three types of basic structural nucleotide units: (a) pentose sugar,
(b) nitrogenous base (pyrimidins/purines) and (c) phosphate residue. They are long,
thread-like polymers, consisting of a linear array of monomers called nucleotides.
Nucleotides are the phosphate ester of nucleosides, which are the basic components of
DNA. The stacks of DNA contain A, G, C, T while RNA contains A, G, C, U. The types
of pentose also distinguish the nucleic acids 2-Deoxyribose is found in DNA while it is
ribose in RNA.
DNA usually consists of two complementary polymeric chains twisted about each
other in the form of a right-handed helix, making a complete turn every 34 0A (3.4 nm),
with a diameter of 20 0A (2 nm). Since the distance between adjacent nucleotides is
3.4 0A, there must be 10 nucleotides per turn. The constant diameter of the helix can be
explained if the bases in each chain face inward and are restricted so that a purine is
13
-
always opposite to a pyrimidine avoiding organization of purine-purine (too thick) or
pyrimidine-pyrimidine (too thin). Irrespective of the actual amounts of each base, the
proportion of G is always the same as the proportion of C in DNA, and the proportion of
A is always the same as that of T. The composition of any DNA can be described by the
proportion of its bases ic., G+C, which ranges from 26% to 74% for different species.
The two chains of DNA (Figure 1.10) are complementary to each other.
Figure 1.10 Structure of right handed double helical DNA (B-Type).
14
-
Since DNA is the basis for the storage, transmission and expression of genetic
information, any reaction or damage caused to it will have important consequences.
There has been substantial interest in exploring the factors that determine kinship and
selectivity in binding of small molecules with DNA [57-59]. A quantitative
understanding of such factors that determine recognition of DNA sites would be valuable
in designing small molecules that binds to specific sites in DNA and finds application in
chemotherapy. A number of metal chelates mostly polypyridyls have been used as
probes of DNA structure in solution [60], as agents for mediation of strand scission of
duplex DNA [61] and as chemotherapeutic agents [62].
The interaction of small molecules like metal complexes with DNA has been an
active area of research at the interface of chemistry and biology [63-68]. These small
molecules are stabilized in binding to DNA through a series of weak interactions, such as
the p-stacking interactions associated with intercalation of a planar aromatic group
between the base pairs, hydrogen-bonding and van der Waals interactions of
functionalities bound along the groove of the DNA helix [69], and the electrostatic
interaction of the cation with phosphate group of DNA [70]. Studies directed toward the
design of site- and conformation- specific reagents provide rationales for new drug design
as well as a means to develop sensitive chemical probes of nucleic acid structure.
Small molecules (metal complexes) bind to DNA double helix by three
distinguished binding modes Figure 1.11. They are,
A. Electrostatic binding / External binding
15
-
B. Groove binding
C. Intercalative binding / Intercalation
A. External binding / Electrostatic binding
Complexes are positively charged and the DNA phosphate sugar backbone is
negatively charged and their interaction is known as electrostatic. This association mode
was proposed for [Ru(bpy)3]2+, due to the luminescence enhancement of this complex
upon binding to DNA. Cations such as Mg2+ usually interact in this way [71].
B. Groove binding
The molecules approach within van der Waals contact and reside in the DNA
groove. Hydrophobic and/or hydrogen-bonding are usually important components of this
binding process, and provide stabilization. The antibiotic netropsin is a model groove-
binder where the methyl groups prevent intercalation [72].
16
-
C. Intercalation
This association involves the insertion of a planar fused aromatic ring system
between the DNA base pairs, leading to significant �-electron overlap. Stacking
interactions stabilizes this mode of binding and is thus less sensitive to ionic strength
relative to the two other binding modes. This mode of binding is usually favored by the
presence of an extended fused aromatic ligand like DPPZ [73]. Indeed with less extended
aromatic systems, the intercalation is usually prevented through clashing of the ancillary
ligands with the phosphodiester backbone, so that only partial intercalation can occur as
in the case for [Ru(phen)3]2+ [74].
17
-
Figure 1.11 Binding modes of small molecules with DNA.
Many metal complexes can bind to DNA in noncovalent modes such as
electrostatic, intercalative and groove binding [75,76]. Varying the substitutive group or
substituent position in the intercalative ligand can create some interesting differences in
the space configuration and the electron density distribution of transition metal
complexes, which will result in some differences in spectral properties and the DNA-
binding behaviors of the complexes and will be helpful to more clearly understand the
binding mechanism of transition metal complexes to DNA [77,78].
18
-
Scope of the present work
Schiff bases, a class of chelators, considered as privileged ligands, attractive due
to their stability, the ease by which modified variations can be obtained, a diverse range
of applications and are flexible both in terms of size and charge.
Schiff base complexes of transition metals having O and N donor atoms
containing phosphine/arsine especially ruthenium complexes, find application in classical
catalytic processes such as hydrogenation, isomerisation, decarbonylation, reductive
elimination, oxidative addition and in making C–C bonds. Transition metal carbonyl
complexes are reactive species in homogeneous catalytic reactions such as
hydrogenation, hydroformylation and carbonylation.
Literature says, though there is a considerable growth of Schiff base complexes
of first row transition metals, the chemistry of ruthenium complexes is less well
developed. But, there has been considerable interest in ruthenium complexes now-a-days
because of their redox stability, excited state life time, excited state reactivities their
ability to act as probes in investigating the structure of DNA and its antimicrobial
activity. The interaction of ruthenium complexes with DNA has received a great deal of
attention during the past decade. Also metal complexes of ruthenium containing nitrogen
and oxygen donor ligands are found to be very effective catalysts for oxidation,
reduction, hydrolysis and other organic and inorganic transformations especially
regioselective oxidation. The redox property of the central ruthenium can be tuned by
changing the substituents in the ligand. The oxidation states of ruthenium complexes can
vary from –II to +VIII. The chemotherapeutic Schiff bases are now attracting the
19
-
attention of inorganic chemists. Reports show that some drugs show increased activity
when it is administered as metal complexes rather than as organic compounds. Yet the
mechanism of antitumour activity of ruthenium compounds is not fully understood, it is
believed that, similar to platinium drugs, the chloride complexes can hydrolyze in vivo,
allowing the Ru to bind to the nucleobases of the DNA. However a deep survey of
literature on Schiff base transition metal complexes of N and O donors reveal that
antimicrobial and DNA binding studies have been largely ignored.
In the present project, which has originated from our interest in the chemistry of
transition metals especially ruthenium in different coordination environments. We have
chosen different types of phenolic ligands to synthesis, characterize and to study their
antibacterial activity and DNA binding properties.
20
-
References
[1] Z. Lu, L. Yang, J. Inorg. Biochem. 95 (2003) 31.
[2] J.Z. Wu, H.Li, J.G. Zhang, H. Xu Ju, Inorg. Chem. Commun. 5 (2002) 71.
[3] H. Schiff, Ann. Chim.(Paris) 131 (1864) 118.
[4] S.A. Sadeek, M.S. Refat, J. Korean Chem. Soc. 50 (2) (2006) 107.
[5] A. Bigotto, V. Galasso, G. Dealti, Spectrochim. Acta 28A (1972) 1581.
[6] S. Ren, R. Wang, K. Komatsu, P. Bonaz-Krause, Y. Zyrianov, C.E. Mckenna,
C. Csipke, Z.A. Tokes, E.J. Lien, J. Med. Chem. 45 (2002) 410.
[7] N. Chitrapriya, V. Mahalingam, L.C. Channels, M. Zeller, F.R. Fronczek,
K. Natarajan, Inorg. Chim. Acta 361 (2008) 2841.
[7] M.S. Refat, S.A. El-Korashy, D.N. Kumar, A.S. Ahmed, Spectrochim. Acta
Part A 70 (2007) 898.
[9] R. Prabhakaran, R. Huang, K. Natarajan, Inorga. Chim. Acta 359 (2006) 3359.
[10] K.P. Balasubramanian, K. Parameswari, V. Chinnusamy, R. Prabhakaran,
K. Natarajan, Spectrochim. Acta Part A 65 (2006) 678.
[11] R. Prabhakaran, A. Geetha, M. Thilagavathi, R. Karvembu, V. Krishnan,
H. Bertagnolli, K. Natarajan, J. Inorg. Biochem. 98 (2004) 2131.
21
-
[12] S. Kannan, R. Ramesh, Polyhedron 25 (2006) 3095.
[13] S. Kannan, K. Naresh Kumar, R. Ramesh, Polyhedron 27 (2008) 701.
[14] M. Sivagamasundari, R. Ramesh, Spectrochim. Acta Part A 67 (2007) 256.
[15] S. Kannan, R. Ramesh, Y. Liu, J. Organomet. Chem. 692 (2007) 3380.
[16] V. Mahalingam, R. Karvembu, V. Chinnusamy, K. Natarajan, Spectrochim. Acta
Part A 64 (2006) 886.
[17] G. Venkatachalam, R. Ramesh, Inorg. Chem. Commun. 9 (2006) 703.
[18] R. Ramesh, Inorg. Chem. Commun. 7 (2004) 274.
[19] R. Karvembu, S. Hemalatha, R. Prabhakaran, K. Natarajan, Inorga. Chem.
Commun. 6 (2003) 486.
[20] M.M. Taqui Khan, R.I. Kureshy, N.H. Khan, Tetrahedron: Asymmetry, 2 (1991)
101.
[21] W.T. Gao, Z. Zhing, Molecules 8 (2003) 788.
[22] M. Verma, S.N Pandeya, K. Singh, T.P. Stables, Acta Pharma. 54 (2004) 49.
[23] K. Naresh Kumar, R. Ramesh, Spcetrochim. Acta Part A 60 (2004) 2913.
[24] M.N. Desai, J.D. Talati, N.K. Shah, Anti-Corrosion Methods and Materials 55
(2008) 27.
22
-
[25] M.N. Ibrahim, S.E. A. Sharif, E-Journal of Chemistry 4 (4) (2007) 531.
[26] J.C. Wu, N. Tang, W.S. Liu, M.Y. Tanchan, A.S. Chin, Chem. Lett. 12 (2001)
757.
[27] L. He, S.H.Q.F. Gou, J. Chem. Crystallogr. 29 (1999) 207.
[28] P. Bhattacharya, J. Parr, A.J. Ross, J. Chem. Soc. Dalton (1998) 3149.
[29] C.M. Liu, R.G. Xiong, X.Z. You, Y.J. Liu, K.K Chiung, Polyhedron 15 (1996)
4564.
[30] A.D. Burrows, Science Progress 85 (3) (2002) 199.
[31] F.N. Castellano, J.D. Dattelbaum, J.R. Lakowicz, Anal. Biochem. 255 (1998) 165.
[32] H.Wolpher, O. Johansson, M. Abrahamson, M. Kritikos, L. Sun, B. Akermark,
Inorg. Chem. Commun. 7 (2004) 337.
[33] T. Urathamkul, J.L. Beck, M.M. Sheil, J.R. Aldrich-Wright, S.F. Ralph, Dalton
Trans (2004) 2683.
[34] H. Chao, J.-G. Liu, L.-N. Ji, X.-Y. Li, J. Biol. Inorg. Chem. 6 (2001) 143.
[35] J.-G. Liu, B.-H. Ye, Q.-L. Zhang, X.-H. Zou, Q.-X. Zhen, X. Tian, L.-N. Ji,
J. Biol. Inorg. Chem. 5 (2000) 119.
[36] A. Anagnostopoulou, E. Moldrheim, N. Katsaros, E. Sletten, J. Biol. Inorg. Chem.
4 (1999) 199.
23
-
[37] R. Hartmann, A. Robert, V. Duarte, B.K. Keppler, B. Meunier, J. Biol. Inorg.
Chem. 2 (1997) 143.
[38] D.B. Hall, R.E. Holmin, J.K. Barton, Nature 382 (1996) 73.
[39] K.P. Balasubramanian, R. Karvembu, R. Prabhakaran, V. Chinnusamy,
K. Natarajan, Spectrochim. Acta Part A 68 (2007) 50.
[40] N. Chitrapriya, V. Mahalingam, M. Zeller, R. Jayabalan, K. Swaminathan,
K. Natarajan, Polyhedron 27 (2008) 939.
[41] C. Dhenaut, I. Ledoux, I.D.W. Samuel, J. Zyss, M. Bourgault, H. Le Bozec,
Nature (London) 374 (1995) 339.
[42] B.J. Coe, G. Chadwick, S. Houbrechts, A. Persoons, J. Chem. Soc., Dalton Trans.
(1997) 1705.
[43] B.J. Coe, S. Houbrechts, I. Asselberghs, A. Persoons, Angew. Chem., Int. Ed.
Engl. 38 (1999) 366.
[44] I.R. Whittall, M.P. Cifuentes, M.G. Mark, B. Luther-Davies, M. Samoc,
S. Houbrechts, A. Persoons, G.A. Heath, D.C.R. Hockless, J. Organomet. Chem.
549 (1997) 127.
[45] A.M. McDonagh, M.G. Humphrey, M. Samoc, B. Luther- Davies, S. Houbrechts,
T. Wadw, H. Sasabe, A. Persoons, J. Am. Chem. Soc. 121 (1999) 1405.
24
-
[46] H. Chao, R.H. Li, B.H. Ye, H. Li, X.L. Feng, J.W. Cai, J.Y. Zhou, L.N. Ji,
J. Chem. Soc., Dalton Trans. (1999) 3711.
[47] R. Karvembu, S. Hemalatha, R. Prabhakaran, K. Natarajan, Inorg. Chem.
Commun. 6 (2003) 486.
[48] S. Kannan, R. Ramesh, Polyhedron 25 (2006) 3095.
[49] J.R.J. Sorenson, Progress in Medicinal Chemistry, G.P. Ellis, and G.B. West,
Ed., Elsevier, New York, Vol. 26 (1989) 437 and references cited therein.
[50] R.H. Holm, P. Kennepohl, Solomon, Chem. Rev. 96 (1996) 2239.
[51] K.D. Karlin, A.D. Zuber buhler, Bioinorganic Catalysis, 2nd Ed., J. Reediijk,
E. Bouwman, Ed., MarcelDekker, NewYork (1999) 469.
[52] S. Srinivasan, J. Annaraj, PR. Athappan, J. Inorg. Biochem. 99 (2005) 876.
[53] D.H. Busch, N.W. Alcock, Chem. Rev. 94 (1994) 585.
[54] J.-L. Tian, L. Feng, W. Gu, G.-J. Xu, S.-P. Yan, D.-Z. Liao, Z.-H. Jiang,
P. Cheng, J. Inorg. Biochem. 101 (2007) 196.
[55] L. Jin, P. Yang, Microchemical Journal 58 (1998) 144.
[56] A.E. Friedman, J.C. Chambron, J.P. Sauvage, J. Am. Chem. Soc. 112 (1990)
4960.
[57] W.S. Wade, P.B. Dervan, J. Am. Chem. Soc. 109 (1987) 1574.
25
-
[58] J.K. Barton, Science 233 (1986) 727.
[59] K. Kissinger, J.b. Dabrowiak, J.W. Lown, Biochemisty 26 (1987) 5590.
[60] J.K. Barton, Inorg. Chem. 7 (1985) 321.
[61] D.S. Sigman, Acc. Chem. Res. 19 (1986) 180.
[62] S.J. Lippand, Acc. Chem. Res. 11 (1978) 211.
[63] P. Nordell, P. Lincoln, J. Am. Chem. Soc. 127 (2005) 9670.
[64] C.C. Cheng, W.C.H. Fu, K.C. Hung, P.J. Chen, W.J. Wang, Y.T. Chen, Nucl.
Acid Res. 31 (2003) 2227.
[65] A.A. Mokhir, R. Kraemer, Bioconjugate Chem. 14 (2003) 877.
[66] W.C. Tse, D.L. Boger, Acc. Chem. Res. 37 (2004) 61.
[67] P. Yang, R. Ren, M.L. Guo, A.X. Song, X.L. Meng, C.X. Yuan, Q.H. Zhou, H.L.
Chen, Z.H. Xiong, X.L. Gao, J. Biol. Inorg. Chem. 9 (2004) 495.
[68] A.Th. Chaviara, P.J. Cox, K.H. Repana, A.A. Pantazaki, K.T. Papazisis,
A.H. Kortsaris, D.A. Kyriakidis, G.S. Nikolov, C.A. Bolos, J. Inorg. Biochem. 99
(2005) 467.
[69] A.M. Pyle, J.P. Rehmann, R. Meshoyrer, C.V. Kumar, N.J. Turro, J.K. Barton,
J. Am. Chem. Soc. 111 (1989) 3051.
26
-
[70] S. Satyanarayana, J.C. Dabrowiak, J.B. Chaires, Biochemistry 31 (1992) 9319.
[71] J. Kelly, A.Tossi, D. McComell, Nucl. Acids. Res. 13 (1985) 6017.
[72] H. Mei, J. Barton, J. Am. Chem. Soc. 108 (1986) 7414.
[73] I. Haq, P. Lincoln, D. Suh, B. Norden, B. Chowdhry, J. Chaires, J. Am. Chem.
Soc. 117 (1995) 4788.
[74] P. Lincoln, B. Norden, J. Phys. Chem. B. 102 (1998) 9583.
[75] J.A. Cowan, Curr. Opin. Chem. Biol. 5 (2001) 634.
[76] L.-N. Ji, X.-H. Zou, J.-G. Liu, Coord. Chem. Rev. 216 (2001) 513.
[77] C. Metcalfe, J.A. Thomas, Chem. Soc. Rev. 32 (2003) 215.
[78] H. Chao, L.N. Ji, Bioinorg. Chem. Appl. 3 (2005) 15 and references cited therein.
27