Vanadium complexes cysteine

Dihydrogen evolves from vanadium(II)-cysteine at pH6.0-9.5. This reduction is first order in V11 and independent of pH in the range 7.5-8.5. If cysteamine or cysteine methyl ester is used, dihydrogen is still evolved. The reaction with serine is 1000 times slower than with cysteine even though the half wave potentials are comparable.156 This reaction may be explained by a hydride pathway similar to that proposed for catechol complexes or alternatively Scheme 8. 

Shaver, A., J.B. Ng, D.A. Hall, B. Soo Lum, and B.I. Posner. 1993. Insulin-mimetic peroxo vanadium complexes Preparation and structure of potassium oxodiper-oxo(pyridine-2-carboxylato)vanadate(V), K2[V0(02)2(C5H4NC00)]-2H20, and potassium oxodiperoxo(3-hydroxypyridine-2-carboxylato)vanadate(V), K2[V0(02)2 (0HC4H3NC00)]3H20, and their reactions with cysteine. Inorg. Chem. 32 3109-3113. 

Cysteine reduces vanadium(V) 803 the kinetics have been studied.804 V02+-cysteine compounds form in the reduction of vanadium(V) with an excess of cysteine805 and a Chinese publication reports K[V0(HCys0)(H20)]S04 and cis- and frans-K2[VO(CysO)2] (H2CysO = cysteine), and ESR as a function of pH. A purple complex from a 5 1 mixture of cysteine... 

Cysteine is a fairly effective reducing agent for vanadate, but even so, under neutral conditions, the V(V) lifetime is sufficiently long that vanadium NMR spectra can be obtained. Four products (-243, -309, -393, and -405 ppm) have been reported. Of these complexes, the -243 and -309 ppm NMR signals apparently correspond to products containing two thiolate groups in the coordination sphere, whereas the -393 and -409 ppm products have one thiolate ligand [43],... 

The reaction chemistry is quite different with cysteine. Under neutral conditions, cysteine reduces vanadate within an hour or so, but vanadate also rapidly forms relatively highly favored complexes with the cysteine that can be studied by NMR spectroscopy within the reduction time. All the complexes studied have sulfur in the coordination sphere. Four such complexes have been identified (Figure 2.2), two bisligand (-243 ppm, -309 ppm) and two monoligand (-393 ppm, 405 ppm) complexes [43], These complexes have not been structurally characterized, but it is quite likely that they are octahedral complexes with a coordination similar to that depicted in Scheme 4.14. Because vanadium(V) displays a general propensity toward five-membered rather than six-membered chelates, coordination of the type depicted in Scheme 4.14b with a nitrogen rather a carboxylate oxygen in the coordination shell seems most likely. 

FIGURE 7.2 NMR spectrum showing the large influence of coordination of S-containing heteroligands on 51V chemical shifts compared to similar O coordinated ligands in bis(N,N-dimethylhydroxylamine)(heteroligand)vanadium(V) complexes at pH 8.50. Experimental conditions total vanadate, 5.0 mM total Af.AI-di methyl hydroxylamine, 40 mM total cysteine, 90 mM KC1, 1.0 M pH, 8.5. 

Evidence is accumulating that vanadium interferes with the proper functioning of the cell cytoskeleton, which could also be involved in its antineoplastic effects. Taxol, a very successful chemotherapeutic drug, inhibits the function of microtubules in the cytoskeleton. In hepatomoa Morris 5123 cells, V(III) complexed with cysteine and derivatives inhibited the growth of these tumor cells and participated in the rearrangement of actin cytoskeleton architecture [166],... 

Osinska-Krolicka, I., H. Podsiadly, K. Bukietynska, M. Zemanek-Zboch, D. Nowak, K. Suchoszek-Lukaniuk, and M. Malicka-Blaszkiewicz. 2004. Vanadium(III) complexes with L-cysteine-stability, speciation and the effect on actin in hepatoma Morris 5123 cells. J. Inorg. Biochem. 98 2087-2098. 

In addition to complexes with ON donor sets, complexes with bidentate N-donor atoms and other donors have been described. For example, after several solution studies the crystal structure of the bis(L-cysteine methyl ester)oxovanadium(IV) complex showed that the vanadium is coordinated by the amido nitrogens and thiolate sulfurs (128).561 The complexes and reactivity of a series of pyridine-2-thiolate complexes of V(IV, III, and II) have been characterized (129-131).651 The mass spectrometric fragmentation patterns of two of these complexes were investigated and show the formation of six 1 1 complexes and one 1 2 complex in the gas phase.651... 

Bidentate ligands containing OS donors, particularly in conjunction with carboxylate moieties, form strong complexes at pH values near the p/y, value for the thiol.584,602,687-689 The reduction of Viv to V111 by cysteine methyl ester in water has been found to be enhanced in the presence of amino polycarboxylates.690 The ligand 2-mercapto-4-methylphenol forms a square-pyramidal five-coordinate complex with the vanadyl cation (150) the reported crystal structure is of the cis isomer.691 The bidentate ligand 2-aminocyclopent-l-ene-l-carbodithioic acid forms non-oxo-Viv complexes based on spectroscopic studies and chemical precedence, an eight-coordinate vanadium atom is inferred.692... 

The Vra complex with L-cysteine was prepared and characterized the crystal structure shows a 1 2 stoichiometry and that the two S-donors are trans to one another while the O- and N-donors are cis to one another (194).810 With three different donor functionalities, this 1 2 complex illustrates key aspects of Vm coordination chemistry. To identify the mode of action of cellular vanadium species and the roles of cysteine and glutathione in cellular redox chemistry, the redox and complexation chemistry of vanadium with sulfur-containing ligands must be better... 

A vanadium(II) tmeda complex with 2,6-dichlorothiophenolate has been reported with both S- and Cl-donor atoms (217).874 The thiolate donor atoms are trans to each other while the Cl atoms are trans to the N atoms in the tmeda ligand.874 The complex will react with azobenzene to give the phenylimido complex where one of the chloro-donor ligands is now trans to the imido nitrogen (218) 874 this complex is structurally similar to other imidovanadium(IV) complexes.643-646 A V11 cysteine methyl ester complex has been shown to reduce water to H2 but the mechanism of this process is not known.875... 

It was suggested that ligands exert a large modulatory role in determining the oxidative ability of these vanadium 0x0 diperoxo complexes affecting both the coordination of cysteine and the reduction potentials of the oxidants. 

NO ligand with a stability constant of 145 at 25°C and 1.5 M ionic strength. The complex decays to [Fe(CN)5NO] and 5RSSR with a rate constant of 1.8 x 10 s but is subject to equilibria involving loss or attack by CN . A purple vanadium(IV) complex has been detected as a product in the vanadium(V) oxidation of cysteine.It is thought to be a bis-cysteine adduct. Acid decomposition of [(en)2Co(SCH2CH2NH2)] is first order in the complex, independent of [H" ], with a rate constant of 2.10 x 10 s ... 

More recently, vanabin-1 and —2 were isolated from vanadocytes of Ascidia sydneiensis satnea. They specifically form complexes with vanadium(IV) but contain neither DOPA nor TOPA (UeH et cd., 2003 Fukui et al, 2003). Vanabin-1 and —2 contain 87 and 91 amino adds, respectively, and have molecular weights of 12.5 and 15 kDa. Each of them contains 18 cysteines but they are not related to vanadimn (Ueki et al, 2003). The structure in aqueous solution of the complex between vanadium(IV) and vana-bin-2 of Ascidia sydneiensis samea was the subject of a detailed study (Hamada et al, 2005). 

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