Vanadium peroxo compounds

Other groups have also examined vanadium(V) catalyzed oxidation of bromide by dihydrogen peroxide in acidic aqueous or aqueous/organic mixtures, although without examining the detailed speciation of the vanadium peroxo compounds in solution [77-82], These reports have focused more on the nature of the substrate brominated and the product distribution under different conditions. 

Figure 3 Structural illustrations of vanadium peroxo compounds (18-35). The charges are given for structure types in which all the complexes have the same charge. For structure types that have differently...

Binuclear vanadium(V) peroxo complexes such as (NH4)5[V202(02)4P04]-H20 are also known.30 They have been implicated as the reactive species in the bromide oxidation by hydrogen peroxide,31 a process which is important in some biological systems (Section 17-B-8). Some stable peroxo compounds display insulin-mimetic activity both in vivo and in vitro.32... 

Labeling studies have clearly shown that the active catalyst is not a peroxo compound but an alkyl peroxide in which the alkyl peroxide group is probably 0,0-triangularly bonded to the metal,as illustrated by the X-ray crystal structure of the vanadium complex (22). The well-characterized d" metal 0,N-bonded N,JV-dialkylhydroxylamino complexes (79), (80) and (81) might be reminiscent of the alkyl peroxide complexes of Mo " , V " and Ti ", which are difiBcult to isolate and involved as reactive intermediates in reactions (64) or (65). 

Cr, Mo and W derivatives. V(V) poly peroxo and polynuclear peroxo species have been characterized both in solution and in the solid state while triperoxo-type vanadium compounds have been isolated and characterized as welP their chemistry has been also accurately analyzed . 

Neither V0(02)+ nor V0(02)2 oxidizes bromide rather they associate to form the dinuclear (V0)2(02)3, which oxidizes bromide (Scheme 3) [76], The association constant for the dinuclear compound is rather small (K3 = 9 M at pH 0-2) this explains why it is not observed by 51V NMR at low concentrations of vanadium [73,76], The dinuclear compound has now been observed by 51V NMR at very high concentrations of vanadium [76], A complex of V202(02)3(HGly)2(H20)2 has been isolated in which a p-peroxo coordination of one peroxide is proposed [76],... 

Conte, V., O. Bortolini, M. Carraro, and S. Moro. 2000. Models for the active site of vanadium-dependent haloperoxidases Insight into the solution structure of peroxo-vanadium compounds. J. Inorg. Biochem. 80 41 -9. 

Studies of the oxidation of organic sulfides with amino acid-derived ligands in acetonitrile revealed very little difference between the mechanism of their oxidation and that of halides, except for one major exception. Despite the fact that acid conditions are still required for the catalytic cycle, hydroxide or an equivalent is not produced in the catalytic cycle, so no proton is consumed [48], As a consequence, there is no requirement for maintenance of acid levels during a catalyzed reaction. Peroxo complexes of vanadium are well known to be potent insulin-mimetic compounds [49,50], Their efficacy arises, at least in part, from an oxidative mechanism that enhances insulin receptor activity, and possibly the activity of other protein tyrosine kinases activity [51]. With peroxovanadates, this is an irreversible function. Apparently, there is no direct effect on the function of the kinase, but rather there is inhibition of protein tyrosine phosphatase activity. The phosphatase regulates kinase activity by dephosphorylating the kinase. Oxidation of an active site thiol in the phosphatase prevents this down-regulation of kinase activity. Presumably, this sulfide oxidation proceeds by the process outlined above. 

Guevara-Garcia, J.A., N. Barba-Behrens, R. Contreras, and G. Mendosa-Diaz. 1998. Bis-peroxo-oxovanadium(V) complexes of histidine-containing peptides as models for vanadium haloperoxidases. In Vanadium Compounds Chemistry, Biochemistry and Therapeutic Applications. A.S. Tracey and D.C. Crans (Eds). American Chemical Society, Washington, D.C. 126-35. 

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