Vanadate-peroxide system

Speciation diagram for the vanadate-peroxide system. c(Vtotai) = lOmM, c(H202)/c(V) = 2, ionic strength 0.15 m Na(Cl), 25°C. Species containing less than 2% of are not shown. Courtesy of L. Pettersson, Umea University, Sweden. 

A triple complex is formed between V-(a-pyridyl)-2-thioquinaldamide (120), vanadate ions and H2O2 that becomes fluorescent in acidic solution (Aex = 340 nm, An = 490 nm). This reaction, originally developed for determination of V(V) in a FIA system, can be adapted for determination of H2O2 and organic peroxides. LOD for H2O2 is 0.05 p,M, with RSD 2.4% (ri = 3) at 1 p,M, with linearity in the 0.2 to 50 p,M range330. 

Analogous to the preceding cw-dioxovanadium(V)-catalyzed system of bromide oxidation by dihydrogen peroxide, Secco carried out a detailed kinetic analysis of vanadate-catalyzed oxidation of iodide by dihydrogen peroxide [75], Peroxovanadate species (i.e., V0[02]+ and V0[02]2 ) or their hydronated forms oxidize iodide in acidic aqueous solution, forming V02+ and V0(02)+, respectively however, once V0(02)+ and V0(02)2 are consumed, iodide reduces... 

It is possible to measure the formation of various radicals such as reactive oxygen species in cells. Reactive oxygen species (ROS) activate the nuclear factor of activated T cell transcription factor (NFAT), which is associated with its dephosphorylation, nuclear translocation, and increased affinity for DNA binding. Vanadium activation of nuclear factor of activated T cells (NFAT) was found to correlate with formation of the ROS H202 and was dependent upon the activity of calcium channels [39], In activated human neutrophiles, vanadium(II), (III), and (IV) increased hydroxyl radical formation and attenuation of myeloperoxidase activity, whereas V(V) did not show these effects. Similar results were seen in a cell-free system [40], Increased lipid peroxidation in liver but not in kidneys was found in normal rats treated with vanadate [41]. 

This book does not follow a chronological sequence but rather builds up in a hierarchy of complexity. Some basic principles of 51V NMR spectroscopy are discussed this is followed by a description of the self-condensation reactions of vanadate itself. The reactions with simple monodentate ligands are then described, and this proceeds to more complicated systems such as diols, -hydroxy acids, amino acids, peptides, and so on. Aspects of this sequence are later revisited but with interest now directed toward the influence of ligand electronic properties on coordination and reactivity. The influences of ligands, particularly those of hydrogen peroxide and hydroxyl amine, on heteroligand reactivity are compared and contrasted. There is a brief discussion of the vanadium-dependent haloperoxidases and model systems. There is also some discussion of vanadium in the environment and of some technological applications. Because vanadium pollution is inextricably linked to vanadium(V) chemistry, some discussion of vanadium as a pollutant is provided. This book provides only a very brief discussion of vanadium oxidation states other than V(V) and also does not discuss vanadium redox activity, except in a peripheral manner where required. It does, however, briefly cover the catalytic reactions of peroxovanadates and haloperoxidases model compounds. 

In contrast to the systems addressed above (i.e. those containing the ligands lactate, citrate or alanylserine), the coordination of alanylhistidine to vanadate is drastically enhanced by concomitant coordination of peroxide, a fact which also applies to the coordination of imidazole, which, in the absence of peroxide, forms only very weak complexes with vanadate. In the ternary system peroxide-vanadate-alanylhistidine, the predominant complex between pH 4 and 9 is V( 2)2(ala-his). In the peroxovanadates, alanylhistidine coordinates through Ne (Figure 2.15).P 1... 

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