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Multiple reactions in vanadyl-V(IV) oxidation by $H_2O_2$

Shankar, Ravi HN and Ramasarma, T (1993) Multiple reactions in vanadyl-V(IV) oxidation by $H_2O_2$. In: Molecular and Cellular Biochemistry, 129 (1). pp. 9-29.

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Abstract

Oxidation of vanadyl sulfate by $H_2O_2$ involves multiple reactions at neutral pH conditions. The primary reaction was found to be oxidation of V(IV) to V(V) using 0.5 equivalent of $H_2O_2$, based on the loss of blue color and the visible spectrum. The loss of V(IV) and formation V(V) compounds were confirmed by ESR and $^{51}V$-NMR spectra, respectively. In the presence of excess $H_2O_2$ (more than two equivalents), the V(V) was converted into diperoxovanadate, the major end-product of these reactions, identified by changes in absorbance in ultraviolet region and by the specific chemical shift in NMR spectrum. The stoichiometric studies on the $H_2O_2$ consumed in this reaction support the occurrence of reactions of two-electron oxidation followed by complexing two molecules of $H_2O_2$. Addition of a variety of compounds—Tris, ethanol, mannitol, benzoate, formate (hydroxyl radical quenching), histidine, imidazole (singlet oxygen quenching), and citrate—stimulated a secondary reaction of oxygen-consumption that also used V(IV) as the reducing source. This reaction requires concomitant oxidation of vanadyl by $H_2O_2$, favoured at low $H_2O_2$:V(IV) ratio. Another secondary reaction of oxygen release was found to occur during vanadyl oxidation by $H_2O_2$ in acidic medium in which the end-product was not diperoxovanadate but appears to be a mixture of $VO^+_3$ (–546 ppm), $VO^{3+}$ (–531 ppm) and $VO_2^+$ (–512 ppm), as shown by the $^{51}V$-NMR spectrum. This reaction also occurred in phosphate-buffered medium but only on second addition of vanadyl. The compounds that stimulated the oxygen-consumption reaction were found to inhibit the oxygen-release reaction. A combination of these reactions occur depending on the proportion of the reactants (vanadyl and $H_2O_2$), the pH of the medium and the presence of some compounds that affect the secondary reactions.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Springer.
Keywords: vanadyl sulfate;H2O2;diperoxovanadate;vanadyl oxidation;O2-consumption;O2-release
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 24 Jun 2008
Last Modified: 19 Sep 2010 04:46
URI: http://eprints.iisc.ernet.in/id/eprint/14620

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