Vanadate coordination, hydrogen peroxide

Coordination of vanadate by hydroxylamines is similar in many respects to coordination by hydrogen peroxide. Various hydroxylamine complexes are known, although only detailed studies of the aqueous chemistry have been carried out with hydroxylamine and its A -melhyl and A,A-dimcthyl derivatives. -substitution apparently has only a small influence on product formation. There is, however, scope for a wider range of isomeric forms with the A-methylated ligand compared to the unsubstituted and dimethylated ligands, and a number of isomers have been observed... 

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. 

Structure and Functions. The VHPOs contain vanadate(V) H2VO4 = V0(0)(0H)2 in their active site. Vanadium is covalently bonded to the Ns of the imidazole moiety of a histidine constituent of the protein, with the vanadium center in a trigonal-bipyramidal environment (Figs. 1 and 2). At pH 8.5, the dissociation constant is ca 45 nM. Oxidant is hydrogen peroxide, which is reduced to water. Hydrogenperoxide is activated by coordination to vanadium, forming a hydroperoxo species V0(0H)(H02)+ (eq. la) in a distorted tetragonal pyramidal... 

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