REACTIONS OF PEROXOVANADATES WITH AMINO-ACIDS AND RELATED-COMPOUNDS IN AQUEOUS-SOLUTION

H-1 and V-51 NMR spectroscopy has been used to study the reactions occ urring between mono- and diperoxovanadate and a number of amino acids in aqueous solution. Concentration and pH studies were undertaken in o rder to establish product stoichiometry and proton requirements. The r esults revealed two distinct modes of interactions, dependent on wheth er the vanadate precursor contained one or two peroxide ligands. Monop eroxovanadate reacted with amino acids such as glycine or proline to g ive two types of bis(amino acid) products. One product had both of the amino acids attached in a bidentate manner while the second type of p roduct had the first amino acid complexed as a bidentate ligand and th e second attached only through the amino group. No reaction of monoper oxovanadate with imidazole or the imidazole ring of histidine was obse rved. In contrast to the results with monoperoxovanadate, no bidentate complexation of amino acids with diperoxovanadate was observed. Compl exation occurred through either the carboxyl or the amino groups, with attachment at the amino position being favored. Imidazole, as the fre e ligand or as the side chain in histidine, was found to complex stron gly to diperoxovanadate, as did N-methylimidazole and also pyridine, t he latter to a lesser extent. Only a weak reaction with tryptophan was observed. The relevance of some aspects of this work to the function of vanadium haloperoxidases is discussed.