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 occurring between mono- and diperoxovanadate and a number of amino acids in aqueous solution. Concentration and pH studies were undertaken in order to establish product stoichiometry and proton requirements. The results revealed two distinct modes of interactions, dependent on whether the vanadate precursor contained one or two peroxide ligands. Monoperoxovanadate reacted with amino acids such as glycine or proline to give 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 product had the first amino acid complexed as a bidentate ligand and the second attached only through the amino group. No reaction of monoperoxovanadate with imidazole or the imidazole ring of histidine was observed. In contrast to the results with monoperoxovanadate, no bidentate complexation of amino acids with diperoxovanadate was observed. Complexation occurred through either the carboxyl or the amino groups, with attachment at the amino position being favored. Imidazole, as the free ligand or as the side chain in histidine, was found to complex strongly to diperoxovanadate, as did N-methylimidazole and also pyridine, the 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.