AN NMR INVESTIGATION OF THE INTERACTIONS OCCURRING BETWEEN PEROXOVANADATES AND PEPTIDES

V-51 nuclear magnetic resonance has been used in the investigation of the reactions which occur between peroxovanadates and simple peptides and other small molecules in aqueous solution. Variation of the concentration of the reactants and changes in the pH of the solutions allowed product stoichiometry, protonation states, and equilibrium constants to be determined. It was found that the diperoxovanadate VO(OO)2(H2O)2- readily formed monodentate complexes with both the amino and carboxylate functionalities of the peptides. A linear free energy relationship between the formation constants of the products and the pk(a) values of the conjugate acids of the reactant groups was observed. This relationship showed that product formation was favored by stronger electron-donating ligands. Inhibition of the vanadate-catalyzed decomposition of hydrogen peroxide by peptides was studied by V-51 NMR and UV spectroscopy. The results were consistent with the formation of a monoperoxopeptidovanadate as the inhibiting species. It was found that the terminal amino and carboxylate functionalities and an amide N-H in the peptide bond were all required for the peptide-induced inhibition to occur. The relevance of these results to some aspects of the biochemical function of peroxovanadates is discussed.