Formation and structure in aqueous solution of complexes between vanadium(V) and aminohydroxamic acids that potentiates vanadium’s insulinomimetic activity: l-glutamic γ-hydroxamic and l-aspartic-β-hydroxamic acids

Abstract

The full speciation of the vanadium(V) complexation systems with two aminohydroxamic acids, aspartic-β- and glutamic-γ-hydroxamic acid, has been determined using potentiometric and spectroscopic techniques. Formation constants were calculated in a systematic study at different ligand to metal molar ratios and the coordination types are proposed. An almost constant value of the 51V NMR signal in neutral medium can be attributed to two (1:1 and 1:2 metal to ligand ratios) similar structures, both of which can be either protonated or deprotonated. The two ligands have a carboxylic group in the structure and show comparable biological activities. In this work analogous complexation behavior at physiological conditions was found despite the presence of two or three methylenic groups between the amino and hydroxamate groups. The carboxylic groups are quite distant from the hydroxamic groups and are not involved directly in the coordination process. Therefore the coordination structures are related to that found in the vanadium(V)-β-alaninehydroxamic acid in which there is not a carboxylic group.