Oxovanadium(IV) and amino acids—IV. The systems l-cysteine or d-penicillamine+VO 2+; a potentiometric and spectroscopic study

Abstract

The aqueous equilibria in the systems l-cysteine or d-penicillamine + VO 2+ have been studied by a combination of pH-potentiometric and spectroscopic methods [electron paramagnetic resonance (EPR), visible absorption and circular dichroism (CD)] in the pH range 1.8–13.5. For pH > 4, high ligand-to-metal ratios were used. The results of the various methods are made self-consistent, then rationalized assuming an equilibrium model including species MLH 2, ML 2H 4, ML 2H 3, ML 2H 2, ML 2H, ML 2, ML 2H −1 and M 2L 2 (where H 2L denotes either l-cysteine or d-penicillamine) and several hydrolysis products; their formation constants and individual electronic spectra (isotropic and CD) are given. Isomeric structures are discussed for each stoichiometry.