Electrochemical reduction of copper complexes with glycine, alanine and valine

Abstract

Basic electrochemical studies of coordination complexes between cupric ions and simple amino acids as ligands (L), namely glycine, alanine and valine, have been carried out to provide insight in the effect of complexation on Cu2+ discharge electrochemistry. The results show that there are strong differences in their cyclic voltammograms, despite the similarities in coordination equilibrium, central atom d electronic structure and inner sphere coordination distances (verified by chemical equilibrium quantification, UV spectroscopy and EXAFS). Evidence of mass transport limitations by diffusion of the neutral CuL2 complexes in solution, and cuprous species generation on the electrode during copper electrodeposition was found, both of which proved to be the main phenomena accounting for the different electrochemical behaviour previously mentioned. Voltammetric studies also showed that, surprisingly, cuprous species are produced not only at the onset of copper electroreduction but at more cathodic potentials. Furthermore, results suggest the existence of a cuprous compound layer beneath the metallic copper deposit. The data gathered in this investigation, leads to the conclusion that the bigger molecular size and organic nature of the ligands induce unexpected processes on the copper electroreduction mechanism.