Synthesis, spectroscopic and voltammetric studies of mixed-ligand copper(II) complexes of amino acids

Abstract

Two Cu-II complexes of the type [Cu(L-1)(L-2)] (where L-1 = tryptophanate or phenylalaninate; L-2 = cysteine thiolate) have been prepared and characterised, and their spectrophotometric and voltammetric behaviour has been investigated. The results obtained by means of FT-IR, e.s.r., u.v.-vis. spectroscopy and by voltammetry revealed the existence of two different [Cu(L-1)(L-2)] complexes. A significance decrease in the g(parallel to) value and, concomitantly, an increase in the d-d transition energy was observed when a mixed-ligand complex is present. The observed anisotropic g-values indicate the presence of Cu-II in a tetragonally distorted octahedral geometry. Formation of a mixed-ligand copper complex can be considered as a type of synergism in the presence of cysteine. The redox state Cu-II or Cu-I of copper in the Cu(L-2) complex depends on the analysing conditions, i.e., cysteine forms a (CuI)-I-I complex under aerobic conditions and a Cu-I complex in anaerobic media. Tryptophan or phenylalanine is bound to Cu-II ions in the Cu(L-1) complexes.