Copper(ii) complexes of amino acid derivatives of the bis(imidazol-2-yl)methyl residue

Abstract

Copper(II) complexes of amino acid derivatives of bis(imidazol-2-yl)methylamine (BIMA), α-Asp–BIMA, α-Glu–BIMA, γ-Glu–BIMA and β-Ala–BIMA, were studied by potentiometric, UV-VIS and EPR techniques. The bis(imidazol-2-yl)methyl residue is the main binding site in strong acidic medium in all cases. The formation of ligand-bridged dinuclear [Cu₂L₂]²⁺ species was detected in an equimolar solution of α-Asp–BIMA and γ-Glu–BIMA with binding of the N-terminal amino and carboxylate groups. The deprotonation of amide nitrogen takes place above pH 6 for the ligands containing an amide group in a chelatable position with terminal amino group (α-Asp–BIMA, α-Glu–BIMA and β-Ala–BIMA), resulting in the formation of dinuclear [Cu₂H₋₂L₂] species with imidazole bridging. For these 3 ligands, deprotonation of the pyrrole-type nitrogen was observed and the existence of a trinuclear species [Cu₃H₋₄L₂] was assumed in alkaline solution. This species contains negatively charged imidazolato bridges.