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

Copper(II) complexes of amino acid derivatives of bis(imidazol-2-yl)methylamine (BIMA), alpha-Asp-BIMA, alpha-Glu-BIMA, gamma-Glu-BIMA and beta-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 [Cu(2)L(2)](2+) species was detected in an equimolar solution of alpha-Asp-BIMA and gamma-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 (alpha-Asp-BIMA, alpha-Glu-BIMA and gamma-Ala-BIMA), resulting in the formation of dinuclear [Cu(2)H(-2)L(2)] species with imidazole bridging. For these 3 ligands, deprotonation of the pyrrole-type nitrogen was observed and the existence of a trinuclear species [Cu(3)H(-4)L(2)] was assumed in alkaline solution. This species contains negatively charged imidazolato bridges.