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), ?-Asp-BIMA, ?-Glu-BIMA, ?-Glu-BIMA and ?-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 ?-Asp-BIMA and ?-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 (?-Asp-BIMA, ?-Glu-BIMA and ?-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.