Electrochemical and SOD activity studies of copper(II) complexes of bis(imidazol-2-yl) derivatives

Ligands containing the bis(imidazol-2-yl) moiety form very stable bis(ligand) [CuHxL2] (x = 0-4) copper(II) complexes, with the coordination of four imidazole nitrogens. Moreover, in the presence of excess metal ion, a trinuclear species with an imidazolato bridge is formed in the case of some amino- and peptide derivatives of the bis(imidazol-2-yl) group (e.g. His-BIMA). The coordination mode of the copper(II) ion in these complexes could mimic the binding of the metal ion in the active centre of the CuZnSOD enzyme. In order to reinforce these assumptions, electrochemical and SOD activity studies of copper(11) complexes of three simple bis(imidazol-2-yl) ligands (BIM, BIMA and BIP) and five amino acid derivatives containing the bis(imidazol-2-yl) group (Z-Gly-BIMA, Z-Ala-BIMA, Gly-BIMA, beta-Ala-BIMA and His-BIMA) were carried out. The measured redox potential values characterizing the [CuHxL2] (x = 0-2) complexes of bis(imidazol-2-yl) derivatives, where the metal ion is bound through imidazole nitrogens, are around 0 V, and a linear trend can be observed between the formal potential and the logarithmic value of the stability constants. It was not possible to determine the redox parameters of the polynuclear complex of His-BIMA. The SOD activity measurements of the bis(ligand) and trinuclear complexes show that the relative activity values characterizing the activity of the four imidazole coordinated bis(ligand) complexes are not so high, in agreement with their stabilities and formal potentials. The relative activity value of the imidazolato bridged [Cu3H-4L2] complex of His-BIMA is, however, higher than the ones published in the literature. (C) 2013 Elsevier Ltd. All rights reserved.