Potentiometric and spectroscopic studies on transition metal complexes of bis(imidazolyl) and bis(pyridyl) derivatives of amino acids.

Copper(II) and zinc(II) complexes of H-Gly-BIMA (glycinamido-bis(imidazol-2-yl)methane) and copper(II), nickel(II), cobalt(II) and zinc(II) complexes of Prodipa (prolineamido-bis(pyridin-2-yl)methane) were studied by potentiometry, electron paramagnetic resonance and visible spectroscopy. The data revealed that both ligands are ambidentate. Imidazole and pyridine nitrogens of H-Gly-BIMA and Prodipa, respectively, are the exclusive binding sites in acidic media, but the metal binding ability of the bis(imidazolyl) residue is much higher than that of the bis(pyridyl) ligand. The coordination of the amino, amide and imidazole/pyridine nitrogens was concluded around physiological pH, which resulted in the formation of an imidazole bridged dimeric species in the case of H-Gly-BIMA.