Potentiometric and spectroscopic studies on the copper(II) complexes formed by oligopeptides containing histidine with a protection at the terminal amino group.

Copper(II) complexes of oligopeptides with protected amino groups (Z-His-OH, Z-HisGly-OH, Z-GlyHis-OH and Z-GlyGlyHis-OH) were studied by potentiometric and spectroscopic methods. The involvement of the imidazole nitrogen in metal binding was proved in slightly acidic media. The deprotonation and coordination of the amide nitrogen atoms from the carbamate or peptide CONH- moieties occurred around pH 7, which resulted in the formation of 2N (Z-His-OH and Z-HisGly-OH), 3N (Z-GlyHis-OH) and 4N (Z-GlyGlyHis-OH) complexes supporting the anchoring ability of the imidazole rings. Ternary complexes with 2.2 ' -bipyridine, L-histidine or glycine (B) were also studied. The major species contained chelated B ligands, whereas the oligopeptide behaved as N-monodentate or ZN-bidentate. The outstanding stability of the 4N complex of Z-GlyGlyHis-OH ([CuH(-3)A](2-)) ruled out mixed complex formation at high pH values.