POTENTIOMETRIC AND SPECTROSCOPIC STUDIES ON THE COPPER(II) AND NICKEL(II) COMPLEXES OF TRIPEPTIDES OF METHIONINE

Copper(II) and nickel(II) complexes of tripeptides containing methioni ne (MetGlyGly, GlyMetGly, GlyGlyMet, MetMetAla, MetGlyMet and MetMetMe t) were studied by potentiometric, UV-Vis and EPR spectroscopic method s. It was found that donor atoms of the peptide backbone (amino and am ide nitrogens and carbonyl or carboxylate oxygens) are the primary bin ding sites in all cases, but the thioether groups of methionyl residue s also make some contribution to metal binding. In the case of copper( II) it was concluded that coordination of sulfur atoms depends on the number and location of methionyl residues in the molecule and S(thioet her) --> Cu(II) charge transfer bands were detected in the species [Cu L](+), [CuLH-1] and [CuLH-2](-) of peptides containing N-terminal meth ionine, internal methionine and C-terminal methionine, respectively. N ickel(II) forms stable square-planar, diamagnetic complexes with all t ripeptides with the stoichiometry of [NiLH-2](-) and metal ion coordin ation of the thioether residue was concluded only in the octahedral [N iL](+) species of peptides containing N-terminal methionine. (C) 1998 Elsevier Science S.A. All rights reserved.