Nickel(II) complexes of oligopeptides containing aspartyl and glutamyl residues. Potentiometric and spectroscopic studies

摘要

Nickel(II) complexes of di-, tri- and tetra-peptides built up from Asp and/or Glu residues have been studied by potentiometric, UV-Vis and circular dichroism spectroscopic methods. The stoichiometry of the complexes are the same as in the case of common oligopeptides, but the presence of the side chain carboxylate groups results in differences in their stabilities and coordination modes. The presence of the beta-carboxylate groups increases the metal binding affinity of the peptides in all cases. This is due to the coordination of the first, second and third aspartic acid residue in the case of the NiL, NiH_1L and NiH_2L complexes, respectively. The high negative charge of Asp(4) suppresses the metal ion coordination of the third amide function, therefore the NiH_3L complex does not form with this tetrapeptide. In the case of peptides containing glutamic acid, no stability enhancement appears because there is only a weak interaction between the nickel(II) ion and the gamma-carboxylate group, which is not able to compensate the disfavoured effect of the increasing negative charge of the complexes. (c) 2006 Elsevier Ltd. All rights reserved.