Reactivity of copper(II) peptide complexes with bioligands (benzimidazole and creatinine)

Abstract

The nature of the peptide seems to be a very important factor for the reactivity of copper(II) peptide complexes with bioligands. Thus, although we have tried to obtain all the ternary complexes derived from the dipeptides l-ala-gly, gly- l-tyr and gly- l-trp with benzimidazole and creatinine, only four new ternary Cu(II) peptide complexes have been obtained: [Cu(gly- l-tyr)(benzimidazole)] · H 2O ( 1), [Cu( l-ala-gly)(benzimidazole)] · 3H 2O ( 2), [Cu(gly- l-trp) (creatinine)] · 1.25H 2O ( 4) and [Cu( l-ala-gly)(H 2O)(creatinine)] · 2H 2O ( 5). Compounds 1, 2 and 4 exist as slightly distorted square planar complexes with the four coordination sites occupied by the tridentate peptide dianion and a nitrogen of the ligand, while compound 5 present a square pyramidal co-ordination in which the axial position is occupied by a water molecule. In the ternary benzimidazole complexes the lateral chain of the peptide moiety seems to determine the relative orientation of the ligand. In contrast, in the creatinine complexes the presence of two important intramolecular hydrogen bonds, involving the exocyclic NH 2 and CO groups of the creatinine molecule, yield a nearly co-planar system which is independent of the nature of the peptidic lateral chain. These compounds do not present catalase-like activity nor remarkable SOD-like activity but the values of IC 50 permit to distinguish a different behavior between benzimidazole and creatinine ternary complexes. Thus, benzimidazole compounds show lower IC 50 (similar to free Cu(II)) values than creatinine ones.