Metal peptide complexes

Abstract

Deprotonated N(peptide) and N(amide) groups are very strong donors which help to stabilize the trivalent oxidation states of copper and nickel. The Cu(III,II) potentials are highly dependent on the nature of the coordinated peptide. The lower the electrode potential the slower the redox decomposition reaction of the Cu(III)-peptide to give Cu(II) and oxidized ligand. Methyl groups in place of hydrogens on α-carbon atoms decrease the thermal decomposition, but increase the photochemical decomposition with relatively high quantum yields (Φ) in both UV and visible. The Φ values and the redox products are wavelength dependent. The copper(III) peptides are four-coordinate, square planar complexes which are slow to undergo equatorial substitution. The Cu(III, II) electron transfer reactions are rapid and are enhanced by an inner-sphere axial path. The Ni(III)-peptide complexes are six-coordinate with tetragonal distortion. Axial substitutions are very labile while equatorial substitutions are sluggish. The Ni(III,II) electron transfer reactions are rapid and are also enhanced by an inner-sphere axial path. The Ni(III) peptides will add a second peptide or other chelating agents to form stable bis-peptide or ternary complexes. © 1983 IUPAC