Potentiometric and spectroscopic studies on transition metal complexes of GlyLys(Gly) and Asp-ε-Lys

Abstract

Copper(II), nickel(II) and zinc(II) complexes of the peptides GlyLys(Gly) and Asp-ε-Lys, containing the amide functions at the ε-amino groups of the lysyl residues were studied by potentiometric, UV-VIS and EPR spectroscopic methods. The stoichiometry of the major species formed in the copper(II)–GlyLys(Gly) system is [CuH₋₁L] and the EPR spectroscopic data indicate the existence of two isomeric forms of the complex. The nickel(II) and zinc(II)–GlyLys(Gly) systems have been characterised by the formation of stable [ML]⁺ complexes containing bis(NH₂,CO) co-ordination and a macrochelate. Deprotonation and co-ordination of the amide groups were detected in the copper(II) and nickel(II) complexes. The co-ordination chemistry of Asp-ε-Lys is best described by the metal binding ability of the amino acid residues and it's high affinity for dimerisation. The stoichiometry of the dinuclear complexes can be given as [M₂L₂], containing only amino acid binding sites. Deprotonation and co-ordination of the amide functions were suggested only in the copper(II)-containing systems, resulting in the formation of the [Cu₂H₋₂L₂]²⁻ dinuclear complex.