Copper coordination by polymers with glycylglycine, phenylalanine or methionine in the side chain: potentiometric and viscosimetric study

The coordination of copper(II) to polymers bearing glycylglycine, phenylalanine or methionine in their side chain was studied by potentiometry and viscosimetry. These polymers, which are not polypeptides, have carboxyl and amide group as potential binding sites in their side chain. They form a 2:1 COO:Cu complex in the lower pH range. The stability of this complex is in the order PPhe > PMet > PGlygly corresponding to the existence and stability of a compact conformation which exists for PPhe and PMet but not for PGlygly. The values of the stability constants decrease while the metal concentration increases. This is linked to the simultaneous viscosity decrease and was explained by increased steric strains in the collapsed polymer complex. At higher pH, potentiometric data indicate that deprotonation of the amide group occurs but the stoichiometry of the corresponding complex(es) cannot be obtained thanks to this technique although one amide group seemed to be deprotonated per copper ion.