Studies on Copper-Acetylglycylglycine System.

Reported here are studies on the copper-acetylgylcylglycine system as a function of pH and the molar ratio between the ligand and the paramagnetic ion, applying potentiometric titration, magnetic resonances (esr and nmr) and spectrophotometric techniques. The results indicate that depending on the pH of the solutions there are three distinct regions characterized by their different species and behavior. In region I (pH less than 6.5), the copper is bound to the carboxylate group of the ligand molecule (the "blue" complex). Precipitation of copper occurs in region II (pH-7). In region III (pH greater than 9), in the presence of excess of ligand, the copper redissolves, forming complexes in which the central copper ion binds to the peptide molecule, through the nitrogens of the deprotonated peptide groups, and to hydroxyl ions. The mutual replacement of the peptide groups of chelated AcGlyGly by OH- and the changes in the structures of the complexes are discussed.