Ternary Coordination Complexes between Glycine, Copper (II), and Glycine Peptides in Aqueous Solution

• Published in: The Journal of biological chemistry Vol. 246; no. 19; pp. 5944 - 5951
• Main Authors: Martin, R P, Mosoni, L, Sarkar, B
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 10.10.1971
• Subjects: Autoradiography; Carbon Isotopes; Chemical Phenomena; Chemistry; Chromatography, Thin Layer; Copper; Dipeptides; Drug Stability; Glycine; Hydrogen-Ion Concentration; Kinetics; Mathematics; Models, Chemical; Models, Structural; Peptides; Potentiometry; Radioisotopes; Spectrophotometry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)61818-6

The equilibria involved in the ternary systems Cu(II)-A'-B and Cu(II)-A''-B (A' = glycylglycine, A'' = diglycylglycine, B = glycine) have been investigated by potentiometry in aqueous solution (1 m NaClO 4 ,25°). In addition to the binary complex species (MA', MH -1 A', MH -2 A', MH -1 A' 2 , M 2 H -3 A' 2 , MB, MB 2 , and MHA'', MA'', MH -1 A'', MH -2 A'', MA'' 2 , MH 2 A'' 2 , MH -1 A'' 2 , MH -2 A'' 2 , MB, MB 2 , respectively) two mixed complexes (MA'B, MH -1 A'B and MA''B, MH -1 A''B) were detected in each system. Their stability constants were refined with a general least squares treatment. In the case of an equimolecular mixture of the constituents, a maximum of about 50% of Cu(II) is present as MH -1 A'B at pH 10 to 10.5 and as MH -1 A''B at pH 8 to 10, when the concentration of each constituent is set equal to 10 -2 m . Mixed coordination enhances the stability of the complexes. The effect is greater in the case of diglycylglycine than glycylglycine. The absorption spectra of the individual species were computed from absorbance measurements made under conditions of pH and ligand ratio which maximized the concentrations of the various species. The position of the absorption bands of the mixed species compared to those of the corresponding binary species was consistent with an increase of the ligand field due to an NH 2 group entering into the coordination sphere of Cu(II). Mixed complex formation was also examined by the radiochromatographic studies utilizing 64 Cu(II), [ 14 C]glycine, and [ 14 C]glycine peptides.