Copper(II) interaction with tetrapeptides containing proline and phenylalanine: A potentiometric and spectrophotometric study

Abstract

The synthesis of four tetrapeptides, L-Phe-L-Pro-Gly-Gly, Gly-L-Pro-L-Phe-Gly, Gly-L-Pro-D-Phe-Gly, and Gly-L-Pro-Gly-L-Phe is described. The hydrogen ion and copper(II) complex formation constants have been measured at 25°C and I = 0.10 mol dm −3 (KNO 3). Circular dichroism spectra have been recorded for copper(II)-peptide mixtures as a function of pH. The potentiometric and Spectrophotometric studies have been combined to ascertain the complex species over a broad pH range. The results obtained support the earlier suggestion on the specific role of a proline residue as a “break-point” in copper complex formation with peptides: the insertion of a proline residue into the second position of a tetrapeptide sequence leads to a novel coordination mode in Cu(II)-tetrapeptide systems.