Copper(II) complexes of opiate-like food peptides

The alpha-casein peptide fragment (90-96) Arg-Tyr-Leu-Gly-Tyr-Leu-Glu, one of the exorphins called "food hormones", is an efficient ligand for Cu-II ions. Potentiometric and spectroscopic studies on aqueous solutions indicate that, depending on the pH range, complex species with different coordination modes (involving the amino and the deprotonated amide groups) are formed. The phenolate side chain of the Tyr residue is not involved in the metal coordination.