Solution Structure of Oligopeptides-Copper(II) Complexes
Combined Potentiometric and spectroscopic studies on the solution equilibria of the copper(II) ion and various hexapeptide-containing systems revealed that CD measurements in the copper(II) d-d transition region are useful for the determination of the coordinating donor groups of the ligand molecules, i.e. the coordination structure . The systematic variation of the place of amino acids with coordinating and non-coordinating side chains in the amino acid sequence as well as the presence and the absence of these resulted in series of CD spectra, the comparison of which gave us the primary information on the coordination mode. The additivity of the chiral contributions of the ligands to the optical activity in the d-d bands have been suggested for some copper(II) tripeptide complexes, assuming that only one complex species exists in the measured solution under specified conditions . But published molar CD spectra are mostly not molar regarding the individual complex species, but characteristic for a mixture of several coexisting species. The relatively good agreement of the spectra of the above mentioned tripeptide systems encouraged us to perform measurements in the systems containing copper(II) and glycine-L-alanine tripeptides of various sequences, such as Gly-Gly-Ala, Gly-Ala-Gly, Ala-Gly-Gly and Ala-Ala-Ala.