Interaction of Cu+ and Cu2+ ions with a-alanine. A density functional study

The Cu+ and Cu2+ preferred binding sites on a-alanine and their affinity values for this amino acid were determined at the density functional level using three different hybrid exchange correlation potentials and the 6–311++G∗∗ basis set. The results demonstrated that the two ions both give stable complexes with a-alanine but the stability order of the metalated species and the coordination sites are different depending on the nature of the cation. In particular, the Cu+ –a-alanine ground-state structure is characterized by an h2-N,O coordination with the nitrogen and oxygen atoms belonging to the amino and carbonyl groups, respectively. In contrast, the most stable complex of the Cu2+ –a-alanine system has an h2-O,O coordination with the cation bonded to the —CO2 − moiety of the zwitterionic form of the amino acid. Comparison with the Cu+ and Cu2+ affinity values for glycine, computed at the same levels of theory, demonstrated that the relative values do not change significantly as different hybrid functionals are used, although the absolute affinities are strongly influenced by the choice of the hybrid potential.