Coordination properties of glycylglycine to Cu+, Ni+ and Co+. Influence of metal cation electronic configuration

The structure, vibrational frequencies and binding energies of the complexes formed by the interaction of Cu+(d10, 1S), Ni+(d9, 2D) and Co+(d8, 3F and 1G) with glycylglycine have been theoretically determined. The most stable structure of Cu+–glycylglycine is bicoordinated with the Cu+ cation interacting with the terminal carbonyl oxygen and the amino group. However, for Ni+–glycylglycine and Co+–glycylglycine the lowest energy structures are tricoordinated, the interaction of the metal cation given by the same groups of Cu+-glycylglycine plus the nitrogen or oxygen atoms of the peptide bond. As for glycine, De values follow the order Ni+ > Co+ (triplet) ∼ Cu+, but the interaction energies are about 11–13 kcal mol−1 larger. Differences on the coordination properties of the metal cations are discussed and interpreted according to their electronic structure.