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

Abstract

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, D_e 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.