Interactions of peptides with metallic cations.: I.: Complexes glycylglycine-M+ (M=Li, Na)

In view of better understanding interactions of aminoacids and peptides with metallic cations, in the isolated state and in water, the model system glycylglycine-M+ (M = Li, Na) has been studied theoretically. The computations have been performed with the help of the density functional theory (DFT) and the B3LYP functional. The extended basis set was the standard 6-31 + + G**. In solution we used a recent model of continuum with a multicentric multipole expansion of the charge distribution. Our study shows that low energy complexes with lithium and sodium are rather similar. In the isolated state, the most stable form corresponds to a bidentate complex in which the cation interacts with two oxygen atoms, one from the terminal COOH and one from the amidic carbonyl. In solution, the coordination of the cation in the most stable form is 3, the nitrogen of the end amino group being the third ligand. The energy range between the lowest energy structure and the highest energy one, in both cases, is slightly reduced under the electrostatic influence of the solvent. (C) 2004 Elsevier B.V. All rights reserved.