Conformations and Metal Ion Affinities of Glutamine Binding with Alkali and Alkaline Earth Metal Cations: an ab initio Study

Conformations and reaction energetics are important for understanding the interactions be-tween biomolecules and metal ions. In this work, we report a systematic ab initio study on the conformations and metal ion affinities of glutamine (Gln) binding with alkali and alkaline earth metal ions. An efficient and reliable method of searching low energy conformations of metalated Gln is proposed and applied to the complexes of Gln.M^+/++ (M^+/++=Li⁺、Na⁺、K⁺、Rb⁺、Cs⁺、Be⁺⁺、Mg⁺⁺、Ca⁺⁺、Sr⁺⁺和Ba⁺⁺). In addition to all conformers known in literatures, many new important conformations are located, demonstrating the power of the new method and the necessity of the conformational search performed here. The metal coordination modes, relative energies, dipole moments, and equilibrium distribu-tions of all important conformations of Gln.M^+/++ are calculated by the methods of B3LYP, BHandHLYP, and MP2. IR spectra and metalation enthalpies and free energies are also pre-sented and compared with the available experiments. The results form an extensive database for systematic examination of the metalation properties of Gln.