Structures and stabilities of glycine and water complexes

Abstract

Structural elucidation, stability, properties and proton transfer processes of neutral and zwitterionic Gly(H2O)1-6 complexes are studied by ab initio calculations. Polarizable continuum model (PCM) is important for energy examination since solvent effects is sensitive to the energy. Glycine is fully solvated by five discrete water molecules under polarizable continuum model (PCM). The structure of neutral and zwitterionic Gly(H2O)1-6 complexes changes from a ring motif to a chain motif, and then to a cubic motif. The binding energy for neutral and zwitterionic Gly(H2O)1-6 complexes increases linearly as function of the number of water molecules increase, indicating Gly(H2O)1-6 complexes exhibit relatively higher stability. However, distortion of water molecules will cost more energy, leading to reduced binding energy per water molecule. The reduction is mainly attributed to the directivity and saturability of H-bonds. Importantly, we find the deprotonation of –NH2 for zwitterionic Gly(H2O)2-4 needs ~10 kcal/mol, which is consistent with the experiments.