Building the first hydration shell of deprotonated glycine by the MCMM and ab initio methods.

The first hydration shell of the deprotonated glycine is built up by the discrete hydration model. The potential energy surfaces (PESs) of the deprotonated glycine and its hydration complexes with different number of water molecules have been scanned by the Monte Carlo multiple minimum (MCMM) conformational search analysis with the MMFFs force field. Then the energy-minimized structures are predicted using the high-level ab initio calculations/MP2/6-311++G(d,p). The results of the structural parameters and the infrared spectra indicate that the first-shell water molecules around the anion of deprotonated glycine play a more important role in determining the hydration process of deprotonated glycine. The competition between the hydrate site I and the hydrate site II represents a dynamic process of hydrated complexes. The vibrational properties of C═O and N-H are determined to characterize the structure of deprotonated glycine in solution by the discrete hydration model and the conductor-like polarizable continuum model (CPCM) in the gas phase, respectively.