A theoretical investigation of the hydrated glycine cation energetics and structures

Using a wide panel of quantum mechanical approaches, we have computed the structures and properties of protonated glycine-water complexes. It turns out that (1) MP2 is the minimum theoretical level to get accurate hydration energies; (2) anharmonicity strongly influences the vibrational spectra but has no impact on the complexation energy; (3) the correction of basis set superposition error significantly modifies both the energetic and entropic terms; and (4) 6-31+G(d) is the necessary minimal basis set. Using our best level of theory, we have obtained theoretical hydration enthalpies that are in perfect agreement with the most recent experimental investigations.