Proton transfer induced by receding water in Glycine---(Water)$_{2}$ Complex

We investigate molecular co-operativity in the zwitterionic configuration of Glycine (Gly) with two proximal water molecules, Gly---(Water)$_{2}$, by deliberately making one of the water molecules recede from the remaining complex. The consequent intra-molecular proton transfer that renders the zwitterionic configuration into a neutral one is viewed under two scalar field descriptors: Molecular Electrostatic Potential (MESP), reflecting the modifications in the environment and the HOMO (highest occupied molecular orbital) electron density. We quantify the process further by energetics, through a many-body analysis of the interaction energy as well as salient IR spectral signatures associated with the proton-transfer. While we employ the decent MP2/aug-cc-pvDZ level of theory to seek optimal structures, it is gratifying that a prescription within density functional theory (DFT) also provides a reliable description of this process.