Thermal stabilities of the microhydrated zwitterionic glycine: a kinetics and dynamics study

Thermal stabilities of the zwitterionic glycine (zg) combined with water molecules are investigated by both ab initio/RRKM calculations and the thermostatic molecular dynamics (MD) simulations. The microhydrated zg clusters, zg-nw (n = 2, 3; w = water), can transfer to the canonical clusters cg-nw through the rapid intramolecular proton transfers (PT), while the proton is shifted via the intermolecular hydrogen bonds for zg-4w --> cg-4w. Both the MD/solution model simulations and the RRKM calculations indicate that the zg and cg conformers hydrated with more water molecules have their respective higher stabilties and the transformation needs to overcome a certain energy barrier. The thermostatic MD simulations show that the dynamic PT processes are significantly influenced by both the temperatures used in the trajectory simulations and the hydrogen bonding arrangements between glycine and water molecules.