Molecular interactions between glycine and H2O affording the zwitterion

Isomerization reactions of glycine were studied computationally. Three water molecules were found to cause the reaction of glycine with the anti carboxyl group. For the glycine with the syn carboxyl group, three and one molecules are concerned with the reaction; one acts as a catalyst to prevent the local proton transfer. A reaction model composed of glycine and eleven water molecules was examined. An "out-of-plane" path was found to be a favorable stepwise channel with two small activation energies. In the path, an ion-pair intermediate was obtained. From the intermediate, a proton may be relayed outward from the hydrogen-bond network. The possibility of this proton dispersal was discussed in relation to experimental evidence of isoelectric points of zwitterions.