Effects of Microsolvating Water on the Stability of Zwitterionic vs. Canonical Diglycine

We present calculations for diglycine - (H2O), (n = 0-3) to examine the effects of microsolvating water on the relative stability of the zwitterionic vs. canonical forms of the dipeptide. We calculate the structures, energies and Gibbs free energies of the conformers at wB97XD/6-311++G** and MP2/aug-cc-pvdz levels of theory level of theory. We predict that microsolvation by up to three water molecules does not give thermodynamic stability of the zwitterion relative to the canonical forms. Our calculations also suggest that zwitterionic diglycine - (H2O)(3) is not stable kinetically in low temperature gas phase environment.