Effects of Microsolvation on the Stability of Zwitterionic Valine

We present calculations for valine (Val) - (H2O)(n) (n = 0-5) to examine the effects of microsolvating water on the relative stability of the zwitterionic vs. canonical forms of Val. We calculate the structures, energies and Gibbs free energies of the conformers at B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p) and MP2/aug-cc-pvdz level of theory. We find that five water molecules are needed to stabilize the zwitterionic form of Val. By calculating the barriers of the canonical <-> zwitterionic pathways of Val - (H2O)(5) conformers, we suggest that both forms of Val - (H2O)(5) may be observed in low temperature gas phase