Microsolvation of Lysine by Water: Computational Study of Stabilized Zwitterion

We present calculations for Lys-(H2O)(n) (n = 2, 3) to examine the effects of microsolvating water on the relative stability of the zwitterionic vs canonical forms of Lys. We calculate the structures, energies, and Gibbs free energies of the conformers at the B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p), and MP2/aug-cc-pvdz levels of theory, finding that three water molecules are required to stabilize the Lys zwitterion. By calculating the barriers of the canonical zwitterionic pathways of Lys-(H2O)(3) conformers, we suggest that both forms of Lys-(H2O)(3) may be observed in low temperature gas phase.