Microsolvation of lysine by water: computational study of stabilized zwitterion.

We present calculations for Lys-(H(2)O)(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-(H(2)O)(3) conformers, we suggest that both forms of Lys-(H(2)O)(3) may be observed in low temperature gas phase.

Efficiency of bulky protic solvent for SN2 reaction.

We calculate and compare the effects of aprotic vs protic solvent on the rate of SN2 reaction [F- + C3H7OMs--> C3H7F + OMs-]. We find that aprotic solvent acetonitrile is more efficient than a small protic solvent such as methanol. Bulky protic solvent (tert-butyl alcohol) is predicted to be quite efficient, giving the rate constant that is similar to that in CH3CN. Our calculated relative activation barriers of the SN2 reaction in methanol, tert-butyl alcohol, and CH3CN are in good agreement with experimental observations.