Stabilizing the zwitter-ionic form of amino acids in the gas phase: An ab initio study on the minimum number of solvents and ions

Second order Moller–Plesset perturbation theory with 6-311++G(d,p) as well as aug-cc-pvtz basis sets is applied to unearth the minimum number of solvent molecules or ions necessary to stabilize the zwitter-ionic form of amino acids by inhibiting the intra-molecular proton transfer. It is observed that the electrostatic interaction between the amino acids and solvents or ions is responsible for the stability of zwitter-ionic form. It is also observed that minimum two solvent (water and methanol) molecules and a single cation or anion are sufficient to stabilize the zwitter-ionic form of all the twenty standard amino acids.