Biosolvation Nature of Ionic Liquids: Molecular DynamicsSimulation of Methylated Nucleobases in Hydrated 1-Ethyl-3-methylimidazoliumAcetate

摘要

Solvation free energies of methylated nucleobases were calculated in pure and hydrated 1-ethyl-3-methylimidazolium acetate, [Emim][Ac], ionic liquid, and pure water using classical molecular dynamics simulations using multistate Bennett’s acceptance ratio method. The calculated solvation free energies in pure water were compared with the previous experimental and theoretical findings and found to be in agreement. We observe that the solvation free energy of methylated nucleobases is more in the pure ionic liquid compared to that in the pure water and on changing the mole fraction of water in the ionic liquid, the solvation free energy decreases gradually. Comparing the Coulombic and van der Waals contribution to the solvation free energy, electrostatic contribution is more compared to that of the latter for all nucleobases. To obtain the atomistic details and explain the solvation mechanism, we calculated radial distribution functions (RDFs), spatial distribution functions (SDFs), and stacking angle distribution of cations to the nucleobases. From RDFs and SDFs, we find that the acetate anions ofthe ionic liquid are forming strong hydrogen bonds with the aminehydrogen atoms of the nucleobases. These hydrogen bonds contributeto the major part of the Coulombic contribution to the solvation freeenergy. Stacking of cations to the nucleobases is primarily due tothe van der Waals contribution to the solvation free energy.