A Monte Carlo simulation study of solvent effect on Ba2+ to Sr2+ ion mutation

Abstract

We have investigated the solvent effects on the relative free energies of solvation for Ba²⁺ to Sr²⁺ ion mutation in the solvents using a Monte Carlo simulation of statistical perturbation theory (SPT) study. For the reliability of our computed results, we compared the relative free energies for interconversion of Ba²⁺ to Sr²⁺, in H₂O (TIP4P) in this study with those of the published works, that in H₂O (TIP4P) is −30.24±0.21 kcal mol⁻¹ in this study, those of the published works in H₂O are −31.3±3.7, −24.9, and −30.3±0.4 kcal mol⁻¹ and that of experimental work is −30.8 kcal mol⁻¹, respectively. There is good agreement among the several studies, taking into account both methods of obtaining hydration free energies and the standard deviations. For the present Ba²⁺ and Sr²⁺ ions, the relative free energies of solvation s. the Onsager dielectric function of bulk solvents decrease with increasing Onsager dielectric function of bulk solvents except for CH₃OH, THF and MEOME. The relative free energies of solvation Ba²⁺ and Sr²⁺ ions in CH₃OH, THF and MEOME could be explained by the strong ion–solvent interactions existing in CH₃OH, THF and MEOME solutions. The strong ion–solvent interactions in CH₃OH, THF and MEOME could be due to the electron pair donor properties of the solvents to the ion i.e., donor number (DN) of CH₃OH, THF and MEOME established by Gutmann (in R. Christian, Solvents and Solvent Effects in Organic Chemistry, VCH, Weinheim, 2nd edn., 1988, p. 20). There is also good agreement between the calculated structural properties in this study and the published works obtained by density functional theory, computer simulations and experiment.