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

We have investigated the solvent effects on the relative free energies of s olvation for Ba2+ to Sr2+ ion mutation in the solvents using a Monte Carlo simulation of statistical perturbation theory (SPT) study. For the reliabil ity of our computed results, we compared the relative free energies for int erconversion of Ba2+ to Sr2+, in H2O (TIP4P) in this study with those of th e published works, that in H2O (TIP4P) is -30.24 +/- 0.21 kcal mol(-1) in t his study, those of the published works in H2O are -31.3 +/- 3.7, -24.9, an d -30.3 +/- 0.4 kcal mol(-1) and that of experimental work is -30.8 kcal mo l(-1), respectively. There is good agreement among the several studies, tak ing 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 vs. the Onsager dielectric function of bulk solvents decrease with increasing Onsager dielectric function of bulk solvents excep t for CH3OH, THF and MEOME. The relative free energies of solvation Ba2+ an d Sr2+ ions in CH3OH, THF and MEOME could be explained by the strong ion-so lvent interactions existing in CH3OH, THF and MEOME solutions. The strong i on-solvent interactions in CH3OH, THF and MEOME could be due to the electro n 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 a nd Solvent Effects in Organic Chemistry, VCH, Weinheim, 2nd edn., 1988, p. 20). There is also good agreement between the calculated structural propert ies in this study and the published works obtained by density functional th eory, computer simulations and experiment.