Solvent effect on Sr 2+ to Ca 2+ ion mutation: Monte Carlo simulation study

Abstract

We have investigated the solvent effects on the relative free energies of solvation and the difference in partition coefficients of Sr 2+/Ca 2+ mutated to each other in solvents using Monte Carlo simulations with statistical perturbation theory study. Comparing the relative free energies for interconversion of Sr 2+ to Ca 2+, in H 2O (TIP3P), in this study with those of the published works, that of H 2O (TIP3P) is −35.60±0.13 kcal/mol in this study, those of the published works in H 2O are −34.7, −37.5, and −38.8 kcal/mol and that of experimental is −34.9 kcal/mol, respectively. There is a good agreement among the several studies. For the present Sr 2+/Ca 2+ ion pair, the relative free energies of solvation vs. Born’s function of the solvents decreased with increasing Born’s function except for CH 3OH, THF and MEOME. The relative free energies of solvation Sr 2+/Ca 2+ pair in CH 3OH, THF and MEOME could be explained by the strong ion–solvent interactions existing in CH 3OH, THF and MEOME solutions. The strong ion–solvent interactions in CH 3OH, THF and MEOME solutions could be due to the electron pair donor properties of the solvents to ion, i.e., donor number of CH 3OH, THF and MEOME established by Gutmann. There is also a good agreement between the calculated structural properties in this study and the published results obtained by ab initio, computer simulations and experimental works.