Abstract :
A Monte Carlo simulation, with statistical perturbation theory (SPT) study, has been applied to explore the solvent effects on the relative free energies of solvation and the difference in partition coefficients (log P) for Na+/Li+ that are mutated to each other in solvents. We compared the relative free energies, for the interconversion of one ion pair, Na+ to Li+, in H2O (TIP4P), obtained in this study with those in the already published work. We found that in H2O (TIP4P), the value is −25.0 kcal/mol in this study and that in the published work, is −23.7±1.1 kcal/mol, obtained from the hydration free energies of Na+ (−98.5±0.5 kcal/mol) and Li+ (−122.2±0.6 kcal/mol), and that in the experimental is −23.9 kcal/mol, respectively. There is a good agreement among the three studies if we consider both the methods that are used to obtain the hydration free energies and standard deviations. There is also a good agreement between the calculated structural properties in this study and the published and experimental results. For the ion pairs considered, the solvent permittivity and the differences of solvation dominate the differences in the relative free energies of solvation and partition coefficients. It is also proved that five Monte Carlo statistical simulations using doublewide sampling are necessary for obtaining the results with precision, and fluid simulations are required in which, Na+ ion is mutated to Li+ ion in several solvents.
