Calculations of hydration entropies of hydrophobic, polar, and ionic solutes in the framework of the Langevin dipoles solvation model

A Langevin dipoles solvation model that can determine the entropies of transfer of molecules from the gas phase to aqueous solution is developed and examined. This computational approach involves the calculation of the hydrophobic part of the hydration entropy using the potential-dependent surface area of the solute. This contribution is augmented by an immobilization entropy term that accounts for the ordering of the solvent dipoles near charged solutes of arbitrary shape. The entropic contributions to the hydration free energies of 55 neutral and 70 ionic solutes at 298 K are calculated using the proposed algorithm and the results are compared to the available experimental data. In addition, it is shown that the hydration entropy contributes significantly to the total activation and reaction entropies of proton transfer and nucleophilic substitution reactions.