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 tran sfer of molecules from the gas phase to aqueous solution is developed and e xamined. This computational approach involves the calculation of the hydrop hobic part of the hydration entropy using the potential-dependent surface a rea of the solute. This contribution is augmented by an immobilization entr opy term that accounts for the ordering of the solvent dipoles near charged solutes of arbitrary shape. The entropic contributions to the hydration fr ee energies of 55 neutral and 70 ionic solutes at 298 K are calculated usin g the proposed algorithm and the results are compared to the available expe rimental data. In addition, it is shown that the hydration entropy contribu tes significantly to the total activation and reaction entropies of proton transfer and nucleophilic substitution reactions.