On the validity of dielectric continuum models in application to solvation in molecular solvents

Abstract

We report Monte Carlo simulations of solvation of a point dipole in dipolar–quadrupolar solvents of varying dipole moment and axial quadrupole. The simulations are carried out to test the prediction of dielectric solvation models of a monotonic increase of the absolute value of the solvation chemical potential |μp| with the solvent dielectric constant ε. Dielectric constants are obtained from pure liquid simulations carried out for each solvent used in solvation simulations. A raising dependence of |μp| on ε, in qualitative agreement with dielectric solvation models, is seen when the solvent dipole moment is varied at constant solvent quadrupole. An increase in the axial quadrupole at constant solvent dipole reduces the dielectric constant at the same time leading to higher |μp| values. The simulations and dielectric models thus give the opposite dependence on the solvent quadrupole for any solvent dipole. We also show that for solvation in dipolar–quadrupolar solvents the saturation limit |μp|→const at ε≫1 predicted by linear response dielectric continuum models actually occurs in the range of nonlinear solvation.