TY - JOUR

T1 - Electrostatic free energy of solvation of an arbitrary charge distribution in the Block-Walker inhomogeneous dielectric

AU - Kono, Hirohiko

AU - Ohtsuki, Yukiyoshi

AU - Abe, Takehiro

PY - 1996/6/6

Y1 - 1996/6/6

N2 - We derive the expressions for the electrostatic free energy and entropy of an arbitrary charge distribution in the dielectric characterized by the distance-dependent Block-Walker (BW) permittivity function ∈r exp(-a In ∈rl r), where a is the solute radius and ∈r is the permittivity of the bulk solvent. This function describes well the effect of dielectric inhomogeneity (e.g., due to nonuniform spatial distribution of dipoles of solvent molecules). As the charge distribution deviates from the center of the solute cavity or as ∈r becomes smaller, the dielectric inhomogeneity gains in importance. The BW function well reproduces the observed free energies and entropies of solvation of univalent ions, without any parametric fittings: its mathematical form leads to appropriate effective radii of solvated ions and produces their sensitive dependence on temperature. We also try to microscopically interpret the BW model by comparing it with the mean spherical approximation (MSA) for the ion-dipolar system and propose the solvent scale BW (SBW) function ∈r exp[-(r2 ln ∈r)/(r - a + r2)], where r2 is the radius of the solvent molecule (when r2 = a, the SBW function is identical with the BW). Although the ion solvation energy for the SBW varies with r2 more moderately than the MSA, both models provide nearly the same effective radius of an ion, i.e., nearly the same free energy (entropy) of ion solvation.

AB - We derive the expressions for the electrostatic free energy and entropy of an arbitrary charge distribution in the dielectric characterized by the distance-dependent Block-Walker (BW) permittivity function ∈r exp(-a In ∈rl r), where a is the solute radius and ∈r is the permittivity of the bulk solvent. This function describes well the effect of dielectric inhomogeneity (e.g., due to nonuniform spatial distribution of dipoles of solvent molecules). As the charge distribution deviates from the center of the solute cavity or as ∈r becomes smaller, the dielectric inhomogeneity gains in importance. The BW function well reproduces the observed free energies and entropies of solvation of univalent ions, without any parametric fittings: its mathematical form leads to appropriate effective radii of solvated ions and produces their sensitive dependence on temperature. We also try to microscopically interpret the BW model by comparing it with the mean spherical approximation (MSA) for the ion-dipolar system and propose the solvent scale BW (SBW) function ∈r exp[-(r2 ln ∈r)/(r - a + r2)], where r2 is the radius of the solvent molecule (when r2 = a, the SBW function is identical with the BW). Although the ion solvation energy for the SBW varies with r2 more moderately than the MSA, both models provide nearly the same effective radius of an ion, i.e., nearly the same free energy (entropy) of ion solvation.

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U2 - 10.1021/jp951759d

DO - 10.1021/jp951759d

M3 - Article

AN - SCOPUS:0030572359

SN - 0022-3654

VL - 100

SP - 9935

EP - 9942

JO - Journal of Physical Chemistry

JF - Journal of Physical Chemistry

IS - 23

ER -