Assessment of free energy expressions in RISM integral equation theory: theoretical prediction of partition coefficients revisited

Abstract

We assess the performance of free energy expressions so far available in the reference interaction site model (RISM) integral equation theory. Free energies of solvation in aqueous and chloroform solutions along with the partition coefficients of them are calculated for 16 organic molecules. Static polarity effects are included using hybrid RISM and Hartree–Fock methods. Our best estimates are obtained from the expression of the distributed partial wave expansion that leads to the standard deviations less than 1.3 kcal mol⁻¹ and 1.1 in the solvation free energies and partition coefficients, respectively.

Keywords:

• PW expansion
• partition coefficients
• LogP
• salvation
• RISM

Notes

Notes

1. A factor 2 is missing in the first term of the PW expression of Sato et al. 23.

2. The number density in the present calculation is 0.03334 molecules Å⁻³.

3. The site–site distances are near experimental values, 1.760 and 2.9044 Å for the CH–Cl and Cl–Cl pairs, respectively. The number density is 0.0074646 molecules Å⁻³.

4. Previously, we actually employed a five-site model with the van der Waals parameters, σ_C = 3.50, σ_H = 2.50, σ_Cl = 3.47 Å, ϵ_C = 0.066, ϵ_H = 0.03, ϵ_Cl = 0.300 kcal mol⁻¹, and the site–site distances, R _CH = 1.100, R _CCl = 1.758, R _HCl = 2.339, R _ClCl = 2.903 Å.

5. According to the previous works 20,23, the modified van der Waals parameters are σ_H = 0.4 Å and ϵ_H = 0.046 kcal mol⁻¹ for the protic hydrogen of solute (phenol) and σ_H = 1.0Å and ϵ_H = 0.04968 kcal mol⁻¹ for the TIP3P water.