Abstract
We describe a simple and accurate method, ESE-PM7, for calculating solvation free energies ΔGsolv° in aqueous and nonaqueous solutions. The method is based on a noniterative COSMO algorithm. Molecular geometries and atomic charges calculated using the semiempirical method PM7 are used to calculate ΔGsolv°. The method has been tested on 92 different solvents and 988 solutes. The mean absolute errors (MAEs) in ΔGsolv° in aqueous solutions estimated by the ESE-PM7 approach are found to be 1.62 kcal/mol for 389 neutral solutes and 3.06 kcal/mol for 139 ions. The MAEs for neutral molecules in organic solvents are 0.97, 0.74, and 0.51 kcal/mol in polar protic, polar aprotic, and nonpolar solvents, respectively. The developed method can be employed to quickly screen ΔGsolv° values of extended molecular systems including pharmaceutical and biological molecules.
Highlights
The solvation free energy ΔGs°olv plays an important role in computational chemistry, since it can make a significant contribution to the total free energy of chemical reactions in solution
Since the PM7 method[43] is widely regarded as the most advanced semiempirical approach, in this work we present a solvation energy scheme based on geometries and atomic charges derived from PM7 calculations
Several other sets were tested: the data set of 464 solutes used by Krıźand Ř ezać ;̌ 54 the subset of 141 solutes from Mobley et al.’s data set[55] (“Mobley”); Guthrie’s SAMPL1 “blind challenge” data set (“Blind”) containing 63 neutral pharmacologically important molecules;[56] reduced Guthrie’s data set (53 molecules)[56] used by Krıźand Ř ezáč[54] (“SAMPL1”); reduced Guthrie’s SAMPL4 data set[57] used by Krıźand Ř ezać 5̌ 4 (“SAMPL4”); ionic data set by Krıźand Ř ezać 5̌ 4 (“C10”)
Summary
The solvation free energy ΔGs°olv plays an important role in computational chemistry, since it can make a significant contribution to the total free energy of chemical reactions in solution. Most practical calculations of ΔGs°olv are based on the continuum solvation (CS) model. The solvation methods in general[2] and PCM methods in particular[1] were reviewed in detail elsewhere. The general idea of the PCM is that the solute placed in a cavity interacts with the solvent represented by a continuum with certain electrical properties. The polarization of the solvent by the solute is described by an electric charge distribution on the surface of the cavity. The charge distribution, in turn, is represented either by a continuous surface charge density σ(r) or by discrete induced charges {qi}. The electrostatic energy Eelst is calculated from the energy of the induced surface charge density σ(r) in the electrostatic potential of the molecule V(r):
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