jp973306+_si_001.pdf (1.54 MB)
Universal Quantum Mechanical Model for Solvation Free Energies Based on Gas-Phase Geometries
journal contribution
posted on 1998-04-04, 00:00 authored by Gregory D. Hawkins, Christopher J. Cramer, Donald G. TruhlarWe present a new solvation model for predicting free energies of
transfer of organic solutes from the gas
phase to aqueous and organic solvents. The model is based on class
II charges, gas-phase geometries, a
generalized Born approximation to the polarization free energy, and
SM5-type atomic surface tensions. The
initial parametrization of the new model was developed to utilize the
MNDO/d Hamiltonian, and we also
present parameters for the MNDO, AM1, and PM3 Hamiltonians. These
parametrizations are based on
reasonably accurate gas-phase geometries for 43 ions and 260 neutral
solute molecules composed of H, C, N,
O, F, S, Cl, Br, and I and containing a wide variety of functional
groups. For aqueous solutions, the
parametrization is based on data for 248 of the neutrals and all of the
ions. For organic solvents, it is based
on 1836 experimental data points for 227 of the neutral solutes in 90
organic solvents. The parametrization
based on the MNDO/d Hamiltonian is called SM5.2R/MNDO/d, and it yields
a mean unsigned error of 3.8
kcal/mol for the free energy of hydration of ions and a mean unsigned
error of 0.38 kcal/mol for the free
energy of solvation of neutral solutes. Gas-phase geometries for
all solute molecules were calculated at the
Hartree−Fock level with a heteroatom-polarized valence-double-ζ
basis set (HF/MIDI!), and we confirmed
that the average errors increase only about 0.1 kcal/mol if we use the
MNDO/d geometries.