Coupled semiempirical quantum mechanics and molecular mechanics (QM/MM) calculations on the aqueous solvation free energies of ionized molecules
✍ Scribed by Cummins, Peter L.; Gready, Jill E.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 240 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
The aqueous solvation free energies of ionized molecules were computed using a coupled quantum mechanical and molecular mechanical Ž . QMrMM model based on the AM1, MNDO, and PM3 semiempirical molecular orbital methods for the solute molecule and the TIP3P molecular mechanics model for liquid water. The present work is an extension of our model for neutral solutes where we assumed that the total free energy is the sum of components derived from the electrostaticrpolarization terms in the Hamiltonian plus an empirical ''nonpolar'' term. The electrostaticrpolarization contributions Ž . to the solvation free energies were computed using molecular dynamics MD simulation and thermodynamic integration techniques, while the nonpolar contributions were taken from the literature. The contribution to the electrostaticrpolarization component of the free energy due to nonbonded interactions outside the cutoff radii used in the MD simulations was approximated by a Born solvation term. The experimental free energies were reproduced satisfactorily using variational parameters from the vdW terms as in the original model, in addition to a parameter from the one-electron integral terms. The new one-electron parameter was required to account for the shortrange effects of overlapping atomic charge densities. The radial distribution