The aqueous solvation thermodynamics of cis- and trans-N-methylacetamide is studied by integral equation theories and molecular dynamics simulations and compared with Monte Carlo results (Jorgensen, W. L.; Gao, J. J. Am. Chem. Soc. 1988, 110, 4212). Although the hypernetted chain (HNC) approximation is generally recommended for polar systems, the solvation free energy derived from the Gaussian fluctuation (GF) approximation gives much better absolute solvation thermodynamics. With the same atomic charges for the two conformers, the difference in solvation free energy between the cis and trans conformers equals 1-2 kcal/mol from the HNC and GF approximations, in approximate agreement with the value of 2.2 kcal/mol from a Monte Carlo simulation with very similar parameters. The simpler superposition approximation introduced by Pettitt and Karplus (Chem. Phys. Lett. 1985, 121, 194) gives results for the relative solvation thermodynamics (cis versus trans conformers) that compare well with the more exact integral equation theories.
ASJC Scopus subject areas
- Colloid and Surface Chemistry