Molecular dynamics simulation of liquid 2-heptanone, pure and saturated with water

Molecular dynamics simulations of liquid 2-heptanone (HPT2) at 300 K were carried out using three different intermolecular potentials. The simulations were performed in two ensembles-the canonical ensemble and the isothermic-isobaric ensemble. Thermodynamic, dynamic, and structural properties were investigated. The results obtained using the three different potentials were very similar. An evaluation of the results obtained against available experimental data was performed and the most realistic potential was then chosen to simulate HPT2 saturated with water (1.41% H2O (w/w)). Radial distribution functions were calculated and a distribution for the number of nearest neighbors was estimated. Dipole associations and other specific group associations were studied. The importance of steric factors in solvation was found to be determinant. Dynamic properties such as diffusion coefficients and orientational correlation times were estimated. It was confirmed that density plays a fundamental role in liquid dynamics. The molecular folding of HPT2 was investigated. It was found that the molecule is more tightly folded in the liquid phase than in the gas phase: as the differences are small, we obtain a picture of a liquid with mostly extended molecules. The structure and dynamics of the water molecules dissolved in HPT2 were also studied. Most water molecules form hydrogen bond-like interactions with the ketone oxygen of the HPT2 molecule, and water dynamics becomes coupled to the HPT2 dynamics. The carbonyl carbon is too hidden by methyl groups to solvate water oxygens. Water associations occur to a small extent. The general statistic properties of HPT2 are not affected by the presence of water, the changes being limited to the HPT2 molecules in close contact with water molecules.