The hydration of aniline: Analysis of spatial distribution functions

摘要

Molecular dynamics simulations of aniline in aqueous infinitely dilute solution are performed fromambient to supercritical conditions. Spatial hydration structures of aniline are examined along theliquid branch of the liquid-vapor coexistence curve of the simple point charge/extended water modelat 298, 373, 473, and 573 K and in the supercritical region at 633, 733, and 833 K with density fixedat 0.3 g / cm~3. The coordination and H-bond numbers of aniline are calculated. The self-diffusioncoefficient of aniline is also evaluated. At room temperature the solvation shell of aniline iscomprised of -32 water molecules. At 298 K, the amino group is hydrated by three water moleculeswith which it forms one strong and two weak (0.6) H bonds acting as an acceptor and donor,respectively. In addition, -1.5 water molecules are identified as 7r-coordinated, forming close to0.75 H bonds with the aromatic ring of aniline. The features of the hydration shell structure ofaniline diminish with temperature and decreasing density. The disappearance of 7r-coordinatedwater molecules is noted at around 473 K, whereas the loss of the hydrophobic solvent cage isobserved near the critical point of water. At supercritical conditions aniline is hydrated byapproximately eight water molecules with the amino group coordinated to roughly two of them,forming less than one H bond in total.