Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India.
Phys Chem Chem Phys. 2018 Jul 11;20(27):18328-18339. doi: 10.1039/c7cp08109j.
Water molecules in different parts of the anisotropic hydration shell of an aromatic molecule experience different interactions. In the present study, we investigate the anisotropic dynamics of water molecules in different non-overlapping conical shells around a benzene solute at sub- and supercritical conditions by means of molecular dynamics simulations using both non-polarizable and polarizable models. In addition to the dynamical properties, the effects of polarizability on the hydration structure of benzene at varying thermodynamic conditions are also investigated in the current study. The presence of πH-bonding in the solvation shell is found to be an important factor that influences the anisotropic dynamics of the benzene hydration shell. The water molecules located axial to the benzene plane are found to be maximally influenced by the πH-bonding. The extent of πH-bonding is found to be somewhat reduced on inclusion of polarizability. The πH-bonded water molecules are found to reorient through large-amplitude angular jumps where the jump-angle amplitude increases at higher temperatures and lower densities. For both non-polarizable and polarizable models, it is found that the water molecules in the axial conical shells possess faster orientational and hydrogen bond dynamics compared to those in the equatorial plane. Water molecules in the axial conical shells are also found to diffuse at a faster rate than bulk molecules due to the relatively weaker benzene-water πH-bonding interactions in the axial region of the hydration shell. The residence dynamics of water molecules in different conical solvation shells around the solute is also investigated in the current study.
水分子在芳香族分子各向异性水合壳的不同部位会经历不同的相互作用。在本研究中，我们通过分子动力学模拟，使用非极化和极化模型，研究了亚临界和超临界条件下，苯溶质周围不同非重叠锥形壳层中水分子的各向异性动力学。除了动力学特性外，本研究还研究了极化对不同热力学条件下苯水合结构的影响。研究发现，溶剂壳层中π氢键的存在是影响苯水合壳层各向异性动力学的一个重要因素。位于苯平面轴向的水分子受到π氢键的最大影响。包含极化后，π氢键的程度有所降低。发现π氢键结合的水分子通过大振幅角跳跃重新取向，随着温度升高和密度降低，跳跃角幅度增加。对于非极化和极化模型，都发现轴向锥形壳层中的水分子的取向和氢键动力学比赤道平面中的水分子更快。由于水合壳层轴向区域的苯-水π氢键相互作用相对较弱，轴向锥形壳层中的水分子也被发现扩散速度比体相分子快。本研究还研究了溶质周围不同锥形溶剂化壳层中水分子的停留动力学。
