Department of Chemistry, Faculty of Science, Okayama University, 700-8530, Okayama, Japan.
Phys Chem Chem Phys. 2011 Nov 28;13(44):19749-58. doi: 10.1039/c1cp22344e. Epub 2011 Sep 13.
The solvation of nonpolar molecules in water and that in simple liquids are compared and contrasted. First, solvation thermodynamics is reviewed in a way that focuses on how the enthalpy and entropy of solvation depend on the choice of microscopic volume change v in the solvation process--including special choices v being zero (fixed-volume condition) and v being the partial molecular volume of a solute molecule (fixed-pressure condition)--and how the solvation quantities are related with temperature derivatives of the solvation free energy. Second, the solvation free energy and the solvation enthalpy of a Lennard-Jones (LJ) atom in model water are calculated in the parameter space representing the solute size and the strength of the solute-solvent interaction, and the results are compared with those for an LJ atom in the LJ solvent. The solvation diagrams showing domains of different types of solvation in the parameter space are obtained both for the constant-volume condition and for the constant-pressure condition. Similarities between water and the simple liquid are found when the constant-volume solvation is considered while a significant difference manifests itself in the fixed-pressure solvation. The domain of solvation of hydrophobic character in the parameter space is large in the constant-volume solvation both for water and for the simple liquid. When switched to the constant-pressure condition accompanying a microscopic volume change, the hydrophobic domain remains large in water but it becomes significantly small in the simple liquid. The contrasting results are due to the smallness of the thermal pressure coefficient of water at low temperatures.
比较和对比了非极性分子在水中和简单液体中的溶解情况。首先，以一种关注溶剂化焓和熵如何取决于溶剂化过程中微观体积变化 v 的选择的方式回顾溶剂化热力学——包括 v 为零（固定体积条件）和 v 为溶质分子的部分分子体积（固定压力条件）的特殊选择——以及溶剂化量如何与溶剂化自由能的温度导数相关。其次，在代表溶质尺寸和溶质-溶剂相互作用强度的参数空间中计算了 Lennard-Jones (LJ) 原子在模型水中的溶剂化自由能和溶剂化焓，并将结果与 LJ 溶剂中的 LJ 原子进行了比较。对于固定体积条件和固定压力条件，都得到了在参数空间中显示不同类型溶剂化的域的溶剂化图。当考虑固定体积溶剂化时，发现水和简单液体之间存在相似性，而在固定压力溶剂化中则表现出明显的差异。在参数空间中，疏水性质的溶剂化域在固定体积溶剂化中对于水和简单液体都是很大的。当切换到伴随微观体积变化的固定压力条件时，疏水域在水中仍然很大，但在简单液体中则显著减小。对比结果归因于低温下水的热压力系数很小。
