Theory of Liquids and Liquid Mixtures, their Structures and Phase Equilibria

康奈尔大学的Benjamin Widom获得了化学理论，模型和计算方法项目的奖项，以研究在水中难以溶解的物质的溶液。 “油和水不相溶”这句话几乎是正确的，但并不完全正确，油和其他物质在水中的轻微溶解度通常至关重要。 它影响着化学加工工业中蒸馏和萃取分离的效率;它是制药工业中药物设计的主要因素;它是水污染和其他环境问题的关注点;它是最基本的生物现象的基础。 例如，人们普遍认为，蛋白质的油状成分与周围的水的相对不相容性是蛋白质折叠成其适当的生物活性形式的原因。 在水中的低溶解度是统称为“疏水”（字面意思是憎水）效应的一个例子。 这些效应是目前理论和计算研究的对象，这些研究旨在了解它们的分子起源和后果：是什么使物质疏水？ 除了低溶解度外，疏水性还表现在哪些方面？ 周围水本身的结构和其他性质如何对溶解的疏水分子的存在作出反应，这种分子尺度的重排会产生什么样的物理和化学后果？这项研究的大部分是针对了解溶剂引起的疏水溶质之间的吸引力，特别是第二渗透维里系数中包含的吸引力的措施。 这是可取的，以调和这个系数的值，发现从状态方程和热力学测量与溶质-溶质对相关函数的积分，所需的Kirkwood-Buff关系之一。 在最近的工作中，它已被证明如何维里系数可以从状态方程中提取的参数设置，以给出现实的纯溶剂的性质和现实的帐户的溶质-溶剂相互作用的影响，如溶质的溶解度和其在溶剂中的部分分子体积。 所得的渗透系数同意以及从实验中提取的溶解度测量。 通过计算机模拟，分别得到了两组分混合物中的几对相关函数。 这些，在被整合，是一致的溶剂的可压缩性，溶质部分分子体积，和气相维里系数，但与先前获得的第二渗透维里系数不一致。 这是一个严重的矛盾，这是重要的解决，为正确理解疏水水化的结构效应，和更一般的疏水效应，取决于它。仍然存在的问题是构建几对相关函数的分析形式，以测试早期的分析指示，溶质-溶质相关函数的幅度，由于溶解度低而难以测量，大大超过了其它两种，使得溶质保持与比溶剂分子更长的距离有效相关，尽管两者具有相同的形式指数衰减长度。 剩余的项目是，确定，通过计算机模拟和分析，溶质-溶质对的相关函数的溶质-穷人的一个闭环共存曲线的一侧，跟踪从熵为基础的演化到基于熵的solvophobicity的温度之间的变化的两个临界溶液点。

Benjamin Widom of Cornell University is supported by an award from the Chemical Theory, Models and Computational Methods program to study solutions, in water, of substances that are hardly soluble. The expression "oil and water don't mix" is almost but not entirely true, and the slight solubility of oils and other substances in water is often of crucial importance. It affects the efficiency of separations by distillation and extraction in the chemical process industries; it is a primary factor in drug design in the pharmaceutical industry; it is a concern in water pollution and other environmental problems; and it underlies the most fundamental biological phenomena. It is widely accepted, for example, that it is the relative incompatibility of the oil-like constituents of a protein and the surrounding water that is responsible for the protein's folding into its proper biologically active form. Low solubility in water is an example of what are known collectively as "hydrophobic" (literally water-hating) effects. These effects are the objects of the present theoretical and computational research, which is directed toward the understanding of their molecular origins and consequences: What makes a substance hydrophobic? In what other ways does hydrophobicity manifest itself in addition to low solubility? How does the structure and other properties of the surrounding water itself respond to the presence of dissolved hydrophobic molecules and what are the physical and chemical consequences of such molecular-scale rearrangements?Much of this research is directed to understanding the solvent-induced attraction between hydrophobic solutes, particularly that measure of the attraction contained in the second osmotic virial coefficient. It is desirable to reconcile the values of this coefficient as found from equations of state and thermodynamic measurements with the integral of the solute-solute pair correlation function, as required by one of the Kirkwood-Buff relations. In recent work it has been shown how the virial coefficient may be extracted from an equation of state with parameters set to give realistic properties of the pure solvent and a realistic account of those effects of the solute-solvent interaction such as on the solubility of the solute and on its partial molecular volume in the solvent. The resulting osmotic coefficient agrees well with that extracted from experimental solubility measurements. Independently, the several pair correlation functions in the two-component mixture are obtained by computer simulation. These, on being integrated, are consistent with the solvent compressibility, the solute partial molecular volume, and the gas-phase virial coefficients, yet inconsistent with the previously obtained second osmotic virial coefficient. This is a serious discrepancy, which is important to resolve, for a proper understanding of structural effects in hydrophobic hydration, and hydrophobic effects more generally, depends on it. There still remains the problem of constructing analytical forms for the several pair correlation functions to test earlier analytical indications that the amplitude of the solute-solute correlation function, which is difficult to measure because of the low solubility, greatly exceeds that of the other two so that the solutes remain effectively correlated to longer distances than do the solvent molecules despite the two having the same formal exponential decay length. A remaining project is that of determining, by computer simulation and analytically, the solute-solute pair correlation function on the solute-poor side of a closed-loop coexistence curve, to trace the evolution from entropy-based to enthalpy-based solvophobicity as the temperature varies between that of the two critical solution points.