Solvation and structure for systems with strong Coulomb interactions

马里兰大学帕克分校的约翰·d·威克斯（John D. Weeks）获得了化学学部理论、模型和计算方法项目的奖励，他对介电流体（如水）和带电离子流体中的溶剂化进行了理论研究。首席研究员和同事们开发了一种新的局部分子场（LMF）理论，该理论将任意外场中具有远程库仑相互作用的非均匀系统的结构与具有短程相互作用的更简单的“模拟系统”的结构联系起来，但在有效或重整的场中，这种相互作用可以解释远程相互作用的平均效应。外场可以表示溶剂与固定的、任意复杂的、可能带电的溶质的相互作用，随着外场的逐渐开启，溶剂化自由能被确定。短程模拟系统的溶剂化过程避免了传统处理库仑相互作用的昂贵计算方法，并推导了完整系统和模拟系统之间溶剂化自由能差的一个非常简单的解析表达式。LMF理论对不同大小的疏水和亲水溶质在水（最重要的溶剂）中的简单球形模型的溶剂化给出了异常准确的结果。正在进行的研究将侧重于这些思想的理论概括，以及应用于生物物理学和材料科学中更复杂的解决问题。准确测定溶剂化过程中的自由能变化是定量了解溶液中大量化学和生物物理过程（从蛋白质折叠到跨细胞膜的药物分配）的必要条件。研究者和同事开发的新的溶剂化理论简单，物理动机，并且非常准确，因此这项研究的结果应该可以为不同背景的实验学家和理论家所接受，并可能为化学，物理和生物学重叠领域的工作提供共同的语言。本提案中的研究直接有助于研究生和博士后的跨学科培训，他们在分析思维，新导出方程的数值解以及使用内部程序和最先进的模拟软件包的计算机模拟的独特组合方面获得经验。

John D. Weeks of the University of Maryland, College Park, is supported by an award from the Theory, Models and Computational Methods program in the Chemistry Division to carry out theoretical research on solvation in dielectric fluids like water and in charged ionic fluids as well. The principal investigator and coworkers have developed a new local molecular field (LMF) theory that relates the structure of a nonuniform system with long-ranged Coulomb interactions in an arbitrary external field to that of a simpler "mimic system" with short ranged interactions but in an effective or renormalized field that accounts for the averaged effects of the long ranged interactions. The external field can represent the interaction of the solvent with a fixed, arbitrarily complicated, and possibly charged solute, and the solvation free energy is determined as the field is gradually turned on. The solvation process in the short ranged mimic system avoids computationally expensive methods used in conventional treatments of Coulomb interactions and a very simple and analytic expression for the difference in solvation free energy between the full and mimic systems has been derived. LMF theory gives exceptionally accurate results for solvation of simple spherical models of hydrophobic and hydrophilic solutes of varying sizes in water, the most important solvent. Ongoing research will focus on theoretical generalizations of these ideas, along with applications to more complex solvation problems of interest in biophysics and materials science.An accurate determination of free energy changes during solvation is required for a quantitative understanding of a vast array of chemical and biophysical processes in solution, ranging from protein folding to drug partitioning across cell membranes. The new solvation theory developed by the investigator and coworkers is simple, physically motivated, and very accurate, so the results of this research should be accessible to experimentalists and theorists with diverse backgrounds and may provide a common language for work in overlapping areas of chemistry, physics, and biology. The research in this proposal contributes directly to the interdisciplinary training of graduate students and postdocs, who gain experience in a unique combination of analytical thinking, numerical solutions of newly derived equations, and computer simulations using both in house programs and state of the art simulation packages.