Spatially-Decomposed Free Energy of Solvation Based on the Endpoint Density-Functional Method
Spatially-Decomposed Free Energy of Solvation Based on the Endpoint Density-Functional Method
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DOI：
10.1021/acs.jctc.8b01309
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发表时间：
2019-05-01
影响因子：
5.5
通讯作者：
Levy, Ronald M.
中科院分区：
文献类型：
--
作者：
Ishii, Yoshiki;Yamamoto, Naoki;Levy, Ronald M.
溶剂化热力学的密度泛函方法的一个空间分辨的版本，提出了通过扩展的自由能功能先前建立在一维，能量表示和制定一个新的表达在一个混合的四维表示（三维的位置和一个维度的能量）。该空间被进一步划分成一组离散的区域相对于溶剂分子从溶质的相对位置，和溶剂化的空间分解的能量进行了分析的小分子与甲基，胺，或羟基基团和丙氨酸二肽在溶剂水。有人观察到，溶剂化自由能的密度是弱依赖于溶质的网站在排除体积区域，是明显有利的溶质原子，可以很容易地与水形成氢键的第一壳层。溶剂重组项减少更快地从溶质的分离比溶质和溶剂之间的直接相互作用，后者支配的第二壳和外部区域的能量。从排除的体积和第一壳的自由能的贡献的总和被发现偏离显着的总和在所有的区域，这意味着溶剂化自由能是不是在定量意义上的溶质附近的空间本地化。尽管如此，一个本地的描述被证明是有效的，证实了自由能的总价值与相应的值通过整合的自由能密度的第二壳的相关性。因此，在本工作中开发的理论框架空间分解的溶剂化自由能可以是有用的，以确定稳定或不稳定的区域溶剂接近溶质和分析的作用，界面水的位移在分子缔合热力学中发挥。
A spatially resolved version of the density-functional method for solvation thermodynamics is presented by extending the free-energy functional previously established in the one-dimensional, energy representation and formulating a new expression in a mixed four-dimensional representation (three dimensions for position and one dimension for energy). The space was further divided into a set of discrete regions with respect to the relative position of a solvent molecule from the solute, and the spatially decomposed energetics of solvation were analyzed for small molecules with a methyl, amine, or hydroxyl group and alanine dipeptide in solvent water. It was observed that the density of the solvation free energy is weakly dependent on the solute site in the excluded-volume region and is distinctively favorable in the first shells of the solute atoms that can readily form hydrogen bonds with water. The solvent-reorganization term reduces faster with the separation from the solute than the direct interaction between the solute and solvent, and the latter governs the energetics in the second shell and outer regions. The sum of the contributions to the free energy from the excluded volume and first shell was found to deviate significantly from the total sum over all the regions, implying that the solvation free energy is not spatially localized near the solute in a quantitative sense. Still, a local description was shown to be valid as confirmed by the correlation of the total value of free energy with the corresponding value obtained by integrating the free-energy density to the second shell. The theoretical framework developed in the present work to spatially decompose the solvation free energy can thus be useful to identify stabilizing or destabilizing regions of solvent proximate to a solute and to analyze the role that the displacement of interfacial water plays in the thermodynamics of molecular association.