Excess chemical potential of small solutes across water--membrane and water--hexane interfaces.
Excess chemical potential of small solutes across water--membrane and water--hexane interfaces.
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DOI：
10.1063/1.471030
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发表时间：
1996-03
期刊：
影响因子：
--
通讯作者：
A. Pohorille;M. Wilson
中科院分区：
文献类型：
--
作者：
A. Pohorille;M. Wilson
用粒子插入法计算了300、310和340K下5种结构相关的小分子溶质CH4、CH3F、CH2F2、CHF3和CF4在水-甘油-1-单油酸酯双层膜和水-正己烷界面上的超额化学势。非极性分子(CH4和CF4)的超额化学势从水到非极性相单调或近乎单调地减小。相反，对于具有永久偶极矩的分子(CH3F、CH2F和CHF3)，多余的化学势表现出界面极小值，该界面极小值是由两个单调和相反变化的贡献叠加产生的：静电和非静电。由产生容纳溶质的空腔的可逆功主导的非静电项减少，而静电项从水到膜内部的界面增加。在水中，二阶微扰理论精确地描述了这一项对偶极矩的依赖关系。为了在界面上达到相同的精度，还必须包括三次项。在界面区域，溶剂的分子结构既影响过剩化学势，又影响溶质取向。界面上的过剩化学势随着温度的升高而增加，但这种影响相当小。我们的分析表明，在水-膜和水-油界面上，许多小的、中等极性的分子应该是表面活性的。讨论了这一结果的生物学和医学意义，特别是与麻醉作用机制有关的意义。
The excess chemical potentials of five small, structurally related solutes, CH4, CH3F, CH2F2, CHF3, and CF4, across the water-glycerol 1-monooleate bilayer and water-hexane interfaces were calculated at 300, 310, and 340 K using the particle insertion method. The excess chemical potentials of nonpolar molecules (CH4 and CF4) decrease monotonically or nearly monotonically from water to a nonpolar phase. In contrast, for molecules that possess permanent dipole moments (CH3F, CH2F, and CHF3), the excess chemical potentials exhibit an interfacial minimum that arises from superposition of two monotonically and oppositely changing contributions: electrostatic and nonelectrostatic. The nonelectrostatic term, dominated by the reversible work of creating a cavity that accommodates the solute, decreases, whereas the electrostatic term increases across the interface from water to the membrane interior. In water, the dependence of this term on the dipole moment is accurately described by second order perturbation theory. To achieve the same accuracy at the interface, third order terms must also be included. In the interfacial region, the molecular structure of the solvent influences both the excess chemical potential and solute orientations. The excess chemical potential across the interface increases with temperature, but this effect is rather small. Our analysis indicates that a broad range of small, moderately polar molecules should be surface active at the water-membrane and water-oil interfaces. The biological and medical significance of this result, especially in relation to the mechanism of anesthetic action, is discussed.