Thermodynamic Properties of Hydration Water around Solutes: Effect of Solute Size and Water-Solute Interaction
Thermodynamic Properties of Hydration Water around Solutes: Effect of Solute Size and Water-Solute Interaction
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DOI：
10.1021/jp306781y
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发表时间：
2012-12-20
影响因子：
3.3
通讯作者：
Brovchenko, I.
中科院分区：
文献类型：
--
作者：
Oleinikova, A.;Brovchenko, I.
研究了不同模型溶质周围水化水的密度、热膨胀和热容随温度和压力的变化规律。球形无结构溶质的半径从3到10埃变化，水-溶质相互作用从强疏水到强亲水变化。将溶质周围的水化水的热力学性质与半径为25埃的大圆柱孔内表面附近的水化水的热力学性质进行了比较。对于所有系统的研究，水化壳层中的水-水相互作用的能量被发现比在散装的负。这是缺失邻居效应的结果，其导致即使在强亲水表面附近的液体密度耗尽。这种效应增强了凹面附近的水化水密度，并减小了凸面附近的水化水密度，从而导致小溶质周围的水化水密度显著增加。表面附近的液体密度耗尽伴随着水化水的热膨胀系数的本质增加：在低温下，它甚至超过强亲水性表面附近的体积值。水化水的定容热容量接近体积值;它实际上对水-表面相互作用不敏感，并且在溶质尺寸减小时略有增加。水化水的恒压热容随水-表面相互作用的减弱而增大，对溶质的大小几乎不敏感。疏水表面附近水的恒压热容的增加被认为是热膨胀系数增加的结果。
Density, thermal expansion, and heat capacity of hydration water around various model solutes have been studied as a function of temperature and pressure. The radius of spherical structureless solute was varied from 3 to 10 angstrom, and the water-solute interaction was varied from strongly hydrophobic to strongly hydrophilic. Thermodynamic properties of hydration water around solutes were compared with those near the inner surface of large cylindrical pores with a radius of 25 angstrom. For all systems studied, the energy of water-water interactions per molecule in the hydration shell is found less negative than in the bulk. This is the result of the missing neighbor effect, which leads to the liquid density depletion even near strongly hydrophilic surfaces. This effect enhances near concave surfaces and diminishes near convex surfaces, which causes an essential increase of hydration water density around small solutes. Liquid density depletion near surfaces is accompanied by an essential increase of the thermal expansion coefficient of hydration water: at low temperatures, it exceeds the bulk value even near strongly hydrophilic surfaces. The constant volume heat capacity of hydration water is close to the bulk value; it is practically not sensitive to water-surface interaction and slightly increases upon decreasing solute size. The constant pressure heat capacity of hydration water increases upon weakening water-surface interaction and is practically not sensitive to solute size. Increase of the constant pressure heat capacity of water near hydrophobic surfaces is found to be the result of the increasing thermal expansion coefficient.