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arXiv 1303.4429cond-mat.softphysics.chem-ph
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水氢键对疏水水化作用长度尺度依赖性的概率探讨

Probabilistic approach to the length-scale dependence of the effect of water hydrogen bonding on hydrophobic hydration

Yuri S. Djikaev, Eli Ruckenstein

摘要:

我们提出了一种水-水氢键的概率方法,该方法允许获得每个水分子的键数作为其与疏水性颗粒的距离和疏水性半径的函数的解析表达式。这种方法可以用于密度泛函理论(DFT)和计算机模拟,以检查粒子的水合作用和溶剂介导的相互作用的颗粒尺寸的影响。例如,它允许一个明确地确定水氢键贡献的外部电位,其中一个水分子受到附近的疏水。该模型的DFT实现预测的水合自由能每单位面积的球形疏水物是急剧敏感的疏水物半径为小半径和弱敏感,大的,这证实了小和大的长度尺度的粒子通过不同的机制发生的水合的愿景。另一方面,该模型预测,即使是足够小的半径的非极性粒子的水合作用可能会成为philically有利的,由于成对(分散)水-水和水-疏水相互作用的能量的相互作用。这揭示了以前的反直觉观察(理论和模拟),两个惰性气体分子更喜欢形成溶剂分离的对,而不是接触的对。

英文摘要:

We present a probabilistic approach to water-water hydrogen bonding that allows one to obtain an analytic expression for the number of bonds per water molecule as a function of both its distance to a hydrophobic particle and hydrophobe radius. This approach can be used in the density functional theory (DFT) and computer simulations to examine particle size effects on the hydration of particles and on their solvent-mediated interaction. For example, it allows one to explicitly identify a water hydrogen bond contribution to the external potential whereto a water molecule is subjected near a hydrophobe. The DFT implementation of the model predicts the hydration free energy per unit area of a spherical hydrophobe to be sharply sensitive to the hydropobe radius for small radii and weakly sensitive thereto for large ones; this corroborates the vision of the hydration of small and large length-scale particles as occurring via different mechanisms. On the other hand, the model predicts that the hydration of even apolar particles of small enough radii may become thermodynamically favorable owing to the interplay of the energies of pairwise (dispersion) water-water and water-hydrophobe interactions. This sheds light on previous counterintuitive observations (both theoretical and simulational) that two inert gas molecules would prefer to form a solvent-separated pair rather than a contact one.

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