Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0580, USA.
J Chem Phys. 2013 Aug 7;139(5):054511. doi: 10.1063/1.4816005.
Hydrophobic interactions are responsible for water-driven processes such as protein folding and self-assembly of biomolecules. Microscopic theories and molecular simulations have been used to study association of a pair of methanes in water, the paradigmatic example of hydrophobic attraction, and determined that entropy is the driving force for the association of the methane pair, while the enthalpy disfavors it. An open question is to which extent coarse-grained water models can still produce correct thermodynamic and structural signatures of hydrophobic interaction. In this work, we investigate the hydrophobic interaction between a methane pair in water at temperatures from 260 to 340 K through molecular dynamics simulations with the coarse-grained monatomic water model mW. We find that the coarse-grained model correctly represents the free energy of association of the methane pair, the temperature dependence of free energy, and the positive change in entropy and enthalpy upon association. We investigate the relationship between thermodynamic signatures and structural order of water through the analysis of the spatial distribution of the density, energy, and tetrahedral order parameter Qt of water. The simulations reveal an enhancement of tetrahedral order in the region between the first and second hydration shells of the methane molecules. The increase in tetrahedral order, however, is far from what would be expected for a clathrate-like or ice-like shell around the solutes. This work shows that the mW water model reproduces the key signatures of hydrophobic interaction without long ranged electrostatics or the need to be re-parameterized for different thermodynamic states. These characteristics, and its hundred-fold increase in efficiency with respect to atomistic models, make mW a promising water model for studying water-driven hydrophobic processes in more complex systems.
疏水相互作用是导致蛋白质折叠和生物分子自组装等水驱动过程的原因。微观理论和分子模拟已被用于研究一对甲烷在水中的缔合，这是疏水吸引的典型例子，并确定熵是甲烷对缔合的驱动力，而焓则不利于缔合。一个悬而未决的问题是，粗粒化水模型在多大程度上仍然可以产生疏水相互作用的正确热力学和结构特征。在这项工作中，我们通过粗粒化单原子水模型 mW 进行分子动力学模拟，研究了温度在 260 至 340 K 之间的一对甲烷在水中的疏水相互作用。我们发现，粗粒化模型正确地表示了甲烷对的缔合自由能、自由能的温度依赖性以及缔合时熵和焓的正变化。我们通过分析水的密度、能量和四面体有序参数 Qt 的空间分布来研究热力学特征与水的结构有序性之间的关系。模拟揭示了甲烷分子的第一和第二水合壳之间区域的四面体有序性增强。然而，四面体有序性的增加远不及溶质周围类似笼形或冰状壳的预期。这项工作表明，mW 水模型在没有长程静电或不需要针对不同热力学状态重新参数化的情况下，再现了疏水相互作用的关键特征。这些特性及其相对于原子模型效率提高了一百倍，使得 mW 成为研究更复杂系统中水驱动疏水过程的有前途的水模型。
