Zangi Ronen, Hagen Morten, Berne B J
Department of Chemistry and Center for Biomolecular Simulations, Columbia University, New York, NY 10027, USA.
J Am Chem Soc. 2007 Apr 18;129(15):4678-86. doi: 10.1021/ja068305m. Epub 2007 Mar 23.
We use molecular dynamics simulations to investigate the solvent mediated attraction and drying between two nanoscale hydrophobic surfaces in aqueous salt solutions. We study these effects as a function of the ionic charge density, that is, the ionic charge per unit ionic volume, while keeping the ionic diameter fixed. The attraction is expressed by a negative change in the free energy as the plates are brought together, with enthalpy and entropy changes that both promote aggregation. We find a strong correlation between the strength of the hydrophobic interaction and the degree of preferential binding/exclusion of the ions relative to the surfaces. The results show that amplification of the hydrophobic interaction, a phenomenon analogous to salting-out, is a purely entropic effect and is induced by high-charge-density ions that exhibit preferential exclusion. In contrast, a reduction of the hydrophobic interaction, analogous to salting-in, is induced by low-charge-density ions that exhibit preferential binding, the effect being either entropic or enthalpic. Our findings are relevant to phenomena long studied in solution chemistry, as we demonstrate the significant, yet subtle, effects of electrolytes on hydrophobic aggregation and collapse.
我们使用分子动力学模拟来研究盐水溶液中两个纳米级疏水表面之间的溶剂介导吸引力和干燥过程。我们将这些效应作为离子电荷密度（即单位离子体积的离子电荷）的函数进行研究，同时保持离子直径不变。当平板靠近时，吸引力通过自由能的负变化来表示，伴随着促进聚集的焓变和熵变。我们发现疏水相互作用的强度与离子相对于表面的优先结合/排斥程度之间存在很强的相关性。结果表明，疏水相互作用的增强，一种类似于盐析的现象，是一种纯粹的熵效应，由表现出优先排斥的高电荷密度离子诱导。相反，疏水相互作用的减弱，类似于盐溶，是由表现出优先结合的低电荷密度离子诱导的，其效应可以是熵效应或焓效应。我们的发现与溶液化学中长期研究的现象相关，因为我们证明了电解质对疏水聚集和塌陷具有显著但微妙的影响。
