Moelbert Susanne, Normand B, De Los Rios Paolo
Institut de théorie des phénoménes physiques, Ecole polytechnique fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Biophys Chem. 2004 Dec 1;112(1):45-57. doi: 10.1016/j.bpc.2004.06.012.
Kosmotropic cosolvents added to an aqueous solution promote the aggregation of hydrophobic solute particles, while chaotropic cosolvents act to destabilise such aggregates. We discuss the mechanism for these phenomena within an adapted version of the two-state Muller-Lee-Graziano model for water, which provides a complete description of the ternary water/cosolvent/solute system for small solute particles. This model contains the dominant effect of a kosmotropic substance, which is to enhance the formation of water structure. The consequent preferential exclusion both of cosolvent molecules from the solvation shell of hydrophobic particles and of these particles from the solution leads to a stabilisation of aggregates. By contrast, chaotropic substances disrupt the formation of water structure, are themselves preferentially excluded from the solution, and thereby contribute to solvation of hydrophobic particles. We use Monte Carlo simulations to demonstrate at the molecular level the preferential exclusion or binding of cosolvent molecules in the solvation shell of hydrophobic particles, and the consequent enhancement or suppression of aggregate formation. We illustrate the influence of structure-changing cosolvents on effective hydrophobic interactions by modelling qualitatively the kosmotropic effect of sodium chloride and the chaotropic effect of urea.
添加到水溶液中的促溶共溶剂会促进疏水性溶质颗粒的聚集，而变性共溶剂则会使此类聚集体不稳定。我们在适用于水的双态穆勒 - 李 - 格拉齐亚诺模型内讨论这些现象的机制，该模型对小溶质颗粒的三元水/共溶剂/溶质系统提供了完整描述。此模型包含促溶物质的主要作用，即增强水结构的形成。由此导致共溶剂分子从疏水颗粒的溶剂化层中优先被排除，以及这些颗粒从溶液中优先被排除，从而使聚集体得以稳定。相比之下，变性物质会破坏水结构的形成，它们自身优先从溶液中被排除，从而有助于疏水颗粒的溶剂化。我们使用蒙特卡罗模拟在分子水平上证明共溶剂分子在疏水颗粒溶剂化层中的优先排除或结合，以及由此导致的聚集体形成的增强或抑制。我们通过定性模拟氯化钠的促溶作用和尿素的变性作用，来说明改变结构的共溶剂对有效疏水相互作用的影响。
