Zangi Ronen, Berne B J
Department of Chemistry and Center for Biomolecular Simulations, Columbia University, New York, New York 10027, USA.
J Phys Chem B. 2006 Nov 16;110(45):22736-41. doi: 10.1021/jp064475+.
The effect of salts on the solvent-induced interactions between hydrophobic particles dispersed in explicit aqueous solution is investigated as a function of the salt's ionic charge density by molecular dynamics simulations. We demonstrate that aggregates of the hydrophobic particles can be formed or dissolved in response to changes in the charge density of the ions. Ions with high charge density increase the propensity of the hydrophobic particles to aggregate. This corresponds to stronger hydrophobic interactions and a decrease in the solubility (salting-out) of the hydrophobic particles. Ions with low charge density can either increase or decrease the propensity for aggregation depending on whether the concentration of the salt is low or high, respectively. At low concentrations of low charge density ions, the aggregate forms a "micelle-like" structure in which the ions are preferentially adsorbed at the surface of the aggregate. These "micelle-like" structures can be soluble in water so that the electrolyte can both increase the solubility and increase aggregation at the same time. We also find, that at the concentration of the hydrophobic particles studied (approximately 0.75 m), the aggregation process resembles a first-order transition in finite systems.
通过分子动力学模拟,研究了盐对分散在显式水溶液中的疏水颗粒之间溶剂诱导相互作用的影响,并将其作为盐离子电荷密度的函数进行考察。我们证明,疏水颗粒的聚集体可根据离子电荷密度的变化而形成或溶解。具有高电荷密度的离子会增加疏水颗粒聚集的倾向。这对应于更强的疏水相互作用以及疏水颗粒溶解度的降低(盐析)。具有低电荷密度的离子根据盐浓度是低还是高,分别可以增加或降低聚集倾向。在低电荷密度离子的低浓度下,聚集体形成一种“胶束状”结构,其中离子优先吸附在聚集体表面。这些“胶束状”结构可溶于水,因此电解质既能增加溶解度又能同时增加聚集。我们还发现,在所研究的疏水颗粒浓度(约0.75 m)下,聚集过程类似于有限系统中的一级转变。