Salting-in and salting-out of hydrophobic solutes in aqueous salt solutions
Salting-in and salting-out of hydrophobic solutes in aqueous salt solutions
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DOI：
10.1021/jp010568
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发表时间：
2001-07-12
影响因子：
3.3
通讯作者：
Garde, S
中科院分区：
文献类型：
--
作者：
Kalra, A;Tugcu, N;Garde, S
我们目前的结果在三个四甲基铵[N（CH 3）（4）（+）]盐溶液中的疏水溶质的水合作用在不同浓度的分子动力学模拟的热力学和结构方面。单价抗衡离子的不同大小的F-，Cl-，和一个相对较大的模型离子BI-的选择，以涵盖一系列的kosmotropic离液行为。使用测试粒子插入获得的硬球溶质的化学势显示盐的类型的盐的盐溶和盐析效果。计算了硬球溶质附近的水和盐离子密度。小的和强水合的F-离子（亲液剂）被排除在疏水溶质附近，导致疏水溶质附近的局部水密度增加（即，优先水合）。这增加了溶液中疏水溶质的过量化学势，导致盐析。对于与疏水溶质强烈缔合的大的、不太有利的水合BI离子（离液剂）观察到相反的行为。由于相邻的水分子，阳离子和阴离子的硬球溶质的表面上的压缩力的计算。我们发现，水分子对总压缩力的贡献最大。这解释了所观察到的溶质表面的优先水合或脱水的程度和盐析或盐溶效应之间的线性相关性。疏水性溶质的水合热力学的趋势，在添加盐的解释在结构水合的个别盐离子。
We present results on the thermodynamic and structural aspects of the hydration of hydrophobic solutes in three tetramethylammonium [N(CH3)(4)(+)] Salt solutions at various concentrations obtained from molecular dynamics simulations. Monovalent counterions of different sizes-F-, Cl-, and a relatively large model ion BI--are chosen in order to cover a range of kosmotropic to chaotropic behaviors. Chemical potentials of hard-sphere solutes obtained using test particle insertions display both salting-in and salting-out effects depending on the type of salt. Water and salt-ion densities in the vicinity of hard-sphere solutes are calculated. Small and strongly hydrated F- ions (kosmotropes) are excluded from the vicinity of hydrophobic solutes, leading to an increase in local water densities near hydrophobic solutes (i.e., preferential hydration). This increases the excess chemical potential of hydrophobic solutes in solution which leads to salting-out. Opposite behavior is observed for large, less favorably hydrated BI- ions (chaotropes) which associate strongly with hydrophobic solutes. Compressive forces due to neighboring water molecules, cations, and anions on the surface of the hard sphere solute are calculated. We find that water molecules make the most significant contribution toward the total compressive force. This explains the observed linear correlation between the extent of preferential hydration or dehydration of the solute surface and salting-out or salting-in effects. The trends in the thermodynamics of hydration of hydrophobic solutes upon addition of salts are explained in terms of the structural hydration of individual salt ions.