Examining the Hofmeister Series through Activation Energies: Water Diffusion in Aqueous Alkali-Halide Solutions
Examining the Hofmeister Series through Activation Energies: Water Diffusion in Aqueous Alkali-Halide Solutions
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通过活化能检查霍夫迈斯特级数：碱卤化物水溶液中的水扩散
DOI：
10.1021/acs.jpcb.0c09965
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Thompson, Ward H.
中科院分区：
文献类型：
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作者：
Borkowski, Ashley K.;Piskulich, Zeke A.;Thompson, Ward H.
离子对水溶液性质的影响通常根据霍夫迈斯特系列进行分类，该系列将它们与离液剂进行排序（“结构破坏者”），削弱周围的氢键网络，（“结构制造者”），这增强了它。在这里，我们研究了Hofmeister系列在101 M钠-卤化物溶液使用分子动力学模拟计算的身份和接近的卤化物阴离子的水扩散系数和活化能的效果。最近开发的方法计算活化能从一个单一的温度模拟，这也允许严格分解成不同的相互作用和运动的贡献。盐对水动力学的影响的机制进行了探索，分别考虑水分子的位置相对于离子。结果表明，水的扩散是加速向下移动的卤素基团从F-到I-。扩散活化能Ea的行为更为复杂，表明熵效应的重要作用。然而，在离子的第一或第二溶剂化壳层中的水分子在向下移动卤化物系列时表现出减少，并且Na+表现出比任何阴离子更大的影响。在离子的第二溶剂化壳层内的水分子的Ea是适度的，表明离子影响的短程性质。
The effect of ions on the properties of aqueous solutions is often categorized in terms of the Hofmeister series that ranks them from chaotropes (“structure-breakers”), which weaken the surrounding hydrogen-bond network to kosmotropes (“structure-makers”), which enhance it. Here, we investigate the Hofmeister series in ∼1 M sodium-halide solutions using molecular dynamics simulations to calculate the effect of the identity and proximity of the halide anion on both the water diffusion coefficient and its activation energy. A recently developed method for calculating the activation energy from a single-temperature simulation is used, which also permits a rigorous decomposition into contributions from different interactions and motions. The mechanisms of the salt effects on the water dynamics are explored by separately considering water molecules based on their location relative to the ions. The results show that water diffusion is accelerated moving down the halide group from F–to I–. The behavior of the diffusion activation energy,Ea, is more complex, indicating a significant role for entropic effects. However, water molecules in the first or second solvation shell of an ion exhibit a decrease inEamoving down the halide series and Na+exhibits a larger effect than any of the anions. TheEafor water molecules within the second solvation shell of an ion are modest, indicating a short-ranged nature of the ion influence.