Di Tommaso Devis, Ruiz-Agudo Encarnación, de Leeuw Nora H, Putnis Andrew, Putnis Christine V
School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
Phys Chem Chem Phys. 2014 May 7;16(17):7772-85. doi: 10.1039/c3cp54923b.
Classical molecular dynamics simulations of several aqueous alkali halide salt solutions have been used to determine the effect of electrolytes on the structure of water and the hydration properties of calcium ions. Compared with the simulations of Ca(2+) ions in pure liquid water, the frequency of water exchange in the first hydration shell of calcium, which is a fundamental process in controlling the reactivity of calcium(ii) aqua-ions, is drastically reduced in the presence of other electrolytes in solution. The strong stabilization of the hydration shell of Ca(2+) occurs not only when the halide anions are directly coordinated to calcium, but also when the alkali and halide ions are placed at or outside the second coordination shell of Ca(2+), suggesting that the reactivity of the first solvation shell of the calcium ion can be influenced by the specific affinity of other ions in solution for the water molecules coordinated to Ca(2+). Analysis of the hydrogen-bonded structure of water in the vicinity of the calcium ion shows that the average number of hydrogen bonds per water molecules, which is 1.8 in pure liquid water, decreases as the concentration of alkali-halide salts in solution increases, and that the temporal fluctuations of hydrogen bonds are significantly larger than those obtained for Ca(2+) in pure liquid water. This effect has been explained in terms of the dynamics of reorganization of the O-H···X(-) (X = F, Cl and Br) hydrogen bond. This work shows the importance of solution composition in determining the hydrogen-bonding network and ligand-exchange dynamics around metal ions, both in solution and at the mineral-water interfaces, which in turn has implications for interactions occurring at the mineral-water interface, ultimately controlling the mobilization of ions in the environment as well as in industrial processes.
通过对几种碱金属卤化物盐水溶液进行经典分子动力学模拟，来确定电解质对水结构和钙离子水合性质的影响。与在纯液态水中对钙离子的模拟相比，在溶液中存在其他电解质的情况下，钙离子第一水合层中水分子交换的频率大幅降低，而水分子交换是控制钙离子水合离子反应活性的一个基本过程。钙离子水合层的强烈稳定不仅发生在卤化物阴离子直接与钙配位时，而且当碱金属和卤化物离子位于钙离子的第二配位层或其外部时也会发生，这表明溶液中其他离子对与钙离子配位的水分子的特定亲和力会影响钙离子第一溶剂化层的反应活性。对钙离子附近水的氢键结构分析表明，每个水分子的平均氢键数（在纯液态水中为1.8）随着溶液中碱金属卤化物盐浓度的增加而减少，并且氢键的时间波动明显大于在纯液态水中钙离子的情况。这种效应已根据O-H···X(-)（X = F、Cl和Br）氢键的重组动力学进行了解释。这项工作表明了溶液组成在确定溶液中和矿物-水界面处金属离子周围的氢键网络和配体交换动力学方面的重要性，这反过来又对矿物-水界面处发生的相互作用有影响，最终控制环境以及工业过程中离子的迁移。
