Division of Theoretical Chemistry , Lund University , P.O. Box 124 , SE-22100 Lund , Sweden.
J Phys Chem B. 2018 May 17;122(19):5094-5105. doi: 10.1021/acs.jpcb.8b02303. Epub 2018 May 3.
The large and sparsely hydrated thiocyanate anion, SCN, plays a prominent role in the study of specific ion effects in biological, colloid, and atmospheric chemistry due to its extreme position in the Hofmeister series. Using atomistic modeling of aqueous SCN solutions, we provide novel insight at the molecular scale into the experimentally observed differences in ion pairing, clustering, reorientation dynamics, mutual diffusion, and solubility between the sodium, Na, and the potassium, K, salt. Compared to KSCN, NaSCN has a less pronounced tendency to ion pairing; nevertheless, at high salt concentrations, we observe a strong attraction between Na cations and the nitrogen end of SCN, resulting in larger and more closely packed ion clusters. To accurately model aqueous SCN solutions in computer simulations, we develop a thermodynamically consistent force field rooted in quantum-chemical calculations and refined using the Kirkwood-Buff theory. The force field is compatible with the extended simple point charge and three-point optimal point charge classical water models and reproduces experimental activity derivatives and air-water surface tension for a wide range of salt concentrations.
大而疏水性的硫氰酸根阴离子（SCN）在生物、胶体和大气化学中特定离子效应的研究中起着突出的作用，这是由于其在 Hofmeister 序列中的极端位置。通过对水合 SCN 溶液的原子建模，我们从分子尺度上为实验观察到的钠离子（Na）和钾离子（K）盐之间的离子配对、聚集、重定向动力学、相互扩散和溶解度的差异提供了新的见解。与 KSCN 相比，NaSCN 的离子配对趋势不那么明显；然而，在高盐浓度下，我们观察到 Na 阳离子与 SCN 的氮端之间存在强烈的吸引力，导致更大和更紧密堆积的离子簇。为了在计算机模拟中准确地模拟水合 SCN 溶液，我们开发了一种热力学一致的力场，该力场基于量子化学计算，并使用 Kirkwood-Buff 理论进行了改进。该力场与扩展的简单点电荷和三点最佳点电荷经典水模型兼容，并为广泛的盐浓度范围重现了实验活性导数和空气-水表面张力。
