Solvation of Magnesium Dication: Molecular Dynamics Simulation and Vibrational Spectroscopic Study of Magnesium Chloride in Aqueous Solutions
Solvation of Magnesium Dication: Molecular Dynamics Simulation and Vibrational Spectroscopic Study of Magnesium Chloride in Aqueous Solutions
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DOI：
10.1021/jp909132a
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发表时间：
2010-04-22
影响因子：
2.9
通讯作者：
Tobias, Douglas J.
中科院分区：
文献类型：
--
作者：
Callahan, Karen M.;Casillas-Ituarte, Nadia N.;Tobias, Douglas J.
镁离子在生物化学中具有重要的作用。虽然海洋和陆地上的矿物盐对环境都是可用的，但它在环境和大气化学中的作用仍然相对未知。一些实验证据表明，在环境条件下，接触离子对在氯化镁溶液中可能不存在，直到饱和浓度。这不是大多数离子的典型情况。关于氯化镁溶液中离子对的存在，分子动力学文献中一直存在分歧。利用本研究中建立的力场，我们证明了接触离子配对在能量上是不利的。此外，我们提出了依赖于浓度的拉曼光谱研究的镁-O-水六水拉伸，明确支持在氯化镁溶液中没有离子对，尽管在0.06x和0.09x之间发生的光谱跃迁表明溶液结构发生了变化。最后，我们比较了实验和计算的观测值，以验证我们的力场以及另外两个常用的镁力场，并在此过程中发现，在较高浓度的氯化镁水溶液中，明显没有观察到镁的离子配对，与镁力场的选择无关，尽管赛纳力场与实验结果更吻合。
Magnesium dication plays many significant roles in biochemistry. While it is available to the environment from both ocean waters and mineral salts on land, its roles in environmental and atmospheric chemistry are still relatively unknown. Several pieces of experimental evidence suggest that contact ion pairing may not exist at ambient conditions in solutions of magnesium chloride up to saturation concentrations. This is not typical of most ions. There has been disagreement in the molecular dynamics literature concerning the existence of ion pairing in magnesium chloride solutions. Using a force field developed during this study, we show that contact ion pairing is not energetically favorable. Additionally, we present a concentration-dependent Raman spectroscopic study of the Mg-O-water hexaaquo stretch that clearly supports the absence of ion pairing in MgCl2 solutions, although a transition occurring in the spectrum between 0.06x and 0.09x suggests a change in solution structure. Finally, we compare experimental and calculated observables to validate our force field as well as two other commonly used magnesium force fields, and in the process show that ion pairing of magnesium clearly is not observed at higher concentrations in aqueous solutions of magnesium chloride, independent of the choice of magnesium force field, although seine force fields give better agreement to experimental results than others.