Role of Hydration in Magnesium versus Calcium Ion Pairing with Carboxylate: Solution and the Aqueous Interface
Role of Hydration in Magnesium versus Calcium Ion Pairing with Carboxylate: Solution and the Aqueous Interface
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DOI：
10.1021/acs.jpcb.1c06108
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发表时间：
2021-10-02
影响因子：
3.3
通讯作者：
Allen, Heather C.
中科院分区：
文献类型：
--
作者：
de Vasquez, Maria G. Vazquez;Rudd, Bethany A. Wellen;Allen, Heather C.
II 族金属阳离子（例如 Ca2+ 和 Mg2+）的结合主要被归类为静电或离子，使用羧酸盐对称和不对称拉伸频率分配，历史上一直使用这些分配，很少考虑水溶液的溶剂化环境。然而，考虑到这些阳离子及其与生物功能相关的结合机制以及揭示海洋到海洋气溶胶转移的表面富集因素的重要性，必须寻求更深入的理解来包括水合效应。此处，将表面和溶液相羧酸盐结合信息的红外反射吸收光谱和拉曼光谱分别与裸露（未结合）羧酸盐和二齿 Zn2+:羧酸盐光谱特征进行比较。光谱非重合效应分析、温度研究以及平均力计算的光谱和电位可以对结合基序进行简明解释，其中包括介导水分子的作用，即接触和溶剂共享离子对。钙直接与接触离子对中的羧酸根结合，而镁很少结合。此外，我们揭示了镁与羧酸盐的溶剂共享离子对在空气-水界面和溶液中的主导地位。
The binding of group II metal cations such as Ca2+ and Mg2+ has been largely categorized as electrostatic or ionic using carboxylate symmetric and asymmetric stretching frequency assignments that have been historically used with little regard for the solvation environment of aqueous solutions. However, given the importance of these cations and their binding mechanisms related to biological function and in revealing surface enrichment factors for ocean to marine aerosol transfer, it is imperative that a deeper understanding be sought to include hydration effects. Here, infrared reflection-absorption and Raman spectra for surface and solution phase carboxylate binding information, respectively, are compared against bare (unbound) carboxylate and bidentate Zn2+:carboxylate spectral signatures. Spectral non-coincidence effect analysis, temperature studies, and spectral and potential of mean force calculations result in a concise interpretation of binding motifs that include the role of mediating water molecules, that is, contact and solvent-shared ion pairs. Calcium directly binds to the carboxylate group in contact ion pairs where magnesium rarely does. Moreover, we reveal the dominance of the solvent-shared ion pair of magnesium with carboxylate at the air-water interface and in solution.