Local Electric Fields in Aqueous Electrolytes
Local Electric Fields in Aqueous Electrolytes
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DOI：
10.1021/acs.jpcb.1c03257
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发表时间：
2021-07-27
影响因子：
3.3
通讯作者：
Cremer, Paul S.
中科院分区：
文献类型：
--
作者：
Drexler, Chad, I;Cracchiolo, Olivia M.;Cremer, Paul S.
研究了含羰基和腈的有机分子水溶液中的振动斯塔克位移。在许多情况下，当盐被引入溶液时，这些部分的振动共振向较低的频率转移。这与基于Onsager反应场理论的蓝移形成了对比。含有水合良好阳离子（如Mg2+或Li+）的盐会导致羰基发生最明显的斯塔克位移，而含有水合不良阳离子（如Cs+）的盐对腈的影响最大。此外，含有I-的盐比含有Cl-的盐产生更大的斯塔克位移。分子动力学模拟表明，阳离子和阴离子都以离子和探针依赖的方式在探针周围积累。离子对通过振动发色团从阳离子指向阴离子产生电场。这是由于离子与探针的溶剂共享结合，与它们在霍夫迈斯特系列中的位置一致。“反昂萨格”斯塔克位移发生在振动光谱和荧光测量中。
Vibrational Stark shifts were explored in aqueous solutions of organic molecules with carbonyl- and nitrile-containing constituents. In many cases, the vibrational resonances from these moieties shifted toward lower frequency as salt was introduced into solution. This is in contrast to the blue-shift that would be expected based upon Onsager's reaction field theory. Salts containing well-hydrated cations like Mg2+ or Li+ led to the most pronounced Stark shift for the carbonyl group, while poorly hydrated cations like Cs+ had the greatest impact on nitriles. Moreover, salts containing I- gave rise to larger Stark shifts than those containing Cl-. Molecular dynamics simulations indicated that cations and anions both accumulate around the probe in an ion- and probe-dependent manner. An electric field was generated by the ion pair, which pointed from the cation to the anion through the vibrational chromophore. This resulted from solvent-shared binding of the ions to the probes, consistent with their positions in the Hofmeister series. The "anti-Onsager" Stark shifts occur in both vibrational spectroscopy and fluorescence measurements.