Terahertz spectroscopy of aqueous ionic solutions to understand the role of hydrogen-bond network breaking and strengthening in the Hofmeister

1888年，Franz Hofmeister在他的论文“Zur Lehre von der Wirkung der Salze”中发现了一系列盐-后来被命名为Hofmeister系列-具有沉淀蛋白质的倾向。随着时间的推移，霍夫迈斯特系列与各种离子溶剂化水的倾向有关变得很清楚。传统的观点认为离子可以被归类为kosmotropes或chaotropes：kosmotropes被认为在周围的水中诱导更像冰的有序，而chaotropes破坏了局部的四面体网络。然而，这一整洁的画面被超快红外研究打乱了，研究表明，水的结构在溶剂化离子周围的第一个溶剂化壳层之外保持不变（“溶剂堡”模型）。在这里，我们建议使用太赫兹拉曼和红外光谱结合时间分辨二维红外光谱（与罗宾Hochstrasser合作）研究飞秒氢键动力学的溶剂化水分子和皮秒扩散动力学离子周围。初步结果表明，太赫兹拉曼数据与以前的泵浦探测实验和各种理论研究不一致，需要对理论模型进行全面检查。我们与凯西海因斯的合作将使我们能够影响离子溶剂化理论工作的发展。

In 1888, Franz Hofmeister in his paper 'Zur Lehre von der Wirkung der Salze' discovered a series of salts -- later named the Hofmeister series -- that have an increasing propensity to precipitate proteins. It became clear over time that the Hofmeister series is related to the propensity of various ions to solvate water. The classical view is that ions may be classed as kosmotropes or chaotropes: kosmotropes are thought to induce a more icelike ordering in the surrounding water whereas chaotropes disrupt the local tetrahedral network. However, this tidy picture was thrown into disarray by ultrafast infrared studies pertaining to show that the water structure remains unaltered beyond the first solvation shell around solvated ions (the 'solventberg' model). Here we propose to use terahertz Raman and infrared spectroscopy combined with time-resolved two-dimensional infrared spectroscopy (in collaboration with Robin Hochstrasser) to study femtosecond hydrogen-bond dynamics of solvated water molecules and picosecond diffusive dynamics around ions. Preliminary results indicate that the terahertz Raman data is at odds with previous pump-probe experiments and various theoretical studies, requiring an overhaul of theoretical models. Our collaboration with Casey Hynes will allow us to influence the development of theoretical work on ionic solvation.