德国马普学会弗里茨哈伯研究所Sajadi Mohsen团队通过时间分辨太赫兹拉曼光谱，揭示了阳离子和阴离子明显地改变了水的分子间相互作用。相关研究成果于2022年6月30日发表在国际顶尖学术期刊《自然—化学》。
离子的溶剂化改变了水的物理、化学和热力学性质，这种行为的微观根源被认为是离子引起的水氢键网络的扰动。
该文中，研究人员使用时间分辨太赫兹拉曼光谱监测盐溶液中的能量耗散来揭示这一微观过程。研究人员使用强太赫兹脉冲共振驱动水分子的低频旋转动力学，并探测其分子间平移运动的拉曼响应。发现，高电荷的阳离子增强了分子间旋转到平移的能量转移，而高电荷的阴离子显著降低了分子间旋转到平移的能量转移，并随离子表面电荷密度和离子浓度而定标。
分子动力学模拟表明，阳离子第一和第二溶剂化壳层之间的水-水氢键强度增加，而阴离子周围的氢键强度降低。阳离子和阴离子对水分子间相互作用的相反影响类似于离子对蛋白质稳定性和变性的影响。
附：英文原文
Title: Time-resolved terahertz–Raman spectroscopy reveals that cations and anions distinctly modify intermolecular interactions of water
Author: Balos, Vasileios, Kaliannan, Naveen Kumar, Elgabarty, Hossam, Wolf, Martin, Khne, Thomas D., Sajadi, Mohsen
Issue&Volume: 2022-06-30
Abstract: The solvation of ions changes the physical, chemical and thermodynamic properties of water, and the microscopic origin of this behaviour is believed to be ion-induced perturbation of water’s hydrogen-bonding network. Here we provide microscopic insights into this process by monitoring the dissipation of energy in salt solutions using time-resolved terahertz–Raman spectroscopy. We resonantly drive the low-frequency rotational dynamics of water molecules using intense terahertz pulses and probe the Raman response of their intermolecular translational motions. We find that the intermolecular rotational-to-translational energy transfer is enhanced by highly charged cations and is drastically reduced by highly charged anions, scaling with the ion surface charge density and ion concentration. Our molecular dynamics simulations reveal that the water–water hydrogen-bond strength between the first and second solvation shells of cations increases, while it decreases around anions. The opposite effects of cations and anions on the intermolecular interactions of water resemble the effects of ions on the stabilization and denaturation of proteins.
DOI: 10.1038/s41557-022-00977-2
