拉曼光谱探究低温对π…H-X氢键的影响

Influence of Low Temperature on π…H-X Hydrogen Bond via Raman Spectroscopy

摘要: π…H-X氢键(以下简称π氢键)作为X-H质子供体与π电子体系间的弱相互作用，广泛存在于生物大分子中，在分子识别、超分子组装与生物结构稳定等过程中起到重要作用。本文以费米共振为分子探针，采用拉曼光谱，系统研究低温对π氢键的调控机制。具体研究结果如下：测量了苯–甲醇浓度梯度实验，得到π氢键与费米共振之间的关系：π氢键数量的增加会导致费米共振强度降低。其次对1:1苯–甲醇进行了变温实验，结果表明，通过降温使样品发生相变进而强化氢键作用：约−10℃苯率先凝固，分子有序度提升，费米双峰峰强上升、半高宽变窄并红移；约−90℃甲醇形成共晶，氢键网络更加致密，π氢键对振动非谐性的调控显著增强，进而使费米共振耦合强度进一步降低。

Abstract: The π…H-X hydrogen bond (hereinafter referred to as π-hydrogen bond) is a weak interaction formed between X-H proton donors and π-electron systems. It widely exists in biomacromolecules and plays a vital role in molecular recognition, supramolecular assembly and biological structural stabilization. Using Fermi resonance as a molecular probe and Raman spectroscopy as the research method, this paper systematically investigates the regulation mechanism of low temperature on π-hydrogen bonds. The main research findings are summarized as follows. Concentration gradient experiments of benzene-methanol mixtures were carried out, revealing the correlation between π-hydrogen bonds and Fermi resonance: an increase in the number of π-hydrogen bonds reduces the intensity of Fermi resonance. Variable-temperature experiments were further performed on benzene-methanol mixtures at a molar ratio of 1:1. The results demonstrate that cooling induces phase transition and strengthens hydrogen bonding interactions. Benzene solidifies first at approximately −10˚C with enhanced molecular orderliness, accompanied by increased intensity, narrowed full width at half maximum and redshift of the Fermi doublet peaks. Methanol forms eutectic crystals at around −90˚C, constructing a denser hydrogen bond network. The regulation effect of π-hydrogen bonds on vibrational anharmonicity is markedly enhanced, which further weakens the coupling strength of Fermi resonance.