随着绿色化学的要求, 更多科研工作者们致力于绿色环保的低共熔溶剂(DES)研究上。 氯化胆碱类DES具有无毒无污染且容易制备的特性, 已被应用于许多不同的领域。 以氯化胆碱(Choline chloride, ChCl)和丙三醇(Glycerine, Gly)形成的DES为研究对象。 对比ChCl, Gly和ChCl/Gly的红外光谱图, 发现NC₄和O—H发生了红移以及特征峰的合并和消失, 这些都表明ChCl/Gly通过N—$\mathrm{H}_{\mathrm{Ch}}^{+}$···Cl^-和Cl^-···H—O_Gly的方式形成DES。 为了探究不同温度下DES变化情况, 以温度为外扰测试25~135 ℃下ChCl/Gly的红外光谱数据, 对比这些数据发现不同温度下NC₄和O—H光谱峰的强度、 宽度和位置都发生了一定程度的改变, 但是这些特征峰都是宽峰具有重叠现象, 很难通过一维光谱分析, 采用二维红外光谱(2D-IR)可以对复杂溶液体系进行更好的图谱分析, 探究其形成机理和分子间结构。 对ChCl/Gly中NC₄和O—H特征峰随温度变化的数据进行2D-IR分析, 获得动态变化顺序, 推测溶液中不同的分子团簇。 研究发现25~65 ℃时O—H在3 539、 3 400、 3 380和3 177 cm^-1有四个自动峰, NC₄也出现不同的自动峰, 这些峰可归属于ChCl/Gly、 ChCl/(Gly)₂、 ChCl/(Gly)₃; 在65~105 ℃时O—H在3 539、 3 400和3 380 cm^-1有三个自动峰, NC₄有相应的变化, 这些峰可归属于ChCl/Gly和ChCl/(Gly)₂; 在105~135 ℃时O—H只在3 380 cm^-1有一个强自动峰, NC₄也只出现一个自动峰, 可归属于ChCl/Gly。 通过2D-IR分析得出随温度上升溶液中分子团簇解离成更稳定的结构, 为了验证这一结论和探究不同团簇分子间Cl^-作为桥梁形成N—$\mathrm{H}_{\mathrm{Ch}}^{+}$···Cl^-和Cl^-···H—O_Gly具体连接方式。 采用密度泛函理论(DFT)在B3LYP/6-311G++(2d, p)理论水平上进行构型几何优化, 计算出相关的热力学数据, 证实了ChCl/Gly中不同分子团簇存在的可能性。 研究表明2D-IR和密度泛函理论计算相结合, 能够很好地用于分析DES中不同分子团簇随温度变化的规律, 较好地解决了一维红外光谱在温度外扰下难以分析重叠峰和宽峰的问题。

With the requirements of green chemistry, more researchers are committed to studying green eutectic solvents (DES). Choline chloride eutectic solvent (DES) has been used in many fields because of its non-toxic, pollution-free and easy preparation. DES formed by choline chloride (ChCl) and glycerol (Gly) was studied in this paper. Comparing the infrared spectra of ChCl, Gly and ChCl/Gly, it was found that NC4 and O—H had red-shift and the combination and disappearance of characteristic peaks, which all indicated that ChCl/Gly formed DES through N—$\mathrm{H}_{\mathrm{Ch}}^{+}$···Cl^- and Cl^-···H—O_Gly. In order to explore the changes of DES at different temperatures, the infrared spectral data of ChCl/Gly at 25~135 ℃ were tested with temperature as an external disturbance. It was found that the intensity, width and position of NC₄ and O—H spectral peaks changed to a certain extent at different temperatures, but these characteristic peaks were all wide peaks with overlapping phenomenon. It is difficult to conduct one-dimensional spectral analysis, but two-dimensional infrared spectroscopy (2D-IR) can better analyze the complex solution system and explore its formation mechanism and intermolecular structure. 2D-IR analysis was performed on the data of NC₄ and O—H characteristic peaks in ChCl/Gly as a function of temperature to obtain the dynamic change sequence and predict the different molecular clusters in the solution. The results Three automatic O—H peaks at 3 539, 3 380 and 3 177 cm^-1 at 25~65 ℃. Different automatic peaks of NC₄ also appear, which can be attributed to ChCl/Gly, ChCl/(Gly)₂ and ChCl/(Gly)₃. At 65~105 ℃, O—H has two automatic peaks at 3 539, 3 380 and 3 400 cm^-1, and NC₄ has corresponding changes, which can be attributed to ChCl/Gly and ChCl/(Gly)₂. At 105~135 ℃, O—H only had a strong automatic peak at 3 380 cm^-1, and NC₄ only had an automatic peak, attributed to ChCl/Gly. Through 2D-IR analysis, it is concluded that molecular clusters in the solution dissociate into a more stable structure with the rise of temperature. In order to verify this conclusion and explore the specific connection mode of N—$\mathrm{H}_{\mathrm{Ch}}^{+}$···Cl^- and Cl^-···H—O_Gly formed by Cl^- between molecules of different clusters as Bridges. The density functional theory (DFT) was used to optimize the configuration geometry at the B3LYP/6-311G++(2d,p) theoretical level, and the relevant thermodynamic data were calculated, which confirmed the possibility of the existence of different molecular clusters in ChCl/Gly. The study shows that the combination of 2D-IR and density functional theory calculation can be well used to analyze the law of different molecular clusters in DES with temperature change, which better solves the problem that it is difficult to analyze overlapping and wide peaks in a one-dimensional infrared spectrum under temperature disturbance.