结构相似单糖和二糖分子的太赫兹时域光谱研究

应用太赫兹时域光谱(THz-TDS)技术结合密度泛函理论(DFT)对两种结构相似的典型单糖和二糖物质(D-葡萄糖和乳糖一水化合物)在0.3~1.7 THz频段的太赫兹吸收光谱进行了实验与理论模拟研究。首先，利用THz-TDS技术分别测量了D-葡萄糖和乳糖一水化合物在0.3~1.7 THz频段的太赫兹特征吸收谱，获得了它们在此太赫兹频率范围内的指纹光谱数据，发现虽然乳糖的组成结构中含有葡萄糖，但THz-TDS技术对糖类分子的结构变化非常敏感，两种物质在所测太赫兹频段内分别表现出各自不同的太赫兹指纹吸收特性。然后，利用DFT方法分别对两种糖类物质单分子和多分子构型的低频集体振动模式进行了理论模拟计算，获得了D-葡萄糖晶胞构型和乳糖一水化合物单分子及晶胞构型的DFT模拟计算结果，并通过简正振动模式分解的PED分析方法，结合GaussView显示的分子振动形式，对两种糖类物质在太赫兹频段吸收峰的简正振动模式进行了指认，发现乳糖一水化合物的振动模式与羟基(-OH)、羟甲基(-CH₂OH)和糖苷键的振动模式密切相关，且D-葡萄糖在1.44 THz处及乳糖一水化合物在1.38 THz处出现的吸收峰主要是由分子间的相互作用(氢键和范德华力)，尤其是相互作用较强的氢键引起。最后，利用约化密度梯度(RDG)分析，可视化地分析了D-葡萄糖和乳糖一水化合物分子间相互作用的位置、类型和强度，进一步证明了两种物质在太赫兹频段的特征吸收峰主要来源于分子间氢键网络支配的集体振动模式。研究结果表明，THz-TDS技术对糖类分子结构的细微变化有着敏锐的感知，虽然D-葡萄糖和乳糖一水化合物的分子结构相似，但太赫兹波对它们之间的结构差异十分敏感，两者在太赫兹波段的特征吸收谱表现出明显差异，这为THz-TDS技术结合DFT方法对糖类物质进行检测识别以及研究糖类分子间的相互作用提供了有价值的实验和理论参考。

A Study of Terahertz Spectra of Monosaccharides and Disaccharides with Structural Similarities

Experimental and theoretical investigations of the terahertz (THz) absorption spectra of two typical monosaccharides and disaccharides (D-glucose and lactose monohydrate), which have similar structures, were carried out by using terahertz time-domain spectroscopy (THz-TDS) and density functional theory (DFT). Firstly, the THz absorption spectra of D-glucose and lactose monohydrate were measured in the frequency range from 0.3 to 1.7 THz by THz-TDS system, and it was found that although the composition of lactose contained glucose, the THz-TDS was very sensitive to the structural changes of carbohydrates. The two carbohydrates showed their special THz fingerprint absorption characteristics in the measured THz band, respectively. Secondly, the vibration frequencies of these two carbohydrates in the THz band were calculated by using the DFT method, and the simulation results, including the unit cell configuration of D-glucose and the isolated-molecule and unit cell configuration of lactose monohydrate, were obtained. At the same time, combining molecular vibration animation displayed by GaussView and potential energy distributions (PED) analysis, the vibrational modes of these two carbohydrates in the THz band were assigned in detail. It was found that the vibrational modes of lactose monohydrate were closely related to the vibrational modes of hydroxyl (-OH), hydroxymethyl (-CH₂OH) and glycosidic bond. The absorption peaks of D-glucose at 1.44 THz and lactose monohydrate at 1.38 THz were mainly caused by intermolecular interactions (hydrogen bonds and van der Waals forces), especially the strong hydrogen bonds. Finally, using the reduced density gradient (RDG) analysis, the type and intensity of the intermolecular interactions of D-glucose and lactose monohydrate were visualized. The experimental results indicated that the THz-TDS technique has a keen perception for the subtle changes in the structure of carbohydrates, which provides an effective method for investigation of intermolecular interactions and detection of carbohydrates.