对比于氨基酸的红外分析法, 太赫兹波的电子能量更低, 可实现无损检测。 氨基酸分子内原子振动、 分子间氢键的作用、 以及晶体中晶格的低频振动均处于太赫兹波段, 使其在太赫兹波段具有吸收峰, 且不同的氨基酸分子太赫兹吸收峰不同, 故可用氨基酸在太赫兹波段的这种“指纹特性”实现氨基酸类物质的定性分析。 量子化学分析方法可以应用量子力学的基本原理和方法, 研究稳定和不稳定分子的结构、 性能及其之间的关系, 还可以针对分子与分子间的相互作用、 相互碰撞及相互反应等问题进行研究。 通过量子化学计算方法计算氨基酸分子的太赫兹吸收谱, 可以为氨基酸分子的太赫兹吸收峰匹配分子振动模式, 对氨基酸定性分析有一定参考性与指向性, 并为实验获取的样品太赫兹时域光谱提供理论支撑, 在实验获得太赫兹吸收谱的基础上进行量子化学计算, 还能为实验结果进行验证。 首先利用太赫兹时域光谱技术获取了谷氨酰胺、 苏氨酸、 组氨酸的太赫兹吸收谱, 分别构建这三种氨基酸样品在实物中以两性离子形式存在的单分子构型, 利用量子化学计算方法在完成结构优化后进行太赫兹吸收谱模拟计算。 计算结果表明三种氨基酸单分子的太赫兹吸收谱计算结果与实验获取的太赫兹吸收谱差异较大, 但在高频段吸收峰峰位基本吻合。 通过GaussView分别查看了这三种氨基酸分子在太赫兹段内的吸收峰对应频率处的振转情况, 发现在高频段内三种氨基酸分子官能团均只发生转动而未见振动, 并且转动模式基本一致。 通过对氨基酸官能团的太赫兹吸收谱进行量子化学计算, 将官能团在高频段内吸收峰对应频率处的振转模式与三种氨基酸分子在该段内吸收峰对应频率处的振转模式做了对比。 研究表明, 在氨基酸单分子构型下由量子化学方法计算所得的太赫兹吸收谱中, 高频段内计算得出的模拟吸收峰与实验获取的太赫兹吸收峰基本吻合; 振转模式分析发现, 谷氨酰胺、 苏氨酸、 组氨酸在太赫兹高频段内的氨基酸官能团振转模式相同, 三种氨基酸分子在高频段内的吸收峰主要来源于氨基酸官能团。 因此, 结合量子化学计算与太赫兹吸收谱可以实现氨基酸类物质的定性分析。

Compared with the infrared analysis of amino acids, terahertz wave has lower electronic energy and can be used for nondestructive testing. The intramolecular atomic vibration, the intermolecular hydrogen bond and the low-frequency vibration of the crystal lattice of amino acids are all in terahertz band, which makes them have absorption peaks in terahertz band, and different amino acid molecules have different Terahertz Absorption peaks. Therefore, this fingerprint characteristic of amino acids in terahertz band can be used for qualitative analysis of amino acids. Quantum chemical analysis methods can apply the basic principles and methods of quantum mechanics to study the structure, properties and relationships of stable and unstable molecules. It can also study the interactions, collisions and reactions between molecules. The Terahertz Absorption Spectra of amino acids can be calculated by quantum chemical calculation method, which can match the molecular vibration mode of the terahertz absorption peaks of amino acids. It has certain reference and directivity for the qualitative analysis of amino acids, and provides theoretical support for the terahertz time domain spectra of samples obtained from experiments. Quantum chemical calculation is carried out on the basis of the terahertz absorption spectra obtained from experiments. It can also validate the experimental results. In this paper, Terahertz Absorption Spectra of glutamine, threonine and histidine were obtained by terahertz time-domain spectroscopy. The monomolecular configurations of these three amino acids in the form of amphoteric ions were constructed respectively. The Terahertz Absorption spectra were simulated by quantum chemical calculation method after the structural optimization was completed. The calculated results showed that the Terahertz Absorption Spectra of three amino acids are quite different from those obtained by experiments, but the peak positions at high frequencies are basically the same. GaussView was used to observe the vibration and rotation of the absorption peaks of the three amino acids at the corresponding frequencies in the terahertz band. It was found that the functional groups of the three amino acids only rotated without vibration in the high frequency band, and the rotation modes were basically the same. The Terahertz Absorption Spectra of amino acid functional groups were calculated quantum chemistry. The vibration and rotation patterns of functional groups at the corresponding frequencies of the absorption peaks in the high frequency band were compared with those of three amino acid molecules at the corresponding frequencies of the absorption peaks in the high frequency band. The results showed that in the terahertz absorption spectra calculated by quantum chemistry method under the single molecular configuration of amino acids, the simulated absorption peaks calculated in the high frequency band are basically consistent with the experimental Terahertz Absorption peaks. Vibration mode analysis showed that the vibrational modes of amino acid functional groups of glutamine, threonine and histidine were the same in the terahertz high frequency band. The absorption peaks of the three amino acid molecules in the high frequency band mainly came from amino acid functional groups. Therefore, the qualitative analysis of amino acids can be realized by combining quantum chemical calculation with Terahertz Absorption spectrum.