为探索用于畜禽饲喂低蛋白日粮的典型氨基酸太赫兹波段指纹特性及其与分子结构相关性, 本文基于太赫兹时域光谱技术和密度泛函理论(DFT)对蛋氨酸等6种饲用氨基酸开展了实验测量和理论振动计算分析。 首先, 制备了氨基酸实验样本, 测量了它们在0.5~2.0 THz的太赫兹吸收光谱, 发现: 蛋氨酸在1.48和1.54 THz、 赖氨酸在0.95和1.67 THz、 色氨酸在1.2和1.4 THz、 苏氨酸在1.42 THz、 组氨酸在1.4 THz、 异亮氨酸在1.41和1.51 THz处呈现明显吸收特性; 然后, 利用GaussView软件构建了6种氨基酸单分子结构, 应用DFT理论的B3LYP杂化泛函方法, 结合6-311G(d, p)基组优化结构, 计算获得其太赫兹波段的频谱特征, 发现: 蛋氨酸在1.51 THz、 赖氨酸在0.89和1.68 THz、 色氨酸在0.67和1.39 THz、 苏氨酸在1.4 THz、 组氨酸在1.4 THz、 异亮氨酸在1.56和1.75 THz处有一定吸收, 与实际实验测量吸收峰位基本吻合; 最后, 利用Gaussian软件分析了6种氨基酸在0.5~2.0 THz波段各吸收峰处的振动模式, 发现: 蛋氨酸1.51 THz处吸收峰源自其甲基团的面内摇摆振动; 赖氨酸0.89和1.68 THz处吸收峰源自其羧基官能团的旋转和氨基官能团的面内摇摆振动; 色氨酸1.39 THz处吸收峰源自其羧基官能团的面外弯曲振动; 苏氨酸1.4 THz处吸收峰源自其羧基官能团的面外弯曲和氨基官能团的面内摇摆振动; 组氨酸1.4 THz处吸收峰源自其氨基官能团的面内摇摆和整体摇摆振动; 异亮氨酸1.56 THz处吸收峰源自其甲基团和氨基官能团的整体摇摆和羧基官能团的面外摇摆振动、 1.75 THz处吸收峰源自其甲基团的整体摇摆和羧基官能团的面外摇摆振动。 该研究为利用太赫兹光谱技术开展典型饲用氨基的快速定性定量研究提供理论参考。

To explore the terahertz band fingerprint properties of typical amino acids used for feeding low-protein diets to livestock and poultry and their correlation with molecular structure, this paper presents experimental analysis and theoretical vibrational calculations of six feed amino acids, including methionine, based on terahertz time-domain spectroscopy technique and Density Functional Theory (DFT). First, experimental samples of amino acids were prepared. Their terahertz absorption spectra were measured from 0.5 to 2.0 THz. It was found that methionine at 1.48 and 1.54 THz, lysine at 0.95 and 1.67 THz, tryptophan at 1.2 and 1.4 THz, threonine at 1.42 THz, histidine at 1.4 THz, isoleucine at 1.41 and 1.51 THz showed significant absorption characteristics; Then, GaussView software was used to construct the single-molecule structures of the six amino acids, and the structure was optimized by applying the B3LYP/6-311G (d, p) level of theory of DFT theory. The spectral properties of their terahertz bands were obtained through theoretical calculations. It was found that methionine at 1.51 THz, lysine at 0.89 and 1.68 THz, tryptophan at 0.67 and 1.39 THz, threonine at 1.4 THz, histidine at 1.4 THz, and isoleucine at 1.56 and 1.75 THz certain absorptionwere present. Which is consistent withthe actual experimental measurement of the absorption peaks. Finally, the vibrational modes of the six amino acids at the absorption peaks in the 0.5~2.0 THz band were analyzed by Gaussian software, and it was found that the absorption peak at 1.51 THz for methionine originated from the in-plane rocking vibration of itsmethyl group; the absorption peaks at 0.89 and 1.68 THz for lysine originated from the rotation of carboxyl group and the in-plane bending vibration of itsamino group; the characteristic peak at 1.39 THz for tryptophan originated from the out-of-plane bending of itscarboxyl group; the absorption peak at 1.4 THz for threonine originated from the out-of-plane bending of itscarboxyl group and the in-plane rocking vibration of itsamino group; the absorption peak at 1.4 THz for histidine originated from the in-plane bending of itsamino group and the overall rocking vibration; the absorption peaks at 1.56 THz for isoleucine originated from the overall rocking of its methyl groupsand amino groups and the out-of-plane rocking vibration of its carboxyl group, and the characteristic peaks at 1.75 THz originated from the overall rocking of its methyl group and out-of-plane rocking vibration of its carboxyl group. This study is a theoretical reference for the rapid qualitative and quantitative studies of typical feedamino acids using terahertz spectroscopy.