亮氨酸与异亮氨酸的低频集体振动的太赫兹光谱研究

太赫兹(THz)波是指频率在0.1~10THz频段的电磁波。太赫兹光谱技术不同于以往的检测手段,可以用于检测氨基酸同分异构体,反映物质的分子结构和构型,对食品安全和药品药性控制有着重要的意义。亮氨酸与异亮氨酸属于同系的同分异构体,它们具有近似的分子结构,但物理化学性质有很大的差别。生物大分子的太赫兹吸收与其分子间氢键和分子内氢键的振动和转动能级相关的偶极跃迁有关,可以利用分子偶极跃迁进行生物分子的指纹识别。采用太赫兹时域光谱(THz-TDS)和傅里叶红外光谱(FTIR),对亮氨酸和异亮氨酸进行了测量。在中红外波段亮氨酸与异亮氨酸的吸收光谱几乎完全重叠,而在太赫兹频波段可以观察到它们的光谱存在明显差异,因此太赫兹光谱能够作为快速准确鉴别这两种物质的方法。采用密度泛函理论(DFT)对亮氨酸和异亮氨酸的低频集体振动模式进行理论模拟,并对其太赫兹光谱进行研究和讨论。通过比较实验和理论结果,计算得到的峰位与实验结果可以互相印证。

Analysis of Leucine and Isoleucine for Low-Frequency Collective Absorption Spectrum Using Terahertz Time-Domain Spectroscopy

Terahertz(THz,1=1012 Hz)wave refers to the frequency in the 0.1～10 THz spectra of electromagnetic radiation.THz time domain spectroscopy(THz-TDS)can provide the structure information of the material and configuration to distinguish different amino acid isomers,and amino acid isomers detection is useful for the quality control of the food and pharmaceutical potency.Leucine and isoleucine are homologous isomers.They have very similar molecular structures,but different chemical and physical properties.Biological macromolecular terahertz absorption is related with intermolecular hydrogen bond vibration and rotational level about the dipole transition,and it can be used for fingerprint identification of molecular dipole transition.In this paper,the terahertz time-domain spectroscopy(THz-TDS)and Fourier transform infrared spectroscopy(FTIR)were used to measure the absorption spectroscopy of leucine and isoleucine at room temperature.A number of different well-resolved THz absorption peaks for the two components were observed,but their infrared absorption peaks were almost overlapped.In parallel with the experiment,the computed vibrational spectra was also obtained by using first principles calculations based on the density functional theory(DFT).The theoretical results fit well with the experimental results.