氨基酸的太赫兹光谱温度相关性研究

采用可调温太赫兹时域光谱(TDS-THz)系统，测量了脂肪族L-天冬酰胺、L-半胱氨酸、L-丙氨酸和芳香族L-酪氨酸四种氨基酸在低温下的温度特性，实验中，分别在降温和升温过程中选取了以下温度节点：常温，250，200，150，100，70，40，10以及4.5 K等，观察样品对太赫兹吸收光谱的异同；结合傅里叶变换红外光谱仪(FTIR)对室温下上述四种氨基酸在低频段(0.5～2 THz)范围内的吸收峰进行了验证，同时采用拉曼光谱仪测试了高频段(3～6 THz)范围内的这四种氨基酸在常温下的拉曼强度，以此来验证了实验的准确性。结果表明：脂肪族和芳香族氨基酸太赫兹光谱对温度变化的响应存在差异，随着温度降低，两类氨基酸的吸收峰位置均发生蓝移现象, 同时部分氨基酸出现新的吸收峰，但是吸收峰线宽的变化略有不同。最后，采用量子化学Gaussian 09软件包，分别选取一种脂肪族氨基酸和一种芳香族氨基酸，通过密度泛函理论对其单分子和晶胞结构进行了计算，对比测试结果可以得出两种氨基酸的振动模式是由分子间作用力形成的。

Temperature Dependence of Terahertz Spectra of Amino Acid

We employed terahertz time domain spectra (THz-TDS) to measure the spectra of L-Asparagine，L-Cysteine，L-Alanine and L-Tyrosine in the frequency range of 0.5～2 THz at different temperatures. We measured the terahertz absorption spectra of amino acids at room temperature, 250, 200, 150, 100, 70, 40, 10 and 4.5 K by cooling the samples. The absorption peaks of the four amino acids in the low frequency range (0.5～2 THz) were demonstrated by Fourier transform infrared spectroscopy (FTIR) at room temperature, and the range of high frequency band (3～6 THz) was measured by Raman strength of these four amino acids at room temperature using Raman spectroscopy. Measurement results indicated that the temperature variation had an important effect on the absorption spectra. When the temperature falled, the absorption peak shifted to higher frequencies, and several new absorption peaks appeared. Aliphatic and aromatic amino acid displayed different responses in the line width and the absorption strength. Furthermore, we used the quantum chemistry Gaussian 09 software package to calculate the THz spectra of one molecule and unit cell of L-Asparagine and L-Tyrosine at room temperature by density functional theory. The calculation results indicate that intermolecular vibration and rotation strongly influence the absorption in THz frequencies for L-Asparagine and L-Tyrosine.