L-天冬酰胺及其一水合物的太赫兹光谱研究*

摘要

Low-frequency collective vibrational modes of biomolecules which often lie in terahertz (THz) band, make the ter-ahertz time-domain spectroscopy (THz-TDS) an important technique for molecular identification and medicine quality inspection. Distinctive THz spectra between L-asparagine and its monohydrate were observed and the dehydration pro-cess of L-asparagine monohydrate was tracked by THz-TDS. Experiments indicate that THz wave is sensitive to phase transitions in crystals, dehydration process, and weak molecular interactions. Multi-techniques including differential scanning calorimetry and thermogravimetry, Fourier transform infrared spectroscopy, and powder X-ray diffraction are performed to investigate the thermodynamic properties, intermolecular and intramolecular vibrations, and molecular packing patterns of L-asparagine and its monohydrate. These measurements support the reliability of THz spectroscopy. To simulate and analyse the vibration modes of L-asparagine monohydrate, density functional theory calculations are per-formed using a Perdew Burke and Ernzerhof generalized gradient approach;the results agree well with the experimental observations.%本文利用太赫兹时域光谱技术测量了室温条件下无水L-天冬酰胺与L-天冬酰胺一水合物的光谱特征，发现二者存在显著的差异，并利用太赫兹时域光谱技术实时检测L-天冬酰胺一水合物受热脱水的动态过程。结果表明太赫兹波对晶体结构变化、含结晶水状况以及分子间弱相互作用敏感。结合差示扫描量热法与热重分析联用、傅里叶变换红外光谱、粉末X射线衍射等多种技术分别从热学性质、分子振动等方面进行了表征，进一步确认了太赫兹实验结果的可靠性。采用基于密度泛函理论(DFT)的第一性原理平面波赝势方法，结合广义梯度近似(GGA)下的PBE交换-关联泛函，对L-天冬酰胺一水合物进行模拟计算，对实验所得太赫兹光谱与分子结构以及相互作用间的关系进行了讨论分析。