基于密度泛函理论的盐酸罂粟碱太赫兹振动光谱计算与分析

为了进一步探究太赫兹振动光谱的理论机理，为违禁药品的太赫兹光谱检测提供完善合理的科学依据，本文以盐酸罂粟碱为例，基于第一性原理的密度泛函理论计算方法，利用BLYP、LC-BLYP、B97-XD、B3LYP和CAM-B3LYP函数并结合6-311++G（d，p）基组，分别讨论其分子构象并对盐酸罂粟碱的光谱吸收特性和振动模式进行了表征和分析。计算结果表明，盐酸罂粟碱是以异喹啉N原子上的质子化阳离子和两个最低质子化构象的形式存在的。四个指纹峰中有三个是由能量最低的分子构象共振引起，另一个是由第二个最低能量的分子构象共振引起的。在该方法中，LC-BLYP函数被证明是五个函数中最合适的一个。研究表明，太赫兹时域光谱技术可以有效地检测非法药物，采用密度泛函理论合理计算振动频率，可以为今后违禁药品及各种衍生物的检验提供依据。

Density Functional Theoretical Calculations and Analysis on Terahertz vibrational Spectra of Papaverine Hydrochloride

In order to further provide basis for the improvement of the computational mechanism and drug terahertz database, taking the papaverine hydrochloride as a detailed example, a scientific and general approach in the theoretical chemistry communities was used to calculate the terahertz vibrational frequencies. Harmonic vibrational frequencies were analyzed using BLYP, LC-BLYP, B97-XD, B3LYP, and CAM-B3LYP functional, combining with the triple-zeta basis set 6-311++G (d,p). The calculational results suggested that papaverine hydrochloride exists as the protonated (on the isoquinoline N atom) cation and two lowest protonated conformers contribute to the spectrum. Three of four fingerprint peaks were resulted from the vibrations of the lowest energy conformer and the other one from the second lowest conformer. As for the method, the LC-BLYP functional is turned out to be the most appropriate one in five functionals examined. The spectral absorption features and vibrational modes of papaverine hydrochloride were also assigned. The results showed significant agreement with experimental results found in the literatures, and indicated that terahertz time-domain spectroscopy (THz-TDS) technique can be an effective way to inspect for illicit drugs. Moreover, the general approach of DFT method above-mentioned should be used to rationally calculate the vibration frequencies, which may be helpful for the inspection of illicit drugs and various derivatives in future.