密度泛函方法研究辣椒碱分子的结构和性质

Studies on structures and properties of capsaicin by density functional theory method

辣椒碱(Capsaicin)在医药、农业和反恐装备方面具有广泛的应用前景。本文用密度泛函理论DFT/B3LYP方法,在6-31+G(d,p)基组水平上对其进行了计算。密度泛函理论方法既考虑了电子相关,又较其他组态相互作用或微扰方法节省机时,其计算结果可靠,被广泛应用于研究各类化合物结构性质。本文获得了辣椒碱分子稳定的几何构象和电荷分布,确定O(12)、N(16)、O(19)、C(37)和C(38)原子,可以作为氢键受体;C(18)与O(19)原子形成一对偶极,它们均是关键药效团的活性部位。通过进行分子轨道特征分析,确定苯环区是参加化学反应时的活性部位。进行的自然键轨道分析结果与分子轨道特征分析结论一致。在振动分析的基础上获得分子的振动频率、IR光谱与实验结论一致;在振动分析的基础上,同时获得不同温度下的热力学性质以及温度对热力学性能影响的关系式,其中,当T>2 542 K时,热容C_(p,m)~θ会随温度的升高而减小,各表达式和热力学量对深入研究辣椒碱分子的其它热力学性质有帮助。探讨了辣椒碱热分解机理,获得该分子热分解时C-N键的断裂能为306.6 kJ·mol^(-1)。本文为研究辣椒碱类化合物的定量构效关系研究提供理论依据。

Capsaicin has a broad application in medicine, agriculture and the anti-terrorism equipment. The properties of Capsaicin were estimated by using density function theory （DNF） method at the B3LYP/6-31 ＋ G （ d, p） level. The density function theory method takes into account the electron correlation and saves computational time compared with configuration interaction （CI） and per- turbation theory （MPn）. The results of density function theory method are credibility and widely used in the study on the characters of various compounds. The stable geometric configuration and the charge distribution have been obtained of Capsaicin. The O atom （12） , N atom （16）, O atom （19）, C atom （37） and C atom （38） can play a role as hydrogen bond receptors. The C atom （18） and O atom （19） form a dipole, which was the active site of the key pharmacophore. The benzene ring district of Capsaicin was the active site of the chemical reaction through the analysis of the characters of frontier molecular orbital. The same results were concluded about the natural bond orbital （NBO） properties with the analysis of frontier molecular orbital. The vibrational frequencies and IR spectra were obtained on the basis of the vibration analysis. The results of frequencies and spectra were consistent with the experimental conclusion. Thermodynamics properties under different temperatures were accessed and the relationship between temperature and thermodynamics properties was deducted from vibrational analysis. When the temperature was higher than 2542K, the heat capacity would reduce with the temperature＇s elevation. The expression and the thermodynamic property were helpful to an in-depth study of Capsaicin and other thermodynamic properties. Pyrolysis mechanism of Capsaicin was discussed. The cracking energy of bond C-N of Capsaicin was 306. 6 kJ · mol^- 1 in the process of thermal decomposition of Capsaicin. These properties are helpful to the further study on the reactions, properties and structure-activity relationship for Capsaicin.