反式辣椒素结构的Ab Initio理论研究

Ab initio SCF study of trans-capsaicin structure

目的研究反式辣椒素(trans-capsaicin)基态、激发态、一价阳离子以及一价阴离子的理论计算结果,分析结果与性质之间的关系,揭示其抗氧化性本质。方法利用HyperChem软件,采用Ab Initio方法,选择3-21G基组对反式辣椒素基态、激发态、一价阳离子以及一价阴离子分别进行计算,并对计算结果中分子能量、轨道以及能级(特别是前线轨道能级)、键长、键级、电荷分布等进行分析。结果计算结果表明,反式辣椒素作为一种抗氧化剂,关键可能是失去基态HOMO中的成键电子,对于反式辣椒素分子稳定性带来的影响最小,能量升高仅有2.38 eV,如果将MP2考虑在内也只有3.11eV;同时将质子论与供氢体对辣椒素抗氧化性的解释,最终归于前线轨道中的电子转移。结论辣椒素作为一种抗氧化剂得到广泛使用,很可能与其HOMO失去成键电子,所需能量最小有关。

Aim To attempt to account for the antioxidation of trans-capsaicin by studying the relations of theoretical results,analysis results and the properties of ground state,excited state,cation（＋1） and anion（-1） of trans-capsaicin.Methods Ab intio（3-21G） SCF along with HyperChem software is used to calculate ground state,excited state,cation（＋1） and anion（-1） of trans-capsaicin respectively,moreover,the calculated results such as total energy,molecular orbitals（MO） and levels of MO（especially the levels of frontier orbitals）,bond length,bond order,charge distribution and others are analyzed.Results The calculated results show that the reason why trans-capsaicin is a widely used as strong antioxidant lies in that the effectiveness may relate with loss one electron in HOMO level,for the required energy in the process is lowest compared with that of excited state and anion（-1）,and the energy increases only 2.38 eV,or the required energy with MP2 energy is also only 3.11 eV for converting trans-capsaicin to trans-capsaicin cation.At the same time,trans-capsaicin donates an electron in the frontier orbital to oxidant,which agrees with protons theory and hydrogen donor for the explanation of trans-capsaicin antioxidation.Conclusion The nature of trans-capsaicin as an antioxidant widely used is probably related with the required minimum energy for the process of losing one bonding electron in its HOMO.