中药黄芪中黄酮类化合物抗氧化活性的DFT研究

Density Functional Theory Investigation on Antioxidant Activity of Flavonoids fromAstragalus

为了研究中药黄芪中黄酮类化合物的抗氧化活性大小,采用密度泛函理论B3LYP方法在6-31+G**水平上,对黄芪中的4个黄酮类化合物毛蕊异黄酮、毛蕊异黄酮苷、芒柄花素和芒柄花苷进行了量子化学计算,获得4个化合物及其相应自由基的最优几何结构。根据量子化学参数酚羟基键长、NBO电荷、酚羟基解离能(BDE)和绝热电离势(IP)等分析化合物的结构与抗氧化活性之间的关系,同时考察了不同溶剂对化合物抗氧化活性的影响。计算结果表明,4个化合物的抗氧化活性顺序为:毛蕊异黄酮>毛蕊异黄酮苷>芒柄花素>芒柄花苷,与实验结论十分吻合,其中毛蕊异黄酮的C3′-OH的抗氧化活性大于C7-OH。在抽氢反应机制中,随着溶剂极性的增大,抗氧化活性减弱;而在单电子转移机制中,随着溶剂极性的增大,抗氧化活性增强。

In order to investigate the antioxidant activity of flavonoids from Astragalus,we performed quantum chemical calculations for four flavonoids including calycosin,calycosin 7 glucoside,formononetin,ononin by density functional theory(DFT)B3LYP method at the 6 31+G**level,and obtained the optimum geometric structures of the four flavonoids and their corresponding free radicals.Moreover,we analyzed the relationship between the structure and antioxidant activity of flavonoids on the basis of the quantum chemical parameters,the bond length of phenolic hydroxyl,the natural bond order(NBO)charges,the bond dissociation energy(BDE)of phenolic hydroxyl,and adiabatic ionization potential(IP).The results show that the sequence of antioxidant activity of the four flavonoids is as follows:calycosin>calycosin 7 glucoside>formononetin>ononin,which is consistent well with the experimental conclusions.Among them,the site of C3′-OH of calycosin is more active than the site of C7-OH.Meanwhile,we investigated the influences of different polar solvents on antioxidant activity.The results indicate that the antioxidant activity decreases with the increasing of solvent polarity in the hydrogen abstraction mechanism.While the antioxidant activity increases with the increasing of solvent polarity in the single electron transfer mechanism.