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甘草中的4种黄酮类化合物甘草素、异甘草素、甘草苷、异甘草苷具有抗氧化、抗肿瘤、抗HIV等生物活性,具有潜在的药用价值。本文采用密度泛函理论(DFT)中的B3LYP方法在6-311G(d,p)基组水平上对甘草中的4种黄酮类化合物甘草素、异甘草素、甘草苷、异甘草苷进行了优化计算,从4个分子的几何结构、氢原子的NBO电荷、羟基解离能、HOMO、LUMO、ΔE_(LUMO-HOMO)等方面分析了4种甘草黄酮类化合物清除自由基的机理。结果表明,4种甘草黄酮类化合物的抗氧化能力大小为异甘草素≧异甘草苷>>甘草素≧甘草苷。C_7位的酚羟基为最大可能活性位点,容易发生抽氢反应,C_(4’)位酚羟基也具有一定的活性,可以增加分子本身的抗氧化活性。C_7位上酚羟基的解离能越小、羟基氢原子带正电荷越大、HOMO能级相对越高、ΔE_(LUMO-HOMO)越小分子的抗氧化活性越高。2、3位C=C双键可以增大分子的共轭体系,从而增大分子的抗氧化活性;糖苷的取代,增加了HOMO、LUMO轨道能级,但是分子失去了4’位酚羟基,所以从整体上降低了分子的抗氧化活性。
Licorice, licorice, isoliquiritigenin, glycyrrhizin and isoliquiritigenin have the biological activity of anti-oxidation, antitumor and anti-HIV, and have potential medicinal value. In this paper, four flavonoids, licorice, isoliquiritigenin, glycyrrhizin and isoliquiritigenin in Glycyrrhiza uralensis were studied by B3LYP method in density functional theory (DFT) at 6-311G (d, p) The mechanism of scavenging free radicals by four kinds of glycyrrhiza flavonoids was analyzed from four geometrical structures, NBO charges of hydrogen atoms, hydroxyl dissociation energies, HOMO, LUMO and ΔE_ (LUMO-HOMO). The results showed that the four kinds of flavonoids glycyrrhizin antioxidant capacity of isoliquiritigenin ≧ isoliquiritigenin >> licorice glycyrrhizin ≧ glycyrrhizin. The phenolic hydroxyl group at C7 position is the most likely active site, and hydrogen abstraction reaction is easy to occur. The phenolic hydroxyl group at C 4 ’position also has certain activity, which can increase the antioxidant activity of the molecule itself. The smaller the dissociation energy of phenolic hydroxyl group at C7, the higher the positive charge of hydroxyl hydrogen atom, the higher the HOMO energy level and the smaller the ΔE_ (LUMO-HOMO), the higher the antioxidant activity of the molecule. 2,3 C = C double bond can increase the molecular conjugation system, thereby increasing the molecular antioxidant activity; glycoside substitution, an increase of HOMO, LUMO orbital energy level, but the molecule has lost 4 ’phenolic hydroxyl group, So as a whole reduces the molecular antioxidant activity.