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绿茶中的4种儿茶素EGCG,ECG,EGC,和EC具有抗氧化、抗癌等生物活性,对人体健康有很好的保护作用。分子的抗氧化机制主要通过酚羟基的抽氢反应直接消除自由基。本文利用密度泛函(DFT)B3LYP法在6-31G~*基组下计算了这4个分子,分别从分子的电荷分布、4个分子与失去带最大正电荷的酚羟基氢原子形成自由基反应的生成热之差(AHOF)、最高占据轨道、最高占据轨道和最低空轨道的能级差等方面分析儿茶素消除自由基的机理。结果表明在4个儿茶素分子中带最大正电荷的氢原子,在不同的酚羟基上。EGCG和EGC分子中位于B环的4′位酚羟基上,ECG分子中位于D环的4″位酚羟基上,EC分子中位于B环的3′位酚羟基上;4个分子中其氢所带正电荷的大小顺序是EGCG>ECG>EGC>EC,与文献记载的消除自由基活性顺序一致;从ΔHOF可以看出,儿茶素消除自由基的反应活性与酚羟基的个数和失去氢原子后形成内氢键的个数有关;另外,最高占据轨道和最低空轨道的能级差在一定程度上也反映4个分子的活性。
The four kinds of catechins in green tea EGCG, ECG, EGC, and EC have biological activities such as anti-oxidation and anti-cancer, and have a good protective effect on human health. The antioxidant mechanism of the molecule directly eliminates free radicals through the hydrogen abstraction reaction of phenolic hydroxyl groups. In this paper, the density functional theory (DFT) B3LYP method is used to calculate the four molecules in the 6-31G ~ * basis set, and the free radicals are formed respectively from the charge distribution of the molecule, the four molecules and the loss of the phenolic hydroxyl hydrogen atom with the maximum positive charge Reaction induced heat of formation (AHOF), the highest occupied orbit, the highest occupied orbital and the lowest level orbital difference between the level of analysis of catechins and other mechanisms to eliminate free radicals. The results show that among the four catechins molecules with the most positively charged hydrogen atoms, different phenolic hydroxyl groups. EGCG and EGC molecules located in the 4 ’position of the B-ring phenolic hydroxyl group, the ECG molecule is located in D ring 4 "phenolic hydroxyl group, EC molecule is located in the B ring 3’ phenolic hydroxyl group; 4 molecules of hydrogen The order of the positive charge is EGCG> ECG> EGC> EC, which is consistent with the order of eliminating free radical activity documented in the literature. From ΔHOF, it can be seen that the catechins eliminate the reaction of free radicals with the number of phenolic hydroxyl groups and lose Hydrogen atoms formed after the number of hydrogen bonds; In addition, the highest occupied orbital and lowest empty orbit level difference to some extent, also reflects the activity of four molecules.