中文摘要：

利用密度泛函理论的B3LYP交换相关泛函对从细梗胡枝子中提取的一种新型黄酮类化合物的分子结构和抗氧化活性进行了研究,获得了该化合物的中性分子、阴离子、自由基和自由基阳离子的稳定几何构型和能量.通过分析前线分子轨道特征,确定了与实验结果一致的现象：A环是参加化学反应的活性部位,并发现A′环也是重要的抗氧化活性部位.为判断其抗氧化活性,预测其水溶液中,中性和阴离子的电离势分别为509.0和432.2kJ.mol^-1,均裂O—H键解离能为347.3kJ.mol^-1,羟基自由基电子亲和势和氢原子亲和势分别为-620.6和-487.5kJ.mol^-1.通过理论分析比较,该黄酮类化合物清除羟基自由基的三种机理即H原子转移、电子转移-质子转移和质子丢失-电子转移在热力学上并存,其中质子丢失-电子转移是热力学最有利的机理.本文为设计新型高效黄酮类抗氧化剂,研究黄酮类化合物的构效关系和抗氧化机理提供了理论依据.

英文摘要：

The molecular structures and antioxidant activities of a novel flavonoid-type compound （lespedezaflavonone） from Lespedeza virgata were studied using density functional theory （DFT） with the B3LYP exchange correlation functional. The optimized geometries of neutral, radical cation, radical, and anion forms of lespedezaflavonone were obtained. Ring A was found to be responsible for the high activity of the flavonoids by an analysis of the character of the frontier molecular orbital, which was consistent with what was observed experimentally. Furthermore, it was noteworthy that ring A＇ was firstly found to be the important part for the potent antioxidant activity of lespedezaflavonone. To quantify the antioxidant activities, we determined the adiabatic ionization potential （IP, 509.0, 432.2 kJ. mol^-1 for the neutral and anion forms, respectively）, the homolytic O--H bond dissociation enthalpy （BDE, 347.3 kJ. mol^-1） for lespedezaflavonone, the adiabatic eleclron affinity （EA, -620.6 kJ. mol^-1） and the H-atom affinity （HA, -4437.5 kJ. mo1-1） for hydroxyl radical in aqueous solution. Our theoretical analysis shows that H-atom transfer, stepwise electron-transfer-proton-transfer, and sequential proton-loss-electron- transfer mechanisms for lespedezaflavonone to scavenge hydroxyl radical may occur thermodynamically in parallel, while the last process is the most favorable. These findings are helpful for further study on the design of novel efficient flavonoid-type antioxidants, the structure-activity relationship and the antioxidant mechanism of flavonoid-type compounds.