Six anthocyanidins of pelargonidin,cyanidin,delphinidin,peonidin,petunidin,malvidin and their radicals were geometri-cally optimized by using the Density Functional Theory B3LYP method with 6-311G(d,p)basis set. The antioxidant activity to scav-enge harmful free radicals of the six anthocyanidins was discussed in detail based on their molecular structures,NBO charges on Phenolic hydroxyl hydrogen atoms,the dissociation enthalpy of phenolic hydroxyl bonds,the energies of the highest occupied molec-ular orbital ( HOMO ) and the low-est unoccupied molecular orbital ( LUMO ) , the energy gap between HOMO and LUMO, and etc. The dissociation enthalpy of phenolic hydroxyl bonds and highest occupied molecular orbital can most explain the antioxidant activity. The 4’-OH has the highest antioxidation activity and the 3-OH is highly glycosylated. In the end,the trans-ition state struc-ture of the pelargonidin scavenging OH free radicals by its C4’sites phenolic hydroxyl was optimi-zed. The reaction activation energy of 14. 6 kJ·mol-1 and reaction heat of -87. 7 kJ·mol-1 were obtained by this work.%本文采用密度泛函理论中的B3LYP方法在6-311G(d,p)水平上对花青素分子中天竺葵色素、矢车菊色素、飞燕草色素、芍药色素、牵牛色素、锦葵色素及相关自由基分子进行了优化计算。从六个分子的结构参数、酚羟基氢原子上的自然键轨道(NBO)电荷数、酚羟基解离能、HOMO和LUMO能级以及其能级差△E(LUMO-HOMO)等方面分析了六种花青素类化合物清除自由基的活性。计算数据表明,酚羟基解离能、最高占据轨道及轨道能级差最能说明抗氧化活性情况,C4’酚羟基清除自由基活性最强,C3位最易发生糖苷化。在相同方法下对天竺葵色素分子C4’位酚羟基与·OH自由基的反应的过渡态进行了计算,发现该反应的反应势垒只有14．6 kJ·mol-1,反应热ΔH=-87．7 kJ·mol-1,该反应为放热反应。
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