茶多酚清除过氧自由基分子机理的量子化学计算研究

为了评价Kondo等的计算结果,用一种组合的密度泛函理论方法计算了EC和EGC各位点的O-H BDE和C-H BDE,结果表明Kondo等的计算结果是不准确的,B环酚羟基,特别是4’位酚羟基,是清除过氧自由基的第一活性位点,2位书氢则是后继抽氢反应的活性位点,这与Kondon等通过实验提出的茶多酚清除自由基的分子机理完全一致.

Quantum Chemical Study of Molecular Mechanism for Green Tea Poly phenols to Scavenge Peroxyl Radicals

Catechins, the main components of green tea polyphenols, are excellent antioxidants. The free radical-scavenging activity of catechins arises from their abstractable phenolic hydrogens,specificall,the cat-echolic hydrogens in ring B. Thus,it is interesting to note Kondo and co-workers proposed that the allylic hydrogens of catechins were more abstractable than the catecholic hydrogens, because the PM3 or AM1 calculated C-H bond dissociation enthalpies (BDEs)of the former were much lower than O-H BDEs of the latter. If this is true,the structure-activity relationships for catechins will have to be re-evaluated,as the allylic hydrogens were taken out of consideration in the most of previous studies. In order to evaluate the calculation results of Kondo and co-workers, we used a combined density functional theory (DFT) method to re-calculate the O-H BDEs and C-H BDEs for catechins. It was revealed that phenolic hydroxyl group,es-peciaaly ,4'-OH should be the active center to scavenge peroxyl radicals,while then 2-allylic hydrogen was the succeeded radical-scavenging point.