类胡萝卜素清除自由基活性构效关系

为探讨类胡萝卜素结构对其自由基清除能力的影响,采用四种自由基清除方法分别测定β-胡萝卜素、叶黄素、虾青素、番茄红素的自由基清除能力,对十三种类胡萝卜素进行了量子化学计算,通过AM1法对其结构进行初步优化后,再用密度泛函方法(Density functional theory,DFT)在B3LYP/6-311(d,p)水平上进一步优化计算。结果表明,不同种类类胡萝卜素对不同的自由基清除能力不同,虾青素最强,其次是番茄红素、叶黄素,β-胡萝卜素最弱;根据前线轨道能级差、NPA净电荷分布发现,类胡萝卜素多个共轭双键的特殊结构是其具有自由基清除能力的重要原因,其端环上的基团能够促进分子的活性,酮基是对其活性影响最大的基团,其次是羟基与环氧基,这与实验结果相吻合,表明前线轨道能级差、NPA电荷分布是表征类胡萝卜素自由基清除能力的重要参数。

The Structure-Activity Relationship of Free Radical Scavenging Ability of Carotenoids

To explore the effect of carotenoid structure on its free radical scavenging ability,quantitative chemical calculations were carried out on 13 kinds of carotenoids. After optimization of the structure by AM1,carotenoids was further optimized by density functional theory(DFT)at B3LYP/6-311(d,p).Four methods were used to determine the free radical scavenging capacity of β-carotene,lutein,astaxanthin and lycopene. The results showed that different carotenoids had different ability to scavenge different free radicals,astaxanthin had the strongest free radical scavenging ability,followed by lycopene,lutein,and β-carotene was the weakest. According to the frontier orbital energy difference and the distribution of NPA charge,the special structure of multiple conjugated double bonds of carotenoids was an important reason for its ability to scavenge free radicals,the groups on the terminal rings could promote the activity of the molecules. The keto group had the greatest effect on carotenoids’ activity,followed by the hydroxyl and epoxy groups,which was consistent with the experimental data,indicating that the frontier orbital energy difference and the distribution of NPA charge were important parameters to characterize the scavenging ability of carotenoids.