4种类胡萝卜素抗氧化性质的量化计算

Density functional theory calculations on antioxidation activity of four carotenoids

类胡萝卜素分子结构中含有一个共轭大π键,可能是这种特殊的结构使它容易与自由基起反应,形成无害的产物,或通过破坏自由基链反应,将自由基清除。运用密度泛函理论方法(density functional theory,DFT)在B3LYP/6-31(d)水平上对虾青素、β-胡萝卜素、玉米黄素和叶黄素四种类胡萝卜素分子进行了优化计算,之后在B3LYP/6-311(d)水平上进行了单点能(single pointenergy,SPE)计算。文章从分子的几何结构、总能量、原子的NBO电荷值、以及前线轨道结构方面详细讨论了它们性质。研究表明,分子的共轭效应使C-C单双键的键长均匀化,同时降低了分子的能量,最高占据轨道与最低空轨道能级间隔ΔE(LUMO-HOMO)变小,光谱移至可见区,从而显出多种颜色。从原子的NBO电荷值,前线轨道ΔE方面分析可见,抗氧化活性理论上虾青素>玉米黄素≈β-胡萝卜素>叶黄素。玉米黄素和叶黄素结构中的羟基的亲水性会增强其与水溶性或脂溶性氧化物反应,导致其清除体内自由基的能力大于β-胡萝卜素。

It is well-known that there is a conjugated π bond in the carotenoid molecular structure, this makes it react with free radicals in the organisms, and eliminate free radicals in the way of forming harmless products or destroying the chain reaction of involving radicals. In this work the Density Functional Theory （DFT） B3LYP / 6-31 （d） method is adopted to optimize the molecular structures of astaxanthin, β-carotene, zeaxanthol and lutein these four carotenes, and then B3LYP / 6-311 （d） method is applied to calculate the Single Point Energy （SPE）. The properties of the carotenoids are discussed based on the molecular structure, the total energy, NBO charge value of the atoms, and the structure of the frontier molecular orbital in detail. The results show that the molecular conjugated effect unifies the length of the C-C bonds in the conjugated system, results in the total energy and the energy differences AE （LUMO-HOMO） declined and the absorptive spectrum shifts to the visible spectrum area. Based on the electronic parameters of the NBO charges and the structure of the molecular frontier orbital, we concluded, theoretically, the antioxidation activity goes along with the series astaxanthin 〉 fl-carotene ~ zeaxanthol 〉 lutein. But the hydroxide radicals on the zeaxanthol and lutein enhance their hydrophilicity and make it easy to react with water-soluble or fat-soluble oxides, so that their ability of eliminating free radicals is higher than that of β-carotene in the organisms.