荷叶黄酮自由基清除活性的量子化学研究

Quantum chemical study on radical scavenging activity of Lotus leaf flavonoids

借助于密度泛函理论,针对荷叶中5种重要的黄酮化合物(槲皮素、山奈酚、异鼠李素、金丝桃苷和紫云英苷)进行结构优化,从捕获DPPH自由基的热力学能量、NBO电荷及半醌自由基的自旋密度分析等方面深入探讨了荷叶黄酮化合物自由基清除活性的构效关系及内在规律.结果表明:5种荷叶黄酮化合物按自由基清除活性排序依次为槲皮素>异鼠李素>山奈酚>金丝桃苷>紫云英苷,酚羟基的位置和分子内氢键的形成是影响荷叶黄酮自由基清除活性差异的主要因素.荷叶黄酮不同位点自由基清除活性的高低与其酚羟基上H原子的电荷分布及黄酮自由基的稳定性成正比关系,自由基单电子的离域程度决定了C(3)—OH是荷叶黄酮的关键活性位点,当C(3)—OH被糖苷基取代时,C(4′)—OH位点接替C(3)—OH成为最高活性位点.

Lotus leaf has shown excellent biological activities and pharmacological effects.Lotus leaf flavonoids are the major active ingredients,and have been found to be important in determining the radical scavenging activity.Nonetheless,the structure-activities relationship between different lotus leaf flavonoids(quercetin,isorhamnetin,kaempferol,astragalin and hyperoside)was rarely studied.Systematic density functional theory(DFT)calculations have been carried out to explore this issue.The optimized geometric configuration,the relative change in energy(ΔH)associated with the formation of various flavonoid radicals,the NBO charges and spin densities analysis of the five aforementioned flavonoids are compared.The results indicate that the order of radical scavenging activity is quercetin>isorhamnetin>kaempferol>hyperoside>astragalin,and the location of phenol hydroxyl group and the intramolecular hydrogen bond both significantly affect the radical scavenging activity of lotus leaf flavonoids.The radical scavenging activity of different reactive site(—OH group)was related to the charges on H atom and the stability of flavonoid radicals,the electron delocalization finally results in the high activity of C(3)—OH of lotus leaf flavonoids.Nevertheless,in the substitution of C(3)—OH with glucoside,the C(4′)—OH could take over the highest active site in lotus leaf flavonoids.