College of Bee Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, P.R. China.
Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing, 100084, P.R. China.
Sci Rep. 2017 Aug 8;7(1):7543. doi: 10.1038/s41598-017-08024-8.
Among the multiple components of propolis, flavonoids contribute greatly to the antioxidant activities of propolis. Flavonoids mainly exist in the form of sugar-conjugated derivatives. Quercetin glycosides represent the predominant flavonoid fraction in propolis. In this work, density functional theory (DFT) calculations were applied to analyze the antioxidative properties of quercetin and its glucosides in the gas and in the liquid phase (ethanol, water). Three main antioxidant mechanisms, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were used to analyze the antioxidative capacity of the investigated compounds. Solvent effects dominantly affect SET-PT and SPLET. Thus, the thermodynamically preferred mechanism can be altered. HAT and SPLET are the thermodynamically dominant mechanisms in gas and solvent phases, respectively. Therefore, in the gas phase, the sequence of the antioxidative capacity is similar with the bond dissociation enthalpy values: quercetin > quercetin-5-O-glucoside > quercetin-7-O-glucoside > quercetin-3-O-glucoside > quercetin-3'-O-glucoside > quercetin-4'-O-glucoside. While, in the solvent phases, the sequence is similar with the proton affinity values: quercetin-4'-O-glucoside > quercetin-5-O-glucoside > quercetin > quercetin-3-O-glucoside > quercetin-7-O-glucoside > quercetin-3'-O-glucoside. OH groups in B-ring and C-ring contribute mainly to the antioxidative activities of quercetin and glucosides compared with A-ring.
在蜂胶的多种成分中，类黄酮对蜂胶的抗氧化活性贡献巨大。类黄酮主要以糖缀合衍生物的形式存在。槲皮素糖苷是蜂胶中主要的类黄酮部分。在这项工作中，应用密度泛函理论（DFT）计算分析了在气相和液相（乙醇、水）中槲皮素及其糖苷的抗氧化性能。三种主要的抗氧化机制，氢原子转移（HAT）、单电子转移后质子转移（SET-PT）和连续质子丢失电子转移（SPLET），被用于分析所研究化合物的抗氧化能力。溶剂效应主要影响 SET-PT 和 SPLET。因此，热力学上更有利的机制可以被改变。HAT 和 SPLET 分别是气相和溶剂相中的热力学主导机制。因此，在气相中，抗氧化能力的顺序与键离解焓值相似：槲皮素>槲皮素-5-O-葡萄糖苷>槲皮素-7-O-葡萄糖苷>槲皮素-3-O-葡萄糖苷>槲皮素-3'-O-葡萄糖苷>槲皮素-4'-O-葡萄糖苷。而在溶剂相中，顺序与质子亲和能值相似：槲皮素-4'-O-葡萄糖苷>槲皮素-5-O-葡萄糖苷>槲皮素>槲皮素-3-O-葡萄糖苷>槲皮素-7-O-葡萄糖苷>槲皮素-3'-O-葡萄糖苷。与 A 环相比，B 环和 C 环上的 OH 基团对槲皮素及其糖苷的抗氧化活性贡献更大。
