黄酮类化合物抗氧化活性的结构因素

用结构化学和量子化学半经验计算方法研究几种典型黄酮类化合物，探讨影响黄酮类化合物抗氧化活性的结构因素。研究结果表明：（1）在分子内形成半醌式自由基时所需能量ΔHOF较低，其形成的自由基较稳定，从而具有较高的抗氧化活性。（2）电子自旋密度分布的均匀性，是黄酮类抗氧化性较强的重要原因。含邻二酚羟基的黄酮形成的半醌式自由基，电子自旋密度分布比较均匀，而且分子中半醌式基团与邻位酚羟基形成分子内氢键使体系能位降低，因而黄酮类化合物中具有邻二羟基酚的品种比含间二羟基酚的抗氧化活性强。（3）分子中的酚羟基的数目和可以形成氢键的数目与分子的抗氧化活性正相关，是黄酮类化合物具有强抗氧化活性的重要因素。研究表明，通过改变黄酮的羟基取代，使黄酮半醌式自由基的电子自旋密度分布更加均匀，用化学修饰增加黄酮类化合物的酚羟基数量以及形成分子内氢键的数目是提高黄酮抗氧化活性的途径。

Structure-Antioxidation Relationship of Flavonoid Antioxidants

The structure-antioxidation relationship of typical flavonoid antioxidants is investigated by means of structural chemistry and the semiempirical calculation method of quantum chemistry. The results suggested that the lesser half-quinone freeradical △HOF make greater antioxidation than the other phenolic hydroxyl in the molecule. The better uniformity of the spin densities distribution of half-quinone freeradical is the essential cause that accounts for the better antioxidation of the flavonoid. Accordingly, the antioxidation of flavonoid containing ortho-substituting hydroxyl is better than that containing meta-substituting hydroxyl，such as the individualization of ortho-dioxy-benzene and meta-dioxy-benzene. The amount of phenol hydroxyl and of intramolecular H-bond in the molecule is in direct relationship with the flavonid antioxidation of the molecule, which contributes to the important factor of the strong antioxidation of flavonoid. While △HOF of half-quinone freeradical of the decorated quercetin discussed is not remarkable minor, and the spin densities is also not noticeable uniform, the antioxidation of the decorated quercetin is better than that of quercetin because the former contains more phenolic hydroxyl and is able to form more intramolecular H-bond. It is shown from the study that the spin densities distribution of half-quinone freeradical is more uniform by changing the locations of hydroxyl substitute, and the increase in the amount of phenol hydroxyl and the amount of intramolecular H-bond in flavonoid molecule by chemical decoration, are the means of improving antioxidation of flavonoid.