Flavonoids widely found in bee products are excellent antioxidants. The structural features are important in evaluating the antiradical activity of flavonoid. In this work, the density functional theory (DFT) methods were applied to investigate the influence of C2C3 double bond on the antiradical activity of flavonoid based on three prevalently accepted radical scavenging mechanisms from the thermodynamic aspect. It is found that the hydroxyl groups in different rings are affected variously by the C2C3 double bond and the 3OH group is most influenced. For the compounds that only differ with the C2C3 double bond, the antiradical activity of flavone or flavonol (possessing C2C3 double bond) is not always stronger than that of flavanone: in the weak polarity phases, only the antiradical activities of chrysin, galangin and morin are stronger than those of pinocembrin, pinobanksin and dihydro-morin, respectively. In polar phases, the C2C3 double bond would weaken the antiradical activity of flavonoid via enlarging the proton affinity and the antiradical activity of flavone or flavonol is weaker than that of flavanone.

中文翻译：

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C2C3双键对黄酮类抗自由基活性的影响：不同机制分析

广泛存在于蜂产品中的黄酮类化合物是极好的抗氧化剂。结构特征对于评价类黄酮的抗自由基活性很重要。在这项工作中，基于三种普遍接受的自由基清除机制，从热力学角度出发，应用密度泛函理论 (DFT) 方法研究了 C2C3 双键对黄酮类化合物抗自由基活性的影响。发现不同环中的羟基受C2C3双键的影响不同，3OH基团的影响最大。对于仅与C2C3双键不同的化合物，黄酮或黄酮醇（具有C2C3双键）的抗自由基活性并不总是强于黄烷酮：在弱极性相中，只有白杨素的抗自由基活性，高良姜素和桑椹素分别强于松香素、松香素和二氢桑椹素。在极性相中，C2C3双键会通过增加质子亲和力来减弱黄酮类化合物的抗自由基活性，并且黄酮或黄酮醇的抗自由基活性弱于黄烷酮。