中文摘要：

黄芩素是黄芩苷的初级代谢产物，二者的分子结构差别仅在于7-位取代基，前者为酚羟基而后者为糖苷．本文通过稳态吸收光谱和循环伏安实验，以及量化计算等方法考察了黄芩素和黄芩苷的酸离解常数（pKa）、脂水分配系数、氧化-还原电位、分子偶极矩等基本物理化学性质，以及清除ABTS^＊＋自由基活性（TEAC）的差异．结果表明，黄芩素酚羟基7-OH的酸性较强（pKa=5．4）；在生理pH下黄芩素的氧化还原电位（0．32Vvs．NHE）略低于黄芩苷，且TEAC值约为黄芩苷的1．8倍．量化计算结果表明，7-取代基对黄酮分子骨架的构型、物理化学性质以及自由基清除活性有显著影响．文中探讨了黄芩素和黄芩苷的微观和宏观分子属性与抗氧化活性之间的关系，得出酚羟基数量及其pK。值、黄酮分子骨架构型以及电子结构是影响类黄酮化合物抗氧化活性主要因素的结论．研究结果可为深入研究类黄酮化合物的抗氧化结构-活性关系提供依据．

英文摘要：

Baicalein, a primary metabolite of baicalin, differs from its mother compound merely by the 7-substituent （i. e. it possesses a phenolic hydroxyl （7-OH） instead of a glucuronic acid）. The present work is intended to compare, by means of steady-state optical absorption spectroscopy, cyclic voltammetry, ESR and quantum chemical calculation, their＇physicochemical properties, such as pKa, log10 partition coefficient, redox potential and dipole moment, as well as their capacities of scavenging ABTS^＊ ＋ （TEAC） and autoxidation of baicalein. Experimental results showed that the 7-OH group of baicalein was rather acidic （pKa =5.4）. In addition, baicalein showed a lower redox potential （0.32 V vs. NHE） and a 1.8-fold higher TEAC with reference to baicalin under physiological pH. Theoretical results showed that the difference in 7 substituent resulted in significantly different molecular structures, physieoehemieal properties and radical scavenging activities of the flavonoids in question, which are discussed in terms of their micro- and macro-molecular properties. It was concluded that the number oF phenolic hydroxyls and the corresponding pKa values, as well as the molecular structures are all important for the antioxidative activity of flavonoids.