【作者】 徐欣荣；

【导师】 何建波；

【作者基本信息】 合肥工业大学 ， 应用化学， 2010， 硕士

【摘要】 类黄酮化合物(Flavonoids)广泛存在于蔬菜、水果和药用植物中,是一类天然抗氧化剂。杨梅素和二氢槲皮素均属于类黄酮化合物,能够清除体内过剩的超氧自由基,具有抗炎、抗肿瘤及抗衰老等药理作用,近年来得到国内外研究者的广泛关注。本文以这两种化合物为模型化合物,采用循环伏安法、微分脉冲伏安法和现场薄层长光程紫外可见光谱电化学方法测试它们的电氧化还原行为和光谱变化,探讨C环2,3碳碳键的饱和性对电氧化机理及抗氧化性能的影响。并采用双电势阶跃计时吸光度法和循环伏吸法对两者的电氧化还原过程进行了现场的动态检测。此外,通过光谱电化学方法对两者与金属离子相互作用的机理进行了研究。电化学测试结果表明,杨梅素和二氢槲皮素在CPE表面有较强的吸附。在较低电势下两种物质均有一对准可逆的氧化还原峰A1和C1,对应于B环上3’,4’-二羟基的两电子两质子反应。不同扫速曲线反映出杨梅素和二氢槲皮素在CPE表面同时受到吸附作用和扩散作用控制。通过pH值的考察发现,酸性条件更利于两者的氧化。循环伏安现场薄层光谱电化学测试表明,在不同的恒电势下氧化还原,杨梅素和二氢槲皮素的UV/Vis特征吸收峰表现出的变化趋势,对应于这两种物质碳环不同位置上的羟基的氧化还原。同时探讨了杨梅素和二氢槲皮素的氧化机理及其抗氧化性构效关系,结果表明杨梅素的氧化遵守随后转化机理,但其分子中B环5’-OH的存在对随后转化步骤有阻碍作用,导致抗氧化性减弱;二氢槲皮素分子中C环2,3位C-C饱和键则完全阻断了随后转化步骤的进行,从而导致抗氧化性大幅度减弱。可见随后转化步骤对黄酮醇抗氧化活性具有十分重要的贡献。本论文用紫外吸收光谱法考察了类黄酮化合物与金属离子(如Fe3+、Cu2+)的相互作用,同时考察了活性氧组分H2O2对类黄酮化合物与金属离子络合作用的影响。研究表明,杨梅素与Cu2+、Fe3+这两种金属离子以1:2的比例络合,3-OH、4-羰基以及B环上的3’,4’-二羟基是其结合位点。二氢槲皮素与金属离子很难络合,很大程度上是受C环2,3位C-C饱和键的影响。酸性条件下,H2O2可以缓慢氧化杨梅素成醌式结构,并在294 nm处出现新的特征吸收峰,同时Fe3+对H2O2的缓慢氧化过程具有显著的促进作用。更多还原

【Abstract】 As a series of natural antioxidants, flavonoids are abundant in vegetables, fruits and medicinal plants. Myricetin and dihydroquercetin belong to flavonoids, which can scavenge superfluous superoxide free radicals in human body and show pharmacological effects in anti-tumour, anti-inflammation and anti-senility, etc. Therefore, they have got great attention in recent years. In this paper, these two compounds were investigated as model compounds to test their electric redox behavior and spectral changes using cyclic voltammetry, differential pulse voltammetry and in situ UV-Vis spectroelectrochemical methods, and then explored the influence of 2,3 C-C saturated bond in electro-oxidation mechanism and anti-oxidation properties. We also used double potential chronoabsorptometry and cyclic voltabsorptometry to test electric redox behavior of the two compounds. In addition, the interactions between metal ions and flavonoids were deeply investigated by spectroelectrochemical methods.Electrochemical tests showed that CPE displayed great power to adsorb myricetin and dihydroquercetin. The two flavonoids both had a couple of reversible redox peaks A1 and C1 at lower potentials, which corresponded to the oxidations of 3’,4’-OHs at B-ring involving 2-electrons and 2-protons. Curves at different scan rates indicated that the reactions of myricetin and dihydroquercetin were both controlled by adsorption and diffusion on CPE surface. Through the examinations at different pH values, we found that acidic conditions were suitable for oxidations of the two flavonoids.Cyclic voltammetry and thin layer spectroelectrochemistry test results indicated that the adsorption and oxidation of myricetin and dihydroquercetin on a CPE in a longoptical-path thin-layer electrochemical cell. The characteristic bands of the two flavonoids showed potential-dependent variations under controlled-potential oxidation. Cyclic voltammetry and in situ UV-Vis spectroelectrochemical methods were used to investigate the electro-oxidation mechanisms of myricetin and dihydroquercetin, in order to understand the relationship between flavonols’antioxidant activity and their chemical structures. The results indicated that the presence of the 5’-OH at the B-ring of myricetin may, to a certain extent, hinder the subsequent chemical transformation, while the 2,3 C-C saturated bond in dihydroquercetin can completely stop the subsequent step, leading to the decrease in antioxidant activity, less for myricetin and more for dihydroquercetin. This suggests that the subsequent chemical transformation gives very important contribution to the antioxidant activity of flavonols.In this work, the interactions between flavonoids and metal ions were studied by spectroelectrochemical methods. We also studied the effect of hydrogen peroxide, one of the reactive oxygen species, on the complexation of flavonoids and metal ions. We have shown that myricetin forms 1:2 complexes with Cu2+, in which 3-OH and 4-oxo groups and 3’,4’-OH groups are coordination sites. The same result was obtained for Fe3+. Spectral changes were hardly obtained for the complexation of dihydroquercetin and metal ions, which corresponded to the 2,3 C-C saturated bond in dihydroquercetin. Hydrogen peroxide can oxidize myricetin to quinine in acidic solutions slowly, whose characteristic absorption peak appears at 294 nm. The slow myricetin oxidation by hydrogen peroxide is accelerated in the presence of Fe3+.更多还原