Chrysin and (±)-taxifolin electrochemical oxidation mechanisms
Chrysin and (±)-taxifolin electrochemical oxidation mechanisms
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DOI：
10.1002/elan.200403216
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发表时间：
2005-06-01
期刊：
影响因子：
3
通讯作者：
Brett, AMO
中科院分区：
文献类型：
--
作者：
Janeiro, P;Corduneanu, O;Brett, AMO
用不同的电化学方法研究了黄酮白杨素和二氢黄酮醇(+/-)-紫杉酯在不同pH值下的电化学行为。二氢黄酮醇(+/-)-紫杉酯有两个氧化峰。(+/-)-紫杉林的一次电氧化反应在整个pH范围内是可逆的。峰电流对pH的依赖关系在中性pH附近出现最大值，在酸性和碱性介质中减小。邻苯二酚基团去质子化对B环的影响与(+/-)-紫杉酯的电子/质子给电子能力及清除自由基的抗氧化活性有关。在白杨素中，其中B环具有未取代的苯基，抗氧化活性部分在A环上，白杨素在比B环上的邻苯二酚部分离子更高的氧化电位下呈现不可逆氧化峰，并具有pH依赖性行为。从7-羟基的较低pK(A)值可以看出，A环上的-OH基团受到4-酮基的影响，表明7-OH基团的酸性较强。紫杉素和白杨素的5-羟基与4-酮基之间的分子内氢键的酸性减弱作用可解释为5-羟基的酸性较弱。
The electrochemical behaviour of the flavone chrysin and the dihydroflavonol (+/-)-taxifolin was investigated by different electrochemical techniques at different pH values. Dihydroflavonol (+/-)-taxifolin presented two oxidation peaks. The first electrooxidation reaction of (+/-)-taxifolin is reversible over the whole pH range. The dependence of peak current on pH showed a maximum around neutral pH values with a decrease in acidic and alkaline media. The influence of the catechol group deprotonation on ring B is related to the electron/proton donating capacity in (+/-)-taxifolin and to its radical scavenging antioxidant activity. In chrysin, where the ring B has an unsubstituted phenyl, the antioxidant active moiety is in ring A. Chrysin presents an irreversible oxidation peak at higher oxidation potentials than those usually obtained for the catechol moiety ion in ring B and a pH dependent behaviour. The -OH groups on ring A are affected by the 4-keto group as shown by the lower pK(a), value of the 7-OH, indicating that the 7-OH group is the more acidic. The 5-OH group is less acid and may be explained by the acidic weakening effect of an intramolecular H-bond between the 5-OH and 4-keto group of taxifolin and chrysin.