Jørgensen L V, Skibsted L H
Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Frederiksberg C, Denmark.
Free Radic Res. 1998 Mar;28(3):335-51. doi: 10.3109/10715769809069285.
Fourteen flavonoid aglycones, and the flavonoid glycoside rutin, with redox potentials ranging from 0.20 (myricetin) to 0.83 V (chrysin) vs. NHE, as determined by cyclic voltammetry at 23 degrees C in aqueous 50 mM phosphate, ionic strength 0.16 (NaCl) with pH = 7.4 and compared with redox potentials determined for four cinnamic acid derivatives, were all found to reduce ferrylmyoglobin, MbFe(IV)=O, to metmyoglobin, MbFe(III). Reaction stoichiometry depends strongly on the number of hydroxyl groups in the flavonoid B-ring. All compounds with 3',4'-dihydroxy substitution reduce 2 equivalents of MbFe(IV)=O, whereas naringenin, hesperitin and kaempferol, with one hydroxyl group in the B-ring, reduce with a one-to-one stoichiometry. As studied spectrophotometrically under pseudo-first-order conditions with flavonoids in excess, rutin and apigenin react with MbFe(IV)=O with very similar and moderately high activation enthalpies of deltaH298++ = 69 +/- 1 kJ mol(-1) and deltaH298++ = 65 +/- 3 kJ mol(-1), respectively, and with positive activation entropies of deltaS298++ = 23 +/- 4 J mol(-1) K(-1) and deltaS298++ = 13 +/- 9 J mol(-1) K(-1), respectively, in agreement with outer-sphere electron transfer as rate determining. For the fifteen plant polyphenols only qualitative relations exist between redox potential and rate constants rather than a linear free energy relationship (r2 = 0.503), and especially the flavone apigenin was found more efficient as reducing agent. For the flavanones, a linear relation (r2 = 0.971) indicate that, in the absence of a 2,3 double bond, removal of the 4-carbonyl group or addition of a 3-hydroxy group only has minor effect on reactivity. The flavonols are the most efficient reducing agents, effectively reducing MbFe(IV)=O to MbFe(III) and establishing a steady state distribution between the flavonol and MbFe(III) and oxymyoglobin, MbFe(II)O2. Oxidised flavonols reduces MbFe(III) to MbFe(II)O2 very efficiently and much faster than the parent flavonol.
通过在23℃下于50mM磷酸盐水溶液中（离子强度0.16（NaCl），pH = 7.4）进行循环伏安法测定，14种黄酮苷元以及黄酮苷芦丁的氧化还原电位范围为相对于标准氢电极（NHE）的0.20（杨梅素）至0.83V（白杨素），并与四种肉桂酸衍生物测定的氧化还原电位进行比较，结果发现它们都能将高铁肌红蛋白（MbFe(IV)=O）还原为高铁血红蛋白（MbFe(III)）。反应化学计量学在很大程度上取决于黄酮B环中的羟基数量。所有具有3'，4'-二羟基取代的化合物可还原2当量的MbFe(IV)=O，而在B环中具有一个羟基的柚皮素、橙皮素和山奈酚则以1:1的化学计量比进行还原。在黄酮过量的伪一级条件下通过分光光度法研究发现，芦丁和芹菜素与MbFe(IV)=O反应时，活化焓分别为非常相似且适中较高的ΔH298++ = 69±1kJ mol⁻¹和ΔH298++ = 65±3kJ mol⁻¹，活化熵分别为正值ΔS298++ = 23±4J mol⁻¹ K⁻¹和ΔS298++ = 13±9J mol⁻¹ K⁻¹，这与外层电子转移作为速率决定步骤一致。对于这15种植物多酚，氧化还原电位与速率常数之间仅存在定性关系，而非线性自由能关系（r² = 0.503），尤其发现黄酮芹菜素作为还原剂更有效。对于黄烷酮，线性关系（r² = 0.971）表明，在不存在2,3-双键的情况下，去除4-羰基或添加3-羟基对反应活性的影响较小。黄酮醇是最有效的还原剂，能有效地将MbFe(IV)=O还原为MbFe(III)，并在黄酮醇与MbFe(III)和氧合肌红蛋白（MbFe(II)O₂）之间建立稳态分布。氧化的黄酮醇将MbFe(III)还原为MbFe(II)O₂的效率非常高，且比母体黄酮醇快得多。
