Kinetic Studies on Retinol Addition Radicals
Kinetic Studies on Retinol Addition Radicals
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视黄醇加成自由基的动力学研究
DOI：
10.1039/c0ob00799d
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
David J McGarvey
中科院分区：
文献类型：
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作者：
Ali El-Agamey;Shunichi Fukuzumi;K.Razi Naqvi;David J McGarvey
视黄醇中性自由基（RS-视黄醇stec）是由视黄醇与4-吡啶基硫基和2-吡啶基硫基自由基在氩饱和的甲醇中反应产生的，它经历β-消除，这可以通过在380 nm处缓慢的次级吸收上升来监测，这归因于不稳定的视黄醇中性加成自由基重排为更稳定的加成自由基。在不同温度下测定了4-PyrS-视黄醇甾体的β-消除反应速率常数（kβ），其Arrhenius方程为log（kβ/s−1）=（12.7 ± 0.2）−（54.3 ± 1.3）/θ，其中θ = 2.3RT kJ mol−1。视黄醇加成自由基（RS-视黄醇stec），从反应产生的视黄醇与各种巯基自由基，对氧的反应性也已在甲醇中进行了研究。在氧存在下，RS-视黄醇的衰变符合双指数动力学，并且所观察到的RS-视黄醇衰变的速率常数都是氧浓度依赖性的。这表明至少有两个由RS stec与视黄醇反应形成的硫基加成自由基进行氧加成反应。根据RS-视黄醇酯和RS-CAR酯（CAR：类胡萝卜素）的氧加成速率常数，讨论了视黄醇的抗氧化-促氧化性质。
Retinol neutral radicals (RS-retinol˙), generated from the reaction of retinol with 4-pyridylthiyl and 2-pyridylthiyl radicals in argon-saturated methanol, undergo β-elimination, which can be monitored via the slow secondary absorption rise at 380 nm attributed to the rearrangement of the unstable retinol neutral addition radicals to the more stable addition radicals. Rate constants for the β-elimination reactions (kβ) of 4-PyrS-retinol˙ were measured at different temperatures and the Arrhenius equation for the reaction is described by log (kβ/s−1) = (12.7 ± 0.2) − (54.3 ± 1.3)/θ, where θ = 2.3RT kJ mol−1. The reactivities of retinol addition radicals (RS-retinol˙), generated from the reaction of retinol with various thiyl radicals, towards oxygen have also been investigated in methanol. In the presence of oxygen, the decay of RS-retinol˙ fits to biexponential kinetics and both observed rate constants for the RS-retinol˙ decay are oxygen-concentration dependent. This suggests that at least two thiyl addition radicals, formed from the reaction of RS˙ with retinol, undergo oxygen addition reactions. In light of the estimated rate constants for oxygen addition to RS-retinol˙ and RS-CAR˙ (CAR: carotenoid), the antioxidant-prooxidant properties of retinol are discussed.