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首页> 外文期刊>Chemistry: A European journal >Kinetic and Thermochemical Study of the Antioxidant Activity of Sulfur-Containing Analogues of Vitamin E
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Kinetic and Thermochemical Study of the Antioxidant Activity of Sulfur-Containing Analogues of Vitamin E

机译：动力学和热化学研究维生素E的含硫类似物的抗氧化活性

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摘要

Sulfur-containing analogues of vitamin E (thiachromanols), either linked or not to a catechol moiety, were synthesized and their hydrogen-atom donating ability evaluated. The determination of the O-H bond dissociation enthalpy (BDE) of the a-toco-pherol analogue 4 by the electron paramagnetic resonance (EPR) equilibration technique provided a value of 78.9 kcal mol~(-1) that is, approximately 1.8 kcal mol~(-1) higher than that of alpha-to-copherol. The kinetic rate constants for the reaction with peroxyl radicals (k_(inh)), measured by inhibited autoxidation studies, showed that thiachromanols react 2.5 times slower than the corresponding tocopherols, in agreement with the higher BDE value. This behavior was explained, on the basis of crystallographic analyses and DFT calculations, in terms of a change in the molecular geometry caused by insertion of a sulfur atom into the framework of vitamin E. This behavior implies a greater deviation of the condensed ring from coplanarity with the aromatic ring, thus giving rise to a decrease in the conjugative stabilization of the phenoxyl radical and consequently to an increase in the O-H bond strength. Although less reactive than tocopherols, thiachromanols may, however, act as bimodal antioxidants as a result of the hydroperoxide decomposing ability of the sulfur atom.
机译：合成或连接或不连接邻苯二酚部分的含维生素E的硫代类似物（硫代铬醇），并评估其氢原子供体能力。通过电子顺磁共振（EPR）平衡技术测定α-生育酚类似物4的OH键解离焓（BDE）提供了78.9 kcal mol〜（-1）的值，约为1.8 kcal mol〜 （-1）高于α-生育酚。通过抑制自氧化研究测量的与过氧自由基反应的动力学速率常数（k_（inh））表明，硫代苯并色酚的反应速度比相应的生育酚慢2.5倍，这与更高的BDE值相符。在晶体学分析和DFT计算的基础上，对这种行为进行了解释，该变化是由于将硫原子插入维生素E的骨架中引起的分子几何结构的变化。这种行为暗示了稠环与共面性的更大偏差与芳环结合，因此降低了苯氧基自由基的共轭稳定性，并因此提高了OH键强度。尽管硫酚的反应活性不如生育酚，但由于硫原子的氢过氧化物分解能力，它们可能充当双峰型抗氧化剂。

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