Buettner G R
ESR Center/EMRB 68, College of medicine, University of Iowa, Iowa City 52242.
Arch Biochem Biophys. 1993 Feb 1;300(2):535-43. doi: 10.1006/abbi.1993.1074.
Free radicals vary widely in their thermodynamic properties, ranging from very oxidizing to very reducing. These thermodynamic properties can be used to predict a pecking order, or hierarchy, for free radical reactions. Using one-electron reduction potentials, the predicted pecking order is in agreement with experimentally observed free radical electron (hydrogen atom) transfer reactions. These potentials are also in agreement with experimental data that suggest that vitamin E, the primary lipid soluble small molecule antioxidant, and vitamin C, the terminal water soluble small molecule antioxidant, cooperate to protect lipids and lipid structures against peroxidation. Although vitamin E is located in membranes and vitamin C is located in aqueous phases, vitamin C is able to recycle vitamin E; i.e., vitamin C repairs the tocopheroxyl (chromanoxyl) radical of vitamin E, thereby permitting vitamin E to function again as a free radical chain-breaking antioxidant. This review discusses: (i) the thermodynamics of free radical reactions that are of interest to the health sciences; (ii) the fundamental thermodynamic and kinetic properties that are associated with chain-breaking antioxidants; (iii) the unique interfacial nature of the apparent reaction of the tocopherol free radical (vitamin E radical) and vitamin C; and (iv) presents a hierarchy, or pecking order, for free radical electron (hydrogen atom) transfer reactions.
自由基的热力学性质差异很大，从强氧化性到强还原性都有。这些热力学性质可用于预测自由基反应的顺序或层级。利用单电子还原电位，预测的反应顺序与实验观察到的自由基电子（氢原子）转移反应一致。这些电位也与实验数据相符，这些数据表明，主要的脂溶性小分子抗氧化剂维生素E和末端水溶性小分子抗氧化剂维生素C协同作用，保护脂质和脂质结构免受过氧化作用。虽然维生素E存在于膜中，维生素C存在于水相中，但维生素C能够使维生素E循环利用；也就是说，维生素C修复维生素E的生育酚氧基（色满氧基）自由基，从而使维生素E能够再次作为自由基链断裂抗氧化剂发挥作用。本综述讨论了：（i）健康科学领域感兴趣的自由基反应的热力学；（ii）与链断裂抗氧化剂相关的基本热力学和动力学性质；（iii）生育酚自由基（维生素E自由基）与维生素C表观反应独特的界面性质；以及（iv）给出自由基电子（氢原子）转移反应的层级或顺序。
