Radicals Generated by ET Redox Reactions

Radicals can also be generated via redox processes either by reduction or oxidation of an appropriate precursor, depending on the nature of the radical precursor. 

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The main oxidative metabolite of a-tocopherol, a-tocopherolquinone, has been quantitated in plasma, erythrocytes and platelets by reversed-phase chromatography and coulometric detection in the redox mode (7,74,78), as outlined in 111.A.3. Levels of a-tocopherolquinone never exceeded 1% of those of a-tocopherol. The most thorough study of the reaction of a-tocopherol with peroxyl radicals, generated by azo-fe/x(amidinopropane) is that by Liebler et al., who used GC-MS to quantitate a-tocopherolquinone, 5,6-epoxy-a-tocopherolquinone, and 2,3-epoxy-a-tocopherolquinone, as well as a-tocopherolhydroquinone in rat liver microsomes (6) (Fig. 2). 

Generation of radicals by redox reactions has also been applied for synthesizing block copolymers. As was mentioned in Section II. D. (see Scheme 23), Ce(IV) is able to form radical sites in hydroxyl-terminated compounds. Thus, Erim et al. [116] produced a hydroxyl-terminated poly(acrylamid) by thermal polymerization using 4,4-azobis(4-cyano pentanol). The polymer formed was in a second step treated with ceric (IV) ammonium nitrate, hence generating oxygen centered radicals capable of starting a second free radical polymeriza-... 

In a study directed to the analysis of the role of Fe and the generation of H2O2 in Escherichia coli (McCormick et al. 1998), hydroxyl radicals were specihcally trapped by reaction with ethanol to give the a-hydroxyethyl radical. This formed a stable adduct with a-(4-pyridyl-l-oxide)-iV-t-butyl nitroxide that was not formed either by superoxide or hydroxyl radicals. The role of redox-reactive iron is to use EPR to analyze the EPR-detectable ascorbyl radicals. 

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