Spin-traps, use

Table 11 summarizes results of spin trapping experiments where PBN-Nu and other ST-Nu" systems have been oxidized anodically at platinum. Originally, all the reactions were suggested to proceed via Nu radicals (Janzen et al., 1980 Walter et al., 1982), but the fact that PBN is oxidized at a lower potential than Cl-, CNO and CN- (Tables 1 and 5) clearly shows that the faster electrochemical process must be PBN— PBN + at the potentials employed. On the other hand, azide ion is oxidized in a faster reaction than any of the spin traps used and thus azide radical is implicated as being trapped. The Cr 4MePyPBN [17] system is a case where possibly Cl is involved in view of the high pa of this spin trap. 

Kochany and Bolton (1992) studied the primary rate constants of the reactions of hydroxyl radicals, benzene, and some of its halo derivatives based on spin trapping using detection by electron paramagnetic resonance (EPR) spectroscopy. The competitive kinetic scheme and the relative initial slopes or signal amplitudes were used to deduce the kinetic model. Based on a previously published rate constant (4.3 x 109 M 1 s ) in the pH range of 6.5 to 10.0 for the reaction of hydroxyl radicals with the spin trap compound 5,5 -d i methy I pyrro I i ne N-oxide (DMPO), rate constants for the reaction of hydroxyl radicals with benzene and its halo derivatives were determined. 

Detection of primary radical anions in microsomal incubations generally is possible only under anaerobic conditions. In the presence of air a redox cycle is set up, as referred to above. Thus, in initially aerobic systems, the primary radical can be detected only after a lag time that corresponds to the time required to deplete oxygen in the medium. During this lag time the superoxide radical is generated, which can be spin trapped using the nitrone 5,5 -dimethylpyrroline-l-oxide (DMPO) [187]. 

As might be predicted on the basis of these data, a number of other thiol compounds have been shown to reduce Fe(IV)=0 Lb to the Fe(III) state with concomitant formation of thiyl radicals (detected by use of EPR spin trapping using 5,5-dimethyl-l-pyrroline IV-oxide) (135). In some cases, however, other species are formed, and these have been identified from their UV-vis absorption spectra as novel sulfur species formed by nucleophilic attack on the tetrapyrrole ring by the thiol group (135). The ability of a thiol to undergo two such competing reactions is dictated by steric and electronic characteristics... 

It was previously shown that oxidation produced a radical cation which could be detected by ESR [111, 112] provided the 4 position was fully substituted. If the 4 position contained a hydrogen atom, then the initial oxidation was followed by deprotonation with the formation of a neutral radical which could undergo further oxidation or dimerisation. In-situ spin trapping using PBN demonstrated the presence of radical intermediates in the electro-oxidation of substituted 1,4-dihydropyridines. That the trapped radicals were the deprotonated neutral radical, and not the primary radical cation, was demonstrated by comparison of the ESR parameters with those of the spin adduct produced by electroreduction of A-methylpyridine ion cations, where only the neutral dihydropyridyl radical would be produced. The work of Volke and co-workers clearly demonstrates how spin trapping may be applied to the study of more complex organic electrode reactions and how comparison of ESR spectra generated from different precursors may be used to reveal the nature of the trapped radical. 

Thermal decomp, of DTBPO Spin trap, using 2-methyl-2-nitroso propane... 

R 298 L.J. Berliner, V. Khramtsov, T.L. Clanton and H. Fujii, NMR and MRI Spin Trapping Using NMR to Learn about Free Radical Reactions , Curr.Top.Biophys., 2002,26,21... 

Recently, evidence for the formation of hydroxyl radicals on BDD has been reported [5] by means of spin-trapping using 5,5-dimethyl- 1-pyrroline-N-oxide (DMPO). 

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