Spin-trapping in vitro

Examples of such reactions in chemical systems together with the symbols used, are given in Table 3.1, and typical adduct spectra are shown in Fig. 3.7. Although a number of other stable radicals could be used in this way, in practice only the nitroxide precursors are important. 

Not all radicals will add to spin traps, and in some cases addition may be too slow to compete with other processes. Also in biological systems, it must be borne in mind that the spin-traps will divert the reactive radicals from their normal role. In fact, they act as radical scavengers. Scavengers are often used as probes of radical reactions, so it is useful to use spin-traps for this purpose as well as for detection by ESR spectroscopy. 

If traps have to be used, identification of the parent radicals obviously becomes more difficult than when these can be detected directly. Thus the discovery of the ideal spin-trap depends in part on the resulting spectrum and its uniqueness for the trapped radical. Ideally there is extra hyperfine coupling characteristic of the trapped species. This is especially convincing if coupling to an enriched isotopic nucleus can be seen, since it establishes the involvement of the enriched specimen in a direct manner (e.g., the use of I3CC14 and l702 discussed below). If such characteristic features are not resolved in the normal spectrum this may be achieved using resolution enhancement, or better, ENDOR spectroscopy. 

If extra splittings characteristic of R rather than the spin-trap are not detected, then one relies on the measured l4N coupling and any H coupling from the trap. Of the traps normally used (Table 3.1) one Me3CNO (NTB) adds the radical directly to nitrogen [3.1]. All the others are nitrones, the radical adding to carbon as in [3.2], (for DMPO). In general the nitrones are 

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A59. Khan, N., C.M. Wilmot, G.M. Rosen, E. Demidenko, 27A74. J. Sun, J. Joseph, J. O Hara, B. Kalyanaraman, and H.M. Swartz Spin traps In vitro toxicity and stability of radical adducts Free Radic. Biol. Med. 34 (2003)... 

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