Trapping agents, radical identification

The sequence of events following the reaction of metMb with hydrogen peroxide has also been investigated through the use of spin trapping agents. Initial studies of this type with 5,5-dimethylpyrroline N-oxide (DMPO) led to the identification of Y103 as the primary site of DMPO adduct formation, a modification that was blocked by specific iodination of this residue 187). The identity of the radical trapped in this reaction... 

Further proof that cyclobutadiene liberated by ceric oxidation of the iron carbonyl complex is completely free of the metal comes from an ingenious new three-phase test for reactive intermediates which resembles the Paneth test for free radicals in its basic flow design. Thus, a cyclobutadiene-iron carbonyl complex bound to a support of polymer beads is treated as a suspension with Ce in the presence of separate polymer beads to which a trapping agent (maleimide) is bound. The resulting adduct is then liberated from the second polymer by hydrolysis for identification, its isolation... 

There is one further e.s.r. technique, spin trapping, which has been developed fairly recently to aid in the identification of radical intermediates that are too short lived to be identified by e.s.r. directly [46]. The electrochemical experiment is carried out in situ in the normal way, but a spin trapping agent is also added to the system. This reacts with any electrogenerated radicals to form a more stable radical which is characteristic of the initial radical and can be identified by e.s.r. The most widely used spin traps are nitrones which react to give stable nitroxide radicals. These nitrones are electroinactive over a wide potential range (+1.2V to up to —l.OV vs SCE) [47] and can therefore be used in many studies. 

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