This method involves the trapping of reactive short-lived free radicals by a diamagnetic spin trap compound via an addition reaction to produce a more stable free radical product or spin adduct. The spin adduct that is formed is paramagnetic and has an ESR spectrum with a hyperfine splitting constant and g-value characteristic of the type of reactive free radical trapped. Thus, the structure of the radical trapped can usually be deduced, although the most difficult aspect of the spin trapping technique is the correct assignment of the nitroxide spectrum to the original radical species. The most commonly used spin trapping agents in biological systems are nitrone derivatives. In general, small R groups have a large aH value.
Solvents can have a major effect on the hyperfine splitting observed for a spin adduct.
In general, increases in solvent polarity produce an increase in the nitrogen-hyperfine splitting as the spin density on the nitrogen increases. Spin trapping reaction of nitrone spin traps DMPO is the most widely used spin trap for the study of oxygen-centred free radicals, due to its solubility in water, its rapid diffusion in biological systems, and the formation of stable adducts. The more lipophilic character of PBN limits its solubility in aqueous environments, but allows it to readily cross membranes and diffuse into cells. As a result of its lipophilicity, PBN has been extensively used to trap lipid-derived radicals. Return to Dr Towner's Research page .