EPR Detection of the Superoxide Free Radical with the Nitrone Spin Traps DMPO and BMPO

acterizing free radicals in chemistry, biology and medicine, is detection by EPR spectroscopy. However, due to their high reactivity and short half-lives, direct EPR detection of many free radicals (e.g., superoxide, hydroxyl radical, alkyl radicals, etc.) is virtually impossible in solution at room temperature. Spin trapping is a technique developed in the late 1960s in which a nitrone or nitroso compound reacts with a target free radical to form a stable and identifiable free radical that is detected by EPR spectroscopy. The spin trapping technique involves the addition of the reactive free radical across the double bond of a diamagnetic ‘‘spin trap’’ to form a much more stable free radical (a ‘‘radical adduct’’) which can then be measured with EPR: other nitrone spin traps. It is very redox inert. DMPO forms radical adducts with O-, C-, N-, S-centered radicals that have very distinguishable EPR spectra. This allows the researcher to identify the type of free radical that was formed in a given reaction. This is not the case for other spin traps such as α-phenyl-N-tert-butylnitrone (PBN) where the EPR spectra for the radical adducts are nearly identical regardless of the radical trapped. The identity of a DMPO radical adduct is then identified using references from a web search of related scientific literature.