Spin Trapping and Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy methodology is a highly selective and sensitive assay for detecting paramagnetic species. Owing to the unpaired electron in the outer orbit, free radicals are paramagnetic species and, when in sufficient quantity, are directly detectable and measurable using EPR spectroscopy. However, many free-radicals species are highly reactive, with relatively short half-lives, and the concentrations found in biochemical systems are usually inadequate for direct detection by EPR spectroscopy. Spin-trapping is a chemical reaction that provides an approach to help overcome this problem. Spin traps are compounds that react covalently with highly transient free radicals to form relatively stable, persistent spin adducts that also possess paramagnetic resonance spectra detectable by EPR spectroscopy. When a spin trap is added to a free radical-generating biochemical reaction, a growing pool of relatively long-lived spin adducts is created as the free radicals react with the spin trap. Detectable EPR spectra are generated by the reaction when the signal strength of the accumulation of adducts reaches the lower limit of sensitivity of the particular spectrometer being utilized.