Introduction:

EPR & "Spin Trapping"
Electron Paramagnetic Resonance (EPR) spectroscopy is the only known method to "visualize" free radicals. However, direct detection of some free radicals (e.g., superoxide and hydroxyl radical) is very difficult or impossible in solution at room temperature. Spin trapping is a technique developed in the late 1960s where a nitrone or nitroso compound reacts with a target free radical to form a stable and distiguishable free radical to be detected by EPR spectroscopy. Spin trapping is the only known method that can detect free radicals such as superoxide and hydroxyl radical specifically in biological systems.

Advantages of BMPO compared to DMPO, DEPMPO and EMPO:
BMPO is a relatively newly discovered nitrone spin trap by Prof. Kalyanaraman's lab at Medical College of Wisconsin. It is most suitable for the specific in-vivo or in-vitro detection of short-lived superoxide, hydroxyl radical and thiyl radical, by forming distinguishable adducts measurable with EPR spectroscopy. Other nitrone spin traps such as DMPO do not distinguish superoxide and hydroxyl radical easily because of spontaneous decay of the DMPO-superoxide adduct (t1/2 = 45 seconds) into the DMPO-hydroxyl adduct. Similar to the recently developed spin traps DEPMPO and EMPO, BMPO-superoxide adduct does not decay into an hydroxyl adduct. The BMPO superoxide spin adduct also has a much longer half-life (t1/2 > = 23 minutes). Additionally, the solid cyclic nitrone BMPO, highly purified by crystallization, can be handled and stored for extended periods of time without fear of decomposition. In comparison, DEPMPO and EMPO are liquid spin traps that are often contaminated with nitroxide impurities and have limited shelf life.

Example Spectra for common Radical Species