NMR Spin Trapping: Insight into the Hidden Life of Free Radical Adducts

In our original work (V. Khramtsov, L.J. Berliner and T. L. Clanton, Magn. Reson. Med. 42:228-234, 1999), a P-31 nuclear magnetic resonance spin trapping (ST NMR) approach aimed to overcome comparatively short lifetimes of the paramagnetic adducts by detecting stable diamagnetic adducts of the degradation of phosphorous-containing nitrone was proposed. High stability of the NMR adducts of the nitrone spin traps with C-centered radicals and the ability to track their origin from paramagnetic adducts make ST NMR a valuable tool for the studies of these radicals in chemical and biological systems. Complementary ST NMR and electron paramagnetic resonance studies of the nitrone adducts derived from the addition of O- and S-centered radicals and nucleophiles revealed new insights into the pathways of the paramagnetic and diamagnetic adduct formation and degradation. In particular, use of ST NMR allowed for observation of reversible nucleophilic addition to the nitrones. On one hand, nucleophilic addition may result in a possible spin trapping artifact via the Forrester-Hepburn mechanism; whereas, on the other hand, the reverse reaction provides the key step in the "recycling" mechanism that is important for the antioxidant actions of the nitrones.