NMR spin trapping: Detection of free radical reactions with a new fluorinated DMPO analog

Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spin trapping were used for detection of free radical reactions utilizing a new fluorinated analog of DMPO, 4-hydroxy-5,5-dimethyl-2-trifluoromethylpyrroline-1-oxide (FDMPO). The parent FDMPO spin trap exhibits a single F-19-NMR resonance at -66.0 ppm. The signal to noise ratio improved 10.4-fold compared to P-31-NMR sensitivity of the phosphorus-containing spin trap, DEPMPO. The spin adducts of FDMPO with (OH)-O-., (CH3)-C-., and (CH2OH)-C-. were characterized. Competitive spin trapping of FDMPO with DMPO showed that both have similar rates of addition of (OH)-O-. and C-centered radicals. The corresponding paramagnetic spin adducts of FDMPO were extremely stable to degradation. In the presence of ascorbate, reaction products from C-centered radicals resulted in the appearance of two additional F-19-NMR signals at -78.6 and -80 ppm for FDMPO/(CH3)-C-. and at -74.6 and -76.75 ppm for FDMPO/(CH2OH)-C-.. In each case, these peaks were assigned to the two stereoisomers of their respective, reduced hydroxylamines. The identification of the hydroxylamines for FDMPO/(CH3)-C-. was confirmed by EPR and F-19-NMR spectra of independently synthesized samples. In summary, spin adducts of FDMPO were highly stable for ESR. For NMR spin trapping, FDMPO showed improved signal to noise and similar spin trapping efficiency compared to DEPMPO. (C) 2001 Elsevier Science Inc.