Nitric oxide (NO), a simple diatomic free radical, is known to play a critical physiological role in diverse organisms. An iron complex, with N-(dithiocarboxy)sarcosine (Fe-DTCS), has a high affinity for endogenous NO and can trap, stabilize, and accumulate it. The stable NO adduct thus formed is detectable at room temperature with electron paramagnetic resonance (EPR) spectrometry. We report in vivo EPR imaging of endogenous NO, trapped by an Fe-DTCS complex, in the abdomen of a live mouse. To our knowledge, this is the first report on EPR imaging of endogenous free radicals produced in vivo. This EPR imaging method will be useful for the noninvasive investigation of the spatial distribution of NO in pathologic organs or tissues.

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The ESR spin-trapping technique using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and N-t-butylbenzylideneamine N-oxide (PBN) as spin-trap reagents has been applied to detect active oxygen radicals generated by the photoexcitation of powdery semiconductors (TiO2, WO3, CdS, and Fe2O3) in non-aqueous solvents such as dimethylsulfoxide (DMSO), benzene, ethanol, and acetonitrile. Appreciable amounts of superoxide ion (O2−) were detected from TiO2, WO3, Fe2O3, and CdS suspensions under photoexcitation. The hyperfine splitting constants (hfsc) of the superoxide ion and carbon(C)-centered radical spin adducts for DMPO and PBN could be determined in various non-aqueous solvents. Some characteristic features for the production of the superoxide ion and C-centered radicals are discussed in connection with the energy-level diagrams of the semiconductors and the redox potentials of the superoxide ion and non-aqueous solvents.

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