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Trichloroethylene radicals generated by ionizing radiation. An EPR/spin trapping study
A J Carmichael1, L Steel-Goodwin
1Applied Cellular Radiobiology Department, Armed Forces Radiobiology Research Institute, Bethesda, Maryland 20889-5603, USA.
Human & Experimental Toxicology
|June 1, 1997
Summary
Ionizing radiation of trichloroethylene (TCE) with linear accelerator or gamma rays generates different carbon-centered radicals. These radicals, identified using spin trapping with N-tert-butyl-alpha-phenyl nitrone (PBN), may explain TCE toxicity in liver slices.
Area of Science:
- Free Radical Chemistry
- Radiation Chemistry
- Toxicology
- Electron Paramagnetic Resonance (EPR) Spectroscopy
Background:
- Trichloroethylene (TCE) is an industrial solvent with known toxicity.
- The exact mechanism of TCE-induced cellular damage, particularly the role of free radicals, remains incompletely understood.
- Spin trapping with N-tert-butyl-alpha-phenyl nitrone (PBN) and EPR spectroscopy are valuable tools for detecting transient radical species.
Purpose of the Study:
- To elucidate the origin of spin-trapped radicals generated from TCE exposure to ionizing radiation.
- To compare radical formation under different radiation conditions (linear accelerator vs. gamma rays).
- To determine if radiation-induced TCE radicals are relevant to those observed in TCE-exposed liver tissue.
Main Methods:
- Exposure of TCE, in the presence of PBN, to ionizing radiation from a linear accelerator (18 MeV electrons) and Cobalt-60 gamma rays.
- Analysis of PBN adducts using Electron Paramagnetic Resonance (EPR) spectroscopy to determine hyperfine coupling constants.
- Use of 13C-labeled TCE to confirm the site of radical formation.
Main Results:
- Linear accelerator radiation of TCE produced three PBN adducts, two indicating carbon-centered radicals and one a PBN decomposition product.
- A predominant, stable carbon-centered radical adduct (aN = 1.61 mT, aH beta = 0.325 mT) was observed, matching adducts from TCE-exposed liver slices.
- Gamma radiation of TCE yielded PBN adducts with different nitrogen hyperfine coupling constants, suggesting radical formation at a different TCE carbon, likely via dechlorination at the CCl2 site.
Conclusions:
- Different ionizing radiation sources produce distinct carbon-centered radicals from TCE.
- The predominant radical observed during linear accelerator irradiation of TCE may be the initial radical species formed during TCE exposure in liver slices.
- Radical formation mechanisms differ, with gamma radiation favoring dechlorination at the CCl2 carbon and linear accelerator radiation potentially involving dechlorination at the CHClCl carbon.
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