Uranium reactions with hydrogen peroxide studied by EPR–spin trapping with DMPO †

Abstract

Uranyl nitrate [UO₂(NO₃)₂] (1.0 × 10^–3M) is reacted with hydrogen peroxide (H₂O₂, 5 × 10^–3M) in the presence of the spin trap 5,5-dimethyl-4,5-dihydro-3H-pyrrole N-oxide (DMPO, 5 × 10^–2M) in acidic solutions. The reaction generates a 1∶2∶2∶1 quartet with hyperfine coupling constants, a_N = a_H^β = 1.50 mT. These values are consistent with reported values for the DMPO–OH spin adduct. It is possible that the uranous ion (UO²⁺), which corresponds to U^IV, generates hydroxyl radicals (˙OH) to give the observed DMPO–OH. This is suggested by two observations: (1) the intensity of the EPR spectrum is dependent on pH, reaching a maximum at pH = 0.6, which is consistent with the formation of UO²⁺ from UO₂²⁺ at lower pH values; and (2) the uranyl ion (UO₂²⁺) corresponds to U^VI and cannot be further oxidized. To determine whether ˙OH radicals generate DMPO–OH, the reaction is carried out in the presence of varying concentrations of ethanol (EtOH). The results indicate that at a low ratio of [EtOH]/[DMPO] the EPR signal corresponds to DMPO–OH, while at a [EtOH]/[DMPO] ratio ca. 1 the signal is mixed and equally intense for DMPO–OH and the hydroxyethyl adduct to DMPO (DMPO–EtOH). When the [EtOH]/[DMPO] ratio is ca. 10 the EPR signal is mainly that of the DMPO–EtOH adduct. This confirms that uranium reacts with H₂O₂ generating hydroxyl radicals.

References

1. B. Shleien, The Health and Radiological Health Handbook, Scinta, Silver Spring, MD, 1992, p. 283.
2. (a) G. L. Diamond, Radiant. Prot. Dosim., 1989, 26, 23; (b) G. L. Diamond, P. E. Morrow, B. J. Panner, R. M. Gelein and R. B. Baggs, Fundam. Appl. Toxicol., 1989, 13, 65.
3. Y. D. La Touche, D. L. Willis and O. I. Dawydiak, Health Physics, 1987, 53, 147.
4. P. Morrow, R. Gelein, H. Beiter, J. Scott, J. Picano and C. Yuile, Health Physics, 1982, 43, 859.
5. (a) A. Ortega, J. L. Domingo, M. Gomez and J. Corbella, Pharmacol. Toxicol., 1989, 64, 247; (b) A. Ortega, J. L. Domingo, J. M. Llobet, J. M. Thomas and J. L. Paternain, Bull. Environ. Contam. Toxicol., 1989, 42, 935.
6. M. E. Wrenn, J. Lipszten and L. Betrtelli, Radiat. Prot. Dosim., 1989, 26, 243.
7. C. A. Castro, K. A. Benson, E. G. Daxon, J. B. Hogan, H. M. Jacocks, M. R. Laudauer, S. A. McBride and C. W. Shehata, Armed Forces Radiobiology Research Institute, Technical Report, #96-3, Bethesda, MD, 1996.
8. C. Voegtlin and H. C. Hodge, Pharmacology and Toxicology of Uranium Compounds, 1949, vol. 1, part 1, p. 91.
9. A. J. Carmichael, Free Radical Res. Commun., 1990, 10, 37.
10. B. Brina and A. G. Miller, Anal. Chem., 1992, 64, 1413.
11. J. J. Fitzgerald and N. D. Chasteen, Anal. Biochem., 1974, 60, 170.
12. I. M. Kolthoff, E. B. Sandell, E. J. Meehan and S. Bruckenstein, Quantitative Chemical Analysis, The Macmillan Company, New York, 1969, 4th edn., pp. 828 and 834.
13. B. Kalyanaraman, C. C. Felix and R. C. Sealy, Photochem. Photobiol., 1982, 36, 5.
14. G. A. Russell, E. G. Janzen and E. T. Strom, J. Am. Chem. Soc., 1964, 86, 1807.
15. C. A. Evans, Aldrichimica Acta, 1979, 12, 23.
16. G. R. Buettner, Free Radical Biol. Med., 1987, 3, 259.
17. R. G. Wilkins, Kinetics and Mechanisms of Reactions of Transition Metal Complexes, VCH, New York, 1991, p. 41.
18. H. G. Claycamp and D. Luo, Radiat. Res., 1994, 137, 114.
19. Farhataziz and A. B. Ross, NSRDS-NBS59. U.S. Govt. Printing Office, Washington, DC, 1997.