Production of hydroxyl-free radical by reaction of hydrogen peroxide with N-methyl-N'-nitro-N-nitrosoguanidine.

Production of a hydroxyl free radical (.OH) by reaction of hydrogen peroxide (H2O2) with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was examined by electron spin resonance using the X OH spin trapping agent 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). The electron spin resonance spectra of the H2O2-MNNG-DMPO system after exposure to light at an intensity of 0.03 mW/cm2 for 5 min, and the DMPO- (.OH) spin adduct (2-hydroxy-5,5-dimethyl-1-pyrroline-1-oxide) generated by use of Fenton's reagent showed the same hyperfine structure and g-value. The signal of the DMPO adduct obtained in the H2O2-MNNG-DMPO system disappeared on addition of the .OH scavenger sodium benzoate. The addition of another .OH scavenger, ethanol, resulted in the appearance of a new signal due to trapping of the alpha-hydroxyethyl radical. These results show that .OH was formed in the H2O2-MNNG-DMPO system. The typical signal of the DMPO-(.OH) spin adduct was not observed in the system in the absence of light. The amount of DMPO-(.OH) spin adduct increased with increase in the concentration of H2O2 when the MNNG level was kept constant, and it changed with the concentration of MNNG at a constant H2O2 level, indicating that .OH was produced by the interaction of MNNG with H2O2. In the absence of H2O2, complicated trapped signals appeared in the spectrum of the MNNG-DMPO system in the light, but these signals were not observed when the system was kept in the dark. In the absence of MNNG, the H2O2-DMPO system did not show any signal, even in the light. These results indicate that interaction of free radicals derived from MNNG with H2O2 on exposure to light resulted in .OH production.