Radiation induced generation of localized highly concentrated hydrogen peroxide in water

It has been reported that an electron paramagnetic resonance (EPR) signal of a nitroxyl radical redox probe in water could be decreased independently with a hydrogen-donor, such as GSH or NAD(P)H, when a relatively high dose X-ray or Carbon beam was irradiated to the sample solution. Since this hydrogen-donor-independent reduction of nitroxyl radial was partly suppressed by catalase, the generation of hydrogen peroxide (H2O2) is related to this reaction. However, the detailed mechanism of this hydrogen-donor-independent reduction of a nitroxyl radical was in progress.Reaction mixtures containing 0.1 mM of a nitroxyl redox probe, TEMPOL or Carbamoyl-PROXYL, were prepared using water solvents containing several different concentrations (1.0 mM‒9.8 M) of H2O2. The reaction mixture was irradiated by 12000 μW/cm2 UVB for 2 min, and the reduction of the EPR signal of the nitorxyl radical was measured. An aliquot (2 µL) of 200 mM K3[Fe(CN)6] solution was added to 200 µL of the reaction mixture, and the time course of the EPR signal of the nitorxyl radical was measured.The UV induced EPR signal loss of the nitorxyl radical was increased with H2O2 higher than 10 mM. The EPR signal of nitorxyl radicals were decreased in the solution containing quite high concentration (M level) of H2O2, when K3[Fe(CN)6] was added to the reaction mixture. Oxidative stimulation by UVB irradiation or addition of K3[Fe(CN)6] could cause nitorxyl radical reduction in a high concentration H2O2 environment. This result suggests that ionizing radiations could prepare a high concentration H2O2 environment, which may be localized.日本放射線影響学会第62回大