Journal Article Localized hydroxyl radical generation at mmol/l and mol/l levels in water by photon irradiation

Ogawa, Yukihiro  ,  Emiko, Sekine-Suzuki  ,  Ueno, Megumi  ,  Nakanishi, Ikuo  ,  Ken-ichiro, Matsumoto

The generation of localized hydroxyl radical (•OH) in aqueous samples by low linear energy transfer (LET) irradiation was investigated. Several concentrations of 5,5-dimethyl-1-pyrroline-N-oxid (DMPO) solution (from 0.5 to 1680 mmol/l) were prepared and irradiated with an identical dose of X-ray or γ-ray. The density of •OH generation in aqueous solution was evaluated by the electron paramagnetic resonance (EPR) spin-trapping technique using DMPO as an EPR spin-trapping agent. The relationship between the molecular density of DMPO in the samples and the concentration of DMPO-OH generated in the irradiated samples was analyzed. Two different characteristic linear trends were observed in the DMPO-OH/DMPO plots, which suggested •OH generation in two fashions, i.e., mmol/l- and mol/l-level local concentrations. The dose, dose rate, and/or the energy of photon irradiation did not affect the shapes of the DMPO-OH/DMPO plots. Moreover, the addition of 5 mmol/l caffeine could cancel the contribution of mmol/l-level •OH generation, leaving a trace of mol/l-level •OH generation. Thus, the localized mmol/l- and mol/l-level generations of •OH, which were independent of experimental parameters such as dose, dose rate, and/or the energy of photon of low LET radiation, were established.

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