Oxygen independent generation of hydrogen peroxide in water irradiated by carbon-ion beam

The oxygen independent formation of hydrogen peroxide (H2O2) in an aqueous solution during carbon-ion beam irradiation was demonstrated. The radiation-induced hydroxyl radical (•OH) generation in an aqueous solution was reported to occur in two different localization densities, which were at the milli-molar (relatively sparse) and/or molar (super-dense) levels. In the milli-molar-level •OH generation atmosphere, •OH generated at a molecular distance of 4.3‒6.6 nm are likely unable to interact each other. However, in the molar-level •OH generation atmosphere, several •OH were generated with a molecular distance of 1 nm or less, and two •OH can react to directly make H2O2.An aliquot of ultra-pure water was irradiated by 290 MeV/nucleon carbon-ion beam at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan). Irradiation experiments were performed under air or hypoxic (100 keV/μm). H2O2 generations in irradiated samples were estimated by two methods below. 1) The •OH synthesized from H2O2 by UVB irradiation was spin-trapped with DMPO, and the •OH adduct of DMPO (DMPO-OH) was then measured as an index of H2O2 using an X-band EPR. 2) A red quinoid dye (absorbance at 505 nm) formed by a reaction of 4-aminoantipyrine and phenol and H2O2 under coexisting peroxidase were measured using the spectrophotometer. Amounts of H2O2 generation per dose was estimated. H2O2 generation under air condition, i.e. total H2O2 generation, decreased with LET H2O2 generation under air condition, i.e. total H2O2 generation, decreased with LET increasing. H2O2 generation under hypoxic condition, i.e. oxygen independent H2O2 generation, increased with LET increasing. The oxygen dependent H2O2 generation, i.e. subtraction of H2O2 generation under hypoxic condition from H2O2 generation under air condition, decreased with LET increasing. Those results suggest that the super-dense •OH generation was increased with LET increasing. High LET beam could make H2O2 oxygen independently.27th Annual Conference of the Society for Redox Biology & Medicine (SfRBM 2020