@misc{oai:repo.qst.go.jp:00083244,
 author = {Yusuke, Makino and Megumi, Ueno and Yoshimi, Shoji and Ken-ichiro, Matsumoto and Ikuo, Nakanishi and Fukui, Koji and Yusuke, Makino and Megumi, Ueno and Yoshimi, Shoji and Kenichiro, Matsumoto and Ikuo, Nakanishi},
 month = {Aug},
 note = {Local density of hydrogen radicals (•H) generated in water during X-ray irradiation to aqueous reaction mixtures were quantified by an electron paramagnetic resonance (EPR) spin-trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin-trapping agent. During water radiolysis process (Eq. 1‒4), the •H could be generated by reaction of hydrated electron (e-aq) and hydrogen ions (H+), which were generated simultaneously with hydroxyl radical (•OH) from ionized water (H2O+).
X-ray  ~~>  H2O  →  H2O+  +  e-[1]
e-  +  nH2O  →  e-aq[2]
H2O+  →  •OH  +  H+[3]
H+  +  e-aq →  •H[4]
Therefore, similar amount of •OH and •H should be expected, however, the G-values reported for •OH and •H are 0.28 and 0.06, respectively. To clarify what could make this difference of yields of •OH and •H, total amount and local densities of X-ray induced •OH and •H were compared.
A concentration series of DMPO aqueous solutions (0.49 mM〜1700 mM) was prepared. The sample solutions were irradiated with 32 Gy of X-ray. Signal intensities of DMPO-OH and DMPO-H caused in the sample were measured by X-band EPR spectrometer. The decay of DMPO-OH and DMPO-H during irradiation was corrected and the net yield was observed [1]. The profiles observed by plotting concentrations of DMPO-OH and DMPO-H against the DMPO density (reciprocal of the intermolecular distance of DMPO) were analysed.
When X-ray was irradiated to DMPO aqueous solutions under an aerobic condition, the profile of DMPO-OH generation showed 3-phase as reported previously [2], however; the profile of DMPO-H showed 2-phase. Both profiles observed for DMPO-OH and DMPO-H were almost overlapped except the DMPO-H lacked 3rd phase. Irradiation under hypoxic condition also showed similar results. The inflection point made by 1st and 2nd phases indicates relatively sparse (mmol/L-level) generation of the target radical. The yields of sparse generations of both •OH and •H were estimated as 200 mmol/L/Gy. Total yields of •OH and •H, which could be expected from end the plots, were 500 mmol/L/Gy or more for •OH and 200 mmol/L/Gy for •H. •H generation is available only from sparse ionization.
References:
[1] Matsumoto K, Ueno M, Shoji Y, Nakanishi I, Radiat. Biol. Res.Commun. 55, 303‒321 (2020).
[2] Matsumoto K, Ueno M, Nakanishi I, Anzai K, Chem. Pharm. Bull.. 63, 195‒199 (2015)., ISMAR-APNMR-NMRSJ-SEST 2021 (a joint meeting of the 22nd International Society of Magnetic Resonance Conference, the 9th Asia-Pacific NMR Symposium, the 60th Annual Meeting of the Nuclear Magnetic Resonance Society of Japan (2021), and the 60th Annual Meeting of the Society of Electron Spin Science and Technology)},
 title = {Generation of Hydrogen Radical in Water Irradiated by X-ray},
 year = {2021}
}