Analysis of redox states of protic and aprotic solutions irradiated by low linear energy transfer carbon-ion beams using a 2,2-diphenyl-1-picrylhydrazyl radical.

The quantitative evaluation of changes in the redox state induced by low linear energy transfer (LET) radiations such as the plateau region of heavy-ion beams via formation of reactive oxygen species is of considerable importance to eliminate the adverse effects of radiation therapy on normal tissues adjacent to a tumour. In this study, a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) was used as a redox probe to estimate the redox states of protic and aprotic solutions irradiated by low LET carbon-ion (C-ion) beams. The dose dependence of the decrease in the absorption band due to DPPH˙ (which was solubilised by β-cyclodextrin (β-CD) in water) after irradiation with low LET C-ion beams (13 keV μm-1 ) was similar to that after X-irradiation. Similar results were obtained when H2 O was replaced with methanol or acetonitrile although the slope values of the plots of the absorbance changes vs. radiation doses were twice larger as compared to the case in β-CD-containing H2 O. Moreover, DPPH˙ was more susceptible to the C-ion beam than to X-rays in isopropyl myristate (IPM), which is one of the saturated fatty acid esters.