Estimation of the Local Concentration of the Markedly Dense Hydroxyl Radical Generation Induced by X-rays in Water

The linear-density (number of molecules on an arbitrary distance) of X-ray-induced markedly dense hydroxyl radicals (center dot OH) in water was estimated based on EPR spin-trapping measurement. A lower (0.13 mM-2.3 M) concentration series of DMPO water solutions and higher (1.7-6.0 M) concentration series of DMPO water solutions plus neat DMPO liquid (8.8 M as DMPO) were irradiated with 32 Gy of X-rays. Then, the yield of DMPO-OH in DMPO water solutions and the total spin-adduct of DMPO in neat DMPO were quantified. For the higher concentration DMPO series, the EPR peak area was estimated by double integration, and the baseline correction of the integral spectrum is necessary for accurate estimation of the peak area. The preparation of a suitable standard sample corresponding to the electric permittivity according to DMPO concentration was quite important for quantification of DMPO-OH, especially in DMPO concentration beyond 2 M. The linear-density of center dot OH generation in water by X-ray irradiation was estimated from the inflection point on the plot of the DMPO-OH yield versus DMPO linear-density. The linear-density of X-ray-induced markedly dense center dot OH was estimated as 1168 mu m(-1), which was converted to 0.86 nm as the intermolecular distance and 2.6 M as the local concentration.

Automated summary

The linear density of X-ray-induced dense hydroxyl radicals (center dot OH) in water was estimated using EPR spin-trapping measurement. The yield of DMPO-OH in different concentrations of DMPO water solutions and the total spin-adduct of DMPO in neat DMPO liquid were quantified. The linear density of center dot OH generation in water by X-ray irradiation was estimated based on the inflection point on the plot of DMPO-OH yield versus DMPO linear density.