Abstract
Spin trapping of the hydroxyl (OH) radical formed by γ-irradiation in ice was performed by using 5, 5-dimethyl pyrroline N-oxide (DMPO) as a trapping agent. A frozen aqueous solution of DMPO was γ-irradiated at -70°C for three days, and ESR spectra were then measured at room temperature as a function of time after melting. A strong four-line absorption characteristic of the spin adduct (DMPO-OH) was observed and the intensity decreased with time, while no signal was observed when γ-irradiation was carried out at room temperature. The intensity of DMPO-OH increased linearly with radiation dose, but it was not changed by the standing time at -70°C after γ-irradiation, suggesting that the OH radical formed by γ-irradiation in ice was trapped by DMPO in the frozen state, DMPO-OH being stable for more than three days in contrast to the case at room temperature. The quantity of DMPO-OH was decreased in the presence of sodium L-ascorbate. The analysis of the intensity change shows that this solid-state spin trapping technique is useful to measure separately the OH radical scavenging and DMPO-OH scavenging abilities of antioxidants.
