Investigation of Hydrated Electron Quenching by Quinone Compounds under Micellar Reaction Environment

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We have studied the hydrated electron (e_<aq>^-) quenching by idebenone (IDB) and the related compound (CoQ_0) in SDS and SOS micellar solutions with 1-propanol (1-PrOH) addition. UV irradiation of IDB with the long side chain in 1-PrOH produced the neutral radical, whereas in the presence of an electron donor (DABCO) the anion radical was formed. On the other hand, UV irradiation of CoQ_0 without the side chain produced the anion radical both in the presence and in the absence of DABCO.In micellar solutions, both compounds produced anion radicals but the EPR (electron paramagnetic resonance) intensity of the IDB radical was very weak even in the presence of DABCO.When 1-PrOH was added to the micellar solution, the signal intensity of the IDB radical increased approximately seven-fold. The effective e_<aq>^- quenching by IDB to form the radical results in decrease of micellar charge density. Therefore, the results obtained suggest that the benzoquinone nucleus of IDB can locate in the … More polar region of the micelle. Furthermore, it was found that IDB quenched e_<aq>^- by the pseudo-first-order kinetic with the rate of 2.1x10^6 sec^<-1> in the micelllar system.Next, the intermediate radicals generated by continuous UV and pulsed UV laser irradiation of antioxidant sesamol in aqueous solutions were investigated. Radical species with the intensity ratio of 1 : 4 : 6 : 4 : 1 was observed using continuous wave Electron Paramagnetic Resonance (CW EPR) with continuous UV irradiation. In order to observe the intermediate radical right after the excitation, Fourier Transform EPR (FT EPR) was used. Trace amount of the same radical was also detected by FT EPR with pulsed UV laser. Based on the hyperfine coupling constant (2.3 G) and g-value (2.0048) together with FT EPR results, this radical was found to be a benzoquinone anion radical. The radical might be produced via multi-step reactions of the excited sesamol in aqueous solution and was stable for at least several minutes. FT EPR showed the detailed behavior of the radicals. Characterization of the intermediate is important to evaluate the antioxidant sesamol. Less