Photochemical reactions of antioxidant sesamol in aqueous solution

Abstract

Antioxidant intermediate radicals generated by continuous ultraviolet (UV) and pulsed UV laser irradiation of sesamol in aqueous solutions were investigated. Radical species with the intensity ratio of 1:4:6:4:1 were observed by using continuous wave electron paramagnetic resonance (EPR) with continuous UV irradiation. The radical was also observed after the irradiation. To observe the intermediate radical right after the excitation, Fourier transform EPR (FT EPR) was used. Trace amounts of the same radical were 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 have been produced via multistep reactions of the excited sesamol in aqueous solution, and it was stable for at least several minutes. In addition to the benzoquinone radical, the formation and dynamics of the sesamolyl radical were investigated by using FT EPR. FT EPR showed the detailed behavior of the radical. Characterization of the intermediate is important to evaluate the antioxidant sesamol.