화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.115, No.29, 8242-8247, 2011
Comparison of the Photochemical Behaviors of alpha-Tocopherol and its Acetate in Organic and Aqueous Mice liar Solutions
Photoionization is known to take place when alpha-tocopherol (TOH) is excited to the S-1 state in a polar medium. It has been previously suggested that TO center dot is formed only as a result of proton release by TOH center dot+, a process that is expected to occur, in a protic solvent, on the subnanosecond time scale. Recent redeterminations of the molar absorption coefficients of e(aq)(-) (Hare et al. J. Phys. Chem. A 2010, 114, 1766) and of TOH center dot and TO center dot (Naqvi et al. J. Phys. Chem. A 2010, 114, 10795) have paved the way for testing the above suggestion, even if subnanosecond time resolution is not available, since it implies the equality of [e(aq)(-)](0) and [TO center dot](0), where [center dot center dot center dot](0) denotes the concentration of the enclosed species immediately after a nanosecond laser pulse. Nanosecond pump-probe spectroscopy of TOH in aqueous micellar solution (AMS) and two organic solvents with similar polarities (acetonitrile and methanol) has revealed that prompt formation of TO center dot through dissociation (TOH + hv -> TO center dot + H-center dot) is not negligible even in AMS. In acetonitrile, TOH center dot and TO center dot are formed with comparable yields, and the former converts quantitatively into TO center dot within 15 mu s. In methanol, TO center dot was observed, but no evidence was found for electron ejection from TOH. Only one photoproduct, namely TO center dot, could be detected when a-tocopherol acetate (TOAc) was excited to the S-1 state in several polar and nonpolar solvents; TOAc has been found to be a more efficient energy degrader than TOH.