Comparison of the Photochemical Behaviors of 伪-Tocopherol and its Acetate in Organic and Aqueous Micellar Solutions

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• 作者：Ye Zhang ; Y. A. Yousef ; Heng Li ; T. B. Mel酶 ; K. Razi Naqvi
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：July 28, 2011
• 年：2011
• 卷：115
• 期：29
• 页码：8242-8247
• 全文大小：821K
• 年卷期：v.115,no.29(July 28, 2011)
• ISSN：1520-5215

文摘

Photoionization is known to take place when 伪-tocopherol (TOH) is excited to the S₁ state in a polar medium. It has been previously suggested that TO^{鈥?/sup> is formed only as a result of proton release by TOH鈥?, 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鈥?/sup> (Hare J. Phys. Chem. A 2010, 114, 1766) and of TOH鈥? and TO鈥?/sup> (Naqvi 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鈥?/sup>]₀ and [TO鈥?/sup>]₀, where [路路路]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鈥?/sup> through dissociation (TOH + h谓 鈫?TO鈥?/sup> + H鈥?/sup>) is not negligible even in AMS. In acetonitrile, TOH鈥? and TO鈥?/sup> are formed with comparable yields, and the former converts quantitatively into TO鈥?/sup> within 15 渭s. In methanol, TO鈥?/sup> was observed, but no evidence was found for electron ejection from TOH. Only one photoproduct, namely TO鈥?/sup>, could be detected when 伪-tocopherol acetate (TOAc) was excited to the S₁ state in several polar and nonpolar solvents; TOAc has been found to be a more efficient energy degrader than TOH.}