Limburg B, Hilbers M, Brouwer A M, Bouwman E, Bonnet S
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University , P.O. Box 9502, 2300 RA Leiden, The Netherlands.
Van 't Hoff Institute for Molecular Sciences, University of Amsterdam , P.O. Box 94157, 1090 GD, Amsterdam, The Netherlands.
J Phys Chem B. 2016 Dec 22;120(50):12850-12862. doi: 10.1021/acs.jpcb.6b09635. Epub 2016 Dec 12.
Recently, the addition of negatively charged liposomes was shown to increase the quantum yield of the photocatalytic reduction of 5,5'-dithio(2-nitrobenzoic acid) (HDTNB) to 2-nitro-5-thiobenzoic acid (HNTB) by triethanolamine using meso-tetra(4-(N-methylpyridinium)porphyrinato zinc chloride as photosensitizer. In this work, we investigate in detail the kinetics of this photocatalytic reaction both in homogeneous solution and at the surface of negatively charged liposomes, to unravel the effects of liposomes on the mechanism of the photoreaction. In homogeneous solution, the reaction is initiated by oxidative quenching. Both static (singlet) and dynamic (triplet) quenching of the photosensitizer contribute to the formation of the photoproduct. In these conditions, the reaction is limited by the low efficiency of reductive regeneration of the photosensitizer, compared to charge recombination. Upon adsorption of the positively charged photosensitizer to the negative surface of the liposomes, however, both static and dynamic oxidative quenching become ineffective due to electrostatic repulsion of the dianionic DTNB from the negatively charged membrane. In such conditions, photoreduction occurs via reductive quenching, showing that the addition of liposomes can truly modify the mechanism of photocatalyzed redox reactions.
最近研究表明，使用氯化锌四（4 - （N - 甲基吡啶）卟啉锌作为光敏剂，添加带负电荷的脂质体可提高三乙醇胺将5,5'-二硫代（2 - 硝基苯甲酸）（HDTNB）光催化还原为2 - 硝基 - 5 - 硫代苯甲酸（HNTB）的量子产率。在本研究中，我们详细研究了该光催化反应在均相溶液和带负电荷脂质体表面的动力学，以阐明脂质体对光反应机理的影响。在均相溶液中，反应通过氧化猝灭引发。光敏剂的静态（单线态）和动态（三线态）猝灭均有助于光产物的形成。在这些条件下，与电荷复合相比，反应受光敏剂还原再生效率低的限制。然而，当带正电荷的光敏剂吸附到脂质体的负表面时，由于二阴离子DTNB与带负电荷膜之间的静电排斥，静态和动态氧化猝灭均无效。在这种条件下，光还原通过还原猝灭发生，这表明脂质体的添加可真正改变光催化氧化还原反应的机理。
