Mechanistic Studies of Photoinduced Electron Transport across Vesicle Bilayers

内层水池中的抗坏血酸（Asc^-）向外层水溶液中的甲基紫素（MV^<2+>）的内能电子传递是由嵌入在囊泡双层中的芘衍生物的辐照驱动的。MV^<2+>的初始还原速率取决于芘环上的取代基；一个亲水官能团通过短亚甲基链与芘环相连，作为电子传递的增敏剂。机理研究表明，电子传递主要是由Asc^-对芘单线态的还原猝灭引起的，并通过位于囊泡双层内外界面的芘之间的电子交换机制进行。设计并合成了一种新型的不对称取代芘，它具有由短亚甲基链连接的亲水性基团和疏水性长烷基基团，是一种很好的电子在囊泡双层间传递的增敏剂。此外，为了提高电子传递效率，研究了内池中脂类和电子给体的分子结构对MV^<2+>还原速率的影响。新合成的长烷基链桥接二聚芘作为增敏剂，提高了电子传递效率。虽然这些系统不幸不能在可见光下工作，但它似乎是自然光合作用最忠实的模型之一，因为电子在光能的帮助下在两个可逆的氧化还原对之间以能量上坡的方向通过脂质双分子层壁转移，防止电荷重组。

Endoergic electron transport across vesicle bilayers from ascorbate (Asc^-) in the inner waterpool to methylviologen (MV^<2+>) in the outer aqueous solution was driven by the irradiation of pyrene derivatives embedded in the vesicle bilayers. The initial rate of MV^<2+> reduction is dependent on the substituent group on the pyrenyl ring ; a hydrophilic functional group linked with the pyrenyl ring by a short methylene chain acts as a sensitizer for the electron transport. Mechanistic studies suggests that the electron transport is mainly initiated by the reductive quenching of the singlet excited state of pyrene by Asc^- and proceeds by a mechanism involving electron exchange between the pyrenes located at the inner and outer interface across the vesicle bilayer. Novel unsymmetrically substituted pyrenes having both a hydrophilic group linked by a short methylene chain and a hydrophobic long alkyl group was designed and synthesized, which acted as an excellent sensitizers for the electron transport across vesicle bilayers. Moreover, in order to enhance the electron transport efficiency, the effects of molecular structure of lipids and electron donors incorporated in the inner waterpool on the MV^<2+> reduction rate were investigated. The use of newly synthesized dimeric pyrenes bridged by a long alkyl chain as sensitizers resulted in the enhancement of electron transport efficiency. Although these systems unfortunately cannot work using visible light, it appears to be one of the most faithful model of natural photosynthesis in that an electron is transferred with the aid of light energy between two reversible redox couples in the energetically uphill direction through lipid bilayer walls preventing a charge recombination.