Photoinduced transmembrane electron transport in DPPC vesicles: Mechanism and application to a hydrogen generation system

Pyrene-sensitized transmembrane electron transport from ascorbate (Asc−) in the inner waterpool to methylviologen (MV2+) in the outer aqueous solution proceeded in gel-phase DPPC vesicles, in which the lateral diffusion of molecules embedded in the vesicle bilayers is totally restricted. Based on the effects of the sensitizer concentration and cholesterol added to DPPC membranes on the efficiency of the electron transport, we propose that the sensitizer clusters play an essential role in the electron transport in DPPC vesicles. The presence of the sensitizer clusters in DPPC vesicles is supported by the temperature dependence of the intensity ratio of the excimer to the monomer fluorescence of the sensitizer. We found that this photoinduced transmembrane electron transport system works using various electron donors that undergo a reversible redox cycle other than Asc−, and that there is a tendency for electron donors having lower oxidation potential to give a larger rate of MV+ formation. Moreover, we accomplished the connection of the system of the photoinduced transmembrane electron transport in DPPC vesicles with the system for hydrogen generation from water using colloidal platinum as a catalyst.