Photoinduced Charge Separation and Recombination at Membrane Water Interface

2 Photoinduced Charge Separation and Recombination at Membrane // Water Interface 

Tollin and his co-workers [145, 146] have observed a number of interesting peculiarities using water-soluble MV2+, AQDS2- and Fe(CN) as redox quenchers of 3Chl. The inner and the outer surface of the vesicles membrane were 

The kinetics of the recombination of Chl+ and MV+ radical ions formed during the quenching of 3Chl, consists of the fast and slow stages. The corresponding rate constants also occurred different at the inner and outer surfaces of the vesicles. The observed difference in the recombination rates was explained by different structural and dynamic characteristics of the inner and outer monolayers of the membrane. 

Note that asymmetry between the inner and outer interfaces was observed also for large unilamellar vesicles [146]. However, the ratios of the rates of 3Chl quenching and the yields of radical-ion products on the inner and outer membrane surface for large unilamellar vesicles are of the opposite character compared with small unilamellar vesicles. 

As follows from the data from Sect. 2, the primary photochemical stage in the majority of the membrane systems studied is the redox quenching of the excited photosensitizer by an electron acceptor or donor leading to electron transfer across the membrane // water interface. For electron transfer to occur from the membrane-embedded photosensitizer to the water soluble acceptor, it is necessary for the former to be located sufficiently close to the membrane surface, though the direct contact of the photosensitizer with the aqueous phase is not obligatory. For example, Tsuchida et al. [147] have shown that electron transfer to MV2 + from photoexcited Zn-porphyrin inserted into the lecithin membrane, is observed only until the distance from the porphyrin ring to the membrane surface does not exceed about 12 A. 

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