Photosensitized electron transport across lipid vesicle walls: quantum yield dependence on sensitizer concentration.

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Abstract
An amphiphilic tris(2,2''-bipyridine)ruthenium(2+) derivative [[N,N''-di(1-hexadecyl)-2,2''-bipyridine-4,4''-dicarboxamide]-bis(2,2''-bipyridine)ruthenium] that is incorporated into the walls of phosphatidylcholine vesicles photosensitizes the irreversible oxidation of EDTA(3-) dissolved in the inner aqueous compartments of the vesicle suspension and the 1-electron reduction of heptylviologen(2+) dissolved in the continuous aqueous phase. The quantum yield of viologen radical production depends on the phospholipid-to-ruthenium complex mole ratio. A kinetic model is used to derive an order-of-magnitude estimate for the rate constant of electron transport across the vesicle walls. The results are inconsistent with a diffusional mechanism for electron transport and are interpreted in terms of electron exchange.