The use of lipid headgroup charge to enhance photoinduced electron transfer in vesicles: reactions of functionalized pyrene with a two component viologen system.

Kinetics of photoinduced electron transfer from a lipid functionalized pyrene, 1-(10-(6(8)-octadecylpyrenyl) decanoyl)-2-hexanoyl-sn-glycero-3-phosphorycholine (OPyPC), to a two component viologen acceptor system have been measured by laser flash photolysis. N,N'-tetramethylene-2,2' -bipyridinium ion (DQ2+) and N,N'-dipropyl-4,4'-bipyridinium sulfonate (PVS), have been utilized as the primary and secondary acceptors. It has been shown that utilization of a lipid with a net negatively charged phosphatidylglycerol headgroup provides a driving force for localizing high concentrations of primary acceptor (DQ2+) in the region of donor. Subsequently, the charged interface can act to maintain long-term separation between the oxidized pyrene donor (OPyPC+) and the reduced secondary acceptor, PVS-. When a dioleoyl lipid is used, reaction of (OPypc+) with the double bond competes significantly with back reaction. However, substitution of diphytylphosphatidylglycerol for the dioleoyl analog results in a cation lifetime of about 0.5 ms and a continued very long-lived reduced species (approximately 4 h). Quantum yields of approximately 0.15 may be obtained in this system.