Pj. Clapp et al., EFFICIENT PHOTOINDUCED ORTHOGONAL ENERGY AND ELECTRON-TRANSFER REACTIONS VIA PHOSPHOLIPID MEMBRANE-BOUND DONORS AND ACCEPTERS, Journal of the American Chemical Society, 116(20), 1994, pp. 9166-9173
A three component, liposome-bound photochemical molecular device (PMD)
consisting of energy and electron transfer reactions is described. Bi
layer membrane surface-associated dyes, akis[4-(trimethylammonio)-phen
yl]-21H,23H-porphine tetra-p-tosylate salt and bis[(3-trimethylammonio
)propyl]thiadicarbocyanine, tribromide, are the energy donor and accep
tor, respectively, in a blue light stimulated energy transfer reaction
along the vesicle surface. The electronically excited cyanine is quen
ched by electron transfer from the phospholipid membrane bound triphen
ylbenzyl berate anion, which is located in the lipid bilayer interior.
The PMD exhibits sequential reactions following electronic excitation
with the novel feature that the steps proceed with orthogonal orienta
tion: energy transfer occurs parallel to the membrane surface, and ele
ctron transfer occurs perpendicular to the surface. Photobleaching and
fluorescence quenching experiments verify the transfer reactions, and
Stern-Volmer analysis was used to estimate the reaction rate constant
s. At the highest concentrations examined of energy and electron accep
tor ca. 60% of the photoexcited porphyrins were quenched by energy tra
nsfer to the cyanine. The use of liposomes of well defined composition
and dimensions in conjunction with molecular components that associat
e with the bilayer in a predictable manner permit the accurate estimat
ion of molecular binding volumes and local concentrations for the anal
ysis.