Energy Interactions and Phospholipid Vesicles

摘要

Luminescence quenching studies of unilamellar phosphatidylcholine vesicles containing a surfactant sensitizer derived from tris(2,2'-bipyridine)ruthenium(II) have shown that only a fraction of these sensitizers is quenchable when ferricyanide is added to the continuous aqueous phase, and that this fraction is made up exclusively of the sensitizers located in the outer monolayer. The size of this fraction is independent of the sensitizer concentration. In contrast to this, the quenching rate constant increases with sensitizer concentration. From these observations, one can conclude that energy transfer occurs among sensitizers located on the same surface of a vesicle, but energy transfer between these sensitizers is not long range enough to reach efficiently across the membrane from inside to outside (and vice versa). The existence of this energy transfer in the first case has important implications on the kinetic scheme for photosensitized electron transport reactions through vesicle walls. The size of the vesicles studied was determined to be approx. 500 angstroms in diameter by exp 14 C-sucrose entrapment. This experimental finding in addition to the fixed fraction of quenchable fluorescence of 0.67 +- 0.02 implies that the surfactant ruthenium molecules extend a considerable distance out of the vesicle into the aqueous phase, and/or they are asymmetrically distributed between inner and outer vesicle surfaces. (ERA citation 07:057699)