Abstract
The interaction of sodium cholate surfactant with phosphatidylcholine unilamellar liposomes was investigated. Alterations in bilayer permeability were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles to the bulk aqueous medium and bilayer solubilization as a decrease in the static light-scattered by liposome suspensions. The value corresponding to the effective surfactant to phospholipid molar ratio parameter ( Re) for each interaction step investigated progressively increased as the surfactant concentration rose, this rise being more pronounced during bilayer solubilization. At the subsolubilizing level, a maximum bilayer/water surfactant partitioning ( K) was reached at 30% of CF release, correlated with the saturation of the outer vesicle leaflet, followed by an abrupt decrease in K up to the complete saturation of these bilayer structures ( Re SAT). At the solubilizing level, the K parameter also drastically increased up to the complete bilayer solubilization ( Re SOL). The fact that the free surfactant concentration at subsolubilizing and solubilizing levels showed values respectively lower than and similar to its critical micelle concentration (CMC) indicates that permeability alterations and bilayer solubilization were determined respectively by the action of surfactant monomer and by the formation of mixed micelles.
Published Version
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