The interactions between ionic surfactants and phosphatidylcholine vesicles: Conductometry

The interaction between ionic surfactants and phosphatidylcholine vesicles, which are prepared without addition of buffer and salt, is investigated by conductivity measurements. On the basis of the vesicle acting as a trap of charge carriers, the bilayer/aqueous phase partition coefficient K and the surfactant/lipid molar ratio Re of nine surfactants are determined. The th ermodynamic consistency is satisfied by the measured parameters. The effect s of the alkyl chain length (C-10-C-16) and ionic head group are then studi ed. The inverse partition coefficient K-1 is linearly related to the critic al micelle concentration. The solubilizing ability Re-b is a consequence of the competition between the surfactant incorporation into the bilayer and the formation of micelles. Consequently, the K parameter rises whereas the Re-b parameter declines as the chain length is increased. The influence due to addition of salt is also discussed. (C) 2001 American Institute of Phys ics.