SOLUBILIZATION OF PHOSPHATIDYLCHOLINE LIPOSOMES BY THE AMPHOTERIC SURFACTANT DODECYL BETAINE

The interaction of the amphoteric surfactant N-dodecyl-N,N-dimethylbet aine (C-12-Bet) with phosphatidylcholine (PC) liposomes was investigat ed. Permeability alterations were detected as a change in 5(6)-carboxy fluorescein (CF) released from the interior of vesicles and bilayer so lubilization as a decrease in the static light-scattering (SLS) of the system. At sublytic level a initial maximum in the bilayer/water part itioning (K) followed by an abrupt decrease of this parameter occurred as the surfactant to lipid molar ratio (Re) rose. At lytic level a di rect dependence was established between both parameters. The fact that the free surfactant concentration at sublytic and lytic levels showed values lower than and similar to its critical micelle concentration i ndicates that permeability alterations and solubilization were determi ned, respectively, by the action of surfactant monomer and by the form ation of mixed micelles. A direct correlation occurred in the initial interaction steps (up to 50% CF release) between the growth of vesicle s their fluidity and Re. A similar direct dependence was established d uring solubilization (up to 30% SLS) between the fall in both the surf actant-lipid aggregate size, the SLS of the system and Re. This surfac tant showed higher capacity to solubilize PC liposomes than that repor ted by the commonly used non-ionic surfactants octyl glucoside and Tri ton X-100 and by the anionic one sodium dodecyl sulfate. (C) 1998 Else vier Science Ireland Ltd. All rights reserved.