SUBSOLUBILIZING ALTERATIONS CAUSED BY ALKYL GLUCOSIDES IN PHOSPHATIDYLCHOLINE LIPOSOMES

The subsolubilizing alterations caused by a series of alkyl glucosides (alkyl chain lengths ranging from C-8 to C-12) in unilamellar phospha tidylcholine (PC) liposomes were investigated. The surfactant to phosp holipid molar ratios (R-e) and the normalized bilayer/aqueous phase pa rtition coefficients (K) were determined by monitoring the increase in the fluorescence intensity of liposome suspensions due to the 5(6)-ca rboxyfluorescein (CF) released from the interior of vesicles to the bu lk aqueous phase. Given that the free surfactant concentrations was al ways lower than the critical micelle concentration (CMC) of the surfac tant tested we may assume that the surfactant-liposome interactions we re mainly ruled by the action of surfactant monomers. In general terms , the decrease in the surfactant alkyl chain length (or the rise in th e surfactant CMC) resulted in an increase in the ability of these surf actants to alter the permeability of liposomes and, inversely, in an a brupt decrease in their affinity with these bilayers structures. The o verall balance of these opposite tendencies shows that at the two inte raction levels studied (50 and 100% of CF release) the nonyl and the o ctyl glucoside showed, respectively, the highest ability to alter the release of the CF trapped in bilayers (lowest R-e values), whereas the dodecyl glucoside showed the highest degree of partitioning into lipo somes or affinity with these bilayer structures (highest K values). (C ) 1998 Elsevier Science B.V.