SOLUBILIZING INTERACTIONS OF OCTYLPHENOL SURFACTANTS WITH LIPOSOMES MODELING THE STRATUM-CORNEUM LIPID-COMPOSITION

The interaction of a series of polyethoxylated octylphenols (ethylene oxide units average 8.5-20.0) with liposomes modeling the stratum corn eum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmit ic acid and 10% of cholesteryl sulfate) was investigated. The surfacta nt/lipid molar ratios (Re) and the bilayer/aqueous-phase partition coe fficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that fr ee concentration for each surfactant tested was always similar to its critical micelle concentration (CMC) indicates that the liposome solub ilization was mainly ruled by the formation of mixed micelles. The Re and K parameters for liposome saturation fell as the surfactant HLB in creased. Thus, at this interaction step the higher the surfactant HLB, the higher the ability of these surfactants to saturate SC liposomes and the lower their degree of partitioning into liposomes. However, th e maximum solubilizing ability was achieved at intermediate HLB values . Thus, the octylphenols with 20 and 12.5 ethylene oxide units showed, respectively, the highest power of saturation and solubilization of S C structures in terms of the total surfactant amounts needed to produc e these effects. Different trends in the interaction of these surfacta nts with SC liposomes were observed when comparing the Re and K parame ters with those reported for PC ones. Thus, whereas the SC liposomes w ere more resistant to the surfactant action, the affinity of these sur factants with these bilayer structures was higher in all cases.