Interaction between Liposomes as a Model of Biomembrane and Nonionic Surfactants

Abstract

The degree of lytic action due to interactions between nonionic surfactants and liposomes was determined in terms of affinity for lipid membranes. The solubilization potential of some surfactants toward liposome membranes was estimated based on physicochemical measurements such as fluorometry to detect the release of fluorescent markers (calcein) from liposomes, turbidimetry in suspensions and surface tensiometry. The lytic action of the alkyl poly (oxyethylene) ether (POE) toward lipid membranes was greatest when the alkyl and ethylene oxide chain lengths were 12 and 8, respectively. The lytic action of nonionic surfactants with various hydrophobic portions (hydrogenated caster oil POE ethers, cholesteryl POE ethers, nonylphenyl POE ethers and POE stearate) was found to depend on structure. Maximum activity in each homologous series was 1.2 I.O.B. (Inorganic Organic Balance).
The critical micelle concentrations (cmc) of dodecyl POE (5) and POE (10) ether in the absence and presence of liposomes were determined using a surface tension meter. Addition of liposomes caused cmc of the surfactants to increase. Dodecyl POE (5) ether causes marker release at lower concentration than cmc without change in turbidity. Dodecyl POE (5) ether concentration increase further, marker release from liposomes greatly increase minor change in turbidity. For dodecyl POE (10) ether, marker release started from cmc with decrease in turbidity. The lytic action of nonionic surfactants on liposomes would thus appear related to their capacity formixed micelle formation with phospholipids.