Membrane-surfactant Interactions in Lipid Micelles Labeled with l-Anilino-8-naphthalenesulfonate

Sonicated lipid micelles, formed from phospholipids isolated from yolks of fresh hen eggs, were used as a model membrane system for studying the effects of several surfactants on membrane properties. The interactions of the surfactants with the model system were followed through the fluorescence of the hydrophobic probe l-anilino-8-naphthalenesulfonate. The surfactants investigated were polyoxyethylene sorbitan monolaurate (Tween 20), polyoxyethylene thioether (Sterox SK), mono-calcium salt of polymerized aryl alkyl sulfonic acids (Daxad 21), and alkylbenzyl quaternary ammonium halide (AHCO DD 50). All surfactants enhanced fluorescence of the membrane-bound probe, and the degree of this enhancement correlated with the previously established phytotoxicity of these substances. The results indicate that surfactants can produce distinct changes in artificial phospholipid membranes and suggest that this lipid interaction may account for altered membrane permeability characteristics in surfactant-treated plants. The effects are observable for surfactant concentrations as low as 0.0001% (w/v), representing an approximate 10-fold increase in sensitivity for detecting surfactant effects compared with previous results on permeability changes in isolated plant cells.