Interactions of Nonionic Polyoxyethylene Alkyl and Aryl Ethers with Membranes and Other Biological Systems

Many nonionic surfactants of the poly(oxyethylene) alkyl and aryl ether class interact with biological membranes increasing their permeability and causing increased trans-membrane solute transport. The mechanisms of such effects are not fully understood. Studies of the interaction of homologous series of nonionic surfactants (varying either in hydrophobic or hydrophilic chain length) with a variety of biological substrates, reviewed here, indicate there to be an optimal lipophilicity for maximal membrane activity. Problems with the hydrophile-lipophile balance (HLB) as an index of lipophilicity result from the structural non-specificity of this value. The biological effects of surfactants are concentration dependent and structure dependent. In many cases C 12 hydrocarbon chain compounds appear to exert maximal effects and in all series a parabolic relationship between membrane activity and lipophilicity is observed. The effects are complex resulting from penetration of the membrane, its fluidization and, at high surfactant concentrations, solubilization of structural components.