Effects of gemini surfactants on egg phosphatidylcholine bilayers in the fluid lamellar phase

Abstract

The influence of 1,4-butanediamonium- N, N′-dialkyl- N, N, N′, N′-tetramethyl dibromides (CmA, m=7–16 is the number of alkyl carbons) on the egg yolk phosphatidylcholine (EYPC) bilayer thickness and lipid surface area at the bilayer–aqueous phase interface is studied using X-ray diffraction on fluid lamellar CmA+EYPC+H 2O phases as a function of CmA:EYPC and H 2O:EYPC molar ratios and the alkyl chain length m. At the constant CmA:EYPC=0.4 and H 2O:EYPC=18 molar ratios, the CmA induced bilayer thickness decrease shows a minimum and the lipid surface area increase a maximum at the alkyl chain length m=9. The obtained results are discussed in the context of a structural perturbation model of the cut-off effect in biological potencies of surfactants which occurs when increasing the alkyl substituent chain length above the critical value.