Interactions between a Synthetic Phospholipid Vesicle and Cationic Surfactants

Abstract

Abstract The interaction between a synthetic phospholipid derivative, the 1,3-ditetradecyl-rac-glycerophosphatidylcholine (2C14–Gly–PC) vesicle, and two cationic surfactants, N-tetradecylpyridinium bromide (TDPBr) and N-tetradecyltrimethylammonium bromide (TDTMABr), were investigated in the hope of obtaining a better understanding of the mechanism of the growth of the vesicle size by the “surfactant-removal” method. The binding isotherms of these surfactants to the lipid vesicle obtained by the surfactant selective electrode were characterized by two-step binding processes; the Langmuir adsorption mechanism in the initial binding, followed by a markedly positive cooperative process. The variation in the hydrodynamic radius, as measured by quasi-elastic light scattering, and the quenching kinetics of pyrene fluorescence with the TDPBr surfactant solution as measured by a stopped-flow method, share a tendency with the binding behavior. The van’t Hoff plots of the initial binding data give a slightly negative enthalpy change, ΔH°, for TDPBr and a relatively large positive ΔH° for TDTMABr. The microenvironmental polarity around pyrene in the molecular assemblies was assessed by means of fluorescence spectroscopy.