Permeability of fluorescent probes at phase transitions from bilayer-coated capsule membranes

Abstract

Ultrathin nylon capsule membranes coated with synthetic bilayers, the hydrophilic head groups of which carried cationic, anionic, and zwitterionic charges, were prepared. The bilayer-coated capsule membranes were used to measure the permeability of 13 water-soluble fluorescent probes, having cationic, anionic, zwitterionic, and non-ionic hydrophilic groups, across the membrane. A bilayer supported on a capsule membrane is more suitable for kinetic studies of permeation and trapping experiments than is a liposomal membrane. The permeability of fluorescent probes was drastically changed near a phase-transition temperature (T_c) of a coating bilayer, depending on the charges on the hydrophilic groups of both bilayers and permeant probes. From both activation energy data and shapes of Arrhenius plots, the permeation process of large probe molecules below and above the T_c is discussed, in comparison with that of a small electrolyte such as NaCl.