ION PERMEABILITY OF DILAUROYLPHOSPHATIDYLETHANOLAMINE MONOLAYER AT THE POLARIZED NITROBENZENE WATER INTERFACE

The phase behavior and ion permeability of dilauroylphosphatidylethanolamine (DLPE) monolayers formed at the polarized nitrobenzene (NB)/water (W) interface have been studied by measuring ac impedance of the interface under the precise control of the potential drop across the interface. With increasing concentration of DLPE in NB, the monolayer formed by adsorption of DLPE from NB undergoes a phase transition from a gaseous to a liquid-expanded state at an occupied area of a DLPE molecule (A) being 0.83 nm2 and from the liquid-expanded to a liquid-condensed state at A = 0.50 nm2. The permeability of the monolayer with respect to ions depends on packing density of the monolayer, surface charge density, and charge and size of transferring ions. When the condensed DLPE monolayer is introduced to the interface, the decrease in the rate of ion transfer is detectable for tetraethylammonium ion (TEA+) transfer, but not ClO4- ion having a smaller ionic radius. The negatively charged DLPE monolayer appreciably reduces the rate of ion transfer for ClO4- ion and accelerates the transfer of TEA+ ion. The effect is reversed in the case of the positively charged DLPE monolayer. These facts clearly indicate the importance of hydrodynamic friction between the condensed monolayer and transferring ions and also of the electrical double layer effect on the kinetics of ion transfer across the DLPE monolayer.