Sodium ion transport through gramicidin-doped bilayers. Influences of temperature and ionic concentration

The dependence on temperature and Na+ concentration of ionic transport in lipid bilayers doped with the antibiotic gramicidin D (GD) were examined using electrochemical impedance spectroscopy (EIS). The experimental system consists of a lipid bilayler obtained from a mixture of phosphatidylcholine and dimethyldioctadecyl-ammonium chloride (DODAC) and supported on gold surfaces modified with a mercaptocarboxylic acid monolayer. This monolayer renders a negatively charged surface upon which spontaneous fusion of lipid vesicles forms the external bilayer attached by electrostatic interactions. A mathematical expression previously derived for the impedance of these membrane processes was used to characterize the system under different experimental conditions. Fitting results yield parameter estimates that confirm the dependence on cation concentration as predicted by the model. A linear behavior in an Arrhenius plot was observed between conductance and temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.