AN INVESTIGATION BY EIS OF GRAMICIDIN CHANNELS IN BILAYER-LIPID MEMBRANES

The influence of Li+, Na+, K+, and Cs+ ions on the characteristics and properties of Black Lipid Membranes (BLM) made of diphytanoylphosphatydilcholine (DPhPC), with thickness thinner than 10 nm, were investigated using electrochemical impedance spectroscopy (EIS). The impedance spectra of the base system including the film and its adjacent chloride ion containing aqueous solutions exhibited for all tested cations a single capacitive contribution. The corresponding time constant can be discussed in terms of a model which includes a dielectric dispersion in the membrane. BLM films doped with a low concentration of Gramicidin A have exhibited values of conductance in contact with electrolytes containing different cations at low aqueous concentration of Gramicidin A, that indicate ionic transference from one side to the other of the membrane. This phenomenon was detected by using either dc or ac voltage perturbations. Data obtained using EIS techniques show two time constants, which can be assigned to the membrane and to the channel/membrane contributions, respectively.