Ion transport across a bilayer lipid membrane in the presence of a hydrophobic ion

The ion transport from one aqueous (W1) to another (W2) across a bilayer lipid membrane (BLM) in the presence of a hydrophobic ion, dipicrylaminate (DPA(-)), was investigated by cyclic voltammetry when the hydrophilic salt such as LiCl, NaCl, KCl or CsCl was used as a supporting electrolyte. Voltammograms for the ion transport at a lower scan rate than 10 mV s(-1) were in steady state and showed sigmoid curves. The magnitude of the ion transport current density at a given potential was proportional to the hydrophobicity of the counter cation. The result supports our proposed mechanism that the hydrophobic ion serves as a carrier compound in the BLM for the ion transfer of the hydrophilic counter ion in the presence of the membrane potential gradient.