Voltammetric Study on the Transport of Ions of Various Hydrophobicity Types through Bilayer Lipid Membranes Composed of Various Lipids

The ion transport from one aqueous medium, W1, to another, W2, through a bilayer lipid membrane, BLM, was investigated voltammetrically by scanning the applied membrane potential, ΔVW1–W2, and monitoring the membrane current, IW1–W2. The shapes of voltammograms observed with a definite BLM depended on the hydrophobicity and the concentration of the ion added into W1 and/or W2, and can be classified into four types. The transport processes involved in each type of voltammogram were elucidated in the light of knowledge about ion transport processes through liquid membranes and by taking into account the conjugated ion transfers at interfaces of W1/BLM and BLM/W2. The shapes of voltammograms were also transformed when BLMs made of different lipids were employed. The spontaneous condensation of objective ions from W1 and/or W2 to the BLM by the partition with counter ions, which depends on the properties of objective ions, counter ions and lipids composing BLMs, is essential for the ion transport through BLMs.