Artificial ion channels of amphiphilic ion pairs composed of oligoether-ammonium and hydrophobic carboxylate or phosphates

Abstract

5,10,15,20-Tetraoxa-tetracosane-1-trimethylammonium cation was paired with anions from stearic acid, dioctadecyl phosphate, l-α-phosphatidic acid and cardiolipin to afford membrane-insertable amphiphilic ion pairs. These ion pairs were incorporated into planar lipid bilayer membranes to observe single ion channel currents. The ion pair with l-α-phosphatidic acid gave the most stable single ion channel currents with cation selectivity. An ion pair with dioctadecyl phosphate also gave a cation selective supramolecular ion channel. Even the stearate pair afforded single ion channel currents, although the cardiolipin did not give any sign of ion channel formation. These examples provide additional support for supramolecular ion channel formation from simple amphiphilic ion pairs. Among these supramolecular ion channels, only the pair with phosphatidic acid afforded a voltage dependent supramolecular ion channel. The combined evidence strongly suggests that the voltage dependence results simply from the incorporation of charges into the membrane phase.