Transmembrane ion channels constructed of cholic acid derivatives

A new class of supramolecular transmembrane ion channels was prepared by li nking two amphiphilic cholic acid methyl ethers through biscarbamate bonds to afford bis(7,12-dimethyl-24-carboxy-3-cholanyl)-N,N'-xylylene dicarbamat e 2 and bis[7,12-dimethyl-24-(N,N,N-trimethylethanaminium-2-carboxylate)-3- cholanyl]-N,N'-xylylene dicarbamate dichloride 3. When incorporated into a planar bilayer membrane, both compounds showed stable (lasting 10 ms to 10 s) single ion channel currents. Only limited numbers of relatively small co nductances were characterized for these channels (5-20 pS for 2 and 5-10 pS for 3, 10 and 17 pS for 2, and 9 pS for 3 in particular). Both channels we re cation selective, and permeability ratios of potassium cation to chlorid e anion were 17 and 7.9 for 2 and 3, respectively, reflecting the differenc e in ionic species of the headgroup. Both channels 2 and 3 showed significa nt potassium selectivity over sodium by a factor of 3.1 and 3.2, respective ly. No Li+ currents were observed for 2, showing sharp discrimination betwe en Na+ or K+.