Supramolecular ion channel containing trans-azobenzene for photocontrol of ionic fluxes

N,N-Dimethyl-N-octadecyl-4-[4-(4′-butyloxy)-trans-azobenzoxy]butyl-ammonium cation was paired with 3,8,13,18,23-pentaoxadocosanoate anion to afford a photo-isomerizable amphiphilic ion pair. When this ion pair in the trans form was incorporated into a planar bilayer phospholipid membrane, single ion channel currents were observed and the ion channel properties could be fully analyzed. The channel showed various conductivity states, as characteristics of supramolecular channels, in the range mostly 2–12 pS. The channel was selective for cation over anion with a permeability ratio PK/PCl of 6.1 and was selective also for metal ion species such as K+/Na+ or K+/Cs+ with selectivity factors of 6.1 and 0.7, respectively. The channel was characterized by a very long open time and stayed in the open state once it appeared. When the trans-azo form was photoirradiated at 367 nm to isomerize to the cis-isomer, no characteristics of single ion channel currents were detected, but leaky currents were observable. When the cis-azo function was isomerized back to the trans form, single channel currents were regenerated. The ionic fluxes of supramolecular channel mechanisms were successfully controlled by photoirradiation.