Supramolecular ion channel containing trans-azobenzene for photocontrol ofionic 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 fo rm was incorporated into a planar bilayer phospholipid membrane, single ion channel currents were observed and the ion channel properties could be ful ly analyzed. The channel showed various conductivity states, as characteris tics of supramolecular channels, in the range mostly 2-12 pS. The channel w as selective for cation over anion with a permeability ratio P-K/P-Cl of 6. 1 and was selective also for metal ion species such as K+/Na+ or K+/Cs+ wit h selectivity factors of 6.1 and 0.7, respectively. The channel was charact erized by a very long open time and stayed in the open stale once it appear ed. When the trans-azo form was photoirradiated at 367 nm to isomerize to t he cis-isomer, no characteristics of single ion channel currents were detec ted, but leaky currents were observable. When the cis-azo function was isom erized back to the trans form, single channel currents were regenerated. Th e ionic fluxes of supramolecular channel mechanisms were successfully contr olled by photoirradiation. (C) 2000 Elsevier Science B.V. All rights reserv ed.