Calixarene-based photoresponsive ion carrier for the control of Na+ flux across a lipid bilayer membrane by visible light

A photoresponsive ion carrier based on calix[4]arene was synthesized for the control of Na+ flux across lipid bilayer membranes by visible light. Calix[4]arene was chosen as a basic skeleton of a photoresponsive ion carrier because its ether derivatives are known to act as Na+ ion carriers in lipid bilayer membranes. For the synthesis of a photoresponsive carrier, dimethylaminoazobenzene was introduced as a photochromic moiety to an ether derivative of p-tert-butylcalix[4]arene. The ion transport ability of the dimethylaminoazobenzene appended calix[4]arene was examined by using a voltage-clamp method. When the calix[4]arene derivative was incorporated into a planar lipid bilayer membrane which separated two chambers filled with 100 mM of NaCl solutions, membrane currents resulting from Na+ flux were observed under applying external voltages between two chambers. The concentration dependence of the calix[4]arene derivative on the membrane currents indicated the formation of a 1:1 complex with Na+ ions for the calix[4]arene-mediated ion transport across the lipid bilayer membrane. By using visible light (> 400 nm), Na+ flux across lipid bilayer membranes containing the dimethylaminoazobenzene appended calix[4]arene derivative could be controlled.