A gramicidin analogue that exhibits redox potential-dependent cation influx

A synthetic analogue of gramicidin A, gram-2-(nicotinamidyl)ethyl carbamate (gAN) was found to regulate the influx of potassium ions depending on its redox state. At potentials less than −0.52 (±0.05) V, the nicotinamide group in gAN is reduced and allows charge- and size-selective influx of cations. In the oxidised state, charge repulsion between the positively charged nicotinamide group and the cations prevents any influx of cations. Chronoamperometric experiments were conducted to determine permeabilities of Eu3+, Tl+, K+ ions in a BLM porated with gAN. Scanning electrochemical microscopy (SECM) experiments were conducted with two ions: permeant K+ ions and the larger (CH3)4N+ ion which blocks the channel. The switching potential for gAN, at which the channel allows flux monovalent cations, is shown to be potential and pH-dependent and temperature-independent.