Artificial Ion Channels Showing Rectified Current Behavior

Abstract

Voltage-dependent artificial ion channels 3 and 4 were synthesized. Two cholic acid derivatives were connected through a m-xylylene dicarbamate unit at 3-hydroxyl groups. Asymmetries were introduced by terminal hydrophilic groups, carboxylic acid and phosphoric acid for 3 and hydroxyl and carboxylic acid for 4. Under basic conditions, these headgroups in 3 and 4 are expected to be dissociate into -1/-2 (pH 8.2) and 0/-1 (pH 7.2), respectively. Single ion channel properties were examined by a planar bilayer lipid membrane method under symmetrical 500 mM KCl at pH 8.2 or 7.2. When 3 and 4 were introduced into the bilayer membrane under application of positive voltage (a positive-shift method), the current values at positive applied voltage were larger than the corresponding ones at the negative applied voltage. The current-voltage plots were fitted by curves through a zero point to show clear rectification properties. The direction of rectification could be controlled by positive- or negative-shift methods. Vectorial alignment of terminal headgroup charges by the voltage-shift incorporation is essential for giving voltage-dependent rectified ion channels.

Ion-Current Rectification in Nanopores and Nanotubes with Broken Symmetry

“…[7] Our measurements suggest that it is indeed the electrostatic asymmetry at the two openings of a nanopore that is responsible for the rectification behavior. The occurrence of rectification seems therefore to be independent of the membrane material as well as of the specific chemistry of charges on the nanopores.…”

“…The resistance is directly proportional to the length of the pore, L, and inversely proportional to its cross-sectional area, A R 1 j L A (7) where j is the specific conductivity of the electrolyte filling the nanopore. In this method we assume that the conductivity of the electrolyte inside the pore is the same as in the bulk solution.…”

“…[1,6] Another rectifying nanoporous system consists of artificial nanopores inserted into a lipid bilayer. [7,8] Our group and others have shown that entirely synthetic systems can also rectify ion current. We have prepared nanopores in polymer films [9][10][11] as well as gold nanotubes [12] that are ion selective and rectify the ion current if they are conical in shape and have excess surface charge.…”

Synthetic multifunctional pores: deletion and inversion of anion/cation selectivity using pM and pH

“…1). Their rare characteristics compared to the other synthetic ion channels/pores, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] i.e. the possibility to install functional groups along the ion-conducting pathway, encouraged the shift of our interest from biomimicry to practical applications.…”

Transmission of Binding Information across Lipid Bilayers

“…From the current study it is very difficult to distinguish between both forms and therefore a certain percentage of U-shaped receptors cannot be fully excluded. However, it has been shown several times by others that introducing rigidity, for example, a dialkyne unit, into the core of specific lipids force them almost exclusively in a transmembrane orientation, [15] even more flexible bolaamphiphilic molecules have been shown to adopt a completely transmembrane conformation. [16] Furthermore, exactly the same transmembrane unit has been reported recently in another transmembrane spanning system [17] and the transmembrane signalling system we reported recently is based on the same dialkyne-cholesterol scaffold as 2 and results obtained with that system clearly suggested a transmembrane orientation.…”