Artificial Chloride-Selective Channel: Shape and Function Mimic of the ClC Channel Selective Pore

Abstract

An artificial channel molecule <b>1</b> that mimics the shape and function of the ClC channel selective pore was described. To facilitate the transport of chloride along a unimolecular pathway, anion-π interactions were introduced as the noncovalent driving force. The hourglass-like shape of <b>1</b> was constructed with 1,3-alternate tetraoxacalix[2]arene[2]triazine as the narrowest (central) unit. Two diglycolamine-linked imide arms were tethered as the extending part, and phenylalanine moieties were fixed as the terminal anchoring groups. The ion transport activity was examined by a combination of vesicle and planar bilayer conductance techniques (BLM). The fluorescence analysis on the vesicle indicated that <b>1</b> is an efficient chloride transporter with high activity (EC₅₀ = 1.50 μM; <b>1</b>/lipid = 1:89). The ion channel characteristics were confirmed by BLM measurements, showing an average conductance of 20.8 ± 1.0 pS in symmetric KCl solutions (<i>cis</i>/<i>trans</i> = 1.0 M/1.0 M). Anion/cation selectivity with a permeability ratio <i>P</i>_Cl^-/<i>P</i>_K⁺ = 1.90 in an asymmetric KCl solution (<i>cis</i>/<i>trans</i> = 1.0 M/0.25 M) and anion/anion selectivity with <i>P</i>_Cl^-/<i>P</i>_Br^- = 22.83 in a KCl/KBr solution (<i>cis</i>/<i>trans</i> = 1.0 M KCl/1.0 M KBr) were demonstrated.