1.D.222.  The TetraCyanoResorcin[4]Arene Ion Channel (TCRA-IC) Family 


Chen et al. 2004 have reported tetracyanoresorcin[4]arene ion channels (44 and 45) that have cup-like structures with free –OH groups at the pore entrance and hydrophobic alkyl chains as tails (see the figure below). The ion channel is a tail-to-tail dimer of the molecule. Titration of 44b with NaOH as monitored by UV-Vis spectroscopy showed characteristic jumps in absorption intensity corresponding to the formation of the monoanionic to tetranionic forms of the macrocycle. Single-ion channel currents at ±100 mV were found to be 0.8 and 0.95 pA at pH = 6 and 7.2, respectively. The channel current increased significantly at pH = 8.5 over the range of 0.7–1.8 pA. The increasing pH deprotonation of the phenolic-OH resulted in an increase in electron density at the benzene rings that might be suitable for pi–cation interactions (see figure b below) (Kumar and Madhavan 2023).


(a) Tetracyanoresorcin[4]arene-based pH switchable ion transporters 44 and 45. (b) Deprotonation of phenolic OH results in increased cation transport.

This family belongs to the Arene Artificial Ion Transporter Superfamily.



Chen, W.H., M. Nishikawa, S.D. Tan, M. Yamamura, A. Satake, and Y. Kobuke. (2004). Tetracyanoresorcin[4]arene ion channel shows pH dependent conductivity change. Chem Commun (Camb) 872-873.

Kumar, N. and N. Madhavan. (2023). Small molecule-derived pH-gated ion transporters. Org Biomol Chem. [Epub: Ahead of Print]