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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.

References associated with 1.D.222 family:

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. 15045106
Kumar, N. and N. Madhavan. (2023). Small molecule-derived pH-gated ion transporters. Org Biomol Chem. [Epub: Ahead of Print] 37404004