1.D.222. The TetraCyanoResorcinArene Ion Channel (TCRA-IC) Family
Chen et al. 2004 have reported tetracyanoresorcinarene 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).