Positive and negative allosteric effects of thiacalix[4]arene-based receptors having urea and crown-ether moieties

Heteroditopic receptors (4a~e) based on a thiacalix[4]arene in the 1,3-alternate conformation, which have two urea moieties linking various phenyl groups substituted with either electron-donating or -withdrawing groups at their m-, or p-positions with a crown-ether moiety at the opposite side of thiacalix[4]arene cavity, have been synthesized. The two examples with p-CH3- (4b) and p-NO2-substituted (4e) (phenyl groups have been characterized by X-ray crystallography. The binding property of receptors 4e was investigated by means of 1H NMR spectroscopic and absorption titration experiments in CHCl3–DMSO (10:1, v/v) solution in the presence of K+ ion and various anions. Interestingly, it was found that receptor 4e, which possesses two p-nitrophenyl ureido moieties, can complex most efficiently in the urea cavity or the crown-ether moiety; and the plausible allosteric effect of receptor 4e was also studied