Urea derivatives of calix[4]arene 1,3-alternate: an anion receptor with profound negative allosteric effect

The complexation behaviour of tetrakis(phenylureido)calix[4]arene in the 1,3-alternate conformation has been studied using NMR titration experiments. It was found that this receptor with two possible binding sites exhibits a strong negative allosteric effect which leads to the exclusive complexation of only one anion.