Tetrakis-(4-carbamoylphenyl)-substituted and tetrakis-(4-amidophenyl)-substituted calix[4]arenes as wellas the monomeric biphenylcarbamate have been synthesized as fluorescent receptors for anion sensing.Their binding properties with various anions including F
-, CH
3COO
-, Ph-COO
-, and H
2PO
4- wereinvestigated by fluorescence titrations, Job plot experiments,
1H NMR spectroscopies, and ESI-MSmeasurements. Importantly, we have found that calix[4]arene-based sensors exhibit greatly enhancedbinding affinity and selectivity toward carboxylates. The binding associations of tetrakis-(4-carbamoylphenyl)-substituted calix[4]arene for carboxylates are 1-2 orders of magnitude greater than those ofthe monomeric biphenylcarbamate sensor. Such an enhancement in the binding affinity and selectivity isattributed to the cooperative binding of the multiple ligating groups as revealed from the ab inito DFTcalculations. Although tetrakis-(4-amidophenyl)-substituted calix[4]arene exhibited relatively weakerbinding affinity toward anions, its superior binding selectivity for acetate ion over fluoride ion is evident.Our results also suggest that carbamate functionality is a useful H-bond donor for hydrogen-bondinginteractions in molecular recognition and supramolecular chemistry.
