Tetrakis-(4-carbamoylphenyl)-substituted and tetrakis-(4-amidophenyl)- substituted calixarenes as well as the monomeric biphenylcarbamate have been synthesized as fluorescent receptors for anion sensing. Their binding properties with various anions including F-, CH3COO-, Ph-COO-, and H2PO4- were investigated by fluorescence titrations, Job plot experiments, 1H NMR spectroscopies, and ESI-MS measurements. Importantly, we have found that calixarene-based sensors exhibit greatly enhanced binding affinity and selectivity toward carboxylates. The binding associations of tetrakis-(4-carbamoylphenyl)-substituted calixarene for carboxylates are 1-2 orders of magnitude greater than those of the monomeric biphenylcarbamate sensor. Such an enhancement in the binding affinity and selectivity is attributed to the cooperative binding of the multiple ligating groups as revealed from the ab inito DFT calculations. Although tetrakis-(4-amidophenyl)- substituted calixarene exhibited relatively weaker binding 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 Ç-bond donor for hydrogen-bonding interactions in molecular recognition and supramolecular chemistry.
Scopus Subject Areas
- Organic Chemistry