Phenyl-calix[4]arene-based fluorescent sensors: cooperative binding for carboxylates.
Tetrakis-(4-carbamoylphenyl)-substituted and tetrakis-(4-amidophenyl)-substituted calix[4]arenes 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 calix[4]arene-based sensors exhibit greatly enhanced binding 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 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 calix[4]arene 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 H-bond donor for hydrogen-bonding interactions in molecular recognition and supramolecular chemistry.
Sun
Xiao Hua
XH
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China.
Li
Wenye
W
Xia
Ping Fang
PF
Luo
Hai-Bin
HB
Wei
Yingli
Y
Wong
Man Shing
MS
Cheng
Yuen-Kit
YK
Shuang
Shaomin
S
D000838:Anions / Q000737:chemistry; D047250:Calixarenes / Q000138:chemical synthesis / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure
D000838:Anions; D002264:Carboxylic Acids; D005456:Fluorescent Dyes; D047250:Calixarenes