Syntheses of Anthryl-Isoxazole Substituted Biscalixarene Derivatives as Fluorogenic Sensors in Molecular Recognition
由單晶結構圖中，我們可以看出雙橋聯雙芳杯化合物46具一扁平長方體孔洞，於是我們取化合物46，對芳香環客體分子和甲基紫精分子進行辨識研究。化合物46對芳香族類客體分子(A1-A6)沒有明顯的辨識效果；然而，化合物46當加入高當量甲基紫精客體分子，有螢光淬熄現象，由Stern-Volmer 方程式，可求得結合常數Ka = 132.9 M-1。|
In this work, we have synthesized biscalixarenes 42-46 using 1,3-dipolor cycloaddittion reactions. Our synthetic strategy for linking two calixarenes involves double and quadruple cycloaddition between aryl dinitrile oxides and propargyl groups to form isoxazole biscalixarenes, 42, 44 and 46. Mo(CO)6–mediated ring opening reaction of isoxazole linked biscalixarenes 42 and 44, led to biscalixarenes with enaminone groups, 43 and 45. Based on 1H□□NMR spectroscopy, we found that compound 45 composed of two atropisomers, because there is a hindered rotation around the C9-C11 bond of the□□-amino□□□□-unsaturated ketones. The binding properties of ligands 44, 45, and 46 toward guests were investigated by UV-Vis and fluorescence spectroscopy. The results showed that ligand 44 was highly selective to recognize Cu2+. Upon titration with Cu2+, the fluorescence of 44 was quenched (On-Off). Cu2+ was found to be reduced to Cu+ by ligand 44 as probed by EPR spectroscopy. Compound 45 showed specific responses to Hg2+ and Cu2+, when addition of Hg2+ to an CH3CN solution of 45, it’s UV-vis absorption was a slightly red shifted; whereas, it did not induced any significant change in UV-vis or fluorescence spectra when various anions were added. An X-ray crystal structure of 46 clearly shows that it’s contains a rectangular cone conformation. Biscailxarene, 46, was used to test its inclusion the binding studies with aromatic guests, however, no inclusion between ligand 46 and aromatic guests (A1-A6) was found. The fluorescence intensity of 46 was decreased with the addition of high equivalent of methyl viologen, and the association constant Ka was determined to be 133□M-1 by Stern-Volmer plot.
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