Pyridine diamide-strapped calix[4]pyrroles with high anion affinity

초록

The anion recognition properties of calix[4]pyrroles strapped with pyridine via either amide or ester linkers were investigated by 1H NMR spectroscopy in CDCl3 and isothermal titration calorimetry (ITC) in acetonitrile, as well as single-crystal X-ray diffraction analysis. In comparison to the parent octamethyl calix[4]pyrrole and the pyridine diester-strapped analogue 1, the pyridine diamide-strapped receptors 2 and 3, incorporating additional hydrogen-bond motifs, exhibited substantially enhanced affinities toward a range of anions. Notably, ITC measurements in acetonitrile revealed that calix[4]pyrrole 3 binds chloride with exceptionally high affinity (Ka = 1.86 & times; 107 M-1) for a calix[4]pyrrole derivative, underscoring the critical role of strategically positioned amide functionalities in strengthening anion-receptor interactions.

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