Abstract
This study comprises the design and development of calix[4] arene-amido-based ionophores by varying structural stringency and steric hindrance at the lower rim to probe the anion sensing properties. The ionophores are prepared, purified, and characterized using various analytical techniques. The molecular structure of the most active ionophore I is established by single-crystal X-ray characterisation. Out of various anions investigated, iodide and cyanide show the highest sensitivity towards the ionophores investigated. Both anions are sensitive enough to give a visibly distinct color change. The binding properties of the ionophores are established with 1H & 127I NMR, fluorescence, and UV-vis spectroscopy, revealing that three ionophores strongly interact with CN− and I−. The binding constants are calculated via Benesi–Hildebrand plots using absorption data. The time-dependent 1H NMR revealed strong hydrogen bonding between the OH and NH groups of the ionophore and cyanide anion. The 127I NMR shows the highest 27.6 ppm shift after 6 h for ionophore I. The crystal structure revealed hydrogen bonding of N–H protons of the amide pendulum and phenolic oxygen of the calix rim. The Job's plot depicted the possibility of a 1 : 1 complex of ionophores with both anions.
Highlights
Supramolecular based anion-selective visual sensors have drawn signi cant attention in the past two decades1 due to their vital role in the environment and biological systems
The absorption spectra of ionophores I, II, and III at variable concentrations of iodide and cyanide are shown in Fig. 2 and 3
The binding constant Ka and stoichiometry of the inclusion complexes of ionophores with iodide and cyanide can be determined by the Benesi–Hildebrand equation (Table 1)
Summary
Supramolecular based anion-selective visual sensors have drawn signi cant attention in the past two decades due to their vital role in the environment and biological systems. Interaction with anions by UV-vis study In UV-vis titration experiment, 1 mL (5 Â 10À3 M) stock solution of tetrabutylammoniumanions (FÀ, ClÀ, BrÀ, IÀ, CNÀ, OHÀ, CH3COOÀ, NO3À, ClO4À and HSO4À) was added to a 1 mL (5 Â 10À5 M) acetonitrile solution of ionophore I–III in ascending order in ten factions (1 : 100 ratio). We have performed competitive binding with other anions (FÀ, ClÀ, BrÀ, IÀ, CNÀ, OHÀ, CH3COOÀ, NO3À, ClO4À and HSO4À) and found that ionophores are showing selective binding and color change towards cyanide. The 1H and 13C NMR spectra of ionophore I–III were recorded before and a er the addition of selected anions (CNÀ and IÀ) in CDCl3 : CD3CN (1 : 2.5).
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