Debasis Kar

Ion conducting cholesterol appended pyridinium bisamide-based gel for the selective detection of Ag+ and Cl− ions

Cholesterol appended bispyridinium isophthalamide dichloride (1) has been designed and synthesized. While compound 1 forms a gel in CHCl3, the cholesterol appended bispyridinium isophthalamide dihexafluorophosphate (1a) analogue that results from 1 on anion exchange does not form a gel in any solvent combination. The chloroform gel of 1 is pH responsive and shows thermally activated ionic conductivity. It serves as a medium for the specific detection of Ag+ ions over a series of examined cations. Compound 1a, on the other hand, acts as a selective Cl− ion detector by forming a gel in chloroform in the presence of tetrabutylammonium chloride.

Fluorometric recognition of both dihydrogen phosphate and iodide by a new flexible anthracene linked benzimidazolium-based receptor

Summary A new flexible anthracene linked benzimidazolium-based receptor 1 has been designed, synthesized and its binding properties have been studied by NMR, UV–vis and fluorescence spectroscopic techniques. While the receptor 1 exhibits a greater change in emission in the presence of tetrabutylammonium dihydrogenphosphate in CH3CN over the other anions studied, iodide is selectively preferred in CHCl3 containing 0.1% CH3CN. Upon complexation of dihydrogen phosphate and iodide, the emission of 1 gradually decreased without showing any other characteristic change in the spectra. Hydrogen bonding and charge–charge interactions interplay simultaneously in a cooperative manner for selectivity in the binding process.

Progress of 3-aminopyridinium-based synthetic receptors in anion recognition

This review describes the overall development on synthetic receptors built on the pyridinium motif with different functionalities at the 3-position in anion recognition. The review covers only the organic systems. In the designs, the pyridinium group along with the other functional motifs plays a crucial role in the binding of various anions of different shapes and sizes. Complexation characteristics are communicated through changes in 1H NMR, emission, color or gelation behaviours.

Fluoride-responsive hydrogel of cholesterol appended pyridinium urea and its metal detecting ability and semi-conducting behaviour

Cholesterol appended pyridinium urea 1 acts as low molecular weight gelator in DMSO:H2O (1:1, v/v) showing distinct colour change in the presence of aqueous solution of KF as well as tetrabutylammonium fluoride and recognises F− specifically. In addition, this hydrogel is noted to detect aqueous solution of Cu2+ and Pb2+ ions over a series of other metal ions and exhibits good semi-conducting property.

Benzimidazolium-based chemosensors: selective recognition of H2PO4−, HP2O73−, F− and ATP through fluorescence and gelation studies

Benzimidazolium-based receptors 1 and 2 have been designed and synthesized. The receptors with identical binding sites exhibit different sensing properties towards different anions under identical conditions. In a lower equivalent amount of guests, receptors 1 and 2 show fluorescence selectivity towards phosphate-based anions. In the presence of higher equivalent amounts of guests, while structure 1 reveals selectivity in sensing of phosphate derivatives such as hydrogen pyrophosphate and dihydrogenphosphate in CH3CN, under identical conditions receptor structure 2 senses F−. Furthermore, compounds 1 and 2 validate the visual sensing of hydrogen pyrophosphate and dihydrogenphosphate, respectively, through the formation of gels. Binding studies have been carried out using fluorescence, UV-vis, 1H NMR and 31P NMR spectroscopic techniques. Experimental results have been correlated with the theoretical findings.

Azaindole-1,2,3-triazole conjugate in a tripod for selective sensing of Cl−, H2PO4− and ATP under different conditions

A new tripodal sensor 1 has been designed and synthesized. The cavity of the tripod selectively recognizes Cl− and H2PO4− over a series of other anions in CH3CN containing 0.01% DMSO by exhibiting a significant change in emission. Between H2PO4− and Cl− ions, H2PO4− is distinguished by 1 through a ratiometric change in emission. In comparison, the indole-based tripod 2 did not show any binding-selectivity with the same anions. Compound 1, furthermore, selectivity recognizes phosphate based biomolecule ATP over ADP and AMP in semi aqueous solvent (CH3CN containing 0.01% DMSO : H2O, 1 : 1, v/v) at pH 7.3. The tripod 1 is cell permeable and detects ATP by showing quenching of emission.

Azaindole-1,2,3-triazole conjugate as selective fluorometric sensor for dihydrogenphosphate

A new receptor 1 has been designed and synthesized. The open cavity of 1 selectively recognizes H2PO4− over a series of other anions in CH3CN containing 0.01% DMSO by exhibiting a ratiometric change in emission. In sensing, the cooperativity of the azaindoles in 1 has been proved using the model compound 2. Also the interaction behavior of the nitrogen in the azaindole has been proved by considering compound 3, which did not show any discrimination towards the anions. Binding studies have been carried out using fluorescence, UV-vis, 1H NMR and 31P NMR spectroscopic techniques.

Benzimidazolium-based new simple ratiometric fluorescent sensor for selective detection of dihydrogenphosphate

A series of pyridine-coupled benzimidazolium-based receptors 1, 2 and 3 have been designed and synthesised. In the series, only receptor 1 is structurally appealing in the selective recognition of H2PO4− in CHCl3 as well as in CH3CN over a series of other anions. The ratiometric change in emission with a triplet band at 420 nm is the distinctive feature of selective recognition of H2PO4− in CHCl3. In CH3CN, a ‘turn on’ response is selectively observed. Binding studies have been carried out using fluorescence, UV–vis, 1H NMR and 31P NMR spectroscopic techniques. Experimental results have been correlated with the theoretical findings. Pyridine-coupled benzimidazolium-based receptor 1, selectively recognises H2PO4− in CHCl3 as well as in CH3CN over a series of other anions. The ratiometric change in emission with a triplet band at 420 nm is the distinctive feature of selective recognition of H2PO4− in CHCl3. In CH3CN, a ‘turn on’ response is selectively observed. Experimental results have been correlated with the theoretical findings.