Santanu Panja

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.

Coumarin-based supramolecular gelator: a case of selective detection of F− and HP2O73−

Coumarin appended 1,2,3-triazole coupled cholesterol 1 which acts as a small molecular gelator has been designed and synthesized. Compound 1 has been noted to form gel from CHCl3–petroleum ether (1:1, v/v). The stable gel is anion responsive. The gel state is transformed into the sol state selectively in the presence of F− and hydrogen pyrophosphate and thus validates their visual sensing over a series of other anions. Fluorescence study in CH3CN containing 0.5% DMSO also reveals substantial change in emission of 1 upon addition of both F− and hydrogen pyrophosphate and distinguishes them from other anions studied.

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.

Naphthalene-cholesterol conjugate as simple gelator for selective sensing of CN- ion

Abstract Cholesterol-based Schiff base 1 has been designed and synthesised. The Schiff base 1 forms yellow coloured gel in DMF:H2O (2:1, v/v) and the gel is anion responsive. Among different anions, the gel phase of 1 is selectively transformed into sol in the presence of CN– ions and validates its visual sensing. 1H NMR, FTIR and HRMS spectroscopic techniques were adopted to study the gelation of 1 and its responsive behaviour towards anions. Cholesterol-based Schiff base 1 has been designed and synthesized. The Schiff base 1 forms yellow colored gel in DMF: H2O (2:1, v/v) and the gel is anion responsive. Among different anions, the gel phase of 1 is selectively transformed into sol in the presence of CN- ions and validates its visual sensing.

Cholesterol-Appended Benzimidazolium Salts: Synthesis, Aggregation, Sensing, Dye Adsorption, and Semiconducting Properties

A series of cholesterol-appended benzimidazolium salts 1-9 have been designed and synthesized. They have been explored in gel chemistry. The gelation of the benzimidazolium salts is dependent on the nature of the counteranions. In addition, the gelation behavior of the gelators is linked with the presence of both π-stacking and cholesteryl motifs. Whereas bisbenzimidazolium salt 2 forms a gel in dimethylsulfoxide/H2O (1:1, v/v) itself, under similar conditions, monobenzimidazolium salts 4 and 6 exhibit gelation in the presence of F- ions and validate the visual sensing of F-. As an application, the gel phase of 2 efficiently removes toxic dyes from waste water. Furthermore, all gels show thermally activated semiconducting property within a wide voltage window.

Naphthalene linked pyridyl urea as a supramolecular gelator: a new insight into naked eye detection of I− in the gel state with semiconducting behaviour

The gelation and anion responsive behavior of some 3-aminopyridine-based urea molecules 1–5 have been examined. Of the different pyridyl ureas, compounds 1 and 2 form an instant gel from DMSO/H2O and DMF/H2O solvents. Between the gels 1 and 2, only the gel state of 2 has been noted, for the first time, to detect iodide ions over a series of other anions through a colour change involving no phase transformation. Furthermore, the gel state of 2 is a poor semiconductor and the presence of iodide ions considerably enhances its conductivity that varies with temperature.

Cholesterol appended bis-1,2,3-triazoles as simple supramolecular gelators for the naked eye detection of Ag+, Cu2+ and Hg2+ ions

Cholesterol coupled bis-1,2,3-triazoles 1–3 have been synthesized and their gelation abilities are examined. Bis triazoles 1–3 form a gel from CHCl3–CH3OH (2 : 1, v/v) mixture solvents. In contrast, compounds 4 and 5, which are devoid of triazoles, are unable to form a gel under similar conditions and thus validate the essential role of triazoles in gelation. While the gel phase of 1 detects Cu2+ ions by showing phase transformation from gel to sol, gels derived from 2 and 3 undergo disintegration in the presence of Ag+, Cu2+ and Hg2+ ions. Such phase changes corroborate the visual sensing of metal ions. Moreover, the fluorescence titration of 3 discriminates Cu2+, Hg2+ and Ag+ ions by exhibiting differential quenching.

Rhodamine-linked pyridyl thiourea as a receptor for selective recognition of F–, Al3+ and Ag+ under different conditions

A new rhodamine-labelled pyridyl thiourea-based compound 1 has been designed and synthesised. While the receptor selectively recognises F– and Al3+ ions in CH3CN, Al3+ and Ag+ ions are selectively screened from other cations in CH3CN/water (4/1, v/v; 10 μM Tris–HCl buffer, pH 6.8) by observing different emission characteristics and colour changes. While Ag+ is sensed through an increase in emission at 416 nm, Al3+ is detected by a ratiometric change in emission of 1 with a band at 585 nm. The receptor shows in vitro detection of both the ions in human cervical cancer (HeLa) cells.

Pyridine coupled mono and bisbenzimidazoles as supramolecular gelators: selective metal ion sensing and ionic conductivity

Pyridine coupled mono and bisbenzimidazoles 1–6 are synthesized and their gelation properties are examined in various polar as well as nonpolar solvents. Among the structures, compounds 1 and 2 form instant gels from DMSO/H2O and MeOH/H2O solvents. The gel states of both 1 and 2 are responsive to Ag+ and Cu2+ ions whereas the gel to sol transition of 2 in DMSO–H2O is additionally caused by Hg2+ ions. On the other hand, compounds 3 and 4 produce gels only in the presence of Ag+ ions under similar conditions and validate their visual readout. In relation to this, the nongelation behavior of p-isomers 5 and 6 (structural isomers) under identical conditions emphasizes the positional role of the pyridyl ring nitrogen with respect to the imidazole ring. Furthermore, metallogels of 3 and 4 exhibit thermally activated ionic conductivity due to movement of Ag+ ions within the gel network.

Pyridine/pyridinium symmetrical bisamides as functional materials: aggregation, selective sensing and drug release

Pyrrole and furan-based pyridine/pyridinium bisamides 1–4 have been designed and synthesized with a view to establishing new supramolecular gelators. The neutral gelators 1 and 2 were explored for cation binding. While the furan analogue 1 forms gel in the presence of Ag+ and Cu2+ ions in DMSO : H2O (1 : 1, v/v), the pyrrole conjugate 2 exhibits metallogel formation selectively with Ag+ ions and corroborates the role of the heteroatom in the spacer that modulates the self assembly behavior of the gelators. As an application, the 1-Cu gel selectively distinguishes thiol-based amino acids from a series of other amino acids as well as effectively discriminates D-glucose from its C2-epimer D-mannose by exhibiting gel to sol transformation. Additionally, encapsulation and subsequent release of the chemopreventive drug curcumin has been studied using the 1-Cu gel. Placement of a cholesterol unit onto the structures 1 and 2 resulted in charged structures 3 and 4 of which compound 4 produced an unambiguous visual readout of F− and AcO− ions by showing gel to sol transition.