Pushap Raj

Benzimidazolium-Based Self-Assembled Fluorescent Aggregates for Sensing and Catalytic Degradation of Diethylchlorophosphate

The unregulated use of chemical weapons has aroused researchers to develop sensors for chemical warfare agents (CWA) and likewise to abolish their harmful effects, the degradation through catalysis has great advantage. Chemically, the CWAs are versatile; however, mostly they contain organophosphates that act on inhibition of acetyl cholinesterase. In this work, we have designed and synthesized some novel benzimidazolium based fluorescent cations and their fluorescent aggregates were fabricated using anionic surfactants (SDS and SDBS) in aqueous medium. The prepared fluorescent aggregates have shown aggregation induced emission enhancement, which was further used as detection of chemical warfare agent in aqueous medium. The aggregates (Benz-2/SDBS and Benz-3/SDBS) have shown significant changes in emission profile upon interaction with diethylchlorophosphate. Contrarily, the pure dipodal receptor Benz-4 has not shown any response in emission after interaction with organophosphate, and consequently, it was concluded that benzimidazolium cation plays a decisive role in sensing. The mechanism of sensing was fully validated using 31P NMR spectroscopy as well as GC-MS, which highlights the transformation of diethylchlorophosphate into diethylhydrogen phosphate. The aggregates selectively interact with diethylchlorophosphate over other biological important phosphates.

Zwitterionic liquid (ZIL) coated CuO as an efficient catalyst for the green synthesis of bis-coumarin derivatives via one-pot multi-component reactions using mechanochemistry

A convenient, solvent free strategy for the synthesis of bis-coumarins has been developed using zwitterionic liquid (ZIL) coated copper oxide (CuO) and mechanical ball milling. The ZIL were fabricated from imidazolium/benzimidazolium and sulfonate/carboxylate based moieties. Use of the ZIL offers an interesting multifunctional opportunity to immobilize them over CuO using the anionic part and the cationic part is left freely available for use in catalytic applications. The hybrid catalysts were fully characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffraction, cyclic voltammetry, solid state ultraviolet-visible absorption and spectroscopic emission methods. The three ZIL-based and CuO coupled hybrid catalysts (ZIL@CuO1–3) generated were found to have diverse sizes, shapes, photophysical signatures and electrochemical properties. The supramolecular assembly of ZIL and CuO in ZIL@CuO1 has extensively enhanced catalytic activity compared to their individual parent components as well as to the two other hybrid materials, ZIL@CuO2–3. The reaction conditions were optimized by varying the number of balls used, the milling time and the milling speed. The reaction mechanism was elucidated using proton–nuclear magnetic spectroscopy and all the final products were fully characterized using spectroscopic methods. Finally, the performance of the reaction at the multigram scale is also detailed and a high EcoScale score and a low E-factor are the most pleasing features of this methodology, and thus, authenticate its use for eco-friendly synthesis of bis-coumarins and offer advancements over other catalysts described in the literature.

An organic–inorganic nanohybrid of a calix[4]arene based chromogenic chemosensor for simultaneous estimation of ADP and NADH

The versatility in the environmental and biological applications of nanohybrids encouraged us to prepare a novel chemosensor based on an organic–inorganic nanohybrid (H1) employing receptor 1 (R1), which was synthesized via the Schiff’s base condensation reaction of a calix[4]arene derivative and an aliphatic amine. Techniques such as DLS and TEM were employed for the characterization of organic nanoparticles (N1) and H1. Further, sensor properties of H1 were explored towards various biologically important molecules in aqueous media using UV-visible spectroscopy. The proposed sensor responded effectively for the selective and simultaneous nanomolar determination of adenosine diphosphate (ADP) and reduced nicotiniamide adenine dinucleotide (NADH). The response was not affected by the presence of each analyte or any other potentially interfering biomolecule or a high concentration of salt. The proposed sensor was also found to show a stable response in an extensive pH range thus widening its practical applicability. H1 was able to detect a minimum concentration (detection limit) of 6.11 × 10−9 M of ADP and 4.87 × 10−9 M of NADH. The prepared hybrid was subjected to real sample analysis for the determination of ADP and NADH in samples prepared artificially by adding known concentrations of NADH and ADP in solution and also in a mixture of both.

Transition metal complexes based chemosensor for organophosphates/chemical warfare agents

The one of most successful approach for sensing of organophosphate/chemical warfare agent in water is the use of metal complexes having one or more vacant coordinated sites for guest. In some cases the coordinated complexes have some labile ligands which can be selectively replaces by the specific analyte. The detection of toxic organophosphates and nerve agents such as Sarin (GB), Soman (GD), and tabun (GA) has been gained remarkable interest due to the overuse of these chemical weapons in battlefield and terrorist attacks. In literature, numerous methods have been developed for rapid detection of nerve agents such as mass spectrometry, gas chromatography, electrochemical sensors, colorimetric and fluoremeteric sensors. However, one of major drawback of reported method is that they were used in organic solvent. To overcome the solvent issue we have synthesized different metal (Ni2+, Cu2+, Zn2+) complexes of naphthalimide/ imine linked ligand for selective and sensitive detection of the organophosphate in water. The architecture of metal complexes is design in such a way that some complexes have vacant coordinated site for selective binding of organophosphates or some have labile ligands for replacement with specific analyte. The single crystal structure of all five complexes has shown that two are dinuclear and three are mononuclear with the distorted octahedral geometry. The coordination spheres of all five complexes were satisfied with chelate ligands and nitrate ions. The organophosphate recognition mechanism was studies with fluorescence and 31PNMR spectroscopy. All five metal complexes have shown nanomolar detection limit for organophosphate.