Regioselective synthesis of functionalized pyrazole-chalcones via a base mediated reaction of diazo compounds with pyrylium salts

A base-mediated reaction of triaryl/alkyl pyrylium tetrafluoroborate salts with α-diazo-phosphonates, sulfones and trifluoromethyl compounds affords the corresponding functionalized pyrazole-chalcones as 5-P-5 and 3-P-3 tautomeric mixture. The reaction proceeds through an initial nucleophilic addition of diazo substrates to pyrylium salts followed by a base-mediated pyrylium ring-opening and intramolecular 1,5-cyclization to afford formal 1,3-dipolar cycloaddition products. The products underwent a Nazarov-type cyclization upon hydride reduction followed by acidic-workup, furnishing the corresponding indenyl-pyrazoles in high yields.

Coumarin functionalized molecular scaffolds for the effectual detection of hazardous fluoride and cyanide

Fluoride and cyanide contamination in drinking water imposes detrimental impacts on human health above their permissible limits. Hence, the quantitative detection of these colourless water-soluble toxins has attracted attention. Even though a plethora of chemosensors have been reported so far for the detection of fluoride and cyanide from various matrices, still their applicability is limited to a few examples. Nevertheless, recent advances in the syntheses of coumarin derivatives have shown significant impact on fluoride and cyanide detection. Therefore, this present review provides a brief overview of the application of coumarin-coupled molecular scaffolds towards the detection of perilous fluoride and cyanide along with their sensing mechanisms in order to develop more innovative, simple, sensitive, real-time responsive and cost-effective coumarin-based supramolecular chemosensors to promote next generation approaches towards the ultra-trace quantitative detection of these toxic anions.

5'-Hydroxymethyl fluorescein: A colorimetric chemosensor for naked-eye sensing of cyanide ion in a biological fluid

A two-step synthetic method to prepare a highly sensitive and selective chemosensor 5'-hydroxymethyl fluorescein (5'-HMF) is described herein. This sensor was explored as a colorimetric sensor for naked-eye detection of cyanide ion in the biological fluid as well as in organic and aqueous media. The addition of cyanide ion to 5'-HMF resulted in a rapid change in color in aqueous medium from light green to dark fluorescent green, and in acetonitrile from light pink to purple. A significant bathochromic shift in the absorption spectra enables cyanide ion to be detected by naked eyes in water and acetonitrile without any interference of the competing anions such as, AcO^-, F^- and SCN^- in aqueous solution. Using the ¹HNMR titration experiments and Job's plot from absorbance spectroscopy, the interaction of CN^- ion with 5'-HMF has been investigated and binding stoichiometry was found to be 1:2 (5'-HMF to CN^-). The limit of detection (LOD) of the sensor for CN^- was 3.68 μM in water with a linearity (R² = 0.9923) in the range of 0.50 to 30.0 μM concentration assuming 1:2 (5'-HMF to CN^-) binding stoichiometry. In addition, the sensor 5'-HMF sensed the CN^- ion in human saliva with the LOD as 7.0 μM in aq. medium.

Mechanochemical synthesis of fluorescein-based receptor for CN- ion detection in aqueous solution and cigarette smoke residue

A facile green method for the mechanochemical synthesis of Schiff base phenylhydrazono-N-methylene fluorescein (PHMF) with 95% yields has been established. The synthesized receptor assists in the naked-eye detection of CN^- ions in organic and aqueous media, and F^- ions in acetonitrile over a series of anions with a color transfer from colorless to pink. A redshift of 160 nm of PHMF-CN^- complex in the absorbance spectrum and a turn-on response in the fluorescence spectrum were observed, respectively, at λmax 345 to 515 and 519 nm. A strong interaction of PHMF with CN^- and F^- ions forming a 1:3 binding stoichiometry has been noted in this study. In an aqueous medium for CN^- ion, the lower limit of detection (LOD) is defined as 9.204 nM, which is quite better in terms of sensitivity. In addition, PHMF's paper-strip sensor for rapid real-time CN^- ion sensing was found to be sufficiently sensitive to successfully detect CN^- ion in water and a solid state, resulting in a portable device for detecting cyanide ions. In acetonitrile, the receptor's ability to detect CN^- ion in cigarette smoke residue was also satisfactorily achieved. Graphical Abstract.

Synthesis of new fluorescent pyrylium dyes and study of their interaction with N-protected amino acids

Six new fluorescent styrylpyrylium dyes have been synthesized and the collisional quenching taking place upon their interaction with Z-protected amino acids has been studied.

Selective fluorescence sensing of H2PO4−by the anion induced formation of self-assembled supramolecular polymers

H₂PO₄⁻anions induced the formation of a fluorescent supramolecular polymer by halogen bonding interactions in a bromoimidazolium based tripodal receptor.

Coumarin-Based Small-Molecule Fluorescent Chemosensors

Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

Roles of Water Molecules and Counterion on HS- Sensing Reaction Utilizing a Pyrylium Derivative: A Computational Study

In this paper, we present a comprehensive computational study on the hydrogen sulfide ion (HS^-) sensing mechanism in aqueous solution using pyrylium-thiopyrylium transformation. Explicit water molecules up to three water molecules are considered using supramolecular models. The effect of water bulk solvent is also taken into account according to the polarizable continuum model. Our results demonstrate that water molecules are directly involved in the sensing reactions by altering reaction mechanisms and dramatically lower the activation energies. The most favorable HS^- sensing mechanism involves a 10-membered ring transition structure formed by three water molecules and one hydronium. The catalytic effects of water molecule(s) due to the alleviation of ring strain and the stabilization from deprotonated hydronium significantly lower the activation energy. The activation energies in aqueous solution decrease from 40.2 kcal/mol for the hydronium-only-catalyzed reaction to 15.7, 14.8, and 7.4 kcal/mol for one-water-, two-water-, and three-water-catalyzed mechanisms, respectively. In addition, the effect of the counterion tetrafluoroborate (BF₄^-) on the reaction mechanisms was also investigated. Our results demonstrate that the counterion BF₄^- most likely behaves as a spectator and has minor influence on the reaction mechanism.

Turn-on fluorescent sensor for the detection of cyanide based on a novel dicyanovinyl phenylacetylene

A novel phenylacetylene derivative (3) was successfully synthesized via Sonogashira coupling and a Knoevenagel reaction for cyanide ion detection.

A simple chemosensor for the dual-channel detection of cyanide in water with high selectivity and sensitivity

By a deprotonated mechanism, the simple chemosensorHYshowed high sensitivity and selectivity for cyanide in aqueous media.