Anil Kuwar

Highly selective turn-on fluorescent sensor for nanomolar detection of biologically important Zn2+ based on isonicotinohydrazide derivative: application in cellular imaging.

A new Zn(2+) selective chemosensor (3) was synthesized by condensation of commercially available substituted salicylaldehyde and isonicotinohydrazide, and characterized by single crystal X-ray crystallography. Receptor 3 with Zn(2+) exhibited a highly selective and pronounced enhancement in the fluorescence emission among different cations by forming a 2:1 complex. The receptor can detect Zn(2+) up to nanomolar level (6.75 nM) with good tolerance of other metal ions and can be used for in vitro cellular imaging.

A two-in-one dual channel chemosensor for Fe3+ and Cu2+ with nanomolar detection mimicking the IMPLICATION logic gate

A novel and easy-to-synthesize colorimetric and fluorescent chemosensor 1 was developed for the highly selective and sensitive recognition of Fe3+ and Cu2+. Receptor 1 showed a detectable color change from yellow to colorless with a blue-shift in the absorption spectra with Cu2+, while Fe3+ induced a color change from yellow to orange and a red-shift in the absorption spectra. In the emission study of 1, Fe3+ showed significant fluorescence enhancement with a slight red-shift while a selective fluorescence quenching was observed with Cu2+ over a wide range of tested metal ions. With Cu2+/Fe3+ as the chemical inputs, the ‘on–off’ emission profile of receptor 1 was developed as an IMPLICATION type logic gate at the molecular level.

A selective and discriminating noncyclic receptor for HSO4− ion recognition

The anion recognition ability of a novel noncyclic dipodalamine phenol receptor L was evaluated using absorption and fluorescence spectroscopic methods. The absorption and fluorescence spectra of L have shown a red shift upon the addition of HSO4− over other surveyed anions in water. The association constant (Ka) of L with HSO4− was calculated using Benesi–Hildebrand plot and Scatchard plot methodology, and it was found to be 3.1 ± 0.2 × 103 M−1.

An amide based dipodal Zn2+ complex: nano-molar detection of HSO4− in a semi-aqueous system

A new chromogenic dipodal Zn2+ complex (4) bearing an amide group has been synthesized. The anion binding profile of this sensor was investigated with fluorescence and UV-Vis spectroscopy. The receptor 4 has high affinity for HSO4 − with a binding constant of 3.5 × 104 M−1 and a detection limit of 50 nM. The binding ability was confirmed with spectroscopic methods and density functional theory calculation (DFT).

A chemosensor showing discriminating fluorescent response for highly selective and nanomolar detection of Cu2+ and Zn2+ and its application in molecular logic gate

A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu(2+) and Zn(2+) in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn(2+) and Cu(2+) ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu(2+) and Zn(2+) ions, respectively. Further, we have effectively utilized the two metal ions (Cu(2+) and Zn(2+)) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm.

Optical chemosensors for water sample analysis

Molecular recognition is an emerging field of Supramolecular Chemistry. The major challenge for supramolecular chemists is detection in an aqueous medium. However, most biological and environmental processes happen in an aqueous medium; therefore, chemosensors that can operate in water are highly demanded. This review mainly focuses on the recognition of analytes (metal, anion and biomolecules) in an aqueous medium (≥90% water) and demonstrates that sensing in an aqueous medium can be achieved without compromising the selectivity and sensitivity. The detail discussion on the design of chemosensors and the mechanism of action for detection of metal ions, anions and biomolecules in an aqueous medium has been provided, reported in the period of 2001–2015.

Highly selective fluorimetric sensor for Cu2+ and Hg2+ using a benzothiazole-based receptor in semi-aqueous media and molecular docking studies

A new chemosensor (Z)-ethyl 2-((Z)-2-(benzo[d]thiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-ylidene)acetate (receptor 1) was designed and synthesized under catalyst-free conditions. Receptor 1 was characterized by various spectroscopic techniques and its structure was solved by single-crystal X-ray diffraction. Receptor 1 was shown to be based on an internal charge transfer mechanism with the benzothiazole unit. These results were complemented by density functional theory calculations. The fluorescent emission of receptor 1 in CH3OH/H2O (50:50 v/v) was significantly quenched in the presence of Cu2+ and Hg2+, but not in the presence of other tested metal ions. Receptor 1 formed complexes in a 1:1 stoichiometry with Cu2+ and Hg2+ and the detection limits were 0.36 and 2.49 μM, respectively. In addition to the sensing study, the nature of the interactions of 1 with aldose reductase inhibitor was investigated using molecular docking studies.

“Turn-on” fluorescent dipodal chemosensor for nano-molar detection of Zn2+: Application in living cells imaging

A malonohydrazide derivative bearing an imine and phenolic group was synthesized and had a high affinity and selectivity towards Zn(2+). The recognition properties of receptor 1 were evaluated using absorbance and fluorescence spectroscopy. The 1:1 stoichiometry of 1.Zn(2+) was confirmed from jobs plot, mass spectra and density functional theory (DFT). The detection of Zn(2+) in intracellular environment of HeLa cell through confocal microscopy was successfully applied for live cell imaging.

2,2′-(Hydrazine-1,2-diylidenedimethylylidene)bis(6-isopropyl-3-methylphenol) based selective dual-channel chemosensor for Cu2+ in semi-aqueous media

A novel receptor based on a substituted salicylaldehyde derivative, 2,2′-(hydrazine-1,2-diylidenedimethylylidene)bis(6-isopropyl-3-methylphenol) (1), was synthesized and characterized using various spectroscopic techniques. The UV-visible spectroscopic studies of the receptor showed selectivity for Cu2+ in the presence of other metal ions by a change in colour from colourless to yellow. A red shift was observed with the appearance of a new absorption band at 450 nm in CH3OH–H2O (60 : 40 v/v). Fluorescence studies of the receptor showed “turn-off” recognition properties for the Cu2+ ion with a 1 : 1 binding stoichiometry and the detection limit was 50 nM.

A highly selective fluorescent ‘turn-on’ chemosensor for Hg2+ based on a phthalazin-hydrazone derivative and its application in human cervical cancer cell imaging

A new phthalazin-hydrazone based fluorescent chemosensor (E)-5-(diethylamino)-2-((2-(phthalazin-1-yl)hydrazono)methyl)phenol (1) was reported. Sensor 1 showed a high selectivity and sensitivity towards Hg2+ by giving significant fluorescence enhancement at 550 nm over other tested cations in DMSO/H2O (80 : 20, v/v) medium. The association constant was 1.0 × 104 M−1 between sensor 1 and Hg2+. Sensor 1 showed a nanomolar detection limit of 26.1 nM Hg2+. Finally, the fluorescence imaging experiments for the detection of intracellular Hg2+ in human cervical cancer HeLa cells showed its practical utility in biological samples.