Hydrazine bridged coumarin-pyrimidine conjugate as a highly selective and sensitive Zn2+ sensor: Spectroscopic unraveling of sensing mechanism with practical application

Coumarin Based Fluorescent Probe for Detecting Heavy Metal Ions

Heavy metals such as Iron, Copper, and Zinc are micro-essential trace metal and involve animportant biological role, but it quickly turns toxic at exceeding the permissible limit, causing gastrointestinal irritation, liver, bone, and kidney damage, as well as disorders including Wilson's, Parkinson's, and Alzheimer's. It is important to detect the metal ions as well as their concentration quickly and affordable cost using organic probes. Among the organic probes,the coumarin fluorescent probe shows a very prominent candidate with heavy metal ions. Therefore, in the present review, we reviewed the very recent literature the identify the heavy metals using modified coumarin fluorescent probes. Readers will get information quickly about the method of preparation of modified coumarin core and their use as fluorescent probes with heavy metals using absorption and emission spectroscopic methods along with the probable mechanistic pathway of detection.

A Practical Hydrazine-Carbothioamide-Based Fluorescent Probe for the Detection of Zn2+: Applications to Paper Strip, Zebrafish and Water Samples

A practical hydrazine-carbothioamide-based fluorescent chemosensor TCC (N-(4-chlorophenyl)-2-(thiophene-2-carbonyl)hydrazine-1-carbothioamide) was applied for Zn2+ detection. TCC exhibited selective fluorescence emission for Zn2+ and did not show any interference with other metal ions. In particular, TCC was utilized for the detection of Zn2+ in paper strips, zebrafish and real water samples. TCC could detect Zn2+ down to 0.39 μM in the solution phase and 51.13 μM in zebrafish. The association ratio between TCC and Zn2+ was determined to be 2:1 by ESI-mass and Job plot. The sensing mechanism of TCC for Zn2+ was illustrated to be a chelation-enhanced fluorescence process through spectroscopic experiments and theoretical calculations.

A Novel Thiosemicarbazide-Based Fluorescent Chemosensor for Hypochlorite in Near-Perfect Aqueous Solution and Zebrafish

A novel thiosemicarbazide-based fluorescent sensor (AFC) was developed. It was successfully applied to detect hypochlorite (ClO−) with fluorescence quenching in bis-tris buffer. The limit of detection of AFC for ClO− was analyzed to be 58.7 μM. Importantly, AFC could be employed as an efficient and practical fluorescent sensor for ClO− in water sample and zebrafish. Moreover, AFC showed a marked selectivity to ClO− over varied competitive analytes with reactive oxygen species. The detection process of AFC to ClO− was illustrated by UV–visible and fluorescent spectroscopy and electrospray ionization–mass spectrometry (ESI–MS).

Developing a new chemosensor targeting zinc ion based on two types of quinoline platform

A chemosensor DQ (2-(2-(quinolin-2-yl)hydrazinyl)-N-(quinolin-8-yl)acetamide), based on two quinoline moieties, has been synthesized. DQ could detect zinc ion through fluorescence turn-on in aqueous media. Limit of detection was calculated as 0.07 μM, far lower than the standard of WHO for zinc ion. The practicality of DQ was demonstrated via the successful results of reusability with EDTA, easy detection on the test strip, and precise quantification in real water samples. Additionally, sensor DQ could be applied to bioimaging of zinc ion in zebrafish. Sensing process of zinc ion by DQ was studied through fluorescence and UV-Vis spectroscopy, ¹H NMR titration, and ESI-mass spectrometry.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

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.

Evaluating the merit of a diethylamino coumarin-derived thiosemicarbazone as an intramolecular charge transfer probe: efficient Zn(ii) mediated emission swing from green to yellow

We report the synthesis and photophysical properties of a coumarin based probe (1E)-1-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl) ethylidene) thiosemicarbazide (DIDOT). DIDOT shows a polarity dependent change in the emission maxima in the solution phase. This is explained by the increased dipole moment in the excited state by an intramolecular charge transfer (ICT) process. DIDOT can successfully detect Zn(ii) in aqueous methanol by a shift in the charge transfer emission maxima from approximately 506 to approximately 535 nm. This shift led to a change in the color of the emission from green to yellow under UV-light. The mechanism of Zn(ii) detection has been delineated using electrospray ionization-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR) and fluorescence time resolved studies coupled with theoretical calculations. The increment in the charge transfer in the Zn(ii) complex of DIDOT over the bare receptor as a consequence of conformational locking was determined to be the underlying cause of the cation detection phenomenon. The limit of detection and binding constant values of DIDOT towards Zn(ii) were approximately 3 × 10^-8 M and 2.35 × 10⁵ M^-1 respectively. Finally, the practical utility of DIDOT has been demonstrated by successful detection and quantification of Zn(ii) in spiked water samples.

A multiple target chemosensor for the sequential fluorescence detection of Zn2+ and S2− and the colorimetric detection of Fe3+/2+ in aqueous media and living cells

A novel multiple target sensor DHIC was developed for the fluorescence detection of Zn²⁺ and S²⁻ and colorimetric detection of Fe^3+/2+. Moreover, DHIC could image sequentially Zn²⁺ and S²⁻ in living cells.

Selective and sensitive fluorescent and colorimetric chemosensor for detection of CO32- anions in aqueous solution and living cells

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin (DHMC). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, ¹H NMR, ¹³C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV-vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO₃^2- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications.

An efficient and sensitive chemosensor based on salicylhydrazide for naked-eye and fluorescent detection of Zn2+

A naked-eye and fluorescent detector for Zn²⁺ was synthesized by the combination of salicylhydrazide and diarylethene with good photochromic properties.