A coumarin derivative with benzothiazole Schiff's base structure as chemosensor for cyanide and copper ions

A Reversible Fluorescent Chemosensor for the Selective Detection of Cu2+ and CN- ions by Displacement Approach

A novel fluorescence chemosensor BDP (2-(1-(benzothiazol-2-yl)-5-(4-(diphenylamino)phenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol) has been synthesized and its sensing behavior has been screened towards various cations by absorption, emission and mass spectroscopic techniques. The probe BDP detects Cu2+ ions preferentially over other metal ions, and the resulting BDP-Cu2+ ensemble acts as a secondary sensor for cyanide anion detection over other anions. The fluorescence intensity of the probe BDP is quenched when it comes into contact with Cu2+ ions, but it is increased reversibly when it comes into contact with cyanide anion, according to spectroscopic measurements. Along with this, optical studies indicate that the sensor BDP has capability to sense Cu2+ and CN- ions selectively over other examined competitive ions with the LOD of 2.57×10-8 M and 2.98×10-8 M respectively. The detection limit of Cu2+ ions is lower than the WHO recommended Cu2+ ions concentration (31.5 µM) in drinking water. On the basis of "on-off-on" fluorescence change of the probe BDP upon interaction with Cu2+ and CN- ions, a possible mechanism for this selective sensing behavior was presented and IMPLICATION logic gate was successfully designed. Furthermore, cell imaging investigations were used to investigate the probe BDP's biological applicability.

Quantitatively analysis and detection of CN- in three food samples by a novel nopinone-based fluorescent probe

Cyanide (CN^-) is one of the most lethal chemical substance and exists in the organisms and environment. Due to the CN^- and CN^--containing chemicals being widely applied in industrial fields and threatening human health, the sensitive and selective detection techniques towards CN^- are still essential. Based on this, a "turn-on" fluorescent probe 2-(4-(5,5-dimethyl-4,5,6,7-tetrahydro-3H-4,6-methanobenzo[d]imidazol-2-yl)styryl)-3-ethylbenzo[d]thiazol-3-ium iodide (NCy) was designed and synthesized for monitoring CN^-. NCy had a distinguishable color change towards CN^- from colorless to yellow under 365 nm UV-light. NCy possessed the merits including low LOD (75 nM), good selectivity, and wide suitable pH range (4-10). The sensing mechanism of NCy towards CN^- was proved by HRMS, ¹H NMR titration and DFT analysis. Furthermore, the probe NCy was successfully utilized in detecting endogenous CN^- in three food samples (green potato, cassava, and bitter almond) quantitatively. In bioimaging aspect, NCy was also successfully applied in detecting the exogenous CN^- in living zebrafish.

Colorimetric and turn-on fluorescent chemosensor with large stokes shift for sensitively probing cyanide anion in real samples and living systems

Cyanide anion is a ubiquitous chemical substance in the ecosystem, however, human daily life is severely threatened by its toxicity at any time. In this paper, a novel colorimetric and turn-on chemosensor 4-(4-(2,2-difluoro-6-methyl-2H-1,3,2-dioxaborinin-4-yl)buta-1,3-dien-1-yl)-N,N-dimethylaniline (NBF) for detecting cyanide anion was synthesized based on the 4-(dimethylamino)cinnamaldehyde and β-diketone difluoroboron complex. This fluorescent probe exhibited excellent spectroscopy properties such as large stokes shift, long emission wavelength, and good sensitivity. The detection limit of NBF towards cyanide ion was determined as low as 2.23 μM. Additionally, the detection mechanism towards cyanide ion was confirmed to be the nucleophilic addition interaction by high resolution mass spectrum (HRMS), ¹H Nuclear Magnetic Resonance (NMR) titration, and quantum chemistry theory calculation. In addition, the probe NBF had been successfully utilized in detecting cyanide ions in water and food samples as well as imaging in the biological system, which broadened its practical application prospects.

Triple Action Sensing Behaviour of a Single Receptor for the Detection of Multiple Analytes via Different Approaches

The thiosemicarbazide based receptor was synthesized with 4-(diethylamino)salicylaldehyde and N- phenyl-thiosemicarbazide by the simple condensation method and the properties were studied under the naked eye, UV-Vis and fluorescence studies etc. The synthesized receptor detects cyanide, cobalt, and mercury in acetonitrile medium. The observed color changes included colourless to yellow for cyanide, colourless to green for cobalt and colourless to yellow for mercury which were seen under naked eye without the aid of any instruments. Furthermore, the cyanide bound receptor detects Cr³⁺ by the relay recognition method. The detection limit of receptor with cyanide, cobalt & mercury was found to be 5.8 × 10^- 7 M, 3.6 × 10^- 7 M and 8.1 × 10^- 7 M respectively. Experimental results were verified by DFT calculations. Receptor was successfully employed in the construction of INHIBIT and IMPLICATION logic gates.

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.

Dual mode detection of CN- & Cu2+ using fluorene moiety with logic gate, DFT studies and real sample analysis applications

A simple colorimetric receptor was synthesized by the condensation of 2-amino fluorene with 2-hydroxy-5-nitrobenzaldehyde and its properties were investigated using colorimetric, fluorescence and DFT studies. The sensing mechanism was ascertained by ¹H NMR titration studies. The synthesized receptor showed two-pronged chemosensing properties and exhibited remarkable colorimetric transitions from colorless to yellow in the presence of CN^- and colorless to green in the presence of Cu²⁺ in 80:20 acetonitrile/water medium, which could be determined by naked eye observations. The detection limit of receptor to CN^- and Cu²⁺ ion was found to be 7.9 × 10^-7 M and 4.5 × 10^-8 M respectively. Receptor was also successfully employed in the construction of molecular INHIBIT and YES logic gates. The synthesized receptor was also efficiently used for real-sample analysis in Finger Millet, also known as Ragi in Tamil. Its scientific name is Eleusine coracana.

Rational design and application of a fluorogenic chemodosimeter for selective detection of cyanide in an aqueous solution via excimer formation

A new quinone-benzothiazole imine based chemodosimeter (R) was rationally designed, synthesized and characterized using NMR and mass spectral techniques. The receptor colorimetrically senses cyanide in aq. HEPES buffer: DMF (2:8 v/v) solution with an instantaneous colour change from yellow to bluish green. An enhancement of fluorescence intensity at 429 nm with excimer formation is also observed after addition of cyanide to the receptor, which is accompanied with a colour change from yellow to blue under UV lamp. Nucleophilic addition of cyanide to imine C-atom inhibits intra-molecular charge transfer (ICT) transition, which is responsible for the excimer formation. This chemical reaction is confirmed by ¹H NMR titration. The receptor binds with two equivalents of cyanide with a binding constant of 5.55 × 10⁴ M^-1. The limit of detection (LOD) of cyanide by the receptor is found to be as low as 69 nM, which is much lower than the acceptable limit of cyanide in drinking water as set by the WHO (1.9 μM). Electrochemical studies support the termination of ICT transition upon addition of cyanide ion. Theoretical studies substantiate experimental findings and excimer formation. The receptor fluorometrically detects cyanide present in tap water and food materials such as cassava flour, almond and potato.

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.

Coumarin based colorimetric and fluorescence on-off chemosensor for F-, CN- and Cu2+ ions

(E)-4-Chloro-3-[{2-(4-nitrophenyl)hydrazono}methyl]-2H-chromen-2-one (C), a coumarin derivative has been studied toward its ion sensing properties for F^-, CN^- and Cu²⁺. A proton-transfer mechanism for F^- sensing has been deduced with the help of ¹H NMR titration alongwith from the changes in the absorption and emission spectra of C in the presence of F^-. C formed 1:1 stoichiometric complex with each of these analytes. Sensing of C toward Cu²⁺ is poor, but interestingly in the presence of F^-or CN^- the sensing ability of Cu²⁺ gets enhanced many folds, and C can act as F^-or CN^- mediated off-on sensor for Cu²⁺. Moreover, colorimetric strip (pre-coated with the coumarin derived compound) tests for F^-and CN^- from their DMSO solution at high temperature (~100°C) opens up the door for easiest naked eye recognition and distinction of these ions, and also for naked-eye detection of F^- and CN^- from its aqueous solution at high temperature (~100°C).