A simple dual-channel sensor for detecting cyanide in water with high selectivity and sensitivity

Taking advantage of the special nucleophilicity of cyanide, a new simple colorimetric chemosensor has been synthesised. This allows a deprotonation reaction to monitoring the cyanide. With the addition of CN^? to the chemosensor aqueous solution, which could induce a change in the solution colour from yellowish to deep yellow, while no colour change could be observed in the presence of other hackneyed anions, by which CN^? can be distinguished from other anions immediate with the naked eye. At the same time, a fluorescence quenching was implemented upon adding cyanide into the chemosensor aqueous solution. The absorption spectra detection limits of the chemosensor for cyanide was 5.35 × 10^?8 M and the fluorescence spectra detection limit was 2.63 × 10^?8 M. The cyanide test strips based on the chemosensor could serve as a convenient cyanide test kits. Furthermore, the chemosensor was successfully applied to detect cyanide in sprouting potatoes.     

Pyridinium‐Fused Pyridinone: A Novel “Turn‐on” Fluorescent Chemodosimeter for Cyanide

A new chemodosimeter based on pyridinium‐fused pyridinone iodide ( PI ) has been obtained through a “clean reaction” method. This compound can detect CN^? in aqueous solution with a high selectivity and rapid response. The detection of CN^? occurs through the nucleophilic attack of CN^? on the C?N bond, which induces the destruction of the π‐conjugation on the pyridinium ring. Support of this detection mechanism was obtained by ¹H NMR titration, HR‐MS, and DFT calculations. Upon the addition of 10 equivalents CN^? to a solution of PI in THF/H₂O (1:1, v/v), a 57‐fold enhancement in fluorescence intensity was observed at the maximum emission wavelength of 457 nm. Meanwhile, the maximum absorption wavelength was also blue‐shifted from 447 nm to 355 nm. Other common anions such as BF₄^?, PF₆^?, F^?, Cl^?, Br^?, I^?, H₂PO₄^?, ClO₄^?, CH₃COO^?, NO₂^?, N₃^?, and SCN^? had little effect on the detection of CN^?. The response time of PI for CN^? was less than 5 seconds. The detection limit was calculated to be 5.4×10^?8 M , which is lower than the maximum permission concentration in drinking water (1.9 μM ) set by the World Health Organization (WHO).     

Coumarin-based urea-amide scaffold in ratiometric fluorescence sensing of CN−

Coumarin-based urea and urea–amide scaffolds 1–3 have been designed and synthesized for the selective and naked eye detection of cyanide ion. Of the three, compound 3 exhibits ratiometric fluorescence change selectively in the presence of CN^? and validates the rationality in designing anion receptor. Upon interaction with CN^?, the color of the solution of 3 in CH₃CN under UV exposure becomes bright yellow, which is beneficial for its naked eye detection. Addition of CN^? of ～10^?4 M brings nice color change from colourless to yellow in ordinary light. The sensing event is supposed to be due to nucleophilic addition of CN^? to the coumarin unit enabling intramolecular charge transfer (ICT) mechanism.     

A novel and synthetically facile coumarin-thiophene-derived Schiff base for selective fluorescent detection of cyanide anions in aqueous solution: Synthesis,anion interactions,theoretical study and DNA-binding properties

A colorimetric and fluorescent chemosensor (chemosensor 2) for the detection of cyanide anions in aqueous solution has been designed and synthesized in high yield. The sensing mechanism of the chemosensor was verified via UV–vis, fluorimetric, and NMR titrations, and was theoretically explained using DFT and TD-DFT calculations. The chemosensor could optically discriminate the presence of fluoride ions over other anions by a color change from yellow to red with an enhancement of pink fluorescence in DMSO. However, it showed strong green fluorescence when CN^? was added to a mixture of DMSO/water (6:4 v/v). Thus, the chemosensor can be employed in selective detecting of CN^? besides other interference anions (F^?, AcO^? and H₂PO₄^?) in aqueous solution. Moreover, 2 can be used to detect CN^? at a concentration as low as 0.32?μM, which is lower than the WHO guideline (2.7?μM) for cyanide. A low quantity of CN^? (1.08?μM) can be detected and quantified using the prepared chemosensor. Moreover, the UV–vis and fluorescence spectroscopy studies of the interactions between 2 and dublex DNA revealed intercalative binding of calf thymus DNA to the chemosensor.     

Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole‐spiropyran conjugate chemosensor molecule ( BISP ) has been synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry (ESI‐MS), and elemental analysis. The two isomeric forms ( BISP ? BIMC ) were shown to be highly selective and sensitive to CN^? among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC . The reaction of CN^? with BIMC was monitored by ¹H NMR spectroscopy, high‐resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au³⁺, Cu²⁺, Ag⁺, and Hg²⁺ with [ BIMC‐CN ] in situ showed that it acts as a secondary recognition ensemble toward Au³⁺ and Cu²⁺ by switch‐on fluorescence. In addition, a reversible logic‐gate property of BIMC has been demonstrated through a feedback loop in the presence of CN^? and Au³⁺ ions, respectively. Furthermore, the use of BIMC to detect CN^? in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN^? test kits.     

Aroyleneimidazophenazine: A Sensitive Probe for Detecting CN− Anion and its Solvatochromism Effect

A novel electron‐deficient heteroacene 15H‐pyrazino[2″,3″:3′,4′]pyrrolo[1′,2′:1,2]imidazo[4,5‐b]phenazin‐15‐one ( 1 ) has been successfully synthesized and characterized. Compound 1 can selectively recognize CN^? and F^? over other 10 anions including BF₄^?, PF₆^?, Cl^?, SO₄^2?, NO₃^?, I^?, H₂PO₄^?, ClO₄^?, Ac^?, and Br^? in CHCl₃/DMF mixed solvents with dual responses, including absorption signals and fluorescent “turn‐off” effects. CN^? and F^? can be distinguished by the completely quenched fluorescence (for CN^?) and partially reduced fluorescence (for F^?). Especially, compound 1 exhibits higher sensitivity to CN^? than F^? with the response concentration as low as 5.0 × 10^?6 mol/L. Moreover, compound 1 shows very interesting solvatochromism effect, and the CHCl₃ solution of compound 1 is sensitive to triethylamine, and its emission could change from green to red upon the addition of triethylamine, which is attributed to the n–π intermolecular charge‐transfer interaction.     

A highly selective and sensitive dual-channel chemosensor for cyanide based on sulfahydrazone derivative

A colorimetric and fluorescent cyanide probe bearing naphthol and sulfahydrazone groups has been designed and synthesized. This structurally simple probe displays a rapid response and high selectivity for cyanide in DMSO/EtOH (v/v = 2:8) solution. The addition of CN^? to the sensor p-toluenesulfonyl-2-hydroxy-1-naphthylhydrazone (L3) induced a remarkable color change from pale-yellow to yellow, and green fluorescence changed to yellow. The ¹H NMR titration and DFT calculations suggested that the selective sensing process is based on a nucleophilic addition reaction of cyanide to imine. Test strips based on sensor L3 were fabricated, which could act as a convenient and efficient test kit to detect CN^? for “in-the-field” measurements.     

Triptycene scaffolds: Synthesis and properties of triptycene-derived Schiff base compounds for the selective and sensitive detection of CN− and Cu2+

A series of triptycene-derived Schiff bases were synthesized by condensation between amino triptycenes with an appropriate aldehyde and were isolated in good to excellent (85–90%) yields. Amongst these, a triptycene-hydroxybenzaldehyde Schiff base compound proved to be a selective sensor for cyanide. It exhibited a “turn-on” fluorescence response at 490 nm to CN^? facilitated by the nucleophilic addition of CN^? to the aldehyde group, accompanied by a visible color change from orange to yellow. Likewise, a triptycene salicylaldehyde adduct was shown to be highly sensitive towards the detection of the CN^? ion with a detection limit of 0.9 μM. On the other hand a triptycene-BODIPY Schiff base compound could be used for the detection of Cu²⁺ ions over other competing, biologically relevant metal ions in acetonitrile. Photophysical studies revealed a 1:1 binding model for the triptycene-BODIPY compound.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

A highly selective chemosensor derived from benzamide hydrazones for the detection of cyanide ion in organic and organic-aqueous media: design,synthesis, sensing and computational studies

ABSTRACT

A new, highly sensitive and selective chemosensing method has been developed for the detection of cyanide ion using benzamide hydrazone receptors (R1-R4). The sensing ability of these compounds towards CN^? in the presence of Br ^?, HSO₄ ^?, Cl^?, OH^?, I^?, F^?, AcO^?, NO₂ ^? and NO₃ ^? in DMF and DMF-Aqueous mixture (DMF:H₂O, 9:1 v/v) was investigated. The binding characteristics of the probe with cyanide ions carried out by ¹ H NMR titrations indicated the deprotonation of N-H group through H-bond interactions between benzamide hydrazones and cyanide ions; it has been theoretically supported by DFT. The binding constant (Ka) and stoichiometry of the host–guest complex formed was calculated by the Benesi–Hildebrand (B–H) plot, and strong interaction of the probe with CN^- ions forming a 1:2 binding stoichiometry has been noted in this study. In a DMF and aqueous medium for CN^? ion, the lower limit of detection (LOD in ppm) is compared to the limit of quantification (LOQ in ppm), which is quite better in terms of sensitivity.     

Schiff base derived from salicylaldehyde‐based azo dye as chromogenic anionic sensor and specific turn‐on emission sensor for cyanide ion

A novel Schiff base has been derived from condensing 4‐aminoantipyrine with diazotized salicylaldehyde. The derived compound acted as a colorimetric sensor for hazardous aqueous anions like CN^?, F^?, and CH₃COO^? among a list of anions. The colorimetric changes were further verified through absorption titrations. The detection limits were of the order of 10^?10 M, which makes the sensor significant. The interaction of the anions with the sensor was stoichiometrically 1:1 with good binding constants. The sensor turns out to be a specific turn‐on emission sensor for CN^? even in competitive environments. The F^? ion sensing ability was extended to the determination of F^? in a commercial toothpaste with good results.     

A Turn‐On Fluorescence Chemosensor for Cyanide in Aqueous Media Based on a Nucleophilic Addition Reaction

We synthesized a new cyanide (CN ⁻) chemosensor CX based on a nucleophilic addition reaction prompted by cyanide ion, which could be used for highly selective and sensitive fluorescence turn‐on detection of cyanide in aqueous media. The CX showed selective fluorescence recognition for CN ⁻, the miscellaneous competitive anions (F⁻, Cl⁻, Br⁻, I⁻, AcO ⁻, H₂PO₄⁻, HSO₄⁻, ClO₄⁻, S^{2 −}, PO₄³⁻, CO₃²⁻ and SCN ⁻) did not lead to any significant interference. The detection limit of the sensor towards CN ⁻ is 1.15 × 10⁻⁷ mol•L⁻¹. The sensor has been successfully applied to estimate the cyanide ion in seeds of cherries. Test strips based on CX were fabricated, which could be used as a convenient and efficient CN ⁻ test kit to detect CN ⁻ in aqueous solution for “in‐the‐field” measurement.     

A Novel Potentiometric Membrane Sensor Based on Aryl Palladium Complex for Selective Determination of Thiocyanate in the Saliva and Urine of Cigarette Smokers

A highly selective potentiometric sensor for thiocyanate ion based on the use of a newly synthesized organo‐palladium ion exchanger complex dispersed in a plasticized poly(vinyl chloride) membrane is described. The sensor displays a Nernstian response (?57.8±0.2 mV decade^?1) over a wide linear concentration range of thiocyanate (1.0×10^?6–1.0×10^?1 mol L^?1 ), low detection limit (6.3×10^?7 mol L^?1), fast response (20 s), stable potential readings (±0.4 mV), good reproducibility (±0.9%), long term stability (8 weeks), high precision (±0.7%) and applicability over a wide pH range (4–10). Negligible interferences are caused by F^?, Cl^?, I^?, Br^?, NO₃^?, NO₂^?, CN^?, SO₄^2?, S₂O₃^2?, PO₄^3?, citrate, acetate and oxalate ions. Under hydrodynamic mode of operation (FIA), the calibration slope is ?51.1±0.1 mV decade^?1, the linear response range is 1.0×10^?5–1.0×10^?1 mol L^?1 SCN^? and the sample throughput is 40–45 per hour. The sensor is satisfactory used for manual and flow injection potentiometric determination of SCN^? in the saliva and urine of cigarette smokers and non smokers. The data agree fairly well with results obtained by the standard spectrophotometric technique. Direct potentiometry and potentiometric titration of SCN^? with Ag⁺ are also monitored with the sensor.     

A coumarin based highly selective fluorescent chemosensor for sequential recognition of Cu2+ and PPi

In this study, we have successfully synthesized a new coumarin based fluorescent chemosensor 1, in which tren and quinolone are introduced as receptors for sequential recognition of Cu²⁺ and PPi. The structure of chemosensor 1 was characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. Sensor 1 showed an obvious “on-off” fluorescence quenching response toward Cu²⁺, and the quenching efficiency reached a maximum of 99.6% with the addition of 20 equiv. of Cu²⁺. The 1-Cu²⁺ complex showed an “off-on” fluorescence enhancement response toward PPi over many competitive anions, especially HPO₄^2? and H₂PO₄^?. The detection limit of sensor 1 was 1.9?×?10^?6?M to Cu²⁺ and 5.96?×?10^?8?M to PPi. In addition, sensor 1 showed a 1:1 binding stoichiometry to Cu²⁺ and sensor 1-Cu²⁺ showed a 2: 1 binding stoichiometry to PPi in CH₃CN/HEPES buffer medium (9:1 v/v, pH?=?7.4). The stable pH range of sensor 1 to Cu²⁺ and 1-Cu²⁺ to PPi was from 4 to 8.     

Novel Fluorescent Chemosensor for Detection of F− Anions Based on a Single Functionalized Pillar[5]arene Iron(III) Complex

Novel fluorescent chemosensor with good selectivity for F^? anion was designed and synthesized. The sensor has a bearing on a single functionalized pillar[5]arene and Fe³⁺ metal complex (PN‐Fe), which showed prominent fluorescent response for F^? anion over other common anions (Cl^?, Br^?, I^?, AcO^?, HSO4^?, H₂PO₄^?, ClO₄^?, CN^? and SCN^?). These results were evaluated by fluorescent method. The detection limit of PN‐Fe to F^? was calculated to be 2.50×10^?7 mol/L. Moreover, the sensor PN‐Fe³⁺ might serve as a recyclable component in sensing materials.     

Reaction‐Based Colorimetric and Ratiometric Fluorescence Sensor for Detection of Cyanide in Aqueous Media

A stilbene‐based compound ( 1 ) has been prepared and was highly selective for the detection of cyanide anion in aqueous media even in the presence of other anions, such as F^?, Cl^?, Br^?, I^?, ClO₄^?, H₂PO₄^?, HSO₄^?, NO₃^?, and CH₃CO₂^?. A noticeable change in the color of the solution, along with a prominent fluorescence enhancement, was observed upon the addition of cyanide. The color change was observed upon the nucleophilic addition of the cyanide anion to the electron‐deficient cyanoacrylate group of 1 . The spectral changes induced by the reaction were analyzed by comparison with two model compounds, such as compound 2 with dimethyl substituents and compound 3 without a cyanoacrylate group. An intramolecular charge‐transfer (ICT) mechanism played a key role in the sensing properties, and the mechanism was supported by DFT/TDDFT calculations.     

A Fluorescent Chemosensor for Dihydrogen Phosphate Ion Based on 2‐[2‐Hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine‐Fe3+ Ensemble

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H₂PO₄^? ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe³⁺ ion, Fe³⁺ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY‐Fe³⁺ ensemble could recover the quenched fluorescence upon the addition of H₂PO₄^? anion resulting in an off‐on‐type sensing with a detection limit of micromolar range in the same medium, and other anions, including F^?, Cl^?, Br^?, I^?, AcO^?, HSO₄^?, ClO₄^? and CN^? had nearly no influence on the probing behavior. The test strips based on 2‐[2‐hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine and Fe³⁺ metal complex ( GY‐Fe³⁺ ) were fabricated, which could act as convenient and efficient H₂PO₄^? test kits.     

Differential Detection of Zn2+ and Cd2+ Ions by BODIPY‐Based Fluorescent Sensors

Two monostyryl BODIPY derivatives that contain one or two bis(hydroxyamido)amino group(s) as the metal chelator have been prepared. The effects of various metal ions on their electronic absorption and fluorescence properties have been studied in detail in MeCN or in phosphate buffered saline (PBS). The results show that the derivative with two hydroxyamide chains can selectively detect Zn²⁺ ions in MeCN. The compound and ions bind in a 1:1 stoichiometry with an association constant of 2.2(±0.1)×10⁴ M ^?1. The intensity of the fluorescence emission increases remarkably and is substantially blue‐shifted from 624 to 572 nm, owing to the inhibition of intramolecular charge transfer, thus allowing its use as a ratiometric fluorescent sensor for Zn²⁺ ions. The derivative with four hydroxyamide chains behaves differently: It responds selectively toward Cd²⁺ ions in phosphate buffered saline. The compound and ions bind in a 1:2 stoichiometry, with first and second association constants of 4.4(±0.9)×10⁴ M ^?1 and 1.3(±0.1)×10⁴ M ^?1, respectively. Upon the addition of 80 equivalents of Cd²⁺ ions, the fluorescence quantum yield increases 15‐fold. Both of these compounds exhibit differential sensing of Zn²⁺ and Cd²⁺ ions and the associated color changes can be easily seen by the naked eye.     

A new benzimidazolium incorporated chemodosimeter affording dual chromogenic and fluorescence switch-on signaling for the selective targeting of cyanide

We have designed and synthesized a new chemodosimeter, Benzolin-A, which selectively responds to toxic cyanide by dual colorimetric and fluorescence turn-on responses in buffered aqueous DMSO. In the presence of cyanide, we observe absorbance red shift of 108 nm (color changing from colorless to yellow) and fivefold fluorescence enhancement. The ¹H NMR studies confirm the nucleophilic addition mechanism, and consistent with the experimental findings, the computational work predicts the feasibility of photoelectron transfer or energy transfer process in the native probe, as well as enhanced internal charge transfer in the Benzolin-A-cyanide adduct. Noteworthily, several background anions, such as F^?, Cl^?, AcO^?, SCN^?, HSO₄ ^?, NO₃ ^?, Br^?, I^? and H₂PO₄ ^? exhibit none or insignificant optical perturbations.     

A Highly Selective Colorimetric Sensor for Cu2+ Based on Phenolic Group Biscarbonyl Hydrazone

A novel copper selective sensor 2 based on hydrazide and salicylaldehyde has been designed and prepared. Sensor 2 behaves a single selectivity and sensitivity in the recognition for Cu²⁺ over other metal ions such as Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Zn²⁺, Pb²⁺, Cd²⁺, Ni²⁺, Co²⁺, Cr³⁺ and Mg²⁺ in DMSO. The distinct color change and the rapid changement of fluorescence emission provide naked‐eyes detection for Cu²⁺. The UV‐vis data indicate that 1:2 stoichiometry complex is formed by sensor 2 and Cu²⁺. The association constant K_s was 3.51×10⁴ mol^?1·L. The detection limitation of Cu²⁺ with the sensor 2 was 2.2×10^?7 mol·L^?1. The sensing of Cu²⁺ by this sensor was found to be reversible, with the Cu²⁺‐induced color being lost upon addition of EDTA.