The benzil-cyanide reaction and its application to the development of a selective cyanide anion indicator

Unexpected Direct Synthesis of Tunable Redox-Active Benzil-Linked Polymers via the Benzoin Reaction

Strategies for the sustainable synthesis of redox-active organic polymers could lead to next-generation organic electrode materials for electrochemical energy storage, electrocatalysis, and electro-swing chemical separations. Among redox-active moieties, benzils or aromatic 1,2-diones are particularly attractive due to their high theoretical gravimetric capacities and fast charge/discharge rates. Herein, we demonstrate that the cyanide-catalyzed polymerization of simple dialdehyde monomers unexpectedly leads to insoluble redox-active benzil-linked polymers instead of the expected benzoin polymers, as supported by solid-state nuclear magnetic resonance spectroscopy and electrochemical characterization. Mechanistic studies suggest that cyanide-mediated benzoin oxidation occurs by hydride transfer to the solvent, and that the insolubility of the benzil-linked polymers protects them from subsequent cyanolysis. The thiophene-based polymer poly(BTDA) is an intriguing organic electrode material that demonstrates two reversible one-electron reductions with monovalent cations such as Li+ and Na+ but one two-electron reduction with divalent Mg2+. As such, the tandem benzoin-oxidation polymerization reported herein represents a sustainable method for the synthesis of highly tunable and redox-active organic materials.

Nucleophilic Approach to Cyanide Sensing by Chemosensors

Cyanide anion has wide use in industrial areas; however, it has a high toxic effect on the environment as waste. Moreover, plant seeds contain cyanide that is often consumed by human beings. Therefore, many studies are carried out to determine cyanide. Especially, optical sensors showing colorimetric and fluorimetric changes have been of considerable interest due to their easy, cheap, and fast responses. This review discusses recent developments in the colorimetric and fluorimetric detection of cyanide by nucleophilic addition to different types of receptors via the chemodosimeter approach. The sensitivity and selectivity of the sensors have been reviewed for changes in absorption and fluorescence, naked-eye detection, real sample application, and detection limits when interacting with cyanide.

An ICT-guided ratiometric naphthalene-benzothiazole-based probe for the detection of cyanide with real-time applications in human breast cancer cells

A methoxynaphthalene benzothiazole conjugate (MNBTZ) armed with CC vinylic double bonds was synthesized and utilized for the selective detection of CN^- ions. The probe showed yellow fluorescence due to ICT from the methoxynaphthalene moiety to benzothiazole, which instantly changed to light purple upon the nucleophilic addition of CN^- to the vinylic double bond, inhibiting ICT due to the break-in conjugation. The effectiveness of the probe was proved by this brilliant ratiometric fluorescence change, which was achieved selectively as observed by experiments with competing anions. ¹H NMR titrations and DFT calculations support this mechanism. A low detection limit of 2.1(±0.0022) × 10^-8 M along with good fluorescence color change on solid TLC plates and human breast cancer cells makes it amenable to CN^- sensing.

Cucurbit[8]uril-Assisted Nucleophilic Reaction: A Unique Supramolecular Approach for Cyanide Detection and Removal from Aqueous Solution

A unique supramolecular approach of preparing and using a cucurbit[8]uril (Q[8])-based dynamic host-guest assembly for cyanide sensing in and removal from water has been successfully developed. The dicyanovinyl-attached cationic guest (1) was designed as the fluorescent response moiety for the detection of the cyanide anion via a nucleophilic addition reaction in the assist of the Q[8]-based 2:2 quaternary complexes. Furthermore, the reaction of cyanide with 1 further switched the Q[8]-based host-guest assemblies from the 2:2 complexes to the 1:1 supramolecular polymers that precipitate in water. Thus, the macrocyclic-based dynamic host-guest assembly has potential use in applications for solving the problem of toxic anion pollutants present in aqueous environments.

Pyrene-Hydrazone-π···Hole Coupled Turn-on Fluorescent and Naked- Eye Colorimetric Sensor for Cyanide: Role of Homogeneous π-Hole Dispersion in Anion Selectivity

A pyrene based probe associated with π···hole - hydrazone as one of the recognizing elements is synthesized and its turn in to a selective colorimetric and turn-on fluorescent sensor, (L³) for cyanide anion. This chemo sensor show high selectivity towards cyanide anion through photo electron transfer (PET) mechanism. The binding strength and sensitivity of the chemo sensor L³ towards cyanide are found to be 2.0 X 10⁴, and 4.44 x 10^-4 respectively. We have compared this high selectivity of the receptor towards cyanide, with our previously reported receptors L¹ and L². The detailed UV-Vis, Emission, ¹H-NMR, IR spectroscopic and Molecular Electrostatic Potential (MEP) studies reveals that the homogeneous π···hole dispersion in the aromatic ring governing the selectivity of the receptor towards cyanide anion. Such a positive π···hole homogeneous dispersion is missing in the case of sensor L², instead we have polarized π···hole dispersion towards 2^nd and 4^th position of di-nitrophenyl chromophoric unit in L².

Fluorescent Sensor for Copper(II) and Cyanide Ions via the Complexation-Decomplexation Mechanism with Di(bissulfonamido)spirobifluorene

A novel spirobifluorene derivative bearing two bissulfonamido groups is successfully synthesized by Sonogashira coupling. This compound exhibits a strong fluorescence quenching by Cu(II) ion in a 50% mixture between acetonitrile and 20 mM pH 7.0 N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer with a detection limit of 98.2 nM. However, this sensor also shows ratiometric signal shifts from blue to yellow in the presence of Zn(II), Pb(II), and Hg(II) ions. The static quenching mechanism is verified by the signal reversibility using ethylenediaminetetraacetic acid (EDTA) and the Stern-Volmer plots at varying temperatures. The Cu(II)-spirobifluorene complex shows a highly selective fluorescence enhancement upon the addition of CN- ion with the detection limit of 390 nM. The application of this complex for quantitative analysis of spiked CN- ion in real water samples resulted in good recoveries.

Cyanobiphenyl-spiropyrane and -hemicyanine conjugates for cyanide detection in organic/aqueous media through reverse ICT direction: Their practical applications

Cyanide is one of the most known toxic substances. It is used in many industries and threats human health and environment through releasing with wastewater. Therefore, it is very important to detect its accurate amount, rapidly. Herein, turn-on and turn-off fluorescence sensors of hybrid cyanobiphenyl-spiropyrane and -hemicyanine were developed for the detection of CN^- ions on the basis of nuchleophilic addition to indolium moiety. Detection behavior of the both probes toward a series of anions was investigated by means of fluorescence, UV-vis, NMR and TOF-MS techniques. The results obviously indicate that both probes show remarkable spectral changes and high selectivity toward CN^- with respect to other tested anions. Cyanide levels in water samples up to 0.208 μM could be quantitatively detected as practical application. A smartphone imaging application was successfully constructed for CN^- detection. Noticeably, production of cotton kids and PSF capsules revealed that the probe could be conveniently used for on-site measurement of cyanide without complicated instruments.

Rational Design of an ICT-Based Chemodosimeter with Aggregation-Induced Emission for Colorimetric and Ratiometric Fluorescent Detection of Cyanide in a Wide pH Range

An alkoxy-substituted 1,3-indanedione-based chemodosimeter 1 with an aggregation-induced emission (AIE) characteristic was rationally designed and synthesized for the ultrasensitive and selective sensing of cyanide in a wide pH range of 3.0-12.0. The nucleophilic addition of cyanide to the β-conjugated carbon of the 1,3-indanedione group obstructs intramolecular charge transfer (ICT) and causes a significant change in the absorption and fluorescence spectra, enabling colorimetric and ratiometric fluorescent detection of cyanide in a 90% aqueous solution. The cyanide-sensing mechanism is supported by single-crystal X-ray diffraction analysis, time-dependent density functional theory (TD-DFT) calculations, and 1H NMR titration experiments. Sensor 1 exhibits strong yellow fluorescence in the solid state due to the AIE effect, and the paper probes containing 1 can be conveniently used to sense cyanide by the naked eye. Furthermore, chemodosimeter 1 was successfully used for sensing cyanide in real environmental water samples.

Name reactions: strategies in the design of chemodosimeters for analyte detection

The design and synthesis of suitable chemodosimeters for the detection of toxic analytes has become challenging for new researchers nowadays in the molecular recognition field.

An Unsymmetric Salamo-like Chemosensor for Fuorescent Recognition of Zn2+

A new unsymmetric tetradentate salamo-like chemical sensor H₂L for fluorescent recognition of Zn²⁺ has been designed and synthesized. The sensor can recognize Zn²⁺ from other metal ions examined with selectivity, anti-interference, reliability and high sensitivity (LOD = 1.89 × 10^-6 M) in ethanol/H₂O solution. The results of UV-Vis and fluorescent spectra analyses, X-ray crystallographic study and DMol³ simulation and calculation (on Materials Studio) indicate that the chelation-enhanced fluorescence (CHEF) recognition mechanism of the sensor H₂L for Zn²⁺ is of its hindered PET process. The sensor H₂L for Zn²⁺ has excellent fluorescence characteristics and has potential application value in biological and environmental systems.

A molecular phototropic system for cyanide: Detection and sunlight driven harvesting of cyanide with molecular sunflower

We are reporting a simple, easy to prepare, and conformation switchable first molecular phototropic system L, "(E)-2-(2,4-dinitrophenyl)-1-((pyren-8-yl)methylene)hydrazine, for cyanide harvesting. This molecular phototropic system behaves as a molecular sunflower in which the conformation of this molecular sunflower can be altered in response to the sunlight. This molecular flower can sense and bind the cyanide anion colorimetrically through its transition state. Further, upon exposure of this transition state cyanide complex 1, under sunlight, this system is capable to release the bound cyanide via -C=N- free rotation to reach its lower energy stable conformation. Similar behaviors were observed for acetate and fluoride with L. The strength of the phototropic system L towards cyanide, acetate and fluoride is found to be 4.5 × 10⁵, 1.53 × 10² and 6.09 × 10² M^-1.

An Efficient Probe of Cyclometallated Phosphorescent Iridium Complex for Selective Detection of Cyanide

A cyclometallated phosphorescent iridium-based probe to detect CN^- was prepared through a cyanide alcoholize reaction based on the C^N type main ligand and N^N type ancillary ligand (2-phenyl pyridine and 1,10-phenanthroline-5-carboxaldehyde, respectively). The efficient probe exhibited good sensitivity in response to CN^- in an CH₃CN and H₂O (95/5) mixture within a 1.23 μM detection limit. The response of PL is directly in line with the concentration of CN^- from 0 to 2.0 equiv. The PL investigation of other reactive anions proved the great selectivity to CN^-. Additionally, upon adding 1.0 equiv. of cyanide, the formation of cyanohydrin was correctly elucidated in ¹H NMR, FT-IR, and mass spectra studies. The conspicuous results indicate that the iridium complex has the potential possibility of application in other biosystems related to CN^-.

Two highly sensitive and efficient salamo-like copper(II) complex probes for recognition of CN. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020;228:117775. [PMID: 31718968 DOI: 10.1016/j.saa.2019.117775]

Two salamo-like copper(II) complex probes, L¹-Cu²⁺ and L²-Cu²⁺, were designed and synthesized for sensitive and efficient identification of CN^-. UV spectroscopy, high resolution mass spectrometry, RGB analysis and naked eye recognition were performed to explore their recognition mechanisms. High resolution mass spectra indicated that the probes L¹-Cu²⁺ and L²-Cu²⁺ formed complexes with CN^-. The two probes could recognize CN^- by the naked eye and the color of the solution changed from light yellow to red. In terms of application, the contents of CN^- in the environmental water samples were tested. In addition, the optimal pH ranges for probe detection of CN^- were investigated by pH value measurement.

Directional Approach to Enantiomerically Enriched Functionalized [7]Oxa-helicenoids and Groove-Based Selective Cyanide Sensing

Several regioselective functionalized mono- and disubstituted [7]oxa-helicenoids have been synthesized in the enantiomerically enriched (90-99% ee) form. These functionalized helicenoids exhibited pronounced spectral and chiroptical properties suitable for sensing applications. In particular, corresponding helicenoid's mono and dialdehydes have been effectively used as chemodosimeters for selective detection of cyanide anions over other anions, while simple aromatic aldehydes do not function as cyanide sensors. The groove available in the helical host plays a crucial role in the sensing. The enantiomerically enriched nature of the sensors allows the use of electronic circular dichroism as an uncommon detection tool for cyanide anions, along with conventional fluorescence and NMR methods.

Chromogenic hydrazide Schiff base reagent: Spectrophotometric determination of CN- ion

A Schiff base reagent, Picolinohydrazide-naphthol (HL), is used for trace level detection of toxic CN^- selectively in presence of eighteen other anions (SCN^-, OCN^-, S₂O₃^2-, HPO₄^2-, H₂PO₄^-, I^-, ClO₄^-, HSO₄^-, SO₄^2-, AsO₄^3-, NO₂^-, AsO₂^-, Cl^-, F^-, HF₂^-, NO₃^-, Br^-, N₃^-) by visual color change, colorless to yellow, in DMSO/H₂O (9:1, v/v) at pH, 7.2 (HEPES buffer) medium. The sensitivity of the probe shows that the limit of detection (LOD) is 7.08 μM. The probable mechanism for the sensing behavior involves the deprotonation of naphthol-OH by CN^- that has been authenticated by ¹H NMR titration and Mass spectra. The composition (1:1 mol ratio) is supported by Job's plot and binding constant (K_a, 1.5 × 10⁴ M^-1) is reported by Benesi-Hildebrand plot. Furthermore, a simple paper strip device is fabricated for the determination of CN^- ion in water. DFT computation is carried out to explain the electronic spectral feature of the sensor.

Catalytic Deacetylation of p-Nitrophenyl Thioacetate by Cyanide Ion and Its Sensor Applications

We demonstrated a simple and rapid deacetylation reaction of p-nitrophenyl thioacetate by cyanide ion. This reaction is caused by the strong nucleophilic tendency of the cyanide ion to the electrophilic substrate and has been previously reported as the most common method for detecting cyanide ions. Tetrabutylammonium cyanide and sodium cyanide can be used as sources of cyanide ions for catalytic deacetylation reactions. Both catalysts showed almost the same catalytic reaction and the catalytic reaction was instantaneous at room temperature with a minimum concentration of cyanide ions of up to 1.0 μM. Cyanide did not catalyze the deacetylation reaction of p-nitropnenyl acetate due to a decrease in the nucleofugality of the leaving group and a decrease in the electrophilicity of carbonyl carbon in the substrate. However, the only disadvantage of this reaction system is the interference with other anions, such as acetate and azide, which also have nucleophilicity toward an electrophilic substrate. If these problems are improved, the system could be applied as a very efficient cyanide ion sensor.

Azaindole-BODIPYs: Synthesis, fluorescent recognition of hydrogen sulfate anion and biological evaluation

The synthesized and sensing capability of two novel azaindole substituted mono and distyryl BODIPY dyes against bisulfate anion were reported. Structural characterizations of the targeted compounds were conducted by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, ¹H and ¹³C NMR spectroscopies. Photophysical properties of the azaindole substituted BODIPY compounds were investigated employing absorption and fluorescence spectroscopies in acetonitrile solution. It was found that the final compounds 3 and 4 exhibited exclusively selective and sensitive turn-off sensor behavior on HSO₄^- anion. Additionally, the stoichiometry ratio of the targeted compounds to bisulfate anion was measured 0.5 by Job's method. Also, density function theory was performed to the optical response of the sensor for targeted compounds. Furthermore, the cytotoxicity of Azaindole-BODIPYs was examined against living human leukemia K562 cell lines.

A Mitochondria-Specific Fluorescent Probe for Visualizing Endogenous Hydrogen Cyanide Fluctuations in Neurons

An ability to visualize HCN in mitochondria in real time may permit additional insights into the critical toxicological and physiological roles this classic toxin plays in living organisms. Herein, we report a mitochondria-specific coumarin pyrrolidinium-derived fluorescence probe (MRP1) that permits the real-time ratiometric imaging of HCN in living cells. The response is specific, sensitive (detection limit is ca. 65.6 nM), rapid (within 1 s), and reversible. Probe MRP1 contains a benzyl chloride subunit designed to enhance retention within the mitochondria under conditions where the mitochondria membrane potential is eliminated. It has proved effective in visualizing different concentrations of exogenous HCN in the mitochondria of HepG2 cells, as well as the imaging of endogenous HCN in the mitochondria of PC12 cells and within neurons. Fluctuations in HCN levels arising from the intracellular generation of HCN could be readily detected.

Two benzoyl coumarin amide fluorescence chemosensors for cyanide anions

Two new benzoyl coumarin amide derivatives with ortho hydroxyl benzoyl as terminal group have been synthesized. Their photophysical properties and recognition properties for cyanide anions in acetonitrile have also been examined. The influence of electron donating diethylamino group in coumarin ring and hydroxyl in benzoyl group on recognition properties was explored. The results indicate that the compounds can recognize cyanide anions with obvious absorption and fluorescence spectral change and high sensitivity. The import of diethylamine group increases smartly the absorption ability and fluorescence intensity of the compound, which allows the recognition for cyanide anions can be observed by naked eyes. The in situ hydrogen nuclear magnetic resonance spectra combining photophysical properties change and job's plot data confirm that Michael addition between the chemosensors and cyanide anions occurs. Molecular conjugation is interrupted, which leads to fluorescence quenching. At the same time, there is a certain extent hydrogen bond reaction between cyanide and hydroxyl group in the compounds, which is beneficial to the recognition.

Lanthanide Complexes that Respond to Changes in Cyanide Concentration in Water

Cyanide ions are shown to interact with lanthanide complexes of phenacylDO3A derivatives in aqueous solution, giving rise to changes in the luminescence and NMR spectra. These changes are the consequence of cyanohydrin formation, which is favored by the coordination of the phenacyl carbonyl group to the lanthanide center. These complexes display minimal affinity for fluoride and can detect cyanide at concentrations less than 1 μm. By contrast, lanthanide complexes with DOTAM derivatives display no affinity for cyanide in water, but respond to changes in fluoride concentration.

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.

Accelerated hydration reaction of an unsymmetrical tolan evidenced by a Hg(ii)-trapped macrocycle and its application as a Hg(ii)-selective indicator

Hg(ii)-mediated hydration reactions of unsymmetrical quinoline type tolans were studied. The observed accelerated reactions of the tolans rely on the additional binding motifs of the tolan, as supported by the X-ray structure of the macrocycle (2b). The analyte-specific reaction allows us to detect Hg(ii) in buffered media.

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium(III) complex, bis[2',6'-difluorophenyl-4-formylpyridinato-N,C4']iridium(III) (picolinate) (IrC), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN(-) on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed IrC was authenticated by single-crystal X-ray diffraction. Notably, the iridium(III) complex exhibits intense red phosphorescence in the solid state at 298 K (ΦPL = 0.16) and faint emission in acetonitrile solution (ΦPL = 0.02). The cyanide anion binding properties with IrC in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV-vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium(III) complex in acetonitrile (c = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of IrC at 480 nm was dramatically enhanced ∼5.36 × 10(2)-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10(-8) M. The cyanohydrin formation mechanism is further supported by results of a (1)H NMR titration of IrC with CN(-). As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with IrC for the trace detection of CN(-) in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium(III) complex probe and its cyanide adduct.

Ratiometric and colorimetric "naked eye" selective detection of CN(-) ions by electron deficient Ni(II) porphyrins and their reversibility studies

Highly electron deficient β-substituted Ni(II) porphyrins (1-5) were synthesized and utilized as novel sensors for selective rapid visual detection of CN(-) ions. This article describes the single crystal X-ray structures, electronic spectral and electrochemical redox properties of these sensors. The ratiometric and colorimetric responses of these porphyrins were monitored by the change in optical absorption spectra. These sensors were found to be highly selective for cyanide ions with extremely high binding constants (10(16)-10(8) M(-2)) through axial ligation of CN(-) ions and are able to detect <0.11 ppm of CN(-) ions. 1-5 were recovered from 1-5·2CN(-) adducts by acid treatment and reused without loss of sensing ability. CN(-) binding strongly perturbs the redox properties of the parent porphyrin π-system. The applicability of 1-5 as practical visible colorimetric test kits for CN(-) ions in aqueous and non-aqueous media has also been explored. The mode of binding was confirmed by single crystal X-ray, spectroscopic studies and DFT calculations.