Fluorescence intensity and lifetime-based cyanide sensitive probes for physiological safeguard

We characterize six new fluorescent probes that show both intensity and lifetime changes in the presence of free uncomplexed aqueous cyanide, allowing for fluorescence based cyanide sensing up to physiological safeguard levels, i.e. <30 μM. One of the probes, m-BMQBA, shows a ≈15-fold reduction in intensity and a ≈10% change in mean lifetime at this level.The response of the new probes is based on their ability to bind the cyanide anion through a boronic acid functional group, changing from the neutral form of the boronic acid group R-B(OH)₂ to the anionic R-B⁻(CN)₃ form, a new cyanide binding mechanism which we have recently reported. The presence of an electron deficient quaternary heterocyclic nitrogen nucleus, and the electron rich cyanide bound form, provides for the intensity changes observed. We have determined the disassociation constants of the probes to be in the range ≈15-84 μM³. In addition we have synthesized control compounds which do not contain the boronic acid moiety, allowing for a rationale of the cyanide responses between the probe isomers to be made.The lifetime of the cyanide bound probes are significantly shorter than the free R-B(OH)₂ probe forms, providing for the opportunity of lifetime based cyanide sensing up to physiologically lethal levels.Finally, while fluorescent probes containing the boronic acid moiety have earned a well-deserved reputation for monosaccharide sensing, we show that strong bases such as CN⁻ and OH⁻ preferentially bind as compared to glucose, enabling the potential use of these probes for cyanide safeguard and determination in physiological fluids, especially given that physiologies do not experience any notable changes in pH.     

Colorimetric detection of cyanide with N-nitrophenyl benzamide derivatives

A series of structurally simple N-nitrophenyl benzamide derivatives have been developed as chemosensors toward cyanide in aqueous environment by taking advantage of the cyanide's strong affinity toward the acyl carbonyl carbon. The high selectivity of these compounds toward CN⁻ makes it a practical system for monitoring CN⁻ concentrations in aqueous samples.     

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.     

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N,N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N,N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag-Ag interaction in [(NHC)₂]Ag⁺[AgX₂]⁻ and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis(N,N′-dibutylbenzimidazolylidene) silver complex [ with non-coordinating nitrate anion.     

A new generation of cyanide ion-selective membranes for flow injection application: part II. Comparative study of cyanide flow-injection detectors based on thin electroplated silver chalcogenide membranes

Using induced cathodic electrodeposition a number of silver chalcogenide thin layer membranes of non-trivial composition have been synthesized and their performance as ion-selective flow-injection potentiometric detectors (FIPDs) for free cyanide has been critically estimated in the context of the stringent requirements for toxic cyanide environmental monitoring. AgSCN/Ag₂S, Ag₂S, Ag_2+δSe, Ag_2+δSe_1−xTe_x (0 < δ < 0.25 and x ≈ 0.13), Ag₂Se and Ag₂Se_1−xTe_x electroplated membranes were selected for the present performance-based comparative study in order to obtain a feedback information about the effect of membrane composition. Both silver selenide and Te-doped silver selenide membranes, irrespective of their stoichiometry with respect to silver, exhibit the lowest detection limit for CN⁻ (52 ppb) with linear double-Nernstian response down to 130 ppb. The type of chalcogene anion in the membrane composition proves to exert dominant effect on the general performance characteristics of the newly developed FIPDs. The silver stoichiometry (intrinsic defects factor) and the inclusion of Te-dopant (extrinsic defects factor) have more pronounced effect on the profile of the output signal and exert moderate control on the detectors selectivity and baseline stability. This new generation of CN⁻—ion-selective membranes for FIPDs exhibits high selectivity against the common interferents present in cyanide effluents such as SCN⁻, S₂O₃²⁻, Cl⁻ and do not get poisoned in the presence of S²⁻. Moreover, their long-term stability and signal reproducibility, which make redundant the regular day-to-day calibration, coupled with the cost-effective technology for membranes preparation and easy re-generation make them attractive candidates for incorporation into automated in-field devices for in situ cyanide toxic species monitoring.     

A rapid responsive and highly selective probe for cyanide in the aqueous environment

A colorimetric and fluorescent cyanide probe based on 7-(trifluoroacetamino)coumarin has been prepared. This structurally simple probe displays rapid response and high selectivity for cyanide over other common anions in the aqueous solution. The sensing of cyanide was performed via the nucleophilic attack of cyanide anion to carbonyl of the probe with a 1:1 binding stoichiometry, which could be confirmed by Job’s plot, ¹H NMR, and MS studies. DFT/TDDFT calculations support that the fluorescence enhancement of the probe is mainly due to the ICT process improvement. The detection limit of the fluorescent assay for cyanide is as low as 0.3 μM in a rapid response of less than 30 s. Thus, the present probe should be applicable as a practical system for the monitoring of cyanide concentrations in aqueous samples.     

Selective fluorescence sensing of cyanide with an o-(carboxamido)trifluoroacetophenone fused with a cyano-1,2-diphenylethylene fluorophore

A novel fluorescence probe has been synthesized, which consists of o-(carboxamido)trifluoroacetophenone moiety as the recognition element and cyano-1,2-diphenylethylene moiety as the signaling unit. Fluorescence titrations of the probe with anions such as F⁻, Cl⁻, I⁻, CN⁻, SCN⁻, AcO⁻, , , and as their Bu₄N⁺ salts in acetonitrile show that CN⁻ is the most efficient quencher, AcO⁻ and F⁻ follow it, and other anions show little changes. In an aqueous medium, MeOH-water (9:1), the probe shows fluorescence quenching only toward cyanide and no changes toward the other anions.     

A selective quinoline-derived fluorescent chemodosimeter to detect cyanide in aqueous medium

A simple quinoline derived probe 3 has been described. Probe 3 having aldehyde function upon interaction with cyanide undergo nucleophilic addition reaction to form cyanohydrin derivative 4 in which fluorescence intensity enhances significantly, ‘turn-on’ by photoinduced electron transfer (PET) OFF–ON mechanism. The color of probe solution switched-on to fluorescent blue which is visible to the naked-eye. Job’s plot analysis revealed a 1:1 stoichiometry for an interaction between 3 and cyanide along with detection limit 0.058 μM (1.5 ppb). The mode of interaction to detect cyanide in aqueous medium through a reaction based chemodosimeter approach has been confirmed by NMR, mass, FTIR, and DFT data analysis.     

Simple Michael acceptor type coumarin derived turn-on fluorescence probes to detect cyanide in pure water

The present article describes design and synthesis of coumarin derived chemical reaction based chemodosimeter to recognize cyanide in aqueous medium. The Michael acceptor type coumarin derived probes 3 and 4 upon interaction with cyanide undergo Michael type nucleophilic addition reaction to form adducts in which fluorescence intensity was significantly enhanced, ‘turn-on’ by the change in intramolecular charge transfer (ICT) mechanism. The nonfluorescent color of solutions changed to a naked-eye sensitive fluorescent blue (switched-on). Job’s plot analysis revealed a 1:1 stoichiometry for the interaction between the probe and cyanide anion with a high detection limit.     

Dual-wavelength β-correction spectrophotometric determination of trace concentrations of cyanide ions based on the nucleophilic addition of cyanide to imine group of the new reagent 4-hydroxy-3-(2-oxoindolin-3-ylideneamino)-2-thioxo-2H-1,3-thiazin-6(3H)-one

A simple, fast, low cost and sensitive direct β-correction spectrophotometric assay of cyanide ions based on its reaction with the reagent 4-hydroxy-3-(2-oxoindolin-3-ylideneamino)-2-thioxo-2H-1,3-thiazin-6(3H)-one, abbreviated as HOTT in aqueous media of pH 7-10 is described. The electronic spectrum of the produced brown-red colored species showed well defined and sharp peak at λ_max = 466 nm. The effective molar absorptivity for the produced cyano compound was 2.5 × 10⁴ L mol⁻¹ cm⁻¹. Beer's law and Ringbom's plots were obeyed in the concentration range 0.05-2.0 and 0.30-1.5 μg mL⁻¹ cyanide ions, respectively. The proposed method offers 16.0 and 50.3 μg L⁻¹ lower limits of detection (LOD) and quantification (LOQ) of the cyanide ion, respectively. The analytical utility of the method for the analysis of cyanide ions in tap and drinking water samples was demonstrated and the results were compared successfully with the conventional cyanide ion selective electrode. The short time response and the detection by the naked eye make the method available for the detection and quantitative determination of cyanide in a variety of samples e.g. fresh and drinking water. Moreover, the structure of the produced colored species was determined with the aid of spectroscopic measurements (UV-Vis, IR, ¹H and ¹³C NMR) and elemental analysis.     

Viscosity B-coefficients of the aqueous cyanide and azide ions

A number of factors have led us to re-examine the literature assignments of the viscosity B-coefficients of the individual cyanide and azide ions in aqueous solutions at 25°C. The revised values, obtained from mutually confirmatory correlations, are: B(CN^–)=–0.020±0.007 and B(N ₃ ^– )=–0.014#±#0.006>dm³-mol^–1     

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 new generation of cyanide ion-selective membranes for flow injection application: Part III. A simple approach to the determination of toxic metal-cyanide complexes without preliminary separation

A new flow injection approach to total weak acid-dissociable (WAD) metal–cyanide complexes is proposed, which eliminates the need of a separation step (such as gas diffusion or pervaporation) prior to the detection. The cornerstone of the new methodology is based on the highly selective flow-injection potentiometric detection (FIPD) system that makes use of thin-layer electroplated silver chalcogenide ion-selective membranes of non-trivial composition and surface morphology: Ag_2 + δSe_1 − xTe_x and Ag_2 + δSe. An inherent feature of the FIP-detectors is their specific response to the sum of simple CN⁻ + Zn(CN)₄²⁻ + Cd(CN)₄²⁻. For total WAD cyanide determination, ligand exchange (LE) and a newly developed electrochemical pre-treatment procedure for release of the bound cyanide were used. The LE pre-treatment ensures complete recovery only when the sample does not contain Hg(CN)₄²⁻. This limitation is overcome by implementing electrochemical pre-treatment which liberates completely the bound WAD cyanide through cathodic reduction of the complexed metal ions. A complete recovery of toxic WAD cyanide is achieved in the concentration range from 156 μg L⁻¹ up to 13 mg L⁻¹. A three-step protocol for individual and group WAD cyanide speciation is proposed for the first time. The speciation protocol comprises three successive measurements: (i) of non-treated, (ii) LE-exchange pre-treated; (iii) electrochemically pre-treated sample. In the presence of all WAD complexes this procedure provides complete recovery of the total bound cyanide along with its quantitative differentiation into the following groups: (1) Hg(CN)₄²⁻; (2) CN⁻ + Cd(CN)₄²⁻ + Zn(CN)₄²⁻; (3) Cu(CN)₄³⁻ + Ni(CN)₄²⁻ + Ag(CN)₂⁻. The presence of a 100-fold excess in total of the following ions: CO₃²⁻, SCN⁻, NH₄⁺, SO₄²⁻ and Cl⁻ does not interferes. Thus the proposed approach offers a step ahead to meeting the ever increasing demand for cyanide-species-specific methods. The equipment simplicity makes the procedure a good candidate for implementing in portable devices for in-field cyanide monitoring.     

Indirect determination of cyanide ion and hydrogen cyanide by adsorptive stripping voltammetry at a mercury electrode

An indirect voltammetric method is described for determination of cyanide ions and hydrogen cyanide, using the effect of cyanide on cathodic adsorptive stripping peak height of Cu-adenine. The method is based on competitive Cu complex formation reaction between adenine at the electrode surface and CN⁻ ions in solution. Under the optimum experimental conditions (pH=6.42 Britton-Robinson buffer, 1×10⁻⁴ M copper and 8×10⁻⁷ M adenine), the linear decrease of the peak current of Cu-adenine was observed, when the cyanide concentration was increased from 5×10⁻⁸ to 8×10⁻⁷ M. The detection limit was obtained as 1×10⁻⁸ M for 60 s accumulation time. The relative standard deviations for six measurements were 4 and 2% for the cyanide concentrations of 5×10⁻⁸ and 2×10⁻⁷ M, respectively. The method was applied to the determination of cyanide in various industrial waste waters such as electroplating waste water and also for determination of hydrogen cyanide in air samples.     

New methods for the detection of cyanide based on displacement of the glutathione ligand of glutathionylcobalamin by cyanide

Glutathionylcobalamin (GSCbl) is a vitamin B₁₂ derivative that contains glutathione as the upper axial ligand to cobalt via a Co–S bond. In the present study, we discovered that cyanide reacted with GSCbl, generating cyanocobalamin (CNCbl) and reduced glutathione (GSH) via dicyanocobalamin (diCNCbl) intermediate. This reaction was induced specifically by the nucleophilic attack of cyanide anion displacing the glutathione ligand of GSCbl. Based on the reaction of GSCbl with cyanide, we developed new methods for the detection of cyanide. The reaction intermediate, violet-coloured diCNCbl, could be applied for naked eye detection of cyanide and the detection limit was estimated to be as low as 520 μg L^?1 (20 μM) at pH = 10.0. The reaction product, CNCbl, could be applied for a spectrophotometric quantitative determination of cyanide with a detection limit of 26 μg L^?1 (1.0 μM) at pH = 9.0 and a linear range of 26–520 μg L^?1 (1.0–50 μM). In addition, the other reaction product, GSH, could be applied for a fluorometric quantitative determination of cyanide with a detection limit of 31 μg L^?1 (1.2 μM) at pH = 9.0 and a linear range of 31–520 μg L^?1 (1.2–20 μM). These new GSCbl-based methods are simple, highly specific and sensitive with great applicability for the detection of cyanide in biological and non-biological samples.     

Pneumatopotentiometric determination of nanogram amounts of cyanide

Hydrogen cyanide is liberated from aqueous samples by reaction with sulphuric acid and transferred by a stream of nitrogen to a silver porous membrane electrode. Some HCN passes through the membrane into an alkaline dicyanoargentate solution; the cyanide ion produced causes a decrease in the equilibrium Ag⁺ concentration and the change of potential is related to the amount of cyanide in the sample. The detection limit is 3.0 ng ml^?1 cyanide in the injected solution; the relative standard deviation is 0.82% for 17 ng of cyanide. Sulphide interferes (as H₂S) but can be removed on a lead acetate column.     

Sequential flow-injection determination of cyanide and weak metal—cyanide complexes with flow-through heterogeneous membrane electrodes

Free cyanide and cyanide present in weak complexes are determined by using two flow- through silver iodide/silver sulphide electrodes with an intervening gas diffusion unit. Under optimal conditions, the linear range is 10^?5?10^?3 mol dm^?3 cyanide, and the relative standard deviations are ca. 2%, with a sampling rate of 20 h^?1. Total cyanide can be determined in the presence of Zn(II), Cu(II) and Cd(II) but results are low with Ni(II), Co(II) or Fe(III) present. Sulphide and thiocyanate must be absent.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

A kinetic study on the bioremediation of sodium cyanide and acetonitrile by free and immobilized cells ofPseudomonas putida

Pseudomonas putida capable of utilizing organic nitrile (acetonitrile) and inorganic cyanide (sodium cyanide) as the sole source of carbon and nitrogen was isolated from contaminated industrial sites and waste water. The bacterium possesses nitrile aminohydrolase (EC 3.5.5.1) and amidase (EC 3.5.1.4), which are involved in the transformation of cyanides and nitriles into ammonia and CO₂ through the formation of amide as an intermediate. Both of the enzymes have a high selectivity and affinity toward the⁻Cn group. The rate of degradation of aceotnitrile and sodium cyanide to ammonia and CO₂ by the calcium-alginate immobilized cells ofP. putida was studied. The rate of reaction during the biodegradation of acetonitrile and sodium cyanide, and the substrate- and product-dependent kinetics of these toxic compounds were studied using free and immobilized cells ofP. putida and modeled using a simple Michaelis-Menten equation.