Showing papers on "Cyanide published in 2001"

Pseudomonas aeruginosa PAO1 kills Caenorhabditis elegans by cyanide poisoning.

Abstract: In this report we describe experiments to investigate a simple virulence model in which Pseudomonas aeruginosa PAO1 rapidly paralyzes and kills the nematode Caenorhabditis elegans . Our results imply that hydrogen cyanide is the sole or primary toxic factor produced by P. aeruginosa that is responsible for killing of the nematode. Four lines of evidence support this conclusion. First, a transposon insertion mutation in a gene encoding a subunit of hydrogen cyanide synthase ( hcnC ) eliminated nematode killing. Second, the 17 avirulent mutants examined all exhibited reduced cyanide synthesis, and the residual production levels correlated with killing efficiency. Third, exposure to exogenous cyanide alone at levels comparable to the level produced by PAO1 killed nematodes with kinetics similar to those observed with bacteria. The killing was not enhanced if hcnC mutant bacteria were present during cyanide exposure. And fourth, a nematode mutant ( egl-9 ) resistant to P. aeruginosa was also resistant to killing by exogenous cyanide in the absence of bacteria. A model for nematode killing based on inhibition of mitochondrial cytochrome oxidase is presented. The action of cyanide helps account for the unusually broad host range of virulence of P. aeruginosa and may contribute to the pathogenesis in opportunistic human infections due to the bacterium.

A plasma membrane-bound enzyme of tobacco roots catalyses the formation of nitric oxide from nitrite.

Abstract: Purified plasma membranes (PMs) of tobacco (Nicotiana tabacum L. cv. Samsun) roots exhibited a nitrite-reducing enzyme activity that resulted in nitric oxide (NO) formation. This enzyme activity was not detected in soluble protein fractions or in PM vesicles of leaves. At the pH optimum of pH 6.0, nitrite was reduced to NO with reduced cytochrome c as electron donor at a rate comparable to the nitrate-reducing activity of root-specific succinate-dependent PM-bound nitrate reductase (PM-NR). The hitherto unknown PM-bound nitrite: NO-reductase (NI-NOR) was insensitive to cyanide and anti-NR IgG and thereby proven to be different from PM-NR. Furthermore, PM-NR and NI-NOR were separated by gel-filtration chromatography and apparent molecular masses of 310 kDa for NI-NOR and 200 kDa for PM-NR were estimated. The PM-associated NI-NOR may reduce the apoplastic nitrite produced by PM-NR in vivo and may play a role in nitrate signalling via NO formation.

Human myeloperoxidase: structure of a cyanide complex and its interaction with bromide and thiocyanate substrates at 1.9 A resolution.

Abstract: The 1.9 A X-ray crystal structure of human myeloperoxidase complexed with cyanide (R = 0.175, Rfree = 0.215) indicates that cyanide binds to the heme iron with a bent Fe−C−N angle of ∼157°, and binding is accompanied by movement of the iron atom by 0.2 A into the porphyrin plane. The bent orientation of the cyanide allows the formation of three hydrogen bonds between its nitrogen atom and the distal histidine as well as two water molecules in the distal cavity. The 1.85 A X-ray crystal structure of an inhibitory complex with thiocyanate (R = 0.178, Rfree = 0.210) indicates replacement of chloride at a proximal helix halide binding site in addition to binding in the distal cavity in an orientation parallel with the heme. The thiocyanate replaces two water molecules in the distal cavity and is hydrogen bonded to Gln 91. The 1.9 A structures of the complexes formed by bromide (R = 0.215, Rfree = 0.270) and thiocyanate (R = 0.198, Rfree = 0.224) with the cyanide complex of myeloperoxidase show how the presenc...

Method for producing double metal cyanide (dmc) catalysts

Abstract: The invention provides an improved process for the preparation of double metal cyanide (DMC) catalysts for the preparation of polyether polyols by polyaddition of alkylene oxides on to starter compounds containing active hydrogen atoms, in which aqueous solutions of a metal salt and a metal cyanide salt are first reacted in the presence of an organic complexing ligand and optionally one or more further complex-forming components to form a DMC catalyst dispersion, this dispersion is then filtered, the filter cake is subsequently washed with one or more aqueous or non-aqueous solutions of the organic complexing ligand and optionally one or more further complex-forming components by a filter cake washing and the washed filter cake is finally dried, after an optional pressing out or mechanical removal of moisture.

A kinetic study that compares the leaching of gold in the cyanide, thiosulfate, and chloride systems

Abstract: Due to the increasing environmental and public concerns over cyanidation, there has been a large amount of research into viable alternative lixiviants. This article presents a detailed kinetic study of gold leaching in cyanide, ammonia/thiosulfate, and chloride/hypochlorite solutions. The gold leach rates were measured using a rotating electrochemical quartz crystal microbalance (REQCM). This instrument allows the mass of a gold sample to be measured in situ, with a sensitivity of less than 10 ng. It will be shown that for the cyanide system, the leach rate of a gold/silver alloy is substantially higher than that of pure gold; for the gold/silver alloy, the reaction is diffusion controlled. For the thiosulfate system, reaction rates which are substantially higher than those for cyanide can be achieved with freshly prepared solutions containing copper(II), although the leach rate decreases as the copper(II) reacts with thiosulfate. A steady-state copper(II) concentration is obtained once the rate of copper(II) reduction by thiosulfate matches the rate of copper(I) oxidation by oxygen; at these steady-state concentrations of copper(II), the leach rates are slower than those obtained for cyanide. It will also be shown that reaction rates similar to the cyanide system can be readily achieved in chloride media at pH 3 with 2.5 mM hypochlorous acid; under these conditions, the reaction is limited by the diffusion of HClO.

Copper(II) catalysis in cyanide conversion into ethyl carbamate in spirits and relevant reactions.

Abstract: The role of copper(II) species in the oxidation of inorganic cyanide to cyanate and in the conversion of cyanate or urea into ethyl carbamate was investigated. The oxidation process has been shown to be independent from the dissolved oxygen. Elemental analysis and infrared spectroscopy have shown the formation of a mixed copper carbonate/hydroxide in the process of oxidation of cyanide to cyanate in water/ethanol. The complexation to CuII of cyanate formed upon cyanide oxidation makes the former more susceptible to nucleophilic attack from ethanol, with conversion into ethyl carbamate. Comparatively, urea has a minor role with respect to cyanide in the formation of ethyl carbamate. Therefore, the urea present in some samples of Brazilian sugar cane spirit (cachaca) has been shown to have almost no influence on the ethyl carbamate content of cachacas, which comes essentially from cyanide. FeII,III affords results similar to those found with CuII. Some suggestions are presented to avoid ethyl carbamate form...

Biogenic production of cyanide and its application to gold recovery.

Abstract: is a cyanogenic (cyanide-producing) microorganism. Cyanide is used on an industrial scale to complex and recover gold from ores or concentrates of ores bearing the precious metal. A potentially useful approach in gold mining operations could be to produce cyanide biologically in relatively small quantities at the ore surface. In this study, C. violaceum grown in nutrient broth formed a biofilm and could complex and solubilize 100% of the gold on glass test slides within 4–7 days. Approximately 50% of the cyanide-recoverable gold could be mobilized from a biooxidized sulfidic-ore concentrate. Complexation of cyanide in solution by gold appeared to have a beneficial effect on cell growth — viable cell counts were nearly two orders of magnitude greater in the presence of gold-coated slides or biooxidized ore substrates than in their absence. C. violaceum was cyanogenic when grown in alternative feedstocks. When grown in a mineral salt solution supplemented with 13.3% v/v swine fecal material (SFM), cells exhibited pigmentation and suspended cell concentrations comparable to cultures grown in nutrient broth. Glycine supplements stimulated production of cyanide in 13.3% v/v SFM. In contrast, glycine was inhibitory when added at the time of inoculation in the more concentrated SFM, decreasing cell numbers and reducing ultimate bulk-solution cyanide concentrations. However, aeration and addition of glycine to stationary phase cells grown on 13.3% v/v SFM anaerobically resulted in rapid production and high concentrations (up to 38 mg l−1) of cyanide. This indicates that biogenesis of cyanide may be supported in remote areas using locally produced and inexpensive agricultural feedstocks in place of commercial media. Journal of Industrial Microbiology & Biotechnology (2001) 26, 134–139.

Sc(BINOL)2Li: a new heterobimetallic catalyst for the asymmetric Strecker reaction

Abstract: The new chiral heterobimetallic complex Sc(BINOL) 2 Li 1 was prepared and used as a catalyst in the enantioselective addition of a cyanide source (HCN or TMSCN) to several imines. High conversion rates and enantiomeric excesses (e.e.s) as high as 95% were obtained.

Potential for error when assessing blood cyanide concentrations in fire victims.

Abstract: The present study explores toxicologic significance of blood cyanide concentrations in fire victims. Headspace gas chromatography was used for cyanide detection. Analysis of blood samples from ten fire victims (postmortem interval = 8 h to 3 to 5 d) detected zero to 11.9 mg/L of cyanide and a large difference in cyanide concentrations among victims. Carboxyhemoglobin (COHb) saturation was in the range of 24.9 to 84.2%. To examine the effects of methemoglobinemia and postmortem interval on blood cyanide concentrations in fire victims, an experiment was carried out using rabbits as the animal model. The rabbits were sacrificed by intramuscular injection of 1 mL/kg 2% potassium cyanide 5 min after intravenous injection of 0.33 mL/kg of 3% sodium nitrite (Group A, n = 3) or physiological saline (Group B, n = 6). Average methemoglobin contents immediately before potassium cyanide administration were 6.9 and 0.8% in Groups A and B, respectively. Average cyanide concentrations in cardiac blood at the time of death were 47.4 and 3.56 mg/L, respectively. When blood-containing hearts of the rabbits (n = 3 for Group B) were left at 46 degrees C for the first 1 h, at 20 to 25 degrees C for the next 23 h and then at 4 degrees C for 48 h, approximately 85 and 46% of the original amounts of blood cyanide disappeared within 24 h in Groups A and B, respectively. After the 72-h storage period, 37 and 10%, respectively, of the original amounts of cyanide remained in the blood. When the other three hearts in Group B were left at 20 to 25 degrees C for the last 48 h without refrigeration, cyanide had disappeared almost completely by the end of the experiment. The present results and those published in the literature demonstrate that the toxic effects of cyanide on fire victims should not be evaluated based solely on the concentration in blood.

Toward the Design of Double Metal Cyanides for the Copolymerization of CO2 and Epoxides

Abstract: Reaction of [KCpFe(CN)2PPh2(CH2)1.5]2 with zinc iodide results in the formation of a nonplanar diamond-shaped arrangement of [FeCNZn]2 with a bridging diphenyl-phosphinopropane, [CpFe(μ-CN)2ZnI(THF)]2-μ-dppp. This double metal cyanide (DMC) is found to mimic the reactivity of the heterogeneous DMC catalysts. That is, it serves to homogeneously catalyze the coupling of CO2 and cyclohexene oxide to afford cyclic cyclohexene carbonate and low molecular weight polycarbonate.

The influence of cyanide on the carbonylation of iron(II): synthesis of Fe-Sr-Cn-Co centers related to the hydrogenase active sites.

Abstract: Thomas B. Rauchfuss,* Stephen M. Contakes,Sodio C. N. Hsu, Michael A. Reynolds, and Scott R. WilsonDepartment of ChemistryUniVersity of Illinois at Urbana-ChampaignUrbana, Illinois 61801ReceiVed April 4, 2001ReVised Manuscript ReceiVed May 30, 2001Recently iron sulfides have been proposed as being central tothe emergence of life.

Photocatalytic production of hydrogen from aqueous solution containing CN− as a hole scavenger

Abstract: The effect of CN− as a hole scavenger on the photocatalytic hydrogen evolution from water was investigated over NiO/TiO2. A considerable amount of hydrogen was produced in the presence of CN−; the total amount of hydrogen evolved was proportional to the total amount of CN− ion in the solution. Quantum yield was 0.12 at 25°C and 0.32 at 75°C; the increment of quantum yield was about 0.048 per 10°C increase of the reaction temperature. Nickel cyanide complex, Ni(CN)42−, was generated from NiO/TiO2 in the presence of CN−. The Ni complex decomposed under UV light in the course of hydrogen evolution, resulting in OCN− formation. In addition to producing valuable hydrogen, this complex decomposition under UV light might be a valuable process to treat wastewater containing harmful cyanide complexes. Heat treatment of NiO/TiO2 catalyst at 700°C was effective for reducing nickel dissolution significantly.

Sequential One-Electron Reduction of Fe(V) to Fe(III) by Cyanide in Alkaline Medium

Abstract: The reduction of Fe(V) by cyanide has been studied anaerobically in alkaline media (pH 10.55−12.10) by using a premix pulse radiolysis technique. The results demonstrated for the first time the spectroscopic evidence for sequential one-electron reductions of Fe(V) to Fe(IV) to Fe(III) in aqueous media. Rates for reductions decrease with an increase in pH and appeared to be related to deprotonation of Fe(V) and Fe(IV) species. The reactivity of the three ferrates (Fe(VI), Fe(V), and Fe(IV)) with cyanide showed that Fe(V) and Fe(IV) are approximately four- and two-orders of magnitude more reactive than Fe(VI), respectively. These rates suggest that Fe(VI) oxidations of compounds may be accelerated if reactions are performed in the presence of one-electron or two-electron reducing substrates.

Surface species during catalytic reduction of NO by propene studied by in situ IR-spectroscopy over Pt supported on mesoporous Al2O3 with MCM-41 type structure

Abstract: The selective catalytic reduction of NO by propene (HC-SCR) in the presence of excess oxygen over Pt/MCM-41 (Al 2 O 3 ) and MCM-41 (Al 2 O 3 ) catalysts has been studied by simultaneous in situ IR-spectroscopy and catalytic activity measurements. IR-spectra of Pt/MCM-41 (Al 2 O 3 ) and MCM-41 (Al 2 O 3 ) were compared during the adsorption of the single reactants (NO and C 3 H 6 ) and during the NO reduction with C 3 H 6 in presence of excess O 2 (NO+C 3 H 6 +O 2 reaction). The adsorption of NO resulted in the formation of surface nitrate species on the Al 2 O 3 support and surface NO species on Pt. Adsorption of propene led to the formation of carboxylate species on Al 2 O 3 . Under reaction conditions nitrates, carboxylates, acetates, hydrocarbon fragments, isocyanate, cyanide species and CO were present on the catalyst surface. The surface concentration of the isocyanate species was found to be strongly correlated to the activity of the Pt/MCM-41 catalyst. Besides the formation of isocyanate, cyanide species were also observed on the surface. Both species increased in concentration with increasing oxygen concentration in the feed. The isocyanate species were found to be a reaction intermediate during the NO reduction, whereas the cyanide species were stable against further reaction. For the cyanide formation, a reaction pathway via isocyanate by abstraction of an oxygen atom by propene was observed.

Rapid Determination of Cyanide and Azide in Beverages by Microdiffusion Spectrophotometric Method

Abstract: A rapid screening method was developed for the determination of the toxic volatile anions, cyanide and azide, in beverages. This method consisted of a microdiffusion extraction combined with spectrophotometry using the K~nig cyanide reaction and ferric azide complex formation in conjugation with cerium azide oxidoreduction. The time required to achieve full recovery in the extraction of hydrogen cyanide and hydrazoic acid from samples was considerably shortened by the diffusion temperature from 25~ to 40~ The time required to achieve saturated color development in the K~nig cyanide reaction was also shortened by incubation temperature to 40~ The interference in both azide color reactions was examined for volatile compounds. Cyanide interfered only the case of ferric azide complex formation. Sulfide, sulfate, nitrite, and acetic acid interfered in both the color reactions. The established method gave a detection limit of 6~M for cyanide and 0.5ram for azide, and it required only 1 h to determine both anions. Cyanide and azide disappeared by evaporation from beverages during 25~ storage under open conditions in a pH-dependent manner as a function of their respective pK a values of 9.2 and 4.6.

Determination of cyanide in waste water by low‐resolution surface enhanced Raman spectroscopy on sol‐gel substrates

Abstract: We introduce the concept of low-resolution surface enhanced Raman spectroscopy (SERS) for cyanide as a potentially highly useful, cost-effective approach to detection and analysis for monitoring water contamination. We present high-sensitivity, low-resolution measurements of cyanide in water using a solid-state gold sol–gel substrate. These data suggest a sensitivity limit for low-resolution SERS detection of cyanide in water in the region of 10 ppb. Copyright © 2001 John Wiley & Sons, Ltd.

The Leaching and Electrochemistry of Gold in High Purity Cyanide Solutions

Abstract: For the last 100 years, cyanidation has been the most important process in the extraction of gold from its ores. However, despite the large number of papers published on the reaction between gold and cyanide, there is little agreement about the kinetics and mechanism of this important reaction. In the present paper, the leaching reaction was studied as a function of solution purity using a rotating electrochemical quartz crystal microbalance. Surprisingly, the experimental results show that pure gold does not leach in highly pure aerated cyanide solutions. On the other hand, gold leaches at a measurable rate in solutions prepared using AR grade reagents. Therefore, it is not surprising that many of the past investigations have resulted in connecting data. A model based on the formation and dissolution of a chain-like film of AuCN has been proposed to account for these results. It is believed that the dissolution of AuCN only occurs at the chain ends, and the presence of impurities in the cyanide solution accelerates this process by depositing on the gold surface and increasing the number of chain ends.

Cyanides and Nitriles

Abstract: Cyanides are among the most acutely toxic of all industrial chemicals and are produced in large quantities and used in many different applications. However, they cause few serious accidents or deaths. This is partly because the word cyanide is synonymous with a highly poisonous substance and a certain amount of care in handling is thereby ensured. The cyanides and nitriles are a disparate group of substances characterized by the presence of a cyanide (CN) group in their molecular structure. The cyanide group consists of a carbon bonded to a nitrogen. In those cases where the cyanide group is readily available, their toxicity is likely to have similarity to hydrogen cyanide (HCN). The chemical and physical characteristics of the compound will affect the potential availability of the cyanide group and therefore the hazards associated with different chemical species. For purposes of the toxicologist, cyanides and nitriles can be classified into the following groups: The inorganic cyanides include (Group 1) hydrogen cyanide, cyanogen, simple salts of hydrogen cyanide that dissociate readily to release CN−1 ions (such as sodium, potassium, calcium, and ammonium cyanide); (Group 2) halogenated compounds such as cyanogen chloride or bromide; and (Group 3) simple and complex salts of hydrogen cyanide that do not dissociate readily to release CN−1 ions (such as cobalt cyanide trihydrate, cupric and cuprous cyanide, silver cyanide, and ferricyanide and ferrocyanide salts). The organic cyanides include (Group 4) cyanide glycosides produced by plants (such as amygdalin and linamarin); and (Group 5) nitriles [such as acetonitrile (methyl cyanide), acrylonitrile and isobutyronitrile]. Keywords: Cyanides; Nitriles; Bhopal; India; Methylisocyanate release

Thermodynamic analysis of gold leaching by ammoniacal thiosulfate using Eh/pH and speciation diagrams

Abstract: Thiosulfate offers a nontoxic alternative to cyanide for processing gold ores. The mechanism of leaching gold using ammoniacal thiosulfate solution is driven by the Cu(II)-Cu(I) redox couple and is complicated by competing ligands such as NH 3 and S 2 O 3 2 - It is shown that an understanding of the copper speciation and sulfur speciation is required to optimize this system. This paper presents Eh-pH and speciation diagrams for varying concentrations of Cu(II), S 2 O 3 2 - and NH 3 and discusses the conditions under which various copper and sulfur species are stable.