Showing papers on "Cyanide published in 1995"

Cyanide detoxification in cassava for food and feed uses

Abstract: Cassava (Manihot esculenta Crantz) is an important tropical root crop providing energy to about 500 million people. The presence of the two cyanogenic glycosides, linamarin and lotaustralin, in cassava is a major factor limiting its use as food or feed. Traditional processing techniques practiced in cassava production are known to reduce cyanide in tubers and leaves. Drying is the most ubiquitous processing operation in many tropical countries. Sun drying eliminates more cyanide than oven drying because of the prolonged contact time between linamarase and the glucosides in sun drying. Soaking followed by boiling is better than soaking or boiling alone in removing cyanide. Traditional African food products such as gari and fufu are made by a series of operations such as grating, dewatering, fermenting, and roasting. During the various stages of gari manufacture, 80 to 95% cyanide loss occurs. The best processing method for the use of cassava leaves as human food is pounding the leaves and cooking the mash in water. Fermentation, boiling, and ensiling are efficient techniques for removing cyanide from cassava peels.

Biological cyanide destruction mediated by microorganisms.

Abstract: Many microorganisms have an inherent capacity to degrade the toxic organic compounds that enter the environment as a result of pollution and natural activities. Significant degradation of these compounds may take many years and it is frequently necessary to consider methods that can accelerate this process. There have been several demonstrations of enhanced biological degradation of toxic wastes, both in the laboratory and under field conditions. The prospects for enhanced biological cyanide degradation are reviewed. Compared with bench-scale processes, there are very few reports of field-scale processes for cyanide bioremediation. The implementation of such field-scale degradation requires inputs from biology, hydrology, geology, chemistry and civil engineering. A conceptual framework is emerging that can be adapted to develop new processes for bioremediation of toxic organic wastes. In terms of cyanide biodegradation, this framework incorporates identification of microbes, determination of the optimal conditions for degradation, establishment of the metabolic pathways involved in cyanide degradation, identification and localization of the genes involved, identification of suitable microbial strains for practical application and development of practical engineering processes. The present review addresses the progress that has been made in each of these aspects of cyanide biodegradation. It also examines the existing field applications of biological cyanide degradation and makes recommendations for future research.

Polyether-containing double metal cyanide catalysts

Abstract: Improved double metal cyanide (DMC) catalysts are disclosed. The catalysts comprise a DMC compound, an organic complexing agent, and from about 5 to about 80 wt. % of a polyether polyol that has tertiary hydroxyl groups. Compared with other DMC catalysts, those of the invention have excellent activity for epoxide polymerization, and they can be used to make polyols having very low unsaturation even at high epoxide polymerization temperatures.

Aerogel materials for photocatalytic detoxification of cyanide wastes in water

Abstract: Ultraviolet-irradiated titania-silica (TiO2SiO2) aerogels were used as photocatalysts to oxidize/degrade aqueous cyanide species to CO2 and N2. TiO2SiO2 aerogel photocatalysts were prepared by the sol-gel technique and supercritical drying. Three types of TiO2SiO2 aerogel were prepared with different SiO2 contents (i.e., TiO2:SiO2 molar ratio = 1:1.3, 1:2.6 and 1:3.9). It was observed that, with increased SiO2 content, shrinkage and apparent density decreased and translucency increased. This resulted in higher photocatalytic activity for oxidation of CN− in dilute solutions (1000 and 522 ppm) of ferric cyanide. Compared with titania powder (i.e., anatase form with TiO2 > 98% and particle diameter < 1 μm), it was proven that the aerogel with highest SiO2 content (i.e. TiO2:SiO2 molar ratio = 1:3.9) had highest efficiency in the photocatalytic oxidation of CN− species under the same experimental conditions. This aerogel photocatalyst was filtered and re-used several times to check for activity loss; no significant change in the activity of the photocatalyst was observed.

Effects of Waterborne Copper, Cyanide, Ammonia, and Nitrite on Stress Parameters and Changes in Susceptibility to Saprolegniosis in Rainbow Trout (Oncorhynchus mykiss).

Abstract: The effects of toxic exposures on the susceptibility of rainbow trout (Oncorhynchus mykiss) to saprolegniosis were evaluated. Fish were exposed to sublethal concentrations of copper (0.25 mg/liter), cyanide (0.07 mg/liter), ammonia (0.5 mg/liter), and nitrite (0.24 mg/liter) for 24 h. After exposure, the fish were challenged by Saprolegnia parasitica (3.6 x 10(sup6) zoospores per liter) for 10 min. Cortisol and cholesterol were used to indicate stress response. Similar increases of cortisol were found for the four tested chemicals. All fish with cortisol levels higher than 370 ng/ml developed the disease, while only 24% of the fish with cortisol levels lower than 370 ng/ml were infected. Cholesterol levels remained unchanged after toxic exposure. Increased susceptibilities to the pathogen were observed for ammonia (71%), copper (57%), nitrite (50%), and cyanide (33%). The increases in susceptibility as a result of cyanide and nitrite exposure could be explained by the stress response. For copper and ammonia, the combination of two different effects, the stress response and specific impairments of the defense mechanism of trout against saprolegniosis, should be considered.

Cyanide and Other Lixiviant Leaching Systems for Gold with Some Practical Applications

Abstract: Selection of a leaching system for gold involves consideration of ore texture and mineralogy, chemical requirements, leaching techniques, the development of flowsheets, and environmental management Aqueous dissolution chemistry for alkaline, neutral, and acid systems is mainly considered here All systems require an oxidant to oxidise gold and a ligand to complex with gold in solution Adjustment of pH is usually necessary Alkaline lixiviant systems (pH > 10)include cyanide, ammonia-cyanide, ammonia, sulphide, nitriles, and a few other minor possibilities Oxygen is the main oxidant Cyanide, which is the main ligand in these systems, forms an anionic complex, “Au(CN)2”, with Au(I) Gold dissolution rates are controlled by oxygen solubility in solution Neutral lixiviant systems (pH 5-9)include thiosulphate, halogens, sulphurous acid, and bacteria plus natural organic acids as the ligand Oxygen is the normal oxidant and either Au(I) or Au(III)complexes are formed Acid leaching systems (pH ⩾ 3)may cont

The clinical experience of acute cyanide poisoning

Abstract: The authors reviewed the clinical manifestations, complications, and the prognosis affected by Lilly Cyanide Antidote in 21 victims of acute cyanide poisoning over a 10-year period. The clinical signs and symptoms in cyanide poisoning are variable. Among 21 cases, loss of consciousness (15), metabolic acidosis (14), and cardiopulmonary failure (9) were the three leading manifestations of cyanide intoxication. Anoxic encephalopathy (6) was not uncommon in the severely intoxicated victims. Diabetes insipidus (1) or clinical signs and symptoms mimicking diabetes insipidus (3) may be an ominous sign to encephalopathy victims. The major cause of fatal cyanide poisoning is the intentional ingestion of cyanide compounds as part of a suicide attempt. Decrease of arteriovenous difference of O2 partial pressure may be a clue for the suspicion of cyanide intoxication. Although the authors cannot show a statistically significant difference (P = .47) for the Lilly cyanide antidote kit in terms of improving the survival rate for victims of cyanide poisoning, the antidote kit was always mandatory in our study in the cases of severely intoxicated victims who survived. Early diagnosis, prompt, intensive therapy with antidote, and supportive care are still the golden rules for the treatment of acute cyanide poisoning, whether in the ED or on the scene.

Isolation and characterization of mutants defective in the cyanide-insensitive respiratory pathway of Pseudomonas aeruginosa.

Abstract: The branched respiratory chain of Pseudomonas aeruginosa contains at least two terminal oxidases which are active under normal physiological conditions. One of these, cytochrome co, is a cytochrome c oxidase which is completely inhibited by concentrations of the respiratory inhibitor potassium cyanide as low as 100 microM. The second oxidase, the cyanide-insensitive oxidase, is resistant to cyanide concentrations in excess of 1 mM as well as to sodium azide. In this work, we describe the isolation and characterization of a mutant of P. aeruginosa defective in cyanide-insensitive respiration. This insertion mutant was isolated with mini-D171 (a replication-defective derivative of the P. aeruginosa phage D3112) as a mutagen and by screening the resulting tetracycline-resistant transductants for the loss of ability to grow in the presence of 1 mM sodium azide. Polarographic studies on the NADH-mediated respiration rate of the mutant indicated an approximate 50% loss of activity, and titration of this activity against increasing cyanide concentrations gave a monophasic curve clearly showing the complete loss of cyanide-insensitive respiration. The mutated gene for a mutant affected in the cyanide-insensitive, oxidase-terminated respiratory pathway has been designated cio. We have complemented the azide-sensitive phenotype of this mutant with a wild-type copy of the gene by in vivo cloning with another mini-D element, mini-D386, carried on plasmid pADD386. The complemented cio mutant regained the ability to grow on medium containing 1 mM azide, titration of its NADH oxidase activity with cyanide gave a biphasic curve similar to that of the wild-type organism, and the respiration rate returned to normal levels. Spectral analysis of the cytochrome contents of the membranes of the wild type, the cio mutant, and the complemented mutant suggests that the cio mutant is not defective in any membrane-bound cytochromes and that the complementing gene does not encode a heme protein.

Cyanide Determination Using an Amperometric Biosensor Based on Cytochrome Oxidase Inhibition

Abstract: An amperometric reagentless biosensor, based on a carbon paste electrode (CPE) modified by asolectin, cytochrome c, and cytochrome oxidase, is described for the sensitive determination of cyanide. The modified CP matrix mimics a biological membrane environment. The sensor, polarized at -0.15 V vs Ag/AgCl, generates the reduced form of cytochrome c, which in turn is oxidized by the enzyme cytochrome oxidase. The resulting current is related to the enzyme activity and is depressed by inhibitors of cytochrome oxidase such as cyanide. Concentrations of cyanide as low as 0.5 μM can be measured with half-maximal response at about 12 μM. The effects of pH, ionic strength, and temperature on this new cyanide biosensor are reported. The inhibition is reversible and reproducible (RSD = 4%), allowing cyanide determination for more than 2 months using the same probe. Possible use of this biosensor in flow systems is illustrated.

Quantification of Cyanogenic Glycosides in Seedlings of Three Macadamia (Proteaceae) Species

Abstract: Members of the genus Macadamia contain cyanogenic compounds, which release hydrogen cyanide (HCN) on hydrolysis. Concentrations of releasable cyanide were measured in tissues of mature nuts and seedlings of Macadamia integrifolia Maiden & Betche, M. tetraphylla L.A.S. Johnson and M. ternifolia F.Muell. Root, cotyledon and leaf samples were assayed at several developmental stages from germination to maturation of the first leaves. All samples contained detectable levels of cyanide. Concentrations were low (0.15 μmol g-1 fresh weight) in cotyledons of mature M. integrifolia and M. tetraphylla seeds, corresponding to the edibility of the seeds of these commercial species, and much higher (9.6 μmol g-1) in the inedible M. ternifolia seeds. Levels in cotyledons of all three species rose dramatically during germination. Root cyanide concentrations of 6-23 μmol g-1 were measured. The immature first leaf of the commercial species contained the highest concentrations (38-77 μmol g-1). Levels decreased with leaf maturity, correlating with toughening of the leaf and possibly a consequent diminished requirement for cyanide as a herbivory deterrent. The significance of the results with respect to plant-insect interactions is discussed.

Highly active double metal cyanide catalysts and epoxide polymerization

Abstract: Highly active double metal cyanide (DMC) catalysts are disclosed. The catalysts comprise a DMC complex, and organic complexing agent, and from about 5 to about 80 wt. %, based on the amount of catalyst, of a polyether having a number average molecular weight greater than about 500. A method of preparing the catalysts is also disclosed. The catalysts are easy to prepare, have exceptional activity, and are readily removed, if desired, from polymer products. The catalysts are used for polymerizing epoxides.

Mixed-Valent Ruthenium Oxide-Ruthenium Cyanide Inorganic Film on Glassy Carbon Electrodes as an Amperometric Sensor of Aliphatic Alcohols

Abstract: A mixed-valent ruthenium oxide-ruthenium cyanide film on glassy carbon (GC/mvRuO-RuCN) electrode exhibits excellent electrocatalytic activity toward oxidation of simple aliphatic alcohols and polyhydric compounds in acidic media. Electrochemical formation of the ruthenium oxide-based chemically modified electrode can be accomplished by potential cycling or potentiostatic control in diluted sulfuric aid solutions. The attractive electrooxidation capabilities of hydroxyl-containing compounds at this moiled electrode are highlighted in terms of sensitivity, stability, and catalytic action. Remarkably, the molar response of the catalytic oxidation increases on increasing the chain length of aliphatic alcohols

Kinetics and mechanism for the binding of HCN to cytochrome c oxidase

Abstract: The kinetics of cyanide binding to cytochrome c oxidase were systematically studied as a function of [HCN], [oxidase], pH, ionic strength, temperature, type and concentration of solubilizing detergent, and monomer-dimer content of oxidase. On the basis of these results a minimum reaction mechanism is proposed in which the spectrally visible rapid and slow cyanide binding reactions are two consecutive first-order reactions, not parallel reactions with different conformers of cytochrome c oxidase. The fast reaction (k'obs) follows saturation type kinetics to form an HCN complex that subsequently undergoes a slow reaction (k'obs). The fast k'obs reaction is independent of ionic strength but is strongly dependent upon pH. Two pK values were evaluated from the bell-shaped rate versus pH profile; one is due to an ionizable group on the protein (pKa = 7.45), while the other is that of HCN (pKHCN = 9.15). Therefore, oxidase is reactive toward HCN only when the group on the protein is unprotonated. The slow k'obs reaction is not a reaction of oxidase with either CN- or HCN; in fact, the product formed by the fast k'obs reaction, the oxidase-HCN complex, still undergoes the slow k" process even if all of the excess KCN is removed. The apparent rate constant of the slower phase (k"obs) is independent of all the variations done in this study, and it probably corresponds to either a slow conformational change in the protein or a change in ligand coordination at one of the metal centers after HCN binds to the bimetallic center of oxidase. Based upon the bell-shaped pH dependence of the fast phase and the pH independence of the slow phase, the mechanism also predicts that a single conformer of cytochrome c oxidase can exhibit either monophasic or biphasic cyanide binding kinetics depending upon the pH. At either very low or very high pH, the two rates become comparable in magnitude, which makes the reaction appear to be monophasic even though both reactions still occur. The amount of monomeric or dimeric oxidase only slightly affects the magnitude of k'obs and k"obs values, and both processes are clearly present in both types of oxidase.

Electrochemical response of poly(vinylferrocenium)-coated Pt electrods to some anions in aqueous media

Abstract: The electrooxidation behavior of iodide, thiocyanate, and cyanide on poly(vinylferrocenium)-coated Pt electrodes was investigated using cyclic voltammetry and differential pulse anodic stripping voltammetry. IR and UV spectroscopic data, and differential scanning calorimetry (DSC) measurements indicated that these anions were incorporated in the polymeric structure as a result of anion exchange. Anodic stripping of these anions from the film was carried out after the initial preconcentration. Cyanide uptake was found to cause an irreversible change in the physical properties of the film, whereas thiocyanate and iodide are merely incorporated in the film structure as counter ions.