Showing papers on "Thiocyanate published in 1998"

Reaction of myeloperoxidase compound I with chloride, bromide, iodide, and thiocyanate.

Abstract: Myeloperoxidase plays a fundamental role in oxidant production by neutrophils. The enzyme uses hydrogen peroxide to oxidize chloride (Cl-), bromide (Br-), iodide (I-), and the pseudohalide thiocyanate (SCN-) to their respective hypohalous acids. This study for the first time presents transient kinetic measurements of the oxidation of these halides and thiocyanate by the myeloperoxidase intermediate compound I, using the sequential mixing stopped-flow technique. At pH 7 and 15 degrees C, the two-electron reduction of compound I to the native enzyme by Cl- has a second-order rate constant of (2.5 +/- 0.3) x 10(4) M(-1) s(-1), whereas reduction of compound I by SCN- has a second-order rate constant of (9.6 +/- 0.5) x 10(6) M(-1) s(-1). Iodide [(7.2 +/- 0.7) x 10(6) M(-1) s(-1)] is shown to be a better electron donor for compound I than Br- [(1.1 +/- 0.1) x 10(6) M(-1) s(-1)]. The pH dependence studies suggest that compound I reduction by (pseudo-)halides is controlled by a residue with a pKa of about 4.6. The protonation of this group is necessary for optimum (pseudo-)halide anion oxidation. These transient kinetic results are underlined by steady-state spectral and kinetic investigations. SCN- is shown to be most effective in shifting the system myeloperoxidase/hydrogen peroxide from the peroxidatic cycle to the halogenation cycle, whereas iodide is shown to be more effective than bromide which in turn is much more effective than chloride. Decreasing pH increases the rate of this transition. Our results show that thiocyanate is an important substrate of myeloperoxidase in most environments and that hypothiocyanate is likely to contribute to leukocyte antimicrobial activity.

Handbook of derivatization reactions for HPLC

Abstract: Acyl Halide. Alcohol. Aldehyde. Alkene. Amide. Amine. Amino Acid. Amino Alcohol. Amino Ketone. Anhydride. Azide. Aziridine. Azo Compound. Boric Acid. Carbamate. Carboxylic Acid. Chelating Agent. Chloramine. Cyanate. Cyanide. Cyanohydrin. Diacid. Dialdehyde. Diene. Diketone. Diol. Enal. Epoxide. Ester. Guanidine. Halide. Haloaldehyde. Halogenated Compound. Hydrazine. Hydroxyl Radical. Hydroxylamine. Imine. Isocyanate. Isothiazole. Ketal. Ketoacid. Ketoalchohol. Ketoaldehyde. Ketone. Lactam. Lactone. Metal. Miscellaneous Reactions. Nitrate. Nitrite. Nitro Group. Nitroprusside Nitrosamide. Nitrosamine. Peracid. Peroxide. Phosphate. Phosphatidylcholine. Phosphonic Acid. Phosphoric Acid. Pyridine Ring. Quinone. Selenium. Sulfate. Sulfide. Sulfite. Sulfonate. Sulfonium Compound. Sulfur Dioxide. Tetrahydropyrimidine. Thiocyanate. Thiol. Thiosulfate. Appendices. Indexes.

A novel pink-pigmented facultative methylotroph, Methylobacterium thiocyanatum sp. nov., capable of growth on thiocyanate or cyanate as sole nitrogen sources

Abstract: The isolation and properties of a novel species of pink-pigmented methylotroph, Methylobacterium thiocyanatum, are described. This organism satisfied all the morphological, biochemical, and growth-substrate criteria to be placed in the genus Methylobacterium. Sequencing of the gene encoding its 16S rRNA confirmed its position in this genus, with its closest phylogenetic relatives being M. rhodesianum, M. zatmanii and M. extorquens, from which it differed in its ability to grow on several diagnostic substrates. Methanol-grown organisms contained high activities of hydroxypyruvate reductase [3 μmol NADH oxidized min–1 (mg crude extract protein)–1], showing that the serine pathway was used for methylotrophic growth. M. thiocyanatum was able to use thiocyanate or cyanate as the sole source of nitrogen for growth, and thiocyanate as the sole source of sulfur in the absence of other sulfur compounds. It tolerated high concentrations (at least 50 mM) of thiocyanate or cyanate when these were supplied as nitrogen sources. Growing cultures degraded thiocyanate to produce thiosulfate as a major sulfur end product, apparently with the intermediate formation of volatile sulfur compounds (probably hydrogen sulfide and carbonyl sulfide). Enzymatic hydrolysis of thiocyanate by cell-free extracts was not demonstrated. Cyanate was metabolized by means of a cyanase enzyme that was expressed at approximately sevenfold greater activity during growth on thiocyanate [V max 634 ± 24 nmol NH3 formed min–1 (mg protein)–1] than on cyanate [89 ± 9 nmol NH3 min–1 (mg protein)–1]. Kinetic study of the cyanase in cell-free extracts showed the enzyme (1) to exhibit high affinity for cyanate (K m 0.07 mM), (2) to require bicarbonate for activity, (3) to be subject to substrate inhibition by cyanate and competitive inhibition by thiocyanate (K i 0.65 mM), (4) to be unaffected by 1 mM ammonium chloride, (5) to be strongly inhibited by selenocyanate, and (6) to be slightly inhibited by 5 mM thiosulfate, but unaffected by 0.25 mM sulfide or 1 mM thiosulfate. Polypeptides that might be a cyanase subunit (mol.wt. 17.9 kDa), a cyanate (and/or thiocyanate) permease (mol.wt. 25.1 and 27.2 kDa), and a putative thiocyanate hydrolase (mol.wt. 39.3 kDa) were identified by SDS-PAGE. Correlation of the growth rate of cultures with thiocyanate concentration (both stimulatory and inhibitory) and the kinetics of cyanase activity might indicate that growth on thiocyanate involved the intermediate formation of cyanate, hence requiring cyanase activity. The very high activity of cyanase observed during growth on thiocyanate could be in compensation for the inhibitory effect of thiocyanate on cyanase. Alternatively, thiocyanate may be a nonsubstrate inducer of cyanase, while thiocyanate degradation itself proceeds by a carbonyl sulfide pathway not involving cyanate. A formal description of the new species (DSM 11490) is given.

The Octahedral M6Y8 And M6Y12 Clusters of Group 4 and 5 Transition Metals

Abstract: Publisher Summary This chapter discusses the octahedral M6Y8 and M6Y12 clusters of group 4 and 5 transition metals. Octahedral clusters of the electropositive metals, groups 3 to 7, are stabilized by π-donor ligands such as halides, chalcogenides, and alkoxides, but the majority accessible to solution chemistry is the halide complexes. Dilution of the pyridine surface with coadsorbed thiolphenol, a noncoordinating moiety, reduces the amount of cluster adsorbed to the surface and the average number of triflate ligands displaced by surface pyridine. The number of triflate ligands remaining on the surface-bound cluster may be adjusted with the thiolphenol/mercaptopyridine ratio. The different coordination environments about the core in the resulting material have been identified with differential pulse voltammetry. Both the α- and β-nitrogens of the azide ligand bind the cations, whereas only the sulfur atoms of the thiocyanate groups coordinate to the alkali metals. In addition to cation bridges, water molecules connect the azide ligands of adjacent clusters via hydrogen bonding.

Cyanex 923 as an extractant for trivalent lanthanides and yttrium

Abstract: The extraction of yttrium and some trivalent lanthanides from thiocyanate and nitrate solutions using Cyanex 923 { TRPO ) in xylene as an extractant has been investigated. It has been found that these trivalent metal ions are extracted from thiocyanate solution as M(SCN)3.n TRPO ; n in general having the values of 4 and 3 for the lighter and the heavier lanthanides respectively. On the other hand, from nitrate solutions these trivalent metal ions are extracted as M(NO3)3 3 TRPO. The equilibrium constants of the extracted complexes have been obtained by non-linear regression analysis. In both the thiocyanate and nitrate systems, the distribution ratios of trivalent lanthanides are found to increase with decreasing ionic radii and the distribution ratio of yttrium lies along with those of the middle lanthanides. The separation factors between these trivalent metal ions were evaluated and compared with those obtained using commercially important extraction reagents like tributylphosphate (TBP), trio...

Cloning of Genes Coding for the Three Subunits of Thiocyanate Hydrolase of Thiobacillus thioparus THI 115 and Their Evolutionary Relationships to Nitrile Hydratase

Abstract: Thiocyanate hydrolase is a newly found enzyme fromThiobacillus thioparus THI 115 that converts thiocyanate to carbonyl sulfide and ammonia (Y. Katayama, Y. Narahara, Y. Inoue, F. Amano, T. Kanagawa, and H. Kuraishi, J. Biol. Chem. 267:9170–9175, 1992). We have cloned and sequenced the scngenes that encode the three subunits of the enzyme. ThescnB, scnA, and scnC genes, arrayed in this order, contained open reading frames encoding sequences of 157, 126, and 243 amino acid residues, respectively, for the β, α, and γ subunits, respectively. Each open reading frame was preceded by a typical Shine-Dalgarno sequence. The deduced amino-terminal peptide sequences for the three subunits were in fair agreement with the chemically determined sequences. The protein molecular mass calculated for each subunit was compatible with that determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. From a computer analysis, thiocyanate hydrolase showed significant homologies to bacterial nitrile hydratases known to convert nitrile to the corresponding amide, which is further hydrolyzed by amidase to form acid and ammonia. The two enzymes were homologous over regions corresponding to almost the entire coding regions of the genes: the β and α subunits of thiocyanate hydrolase were homologous to the amino- and carboxyl-terminal halves of the β subunit of nitrile hydratase, and the γ subunit of thiocyanate hydrolase was homologous to the α subunit of nitrile hydratase. Comparisons of the catalytic properties of the two homologous enzymes support the model for the reaction steps of thiocyanate hydrolase that was previously presented on the basis of biochemical analyses.

Early Events in Decatungstate Photocatalyzed Oxidations: A Nanosecond Laser Transient Absorbance Reinvestigation

Abstract: Transient absorbance changes following nanosecond flash excitation of M4[W10O32] (M = Na+ or (n-C4H9)4N+ ≡ Q+) in acetonitrile reveal a long-lived ligand-to-metal charge-transfer (LMCT) intermediate [W10O32]4-† (φ ∼ 0.50, τ > 74 ns) as the reactive species in photocatalyzed organic oxidations. From its long lifetime and the lack of detectable emission between 400 and 900 nm, this LMCT intermediate is assigned to a “hot” ground-state isomer which is quenched reductively to [W10O32]5- or its protonated derivative [HW10O32]4-. Up to 1 μs after flash excitation of Na4[W10O32], the kinetics and quantum yields are measured for the reductive quenching of [W10O32]4-† by thiocyanate and four classes of organic substrates. Aromatic amines, thianthrene, and thiocyanate quench [W10O32]4- † by electron transfer at or near diffusion-controlled rates, and the alkanes and 2-butanol quench [W10O32]4- † by hydrogen atom transfer with rate constants in the range 107−108 M-1 s-1. High yields of the geminate pairs do not requ...

Aqueous Calcium Thiocyanate Solution as a Cellulose Solvent. Structure and Interactions with Cellulose

Abstract: Dissolution of cellulose into aqueous (aq) calcium thiocyanate solution was investigated with emphasis on solvent structure and interactions with cellulose. The aq calcium thiocyanate (Ca(SCN)2) solution with concentration (CCaT) more than 48.5 wt% could dissolve any celluloses. Solvation measurement revealed that in CCaT≧48.5 wt%, the solvent system is formulated by Ca(NCS)2·xH2O (x≦4)+yH2O (y≦6), which exhibits mainly non-dissociated thiocyanate with high specific viscosity, as proved by electric conductivity, specific viscosity and IR or 13C NMR measurements on solvent as a function of concentration of calcium thiocyanate. In this regard, the most stable 4 hydrate calcium thiocyanate is concluded from energy calculation as trans-trans configuration of Ca(–N=C=S)·4H2O. DSC and IR analyses suggested that dissolution of cellulose takes place by first attack of Ca(NCS)2·xH2O (x≦4) towards ring oxygen in cellulose. Ca(NCS)2·xH2O (x≦4) becomes 4-hydrates-like structure (sixcoordinate complex of Ca) and cellulose forms a 5-membered ring by coordinating two oxygen atoms (O(5) and O(6)) in the glucopyranose unit, and then cellulose dissolves on heating. In this process, some ligand exchange might occur if the hydration number is more than 2. This coordination of cellulose is quite characteristic, compared with other solvents, such as cuprammonium hydroxide, which coordinate with O(2) and O(3) hydroxyl groups.

Structure-activity relationship of new growth inhibitors of Trypanosoma cruzi

Abstract: Several drugs bearing the 4-phenoxyphenoxy skeleton and other closely related structures were designed, synthesized, and evaluated as antiproliferative agents against Trypanosoma cruzi, the etiologic agent of Chagas' disease. The new class of drugs was envisioned by modifying the nonpolar 4-phenoxyphenoxy moiety replacing selected aromatic protons by different groups via electrophilic aromatic substitution reactions as well as introducing a sulfur atom at the polar extreme. Of the designed compounds, sulfur-containing derivatives were shown to be potent antireplicative agents against T. cruzi. Among these drugs, 4-phenoxyphenoxyethyl thiocyanate (compound 56) proved to be an extremely active growth inhibitor of the epimastigote forms of T. cruzi and displayed an IC50 of 2.2 microM. Under the same assay conditions, this drug was much more active than Nifurtimox, one of the drugs currently in clinical use to control this disease. This thiocyanate derivative was also a very active inhibitor against the intracellular form of the parasite at the nanomolar level. Other sulfur derivatives prepared also exhibited very potent antiproliferative action against T. cruzi. The presence of a sulfur atom at the polar extreme for this family of compounds seems to be very important for biological action because this atom was always associated with high inhibition values. 4-Phenoxyphenoxyethyl thiocyanate presents very good prospective not only as a lead drug but also as a potential chemotherapeutic agent.

Stripping Voltammetric Determination of Iodide with Synergistic Accumulation at a Carbon Paste Electrode

Abstract: Carbon paste electrodes (CPEs) of various compositions were studied to elucidate the stripping voltammetric behavior of iodide. At an accumulation potential of +0.7 V (vs. Ag/AgCl), the CPE containing tricresyl phosphate as a pasting liquid was able to preconcetrate iodide effectively via ion-pairing reaction followed by oxidation to iodine and its extraction onto pasting liquid. In a supporting electrolyte containing 0.5 M NaCl and 0.1 M HCl, the reduction signal was proportional to iodide concentration from 5 × 10−6 to 5 × 10−7 mol/L with a detection limit of approximately 2.5 × 10−7 mol/L (accumulation for 5 min). Other halides and pseudohalides did not interfere with the determination, except for a high concentration excess of thiocyanate and bromide (100:1). The method was tested on model solutions and was applied to determine total iodine in samples of table salts and mineral water. The results were compared to those obtained by reference methods.

Biodegradation of free cyanide, thiocyanate and metal complexed cyanides in solutions with different compositions

Abstract: The feasibility of using biological processes for the detoxification of cyanide solutions was established in the 1980's. However, most of the proposed schemes of treatment have been developed for relatively low concentrations. The present work reports on a biological sludge acclimatisation procedure and the process performance when treating cyanide solutions with different compositions, including the elimination of a carbon source in the influent. The experiments were carried out in continuous bench scale stirred reactors (5 litres). The following parameters were monitored for evaluation purposes: chemical oxygen demand (COD), free cyanide, thiocyanate, copper, iron and zinc concentrations. The acclimatisation time to obtain a specific biological sludge was (reduced from 12 to) 6 months. Microbial activity was found to be the main mechanism of free cyanide and thiocyanate degradations, copper and iron removal. An organic carbon source was necessary in the influent to the system to improve process performa...

Solubility and Dissolved Cellulose in Aqueous Calcium- and Sodium-Thiocyanate Solution

Abstract: Attempt was made to investigate the solubility and the dissolved state of various celluloses in aqueous (aq) calcium- and sodium-thiocyanate solution. Almost all celluloses used in this study were soluble in 55 wt% aq calcium thiocyanate (Ca(SCN)2) soln. at about 100°C, while 60 wt% aq sodium thiocyanate (NaSCN) soln. dissolves only limited cellulose mainly regenerated from cellulose solution. The solubility of cellulose in 60 wt% aq NaSCN was independent of the crystal form, crystallinity and the degree of polymerization of cellulose and this was explained only in terms of the degree of breakdown of intramolecular hydrogen bonds in the cellulose solid. Using 2-dimensional NMR six carbon peaks in 13C NMR spectra of cellulose in two solvents were successfully assigned. The comparison of chemical shifts of cellulose in 55 wt% aq Ca(SCN)2 solution and 10% sodium hydroxide (NaOH) solution strongly suggested that calcium atoms as electron acceptors coordinate with oxygen atoms in glucose ring and primary alcohol at C(6) position, in the same manner of cellulose dipped in 55 wt% aq Ca(SCN)2 solution at room temperature. In the 13C NMR spectrum of cellulose-60% aq NaSCN solution system, C(3), C(2), and C(6) peaks were observed at lower magnetic field side, implying that sodium atoms interact with hydroxide groups at C(2), C(3), and C(6) positions of glucopyranose in cellulose molecules.

Method for treating the surfaces of plastic substrates

Abstract: The substrate is exposed to a noble gas or nitrogen plasma in a vacuum chamber and the vapor of an adhesion-promoting compound (I). (I) is a free radical polymerization or addition compound. It has a (cyclo)aliphatic or (hetero)aromatic structure and contains a nitrile, mercapto, thiocyanate, imidazole, carboxyl, carbonyl or beta -carbonyl group as metal-complexing function. Independent claims are also included for 2 variants using adhesion-promoting compounds (II) or (III).

Resonant Rayleigh scattering for the determination of trace amounts of mercury (II) with thiocyanate and basic triphenylmethane dyes

Abstract: Intense resonance Rayleigh scattering (RRS) appears when mercury (II) reacts with thiocyanate and a basic triphenylmethane dye (BTPMD), such as crystal violet (CV), ethyl violet (EV), brilliant green (BG), malachite green (MG) or indine green (IG), to form an ion-association complex of the type (BTPMD)2[Hg(SCN)4]. The characteristics of RRS spectra of the ion-association complexes and suitable conditions for the reactions were investigated. The intensity of RRS is directly proportional to the concentration of mercury (II) in the range of 0±2.0 μg/25 ml. The RRS methods have very high sensitivities for determination of mercury (II); their detection limits are between 1.68 ng/ml and 6.00 ng/ml on different dye systems. The effects of foreign ions and ways to improve the selectivity were studied. The new highly sensitive methods for the determination of trace amounts of mercury based on the RRS of the ion-association complexes have been developed.

THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) FROM NITRATE AND THIOCYANATE MEDIA WITH OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE

Abstract: The extraction of Am(III) and Eu(III) from 1.0 M NH4NO3 and NHS4SCN at pH 2.60 into octyl(pheriyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in n-dodecane has been studied in the temperature range 15.0 to 45.0°C. Under all conditions, the species ML3·CMPO is the dominant extracted complex. The extraction equilibrium constants are at least 103 higher in the SCN- systems than in the NO3 - systems. This difference is attributed to the relative energy associated with transfer of the anions from the aqueous to the: extractant phase. Extraction enthalpies and entropies have been calculated in each system from the temperature dependence of Kex. Enthalpies are considerably more exothermic in the thiocyanate system for both metal ions. Comparison of ΔHAm SCN with ΔHEU SCN gives a possible indication of enhanced Am-SCN bond strength in the extracted complex.

Structural Changes in Wood Pulp Treated by 55 wt% Aqueous Calcium Thiocyanate Solution

Abstract: Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN) 2 ) solution at room temperature. For this purpose, X-ray, DSC, and CP/MAS 13 C NMR were used to measure changes of crystalline structure and formation of cellulose-solvent complex. X-Ray data indicated that 55 wt% aq Ca(SCN) 2 soln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose-calcium thiocyanate addition compound. The interplanar spacing of (110), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time t d of 90 min. From DSC thermograms of cellulose-55wt% aq Ca(SCN) 2 soln. mixture, exothermic heat ΔH for the formation of the addition compound was estimated to be ca. 11 kcal mol -1 , which was far lower than that for generation of cellulose sodium salt. The cellulose recovered from the system has quite different crystalline structure depending on treatment time and the reagents used for recovery. Up to t d = 90 min, water recoverd the mixture of natural cellulose crystal (Cell-1) and hydrated cellulose (Cell-11), while the methanol and acetone recovered only Cell-I. After one day the structure of the recovered cellulose from the system was: water, Cell-II; methanol, Cell-I; acetone, almost amorphous cellulose.