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Reductant
Selected Abstracts[bmim]PF6/H2O Biphasic System Promoted Chemoselective Reduction of Aldehydes and Ketones with Potassium Borohydride as Reductant.CHEMINFORM, Issue 35 2005Hui-Mou Luo Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Molybdenum and Vanadium-Based Mixed Oxide Catalysts with Metastable Structure: Easy Access to the MoVNbTe(Sb)Ox Catalytically Active Structure Using Reductant and Oxoacid.CHEMINFORM, Issue 36 2003Hideto Tsuji Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Gold Microplates Using Bovine Serum Albumin as a Reductant and a StabilizerCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2010Leslie Au Abstract Gold microplates were synthesized in aqueous solutions by reducing HAuCl4 with the hydroxyl groups in both serine and threonine of bovine serum albumin (BSA), which is a globular protein in its native state. In this article, we systematically investigated the effects of temperature, pH value, the concentration of BSA, and ionic species on the reduction kinetics and thus the size and morphology of the final product. The optimal experimental conditions for producing uniform Au microplates include the following: an elevated temperature in the range of 55,65,°C, an acidic solution with pH,3, and the presence of NaCl (0.14,M). We found that if any one of these parameters was deviated from the optimal condition, Au microplates would not be formed in high yields. We also found that the surfaces of the as-synthesized Au microplates were covered by a dense array of BSA bumps. [source] Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometryELECTROPHORESIS, Issue 11 2005Feng Li Abstract This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg·L,1 Hg(II) and 4 mg·L,1 MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 µg·L,1 (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%. [source] Isolation and properties of methanesulfonate-degrading Afipia felis from Antarctica and comparison with other strains of A. felisENVIRONMENTAL MICROBIOLOGY, Issue 1 2005S. Azra Moosvi Summary Three novel strains of methylotrophic Afipia felis were isolated from several locations on Signy Island, Antarctica, and a fourth from estuary sediment from the River Douro, Portugal. They were identified as strains of the ,-2 proteobacterium A. felis by 16S rRNA gene sequence, analysis., Two, strains, tested, were, shown to contain the fdxA gene, diagnostic for A. felis. All strains grew with methanesulfonate (and two strains with dimethylsulfone) as sole carbon substrate. Growth on methanesulfonate required methanesulfonate monooxygenase (MSAMO), using NADH as the reductant and stimulated by reduced flavin nucleotides and Fe(II). Polymerase chain reaction amplification of DNA from an Antarctic strain showed a typical msmA gene for the ,-hydroxylase of MSAMO, and both Antarctic and Portuguese strains contained mxaF, the methanol dehydrogenase large subunit gene. This is the first report of methanesulfonate-degrading bacteria from the Antarctic and of methylotrophy in Afipia, and the first description of any bacterium able to use both methanesulfonate and dimethylsulfone. In contrast, the type strain of A. felis DSM 7326T was not methylotrophic, but grew in defined mineral medium with a wide range of single simple organic substrates. Free-living Afipia strains occurring widely in the natural environment may be significant as methylotrophs, degrading C1 -sulfur compounds, including the recalcitrant organosulfur compound methanesulfonate. [source] Kinetics of the reduction of chromium(VI) by vitamin CENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2005Xiang-Rong Xu Abstract The kinetics of the reduction of Cr(VI) to Cr(III) by vitamin C was studied using potassium dichromate solution as the model pollutant. Effects of the concentration of vitamin C, pH, temperature, and irradiation on the reduction of Cr(VI) were examined. The kinetics of Cr(VI) reduction by vitamin C can be described as - d[Cr(VI)]/dt = 0.0156 (,M s,1).[Cr(VI)][vitamin C] (pH 5), where dt is the differential function (d) of time (t). The activation entropy (,S,) and enthalpy (,H,) are 42.4 kJ mol,1 and -71.0 J mol,1 K,1, respectively, and the activation energy at 298 K is 63.5 kJ mol,1. The advantages of vitamin C as a reductant are as follows: It is an important biological reductant in humans and animals, and it is not toxic. Toxic Cr(VI) can be reduced by vitamin C not only in acidic conditions but also in alkaline solutions (pH 9); furthermore, the reduction was shown to occur both under the irradiation and in the dark. The present results suggest that vitamin C could be used effectively in the remediation of Cr(VI)-contaminated soil and groundwater in a wide range of pH, with or without sunlight. [source] Generation and Reactions of Overcrowded Diaryldilithiostannane and DiaryldipotassiostannaneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2005Tomoyuki Tajima Abstract Exhaustive reduction of an overcrowded dibromostannane bearing two bulky aromatic substituents, Tbt(Dip)SnBr2 {Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl; Dip = 2,6-diisopropylphenyl}, with an excess amount of lithium naphthalenide in THF at ,78 °C gave the corresponding dilithiostannane, Tbt(Dip)SnLi2, the generation of which was confirmed by trapping experiments with some electrophiles together with 119Sn and 7Li NMR spectroscopy. The diaryldilithiostannane was found to be stable in solution under an inert gas below ,25 °C. The potassium analogue, Tbt(Dip)SnK2, was also generated by the reduction of the dibromostannane in THF at ,78 °C by the use of KC8 as a reductant. The reactions of dilithiostannane and dipotassiostannane obtained with o -dibromobenzene did not give a stannacyclopropabenzene derivative but an unexpected cyclization product, a stannacyclobutabenzene derivative, in contrast to thereactions of the corresponding dilithiosilane and dilithiogermane, Tbt(Dip)ELi2 (E = Si, Ge), with o -dibromobenzene leading to the formation of the corresponding metallacyclopropabenzenes as stable crystalline compounds. A preliminary result of the synthesis of a tin,tellurium double-bond compound from the dilithiostannane is also presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Interflavin electron transfer in human cytochrome P450 reductase is enhanced by coenzyme bindingFEBS JOURNAL, Issue 12 2003Relaxation kinetic studies with coenzyme analogues The role of coenzyme binding in regulating interflavin electron transfer in human cytochrome P450 reductase (CPR) has been studied using temperature-jump spectroscopy. Previous studies [Gutierrez, A., Paine, M., Wolf, C.R., Scrutton, N.S., & Roberts, G.C.K. Biochemistry (2002) 41, 4626,4637] have shown that the observed rate, 1/,, of interflavin electron transfer (FADsq , FMNsq,FADox , FMNhq) in CPR reduced at the two-electron level with NADPH is 55 ± 2 s,1, whereas with dithionite-reduced enzyme the observed rate is 11 ± 0.5 s,1, suggesting that NADPH (or NADP+) binding has an important role in controlling the rate of internal electron transfer. In relaxation experiments performed with CPR reduced at the two-electron level with NADH, the observed rate of internal electron transfer (1/, = 18 ± 0.7 s,1) is intermediate in value between those seen with dithionite-reduced and NADPH-reduced enzyme, indicating that the presence of the 2,-phosphate is important for enhancing internal electron transfer. To investigate this further, temperature jump experiments were performed with dithionite-reduced enzyme in the presence of 2,,5,-ADP and 2,-AMP. These two ligands increase the observed rate of interflavin electron transfer in two-electron reduced CPR from 1/, = 11 s,1 to 35 ± 0.2 s,1 and 32 ± 0.6 s,1, respectively. Reduction of CPR at the two-electron level by NADPH, NADH or dithionite generates the same spectral species, consistent with an electron distribution that is equivalent regardless of reductant at the initiation of the temperature jump. Spectroelectrochemical experiments establish that the redox potentials of the flavins of CPR are unchanged on binding 2,,5,-ADP, supporting the view that enhanced rates of interdomain electron transfer have their origin in a conformational change produced by binding NADPH or its fragments. Addition of 2,,5,-ADP either to the isolated FAD-domain or to full-length CPR (in their oxidized and reduced forms) leads to perturbation of the optical spectra of both the flavins, consistent with a conformational change that alters the environment of these redox cofactors. The binding of 2,,5,-ADP eliminates the unusual dependence of the observed flavin reduction rate on NADPH concentration (i.e. enhanced at low coenzyme concentration) observed in stopped-flow studies. The data are discussed in the context of previous kinetic studies and of the crystallographic structure of rat CPR. [source] Synthesis of High-Surface-Area Platinum Nanotubes Using a Viral TemplateADVANCED FUNCTIONAL MATERIALS, Issue 8 2010. Górzny, Marcin Abstract A novel method for the synthesis of high-active-surface-area, platinum,tobacco mosaic virus (Pt,TMV) nanotubes is presented. A platinum salt is reduced to its metallic form on the external surface of a rod-shaped TMV by methanol, which serves as a solvent and reductant simultaneously. It was found that for the same Pt loading the Pt,TMV nanotubes had an electrochemically active surface area between 4 to 8 times larger than similarly sized Pt nanoparticles. A Pt,TMV catalyst displays greater stability in acidic conditions than those based on nanoparticles. When used as a catalyst for methanol oxidation, these Pt nanotubes display a 65% increase in catalytic mass activity compared to that based on Pt nanoparticles. [source] One-Pot Preparation of Polymer,Enzyme,Metallic Nanoparticle Composite Films for High-Performance Biosensing of Glucose and GalactoseADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Yingchun Fu Abstract New polymer,enzyme,metallic nanoparticle composite films with a high-load and a high-activity of immobilized enzymes and obvious electrocatalysis/nano-enhancement effects for biosensing of glucose and galactose are designed and prepared by a one-pot chemical pre-synthesis/electropolymerization (CPSE) protocol. Dopamine (DA) as a reductant and a monomer, glucose oxidase (GOx) or galactose oxidase (GaOx) as the enzyme, and HAuCl4 or H2PtCl6 as an oxidant to trigger DA polymerization and the source of metallic nanoparticles, are mixed to yield polymeric bionanocomposites (PBNCs), which are then anchored on the electrode by electropolymerization of the remaining DA monomer. The prepared PBNC material has good biocompatibility, a highly uniform dispersion of the nanoparticles with a narrow size distribution, and high load/activity of the immobilized enzymes, as verified by transmission/scanning electron microscopy and electrochemical quartz crystal microbalance. The thus-prepared enzyme electrodes show a largely improved amperometric biosensing performance, e.g., a very high detection sensitivity (99 or 129,µA cm,2 mM,1 for glucose for Pt PBNCs on bare or platinized Au), a sub-micromolar limit of detection for glucose, and an excellent durability, in comparison with those based on conventional procedures. Also, the PBNC-based enzyme electrodes work well in the second-generation biosensing mode. The proposed one-pot CPSE protocol may be extended to the preparation of many other functionalized PBNCs for wide applications. [source] Reactive Template Method to Synthesize Gold Nanoparticles with Controllable Size and Morphology Supported on Shells of Polymer Hollow Microspheres and Their Application for Aerobic Alcohol Oxidation in WaterADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Jie Han Abstract A novel method has been developed to synthesize gold nanoparticles with tunable size and morphology supported on both inner and outer surfaces of poly(o -phenylenediamine) (PoPD) hollow microspheres, which act as both reductant and template/stabilizer. The size of gold nanoparticles supported on shells of PoPD hollow microspheres can be tuned from 3 to 15,nm by changing the concentration of the gold source, HAuCl4. Gold nanorods supported on shells of PoPD hollow microspheres can also be fabricated by introducing a well-known seed-growth strategy. In addition, silver nanoparticles supported on shells of PoPD hollow microspheres can also be successfully fabricated using the same strategy, which indicates the diversity of this proposed method for polymer hollow microspheres supporting noble metal nanoparticles. The products are characterized by X-ray diffraction and contact angle analysis. Furthermore, the catalytic activity of the obtained PoPD-microsphere-supported gold nanoparticles for aerobic alcohol oxidation is investigated. The results demonstrate that such polymer-supported gold nanoparticles can be used as reusable catalysts with high catalytic activity for aerobic alcohol oxidation in water. [source] Template Synthesis of Aligned Carbon Nanotube Arrays using Glucose as a Carbon Source: Pt Decoration of Inner and Outer Nanotube Surfaces for Fuel-Cell Catalysts,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2008Zhenhai Wen A facile method is developed to synthesize aligned arrays of open-ended carbon nanotubes (CNTs) via in situ glucose polymerization in the inner pores of anodic aluminum oxide templates under hydrothermal conditions, followed by carbonization at high temperature. Pt nanoparticles are decorated on the surfaces of the as-prepared CNTs using the incipient wet method based on the use of NaBH4 as a reductant. Characterization of the resulting structures by transmission electron microscopy and field-emission scanning electron microscopy demonstrates that the Pt nanoparticles are anchored on both the inner and outer walls of CNTs, thus giving rise to a shell,core,shell-like nanotube composite. The electrocatalytic properties of the Pt,CNT,Pt electrodes are investigated for methanol oxidation by cyclic voltammetry and chronoamperometric measurements. It is found that the hybrid electrodes show superior catalytic performance compared to commercial carbon-black-supported Pt. The increased catalytic efficiency of Pt might be a result of the unique morphology of these structures. [source] Kinetics and mechanism of the oxidative regeneration of carbonyl compounds from oximes by pyridinium bromochromateINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 6 2006Pradeep K. Sharma The oxidative deoximination of several aldo- and keto-oximes by pyridinium bromochromate (PBC), in dimethylsulfoxide, exhibited a first-order dependence on both the reductant (oxime) and the oxidant (PBC). The oxidation of ketoximes is slower than that of aldoximes. The rates of oxidation of aldoximes correlated well in terms of the Pavelich,Taft dual substituent-parameter equation. The low positive value of polar reaction constant indicated a nucleophilic attack by a chromate-oxygen on the carbon. The reaction is subject to steric hindrance by the alkyl groups. The reaction of acetaldoxime has been studied in 19 different organic solvents. The solvent effect has been analyzed by Taft's and Swain's multiparametric equations. A mechanism involving the formation of a cyclic intermediate, in the rate-determining step, has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 364,368, 2006 [source] Kinetics of Fe(II) reduction of cis -halogeno(dodecylamine) bis(ethylenediamine)- cobalt(III) complex ion in aqueous solutionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2006K. Santhakumar Kinetics of reduction of the surfactant complex ions, cis -chloro/bromo (dodecylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous solution was studied at 303, 308, and 313 K by spectrophotometry method under pseudo-first-order conditions, using an excess of the reductant. The second-order rate constant remains constant below critical micelle concentration (cmc), but increases with cobalt(III) concentration above cmc, and the presence of aggregation of the complex itself alters the reaction rate. The rate of reaction was not affected by the added [H+]. Variation of ionic strength (,) influences the reaction rate. Activation and thermodynamic parameters have been computed. It is suggested that the reaction of Fe2+ (aq) with cobalt(III) complex proceeds by the inner-sphere mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 98,105, 2006 [source] Kinetics and mechanism of oxidation of 2-mercaptosuccinic acid by bis(,-oxo)- manganese(III,IV)-cyclam complex in aqueous medium: Influence of externally added copper(II)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2004Nizamuddin Shaikh Kinetic studies on the oxidation of 2-mercaptosuccinic acid by dinuclear [Mn2III/IV(,-O)2(cyclam)2](ClO4)3] (1) (abbreviated as MnIII,MnIV) (cyclam = 1,4,8,11-tetraaza-cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0,6.0, in the presence of acetate buffer at 30°C by UV,vis spectrophotometry. In the pH region, two species of complex 1 (MnIII,MnIV and MnIII,MnIVH, the later being ,-O protonated form) were found to be kinetically significant. The first-order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first-order dependence on [Cu2+] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of ,-O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV,vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer-sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170,177 2004 [source] Kinetics and mechanism of oxidation of antimony(III) by keggin-type 12-tungstocobaltate(III) in aqueous hydrochloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003B. D. Bhosale The reaction between Sb(III) and [CoIIIW12O40]5, proceeds with two, one-electron steps; formation of unstable Sb(IV) is the slow first step followed by its reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H+] as there are no protonation equlibria involved with both the reactants, whereas the accelerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl63,. Increase in the ionic strength and decrease in the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters were also determined and these values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 9,14, 2003 [source] Kinetics and mechanism of oxidation of aurate(I) by peroxydisulphate in aqueous hydrochloric acidINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2002R. M. Babshet The reaction between Au(I), generated by reaction of thallium(I) with Au(III), and peroxydisulphate was studied in 5 mol dm,3 hydrochloric acid. The reaction proceeds with the formation of an ion-pair between peroxydisulphate and chloride ion as the Michealis,Menten plot was linear with intercept. The ion-pair thus formed oxidizes AuCl2, in a slow two-electron transfer step without any formation of free radicals. The ion-pair formation constant and the rate constant for the slow step were determined as 113 ± 20 dm,3 mol,1 and 5.0 ± 1.0 × 10,2 dm3 mol,1 s,1, respectively. The reaction was retarded by hydrogen ion, and formation of unreactive protonated form of the reductant, HAuCl2, causes the rate inhibition. From the hydrogen ion dependence of the reaction rate, the protonation constant was calculated to be as 0.6 ± 0.1 dm3 mol,1. The activation parameters were determined and the values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 589,594, 2002 [source] Kinetics and mechanism of the oxidation of 4-methyl-3-thiosemicarbazide by acidic bromate,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2002Sreekantha B. Jonnalagadda The oxidation of 4-methyl-3-thiosemicarbazide (MTSC) by bromate and bromine was studied in acidic medium. The stoichiometry of the reaction is extremely complex, and is dependent on the ratio of the initial concentrations of the oxidant to reductant. In excess MTSC and after prolonged standing, the stoichiometry was determined to be H3CN(H)CSN(H)NH2 + 3BrO3, , 2CO2 + NH4+ + SO42, + N2 + 3Br, + H+ (A). An interim stoichiometry is also obtained in which one of the CO2 molecules is replaced by HCOOH with an overall stoichiometry of 3H3CN(H)CSN(H)NH2 + 8BrO3, , CO2 + NH4+ + SO42, + HCOOH + N2 + 3Br, + 3H+ (B). Stoichiometry A and B are not very different, and so mixtures of the two were obtained. Compared to other oxidations of thiourea-based compounds, this reaction is moderately fast and is first order in both bromate and substrate. It is autocatalytic in HOBr. The reaction is characterized by an autocatalytic sigmoidal decay in the consumption of MTSC, while in excess bromate conditions the reaction shows an induction period before autocatalytic formation of bromine. In both cases, oxybromine chemistry, which involves the initial formation of the reactive species HOBr and Br2, is dominant. The reactions of MTSC with both HOBr and Br2 are fast, and so the overall rate of oxidation is dependent upon the rates of formation of these reactive species from bromate. Our proposed mechanism involves the initial cleavage of the CN bond on the azo-side of the molecule to release nitrogen and an activated sulfur species that quickly and rapidly rearranges to give a series of thiourea acids. These thiourea acids are then oxidized to the sulfonic acid before cleavage of the CS bond to give SO42,, CO2, and NH4+. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 237,247, 2002 [source] Studies of the micellar effect on photogalvanics: Solar energy conversion and storage,EDTA,safranine O,DSS systemINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2010Prerna Gangotri Abstract The studies of the micellar effect on photogalvanics was done for solar energy conversion and storage in photogalvanic cell containing dioctyl sodium sulphosuccinate as anionic micellar species, EDTA as reductant and safranine O as photosensitizer. The photopotential and photocurrent generated were 800.0,mV and 65.0,µA respectively. The observed conversion efficiency was 0.2532 per cent, the fill factor was 0.38 and the maximum power of the cell was 52.0,µW whereas the power at power point of the photogalvanic cell was 26.34,µW. The rate of initial generation of current was 37.5,µA,min,1. The photogalvanic cell can be used for 80.0,minutes in the dark. The effects of different parameters on the electrical output of the photogalvanic cell were observed and a mechanism has also been proposed for the generation of photocurrent in the photogalvanic cell. Copyright © 2009 John Wiley & Sons, Ltd. [source] A closed-loop proposal for hydrogen generation using steel waste and a prototype solar concentratorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009Abdul-Majeed Azad Abstract An economically viable and environmental-friendly method of generating PEM grade hydrogen has been proposed and is by the reaction of certain metals with steam, appropriately called ,metal,steam reforming',MSR. The drawbacks of conventional processes (hydrogen and carbothermic reduction schemes) are overcome by resorting to solution-based reduction schemes and are made economically feasible using iron oxides from steel industry's mill-scale waste. A novel aqueous-based room temperature technique using sodium borohydride (NaBH4) as the reducing agent has been developed that produces highly active nanoscale iron particles (,40,nm). By using hydrazine as an inexpensive and, compared with NaBH4, more stable reductant, body centered cubic iron particles with ,5,nm edges were obtained via solvothermal process under mild conditions from acid digested mill-scale waste. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation than the coarser microscale iron. The rate constants for the MSR were obtained for all the reduction schemes employed in this work and are given by khydrogen=0.0158,min,1kcarbon=0.0248,min,1ksodiumborohydride=0.0521,min,1 and khydrazine=0.1454,min,1, assuming first order kinetics. Another innovative effort converted the magnetite waste directly into nZVI under solvothermal conditions, thus obviating the sluggish and time-consuming acid dissolution step. This particular aspect has significant ramification in terms of time and cost of making the iron precursor. To initiate and sustain the somewhat endothermic MSR process, a solar concentrator consisting of a convex polyacrylic bowl with reflective aluminum coating was fabricated and evaluated. This unique combination of mill-scale waste as iron source, hydrazine as reductant, mild process conditions and solar energy as the MSR actuator obviates several drawbacks plaguing the grand scheme of producing and delivering pure and humidified H2 to a PEMFC stack. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hydroxypropyl-,-Cyclodextrin-Capped Palladium Nanoparticles: Active Scaffolds for Efficient Carbon-Carbon Bond Forming Cross-Couplings in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Jaqueline Abstract A new approach for the preparation of palladium nanoparticles in water from a renewable source, 2-hydroxypropyl-,-cyclodextrin (,-HPCD), which acts both as a reductant and capping agent, is presented. The palladium nanoparticles were characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), which revealed the formation of spherical particles in the size range of 2,7,nm. Further analysis by Fourier-transform infrared spectroscopy (FT-IR) and 1H,NMR did not show covalent bonds between cyclodextrins and palladium nanoparticles, suggesting that ,-HPCD is only physically adsorbed on the nanoparticle surface, presumably through hydrophobic interactions which limit the mutual coalescence of nanoclusters. The catalytic activity was tested in Suzuki, Heck and Sonogashira reactions in neat water, providing good yields and selectivities of coupling products under very low Pd loadings (0.5,0.01,mol%). Remarkably, the nanocatalyst showed significant stability hence the aqueous phase remained active for four subsequent runs. The combination of a binding site for substrates (the HPCD cavity) and a reactive centre (Pd core) provides a potential to explore functional catalysis in aqueous medium. [source] Structure,function studies of glutamate synthases: A class of self-regulated iron-sulfur flavoenzymes essential for nitrogen assimilationIUBMB LIFE, Issue 5 2008Maria Antonietta Vanoni Abstract Glutamate synthases play with glutamine synthetase an essential role in nitrogen assimilation processes in microorganisms, plants, and lower animals by catalyzing the net synthesis of one molecule of L -glutamate from L -glutamine and 2-oxoglutarate. They exhibit a modular architecture with a common subunit or region, which is responsible for the L -glutamine-dependent glutamate synthesis from 2-oxoglutarate. Here, a PurF- (Type II- or Ntn-) type amidotransferase domain is coupled to the synthase domain, a (,/,)8 barrel containing FMN and one [3Fe-4S]0,+1 cluster, through a ,30 Å-long intramolecular tunnel for the transfer of ammonia between the sites. In bacterial and eukaryotic GltS, reducing equivalents are provided by reduced pyridine nucleotides thanks to the stable association with a second subunit or region, which acts as a FAD-dependent NAD(P)H oxidoreductase and is responsible for the formation of the two low potential [4Fe-4S]+1,+2 clusters of the enzyme. In photosynthetic cells, reduced ferredoxin is the physiological reductant. This review focus on the mechanism of cross-activation of the synthase and glutaminase reactions in response to the bound substrates and the redox state of the enzyme cofactors, as well as on recent information on the structure of the ,, protomer of the NADPH-dependent enzyme, which sheds light on the intramolecular electron transfer pathway between the flavin cofactors. © 2008 IUBMB IUBMB Life, 60(5): 287,300, 2008 [source] Asymmetric Carbonyl Reductions with Microbial KetoreductasesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2008Menno Abstract The biocatalytic reduction of ,-keto esters and some aromatic ketones in the presence of a variety of ketoreductases from different microbial origins was investigated. The prochiral selectivity was generally high and both product enantiomers could be obtained by a proper choice of enzyme. Aromatic ketones reacted slower than the esters but the prochiral selectivity was often high. The organic cosolvent tolerance of these enzymes was rather variable but useful activity could be maintained in a number of cases. Reduction of the oxidized cofactors NAD and NADP, employing 2-propanol as a sacrificial reductant, was catalyzed by the ketoreductases from Rhodococcus erythropolis and Lactobacillus kefir, respectively. [source] Effect of weak reductant on properties of electroless copper polyacrylonitrile nanocomposites for electromagnetic interference shieldingJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010Keng-Yu Tsao Abstract In this work, the electroless copper method with different reductant compositions (NaHSO3/Na2 S2O3·5H2O and Na2S2O3·5H2O) without sensitizing and activating, was used to deposit copper-sulfide deposition on the polyacrylonitrile (PAN) surface for electromagnetic interference (EMI) shielding materials. The weak reductant, NaHSO3, in the electroless copper method was used to control the phase of copper-sulfide deposition. The Cux(x=1,1.8)S was deposited on the PAN (CuxS-PAN) by reductant composition (NaHSO3/Na2S2O3·5H2O) and the Cux(x=1,1.8)S deposition of CuxS-PAN possesses three kinds of copper-sulfide phases (CuS, Cu1.75S and Cu1.8S). However, the electroless copper with reductant was only Na2S2O3·5H2O (without weak reductant, NaHSO3), the hexagonal CuS deposition was plated on the PAN (CuS-PAN) and increased the EMI shielding effectiveness of CuS-PAN composites about 10,15 dB. In this study, the best EMI SE of CuS-PAN and CuxS-PAN composites were about 27,30 dB and 15,17 dB respectively, as the cupric ion concentration was 0.24 M. The volume resistivity of CuS-PAN composite was about 1000 times lower than that of CuxS-PAN composite and lowest volume resistivity of CuS-PAN composites was 0.012 , cm, as the cupric ion concentration was 0.24 M. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] The use of sodium formate for the recovery of precious metals from acidic base metal effluentsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2001Herman G Julsing Abstract Zinc was used for the reduction of the platinum group metals (PGMs) in acidic effluents. Due to the increasing cost of zinc, sodium formate was investigated as an alternative reductant. In a base metal-containing acidic effluent, called diethylenetriamine barren, sodium formate was used to precipitate the PGMs. This effluent was the filtrate obtained after a precipitation procedure had been used to remove rhodium and iridium. It was found that pH 1.5 was the optimum starting pH for sodium formate reduction. The pH increased to approximately 4.5 after the addition of sodium formate. The optimum concentration of sodium formate was found to be 30,g,dm,3 at a temperature of 100,°C where the process time was 6,h. Platinum and palladium were the most effectively reduced PGMs, both exhibiting an average precipitation efficiency of greater than 99%. Difficulty was experienced with the precipitation of iridium (average precipitation efficiency of 76%). The precipitated PGMs readily dissolved in hydrochloric acid (6,M) and sodium chlorate (2%). A reduction in costs resulted from the discontinuation of the use of zinc for reduction purposes. An additional advantage was that zinc was no longer introduced into the PGM refinery circuits. © 2001 Society of Chemical Industry [source] IN VITRO COMPARISON OF ANAEROBIC AND AEROBIC GROWTH RESPONSE OF SALMONELLA TYPHIMURIUM TO ZINC ADDITIONJOURNAL OF FOOD SAFETY, Issue 4 2002S.Y. PARK ABSTRACT Zinc supplemented diets have been used to provide zinc as a nutrient and higher concentrations have been used to induce molt in laying hens. It is not known if the zinc in these diets would inhibit Salmonella spp growth. This study examines the effects of zinc compounds on the growth of S. typhimurium poultry isolate under aerobic and anaerobic conditions. The aerobic growth response of S. typhimurium was determined either in tryptic soy broth (TSB) or minimal (M9) broth containing five different concentrations (0.67, 2.01, 3.35, 4.69, and 6.03% [wt/vol]) of either Zn acetate [Zn(C2H2O2)22H2O] or Zn sulfate [ZnSO47H2O] while anaerobic growth response was determined in M9 broth with or without reductants (L-cysteine hydrochloride [C3H7NO2SHCl], and sodium sulfide [Na2S 9H2O]). Aerobic growth rates inhibited (P < 0.05) by Zn acetate than by Zn sulfate in TSB medium. The Zn source and concentration decreased (P < 0.05) aerobic growth response of S. typhimurium poultry isolate in M9 medium. The growth rates of S. typhimurium under anaerobic growth conditions were less responsive to Zn salts but were generally lower (P < 0.05) in the presence of reductant than in the absence of reductants at each concentration of Zn compound. The results in this study provide evidence that Zn may inhibit S. typhimurium under in vitro aerobic or anaerobic atmospheric conditions and S. typhimurium grows less optimally under anaerobic growth conditions. [source] Performance features of Pt/BaO lean NOx trap with hydrogen as reductantAICHE JOURNAL, Issue 3 2009Robert D. Clayton Abstract The performance of a model Pt/BaO/Al2O3 monolith catalyst was studied using H2 as the reductant. The dependence of product selectivities on operating parameters is reported, including the durations of regeneration and storage times, feed composition and temperature, and monolith temperature. The data are explained in terms of a phenomenological model factoring in the transport, kinetic, and spatio-temporal effects. The Pt/BaO catalyst exhibits high cycle-averaged NOx conversion above 100°C, generating a mixture of N2 and byproducts NH3 and N2O. The cycle-averaged NOx conversion exhibits a maximum at about 300°C corresponding to the NOx storage maximum. The N2 selectivity exhibits a maximum at a somewhat higher temperature, at which point the NH3 selectivity exhibits a minimum. This trend conveys the intermediate role of NH3 in reacting with stored NOx. Both N2 and N2O are also formed during the storage steps from the oxidation of NHx species produced during the regeneration. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] NOx storage and reduction with propylene on Pt/BaO/aluminaAICHE JOURNAL, Issue 10 2004Rachel L. Muncrief Abstract An experimental study was carried out of periodically operated NOx (NO + NO2) storage and reduction on a model Pt/BaO/Al2O3 catalyst powder. The effect of the reductant (propylene) injection policy on time-averaged NOx conversion was evaluated in terms of feed composition and temperature, reductant pulse duration, and overall cycle time. Conditions giving time-averaged NOx conversions exceeding 90% were identified. The reductant-to-oxidant ratio during the injection and the total cycle time are both found to be critical factors to achieve high conversion. The time-averaged conversion is bounded above and below by the steady-state conversions obtained with feeds having the same compositions as that during the rich and lean part of the cycle, respectively. For a fixed supply of propylene, short pulses of high concentration are much more effective than longer pulses of reduced concentration. The NOx conversion achieves a maximum value at an intermediate overall cycle time when the propylene pulse of fixed duty fraction is net reducing. High conversions are sustained over a wide temperature window (200,400°C). A simple storage,reduction cycle is proposed that elucidates the main findings in the study. The key factor for high NOx conversion is the temporal production of oxygen-deficient conditions coupled with high catalyst temperatures, both resulting from the intermittent catalytic oxidation of propylene. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2526,2540, 2004 [source] INORGANIC CARBON REPLETION DISRUPTS PHOTOSYNTHETIC ACCLIMATION TO LOW TEMPERATURE IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS,JOURNAL OF PHYCOLOGY, Issue 2 2005Robert A. Burns Acclimation of cyanobacteria to ambient fluctuations in inorganic carbon (Ci) and temperature requires reorganization of the major protein complexes involved in photosynthesis. We grew cultures of the picoplanktonic cyanobacterium Synechococcus elongatus Naegeli across most of its range of tolerable temperatures from 23 to 35°C at both low (<0.1 mM) and high Ci (approximately 4 mM). Over that range of temperatures, the chl-based doubling time did not differ between low and high Ci grown cells but did increase with decreasing temperature. Cells grown at 23°C high Ci showed an elongated morphology, which was not present in 23°C low Ci cells nor at 35°C high and low Ci. Furthermore, 23°C high Ci cells showed premature senescence and death compared with all other treatments. Phycocyanin per cell was greater in high Ci grown cells at all temperatures but showed a characteristic decrease with decreasing temperature. Functional PSII determination showed that 23°C high Ci cells had 1.5 × 105 PSII·cell,1 compared with only 6.9 × 104 PSII·cell,1 for 23°C low Ci. The 35°C high and low Ci cells had 7.7 × 104 and 6.4 × 104 PSII·cell,1, respectively. These data were supported by immunoblot determinations of PsbA content·cell,1. As a result of their high PSII·cell,1, 23°C high Ci cells generated more reductant from PSII than could be accommodated by downstream assimilative metabolism, resulting in early senescence and death of 23°C high Ci cells, probably as a result of the generation of reactive byproducts of electron transport. [source] Effects of non-steady-state iron limitation on nitrogen assimilatory enzymes in the marine diatom thalassiosira weissflogii (BACILLARIOPHYCEAE)JOURNAL OF PHYCOLOGY, Issue 1 2000Allen J. Milligan Since the recognition of iron-limited high nitrate (or nutrient) low chlorophyll (HNLC) regions of the ocean, low iron availability has been hypothesized to limit the assimilation of nitrate by diatoms. To determine the influence of non-steady-state iron availability on nitrogen assimilatory enzymes, cultures of Thalassiosira weissflogii (Grunow) Fryxell et Hasle were grown under iron-limited and iron-replete conditions using artificial seawater medium. Iron-limited cultures suffered from decreased efficiency of PSII as indicated by the DCMU-induced variable fluorescence signal (Fv/Fm). Under iron-replete conditions, in vitro nitrate reductase (NR) activity was rate limiting to nitrogen assimilation and in vitro nitrite reductase (NiR) activity was 50-fold higher. Under iron limitation, cultures excreted up to 100 fmol NO2,·cell,1·d,1 (about 10% of incorporated N) and NiR activities declined by 50-fold while internal NO2, pools remained relatively constant. Activities of both NR and NiR remained in excess of nitrogen incorporation rates throughout iron-limited growth. One possible explanation is that the supply of photosynthetically derived reductant to NiR may be responsible for the limitation of nitrogen assimilation at the NO2, reduction step. Urease activity showed no response to iron limitation. Carbon:nitrogen ratios were equivalent in both iron conditions, indicating that, relative to carbon, nitrogen was assimilated at similar rates whether iron was limiting growth or not. We hypothesize that, diatoms in HNLC regions are not deficient in their ability to assimilate nitrate when they are iron limited. Rather, it appears that diatoms are limited in their ability to process photons within the photosynthetic electron transport chain which results in nitrite reduction becoming the rate-limiting step in nitrogenassimilation. [source] | |||||||||||||||||||||||||||||||