Enzymatic reduction of chromium(VI) by human hepatic microsomes

The reduction of chromium(VI) by human hepatic microsomes was investigated. The reduction rates were proportional to the amount of microsomes added and reduction was mediated by an NADPH-dependent enzymatic system which exhibited a Km for chromate of 1.04 +/- 0.18 microM and a Vmax of 5.03 +/- 0.49 nmol/min/mg protein. Relative to incubation under 0% O2, 21% O2 inhibited microsomal Cr(VI) reduction in three individuals by 53, 36 and 37%. Cr(VI) reduction was not inhibited by metyrapone, carbon monoxide, aminopyrine, piperonyl butoxide or chloroform, suggesting that cytochrome P450s did not play a major role. Thallium trichloride (0.13 and 0.26 mM), a known flavoprotein inhibitor, caused a complete inhibition of both Cr(VI) reduction and NADPH:cytochrome P450 (c) reductase activity. A partial inhibition of Cr(VI) reduction was seen in the presence of n-octylamine, which may suggest a possible role for flavin-containing monooxygenase (FMO). Overall, human microsomal Cr(VI) reduction is very different from the P450-mediated microsomal reduction observed in rodents. Specifically, the human system is much less oxygen-sensitive, has a much greater affinity for chromate and is apparently mediated by flavoproteins.     

Recent studies of convection in commercial aluminum reduction cells

Convection rates and patterns in the bath electrolyte and the cathode metal of 150 kA prebaked anode aluminum reduction cells have been studied by means of radioactive tracers. Gamma radiation probes have been used for a continuousin situ determination of the radiotracer activity in the bath and liquid metal. The measurements are compared with predicted convection patterns from model magnetodynamic calculations for both magnetically compensated and uncompensated reduction cells. The measurements give evidence of a strong coupling between the convection currents in the metal and bath phases. The recorded activity vs time data further allow an estimation of the degree of turbulence in the reduction cells. From these investigations attempts are made to correlate data from the convection studies with current efficiency, as determined by the method of isotope dilution. The same method has also been used to determine liquid bath volume and the melting-out of solid bath electrolyte during periods with anode effect.     

Fundamental studies on the continuous electrolytic reduction of uranyl sulfate

With the aim of developing a process for continuous electrolytic reduction of uranyl sulfate, the effects of temperature and HF concentration on the electrolytic reduction were investigated using both a rectangular cell and a bipolar cell. Some tests on the semicontinuous-type elec-trolytic reduction of U(VI) and the continuous monitoring of U(VI) in a catholyte were carried out to examine the feasibility of a process for continuous electrolytic reduction. The reduction rate and current efficiency of the electrolysis were increased with increasing temperature up to 333 K, due to an increase in the diffusion coefficient of uranyl sulfate. The presence of a small amount of HF in the catholyte improved the polarization characteristics of the electrolysis. The precipitation of uranous sulfate occurring in electrolysis above 323 K was eliminated by the addition of HF of 2.3 g dm^-3. However, the addition of the excess amount of HF causes the precipitation of UF₄ on the cathode surface during electrolysis. Increase in electric current was not effective in the semicontinuous electrolytic reduction of U(VI) for catholytes with high reduction ratios, and a catholyte with a composition of around 50 pct reduction ratio is pref-erable for continuous operation. The concentration of U(VI) in a catholyte can be monitored continuously either in the absence or in the presence of HF by using a device consisting of three small electrodes. Formerly Graduate Student in the Department of Metallurgy, Kyoto University Formerly Director, Mining and Ore Processing Division, Ningyo-toge Works, PNC Japan     

Kinetic studies of reduction of CoO and CoWO4 by hydrogen

The present work deals with the studies of the kinetics of reduction of CoO and CoWO₄ in flowing hydrogen gas by thermogravimetric method. The reduction studies for CoO were carried out in the temperature range of 637 to 837 K, while for CoWO₄ reduction, the temperature range was 837 to 1173 K. In the case of the reduction of CoWO₄, the reaction products after reduction were analyzed by X-ray diffraction as well as scanning electron microscopy. The activation energy for the reduction of CoO was found to be of 54.3 kJ/mol. Cobalt tungstate was reduced to a mixture of Co₇W₆ and W, and the activation energy for the reaction is 90.0 kJ/mol. The results are discussed in the light of the reduction kinetics of other transition metal oxides and tungstates under similar conditions.     

Fundamental studies related to the development of the smelting reduction of iron oxide and carbon-constant volume studies

Abstract

Today, most of the iron-making capacity of the world is still dependent upon the blast furnace process, although the production of sponge iron by direct reduction processes is gaining acceptance in many areas. Another method of making iron, known as smelting reduction, is receiving attention, and pilot-plant scale operations are being developed in Europe and possibly elsewhere. In this method, iron oxide is reduced with carbon (coal) by a fast reaction such that liquid iron is the product, heat being provided to the reaction by the exothermic oxidation of carbon monoxide by oxygen within the reaction vessel.

In the present investigation, an attempt has been made to study the behaviour of composite pellets of wüstite and carbon in the region of 1500°C in various gas atmospheres at constant volume. Reaction rates were followed within the constant-volume system by measuring the increase in pressure with time using a pressure transducer. Composite pellets containing slightly more than the stoichiometrically required amount of carbon were reacted to form liquid iron in an argon atmosphere; to achieve melting, good mixing of the pellets was a critical requirement. Melting conditions were also obtained in carbon monoxide-carbon dioxide mixtures between 100 per cent CO and 100 per cent CO₂ When composite pellets, surrounded by a protective layer of carbon, were introduced into an atmosphere containing free oxygen, it was again possible to obtain melting and reduction to liquid iron. The activation energy for the reaction was approximately 15 kcal/mole. Possible reaction mechanisms are discussed.

Résumé

De nos jours, la réduction des oxydes de fer s'accomplit en grande partie au haut foumeau. On note toutefois une implantation graduelle des procédés de réduction directe des oxydes en fer éponge. Une autre méthode de production du fer, connue sous Ie nom de smeltage réducteur, est actuellement à l'étude. Des essais à l'échelle de l'usine pilote se font actuellement en Europe et possiblement ailleurs. La méthode consiste à produire du fer liquide en réduisant rapidement l'oxyde de fer par du carbone. L'énergie requise pour la réaction vient de l'oxydation exothermique du monoxyde de carbone par l'oxygène présént dans l'enceinte réactionnelle.

Les auteurs ont étudié le comportement de boulet1es composées de wüstite et de carbone en présence de diverses atmosphères gazeuses dans une enceinte fermée à 1,500°C. Les vitesses de réaction ont été détérminées en mesurant l'augmentation de la pression dans l'enceinte au moyen d'un transducteur de pression. Des boule1tes composées comportant un peu plus que la quantité stoechiométrique de carbone ont été réduites en fer liquide dans une atmosphère d'argon. La fusion n'avait lieu que si les constituants des boulet1es étaient intimement mélangés. La fusion de boulet1es a été réalisée dans des atmosphères constituées de melanges CO-CO₂, les proportions variant entre 100% CO et 100% CO₂. Le fer liquide a aussi été obtenu en faisant réagir des boulettes d'oxyde et de carbone entourées d'une couche protectrice de carbone, dans une atmosphère contenant de l'oxygène libre. L' énergie d'activation de la réaction était d'environ 15 kcal/mole. En fin, les auteurs discutent des mécanismes de la réaction.     

Kinetic studies of the reduction of FeO and FeWO4 by hydrogen

The kinetics of the reduction of FeO and FeWO₄ have been investigated by thermogravimetric method in the temperature ranges of 1023 to 1173 K and 823 to 1173 K, respectively. The experiments were conducted under isothermal conditions in flowing hydrogen gas. The activation energies for the reduction of the pure iron oxide and iron tungstate were found to be 42.7 kJ/mol and 85.1 kJ/mol, respectively. The results obtained show that the reduction of iron tungstate proceeds in one single step from FeWO₄ to Fe₃W₂ and W. The experimental data are compared with the information available in the literature, and the correlations between the results obtained in pure oxide systems and complex systems are discussed.     

Thermogravimetric and mass spectrometric studies of the reduction of iron niobate by carbon

X-ray diffraction, thermogravimetric, differential thermal, and mass spectrometric analyses are used to study the sequence of phase transformations that occur during the carbothermic reduction of iron niobate FeNb₂O₆ in nonisothermic heating to 1500°C in a flowing argon atmosphere.     

Laboratory reduction rate and current efficiency studies of batch type electrolytic reduction of U(VI) in a sulfate system

The electrolytic reduction of U(VI) was investigated to improve the batch type electrolytic reduction of uranyl sulfate. For this purpose, theoretical considerations were made on the time variation of reduction rate and of current efficiency. A monitoring device consisting of two titanium electrodes and one platinum electrode was developed to determine the reduction ratio and to detect the end point of the reduction of U(VI). The monitoring device worked well for these purposes. The reduction rate in a batch type electrolytic reduction of U(VI) at constant current was larger than theoretically expected. This phenomenon was attributed to the increase in the mass transfer rate of U(VI) species toward the cathode due to the disturbance of the concentration boundary layer by hydrogen gas evolved from the cathode surface. The deterioration of titanium cathode experienced in an operating plant was investigated, and was found to be caused by platinum plating onto the titanium cathode surface during the operation. The deteriorated cathode could be restored by immersing it in a hot aqua regia or a mixture of hydrofluoric acid and phosphoric acid for a few minutes.     

Characterization of striped bass growth hormone receptors by disulfide-bond reduction and cross-linking studies

Growth hormone (GH) receptors were analyzed in striped bass (Morone saxatilis) by addition of disulfide-bond reducing agents to radioreceptor assays and by cross-linking both striped bass and coho salmon (Oncorhynchus kisutch) crude membrane preparations to radiolabeled hormone. Dithiothreitol (DTT) caused a dose-dependent increase in specific binding of 125I-tilapia (Oreochromis mossambicus) GH to striped bass membrane preparations. Maximal enhancement of 3.4-fold was obtained with 1 mM DTT and 0.03 trypsin inhibitor units/ml of aprotinin. Addition of N-ethylmaleimide (NEM), which binds covalently to free sulfhydryl groups, decreased specific binding. Scatchard analysis of striped bass membrane preparations indicated a single class of GH receptors. Addition of DTT with aprotinin increased GH-binding site concentration from 278 to 507 fmol/mg, while the dissociation constant of 0.56 nM remained unchanged. Cross-linking 125I-tilapia GH to striped bass hepatic membrane preparations and 125I-salmon GH to coho salmon membrane preparations yielded two to three specifically labeled proteins on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Endoglycosidase H treatment was without effect on specifically labeled proteins from either species. Following digestion with N-glycosidase F, relative molecular weights of specifically labeled 125I-GH complexes were reduced, suggesting that hepatic GH-binding proteins in striped bass and salmon are N-linked glycoproteins.     

MnO2 reduction by calcium lignosulfonate: the kinetics and mechanism studies

ABSTRACT

The kinetics and mechanism of the reduction of manganese dioxide ore by calcium lignosulfonate (CLS) in acid solution were investigated. The results showed that the reducing process mainly occurred after the adsorption and then decomposition of CLS by ore and the concentration of sulphuric acid exerted an enhancing effect on both CLS adsorption and manganese extraction. The effects of leaching temperature, the mass ratio of CLS to MnO₂ in ore, concentration of sulphuric acid as well as leaching time on per cent leached of Mn were also discussed. The experimental data were well interpreted with a shrinking core model of internal diffusion, and an overall kinetic model was established. The reaction rate constant was found to be proportional to the mass ratio of CLS to MnO₂ in ore and concentration of sulphuric acid, and the apparent activation energy was determined to be 69.4?kJ?mol^?1 by using Arrhenius expression.     

Enzymatic analysis of acetylpolyamine

An enzymatic method was proposed for measuring acetylpolyamine (AcPA) alone, even when non-acetylated polyamine co-exists. The method consisted of four enzymatic reactions. First, AcPA was hydrolysed by acylpolyamine amidohydrolase to yield acetate; followed by the other three reactions coupled with three enzymes, respectively, acetate kinase, pyruvate kinase, and lactate dehydrogenase; the acetate formation caused a decrease in NADH. The quantity of AcPA was then evaluated as the change in absorbance at 340 nm. The reagent composition of the reaction mixture was determined, and characteristics of the method were investigated. The validation tests produced satisfactory results. The co-existence of non-acetylated polyamine gave no effect on the measurement. The present method was found to be used easily, rapidly and reliably for the selective determination of AcPA itself.     

Hot extrusion of aluminum powder at low reduction ratios: Analytical and metallographic studies

This paper deals with an investigation into the flow of aluminum powder billet during hot extrusion at low reduction ratios through square edge die under axisymmetric conditions. Analytical studies using the finite element method as well as the experimental observations are reported for various low reduction ratios ranging from 1.3:1 to 3.2:1 at extrusion temperatures, 300, 400, and 500 °C; friction effects have also been included. Extrusion pressures, velocity vectors, average pressure contours, and effective strain-rate contours are obtained using a velocity-pressure relationship. Analytical extrusion pressures agree quite well with experimental values. Metallographic investigations of the longitudinal section of partially extruded billets reveal very clearly the flow of the material in the different regions,viz., inside the container, near the die and the extruded portion, and are correlated with analytical results.     

吡咯/炭黑氧化物复合氧阴极材料的制备及催化性能

氧还原反应(ORR) 是碱性燃料电池和金属-空气电池的重要阴极反应.由于常见的铂基氧阴极材料存在价格昂贵、稳定性较低等问题, 因此, 开发低成本、高效率的非贵金属基氧阴极材料具有重要的研究意义和应用价值.氮掺杂碳材料是目前氧阴极材料研究的热点, 炭黑中碳原子的排列方式类似于石墨, 由于其价格低廉、来源广泛, 在碳材料的研究中具有独特的优势.本文基于炭黑, 采用化学法制备了氮掺杂炭黑氧阴极材料, 研究了其氧还原反应催化活性, 并进行了相关表征.结果显示炭黑-吡咯复合材料具有极好的氧还原反应活性, 700℃热处理后性能最优, 在1 mol·L-1KOH中其起峰电位约为0. 9 V, 极限扩散电流密度为2. 6 m A·cm-2, 转移电子数高于3. 5, 这些特性使得这类材料具有广阔的应用前景.      

Enzymatic amplification of lactate dehydrogenase-elevating virus

To improve the detection of lactate dehydrogenase-elevating virus (LDV), we developed a PCR assay. Primers were selected from ORF7, encoding nucleocapsid protein VP1. No specific amplification was observed with any other common murine virus or with RNAs from the closely related Lelystad virus and equine arteritis virus. In experimentally infected mice, LDV could be detected in plasma in both the acute and the persistent phases. LDV was also detected by the PCR in contaminated pools of Plasmodium berghei parasites which were maintained in mice, both by a direct analysis of the samples and by testing of plasma from mice inoculated with these pools. There was a complete agreement between the results of the PCR assay and the lactate dehydrogenase (LDH) enzyme assay of plasma from the inoculated mice. In contrast to the results of the LDH enzyme assay, no false-positive reactions were obtained in the PCR assay with negative control samples showing visible hemolysis. Storage of plasma samples at room temperature and at 4, -20, and -80 degrees C for up to 8 days did not influence the results of the PCR. These results show that the PCR is a valuable technique which may replace the LDH test as a diagnostic tool.     

Enzymatic assay of D-mannose in serum

We describe a new and improved enzymatic assay for determining the concentration of D-mannose in sera. Serum D-glucose is selectively converted to glucose-6 phosphate with the highly specific thermostable glucokinase (EC 2.7.1.2) from Bacillus stearothermophilus. The anionic reaction products and excess substrates are removed by a rapid and simple anion-exchange chromatography step in microcentrifuge spin columns. D-Mannose in the glucose-depleted sample is then assayed spectrophotometrically by using coupled enzymatic reactions. The quantitative elimination of glucose from the serum samples allowed the accurate and reproducible assay of serum mannose in the 0-200 mumol/L range. Recovery of mannose added to serum (5-200 mumol/L) was 94% +/- 4.4%. The intraassay CV was 6.7% at 40 mumol/L mannose (n = 5; 39.6 +/- 1.6 mumol/L) and 4.4% at 80 mumol/L (n = 11; 75.0 +/- 1.8 mumol/L); the interassay CV at these concentrations was 12.2% (n = 7; 36.9 +/- 2.1 mumol/L) and 9.8% (n = 7; 74.2 +/- 2.7 mumol/L), respectively. Sera from 11 healthy human volunteers contained an average of 54.1 +/- 11.9 mumol/L mannose (range 36-81 mumol/L).     

The assessment of human body composition during weight reduction: evaluation of a new model for clinical studies

Adipose tissue, the logical target component in weight reduction regimens, was measured in five obese subjects during weight reduction, and in four normal weight controls. The two compartment model of Ljunggren, consisting of adipose tissue (AT) and adipose tissue-free mass (AFM), was further developed by finding experimental values for total water, extracellular water (ECW), lipid, and cell solids in 16 biopsied subjects. The AFM was estimated from body potassium content (40K counting) by use of an age/sex specific constant for the K content in the fat free body. Five obese subjects maintained for 46 days on regimens averaging 800 kcal/day had initial AT from 48% to 60% of body weight compared with AT 27% to 46% in four normal controls. Weight reductions averaged 17.4 kg (12% of initial weight), with approximately equal reductions in adipose tissue, adipose-free mass, and water. Initial fluid compartment ratios in the obese were unusually high (ECW:ICW in AFM was 0.74 +/- 0.23 [S.D.] compared with 0.42 +/- 0.05 in normals); these values returned toward normal (to 0.59 +/- 0.06) with weight reduction. The fact that it was possible to disclose a hitherto unappreciated abnormality of hydration in the adipose-free mass of obese subjects and its change toward normal with weight reduction, suggests that the adipose:adipose-free model may have a special utility when body composition measurements are used to monitor the effects of weight reduction regimens on various body constituents.     

Enzymatic properties of neuraminidase from corynebacterium diptherial

Enzymatic properties of neuraminidase isolated from non-toxigenic strain C7 of diphteritic bacteria are studied. The enzyme has the pH optimum 5.5--6.0 in acetate buffer and the temperature optimum 38 degrees C. Neuraminidase has the highest substrate affinity to glycoproteins of equine blood serum, the lowest affinity--to 3-N-acetylneuraminosyllactose and ovomucin. The Km values was 4.3-10(-4) at optimal conditions under the hydrolysis of 3-N-acetylneuraminosyllactose, Vm was 0.05+/-0.02 muM NANA/hour/mg of protein. The following esters of N-glyconoyl-glycine were shown to be competitive inhibitors of neuraminidase: 1) methyl ester of 3-aza-4-oxo-2,3,4-trideoxy-D-arabinooctonic acid; 2) methyl ester of 3-aza-4-oxo-2,3,4-trideoxy-D-glucoheptodecanic acid; 3) methyl ester of 3-aza-4-oxo-2,3,4-trideoxy-D-galactonic acid; 4) methyl ester of 3-aza-4-oxo-2,3,4-trideoxy-D-gluconic acid, Ki values being 6.5-10(-4), 4.5-10(-4); 9.5-10(-4) and 7.1-(10-3) M, respectively.