Initial Reduction Rate Research Articles

The oxidative dehydrodimerization of propylene over BiSn oxide catalysts: III. Reduction and temperature-programmed reoxidation of the catalyst

A bismuth-tin oxide catalyst, which is active for the oxidative dehydrodimerization of propylene, was studied with the objective of characterizing its redox properties. The redox properties were investigated by kinetic methods and temperature-programmed reoxidation. The initial rate of reduction of the catalyst exhibited a first-order dependence on propylene partial pressure and an activation energy of 22 kcal/mol. The results of the temperature-programmed reoxidation investigation suggested a low-temperature reoxidation region and a high-temperature reoxidation region. The activation energy for the low-temperature reoxidation was 23 kcal/mol; the activation energy for the high-temperature reoxidation was 45 kcal/mol. Additional information regarding the physicochemical changes which occur in the catalyst in the two temperature regions was obtained from an examination of the catalyst by Auger and ESCA. The results obtained from these investigations suggested that the tin cations are more resistent to reduction than the bismuth cations. In addition, the low-temperature reoxidation appears to be associated with the transformation of Sn 0 to Sn 4+ and Bi 0 to possibly an intermediate oxidation state. The high-temperature reoxidation appears to be associated with the full reoxidation of Bi to Bi 3+. The redox properties and the physicochemical changes also correlated with the mechanism suggested for the oxidative dehydrodimerization of propylene in the earlier studies.

Nitrogenase Activity (C2H2) of Isolated Peanut and Cowpea Bacteroids under Nitrogen, Argon, and Helium Atmospheres

Peanut nodules have been reported to have several times higher nitrogenase activity (C2H2) than cowpea and siratro nodules induced by the same rhizobial strains. The unique morphological modification of the peanut bacteroids has been considered to be the cause for such enhanced activity. To investigate this possibility, nitrogenase activities of isolated peanut and cowpea bacteroids were compared. Peanut bacteroids showed low initial rates of C2H2 reduction which increased with time, but for cowpea bacteroids higher initial rates decreased with time. Moreover, the gases used as diluent for 02 (N2, Ar, or He) were found to influence 02 tolerance and

Ethylene oxidation to acetic acid with Pd-V 2O 5 type catalysts : I. Gas-solid reactions

Palladium added to V 2O 5 enhances the reducibility of this oxide. The reduction can then be performed at low temperature so as to produce selectively a reduced phase with the formula V 4O 9. The influence of ethylene partial pressure on the initial reduction rate of Pd-V 2O 5 and the influence of oxygen partial pressure on the initial oxidation rate of the reduced phase have been established. Kinetic equations are proposed for these two gas-solid reactions. The selective formation of acetaldehyde and acetic acid occurs during the reduction. In the presence of both ethylene and oxygen reactants, i.e., for the condition of catalytic reaction, we observe a change of the initial composition of the solid toward a final state which depends on the partial pressure of the reactants. Qualitatively, from an initially oxidized form, there is a partial reduction, while from an initially reduced form, V 4O 9, there is a partial oxidation.

Flavocytochrome b2 (Baker's yeast). Deuterium isotope effect studied by rapid-kinetic methods as a probe for the mechanism of electron transfer.

The use of DL-[2-2H]lactate in steady-state measurements of ferricyanide reduction by flavocytochrome b2 at 30 degrees C has previously yielded an isotope effect of 5 [F. Lederer (1974) Eur. J. Biochem. 46, 393--399]. We report here studies carried out at 5 degrees C with L-[2-2H]lactate, where flavin and heme reduction were observed in the stopped-flow apparatus, in the absence of acceptor. The generally biphasic reduction curves were analysed according to a new mathematical treatment which allowed us to derive microscopic constants from initial reduction rates. It has thus been possible to determine an isotope effect of 8 on flavin reduction, 6 on heme reduction, compared to 4 in the steady state. Consequently, two slightly rate-limiting steps occur after the first one where the alpha-hydrogen is abstracted. It has also been possible to calculate the substrate association and dissociation rate constants for intact enzyme. The studies were carried out in parallel on intact and cleaved cytochrome b2. The results suggest that proteolysis affects essentially the steps involved in flavin reduction, and not intramolecular electron transfer steps. Moreover, the experimental data obtained at low rates of electron entry have led us to reexamine a previously proposed scheme for electron transfer [Capeillère-Blandin, Bray, Iwatsubo and Labeyrie (1975) Eur. J. Biochem. 54, 549--566]. An alternative model based on computer-simulation studies will be presented in a paper in this journal.

Bacterial cycling of sulfur in a Baltic sediment: An in situ study in closed systems

Bacterial cycling of sulfur at the sediment‐water interface was studied in situ at 10‐m water depth in both transparent and opaque closed‐box systems over a period of 245 days. Reducing processes dominated at Eh values below +200 mV. In the transparent systems, oxygen was produced because of photosynthesis and the redox turnover was delayed 30 days compared to the opaque systems in which reducing conditions were established in 10 days. The initial rates of bacterial sulfate reduction were 0.22 and 0.35 g SO4‐S m‐2 day‐1 for the opaque and transparent systems, respectively. The bacteria generated sulfide at rates corresponding to the depletion of sulfate. Photosynthetic sulfur bacteria developed in the transparent systems, and sulfide was oxidized at twice the rate of its formation, equal to 0.7 g sulfide‐S m‐2day‐1. A stepwise oxidation of sulfide, via elemental sulfur to sulfate, was demonstrated. Sulfate reduction dominated the opaque systems and also the transparent ones with insufficient light.

The control of 3-phosphoglycerate reduction in isolated chloroplasts by the concentrations of ATP, ADP and 3-phosphoglycerate

1. 1. Oxygen evolution by reconstituted chloroplasts with 3-phosphoglycerate as substrate was inhibited by ADP. This inhibition was overcome by increased concentrations of 3-phosphoglycerate or by the addition of excess ATP. 2. 2. The initial rate of 3-phosphoglycerate reduction by chloroplast stromal extracts, measured as 3-phosphoglycerate-dependent oxidation of NADPH, was also dependent on the concentrations of 3-phosphoglycerate, ADP and ATP. 3. 3. Within the range of concentrations of 3-phosphoglycerate, ADP and ATP expected to occur within intact chloroplasts, the rate of 3-phosphoglycerate (PGA) reduction by stromal extract was proportional to the ratio [ATP] [PGA]/[ADP]. 4. 4. These results are consistent with the notion that the substrates and products of 3-phosphoglycerate kinase control the rate of 3-phosphoglycerate reduction via a mass action effect.

Réduction catalytique de cétones α,β-éthyléniques à température modérée par

The use of the catalyst [Formula: see text] in the reduction of the ethylenic system of styryl ketones by 1-phenylethanol permits the hydrogenation reaction to proceed at 50 °C. Some substituent effects in the α,β-unsaturated ketones were demonstrated at this temperature. These showed an increase in the initial rate of reduction for electron-attracting groups and the inverse effect for electron-donating groups. The observation of a relation between the electrochemical reduction potential of these ketones and their rate of hydrogenation suggests a transfer of hydrogen to the ketone by a hydride ion intermediate. [Journal translation]

Interaction of β-lactoglobulin and cytochrome c: Complex formation and iron reduction

β-Lactoglobulin forms a soluble complex with cytochrome c in mildly alkaline solutions of low ionic strength. Sedimentation velocity experiments suggest that the complex (maximum s 20 = 3.7) consists of one cytochrome c molecule per β-lactoglobulin monomer unit. At pH 8 or higher, the presence of β-lactoglobulin causes reduction of ferri- to ferrocytochrome c. The initial rate of reduction at a single temperature depends primarily on the concentration of β-lactoglobulin, although the final percentage ferrocytochrome c obtained is constant at molar ratios of three or more β-lactoglobulin monomers to one cytochrome c molecule. The temperature dependence of the initial rate of iron reduction resembles that for alkaline denaturation of β-lactoglobulin. The displacement of N-dansylaziridine, a sulfhydryl specific dye, from bovine β-lactoglobulin during iron reduction, and the formation of nonreducing complexes between the analogous swine protein (no sulfhydryls) and cytochrome c suggest that the sulfhydryl group of β-lactoglobulin is the electron donor.

Relation between propylene oxidation performance of copper-based bimetallic catalysts and the redox behaviour of their surfaces

Propylene oxidation and surface oxidation–reduction rate processes on supported bimetallic catalysts which consist of Cu as substrate with small amounts of adherent Ag, Au or Rh have been studied and the relation between them discussedThe adhering components enhanced the rates of both the reduction of a preoxidized surface and of propylene oxidation in the order Rh Au > Ag, but exerted no effect on the oxidation rate of a prereduced surface.The reduction processes were kinetically divided into three stages as follows: (1) the accelerating reduction rate period (ARP; fraction reduced x [graphic omitted] 0–0.3), (2) the maximal reduction rate period (MRP; x [graphic omitted] 0.3–0.8), (3) the decelerating reduction rate period (DRP; x [graphic omitted] 0.65–0.95).For all the catalysts, Arrhenius parameters of each reduction rate coefficient in the period MRP and DRP, and the rate of propylene oxidation showed compensation effects: log A=E/(2.3 RTs)+ log Cs and indicated the same isokinetic temperature Ts, (615 ± 9 K). E for the initial reduction rate (Ek) was correlated with that of the rate of propylene oxidation (Eo) for each catalyst by the expression Ek=Eo+(8.5 ± 0.9) kcal mol–1.The accelerating effects of the adhering components were observed during the incubation period in the early stages of ARP. This indicates that small amounts of a metal which is more difficult to oxidize than Cu, having a dispersed structure on the surface of Cu substrate exhibit a spillover of the reductant gas, and perform the role of initiation nuclei for reaction with the surface oxygen.

Surface Charge Variation in Aging Ferric Hydroxide

AbstractThe variation with time of exchangeable surface charge of amorphous ferric hydroxide in aqueous suspension was monitored by a titration technique. After 120 days, the surface charge of suspensions with initial pH from 8.5 to 10.5 was about one-fourth of the initial value, and goethite had formed from the ferric hydroxide. After the same time interval, the exchangeable surface charge of suspensions with initial pH from 5.5 to 8.0 was about two thirds the original value and the ferric hydroxide was still largely amorphous. The initial rate of crystallization and surface charge reduction increased with initial pH for suspensions with pH from 8.5 to 10.5, whereas the rate of surface charge reduction appeared to be independent of pH for suspensions with initial pH between 5.5 and 8.0. Based on these results it is suggested that at pH from 8.5 to 10.5 ferric hydroxide ages to goethite via a solution stage involving the Fe(OH)4- ion, whereas at pH values below 8.5 ferric hydroxide aging proceeds via mechanisms which do not involve the particle surface or bulk solution.

Differences Caused by Different Inducing Substances in the Specificity of Hydroxylases and in the Type of Hydroxylating Cytochrome in Liver Microsomal Fractions

(ethanol and phenacetin) were added to liver microsomal preparations (all at a concentration of 1 mM) to determine their effects on both the initial rate of reduction and the final absorbance (45W90nm) change. It was found that type I1 compounds inhibited the initial rate by over 50% and also decreased the final absorbance change (i.e. inhibited CO binding to the reduced cytochrome). RI compounds, however, had either no effect or inhibited the initial rate to a lesser degree and barely affected the final 450-490nm absorbance change (Fig. 1). Results from this approach agreed with the preliminary classification of the benzimidazoles into type I1 and RI compounds. It appears that the type of binding of the 2-substituted benzimidazoles is determined by the nature of the substituent in the 2-position. If the 2-position is unsubstituted or contains a primary amino or carboxylic acid grouping, then a type I1 spectrum is observed. However, any other substituent. even a methyl group leads to the observation of a RI spectrum.

NO2-Tyr82 and NH2-Tyr82 derivatives of adrenodoxin. Effects of chemical modification on electron transferring activity

Bovine apoadrenodoxin was treated with tetranitromethane to introduce a nitro group into the tyrosyl residue at position 82 of this protein. The degrees of nitration under the best conditions were estimated to be 90% and nearly 100% on the basis of amino acid analysis and the spectrophotometric method, respectively. An amino derivative was prepared by reducing the nitro group with sodium dithionite. The apoadrenodoxin derivatives could be reconstituted to have an iron-sulfur chromophore similar to the native adrenodoxin which contains a 1:1 molar ratio of labile sulfur to iron content and displays absorption peaks at 414 and 450 nm. The enzymatic acitivies of these reconstituted nitro and amino derivatives toward cytochrome c reduction in the presence of adrenodoxin reductase and NADPH were 19 and 7% of native adrenodoxin, respectively. We studied the kinetics of the direct reduction of the reconstituted amino derivative in the presence of NADPH and adrenodoxin reductase under anaerobic conditons. The initial rate of reduction for the amino derivative was 7% of the native adrenodoxin, which is in good agreement with its activity toward cytochrome c reduction. From these results, it is concluded that by modifying the tyrosyl residue at position 82 of the adrenodoxin polypeptide, the electron-transferring activity of the molecule is largely diminished.

43] Glucose-6-phosphate dehydrogenase from cow adrenal cortex

Publisher Summary This chapter explains the glucose-6-phosphate dehydrogenase from cow adrenal cortex. During the purification procedure, dehydrogenase activity is measured by monitoring the initial rate of reduction of NADP + or NAD + . Increase in absorbance at 340 nm is followed using a Beckman spectrophotometer with recorder. The reactions are initiated with glucose 6-phosphate or 6-phosphate gluconate. All assays are made with the enzyme diluted to 1–20 μ g protein per 3 ml and were performed under the conditions of zeroorder kinetics for substrates. A typical purification of adrenal glucose 6-phosphate dehydrogenase is summarized. Purification of fresh adrenal tissue was carried through to fraction IV, since this fraction could be stored frozen for several weeks with minimum loss of enzyme activity. The pH is kept between pH 6 and 7 with the early fractions, possibly because of proteases that may be less active at a lower pH. Adrenal glucose-6-phosphate dehydrogense is most stable in the presence of either NADP + or glucose 6-phosphate. Phosphate buffers are used during purification. The ten fractionation steps (step 4 was a storage step) produced a 250-fold purification with a 20% yield. The entire procedure usually required a 3-week period of collecting and processing to the fraction IV stage and 1 week between fraction IV and preparation of crystals. The final specific activity is 340 μ moles of NADP + reduced per minute per milligram of protein in 37° in 0.1 M Tris buffer at pH 8.0 with Mg 2+ .

Gaseous reduction of magnetite superconcentrate compacts

The reduction rate of superconcentrate magnetite compacts in the form of small discs has been investigated in the temperature range of 4000–1250°C using hydrogen as the reducing agent, andfrom 1000° to 1250°C using mixtures of hydrogen and carbon monoxide as the reducing agent. The maximum reduction rate for 100% reduction occurred at 570°C and a reduction rate minimum occurred at 750°Cfollowed by a second rate minimum at 960°C when hydrogen was the reducing gas. The initial rate of reduction increased with temperature over the complete temperature range but during the final stages of reduction the rate rapidly decreased. For 100% reduction at 570°C, the reduction rate with hydrogen wasfaster than at any other temperature with hydrogen or 100% carbon monoxide. Mixtures of hydrogen and carbon monoxide gave the fastest reduction rate and the time for total reduction decreased with increasing temperature. Increases in thickness of the superconcentrate discs increased the reduction time but at a rate less than direct proportionality. The calculated activation energies correspond with values determined by other investigators.

Involvement of the superoxide free radical ion in photosynthetic oxygen reduction.

Abstract Photosynthetic oxygen reduction by isolated chloroplast lamellar systems has been studied with the aid of superoxide dismutase. Two mechanisms of oxygen reduction by illuminated chloroplast lamellar systems can be differentiated: 1. In the presence of low potential electron acceptors like AQ or MV the superoxide free radical ion is the product of autooxidation of the reduced acceptor. Addition of superoxide dismutase has no influence on the initial rates of oxygen reduction. 2. Stimulation of photosynthetic oxygen reduction by o-diphenols is only observed in the absence of superoxide dismutase and ascorbate; apparently the superoxide free radical ions is involved in both initiation and propagation of a chain reaction. If the ferredoxin-stimulated photosynthetic oxygen reduction is measured, both ascorbate and superoxide dismutase are active as inhibitors. By heating suspensions of chloroplast lamellar systems, a substance is released into the supernatant which exhibits the activity of an oxygen reducing factor (ORF) with properties similar to o-diphenols: The stimulation of photosynthetic oxygen reduction is reversed by addition of either SDM or ascorbate. A reaction sequence for photosynthetic oxygen reduction in the presence of ferredoxin is considered, which is initiated by the superoxide free radical ion produced by autooxidation of reduced ferredoxin; the superoxide free radical ion "activates" an endogenous oxygen reducing factor, which in this "active" state can reduce oxygen to O2·-. The presence of either superoxide dismutase or ascorbate yields in chain termination by scavenging the superoxide free radical ion

Diminution of acetylene reduction during assay of detached soybean nodules

Initial rates of acetylene reduction were observed to decline after about 2 h at a given ratio of detached soybean nodule mass to assay vessel vol. Such decreases occurred despite final concentrations of oxygen at 20–30 per cent. and could not be attributed to depletion of acetylene or to accumulation of hydrogen or carbon dioxide. Nodules held briefly at high nodule mass to container vol. ratio gave evidence of progressive inactivation with holding time when subsequently assayed. A search for possible gaseous inhibitors revealed several unknown products that occurred consistently during prolonged acetylene reduction assay. One product observed during assay gave a peak on the gas chromatogram that was determined by the initial concentration of oxygen, and varied inversely with the ethylene peak. The compound responsible for this peak was identified as ethanol. Ethanol vapor added to the assay system inhibited acetylene reduction after 2 h. A high initial oxygen concn depressed somewhat the inhibitory effect of ethanol.

Reaction Mechanism of Ribonucleoside Diphosphate Reductase from Escherichia coli: OXIDATION-REDUCTION-ACTIVE DISULFIDES IN THE B1 SUBUNIT

Abstract Ribonucleoside diphosphate reductase consists of two nonidentical subunits, proteins B1 and B2. The enzyme catalyzes the reduction of ribonucleotides to the corresponding deoxyribonucleotides. The electrons required in this reduction are transported from NADPH via a flavoprotein, thioredoxin reductase, to a low molecular weight protein, thioredoxin. The reduced form of thioredoxin acts as hydrogen donor in ribonucleotide reduction. Both thioredoxin and thioredoxin reductase contain oxidation-reduction active disulfides participating as electron carriers during catalysis. In this paper, data are presented which show that in the absence of hydrogen donor, ribonucleotide reductase reduces a limited amount of ribonucleotides at the expense of sulfhydryls of protein B1. A maximal value of 3 moles of deoxyribonucleotide was obtained per mole of B1 and at the same time 6 moles of sulfhydryls were oxidized. The reaction requires the presence of protein B2. The same initial rate of cytidine diphosphate reduction was obtained in the presence and in the absence of reduced thioredoxin. Electron transfer occurred readily between fully reduced B1 and the oxidation-reduction active disulfide of thioredoxin. Steady state kinetics of ribonucleotide reductase indicated that the enzyme acted by a ping-pong mechanism, i.e. alternated between two stable forms during catalysis. Based on these results it is proposed that in the reduction of ribonucleotides, electrons flow from thioredoxin to oxidationreduction active disulfides of protein B1. The dithiols formed interact by unknown mechanisms with a free radical species in protein B2 (Atkin, C. L., Thelander, L., Reichard, P., and Lang, G. (1973) J. Biol. Chem. 248, 7464–7472) to reduce the ribonucleotide.

Effects of anti-human neutrophil antibodies in vitro. Quantitative studies.

Opsonic, antiphagocytic, cytotoxic, and metabolic effects of homologous and heterologous antibodies against human neutrophils were analyzed by means of quantitative assays to facilitate detection of antibody activity, and to probe membrane function of these cells. Normal human neutrophils were purified by gradient centrifugation, sensitized with heat-inactivated antineutrophil antisera, and incubated with rabbit alveolar macrophages in balanced salt solution containing nitroblue tetrazolium. The macrophages engulfed sensitized neutrophils and reduced nitroblue tetrazolium to formazan in phagocytic vacuoles. The initial rate of nitroblue tetrazolium reduction by macrophages ingesting the neutrophils was measured spectrophotometrically. Neutrophils treated with rabbit anti-human leukocyte antiserum or IgG, with sera from mothers of infants with neonatal isoimmune neutropenia, and with 27% of sera from frequently transfused patients promoted rapid rates of nitroblue tetrazolium reduction by alveolar macrophages. This indicates that antineutrophil antibodies without added complement opsonized neutrophils for ingestion by the macrophages. Some sera from frequently transfused patients with opsonic activity for certain donors' neutrophils did not agglutinate these neutrophils (44%), did not lyse them in the presence of fresh plasma (47%), and did not inhibit phagocytosis of particles by the neutrophils (26%). The reverse was not observed. The opsonic activity of antineutrophil antiserum appears to be the most sensitive and a quantitative means of detecting antibody activity in vitro.Low concentrations of rabbit anti-human leukocyte antisera or IgG stimulated the ingestion rate of unopsonized or opsonized particles by human neutrophils, and, as previously reported by others, enhanced rates of oxidation of [1-(14)C]glucose by the cells. High concentrations of the antisera or IgG inhibited ingestion. All concentrations of homologous antineutrophil antisera tested only inhibited ingestion of particles by neutrophils and none altered rates of resting glucose oxidation by the cells. The findings suggest that heterologous antibodies disturb membrane antigens that trigger oxidative metabolism and enhance as well as inhibit ingestion, and that these antigens are common to all human neutrophils. In contrast to other studies with antimacrophage antibodies, antineutrophil antibodies altered phagocytic rates of both unopsonized and opsonized particles although there were differences in dose-response curves depending on the type of particle tested. Thus, antineutrophil antibodies do not merely cover selected receptor sites.

Phagocytosis of Antibody-Coated Platelets by Human Granulocytes

To determine whether anti-platelet antibodies act as opsonins to promote phagocytosis of sensitized platelets, normal human platelets were exposed to a variety of serums containing anti-platelet antibodies, and then incubated with autologous granulocytes. Phagocytosis was observed microscopically, by uptake of 51Cr-labeled platelets, and by initial rate of reduction of nitroblue tetrazolium. Phagocytosis and the initial rate of dye reduction were increased as compared to control serums, by serums from 14 patients with idiopathic thrombocytopenic purpura, from 13 patients refractory to platelet transfusion, and from rabbits immunized with washed human platelets. The opsonic activities of serums from patients with idiopathic thrombocytopenic purpura persisted after treatment with steroids or splenectomy. Thus antibody-mediated phagocytosis may be important in the pathogenesis of idiopathic thrombocytopenic purpura and in the clearance of sensitized platelets. (N Engl J Med 290:989–993, 1974)

Glucose release measurements from liposomes with an oxygen electrode

A method for measuring glucose release from liposomes by means of an oxygen electrode is described. The glucose concentration is determined from the initial rates of oxygen reduction catalysed by glucose oxidase. The reduction is directly proportional to either glucose (0.066–3.0 mM) or enzyme concentration (0.3–10 μg). The enzyme does not penetrate lipid bilayers and free glucose can be measured directly. Trapped glucose can be released and measured in the presence of detergents which do not interfere with the assay. By using appropriate calibration curves, glucose concentrations could be determined under extreme conditions of pH (3–9.5), temperature (10–51 °C), and in the presence of various salts and buffers. The application of polarographic methods for studies of the permeability of amino acids and other sugars is discussed.