Decomposition of aqueous dithionite. Part II. A reaction mechanism for the decomposition of aqueous sodium dithionite

1970 ◽  
Vol 48 (5) ◽  
pp. 782-787 ◽  
Author(s):  
M. Wayman ◽  
W. J. Lem
Keyword(s):  
Induction Period ◽  
Sodium Dithionite ◽  
Side Reactions ◽  
Induction Phase ◽  
Time Curve ◽  
Rapid Phase ◽  
Aqueous Sodium ◽  
Ph Values ◽  
Decomposition Time ◽  
Rate Limiting

The decomposition of dilute aqueous sodium dithionite has been studied in unbuffered solutions by means of continuous polarography, accompanied by recorded pH values. The decomposition–time curve began with a slow "induction" period followed by an S-shaped rapid phase. The pH values decreased slightly during the induction period and increased considerably during the rapid phase. The addition of a solution of fresh decomposition products eliminated the induction phase. The addition of sulfide also eliminated the induction period and catalyzed the reaction. The accepted stoichiometry (2) of the reaction was confirmed. The following sequence of reactions is proposed[Formula: see text][Formula: see text]In the presence of H2S and possibly S formed in side reactions which consume H+, reaction [5] is catalyzed and may be represented as[Formula: see text]and[Formula: see text]The rate equation is represented as[Formula: see text]Reaction [4] is rate limiting during the induction period and reaction [5] (catalyzed), during the rapid phase of decomposition.

Study on desorption of Mn, Fe, and Mg from TMP and evaluation of the complexing strength of different chelating agents using side reaction coefficients 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Holzforschung ◽  
2009 ◽  
Vol 63 (6) ◽  
Author(s):  
Kim Granholm ◽  
Pingping Su ◽  
Leo Harju ◽  
Ari Ivaska
Keyword(s):  
Citric Acid ◽  
Metal Ions ◽  
Chelating Agents ◽  
Side Reaction ◽  
Sodium Dithionite ◽  
Thermomechanical Pulp ◽  
Peroxide Bleaching ◽  
Ph Values ◽  
Reducing Environment ◽  
Ph Range

Abstract Chelation of thermomechanical pulp (TMP) was studied in this work. The desorption of Mn, Fe, and Mg due to their impact on peroxide bleaching was investigated. The desorption experiments were performed with EDTA, citric acid, oxalic acid, and formic acid as chelating agents at different pH. Chelation experiments with EDTA were carried out at pH 3–11. Sodium dithionite was used as the reducing agent in studying chelation with EDTA in a reducing environment. Mn was very effectively desorbed with EDTA from TMP at pH <10 and the reducing environment further improved the removal of all the studied metal ions from TMP with EDTA. Citric acid also removed Mn effectively from TMP at pH 5. The thermodynamic stability constants of different metal chelates do not present the correct picture of how strongly the metal ions are bound by the chelating agents in different conditions. But by means of the side reaction coefficients (α M(L)-coefficients) it is also theoretically possible to evaluate and compare the real binding strengths between the metal ions and different chelating agents at varying pH values and other solution conditions. In this study, a theory is given for the calculation of side reaction coefficients. Values of the α M(L)-coefficients, for the pH range 0–14, are presented for EDTA, DTPA, and also for some other new potential environmentally friendly chelating agents.

scholarly journals Mechanism of d-fructose isomerization by Arthrobacterd-xylose isomerase

1992 ◽  
Vol 283 (1) ◽  
pp. 223-233 ◽  
Author(s):  
M Rangarajan ◽  
B S Hartley
Keyword(s):  
Ring Opening ◽  
Ph Dependence ◽  
Xylose Isomerase ◽  
Competitive Inhibitor ◽  
Apparent Dissociation Constant ◽  
Ph Values ◽  
Rate Limiting Step ◽  
Competitive Inhibitors ◽  
Rate Limiting ◽  
Very High

The mechanism of D-fructose isomerization by Arthrobacter D-xylose isomerase suggested from X-ray-crystallographic studies was tested by detailed kinetic analysis of the enzyme with various metal ions at different pH values and temperatures. At D-fructose concentrations used in commercial processes Mg2+ is the best activator with an apparent dissociation constant of 63 microM; Co2+ and Mn2+ bind more strongly (apparent Kd 20 microM and 10 microM respectively) but give less activity (45% and 8% respectively). Ca2+ is a strict competitive inhibitor versus Mg2+ (Ki 3 microM) or Co2+ (Ki 105 microM). The kinetics show a compulsory order of binding; Co2+ binds first to Site 2 and then to Site 1; then D-fructose binds at Site 1. At normal concentrations Mg2+ binds at Site 1, then D-fructose and then Mg2+ at Site 2. At very high Mg2+ concentrations (greater than 10 mM) the order is Mg2+ at Site 1, Mg2+ at Site 2, then D-fructose. The turnover rate (kcat.) is controlled by ionization of a residue with apparent pKa at 30 degrees C of 6.0 +/- 0.07 (Mg2+) or 5.3 +/- 0.08 (Co2+) and delta H = 23.5 kJ/mol. This appears to be His-219, which is co-ordinated to M[2]; protonation destroys isomerization by displacing M[2]; Co2+ binds more strongly at Site 2 than Mg2+, so competes more strongly against H+. The inhibition constant (Ki) for the two competitive inhibitors 5-thio-alpha-D-glucopyranose and D-sorbitol is invariant with pH, but Km(app.) in the Mg[1]-enzyme is controlled by ionization of a group with pKa 6.8 +/- 0.07 and delta H = 27 kJ/mol, which appears to be His-53. This shows that Km(app.) is a complex constant that includes the rate of the ring-opening step catalysed by His-53, which explains the pH-dependence. In the Mg[1]Mg[2]-enzyme or Co[1]Co[2]-enzyme, the pKa is lower (6.2 +/- 0.1 or 5.6 +/- 0.08) because of the extra adjacent cation. Hence the results fit the previously proposed pathway, but show that the mechanisms differ for Mg2+ and Co2+ and that the rate-limiting step is isomerization and not ring-opening as previously postulated.

scholarly journals Outdoor Large-Scale Cultivation of the Acidophilic Microalga Coccomyxa onubensis in a Vertical Close Photobioreactor for Lutein Production

Processes ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 324 ◽  
Author(s):  
Juan-Luis Fuentes ◽  
Zaida Montero ◽  
María Cuaresma ◽  
Mari-Carmen Ruiz-Domínguez ◽  
Benito Mogedas ◽  
...  
Keyword(s):  
Biomass Production ◽  
Large Scale ◽  
Culture Conditions ◽  
High Concentration ◽  
Ph Values ◽  
Lutein Content ◽  
Acidic Waters ◽  
Large Scale Cultivation ◽  
Rate Limiting ◽  
Lutein Production

The large-scale biomass production is an essential step in the biotechnological applications of microalgae. Coccomyxa onubensis is an acidophilic microalga isolated from the highly acidic waters of Río Tinto (province of Huelva, Spain) and has been shown to accumulate a high concentration of lutein (9.7 mg g−1dw), a valuable antioxidant, when grown at laboratory-scale. A productivity of 0.14 g L−1 d−1 was obtained by growing the microalga under outdoor conditions in an 800 L tubular photobioreactor. The results show a stable biomass production for at least one month and with a lutein content of 10 mg g−1dw, at pH values in the range 2.5–3.0 and temperature in the range 10–25 °C. Culture density, temperature, and CO2 availability in highly acidic medium are rate-limiting conditions for the microalgal growth. These aspects are discussed in this paper in order to improve the outdoor culture conditions for competitive applications of C. onubensis.

High Rate Electrochemical Machining

1973 ◽  
Vol 95 (4) ◽  
pp. 992-996 ◽  
Author(s):  
S. P. Loutrel ◽  
N. H. Cook
Keyword(s):  
Theoretical Model ◽  
Ion Mobility ◽  
Electrochemical Machining ◽  
High Flow ◽  
High Rate ◽  
Aqueous Sodium ◽  
Electrolyte Conductivity ◽  
High Temperature And Pressure ◽  
Temperature And Pressure ◽  
Rate Limiting

This is the first of three papers on high rate Electrochemical Machining. Feed rate limiting mechanisms are discussed along with qualitative predictions. Methods of increasing feed rates are studied theoretically and experimentally. The use of high supply voltages (118 volts) high electrolyte pressures (330 bars (4800 psi)) and high flow velocities (192 M/sec) when machining iron in aqueous sodium chloride electrolyte led to feed rates of 10.8 cm/min (4.25 in/min). The following two papers will discuss a theoretical model of the ECM process and present high temperature and pressure electrolyte conductivity and ion mobility.

The gaseous oxidation of aliphatic alcohols. III. n - and iso -propyl alcohols

1960 ◽  
Vol 257 (1290) ◽  
pp. 402-412 ◽  
Keyword(s):  
Hydrogen Peroxide ◽  
Carbon Monoxide ◽  
Free Radicals ◽  
Induction Period ◽  
Isopropyl Alcohol ◽  
Side Reactions ◽  
Chain Mechanism ◽  
Complete Elimination ◽  
Chain Branching ◽  
A Chain

A study of the gaseous oxidation of n -propyl alcohol (1-propanol) at 264°C shows that, after an induction period during which higher aldehydes and hydrogen peroxide are apparently the only products formed, the pressure starts to rise autocatalytically and methanol, formaldehyde and carbon monoxide become detectable. Additions of higher aldehydes reduce the induction period but the amounts required for its complete elimination are considerably greater than those normally present at the end of the induction period. A chain mechanism is proposed which involves initially abstraction of hydrogen from 1-propanol by HO 2 radicals followed by interaction of the resulting hydroxypropyl radicals with oxygen to yield propionaldehyde. Further reactions of this aldehyde are believed to be responsible for chain-branching and for the formation of the various C 1 products. Isopropyl alcohol (2-propanol) is much less readily oxidized than 1-propanol. At 330°C the main oxidation product is acetone which is formed together with hydrogen peroxide in somewhat smaller quantities. Minor products include methanol, acetaldehyde and formaldehyde. The course of the oxidation of 2-propanol is little affected by additions of acetone or formaldehyde but the induction period is markedly reduced by added acetaldehyde. The chain cycle suggested for the initial stages of oxidation involves attack by HO 2 radicals at the tertiary C─H bond of the alcohol followed by reaction of the resulting free radicals with oxygen to give acetone. The intermediate responsible for chain-branching is believed to be acetaldehyde which is produced by side reactions. C 1 compounds are formed partly by oxidation of this aldehyde and partly by further reactions of acetone.

The influence of pH on kinetic parameters of coleoptile phosphoenolpyruvate carboxylase. Relationship to auxin-stimulated dark fixation

1979 ◽  
Vol 57 (5) ◽  
pp. 543-547 ◽  
Author(s):  
Ceredwyn Smith ◽  
Ahmed Doo ◽  
Alan W. Bown
Keyword(s):  
Binding Affinity ◽  
Catalytic Efficiency ◽  
Enzymic Activity ◽  
Carboxylase Activity ◽  
Pep Carboxylase ◽  
Ph Values ◽  
Dark Fixation ◽  
Rate Limiting ◽  
Cytosol Ph

In vitro phosphoenolpyruvate (PEP) carboxylase activity from Avena coleoptile tissue was investigated over a range of pH values which include cytosol pH values. Increasing the pH from 7.0 to 7.5 increased optimal PEP carboxylase activity (Vmax) by over 100%. In the presence of rate-limiting 0.07 mM PEP, noncompetitive inhibition by 0.1 mM malate decreased from 80% at pH 7.1 to 50% at pH 7.5. The Km for PEP was not influenced by malate, but as the pH was increased from 7.1 to 7.5, the Km decreased from 0.16 to 0.08 mM. Over the same pH rise, the KI for malate inhibition increased from 0.04 mM to 0.09 mM. Fusicoccin had no detectable influence on enzymic activity. These results are discussed in relation to the stimulation of H+ excretion and dark CO2 fixation by indoleacetic acid and fusicoccin. The data indicate that any increase in cytosol pH, resulting from H+ excretion, would stimulate PEP carboxylase activity by promoting catalytic efficiency and binding affinity for PEP and by reducing the binding affinity for the inhibitor malate.

scholarly journals The binding of cyanide to ferroperoxidase

1971 ◽  
Vol 122 (1) ◽  
pp. 79-87 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini ◽  
Maurizio Brunori
Keyword(s):  
Sodium Dithionite ◽  
Affinity Constant ◽  
Kinetic Measurements ◽  
First Order ◽  
Ph Values ◽  
Cyanide Binding ◽  
Single Process ◽  
Ph Jump ◽  
Equilibrium And Kinetics ◽  
Kinetics Of

1. The equilibrium and kinetics of cyanide binding to ferroperoxidase were investigated. At pH9.1 the equilibrium and kinetic measurements agree closely and disclose a single process with an affinity constant of 1.1×103m@!-1 and combination and dissociation velocity constants of 29m-1·s-1 and 2.5×10-2s-1 respectively. 2. At pH values below 8 the affinity constant falls until at pH6.0 the ferroperoxidase·cyanide complex is no longer formed. This is shown to be associated with the formation of ferriperoxidase·cyanide complex in the mixture even in the presence of excess of sodium dithionite. 3. Rapid-pH-jump experiments show a fast pseudo-first-order interconversion between ferroperoxidase·cyanide complex at pH9.1 and ferriperoxidase·cyanide complex at pH6.0. 4. The kinetics of binding of cyanide to dithionite-reduced peroxidase at pH6.0 are complicated and radically different from those observed at pH9.1. 5. Above pH8 the change of affinity constant with pH is consistent with the undissociated species, HCN, being bound by the ferroperoxidase. The enthalpy for this process measured both by equilibrium and kinetic methods is about -8kcal/mol. 6. The binding of cyanide to reconstituted peroxidases, proto, meso and deutero, was investigated. 7. The results are discussed in relation to known data on cyanide binding to other haemoproteins.

scholarly journals Kinetics of the diamine oxidase reaction

1973 ◽  
Vol 131 (3) ◽  
pp. 459-469 ◽  
Author(s):  
William G. Bardsley ◽  
M. James C. Crabbe ◽  
Julian S. Shindler
Keyword(s):  
Diamine Oxidase ◽  
Experimental Conditions ◽  
Ph Values ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Deuterium Substitution ◽  
Effects Of Temperature ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Oxidase Reaction

1. The oxidation of p-dimethylaminomethylbenzylamine was followed spectrophotometrically by measuring the change in E250 caused by the p-dimethylaminomethylbenzaldehyde produced under a wide variety of experimental conditions. 2. The effect of variations in concentrations of both substrates (amine and oxygen) and all products (aminoaldehyde, hydrogen peroxide and ammonia) on this reaction was studied and the results used to develop a formal mechanism. 3. The nature of the rate-limiting step was elucidated by studying the effects of alterations in ionic strength, dielectric constant and deuterium substitution on the velocity of the forward reaction. 4. Thermodynamic activation energy parameters were obtained at several pH values from the effects of temperature on the reaction.

STUDIES IN THE POLYOXYPHENOL SERIES: VIII. THE OXIDATION OF SUBSTANCES RELATED TO VANILLIN WITH SODIUM CHLORITE AND CHLORINE DIOXIDE

1955 ◽  
Vol 33 (1) ◽  
pp. 82-96 ◽  
Author(s):  
C. D. Logan ◽  
R. M. Husband ◽  
C. B. Purves
Keyword(s):  
Hydrogen Peroxide ◽  
Chlorine Dioxide ◽  
Sodium Chlorite ◽  
Veratric Acid ◽  
Simultaneous Formation ◽  
Aqueous Sodium ◽  
Sharp Distinction ◽  
Slow Reaction ◽  
Ph Values ◽  
Chlorous Acid

The research confirmed the fact that chlorine dioxide and sodium chlorite were not equivalent in their oxidizing properties. At 22 °C. or less, the oxidation of pyrogallol by aqueous sodium chlorite at pH 6 was very slow, but became very rapid on the acid side of pH 3.5. The amorphous, colored products probably did not include purpurogallin. Under similar circumstances p-hydroxybenzaldehyde was unaffected at pH 6; 22% was oxidized to p-benzoquinone (Dakin's reaction) at pH 5, and this amount increased to 39% at pH 1. The yield of benzoquinone was about 24% regardless of pH within the above range when aqueous chlorine dioxide was the oxidant. Sodium chlorite at pH 0.9 produced a 91% yield of methoxy-p-quinone from methoxy-p-hydroquinone; at pH 4 this product was mixed with 56% of 4,4′-dimethoxydiquinone, but near pH 6 a slower oxidation did not proceed beyond 4,4′-dimethoxyquinhydrone. Aqueous chlorine dioxide yielded at least 92% of monomeric methoxyquinone at all pH values between 1 and 6, probably in accord with the equation,[Formula: see text] The simultaneous formation of hydrogen peroxide was suspected, but not proved. In sharp distinction to the behavior of free phenols, veratraldehyde was not oxidized by aqueous chlorine dioxide between pH 6 and pH 3, but at pH 1 a slow reaction yielded up to 15% of veratric acid. Sodium chlorite produced about 92% of the same acid at pH 1 and pH 4, but its action was negligible at pH 5. Since by-product chlorine dioxide was ineffective at pH 4, it was possible to confirm the validity of the Jeanes–Isbell equation for the reduction of chlorous acid:[Formula: see text]The oxidation of acetylated vanillin was complicated by the occurrence of deacetylation. Red, chlorinated oils with quinoidal properties were also formed in most of the above oxidations.

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