Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 2. The Kinetics of Dioxygen Uptake

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 171-175 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Reaction Time ◽  
Initial Phase ◽  
Cation Radical ◽  
Kinetic Studies ◽  
Veratryl Alcohol ◽  
Second Phase ◽  
Stoichiometric Ratio ◽  
Rate Law ◽  
Order Rate ◽  
Kinetics Of

Summary The kinetics of dioxygen uptake in the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of ABTS, the mediator, was studied. The kinetics of dioxygen uptake consists of two phases: (1) the initial phase up to a reaction time of one hour, and (2) the second phase, after a reaction time of one hour. In the initial phase, ABTS is mainly oxidized to the corresponding cation radical. The kinetics of dioxygen uptake follows a pseudo-zero order rate law. The dioxygen uptake under the reaction condition correlates with the initial ABTS concentration according to the stoichiometric relationship of 0.25 moles dioxygen per mole ABTS. In the second phase, veratryl alcohol is mainly oxidized to veratraldehyde. The kinetics of the dioxygen uptake follows a pseudo-first order rate law. The dioxygen uptake correlates linearly with the yield of veratraldehyde. The stoichiometric ratio between the formation of veratraldehyde and the consumption of dioxygen differs slightly at different M/S ratios. On average, however, it is 0.42 moles of dioxygen per one mole of veratraldehyde formed. The reaction mechanism is discussed on the basis of the kinetic data.

Biobleaching of Pulp with Dioxygen in the Laccase-Mediator System. Part 1. Kinetics of Delignification

Holzforschung ◽  
2000 ◽  
Vol 54 (4) ◽  
pp. 390-396 ◽  
Author(s):  
Mikhail Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Reaction Time ◽  
Kappa Number ◽  
Acetate Buffer Solution ◽  
Alkaline Extraction ◽  
Residual Lignin ◽  
Rate Law ◽  
Order Rate ◽  
Mediator System ◽  
Laccase Mediator System ◽  
Kinetics Of

SummaryKinetics of pine kraft-AQ pulp delignification with the laccase-mediator system (LMS) and the effects of variable factors on the delignification were studied. The delignification was conducted in acetate buffer solution at pH 4.5 and at 40°C under atmospheric pressure. Only a part of the residual lignin could be removed in one-stage processes. Kinetics of kappa number reduction follows a pseudo-second order rate law with pulp consistency of 10 %, mediator charge of 0.1 mmole HOBT/g pulp and laccase charage of 10 UCorioluslaccase/g pulp. Kinetics of dioxygen uptake follows a pseudo-first order rate law up to first 8 hours of the reaction and a pseudo-zero order rate law at the reaction time of 8–24 hours. The amounts of dioxygen consumed per removal of one C9-unit equivalent of residual lignin is rather high, 1.5–2.5 mole, and increases with increasing reaction time. Experimental data show that side reactions between the Laccase-Mediator System and products of oxidative degradation of lignin strongly inhibit the delignification either by chemical or physical means or both. Removal of the degraded lignin fragments by alkaline extraction effectively restores the delignification of pulp with LMS. A four-stage process consisting of consecutive treatment of pulp with dioxygen-laccase-HOBT (LMS) followed by alkaline extraction (E), (LMS-E)4, decreased kappa number of a pine kraft-AQ pulp from 21.8 to less than 5. On the basis of the kinetic data, the mechanism of the pulp delignification with LMS is discussed.

Oxidation of Benzyl Alcohols by the Laccase-Mediator System (LMS) a Comprehensive Kinetic Description

Holzforschung ◽  
2001 ◽  
Vol 55 (1) ◽  
pp. 47-56 ◽  
Author(s):  
A. Potthast ◽  
T. Rosenau ◽  
K. Fischer
Keyword(s):  
Benzyl Alcohol ◽  
Cation Radical ◽  
Product Formation ◽  
Zero Order ◽  
Enzymatic Oxidation ◽  
Second Phase ◽  
Rate Law ◽  
Zero Order Kinetics ◽  
Mediator System ◽  
Laccase Mediator System

SummaryInvestigations into the reaction kinetics of the laccase-mediator system (LMS) have been carried out. Two widely used mediators, 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS,3) and 1-hydroxybenzotriazole (HOBT,4), were compared by means of a model reaction, the oxidation of 2,4-dimethoxybenzyl alcohol (DMBA,1) to 2,4-dimethoxybenzaldehyde (DMA,2). The consumption of dioxygen was recorded electrochemically, substrate consumption and product formation were monitored by GLC.With ABTS as the mediator, the LMS reaction proceeded in two clearly distinguishable stages. The first phase is characterized by a fast decrease in oxygen with zero-order kinetics and no detectable formation of 2,4-dimethoxybenzaldehyde (2). ABTS is converted into oxidized species, the cation radical6and the dication7, respectively. In the second phase, oxygen consumption was considerably slower and followed a second-order kinetics, while the benzaldehyde was produced according to a zero-order rate law. According to the kinetic studies, the ABTS dication, but not the enzyme itself, is acting as the actual oxidant. The rate of oxidation product formation increased with increasing mediator / benzyl alcohol ratio. Less oxygen than the equivalent amount was consumed in the second reaction stage indicating that the oxidized ABTS formed in the first stage acts as an oxidant reservoir, being reduced to ABTS in turn.The LMS reaction with HOBT (4) as the mediator did not exhibit distinguishable phases, and was characterized by a comparatively slow oxygen uptake with zero-order kinetics throughout. Enzymatic oxidation of HOBT to the HOBT radical (5), which acts as the actual oxidant towards the benzyl alcohol, was the rate-determining step. The production of 2,4-dimethoxybenzaldehyde thus followed a zeroorder rate law as well. The reaction rate increased with increasing HOBT / benzyl alcohol ratios. Increasing concentrations of4caused less oxygen to be consumed per equivalent of benzaldehyde formed, indicating the occurrence of another reaction pathway at high mediator charges. At low HOBT / benzyl alcohol ratios the HOBT radical (5) acts as one-electron oxidant and is reduced to HOBT in a reversible process. In contrast, at higher HOBT / benzyl alcohol ratios5acts as a three-electron oxidant, being irreversibly reduced to benzotriazole. At commonly employed mediator concentrations, a superposition of both mechanisms results. The pure borderline cases can only be observed at HOBT / benzyl alcohol ratios below 1 and above 6, respectively.

Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 1. Effects of Mediator Concentration

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Kinetic Studies ◽  
Veratryl Alcohol ◽  
Alcohol Oxidation ◽  
Order Rate Constant ◽  
Molar Ratio ◽  
Active Centers ◽  
First Order ◽  
System Part ◽  
Kinetics Of

Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.

Die Kinetik des Zerfalls von tert. Butylperoxypivalat bei hohen Drücken und Temperaturen / The Kinetics of the Decomposition of tert.Butylperoxypivalate up to High Pressures and Temperatures

1981 ◽  
Vol 36 (12) ◽  
pp. 1371-1377 ◽  
Author(s):  
M. Buback ◽  
H. Lendle
Keyword(s):  
Activation Energy ◽  
High Pressure ◽  
High Pressures ◽  
Activation Volume ◽  
Rate Law ◽  
First Order ◽  
Order Rate ◽  
High Pressures And Temperatures ◽  
Kinetics Of

AbstractThe decomposition of tert. butylperoxypivalate dissolved in n-heptane has been measured ir-spectroscopically in optical high-pressure cells up to 2000 bar at temperatures between 65 °C and 105 °C. The reaction follows a first order rate law with an activation energy Ea = 122.3 ±3.0 kJ · mol-1 and an activation volume ⊿V≠ = 1.6 ± 1.0 cm3 mol-1 .

scholarly journals Pressure-induced depolymerization of spindle microtubules. I. Changes in birefringence and spindle length.

1975 ◽  
Vol 65 (3) ◽  
pp. 603-614 ◽  
Author(s):  
E D Salmon
Keyword(s):  
Initial Phase ◽  
Polarized Light ◽  
Meiotic Metaphase ◽  
Second Phase ◽  
Complete Disappearance ◽  
Spindle Microtubule ◽  
Spindle Microtubules ◽  
Optical Pressure ◽  
Two Phases ◽  
Kinetics Of

Changes in birefringence retardation (BR) and length of Chaetopterus meiotic metaphase-arrested spindles produced by increased hydrostatic pressure were observed with polarized-light microscopy using a newly developed optical pressure chamber. Increased pressure produced rapid, reversible decreases in spindle BR and length. Pressures of 3,500 psi or higher at 22 degrees C caused complete disappearance of spindle BR within 3 min. Up to 6,000 psi, the rates of both BR decay and spindle shortening increased progressively with increasing pressure. At 6,000 psi or above, the BR decreased rapidly but there was no evidence of spindle shortening. The general observations are consistent with results of earlier classical experiments on effects of pressure on mitosis, and with experiments that used colchicine or low temperature as microtubule-depolymerizing agents. The kinetics of spindle depolymerization and repolymerization showed two phases: an initial phase of rapid decreases or increase in half-spindle microtubule BR; and a second phase of nearly constant BR during which most of the spindle shortening or growth occurs. BR is assumed to be directly related to the number of microtubules in a spindle cross section. It is hypothesized that microtubules in the spindle have different stabilities depending on the attachment of nonattachment of their ends. This hypothesis is used to explain the two phases of spindle depolymerization and repolymerization as well as several other observations.

Thallic Ion Oxidation of Styrene: Kinetics of Decomposition of the Oxythallation Adduct C6H5—CH(OCH3)—CH2Tl(OAc)2

1974 ◽  
Vol 52 (15) ◽  
pp. 2667-2672 ◽  
Author(s):  
Louise Nadon ◽  
Miklos Zador
Keyword(s):  
Kinetic Parameters ◽  
Reactive Species ◽  
Rate Law ◽  
First Order ◽  
Order Rate ◽  
Rate Determining Step ◽  
Kinetics Of Decomposition ◽  
Low Concentrations ◽  
Kinetics Of

The kinetics of decomposition of the organo-thallic adduct formed in methanol between styrene and Tl(OAc)3, (C6H5—CH(OCH3)—CH2—Tl(OAc)2) has been studied in a water–methanol solvent. The reaction follows a first order rate law. The organo-thallic compound, RTl(OAc)2, is shown to be dissociated at low concentrations yielding two reactive species, RTlOH+ and RTl2+. The influence of acidity on the rate of decomposition shows that RTl2+ is much more reactive than RTiOH+. The kinetic parameters have been determined. The implication of the results on the rate-determining step of Tl(III) oxidation of styrene is discussed.

Kinetic Study on Delignification of Kraft-AQ Pine Pulp with Hydrogen Peroxide Catalyzed by Mn(IV)-Me4DTNE

Holzforschung ◽  
2000 ◽  
Vol 54 (4) ◽  
pp. 413-419 ◽  
Author(s):  
Yu Cui ◽  
Pratuang Puthson ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman
Keyword(s):  
Hydrogen Peroxide ◽  
Initial Phase ◽  
Model Compound ◽  
Kinetic Studies ◽  
Kappa Number ◽  
Lignin Model Compound ◽  
First Order Kinetics ◽  
Residual Phase ◽  
Lignin Model ◽  
Kinetics Of

Summary The kinetics of delignification of a kraft-AQ southern pine pulp with hydrogen peroxide catalyzed by [LMn(IV)(μ-O)3Mn(IV)](ClO4)2 (1), where L = 1,2-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane was studied. The degree of delignification was significantly improved by using the catalyst. The pulp was bleached for 2 hours at 80°C, in 10% consistency with 2% NaOH, 4% H2O2 and 60 ppm catalyst charges on pulp (O.D.). Kappa number of the pulp was reduced from 31.6 to 16.8 corresponding to a degree of delignification of approximately 4%, while GE brightness was increased from 24.2 to 44.7. At the same time, viscosity of the resulting pulp was reduced from 31.1 mPa•s to 20.1 mPa•s compared to the reduction from 31.1 mPa•s to 20.1 mPa•s in the uncatalyzed bleaching under the same reaction condition. This indicates that the degradation of the carbohydrates was moderate in the catalyzed bleaching compared to the uncatalyzed bleaching. The delignification was found to follow pseudo first order kinetics with respect to kappa number, i.e., residual lignin, in the initial phase and quickly slowed down after 30 minutes (residual phase) under all the reaction temperatures investigated. The delignification rate constants in the initial phase were 0.17, 0.18, and 0.21 min−1 at 50, 60, and 80°C, respectively. Degree of delignification at the delignification time of 30 minutes is approximately 40% at 80°C. The possible delignification mechanism was discussed on the basis of the kinetic studies and lignin model compound experiments.

Oxidative Ammonolysis of Technical Lignins. Part 1. Kinetics of the Reaction under Isothermal Condition at 130°C

Holzforschung ◽  
2001 ◽  
Vol 55 (4) ◽  
pp. 397-404 ◽  
Author(s):  
Ewellyn A. Capanema ◽  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman
Keyword(s):  
Reaction Time ◽  
Isothermal Condition ◽  
Reaction Times ◽  
Molar Ratio ◽  
Second Phase ◽  
Spectroscopic Techniques ◽  
Oxidative Ammonolysis ◽  
Nitrogen Incorporation ◽  
Two Phases ◽  
Kinetics Of

Summary Investigations were conducted on the oxidative ammonolysis of REPAP organosolv lignin at 130 °C in 0.8M NH4OH solution under oxygen pressure of 12 bar. The lignin was completely solubilized at the reaction time of 165 min. The kinetics of the nitrogen incorporation consists of two phases. The first phase is up to the reaction time of approximately 35 min including 15 min heating up period. The rate of nitrogen incorporation in the first phase is 2.3 times higher than that in the second phase: κ1 = 4.58 × 10−4 s−1 versus κ2 = 1.90 × 10−4 s−1. The oxygen uptake and CO2 formation in the reaction is rather high. When the nitrogen incorporation was ceased after reaction for 255 minutes, more than 4 moles of oxygen/C9-unit of lignin were consumed and approximately 1.5 moles of carbon dioxide/C9-unit of lignin were released. In addition, extensive O-demethylation of methoxyl groups occurred. The molar ratio of the nitrogen incorporation to the methoxyl group eliminated is approximately 1.4 and 0.7 for the soluble and insoluble N-modified lignins, respectively. Structural analyses of the soluble N-modified lignins by FTIR and 1H NMR spectroscopic techniques showed only quantitative differences in the spectra obtained at different reaction times. This indicates that the reaction pathways do not change in the course of the oxidative ammonolysis. Possible reaction mechanisms of the oxidative ammonolysis are discussed on the basis of the experimental data.

scholarly journals Kinetics of Reactive Blue 21 Decolorization Using Peracetic Acid

2017 ◽  
Vol 33 (3) ◽  
Author(s):  
Vu Duy ◽  
Le Van Chieu ◽  
Cao The Ha
Keyword(s):  
Aqueous Solutions ◽  
Reaction Kinetics ◽  
Peracetic Acid ◽  
Light Absorption ◽  
Second Order ◽  
Catalytic Reactions ◽  
Rate Law ◽  
Order Rate ◽  
Decolorization Rate ◽  
Kinetics Of

Decolorization rate of Reactive Blue 21 by peracetic acid in aqueous solutions was measured at pH 6.0. Concentrations of peracetic acid were applied in the range of 1 - 3 mM. The reaction kinetics were monitored by recording the light absorption of the Reactive Blue 21 at 660 nm. The obtained results showed that the decolorization happened via non-catalytic and auto-catalytic reactions. Both the reactions were proposed to obey the second-order rate law.

KINETIC STUDIES ON METHYL-BIS-β-CHLOROETHYLAMINE: II. THE KINETICS OF THE ACTION OF SODIUM THIOSULPHATE ON THE PIPERAZINIUM DIMER

1948 ◽  
Vol 26b (2) ◽  
pp. 170-174
Author(s):  
C. A. Winkler ◽  
A. L. Thompson ◽  
T. J. Hardwick
Keyword(s):  
Rate Constants ◽  
Initial Rate ◽  
Kinetic Studies ◽  
Ionization Mechanism ◽  
Sodium Thiosulphate ◽  
First Order ◽  
Rate Expression ◽  
Order Rate ◽  
Kinetics Of ◽  
Rate Controlling Step

It has been shown analytically that for this reaction the formation of Cl− agrees with S2O3− disappearance. The approximate first order rate-controlling step is postulated to be dependent on an ionization mechanism. The rate expression calculated from initial rate constants is given approximately by k = 4.0 × 1015e−25,500/RT hr.−1.

Sign in / Sign up

Export Citation Format

Share Document