Three-Factor Kinetic Equation of Catalyst Deactivation

The three-factor kinetic equation of catalyst deactivation was obtained in terms of apparent kinetic parameters. The three factors correspond to the main cycle with a linear, detailed mechanism regarding the catalytic intermediates, a cycle of reversible deactivation, and a stage of irreversible deactivation (aging), respectively. The rate of the main cycle is obtained for the fresh catalyst under a quasi-steady-state assumption. The phenomena of reversible and irreversible deactivation are presented as special separate factors (hierarchical separation). In this case, the reversible deactivation factor is a function of the kinetic apparent parameters of the reversible deactivation and of those of the main cycle. The irreversible deactivation factor is a function of the apparent kinetic parameters of the main cycle, of the reversible deactivation, and of the irreversible deactivation. The conditions of such separability are found. The obtained equation is applied successfully to describe the literature data on the reversible catalyst deactivation processes in the dehydration of acetaldehyde over TiO2 anatase and in crotonaldehyde hydrogenation on supported metal catalysts.

Expression and Biochemical Characterization of a Novel Marine Chitosanase from Streptomyces niveus Suitable for Preparation of Chitobiose

It is known that bioactivities of chitooligosaccharide (COS) are closely related to the degree of polymerization (DP); therefore, it is essential to prepare COS with controllable DP, such as chitobiose showing high antioxidant and antihyperlipidemia activities. In this study, BLAST, sequence alignment and phylogenetic analysis of characterized glycoside hydrolase (GH) 46 endo-chitosanases revealed that a chitosanase Sn1-CSN from Streptomyces niveus was different from others. Sn1-CSN was overexpressed in E. coli, purified and characterized in detail. It showed the highest activity at pH 6.0 and exhibited superior stability between pH 4.0 and pH 11.0. Sn1-CSN displayed the highest activity at 50 °C and was fairly stable at ≤45 °C. Its apparent kinetic parameters against chitosan (DDA: degree of deacetylation, >94%) were determined, with Km and kcat values of 1.8 mg/mL and 88.3 s−1, respectively. Cu2+ enhanced the activity of Sn1-CSN by 54.2%, whereas Fe3+ inhibited activity by 15.1%. Hydrolysis products of chitosan (DDA > 94%) by Sn1-CSN were mainly composed of chitobiose (87.3%), whereas partially acetylated chitosan with DDA 69% was mainly converted into partially acetylated COS with DP 2-13. This endo-chitosanase has great potential to be used for the preparation of chitobiose and partially acetylated COS with different DPs.

EFFECT OF AFLATOXIN B-CONTAMINATED FEED ON GOAT ERYTHROCYTE MEMBRANE CALCIUM ADENOSINE TRIPHOSPHATASE IN VITRO

Aflatoxin B1 (AFBI) 2, a food/feed contaminant in the tropics, stimulated the activity of gout erythrocyte membrane ion motive calcium adenosine triphosphatase (Ca-ATPase). The stimulatory action was concentration-dependent, typical of a saturation kinetic effect. The degree of stimulation varied from 20% to more than 90% between the lowest (0.1 M) and highest (1000 M) contentrations. AFB1 induced changes in the apparent kinetic parameters, Km and Vmax, of the erythrocyte membrane-bound enzyme. This could affect erythrocyte structure, and thus, the erythrocyte function in oxygen and delivery to the cells.

Kinetic and substrate complex characterization of RamA, a corrinoid protein reductive activase from Methanosarcina barkeri

ABSTRACT In microbial corrinoid-dependent methyltransferase systems, adventitious Co(I)-corrinoid oxidation halts catalysis and necessitates repair by ATP-dependent reductive activases. RamA, an activase with a C-terminal ferredoxin domain with two [4Fe-4S] clusters from methanogenic archaea, has been far less studied than the bacterial activases bearing an N-terminal ferredoxin domain with one [2Fe-2S] cluster. These differences suggest RamA might prove to have other distinctive characteristics. Here, we examine RamA kinetics and the stoichiometry of the corrinoid protein:RamA complex. Like bacterial activases, K+ stimulates RamA. Potassium stimulation had been questioned due to differences in the primary structure of bacterial and methanogen activases. Unlike one bacterial activase, ATP is not inhibitory allowing the first determination of apparent kinetic parameters for any corrinoid activase. Unlike bacterial activases, a single RamA monomer complexes a single corrinoid protein monomer. Alanine replacement of a RamA serine residue corresponding to the serine of one bacterial activase which ligates the corrinoid cobalt during complex formation led to only moderate changes in the kinetics of RamA. These results reveal new differences in the two types of corrinoid activases, and provide direct evidence for the proposal that corrinoid activases act as catalytic monomers, unlike other enzymes that couple ATP hydrolysis to difficult reductions.

Thermogravimetric Study on the Co-Pyrolysis Characteristics of Bituminous Coal and Wheat Straw

In this work, the pyrolysis behavior of bituminous coal (BC) wheat straw (WS) and the blends were investigated by thermogravimetric analysis. It was found that the main thermal degradation stage of BC and WS lies in different temperature range and there is nearly no overlapping. Interaction was observed during the co-pyrolysis process of BC and WS. At high temperatures, the volatile releasing is slightly inhibited by WS addition. Coats-Redfern method was used to analyze the apparent kinetic parameters. The results indicated that both the two reaction stages during pyrolysis process are well correlated by first-order reaction. The variation trend of activation energy value further confirm the synergistic effects between BC and WS. The experimental results may provide useful data for co-thermochemical utilization of biomass with coal.

Kinetics Study of Vitamin A Precursor Synthesis by Immobilized Lipase-Catalyzed Regioselective Monoacetylation in n-Hexane

Vitamin A is an essential nutrient element in animal and human growth, which is usually produced by partially acetylating and transforming retinyl diol. The lipase-catalyzed mono-acetylation can obtain pure monoacetate compared with the classical chemistry process. In the current work, the synthesis of vitamin A precursor of Candida antarctica lipase B catalyzed by regioselective monoacetylation of primary hydroxyl of diol in n-hexane was studied. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both substrates. A kinetic model was developed, and the apparent kinetic parameters were calculated as: Vmax =8.45 mmol/ (L•h); K m, vinyl =0.997 mmol/L; K m, diol =161.28 mmol/L; K i, diol =287.32 mmol/L; K i, monoacetate=18.13 mmol/L; and K I, diol =427.40 mmol/L. The current study indicates a competitive enzyme inhibition of highly concentrated diol during lipase-catalyzed acetylation reaction. When the diol concentration in the medium was low, there was a good conformity between the experimental and simulated values with 4.73% average relative error.

The kinetics of the hydrogen chloride oxidation

Hydrogen chloride (HCl) oxidation has been investigated on technical membrane electrode assemblies in a cyclone flow cell. Influence of Nafion loading, temperature and hydrogen chloride mole fraction in the gas phase has been studied. The apparent kinetic parameters like reaction order with respect to HCl, Tafel slope and activation energy have been determined from polarization data. The apparent kinetic parameters suggest that the recombination of adsorbed Cl intermediate is the rate determining step.

Kinetics of thermal decomposition of aseptic packages

Kinetics of thermal decomposition of aseptic packages (e.g. Tetrapak cartons) and pyrolysis of this waste in a laboratory flow reactor was studied. Three different models for the calculation of the reaction rate and the determination of apparent kinetic parameters of thermal decomposition were used. The first method assumes a two stage thermal decomposition and the kinetic parameters were determined by fitting a derivative thermogravimetric (DTG) curve to experimentally determined thermogravimetric data of whole aseptic cartons. The second method uses kinetic parameters determined by fitting DTG curves to thermogravimetric data of individual components of aseptic packages. The last method was a multi-curve isoconversion method assuming a change of kinetic parameters with the increasing conversion. All types of the determined kinetic parameters were used in a mathematical model for thermal decomposition of mini briquettes made from aseptic packages at the temperature of 650°C. The model calculated also the heat conduction in the particles and it was verified by an independent set of experiments conducted in a laboratory screw type flow reactor.