Cascade Biocatalysis Designed for the Allylic Oxidation of α-Pinene

A biocatalytic cascade system using a cocktail of oxidoreductase enzymes (2-1B peroxidase and M120 laccase) was designed for the allylic oxidation of (+)-α-pinene into value-added products (e.g., verbenol and verbenone). The oxidative transformation involved a two-step process as follows: (+)-α-pinene was (i) oxidized on the allylic position with H2O2 mainly assisted by 2-1B peroxidase leading to verbenol as the principal reaction product, and (ii) directed to verbenone in the presence of M120 laccase responsible for further oxidation of verbenol to verbenone. The reaction environment was ensured by the acetate buffer (0.1 M, pH = 5). Optimum values for the experimental parameters (e.g., concentration of 2-1B peroxidase, M120 laccase, and H2O2) were set up. The biocatalytic cascade process was monitored for 24 h in order to evaluate the process pathway. Maximum performance under optimum conditions was reached after 5 h incubation time (e.g., 80% (+)-α-pinene conversion and 70% yield in verbenol). Therefore, the developed biocatalytic cascade system offered promising perspectives for (+)-α-pinene valorization.

ABTS/PP Decolorization Assay of Antioxidant Capacity Reaction Pathways

The 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+) radical cation-based assays are among the most abundant antioxidant capacity assays, together with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-based assays according to the Scopus citation rates. The main objective of this review was to elucidate the reaction pathways that underlie the ABTS/potassium persulfate decolorization assay of antioxidant capacity. Comparative analysis of the literature data showed that there are two principal reaction pathways. Some antioxidants, at least of phenolic nature, can form coupling adducts with ABTS•+, whereas others can undergo oxidation without coupling, thus the coupling is a specific reaction for certain antioxidants. These coupling adducts can undergo further oxidative degradation, leading to hydrazindyilidene-like and/or imine-like adducts with 3-ethyl-2-oxo-1,3-benzothiazoline-6-sulfonate and 3-ethyl-2-imino-1,3-benzothiazoline-6-sulfonate as marker compounds, respectively. The extent to which the coupling reaction contributes to the total antioxidant capacity, as well as the specificity and relevance of oxidation products, requires further in-depth elucidation. Undoubtedly, there are questions as to the overall application of this assay and this review adds to them, as specific reactions such as coupling might bias a comparison between antioxidants. Nevertheless, ABTS-based assays can still be recommended with certain reservations, particularly for tracking changes in the same antioxidant system during storage and processing.

Optimization of Pd Membrane Reactor for Direct Oxidation of Aromatic Compounds

Computational fluid dynamic has already become a widely used and indispensable design and optimization tool in many technical areas. In the present work, the CFD simulations have been coupled with complex chemical reactions to model a membrane tubular reactor which is used to produce phenol from benzene in the vapor phase. Hydrogen dissociates on the palladium layer and reacts with oxygen to give active oxygen species, which attack benzene to produce phenol. In principal, reaction occurs in the surface of palladium and conversion of benzene is increased by changing the length and diameter of the Pd coated PSS tubes. The reactor length and diameter are two geometrical factors which are concerned in the present study. Although increasing the reactor length increase the conversion of benzene to phenol but the concentration of the phenol start to decrease. Based on the data provided by the experiments, a mathematical model has been constructed to conduct a simulation which leads us to an optimum design of a new tubular membrane micro-reactor.

Ionic Liquid-Aided Carboxymethylation of Kraft Pulp

Different ionic liquids containing the cation such as 1-N-butyl-3-methylimida-zolium (Bmim+) are able to efficiently dissolve cellulose. The ability of ionic liquids to truly dissolve cellulose is significant when cellulose derivatization is attempted. A series of experiments on etherification (carboxymethylation) of cellulose was performed, using both the conventional suspension approach (slurry) with 2-propanol as the principal reaction media and a totally homogenous reaction approach utilizing ionic liquids as a reaction media capable of dissolving cellulose. It was observed that a pre-treatment with the ionic liquid 1-N-butyl-3-methylimidazolium iodide ([Bmim][I]) seems to promote substitution in line with the conventional, heterogeneous suspension process. Under carefully chosen reaction conditions, a higher degree of substitution was obtained when wetting the cellulose with [Bmim][I] prior to classical derivatization than without this pre-treatment. It was also observed that the substitution pattern was changing upon use of the ionic liquid [Bmim][I]. Upon a totally homogenous etherification, it was found that the ionic liquid 1-N-butyl-3-methylimidazolium acetate ([Bmim][oAc]) gave the highest degree of substitution. The product obtained was water-soluble and had a DS (degree of substitution) of 0.59. The substitution pattern of the products obtained from the homogenous reactions follow the same substitution pattern as the products obtained from the conventional suspension process. This indicates that the properties of the products are in line with products prepared via the conventional reaction route.

Theoretical Study of Vanadium Oxides Interaction with Y-Zeolite

A current problem about oils and feedstock in fluid catalytic cracking (FCC) is the continuous cumulative deposition of metal contaminants on the catalyst, resulting in important modifications of its properties. Vanadium plays a detrimental role on the catalyst components because enhances the destruction of the Y-zeolite structure during regeneration stage when it is exposed by steam and oxygen at high temperatures. Knowledge of the mechanism interaction of vanadium with the catalyst is important to improve FCC performance. Quantum Molecular Dynamics calculations were done introducing the VO, V2O3, VO2 or V2O5 molecules at the center of a Y-zeolite ring simulating regeneration conditions. The results indicate that the principal reaction is carried out among the zeolite and the vanadium atoms of molecules. This happens, when interaction is presented, since the loss of a hydrogen atom of the active place causes high degree of oxygen reactivity.

THE COMPETITIVE REACTION MECHANISM IN EXOTIC NUCLEAR REACTIONS

Two principal reaction dynamics are introduced. One is the spin displacement, which is caused from the spin-dependence of the interaction, and the other is the isovector displacement, which is caused from the isospin-dependence of it. The competition of these two dynamics is a rather important factor as the target or projectile has more excess neutrons or protons. In this paper the competitive reaction mechanism is theoretically formulated, where the time-dependent mean field calculations are performed for justification.

Chemical Reactions in a Soda-Lime Silicate Batch

Primary chemical reactions among the raw materials composing the batch give rise to various transitory intermediate products. Their physical properties influence the character of the glass melting process. The reaction pathway can be controlled by selecting the conditions, e.g. the grainsize composition of raw materials or the heating rate, which will influence the efficacy of the subsequent fining process. The present contribution describes practical technological properties of a couple of principal reaction pathways. A relationship between the practical monitoring of the actual glass melting process and the occurrence of peculiar chemical specimens is also mentioned.

Cesium Extraction from Cs0.8Ba0.4Ti8O16 Hollandite Nuclear Waste Form Ceramics in Nitric Acid Solutions

The leaching of Cs from well-characterized Cs-bearing hollandite powders with ideal formula Cs0.8Ba0.4Ti8O16 was studied at 200 °C under static oxidizing conditions achieved using dilute nitric acid solutions. A variety of techniques were used to elucidate the leaching mechanism including x-ray powder diffraction, magnetic susceptibility, x-ray absorption near edge structure, and electron microscopy. Under the conditions of the study, Cs is leached from Cs-hollandite according to a deceleratory rate law with contracting geometries. The principal reaction products are rutile and brookite. The leaching mechanism involves the formation of a quasi-continuous, and hence relatively impermeable, secondary titanium oxide phase (rutile and/or brookite) on the surfaces of the hollandite crystallites. The driving force for the leaching reaction appears to be the oxidation of Ti3+ in the structure by the oxidizing acid, which then promotes extraction of Cs and Ba from the hollandite tunnels followed by tunnel destabilization and transformation to rutile and brookite.

Landfill codisposal of pentachlorophenol (PCP)-treated waste wood with municipal solid waste

Pentachlorophenol (PCP) has been used as a biocide and preservative for wood power poles and crossarms. If disposed in landfills, the natural capacity of landfills to transform hazardous constituents to less hazardous or inert substances may also apply to such PCP-treated materials. The principal reaction of interest in the anaerobic environment of a landfill is reductive dechlorination. The fate and transformation of PCP-treated wood was investigated in simulated landfill bioreactors operated under single pass leaching and leachate recirculation. The wood samples consisted of 2% of the total mass by weight loaded into the bioreactors. The PCP leaching potential was examined at varying pH conditions with TCLP and Soxhlet extractions. Adsorption of PCP to the synthetic solid waste was used to determine its role in immobilizing leachate PCP. Routine indicator parameters were used to describe the acidogenic and methanogenic phases of landfill stabilization. Leached PCP was transformed without inhibitory effects on landfill stabilization, thereby affirming the acceptability of such a codisposal practice.

Propargylic Terminated Prepolymers. 2. Molten State Mechanisms and Kinetics of Difunctional Systems

We have synthesized five dipropargylic compounds containing electron donor and acceptor substituents between the two phenyl groups. Based on physicochemical data obtained it is shown that heat-induced polymerization depends on the nature of the substituent. Thus, reaction kinetics are modified while molten state mechanisms involved remain identical (principal reaction: intramolecular ring formation; secondary reaction: formation of phenolic entities). The physicochemical techniques used to obtain these results were Fourier transform infrared spectroscopy (FT-IR) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, correlated with chromatographic separation.