Complex Reaction Mechanisms Research Articles

Catalytic pyrolysis of pine needles with nickel doped gamma-alumina: Reaction kinetics, mechanism, thermodynamics and products analysis

The present study aims to explore the catalytic effect of nickel doped gamma-alumina on thermal decomposition behavior of waste pine needle (PN) biomass. Effect of catalysts on pyrolysis behavior was firstly investigated through thermogravimetric (TG) analysis to determine the kinetics and mechanism of the process and then laboratory scale semi-batch reactor was used to determine the distribution and composition of the pyrolysis products. The kinetic parameters (such as activation energy (Ea) and pre-exponential parameter (A)) were evaluated using isoconversional (Ozawa Flynn Wall (OFW) and Kissinger Akahira Sunose (KAS)) methods, while reaction mechanism was elucidated using Criado plots. The results showed a significant reduction in activation energy and an improvement in reaction rate after incorporation of catalysts in the process. Comparison of experimental curves with theoretical Criado plots showed a multistep complex reaction mechanism. Thermodynamic parameters (such as Gibbs free energy, enthalpy and entropy) were also determined for the process. Pyrolysis experiments showed that catalysts addition also effected the distribution and quality of the products. Inclusion of catalysts increased the hydrocarbon and phenolic content in the bio-oil and reduced oxygen content. Ni/Al2O3 is more promising catalyst in terms of oxygen reduction potential and production of hydrocarbon and phenolic compounds as compared to Al2O3 catalyst. Catalytic pyrolysis requires less energy and produces higher quality bio-oil, which makes it a cleaner option for the sustainable utilization of harmful pine needles. The study will assist in the design, optimization and scale-up of the process at large industrial level.

Thermal degradation characteristics, kinetics, thermodynamic, and reaction mechanism analysis of pistachio shell pyrolysis for its bioenergy potential

The research work aims to estimate the bioenergy potential of pistachio shell and study its degradation kinetics which is necessary for the efficient design and optimization of thermochemical processes for bioenergy generation. Initial characterizations (proximate, ultimate, higher heating value, and compositional analysis), kinetic study, and thermodynamic analysis accompanied by reaction mechanism are investigated. Physicochemical characterization results confirmed high volatile matter (~ 79.8 wt%) and high heating value (16.85 MJ/kg) of pistachio shell. Thermogravimetric analysis (TGA) is performed at four different heating rates of 10, 20, 30, and 40 °C/min under nitrogen gas flow rate from ambient temperature to 900 °C. TGA results show the three-stage pyrolysis reaction which involves removal of moisture and light volatiles, degradation of cellulose and hemicellulose, and decomposition of lignin. The result also reveals that maximum degradation occurred in the temperature range of 200–400 °C. For calculating the kinetic (activation energy and pre-exponential factor) and thermodynamic parameters (enthalpy, entropy, and Gibbs free energy), different iso-conversional models, i.e. Flynn-wall-Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Starink, and Friedman, are employed which gives the average value of activation energy as 168.86, 165.80, 166.29, and 190.10 kJ/mol, respectively and the pre-exponential factor values lie in the range of 107-1021 s−1. The average values of Gibbs free energy calculated for FWO, KAS, Starink, and Friedman methods are 182.09, 182.15, 182.13, and 181.42 kJ/mol, respectively. Criado method and Z plot are showing complex reaction mechanism. The results of kinetics and thermodynamic study reveal pistachio shell is an efficient biomass for bioenergy production.

Genome-wide identification and expression analysis of the ERF transcription factor family in pineapple (Ananas comosus (L.) Merr.).

Pineapple (Ananas comosus (L.) Merr.) is an important tropical fruit with high economic value. The quality and yield of pineapple will be affected by various environmental conditions. Under adverse conditions, plants can produce a complex reaction mechanism to enhance their resistance. It has been reported that the member of ethylene responsive transcription factors (ERFs) plays a crucial role in plant developmental process and stress response. However, the function of these proteins in pineapple remains limited. In this study, a total of 74 ERF genes (AcoERFs) were identified in pineapple genome, named from AcoERF1 to AcoERF74, and divided into 13 groups based on phylogenetic analysis. We also analyzed gene structure, conserved motif and chromosomal location of AcoERFs, and the AcoERFs within the same group possess similar gene structures and motif compositions. Three genes (AcoERF71, AcoERF73 and AcoERF74) were present on unanchored scaffolds, so they could not be conclusively mapped on chromosome. Synteny and cis-elements analysis of ERF genes provided deep insight into the evolution and function of pineapple ERF genes. Furthermore, we analyzed the expression profiling of AcoERF in different tissues and developmental stages, and 22 AcoERF genes were expressed in all examined tissues, in which five genes (AcoERF13, AcoERF16, AcoERF31, AcoERF42, and AcoERF65) had high expression levels. Additionally, nine AcoERF genes were selected for functional verification by qRT-PCR. These results provide useful information for further investigating the evolution and functions of ERF family in pineapple.

A review of in situ upgrading technology for heavy crude oil

With the growing demand of oil worldwide, heavy oil has increasingly become vital in the world energy market. However, further development of heavy oil reservoirs are limited by regular enhanced oil recovery (EOR) methods. In situ upgrading technology provides potential for the development of heavy oil and bitumen reservoirs. This study reviews three categories of in situ upgrading methods: solvent-based, in situ combustion (ISC), and catalytic. Solvent-based methods, including cyclic solvent injection, vapor extraction, and hybrid processes, have recently received attention and have been progressed in both laboratory and field applications. However, high solvent costs in relation to the low price of heavy oil have continued to limit the field applications of these techniques. ISC, which may have the potential to develop particularly harsh reservoirs with extremely viscous crude oil, involves complex reaction mechanisms and consists of three main steps: oxidation, combustion, and gas flooding. Yet, complex operating conditions and a low success rate have restricted its application. Catalytic methods, which have demonstrated the potential to refine and upgrade crude oil in a more economic and environmentally friendly way, are often accompanied by conventional thermal EOR methods, such as steam flooding and ISC, and involve a series of hydroprocessing or hydrotreating reactions, such as hydrocracking, hydrodesulfurization, hydrodenitrogenation, hydrodeoxygenation, and hydrodemetallization. However, the high cost and complexity of the reaction mechanisms have limited their applications.

Kinetic Characteristic Features of the Fast Relaxations of Chemical Reactions

Fast changes in the kinetic characteristics occur at the beginning of the transition processes of nonlinear chemical reactions, which are often not observed during nonstationary experiments. These periods of fast relaxations may carry important information about the mechanisms of complex reactions. The evolution of the period of fast relaxations of typical chemical reactions as they move away from equilibrium is studied in this paper. A three-level classification of the forms of nonequilibrium kinetic dependences with respect to the level of informativity is introduced. Nonmonotonic curves with bends (ravines, hills) have the maximum informativity, monotonic curves with bends (waves) have the average informativity, and monotonic curves without bends (descents, ascents) have the minimum informativity. The criterion of existence of the period of fast relaxations, during which the informative forms of the kinetic curves (ravines, hills, waves) exist, is formulated. It is shown that the states of false equilibrium can be observed during their study in which kinetic curves seem to be constant far from the equilibrium. The obtained results may be useful in the reconstruction of the mechanisms of chemical reactions.

Protein quantification by bicinchoninic acid (BCA) assay follows complex kinetics and can be performed at short incubation times

Amongst the available methodologies for protein determination, the bicinchoninic acid (BCA) assay highlights for its simplicity, sensitivity, repeatability and reproducibility. Nevertheless, in spite that the general principle behind this methodology is known, there are still unanswered questions regarding the chemistry behind the assay and the experimental conditions commonly employed. The present work explored the kinetics, and the analytical response of the assay to free amino acids, peptides (containing tryptophan and tyrosine), and proteins. Results revealed kinetic profiles characterized by the absence of plateaus, with behaviors depending on the type of the sample. The latter, along with contribution to the BCA index elicited by oxidation products generated at the side chain of tryptophan and tyrosine, as well as pre-oxidized β-casein, evidenced the presence of complex reaction mechanisms. In spite of such complexity, our results showed that the BCA index is not modulated by the incubation time. This applies for responses producing absorbance intensities (at 562 nm) higher than 0.1. Therefore, we propose that the assay can be applied at shorter incubation times (15 min) than those indicated in manufactures specifications, and usually used by researches and industry (30 min at 37 °C).

Lithiated bimetallic oxide, Li3Fe(MoO4)3, as a high-performance anode material for lithium-ion batteries and its multielectron reaction mechanism

The lithiated bimetallic oxide, Li3Fe(MoO4)3, is successfully synthesized by a glycine-assisted sol-gel combustion method at a low temperature in short time. Attributed to the large amount of gas generated in the combustion reaction, the morphology of the sample exhibits a fluffy porous nature like a coral, which is helpful for buffering the volume expansion in the charge/discharge process and improving the structural stability of the electrode material. Combined with the fluffy porous nature and the realization of a multielectron reaction, as-prepared Li3Fe(MoO4)3 exhibits an excellent electrochemical performance, where a high reversible capacity of 988.2 mAh g−1 can be obtained at a current density of 100 mA g−1. Using in situ X-ray diffraction and high-resolution transmission electron microscopy technologies, the complex reaction mechanism of Li3Fe(MoO4)3 during the lithium insertion/extraction process is discussed in detail for the first time. For the Li3Fe(MoO4)3 electrode, the reversible reaction mechanism is a typical conversion reactions between the metal element and the corresponding oxide amorphous phase. In addition, the practical application of Li3Fe(MoO4)3 as anode material is also studied. When combined with a layered structure LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode in full cells, Li3Fe(MoO4)3 presents good capacity and cycling stability.

Detection of Hg(II) in adsorption experiment by a lateral flow biosensor based on streptavidin-biotinylated DNA probes modified gold nanoparticles and smartphone reader

The increased occurrence of Mercury (Hg II) contaminant has caused environmental and health concerns worldwide. Removal of Hg(II) from water is of significant interest, in particular if these can be coupled in a manner of detection. Here, a novel activated carbon (AC) adsorbent and a fast detection device to form a closed-cycle strategy was developed. The synthesis of conjugates of streptavidin-biotinylated DNA probes modified gold nanoparticle was used with lateral flow biosensors for Hg(II) detection. A quantification was completed via a self-developed smartphone app and its limit of detection was 2.53 nM. Moreover, AC was activated with a new activating agent of diammonium hydrogen phosphate. The adsorbent was characterized and determined to have an amorphous microporous structure with a high surface area (1076.5 m2 g−1) and demonstrated excellent removal efficiency (99.99%) and adsorption capacity (∼100 mg g−1) for Hg(II). The kinetics of the pseudo-second-order model and the mechanisms of electrostatic adsorption, ion exchange, and complex reactions are provided. The proposed closed-cycle strategy can be useful for early, fast, and mobile detection of Hg (II) pollution, followed by its effective removal during water treatment.

Simultaneous determination of transient free radicals and reaction kinetics by high-resolution time-resolved dual-comb spectroscopy

Quantitative determination of multiple transient species is critical in investigating reaction mechanisms and kinetics under various conditions. Dual-comb spectroscopy, a comb-laser-based multi-heterodyne interferometric technique that enables simultaneous achievement of broadband, high-resolution, and rapid spectral acquisition, opens a new era of time-resolved spectroscopic measurements. Employing an electro-optic dual-comb spectrometer with central wavelength near 3 µm coupled with a Herriott multipass absorption cell, here we demonstrate simultaneous determination of multiple species, including methanol, formaldehyde, HO2 and OH radicals, and investigate the reaction kinetics. In addition to quantitative spectral analyses of high-resolution and tens of microsecond time-resolved spectra recorded upon flash photolysis of precursor mixtures, we determine a rate coefficient of the HO2 + NO reaction by directly detecting both HO2 and OH radicals. Our approach exhibits potential in discovering reactive intermediates and exploring complex reaction mechanisms, especially those of radical-radical reactions.

Red Wine Oxidation: Accelerated Ageing Tests, Possible Reaction Mechanisms and Application to Syrah Red Wines.

Wine oxidation and ageing involve many complex chemical pathways and reaction mechanisms. The purpose of this study is to set up new and reproducible accelerated red wine ageing tests and identify chemical oxidation or ageing molecular markers. Three accelerated and reproducible ageing tests were developed: a heat test (60 °C); an enzymatic test (laccase test; a chemical test (hydrogen peroxide test). Depending on the test, oxygen consumption was significantly different. For a young wine (2018), the oxygen consumption rate moved from 2.40 ppm·h−1 for the heat test to 3.33 ppm·h−1 for the enzymatic test and 2.86 ppm·h−1 for the chemical test. Once applied to two other vintages (2010 and 2014) from the same winery, the tests revealed different comportments corresponding to wine natural evolution. High resolution UPLC-MS was performed on forced ageing samples and compared to naturally aged red wines. Specific oxidation or ageing ion markers were found with significant differences between tests, revealing the specificity of each test and different possible molecular pathways involved. The hydrogen peroxide test seems to be closer to natural oxidation with an important decrease in absorbance at 520 nm and similar molecular ion variations for [M+H]+ = 291, 331, 347, 493, 535, 581, 639 Da.

Determination of pre-exponential factor and reaction mechanism in a model-free way

Four methods to compute the pre-exponential factor and the mathematical function that describe the reaction mechanism in a model-free way are proposed and their accuracies were estimated using a complex (multi-step) reaction mechanism that has been simulated. It is shown that the use of the compensation effect in association with Friedman’s or Vyazovkin’s isoconversional methods gives accurate results. Model-free estimation of these parameters can be an efficient tool for the elucidation of complex reaction mechanisms, in complementarity to the estimation of the effective activation energy dependency with temperature and extent of conversion.

The C-matrix augmentation in a multi-route reaction mechanism

When the dimensional complexity of the chemical reaction mechanism arises, it needs special arrangements to deal with such issues. We propose an effective linear algebraic technique to split a complex reaction mechanism into different reaction completion routes to overcome this complexity. Here, three key matrices, the molecular, stoichiometric, and Horiuti matrices, are discussed in detail to deal with the whole mechanism as well as the different reaction routes. The C-matrix procedure is based on calculating the Reduced Row Echelon Form (RREF) for reducing each augmented matrix. This approach is efficient to find the typical results in chemical kinetics and engineering of chemical reactions, i.e., reaction routes, key, and non-key components, key and non-key elements, dependent and independent reaction steps, and overall reaction free from the catalyst. This procedure is very useful to develop new software tools for analyzing complex chemical networks.

Active Intermediates in Copper Nitrite Reductase Reactions Probed by a Cryotrapping-Electron Paramagnetic Resonance Approach.

Redox active metalloenzymes catalyse a range of biochemical processes essential for life. However, due to their complex reaction mechanisms, and often, their poor optical signals, detailed mechanistic understandings of them are limited. Here, we develop a cryoreduction approach coupled to electron paramagnetic resonance measurements to study electron transfer between the copper centers in the copper nitrite reductase (CuNiR) family of enzymes. Unlike alternative methods used to study electron transfer reactions, the cryoreduction approach presented here allows observation of the redox state of both metal centers, a direct read‐out of electron transfer, determines the presence of the substrate/product in the active site and shows the importance of protein motion in inter‐copper electron transfer catalyzed by CuNiRs. Cryoreduction‐EPR is broadly applicable for the study of electron transfer in other redox enzymes and paves the way to explore transient states in multiple redox‐center containing proteins (homo and hetero metal ions).

Active Intermediates in Copper Nitrite Reductase Reactions Probed by a Cryotrapping‐Electron Paramagnetic Resonance Approach

AbstractRedox active metalloenzymes catalyse a range of biochemical processes essential for life. However, due to their complex reaction mechanisms, and often, their poor optical signals, detailed mechanistic understandings of them are limited. Here, we develop a cryoreduction approach coupled to electron paramagnetic resonance measurements to study electron transfer between the copper centers in the copper nitrite reductase (CuNiR) family of enzymes. Unlike alternative methods used to study electron transfer reactions, the cryoreduction approach presented here allows observation of the redox state of both metal centers, a direct read‐out of electron transfer, determines the presence of the substrate/product in the active site and shows the importance of protein motion in inter‐copper electron transfer catalyzed by CuNiRs. Cryoreduction‐EPR is broadly applicable for the study of electron transfer in other redox enzymes and paves the way to explore transient states in multiple redox‐center containing proteins (homo and hetero metal ions).

Computational analysis of the slow invariant manifold for single and multi-route reaction mechanisms

The complexity behavior lies in many natural phenomena’s, such as our ecosystems, the earth’s climate, the behavior of the animal group, living cells and our brain. Therefore, a new field of “systems chemistry” is emerging, which aims to capture the complexity observed in natural systems within a synthetic chemical framework. To understand the physical behavior of the chemical components in a reaction mechanism (system), we need to understand the overall (complete) reactions network as well as different available reaction-paths. We propose the development of a multi-route reaction mechanism for a complex chemical reaction mechanism which is unsolvable through a common way. Further, invariant manifold approximation has been constructed through the Quasi Equilibrium Manifold. The numerical results have been tabulated along with the graphical view through MATLAB

Pyrolysis of almond shells waste: effect of zinc oxide on kinetics and product distribution

In the present work, plain and zinc oxide-loaded almond shells were pyrolyzed in an indigenously manufactured pyrolysis system. The bio-oil produced as a result of catalytic and non-catalytic pyrolysis was characterized using gas chromatography mass spectrometry (GC-MS). Bio-oil produced from non-catalytic pyrolysis consists mainly of ethanol, acetic acid, 1-hydroxy-2-butanone, and 9-octadecenoic acid, methyl ester while bio-oil produced from catalytic pyrolysis consists of a large number of components ranging from C5 to C57. In order to study the kinetics of pyrolysis reaction, both the samples were subjected to thermogravimetric analysis (TGA) at heating rate of 5, 10, 15, and 20 °C/min from room temperature to 600 °C. A four steps degradation was observed, i.e., the first weight loss refers to removal of water molecules, the second weight loss is due to decomposition of hemicellulose, the third weight loss is owed to degradation of cellulose, while the last one is attributed to decomposition of lignin. Kinetic parameters were determined applying Ozawa-Flynn-wall (OFW) and Coats-Redfern (CR) equations. Activation energy (Ea) and frequency factor (A) were observed to increase with increase in fraction conversion which shows complex mechanism of reaction. It has been concluded that zinc oxide proved to be an effective catalyst vis-a-vis decrease in activation energy and quality of bio-oil produced.

Kinetics of Alizarin Dye Hydrolysis in Alkaline Medium for Wastewater Treatment

The kinetics of the hydrolysis of Alizarin dye (ALZ) in basic medium is investigated for the purpose of wastewater treatment. ALZ represents a group of aromatic dyes, that are heavy, toxic, and non-biodegradable. The kinetics of the reaction was followed by UV-Vis spectrophotometry and ab-initio computational methods. The effects of initial concentration, ionic strength, and temperature were studied. The kinetic salt effect (ionic strength) demonstrated that OH– is part of the rate determining step of the reaction. Unlike common reactions, anti-Arrhenius behavior was observed within the temperature range of 25-50°C. Therefore, the apparent activation energy was determined to be -23.91 kcal/mol. Using theoretical quantum calculations, the reaction under study was investigated using the density functionals B3LYP and B97D3, and final energies were obtained using the 2nd order Moller−Plesset (MP2) theory. A complex reaction mechanism is suggested that involves the formation of an intermediate that combines the ALZ anion and water molecule attached by H-bonding. The mechanism accounted for the anti-Arrhenius behavior and the negative Ea. The standard reaction enthalpy (ΔH298) obtained using the B97D3 Grimme’s functional was within the range of the experimental Ea value.

Integrated Metabolic and Kinetic Modeling for Lysine Production

The existing modeling methods for lysine production usually ignore the complex reaction mechanism, lacking microbial insights into intracellular behavior. In this paper, a novel integrated modeling...

Investigating protein thiol chemistry associated with dehydroascorbate, homocysteine and glutathione using mass spectrometry.

Oxidative stress is an imbalance between reactive free radical oxygen species and antioxidant defenses. Its consequences can lead to numerous pathologies. Regulating oxidative stress is the complex interplay between antioxidant recycling and thiol-containing regulatory proteins. Understanding these regulatory mechanisms is important for preventing onset of oxidative stress. The aim of this study was to investigae S-thiol protein chemistry associated with oxidized vitamin C (dehydroascorbate, DHA), homocysteine (HcySH) and glutathione (GSH) using mass spectrometry. Glutaredoxin-1 (Grx-1) was incubated with DHA, with and without GSH and HcySH. Disulfide formation was followed by electrospray ionization mass spectrometry (ESI-MS) of intact proteins and by LC/ESI-MS/MS of peptides from protein tryptic digestions. The mechanism of DHA-mediated S-thiolation was investigated using two synthetic peptides: AcFHACAAK and AcFHACE. Three proteins, i.e. human hemoglobin (HHb), recombinant peroxiredoxin 2 (Prdx2) and Grx-1, were S-homocysteinylated followed by S-transthiolyation with GSH and investigated by ESI-MS and ESI-MS/MS. ESI-MS analysis reveals that DHA mediates disulfide formation and S-thiolation by HcySH as well as GSH of Grx-1. LC/ESI-MS/MS analysis allows identification of Grx-1 S-thiolated cysteine adducts. The mechanism by which DHA mediates S-thiolation of heptapeptide AcFHACAAK is shown to be via initial formation of a thiohemiketal adduct. In addition, ESI-MS of intact proteins shows that GSH can S-transthiolate S-homocysteinylated Grx-1_ HHb and Prdx2. The GS-S-protein adducts over time dominate the ESI-MS spectrum profile. Mass spectrometry is a unique analytical technique for probing complex reaction mechanisms associated with oxidative stress. Using model proteins, ESI-MS reveals the mechanism of DHA-facilitated S-thiolation, which consists of thiohemiketal formation, disulfide formation or S-thiolation. Furthermore, protein S-thiolation by HcySH can be reversed by reversible GSH thiol exchange. The use of mass spectrometry with in vitro models of protein S-thiolation in oxidative stress may provide significant insight into possible mechanisms of action occurring in vivo.

Balancing the chemical equations and their steady-state approximations in the complex reaction mechanism: linear algebra techniques

Mathematically, the complex reactions can be simplified through different linear/non-linear algebraic techniques that are the easiest way to balance the complex models. Furthermore, the complex chemical equations can be balanced with the linear algebraic technique based on matrix-inversion applications. That is the other way for the researchers and chemists to balance the complex chemical equation. In this article, we provide information about coefficients that balance the chemical equations through null-space methodology and the steady-state approximation by applying linear algebra technique. The purpose is not only to identify the undetermined coefficients but also to compute the kernel matrix or null spaces. Furthermore, the steady state for a two-step reaction mechanism is established.