Individual Rate Constants Research Articles

Theoretical kinetics study of key reactions between ammonia and fuel molecules, part II: H-atom abstraction from alcohols and ethers by ṄH2 radicals

Ammonia, as a carbon-free fuel, is expected to be a carbon-neutral alternative fuel to control pollution emissions. However, with lower reactivity, pure ammonia needs to be blended with highly reactive biofuels including alcohols and ethers, for a better combustion performance. Alcohols and ethers can be produced from various sources, including renewable materials and fossil fuels. Therefore, the combination of ammonia with alcohols/ethers is a promising choice for developing carbon-neutral energy solutions. As an important intermediate, ṄH2 radicals can easily be formed during the pyrolysis or oxidation processes for ammonia combustion. The H-atom abstraction reaction between ṄH2 radicals and fuel molecules is vital in determining the blending fuel reactivity. High-level ab initio calculations have been carried out in this study to perform a systematic theoretical chemical kinetic investigation of H-atom abstraction by ṄH2 radicals from C1–C5 alcohols, 2,3-dimethyl-2-butanol, C1–C4 ethers and methyl isobutyl ether with a total of 61 H-atom abstraction reaction channels. The QCISD(T)/CBS//M06–2X/6–311++G(d, p) level of theory was employed to investigate the potential energy surfaces of the title reactions involved. Electronic geometry optimization, frequency analysis, and zero-point energy correction were performed for reactants, transition states and products related to 61 reaction channels at the M06–2X/6–311++G(d, p) level of theory. Single-point energy calculations were performed at the QCISD(T)/cc-pVXZ (X = D, T) and MP2/cc-pVYZ (Y = D, T, Q) level of theory and then extrapolated to the complete basis set. Conventional transition state theory was used to calculate the rate constants for different channels in the temperature range from 500 to 2000 K. The calculated individual and average rate constants for H-atom abstraction from different sites of alcohols and ethers were also obtained to explore the kinetic influence from the functional group. This is the first systematic study providing the rate constants for the title reactions which can be used to develop the combustion kinetic models for ammonia/alcohols and ammonia/ethers blends.

Transacylation and hydrolysis of the acyl glucuronides of ibuprofen and its α-methyl-substituted analogues investigated by 1H NMR spectroscopy and computational chemistry: Implications for drug design

Drugs and drug metabolites containing a carboxylic-acid moiety can undergo in vivo conjugation to form 1-β-O-acyl-glucuronides (1-β-O-AGs). In addition to hydrolysis, these conjugates can undergo spontaneous acyl migration, and anomerisation reactions, resulting in a range of positional isomers. Facile transacylation has been suggested as a mechanism contributing to the toxicity of acyl glucuronides, with the kinetics of these processes thought to be a factor. Previous 1H NMR spectroscopic and HPLC-MS studies have been conducted to measure the degradation rates of the 1-β-O-AGs of three nonsteroidal anti-inflammatory drugs (ibufenac, R-ibuprofen, S-ibuprofen) and a dimethyl-analogue (termed here as “bibuprofen”). These studies have also determined the relative contributions of hydrolysis and acyl migration in both buffered aqueous solution, and human plasma. Here, a detailed kinetic analysis is reported, providing the individual rate constants for the acyl migration and hydrolysis reactions observed in buffer for each of the 4 AGs, together with the overall degradation rate constants of the parent 1-β-O-AGs. Computational modelling of the reactants and transition states of the transacylation reaction using density functional theory indicated differences in the activation energies that reflected the influence of both substitution and stereochemistry on the rate of transacylation/hydrolysis.

Phase plane dynamics of ERK phosphorylation

The extracellular signal-regulated kinase (ERK) controls multiple critical processes in the cell and is deregulated in human cancers, congenital abnormalities, immune diseases, and neurodevelopmental syndromes. Catalytic activity of ERK requires dual phosphorylation by an upstream kinase, in a mechanism that can be described by two sequential Michaelis-Menten steps. The estimation of individual reaction rate constants from kinetic data in the full mechanism has proved challenging. Here, we present an analytically tractable approach to parameter estimation that is based on the phase plane representation of ERK activation and yields two combinations of six reaction rate constants in the detailed mechanism. These combinations correspond to the ratio of the specificities of two consecutive phosphorylations and the probability that monophosphorylated substrate does not dissociate from the enzyme before the second phosphorylation. The presented approach offers a language for comparing the effects of mutations that disrupt ERK activation and function invivo. As an illustration, we use phase plane representation to analyze dual phosphorylation under heterozygous conditions, when two enzyme variants compete for the same substrate.

Real-Time Monitoring and Control of Nanoparticle Formation.

Methods capable of controlling synthesis at the level of an individual nanoparticle are a key step toward improved reproducibility and scalability in engineering complex nanomaterials. To address this, we combine the spatially patterned activation of the photoreductant sodium pyruvate with interferometric scattering microscopy to achieve fast, label-free monitoring and control of hundreds of gold nanoparticles in real time. Individual particle growth kinetics are well-described by a two-step nucleation-autocatalysis model but with a distribution of individual rate constants that change with reaction conditions.

Statistical prediction and sensitivity analysis of kinetic rate constants for efficient thermal valorization of plastic waste into combustible oil and gases

Sensitivity analyses of rate constants for chemical kinetics of the pyrolysis reaction are essential for the efficient valorization of plastic waste into combustible liquids and gases. Finding the role of individual rate constants can provide important information on the process conditions, quality, and quantity of the pyrolysis products. The reaction temperature and time can also be reduced through these analyses. For sensitivity analysis, one possible approach is to estimate the kinetic parameters using MLRM (multiple linear regression model) in SPSS. To date, no research reports on this research gap are documented in the published literature. In this study, MLRM is applied to kinetic rate constants, which slightly differ from experimental data. The experimental and statistically predicted rate constants varied up to 200% from their original values to perform sensitivity analysis using MATLAB software. The product yield was examined after 60 min of thermal pyrolysis at a fixed temperature of 420 °C. The predicted rate constant “k(8)” with a slight difference of 0.02 and 0.04 from the experiment revealed 85% oil yield and 40% light wax after 60 min of operation. The heavy wax was missing from the products under these conditions. This rate constant can be utilized to maximize the commercial-scale extraction of liquids and light waxes from thermal pyrolysis of plastics.

Numerical sensitivity analysis of temperature‐dependent reaction rate constants for optimized thermal conversion of high‐density plastic waste into combustible fuels

AbstractThe use of experimental rate constants for producing a high yield of liquid fuels from the pyrolysis of plastic waste is not widely accepted owing to a lack of compatibility between the different kinetic rate constants responsible for successful conversion reactions. In R software, the Arrhenius law can forecast the ideal combination of reaction rate constants and frequency factors and then perform sensitivity analysis on individual rate constants to estimate the selectivity and quantity of primary pyrolysis products. Sensitivity analysis is a way of determining the effectiveness of individual rate constants in the reaction. This research element is currently lacking in the literature for the cost‐effective valorization of plastics into combustible fuels. We are the first to use R software to perform sensitivity analysis on specific rate constants by reducing or raising their initial values to a point where maximum oil yield is attainable in the temperature range of 340–370°C. The primary focus was to save time and cost of extracting empirical rate constants from experiments to produce commercial‐scale pyrolytic oil. The H‐abstraction, chain fission, polymerization, and scission reactions were chosen due to the high availability of free radicals for maximum oil production. The oil recovery rate improved drastically to 90% at the end of processing time, while the number of by‐products gradually decreased. The k8 rate constant driven reaction is the best‐suited condition for industrial‐scale pyrolysis of high‐density plastics into liquid fuels, with 74% improvement in oil production and 14% improvement in light wax during sensitivity analysis.

An exploratory steady-state redox model of photosynthetic linear electron transport for use in complete modelling of photosynthesis for broad applications.

A photochemical model of photosynthetic electron transport (PET) is needed to integrate photophysics, photochemistry, and biochemistry to determine redox conditions of electron carriers and enzymes for plant stress assessment and mechanistically link sun-induced chlorophyll fluorescence to carbon assimilation for remotely sensing photosynthesis. Towards this goal, we derived photochemical equations governing the states and redox reactions of complexes and electron carriers along the PET chain. These equations allow the redox conditions of the mobile plastoquinone pool and the cytochrome b6 f complex (Cyt) to be inferred with typical fluorometry. The equations agreed well with fluorometry measurements from diverse C3 /C4 species across environments in the relationship between the PET rate and fraction of open photosystem II reaction centres. We found the oxidation of plastoquinol by Cyt is the bottleneck of PET, and genetically improving the oxidation of plastoquinol by Cyt may enhance the efficiency of PET and photosynthesis across species. Redox reactions and photochemical and biochemical interactions are highly redundant in their complex controls of PET. Although individual reaction rate constants cannot be resolved, they appear in parameter groups which can be collectively inferred with fluorometry measurements for broad applications. The new photochemical model developed enables advances in different fronts of photosynthesis research.

From electronic structure to model application of key reactions for gasoline/alcohol combustion: Hydrogen-atom abstraction by CH3OȮ radicals

Hydrogen atom abstraction by methyl peroxy (CH3OȮ) radicals can play an important role in gasoline/ethanol interacting chemistry for fuels that produce high concentrations of methyl radicals. Detailed kinetic reactions for hydrogen atom abstraction by CH3OȮ radicals from the components of FGF-LLNL (a gasoline surrogate) including cyclopentane, toluene, 1-hexene, n-heptane, and isooctane have been systematically studied in this work. The M06–2X/6–311++G(d,p) level of theory was used to obtain the optimized structure and vibrational frequency for all stationary points and the low-frequency torsional modes. The 1-D hindered rotor treatment for low-frequency torsional modes was treated at M06–2X/6–31G level of theory. The UCCSD(T)-F12a/cc-pVDZ-F12 and QCISD(T)/CBS level of theory were used to calculate single point energies for all species. High pressure limiting rate constants for all hydrogen atom abstraction channels were performed using conventional transition state theory with unsymmetric tunneling corrections. Individual rate constants are reported in the temperature range from 298.15 to 2000 K. Our computed results show that the abstraction of allylic hydrogen atoms from 1-hexene is the fastest at low temperatures. When the temperature increases, the hydrogen atom abstraction reaction channel at the primary alkyl site gradually becomes dominant. Thermodynamics properties for all stable species and high-pressure limiting rate constants for each reaction pathway obtained in this work were incorporated into the latest gasoline surrogate/ethanol model to investigate the influence of the rate constants calculated here on model predicted ignition delay times.

PH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes.

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pK a of 7.0, close to the pK a of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

PH Dependence of Amyloid-β Fibril Assembly Kinetics: Unravelling the Microscopic Molecular Processes.

Central to Alzheimer's disease (AD) is the assembly of the amyloid-beta peptide (Aβ) into fibrils. A reduction in pH accompanying inflammation or subcellular compartments, may accelerate fibril formation as the pH approaches Aβ's isoelectric point (pI). Using global fitting of fibril formation kinetics over a range of pHs, we identify the impact net charge has on individual fibril assembly microscopic rate constants. We show that the primary nucleation has a strong pH dependence. The titration behaviour exhibits a mid-point or pKa of 7.0, close to the pKa of Aβ histidine imidazoles. Surprisingly, both the secondary nucleation and elongation rate constants are pH independent. This indicates the charge of Aβ, in particular histidine protonation, has little impact on this stage of Aβ assembly. These fundamental processes are key to understanding the forces that drive the assembly of Aβ into toxic oligomers and fibrils.

Temperature and Pressure-Dependent Rate Constants for the Reaction of the Propargyl Radical with Molecular Oxygen.

Ab initio CCSD(T)/CBS(T,Q,5)//B3LYP/6-311++G(3df,2p) calculations have been conducted to map the C3H3O2 potential energy surface. The temperature- and pressure-dependent reaction rate constants have been calculated using the Rice–Ramsperger–Kassel–Marcus Master Equation model. The calculated results indicate that the prevailing reaction channels lead to CH3CO + CO and CH2CO + HCO products. The branching ratios of CH3CO + CO and CH2CO + HCO increase both from 18 to 29% with reducing temperatures in the range of 300–2000 K, whereas CCCHO + H2O (0–10%) and CHCCO + H2O (0–17%) are significant minor products. The desirable products OH and H2O have been found for the first time. The individual rate constant of the C3H3 + O2 → CH2CO + HCO channel, 4.8 × 10–14 exp[(−2.92 kcal·mol–1)/(RT)], is pressure independent; however, the total rate constant, 2.05 × 10–14 T0.33 exp[(−2.8 ± 0.03 kcal·mol–1)/(RT)], of the C3H3 + O2 reaction leading to the bimolecular products strongly depends on pressure. At P = 0.7–5.56 Torr, the calculated rate constants of the reaction agree closely with the laboratory values measured by Slagle and Gutman [Symp. (Int.) Combust.1988, 21, 875−883] with the uncertainty being less than 7.8%. At T < 500 K, the C3H3 + O2 reaction proceeds by simple addition, making an equilibrium of C3H3 + O2 ⇌ C3H3O2. The calculated equilibrium constants, 2.60 × 10–16–8.52 × 10–16 cm3·molecule–1, were found to be in good agreement with the experimental data, being 2.48 × 10–16–8.36 × 10–16 cm3·molecule–1. The title reaction is concluded to play a substantial role in the oxidation of the five-member radicals and the present results corroborate the assertion that molecular oxygen is an efficient oxidizer of the propargyl radical.

Kinetic model for reversible radical transfer in ribonucleotide reductase

The enzyme ribonucleotide reductase (RNR), which catalyzes the reduction of ribonucleotides to deoxynucleotides, is vital for DNA synthesis, replication, and repair in all living organisms. Its mechanism requires long-range radical translocation over ∼32 Å through two protein subunits and the intervening aqueous interface. Herein, a kinetic model is designed to describe reversible radical transfer in Escherichia coli RNR. This model is based on experimentally studied photoRNR systems that allow the photochemical injection of a radical at a specific tyrosine residue, Y356, using a photosensitizer. The radical then transfers across the interface to another tyrosine residue, Y731, and continues until it reaches a cysteine residue, C439, which is primed for catalysis. This kinetic model includes radical injection, an off-pathway sink, radical transfer between pairs of residues along the pathway, and the conformational flipping motion of Y731 at the interface. Most of the input rate constants for this kinetic model are obtained from previous experimental measurements and quantum mechanical/molecular mechanical free-energy simulations. Ranges for the rate constants corresponding to radical transfer across the interface are determined by fitting to the experimentally measured Y356 radical decay times in photoRNR systems. This kinetic model illuminates the time evolution of radical transport along the tyrosine and cysteine residues following radical injection. Further analysis identifies the individual rate constants that may be tuned to alter the timescale and probability of the injected radical reaching C439. The insights gained from this kinetic model are relevant to biochemical understanding and protein-engineering efforts with potential pharmacological implications.

On the Scavenging Ability of Scutellarein against the OOH Radical in Water and Lipid-like Environments: A Theoretical Study

The antioxidant capability of scutellarein, a flavonoid extracted from different plants of the Scutellaria family, was computationally predicted by considering its reaction with the OOH radical in both lipid-like and water environments. The pKa and equilibrium behavior in the aqueous phase were also calculated. Different reaction mechanisms involving the most populated species were considered. The work was performed by using the density functional level of theory. The individual, total, and fraction-corrected total rate constants were obtained. The results show that scutellarein has scavenging power against the hydroperoxyl radical similar to that of Trolox, which is generally used as a reference antioxidant.

Degradation of 2,6-dichlorophenol by ferrate (VI) oxidation: Kinetics, performance, and mechanism

• Complete removal of 2,6-DCP by Fe(VI) was achieved at a 6:1 or higher molar ratio. • The reaction activation energy was obtained using temperature dependence of rate constants. • The reaction rate constants were found to decrease non-linearly as pH increases. • Species-specific rate constants were calculated using pH dependence of speciation. • A detailed dechlorination and ring-opening mechanism of 2,6-DCP degradation by Fe(VI) was proposed. The kinetics, performance and mechanism of the oxidative degradation of 2,6-dichlorophenol (2,6-DCP) by ferrate(VI) (Fe(VI)) were investigated in this study. The kinetics of oxidation of 2,6-DCP with Fe(VI) were studied as a function of pH (8.23–10.45) and temperature (20.0–33.5 ℃). The reaction follows a second-order rate law with first order in each reactant. The reaction rate constants were found to decrease non-linearly from 265.14 ± 14.10 M −1 ·s −1 at pH 8.23 to 9.80 ± 0.72 M −1 ·s −1 at pH 10.45. The individual species-specific second-order rate constants were calculated using pH dependence of species distributions of Fe(VI) (HFeO 4 - and FeO 4 2- ) and 2,6-DCP (2,6-DCP and 2,6-DCP - ). The reaction of deprotonated 2,6-DCP with protonated Fe(VI) was found to occur fastest among four parallel reactions between Fe(VI) and 2,6-DCP species. The correlation between temperature and rate constant showed that the activation energy of the reaction was 19.00 ± 1.82 kJ·mol −1 . Removal performance depends on pH and molar ratio of Fe(VI) to 2,6-DCP. 2,6-DCP degradation efficiency decreased with increasing pH, which was in accord with pH dependence of the reaction constants. Complete removal of 2,6-DCP by Fe(VI) was achieved at a 6:1 or higher molar ratio. The oxidized products (OPs) of 2,6-DCP were identified using high performance liquid chromatography - mass spectrometry (HPLC-MS) and ion-selective electrode (ISE), and a dechlorination and ring-opening mechanism of 2,6-DCP degradation by Fe(VI) was proposed in detail. The results indicate that it is feasible and highly efficient for 2,6-DCP degraded by Fe(VI) to form nontoxic products.

Coordinated Actions of Cas9 HNH and RuvC Nuclease Domains Are Regulated by the Bridge Helix and the Target DNA Sequence.

CRISPR-Cas systems are RNA-guided nucleases that provide adaptive immune protection in bacteria and archaea against intruding genomic materials. Cas9, a type-II CRISPR effector protein, is widely used for gene editing applications since a single guide RNA can direct Cas9 to cleave specific genomic targets. The conformational changes associated with RNA/DNA binding are being modulated to develop Cas9 variants with reduced off-target cleavage. Previously, we showed that proline substitutions in the arginine-rich bridge helix (BH) of Streptococcus pyogenes Cas9 (SpyCas9-L64P-K65P, SpyCas92Pro) improve target DNA cleavage selectivity. In this study, we establish that kinetic analysis of the cleavage of supercoiled plasmid substrates provides a facile means to analyze the use of two parallel routes for DNA linearization by SpyCas9: (i) nicking by HNH followed by RuvC cleavage (the TS (target strand) pathway) and (ii) nicking by RuvC followed by HNH cleavage (the NTS (nontarget strand) pathway). BH substitutions and DNA mismatches alter the individual rate constants, resulting in changes in the relative use of the two pathways and the production of nicked and linear species within a given pathway. The results reveal coordinated actions between HNH and RuvC to linearize DNA, which is modulated by the integrity of the BH and the position of the mismatch in the substrate, with each condition producing distinct conformational energy landscapes as observed by molecular dynamics simulations. Overall, our results indicate that BH interactions with RNA/DNA enable target DNA discrimination through the differential use of the parallel sequential pathways driven by HNH/RuvC coordination.

Experimental and Computational Insight into the Mechanism of NO Binding to Ferric Microperoxidase. The Likely Role of Tautomerization to Account for the pH Dependence.

According to the current paradigm, the metal-hydroxo bond in a six-coordinate porphyrin complex is believed to be significantly less reactive in ligand substitution than the analogous metal-aqua bond, due to a much higher strength of the former bond. Here, we report kinetic studies for nitric oxide (NO) binding to a heme-protein model, acetylated microperoxidase-11 (AcMP-11), that challenge this paradigm. In the studied pH range 7.4-12.6, ferric AcMP-11 exists in three acid-base forms, assigned in the literature as [(AcMP-11)FeIII(H2O)(HisH)] (1), [(AcMP-11)FeIII(OH)(HisH)] (2), and [(AcMP-11)FeIII(OH)(His-)] (3). From the pH dependence of the second-order rate constant for NO binding (kon), we determined individual rate constants characterizing forms 1-3, revealing only a ca. 10-fold decrease in the NO binding rate on going from 1 (kon(1) = 3.8 × 106 M-1 s-1) to 2 (kon(2) = 4.0 × 105 M-1 s-1) and the inertness of 3. These findings lead to the abandonment of the dissociatively activated mechanism, in which the reaction rate can be directly correlated with the Fe-OH bond energy, as the mechanistic explanation for the process with regard to 2. The reactivity of 2 is accounted for through the existence of a tautomeric equilibrium between the major [(AcMP-11)FeIII(OH)(HisH)] (2a) and minor [(AcMP-11)FeIII(H2O)(His-)] (2b) species, of which the second one is assigned as the NO binding target due to its labile Fe-OH2 bond. The proposed mechanism is further substantiated by quantum-chemical calculations, which confirmed both the significant labilization of the Fe-OH2 bond in the [(AcMP-11)FeIII(H2O)(His-)] tautomer and the feasibility of the tautomer formation, especially after introducing empirical corrections to the computed relative acidities of the H2O and HisH ligands based on the experimental pKa values. It is shown that the "effective lability" of the axial ligand (OH-/H2O) in 2 may be comparable to the lability of the H2O ligand in 1.

Quantum chemical study of the mechanisms, kinetics, and ecotoxicity assessment of OH radical-initiated reactions of 2,2′,4,4′,5,5′ -hexabrominated diphenyl ether (BDE-153) in atmosphere and wastewater

2,2′,4,4′,5,5′-hexabrominated diphenyl ether (BDE-153) and its OH radical addition products are considered potentially harmful to ecological systems. Therefore, the oxidation reactions mechanisms of BDE-153 initiated by OH radical, the reaction kinetics and the ecotoxicity of BDE-153 assessment in the gas and the aqueous phase were investigated using quantum chemical methods. It is more feasible for the OH radical to add at the nonbromine substituted carbon atoms of the aromatic ring in the BDE-153 molecule to create OH addition intermediates. The secondary reactions involving OH addition intermediates in the presence of O2/NO would generate preferred tribromophenol and OH-addition products. Most of the transformation products are still toxic to aquatic organisms. The total and individual rate constants were evaluated by using the KiSThelP program in a suitable temperature range (198–338 K) and a pressure of 1 atm. At 298 K and 1 atm, the total rate constants in atmosphere and wastewater are 2.90 × 10-13 cm3 molecule-1 s−1 and 9.61 × 106 M−1 s−1, and the half-lives are 39.9 days and 72.1–7.21 × 1010 s, respectively. The implicit and explicit solvent models were used to examine the solvent effect on the total reaction. These results clarify the transformation mechanism, atmospheric fate, and ecotoxicity of BDE-153 in advanced oxidation processes. The calculations provided a basis for designing experimental and industrial applications of BDE-153.

Data driven reaction mechanism estimation via transient kinetics and machine learning

• Reaction mechanism characterization via experimental transient kinetic measurements. • Integration of well-defined reactor physics and machine learning. • Data-driven kinetic coefficients estimation via machine learning. • Reaction mechanism classification through rate and gas concentration correlation. • Validation of reaction mechanism applied to CO oxidation on platinum. Understanding the set of elementary steps and kinetics in each reaction is extremely valuable to make informed decisions about creating the next generation of catalytic materials. With structural and mechanistic complexities of industrial catalysts, it is critical to obtain kinetic information through experimental methods. As such, this work details a methodology based on the combination of transient rate/concentration dependencies and machine learning to measure the number of active sites, the individual rate constants, and gain insight into the mechanism under a complex set of elementary steps. This new methodology was applied to simulated transient responses to verify its ability to obtain correct estimates of the micro-kinetic coefficients. Furthermore, data from an experimental CO oxidation on a platinum catalyst was analyzed to reveal that Langmuir-Hinshelwood mechanism drives the reaction. As oxygen accumulated on the catalyst, a transition in the apparent kinetics was clearly defined in the machine learning analysis due to the large amount of kinetic information available from transient reaction techniques. This methodology is proposed as a new data driven approach to characterize how materials control complex reaction mechanisms relying exclusively on experimental data.

Atmospheric oxidation of 4‐(2‐methoxyethyl) phenol initiated by OH radical in the presence of O2 and NOx: A mechanistic and kinetic study

Abstract4‐(2‐Methoxyethyl) phenol (MEP) plays an important role in the formation of secondary organic aerosols (SOA). The gas‐phase mechanism and kinetics of MEP with OH reaction are studied by the density functional theory (DFT). The initial reactions of MEP with OH radical produce two different channels: OH addition and H abstraction. Subsequent reaction schemes of the main intermediates are investigated by using M06‐2X/6‐311++G(3df,2p)//M06‐2X/6‐311+G(d,p) level. Ketene, diketones and nitrophenol compounds are demonstrated to be the dominant oxidation products in the presence of high O2 and NOx. The total and individual rate constants are calculated by using the traditional transition state theory (TST) at 298K and 1atm. The calculated value of 5.62×10−11 cm3 molecule−1 s−1 is close to experimental data of similar systems. The lifetime of MEP is estimated to be 4.94 hours. These results provide a comprehensive explanation for atmospheric oxidation pathways of MEP.

Thermokinetic parameters evaluation using reaction calorimetry: Application to butyl methacrylate solution radical polymerization

This study investigates the possibility to use reaction calorimetry to estimate thermokinetic parameters of an industrial reaction. The synthesis chosen in this study is the radical polymerization of butyl methacrylate in different organic solvents. The kinetic parameters estimation method is based on the comparison of experimental thermal power profiles released during polymerization and measured using a reaction calorimeter RC1-RTCal with calculated power profiles by means of a simplified model. Individual kinetic parameters of the three main steps (initiation, propagation, termination) were estimated using a minimization method based on a genetic algorithm. Contrary to classical methods, in this paper the three kinetic parameters are estimated simultaneously and at high conversion. The measurement of physical properties, average molecular mass, polydispersity index and viscosity, made it possible to understand the effect of the solvents nature on individual kinetic rate constants. Estimated results are in good consistency with those encountered in the literature obtained by classical methods.