Reaction Constants Research Articles

Absorption in a pseudo-first-order regime with two irreversible reactions: Influence of the second reaction on the transfer rate

Gas-absorbing liquids such as CO2 often undergo two reactions: a main reaction and a secondary reaction. The solute flux transferred is a result of both reactions. Kinetics is one of the most important properties in the design of an absorber. To access the rate constant of the main reaction, the assumption of a pseudo-first-order (PFO) regime is often made, but the criteria for the system to be in a pseudo-first-order regime change between researchers. Furthermore, the impact of the secondary reaction is either neglected or overestimated. Recently, some researchers carried out simulations of multiple parallel gas–liquid reactions in the instantaneous regime and developed generalized criteria for this regime. In this study, to estimate the impact of the secondary reaction in a PFO regime, hundreds of simulations were carried out with two irreversible reactions within the framework of the film theory. This work proves that for Ha1 > 10, Ha2 > 10, Ha1/E∞,1 < 0.5, Ha2/E∞,2 < 0.5, normalized concentration profiles depend only on three factors: Ha1/ E∞,1, Ha2/ E∞,2, and Ha1/Ha2. Curves and generalized equations are provided enabling the estimation of the concentrations of reactants at the interface, the enhancement factor, and the influence of each reaction on the gas transfer flux (average absolute relative deviation ≤ 0.50 %). New criteria for determining whether the system can be considered in a pseudo-first-order regime are defined, giving accurate predictions with a success rate of 96.2 %.

Synthesis of ZnV2O6 nanosheet photocatalysts for efficient photodegradation of Rhodamine B: Experimental and RSM modeling

A ZnV2O6 photocatalyst with nano-sheet morphology was synthesized using a facile solvothermal approach. To optimize the photo-decomposition of Rhodamine B (RhB), a new surface response methodology (RSM) based on the Central Composite Design (CCD) approach was employed. Several structural/microstructural and spectroscopic characterization techniques were utilized to describe the physical and chemical characteristics of ZnV2O6 (ZVO) nanosheet such as XRD, Raman, SEM-TEM, DRS, PL/TRF. The optimal conditions for RhB photo-decomposition were mathematically discussed as a function of four variables such as pollutant dose, pH values, photocatalyst-weight, and irradiation time, which were modeled by CCD-RSM employing a quadratic statistical model and an optimization approach (ANOVA analysis). RhB degradation efficiency of 97 % was achieved for the optimal conditions of pH = 8, photocatalyst mass = 95 mg, RhB concentration = 9 ppm, and irradiation time = 120. The registered reaction constant was 0.029 min−1. The removal efficiencies of TOC and COD when using the ZVO photo-catalyst for the RhB degradation were 83 % and 88 % respectively. The re-usability of ZnV2O6 samples has been assessed in 4 consecutive series revealing a high stability of the material after extended periods of photo-catalytic reaction. Furthermore, the active radical species involved in the breakdown of RhB were further confirmed through quenching tests in which hydroxyls and holes were found to be the major species contributing to the decomposition of RhB.

Reinforcing the photocatalytic removal of ibuprofen antibiotic over S-scheme 2D/1D Bi12O17Cl2/V2O5 heterojunction under solar light illumination

In our work, the Bi12O17Cl2/V2O5 hybrid with a favorable S-scheme mechanism was prepared via a simple self-assembly procedure for ibuprofen (IBF) oxidation under solar light energy. The 2D Bi12O17Cl2 provides abundant active sites to immobilize 1D V2O5 nanorods, enhancing the interaction between two semiconductors. The establishment of the 2D/1D structure reflected a positive effect on the surface area of Bi12O17Cl2/V2O5-10 %, which was linked to the reduction in the aggregation rate of V2O5 nanorods. Amazingly, optimal Bi12O17Cl2/V2O5 photocatalysts achieved exceptional IBF degradation capacities of 88.6 % and 71.3 % under LED and direct solar light irradiation, respectively. Among the samples, the optimized Bi12O17Cl2/V2O5-10 % reflected the best IBF oxidation kinetic with a reaction constant of 0.03894 min− 1, which is stronger than pristine Bi12O17Cl2 (0.00885 min− 1) and V2O5 (0.0119 min− 1) by 4.4 and 3.27 times, respectively. The promoted catalytic activity was correlated to the S-scheme heterojunction between Bi12O17Cl2 and V2O5 that could upgrade the solar light absorbance, facilitate the separation and transportation of charge carriers, and strengthen the redox potential of Bi12O17Cl2/V2O5. Furthermore, the parameters revealed the best IBF treatment at a catalyst dosage of 0.6 g/L and a pH value of 7. Besides, Bi12O17Cl2/V2O5-10 % recorded outstanding catalytic stability in six cycles without notable alteration in its structure, morphology, or optical properties. On the other hand, the radical quenching tests declared that •O2− and •OH play major contributions in IBF photooxidation over Bi12O17Cl2/V2O5-10 %. Finally, our work offers vital guidance towards designing robust bismuth-based heterojunctions for efficient degradation of IBF antibiotics in a sustainable and cost-effective strategy.

Mechanistic and kinetic insights of the formation of allene and propyne from the C3H3 reaction with water.

Allene (H2C = C = CH2) and propyne (CH3-C≡CH) are important compounds in the combustion chemistry. They can be created from the reaction of proparyl radicals with water. In this study, therefore, a computational study into the C3H3 + H2O potential energy landscape has been carefully conducted. The computed results indicate that the reaction paths forming the products (allene: CH2CCH2 + •OH) and (propyne: HCCCH3 + •OH) prevail under the 300-2000K temperature range, where the latter is much more predominant compared to the former. However, these two products are not easily formed under ambient conditions due to the high energy barriers. In the 300 - 2000K temperature range, the branching ratio for the propyne + •OH product declines from 100 to 86%, whereas the allene + •OH product shows an increase, reaching 14% at 2000K. The overall bimolecular rate constant of the title reaction can be presented by the modified Arrhenius expression of ktotal = 1.94 × 10-12 T0.14 exp[(-30.55kcal.mol-1)/RT] cm3 molecule-1s-1. The total rate constant at the ambient conditions in this work, 2.37 × 10-34 cm3 molecule-1s-1, was found to be over five orders of magnitude lower than the total rate constant of the C3H3 + NH3 reaction, 7.98 × 10-29 cm3 molecule-1s-1, calculated by Hue et al. (Int. J. Chem. Kinet. 2020, 4(2), 84-91). The results in this study contribute to elucidating the mechanism of allene and propylene formation from the C3H3 + H2O reaction, and they can be used for modeling C3H3-related systems under atmospheric and combustion conditions. All the geometric structures of the C3H3 + H2O system were optimized by the B3LYP method in conjunction with the 6-311 + + G(3df,2p) basis set. Single-point energies of these species were calculated at the CCSD(T)/6-311 + + G(3df,2p) level of theory. The CCSD(T)/CBS level has also been used to compute single-point energies for the two major reaction channels (C3H3 + H2O → allene + •OH and C3H3 + H2O → propyne + •OH). Rate constants and branching ratios of the key reaction channels were calculated in the 300-2000K temperature interval using the Chemrate software based on the transition state theory (TST) with Eckart tunneling corrections.

Linear Free Energy Analysis on the Ring‐Expansion of Arylthiiranes with Ketenes

AbstractThe ring‐expansion of arylthiiranes and phenoxyacetyl chloride was performed in the presence of triethylamine and provided a novel strategy for the synthesis of 4,5‐dihydrobenzo[d]thiepin‐2(1H)‐ones, benzo[d]‐ϵ‐thiolactones, directly without catalysts or additives. Its linear free energy analysis was conducted on the basis of competitive experiments. The results indicate that both reaction constants are close to zero (0.14 for σm and 0.20 for σp), supporting the proposed sulfur‐shifted ene mechanism. The current reaction features atom and step‐economic one‐pot characteristic via a tandem sequence of in situ ketene generation, sulfur‐shifted ene reaction, and aromatization.

A consistent explanation of seemingly inconsistent experimental and theoretical data for N[formula omitted]O + O via MultiScale Informatics

The N2O + O reaction plays a critical role in NOx formation at high pressures and low peak temperatures, in the “dark zone” region of deflagration waves of organic energetic materials, and in N2O consumption in NH3 combustion. While the rate constant for N2O + O = NO + NO (R3) is considered reasonably well established, viewpoints regarding the rate constants for N2O + O = N2 + O2 (R2)—and even the main products of the N2O + O reaction—have not reached a consensus, with studies from the past few years continuing to reach drastically different conclusions. To date, no single model has been presented that can reproduce all key datasets on both sides of the debate. Using the MultiScale Informatics (MSI) approach, we identified a model consistent with a vast catalog of theoretical and experimental data previously used to determine rate constants for R2, R3, and other key reactions influencing experimental interpretations. Notably, this MSI model (presented herein) reproduces all experimental datasets previously used to anchor low-activation-energy k2 expressions that greatly favor R2 at intermediate temperatures. However, its kinetic parameters are also consistent with theoretical calculations that instead show high activation energy for R2 and k2 values many orders of magnitude lower—such that R3 is the main channel at essentially all temperatures. This model is also consistent with our new experimental data (presented in our companion paper) at optimally selected conditions that avoid the interpretation ambiguities that have hindered definitive conclusions from previous experimental data. The present analysis elucidates the role of secondary reactions that would have artificially inflated the apparent k2/k3 ratio previously deduced from experiments in a manner that may not have been detectable from even multi-species measurements at typical conditions—and may, therefore, explain the persistent historical difficulties in establishing the main products of N2O + O.Novelty and significance statementDespite decades of research, viewpoints regarding the rate constants for N2O + O = N2 + O2 (R2)—and even the main products of the N2O + O reaction—have not reached a consensus, with studies from the past few years still reaching drastically different conclusions. To date, no single model has been presented that can reproduce all key datasets on both sides of the debate. Here, we present a single model consistent with a vast catalog of theoretical and experimental data, including all experimental datasets previously used to anchor low-activation-energy expressions for k2 that greatly favor R2 as the main channel at intermediate temperatures—but with kinetic parameters consistent with theoretical calculations that instead show high activation energy for R2 and N2O + O = NO + NO (R3) as the main channel at essentially all temperatures.

Folding and Binding Kinetics of the Tandem of SH2 Domains from SHP2.

The SH2 domains of SHP2 play a crucial role in determining the function of the SHP2 protein. While the folding and binding properties of the isolated NSH2 and CSH2 domains have been extensively studied, there is limited information about the tandem SH2 domains. This study aims to elucidate the folding and binding kinetics of the NSH2-CSH2 tandem domains of SHP2 through rapid kinetic experiments, complementing existing data on the isolated domains. The results indicate that while the domains generally fold and unfold independently, acidic pH conditions induce complex scenarios involving the formation of a misfolded intermediate. Furthermore, a comparison of the binding kinetics of isolated NSH2 and CSH2 domains with the NSH2-CSH2 tandem domains, using peptides that mimic specific portions of Gab2, suggests a dynamic interplay between NSH2 and CSH2 in binding Gab2 that modulate the microscopic association rate constant of the binding reaction. These findings, discussed in the context of previous research on the NSH2 and CSH2 domains, enhance our understanding of the function of the SH2 domain tandem of SHP2.

Solubility, pH-Solubility Profile, pH-Rate Profile, and Kinetic Stability of the Tyrosine Kinase Inhibitor, Alectinib.

Alectinib HCl (ALBHCl) is a tyrosine kinase inhibitor used for non-small cell lung carcinoma (NSCLC). The aim of this study is to unlock some of the physicochemical properties of ALBHCL that serve as a database for any future studies. A solubility study of ALBHCL was performed in different solvents. Also, photostability was tested in the solution and solid states, and the order of reaction and rate constant were calculated. In addition to the pH solubility relation, the pH-rate relation at different temperatures was also studied, and the profiles were constructed. A solubility study was also performed in different media for the purpose of optimizing suitable sink conditions for the in vitro dissolution testing of solid dosage forms. Solubility tests in multiple solvents and pH conditions revealed that the highest solubility was in DMSO, methanol, and chloroform, with acidic media yielding the maximum solubility but degrading at rather low pH levels. ALBHCL proved unstable at high temperatures and under light exposure, with varying stability across different pH levels. The optimal dissolution media for in vitro oral dosage form evaluation were determined, achieving sink conditions at pH levels of 6.8 and 4.5 with specific additives. This study enhances the existing database on ALBHCL's physicochemical properties, emphasizing the importance of pH optimization in pharmaceutical processes and providing valuable insights into its pharmaceutical application.

New QSPR molecular descriptors based on low-cost quantum chemistry computations using DFT/COSMO approach

This work presents a simple computational methodology to determine new theoretical molecular descriptor scales convenient for use in QSPR correlations and the analysis of solvation-related properties. On the basis of low-cost quantum chemical computations using DFT/COSMO approach, in particular that implemented in the ADF/COSMO-RS module of the Amsterdam Modeling Studio program package, optimized geometry and local screening charge density of a considered molecule are obtained and related to the proposed descriptors through an a priori simple reasoning. Values of four molecular descriptors, namely volume VCOSMO∗, hydrogen bond/Lewis acidity αCOSMO and basicity βCOSMO, and charge asymmetry of the nonpolar region of the molecule δCOSMO have been calculated and are presented for sets of 128 non-ionic organic molecules and 47 ions composing ionic liquids. Relation of the proposed scales to some others that are widely known or presented recently in the literature has been examined. Although the present methodology is completely independent of any experimental data, the theoretical descriptor scales proposed here have been found to correlate linearly quite well with the respective empirical scales (mostly R2 > 0.8, and for some R2 > 0.9). For non-ionic organics, just the direct proportionality provided adequate fits of the well-established prominent scales such as those of Abraham, Klamt, Kamlet-Taft, Catalan, Gutmann, and Laurence and showed only a few statistically justifiable outliers. For ions composing ILs, the linear fits of seven acidity or basicity scales presented previously with those proposed in this work were of similar quality. Examining the observed outliers, several descriptor values reported in the literature were identified as being in error. Good performance of the new descriptor scales has been demonstrated by employing them for LSER fitting of various solvation-related thermodynamic and kinetic properties such as standard vaporization enthalpy, standard hydration enthalpy, air–water partition coefficient, air-IL partition coefficient, and solvent effects on the activation Gibbs energy or rate constant of SN1 and SNAr reactions. The quality of these correlations appears to be comparable to that of the correlations currently available for these properties, regardless of the role, solute or solvent, the involved molecules played.

Photomediated synthesis of stabilizer-free silver nanoprisms with a tunable plasmon wavelength for enhanced catalytic activity

Herein, we introduce a simplified photomediated method for fabricating silver nanoprisms (AgNPrs) with controllable surface plasmon resonance. The Ag nanoparticles (Ag seeds), Ag+, and citrate ions were used to control AgNPrs growth. Citrate ions served as a reducing agent and a stabilizer. The optimized [citrate]/[Ag+] ratio of 10 was sufficient to stabilize the final AgNPrs. Sodium borohydride (NaBH4) was used as a strong reducing agent to generate the initial Ag seed amount, then controlled by the [BH4−]/[Ag+] ratio. A ratio of 0.0005–0.005 ([BH4−]/[Ag+]) yielded a 545–702 nm plasmon band of AgNPrs. AgNPrs displayed an irregular plate shape in their morphological structure, featuring lateral dimensions spanning from 30.7 ± 4.3 to 51.0 ± 10.8 nm and a thickness ranging from 7.2 ± 0.8 to 10.7 ± 1.3 nm. The synthesized AgNPrs exhibited excellent stability in the dark at 4 °C without any additional polymeric stabilizer and presented negligible variations in their absorbance UV–visible spectra for at least 1 month. They demonstrated an enormous (111) facet potentially serving as an active catalytic site for reducing 4-nitrophenol to 4-aminophenol. With synthesized AgNPrs, the rate constant of the reduction reaction increased to 0.2440 min−1, which was 120 times greater than that without the catalyst or with spherical Ag nanoparticles. These AgNPrs can be reutilized for at least five catalytic cycles without losing their catalytic efficiency.

Determination of physicochemical parameters of (bio)molecules and (bio)particles by capillary electromigration methods.

The review provides an overview of recent developments and applications of capillary electromigration (CE) methods for the determination of important physicochemical parameters of various (bio)molecules and (bio)particles. These parameters include actual and limiting (absolute) ionic mobilities, effective electrophoretic mobilities, effective charges, isoelectric points, electrokinetic potentials, hydrodynamic radii, diffusion coefficients, relative molecular masses, acidity (ionization) constants, binding constants and stoichiometry of (bio)molecular complexes, changes of Gibbs free energy, enthalpy and entropy and rate constants of chemical reactions and interactions, retention factors and partition and distribution coefficients. For the determination of these parameters, the following CE methods are employed: zone electrophoresis in a free solution or in sieving media, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography. In the individual sections, the procedures for the determination of the above parameters by the particular CE methods are described.

Synthesis of 3D Sb2O3-based heterojunction reinforced by SPR effect and photo-Fenton mechanism for upgraded oxidation of metronidazole in water environments

The traditional homogenous and heterogenous Fenton reactions have frequently been restrained by the lower production of Fe2+ ions, which significantly obstructs the generation of hydroxyl radicals from the decomposition of H2O2. Thus, we introduce novel photo-Fenton-assisted plasmonic heterojunctions by immobilizing Fe3O4 and Bi nanoparticles onto 3D Sb2O3 via co-precipitation and solvothermal approaches. The ternary Sb2O3/Fe3O4/Bi composites offered boosted photo-Fenton behavior with a metronidazole (MNZ) oxidation efficiency of 92% within 60 min. Among all composites, the Sb2O3/Fe3O4/Bi-5% hybrid exhibited an optimum photo-Fenton MNZ reaction constant of 0.03682 min− 1, which is 5.03 and 2.39 times higher than pure Sb2O3 and Sb2O3/Fe3O4, respectively. The upgraded oxidation activity was connected to the complementary outcomes between the photo-Fenton behavior of Sb2O3/Fe3O4 and the plasmonic effect of Bi NPs. The regular assembly of Fe3O4 and Bi NPs enhances the surface area and stability of Sb2O3/Fe3O4/Bi. Moreover, the limited absorption spectra of Sb2O3 were extended into solar radiation by the Fe3+ defect of Fe3O4 NPs and the surface plasmon resonance (SPR) effect of Bi NPs. The photo-Fenton mechanism suggests that the co-existence of Fe3O4/Bi NPs acts as electron acceptor/donor, respectively, which reduces recombination losses, prolongs the lifetime of photocarriers, and produces more reactive species, stimulating the overall photo-Fenton reactions. On the other hand, the photo-Fenton activity of MNZ antibiotics was optimized under different experimental conditions, including catalyst loading, solution pH, initial MNZ concentrations, anions, and real water environments. Besides, the trapping outcomes verified the vital participation of •OH, h+, and •O2− in the MNZ destruction over Sb2O3/Fe3O4/Bi-5%. In summary, this work excites novel perspectives in developing boosted photosystems through integrating the photocatalysis power with both Fenton reactions and the SPR effects of plasmonic materials.

A Numerical Time Integration Procedure for Secondary Dendrite Arm Spacing in Hyper-Peritectic Steel Alloys

AbstractA numerical time integration procedure for the calculation of the secondary dendrite arm spacing (SDAS) in FeC hyper-peritectic alloys is presented, a preferred group of low-carbon casting steel. The procedure incorporates a three-stage thin arm dissolution model, which is solved at each time step using Newton–Raphson iteration. This is coupled to a coarsening model based on the integral forms of the dissolution model, which are solved using Gaussian quadrature, as well as a growth model for solid fraction evolution. The procedure can easily be embedded into numerical models for solidification, in which the space–time evolution of the SDAS is required for determining the dynamic permeability in the mushy zone. Higher order approximations for both growth and solute concentration evolution can easily be incorporated. Temperature dependence of thermophysical parameters is taken into account using inter-dendritic solidification empirical models, and an alloy-specific peritectic reaction constant is used to determine the isothermal peritectic holding time. The procedure is validated against experimental data presented in literature. Various cases of SDAS as a function of local solidification time, cooling rate and carbon composition are investigated. The method is compared to experimental results of SDAS obtained from test castings of a hyper-peritectic steel alloy and can be used to iteratively determine the alloy-specific peritectic reaction constant by comparing the solid fraction evolution during the peritectic reaction with that found from the experimental cooling curve.

Characteristics of Aqueous Chemical Species Generation in Plasma-Facing Liquid Systems Using Helium Jet Plasma.

Plasma-facing liquids (PFLs) facilitate the storage of reactive O and N species (RONS), including H2O2 and NO2 -, which remain in the PFL after plasma treatment, and they can continuously influence the target immersed in the liquid. However, their behaviors and levels of generation and extinction depend strongly on the plasma characteristics and liquid condition. Therefore, understanding the effects of the liquid type on the plasma discharge characteristics and the RONS generated via plasma discharge is necessary. We compared the RONS generation and storage trends of deionized H2O and a high-conductivity PFL, RPMI 1640, which is a well-known cell culture medium commonly used to culture mammalian cells. RPMI 1640 acted as an electrode and enhanced the plasma discharge power by supplying abundant radicals and RONS. The production of gaseous hydroxyl radicals and NO markedly increased, which facilitated H2O2 and NO2 - production in the PFL for the first 200 s, and then the increase in the RONS concentration stagnated. With respect to storage, as the components within RMPI 1640 exhibited high reaction constants for their reactions with H2O2, H2O2 elimination was completed in <30 min. Unlike H2O2, the concentration of NO2 - in the PFL was unchanged.

Photo-Oxidation of α-Pinene Oxidation Products in Atmospheric Waters - pH- and Temperature-Dependent Kinetic Studies.

The atmospheric α-pinene oxidation leads to three carboxylic acids: norpinonic acid (NPA), pinic acid (PA), and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA). In this study, the OH radical kinetics in the aqueous phase of these carboxylic acids were investigated at different temperatures and pH values of solutions. Activation parameters and the corresponding atmospheric lifetimes of the acids in the troposphere were derived. The overall second-order rate constants for the individual speciation forms of the acids (AH and A- for NPA; AH2, AH- and A2- for PA; and AH3, AH2-, AH2- and A3- for MBTCA) were determined. At 298 K, the rate constants for reactions of protonated forms (AHx) of NPA, PA, and MBTCA with •OH, were (1.5 ± 0.2) × 109 L mol-1 s-1, (2.4 ± 0.1) × 109 L mol-1 s-1, and (4.1 ± 0.6) × 108 L mol-1 s-1, respectively. For the fully deprotonated forms (Ax-) of studied acids, the second-order rate constants were (2.2 ± 0.2) × 109 L mol-1 s-1, (2.8 ± 0.1) × 109 L mol-1 s-1, and (10.2 ± 0.7) × 108 L mol-1 s-1 at 298 K, respectively. It was found that the reactions of NPA and PA with OH radicals are faster than with MBTCA. For MBTCA, the reaction rate depends on pH more strongly at elevated temperatures (>298 K). The atmospheric lifetimes of the acids considered due to their reactivity with •OH were calculated for different model scenarios at a temperature of 283 K and pH = 2 in the aqueous phase. For this purpose, liquid water content (LWC) was used for aerosols and clouds under storm conditions and at various aqueous-phase concentrations of OH radicals. The lifetimes decreased with increasing LWC (from 10-12 m3 m-3 in aerosol to 10-5 m3 m-3 in storms), indicating that the acids undergo significant aqueous processing under realistic atmospheric conditions. Besides, the aerosol systems appeared less effective in removing PA and NPA, with lifetimes ranging from hundreds of days to tens and hundreds of hours, respectively. Clouds were more effective, with lifetimes ranging from tens of hours to a single second or less. MBTCA, which dissolves better in water, was effectively removed in all systems, with the longest lifetime of approximately 90 min.

Study of the influence of ionizing radiation on the activity of the neurotoxin Vipoxin in a model monolayer system at the water/air interface

The main components of the cell membrane are phospholipids, and the enzymes that hydrolyze them for the purposes of many important physiological functions are the phospholipases whose properties strongly depend on the phospholipids’ structural organization. Here, we propose a proper experimental approach to study the effect of ionizing radiation on the catalytic action of the neurotoxin Vipoxin, a heterodimeric protein complex composed of an active basic secretory phospholipase A2 (PLA2) and an inactive acidic component, known as “inhibitor”, on the phospholipid substrate such as α-L-dilauroylphosphatidylcholine (DLPC) using as a model system Langmuir monolayer. First, the Vipoxin dissolved in buffer solution was irradiated in a controlled manner with radiation doses varying from 0.1 to 10 Gy, next, the Vipoxin PLA2 activity was followed in real-time, using a modified Langmuir trough, measuring the surface area change of the monolayer. This approach allowed us to obtain the dependence of the neurotoxin catalytic activity at a particular surface pressure and to determine the fundamental constants of the enzyme reaction. It was found that the activity of Vipoxin was influenced in a dose dependent manner. We also found that at higher irradiation doses the enzymatic activity increased, hypothetically due to dissociation of its dimeric Vipoxin complex.

Modulating the channel structure of iron-based catalysts with β-cyclodextrin for enhanced degradation of 2,4,6-trichlorophenol via peroxymonosulfate activation: Performance, mechanism and transformation pathways

Rationally regulating the structure of catalysts in Fenton-like reactions provides abundant opportunities for the efficient remediation of organic micropollutants from the aqueous environment, yet it is challenging to achieve superior reactivity and the catalytic mechanisms have rarely been systematically elucidated. Herein, we present a simple strategy to synthesize confined catalysts with different pore-size distributions by modulating the proportion of β-cyclodextrin (β-CD) with a cavity. The degradation performance of the confined catalyst MCF with the smallest pore size (5.9 nm) was remarkably enhanced compared to the unconfined catalyst NCF, mainly by 1O2 and electron transfer. As the cavity content increases, the reactivity displayed an unexpected volcanic peak tendency. The pseudo-first-order reaction constant of MCF was 2.6 times higher than that of HCF (8.2 nm) in Fenton-like oxidation with peroxymonosulfate (PMS). Comparative control experiments demonstrated that the appropriate structure can significantly facilitate the diffusion and degradation process of pollutants that are adsorbed in the confined channels. The MCF/PMS system exhibited strong adaptability to coexisting ions and pH in the water matrix, and the intermediate products were harmless to the environment. This unusual catalytic mechanism and the structural regulation strategy will establish new insights into boosting the catalytic performance for the efficient removal of organic micropollutants.

Adsorption properties and catalytic activity of Fe3O4-Ag nanostructures

The morphology and magnetic properties as well as adsorption capacity and catalytic activity of Fe3O4-Ag nanoparticles synthesized by the solvothermal method were studied in dependence on the duration of the thermolysis process (3, 6, and 8 h). X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy measurements showed that the morphology of nanoparticles changed strongly as the duration of thermolysis increased. At 6 and 8 h duration, Fe3O4 nanocrystals grow and assemble into porous spherical globules with an Ag core (samples 2 and 3). These samples demonstrate high magnetization value and very low coercivity. The adsorption capacity of nanoparticles was studied with respect to two organic dyes: cationic methylene blue (MB) and anionic Congo red (CR). The particles showed preferential adsorption of the cationic dye. High catalytic activity towards four dyes: MB, methyl orange (MO), CR, and Rhodamine C (RhC) at the presence of NaBH4 is the remarkable property of these samples. The rate constant of the catalytic reaction was 1.4 min−1. Simultaneous exposure of CR and MO dyes to nanoparticles and NaBH4 caused their irreversible 100 % degradation while in the case of MB and RhC, a transition to their leuco form occurred.

Initial precursor reaction mechanism of CVD-HfC coating based on density functional theory

Recently, the preparation of ultra-high temperature HfC ceramic coating has gained significant attention, particularly through the application of the HfCl4-CH4-H2-Ar system via Chemical Vapor Deposition (CVD), which has been found widely applied to C/C composites. Herein, an analysis of the reactions that occur in the initial stage of the CVD-HfC coating process is presented using Density Functional Theory (DFT) and Transition State Theory (TST) at the B3LYP/Lanl2DZ level. The results reveal that HfCl4 can only cleave to produce hypochlorite, which will further react with methyl to synthesize intermediates to form HfC. According to the analysis of the energy barrier and reaction constant, HfCl preferentially reacts with methyl groups to form complex adsorptive intermediates at 1573 K. With a C—Hf bond production energy of 212.8 kcal/mol (1 kcal = 4.18 kJ), the reaction rate constant of HfCl + CH is calculated to be 2.15 × 10−18 cm3/s at 1573 K. Additionally, both the simulation and experimental results exhibit that the upward trend of reaction rate constants with temperature is also consistent with the deposition rate, indicating that the growth curve of the reaction rate constants tends to flatten out. The proposed reaction model of the precursor’s decomposition and reconstruction during deposition process has significant implication for the process guidance.

Kinetic Computation of Cyclization Reactions of Large Keto-Hydroperoxide Radicals in Low Temperature Combustion.

The cyclization reactions of keto-hydroperoxide (KHP) radicals leading to the formation of keto cyclic ethers and OH radicals play an important role in low temperature combustion for hydrocarbon fuels or oxygenated hydrocarbon fuels. However, due to the lack of kinetic data of cyclization reactions of KHP radicals, researchers often derive high-pressure-limit rate constants of cyclization reactions of KHP radicals from analogous cyclization reactions of hydroperoxyl alkyl radicals during construction of the combustion mechanism. This study aims to systematically investigate the kinetics of cyclization reactions of KHP radicals involving short-to-large-sized radicals. The studied reactions are divided into 7 reaction classes, according to the size of the cyclic transition state, the conjugative effect (whether KHP radicals are resonance-stabilized or not), and the position of the carbonyl group (whether the carbonyl group is inside or outside of the reaction center). The isodesmic reaction method, in conjunction with transition state theory, is utilized for each reaction class to compute the energy barriers and high-pressure-limit rate constants at the DFT level. The study revealed that energy barriers calculated at the DFT level with correction by the isodesmic reaction method are close to the results from the benchmark CCSD(T) method. To develop more accurate rate rules, these reaction classes are further divided into subclasses based on the relative site of the OOH group with the carbonyl group, the type of carbon atoms where the OOH group is located, and the type of carbon atoms where the radical site is located. For each subclass, high-pressure-limit rate rules are derived by averaging the rate constants of reactions in the subclass, and it is found that the maximum absolute deviation of the energy barrier and the ratio of the largest rate constant to the smallest rate constant among reactions in each subclass are within chemical accuracy limits, indicating acceptable use of the developed rate rules. A comparison of the rate constants for cyclization reactions of KHP radicals with the values of analogous cyclization reactions of hydroperoxyalkyl radicals as provided in reported mechanisms is made. Additionally, a comparison is drawn between our developed rate rules for subclasses of the cyclization reactions of KHP radicals and the rate rules for analogous subclasses of cyclization reactions of hydroperoxyl alkyl radicals. These comparisons demonstrate significant differences and highlight the necessity for improved rate rules for cyclization reactions of KHP radicals to enhance the automatically generated combustion mechanisms for hydrocarbon and oxygenated hydrocarbon fuels.