Kinetic Analysis Research Articles

On the Mechanisms of Hypohalous Acid Formation and Electrophilic Halogenation by Non-Native Halogenases.

Enzymatic electrophilic halogenation is a mild tool for functionalization of diverse organic compounds. Only a few groups of native halogenases are capable of catalyzing such a reaction. In this study, we used a mechanism-guided strategy to discover the electrophilic halogenation activity catalyzed by non-native halogenases. As the ability to form a hypohalous acid (HOX) is key for halogenation, flavin-dependent monooxygenases/oxidases capable of forming C4a-hydroperoxyflavin (FlC4a-OOH), such as dehalogenase, hydroxylases, luciferase and pyranose-2-oxidase (P2O), and flavin reductase capable of forming H2O2 were explored for their abilities to generate HOX in situ. Transient kinetic analyses using stopped-flow spectrophotometry/fluorometry and product analysis indicate that FlC4a-OOH in dehalogenases, selected hydroxylases and luciferases, but not in P2O can form HOX; however, the HOX generated from FlC4a-OOH cannot halogenate their substrates. Remarkably, in situ H2O2 generated by P2O can form HOI and also iodinate various compounds. Because not all enzymes capable of forming FlC4a-OOH can react with halides to form HOX, QM/MM calculations, site-directed mutagenesis and structural analysis were carried out to elucidate the mechanism underlying HOX formation and characterize the active site environment. Our findings shed light on identifying new halogenase scaffolds besides the currently known enzymes and have invoked a new mode of chemoenzymatic halogenation.

Sustainable approach to dye adsorption: hemp-based activated carbon as an effective adsorbent

ABSTRACT In industry, the use of dyes that threaten human health is increasing day by day. RB 19 (Reactive Blue 19, Remazol brilliant blue R), one of the most common dyes that adversely affect natural life, is the subject of this article. In this article, the waste parts of the hemp plant (root, stem and other) were evaluated for use in scientific studies. Hemp wastes were carbonised at 500°C at a heating rate of 10°C/min for 1 hour in the N2 atmosphere. Chemical activation was then carried out with 1:4 potassium hydroxide (KOH) at 800°C under the same conditions. Activated carbon (AC) used as an adsorbent was characterised by elemental analysis (73.3% C, 0.3% H, 0.46% N, 0.02% S and 25.92% O), XRD, SEM, BET and FT-IR analysis. Activated carbon (AC) with 850 μm size, 1858.70 m2/g surface area was obtained by chemical activation of carbonised hemp waste with KOH. SEM images showed that the activated carbon is structurally similar to a honeycomb. Kinetic parameters were analysed with six different equations (Intra Particle Diffusion, Pseudo First, Pseudo Second, Elovich, Avrami, Bangham) and adsorption mechanism with eight different equations (Henry, Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Koble-Corrigan, Flory-Huggins, Harkin-Jura). According to the calculated diffusion coefficient (19.299), it is concluded that diffusion is externally controlled. The Intra-Particle Diffusion constant (75.34) indicated that the outer adsorption layer of activated carbon was thick. When the correlation coefficients of the equations were examined according to the kinetic analysis results, the highest correlation coefficient was observed in the Pseudo-First kinetic model for all temperatures. However, it was determined that it also fits the Bangham and Avrami models. Since Bangham and Avrami models have high regression coefficients (0.96–0.99), it can be said that adsorption also fits these models. Also, the negative Gibbs Free Energy values indicate that adsorption can occur spontaneously and is thermodynamically favourable.

Investigation of Direct Reduction of Copper Slag Using Castor Oil as a Green Reductant: Metal Recovery, Reduction Characterization and Kinetic Analysis

Investigation of Direct Reduction of Copper Slag Using Castor Oil as a Green Reductant: Metal Recovery, Reduction Characterization and Kinetic Analysis

Kinetic and biosorption analysis of ammonia‑nitrogen (NH3−N) by Bacillus subtilis strain ON358108, isolated from eutrophicated Dal Lake waters in Srinagar, India

Ammonia‑nitrogen (NH3-N) is pivotal in aquatic ecosystems, yet its excess poses ecological and health risks. Through batch experiments, this study investigates Bacillus subtilis' efficacy in degrading ammonia‑nitrogen (NH3-N) Bacillus subtilis adapted to concentrations up to 150 mg/L over days, influenced by temperature, pH, initial ammonia‑nitrogen (NH3-N) concentration, and biomass abundance. In the present investigation, the biosorption of ammonia nitrogen (NH3-N) (from 100 ppm concentration of ammonia nitrogen solution) was maximum (about 89 % ± 1.5 mgg) under conditions: pH 7, adsorbent dosage 0.5 g in 50 mL of ammonia‑nitrogen solution, and temperature of 30 °C. Analytical techniques including SEM, XRD, BET, TEM, and FTIR corroborated findings. Pseudo-second-order kinetics and Langmuir model fitting indicated physical and chemical involvement in biosorption. This study underscores Bacillus subtilis' potential for ammonia‑nitrogen (NH3-N) remediation, providing insights into optimized conditions and mechanistic understanding crucial for water quality management and ecosystem preservation.

Antibiotic Chloramphenicol degradation using submerged thermal plasma synergized with LaMnO3 catalyst

The present study focused on the degradation of antibiotic Chloramphenicol (CAP), an emerging contaminant, using submerged thermal plasma (STP) technology. Almost 99 % degradation and 82 % mineralization were achieved within 20 min of treatment by Ar/CO2 plasma, generated at 6.2 kW discharge power using a customized thermal plasma torch inside the aqueous solution. Kinetic analysis revealed first-order reaction for CAP degradation with a rate constant of 0.257 min−1. Long-lived species, such as H2O2, O3, NO2–, NO3–, and Cl- formed during plasma treatment were quantified. LaMnO3 perovskite (LMO) nanopowder prepared through a novel thermal plasma route, was introduced as catalyst into the treatment system which enhanced the degradation and mineralization efficiency by 34 % and 17 %, respectively, showing a strong synergetic effect between STP and catalyst. The energy yield was elevated from 102 mg/kWh to 144 mg/kWh with the addition of catalyst into the STP treatment system. Liquid chromatography-mass spectroscopy was used to identify the various degradation intermediates produced during thermal plasma treatment and correspondingly possible degradation pathways were proposed. The antibacterial activity assessment results revealed a significant reduction in the antimicrobial activity of all treated solutions against Gram-positive Bacillus cereus and Gram-negative Pseudomonas aeruginosa bacteria. Additionally, seed germination and growth assessment revealed a reduction in phytotoxicity of the treated solutions. STP, combined with the LMO, proved highly effective in treating pharmaceutical contamination in aqueous medium.

Dual‐functional and polydopamine‐coated vanadium disulfide for “fast‐charging” lithium‐ion batteries

AbstractAs a typical representative of vanadium‐based sulfides, vanadium disulfide has attracted the attention of researchers ascribed to its high theoretical capacity and unique crystal structure. However, overcoming its structural collapse while achieving dual functionalization that serves as both active material and binder remains challenging. This study designs a dopamine‐coating vanadium disulfide core‐shell structure through the synergistic effect of V‐O bonds and hydrogen bonds between vanadium disulfide and dopamine, which is further employed as a dual‐function electrode material. The polydopamine‐coated vanadium disulfide without binder exhibits specific capacity of 682.03 mAh g−1, and the Coulombic efficiency of 99.78% at a current density of 200 mA g−1 after 400 cycles. More importantly, at a larger current density of 1000 mA g−1, the specific capacity is 385.44 mAh g−1 after 1500 cycles. After 3150 cycles, the specific capacity is 200.32 mAh g−1 at 2000 mA g−1. Electrochemical kinetics analysis displays that the polydopamine‐coated vanadium disulfide without binder exhibits fast ion‐diffusion kinetics, with the order of magnitude of ion‐diffusion coefficients ranging from 10−11 to 10−12. This kind of material has the potential to be a significantly promising electrode material for “fast‐charging” lithium‐ion batteries.

Carbothermal reduction between MOF-derived carbon and spent battery powder for metal recovery: Thermogravimetric behavior and kinetic analysis

The combined hydrometallurgical and pyrometallurgical process is an innovative method for recycling spent batteries. This process includes a carbothermic reduction step that reduces the valence of valuable metals in the batteries, facilitating subsequent leaching, which is a crucial stage in the recycling process. Additionally, the use of new carbon materials in electrode materials for ternary lithium batteries, referred to as LIBs, is increasing. These materials typically have high porosity and a large specific surface area. In this study, two types of nanoporous carbon (NC) commonly used in electrodes, namely Al-PCP-800 and ZIF-8–800, were prepared to investigate their effects on the carbothermic reduction stage of recycling spent batteries. The carbothermal reduction reactions of spent LIBs powder mixed with activated carbon and the two types of NC were examined using a thermogravimetric balance (TG/DTG). Kinetic characteristics were calculated in the interval of maximum weight loss rate using five kinetic models: VM, RPM, URCM, KAS, and FWO. The kinetic analysis revealed that the KAS and FWO models, which exhibited higher correlation coefficients, more accurately described the carbothermic reduction reactions. TG analysis showed that the sample mixed with 25 % ZIF-8–800 achieved the lowest temperature at the weight loss peak for the maximum weight loss rate, 769°C at a heating rate of 20 °C/min. Additionally, the reaction activity of NC with the positive material in the spent LIBs powder was stronger than that of activated carbon. Among the models, the sample mixed with 25 % ZIF-8–800 exhibited the lowest activation energies, recorded at 171.83, 28.48, 122.22, 199.49, and 143.45 kJ/mol, respectively. XRD and XPS characterizations of the roasted products from the spent LIBs powder mixed with the three carbon materials at various roasting end temperatures demonstrated that the cathode materials initially decomposed into Mn3O4, NiO, CoO, Li2O, and Li2CO3. At higher temperatures, Mn3O4, NiO, and CoO were further reduced to MnO, pure metallic Co, and pure metallic Ni, respectively. The sample mixed with ZIF-8–800 showed the most substantial reduction of metallic elements, with the relative contents of pure metallic Ni, pure metallic Co, and low-valent Mn elements reaching 5.50 %, 4.41 %, and 71.29 %, respectively, at a final roasting temperature of 800 °C. Therefore, NC demonstrated greater reactivity in the reduction reactions with the cathode material in the spent LIBs powder, ranking in the order of ZIF-8–800 > Al-PCP-800 > activated carbon.

Inhibition of RNA Phosphodiester Backbone Cleavage in the Presence of Organic Cations of Different Sizes.

Living cells contain various types of organic cations that may interact with nucleic acids.In order to understand thenucleic acid-binding properties oforganic cations of different sizes, we investigated the ability ofsimple organic cations to inhibit the RNA phosphodiester bond cleavage promoted by Mg2+, Pb2+, and RNA-cleaving serum proteins. Kinetic analysis using chimeric DNA-RNA oligonucleotides showed that the cleavage at ribonucleotide sites was inhibited in the presence of monovalent cations comprising alkyl chains or benzene rings. The comparison of thecleavage rates in the presence ofquaternary ammonium and phosphonium ionsindicated thatthe steric hindrance effect of organic cations on their binding tothe RNA backboneis significant when the cation size is larger than the phosphate-phosphate distance of a single-stranded nucleic acid.The cleavage inhibition was also observed for ribonucleotides located in long loops but not in short loopsof oligonucleotide structures, indicating less efficient binding of bulky cationsto structurally constrained regions.Theseresults revealtheunique nucleic acid-binding properties of bulky cations distinct from those of metal ions.

Constructing sustainable keratin/algae biohydrogels for efficient removal of aniline blue via a pre-extrusion induced self-crosslinking strategy

Two environmentally friendly hierarchical porous biohydrogels, honeycomb keratin hydrogel (HKH) and spongy keratin-algae hydrogel (SKAH), were fabricated using an extrusion approach by using extruded keratin with or without algae. The extruded keratin exhibits exceptional self-crosslinking properties, making the biohydrogels behave with excellent adsorption performance for aniline blue dye removal from wastewater. In addition, the SKAH demonstrated a significantly higher maximum uptake capacity of 442.56 mg/g, surpassing that of the HKH (134.63 mg/g). This enhancement can be attributed to the looser porous structure of the SKAH, which enables better exposure of active groups within the material, which indicates the introduction of algae led to noticeable variations in the microstructure and performance of the adsorbent. Systematic investigation on the adsorption performance of isotherm and kinetics analyses indicated that chemisorption played a predominant role in governing the overall rate of adsorption. Overall, this extrusion approach allows for a simplified and non-toxic method of synthesizing these biohydrogels without the need for additional chemical reagents or biocross-linkers, promoting their eco-friendliness and reducing potential environmental impacts. The unique feature presents significant opportunity to fabricate sustainable and eco-friendly biohydrogel adsorbent for wastewater treatment.

KINETICS AND THERMODYNAMIC ASSESSMENT OF RICE HUSK IN AN INERT ATMOSPHERE AS A FEEDSTOCK FOR ALTERNATIVE FUEL PRODUCTION

The utilisation of rice husk as a feedstock for alternative fuel production is an area of growing interest due to its abundance and potential as a renewable energy source. This study reports investigation of kinetics and thermodynamics of rice husk pyrolysis in an inert atmosphere. Experimental analysis, including proximate, ultimate, structural composition and thermogravimetric analyses (TGA), were conducted to determine the proxanal, ultanal, chemical composition and pyrolysis characteristics of rice husk under inert conditions. Kinetics of the pyrolysis process was evaluated using distributed activation energy model (DAEM) while thermodynamic parameters such as activation energy (E A), changes in enthalpy (ΔH), entropy (ΔS),and Gibbs free energy (ΔG) were computed to provide insights into the reaction mechanisms. The feedstock exhibited ash content, fixed carbon, volatile matter, and higher heating value on dry basis of 13.56wt%, 16.37wt%, 70.07wt% and 15.22MJ/kg respectively while the result of ultimate analysis showed carbon, hydrogen, nitrogen, sulphur and oxygen content of 40.95, 5.67, 0.22, 0.09 and 52.17wt%. The chemical composition result (water extractives-free) indicated cellulose, hemicellulos and lignin content of 39.12, 17.56 and 22.43 wt%. The kinetics analysis revealed that the pyrolysis process followed a single-order reaction mechanism and irreversible, suggesting that the pyrolysis reactions proceed in a direction that favors the formation of products. The average E A, ΔH, ΔS and ΔG required for the pyrolysis reactions was established to be 140.56 kJ/mol, 137.00 kJ/mol, -135.25 J/mol and 222.38 kJ/mol respectively. The comprehensive assessment of the feedstock affirms its suitability for alternative fuel production towards a greener energy landscape.

Chemical insight into thermal degradation, chemical kinetics, and thermodynamics behavior of sewage sludge through thermogravimetry and Fourier transform infrared analysis

Pyrolysis emerges as a promising path for sewage sludge (SS) management and value creation by producing compounds with enhanced utility. This study focuses on a comprehensive analysis of the thermal decomposition of SS using thermogravimetric analysis (TGA) and Fourier transform infrared spectrometry (FTIR). The TGA and FTIR were employed to evaluate the pyrolysis behavior, kinetics, and characteristics during pyrolysis of SS. The process revealed three distinct stages: 1st stage ranged between 30–185 °C with the removal of moisture, 2nd stage saw devolatilization of SS in the range of 185–595 °C, and the 3rd stage was mainly the formation of char in the temperature range of 595–900 °C. Pyrolysis kinetics, reaction mechanisms, and thermodynamic properties were extensively investigated at three different heating rates of 10, 20, and 30 °C /min. It was observed that with the temperature rise, the decomposition rate also increased rapidly, notably for the heating rate of 30 °C/min. Using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Tang methods, activation energies for SS pyrolysis were estimated for α in the range of 0.2–0.85, and the average value for that range was found to be 84.72, 92.29, 91.99, and 91.76 kJ/mol, respectively for different iso-conversional methods. The chemical kinetics analysis through Coats-Redfern methods identified that 3-D diffusion-reaction mechanisms have the highest coefficient of determination among the other models. Criado z-master plot emphasizes the prevalence of Avrami-Erofeev (A4) as the bestsuited reaction model in combination with α, providing a detailed examination that illuminates the complex processes and mechanisms inherent in the pyrolysis of sewage sludge.

Role of oxygen vacancy in high-entropy Cu1Zn1Al0.5Ce5Zr0.5Ox for CO2 hydrogenation reaction

High-entropy oxides (HEOs) have garnered significant attention in catalysis due to their excellent redox properties and superior stability. In this study, we prepared and investigated a high-entropy oxide, Cu1Zn1Al0.5Ce5Zr0.5Ox, to elucidate the impact of oxygen vacancy density on the CO2 hydrogenation reaction. Comparisons were made with binary or ternary solid solutions composed of the same cations present in this HEO, and possessing the same phase structure. The HEO exhibits a higher surface oxygen vacancy density as evidenced by Raman spectroscopy and XPS. The increased number of oxygen vacancies significantly increases the active sites and enhances the strength for CO2 adsorption. Combined with kinetic analysis, it is suggested that the enhanced CO2 adsorption leads to improved CO2 conversion on the HEO. Moreover, the formation of oxygen vacancies facilitates H2 dissociation and supply, which is pivotal for methanol formation on the HEO. The stability of the HEO Cu1Zn1Al0.5Ce5Zr0.5Ox surpasses that of the medium entropy oxide, showing no significant deactivation after 100 hours of reaction.

For regenerated graphite: Tailoring sub-surface architecture with strong pre-storage abilities towards high-rate properties

Captured by the economic value and environmental friendliness, the high-value recycling of spent batteries has been devoted plenty of attention. However, the regenerated graphite is still limited by large anisotropy and inferior rate abilities. Through the tailoring of low-temperature ionic liquid, the further regenerated graphite displayed rich sub-surface pores and improved crystalline degree, bringing about strong wettability and enhanced isotropy. Utilizing as lithium-storage anode, the optimized sample could deliver a capacity of 321 mAh/g after 300 loops at 1.0 C. Even at 2.0 C after 400 cycles, their capacity could also remain about 278 mAh/g. Supported by the detailed kinetic analysis, the abundant pores of sub-surface served significant roles in the enhancements of diffusion/surface-controlling behaviors. Their pre-storage advantages would be beneficial for the alleviation of voltage dropping, resulting in improved rate properties. Meanwhile, its activation energy was calculated at about 14.52 KJ mol−1, revealing its relatively small ion-diffusion energy barrier. More significantly, assisted by economic analysis, its revenue could also reach up to 5700$ t−1, with a promising recycling value. Given this, the work is expected to offer significant cooperative regeneration manners and shed light on the significant effect of sub-surface designing.

Human Plasma Butyrylcholinesterase Hydrolyzes Atropine: Kinetic and Molecular Modeling Studies.

The participation of butyrylcholinesterase (BChE) in the degradation of atropine has been recurrently addressed for more than 70 years. However, no conclusive answer has been provided for the human enzyme so far. In the present work, a steady-state kinetic analysis performed by spectrophotometry showed that highly purified human plasma BChE tetramer slowly hydrolyzes atropine at pH 7.0 and 25 °C. The affinity of atropine for the enzyme is weak, and the observed kinetic rates versus the atropine concentration was of the first order: the maximum atropine concentration in essays was much less than Km. Thus, the bimolecular rate constant was found to be kcat/Km = 7.7 × 104 M-1 min-1. Rough estimates of catalytic parameters provided slow kcat < 40 min-1 and high Km = 0.3-3.3 mM. Then, using a specific organophosphoryl agent, echothiophate, the time-dependent irreversible inhibition profiles of BChE for hydrolysis of atropine and the standard substrate butyrylthiocholine (BTC) were investigated. This established that both substrates are hydrolyzed at the same site, i.e., S198, as for all substrates of this enzyme. Lastly, molecular docking provided evidence that both atropine isomers bind to the active center of BChE. However, free energy perturbations yielded by the Bennett Acceptance Ratio method suggest that the L-atropine isomer is the most reactive enantiomer. In conclusion, the results provided evidence that plasma BChE slowly hydrolyzes atropine but should have no significant role in its metabolism under current conditions of medical use and even under administration of the highest possible doses of this antimuscarinic drug.

Inhibition of QDPR synergistically modulates intracellular tetrahydrobiopterin profiles in cooperation with methotrexate

Tetrahydrobiopterin (BH4) is an essential cofactor for dopamine and serotonin synthesis in monoaminergic neurons, phenylalanine metabolism in hepatocytes, and nitric oxide synthesis in endothelial and immune cells. BH4 is consumed as a cofactor or is readily oxidized by autooxidation. Quinonoid dihydropteridine reductase (QDPR) is an enzyme that reduces quinonoid dihydrobiopterin (qBH2) back to BH4, and we have previously demonstrated the significance of QDPR in maintaining BH4 in vivo using Qdpr-KO mice. In addition to the levels of BH4 in the cells, the ratios of oxidized to reduced forms of BH4 are supposed to be important for regulating nitric oxide synthase (NOS) via the so-called uncoupling of NOS. However, previous studies were limited due to the absence of specific and high-affinity inhibitors against QDPR. Here, we performed a high-throughput screening for a QDPR inhibitor and identified Compound 9b with an IC50 of 0.72 μM. To understand the inhibition mechanism, we performed kinetic analyses and molecular dynamics simulations. Treatment with 9b combined with methotrexate (MTX), an inhibitor of another BH4-reducing enzyme, dihydrofolate reductase (DHFR), significantly oxidized intracellular redox states in HepG2, Jurkat, SH-SY5Y, and PC12D cells. Collectively, these findings suggest that 9b may enhance the anticancer and anti-autoimmune effects of MTX.

Phosphorescence of beta irradiated Sr4Al14O25:Eu2+,Dy3+ ─ A persistent luminescence phosphor

Phosphorescence of beta irradiated Sr4Al14O25:Eu2+,Dy3+ has been analysed. The persistent luminescence that defines this phosphor is phosphorescence hence the justification for this study. A set of phosphorescence decay curves were measured at various temperatures Tph between 20 and 352 °C following irradiation to 2 Gy. The residual thermoluminescence (R-TL) was recorded at 1 °C/s after the phosphorescence decay. A conventional TL glow curve recorded at the same rate following irradiation to 2 Gy produces two composite glow peaks P1 and P2 at 63 and 252 °C respectively. The decay curves measured between Tph = 28–60 °C and 200–240 °C associated with peaks P1 and P2 respectively give the values of the activation energy of peaks P1 and P2 as 0.59 ± 0.01 and 0.80 ± 0.04 eV. The effective frequency factors associated with the traps are 6.2 × 109 and 6.4 × 105 s−1 respectively. Peaks P1 and P2 are affected by thermal quenching with activation energy W = 0.69 ± 0.06 eV and 0.66 ± 0.03 eV respectively. The R-TL glow curves show two maxima R1 and R2 at ∼72 and 260 °C respectively. Kinetic analysis of R-TL peak R2 shows a Gaussian distribution of trap energy whereas the same analysis on R-TL peak R1 shows a non-Gaussian distribution of trap energy. The mean values of activation energy corresponding to the respective electron traps of R1 and R2 are estimated to be 0.62 ± 0.07 and 1.04 ± 0.06 eV. For peak R2, the Gaussian distribution curve shows the maximum at ∼1.06 eV which indicates that most electron traps corresponding to peak R2 have this trap depth.

Gene cloning, expression, and enzyme kinetics analysis of Eimeria tenella 2- methylcitrate synthase

In prokaryotes and lower eukaryotes, 2-methylcitrate cycle (2-MCC) is the main pathway for propionate decomposition and transformation, but little is known about the 2-MCC pathway of Eimeria tenella. The analysis of genomic data found that the coding gene of 2- methylcitrate synthase (EC 2.3.3.5, PrpC) exists in E. tenella, which is a key enzyme of 2-MCC pathway. Through the search analysis of the database (ToxoDB), it was found that ETH_ 00026655 contains the complete putative sequence of EtprpC. In this study, we amplified the ORF sequence of EtprpC based on putative sequence. Then, prokaryotic expression, enzyme activity and kinetic analysis was performed. The results showed that the EtprpC ORF sequence was 1272 bp, encoding a 46.3 kDa protein comprising 424 amino acids. Enzyme activity assays demonstrate linearity between the initial reaction rate (OD/min) and EtPrpC concentration (ranging from 1.5 to 9 µg/reaction), with optimal enzyme activity observed at 41°C and pH 8.0. The results of enzymatic kinetic analysis showed that the Km of EtPrpC for propionyl-CoA, oxaloacetic acid, and acetyl-CoA was 5.239 ± 0.17 mM, 1.102 ± 0.08 μM, and 5.999 ± 1.24 μM, respectively. The Vmax was 191.11 ± 19.1 nmol/min/mg, 225.48 ± 14.4 nmol/min/mg, and 370.02 ± 25.8 nmol/min/mg when EtPrpC concentration at 4, 6, and 8 μg, respectively. Although the ability of EtPrpC to catalyze acetyl-CoA is only 0.11% of its ability to catalyze propionyl-CoA, it indicates that the 2-MCC pathway in E. tenella is similar to that in bacteria and may have a bypass function in the TCA cycle. This study can provide the theoretical foundation for the new drug targets and the development of new anticoccidial drugs.

Unraveling selectivity in non-noble metal-catalyzed hydrogenation of 5-hydroxymethylfurfural (HMF) through mechanistic insights

The development of heterogeneous catalysts for converting abundant biomass feedstocks to higher value products is one of the most challenges these days. 2,5-dihydroxymethylfuran (DHMF) and 2,5-dihydroxymethyltetrahydrofuran (DHMTHF), synthesized from HMF hydrogenation, serve as crucial precursors in various applications. Non-noble metal catalysts are particularly attractive for this reaction, given their affordability and impressive catalytic efficiency. This work unveils the origin of the unique selectivity over Ni and Cu through mechanistic investigation using density functional theory (DFT), thermodynamic and kinetic analyses. The results emphasize that temperature and solvent play a crucial role in altering the energetic stabilities of intermediates, thereby influencing the energetic span (δG), turnover frequency (TOF), and selectivity of the reaction. The theoretical results align well with experimental observations. At 373.15 K, the highest TOF values over Ni and Cu are predicted in the HMF-to-DHMTHF path (1.79 × 103h−1) and the HMF-to-DHMF path (4.01 × 105h−1), respectively, in gas phase—under low dielectric constant ε condition. In contrast, the highest TOF value for Ni is observed in the HMF-to-DHMF path under implicit water condition (ε = 78.4) at 298.15 K. Competitive DHMF desorption and further hydrogenation influence the reaction’s selectivity. These insightful fundamental findings reveal key descriptors essential for designing new heterogeneous catalysts or enhancing existing ones, with the aim of potentially impacting biomass upgrading and other hydrogenation reactions.

Evolution of morphology, structure, and performance of the COF membranes with monomer concentrations: Enabling effective desalination and kinetics analysis

Fabricating crystalline covalent organic framework (COF) membrane with sub-nanopores for desalination remains challenging. Monomer (p-phenylenediamine (Pa) and 1,3,5-triformylphloroglucinol (Tp)) concentration was crucial to tailor the diffusion-reaction process in the p-toluenesulfonic acid (PTSA)-mediated interfacial catalytic polymerization process for crystalline TpPa-COF membrane fabrication. By increasing monomer concentration, membrane surface color evolved from light yellow to dark orange. TpPa-COF layers with adjustable thickness (90.47–436 nm) transformed from amorphous to crystalline with crystalline and cross-linking degree increasing from 16.47 % to 73.90 %, and 66.40 % to 87.60 %, respectively. Pore size decreased from 1.69 to 0.17 nm, while Na2SO4 rejection significantly increased from 26.7 % to 90.4 %. A 3-day filtration test for RO concentrate demonstrated the stability and robust desalination performance with SO42− rejection ratio of 74.3 ± 1.08 % and Mg2+ rejection ratio of 65.6 ± 1.33 %. Diffusion behavior experiments demonstrated that diffusion coefficient for Pa-PTSA complex (6.49 × 10−5–8.87 × 10−5 cm2 s−1, Pa > 0.05 wt%) higher than Tp (3.53 × 10−6–6.39 × 10−6 cm2 s−1, Tp > 0.006 wt%) by one order of magnitude promoted structural crystallinity and regulated assembly at the interface, resulting in TpPa-COF layer with sub-nanopores. This study highlighted the importance of monomer concentration on the COF membrane formation, providing valuable insights for the highly crystalline COF membrane fabrication.

Synthesis of carboxymethyl starch co (polyacrylamide/ polyacrylic acid) hydrogel for removing methylene blue dye from aqueous solution

Natural polysaccharides, notably starch, have garnered attention for their accessibility, cost-effectiveness, and biodegradability. Modifying starch to carboxymethyl starch enhances its solubility, swelling capacity, and adsorption efficiency. This research examines the synthesis of an effective hydrogel adsorbent based on carboxymethyl starch for the elimination of methylene blue from aqueous solutions. The hydrogel was synthesized using polyacrylamide and polyacrylic acid as monomers, ammonium persulfate as the initiator, and N,N′-methylenebisacrylamide as the cross-linker. Through FESEM, swelling morphology was evaluated in both distilled water and methylene blue dye. The adsorption data elucidated that the adsorption capacity of the hydrogel significantly depends on the dosage of the adsorbent, pH, and concentration of the MB dye. At a pH of 7 and a dye concentration of 250 mg/L, the hydrogel exhibited an impressive 95 % removal rate for methylene blue. The results indicate that the adsorption process follows pseudo-second-order kinetics and conforms well to the Langmuir adsorption isotherm, indicating a maximum adsorption capacity of 1700 mg/g. According to the pseudo-second-order kinetic model and FTIR analysis, methylene blue chemisorbs to the adsorbent material. Hydrogel absorbents regulate adsorption through both intra-particle diffusion and liquid film diffusion. These results highlight the potential of the new hydrogel absorber for water purification.