Kinetic Analysis Research Articles

Characterization of δ-PuGa (1 at%. Ga) Oxidation Under Dry Oxygen Atmosphere Exposure

AbstractThe oxidation of δ-stabilized plutonium alloy was studied under dry oxygen exposures for temperatures varying from 100 up to 300 °C and oxygen partial pressures varying from 10–4 up to 500 mbar. The coupling of X-ray diffraction, Raman spectroscopy and FIB-SEM has allowed to show that the oxide scale is composed of an outer layer of PuO2 and an inner mixed layer of α + β-Pu2O3 platelets propagating into a metallic zone corresponding to the stable phase of unalloyed Pu. Furthermore, the analysis of Pu oxidation kinetics has displayed first a parabolic growth governed by the diffusion of interstitial oxygen. This step consists of the thickening of the Pu2O3 layer with a decrease in α-Pu2O3 ratio in favor of β-Pu2O3. Then, a second step occurs consisting of a linear growth of the PuO2-layer with the formation of thick nodules which tend to cover the whole oxide surface. Based on the results of this work, a general oxidation mechanism for δ-Pu alloy is provided.

Kinetic Diagram Analysis: A Python Library for Calculating Steady-State Observables of Biochemical Systems Analytically.

Kinetic diagrams are commonly used to represent biochemical systems in order to study phenomena such as free energy transduction and ion selectivity. While numerical methods are commonly used to analyze such kinetic networks, the diagram method by King, Altman and Hill makes it possible to construct exact algebraic expressions for steady-state observables in terms of the rate constants of the kinetic diagram. However, manually obtaining these expressions becomes infeasible for models of even modest complexity as the number of the required intermediate diagrams grows with the factorial of the number of states in the diagram. We developed Kinetic Diagram Analysis (KDA), a Python library that programmatically generates the relevant diagrams and expressions from a user-defined kinetic diagram. KDA outputs symbolic expressions for state probabilities and cycle fluxes at steady-state that can be symbolically manipulated and evaluated to quantify macroscopic system observables. We demonstrate the KDA approach for examples drawn from the biophysics of active secondary transmembrane transporters. For a generic 6-state antiporter model, we show how the introduction of a single leakage transition reduces transport efficiency by quantifying substrate turnover. We apply KDA to a real-world example, the 8-state free exchange model of the small multidrug resistance transporter EmrE of Hussey et al. (J. Gen. Physiol., 2020, 152, e201912437), where a change in transporter phenotype is achieved by biasing two different subsets of kinetic rates: alternating access and substrate unbinding rates. KDA is made available as open source software under the GNU General Public License version 3.

Catalytic efficiency and kinetic analysis of manganese Polyoxometalate Heterogenized in MIL-100-Fe for selective Olefin oxidation using H2O2

In our previous study, we introduced a heterogeneous catalyst, denoted as H5[PMo11MnO39(H2O)]0.30@ [Fe3O(OH)(H2O)2[C6H3(CO2)3]2·8H2O (C1), through the encapsulation of a homogeneous polyoxometalate, H5[PMo11Mn(H2O)O39] (MnP), within a metal–organic framework [Fe3O(OH)(H2O)2[C6H3(CO2)3]2·14H2O (MIL-100-Fe). In the present study, we utilized the same catalyst for the oxidation of cyclohexene (CyH), cis-cyclooctene (CyO), styrene (Sty), and geraniol (Ger) in acetonitrile, employing H2O2 as a green oxidant. Kinetic studies were carried out to investigate the influence of substrate, H2O2, catalyst concentration, reaction time, temperature, and total H2O2 decompositions on oxidation and selectivity. C1 exhibited significantly higher efficiency in catalyzing the allylic oxidation of all substrates compared to individual components MnP and MIL-100-Fe, in terms of conversion percentage, rate constants, turnover numbers (TONs), H2O2 efficiencies, and product selectivity. Under optimized conditions, C1 achieved overall conversions of 85 %, 96 %, 98 %, and 100 % for CyH, CyO, Sty, and Ger, respectively. The harmonious catalytic function of polyoxometalates (POM) and metal-organic frameworks (MOF) in C1 also reduced the auto-decomposition of H₂O₂ which resulted into higher H2O2 efficiencies. Notably, the catalyst exhibited complete recoverability and reusability without any structural changes or loss of activity.

Localized nitride strategy to construct interfacial and electronic modulated WO3/WN nanoparticles for superior lithium-ion storage

The interfacial effect is important for the tungsten trioxide (WO3)-based anode to achieve superior lithium-ion storage performance. Herein, the interfacial effect was constructed by in-situ surface direct nitridation reaction at 600 ℃ for 30 min of the as-synthesis WO3 nanoparticles (WO3/WN). X-ray photoelectron spectroscopy (XPS) analysis confirms evident chemical interaction between WO3 and WN via the interfacial covalent bond (WON). This WO3/WN anode shows a distinct interfacial effect for an efficient interatomic electron migration. Electrochemical kinetic analysis shows enhanced pseudocapacitance contribution. The galvanostatic intermittent titration technique (GITT) result demonstrates improved charge transfer kinetics. Ex-situ X-ray diffraction (XRD) analysis reveals the reversible oxidation and reduction reaction of the WO3/WN anode. The density functional theory (DFT) result shows that the evident interfacial bonding effect can enhance the electrochemical reaction kinetics of the WO3/WN anode. The discharge capacity can reach up to 546.9 mA h g−1 at 0.1 A g−1 after 200 cycles. After 2000 cycles, the capacity retention is approximately 85.97 % at 1.0 A g−1. In addition, the WO3/WN full cell (LiFePO4/C//WO3/WN) demonstrates excellent rate capability and capacity retention ratio. This in-situ surface nitridation strategy is an effective solution for designing an oxide-based anode with good electrochemical performance and beyond.

Zn-MOF-5-Modified biochar derived from KMnO4-activated waste corncob for enhanced adsorption of gaseous ammonia

Ammonia (NH3) is an odor gas pollutant which has serious harm to the environment and human health. The development of advanced adsorbents to remove NH3 is of great significance. Herein, a new adsorbent for NH3 adsorption with high efficiency was prepared by in-situ growth of Zn-MOF-5 on the KMnO4-activated waste corncob-derived porous biochar (KCB). The optimized M0.6K0.1CB-400 sample was obtained by optimizing the mass ratio of KMnO4 to corncob at 0.1, activation temperature at 400 °C, and the dosage ratio of Zn-MOF-5 to porous biochar at 0.6. The M0.6K0.1CB-400 demonstrated an excellent NH3 adsorption capacity of 6.88 mmol/g at 298.15 K and 1 bar, exhibiting a fast adsorption kinetics with 94 % of the equilibrium adsorption capacity reached in just 10 min. The M0.6K0.1CB-400 composite demonstrated good regeneration functionality by maintaining a NH3 removal capacity of 3.44 mmol/g after 6 regeneration cycles. Based on the thermodynamic and kinetic analyses, along with characterization of the chemical composition and physical structure of the NH3-adsorbed samples, the adsorption process of MKCB on NH3 was proven to involve a combination of physical and chemical adsorption. This study introduces a novel method for synthesizing MOF-modified biochar as a highly efficient NH3 adsorbent, offering new insights into the underlying mechanisms of gas purification.

Negative Reaction Order for CO during CO2 Electroreduction on Au.

The potential-dependent negative fractional reaction orders with respect to the CO partial pressures were measured for CO2 electroreduction (CO2R) on Au under mass-transfer-controlled conditions using a rotating ring-disk electrode setup. At high overpotentials, the CO reaction order approaches -1 due to enhanced CO adsorption on Au, which is supported by kinetic analysis and density functional theory (DFT) simulations. This work illustrates that the CO site-blocking effect cannot be ignored, even on a weak CO-binding metal such as Au in the electrochemical environment. The CO site-blocking effect can greatly hamper the activity and the selectivity of the CO2R to CO. This observation enriches the current mechanistic understanding of the CO2R and could have significant implications not only in the theoretical modeling of the CO2R but also in the evaluation of intrinsic CO2R activity at practical current density and high conversion conditions.

Biochar Microparticles from Pomegranate Peel Waste: Literature Review and Experiments in Isotherm Adsorption of Ammonia

This research aimed to synthesize biochar microparticles from pomegranate peel waste for ammonia adsorption. This research also focused on analyzing adsorption isotherm and kinetics models to understand the mechanism of ammonia adsorption on the biochar. The experiments were conducted by carbonizing pomegranate peel waste. The carbonized material was then milled and sieved to obtain biochar microparticles with a certain size (i.e. 500, 1000, and 2000 μm). The particles were then characterized using microscopy and infrared spectroscopy (FTIR) to identify particle morphology and functional groups. The prepared particles were then used for the ammonium adsorption process, and compared with ten isotherm models (such as Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Jovanovic, Halsey, Harkin-Jura, Flory-Huggins, Fowler-Guggenheim, and Hill-Deboer) to identify the adsorption mechanism. Adsorption kinetic analysis was also performed to identify the adsorption rate of the prepared particles using first-order and second-order pseudo-kinetic models. The adsorption isotherm model informed that ammonia adsorption on biochar with sizes of 2000 μm (large) and 1000 μm (medium) occurs in a multilayer process with physical interaction accompanied by pore filling. Meanwhile, small biochar (500 μm) indicates that the ammonia adsorption process occurs on homogeneous sites with physical interaction through pore filling. From the results of fitting the isotherm model, information about the maximum adsorption capacity for each size of 2000, 1000, and 500 μm are 65.631, 62.231, and 50.086 mg/g, respectively. Overall, the adsorption mechanism occurring on biochar involves interactions among ammonia molecules that repel each other under endothermic conditions. The largest adsorption capacity was obtained for biochar with sizes of 2000 μm. Analysis of adsorption kinetics showed that the adsorption process follows a first-order pseudo-kinetic model, indicating an adsorption mechanism controlled by intraparticle diffusion. This study concludes that biochar from pomegranate peel is prospective for use as an environmentally friendly adsorbent for ammonia removal applications from wastewater, offering a sustainable and effective alternative adsorbent to existing water treatment technologies and solving current issues in the sustainable development goals (SDGs).

Effects of hydrogen volume fraction, air fuel ratio, and compression ratio on combustion and emission characteristics of an SI ammonia-hydrogen engine

An effective approach to reducing greenhouse gas emissions is to utilize low/zero carbon fuels. This study simulated the combustion of a marine spark ignition (SI) ammonia-hydrogen engine, focusing on the effects of hydrogen volume fraction (XH2), air fuel ratio (λ), and compression ratio (CR) on the combustion and emission characteristics. The pathways of nitrogen-based pollutants such as NH3, NO, and N2O were explained. The results show that increasing XH2 improves Pmax, heat release rate, thermal efficiency, and power. Regarding emission characteristics, when XH2 rises, NH3 emissions drop; NOx emissions remain almost constant at λ ≤ 1 (2100 ppm at λ = 1) and considerably increase at λ > 1, peaking at 5245 ppm. Moreover, as CR rises, the engine power and thermal efficiency increase, NOx emissions decrease by 10%, and N2O emissions are below 20 ppm. Furthermore, chemical kinetic analysis shows that NO comes from N and N2, diffuses from the flame front toward the center in the cylinder under λ = 1.2. And NO comes from HNO and is generated in the flame front and the center under λ = 0.9, respectively. N2O is produced by NH and NH2 and is only generated in the flame front.

Structural evolution in desalting Merluccius hubbsi fillets: comparative analysis of varied salting techniques

SummaryThis study investigates the reversible and irreversible structural changes in proteins induced by different salting methods (brining, mixed salting, and dry salting) during the desalting process of Merluccius hubbsi fillets. We focused on mass changes, water content, and NaCl content, employing mathematical models for kinetic analysis and sorption isotherms. Image analysis was utilised to examine tissue microstructure and texture profile analysis assessed the mechanical properties. Our results indicate that salting methods significantly influence mass changes and yield during desalting. Specifically, brining led to the highest weight gain due to controlled salt absorption and enhanced water retention. The Peleg model accurately described NaCl and water content dynamics during desalting. Microscopic analysis revealed substantial structural alterations, while mechanical properties showed significant differences; dry and mixed salting methods caused notable tissue damage and protein denaturation. These findings provide valuable insights for enhancing salting processes and improving the quality of desalted seafood products.

Hydrolysis kinetics of self-degradable diverters for well stimulation

Self-degradable diverters have gained increased popularity in well stimulation as an environmentally friendly and robust fluid diversion technology. As of now, limited data and conflicting information exist in the literature regarding the hydrolytic degradation rates of diverters under field-representative conditions, and knowing these rates is crucial for optimizing well stimulation designs. In this work, we systematically measured the degradation rates of commercial self-degradable diverters in aqueous solutions spanning a wide solution pH range of 0.3–13.6 and a wide temperature range of 60–110 °C. We first demonstrated that existing bottle degradation test protocols might return misleading results due to the alteration of solution pH by degradation products, and we developed a more reliable experimental protocol using buffer solutions instead. Using this procedure, we found that as the solution pH increased, the hydrolysis rate of diverters first decreased and then increased, with a minimal degradation rate at around pH = 4. Elevated temperatures yielded faster hydrolysis. The collected kinetic data fit reasonably well to a published kinetic model that was originally developed for pure polylactic acid in deionized water, with an R2 value over 0.98 for all pH and temperature conditions. This comparison suggests that the model can be more widely applied to describe the degradation kinetics of commercial diverters over broad temperature and pH ranges. The test protocol, experimental data, and kinetic analysis in this work provide important guidance on improving the efficiency of fluid diversion and well stimulation operations.

Indole derivatives efficacy and kinetics for inhibiting carbon steel corrosion in sulfuric acid media

The global prevalence of metal corrosion is a significant challenge due to its detrimental effect. Environmentally friendly and non-hazardous alternatives for harmful and poisonous synthetic corrosion inhibitors are urgently necessary due to increasing environmental concerns and regulations prohibiting their application. In this study, indole molecules were employed as carbon steel corrosion inhibitors in acidic conditions. Gravimetrical and scanning electronic microscope (SEM) analysis was used in a preliminary investigation of indole as an organic inhibitor. The results revealed that adding indole to carbon steel before exposing it to sulfuric acid slowed and induced resistance to corrosion. The indole affixed themselves to the steel carbon surfaces, producing a barrier/protection for carbon steel. The efficacy of the indole in preventing corrosion was determined through the weight loss method. Temperature and inhibitory concentration effects on inhibition effectiveness under varying parameters were also reported. The temperatures employed were between 298 K and 328 K, while the inhibitor concentrations ranged from 1.2 × 10−3 M to 7.6 × 10−3 M, and both parameters significantly influenced corrosion inhibition effectiveness. The inhibitory mixture attained optimum efficacy in inhibiting corrosion, at 81 %, when the lowest and highest respective temperature and concentration were applied. The kinetic analysis was conducted under a range of temperatures to determine the reaction mechanisms of the inhibitor. The thermal adsorption isotherm of the inhibitor indicated that the surface adhered to Langmuir's adsorption isotherm. Additionally, investigations on corrosion and inhibition using the electrochemical impedance spectroscopy method (EIS) were conducted. This study can provide in-depth knowledge for advancing inhibitory science and engineering to enhance corrosion resistance in acidic media.

Enzyme Catalyzed Formation of CoA Adducts of Fluorinated Hexanoic Acid Analogues using a Long-Chain acyl-CoA Synthetase from Gordonia sp. Strain NB4-1Y.

Per and polyfluoroalkyl substances (PFAS) are a large family of anthropogenic fluorinated chemicals of increasing environmental concern. Over recent years, numerous microbial communities have been found to be capable of metabolizing some polyfluoroalkyl substances, generating a range of low-molecular-weight PFAS metabolites. One proposed pathway for the microbial breakdown of fluorinated carboxylates includes β-oxidation, this pathway is initiated by the formation of a CoA adduct. However, until recently no PFAS-CoA adducts had been reported. In a previous study, we were able to use a bacterial medium-chain acyl-CoA synthetase (mACS) to form CoA adducts of fluorinated adducts of propanoic acid and pentanoic acid but were not able to detect any products of fluorinated hexanoic acid analogues. Herein, we expressed and purified a long-chain acyl-CoA synthetase (lACS) and a A461K variant of mACS from the soil bacterium Gordonia sp. strain NB4-1Y and performed an analysis of substrate scope and enzyme kinetics using fluorinated and nonfluorinated carboxylates. We determined that lACS can catalyze the formation of CoA adducts of 1:5 fluorotelomer carboxylic acid (FTCA), 2:4 FTCA and 3:3 FTCA, albeit with generally low turnover rates (<0.02 s-1) compared with the nonfluorinated hexanoic acid (5.39 s-1). In addition, the A461K variant was found to have an 8-fold increase in selectivity toward hexanoic acid compared with wild-type mACS, suggesting that Ala-461 has a mechanistic role in selectivity toward substrate chain length. This provides further evidence to validate the proposed activation step involving the formation of CoA adducts in the enzymatic breakdown of PFAS.

Large eddy simulation of round jets with mild temperature difference

Understanding the behaviour of hot jets is crucial for various engineering and environmental applications. The present work studies the influence of heat transfer on the dynamics of horizontal round hot jets through Large Eddy Simulations (LES). Our focus lies on trajectory development, large-scale coherent structures, and turbulent kinetic budget analysis in the near-field and intermediate-field regions. LES of two horizontal round hot jets with Reynolds numbers (3934 and 5100) and corresponding Froude numbers (32.98 and 17.07) were carried out using buoyantPimpleFoam solver in OpenFOAM, and the simulation on an isothermal jet was also performed as a baseline for comparison. The results reveal that the jet core temperature decays faster in the streamwise direction but more slowly in the radial direction, indicating a wider temperature spread than velocity, and the maximum difference between the temperature and velocity spread is about 0.5D. Moreover, the energy associated with the large-scale coherent structure decreases with increasing initial jet temperature. The energy of the first two modes of snapshot Proper Orthogonal Decomposition (POD) and extended POD dropped by 12% and 14%, respectively. The coherent motion with the greatest correlation between the temperature and velocity fluctuations is identified as four pairs of Q1 and Q3 events, which are Reynolds shear stress dominant events. Furthermore, compared with the isothermal jet, the turbulent kinetic energy budgets of the hot jets indicate that the diffusion and generation terms are both reduced by approximately 50%, suggesting a transfer of more kinetic energy into potential energy rather than turbulence. The finding highlights the potential of heightened temperatures to mitigate instabilities associated with large-scale motions in hot jets. This study fills the gap on a comprehensive analysis of heat transfer effects on jet dynamics, and quantitative insights into the large-scale coherent structures are provided, contributing to a better understanding of hot jet behaviour.

Harnessing a thermo-active and alkaline lipase from novel strain of Brevibacillus borstelensis gp-1, for application in biodiesel synthesis

A novel thermo-active and alkaliphilic strain of Gp-1, isolated from hot water springs of Ganeshpuri, Maharashtra, India, identified as Brevibacillus borstelensis based on 16SrDNA characterization, with accession no. MT292327, at NCBI database. Statistical optimization of lipase production was done using Plackett-Burman algorithm and response surface methodology. Fermentative production of Gp-1 lipase was followed by partial purification, with 24.10 fold purification. Gp-1 lipase has molecular mass of 31 kDa, as determined by SDS-PAGE. Gp-1 lipase exhibited maximal specific activity at pH 10 and 55 °C, with stability up to 70 °C. Kinetic parameters analysis revealed Gp-1 lipase has Km and Vmax values of 1.544 mM and 31.25 μM/mg. min, and specificity constant of 281.13 sec-1, with pNP caprylate as the base suited substrate. Gp-1 lipase was found to be retain more than 90% activity in presence of various organic solvents, and various commercial detergent formulations. The Gp-1 lipase was also tested for transesterification reactions, which revealed successful transesterification of coconut oil, olive oil and waste cooking oil, and conversion in esters. Hence, Gp-1 lipase stands out as a prospective candidate in biodiesel synthesis, a green energy alternative.

Adsorption dynamics of Eriochrome Black dye removal using raw and ultrasonicated Pithecellobium seed biomass: ANN modeling and mechanisms

Utilization of Ultrasonic modified Pithecellobium dulce seed biomass, proved the efficacy in Eriochrome black dye remediation. The study investigates the sorption dynamics of Eriochrome Black (EB) dye removal using raw and ultrasonicated Pithecellobium seed biomass combined with Artificial Neural Network (ANN) modeling for the elucidation of underlying mechanisms. To improve the adsorption performance, Pithecellobium dulce biomass has been subjected to ultrasonication. The characterization of modified seed adsorbent revealed the adsorptive properties of biomass for the removal process. Varying impacts of dye adsorption were studied revealing the optimal parameters to be pH of 5, temperature of 303 K, contact time of 40 min-Ultrasonicated Pithecellobium dulce (UPDB) biomass; 80 min – Raw Pithecellobium dulce biomass (RPDB), and dose of 5 g/L and 2.5 g/L for RPDB and UPDB respectively. Isotherm and Kinetic analysis revealed the Freundlich and pseudo-first order models to be best fitting for the current system. Ultrasonicated seed biomass exhibited enhanced adsorption capacity of 126.9 mg/g compared to 83.8 mg/g for raw seed biomass. Thermodynamic investigation infers the spontaneity and exothermic nature of adsorption process. The ANN model for the prediction of eriochrome black dye adsorption onto ultrasonic modified Pithecellobium dulce seed biomass exhibited better correlation coefficient of 0.9559 indicating the better prediction of trained model for dye removal process. Thus, ANN model provides a better prediction of the relation between operational factors and dye removal.

Inhibition of Soluble Epoxide Hydrolase by Cembranoid Diterpenes from Soft Coral Sinularia maxima: Enzyme Kinetics, Molecular Docking, and Molecular Dynamics.

Soluble epoxide hydrolase (sEH) is essential for converting epoxy fatty acids, such as epoxyeicosatrienoic acids (EETs), into their dihydroxy forms. EETs play a crucial role in regulating blood pressure, mediating anti-inflammatory responses, and modulating pain, making sEH a key target for therapeutic interventions. Current research is increasingly focused on identifying sEH inhibitors from natural sources, particularly marine environments, which are rich in bioactive compounds due to their unique metabolic adaptations. In this study, the sEH inhibitory activities of ten cembranoid diterpenes (1-10) isolated from the soft coral Sinularia maxima were evaluated. Among them, compounds 3 and 9 exhibited considerable sEH inhibition, with IC50 values of 70.68 μM and 78.83 μM, respectively. Enzyme kinetics analysis revealed that these two active compounds inhibit sEH through a non-competitive mode. Additionally, in silico approaches, including molecular docking and molecular dynamics simulations, confirmed their stability and interactions with sEH, highlighting their potential as natural therapeutic agents for managing cardiovascular and inflammatory diseases.

Indole alkaloids from Ochreinauclea maingayi (Rubiaceae) as butyrylcholinesterase inhibitors and their paralysis effect in transgenic Caenorhabditis elegans

This study investigated the butyrylcholinesterase (BChE) inhibitory activity of harmane (1), naucledine (2), and dihydrodeglycocadambine (3) isolated from fractions F7 and F9 of Ochreinauclea maingayi. Both fractions demonstrated significant inhibition, exceeding 80%, against BChE at 100 µg/mL. Compound 2, is the most potent inhibitor, exhibiting an IC50 value of 22.08 µM, followed by 1 and 3 (IC50 23.96 and 30.32 µM, respectively). Docking studies revealed that 1 and 2 effectively bind to BChE, with binding energies of −51.24 and −57.17 kcal/mol, respectively. Kinetic analysis of 2 indicated mixed-mode inhibition of BChE, with a Ki of 6.08 μM. In the paralysis assay, 1 showed a weak delay in paralysis and reduced the paralysis ratio from 72.59 ± 4.7% to 60.00 ± 7.0% (12.59% reduction) followed by 2 with 70.00 ± 1.7% (2.59% reduction) compared with negative standard (DMSO 0.1%) on human amyloid β-protein in a transgenic Caenorhabditis elegans (CL4176) model.

Kinetics, thermodynamics, and optimization analyses of lipid extraction from discarded beef tallow for bioenergy production

ABSTRACT The wide expansion of the meat industry generated tremendous amounts of animal-based waste. Discarded beef tallow (DBT) is one of those prevalent lipid-rich wastes disposed of by slaughterhouses, meat processing units, and tanneries. The current study utilized the advanced technology of supercritical CO2 (SC-CO2) to extract lipid content from DBT for biodiesel production through transesterification. The effects of SC-CO2 parameters on the extraction rate were investigated over ranges of (32–80°C) for temperature, (10–50 MPa) for pressure, and (15–150 min) for treatment time. Using response surface methodology (RSM), both processes of SC-CO2 and transesterification were optimized. The highest extraction rate was 86.10%, obtained at the experimental conditions of 60°C for temperature, 30 MPa for pressure, and 120 min for treatment time. For the transesterification, the maximum yield of biodiesel was 95.15%, obtained at the reaction conditions of 1:7.5, 1.16 wt%, 58°C, and 72 min for lipid to methanol molar ratio, catalyst ratio, temperature, and time, respectively. The outcomes of the kinetic and thermodynamic analyses showed that the SC-CO2 extraction was an endothermal, unspontaneous, and temperature-dependent process. The characteristics of the synthesized biodiesel largely comply with the ASTM D6751 and EN 14,214 standards. The findings of the current study confirm the viability of SC-CO2 to extract lipids from DBT as a low-cost feedstock for biodiesel production.

Rational Construction of Honeycomb-like Carbon Network-Encapsulated MoSe2 Nanocrystals as Bifunctional Catalysts for Highly Efficient Water Splitting.

The scalable fabrication of cost-efficient bifunctional catalysts with enhanced hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance plays a significant role in overall water splitting in hydrogen production fields. MoSe2 is considered to be one of the most promising candidates because of its low cost and high catalytic activity. Herein, hierarchical nitrogen-doped carbon networks were constructed to enhance the catalytic activity of the MoSe2-based materials by scalable free-drying combined with an in situ selenization strategy. The rationally designed carbonaceous network-encapsulated MoSe2 composite (MoSe2/NC) endows a continuous honeycomb-like structure. When utilized as a bifunctional electrocatalyst for both HER and OER, the MoSe2/NC electrode exhibits excellent electrochemical performance. Significantly, the MoSe2/NC‖MoSe2/NC cells require a mere 1.5 V to reach a current density of 10 mA cm-2 for overall water splitting in 1 M KOH. Ex situ characterizations and electrochemical kinetic analysis reveal that the superior catalytic performance of the MoSe2/NC composite is mainly attributed to fast electron and ion transportation and good structural stability, which is derived from the abundant active sites and excellent structural flexibility of the honeycomb-like carbon network. This work offers a promising pathway to the scalable fabrication of advanced non-noble bifunctional electrodes for highly efficient hydrogen evolution.

Mechanistic conformational and substrate selectivity profiles emerging in the evolution of enzymes via parallel trajectories

Laboratory evolution studies have demonstrated that parallel evolutionary trajectories can lead to genetically distinct enzymes with high activity towards a non-preferred substrate. However, it is unknown whether such enzymes have convergent conformational dynamics and mechanistic features. To address this question, we use as a model the wild-type Homo sapiens kynureninase (HsKYNase), which is of great interest for cancer immunotherapy. Earlier, we isolated HsKYNase_66 through an unusual evolutionary trajectory, having a 410-fold increase in the kcat/KM for kynurenine (KYN) and reverse substrate selectivity relative to HsKYNase. Here, by following a different evolutionary trajectory we generate a genetically distinct variant, HsKYNase_93D9, that exhibits KYN catalytic activity comparable to that of HsKYNase_66, but instead it is a “generalist” that accepts 3’-hydroxykynurenine (OH-KYN) with the same proficiency. Pre-steady-state kinetic analysis reveals that while the evolution of HsKYNase_66 is accompanied by a change in the rate-determining step of the reactions, HsKYNase_93D9 retains the same catalytic mechanism as HsKYNase. HDX-MS shows that the conformational dynamics of the two enzymes are markedly different and distinct from ortholog prokaryotic enzymes with high KYN activity. Our work provides a mechanistic framework for understanding the relationship between evolutionary mechanisms and phenotypic traits of evolved generalist and specialist enzyme species.