Reaction Constants Research Articles

Nano gold catalyst preparation and it’s p-nitrophenol catalytic degradation properties

Abstract Cacumen platyclade extracts were utilized as the reducing agent to prepare Au/Al2O3 composites. XRD, BET, SEM, TEM were employed to characterize the properties of the catalyst. The catalytic activity of Au/Al2O3 was studied by using NaBH4 as the reducing agent and nitrophenol as the pollutant. The results showed that the Au/Al2O3 catalyst, calcinated at 400 °C, exhibited the highest catalytic activity. With a catalyst dosage of 1 g L−1, 2 mL NaBH4 of 0.15 mol L−1 could degrade 96.5 % nitrophenol in 21 min at 298 K, with a reaction constant of 0.16 min−1. Furthermore, the p-nitrophenol degradation ratio decreased by 0.8 % after ten cycles.

Possible formation of long-lived photo-oxidants by photolysis of organic matter phenols in sunlit waters

AbstractPhotodegradation in sunlit waters is a major process of contaminant abatement, yet underlying chemical processes in the presence of dissolved organic matter are poorly known. Long-lived photo-oxidants are reactive species formed when the chromophoric dissolved organic matter absorbs sunlight, and they are involved in the degradation of contaminants. Previous works identified long-lived photo-oxidants with phenoxy radicals, which could be formed upon oxidation of natural phenols by the excited triplet states of chromophoric dissolved organic matter. Here, we generated reactive phenoxy radicals by direct ultraviolet-A photolysis of 2-nitrophenol and 4-nitrophenol. We measured the second-order rate constants for reaction of these phenoxy radicals with 2,4,6-trimethylphenol, a model electron-rich phenol. Results show rate constants of 9.39 × 108(M−1s−1) for the 2-nitrophenoxyl radical, and 1.56 × 108(M−1s−1) for the 4-nitrophenoxyl radical. These values are slightly lower than the typical rate constant of the reaction between 2,4,6-trimethylphenol and the excited triplet states of chromophoric dissolved organic matter, of 3 × 109(M−1s−1). This means that 2,4,6-trimethylphenol would not be degraded to comparable extents by the excited triplet states of chromophoric dissolved organic matter and by long-lived photo-oxidants, if long-lived photo-oxidants were generated solely by the triplet states of chromophoric dissolved organic matter. Overall, findings suggest the occurrence of new pathway involving the direct photolysis of organic matter phenols that generates long-lived photo-oxidants.

Analytical justification of the thermochemical interaction between blast reagents and carbon-containing products under the influence of magnetic fields

Purpose. To justify and develop a model that describes the effect of magnetic treatment of blast reagents and carbon-containing products on the gasification process for predicting the intensification of gas formation. Methodology. The study involves theoretical modeling based on experimental data to investigate the influence of magnetic fields on the underground coal gasification process and co-gasification of coal and carbon-containing products. The Arrhenius equation was used to estimate the rate constants of gasification reactions in the temperature range of 800–1,000 °C. The effect of the magnetic field was incorporated by adjusting the activation energy (Ea). The results of analytical and experimental studies were processed using methods of computer and mathematical modeling. Findings. The results show that the application of magnetic fields significantly intensifies the gasification process of carbon containing products. Increasing the reactivity of the blast reagents, particularly water and oxygen, leads to a higher overall yield of combustible gases. The use of magnetic fields in the gasification process substantially increases the reaction rate (k) due to the reduction in activation energy (Ea), improving the overall efficiency of gasification. Originality. For the first time, an analytical model has been developed to describe the effect of magnetic treatment of blast reagents and carbon-containing products on the gasification process in the temperature range of 800–1,000 °C. The obtained reaction rates follow an exponential trend. The established and correlation-validated pattern shows the relationship between changes in the approximation coefficient (F ) and the change in the carbon fraction (C, %) during the magnetic treatment of blast components within the specified temperature range. Practical value. The results of this study can be applied to enhance the efficiency of industrial gasification processes, particularly underground coal gasification and co-gasification of coal and carbon-containing productss.

In Situ Uranium Extraction through the Synthesis of the Uranyl Peroxide Studtite Using a Nonthermal Plasma.

Extraction of uranium from water is an essential step in in situ leach (ISL) mining and environmental decontamination. This is often done by precipitating uranium in solution as the uranyl peroxide studtite, [(UO2)(O2)(H2O)2](H2O)2, by adding hydrogen peroxide, which is energy-intensive to produce and hazardous to transport. Here, we present a method for synthesizing studtite, by generating reactive oxygen species in solution using a nonthermal plasma. Precipitation of studtite is observed within 5 min of the onset of plasma treatment as confirmed by X-ray diffraction and Raman spectral analysis. The faradaic efficiency of studtite formation is analyzed to estimate the values of hydrogen peroxide yield, 1.23 molecules per incident ion, and the rate constant of the studtite-forming reaction, 4.44 × 107 M-1 s-1. This work is a proof of concept and identifies significant parameters for the future development of a larger scale, higher throughput system.

Mechanism of β-MnO2 particle for the peroxymonosulfate activation under electric field: the promoting effect of carbamazepine on Mn(III) and reactive oxygen species production

In this study, β-MnO2 was introduced into electro-peroxymonosulfate process as particle electrodes (E/PMS/β-MnO2) to reveal the pathway of reactive manganese species (RMnS) and its promoting effect on reactive oxygen species (ROS) production. A significant synergistic was observed in the E/PMS/β-MnO2 process, the reaction constant was 3 times higher than that in the E/PMS process. The mechanism experiments revealed the generation pathway of Mn(III)aq during the E/PMS/β-MnO2 process. The pyrophosphate complex experiments and electrochemical analysis demonstrated that Mn(III)aq was dominantly generated through the electron transfer between carbamazepine (CBZ) and Mn(IV) under electric field conditions, rather than the reduction process in the cathode area. Furthermore, quenching experiments and competition kinetics method demonstrated the production of Mn(III)aq has the potential to enhance the formation of reactive oxygen species (ROS), especially •OH and SO4•−. In addition, Mn(V)aq and Mn(VI)aq was proved unable to be produced during the E/PMS/β-MnO2 process. Different from other similar electrochemical studies, 1O2 was mainly generated by the reaction betweenO2•− and •OH in this research. It was observed that the inclusion of Cl— facilitated the removal of CBZ, whereas the addition of humic acid (HA) had negligible impact on CBZ removal during the E/PMS/β-MnO2 process. At last, the results of various water matrices effects and toxicology analysis showed that the E/PMS/β-MnO2 process has satisfactory performance in practical application. This study could provide new insights for electro-persulfate treatment processes.

Selective methanol production via CO2 reduction on Cu2O revealed by micro-kinetic study combined with constant potential model

High efficiency electrocatalysis of greenhouse gas CO2 to liquid fuel methanol attracts great attentions that allows energy transformation from renewable electric energy to storable chemical energy. Catalytically converting CO2 to methanol using green hydrogen is a promising pathway to achieve carbon neutrality. In this work, the catalytic activity and product selectivity of the electrochemical CO2 reduction reaction on Cu2O were studied using a micro-kinetic model based on Marcus charge transfer theory. The constant potential model under the grand-canonical ensemble enables the accurate description of binding energies and ground-state charge transfer upon surface adsorption as a function of electrode potential. Firstly, the potential-dependent activation energies and rate constants of all possible elementary reactions involved in CO2 reduction are calculated. Then, the surface coverage and its derivative can be obtained in a steady-state approximation. Finally, the total reaction rate and partial reaction rate can be deduced, allowing for direct comparison with catalytic activity (current density) and product selectivity (Faradaic efficiency). It is found that CH3OH is the dominant product on the Cu2O(111) surface, while CO is the main product on the Cu2O(110) surface. Based on the derived total and partial reaction rates under the steady-state approximation, it is demonstrated that Cu2O(111) exhibits the highest electrocatalytic activity and methanol selectivity at U = −0.6 V vs. SHE. This research presents a methodology for predicting apparent electrocatalytic performance from microscopic reaction energy calculations, which can be applied to other important electrocatalytic reaction mechanisms and performance predictions.

Investigation of the reaction of hydrogen iodide with a chlorine atom in the atmosphere above the sea

By the method of resonant fluorescence (RF) of chlorine atoms and iodine atoms, the rate constant of the reaction of a chlorine atom with hydrogen iodide at a temperature of 298 K. The values of the reaction constants measured by both methods turned out to be quite close. The role of this reaction in the chemistry of the troposphere above the surface of the oceans is discussed.

Exploration of catalytic activities of Caesalpinia bonduc (L.) Roxb. ash on green-oxidation of small organic substrates: an effective way to reduce the use of harsh chemicals

In this modern era, large-scale industrial use of harsh chemicals is an alarming problem as it can cause serious environmental damage. Among industrial pollutants, harsh chemical oxidizing agents are one of the leading chemicals that can cause severe environmental threats. These harmful harsh chemicals are practically omnipresent in industries and are used to oxidize numerous small organic substrates. Replacement of these harsh chemicals with some plant-based products might be helpful to safeguard our environmental damage. In this study, Caesalpinia bonduc (L.) Roxb. ash is used as a catalyst to activate aerial oxygen for promoting the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) and o-aminophenol (OAPH) like small organic substrates. Detailed kinetic studies for these catalytic oxidation reactions have been performed spectrophotometrically, which confirms that catalytic reactions follow Michaelis–Menten kinetics. Several enzyme-kinetics plots such as the Michaelis–Menten plot, Lineweaver–Burk plot, Hanes–Woolf plot, and Eadie–Hofstee plot have been used to determine the maximum rate achieved by the reaction (Vmax) and Michaelis constant (KM) like kinetic parameters. The average values of Vmax and KM for catalytic oxidation of 3,5-DTBC are (8.6669 ± 0.6519) × 10–5 M S−1 and (21.4289 ± 0.4741) × 10–4 M, respectively. Similarly, the average values of Vmax and KM for catalytic oxidation of OAPH are (2.1781 ± 0.2071) × 10–5 M S−1 and (20.1062 ± 1.2690) × 10–3 M, respectively. The mineral composition of Caesalpinia bonduc (L.) Roxb. ash has also been evaluated by using inductively coupled plasma optical emission spectroscopy (ICP-OES).Graphical

Patterns of interaction between peptides of various structures and pyrimidine nucleic bases in a buffered saline medium according to the analysis of thermodynamic parameters

Complexation of cytosine, uracil and thymine with the dipeptides glycyl-glycine, glycyl-l-phenylalanine, alanyl-l-glutamine and with the tripeptide γ-l-glutamyl-l-cysteinyl-glycine in a buffered saline has been studied using dissolution calorimetry. The values of the reaction constant, the change in Gibbs energy, enthalpy, and entropy have been found (log Kr, ΔrG, ΔrH, TΔrS). By analyzing the obtained data together with previous results for other peptides, it was found that peptides bind to pyrimidine nucleic bases in a solution in several important patterns. No pattern depending on the charge of the peptide is observed in the obtained thermodynamic values, which indicates a minor role of electrostatic interaction in their binding by the nucleic base. The effect of the structure of the peptide and the nucleobase on the thermodynamic parameters of complexation is manifested in the fine balance of the enthalpy and entropy factors of the process. The Gibbs energy of complexation depends on the number of potential H-bonding sites of the peptide, which shows the major contribution of H-bonding between the reagents. The reduction in the favorable entropy factor is responsible for the tendency of negative ΔrG values to decrease with increasing number of sites. It was found that positive values of entropy change during complex formation increase with increasing hydrophobicity index of the peptide, which is interpreted within the framework of the overlapping hydration sphere model. Strengthening the hydrophobic properties of the nucleic base from uracil to thymine due to the additional CH3 group slightly changes the enthalpy and entropy of the process of binding the +AlaGln− zwitterion but significantly affects the thermodynamic parameters of binding the anion of peptide +/−GluCysGly−.

GREEN ROUTE SYNTHESIS OF COPPER OXIDE (CuO) NANOPARTICLES FOR THE DEGRADATION OF COMMERCIAL DYES USING VICIA FABA LEAF EXTRACT

The release of toxic dyes into water effluents by various industries has become a global concern. Therefore, developing novel, straightforward, and economically viable methods or materials for purifying these hazardous pigments is imperative. This study aims to synthesize copper oxide nanoparticles (CuO-NPs) through a green route using Vicia faba leaf extract. UV-Vis spectroscopy reveals an absorption band ranging from 200 nm to 300 nm, with a major absorption peak at 212 nm and an energy band gap of 5.29 eV. FTIR, SEM, EDX, and XRD techniques characterise the synthesised CuO nanoparticles. FTIR analysis identifies functional groups including hydroxyl (OH), aromatic C-H, C=C stretching, carbonyl (C=O), and Cu-O stretching vibrations. Scanning electron microscopy reveals flower-like particles, while EDX analysis confirms the formation of CuO nanoparticles. The XRD pattern indicates a crystalline structure with an average particle size of 27.44 nm. A plot of (αhν)² versus photon energy (hν) was generated to determine the energy band gap, yielding a value of 5.29 eV. Rhodamine-B and methylene blue (MB) dyes were employed to evaluate the photocatalytic degradation of the synthesized CuO-NPs, resulting in correlation coefficients of 0.7154and 0.9702, respectively. Furthermore, the rate constants of these dye reactions were found to be 0.0406min-¹ and0.0343 min-¹.

Efficient removal of Congo red by BiOCl/TiO2/montmorillonite photocatalytic material

A series of BiOCl/TiO2/montmorillonite photocatalytic material (BTM) were prepared by sol-gel method combined with calcination process, and were used for the degradation of Congo red. The phase composition, morphology, and optical properties of the as-prepared materials were characterized by XRD, SEM, BET and UV–vis DRS. Compared with BiOCl and TiO2, BTM has a better removal effect on Congo red, in which BTM-20 has the highest photocatalytic activity. After 120 min of illumination, the degradation rate of Congo red by BTM-20 reached 94.04 %. The photocatalytic degradation process of Congo red by BTM-20 conformed to the pseudo-first-order kinetic model with a reaction constant of 0.00803 min−1. The type-Ⅱ heterojunction between BiOCl and TiO2 promotes the separation of photogenerated electron-hole pairs of BTM-20 and enhances the absorption for visible light. The experiment of the free radical capture indicated that superoxide radical played a leading role in photocatalytic degradation of Congo red, followed by hydroxyl radical. This study provides a new treatment ideas for environmental remediation, and provides an efficient photocatalytic material for the degradation of pollutant.

Atmospheric Degradation Mechanism of Isoamyl Acetate Initiated by OH Radicals and Cl Atoms Revealed by Quantum Chemical Calculations and Kinetic Modeling.

Isoamyl acetate is one of the volatile organic compound class molecules relevant to agricultural and industrial applications. With the growing interest in isoamyl acetate applications in industry, the atmospheric fate of isoamyl acetate must be considered. Reaction mechanisms, potential energy profiles, and rate constants of isoamyl acetate reaction with atmospheric relevant oxidant OH radicals and Cl atoms have been obtained from the quantum chemical calculations and kinetic modeling. The geometry optimizations were conducted using M06-2X/6-311++G(3df,3pd) followed by single point-energy calculations at the DLPNO-CCSD(T) method with an extrapolated complete basis set. The rate constants were calculated by solving the master equation. A hydrogen-abstraction reaction dominates the first step of isoamyl acetate degradation, while the addition-substitution reaction plays a small role in the degradation products. The kinetic study was conducted to evaluate the rate constants within a temperature range of 200-400 K. The total rate constants for the isoamyl acetate degradation reactions initiated by the OH radical and Cl atom were determined to be 6.96 × 10-12 and 1.27 × 10-10 cm3 molecule-1 s-1, respectively, under standard temperature and pressure conditions. The product degradation mechanism, ozone formation potential, and atmospheric impacts were discussed.

Reaction Rate Rules of Intramolecular H-Migration Reaction Class for RIORIIOO·Radicals in Ether Combustion.

The intramolecular H-migration reaction of RIORIIOO· radicals constitute a key class of reactions in the low-temperature combustion mechanism of ethers. Despite this, there is a dearth of direct computations regarding the potential energy surface and rate constants specific to ethers, especially when considering large molecular systems and intricate branched-chain structures. Furthermore, combustion kinetic models for large molecular ethers generally utilize rate constants derived from those of structurally similar alcohols or alkane fuels. Consequently, chemical kinetic studies involve the calculation of energy barriers and rate rules for the intramolecular H-migration reaction class of RIORIIOO· radicals, which are systematically conducted using the isodesmic reaction method (IRM). The geometries of the species participating in these reactions are optimized, and frequency calculations are executed using the M06-X method in tandem with the 6-31+G(d,p) basis set by the Gaussian 16 program. Moreover, the M06-2X/6-31+G(d,p) method acts as the low-level ab initio method, while the CBS-QB3 method is utilized as the high-level ab initio method for calculating single-point energies. Rate constants at the high-pressure-limit are computed based on the reaction class transition state theory (RC-TST) by ChemRate program, incorporating asymmetric Eckart tunneling corrections for intramolecular H-migration reactions across a temperature range of 500 to 2000 K. It was found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the rate constants of the H-migration reaction for RIORIIOO· radicals diverge from those of comparable reactions in alkanes and alcohol fuels. There are significant disparities in energy barriers and rate constants across the entire reaction classes of the H-migration reaction for RIORIIOO· radicals, necessitating the subdivision of the H-migration reaction into subclasses. Rate rules are established by averaging the rate constants of representative reactions for each subclass, which is pivotal for the advancement of accurate low-temperature combustion reaction mechanisms for ethers.

Quantitative and mechanistic elucidation of the reactive oxygen species for effective sulfamethoxazole removal in heterogeneous peroxymonosulfate activated by MOFs-derived cladding structure CoZn/NC@UiO

In cobalt-based catalyst/peroxymonosulfate (PMS) systems, the key issues are the leaching of metals and the stability of catalysts. In this study, a NH2-UiO-66 cladded CoZn/NC catalyst was synthesized for efficient degradation of sulfamethoxazole (SMX) using activated PMS. The removal efficiency of SMX could achieve 100% within 30 min. The leaching of Co2+ was inhibited to 0.05 ppm and the anti-interference and cyclic stability of the catalyst were enhanced by the NH2-UiO-66 shell. In addition, the quenching experiment, electron paramagnetic resonance (EPR) technique and probe experiment were used to analyze the reactive oxygen species (ROSs) qualitatively and quantitatively. The findings demonstrated that singlet oxygen (1O2) had the highest steady-state and cumulative concentration. However, 1O2 could only participate in the degradation of SMX through single electron transfer or addition reaction, resulting in a lower second-order rate constant of the SMX reaction with 1O2. Sulfate radical (SO4·-) contributed the most to the degradation of SMX due to the high reactivity of the sulfonamide structure in SMX to SO4·-. Finally, possible pathways for SMX degradation were proposed. The two primary mechanisms of SMX degradation were S-N cleavage and amino hydroxylation/oxidation. The toxicity of most of the intermediates was less than that of SMX through ecological structure–activity relationship analysis. Overall, a novel approach to synthesize low leaching and efficient cobalt based catalyst was put forward, and the activation mechanism of PMS was also revealed.

Hydration kinetics of C3A: effect of lithium, copper and sulfur-based mineralizers

AbstractCalcium aluminate phases have a particular effect on the early heat release during setting initiation and have a substantial influence on the further workability of ordinary Portland cement. The nature of the calcium aluminate hydration products and its kinetics strongly depends on sulfate content and humidity. The effect of mineralisers on melt formation and viscosity is well described for calcium silicate systems, but information is still lacking for calcium aluminates. Therefore, the synergistic effect on the crystal structure and hydration mechanism of the tricalcium aluminate phase of the addition of mineralizers, i.e. Li2O, CuO, SO3 to the raw meal is here investigated. Co-doped calcium aluminate structures were formed during high-temperature treatment. Thermal analysis (TG–DTA and heating microscopy) was used to describe the ongoing high-temperature reaction. Resulting phase composition was dependent on the concentration of the mineralizer. While phase pure system was prepared with low mineralizer concentrations, with increasing mineralizer content the secondary phases were formed. Raman spectroscopy and XPS analysis were used to investigate the cation substitution and to help describe the cations bonding in co-doped calcium aluminate system. Prepared powders have been hydrated in a controlled manner at different temperatures (288, 298, 308 K). The resulting calorimetric data have been used to investigate the hydration kinetics and determine the rate constant of hydration reaction. First-order reaction (FOR) model was here applied for the activation energy and frequency factor calculations. The metastable and stable calcium aluminate hydrates were formed according to initial phase composition. In phase pure systems with low S content, the formation of stable and metastable hydrates was depended on the reaction temperature. Conversely, in systems with secondary phases and higher S content, the hydration mechanism resembled that which appears in calcium sulfoaluminates.

Recombinant laccase biosynthesis for efficient polydopamine coating

Laccases are versatile biocatalysts with interest for various industrial applications. This study reports the expression of Trametes versicolor laccase in Komagataella phaffii X33. The cultivation parameters (methanol and CuSO4 concentration, and temperature) for recombinant laccase production were studied in an orbital shaker. Enhanced laccase production was achieved by adding 1 % (v/v) methanol daily, supplementing 0.1 mM CuSO4 and incubating at 25 °C. Under these conditions, laccase production was scaled-up in a 4 L stirred tank bioreactor. Subsequently, laccase was concentrated and purified using a combined protocol of ultrafiltration and acetone precipitation, achieving a purification factor of 3.02. The laccase produced exhibited robust stability within a pH range from 4.0 to 8.0 and thermal stability up to 30 °C. Michaelis Menten kinetic revealed Michaelis constant (KM) and maximum rate of reaction (Vmax) values of 44.5 µM and 110.9 µM/min, respectively. Finally, laccase was employed as a biocatalyst to assist the polymerization of dopamine to polydopamine, allowing the one-step coating of cellulose filter paper, as confirmed by diffuse reflectance spectroscopy (UV-Vis DRS) and scanning electron microscopy (SEM). This work represents an advance in the field of laccase production in both orbital shaker and bioreactor, while demonstrating, for the first time, the laccase-assisted polymerization of dopamine for the coating of filter paper with polydopamine.

THERMODYNAMICS OF CARBOTHERMAL REDUCTION PROCESS COPPER SLAG

The article analyses the thermodynamic laws of processing iron-based compounds contained in copper production slag using the method of carbothermic recovery. Evaluation of the probable direction of carbothermic reactions occurring between oxidized compounds and carbon in the slag was carried out by changing the thermodynamic values of the system. In the thermodynamic scientific justification of the physic-chemical processes occurring in the carbothermic recovery of metal oxides in slag, the change of Gibbs energy of the system with temperature increases and the estimation of equilibrium constants of chemical reactions based on Gibbs energy and the method of determining the slowest (limiting) chemical process among them were used. The Microsoft Excel program was used to determine the thermodynamic values of the chemical reactions occurring in the slag and reducing agent system and to compile their Ellingham graphs.

Insight into the Kinetics of Isomerization and β-Scission Reactions Following H-Abstraction in 2-Pentanone Combustion.

2-Pentanone is a significant carbon-neutral fuel. To better understand 2-pentanone combustion, the CCSD(T)/CBS method was used to calculate the potential energy surfaces (PES) for H-abstraction, isomerization, and β-scission reactions of 2-pentanone. Rate constants for the above reactions were calculated by the MESS employing conventional transition state theory (CTST) at 300-2000 K. The findings reveal adherence to the Evans-Polanyi principle in the H-abstraction reactions of 2-pentanone by H atoms. Specifically, the 2-site shows more competitive kinetics due to having the lowest energy barrier of 7.8 kcal/mol. The 4-position has the highest energy barrier, making the reaction difficult to occur. In the subsequent reactions, the breaking of C-H bonds is most competitive at low temperatures. In particular, the H transfer from INT1 to INT3 has a potential well height of 24.8 kcal/mol. The β-scission reactions become the main pathway for the depletion of pentanone radicals with increasing temperature. This study significantly extends the kinetic parameters of 2-pentanone combustion over a wide range of temperatures and pressures, which is expected to contribute to the development of 2-pentanone combustion models.

Plasma simulation of HF plasma generated in dual-frequency chamber for high aspect ratio dielectric etching

For the 3D NAND memory hole with a high aspect ratio above 100, the etching process with hydrogen-fluoride (HF) contained plasmas has been proposed. We have developed a simulation model for gas-phase reactions that reproduces the HF plasma in experiments. The HF plasma was generated using a power supply of 100 MHz frequency, and electron and F densities were measured. The simulation model was constructed on the basis of the collision cross sections and reaction constants reported in the previous papers, and the F density in the simulation was calibrated by comparing it with that in the experiments. As a result of the plasma simulation, the densities of F and the electrons were determined to be 7.52 × 1016 m–3 and 8.50 × 1016 m–3, respectively. Taking into consideration the errors in the experiment, we considered that the simulation model is able to reproduce the experimental HF plasma well.

Structural and functional analysis of a bile salt hydrolase from the bison microbiome

The bile salt hydrolases (BSHs) are significant constituents of animal microbiomes. An evolving appreciation of their roles in health and disease has established them as targets of pharmacological inhibition. These bacterial enzymes belong to the N-terminal nucleophile superfamily and are best known to catalyze the deconjugation of glycine or taurine from bile salts to release bile acid substrates for transformation and or metabolism in the gastrointestinal tract. Here, we identify and describe the BSH from a common member of the Plains bison microbiome, Arthrobacter citreus (BSHAc). Steady-state kinetic analyses demonstrated that BSHAc is a broad-spectrum hydrolase with a preference for glycine-conjugates and deoxycholic acid (DCA). Second-order rate constants (kcat/KM) for BSHAc-catalyzed reactions of relevant bile salts-glyco- and tauro-conjugates of cholic acid and DCA- varied by ∼30-fold and measured between 1.4× 105 and 4.3× 106M-1s-1. Interestingly, a pan-BSH inhibitor named AAA-10 acted as a slow irreversible inhibitor of BSHAc with a rate of inactivation (kinact)of ∼2h-1 and a second order rate constant (kinact/KI) of ∼24M-1s-1 for the process. Structural characterization of BSHAc reacted with AAA-10 showed covalent modification of the N-terminal cysteine nucleophile, providing molecular details for an enzyme-stabilized product formed from this mechanism-based inhibitor's α-fluoromethyl ketone warhead. Structural comparison of the BSHs and BSH:inhibitor complexes highlighted the plasticity of the steroid-binding site, including a flexible loop that is variable across well-studied BSHs.