Kinetic Steps Research Articles

Influence of Acylation by Hydroxycinnamic Acids on the Reversible and Irreversible Processes of Anthocyanins in Acidic to Basic Aqueous Solution.

In this work, the thermodynamics and kinetics of the reversible and irreversible processes of cyanidin 3,5-O-diglucoside and cyanidin 3-O-(2-O-glucosyl, 6-O-sinapoyl)glucoside-2-O-glucoside, 5-O-glucoside were studied by covering all pH range (holistic approach). The acylation (i) decreases the mole fraction of the colorless hemiketal in acidic medium and increases that of the colored quinoidal base, (ii) expands the pH domain of the flavylium cation, and (iii) moderately decreases the rate of tautomerization and isomerization of the neutral and monoanionic species. Degradation of cyanidin-3,5-O-diglucoside in a basic medium occurs in two distinct stages. After the formation of the anionic quinoidal bases (double proton loss from flavylium cation), a fast kinetic step, only observed by stopped flow, gives rise to the B4n- hydroxide adducts (n = 2,3) in equilibrium with the respective quinoidal bases An- (n = 1,2), leading to a first transient state. The quinoidal bases and B4n- adducts disappear completely from the first to a second transient state by means of two parallel reactions: (i) one reversible, giving the anionic cis- and trans-chalcones, (ii) the other irreversible, giving degradation products and exhibiting a pH-dependent bell-shaped mole fraction with maximum around pH = 12. From the second transient state, the anionic chalcones disappear completely in a few days. Acylation prevents formation of the first transient state. All of these effects are compatible with anthocyanidin-acyl π-stacking interactions (intramolecular copigmentation).

Balancing the elementary steps via photo-assisted thermal catalysis for boosting propane dehydrogenation

Balancing kinetics behavior is a significant priority in chemical reactions especially involving two or more elementary steps. Propane dehydrogenation (PDH), usually involves a slower 2nd C-H activation step at a low temperature, resulting in heat waste for overcoming a higher energy barrier of the 2nd dehydrogenation. Herein, we develop one Photo-assisted Thermal PDH process (PTPDH) based on PtZn clusters encapsulated in porous MFI zeolite, which effectively balances the kinetic elementary steps via exciting the ground state electrons of the active sites to the positively charged -C3H7 fragments, achieving a 23.4 % growth ratio (from 39.6 to 51.3·10−8 mol·g−1·s−1) with the assistance of ∼5 suns light intensity at 400 °C. The comparison between the temperature-dependent and light intensity-dependent kinetic parameters confirmed that the non-thermal effect instead of the photo-to-thermal effect dominates the PTPDH process. Furthermore, the Lewis acidity-activity correlation experiments, in-situ radiation mass spectrometry and the H2 co-feeds experiment indicate that the hot electrons instead of the holes play a more significant role in propylene production. Last, the in-situ Drifts-MS technique and DFT calculations demonstrate light radiation conduce to the electron transition from metal to the unpopulated electronic states of -C3H7 fragments, while not conducing to the adsorbed C3H8 molecule, thus selectively promoting the 2nd dehydrogenation process and achieving a balanced chemical kinetic condition. Our findings demonstrate that Photo-assisted Thermal PDH is a promising method for balancing the 1st and 2nd dehydrogenation processes.

Elucidating redox pathways for N2O selective catalytic reduction with NO and NH3 over Fe-chabazite zeolites

We combined kinetics and in situ X-ray absorption spectroscopy to investigate redox pathways of N2O-selective catalytic reduction (SCR) by NH3 and NO over Fe-exchanged Chabazite zeolites, a strategy to mitigate emissions of greenhouse gas N2O and toxic NOx from sources such as NH3 engines. N2O-SCR occurs via FeII/FeIII redox cycles with N2O as the oxidant, and parallel reactions involving NO+NH3 or NH3 as reductants, where in situ XAS shows that most Fe ions are redox-active. NO co-reduces FeIII with NH3 rather than oxidizing to NO2. Net rates of N2O-SCR in gas mixtures containing NH3 versus NO+NH3 are both limited by FeII oxidation, resulting in similar apparent activation energies. In contrast, reduction pathway selectivity reflects the intrinsic kinetics of FeIII reduction steps with NO+NH3 versus NH3, implying that reduction involving NO+NH3 dominates at lower temperatures and higher NO pressures. This work provides fundamental insights into kinetics and mechanisms of N2O-SCR.

Cargo adaptor identity controls the mechanism and kinetics of dynein activation.

Cytoplasmic dynein-1 (dynein), the primary retrograde motor in most eukaryotes, supports the movement of hundreds of distinct cargos, each with specific trafficking requirements. To achieve this functional diversity, dynein must bind to the multi-subunit complex dynactin and one of a family of cargo adaptors to be converted into an active, processive motor complex. Very little is known about the dynamic processes that promote the formation of this complex. To delineate the kinetic steps that lead to dynein activation, we developed a single-molecule fluorescence assay to visualize the real-time formation of dynein-dynactin-adaptor complexes in vitro. We found that dynactin and adaptors bind dynein independently rather than cooperatively. We also found that different dynein adaptors promote dynein-dynactin-adaptor assembly with dramatically different kinetics, which results in complex formation occurring via different assembly pathways. Despite differences in association rates or mechanism of assembly, all adaptors tested can generate a population of tripartite complexes that are very stable. Our work provides a model for how modulating the kinetics of dynein-dynactin-adaptor binding can be harnessed to promote differential dynein activation and reveals a new facet of the functional diversity of the dynein motor.

Multi-response kinetic modelling of the formation of five Strecker aldehydes during kilning of barley malt

Control of aroma formation during production of barley malt is critical to provide consistent and high-quality products for the brewing industry. Malt quality can be affected by the inherent variability of raw material and processing conditions, leading to inconsistent and/or undesirable profiles. Dried green malts were cured isothermally at 65, 78 and 90 °C for 8.4 h, and characteristic aroma compounds (Strecker aldehydes), precursors and intermediate compounds were analysed over time. By kinetic modelling of Strecker aldehydes, based on fundamental chemical pathways, we showed that degradation of Amadori rearrangement products and short-chain dicarbonyls was more sensitive to temperature change due to their higher activation energies compared to other kinetic steps. This study can help maltsters to manipulate formation of Strecker aldehydes, via raw material screening and process control, and hence optimise the organoleptic quality of malts and their products, such as non-alcoholic beers, where these aldehydes play a key role.

Experimental analysis of hyper power impulse magnetron discharge with long pulse operation

Abstract Glow discharges are known to be limited for running at high current densities (typically below 0.1 A ⋅ c m − 2 ). Magnetically enhanced plasmas overcome this limitation, reaching up to two orders of magnitude higher current densities. However, the highest reported discharge current density hardly reaches 10 A ⋅ c m − 2 even in high power impulse magnetron sputtering (HiPIMS). Here, we report on the long (∼1 ms) pulsed operation of the magnetron in helium with an over-dense current (∼30 A ⋅ c m − 2 , usual for arcs) while preserving the glow mode. This regime defying the arcs was called hyper power impulse magnetron (HyPIM) because the power injected per pulse is several times higher than in HiPIMS for the same average power and pulse duration. HyPIM operation mode is distinguished from HiPIMS by the limited pulse voltage and is unsuitable for thin film deposition but may interest plasma switches. These huge currents were obtained for two cathode materials, molybdenum (Mo) and tungsten (W). Different experimental diagnostics bring insights into the physical phenomena governing the HyPIM plasma. A discussion on the role played by the metal atoms on the current unveils the origin of such exceptional glow current all along the pulse and the key role of the helium metastable atoms. A schematic of the kinetic steps of the HyPIM discharge is proposed.

Early Events in G-quadruplex Folding Captured by Time-Resolved Small-Angle X-Ray Scattering.

Time-resolved small-angle X-ray experiments (TR-SAXS) are reported here that capture and quantify a previously unknown rapid collapse of the unfolded oligonucleotide as an early step in G4 folding of hybrid 1 and hybrid 2 telomeric G-quadruplex structures. The rapid collapse, initiated by a pH jump, is characterized by an exponential decrease in the radius of gyration from 20.6 to 12.6 Å. The collapse is monophasic and is complete in less than 600 ms. Additional hand-mixing pH-jump kinetic studies show that slower kinetic steps follow the collapse. The folded and unfolded states at equilibrium were further characterized by SAXS studies and other biophysical tools, to show that G4 unfolding was complete at alkaline pH, but not in LiCl solution as is often claimed. The SAXS Ensemble Optimization Method (EOM) analysis reveals models of the unfolded state as a dynamic ensemble of flexible oligonucleotide chains with a variety of transient hairpin structures. These results suggest a G4 folding pathway in which a rapid collapse, analogous to molten globule formation seen in proteins, is followed by a confined conformational search within the collapsed particle to form the native contacts ultimately found in the stable folded form.

Interfacial engineering for the construction of iron sulfide/boride nanosheets heterostructure bifunctional electrocatalysts for high-efficiency overall water splitting

Iron-based materials have been extensively studied and applied as electrocatalysts. However, the electronic structure of iron itself is not conducive to effectively activating adsorbed intermediates, leading to slower kinetic steps. In this study, a heterogeneous composite catalyst with a nano-sheet array structure consisting of iron boron/sulfide (FeS@Fe2B/IP) was successfully prepared through a two-step process involving boriding and sulfidation of iron plates. The nanosheet array structure provides numerous catalytic active sites, promotes effective contact between electrolytes and catalytic sites, and enhances the apparent reaction rate of the catalyst. Additionally, the heterogeneous interface of FeS/Fe2B plays a crucial role in regulating the electronic structure of the metal Fe site, improving charge transfer rates, and accelerating electrocatalytic reaction kinetics. Ultimately, FeS@Fe2B/IP demonstrates outstanding water splitting performance, with only 177 and 191 mV overpotential providing 10 mA cm−2 toward HER and OER, respectively. Furthermore, it achieves a high current density of 500 mA cm−2 at 473 and 520 mV overpotentials for HER and OER, respectively. In addition to its excellent performance in water splitting applications, a bipolar alkaline cell was constructed using the FeS@Fe2B/IP bifunctional catalyst. This achieved current densities of 10 and 100 mA cm−2 at potentials of 1.63 and 1.75 V. Moreover, the catalytic stability of the FeS@Fe2B/IP system remained consistent for nearly 50 hours at current densities of 10 and 100 mA cm−2. These results confirm that FeS@Fe2B/IP is indeed a high-performance bifunctional electrocatalytic material which can significantly improve energy utilization efficiency in various applications.

Ultrafine ruthenium-based nanoclusters regulated by a three-phase heterogeneous interface exhibiting superior mass activity for alkaline hydrogen evolution

Platinum-based catalysts are considered the most effective catalysts for the hydrogen evolution reaction (HER) in acidic media; however, they exhibit poor performance in alkaline electrolysis waters, which are currently more commercially developed, due to their sluggish water dissociation ability. Small-sized metal Ru nanoparticles, with metal-hydrogen bond strength close to Pt (approximately 65 kcal/mol) and a relatively lower water dissociation barrier, are considered one of the most promising alternatives to the noble metal Pt for alkaline HER. Based on the above statements, the present study innovatively combines the effective strategies of "heterogeneous interface engineering" and "construction of ultrafine active sites" to develop a highly efficient Ru-based catalyst with a three-phase heterogeneous interface, aiming to form its application in alkaline HER. Characterization analysis and DFT calculations demonstrated that the "Rux-Ni(OH)2NiO" three-phase heterogeneous interface constructed around ultrafine Rux clusters effectively modulated the electronic structure of the overall material and optimized the HER kinetic steps. This catalytic material, Rux@NOH/NO, exhibited outstanding electrocatalytic activity in alkaline HER, requiring only 44.2 mV to drive a current density of 10 mA·cm−2, with excellent long-term stability and extremely low active material loading (1.36 wt%-Ru). Specially, its mass activity reached an impressive 18,897.1 A/gRu at 150 mV, which is 10.2 times higher than that of commercial 20wt% Pt/C. In summary, this study synergistically constructs an ultrafine metal ruthenium-based catalyst based on a three-phase heterogeneous interface using a composite strategy, which provides an effective catalyst system for alkaline HER catalytic reactions and holds significance for the rational construction and design of efficient heterogeneous interface electrocatalysts.

Damage kinetics in high-temperature irradiated Ni crystals

High-temperature (∼800 K) ion irradiation with 380 keV Ar ions was used to modify the surface of Ni single crystals in order to generate radiation defects and mimic the effect of neutrons avoiding sample activation. The modified 800 nm thick layer was analyzed regarding structural and mechanical properties utilizing a combination of experimental and simulation techniques. The ion implantation fluence ranged from 1 × 1014 cm−2 up to 1 × 1016 cm−2, which corresponds to values of displacements per atom from 0.25 to 25, respectively. The structural characterization was performed by Rutherford Spectroscopy in Channeling mode (RBS/C) associated with scanning (SEM) and transmission electron microscopy (TEM). The experimental results were supported by Monte Carlo (McChasy) and Molecular Dynamics (MD-LAMMPS) simulations. The simulations performed using the second generation of the McChasy code show that the influence of bubbles formed inside the material is not negligible and affects the quantitative analysis of defects in the simulated spectra. A second step in damage kinetics was revealed for the highest dose (i.e., 25 dpa) as a consequence of the entanglement of dislocations and agglomeration of noble gas bubbles, which was confirmed by TEM analysis. Moreover, nanomechanical results confirm that Ar bubbles deteriorate mechanical properties such as hardness.

Machine Learning Accelerated Identification of Bifunctional Active Sites in Metal-Organic Framework Derived Metal Oxide Heterostructures for High-Performance Zinc-Air Batteries

The demand for electrochemical energy storage (ESS) systems and their market size has drastically increased in many applications ranging from portable devices through electric vehicles to large-scale grid systems over the past decades. Yet, a more advanced ESS is required due to the safety issues and limited energy density of currently commercialized lithium-ion batteries (LIBs) for wide and matured applications. As a solution to this challenge, zinc-air batteries (ZABs) have gained tremendous attention due to their high energy density, low cost, environmental friendliness, and much lower fire risk characteristics. ZABs utilize oxygen from the atmosphere at their cathode during discharge, where the atmospheric oxygen is reduced to hydroxide via an oxygen reduction reaction (ORR). On the other hand, hydroxide is released as oxygen via oxygen evolution reaction (OER) during charge. The fact that oxygen is drawn directly from the air enables high gravimetric and volumetric energy densities of ZABs compared to those of commercial LIBs. However, the sluggish kinetics of the four-electron transfer steps in ORR and the mass transport of oxygen in OER remain major challenges for the practical application of ZABs. Meanwhile, precious metal-based catalysts such as Pt/C and RuO2 are known to have good catalytic activity towards ORR and OER. However, the integration of different catalysts into the same cathode is very difficult. Additionally, the high cost and natural scarcity of novel metals limit their usage for practical applications.We synthesized a bifunctional CoO/Mn3O4 heterostructure (CMH) OER/ORR electrocatalyst which was derived from metal-organic framework (MOF) for excellent activities in ZABs. The CMH cathode exhibited high ORR and OER performances, as demonstrated by the higher ORR current density than that of the Pt/C catalyst as well as the low OER overpotential exceeding those of the RuO2 catalyst. Remarkably, atomic structures of the CMH were elucidated using global optimization of genetic algorithm integrated with the machine learning force field. By adopting first-principles electronic structure calculations, we further revealed the charge transfer and active sites for both reactions in the identified heterojunction. Furthermore, assembling CMH cathode and Zn metal anode into a ZAB full-cell configuration achieves a ~5.5-fold higher energy density of 879 Wh kg-1 exceeding those of commercial lithium-ion batteries (LIBs), a high-discharge outstanding power density that is 1.39 times higher than novel metal catalysts, and robust cycle stability with negligible voltage decay which is far superior to that of benchmark Pt/C+RuO2 electrocatalysts.

(Invited) Resolving Catalytic Mechanism at an Electrode Surface: Thermodynamics & Kinetics of Reaction Steps

Computationally, often the energetics of intermediate reaction steps differentiate the efficiency of heterogeneous catalysts for product evolution. Yet, when compared to experiment, kinetic models are applied. For example, a material’s activity measured by one rate of product evolution is plotted as a function of the calculated formation energies of intermediate chemical forms. A critically important reaction for which this dichotomy between experiment and theory exists is the oxygen evolution reaction (OER) from water. In the laboratory group, we employ time-resolved optical and vibrational spectroscopy to deconstruct OER into its individual reaction steps on an electrode surface. In the presentation, I will describe the experimental methodology and the chosen model system, the n-doped SrTiO3/aqueous interface. I’ll show how these experiments identify both the rates and energetics of the first reaction step, the release of a proton and electron from an absorbed water species, denoted by OH* or O*. A recent success was to isolate a Langmuir isotherm of the intermediate population arising within < 2 ps on the SrTiO3 surface. The intermediate population is of trapped holes measured by emission from the conduction band into unoccupied states in the middle of the semi-conductor bandgap. The isotherm is tuned by the pH of the electrolyte. The pH-dependent formation of these intermediates are connected to their pH-dependent decay at microsecond timescales, presumably related to later reaction steps of OER. I'll also present work on the side of vibrational spectroscopy that looks at how the potential energy surface of a particular trapped hole, the terminal oxyl radical, arises in time through the spectral kinetics of its normal mode. A growing area is to apply the particular experimental methodology to a surface of similar electronic structure but diverse crystal geometries, namely polymorphs of TiO2.

Biaxial strain induced OH engineer for accelerating alkaline hydrogen evolution

The sluggish kinetics of Volmer step in the alkaline hydrogen evolution results in large energy consumption. The challenge that has yet well resolved is to control the water adsorption and dissociation. Here, we develop biaxially strained MoSe2 three dimensional nanoshells that exhibit enhanced catalytic performance with a low overpotential of 58.2 mV at 10 mA cm−2 in base, and long-term stable activity in membrane-electrode-assembly based electrolyser at 1 A cm−2. Compared to the flat and uniaxial-strained MoSe2, we establish that the stably adsorbed OH engineer on biaxially strained MoSe2 changes the water adsorption configuration from O-down on Mo to O-horizontal on OH* via stronger hydrogen bonds. The favorable water dissociation on 3-coordinated Mo sites and hydrogen adsorption on 4-coordinated Mo sites constitute a tandem electrolysis, resulting in thermodynamically favorable hydrogen evolution. This work deepens our understanding to the impact of strain dimensions on water dissociation and inspires the design of nanostructured catalysts for accelerating the rate-determining step in multi-electron reactions.

Crossing the Halfway Point: Aptamer-Based, Highly Multiplexed Assay for the Assessment of the Proteome.

Measuring responses in the proteome to various perturbations improves our understanding of biological systems. The value of information gained from such studies is directly proportional to the number of proteins measured. To overcome technical challenges associated with highly multiplexed measurements, we developed an affinity reagent-based method that uses aptamers with protein-like side chains along with an assay that takes advantage of their unique properties. As hybrid affinity reagents, modified aptamers are fully comparable to antibodies in terms of binding characteristics toward proteins, including epitope size, shape complementarity, affinity and specificity. Our assay combines these intrinsic binding properties with serial kinetic proofreading steps to allow highly effective partitioning of stable specific complexes from unstable nonspecific complexes. The use of these orthogonal methods to enhance specificity effectively overcomes the severe limitation to multiplexing inherent to the use of sandwich-based methods. Our assay currently measures half of the unique proteins encoded in the human genome with femtomolar sensitivity, broad dynamic range and exceptionally high reproducibility. Using machine learning to identify patterns of change, we have developed tests based on measurement of multiple proteins predictive of current health states and future disease risk to guide a holistic approach to precision medicine.

Hierarchical Modeling of the Local Reaction Environment in Electrocatalysis.

ConspectusElectrocatalytic reactions, such as oxygen reduction/evolution reactions and CO2 reduction reaction that are pivotal for the energy transition, are multistep processes that occur in a nanoscale electric double layer (EDL) at a solid-liquid interface. Conventional analyses based on the Sabatier principle, using binding energies or effective electronic structure properties such as the d-band center as descriptors, are able to grasp overall trends in catalytic activity in specific groups of catalysts. However, thermodynamic approaches often fail to account for electrolyte effects that arise in the EDL, including pH, cation, and anion effects. These effects exert strong impacts on electrocatalytic reactions. There is growing consensus that the local reaction environment (LRE) prevailing in the EDL is the key to deciphering these complex and hitherto perplexing electrolyte effects. Increasing attention is thus paid to designing electrolyte properties, positioning the LRE at center stage. To this end, unraveling the LRE is becoming essential for designing electrocatalysts with specifically tailored properties, which could enable much needed breakthroughs in electrochemical energy science.Theory and modeling are getting more and more important and powerful in addressing this multifaceted problem that involves physical phenomena at different scales and interacting in a multidimensional parametric space. Theoretical models developed for this purpose should treat intrinsic multistep kinetics of electrocatalytic reactions, EDL effects from subnm scale to the scale of 10 nm, and mass transport phenomena bridging scales from <0.1 to 100 μm. Given the diverse physical phenomena and scales involved, it is evident that the challenge at hand surpasses the capabilities of any single theoretical or computational approach.In this Account, we present a hierarchical theoretical framework to address the above challenge. It seamlessly integrates several modules: (i) microkinetic modeling that accounts for various reaction pathways; (ii) an LRE model that describes the interfacial region extending from the nanometric EDL continuously to the solution bulk; (iii) first-principles calculations that provide parameters, e.g., adsorption energies, activation barriers and EDL parameters. The microkinetic model considers all elementary steps without designating an a priori rate-determining step. The kinetics of these elementary steps are expressed in terms of local concentrations, potential and electric field that are codetermined by EDL charging and mass transport in the LRE model. Vital insights on electrode kinetic phenomena, i.e., potential-dependent Tafel slopes, cation effects, and pH effects, obtained from this hierarchical framework are then reviewed. Finally, an outlook on further improvement of the model framework is presented, in view of recent developments in first-principles based simulation of electrocatalysis, observations of dynamic reconstruction of catalysts, and machine-learning assisted computational simulations.

Simulation-Guided Conformational Space Exploration to Assess Reactive Conformations of a Ribozyme.

Self-splicing ribozymes are small ribonucleic acid (RNA) enzymes that catalyze their own cleavage through a transphosphoesterification reaction. While this process is involved in some specific steps of viral RNA replication and splicing, it is also of importance in the context of the (putative) first autocatalytic RNA-based systems that could have preceded the emergence of modern life. The uncatalyzed phosphoester bond formation is thermodynamically very unfavorable, and many experimental studies have focused on understanding the molecular features of catalysis in these ribozymes. However, chemical reaction paths are short-lived and not easily characterized by experimental approaches, so molecular simulation approaches appear as an ideal tool to unveil the molecular details of the reaction. Here, we focus on the model hairpin ribozyme. We show that identifying a relevant initial conformation for reactivity studies, which is frequently overlooked in mixed quantum-classical studies that predominantly concentrate on the chemical reaction itself, can be highly challenging. These challenges stem from limitations in both available experimental structures (which are chemically altered to prevent self-cleavage) and the accuracy of force fields, together with the necessity for comprehensive sampling. We show that molecular dynamics simulations, combined with extensive conformational phase space exploration with Hamiltonian replica-exchange simulations, enable us to characterize the relevant conformational basins of the minimal hairpin ribozyme in the ligated state prior to self-cleavage. We find that what is usually considered a canonical reactive conformation with active site geometries and hydrogen-bond patterns that are optimal for the addition-elimination reaction with general acid/general base catalysis is metastable and only marginally populated. The thermodynamically stable conformation appears to be consistent with the expectations of a mechanism that does not require the direct participation of ribozyme residues in the reaction. While these observations may suffer from forcefield inaccuracies, all investigated forcefields lead to the same conclusions upon proper sampling, contrasting with previous investigations on shorter timescales suggesting that at least one reparametrization of the Amber99 forcefield allowed to stabilize aligned active site conformations. Our study demonstrates that identifying the most pertinent reactant state conformation holds equal importance alongside the accurate determination of the thermodynamics and kinetics of the chemical steps of the reaction.

Direct Electron Transfer-Driven Nontoxic Oligomeric Deposition of Sulfonamide Antibiotics onto Carbon Materials for In Situ Water Remediation.

The rising in situ chemical oxidation (ISCO) technologies based on polymerization reactions have advanced the removal of emerging contaminants in the aquatic environment. However, despite their promise, uncertainties persist regarding their effectiveness in eliminating structurally complex contaminants, such as sulfonamide antibiotics (SAs). This study elucidated that oligomerization, rather than mineralization, predominantly governs the removal of SAs in the carbon materials/periodate system. The amine groups in SAs played a crucial role in forming organic radicals and subsequent coupling reactions due to their high f- index and low bond orders. Moreover, the study highlighted the robust adhesion of oligomers to the catalyst surface, facilitated by enhanced van der Waals forces and hydrophobic interactions. Importantly, plant and animal toxicity assessments confirmed the nontoxic nature of oligomers deposited on the carbon material surface, affirming the efficacy of carbon material-based ISCO in treating contaminated surface water and groundwater. Additionally, a novel classification approach, Δlog k, was proposed to differentiate SAs based on their kinetic control steps, providing deeper insights into the quantitative structure-activity relationship (QSAR) and facilitating the selection of optimal descriptors during the oligomerization processes. Overall, these insights significantly enhance our understanding of SAs removal via oligomerization and demonstrate the superiority of C-ISCO based on polymerization in water decontamination.

Regulatory properties of transcription factors with diverse mechanistic function.

Transcription factors (TFs) regulate the process of transcription through the modulation of different kinetic steps. Although models can often describe the observed transcriptional output of a measured gene, predicting a TFs role on a given promoter requires an understanding of how the TF alters each step of the transcription process. In this work, we use a simple model of transcription to assess the role of promoter identity, and the degree to which TFs alter binding of RNAP (stabilization) and initiation of transcription (acceleration) on three primary characteristics: the range of steady-state regulation, cell-to-cell variability in expression, and the dynamic response time of a regulated gene. We find that steady state regulation and the response time of a gene behave uniquely for TFs that regulate incoherently, i.e that speed up one step but slow the other. We also find that incoherent TFs have dynamic implications, with one type of incoherent mode configuring the promoter to respond more slowly at intermediate TF concentrations. We also demonstrate that the noise of gene expression for these TFs is sensitive to promoter strength, with a distinct non-monotonic profile that is apparent under stronger promoters. Taken together, our work uncovers the coupling between promoters and TF regulatory modes with implications for understanding natural promoters and engineering synthetic gene circuits with desired expression properties.

Study on high-efficiency sulfide removement using sulfate radical-based AOPs and its oxidation mechanism of refractory gold ore

Pyrite enclosure poses a significant challenge in refractory gold ore processing, inhibiting gold leaching. This study explores Sulfate Radical-based Advanced Oxidation Processes (SR-AOPs) as an effective alternative for pretreating such ores. The oxidation pretreatments were performed under heat and ultrasound activation methods, including heat and ultrasound, and the influences of pretreatment time, pH, ultrasound power, pretreatment temperature, and precursor (PDS) concentration were investigated. Both ultrasonic and heat activation effectively mitigate the negative impact of pyrite enclosure on gold leaching. Specifically, the gold leaching rate improved from 21.9 % to 46.1 % and 74.9 % with heat and ultrasound activation, respectively The and generated by PDS dominate the pyrite oxidation according to EPR and quenching tests. Meanwhile, the SR-AOPs treatment also promotes the interactions between pyrite enclosure and leaching agent, reducing the negative influences of pyrite. Kinetic studies indicated that the oxidation processes are different under heat and ultrasound activation. Heat activation is governed by an interfacial chemical reaction, with an activation energy of 25.57 kJ/mol. In contrast, ultrasound-induced cavitation and microjets remove the oxidation layer, disrupt the pyrite crystal structure, and expose encapsulated gold. These effects accelerate pyrite oxidation, shifting the kinetic control step from interfacial chemical reaction to internal diffusion, with a reduced activation energy of 35.06 kJ/mol.

Carbon Corrosion Induced by Surface Defects Accelerates Degradation of Platinum/Graphene Catalysts in Oxygen Reduction Reaction.

Graphene supported electrocatalysts have demonstrated remarkable catalytic performance for oxygen reduction reaction (ORR). However, their durability and cycling performance are greatly limited by Oswald ripening of platinum (Pt) and graphene support corrosion. Moreover, comprehensive studies on the mechanisms of catalysts degradation under 0.6-1.6V versus RHE (Reversible Hydrogen Electrode) is still lacking. Herein, degradation mechanisms triggered by different defects on graphene supports are investigated by two cycling protocols. In the start-up/shutdown cycling (1.0-1.6V vs.RHE), carbon oxidation reaction (COR) leads to shedding or swarm-like aggregation of Pt nanoparticles (NPs). Theoretical simulation results show that the expansion of vacancy defects promotes reaction kinetics of the decisive step in COR, reducing its reaction overpotential. While under the load cycling (0.6-1.0V vs.RHE), oxygen containing defects lead to an elevated content of Pt in its oxidation state which intensifies Oswald ripening of Pt. The presence of vacancy defects can enhance the transfer of electrons from graphene to the Pt surface, reducing the d-band center of Pt and making it more difficult for the oxidation state of platinum to form in the cycling. This work will provide comprehensive understanding on Pt/Graphene catalysts degradation mechanisms.