Catalytic Action Research Articles

Heterojunction semiconductor nanocatalysts as cancer theranostics.

Cancer nanotechnology is a promising area of cross-disciplinary research aiming to develop facile, effective, and noninvasive strategies to improve cancer diagnosis and treatment. Catalytic therapy based on exogenous stimulus-responsive semiconductor nanomaterials has shown its potential to address the challenges under the most global medical needs. Semiconductor nanocatalytic therapy is usually triggered by the catalytic action of hot electrons and holes during local redox reactions within the tumor, which represent the response of nontoxic semiconductor nanocatalysts to pertinent internal or external stimuli. However, careful architecture design of semiconductor nanocatalysts has been the major focus since the catalytic efficiency is often limited by facile hot electron/hole recombination. Addressing these challenges is vital for the progress of cancer catalytic therapy. In recent years, diverse strategies have been developed, with heterojunctions emerging as a prominent and extensively explored method. The efficiency of charge separation under exogenous stimulation can be heightened by manipulating the semiconducting performance of materials through heterojunction structures, thereby enhancing catalytic capabilities. This review summarizes the recent applications of exogenous stimulus-responsive semiconducting nanoheterojunctions for cancer theranostics. The first part of the review outlines the construction of different heterojunction types. The next section summarizes recent designs, properties, and catalytic mechanisms of various semiconductor heterojunctions in tumor therapy. The review concludes by discussing the challenges and providing insights into their prospects within this dynamic and continuously evolving field of research.

Photocatalytic magnetic bimetallic ferrite synergistically activates ammonium persulfate for the efficient degradation of tetrachlorobisphenol A(TCBPA)

The presence of tetrachlorobisphenol A(TCBPA) in the environment is continually increasing, which has potential negative effects on human health. Therefore, it is important to develop new materials that can degrade these compounds using various modification techniques. Recently, the photocatalytic degradation of organic pollutants using peroxides has been widely used as the focus of several research studies. This study synthesized Zr-doped NiFe2O4 (Zr-NiFe2O4) metal complex materials using a co-precipitation method and applied them to catalyze the degradation of a typical halogenated bisphenol A pollutant using different phase-catalyzed peroxydisulfate (PS) compounds. The results showed that Zr-NiFe2O4 significantly enhances the nitrogen-active adaptive catalytic action between the reactive species and (NH4)2S2O8, exhibiting an excellent catalytic performance (99 %). The degradation rate could reach 90 % after 30 mins with the low concentration of TCBPA (20 mg•L–1). Furthermore, the degradation of TCBPA in the Zr-NiFe2O4/LED/(NH4)2S2O8 system occurred over a wide pH range of 3–11. The results of leaching metals were detected that the concentrations of the leached zirconium, nickel and iron ions declined to 0.018 mg•L−1. In addition, the tri-metal synergistic effect of Zr-NiFe2O4 not only significantly improved the TCBPA removal efficiency, but also enhanced the long-term stability of the composite material. Mechanistic studies revealed that ·OH and SO4·– were involved in the TCBPA degradation process with ·OH being the primary active species, and the possible degradation pathways were deduced using mass spectrometry. The on-line infrared test experiments showed the disappearance of the hydroxyl and double bond within approximately 120 seconds. Moreover, the magnetic properties of Zr-NiFe2O4 met the water recovery requirements, effectively reducing secondary pollution, and aligned with the practical needs for water treatment, providing data for the construction of efficient magnetic catalysts.

Catalytic Biomaterials-Activated In Situ Chemical Reactions: Strategic Modulation and Enhanced Disease Treatment.

Chemical reactions underpin biological processes, and imbalances in critical biochemical pathways within organisms can lead to the onset of severe diseases. Within this context, the emerging field of "Nanocatalytic Medicine" leverages nanomaterials as catalysts to modulate fundamental chemical reactions specific to the microenvironments of diseases. This approach is designed to facilitate the targeted synthesis and localized accumulation of therapeutic agents, thus enhancing treatment efficacy and precision while simultaneously reducing systemic side effects. The effectiveness of these nanocatalytic strategies critically hinges on a profound understanding of chemical kinetics and the intricate interplay of reactions within particular pathological microenvironments to ensure targeted and effective catalytic actions. This review methodically explores in situ catalytic reactions and their associated biomaterials, emphasizing regulatory strategies that control therapeutic responses. Furthermore, the discussion encapsulates the crucial elements-reactants, catalysts, and reaction conditions/environments-necessary for optimizing the thermodynamics and kinetics of these reactions, while rigorously addressing both the biochemical and biophysical dimensions of the disease microenvironments to enhance therapeutic outcomes. It seeks to clarify the mechanisms underpinning catalytic biomaterials and evaluate their potential to revolutionize treatment strategies across various pathological conditions.

Insight into lignin-carbohydrate ester change in pretreated corn bran and its enzymatic hydrolysis by three glucuronoyl esterases from Sordaria brevicollis

Lignin-carbohydrate esters (LC-esters) formed by glucuronoarabinoxylan and lignin are a key factor for the recalcitrance of corn bran, understanding LC-esters change during pretreatment and enzymatic hydrolysis by glucuronoyl esterases (GEs) is essential to the sustainable utilization of corn bran. Herein, hydrolysis performances of three GEs, SbGE15A, SbGE15B, and SbGE15C from Sordaria brevicollis with different subclades and modularity, and changes in enzyme-reachable LC-esters during different pretreatments of corn bran have been comprehensively compared. FB enzymes, SbGE15B and SbGE15C showed higher catalytic activity towards model and natural substrates than FA enzyme, SbGE15A. Particularly, SbGE15C harboring carbohydrate-binding module 1 (CBM1) exhibited much superior catalytic performance and synergistic effect with GH10 endo-xylanase EpXYN1 from Eupenicillium parvum on pretreated residues than SbGE15A and SbGE15B without CBM1. Autohydrolysis and DES (ChCl-LA) pretreatment could decrease the content of enzyme-reachable LC-esters and depolymerize its structure, transitioning from Lignin-(Me)GlcA-Xylan to Lignin-(Me)GlcA-XOS, and eventually to Lignin-(Me)GlcA with increasing pretreatment time. These changes consequently cause a decrease in synergy between SbGE15s and EpXYN1 or commercial enzyme cocktails on pretreated residues. The findings provide new insights into significant changes in enzyme-reachable LC-esters depending on the pretreatment method and intensity and the consequent influence of these changes on the catalytic action of GEs.

Ultramarine blue containing paint layers: Further study of the photo-catalytic degradation of binding media

Photo-catalytic degradation of a linseed oil binder by natural ultramarine (Lapis Lazuli or Lazurite) and Sodalite in paint layers was studied. Both pigments degrade the binder under xenon arc exposure, leading to erosion of the binder at the surface, increased roughness, light scattering and desaturation of the color. Both pigments behave similarly to synthetic ultramarine blue studied earlier. The results for Sodalite provide further proof that the zeolitic nature of the aluminosilicate cage causes the catalytic degradation and that the enclathrated polysulfur radical anions S2-. and S3-. trapped inside the cage are not responsible for the catalytic action. Relatively stable synthetic binders are less affected by the presence of synthetic ultramarine blue. The paints were aged in a xenon arc apparatus using a simulated indoor environment (radiation > ca. 320 nm). The samples were analyzed using diffuse reflectance spectroscopy in the UV–vis and short wavelength infrared (SWIR) ranges, Raman spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM) and FTIR.

Self‐Oxygenated Biomimetic Nanozyme for Tumor Catalytic Immunotherapy

AbstractThe treatment of solid tumors remains a significant challenge due to the complex, immunosuppressive tumor microenvironment (TME). This manuscript introduces the self‐oxygenated biomimetic nanozyme system, SS‐MSN@Au‐BOM, which innovatively combines catalytic therapy with immunotherapy to modulate the TME for enhanced therapeutic efficacy. Employing mesoporous silicon nanoparticles doped with disulfide bonds, the system integrates gold nanozymes that exhibit glucose oxidase (GOx)‐like and peroxidase (POD)‐like activities, along with a catalase (CAT) function derived from bacterial outer membrane (BOM) coatings. SS‐MSN@Au‐BOM significantly disrupted tumor growth by catalyzing endogenous hydrogen peroxide to generate cytotoxic ROS and essential oxygen, enhancing intratumoral ROS levels while alleviating hypoxia. This catalytic action facilitates immunogenic cell death, enhances dendritic cell maturation, and T‐cell activation. Notably, the system shows excellent biocompatibility, effective tumor targeting, and prolonged systemic circulation. SS‐MSN@Au‐BOM offers a dual‐functional approach that effectively disrupts the TME and promotes robust antitumor immunity. This study paves the way for further clinical investigation and the development of enzyme‐based therapeutics, potentially transforming the landscape of cancer treatment.

Construction and demolition waste as a low-cost adsorbent for water treatment: kinetics, isotherm, thermodynamics, and Fenton regeneration.

The present study proposes to investigate the feasibility of using construction and demolition waste (CDW) as an aqueous remediation agent through adsorption. The CDW, with and without chemical and thermal pre-activation, was evaluated to remove the methylene blue (MB) dye from the water solution. Variables interfering with adsorption processes, such as adsorbent dosage, solution pH, and particle size, were evaluated. The material was characterized by pHZPC, FTIR, XRD, SEM, EDS, and TG. The kinetic and equilibrium data better fitted the Elovich and Sips models, respectively. A maximum adsorption capacity of 18.62mgg-1 at 60°C was observed. Thermodynamic data indicated that adsorption occurred through a spontaneous and favorable process governed mainly by physical processes. The regeneration studies were carried out using processes based on the Fenton reaction, where the catalytic action of the iron naturally present in the CDW was evaluated. The results showed that the desorption balance was the main limiting factor for the effective regeneration of the saturated material. Adding Fe2+ to the system made this process suitable for the regeneration of the CDW and degradation of the pollutant in the aqueous phase. A regeneration efficiency of 65%, maintained practically constant during five adsorption-regeneration cycles, was observed. These results highlight the high potential of using CDWs as an adsorbent material.

High Response and ppb-Level Detection toward Hydrogen Sensing by Palladium-Doped α-Fe2O3 Nanotubes.

Developing hydrogen sensors with parts per billion-level detection limits, high response, and high stability is crucial for ensuring safety across various industries (e.g., hydrogen fuel cells, chemical manufacturing, and aerospace). Despite extensive research on parts per billion-level detection, it still struggles to meet stringent requirements. Here, high performance and ppb-level H2 sensing have been developed with palladium-doped iron oxide nanotubes (Pd@Fe2O3 NTs), which have been prepared by FeCl3·6H2O, PdCl2, and PVP electrospinning and air calcination techniques. Various characterization techniques (FESEM, TEM, XRD, and so forth) were used to prove that the nanotube structure was successfully prepared, and the doping of Pd nanoparticles was realized. The experiments show that palladium doping can significantly improve the gas response of iron oxide nanotubes. Specifically, 0.59 wt % Pd@Fe2O3 NTs have high response (Ra/Rg = 41,000), high selectivity, and excellent repeatability for 200 ppm hydrogen at 300 °C. Notably, there was still a significant response at a low detection limit (LOD) of 50 ppb (Ra/Rg = 16.8). This excellent hydrogen sensing performance may be attributed to the high surface area of the nanotubes, the p-n heterojunction of PdO/Fe2O3, which allows more oxygen to be adsorbed on the surface, and the catalytic action of Pd nanoparticles, which promotes the reaction of hydrogen with surface-adsorbed oxygen.

Sulfur doped hollow cobalt–nitrogen–carbon oxidase-mimicking nanozyme enable sensitive chemiluminescence sensing serum total antioxidant capacity

Heteroatom doping is one of most important methodology for heightening catalytic activity of a nanozyme through modulating electronic configuration and coordinated environment of metal atoms. Here, a nitrogen/sulfur co-doped cobalt-decorated hollow carbon structure (CoS/NC) was fabricated through a simple and manageable template-assisted synthetic strategy, following high-temperature carbonization treatment. Remarkably, the CoS/NC has superior oxidase-mimicking activity than its counterparts and displays excellent catalytic action on the chemiluminescence (CL) reaction between luminol and dissolved oxygen (O2). The CoS/NC nanozyme-based CL system is highly sensitive to physiologically relevant antioxidants of both species including single electron transfer and hydrogen atom transfer. The detection limits can be reached as low as 3 nmol·L−1 ascorbic acid, 30 nmol·L−1 uric acid, 16 nmol·L−1 glutathione, and 28 nmol·L−1 cysteine. The total antioxidant capacity (TAC) of human serums has been determined in order to assess the feasibility of the CL system. The results of serum TAC, with ascorbic acid as an equivalent model, show a good consistency with those obtained by the standard CUPRAC method. This work not only benefits the rational design of a high catalytic functionality nanozyme, but also constructs a robust TAC detection platform for monitoring oxidative stress-related diseases.

Kinetic analysis of landfill stale garbage (LSG) pyrolysis and combustion behaviour using thermogravimetry coupled MS and FTIR technique

The environmental impact of landfill stale garbage (LSG), particularly concerning methane emissions and the depletion of valuable resources, presents a significant challenge to environmental sustainability. This research examines the thermochemical properties of LSG, establishing a foundation for the development of efficient treatment methods focused on energy and resource recovery. The TG-FTIR-MS technique and the modified Coast Redfern model were used to evaluate thermal behaviour, gas emissions, and decomposition during the pyrolysis and combustion processes of LSG, both individually and in blends. The study demonstrates that blended component pyrolysis attains a conversion efficiency of up to 85 %, in contrast to 65 % for individual components. This indicates a synergistic effect that implies catalytic actions, which notably improve the decomposition process and decrease pollutants such as sulphur, fluorine, nitrogen compounds, and hazardous halogens that may generate dioxins and furans during combustion. Analysis indicated that the activation energy necessary for the pyrolysis of individual LSG components exhibited significant variation, with values ranging from 7.6 to 217.3 kJ/mol. The blended components demonstrated an activation energy range of 20–178.5 kJ/mol for pyrolysis and 14.1–167.7 kJ/mol for combustion. This study suggests that pyrolysis of blended LSG components is preferable to combustion, as it offers greater efficiency and reduced pollutant emissions, despite combustion's notable energy yield and volume reduction. Our research indicates significant advancements in conversion efficiency and pollutant reduction, prompting a strong recommendation for pyrolysis as the optimal method for LSG treatment. This method demonstrates a balance between resource recovery and environmental responsibility.

Peptides inhibiting the assembly of monomeric human l-lactate dehydrogenase into catalytically active homotetramer decrease the synthesis of lactate in cultured cells.

The energetic metabolism of cancer cells relies on a substantial commitment of pyruvate to the catalytic action of lactate-generating dehydrogenases. This coupling mainly depends on lactate dehydrogenase A (LDH-A), which is overexpressed in different types of cancers, and therefore represents an appealing therapeutic target. Taking into account that the activity of LDHs is exclusively exerted by their tetrameric forms, it was recently shown that peptides perturbing the monomers-to-tetramer assembly inhibit human LDH-A (hLDH-A). However, to identify these peptides, tetrameric hLDH-A was transiently exposed to strongly acidic conditions inducing its dissociation into monomers, which were tested as a target for peptides at low pH. Nevertheless, the availability of native monomeric hLDH-A would allow performing similar screenings under physiological conditions. Here we report on the unprecedented isolation of recombinant monomeric hLDH-A at neutral pH, and on its use to identify peptides inhibiting the assembly of the tetrameric enzyme. Remarkably, the GQNGISDL octapeptide, mimicking the 296-303 portion of hLDH-A C-terminal region, was observed to effectively inhibit the target enzyme. Moreover, by dissecting the action of this octapeptide, the cGQND cyclic tetrapeptide was found to act as the parental compound. Furthermore, we performed assays using MCF7 and BxPC3 cultured cells, exclusively expressing hLDH-A and hLDH-B, respectively. By means of these assays we detected a selective action of linear and cyclic GQND tetrapeptides, inhibiting lactate secretion in MCF7 cells only. Overall, our observations suggest that peptides mimicking the C-terminal region of hLDH-A effectively interfere with protein-protein interactions responsible for the assembly of the tetrameric enzyme.

Research on the modification of magnesium hydride by two-dimensional layered Mo2Ti2C3 MXene

One of the most important technologies for the sustainable development of energy in the future is solid-state hydrogen storage. This study employed etching methods to fabricate two-dimensional layered catalyst Mo2Ti2C3 MXene, which was compared with unetched MAX phases Mo2Ti2AlC3 and Ti3C2, as well as Mo2C. Through mechanical ball milling, these materials were mixed with MgH2 to prepare composite materials, including MgH2 + Ti2C3, MgH2 + Mo2C, MgH2 + Mo2Ti2AlC3, and MgH2 + Mo2Ti2C3. According to the study, Mo2Ti2C3 demonstrates the synergistic catalytic actions of Ti and Mo in contrast to Ti2C3 and Mo2C. The composite material MgH2 + Mo2Ti2C3 lowers the initial dehydrogenation temperature of MgH2 to 180 °C, which is 165 °C lower than pure MgH2. After 30 min at 250 °C, the dehydrogenation amount is approximately 5.85 wt%. Hydrogen absorption begins at 40 °C and reaches approximately 5.75 wt% at 150 °C. Additionally, it maintains a reversible hydrogen storage capacity of up to 96 % even after 20th cycles at 300 °C. This is because Mo2Ti2C3 has one less layer of Al than Mo2Ti2AlC3, which results in a wider interlayer spacing, more active sites for MgH2, and facilitates hydrogen molecule dissociation and recombination.

Effect of Electric Fields on the Decomposition of Phosphate Esters.

Phosphate esters decompose on metal surfaces and form protective polyphosphate films. For many applications, such as in lubricants for electric vehicles and wind turbines, an understanding of the effect of electric fields on molecular decomposition is urgently required. Experimental investigations have yielded contradictory results, with some suggesting that electric fields improve tribological performance, while others have reported the opposite effect. Here, we use nonequilibrium molecular dynamics (NEMD) simulations to study the decomposition of tri-n-butyl phosphate (TNBP) molecules nanoconfined between ferrous surfaces (iron and iron oxide) under electrostatic fields. The reactive force field (ReaxFF) method is used to model the effects of chemical bonding and molecular dissociation. We show that the charge transfer with the polarization current equalization (QTPIE) method gives more realistic behavior compared to the standard charge equilibration (QEq) method under applied electrostatic fields. The rate of TNBP decomposition via carbon-oxygen bond dissociation is faster in the nanoconfined systems than that in the bulk due to the catalytic action of the surfaces. In all cases, the application of an electric field accelerates TNBP decomposition. When electric fields are applied to the confined systems, the phosphate anions are pulled toward the surface with high electric potential, while the alkyl cations are pulled to the surface with lower potential, leading to asymmetric film growth. Analysis of the temperature- and electric field strength-dependent dissociation rate constants using the Arrhenius equation suggests that, on reactive iron surfaces, the increased reactivity under an applied electric field is driven mostly by an increase in the pre-exponential factor, which is linked to the number of molecule-surface collisions. Conversely, the accelerated decomposition of TNBP on iron oxide surfaces can be attributed to a reduction in the activation energy with increasing electric field strength. Single-molecule nudged-elastic band (NEB) calculations also show a linear reduction in the energy barrier for carbon-oxygen bond breaking with electric field strength, due to stabilization of the charged transition state. The simulation results are consistent with experimental observations of enhanced and asymmetric tribofilm growth under electrostatic fields.

Binding Modalities and Phase-Specific Regulation of Cyclin/Cyclin-Dependent Kinase Complexes in the Cell Cycle.

Cyclin-dependent kinases (CDKs) are activated upon cyclin-binding to enable progression through the cell cycle. Dominant CDKs and cyclins in mammalian cells include CDK1, CDK2, CDK4, and CDK6 and corresponding cyclins A, B, D, and E. While only certain, "typical" cyclin/CDK complexes are primarily responsible for cell cycle progression, "atypical" cyclin/CDK complexes can form and sometimes perform the same roles as typical complexes. We asked what structural features of cyclins and CDKs favor the formation of typical complexes, a vital yet not fully explored question. We use computational docking and biophysical analyses to exhaustively evaluate the structure and stability of all CDK and cyclin complexes listed above. We find that binding of the complexes is generally stronger for typical than for atypical complexes, especially when the CDK is in an active conformation. Typical complexes have denser clusters, indicating that they have more defined cyclin-binding sites than atypical complexes. Our results help explain three notable features of cyclin/CDK function in the cell cycle: (i) why CDK4 and cyclin-D have exceptionally high specificity for each other; (ii) why both cyclin-A and cyclin-B strongly activate CDK1, whereas CDK2 is only strongly activated by cyclin-A; and (iii) why cyclin-E normally activates CDK2 but not CDK1. Overall, this work reveals the binding modalities of cyclin/CDK complexes, how the modalities lead to the preference for typical complexes versus atypical complexes, and how binding modalities differ between typical complexes. Our observations suggest targeting CDK catalytic actions through destabilizing their native differential cyclin interfaces.

Catalytic Effect of Titanium Ions on the Cathodic Reduction of Selenium (VI), Copper (II), Uranium (VI) Ions and Other Metals in an Aqueous Solutions

It is known that catalytic processes are widely applied in the field of organic chemistry; however they also play a significant role in inorganic chemistry. Nonetheless, numerous unresolved issues persist in the technology of inorganic substances and the extraction of metals and nonmetals in their elemental states. This publication aims to consolidate the results of our pioneering research utilizing the redox Ti (IV)–Ti (III) system, which demonstrates a catalytic action on the cathodic reduction of selenium (VI), copper (II), platinum (IV), palladium (IV), bismuth, arsenic (V) ions, uranium (VI), as well as manganese dioxide suspension. It has been demonstrated that in the presence of the redox Ti (IV)–Ti (III) system, hard-to-reduce selenate ions can be reduced at room temperature. The catalytic action of the redox Ti (IV)–Ti (III) system has been reliably demonstrated, and the reaction mechanism has been established. In the electrochemical production of metal powders (Cu, Pt, Pd, Bi) at cathode current densities exceeding the limiting value, a portion of the current is irreversibly lost to the discharge of hydrogen ions. Consequently, the current efficiency (CE) for powder production does not exceed 80 %. We have established that in the presence of titanium (IV) ions, due to their catalytic action, the CE increases by more than 15 %. It has also been shown that during the cathodic polarization of hexavalent uranium its reduction to uranium (IV) in the presence of the catalyst increases by more than 50 %. The reduction of hard-to-reduce arsenate ions in the presence of titanium (IV) ions proceeds with high CE to the active trivalent state, and further reduction can proceed electrochemically. The cathodic reduction of a manganese dioxide suspension was investigated. In the presence of a catalyst — titanium (IV) ions, manganese in this dioxide is reduced to the divalent state with a current efficiency exceeding 90 %.

Synthesis and properties of oligopropylamines with photosensitive o-nitrobenzyl ester core

The o-nitrobenzyl ester group is known for more than 50 years as a convenient protecting group and fragment for the design of photosensitive systems, including drug delivery agents. Polymeric amines with these groups are promising systems for medical applications, but the lack of basic knowledge about the possible degradation of these compounds under physiological conditions restrains the development of real preparations. We synthesized five new polyamines with the insertion of the o-nitrobenzyl ester group into the chain, including an oligomeric mixture with a weight average number of amine groups equal to 21. The ester group in the polyamine chain was found to be sensitive to hydrolysis at neutral and alkaline pH values. The presence of an amine group near the ester group facilitates hydrolysis through coordination with a hydroxyl ion or water molecule. The catalytic action of the amine moieties is prevented by protonation of the amine at low pH values or by interaction with polymeric acid. The study of photodegradation of new polyamines by HPLC-MS showed the formation of a number of products, most of which were not considered in previous works with o-nitrobenzyl ester derivatives. The o-nitrobenzyl ester group is used in the design of gene delivery systems and other biomedical preparations as a fragment that can be degraded by light. Our results indicate that photodegradation of o-nitrobenzyl esters can produce a number of compounds whose structure and safety for living organisms must be evaluated before use. On the other hand, the discovered hydrolyzability of o-nitrobenzyl esters catalyzed by a neighboring amine group may find application in the development of drug delivery systems. We have shown that the lifetime of o-nitrobenzyl ester containing polyamines is sufficient for gene delivery. Self-degradation of the delivery agent after penetration into a living cell is a desirable case for the release of the delivered agent.

Escherichia coli alcohol dehydrogenase YahK is a protein that binds both iron and zinc.

Previous studies have highlighted the catalytic activity of Escherichia coli alcohol dehydrogenase YahK in the presence of coenzyme nicotinamide adenine dinucleotide (NAD) and metal zinc. Notably, competitive interaction between iron and zinc ligands has been shown to influence the catalytic efficiency of several key proteases. This study aims to unravel the intricate mechanisms underlying YahK's catalytic action, with a particular focus on the pivotal roles played by metal ions zinc and iron. The purified YahK protein from E. coli cells cultivated in LB medium was utilized to investigate its metal-binding properties through UV-visible absorption measurements and determination of metal content. Subsequently, the effects of excess zinc and iron on the metal-binding ability and alcohol dehydrogenase activity of the YahK protein were explored using M9 minimal medium. Furthermore, site-directed mutagenesis technology was employed to determine the iron-binding site location within the YahK protein. Polyacrylamide gel electrophoresis was conducted to examine the relationship between iron and zinc with respect to the YahK protein. The study confirmed the presence of iron and zinc in the YahK protein, with the zinc-bound form exhibiting enhanced catalytic activity in alcohol dehydrogenation reactions. Conversely, the presence of iron appears to play a pivotal role in maintaining overall stability of the YahK protein. Furthermore, experimental findings indicate that excessive zinc within M9 minimal medium can competitively bind to iron-binding sites on YahK, thereby augmenting its alcohol dehydrogenase activity. The dynamic binding of YahK to iron and zinc unveils its intricate regulatory mechanism as an alcohol dehydrogenase, thereby highlighting the possible physiological role of YahK in E. coli and its significance in governing cellular metabolic processes. This discovery provides a novel perspective for further investigating the specific impact of metal ion binding on YahK and E. coli cell metabolism.

Study on Attenuation Mechanism and Durability Improvement of Platinum-Carbon Catalysts for Proton Exchange Membrane Fuel Cells

The relationship between Pt particle size and activity and durability of Pt/C electrocatalysts on rotating disk electrodes is established and the results show that Pt/C electrocatalysts with particle size over 3.5 nm have excellent resistance to Pt particle decay and carbon corrosion. Further, the research results on the mechanism of Pt particle decay and carbon corrosion show that the Pt particle attenuation is composed of 80% Ostwald ripening and 20% particle agglomeration, and the carbon corrosion is affected by the catalytic action of Pt particles. Therefore, the above results show that regulating the Pt particle size to 3.5–4.0 nm can improve the durability of Pt/C electrocatalysts on RDE. To verify the accuracy of this conclusion and determine the optimal particle size range in practical application, single cells with 5 × 5 cm2 is assembled to evaluate the performance and durability of cathode Pt/C electrocatalysts under H2/air. The results show that cathode Pt/C electrocatalysts with particle size between 3.5 nm and 3.8 nm have high single cell performance (2.3 A cm−2@0.65 V) and durability (A loss of 15 mV@0.8 A cm−2 after 30000 cycles). These findings reveal the attenuation mechanism of Pt/C electrocatalysts and provide ideas for the development of high-durability Pt-based electrocatalysts for practical applications.

Role of oxidants in the anodic oxidation of 2024 aluminum alloy by dominating anodic and cathodic processes

The addition of oxidants into the electrolyte of Al anodic oxidation can alter the anodic and cathodic reactions, further affects the quality of the oxide film. In this paper, the role of two typical oxidants of H2O2 and Na2MoO4 in the microstructure and corrosion resistance of the oxide film on 2024 aluminum alloy was investigated by the scanning electron microscopy (SEM), Mott Schottky plots and electrochemical impedance spectroscopy (EIS). The addition of H2O2 increases the oxygen evolution amount on the anode Al and more oxygen can participate in the oxide film formation to improve the compactness. The addition of Na2MoO4 results in the deposit of MoO2 on the cathode plate to accelerate the hydrogen evolution reaction by the catalytic action of the MoO2, which further accelerates the anodic reaction to form a thick oxide film. As a result, the corrosion resistance of the oxide film is significantly improved by adding H2O2 or Na2MoO4 due to the promotion of film thickness and compactness.

Effect of Ionizing Radiation on the Activity of the Enzyme Invertase Studied by Polarimetry

The effect of ionizing radiation on biological systems, and particularly the enzymes which are responsible for most cellular functions, leads to chemical alterations in their molecular structure, and as a subsequent result often causes inhibition of their activities. Of particular importance for understanding the molecular and kinetic mechanisms of action of ionizing radiation on these systems is to find suitable experimental protocols and kinetic models applicable to specific enzymes and their substrates. In the present study we offer a convenient experimental approach by applying polarimetric measurements to study the influence of ionizing radiation on the catalytic action of the enzyme invertase. Following the Michaelis- Menten kinetic model we determined the values of the kinetic constants Km и Vmax for the reactions catalyzed either by the native or irradiated invertase and made some conclusions about possible changes either in the active centre or in the molecular structure of the enzyme under the action of ionizing radiation.