Important Reactions Research Articles

Unraveling FeOx Nanoparticles Confined on Fibrous Mesoporous Silica Catalyst Construction and CO Catalytic Oxidation Performance

Catalytic oxidation is used to control carbon monoxide (CO) emissions from industrial exhaust. In this study, a mesoporous silica material, KCC-1, was synthesized and used as a carrier with a high specific surface area to confine active component FeOx nanoparticles (NPs), and the CO catalytic oxidation performance of x%Fe@KCC-1 catalysts (x represents the mass loading of Fe) was studied. The experimental results showed that due to its large specific surface area and abundant mesopores, the FeOx NPs were highly dispersed on the surface of the KCC-1 carrier. The particle size of FeOx was very small, resulting in strong interactions between FeOx NPs and KCC-1, which enhanced the catalytic oxidation reaction on the catalyst. The FeOx loading improved the CO adsorption capability of the catalyst, which facilitated the catalytic oxidation of CO, with the 7%Fe@KCC-1 catalyst achieving 100% CO conversion at 160 °C. The CO catalytic removal mechanism was investigated by a combination of in-situ DRIFTS and DFT calculations. This study advances scientific understanding of the application potential of nano-catalysts in important oxidation reactions and provides valuable insights into the development of efficient CO oxidation catalysts.

The sweat rate as a digital biomarker in clinical medicine beyond sports science

Sweating is an important physiological reaction and a clinical symptom in a variety of diseases. However, it remains underrated in clinical use. Gold standards to measure the sweat rate are neither continuous nor easily or lab-independently applicable. With the emergence of novel wearable devices, using the sweat rate as a digital biomarker shows promise for clinical monitoring and diagnostics. In this Commentary, we discuss the potential and importance of the sweat rate as a digital biomarker in clinical medicine beyond sports science.

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2− and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Cooperative Triple Catalysis Enables Deaminative α-Indolmethylation of Carbonyl Compounds with Gramines.

α-Functionalization of carbonyl compounds is an important reaction in synthetic chemistry. However, the development of novel synthetic strategies to realize this reaction is challenging. This study describes the α-indolmethylation of carbonyl compounds using cooperative copper, amine, and hydrogen-bond catalysis. This reaction provides a novel and efficient strategy for developing indolmethylated carbonyl compounds by deaminative coupling of gramines.

L-proline-based deep eutectic solvents as green and enantioselective organocatalyst/media for aldol reaction

The use of chiral deep eutectic solvents (DESs) based on the natural amino acid L-proline and various glycols presents an environmentally friendly approach for important CC bond formation reactions. These DESs serve as both organocatalysts and reaction media in the aldol reaction, reducing the need for additional toxic or hazardous chemicals. By employing these DESs, we were able to activate the desired reaction through the condensation of ketones and L-proline via enamine activation. This approach eliminates the requirement for traditional, often environmentally harmful, organic solvents. Notably, diethylene glycol played a crucial role in modulating the reaction performance, including conversion and enantioselectivity. Diethylene glycol is a relatively safer alternative compared to other commonly used solvents or additives with potential environmental and health risks. Moreover, reducing the L-proline content in the DESs led to a slight increase in the enantiomeric excess of the predominant diastereomeric product. This finding suggests the possibility of minimizing the use of L-proline, which can be advantageous from both cost and environmental perspectives.The results of these reactions demonstrate promising green outcomes, with a diastereomeric ratio up to 25:1 for the major anti-isomer, showcasing excellent selectivity (>90 % ee). In addition to these high enantiomeric excess values, quantitative yields in the aldol reaction highlight the potential for high efficiency and reduced waste production.Overall, the utilization of chiral DESs based on L-proline and glycols offers a greener alternative for enantioselective organocatalytic reactions. This approach minimizes the use of hazardous catalysts, reduces waste generation, and demonstrates impressive selectivity, paving the way for more sustainable synthetic methodologies.

The Relevance of the Interfacial Water Reactivity for Electrochemical CO Reduction on Copper Single Crystals.

The electrochemical reduction of CO2 is an important electrolysis reaction that enables the conversion of a waste gas to fuels or value-added chemicals. To make this reaction viable, a profound understanding of central intermediate steps, such as the CO electroreduction, is required. On Cu, the CO reduction reaction (CORR) is intimately linked to the hydrogen evolution reaction (HER) that proceeds via the reduction of water in alkaline or neutral electrolytes. Here, we demonstrate that the interaction of water or more specifically the water reduction kinetics on differently smooth Cu(100) and Cu(111) surfaces during the CORR in alkaline media significantly governs the CORR. On Cu(111), faster HER kinetics and the highest CORR activity are observed, even though HER and CORR onsets are more negative. While on Cu(100) small Cu ad-island clusters form in the cathodic potential range only when CO is present, structural changes appear on a larger length scale on Cu(111) both under CORR conditions and when no CO is present. These differences in the reconstruction characteristics may be attributed to the dominance of either the CORR and its intermediates or the HER on the different Cu surfaces. Therefore, the interfacial water reactivity is considered an essential activity descriptor for the CORR on Cu in alkaline media.

A numerical study of NOX and soot emissions in ethylene-ammonia diffusion flames with oxygen enrichment

Blending ammonia with hydrocarbon fuels is gaining interest due to its potential to significantly reduce carbon emissions from the combustion of these blends. Additionally, studies have provided strong evidence of oxygen enhanced combustion to reduce soot emissions and improve flame stability. The present work attempts to leverage the benefits of both strategies, ammonia doping and oxygen enhanced combustion, by considering ethylene diffusion flames. Simulations are performed using the CHEMKIN-Pro software. A reaction mechanism with 372 species and 13,847 reactions is developed by combining gas phase chemistries for ethylene, NH3 and NOX, along with a detailed soot mode. The mechanism is extensively validated for a range of fuel blends in terms of flame structure, intermediate hydrocarbons, soot precursors and soot. Oxygen enrichment is achieved by removing certain amount of nitrogen from oxidizer stream and adding it to fuel stream, and thereby maintaining a nearly constant flame temperature. Extensive analysis is carried out to characterize the chemical and dilution effects of ammonia doping on flame structure, soot precursors, soot, and NOX in ethylene flames with varying levels of oxygenation. Further, dominant reaction pathways for several soot precursors and NOx are identified through detailed rate of production analyses. Results indicate that ammonia doping in ethylene flames leads to substantial increase in NOX emissions, while oxygenation has negligible influence on NOX emissions. In contrast, both NH3 doping and oxygenation provide significant reduction in the formation of soot precursors and soot. Oxygenation achieves this reduction through both hydrodynamic and flame structure effects, as the flame shifts from oxidizer side to fuel side. On the other hand, NH3 doping reduces the rates of important reactions for the formation of soot precursors, as the concentrations of relevant species (C2H2, C3H3, C3H3-P, C3H3-A etc.) decrease due to their consumption through reactions with species like NCO and CN formed from NH3. Moreover, the effectiveness of NH3 doping is further enhanced when combined with oxygenation. Hence, NH3 doping and oxygenation are found to be effective and synergistic strategies in reducing soot emissions, and their proper combination could provide near zero soot emissions.

Experimental study on the preparation of monodisperse nano-silver by hydrothermal synthesis

As a new material with wide application prospect, nano-silver is getting high attention. Hydrothermal synthesis has the advantages of green, easy operation and low cost, and is a promising technology for the preparation of nano-silver. In this paper, the effects of reaction time, reaction temperature, precursor concentration, PVP concentration and modifier addition on the particle size distribution and surface morphology of nano-silver during the subcritical hydrothermal reaction were optimized by comparing the supercritical and subcritical hydrothermal methods. Then, the important role and reaction mechanism of PVP as a modifier and the formation mechanism of spherical nano-silver particles were analyzed. The experimental results showed that the average particle size of 23.68 nm can be obtained by using NaHCO3 and PVP as reducing and dispersing agents, the reaction time is 5 h, the reaction temperature is 180 °C, and the concentrations of AgNO3 and PVP are 0.1 M and 0.3 M, respectively, to obtain the more uniformly dispersed silver nanoparticles. The results provide an important reference for future research on the preparation of conductive pastes.

Hydrogen Storage System Attained by HCOOH-CO2 Couple: Recent Developments in Pd-Based Carbon-Supported Heterogeneous Catalysts

The present review revisits representative studies addressing the development of efficient Pd-based carbon-supported heterogeneous catalysts for two important reactions, namely, the production of hydrogen from formic acid and the hydrogenation of carbon dioxide into formic acid. The HCOOH-CO2 system is considered a promising couple for a hydrogen storage system involving an ideal carbon-neutral cycle. Significant advancements have been achieved in the catalysts designed to catalyze the dehydrogenation of formic acid under mild reaction conditions, while much effort is still needed to catalyze the challenging CO2 hydrogenation reaction. The design of Pd-based carbon-supported heterogeneous catalysts for these reactions encompasses both the modulation of the properties of the active phase (particle size, composition, and electronic properties) and the modification of the supports by means of the incorporation of nitrogen functional groups. These approaches are herein summarized to provide a compilation of the strategies followed in recent studies and to set the basis for a hydrogen storage system attained using the HCOOH-CO2 couple.

Characterization of Dominant Hydrogeochemical Processes in Groundwater in Onitsha Area, Southeastern Nigeria

The characterization of the dominant hydrogeochemical processes in groundwater in Onitsha area, southeastern Nigeria was carried out. This is to identify the dominant mechanisms responsible for the evolution and the chemical composition of the water sources. A total of fifteen (15) groundwater samples were collected from different locations in the study area in August 2022 and these samples were subjected to chemical analysis using standard methods. The results indicated that the water quality parameters were within the World Health Organization acceptable limits for drinking quality although turbidity in six of the samples exceeded the guideline values. The hydrochemical facies were determined using various plots. Piper diagrams indicated that Ca2+ - Mg2+ - Cl- – SO42- was the dominant facies with Ca2+ and Cl- as the dominant ions. The Durov diagram indicate recharge water in limestone and sandstone aquifers and influenced by important ion exchange reactions. However, the Gibbs plots mainly plotted in the rock dominance zone indicating that the major processes controlling water chemistry in the study area were water-rock interaction and dissolution of rock minerals. The ionic ratio plots were employed to determine the mechanisms and reactions prevalent in the study area that influenced the water chemistry. Na/Cl plot indicated that the excess of Cl- over Na+ was balanced by Ca2+ and Mg2+ while the depletion of Na+ with respect to Clindicated ion exchange reaction which could be attributed to silicate weathering confirming the Na/Cl plot conclusions. The relative abundance of anionic facies shows that Cl- + SO42- were more abundant than HCO3- and the plot of Ca2+ + Mg2+ ions against HCO3- ions depict samples with excess Ca2+ + Mg2+. However, Ca2+ +Mg/HCO3 ratio was less than one (<1) and indicated fresh recharge water.

Development of supported intermetallic compounds: advancing the Frontiers of heterogeneous catalysis.

Intermetallic compound (IMC) catalysts have garnered significant attention due to their unique surface and electronic properties, which can lead to enhanced catalytic performance compared to traditional monometallic catalysts. However, developing IMC materials as high-performance catalysts has been hindered by the inherent complexity of synthesizing nanoparticles with well-defined bulk and surface compositions. Achieving precise control over the composition of supported bimetallic IMC catalysts, especially those with high surface area and stability, has proven challenging. This review provides a comprehensive overview of the recent progress in developing supported IMC catalysts. We first examine the various synthetic approaches that have been explored to prepare supported IMC nanoparticles with phase-pure bulk structures and tailored surface compositions. Key factors influencing the formation kinetics and compositional control of these materials are discussed in detail. Then the strategies for manipulating the surface composition of supported IMCs are delved into. Applications of high-performance supported IMCs in important reactions such as selective hydrogenation, reforming, dehydrogenation, and deoxygenation are comprehensively reviewed, showcasing the unique advantages offered by these materials. Finally, the prevailing research challenges associated with supported IMCs are identified, including the need for a better understanding of the composition-property relationships and the development of scalable synthesis methods. The prospects for the practical implementation of these versatile catalysts in industrial processes are also highlighted, underscoring the importance of continued research in this field.

Unlocking the secrets of porous silicon formation: insights into magnesiothermic reduction mechanism using in situ powder X-ray diffraction studies.

The magnesiothermic reduction of SiO2 is an important reaction as it is a bulk method that produces porous Si for a wide range of applications directly from SiO2. While its main advantage is potential tunability, the reaction behavior and final product properties are heavily dependent on many parameters including feedstock type. However, a complete understanding of the reaction pathway has not yet been achieved. Here, using in situ X-ray diffraction analysis, for the first time, various pathways through which the magnesiothermic reduction reaction proceeds were mapped. Further, the key parameters and conditions that determine which pathways are favored were determined. It was discovered that the reaction onset temperatures can be as low as 348 ± 7 °C, which is significantly lower when compared to previously reported values. The onset temperature is dependent on the size of Mg particles used in the reaction. Further, Mg2Si was identified as a key intermediate rather than a reaction byproduct during the reduction process. Its rate of consumption is determined by the reaction temperature which needs to be >561 °C. These findings can enable process and product optimization of the magnesiothermic reduction process to manufacture and tune porous Si for a range of applications.

The Prothrombin-Prothrombinase Interaction.

The hemostatic response to vascular injury entails a sequence of proteolytic events where several inactive zymogens of the trypsin family are converted to active proteases. The cascade starts with exposure of tissue factor from the damaged endothelium and culminates with conversion of prothrombin to thrombin in a reaction catalyzed by the prothrombinase complex composed of the enzyme factor Xa, cofactor Va, Ca2+, and phospholipids. This cofactor-dependent activation is paradigmatic of analogous reactions of the blood coagulation and complement cascades, which makes elucidation of its molecular mechanism of broad significance to the large class of trypsin-like zymogens to which prothrombin belongs. Because of its relevance as the most important reaction in the physiological response to vascular injury, as well as the main trigger of pathological thrombotic complications, the mechanism of prothrombin activation has been studied extensively. However, a molecular interpretation of this mechanism has become available only recently from important developments in structural biology. Here we review current knowledge on the prothrombin-prothrombinase interaction and outline future directions for the study of this key reaction of the coagulation cascade.

Spin-polarized p-block antimony/bismuth single-atom catalysts on defect-free rutile TiO2(110) substrate for highly efficient CO oxidation.

Developing high-loading spin-polarized p-block-element-based single-atom catalysts (p-SACs) upon defect-free substrates for various chemical reactions wherein spin selection matters is generally considered a formidable challenge because of the difficulty of creating high densities of underpinning stable defects and the delocalized electronic features of p-block elements. Here our first-principles calculations establish that the defect-free rutile TiO2(110) wide-bandgap semiconducting anchoring support can stabilize and localize the wavefunctions of p-block metal elements (Sb and Bi) via strong ionic bonding, forming spin-polarized p-SACs. Cooperated by the underlying d-block Ti atoms via a delicate spin donation-back-donation mechanism, the p-block single-atom reactive center Sb(Bi) exhibits excellent catalysis for spin-triplet O2 activation and CO oxidation in alignment with Wigner's spin selection rule, with a low rate-limiting reaction barrier of ∼0.6 eV. This work is crucial in establishing high-loading reactive centers of high-performance p-SACs for various important physical processes and chemical reactions, especially wherein the spin degree of freedom matters, i.e., spin catalysis.

Anomalous proton transfer of a photoacid HPTS in nonaqueous reverse micelles.

The proton transfer reaction is one of the fundamental chemical reactions where the reaction dynamics strongly depend on solvent properties such as acidity or basicity. A photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) shows a sharp decrease of pKa (7.7 → 0.5) upon photoexcitation, and the excited-state proton transfer (ESPT) occurs with ultrafast time constants of 2.5 and 89 ps in bulk aqueous solution. However, the two-step proton transfers via the contact ion pair formation and the proton diffusion are strongly limited inside the nanopools of reverse micelles (RMs). The confinement in small RMs strongly impeded the proton transfer reactions. In this work, we report the ESPT of HPTS confined in methanol-in-oil RMs by steady-state and time-resolved electronic spectroscopy. Interestingly, HPTS shows substantial deprotonation in the excited state only in small RMs, while the ESPT of HPTS does not occur in bulk methanol solution due to the low basicity of aliphatic alcohols. The kinetic analysis of time-resolved fluorescence and transient absorption measurements will compare the proton transfer dynamics of HPTS in the water-in-oil and methanol-in-oil RMs. The ESPT of photoacids, especially in the nonaqueous RMs, can be crucial in understanding many important chemical reactions involving proton transfer in the confined environments of cells and membranes.

Calculation of astrophysical reaction rate and uncertainty for T(d,n)4He using Bayesian statistical approach

Abstract One of the best methods to investigate and calculate a desired quantity using available limited data is the Bayesian statistical method, which has been recently entered the field of nuclear astrophysics and can be used to evaluate the astrophysical S-factors, the cross sections and, as a result, the nuclear reaction rates of Big Bang Nucleosynthesis. This study tries to calculate the astrophysical S-factor and the rate of reaction T(d,n)4He as an important astrophysical reaction with the help of this method in energies lower that electron repulsive barrier, and for this purpose, it uses the R-Software, which leads to improved results in comparison with the non-Bayesian methods for the mentioned reaction rate.

Theoretical study on hydroformylation catalyzed by cationic cobalt(II) complexes.

Hydroformylation is one of the most important homogeneous reactions in industrial production. Herein, a density functional theory (DFT) method was employed to investigate two proposed reaction mechanisms of hydroformylation catalyzed by cationic cobalt(II) complexes, the carbonyl dissociative mechanism and the associative mechanism. The calculated results showed that the heterolytic H2 activation is the rate-determining step for both the dissociative mechanism and the associative mechanism, with energy barriers of 26.8 kcal mol-1 and 40.5 kcal mol-1, respectively. Meanwhile, the regioselectivity, the spin multiplicity of the catalyst and the substituent effects on the reaction were also investigated. The most stable cobalt(II) catalyst has a doublet state and the linear aldehyde is the dominant product. In addition, it was found that the energy barrier of the reaction decreased when the electron density of the Co center of the catalyst was increased by changing the ligand. The catalytic activity of the catalyst was proposed to be the best when the PEt2 group of the ligand is replaced by the P(tBu)2 group. This study might not only provide new insights for hydroformylation catalyzed by cobalt but also facilitate theory-guided design of novel transition metal catalysts for hydroformylation.

A comparative study of two aldehyde dehydrogenases from Sphingobium sp.: the substrate spectrum and catalytic mechanism.

Biocatalytic oxidation is one of the most important and indispensable organic reactions for the development of green and sustainable biomanufacturing processes. NAD(P)+-dependent aldehyde dehydrogenase (ALDH) catalyzes the oxidation of aldehydes to carboxylic acids. Here, two ALDHs, SpALDH1 and SpALDH2, were identified from Sphingobium sp. SYK-6. They belong to different ALDH families and share only 32.30% amino acid identity. Interestingly, SpALDH1 and SpALDH2 exhibit significantly different enzymatic properties and substrate profiles. SpALDH2 has better thermostability than SpALDH1. SpALDH1 is a metalloenzyme and is activated by potassium ions, while SpALDH2 is not metallic-dependent. Compared with SpALDH1, SpALDH2 has a relatively broad substrate spectrum toward aromatic aldehydes. Based on homology modeling and molecular docking analysis, mechanisms underlying the substrate specificity of ALDHs were elucidated. For both ALDHs, hydrophobicity of substrate binding pockets is important for the catalytic properties, especially substrate specificity. Notably, optimization of the flexible loop 444-457 reforms a hydrogen bond between pyridine substrates and SpALDH1, contributing to the high catalytic activity. Finally, a coupling reaction catalyzed by ALDHs and NOX was constructed for efficient production of aromatic carboxylic acids.

Обзор спектрофлуориметрических исследований кожных покровов

Background. Nicotinamide adenine dinucleotide (NADN) is involved in many important biochemical reactions in human metabolism, including participation in mitochondrial energy production. Mitochondrial activity, which affects skin microcirculation and the efficiency of local blood supply, can be indirectly assessed by the fluorescence of NADH in its reduced form. Changes in major skin fluorophores have been studied in both animals and humans, at rest and under different conditions, using spectrofluorimetry. The purpose of the work is, based on scientific literature data, to evaluate the possibility of using a spectrofluorimetric study of NADH levels, as well as the NADH/FAD ratio when assessing the condition of both free skin flaps and pedicled flaps after reconstructive operations, in particular in ophthalmology. Materials and methods. A search of scientific publications in PubMed, Google Scolar and Elibrary was conducted, as a result 61 articles for the period of 1957-2022 were selected for the final scientific review. Results and discussion. A brief historical background of the first spectrofluorimetric studies is presented. A brief overview of spectrofluorimetric methods for studying the skin of both humans and experimental animals, as well as other organs and systems, is given. The disadvantages and advantages of various research methods are listed. A review of changes in spectrofluorimetric parameters of the skin in patients with various somatic diseases of organs and systems was carried out. Conclusion. A review of the abovementioned methods for assessing tissue metabolism is applicable in surgical treatment, plastic surgery and onco-ophthalmology. Of particular value for surgery will be research methods that make it possible to predict the likelihood of rejection of transplanted skin flaps and their cicatricial changes. The presented literature review confirms the effectiveness of spectrofluorimetry for assessing metabolic disorders in the skin. The relevance of the method for predicting cosmetic outcomes during plastic surgery, including on the adnexal apparatus of the eye, requires continued research into the main fluorophores of the skin.

Effects of radiative heat loss on extinction limits of counterflow premixed ammonia-air flames

The effect of radiative heat loss on counterflow premixed ammonia-air flames has been investigated as a function of equivalence ratio and system pressure. Non-adiabatic counterflow premixed flame simulations incorporating detailed chemistry, transport, and radiative heat transfer in the optically thin limit have been employed to elucidate important underlying physics and extinction characteristics. Similar to methane-air flame systems, non-adiabatic counterflow premixed computations show that the combined effects of positive flame stretch, sub-unity Lewis number, and radiative heat loss lead to the extension of the lean flammability limit for ammonia-air flames, revealing a C-shaped curve near the lean flammability limit that exhibits both radiation-induced and stretch-induced extinction states. The computations compare favorably with the experimentally determined extinction stretch rate values for the stretch-induced extinction states over a wide range of equivalence ratios at different pressures up to 5 atm. A novel feature sensitivity analysis has also been developed to highlight important sensitive reactions for the stretch- and radiation-induced extinction states. Furthermore, the controlling chemistry at the dual-extinction states and at varying pressures are compared and discussed.