Mild Oxidation Research Articles

Metal‐Free Nitration of Indazoles with tert‐Butyl Nitrile in Air to Prepare 3‐Nitroindazoles and 3‐Aminoindazoles

Comprehensive SummaryA variety of 3‐nitroindazoles and 3‐aminoindazoles were prepared in good to excellent yields with high regioselectivity through TBN‐mediated nitration at the C3‐position of indazoles under the air conditions and sequential reduction. Mechanistic studies revealed that TBN played crucial roles to produce •NO2 radical source in the presence of air conditions and C3‐nitration of indazoles was initiated by N1‐nitration and sequential migration of NO2 group to C3‐position. Moreover, this method could be easily applied in the gram scalable synthesis of ibuprofen and ciprofibrate‐derived 3‐aminoindazoles. The present method highlights air as mild oxidant, metal‐free radical nitration of indazole, N—N bond formation and cleavage, and late‐stage modification of drugs.

Halide Perovskite Induces Halogen/Hydrogen Atom Transfer (XAT/HAT) for Allylic C−H Amination

AbstractAllylic C−H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C−H activation but furnishes reductive amines, inferring mild oxidants’ inactivity for C−H oxidation but strong oxidants’ detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen‐vacancies of perovskite photocatalyst and exploits halogenated‐solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C−H allyl amination with 19,376 turnovers. CsPbBr3 nanocrystals induce cooperative hydrogen‐atom‐transfer (HAT, C−H oxidation, and halogen‐vacancy CsPbBr3−x formation) and halogen‐atom‐transfer (XAT, CsPbBr3−x‐induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives.

Microstructure and corrosion property evolution of a surface-nanostructured 15–15Ti austenitic steel during immersion in liquid LBE at 550 °C

This study investigated the compatibility of surface-nanostructured 15–15Ti austenitic steel in 550 °C LBE with an oxygen concentration of 5 × 10−7 wt.% for various exposure durations (759, 1638, 2404, and 3012 h). The results demonstrate that the grain size was reduced from 33.50 μm to the nano-scale after shot-peening (SP), achieving 17.62, 15.44, and 14.25 nm under SP pressures of 0.06, 0.15 and 0.25 MPa, respectively. The untreated steel experienced severe oxidation and dissolution corrosion, whereas the surface-nanostructured steel exhibited only mild oxidation and was resistant to dissolution corrosion. The enhanced corrosion resistance of surface-nanostructured steel is attributed to the higher protectiveness of the Cr-rich spinel layer and the less defective Ni-rich layer beneath it. Recrystallization occurred exclusively in the Ni-rich region, while the deformed steel underwent recovery during exposure. The thickness of the recrystallization layer was 2.9 μm at 759 h, increased to 8 μm at 1638 h, and remained stable thereafter. The size of recrystallized grains in SP-samples processed under pressure of 0.06 MPa and 0.15 MPa was approximately 2.92 μm, whereas it was about 1.32 μm for 0.25 MPa processed sample.

Cu12-Methylsilsesquioxane Cage Decorated with Cu(dppe)2 Moieties for Mild Oxidative Functionalization of Alkanes.

We report a high nuclear (Cu14) complex synthesized via the self-assembly of copper-methylsilsesquioxane induced by the complexation with 1,2-bis(diphenylphosphino)ethane (dppe). The structure includes two cationic CuI(dppe)2 moieties and an anionic silsesquioxane cage of an unprecedented CuII12 structural type. The Cu12 cage fragment exhibits a unique (i) combination of Si4-cyclic/Si2-acyclic silsesquioxane ligands and (ii) encapsulation of two different chloride and carbonate species. This complex acts as a promising precatalyst in the mild oxidation and carboxylation of light alkanes to produce alkyl hydroperoxides, alcohols, ketones, or carboxylic acids. The present study widens the family of copper-methylsilsesquioxane clusters with prospective use in oxidation catalysis.

Synthesis of Hetaryl Substituted Pyrazolo[3,4-b]Quinolinone Systems by Multicomponent Cyclocondensation Reaction

In this study, the synthesis of pyrazolo[3,4-b]quinolinone compounds was carried out via one-pot three-component reactions. These reactions proceed as domino processes, making them easier to occur than the conventional multistep organic reactions. By employing this method, new organic molecules can be synthesized in a single step, using minimal time and number of trials. In the first phase of this two-step study, heteroaromatic carbaldehydes (quinoline-8-carboxaldehyde and quinoline-4-carboxaldehyde) were prepared to be used as substrates in subsequent reactions by oxidation of 8-methylquinoline and 4-methylquinoline with selenium dioxide, a mild oxidant. In the second step, heteroaromatic carbaldehyde reacted with aminopyrazole and dimedone in anhydrous ethanol by one-pot multicomponent condensation method to synthesize six new compounds with heteryl-substituted pyrazolo[3,4-b]quinolinone ring system. The crude products were obtained in excellent yields and further purified by crystallization. The structures of the compounds, which were found to be completely pure as a result of chromatographic studies, were elucidated by spectroscopic methods and elemental analysis.

Valence-engineered catalysis-selectivity regulation of molybdenum oxide nanozyme for acute kidney injury therapy and post-cure assessment.

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H2O2-associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H2O2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases.

Steam-Assisted Selective CO2 Hydrogenation to Ethanol over Ru-In Catalysts.

Multicomponent catalysts can be designed to synergistically combine reaction intermediates at interfacial active sites, but restructuring makes systematic control and understanding of such dynamics challenging. We here unveil how reducibility and mobility of indium oxide species in Ru-based catalysts crucially control the direct, selective conversion of CO2 to ethanol. When uncontrolled, reduced indium oxide species occupy the Ru surface, leading to deactivation. With the addition of steam as a mild oxidant and using porous polymer layers to control In mobility, Ru-In2O3 interface sites are stabilized, and ethanol can be produced with superior overall selectivity (70 %, rest CO). Our work highlights how engineering of bifunctional active ensembles enables cooperativity and synergy at tailored interfaces, which unlocks unprecedented performance in heterogeneous catalysts.

Interface and doping engineering of V2C‐MXene‐based electrocatalysts for enhanced electrocatalysis of overall water splitting

AbstractThe restacking and oxidizable nature of vanadium‐based carbon/nitride (V2C‐MXene) poses a significant challenge. Herein, tellurium (Te)‐doped V2C/V2O3 electrocatalyst is constructed via mild H2O2 oxidation and calcination treatments. Especially, this work rationally exploits the inherent easy oxidation characteristic associated with MXene to alter the interfacial information, thereby obtaining stable self‐generated vanadium‐based heterointerfaces. Meanwhile, the microetching effect of H2O2 creates numerous pores to address the restacking issues. Besides, Te element doping settles the issue of awkward levels of absorption/desorption ability of intermediates. The electrocatalyst obtains an unparalleled hydrogen evolution reaction and oxygen evolution reaction with the overpotential of 83.5 and 279.8 mV at −10 and 10 mA cm−2, respectively. In addition, the overall water‐splitting device demonstrates a low cell voltage of 1.41 V to obtain 10 mA cm−2. Overall, the inherent drawbacks of MXene can be turned into benefits based on the planning strategy to create these electrocatalysts with desirable reaction kinetics.

Stereoselective Synthesis of AB‐5,15‐Porphyrinquinone Platinum(II) Complexes

5,15‐Porphyrinquinone is a non‐aromatic and electron‐deficient porphyrinoid that acts as an important framework for the synthesis of porphyrinoid derivatives. Generally, meso‐functionalized A2‐porphyrinquinone is synthesized via the oxidation of A2‐porphyrin. Herein, we present the stereoselective synthesis of AB‐porphyrinquinone Pt(II) complexes using the corresponding dipyrrinato‐Pt complexes and bisformyldipyrrins. The reaction involves cyclization and oxidative aromatization induced by the Pt template, followed by oxidation using a mild MnO2 oxidant.

α,β-Dehydrogenation Adjacent to Sulfur- and Phosphorus- Containing Compounds.

Here, we report a robust nickel-catalyzed α,β-dehydrogenation process designed for substrates that contain electron-withdrawing sulfur and phosphorus groups. Leveraging the formation of organozinc intermediates and the utilization of a mild oxidant, allyl methyl carbonate, this methodology exhibits remarkable efficiency and outstanding diastereoselectivities across a diverse array of substrates, achieving E:Z ratios exceeding 20:1. Investigation through deuterium incorporation studies and an analysis of the reaction sequence leading to the formation of the dehydrogenative allylation side product, provide useful insights into reaction optimization.

Oxidation-Controlled, Strain-Promoted Tellurophene-Alkyne Cycloaddition (OSTAC): A Bioorthogonal Tellurophene-Dependent Conjugation Reaction.

Tellurophene-bearing small molecules have emerged as valuable tools for localizing cellular activities in vivo using mass cytometry. To broaden the utility of tellurophenes in chemical biology, we have developed a bioorthogonal reaction to facilitate tagging of tellurophene-bearing conjugates for downstream applications. Using TePhe, a tellurophene-based phenylalanine analogue, labeled recombinant proteins were generated for reaction development. Using these proteins, we demonstrate an oxidation-controlled, strain-promoted tellurophene-alkyne cycloaddition (OSTAC) reaction. Mild oxidation of the tellurophene ring with N-chlorosuccinimide produces a reactive Te(IV) species which undergoes rapid (k > 100 M-1 s-1) cycloaddition with bicyclo[6.1.0]nonyne (BCN) yielding a benzo-fused cyclooctane. Selective labeling of TePhe-containing proteins can be achieved in complex protein mixtures and on fixed cells. OSTAC reactions can be combined with strain-promoted azide alkyne cycloaddition (SPAAC) and copper-catalyzed azide alkyne click (CuAAC) reactions. Demonstrating the versatility of this approach, we observe the expected staining patterns for 5-ethynyl-2'-deoxyuridine (DNA synthesis-CuAAC) and immunohistochemistry targets in combination with TePhe (protein synthesis-OSTAC) in fixed cells. The favorable properties of the OSTAC reaction suggest its broad applicability in chemical biology.

CO2-mediated oxidative dehydrogenation of propane to propylene and syngas: Reaction and energy performance matrices

The performance of CO2-assisted oxidative dehydrogenation of propane to propylene is investigated. The energy performance matrices are defined as energy efficiency and exergy efficiency at both the reactor level and the overall system level. Oxidants are the main factor that dictates the performance of the dehydrogenation of propane. Oxygen is a strong oxidant which helps in promoting the endothermic dehydrogenation of propane. CO2 is considered a mild oxidant that hinders the over-oxidation of propane. The addition of CO2 promotes propane conversion but sacrifices the other performance matrices including propylene selectivity and the H2/CO ratio of the syngas. Consequently, the energy and exergy efficiencies of the reactor as well as the DHP system decrease with increasing CO2 supply. The addition of O2 has positive impacts on the energy performance matrices at a certain temperature range (from 863 K to 1273 K). However, the addition of O2 leads to an adverse impact on the propylene selectivity and H2/CO ratio of the syngas. Under the absence of O2, the DHP exhibits a propane conversion of 91% with the propylene selectivity and system exergy efficiency of 90% and 86%, respectively when the CO2/C3H8 ratio of 0.25 at 973.15 K. This work provides strong evidence that the reaction performance matrices have a strong relation to the energy performance matrices and offers a baseline for future research and optimization in the presence of O2 and CO2.

Eco-friendly sustainable fluorescent coal-based carbon dots as a highly selective probe for Cu2+detection

Carbon dots as fluorescent probes exhibit brilliant sensitivity and selectivity in copper ion detection, which greatly depends on their microstructure. Herein, a mild oxidation method was adopted to tailor the organic macromolecules of coal and its derivatives for preparing coal-based carbon dots. Such coal-based carbon dots comprise a carbonaceous center dominated by sp2 microcrystalline carbon, surface defects formed by sp3 amorphous carbon, and oxygen/nitrogen-containing functional groups. The coal-based humic acid-based carbon dots (HA-CDs) exhibit high dispersity (∼7.6 nm), high sp2 microcrystalline carbon (61.73 %), abundant carboxyl groups (2.09 %), hydroxy groups (8.93 %), and pyridinic nitrogen (1.06 %). Due to their unique microstructure, the HA-CDs in aqueous solutions exhibit prominent fluorescence stability under different pH conditions and show superior selectivity and sensitivity to Cu2+ even in the existence of other metal ions. Within the concentration range of 0–40 µmol/L, the fluorescence intensity of HA-CDs linearly correlates with the concentration of Cu2+. The limit of detection is 0.014 µmol/L, allowing for tracing the Cu2+ concentration in flowing water. This work affords a novel idea for the microstructure design of high-sensitivity carbon dots for Cu2+ detection in the water environment.

Effect of cyclic oxidation temperature on compressive strength of Cu-based brake pad for high-speed train

The cyclic oxidation tests of Cu-based brake pads at temperatures of 25, 300, 400, 500, 550, 600, 650 and 700 °C were conducted to simulate the oxidation of the friction surface under different braking speeds. Furthermore, the effect of cyclic oxidation temperature on the compressive strength was investigated. The results show that the cyclic oxidation process of Cu-based brake pads can be divided into three stages: mild oxidation (≤400 °C), moderate oxidation (500–600 °C) and severe oxidation (≥650 °C). Mild oxidation results in the formation of spherical Cu2O particles. The surface is covered by Cu2O and Fe2O3 nanosheets for moderate oxidation. Severe oxidation is characterized by a continuous thick CuO film, Fe2O3 nanosheets, and eroded graphite particles. The compressive strength and toughness of Cu-based brake pads show a declining trend as the cyclic oxidation temperature rises. The compressive strength of the Cu-based brake pad after oxidized at 700 °C, recorded at 30.56 MPa, is considerably lower than that of the original samples, which was 132.2 MPa. This reduction in compressive strength is attributed to the embrittlement of the metallic matrix and the formation of pores from graphite oxidation.

Diastereoselective Synthesis of Sulfoxide-Functionalized N-Heterocyclic Carbene Ruthenium Complexes: An Experimental and Computational Study.

The synthesis of sulfoxide-functionalized NHC ligand precursors were carried out by direct and mild oxidation from corresponding thioether precursors with high selectivity. Using these salts, a series of cationic [Ru(II)(η6-p-cymene)(NHC-SO)Cl]+ complexes were obtained in excellent yields by the classical Ag2O transmetallation route. NMR analyses suggested a chelate structure for the metal complexes, and X-ray diffractometry studies of complexes 4 b, 4 c, 4dBArF and 4 e unambiguously confirmed the preference for the bidentate (κ2-C,S) coordination mode of the NHC-SO ligands. Interestingly, only one diastereomer, in the form of an enantiomeric pair, was observed both in 1H NMR and in the solid state for the complexes. DFT calculations showed a possible intrinsic energy difference between the two pairs of diastereomer. The calculated energy barriers suggested that inversion of the sulfoxide is only plausible from the higher energy diastereomer together with bulky substituents. Inverting the configuration at the Ru center instead shows a lower and accessible activation barrier to provide the most stable diastereomer through thermodynamic control, consistent with the observation of a single species by 1H NMR as a pair of enantiomers. All these complexes catalyse the β-alkylation of secondary alcohols. Complex 4dPF6 bearing an NHC-functionalised S-Ad group has been further studied with different primary and secondary alcohols as substrates, showing high reactivity and high to moderate β-ol-selectivities.

Study of ignition and combustion of aluminum/ethanol nanofluid based on reactive molecular dynamics simulation

Aluminum/ethanol nanofluid fuel offers high energy density, high combustion efficiency, and low pollutant emissions, making it highly promising for aerospace applications. In recent years, the fundamental combustion characteristics for aluminum/ethanol nanofluid fuel have been extensively studied. However, current experimental techniques are still difficult to reveal the micro-mechanisms ignition and combustion of aluminum/ethanol nanofluid fuel. Hence, the ignition and combustion mechanisms of aluminum/ethanol nanofluid fuel were investigated from a microscopic point of view through reactive molecular dynamics simulation. The simulation results show that the mechanisms of enhanced ethanol combustion by aluminum nanoparticles mainly consists of micro-explosion at high temperature and small particle size, chain reaction at low temperature and large particle size, melt-dispersion in the mild oxidation state and diffusive oxidation in the moderate and heavy oxidation states. In addition, the initial stage of the combustion of aluminum nanoparticles with core-shell structure in ethanol is mainly a non-homogeneous surface reaction. This work reveals the combustion characteristics and mechanisms of aluminum/ethanol nanofluid fuel from an atomic perspective, which is expected to provide insights for the exploration and application of ethanol-based nanofluid fuel in the future.

Ga2O3/La2O3-γAl2O3 catalysts for CO2-assisted propane oxidative dehydrogenation to propylene

Novel Ga2O3/La2O3-γAl2O3 was investigated for ODH of propane to propylene using CO2 as a mild oxidant in a batch scale fluidized CREC Riser Simulator. La2O3 in the catalysts provided a control of both the reducibility and acidity, as shown by H2-TPR and NH3-TPD, respectively. The propane conversion and products selectivity were strong function of La2O3 content in the Ga2O3/La2O3-γAl2O3 catalysts. With increasing La2O3 content in the catalyst, propane conversion dropped slightly but the propylene selectivity and yields increased. It was proposed that the presence of La2O3 reduced the non-selective sites and the acidity of the catalysts, that contributed towards deep oxidation of propane and propylene. The improved activity and selectivity with CO2 addition implied that the as-synthesized catalyst possesses CO2 activation capability required for ODH reactions. Among the investigated catalysts, Ga2O3/La2O3-γAl2O3(1:1) exhibited the highest propane conversion (92 %) and propylene yield (56 %) at 600 ℃ in the presence of CO2.

Structural Characterization of Disulfide-Linked p53-Derived Peptide Dimers.

Disulfide bonds provide a convenient method for chemoselective alteration of peptide and protein structure and function. We previously reported that mild oxidation of a p53-derived bisthiol peptide (CTFANLWRLLAQNC) under dilute non-denaturing conditions led to unexpected disulfide-linked dimers as the exclusive product. The dimers were antiparallel, significantly α-helical, resistant to protease degradation, and easily reduced back to the original bisthiol peptide. Here we examine the intrinsic factors influencing peptide dimerization using a combination of amino acid substitution, circular dichroism (CD) spectroscopy, and X-ray crystallography. CD analysis of peptide variants suggests critical roles for Leu6 and Leu10 in the formation of stable disulfide-linked dimers. The 1.0 Å resolution crystal structure of the peptide dimer supports these data, revealing a leucine-rich LxxLL dimer interface with canonical knobs-into-holes packing. Two levels of higher-order oligomerization are also observed in the crystal: an antiparallel "dimer of dimers" mediated by Phe3 and Trp7 residues in the asymmetric unit and a tetramer of dimers mediated by Trp7 and Leu10. In CD spectra of Trp-containing peptide variants, minima at 227 nm provide evidence for the dimer of dimers in dilute aqueous solution. Importantly, and in contrast to the original dimer model, the canonical leucine-rich core and robust dimerization of most peptide variants suggests a tunable molecular architecture to target various proteins and evaluate how folding and oligomerization impact various properties, such as cell permeability.

Structural model of oxidatively unzipped narrow single-walled carbon nanotubes

In this study, we present a synthetic method for the preparation of oxo-graphene nanoribbons (oxo-GNRs) by oxidative cleavage of C–C bonds of enriched (6,5)-single-walled carbon nanotubes (SWCNTs). We applied a mild oxidation protocol to oxidize SWCNTs involving sulfuric acid as dispersion medium and potassium permanganate as oxidant. The obtained oxo-GNRs exhibit stunning fluorescence properties with emission maxima of about 300 nm and 400 nm, respectively, depending on oxidation time. The analyses reveal that functional oxo-groups are predominantly located at the rims of oxo-GNRs. Next to lactones, 1,3-ketones are identified, which can be further reacted with hydrazine, most likely forming pyrazoline groups. Based on our data, we propose a chemical structure model for the oxo-GNRs. The model is based on an intact inner π-system, responsible for photoluminescence properties and oxo-functionalized rims of GNRs.

An Organic Molecular Mimetic Metal-Free Heterogeneous Catalyst for Electrocatalytic Alkyne Semihydrogenation.

The direct construction of metal-free catalysts on conductive substrates for electrocatalytic organic hydrogenation reactions is significant but still unexplored. Here, learning from the homogeneous molecular catalysts, an organic molecular mimetic metal-free heterogeneous catalyst is designed and constructed in situ on a graphite flake electrode via a mild electrochemical oxidation-reduction relay strategy. The as-prepared -COOH- and -OH-functionalized metal-free catalyst exhibits an electrocatalytic alkyne semihydrogenation performance with a 72 % Faradaic efficiency, 99 % selectivity and 96 % yield of the alkene product, which is comparable to that of noble metal catalysts. The removal of these oxygen-containing groups leads to negligible activity. The experimental and calculation results reveal that the origin of the high activity can be assigned to the -COOH and -OH groups on graphite. A flow electrolytic cell delivers ten grams of hydrogenated products with 81 % Faradaic efficiency. This metal-free catalyst is also suitable for gas-phase acetylene semihydrogenation and other electrocatalytic hydrogenation reactions.