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An iron-mediated bromination/cyclization for the synthesis of bromobenzoxazines from olefinic amides has been successfully developed. In this protocol, the simple iron salt FeBr3 was employed as a bromination reagent, giving the bromobenzoxazine products in moderate to excellent yields. This methodology features good functional group tolerance, gram-scale synthesis, and green reaction conditions by the use of air as the terminal oxidant. Preliminary mechanistic studies suggest that a free radical pathway is involved. [ABSTRACT FROM AUTHOR]

Efficient spontaneous molecular oxygen (O2) activation is expected in advanced oxidation processes. However, it remains a great challenge to promote the reactants adsorption and accelerate the interfacial electron transfer to boost the activation kinetic of O2. Herein, defect‐rich N‐doped reduced graphene oxide/CoFe2O4 (NGCF‐OV) membrane containing asymmetric Co‐OV‐Fe sites is prepared for O2 activation. The intrinsic catalytic activity is that the asymmetric Co‐OV‐Fe sites regulate the O─O bond length, promoting more and faster electron transfer to O2 for selectively producing 1O2. Meanwhile, the adjacent graphitic N sites help confine organics to the surface and thus greatly shorten the reaction distance of 1O2 and improve its utilization efficiency. The NGCF‐OV membrane demonstrates complete degradation of bisphenol A within a retention time of 86 ms, achieving a k‐value of 0.047 ms−1, which exceeds the performance of most Fenton‐like systems. This work provides new horizons for designing an efficient and stable catalytic membrane, enriching the domain of advanced wastewater treatment strategies. [ABSTRACT FROM AUTHOR]

Aerobic oxidation of olefins without any co‐reductant and high temperature was studies in the presence of nano and bulky Fe‐porphyrin in a comparative manner. Nano‐particles of Fe‐porphyrin were obtained via ultrasound irradiation. The results show higher catalytic efficiency of nano‐catalyst (turnover number of 1300) with respect to the bulk catalyst (turnover number of 600) in the oxidation of cyclohexene with molecular oxygen at room temperature. [ABSTRACT FROM AUTHOR]

Strategic design for the construction of contiguous tetrasubstituted carbon centers represents a daunting challenge in synthetic organic chemistry. Herein, we report a combined experimental and computational investigation aimed at developing catalytic aerobic carbooxygenation, involving the intramolecular addition of tertiary radicals to geminally disubstituted alkenes, followed by aerobic oxygenation. This reaction provides a straightforward route to various α,α,β,β‐tetrasubstituted γ‐lactones, which can be readily transformed into hexasubstituted γ‐lactones through allylation/translactonization. Computational analysis reveals that the key mechanistic foundation for achieving the developed aerobic carbooxygenation involves the design of endothermic (energetically uphill) C−C bond formation followed by exothermic (energetically downhill) oxygenation. Furthermore, we highlight a unique fluorine‐induced stereoelectronic effect that stabilizes the endothermic stereodetermining transition state. [ABSTRACT FROM AUTHOR]

The chemoselective epoxidation of electron-deficient olefins in the presence of electron-rich alkene moieties is reported. This chemoselective epoxidation strategy undergoes a conjugated olefin epoxidation and BHT hydroxylation process to give various useful oxiranes in high yields, especially for the 2-substituted 2-trifluoromethyloxiranes. Importantly, this protocol features mild conditions, is transition-metal free, operationally simple, and gram-scalable, and tolerates diverse functional groups. Drug candidate HSD-16 is synthesized smoothly by this protocol. Mechanism studies indicate molecular oxygen is the terminal oxidant and the O-source of the oxiranes. [ABSTRACT FROM AUTHOR]

The development of green route for preparing propylene oxide (PO) with molecular oxygen is of significance both in academic and industrial. In this work, propylene epoxidation coupled with furfural oxidation catalyzed by platinum meso-tetraphenylporphyrin (Pt (II)TPP) has been developed. Propylene conversion and PO selectivity reached up to 56% and 83%, respectively. Meanwhile, furfural was almost completely converted to furoic acid. Based on operando characterizations and electron paramagnetic resonance (EPR) tests, a mechanism involved high-valent Pt species was proposed. This work is expected to provide a potential application prospects for producing PO and furoic acid simultaneously in chemical industry.

Micro-nanobubbles (MNBs) can form reactive oxygen species (ROS) with high oxidizing potential. In this study, nickel-doped metal–organic framework materials (MOFs) capable of activating molecular oxygen were synthesized using trivalent arsenic (As(III)) as a target pollutant and combined with peroxymonosulfate (PMS) to construct a MOF/MNB/PMS system. The results included the rapid oxidation of As(III), the successful absorption of oxidized As(V), and finally the efficient removal of As. The effects of pH, amount of PMS used, and preparation time of MNBs on the As removal performance of the MOF/MNB/PMS system were investigated experimentally. The changes in the properties of the materials before and after the reaction were analyzed by XPS, and it was found that the main active sites on the surface of the MOFs were the metal elements and the pyridine nitrogen near the carbon atom. The regular morphology and elemental composition of the MOFs were determined by TEM scanning and EDS test, which indicated the presence of nickel. XRD tests before and after the reaction showed that the MOFs were structurally stable. The results of the free radical burst experiments show that the single linear oxygen (1O2) is the main active substance in the system, and that the MNBs are key factors by which the system achieves efficient oxidation performance. In addition to providing a sustainable supply of molecular oxygen to the MOFs during the reaction process, coupling the MNBs with PMS was found to improve the oxidation capacity of the system. The results of this study thus provide a new concept for As removal and advanced oxidation in water bodies. [ABSTRACT FROM AUTHOR]

[Display omitted] Developing efficient catalysts for the selective oxidation of sulfides to sulfoxides using molecular oxygen as the oxidant is a challenging task. Here, we report a novel catalyst comprising a single atom palladium engineered cobalt nanocomposite (denoted as PdCo@NC-800–0.01) for this reaction. The incorporation of single atom palladium effectively transforms an originally inactive cobalt nanocomposite into a highly efficient and selective catalyst for the oxidation of sulfides. This catalyst PdCo@NC-800–0.01 exhibited outstanding performance in the selective oxidation of sulfides to sulfoxides using O 2 as the oxidant in the presence of isobutyraldehyde (IBA) under mild conditions, demonstrating high activity and excellent selectivity for a broad spectrum of sulfides with good tolerance toward various functional groups, including those susceptible to oxidation. Furthermore, the catalyst could be easily recovered and reused up to 10 times without any significant loss in activity and selectivity. Comprehensive characterizations and theoretical calculations revealed that the engineering of cobalt nanocomposite with single atom Pd greatly enhanced the ability to adsorb and activate IBA, leading to the generation of the key acyl radical. This radical then reacted with singlet oxygen 1O 2 derived from molecular oxygen, producing reactive oxygen species peroxy radical, which ultimately promoted the catalytic performance. [ABSTRACT FROM AUTHOR]

Herein, we report a copper‐catalyzed intramolecular benzylic C(sp3)−H oxidation of unprotected aniline derivatives under aerobic conditions, which enables the preparation of phenanthridine compounds. To the best of our knowledge, this is the pioneering reaction of dehydrogenative C(sp3)−N bond formation from unprotected anilines under a Cu/O2 system. Notably, various anilines possessing alkyl, methoxy, halogen (fluoride, chloride, bromide, and iodide), trifluoromethyl, trifluoromethoxy, cyano, ester, and acetal groups can also participate in the reaction. [ABSTRACT FROM AUTHOR]

Inner membranes of mitochondria are extensively folded, forming cristae. The observed overall correlation between efficient eukaryotic ATP generation and the area of internal mitochondrial inner membranes both in unicellular organisms and metazoan tissues seems to explain why they evolved. However, the crucial use of molecular oxygen (O2) as final acceptor of the electron transport chain is still not sufficiently appreciated. O2 was an essential prerequisite for cristae development during early eukaryogenesis and could be the factor allowing cristae retention upon loss of mitochondrial ATP generation. Here I analyze illuminating bacterial and unicellular eukaryotic examples. I also discuss formative influences of intracellular O2 consumption on the evolution of the last eukaryotic common ancestor (LECA). These considerations bring about an explanation for the many genes coming from other organisms than the archaeon and bacterium merging at the start of eukaryogenesis. [ABSTRACT FROM AUTHOR]

We use the extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft to determine the first quantification of vertical variation in O2 mole fraction separately for day and night in the ∼90–130 km altitude range. The upper atmospheric O2 variation is expected to be due to the interplay between diffusion and advection because of its long photochemical lifetime. It is therefore a useful tracer of the state of atmospheric mixing and circulation. The altitude‐averaged mixing ratio is measured to be 2.69(±0.03) × 10−3 for the nightside and 2.05(±0.03) × 10−3 for the dayside. The average O2 mole fraction for day and night are nearly identical below 105 km, consistent with the value of 1.61 × 10−3 derived from the Mars Curiosity Rover/Sample Analysis at Mars near‐surface measurements. At higher altitudes, dominated by molecular diffusive separation, the measured O2 mole fraction demonstrates a vertical gradient with a local time dependence. The nightside mole fraction is a factor of 1.37 ± 0.04 larger than the dayside value at ∼125 km. This nightside enhancement is explained in terms of the relative role of solar‐driven rapid horizontal winds at high altitudes and slower vertical diffusion, resulting in a nightside (dayside) downward (upward) diffusive flux. Using the 1‐D diffusion model, the measured profiles correspond to a vertical eddy diffusion coefficient K = 3.5(±1.5) × 106 cm2/s. The Mars Climate Database predicts comparable but lower day‐night differences in oxygen mole fraction due to an overestimated K = 7.0(±1.0) × 106 cm2/s, which affects atmospheric mixing as well as the rate of atmospheric escape to space. Plain Language Summary: Molecular oxygen in the martian atmosphere is produced photochemically and behaves like an inert trace gas due to its long photochemical lifetime (∼60 Earth years). Its variations in the upper atmosphere are therefore governed by diffusion and dynamics and are indicative of the changes in atmospheric mixing and circulation. Other data sets have only provided a glimpse of O2 abundance in the upper atmosphere due to limited spatial and temporal coverage. The extensive stellar occultation data set of the Imaging Ultraviolet Spectrograph aboard the Mars Atmosphere and Volatile EvolutioN spacecraft can help fill this knowledge gap. This study shows the first quantification of vertical variation in O2 mixing ratio separately for day and night in the ∼90–130 km altitude range. While the day and night O2 mixing ratio is measured to be identical below 105 km in the well‐mixed atmosphere, significant local time dependence is seen under molecular diffusive separation, with a nightside enhancement and a dayside depletion. This is explained in terms of diffusive flux from the dayside to the nightside. However, the Mars Climate Database output is inconsistent with these measurements, which therefore have important implications for how species diffuse through the martian atmosphere and escape to space. Key Points: Stellar occultations observed by Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph allow the most complete study of molecular oxygen in the upper atmosphereSignificant day/night differences reveal the importance of diurnal circulation and molecular diffusionObserved day/night differences exceed those in models, suggesting mixing is significantly overestimated in those models [ABSTRACT FROM AUTHOR]

Molecular oxygen (O2) is an environmentally friendly, cost-effective, and non-toxic oxidant. Activation of O2 generates various highly oxidative reactive oxygen species (ROS), which efficiently degrade pollutants with minimal environmental impact. Despite extensive research on the application of O2 activation in environmental remediation, a comprehensive review addressing this topic is currently lacking. This review provides an informative overview of recent advancements in O2 activation, focusing on three primary strategies: photocatalytic activation, chemical activation, and electrochemical activation of O2. We elucidate the respective mechanisms of these activation methods and discuss their advantages and disadvantages. Additionally, we thoroughly analyze the influence of oxygen supply, reactive temperature, and pH on the O2 activation process. From electron transfer and energy transfer perspectives, we explore the pathways for ROS generation during O2 activation. Finally, we address the challenges faced by researchers in this field and discuss future prospects for utilizing O2 activation in pollution control applications. This detailed analysis enhances our understanding and provides valuable insights for the practical implementation of organic pollutant degradation.

The exploitation of highly efficient solvent-free catalytic systems for the selective aerobic oxidation of benzylic compounds to produce corresponding ketones with molecular oxygen under mild conditions remains a great challenge in the chemical industry. In this work, Au-Pd nanoparticles supported on porous carbon catalysts were fabricated by the borax-mediated hydrothermal carbonization method and the chemical reduction method. The physicochemical properties of Au-Pd bimetallic samples were examined by XRD, N2 sorption, SEM, TEM, and XPS techniques. The Au-Pd nanoparticles have successfully immobilized on the spherical carbon support with a porous structure and large surface area. A solvent-free catalytic oxidation system was constructed to selectively convert indane into indanone with Au-Pd nanocatalysts and O2. In contrast with a monometallic Au or Pd catalyst, the resulting bimetallic Au-Pd catalyst could effectively activate O2 and exhibit improved catalytic activity in the controlled oxidation of indane into indanone under 1 bar O2. A total of 78% conversion and >99% selectivity toward indanone can be achieved under optimized conditions. The synergistic effect of Au and Pd and porous carbon support contributed to the high catalytic activity for aerobic benzylic compound oxidation. This work offers a promising application prospect of efficient and recyclable Au-Pd nanocatalysts in functional benzylic ketone production. [ABSTRACT FROM AUTHOR]

A Special Issue of Microorganisms devoted to 'Microbial Biocatalysis and Biodegradation' would be incomplete without some form of acknowledgement of the many important roles that dioxygen-dependent enzymes (principally mono- and dioxygenases) play in relevant aspects of bio-oxygenation. This is reflected by the multiple strategic roles that dioxygen -dependent microbial enzymes play both in generating valuable synthons for chemoenzymatic synthesis and in facilitating reactions that help to drive the global geochemical carbon cycle. A useful insight into this can be gained by reviewing the evolution of the current status of 2,5-diketocamphane 1,2-monooxygenase (EC 1.14.14.108) from (+)-camphor-grown Pseudomonas putida ATCC 17453, the key enzyme that promotes the initial ring cleavage of this natural bicyclic terpene. Over the last sixty years, the perceived nature of this monooxygenase has transmogrified significantly. Commencing in the 1960s, extensive initial studies consistently reported that the enzyme was a monomeric true flavoprotein dependent on both FMNH2 and nonheme iron as bound cofactors. However, over the last decade, all those criteria have changed absolutely, and the enzyme is currently acknowledged to be a metal ion-independent homodimeric flavin-dependent two-component mono-oxygenase deploying FMNH2 as a cosubstrate. That transition is a paradigm of the ever evolving nature of scientific knowledge. [ABSTRACT FROM AUTHOR]

2,2,6,6‐Tetramethylpiperidinium‐nitroxide (TEMPO) is a mild and efficient catalyst, which is important in the industrial production of selective oxidation of alcohols to the corresponding aldehyde or ketone compounds. However, it is a challenge to recover the expensive TEMPO catalyst in homogeneous catalytic systems. In this study, a novel polymer‐supported catalyst was prepared using 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxy (4‐OH‐TEMPO) and polyaromatic ether sulfone (PAES). The successful grafting of 4‐OH‐TEMPO in PAES‐C was demonstrated by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT‐IR), load capacity can be calculated by elemental analysis (EA). BET and scanning electron microscopy (SEM) to depict the structure‐performance relationship. Herein, SEM images revealed the existence of porous structure. This structure can effectively adsorb NO molecules to form a PAES‐TEMPO/NOx catalytic system to selectively oxidize benzyl alcohol. The experimental results indicated the high activity, the subsequent benzyl alcohol oxidation cycle can reach more than 93% conversion without showing a large loss of selectivity. More importantly, the as‐prepared catalyst exhibited the attractive recyclability (recovery rate is 98%). After 10 consecutive runs, no significant loss of conversion and selectivity was observed (the conversion rate of benzyl alcohol was more than 93% and the selectivity was more than 95%). This study might provide some recommendation on the development of highly efficient catalysts for alcohol oxidation. [ABSTRACT FROM AUTHOR]

While amide‐linked covalent organic frameworks (COFs) have gained significant research attention due to their stability, there is currently no universal method for creating amide‐linked COFs with diverse chemical structures. Here, we present a gentle, precise, and versatile synthetic approach to amide‐linked COFs using N‐heterocyclic carbene (NHC)‐mediated oxidation with molecular oxygen as the oxidant. This approach is gentle and selective, and even fragile functional groups like thioethers are able to survive the transformation. Additionally, this method does not require dangerous conditions such as high pressure or strong oxidants, making it a promising way to create functional amide‐linked COFs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two CMPs based on fused thiophenes are designed as photocatalysts. • Red lightdrives the oxidation of amines over DTT–Py–CMP. • Extensive π-conjugation attributes to a better absorption of visible light. • Outstanding photocatalytic performance is achieved. • General applicability for the oxidation of benzyl amines is presented. By virtue of tailorable building blocks, the band gaps and electronic structures of conjugated microporous polymers (CMPs) can be readily adjusted at the molecular level. Generally, the building blocks possessing extended π-conjugations result in exceptional photocatalytic performances. In this work, the direct C H arylation of fused thiophenes, thieno[3,2- b ]thiophene (TT) and dithieno[3,2- b :2′,3′- d ]thiophene (DTT), with 1,3,6,8-tetrabromopyrene affords two CMPs, namely TT-Py-CMP and DTT-Py-CMP. The expansion of π-conjugations of the fused thiophenes from TT to DTT gives rise to a bathochromic shift about 30 nm from TT-Py-CMP to DTT-Py-CMP. Besides, systematic characterizations suggest the optoelectronic properties of DTT-Py-CMP are better than that of TT-Py-CMP. Furthermore, DTT-Py-CMP drives better red light photocatalysis than TT-Py-CMP for the selective oxidation of amines with molecular oxygen. The selective oxidation of benzyl amines by red light photocatalysis of DTT-Py-CMP progresses via an electron transfer pathway with high selectivities for imines. This work provides new insights that fused thiophenes could be the stepping stone in designing CMPs for expansive visible light photocatalysis. [ABSTRACT FROM AUTHOR]

Benzyl benzoate (BB), an important ester, still demands for green synthesis routes. In this work, by size regulation and proper functionalization of carbon nanotubes (CNTs) as the support of gold catalyst, this ester can be synthesized very efficiently directly from benzyl alcohol via oxidative coupling. More attractively, the reaction is performed using water as green solvent and molecular oxygen as green oxidant. Simultaneously, very high selectivity to BB can be obtained near full conversion within very short reaction time (just 0.5 h), while the low-value benzoic acid byproduct is negligible. This is very different from many reported gold catalysts that yield much benzoic acid and/or benzaldehyde in water. The results show that, besides the size of CNTs (length and diameter), the functionalization of CNTs is also critical for improving both conversion and the selectivity to BB. In addition, the reaction mechanism for forming BB ester is put forward as well.

This review article describes a historical perspective of elucidation of the nature of the chemical bonds of the high-valent transition metal oxo (M=O) and peroxo (M-O-O) compounds in chemistry and biology. The basic concepts and theoretical backgrounds of the broken-symmetry (BS) method are revisited to explain orbital symmetry conservation and orbital symmetry breaking for the theoretical characterization of four different mechanisms of chemical reactions. Beyond BS methods using the natural orbitals (UNO) of the BS solutions, such as UNO CI (CC), are also revisited for the elucidation of the scope and applicability of the BS methods. Several chemical indices have been derived as the conceptual bridges between the BS and beyond BS methods. The BS molecular orbital models have been employed to explain the metal oxyl-radical character of the M=O and M-O-O bonds, which respond to their radical reactivity. The isolobal and isospin analogy between carbonyl oxide R2C-O-O and metal peroxide LFe-O-O has been applied to understand and explain the chameleonic chemical reactivity of these compounds. The isolobal and isospin analogy among Fe=O, O=O, and O have also provided the triplet atomic oxygen (3O) model for non-heme Fe(IV)=O species with strong radical reactivity. The chameleonic reactivity of the compounds I (Cpd I) and II (Cpd II) is also explained by this analogy. The early proposals obtained by these theoretical models have been examined based on recent computational results by hybrid DFT (UHDFT), DLPNO CCSD(T0), CASPT2, and UNO CI (CC) methods and quantum computing (QC). [ABSTRACT FROM AUTHOR]

Many redox reactions are being catalyzed by oxidoreductase enzymes. Although they have high structural similarity, these enzymes undergo different reaction mechanisms and rates depending on the types of substrate, structure, and protonation state. Many pharmaceutical and food industry applications of these enzymes depend on the structural characterization and elucidation of the reaction mechanisms. Combined experimental studies with computational tools provided evidence on the isoalloxazine ring of the oxidoreductase's flavin cofactor reacting through a step-wise process of consecutive single-electron transfers. Moreover, a reaction mechanism is enabled due to the protonation state of the proximity of the cofactor and substrate binding pocket. This paper aims to review the recent advances concerning the structural aspects and factors affecting the mechanism of reactions involving several representatives of the flavin-dependent oxidase family. [ABSTRACT FROM AUTHOR]

Aerobic oxidative cross‐coupling represents one of the most straightforward and atom‐economic methods for construction of C−C and C−X (X=N, O, S, or P) bonds using air as a sustainable external oxidant. The oxidative coupling of C−H bonds in heterocyclic compounds can effectively increase their molecular complexity by introducing new functional groups through C−H bond activation, or by formation of new heterocyclic structures through cascade construction of two or more sequential chemical bonds. This is very useful as it can increase the potential applications of these structures in natural products, pharmaceuticals, agricultural chemicals, and functional materials. This is a representative overview of recent progress since 2010 on green oxidative coupling reactions of C−H bond using O2 or air as internal oxidant focus on Heterocycles. It aims to provide a platform for expanding the scope and utility of air as green oxidant, together with a brief discussion on research into the mechanisms behind it. [ABSTRACT FROM AUTHOR]

Interaction of molecular oxygen 3O2 with the flavin-dependent protein miniSOG after light illumination results in creation of singlet oxygen 1O2 and superoxide O2●−. Despite the recently resolved crystal structures of miniSOG variants, oxygen-binding sites near the flavin chromophore are poorly characterized. We report the results of computational studies of the protein−oxygen systems using molecular dynamics (MD) simulations with force-field interaction potentials and quantum mechanics/molecular mechanics (QM/MM) potentials for the original miniSOG and the mutated protein. We found several oxygen-binding pockets and pointed out possible tunnels bridging the bulk solvent and the isoalloxazine ring of the chromophore. These findings provide an essential step toward understanding photophysical properties of miniSOG—an important singlet oxygen photosensitizer.

The exploitation of highly efficient solvent-free catalytic systems for the selective aerobic oxidation of benzylic compounds to produce corresponding ketones with molecular oxygen under mild conditions remains a great challenge in the chemical industry. In this work, Au-Pd nanoparticles supported on porous carbon catalysts were fabricated by the borax-mediated hydrothermal carbonization method and the chemical reduction method. The physicochemical properties of Au-Pd bimetallic samples were examined by XRD, N2 sorption, SEM, TEM, and XPS techniques. The Au-Pd nanoparticles have successfully immobilized on the spherical carbon support with a porous structure and large surface area. A solvent-free catalytic oxidation system was constructed to selectively convert indane into indanone with Au-Pd nanocatalysts and O2. In contrast with a monometallic Au or Pd catalyst, the resulting bimetallic Au-Pd catalyst could effectively activate O2 and exhibit improved catalytic activity in the controlled oxidation of indane into indanone under 1 bar O2. A total of 78% conversion and >99% selectivity toward indanone can be achieved under optimized conditions. The synergistic effect of Au and Pd and porous carbon support contributed to the high catalytic activity for aerobic benzylic compound oxidation. This work offers a promising application prospect of efficient and recyclable Au-Pd nanocatalysts in functional benzylic ketone production.

A Special Issue of Microorganisms devoted to ‘Microbial Biocatalysis and Biodegradation’ would be incomplete without some form of acknowledgement of the many important roles that dioxygen-dependent enzymes (principally mono- and dioxygenases) play in relevant aspects of bio-oxygenation. This is reflected by the multiple strategic roles that dioxygen -dependent microbial enzymes play both in generating valuable synthons for chemoenzymatic synthesis and in facilitating reactions that help to drive the global geochemical carbon cycle. A useful insight into this can be gained by reviewing the evolution of the current status of 2,5-diketocamphane 1,2-monooxygenase (EC 1.14.14.108) from (+)-camphor-grown Pseudomonas putida ATCC 17453, the key enzyme that promotes the initial ring cleavage of this natural bicyclic terpene. Over the last sixty years, the perceived nature of this monooxygenase has transmogrified significantly. Commencing in the 1960s, extensive initial studies consistently reported that the enzyme was a monomeric true flavoprotein dependent on both FMNH2 and nonheme iron as bound cofactors. However, over the last decade, all those criteria have changed absolutely, and the enzyme is currently acknowledged to be a metal ion-independent homodimeric flavin-dependent two-component mono-oxygenase deploying FMNH2 as a cosubstrate. That transition is a paradigm of the ever evolving nature of scientific knowledge.

Molecular oxygen (O2) migration in isolated β-chains of human hemoglobin was studied using molecular dynamics simulations and laser kinetic absorption spectroscopy. Insertion of xenon (Xe) atoms into the isolated chains was found to decrease the time constant of the slowest component of geminal O2 rebinding to the protein. This change was caused by a decrease in the intra-protein space available for O2 migration after insertion of the inert gas into the Xe-binding sites of the protein. Molecular dynamics simulations revealed that the O2 molecule occupied both the Xe2 and Xe1 sites of the protein during geminal recombination to the isolated β-chains. The amino acids involved in formation of the primary and secondary docking sites of the protein were determined. The results are important for understanding the mechanism of O2 binding by both native tetrameric human hemoglobin and artificial oxygen carriers based on heme proteins. [ABSTRACT FROM AUTHOR]

In this article, the biocatalytic oxidation of ethanol into acetaldehyde was studied using a catalase entrapped within a monolithic polyampholyte cryogel, p(APTAC-co-AMPS), as catalyst. When an anionic monomer, 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS), was mixed with a cationic monomer, (3-acrylamidopropyl) trimethylammonium chloride (APTAC), under cryo-polymerization conditions at a molar ratio of monomers [APTAC]:[AMPS] = 75:25 mol.% in the presence of 10 mol.% cross-linking agent, N,N-methylenebisacrylamide (MBAA), the macroporous polyampholyte cryogels containing various amounts of catalase were synthesized in situ. The conversion of ethanol into acetaldehyde in good-to-high yields was observed in flow-through and batch-type reactors under optimal conditions: at T = 10–20 °C, pH = 6.9–7.1, [C2H5OH]:[H2O2] = 50:50 vol.%. According to the SEM images, the pore sizes of the p(AMPS-co-APTAC) cryogel vary from 15 to 55 μm. The catalytic activity of catalase entrapped within a monolithic polyampholyte cryogel in the conversion of ethanol into acetaldehyde was evaluated through the determination of kinetic parameters such as the Michaelis constant (Km), maximum enzymatic rate (Vmax), activation energy (Ea), turnover number (TON) and turnover frequency (TOF). The catalase encapsulated within the monolithic polyampholyte cryogel exhibits a high conversion of ethanol into acetaldehyde. The key parameters of ethanol oxidation in flow and batch reactors in the presence of the cryogel monolith were calculated. [ABSTRACT FROM AUTHOR]

Nitrogen-containing heterocycles such as morpholin-2-ones are structural elements of many biologically active substances, as well as useful synthetic intermediates. To be able to functionalize them regioselectively in an easy, atom-efficient, and environmentally friendly manner is highly desirable. A procedure for cross-dehydrogenative coupling between morpholinones and cyclic imides was developed addressing these requirements. An earth-abundant metal catalyst, copper(I) chloride, in the presence of acetic acid, and with molecular oxygen as the sole oxidant, operating under mild conditions, afforded the desired C–N coupled products in high yields. Besides being potentially biologically active, as many members of both families of compounds are, the products themselves may be suitable substrates for functionalized polymers, e.g., poly(β-aminoesters) or even for PROTACs. [ABSTRACT FROM AUTHOR]

Meso-tetrakis(4-carboxyphenyl)porphyrinatomanganese(III) acetate has been immobilized onto the modified silica-coated Fe3O4 nanoparticles with linkers using different chain lengths (short, Fe3O4@SiO2-MnTCPP (C-1), medium, Fe3O4@SiO2-NH2-MnTCPP (C-2), and long length, Fe3O4@SiO2-NHCO-NH2-MnTCPP (C-3)). The catalysts have been fully characterized using FT-IR, UV-Vis, XRD, FE-SEM, TEM, TGA, and VSM. A comparative study based on the difference in chain length of the linker in the oxidation of olefins with molecular oxygen was performed. The new long-chain linker was designed to improve the performance of the catalytic activity including complete conversion of the α-methyl styrene, 4-methyl styrene, and 4-chloro styrene achieved after 2 h. The new heterogenized catalyst of Fe3O4@SiO2-NHCO-NH2-MnTCPP shows higher catalytic activity in the oxidation of different olefins as well as better reusability of the catalyst. [ABSTRACT FROM AUTHOR]

Interaction of molecular oxygen 3O2 with the flavin-dependent protein miniSOG after light illumination results in creation of singlet oxygen 1O2 and superoxide O2●−. Despite the recently resolved crystal structures of miniSOG variants, oxygen-binding sites near the flavin chromophore are poorly characterized. We report the results of computational studies of the protein−oxygen systems using molecular dynamics (MD) simulations with force-field interaction potentials and quantum mechanics/molecular mechanics (QM/MM) potentials for the original miniSOG and the mutated protein. We found several oxygen-binding pockets and pointed out possible tunnels bridging the bulk solvent and the isoalloxazine ring of the chromophore. These findings provide an essential step toward understanding photophysical properties of miniSOG—an important singlet oxygen photosensitizer. [ABSTRACT FROM AUTHOR]

A method has been developed for the sol–gel encapsulation of hemoglobin in the deoxygenated T-conformation followed by saturation of the protein with molecular oxygen (O2). A device for the sol–gel encapsulation of hemoglobin under anaerobic conditions has been constructed. Kinetic data for the bimolecular recombination of O2 with encapsulated hemoglobin stabilized predominantly in the oxygenated T-conformation (in an ensemble of oxygenated T-conformers were measured for the first time using time-resolved absorption spectroscopy. This method permits detailed study of the O2-binding properties of the nonequilibrium conformational states of hemoglobin, which significantly contributes to our understanding of the mechanism of the regulation of O2 binding by both native human hemoglobin and artificial oxygen carriers. [ABSTRACT FROM AUTHOR]

Total parenteral nutrition (TPN) is a life-saving therapy for patients with intestinal failure, but it carries the risk of complications, including an increase in liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST) after long-term use. Patients receiving chronic TPN are also exposed to metabolic stress from both the underlying disease and parenteral nutrition. The aim of this study was to compare the concentration of liver transaminases AST and ALT in relation to the rate of oxygen consumption in platelet mitochondria in patients receiving long-term TPN with the degree of oxidative stress induced by lipid emulsions, and to explain their role in cellular energy metabolism and changes in the liver based on the percentage of genomic DNA damage. The study group consisted of 86 TPN patients, while the control group consisted of 86 healthy volunteers who were fed only orally. The results of the study showed that the percentage of molecular oxygen depended on the type of lipid emulsion supplied. Analyzing time on TPN as a factor, we observed a decrease in percentage genomic DNA damage and an increase in percentage molecular oxygen in cells. It remains unclear whether TPN has a direct effect on genomic DNA damage and the level of molecular oxygen in cells during the course of treatment. In conclusion, this study provides important insights into the potential effects of TPN on liver enzymes and cellular metabolism. Further research is needed to better understand the underlying mechanisms and to develop strategies to minimize the risk of complications associated with TPN. [ABSTRACT FROM AUTHOR]

As a key branch of the cross-discipline biophotonics, phototherapy, including photodynamic therapy (PDT), and photothermal therapy (PTT), is promising in biomedicine and visible light-driving PDT has been applied to clinical treatment. However, extensive applications of phototherapy are limited by the hypoxic microenvironment, laser penetration depth, and potential complexity for combined PDT/PTT. Thus, NIR-responsive oxygen self-supply nanocomposites functionalized with photosensitizers for achieving simultaneous in-depth PDT/PTT are urgently required. Herein, a multifunctional platform has been fabricated by co-immobilizing monodispersed ultrasmall Pd nanoclusters and a photosensitizer 5,10,15,20-Tetrakis (4-Aminophenyl)-21H,23H Porphyrin (Thp) on the surface of Ti3C2Tx MXene nanosheets, generating the Pd-Thp-Ti3C2Tx nanocomposite. Material characterization demonstrated that Pd nanoclusters and Thp were well-distributed on the MXene surface while MXene maintained its photothermal conversion efficiency and broad absorption. In this nanoplatform, irradiated by the single 808 nm laser, Pd selectively catalyzed the decomposition of H2O2 to O2, and O2 was continuously supplied to Thp for enhanced NIR-driving PDT. The in vivo fluorescence and photothermal imaging demonstrated the pronounced accumulation of nanocomposites in the tumor site. Both in vitro and in vivo results clearly demonstrated the nanocomposite had good biocompatibility, and that the synergistic PTT and enhanced PDT made apoptosis of the tumor cell achievable. This work not only proves this Pd-Thp-Ti3C2Tx nanocomposite serves a promising solution for tumor hypoxia by inducing apoptosis of tumor cells with synergistic PTT and PDT, but also broadens the application of promising optical materials in biomedical field.

Molecular oxygen (O2) is the perfect probe molecule for membrane studies carried out using the saturation recovery EPR technique. O2 is a small, paramagnetic, hydrophobic enough molecule that easily partitions into a membrane’s different phases and domains. In membrane studies, the saturation recovery EPR method requires two paramagnetic probes: a lipid-analog nitroxide spin label and an oxygen molecule. The experimentally derived parameters of this method are the spin–lattice relaxation times (T1s) of spin labels and rates of bimolecular collisions between O2 and the nitroxide fragment. Thanks to the long T1 of lipid spin labels (from 1 to 10 µs), the approach is very sensitive to changes of the local (around the nitroxide fragment) O2 diffusion-concentration product. Small variations in the lipid packing affect O2 solubility and O2 diffusion, which can be detected by the shortening of T1 of spin labels. Using O2 as a probe molecule and a different lipid spin label inserted into specific phases of the membrane and membrane domains allows data about the lateral arrangement of lipid membranes to be obtained. Moreover, using a lipid spin label with the nitroxide fragment attached to its head group or a hydrocarbon chain at different positions also enables data about molecular dynamics and structure at different membrane depths to be obtained. Thus, the method can be used to investigate not only the lateral organization of the membrane (i.e., the presence of membrane domains and phases), but also the depth-dependent membrane structure and dynamics and, hence, the membrane properties in three dimensions.

The oxidative [3+2+1] annulation reaction of aldehydes, 5‐aminopyrazoles, and nitriles is achieved under the oxidation of I2/O2, affording various valuable pyrazolo[3,4‐d]pyrimidines in 27%–91% yields. The salient feature of this reaction is transition‐metal free, operationally simple, broad substrate scope, good functional group tolerance, and gram‐scalable. Remarkably, the corresponding products exhibited intriguing photophysical properties such as Aggregation‐Induced Emission (AIE) and intramolecular charge transfer (ICT) and showed good potential to specifically light up lipid droplets (LDs) in living cells with bright fluorescence, low cytotoxicity, and good photostability. [ABSTRACT FROM AUTHOR]

As a clean fossil energy and chemical feedstock, development of breakthrough strategies for direct conversion of methane (CH4) into various chemicals under mild reaction conditions is highly desired. Herein, Rh/ZSM‐5 catalyst was reported to convert CH4 to oxygenates with molecular oxygen (O2) in the presence of CO at low temperature with promising catalytic performance. The oxygenates productivity reached as high as 5638.0 μmol gcat.−1 h−1. Structure characterization confirmed the existence of highly dispersed Rh2O3 nanoparticles with an average diameter of 2.4 nm in the Rh/ZSM‐5 catalyst. Based on control experiments and mechanism study, it was suggested that CO plays a pivotal role over the Rh/ZSM‐5 catalyst to boost direct oxidation of methane. CO participates in water‐gas‐shift reaction to produce in‐situ H species, which enables to form *OH, *OOH and H2O2 active species by reacting with O2. The as‐obtained *OH, *OOH and H2O2 species will thus render high activity for methane oxidation. [ABSTRACT FROM AUTHOR]

Nano-zero-valent copper (nZVC) is a superior molecular oxygen (O2) activator for the abatement of organic pollutants due to its high electron utilization rate. However, the activation efficiency of O2 is compromised by the agglomeration tendency of nZVC particles and the concomitant reduction of the available active sites. To address this problem, the biochar (BC) with porous structure and abundant surface functional groups is utilized to disperse and stabilize nZVC for O2 activation (simplified as the nZVC/BC/O2 system) for efficient removal of tetracycline (TC). The nZVC/BC composite possesses a high specific area with well-distributed nZVC particles on the BC surface, which guarantees the superior dispersion and high reactivity in the activation of O2. The efficacy of the nZVC/BC/O2 system for TC abatement is evaluated and the underlying mechanism is elucidated. The results show that nZVC/BC/O2 system can achieve excellent removal of TC with the efficiencies of more than 85% in the pH range of 4.0–9.0, which originated from the combined action of complexation and degradation. The degradation is dominated by reactive oxygen species (ROS) including •OH, •O2− and 1O2 generated by Cu0/Cu+ activated O2 while the generation of Cu2+ via oxygen oxidation on the surface of nZVC/BC can remove TC by complexation adsorption. This study highlights the complexation and degradation in the removal of TC and can be expected to exhibit application prospects in the water and wastewater treatment. [ABSTRACT FROM AUTHOR]

Oxygenase activity of the flavin-dependent enzyme RutA is commonly associated with the formation of flavin-oxygen adducts in the enzyme active site. We report the results of quantum mechanics/molecular mechanics (QM/MM) modeling of possible reaction pathways initiated by various triplet state complexes of the molecular oxygen with the reduced flavin mononucleotide (FMN) formed in the protein cavities. According to the calculation results, these triplet-state flavin-oxygen complexes can be located at both re-side and si-side of the isoalloxazine ring of flavin. In both cases, the dioxygen moiety is activated by electron transfer from FMN, stimulating the attack of the arising reactive oxygen species at the C4a, N5, C6, and C8 positions in the isoalloxazine ring after the switch to the singlet state potential energy surface. The reaction pathways lead to the C(4a)-peroxide, N(5)-oxide, or C(6)-hydroperoxide covalent adducts or directly to the oxidized flavin, depending on the initial position of the oxygen molecule in the protein cavities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ag particles (40–170 nm) supported on α-Al 2 O 3 are composed of multiple crystallites. • Increasing Ag particle size increases the apparent TOF. • EO selectivity nearly constant with Ag particle size (at zero residence time). • Raman bands at 815 and 880 (Ag > 100 nm) cm−1 identified as active oxygen species. • 880 cm−1 band most likely responsible for higher apparent TOF in large Ag particles. In situ Raman spectroscopy and parallel fixed bed reactor studies were conducted under ethylene epoxidation conditions with O 2 at 1 atm and 200 ℃ on unpromoted Ag/α-Al 2 O 3 catalysts with different Ag particle sizes. It was found that for Ag particles of 20–50 nm, the weight normalized conversion rate decreased rapidly with increasing Ag particle size but remained almost constant above 50 nm. On the other hand, the apparent TOF increased with increasing Ag particle sizes in the 20–170 nm studied range, while ethylene oxide selectivity at zero residence time was nearly constant (55 ± 4%). Raman bands at 815 (all Ag sizes) and 880 (Ag sizes > 100 nm) cm−1 were identified and assigned to active molecular oxygen species. The 880 cm−1 species was assigned to a molecular oxygen complex structure stabilized by subsurface oxygen. The presence of the 880 cm−1 oxygen species likely explain the higher apparent TOF in larger Ag particles (>100 nm). [ABSTRACT FROM AUTHOR]

In this work, liquid-phase catalytic oxidation of toluene was carried out under solvent-free conditions, and highly selective synthesis of benzaldehyde (BAL) and benzyl alcohol (BOL) and benzoic acid (BAC) in the presence of Mn@ZIF-8 calcined material as catalyst with oxygen molecules. As a heterogeneous catalyst, the zeolitic imidazolate framework Mn@ZIF-8 derived material exhibited reasonable substrate-product selectivity (70.3% of selectivity to BAL and BOL, 95.1 % of selectivity to BAL, BOL and BAC) and conversion (6.5%) under optimum reaction conditions. The catalysts were characterized by BET-specific surface area determination, XRD, XPS, FT-IR, TG-DTG and SEM-EDS-Mapping. The results demonstrated that the catalytic capacity of the catalysts was enhanced by the good dispersion of amorphous Mn species in ZIF-8 derivatives and high specific surface area. The possible reaction pathway for the catalytic oxidation of toluene was also suggested. Maybe this method employing Mn@ZIF-8 as efficient catalyst affords a new and environmentally friendly route for the synthesis of BOL and BAL from the selective oxidation of toluene.

Peroxo-heteropoly compound PO4[W(O)(O2)2] was synthesized on calcium-deficient hydroxyapatite using a reaction of surface [HPO4]2− groups on hydroxyapatite with a Na2[W2O3(O2)4] aqueous solution. The vibration of [HPO4]2− at 875 cm−1 became very weak, and the vibration of the peroxo-oxygen bond [O–O]2− at 845 cm−1 appeared in the FT-IR spectrum of the solid product, indicating that PO4[W(O)(O2)2] was formed on the surface of hydroxyapatite. The formed solid sample was further reacted with PdCl2(PhCN)2 in an acetone solution to fix PdCl2 between the O sites on the hydroxyapatite. Elemental analyses proved that the resultant solid contained 1.2 wt.% Pd, implying that PdCl2 molecules were immobilized on the surface of hydroxyapatite. The hydroxyapatite-based hybrid compound containing Pd and PO4[W(O)(O2)2] was used as a heterogeneous catalyst in a methanol solvent for propylene epoxidation by molecular oxygen in an autoclave batch reaction system. A propylene conversion of 53.4% and a selectivity for propylene oxide of 88.7% were obtained over the solid catalyst after reaction at 363 K for 8 h. The novel catalyst could be reused by a simple centrifugal separation, and the yield of propylene oxide did not decrease after the reaction for five runs. By prolonging the reaction time to 13 h, the highest yield of propylene oxide at 363 K over the solid catalyst was obtained as 53.8%, which was almost the same as that of the homogeneous catalyst containing PdCl2(PhCN)2 and [(C6H13)4N]2{HPO4[W(O)(O2)2]2} for the propylene epoxidation. Methanol was used as a solvent as well as a reducing agent in the propylene epoxidation by molecular oxygen. Small particles of Pd metal were formed on the surface of the hybrid solid catalyst during the reaction, and acted as active species to achieve the catalytic turnover of PO4[W(O)(O2)2] in the propylene epoxidation by molecular oxygen in methanol. [ABSTRACT FROM AUTHOR]

Simultaneous nitric oxide (NO) laser-induced fluorescence (LIF), atomic oxygen (O) two-photon LIF (TPLIF), and molecular oxygen (O 2) LIF were demonstrated using a single broadband femtosecond (fs) laser in methane- and hydrogen-fueled flames. An amplified Ti:Sapphire laser with ∼80-fs pulse duration was used to pump an optical parametric amplifier (OPA) to generate 226.1-nm pulses having 2.3 nm (∼450 cm−1) bandwidth to excite all three species simultaneously. The specific excitation transitions are NO A-X (0,0) system, O 3 p 3 P ← ← 2 p 3 P two-photon transition, and O 2 B 3 Σ u − − X 3 Σ g − Schumann-Runge system. Detailed emission characterization was performed using a 1D imaging spectrometer to identify suitable emission bands for interference-free detection of each species. A simultaneous detection system consisting of a visible and a UV camera provided the optimal detection of all three species. Imaging studies revealed high concentrations of NO, O, and O 2 at the edge of the flame cone of Bunsen flames because NO and O are produced at the hot flame front. O 2 LIF signal was present only at the flame front because of the strong temperature dependence of the O 2 Schumann-Runge system. Direct imaging of O TPLIF enabled single-shot as well as high-fidelity shot-averaged line images in stable laminar flames. Equivalence ratio scans in the CH 4 /air Hencken flames showed good agreements for O and O 2 with Cantera equilibrium predictions performed using GRI-Mech 3.0. Although the NO measurements deviated from the equilibrium calculations on the fuel-rich side, it agreed well with previously reported NO LIF measurements in a similar flame. This discrepancy is likely due to Prompt NO, which was not considered in the simulation. NO LIF measurements as a function of height-above-the-burner in the H 2 /air Hencken flames agreed well with calculated NO mole fractions using the UNICORN flame code. The present study lays the foundation for single-laser imaging of three critical flame species in NO formation pathways in combustion systems. [ABSTRACT FROM AUTHOR]

Bio‐catalysis is a versatile and powerful tool in organic synthesis, hazardous chemical remediation, biosensors, and industrial sectors. It has been claimed that laccases can function as an intriguing class of biocatalyst in organic chemistry. They are highly favourable catalysts and offer advantages over conventional oxidants and toxic metal catalysts by exhibiting high activity in aqueous media under mild conditions and also work on diverse functional groups possessing substrates maintaining the atom economy. They coordinate well with molecular oxygen and perform chemo selective oxidation reactions, as well as a plethora of other reactions. However, this review is intended to cover molecular oxygen‐assisted laccase catalysis in organic transformations and its significance in industry. [ABSTRACT FROM AUTHOR]

A metal-free catalyzed oxidation of 2-nitro-4-methylsulfonatotoluene(NMST) to produce 2-nitro-4-methylsulfonatobenzoic acid(NMSBA) under Taylor flow regimes is introduced. N,N′,N″- trihydroxyisocyanuric acid (THICA) as the catalyst and nitric acid as promoter, molecular oxygen as oxidant. The related parameters, such as residence time (τ), reaction temperature (T), and molar flow ratio of oxygen/substrate were investigated systematically. A good yield and selectivity were obtained by taking advantages of continuous flow system. Compared with the traditional batch oxidation process, the new continuous process is more safe and environmentally friendly. [ABSTRACT FROM AUTHOR]

The process of oxidative dehydrogenation of ethane (ODE) at an elevated pressure over a MoVNbTeOx mixed oxide catalyst is studied. It is found that when the reaction is carried out at 280°C, the fraction of the total amount of reacted oxygen consumed for the formation of ethylene decreases from 100 to 68% with the increase in pressure from 0.1 to 10.0 MPa, which may indicate an increase in the role of chemisorbed oxygen in the ODE process at a high pressure. Here, the productivity with respect to ethylene at 280°C and 10.0 MPa is higher in comparison with the value obtained at 360°C and 0.1 MPa. [ABSTRACT FROM AUTHOR]

A binary system (BS) of styrene epoxide–p-toluenesulfonic acid (SE–TSA) oxidized in a solution of isopropyl alcohol (ISA) initiates its radical chain oxidation (RCO). For the correct measurement of the oxygen uptake by the binary system itself, RCOs are blocked by introducing small (~10–5 mol/L) concentrations of Cu2+ acetate, a catalyst for breaking solvent oxidation chains. The oxidation rate measured using this technique is expressed as V = k [SE]0 [TSA]1 at [SE] [TSA]1, where SE is styrene epoxide and TSA is p‑toluenesulfonic acid. The Arrhenius form of the effective rate constant has the form k [s–1] = 5.2 × 1010exp(–85.0 kJ mol–1/RT) at 333–348 K. [ABSTRACT FROM AUTHOR]

The in‐depth mechanism on the simultaneous activation of O2 and surface lattice O2− on one active metallic site has not been elucidated yet. Herein, we report a strategy for the construction of abundant oxygen activation sites by rational design of Cu1/TiO2 single atom catalysts (SACs). The charge transfer between isolated Cu and TiO2 support generates abundant CuI and 2‐coordinated Olat sites in Cu1−O−Ti hybridization structure, which facilitates the chemisorption and activation of O2 molecules. Simultaneously, the Cu1−O−Ti induced TiO2 lattice distortion activate the adjacent surface lattice O2−, achieving the dual activation of O2 and surface lattice O2−. The Cu1−O−Ti active site switches the CO oxidation mechanism from Eley‐Rideal (80 °C) to Mars–van Krevelen route (200 °C) with the increase of reaction temperature. The dual activation of O2 and surface lattice O2− can by modulating the electron properties of SACs can boost the heterogeneous catalytic oxidation activity. [ABSTRACT FROM AUTHOR]

Mg 2 Fe layered double hydroxide was prepared by the coprecipitation method and was used as an efficient catalyst for the Baeyer–Villiger oxidation of cyclohexanone to caprolactone in the presence of molecular oxygen and benzaldehyde. The obtained catalyst was characterized by XRD, FTIR, SEM, TG, XPS, and Hammett indicator method. The effects of solvent, benzaldehyde dosage. reaction temperature, O 2 flow rate, catalyst dosage, and reaction time on the reaction were examined. Mg 2 Fe-LDH catalyst shows good catalytic results in the catalytic process which could also selectively convert a variety of cyclic ketone derivatives to their corresponding lactone with high yields. A series of controlled experiments were conducted to reveal the reaction mechanism. The results imply that the catalyst is bifunctional, possessing both alkalinity and redox properties. The alkalinity of Mg 2 Fe-LDH catalyzes the oxygen transfer from perbenzoic acid to cyclohexanone, iron with its highest oxidation state could catalyze the autoxidation of benzaldehyde to perbenzoic acid. In addition, the catalysts can be reused at least five times without significant decrease in catalytic activity. [Display omitted] • An environmentally Mg 2 Fe-LDH catalyst was prepared using inexpensive materials through a mild method of coprecipitation. • Mg 2 Fe-LDH as a bifunctional catalyst possesses both alkalinity and redox property. • This catalytic system selectively converts a wide scope of ketone derivatives to their corresponding lactones with high yields. [ABSTRACT FROM AUTHOR]

• Transition metal-free visible light-mediated method for the construction of various N -heterocycles at room temperature. • 4CzIPN was used as photocatalyst with molecular oxygen as terminal oxidant. • This photocatalytic system exhibits good functional group tolerance. • Biologically active natural product Schizocommunin and its derivatives were successfully synthesized. • A plausible reaction mechanism involving a radical process was proposed. A novel, transition metal-free visible light-mediated method for the construction of N -heterocycles from easily available aldehydes and o -substituted anilines in the presence of 4CzIPN under oxygen atmosphere has been developed. This photocatalytic system is a sustainable and atom-economical methodology that avoids toxic chemical additives and transition metals under ambient conditions. A variety of functionalized nitrogenous heterocyclic compounds are obtained in good to excellent yields. Notably, the biologically active natural product Schizocommunin and its derivatives are successfully synthesized, which might indicate this protocol has more applications in the future. In addition, a plausible reaction mechanism involving a radical process has been proposed based on control experiments and mechanism exploration, and further applications of this catalytic system are under way in our laboratory. A novel, transition metal-free visible light-mediated method for the construction of N-heterocycles from easily available aldehydes and o -substituted anilines in the presence of 4CzIPN under oxygen atmosphere has been developed. [Display omitted] [ABSTRACT FROM AUTHOR]

This review article describes a historical perspective of elucidation of the nature of the chemical bonds of the high-valent transition metal oxo (M=O) and peroxo (M-O-O) compounds in chemistry and biology. The basic concepts and theoretical backgrounds of the broken-symmetry (BS) method are revisited to explain orbital symmetry conservation and orbital symmetry breaking for the theoretical characterization of four different mechanisms of chemical reactions. Beyond BS methods using the natural orbitals (UNO) of the BS solutions, such as UNO CI (CC), are also revisited for the elucidation of the scope and applicability of the BS methods. Several chemical indices have been derived as the conceptual bridges between the BS and beyond BS methods. The BS molecular orbital models have been employed to explain the metal oxyl-radical character of the M=O and M-O-O bonds, which respond to their radical reactivity. The isolobal and isospin analogy between carbonyl oxide R2C-O-O and metal peroxide LFe-O-O has been applied to understand and explain the chameleonic chemical reactivity of these compounds. The isolobal and isospin analogy among Fe=O, O=O, and O have also provided the triplet atomic oxygen (3O) model for non-heme Fe(IV)=O species with strong radical reactivity. The chameleonic reactivity of the compounds I (Cpd I) and II (Cpd II) is also explained by this analogy. The early proposals obtained by these theoretical models have been examined based on recent computational results by hybrid DFT (UHDFT), DLPNO CCSD(T0), CASPT2, and UNO CI (CC) methods and quantum computing (QC).