Oxygen Insertion Research Articles

Mechanistic Studies on Oxygen-Insertion into Osmium(III)–Carbon Bond via High-Valent Oxido-Osmium(V) Complex

Abstract An osmium(III)-metalacycle complex consisting of 2-phenylpyridine is converted to the 2-phenoxidopyridine-osmium(III) complex upon treatment with a tertiary amine N-oxide, where a high-valent oxido-osmium(V) complex is proposed as a key reactive intermediate (H. Sugimoto et al. Organometallics, 2021, 40, 102–106). To gain insight into the reaction mechanism, substituent effects of 2-phenylpyridine moiety on the oxygen atom insertion reaction are examined using a series of 2-(4-X-phenyl)pyridines. All the cyclometalated complexes react with the tertiary amine N-oxide to produce the phenoxido-osmium(III) complexes. Kinetic analyses are conducted on the adduct formation process and the oxygen insertion reaction. In the former process, the binding constant of the amine N-oxide to the osmium(III) center is not influenced by electron withdrawing nature of the substituent X, but decrease of the reaction rate is observed in the latter process as electron withdrawing nature of X increases. Furthermore, the electronic effects of the amine N-oxides are examined using p-substituted N,N-dimethylaniline N-oxide (p-Y-C6H4N(O)(Me)2) to find that reaction rates increase as the electron withdrawing nature of Y increases. These results are consistent with the proposed mechanism in which the C–O bond formation involves conversion of the osmium(III)-N-oxide adduct to its oxido-osmium(V) species as the active oxidant.

New insights into the mechanisms of TiB[formula omitted](001) thermal oxidation combining molecular dynamics and density functional theory calculations

Using reactive force field molecular dynamics and Density Functional Theory, this study unravels the early stages of TiB2 oxidation. Overall, it is found that the TiB2 boron sheets hinder the oxidation until a temperature of 800 K is reached, above which a complex sequence of chemical mechanisms leads to the formation of a titanium oxide at the top surface and agglomeration of pure boron underneath, preventing further TiO2 growth below 900 K. It is demonstrated that titanium oxidation is possible after the softening and distortion of boron sheets due to oxygen adsorbate presence; mostly BO radicals, no B2O3-like structure is formed. The local distortions of boron aromatic rings allow oxygen insertion into the subsurface, which is followed by titanium extraction and migration towards the outer surface in contact with the molecular oxygen atmosphere. Mechanistic details of these complex extraction–oxidation processes and their relation to cooperative oxygen atoms and molecules are detailed in terms of pathways and corresponding energetics. Interestingly different reaction stages are identified, that do not exceed 2 eV activation. The proposed hierarchical scenario of oxidation of titanium and boron in TiB2 might benefit to the general understanding of metal diboride oxidation.

Symmetrical and Unsymmetrical Dicopper Complexes Based on Bis-Oxazoline Units: Synthesis, Spectroscopic Properties and Reactivity

Copper–oxygen adducts are known for being key active species for the oxidation of C–H bonds in copper enzymes and their synthetic models. In this work, the synthesis and spectroscopic characterizations of such intermediates using dinucleating ligands based on a 1,8 naphthyridine spacer with oxazolines or mixed pyridine-oxazoline coordination moieties as binding pockets for copper ions have been explored. On the one hand, the reaction of dicopper(I) complexes with O2 at low temperature led to the formation of a µ-η2:η2 Cu2:O2 peroxido species according to UV-Vis spectroscopy monitoring. The reaction of these species with 2,4-di-tert-butyl-phenolate resulted in the formation of the C–C coupling product, but no insertion of oxygen occurred. On the other hand, the synthesis of dinuclear Cu(II) bis-µ-hydroxido complexes based on pyridine–oxazoline and oxazoline ligands were carried out to further generate CuIICuIII oxygen species. For both complexes, a reversible monoelectronic oxidation was detected via cyclic voltammetry at E1/2 = 1.27 and 1.09 V vs. Fc+/Fc, respectively. Electron paramagnetic resonance spectroscopy (EPR) and UV-Vis spectroelectrochemical methods indicated the formation of a mixed-valent CuIICuIII species. Although no reactivity towards exogeneous substrates (toluene) could be observed, the CuIICuIII complexes were shown to be able to perform hydroxylation on the methyl group of the oxazoline moieties. The present study therefore indicates that the electrochemically generated CuIICuIII species described herein are capable of intramolecular aliphatic oxidation of C–H bonds.

Oxidation of chlortetracycline and its isomers by Botrytis aclada laccase in the absence of mediators: pH dependence and identification of transformation products by LC-MS.

Tetracyclines are antibiotics considered emerging pollutants and currently, wastewater treatment plants are not able to remove them efficiently. Laccases are promising enzymes for bioremediation because they can oxidize a wide variety of substrates. The aim of this study was to evaluate the Botrytis aclada laccase for the oxidation of chlortetracycline and its isomers in the absence of a mediator molecule, at a pH range between 3.0 to 7.0, and to characterize the transformation products by LC-MS. Chlortetracycline and three isomers were detected in both, controls and reaction mixtures at 0h and in controls after 48h of incubation but in different proportions depending on pH. An additional isomer was also detected, but only in the presence of BaLac. Based on the transformation products identified in the enzymatic reactions and information from literature, we assembled a network of transformation pathways starting from chlortetracycline and its isomers. The spectrometric analysis of the products indicated the probable occurrence of oxygen insertion, dehydrogenation, demethylation and deamination reactions. Four new products were identified, and we also described a novel transformation product without the chloro group. We observed that increasing pH led to higher diversity of main products. This is the first study using the laccase from fungi Botrytis aclada to oxidate chlortetracycline and its isomers and it can be considered as an ecological alternative to be used in bioremediation processes such as wastewater.

Unraveling Exclusive In-Plasma Initiated Oxidation Processes Occurring at Polymeric Surfaces upon O2 Admixtures to Medium Pressure Ar and N2 DBD Treatments.

Polymeric surfaces have been increasingly plasma-activated to adopt adequate chemistries, enabling their use in different applications. An unavoidable surface oxygen insertion upon exposure to non-oxygen-containing plasmas was always observed and mainly attributed to in-plasma oxidation stemming from O2 impurities in plasma reactors. Therefore, this work investigates exclusive in-plasma oxidation processes occurring on polyethylene surfaces by purposely admixing different O2 concentrations to medium-pressure Ar and N2 dielectric barrier discharges (base pressure: 10-7 kPa). Hence, distinctive optical emission spectroscopy and in-situ X-ray photoelectron spectroscopy (XPS) data were carefully correlated. Pure N2 discharge triggered an unprecedented surface incorporation of large nitrogen (29%) and low oxygen (3%) amounts. A steep rise in the O-content (10%) at the expense of nitrogen (15%) was detected upon the addition of 6.2 × 10-3% of O2 to the feed gas. When the added O2 exceeded 1%, the N content was completely quenched. Around 8% of surface oxygen was detected in Ar plasma due to high-energy Ar metastables creating more surface radicals that reacted with O2 impurities. When adding only 6.2 × 10-3% of O2 to Ar, the surface O content considerably increased to 12%. Overall, in-plasma oxidation caused by O2 impurities can strikingly change the surface chemistry of N2 and Ar plasma-treated polymers.

Dual factors required for cytochrome-P450-mediated hydrocarbon ring contraction in bacterial gibberellin phytohormone biosynthesis

Cytochromes P450 (CYPs) are heme-thiolate monooxygenases that prototypically catalyze the insertion of oxygen into unactivated C-H bonds but are capable of mediating more complex reactions. One of the most remarked-upon alternative reactions occurs during biosynthesis of the gibberellin A (GA) phytohormones, involving hydrocarbon ring contraction with coupled aldehyde extrusion of ent-kaurenoic acid to form the first gibberellin intermediate. While the unusual nature of this reaction has long been noted, its mechanistic basis has remained opaque. Building on identification of the relevant CYP114 from bacterial GA biosynthesis, detailed structure-function studies are reported here, including development of invitro assays as well as crystallographic analyses both in the absence and presence of substrate. These structures provided insight into enzymatic catalysis of this unusual reaction, as exemplified by identification of a key role for the "missing" acid from an otherwise highly conserved acid-alcohol pair of residues. Notably, the results demonstrate that ring contraction requires dual factors, both the use of a dedicated ferredoxin and absence of the otherwise conserved acidic residue, with exclusion of either limiting turnover to just the initiating and more straightforward hydroxylation. The results provide detailed insight into the enzymatic structure-function relationships underlying this fascinating reaction and support the use of a semipinacol mechanism for the unusual ring contraction reaction.

Investigation of the Model-Dependent Reactivity of the Char-Bound Nitrogen Surface: A DFT Study.

The concern of energy and the environment provides great inducement for fundamental research on the mechanisms of oxidation of char-bound nitrogen (char(N)). In the present study, based on the armchair(N) model, we investigated its reaction mechanism at an atomistic level and with a comprehensive study of the effect of the model surface. Several pathways are found by density functional theory (DFT) calculations for the oxidation of armchair(N). The main gaseous species released during the oxidation are NO, HCN, CO, and CO2. The evaluated optimal reaction pathways are selected to investigate the model-dependent reactivity. According to our calculations, the oxidation of the simplified top armchair(N) model (TM) will be much more competitive than that of the simplified edge armchair(N) model (EM). In the route giving NO, the decreased stability of the intermediates makes the reaction of TM more favorable. In the route giving HCN, the described reduced mechanism and the larger exothermicity and lower highest-energy transition state will be responsible for the priority. Further analysis of the kinetics gives the evidence for the competitiveness: the rate constants for most of the steps of the TM, such as HCN desorption, surface bond dissociation, ring closure and opening, and oxygen insertion and migration, are higher than that of the EM. Therefore, a conclusion can be drawn that the oxidation of the armchair(N) will mainly take place from the top surface rather than the edge surface. The results can be used to supplement present understanding of the oxidation of armchair structure, which is extremely crucial for the development of the kinetics model to better predict the NOx emissions during the air-staged combustion.

Structural modulation and spin glassiness upon oxidation in oxygen storage material LnFeMnO4+x for Ln = Y, Lu, and Yb

The mixed valence multiferroic LnFe2+Fe3+O4 (where Ln = Y, Lu, and Yb) can reversibly uptake oxygen into its lattice, which is evidenced by a crystallographic phase transition along with the appearance of structural modulations. In this study, we show that the Mn-substituted version of this multiferroic can also be readily oxidized to LnFe3+Mn3+O4.5 revealing similar oxygen storage behavior. Through neutron, electron, and synchrotron x-ray diffraction studies, we observe a structural modulation that we attribute to a displacement wave in the fully oxidized compound. This wave exhibits commensurability with a wavevector q = (−2/7, 1/7, 0). Bond valence summation analysis of plausible interstitial oxygen positions suggests that oxygen insertion likely occurs at the middle of the Fe/Mn–O bipyramid layers. The structural modulation of LnFeMnO4.5 is two-dimensional, propagates along the ab-plane, and is highly symmetric as 12 identical modulation vectors are observed in the diffraction patterns. The nature of the lanthanide, Ln3+, does not seem to influence such modulations since we observe identical satellite reflections for all three samples of Ln = Y, Lu, and Yb. Both LnFeMnO4 and LnFeMnO4.5 display spin glassy behavior with 2D short-range magnetic ordering being observed in LnFeMnO4. Analysis of the neutron diffraction data reveals a correlation length of ∼10 nm. Upon oxidation to LnFeMnO4.5, the short-range magnetic order is significantly suppressed.

Ozonative epoxidation of ethylene: A novel process for production of ethylene oxide

Here we report a novel reaction for ethylene oxide production using catalytic reaction of ethylene with ozone at room temperature. A key aspect of this path is boosting selective oxygen coverage on the surface of the catalyst which enables achieving high ethylene oxide selectivity and maintaining high conversion. Comparing the structural changes of the catalyst before and after the reaction suggested that the process allows facile generation of the catalytic active sites and selective oxygen species on the Ag/Al2O3 catalyst. With this novel process and under kinetically controlled regime, single-pass ethylene conversion of 98% and selectivity of 56% were achieved at room temperature. The low apparent activation energy of 22.1 kJmol-1 indicated the feasibility and high rate of this reaction at room temperature. This approach is believed to deliver a new class of processes for other oxygen insertion reactions.

Discovery and Characterization of a Baeyer-Villiger Monooxygenase using Sequence Similarity Network Analysis.

Baeyer-Villiger monooxygenases(BVMOs) are important flavin-dependent enzymes which perform oxygen insertion reactions leading to valuable products. As reported in many studies, BVMOs are usually unstable during application, preventing a wider usage in biocatalysis. Here, we discovered a novel NADPH-dependent BVMO which originates fromHalopolyspora algeriensisusing sequence similarity networks (SSNs). The enzyme is stable at temperatures between 10°C to 30°C up to five days after the purification, and yields the normal ester product. In this study,the substrate scope was investigated for a broad range of aliphatic ketones and the enzyme was biochemically characterized to identify optimum reaction conditions. The best substrate (86% conversion) was 2-dodecanone using purified enzyme. This novel BVMO could potentially be applied as part of an enzymatic cascade or in bioprocesses which utilize aliphatic alkanes as feedstock.

Impact of diabetes on emergency care of acute myocardial infarction patients during the coronavirus disease 2019 pandemic: a nationwide population-based study.

Although acute myocardial infarction (AMI) requires timely intervention, limited nationwide data is available regarding the association between disruption of emergency services and outcomes of patients with AMI during the coronavirus disease 2019 (COVID-19) pandemic. Moreover, whether diabetes mellitus (DM) adversely affects disease severity in these patients has not yet been investigated. This nationwide population-based study analyzed 45,648 patients with AMI, using data from the national registry of emergency departments (ED) in Korea. Frequency of ED visits and disease severity were compared between the COVID-19 outbreak period (year 2020) and the control period (the previous year 2019). The number of ED visits by patients with AMI decreased during the first, second, and third waves of the outbreak period compared to the corresponding time period in the control period (all p-values < 0.05). A longer duration from symptom onset to ED visit (p = 0.001) and ED stay (p = 0.001) and higher rates of resuscitation, ventilation care, and extracorporeal membrane oxygen insertion were observed during the outbreak period than during the control period (all p-values < 0.05). These findings were exacerbated in patients with comorbid DM; Compared to patients without DM, patients with DM demonstrated delayed ED visits, longer ED stays, more intensive care unit admissions (p < 0.001), longer hospitalizations (p < 0.001), and higher rates of resuscitation, intubation, and hemodialysis (all p-values < 0.05) during the outbreak period. While in-hospital mortality was similar in AMI patients with and without comorbid DM during the two periods (4.3 vs. 4.4%; p = 0.671), patients with DM who had other comorbidities such as chronic kidney disease or heart failure or were aged ≥ 80 years had higher in-hospital mortality compared with those without any of the comorbidities (3.1 vs. 6.0%; p < 0.001). During the pandemic, the number of patients with AMI presenting to the ED decreased compared with that of the previous year, while the disease severity increased, particularly in patients with comorbid DM.

Hexaniobate as a Recyclable Solid Base Catalyst to Activate C–H Bonds in Lignin Linkage Boosting the Production of Aromatic Monomers

The targeting cleavage of lignin into value-added aromatic monomers has attracted increasing attention. Although the base-catalyzed depolymerization of lignin has been developed, the use of excess corrosive bases and their poor recyclability limit their industrial implementation. Herein, a catalytic amount of solid base K7HNb6O19 (KNb6) coupled with copper-modified graphitic carbon nitride (Cu/C3N4) shows enhanced catalytic performance for the oxidative cleavage of β-O-4 lignin linkages using molecular oxygen. Due to the synergetic effect between KNb6 and Cu/C3N4, 96% of the β-O-4 ketone model was converted under relatively mild conditions, and phenol (yield: 90%) and other aromatic monomers (yield: 90%) were obtained. Moreover, KNb6–Cu/C3N4 is robust, and its catalytic activity is basically maintained after five cycles. Experimental and theoretical studies (spectroscopic analysis, control experiments, kinetic study, density functional theory calculations, etc.) reveal that the surface basic O atoms of KNb6 can simultaneously activate the Cβ–H bond of β-O-4 ketone to promote the insertion of molecular oxygen, and subsequently, Cu/C3N4 catalyzes the selective cleavage of the Cα–Cβ bond. The catalysts were also active for the oxidative cleavages of other lignin models and oxidized organosolv lignin.

Monitoring Light‐Driven Oxygen Insertion Reactions into Metal Carbon Bonds by LED‐NMR Spectroscopy

AbstractThe facile light‐driven insertion reaction of oxygen into metal carbon bonds of the BPI (1,3‐bis(2‐pyridylimino)isoindole) complexes [Pt(BPI)Me] and [Pd(BPI)Me] has been investigated by LED‐NMR in CDCl3. The initial insertion reaction leads to peroxo complexes [Pt(BPI)OOMe] and [Pd(BPI)OOMe], which undergo further reactions over time. Spectra were recorded at 1 minute time intervals, which enabled the tracking of the methyl substituent, which eventually generates formaldehyde (and methanediol) and methanol in almost equal proportions. Degradation of the solvent CDCl3 to phosgene and DCl in the presence of oxygen and light leads to several side reactions. DCl reacts with [M(BPI)Me] and [M(BPI)OOMe] to form [M(BPI)Cl], whereas phosgene reacts with in situ generated methanol to chloro methylformate and dimethyl carbonate.

Uncovering the Enhancement Mechanism of the Oxygen Reduction Reaction on Perovskite/Ruddlesden–Popper Oxide Heterostructures (Nd,Sr)CoO3/(Nd,Sr)2CoO4 and (Nd,Sr)CoO3/(Nd,Sr)3Co2O7

Although the perovskite (Nd,Sr)CoO3 (NSC113)/Ruddlesden-Popper (R-P) oxide (Nd,Sr)2CoO4 (NSC214) heterostructure is reported to improve the oxygen reduction reaction (ORR) activity by 2-3 orders of magnitude, the enhancement mechanism remains unclear. For the first time, we conclude that there are two main factors that can enhance the ORR activity: (1) Oxygen adsorbed on such heterostructures would gain more electrons, promoting the oxygen adsorption. (2) The more distant rock-salt layers on the heterointerfaces can facilitate the insertion of interstitial oxygen and form a high-speed transport channel of interstitial oxygen. Moreover, the perovskite/double-layered R-P oxide heterostructure, which has not been reported yet, is predicted to have better ORR performance than the perovskite/single-layered R-P oxide heterostructure. Our work elucidates the ORR enhancement mechanism on perovskite/R-P oxide heterostructures from the atomic level, which is demonstrated by experiments and, thus, is very meaningful for the development of high-performance electrochemical devices.

Cyclopalladates of 1-(2′-hydroxynaphthylazo) naphthalene complexes: Oxygen insertion into the Palladium-Carbon (Naphthyl) bond

Cyclopalladates of 1-(2′-hydroxynaphthylazo) naphthalene complexes: Oxygen insertion into the Palladium-Carbon (Naphthyl) bond

Experimentally revealed and theoretically certified synergistic electronic interaction of V-doped CoS for facilitating the oxygen evolution reaction.

Since electrocatalytic oxygen evolution (OER) is a four-electron transfer reaction with very slow kinetics, there is great competition to develop cheap, durable and efficient catalysts for oxygen evolution. A molecular model is designed for density functional theory (DFT) simulation calculations to guide the experiment, and this hypothesis is fully supported by the experimental data. Herein, regulating the composition and morphology of the bimetallic VCo and MoCo sulfide and monometallic sulfide nanoparticles (NPs) at the oil-water interface was achieved via a one-step hydrothermal method for efficient and durable OER electrocatalysts. Compared to CoS and MoCoS, the VCoS NPs show superior OER performance. By adjusting the atomic composition ratio of the VCoS nanoparticles, the VCoS NPs (1 : 2 : 1.5 mole ratio) showed a significant OER overpotential η = 255 mV (10 mA cm-2), and their outstanding stability was demonstrated after 48 h of continuous testing. The CoS and MoCoS NPs were also tested for comparison. Density functional theory (DFT) calculations showed that appropriate V doping (VCoS) can heighten the density of states (DOS) of the Fermi level, which generates more charge density and reduces the intermediate adsorption energy. This study not only provides efficient and powerful integrated catalysts, but also details a DFT calculation model guided by experiments to regulate the oxygen insertion technology, thus leading to the design of ideal materials and enabling more far-reaching applications in electrocatalysis.

Correlation between the twinning process and oxygen insertion in CeNbO4+x phases

This reinvestigation study presents the structural link between the twinning process in the CeNbO4 phase and the commensurate and incommensurate modulations in the CeNbO4+x phases, resulting from their oxidation. The anionic insertion occurs with the formation of oxygen clusters propagating through the structure via a small distortion of the cationic sub-structure associated with the rotation of the coordinating oxygen edges of some niobium sites. These cationic distortions and O–O rotations appear to be a common feature of the twinned CeNbO4 and CeNbO4+x phases. The location of the inserted oxygens is related to a local distortion of the cationic sub-structure, similar to that observed in “nano-twinned” areas, which explains why the directions of the incommensurate vectors of CeNbO4.08 are related to those of the twinning walls. The CeNbO4.08 and CeNbO4.25 phases are discrete and the continuity of the oxidation/reduction process is the result of the mixing of these two phases, which have in common their link with the distortions induced by the twinning process that guides the distribution of the distorted areas.

Lipoxygenase (LOX) in Sweet and Hot Pepper (Capsicum annuum L.) Fruits during Ripening and under an Enriched Nitric Oxide (NO) Gas Atmosphere

Lipoxygenases (LOXs) catalyze the insertion of molecular oxygen into polyunsaturated fatty acids (PUFA) such as linoleic and linolenic acids, being the first step in the biosynthesis of a large group of biologically active fatty acid (FA)-derived metabolites collectively named oxylipins. LOXs are involved in multiple functions such as the biosynthesis of jasmonic acid (JA) and volatile molecules related to the aroma and flavor production of plant tissues, among others. Using sweet pepper (Capsicum annuum L.) plants as a model, LOX activity was assayed by non-denaturing polyacrylamide gel electrophoresis (PAGE) and specific in-gel activity staining. Thus, we identified a total of seven LOX isozymes (I to VII) distributed among the main plant organs (roots, stems, leaves, and fruits). Furthermore, we studied the FA profile and the LOX isozyme pattern in pepper fruits including a sweet variety (Melchor) and three autochthonous Spanish varieties that have different pungency levels (Piquillo, Padrón, and Alegría riojana). It was observed that the number of LOX isozymes increased as the capsaicin content increased in the fruits. On the other hand, a total of eight CaLOX genes were identified in sweet pepper fruits, and their expression was differentially regulated during ripening and by the treatment with nitric oxide (NO) gas. Finally, a deeper analysis of the LOX IV isoenzyme activity in the presence of nitrosocysteine (CysNO, a NO donor) suggests a regulatory mechanism via S-nitrosation. In summary, our data indicate that the different LOX isozymes are differentially regulated by the capsaicin content, fruit ripening, and NO.

Ni-Catalyzed Oxygen Transfer from N2O onto sp3-Hybridized Carbons.

Herein we disclose a catalytic synthesis of cycloalkanols that harnesses the potential of N2O as an oxygen transfer agent onto sp3-hybridized carbons. The protocol is distinguished by its mild conditions and wide substrate scope, thus offering an opportunity to access carbocyclic compounds from simple precursors even in an enantioselective manner. Preliminary mechanistic studies suggest that the oxygen insertion event occurs at an alkylnickel species and that N2O is the O transfer reagent.

Self-sacrificial tyrosine cleavage by an Fe:Mn oxygenase for the biosynthesis of para-aminobenzoate in Chlamydia trachomatis

Chlamydia protein associating with death domains (CADD) is involved in the biosynthesis of para-aminobenzoate (pABA), an essential component of the folate cofactor that is required for the survival and proliferation of the human pathogen Chlamydia trachomatis. The pathway used by Chlamydiae for pABA synthesis differs from the canonical multi-enzyme pathway used by most bacteria that relies on chorismate as a metabolic precursor. Rather, recent work showed pABA formation by CADD derives from l-tyrosine. As a member of the emerging superfamily of heme oxygenase-like diiron oxidases (HDOs), CADD was proposed to use a diiron cofactor for catalysis. However, we report maximal pABA formation by CADD occurs upon the addition of both iron and manganese, which implicates a heterobimetallic Fe:Mn cluster is the catalytically active form. Isotopic labeling experiments and proteomics studies show that CADD generates pABA from a protein-derived tyrosine (Tyr27), a residue that is ∼14 Å from the dimetal site. We propose that this self-sacrificial reaction occurs through O2 activation by a probable Fe:Mn cluster through a radical relay mechanism that connects to the "substrate" Tyr, followed by amination and direct oxygen insertion. These results provide the molecular basis for pABA formation in C. trachomatis, which will inform the design of novel therapeutics.