Subsequent Oxidation Research Articles

Photochemical Ring Expansion of Cyclic Sulfoximines with Aryl Diazoacetates and Subsequent Diastereoconvergent Oxidation

Photochemical Ring Expansion of Cyclic Sulfoximines with Aryl Diazoacetates and Subsequent Diastereoconvergent Oxidation

Photocatalytic Silylation of Aryl Alkynoates: Synthesis of Silylated Coumarins

AbstractHerein, we report the photocatalytic synthesis of 3‐silyl coumarins using hydrosilanes as the silyl radical source with aryl alkynoates. Readily prepared N‐aminopyridinium salts act as hydrogen atom transfer reagents for generating silyl radicals under photoredox catalysis. The reaction proceeds through a silyl radical addition to alkyne followed by radical cascade cyclization/migration with subsequent oxidation and aromatization to give the desired 3‐silyl coumarins in 34–89% yield.

Iron Oxide Clusters as Electron Donors Under Light Enhance Oxygen Reduction Kinetics at Atomically Dispersed Fe for Photocatalytic CH4 Partial Oxidation

AbstractPhotocatalytic CH4 oxidation to CH3OH emerges as a promising strategy to sustainably utilize natural gas and mitigate the greenhouse effect. However, there remains a significant challenge for the synthesis of methanol by using O2 at low temperature. Inspired by the catalytic structure in soluble methane monooxygenase (MMO) and the corresponding reaction mechanism, we prepared a biomimetic photocatalyst with the decoration of Fe2O3 nanoclusters and satellite Fe single atoms immobilized on carbon nitride. The catalyst demonstrates an excellent CH3OH productivity of 5.02 mmol ⋅ gcat−1 ⋅ h−1 with CH3OH selectivity of 98.5 %. Mechanism studies reveal that the synergy between Fe2O3 nanoclusters and Fe single atoms establishes a dual‐Fe site as MMO for O2 activation and subsequent CH4 partial oxidation. Moreover, the light excitation of Fe2O3 nanoclusters with a relative narrow band gap could deliver the electrons and protons to atomic Fe that facilitating the oxygen reduction kinetics for the robust of CH3OH synthesis.

Distinct Pathways Determined by Photocatalytic C─H or O─H Bond Activation for Hydroxyl Compounds Conversion Paired With Hydrogen Production

AbstractSelective control of C─H or O─H bond activation in photocatalytic conversion coupled with hydrogen production is a promising yet challenging goal. Here, an efficient photocatalytic system is reported that can produce high‐valued tartaric acid or formaldehyde and simultaneous producing hydrogen. At optimized conditions, the directional conversion of glycolic acid into tartaric acid is achieved with a selectivity of 76.24%, and the selectivity of methanol oxidation into formaldehyde reaches 88.21%. A high hydrogen production rate of 21.43 mmol·g−1·h−1 is obtained using glycolic acid as substrate. Mechanism studies reveal that α‐C─H bond is preferentially activated in glycolic acid adsorbed on the photocatalyst, while O─H bond is preferentially activated in methanol, forming carbon‐centered radical (•CH(OH)COOH) or oxygen‐centered radical (CH3O•) for subsequent coupling or oxidation reactions. This work demonstrates the selective control of the photocatalytic conversion process of different hydroxyl compounds, providing a new perspective for achieving organic compounds selective activation coupled with hydrogen production.

Tetratellura[36]octaphyrin(1.1.1.1.1.1.1.1) Metalation: From Dynamic Behavior to Rigid Chiral Figure-of-Eight Molecule; Activation of the C-Te Bond by Ruthenium.

The large expanded telluraporphyrin, tetratellura[36]octaphyrin(1.1.1.1.1.1.1.1), was synthesized in 7% yield by acid-catalyzed condensation of pyrrole with 2,5-bis(phenylhydroxymethyl)tellurophene and subsequent oxidation. The macrocycle acquires the chiral figure-eight conformation with two alternative spatial arrangements of the heterocyclic rings. The molecule exhibits dynamic behavior in solution, which was studied by means of 1H NMR spectroscopy. The reaction with chlorine led to a reversible oxidative addition at two distant tellurium atoms, which altered the preferred conformations. Metalation of the tetratellura[36]octaphyrin with triruthenium dodecacarbonyl selectively activated two of the eight Te-C bonds, resulting in the formation of an organometallic diruthenium compound. During the reaction, two tellurophene rings were converted to 1-ruthena-2-telluracyclohexadiene units containing octahedral ruthenium(II) centers. The rigid structure of this chiral complex allowed the separation of enantiomers.

Exploring Ultrafast Carrier Dynamics in Photoelectrochemical Water Splitting Using Transient Absorption Spectroscopy

AbstractHydrogen fuel produced from water splitting using sunlight remains one of the cleanest and most sustainable energy sources. However, photoelectrochemical hydrogen production faces several challenges, including poor sunlight absorption, deficient charge carrier lifetime and transfer rates, and very sluggish kinetics of the water oxidation half‐reaction. To address these challenges, researchers have concentrated on enhancing the efficiency of photoelectrochemical water splitting. A critical factor in this enhancement is a deeper understanding of the fundamental processes involved in photoabsorption and the subsequent oxidation evolution reaction. The advent of ultrafast lasers has enabled the detailed tracking of charge carriers within materials after sunlight absorption, including their separation and migration to the surface for water oxidation. Ultrafast transient absorption spectroscopy is a powerful technique that allows real‐time observation of the behavior of excited states and charge carriers on femtosecond to nanosecond timescales. Recent studies utilizing ultrafast transient absorption spectroscopy are explored to investigate the dynamics of charge carriers in photoelectrochemical water splitting, providing insights into the mechanisms that lead to the design of enhanced photoanodes with improved efficiency.

Enhanced 3D-printed Matrix for Electrocatalytic Detection: A Practical and Simple Electrochemical Platform

AbstractIn this work, we proposed a novel 3D-printed manufactured electrode system. A project was developed and optimized, compatible with commercially available potetiostats. Additive manufacturing included the modification of the pseudo-reference electrode by electrodeposition of silver and its subsequent oxidation to the Ag/AgCl form. Then the system was tested using electrochemical techniques to check the application as a universal electroactive platform. As an example, we checked the detection of paracetamol as a common substance from non-steroidal anti-inflammatory drugs (NSAIDs). Finally, the system was compared to available commercial carbon electrodes, considering the screen-printed electrode (SPE no.1 and SPE no.2) and the glassy carbon electrode (GCE), showing higher sensitivity and linearity range compared to commercial screen-printed systems. The novelty of the proposed platform unveils a new way of common, simple, budget, and fast obtaining a universal electroactive platform for electrochemical research, keeping high-performance parameters.

Catalytic oxidation of Mn(II) on ferrihydrite and goethite surfaces and the subsequent oxidation and immobilization of coexisting Cr(III)

Catalytic oxidation of Mn(II) on ferrihydrite and goethite surfaces and the subsequent oxidation and immobilization of coexisting Cr(III)

Efficient catalytic oxidation of xylose to formic acid with the oxygen vacancies of CeO2 promoted the vanadium catalysts anchored on biochar

The catalytic oxidation of carbohydrates for the preparation of formic acid (FA) is an prominent route for high-value utilisation of biomass. Reforming xylose, a biomass derivative, into FA with high efficiency is essential for the advancement of non-homogeneous V-type catalysts. Here, we present the self-assembly of V and Ce onto a cellulose pulp for the synthesis of oxygen vacancy (Ov)-rich non-homogeneous-bimetallic catalysts (5Ce-VOx/BC-600). Under the optimised conditions, 71.46 % FA was obtained, which far exceeded the catalytic performance of the single-metal catalyst. Furthermore, the 5Ce-VOx/BC-600 catalyst showed excellent stability and reusability. Kinetic studies revealed that glyceric and glycolic acids served as the pivotal intermediates, undergoing subsequent deacidification and oxidation processes to yield FA and CO2. The analysis of the catalytic mechanism indicated that the incorporation of Ce enhanced the quantity of acidic sites and the concentration of Ov in the 5Ce-VOx/BC-600 catalyst, which promoted substrate adsorption and O2 activation. Meanwhile, the catalyst showed high lattice oxygen (OL) mobility and assisted the redox cycle of V5+/V4+ to oxidise xylose to FA. Significantly, the synergistic effect of Ce, V species and Ov enhances the OL mobility of the catalysts, thus promoting the efficient oxidation of xylose. The catalytic system was further extended to the oxidation of other biomass derivatives to FA, demonstrating excellent catalytic performance.

Photoredox-Catalyzed Markovnikov Hydroamination of Alkenes with Azoles.

A visible-light induced intermolecular hydroamination of alkenes with azoles is reported, delivering pharmaceutically valuable N-benzyl azoles in high yields with excellent Markovnikov selectivity. Mechanistic studies suggest that the process is initiated by the energy transfer of the excited photocatalyst with alkenes, followed by the single electron reduction, protonation, and subsequent single electron oxidation to afford the key alkyl carbocation intermediate. This protocol exhibits advantages of broad functional group tolerance, excellent atom economy, high efficiency, and mild reaction conditions.

Unexpectedly high degradation efficiency for MB on Bi3O4Br photocatalyst obtained from bismuth citrate

For the first time, pure Bi3O4Br with a uniform square sheet-like structure was synthesized using a hydrothermal method at 180 °C and pH of 12.5 by employing bismuth citrate as the bismuth source without any surfactant. The photocatalytic activity of Bi3O4Br for the degradation of methylene blue (MB), tetracycline (TC), methyl violet (MV), and rhodamine B (RhB) was evaluated under visible light illumination and the results showed that the as-prepared Bi3O4Br exhibited excellent photodegradation efficiency for MB with an apparent rate constant (ka) of 0.02676 min−1, superior to TC, MV and RhB with ka = 0.00899 min−1, 0.00073 min−1 and 0.00409 min−1, respectively. Since the direct oxidation of the holes predominates in the degradation process, the study on the photocatalytic mechanism suggested that a more positive valence band (VB) potential of Bi3O4Br than HOMO orbital position of MB was prerequisite and also, the smaller the difference between VB potential of a photocatalyst and HOMO energy level of a pollutant, the faster the migration of the holes and subsequent oxidation of pollutant.

Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere.

Earth is expected to have acquired a reduced proto-atmosphere enriched in H2 and CH4 through the accretion of building blocks that contain metallic Fe and/or the gravitational trapping of surrounding nebula gas. Such an early, wet, reduced atmosphere that covers a proto-ocean would then ultimately evolve toward oxidized chemical compositions through photochemical processes that involve reactions with H2O-derived oxidant radicals and the selective escape of hydrogen to space. During this time, atmospheric CH4 could be photochemically reprocessed to generate not only C-bearing oxides but also organics. However, the branching ratio between organic matter formation and oxidation remains unknown despite its significance on the abiotic chemical evolution of early Earth. Here, we show via numerical analyses that UV absorptions by gaseous hydrocarbons such as C2H2 and C3H4 significantly suppress H2O photolysis and subsequent CH4 oxidation during the photochemical evolution of a wet proto-atmosphere enriched in H2 and CH4. As a result, nearly half of the initial CH4 converted to heavier organics along with the deposition of prebiotically essential molecules such as HCN and H2CO on the surface of a primordial ocean for a geological timescale order of 10-100 Myr. Our results suggest that the accumulation of organics and prebiotically important molecules in the proto-ocean could produce a soup enriched in various organics, which might have eventually led to the emergence of living organisms.

Core‐Fluorinated BODIPYs – a New Family of Highly Efficient Luminophores

AbstractA modular synthesis of novel series of 1,7‐difluorinated BODIPYs has been elaborated. First, the acid‐catalyzed condensation of ethyl 3‐aryl‐4‐fluoro‐1H‐pyrrole‐2‐carboxylates with aromatic aldehydes gives the corresponding dipyrromethane‐1,9‐dicarboxylates. The latter are subjected to the exhaustive reduction with lithium aluminum hydride to transform the ester moieties into methyl groups. The subsequent oxidation of the resulting 1,9‐dimethylated dipyrromethanes followed by the boron difluoride complexation afforded a family of novel core‐fluorinated BODIPYs in up to 74 % yield. Photophysical properties of the resulting BODIPYs were tuned by varying of the starting fluoropyrroles and aromatic aldehydes and were studied by UV‐visible and fluorescence spectroscopy. As a result, the fluorescence quantum yields of the obtained compounds reached up to 99 %. In addition, their ability to generate singlet oxygen and electrochemical properties were also evaluated. As a result, a new promising family of fluorophores with a good combination of the fluorescence and photosensitizing properties was obtained. It was found that conversion of ester groups into methyl ones at the 3,5‐positions of the BODIPY core is a crucial step toward fluorescence enhancement. In addition, DFT calculations were performed to elucidate a relationship between electronic structure, geometry and photophysical properties of these BODIPYs.

Iron Oxide Clusters as Electron Donors Under Light Enhance Oxygen Reduction Kinetics at Atomically Dispersed Fe for Photocatalytic CH4 Partial Oxidation.

Photocatalytic CH4 oxidation to CH3OH emerges as a promising strategy to sustainably utilize natural gas and mitigate the greenhouse effect. However, there remains a significant challenge for the synthesis of methanol by using O2 at low temperature. Inspired by the catalytic structure in soluble methane monooxygenase (MMO) and the corresponding reaction mechanism, we prepared a biomimetic photocatalysts with the decoration of Fe2O3 nanocluster and satellite Fe single atom immobilized on carbon nitride. The catalyst demonstrates an excellent CH3OH productivity of 5.02 mmol·gcat-1·h-1 with methanol selectivity of 98.5%. Mechanism studies reveal that the synergy between Fe2O3 nanocluster and Fe single atom establishes a dual-Fe site as MMO for O2 activation and subsequent CH4 partial oxidation. Moreover, the light excitation of Fe2O3nanoclusters with a relative narrow bandgap could deliver the electrons and protons to atomic Fe that facilitating the oxygen reduction kinetics for the robust of methanol synthesis.

Boosting electrocatalytic oxygen reduction of Fe-Co polyphthalocyanine via the synergy of metal component optimization and axial ligand modification

Conjugated metal polyphthalocyanine (MPPc) organic skeletons, a kind of novel porous materials containing inherent M−N4 highly active sites, are of great significance for oxygen reduction reaction (ORR). Herein, bimetallic Fe-Co phthalocyanine covalent polymers (denoted as FeCoPPc) were prepared as ORR electrocatalysts through a solvothermal process and subsequent oxidation treatment. Meanwhile, the effect of axial oxygen-containing ligands of metal centers on the catalytic kinetic processes was also investigated. Benefiting from the highly exposed bimetal active sites and the finely designed ligand structure, FeCoPPc with optimized Fe/Co ratio and ClO3− coordination (Fe0.9Co0.1PPc-ClO3) displayed an outstanding ORR electrocatalytic activity and superior durability compared to 20 % Pt/C, manifested by an onset potential of 0.986 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.923 V vs. RHE in a 0.1 M KOH solution. This work may guide the rational design of high-performance electrocatalysts to regulate the catalytic activity.

Rhodium(III)-Catalyzed Atroposelective Indolization to Access Planar-Chiral Macrocycles.

Macrocycles incorporating conformationally defined indoles are widely found in bioactive natural products. However, the catalytic enantioselective synthesis of planar-chiral indoles via indolization involving macrocyclization remains elusive. Herein, we present the first rhodium(III)-catalyzed atroposelective macrocyclization, which involves the C-H activation of aniline, and a subsequent oxidation [3 + 2] annulation reaction with an intramolecular alkyne. This protocol achieves the construction of indoles, macrocyclization, and planar chirality control in a single step. Importantly, this strategy produces macrocyclic atropisomers bearing full-carbon ansa chains, which represent challenging targets in organic synthesis. Thermodynamic experiments revealed that the rotational barrier of the full-carbon ansa chain-linked macrocyclic atropisomer was lower than that of the atropisomer bearing an oxa-ansa chain. The reaction mechanism was elucidated by computational studies, which revealed that the C-H activation and intramolecular alkyne insertion steps collectively determined the enantioselectivity.

Oxide Acidity Modulates Structural Transformations in Hydrogen Titanates during Electrochemical Li-Ion Insertion.

Hydrogen titanates (HTOs) form a diverse group of metastable, layered titanium oxides with an interlayer containing both water molecules and structural protons. We investigated how the chemistry of this interlayer environment influenced electrochemical Li+-insertion in a series of HTOs, H2TiyO2y+1·nH2O (y = 3, 4, and 5). We correlated the electrochemical response with the physical and chemical properties of HTOs using operando X-ray diffraction, in situ differential electrochemical mass spectroscopy, solid-state proton nuclear magnetic resonance, and quasi-elastic neutron scattering. We found that the potential for the first reduction reaction trended with the relative acidity of the structural protons. This mechanism was supported with first-principles density functional theory (DFT) calculations. We propose that the electrochemical reaction involves reduction of the structural protons to yield hydrogen gas and formation of a lithiated hydrogen titanate (H2-xLixTiyO2y+1). The hydrogen gas is confined within the HTO lattice until the titanate structure expands upon subsequent oxidation. Our work has implications for the electrochemical behavior of insertion hosts containing hydrogen and structural water molecules, where hydrogen evolution is expected at potentials below the hydrogen reduction potential and in the absence of electrolyte proton donors. This behavior is an example of electrochemical electron transfer to a nonmetal element in a metal oxide host, in analogy to anion redox.

Accessing Homo- and Heterobimetallic Complexes with a Dianionic Pentadentate Ligand.

The tetrapyrazolylpyridyl diborate (B2Pz4Py) ligand provides a suitable platform for the isolation of heterobimetallic main-group element compounds as well as homotetrametallic copper complexes. The heterobimetallic tin(II)-lithium(I) (1) and tin(II)-thallium(I) (2) complexes have been synthesized, isolated, and fully characterized including single-crystal X-ray diffraction analysis. When reacted with copper(I) sources, complex 2 grants access to a homotetrametallic copper(I) complex (4). Upon subsequent oxidation, 4 gives rise to the bimetallic copper(II) complex 5, in which the two copper(II) centers are connected via a bridging bromido ligand (CuII-μ-Br-CuII).

CHARACTERIZATION OF FINE CARBONACEOUS AEROSOLS FROM THE EASTERN MEDITERRANEAN: CONTRIBUTIONS OF FOSSIL AND NON-FOSSIL CARBON SOURCES

ABSTRACT In order to better characterise carbonaceous components in atmospheric aerosols and to assess the contributions of fossil carbon (FC) and non-fossil carbon (NFC) sources and their seasonality in the Eastern Mediterranean, we collected fine (PM1.3) aerosols at a remote marine background site, the Finokalia Research Station, Crete, Greece, over a period of one-year. PM1.3 samples were analysed for elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC), and stable carbon isotope ratio (δ13CTC) and radiocarbon content (14CTC) (pMC) of total carbon (TC). All the parameters, i.e., PM1.3, δ13CTC and 14CTC showed a clear temporal pattern with higher values in summer and lower values in autumn. The 14CTC ranged from 54.7 to 99.1 pMC with an average of 74.5 pMC during the entire year. The FC content in TC (FCTC) was found to be slightly lower in winter and almost stable in other seasons, whereas the NFC contents (NFCTC) showed a clear seasonality with the highest level in summer followed by spring and the lowest level in winter. Based on these results together with the seasonal distributions of organic tracers, we found that biomass burning (BB) and soil dust are two major sources of the fine aerosols in winter. Although biogenic emissions of VOCs followed by subsequent secondary oxidation processes are significant in summer followed by spring and autumn, pollen is a significant contributor to TC in spring. This study showed that emissions from fossil fuel combustion are significant (25.5%) but minor compared to NFC sources in the eastern Mediterranean.

Direct mitochondrial import of lactate supports resilient carbohydrate oxidation.

Lactate is the highest turnover circulating metabolite in mammals. While traditionally viewed as a waste product, lactate is an important energy source for many organs, but first must be oxidized to pyruvate for entry into the tricarboxylic acid cycle (TCA cycle). This reaction is thought to occur in the cytosol, with pyruvate subsequently transported into mitochondria via the mitochondrial pyruvate carrier (MPC). Using 13 C stable isotope tracing, we demonstrated that lactate is oxidized in the myocardial tissue of mice even when the MPC is genetically deleted. This MPC-independent lactate import and mitochondrial oxidation is dependent upon the monocarboxylate transporter 1 (MCT1/ Slc16a1 ). Mitochondria isolated from the myocardium without MCT1 exhibit a specific defect in mitochondrial lactate, but not pyruvate, metabolism. The import and subsequent mitochondrial oxidation of lactate by mitochondrial lactate dehydrogenase (LDH) acts as an electron shuttle, generating sufficient NADH to support respiration even when the TCA cycle is disrupted. In response to diverse cardiac insults, animals with hearts lacking MCT1 undergo rapid progression to heart failure with reduced ejection fraction. Thus, the mitochondrial import and oxidation of lactate enables carbohydrate entry into the TCA cycle to sustain cardiac energetics and maintain myocardial structure and function under stress conditions.