Oxygen Molecules Research Articles

Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag−ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry

AbstractPhotocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (⋅CH3) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of ⋅CH3 and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR‐PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag−ZnO. Gas phase ⋅CH3 generated by photogenerated holes (O−) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH3O⋅) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO2. The gas‐phase self‐coupling reaction of ⋅CH3 contributes to the formation of ethane, which indicates the key role of ⋅CH3 desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from ⋅CH3 of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.

Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag-ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry.

Photocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (⋅CH3 ) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of ⋅CH3 and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag-ZnO. Gas phase ⋅CH3 generated by photogenerated holes (O- ) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH3 O⋅) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO2 . The gas-phase self-coupling reaction of ⋅CH3 contributes to the formation of ethane, which indicates the key role of ⋅CH3 desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from ⋅CH3 of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.

Unraveling Pathways of Photocatalytic Oxygen Evolution on Fluorinated Anatase TiO2

Recent experiments reported that the efficiency of the oxygen evolution reaction (OER) was greatly improved in fluorinated TiO2 by forming the surface hydrogen bonds, but the mechanism remains ambiguous. Herein, we systematically investigated dual OER pathways on the fluorinated anatase TiO2(101) surface by using the first-principles calculations. The dual H-bonding water is significantly activated by trapping a first hole in the system and facilitates its proton transfer in pathway I. The inactive Ti-coordinated water also transfers a proton to a bridge O2– ion with a similar barrier and simultaneously traps the first hole in pathway II. Both ·OH radicals separately transfer a proton to the F– ion and bridge O2– ion very quickly and trap the second hole to produce the ·O radical. Consequently, the ·O radical directly couples with the bridge O2– ions with a high barrier of about 0.72 eV to produce the flat peroxo dimer (O22–) in pathway I. The Ti-coordinated ·O radical undergoes two steps of the proton transfer and O–O coupling with both high barriers of about 0.75 eV to produce the oblique O22– species in pathway II. Finally, the O22– spontaneously and successively traps the third and fourth holes to quickly form the oxygen molecule. Additionally, the fluorine atoms are further demonstrated to accelerate the proton transfer and the O–O coupling steps by comparing the pathways on the fluorinated and pure TiO2 surfaces. These results may provide new insights into the OER mechanism in fluorinated TiO2 and roles of the dopant in improving OER efficiency of the TiO2 photocatalysts.

Iron-palladium supported graphene as an efficient bimetallic catalyst for the selective oxidation of benzyl alcohol to benzaldehyde

The catalytic oxidation of benzyl alcohol (OBA) is one of the significant methods to produce benzaldehyde, an essential reagent in the chemical and pharmaceutical industries. However, developing an active and efficient catalyst for OBA is a tremendous challenge in commercialization. This research describes a simple, eco-friendly method for producing Fe, Pd, and Fe: Pd bimetallic nanoparticles fabricated by sol immobilization over graphene to conduct OBA. The resulting composite nano-alloys were then characterized using X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The oxidation state and elemental composition of as-fabricated nanoparticles were analyzed using XPS. The point of zero charges (pHPZC) was analyzed and the PZC value indicated that the proposed adsorbent material tends to have a positive charge. The OBA reaction efficiency (87%) of bimetallic nanocatalysts stabilized in graphene support was increased through surface modification of the ratio of both metals. The experimental error was based on three parallel tests and the carbon balance (99.6%) was analyzed during the experiments A proposed reaction mechanism of OBA validated the β-hydride step's elimination by molecular oxygen converting the metal hydride into a water molecule, forming a peroxide intermediate to form water and oxygen molecules. The Fe on the nanocatalyst’s surface is preferentially responsible for the adsorption of the substrate molecule, resulting in the formation of metal-alkoxide. Since it lacks electrons, Fe is more likely to be oxidized, allowing it to perform better than monometallic catalysts in terms of catalytic activity. The present study has great potential to be applied on an industrial scale and studied for industrialists, researchers, and academicians.

Exploring the Potential of Lignocellulosic Biomass-Derived Polyoxymethylene Dimethyl Ether as a Sustainable Fuel for Internal Combustion Engines

The most effective way to reduce internal combustion engine emissions is to use a sustainable alternative fuel that contains oxygen molecules. Alternative fuels may be used to address a future global energy crisis. Different oxygenated alternative fuels have been investigated in internal combustion engines. Polyoxymethylene di-methylene ether (PODE), which contains 3–5 CH2O groups, is currently superior in the field of oxygenated fuels due to its physical and chemical properties. Furthermore, using PODE as a fuel does not necessitate any significant engine modifications. When compared to standard diesel fuel, the use of PODE results in near stoichiometric combustion with less hazardous exhaust gas. It also significantly reduces NOx emissions due to the lack of C-to-C bonds. Several articles in the literature were found on the manufacturing and application processes for the production of PODE. However, the current review focuses primarily on simplifying the various production technologies, the physical and chemical properties of PODEn and its advantages and disadvantages in ICEs, PODEn application in internal combustion engines and its characteristics, PODE spray analysis, and measurements of the fuel’s physical and chemical characteristics. This review emphasizes the fact that PODE can be used as a sole fuel or in conjunction with fossil fuels and advanced combustion technologies. Because C-C bonds and higher oxygen molecules are not available, the trade-off relationship between nitrogen oxides and soot production is avoided when PODEn is used as a fuel, and combustion efficiency is significantly improved.

Effect of Pd crystal facet on the reaction of oxygen-promoted hydrogen evolution from formaldehyde driven by visible light

For heterogeneous catalysis reaction, the facet effect plays an important role in affecting the activity of the catalyst. In this paper, we prepared Pd catalysts exposed to (111) and (100) crystal planes by controlling the type of end capping agent and the structure of the catalysts were characterized using techniques such as TEM, XRD, XPS. The eosin Y (EY) sensitized Pd catalysts were used to catalytic hydrogen production from formaldehyde driven by visible light under alkaline conditions. The experimental results show that the Pd(100)/RGO catalyst exhibits highest catalytic performance, the hydrogen evolution rate was 86.85μmol/h. This can be attributed to the strong interaction between the Pd(100) facet and graphite oxide, which is conducive to improving the transfer rate on the catalyst surface. In addition, the dissociation energy barrier of oxygen molecules on the surface of the Pd(100) catalyst is an important reason for the high activity of the catalyst. Our results give a new viewpoint to the development of high efficiency catalysts for hydrogen evolution from formaldehyde.

Waste Cigarette Butts-Derived Nitrogen-Doped Carbon Fibers Loaded with Ru Nanoparticles as an Efficient Cathode Catalyst for Lithium-Oxygen Batteries

Low catalytic activity and high cost of cathode catalysts hinder the large-scale commercial application of lithium-oxygen (Li-O2) batteries. In this work, waste cigarette butts, which inherently have a porous fiber structure, were selected as the precursor of the carbon material for the cathode catalyst of Li-O2 batteries. The porous nitrogen-doped carbon material was prepared by simple heat treatment of waste cigarette butts. The rich porous structure of the obtained carbon fiber material effectively enhances the diffusion of oxygen molecules and provides ample space for the discharge products. N doping in carbon fibers enhances the bifunctional catalytic activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which was corroborated by density functional theory (DFT) calculation. The assembled Li-O2 battery with C–N fibers-loaded Ru nanoparticles catalyst delivers an initial discharge capacity of up to 12 036.3 mA h g–1 and can be cycled stably for more than 800 cycles (4000 h) at a current density of 200 mA g–1 and a cutoff capacity of 500 mA h g–1. Even at a high current density of 500 mA g–1, the cells still show a high average discharge voltage of 2.28 V with excellent cycle stability and rate capability. XPS analysis proves that the cathode material can effectively inhibit the formation of Li2CO3 and Li2O byproducts. This work provides a cost-effective solution to solve the cathode catalyst problem of Li-O2 batteries and improve their cycling stability as well as environment protection.

Stabilizing MXene suspension with polyhydric alcohols

MXenes have promises in myriad applications by virtue of two-dimensional nature and adjustable functional groups. To achieve the applications, MXenes are always first prepared in the form of aqueous suspension. However, fast degradation caused by the attack of dissolved oxygen and water molecules is the main obstacle to the application of MXenes. It has come to light that the degradation preferentially takes place at defective sites and edges where defects enrich. To tackle this problem and increase the stability, herein, using Ti3C2Tx MXene as a model material, we report a simple yet efficient strategy for long term storage of MXene suspension by introducing glycerol, a typical polyhydric alcohol. The effectiveness of the strategy is evidenced by structural compositional and morphological investigations. Glycerol protects the defective sites of MXene flakes through restricting water and/or oxygen molecules from reactive sites. This is supported by ab initio molecular dynamics simulations that form hydrogen bonds between MXene and glycerol molecules just over defective sites. Following this mechanism, other polyhydric alcohols, such as ethylene glycol and propylene glycol, are also effective in stabilizing Ti3C2Tx MXene suspension. The strategy based on polyhydric alcohols has the potential to be extended to other MXenes, solving the most urgent challenge in the field of MXene engineering.

Room-temperature X-ray induced photochromic properties of tungsten oxide

The transformation of tungsten oxide from yellow (without X-ray) to blue green (60 min) under X-ray radiation of varying duration, and it is a continuous process. Under X-ray irradiation treatment, some of the W-O bonds break, causing the oxygen molecules to leave the surface lattice and creating oxygen vacancies. One oxygen vacancy in WO3 generally causes two electrons, which reduces W6+ ions into W5+. The product is HxWO3, resulting in a reduction in the crystalline volume and band gap of the sample. Simultaneously thermally annealed pre- and post-X-ray irradiation samples, both of which are the same color after cooling. This new finding extends the photochromic energy range of tungsten oxide and has important implications for the design and fabrication of other X-ray-induced photochromic materials for charge transfer, which will certainly benefit the development of next-generation X-ray detection materials.

Adaptive design for the connection of multicell HHO generator with solar photovoltaic panels

Hydrogen is considered a new source of energy and one of the sources of clean energy. One of the most widely used methods of hydrogen production is water electrolysis. Water electrolysis causes water molecules to break down into hydrogen and oxygen by passing an electric current through water molecules and using an intercellular membrane. If the intercellular membrane is removed, hydrogen gas and oxygen are mixed to produce hydroxy gas. This gas, which contains hydrogen and oxygen molecules, has been considered an auxiliary fuel and combustion enhancer. In this research, the design and construction of a multi-cell electrolyzer producing hydroxy gas without a membrane was carried out using 316 stainless steel sheets. Potassium hydroxide (KOH) solution was used as an electrolyte to increase water conductivity, and solar panels were used to supply the energy required for the electrolyzer. Adjusting the number of electrolyzer plates with the voltage of the solar panels is one of the most critical points in the optimal design of this combined system. The effect of parameters on the amount of hydroxy gas production, energy intensity, and production per electrolyzer surface has been evaluated. The experimental results show that due to the internal resistance of each electrolyzer cell, the voltage of each cell varies between 2 and 3 V in different currents. The number of series cells in the electrolyzer determines its total voltage, which should be matched to the solar system to stay at the optimum point of operation. In the studied electrolyzer, optimized design of electrolizer have 18, 17 and, 15 plates, when one, two, and three 325W solar panels is used, respectively. In the next step, the daily test is performed for optimized electrolyzers. Daily production per surface of the solar panel for the three states was 530, 600 and 533L/m2, respectively. This indicates that daily production increases with increasing the number of panels but specific production per solar panel area may not increase and will have an optimal value. So, in the combination of an HHO generator with a solar system, the number of electrolyzer plates and also the surface area of solar panels should be optimally selected to achieve the optimum operation. This issue can be completed with accurate modeling in future studies.

The molecular chemistry of Type Ibc supernovae and diagnostic potential with the James Webb Space Telescope

Context. A currently unsolved question in supernova (SN) research is the origin of stripped-envelope supernovae (SESNe). Such SNe lack spectral signatures of hydrogen (Type Ib), or hydrogen and helium (Type Ic), indicating that the outer stellar layers have been stripped during their evolution. The mechanism for this is not well understood, and to disentangle the different scenarios’ determination of nucleosynthesis yields from observed spectra can be attempted. However, the interpretation of observations depends on the adopted spectral models. A previously missing ingredient in these is the inclusion of molecular effects, which can be significant. Aims. We aim to investigate how the molecular chemistry in SESNe affect physical conditions and optical spectra, and produce ro-vibrational emission in the mid-infrared (MIR). We also aim to assess the diagnostic potential of observations of such MIR emission with JWST. Methods. We coupled a chemical kinetic network including carbon, oxygen, silicon, and sulfur-bearing molecules into the nonlocal thermal equilibrium (NLTE) spectral synthesis code SUMO. We let four species – CO, SiO, SiS, and SO – participate in NLTE cooling of the gas to achieve self-consistency between the molecule formation and the temperature. We applied the new framework to model the spectrum of a Type Ic SN in the 100–600 days time range. Results. Molecules are predicted to form in SESN ejecta in significant quantities (typical mass 10−3 M⊙) throughout the 100–600 days interval. The impact on the temperature and optical emission depends on the density of the oxygen zones and varies with epoch. For example, the [O I] 6300, 6364 feature can be quenched by molecules from 200 to 450 days depending on density. The MIR predictions show strong emission in the fundamental bands of CO, SiO, and SiS, and in the CO and SiO overtones. Conclusions. Type Ibc SN ejecta have a rich chemistry and considering the effect of molecules is important for modeling the temperature and atomic emission in the nebular phase. Observations of SESNe with JWST hold promise to provide the first detections of SiS and SO, and to give information on zone masses and densities of the ejecta. Combined optical, near-infrared, and MIR observations can break degeneracies and achieve a more complete picture of the nucleosynthesis, chemistry, and origin of Type Ibc SNe.

The theory of oxygen hemoglobin association

We develop a theory of oxygen hemoglobin association and derive the oxygen hemoglobin association equation and determine the values of the four association constants by curve fitting four commonly accepted data points that relate oxygen saturation and oxygen partial pressure (PO2) in the blood using mathematical reasoning and chemical kinetics. The four association constants come from the progression of oxygen binding to each of the four subunits on the hemoglobin molecule in a cooperative manner. The binding of oxygen alters the affinity of subsequent binding of additional oxygen molecules, which is reflected in changing magnitudes of the association constants. We also demonstrate rather surprisingly that the value of the third association constant is significantly smaller than all other association constants and offer some conjecture about this puzzling finding. With our equation, we can compute the distributions of all five oxyhemoglobin species at various PO2 levels that are published for the first time in the history of hemoglobin research. After examining the distributions, we find the triply bound oxyhemoglobin exists in very low concentration, consistent with the small third association constant. In addition, we present the oxygen levels where maximal concentrations of various oxyhemoglobin species occur, another unexpected finding that was never published before. Finally, we determine the inflection point of the hemoglobin association curve, a defining property to a specific sigmoid curve, representing the steepest portion of the curve.

P‐153: Late‐News Poster: Temporal Photo‐Response Analysis of Inkjet‐Printed Transparent Single‐Walled Carbon Nanotube Thin‐Film Transistors

We demonstrated the temporal photo‐response of transparent and flexible carbon nanotube thin‐film transistors. Fabricated carbon nanotube thin film transistors showed exponential degradation with light illumination and linear recovery after light off. The result indicates that the principal mechanism of photo‐response in carbon nanotube transistors is photo‐desorption of oxygen molecules.

Facet-Controlled Cu2O Support Enhances Catalytic Activity of Pt Nanoparticles for CO Oxidation.

The metal-support interaction plays a crucial role in determining the catalytic activity of supported metal catalysts. Changing the facet of the support is a promising strategy for catalytic control via constructing a well-defined metal-support nanostructure. Herein, we developed cubic and octahedral Cu2O supports with (100) and (111) facets terminated, respectively, and Pt nanoparticles (NPs) were introduced. The in situ characterizations revealed the facet-dependent encapsulation of the Pt NPs by a CuO layer due to the oxidation of the Cu2O support during the CO oxidation reaction. The CuO layer on Pt at cubic Cu2O (Pt/c-Cu2O) significantly enhanced catalytic performance, while the thicker CuO layer on Pt at octahedral Cu2O suppressed CO conversion. The formation of a thin CuO layer is attributed to the dominant Pt-O-Cu bond at the Pt/c-Cu2O interface, which suppresses the adsorption of oxygen molecules. This investigation provides insight into designing high-performance catalysts via engineering the interface interaction.

Structure evolution and properties enhancement of polyamide‐6/polyamide‐1010 films under uniaxial and biaxial stretching

AbstractThe effect of stretching process on the structures and properties of the stretch‐oriented PA6/PA1010 film was investigated during the uniaxial and biaxial stretching. The results showed that the PA6/PA1010 cast film exhibited β‐form crystals, and the uniaxial stretching induced the β → α + γ phase transition and preferential orientation along the stretching direction, while the β → α phase transition and no preferential orientation were observed during the biaxial stretching process. Meanwhile, the melting temperature and crystallinity of PA6 in uniaxially and biaxially stretched PA6/PA1010 films were improved with the increasing stretching ratios, thus creating a much more tortuous pathway for the diffusion of oxygen molecules to enhance the oxygen barrier property of the stretched films after uniaxial and biaxial stretching. The morphological analysis showed that the PA1010 particles were oriented and deformed along the stretching direction and no obvious debonding and voids were observed at the interface. In addition, the mechanical properties of the stretched films were closely dependent upon the stretching ratios. It was found that the tensile strength of the biaxially stretched PA6/PA1010 films with stretching ratio of 3.5 × 3.5 in MD and TD exhibited about 1.7 times and 2.2 times higher than that of the PA6/PA1010 cast film, respectively.

Aurozyme: A Revolutionary Nanozyme in Colitis, Switching Peroxidase-Like to Catalase-Like Activity.

A therapeutic strategy that could address colitis of multiple etiologies while restoring the dysbiosis of gut microbiota is attractive. Here, Aurozyme, a novel nanomedicine comprised of gold nanoparticles (AuNPs) and glycyrrhizin (GL) with a glycol chitosan coating layer, as a promising approach for colitis, is demonstrated. The unique feature of Aurozyme is the conversion of harmful peroxidase-like activity of AuNPs to beneficial catalase-like activity due to the amine-rich environment provided by the glycol chitosan. This conversion process enables Aurozyme to oxidize the hydroxyl radicals derived from AuNP, producing water and oxygen molecules. In fact, Aurozyme effectively scavenges reactive oxygen/reactive nitrogen species (ROS/RNS) and damage-associated molecular patterns (DAMPs), which can attenuate the M1 polarization of macrophage. It exhibits prolonged adhesion to the lesion site, promoting sustained anti-inflammatory effects and restoring intestinal function in colitis-challenged mice. Additionally, it increases the abundance and diversity of beneficial probiotics, which are essential for maintaining microbial homeostasis in the gut. The work highlights the transformative potential of nanozymes for the comprehensive treatment of inflammatory disease and represents an innovative switching technology of enzyme-like activity by Aurozyme.

Effect of particle size on ignition and oxidation of single aluminum: molecular dynamics study

Alumina nanoparticle is one of the attractive nanoparticles synthesized by the plasma method. The oxidation step in this method is challenging to explain experimentally. This work was to perform a molecular dynamics simulation to determine the oxidation mechanism of aluminum nanoparticles with different sizes and oxidation levels in the oxide layer. This work was to perform a molecular dynamics simulation to determine the oxidation mechanism of aluminum nanoparticles with different sizes and oxidation levels in the oxide layer. The simulation method employed the ReaxFF potential. The material used is aluminum nanoparticles in three different sizes (8, 12, and 16 nm) with an oxide layer thickness of 0.5 nm. Aluminum nanoparticles were given a relaxation treatment of 300 K for 1 ps and then heated to a temperature of 3250 K with a heating rate of 5×1013 K/s and cooled to 300 K. The ensemble used is a canonical ensemble with the Nose/Hoover thermostat method. The result shows that the higher the temperature applied to the system, the more oxygen molecules adsorption occurs on the surface of the oxide layer and the diffusion of oxygen to the particle core. The higher temperature applied also causes gaps, or void spaces, between the core and the shell. The reaction barrier for diffusion of oxygen also decreased significantly due to void space, and the surface of the aluminum core dissociates to the surface (alumina shell). Particles with a smaller size have a shorter ignition delay time. In addition, the smaller the particle size, the more oxygen molecules' reacted with aluminum particles in the particle core

Symmetric Electronic Structures of Active Sites to Boost Bifunctional Oxygen Electrocatalysis by MN4+4 Sites Directly from Initial Covalent Organic Polymers

AbstractTransition metal‐nitrogen‐carbon (M‐N‐C) catalysts with CoN4 centers have attracted great attention as a potential alternative to precious metal catalysts for bifunctional oxygen electrocatalysis. However, the asymmetric charge environment of the active site of MN4 obtained by conventional pyrolysis strategy makes the unbalanced adsorption of oxygen molecules, which restricts the activities of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, a series of well‐defined quasi‐phthalocyanine conjugated 2D covalent organic polymer (COPBTC‐M) is developed with MN4+4 active sites through a pyrolysis‐free strategy. Compared to CoN4 site, the additional subcentral N4 atoms in MN4+4 site in COPBTC‐Co catalyst balance the charge environment and form a symmetric charge distribution, which changes the antibonding orbital of the active metal and regulate the oxygen species adsorption, thus improving the activity of the bifunctional oxygen electrocatalysis. In Silico screening demonstrates that cobalt has the best ORR and OER activity for COPBTC‐M with MN4+4 sites, which can be attributed to the fewer anti‐bonding orbital below the Fermi level, which weakens the oxygen species adsorption. Both theoretical and experimental results verify that the COPBTC‐Co possesses unique CoN4+4 active sites and the harmonious coordinating environment can lead to superior bifunctional oxygen catalytic activity with a high bifunctional oxygen catalytic activity (ΔE [Ej10 – E1/2] = 0.76 V), which is comparable with the benchmark Pt/C‐IrO2 pairs. Accordingly, the as‐assembled Zn–air battery exhibits a maximum power density of 157.7 mW cm −2 with stable operation for >100 cycles under an electric density of 10 mA cm −2. This study provides a characteristic understanding of the intrinsic active species toward MNx centers and could inspire new avenues for designation of advanced bifunctional electrocatalysts that catalyze ORR and OER processes simultaneously.

Modeling the Enzyme Specificity by Molecular Cages through Regulating Reactive Oxygen Species Evolution.

Mimicking the active site and the substrate binding cavity of the enzyme to achieve specificity in catalytic reactions is an essential challenge. Herein, porous coordination cages (PCCs) with intrinsic cavities and tunable metal centers have proved the regulation of reactive oxygen species (ROS) generating pathways as evidenced by multiple photo-induced oxidations. Remarkably, in the presence of the Zn4 -μ4 -O center, PCC converted dioxygen molecules from triplet to singlet excitons, whereas the Ni4 -μ4 -O center promoted the efficient dissociation of electrons and holes to conduct electron transfer towards substrates. Accordingly, the distinct ROS generation behavior of PCC-6-Zn and PCC-6-Ni enables the conversion of O2 to 1 O2 and O2 ⋅- , respectively. In contrast, the Co4 -μ4 -O center combined the 1 O2 and O2 ⋅- together to generate carbonyl radicals, which in turn reacted with the oxygen molecules. Harnessing the three oxygen activation pathways, PCC-6-M (M=Zn/Ni/Co) display specific catalytic activities in thioanisole oxidation (PCC-6-Zn), benzylamine coupling (PCC-6-Ni), and aldehyde autoxidation (PCC-6-Co). This work not only provides fundamental insights into the regulation of ROS generation by a supramolecular catalyst but also demonstrates a rare example of achieving reaction specificity through mimicking natural enzymes by PCCs.

Modeling the Enzyme Specificity by Molecular Cages through Regulating Reactive Oxygen Species Evolution

AbstractMimicking the active site and the substrate binding cavity of the enzyme to achieve specificity in catalytic reactions is an essential challenge. Herein, porous coordination cages (PCCs) with intrinsic cavities and tunable metal centers have proved the regulation of reactive oxygen species (ROS) generating pathways as evidenced by multiple photo‐induced oxidations. Remarkably, in the presence of the Zn4‐μ4‐O center, PCC converted dioxygen molecules from triplet to singlet excitons, whereas the Ni4‐μ4‐O center promoted the efficient dissociation of electrons and holes to conduct electron transfer towards substrates. Accordingly, the distinct ROS generation behavior of PCC‐6‐Zn and PCC‐6‐Ni enables the conversion of O2 to 1O2 and O2⋅−, respectively. In contrast, the Co4‐μ4‐O center combined the 1O2 and O2⋅− together to generate carbonyl radicals, which in turn reacted with the oxygen molecules. Harnessing the three oxygen activation pathways, PCC‐6‐M (M=Zn/Ni/Co) display specific catalytic activities in thioanisole oxidation (PCC‐6‐Zn), benzylamine coupling (PCC‐6‐Ni), and aldehyde autoxidation (PCC‐6‐Co). This work not only provides fundamental insights into the regulation of ROS generation by a supramolecular catalyst but also demonstrates a rare example of achieving reaction specificity through mimicking natural enzymes by PCCs.