Coupling Route Research Articles

Carbonate-carbonate coupling on platinum surface promotes electrochemical water oxidation to hydrogen peroxide

Water electro-oxidation to form H2O2 is an important way to produce H2O2 which is widely applied in industry. However, its mechanism is under debate and HO(ads), hydroxyl group adsorbed onto the surface of the electrode, is regarded as an important intermediate. Herein, we study the mechanism of water oxidation to H2O2 at Pt electrode using in-situ Raman spectroscopy and differential electrochemical mass spectroscopy and find peroxide bond mainly originated from the coupling of two CO32- via a C2O62- intermediate. By quantifying the 18O isotope in the product, we find that 93% of H2O2 was formed via the CO32- coupling route and 7% of H2O2 is from OH(ads)-CO3•− route. The OH(ads)-OH(ads) coupling route has a negligible contribution. The comparison of various electrodes shows that the strong adsorption of CO3(ads) at the electrode surface is essential. Combining with a commercial cathode catalyst to produce H2O2 during oxygen reduction, we assemble a flow cell in which the cathode and anode simultaneously produce H2O2. It shows a Faradaic efficiency of 150% of H2O2 at 1 A cm−2 with a cell voltage of 2.3 V.

Interface coupling of octahedron Cu2O with reduced graphene oxide for enhanced photocatalytic and photoelectrochemical activity

Graphene oxide (GO) has been recognized as an ideal substrate material of semiconductor photocatalysts to achieve superior properties. Herein, Cu2O/reduced graphene oxide hetero-structures (Cu2O/rGO), featured by octahedron Cu2O with highly exposed {111} facets in-situ anchored on the framework of rGO nanosheets, were constructed via a green wet chemistry route at room temperature. During the reactions, Cu2+ ions that were adsorbed on GO could act as the nucleation sites of Cu2O while GO was further converted into rGO under the reduction of glucose, forming a robust hetero-interface of C–O–Cu bonding. Owning to the improved photon capture ability and carrier separation efficiency, the optimized Cu2O/rGO exhibits about 3.5 and 9.3 times enhancement of photocurrent intensity and photocatalytic activity, respectively, as compared to those of pure Cu2O. Meanwhile, the correlation among rGO content, structure and photocatalytic activity of Cu2O/rGO was demonstrated. This work presents a rational route and deep insight for the interface coupling within metal oxide/carbon material hetero-structures for advanced catalytic applications.

Available Strategies for Improving the Biosynthesis of Methionine: A Review.

Methionine is the only nonpolar α-amino acid containing sulfur among the eight essential amino acids and is closely related to the metabolism of sulfur-containing compounds in the human body. Widely used in feed, medicine, food, and other fields, the market demand is increasing annually. However, low productivity and high cost largely limit the industrial production of methionine, and many novel production methods still have their own disadvantages. In this paper, the available methods for synthesizing methionine are reviewed and discussed. The latest strategies for improving methionine production are further introduced, including culture medium optimization, mutation technology, expression of key genes in the metabolic pathway, knockout and recombination, as well as the engineering of membrane transporters, the fermentation-enzymatic coupling route, and innovation of CO2 biotransformation.

A Distibene with Extremely Long Sb=Sb Distance and Related Heavier Dipnictenes from Salt‐Free Metathesis Reactions

AbstractConversions of organoelement diamides, ArDippE(NMe2)2 (E=Sb, Bi; ArDipp=C6H3‐2,6‐Dipp2), with Ph2SnH2 as reducing agent gave access to low‐valent, heavier group 15 dimers ArDippSb=SbArDipp and ArDippBi=BiArDipp, while only readily removable byproducts (i. e. dihydrogen, amines) and cyclo‐(Ph12Sn6) are generated during the reaction. Moreover, experiments involving the reaction of organoantimony hydride species Ar*2SbH (Ar*=C6H2‐2,6‐(Ph2CH)2‐4‐iPr) with Bi(NEt2)3 yielded a second novel distibene, Ar*Sb=SbAr*, with the currently longest Sb−Sb bond distance of 2.8605(5) Å in a distibene. In conversions of TbbSnH3 (Tbb=C6H2‐2,6‐(CH(SiMe3)2)2‐4‐tBu) with Bi(NEt2)3, ligand migration resulted in the isolation of TbbBi=BiTbb. Remarkably, the herein reported novel inorganic coupling route enables preparation and isolation of heavier dipnictenes without the formation of inorganic salts. All four low‐oxidation state compounds were isolated and subsequently characterized using state of the art techniques, i. e. X‐ray crystallography, NMR and UV/Vis spectroscopy.

Boosting photocatalytic antibiotic degradation with simultaneous H2O2 production of g-C3N4 by building dual-dragging force for efficient charge separation

Graphitic carbon nitride (g-C3N4) is a promising candidate for photocatalytic antibiotic degradation with simultaneous H2O2 production. However, g-C3N4 suffers from a high charge recombination and insufficient visible-light absorption. Herein, the benzene-ring and cyano groups were successfully grafted onto the surface of g-C3N4 (BCN-ND) by a simple coupling route involving copolymerization and secondary calcination, which provided a dual-dragging force was generated for the directional separation of photogenerated electrons and holes. The benzene-ring establishes a mid-state slightly above the valence band, which results in a dragging force for holes and extends the response of g-C3N4 to visible light. Moreover, the cyano group exhibits a powerful electron-withdrawing capacity, acting as an electron-dragging force and narrowing the intrinsic bandgap. Therefore, BCN-ND exhibits remarkable photocatalytic activity with a sulfamethoxazole degradation percentage of 99.5 % and simultaneous H2O2 production of 62 μmol/L after 80 min of visible light irradiation. This work provides new perspectives for enhancing photocatalytic activity by constructing of a dual-dragging center for oppositely directional charge separation.

Suzuki-Miyaura Type Regioselective C-H Arylation of Aromatic Aldehydes by a Transient Directing Strategy.

Herein, we disclose a common approach for palladium-catalyzed direct coupling of the ortho-C-H bond of aromatic aldehydes with various organoboronic reagents by a transient directing strategy. In contrast to widely used cross-coupling reactions of C-H bonds with aryl halides, which generally need silver salt as a halide removal reagent, the method which used BQ/TFA as weak oxidation system for the PdII/Pd0 redox cycle is cost-effective, ecofriendly, and more aligned with green catalysis. This broadly applicable method opens up a new and efficient Suzuki-Miyaura coupling route for the direct formation of carbon-carbon bonds by C-H bond activation.

Building Porous Ni(Salen)-Based Catalysts from Waste Styrofoam via Autocatalytic Coupling Chemistry for Heterogeneous Oxidation with Molecular Oxygen.

The development of robust and industrially viable catalysts from plastic waste is of great significance, and the facile construction of high performance heterogeneous catalyst systems for phenol-quinone conversions remains a grand challenge. Herein, a feasible strategy is demonstrated to reclaim Styrofoam into hierarchically porous nickel-salen-loaded hypercrosslinked polystyrene (PS@Ni-salen) catalysts with high activities through an unusual autocatalytic coupling route. The salen is immobilized onto PS chain by Friedel-Crafts alkylation of benzyl chloride derivatives, and the generated hydrogen chloride coordinately promotes the simultaneous crosslinking and bridge formation between aromatic rings via a Scholl coupling route, leading to hierarchically porous networks. After the metallization with Ni, the resultant networks exhibit high catalytic activity for the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-1,4-benzoquinone under mild conditions (303 K, 1bar of O2 ). This catalyst also demonstrates attractive recycling performance without an obvious loss of catalytic efficiency over five consecutive cycles. This methodology might provide a potential sustainable alternative to construct environmentally benign and cost-effective catalysts for specific organic transformation.

New Radical Route and Insight for the Highly Efficient Synthesis of Benzimidazoles Integrated with Hydrogen Evolution.

Benzimidazoles are a versatile class of scaffolds with important biological activities, whereas their synthesis in a lower-cost and more efficient manner remains a challenge. Here, we demonstrate a conceptually new radical route for the high-performance photoredox coupling of alcohols and diamines to synthesize benzimidazoles along with stoichiometric hydrogen (H2 ) over Pd-decorated ultrathin ZnO nanosheets (Pd/ZnO NSs). The mechanistic study reveals the unique advantage of ZnO NSs over other supports and particularly that the features of Pd nanoparticles in facilitating the cleavage of the α-C-H bond of alcohols and adsorbing subsequently-generated C-centered radicals hold the key to turning on the reaction. This work highlights a new insight into radical-induced efficient benzimidazole synthesis pairing with H2 evolution by rationally designing semiconductor-based photoredox systems.

Synergistic electrocatalysis of crystal facet and O-vacancy for enhancive urea synthesis from nitrate and CO2

One-pot green urea electrosynthesis from CO2 and nitrogenous pollutants via the co-reductive C−N coupling route under ambient conditions is prospective to replace the traditional urea synthesis process. Here, a bifunctional indium hydroxide (Vo-S-IO-6) bearing oxygen vacancy (Vo) sites on {100} facets was developed to markedly enable urea synthesis (unprecedented faradaic efficiency of 60.6% with a high production rate of 910.4 μg h-1 mg-1cat.) from NO3− and CO2 by subtly integrating facet and defect engineering. ln-O-x-O-ln (x = C or N) configuration and Vo in Vo-S-IO-6 provided dual active sites for the adsorption and activation of NO3− and CO2 to exclusively form *NO2 and *CO2 species, respectively, which ensured highly selective C−N coupling. Moreover, theoretical calculations elaborated that Vo-induced local electron reconstruction accelerated the protonation rate-determining step, thus lowering overall energy barriers. This work offers a design strategy of synergistic electrocatalysts based on geometrical nature for efficient urea synthesis.

Engineering O‐Succinyl‐L‐Homoserine Mercaptotransferase for Efficient L‐Methionine Biosynthesis by Fermentation‐Enzymatic Coupling Route

AbstractL‐Methionine is the unique sulfur‐containing amino acid essential for humans and animals, which is widely used in pharmaceutical, food and feed industries. Its green and efficient production has attracted a great deal of attention. Fermentation‐enzymatic coupling route is regarded to be promising for L‐methionine biosynthesis, while O‐succinyl‐L‐homoserine mercaptotransferase (MetZ) is the key biocatalyst. Exploring and engineering of MetZ with ideal catalytic properties is highly desired. Herein, the MetZ from Chromobacterium violaceum (CvMetZ) was screened and through in silico analyses, potential beneficial amino acid residues both at the access channel and around the oxygen anion holes were anchored for site‐saturation mutagenesis. The positive mutants were obtained with improved activity for L‐methionine biosynthesis using O‐succinyl‐L‐homoserine (OSH) and methyl mercaptan as substrate. The best mutant was further applied for L‐methionine production and supply of methyl mercaptan was optimized in a fed‐batch approach. The conversion of 100 g/L OSH reached 92% with L‐methionine yield of 62.6 g/L, which was well coupled with the OSH fermentation level.magnified image

Theoretical Assessment of the Mechanism and Active Sites in Alkene Dimerization on Ni Monomers Grafted onto Aluminosilicates: (Ni-OH)+ Centers and C-C Coupling Mediated by Lewis Acid-Base Pairs.

Ni-based solids are effective catalysts for alkene dimerization, but the nature of active centers and identity and kinetic relevance of bound species and elementary reactions remain speculative and based on organometallic chemistry. Ni centers grafted onto ordered MCM-41 mesopores lead to well-defined monomers that are rendered stable by the presence of an intrapore nonpolar liquid, thus enabling accurate experimental inquiries and indirect evidence for grafted (Ni-OH)+ monomers. Density functional theory (DFT) treatments presented here confirm the plausible involvement of pathways and active centers not previously considered as mediators of high turnover rates for C2-C4 alkenes at cryogenic temperatures. (Ni-OH)+ species act as Lewis acid-base pairs that stabilize C-C coupling transition states by polarizing two alkenes in opposite directions via concerted interactions with the O and H atoms in these pairs. DFT-derived activation barriers for ethene dimerization (59 kJ mol-1) are similar to measured values (46 ± 5 kJ mol-1) and the weak binding of ethene on (Ni-OH)+ is consistent with kinetic trends that require sites to remain essentially bare at subambient temperatures and high alkene pressures (1-15 bar). DFT treatments of classical metallacycle and Cossee-Arlman dimerization routes (Ni+ and Ni2+-H grafted onto Al-MCM-41, respectively) show that such sites bind ethene strongly and lead to saturation coverages, in contradiction with observed kinetic trends. These C-C coupling routes at acid-base pairs in (Ni-OH)+ differ from molecular catalysts in (i) the type of elementary steps; (ii) the nature of active centers; and (iii) their catalytic competence at subambient temperatures without requiring co-catalysts or activators.

CO2 methanation over Ni/Al2O3-ZrO2 catalysts: Optimizing metal-oxide interfaces by calcinating-induced phase transformation of support

A new strategy to prepare the NiO/Al2O3-ZrO2 catalyst with various interfacial structures by inducing different phase transitions of Al2O3 and ZrO2 via varying the precursor calcination temperature was proposed, and their CO2 methanation performance was subsequently investigated. The characterization of the catalyst showed that Ni was prone to bonding with Al ion during the calcination process and forming NiAl2O4 or strong interaction between Al2O3 and NiO. The reduced metallic nickel (Ni0) and partially unreduced NiAl2O4 exist in the state of Ni-NiAl2O4/Al2O3-ZrO2, forming a multi-interface system of Ni-O-Al, Al-O-Zr, and Ni-O-Zr. Moreover, this supplies medium-strength adsorption sites that play a key role in CO2 activation. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis and catalytic activity revealed that the CO2 methanation was completed in a two-step coupling route of Reverse Water Gas Shift (RWGS) and CO methanation. The abundant interfaces of the catalyst effectively suppressed the sintering of Ni.

Systematic Design Method for Mutual Coupling Reduction in Closely Spaced Patch Antennas

In this article, a systematic design approach is presented to reduce the mutual coupling between a pair of closely spaced microstrip patch antennas (MPAs). This method can effectively overcome the main drawback of previous two-path cancellation methods, i.e., lack a systematic design guideline and heavily rely on the time-expensive trial-and-error procedure to mitigate mutual coupling in a best-effort manner. To this end, we first propose the concept and workflow of the systematic design method, and introduce the circuit-level modeling upon the proposed two coupling routes. Then, prototyped on a practical and simple physical structure, we perform certain accurate extractions and derive the rigorous conditions for both of isolation between two patches and impedance matching of a single patch based on these two paths. Afterwards, according to the circuit-level discussion on lumped elements, the corresponding decoupling structure could be implemented substantially and designed quantitatively at the antenna level for particularized closely spaced MPAs. Finally, a prototype is simulated, fabricated, and measured to validate the proposed method. The results show that the circuit-model calculation, full-wave simulation, and measurement are in good agreement. By virtue of such a simple decoupling structure, the poor 7-dB isolation is dramatically improved to 58 dB, and the isolation is enhanced beyond 20 dB in the entire impedance matching bandwidth range of 4.38 4.60 GHz (4.9%), with the closely center-to-center spacing of 0.37 λ0.

In situ SERS reveals the route regulation mechanism mediated by bimetallic alloy nanocatalysts for the catalytic hydrogenation reaction.

Synthesizing arylamines with high selectivity via hydrogenation of nitroaromatics is a long-standing challenge because of the complex reaction pathways. Revealing the route regulation mechanism is the key to obtain high selectivity of arylamines. However, the underlying reaction mechanism of route regulation is uncertain owing to a lack of direct in situ spectral evidence of the dynamic transformation of intermediate species during the reaction process. In this work, by using in situ surface-enhanced Raman spectroscopy (SERS), we have employed 13 nm Au100-x Cu x nanoparticles (NPs) deposited on a SERS-active 120 nm Au core to detect and track the dynamic transformation of intermediate species of hydrogenation of para-nitrothiophenol (p-NTP) into para-aminthiophenol (p-ATP). Direct spectroscopic evidence demonstrates that Au100 NPs exhibited a coupling route with the in situ detection of the Raman signal assigned to coupling product p,p'-dimercaptoazobenzene (p,p'-DMAB). However, Au67Cu33 NPs displayed a direct route without the detection of p,p'-DMAB. The combination of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations reveals that Cu doping can favor the formation of active Cu-H species owing to the electron transfer from Au to Cu, which can promote the formation of phenylhydroxylamine (PhNHOH*) and favor the occurrence of the direct route on Au67Cu33 NPs. Our study provides direct spectral evidence demonstrating the critical role of Cu in route regulation for the nitroaromatic hydrogenation reaction at a molecular level and clarifies the route regulation mechanism. The results have significant implications for revealing multimetallic alloy nanocatalyst mediated reaction mechanisms and help to guide the rational design of multimetallic alloy catalysts for catalytic hydrogenation reactions.

The preparation of chiral carbon dots and the study on their antibacterial abilities

Chirality is one of the most widespread properties in nature. After the successful application of non-optical active carbon dots (CDs) in the fields of detection, imaging, and antibacterial, the researchers turned more attention to the preparation and applications of chiral CDs. This paper reports the preparation of several chiral CDs with chiral amino acids as carbon sources through two different methods (one-step hydrothermal route and two-step coupling route), and further explores the difference in antibacterial abilities of these chiral CDs prepared by different carbon sources and synthesis methods. The experiments results showed that chiral D/LGU which are prepared through one-step method and with glutamic acid (Glu), are superior to those prepared by two-step method (NLDU/NDGU), or those prepared with cysteine as raw material (D/LCS). For D/LCS, the antibacterial ability of the L type is superior to that of the D type, proving that the synthesis method and the chirality of raw material are both important in the antibacterial behavior of prepared CDs. The chirality and optical properties of prepared CDs have been characterized by UV–vis spectrophotometer, fluorescence spectrology, and circular dichroism. Through MurA enzyme inhibition tests, SEM, and molecular docking design, the antibacterial mechanism of chiral CDs has been investigated. The research provides a sound foundation for the preparation, characterization, and application of chiral CDs, as well as the novel targeting antibacterial applications.

Co-electrolysis of CO2 and formaldehyde to ethanol: An inspiring asymmetric C−C coupling pathway

Selectively producing a target ethanol product is highly desired but challenging, especially when using CO 2 as a feedstock only. In this issue of Chem Catalysis , Han and co-workers describe a co-electrocatalytic conversion of CO 2 and formaldehyde (FA) toward ethanol, which expands the scopes of C−C coupling routes for CO 2 utilization. Selectively producing a target ethanol product is highly desired but challenging, especially when using CO 2 as a feedstock only. In this issue of Chem Catalysis , Han and co-workers describe a co-electrocatalytic conversion of CO 2 and formaldehyde (FA) toward ethanol, which expands the scopes of C−C coupling routes for CO 2 utilization.

Coupling photocatalytic water oxidation on decahedron BiVO4 crystals with catalytic wet peroxide oxidation for removing organic pollutions in wastewater

Catalytic wet peroxide oxidation (CWPO) is widely used to remove organic pollutants in industrial wastewater, however, the remained challenges in circulating Fe3+/Fe2+ ions, inevitably forming iron sludge and massively consuming H2O2 limit its applications. Herein, the coupling of CWPO and photocatalytic water oxidation on decahedron BiVO4 crystals was reported to solve the above challenges. Using spatial photogenerated charge separation between different facets of BiVO4, efficiently circulating Fe3+ to Fe2+ was realized with a selectivity of ~100%, which greatly inhibits the formation of iron sludge. Moreover, in-situ formation of H2O2 through two-hole-involved photocatalytic water oxidation on BiVO4 replenishes the H2O2 consuming in the CWPO process. The coupling system exhibits a much higher total organic carbon (TOC) removal than the CWPO process in various pollutants, giving an improvement of rate constant to more than 10 times. This work provides a potential coupling route for advanced degradation of organic pollutants in wastewater treatment.

Heptazine‐Based TADF Materials for Nanoparticle‐Based Nonlinear Optical Bioimaging

Abstracts‐Heptazines are emerging as strong electron acceptors for efficient thermally activated delayed fluorescent (TADF) materials, yet the difficulties in synthesizing them have limited their practical use. Here, three novel s‐heptazine TADF materials with green to deep‐red emission (λmax = 525–664 nm) and high photoluminescence quantum yields, synthesized by either pseudoelectrophilic substitution or Negishi coupling routes, are described. These materials also demonstrate strong nonlinear optical absorption, with two‐photon cross sections up to 1260 GM. With deep‐red fluorescence, strong two‐photon absorption, high quantum yield, and delayed fluorescence, the emitter HAP‐3MeOTPA is ideally suited for use in nanoparticle‐based bioimaging experiments. The two kinds of luminescent nanoparticle are prepared, namely hostless, aggregate‐based organic dots (a‐Odots) and rigid, glassy Odots (g‐Odots) as biocompatible and water‐dispersible TADF probes. The g‐Odots are shown to retain the nonlinear optical properties, high photoluminescence quantum yield, and TADF observed in the constituent heptazine dye. These g‐Odots are then used as biological imaging probes with immortalized human kidney cancer (HEK293) cells, and single and multi‐photon‐excited microscopy coupled with time‐gated luminescence measurements are demonstrated. This work not only describes new routes to efficient heptazine‐based TADF materials, but also demonstrates their potential as nanoparticle‐based bioimaging probes combining several advanced optical functions.

Organocatalytic One‐Pot Synthesis of Pseudo‐Terpenoids

AbstractStructurally complex cedrane scaffolds were synthesized in very good yields with high chemo‐ and diastereoselectivities in a sequential one‐pot manner. A combination of intermolecular olefination, intramolecular Michael and Michael reactions or intermolecular olefination, intramolecular Michael and aldol reactions were used as the key steps from the readily available hydroxy‐p‐quinone butanals and phosphoranes with catalytic amounts of quinine at ambient temperatures for a few hours. This is a unique one‐pot combination of coupling and annulation routes for the green synthesis of a library of tricyclic pseudo‐terpenoids (cedrane scaffolds) with high selectivity and yields. Organocatalytic ring isomerization was highlighted through transforming one ring into another one by retro‐cyclization. We have discussed thoroughly mechanistic aspects of these tandem coupling/annulation and ring isomerization reactions based on control experiments and X‐ray crystal structure analysis.

Light-Induced Structural Dynamic Evolution of Pt Single Atoms for Highly Efficient Photocatalytic CO2 Reduction.

Revealing the structural evolution of the real active site during photocatalysis is very important for understanding the catalytic mechanism, but it remains a great challenge. By employing single atoms (SAs) as the mechanism research platform, we investigated the variation of the SA structure under light and the corresponding reaction pathway controlment mechanism. In particular, taking the defect anchoring strategy, Pt SAs are anchored on the metal ion vacancy-rich ZnNiTi layered double hydroxide-etched (ZnNiTi-LDHs-E) support. It is proved by CO-Fourier transform infrared and X-ray absorption fine structure characterization methods that the Pt SAs could gain photoelectrons to form cationic Pt(IV), electron-rich Pt(II), and near-neutral Ptδ+ species at different light intensities. By in situ inducing the above different Pt SAs in photocatalytic CO2 reduction, a dramatic product distribution is observed: (1) under weak light, Pt(IV) SAs cannot activate CO, so CO cannot be further transformed into hydrocarbons; (2) under the moderate light, electron-rich Pt(II) SAs could cooperate with adjacent LDH surface sites (Ni2+/Ti4+) to open up the C-C coupling route for C2H6 generation; and (3) Pt SAs in the state of near-neutral Ptδ+ could directly hydrogenate CO into CH4. This work reveals the structural evolution of Pt SAs in photocatalysis and the corresponding effect on catalytic performance, which provides a new idea for the construction of highly efficient photocatalysts.