Semiconductor polymeric graphitic carbon nitride (g-C
3
N
4
) photocatalysts have attracted dramatically growing attention in the field of the visible-light-induced hydrogen evolution reaction (HER) ...because of their facile synthesis, easy functionalization, attractive electronic band structure, high physicochemical stability and photocatalytic activity. This review article presents a panorama of the latest advancements in the rational design and development of g-C
3
N
4
and g-C
3
N
4
-based composite photocatalysts for HER application. Concretely, the review starts with the development history, synthetic strategy, electronic structure and physicochemical characteristics of g-C
3
N
4
materials, followed by the rational design and engineering of various nanostructured g-C
3
N
4
(
e.g.
thinner, highly crystalline, doped, and porous g-C
3
N
4
) photocatalysts for HER application. Then a series of highly efficient g-C
3
N
4
(
e.g.
, metal/g-C
3
N
4
, semiconductor/g-C
3
N
4
, metal organic framework/g-C
3
N
4
, carbon/g-C
3
N
4
, conducting polymer/g-C
3
N
4
, sensitizer/g-C
3
N
4
) composite photocatalysts are exemplified. Lastly, this review provides a comprehensive summary and outlook on the major challenges, opportunities, and inspiring perspectives for future research in this hot area on the basis of pioneering works. It is believed that the emerging g-C
3
N
4
-based photocatalysts will act as the "holy grail" for highly efficient photocatalytic HER under visible-light irradiation.
Graphitic carbon nitrides and their composites with various morphologies and bandgaps engineered for the hydrogen evolution reaction under visible light are reviewed.
A series of highly active organoboron catalysts for the coupling of CO2 and epoxides with the advantages of scalable preparation, thermostability, and recyclability is reported. The metal‐free ...catalysts show high reactivity towards a wide scope of cyclic carbonates (14 examples) and can withstand a high temperature up to 150 °C. Compared with the current metal‐free catalytic systems that use mol % catalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat.=200 000/1, mole ratio) in the presence of a cocatalyst. This feature greatly narrows the gap between metal‐free catalysts and state‐of‐the‐art metallic systems. An intramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures, structure–performance relationships, kinetic studies, and key reaction intermediates.
A highly active bifunctional organoboron catalyst with the advantages of scalable preparation, thermostability, and recyclability was reported for the cyclization of CO2 and epoxides. An intramolecular cooperative mechanism was substantiated by investigations into the crystal structure of the catalysts, structure– performance relationships, kinetic studies, and the key reaction intermediates.
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Quinoline and quinazoline alkaloids, two important classes of N‐based heterocyclic compounds, have attracted tremendous attention from researchers worldwide since the 19th century. Over the past 200 ...years, many compounds from these two classes were isolated from natural sources, and most of them and their modified analogs possess significant bioactivities. Quinine and camptothecin are two of the most famous and important quinoline alkaloids, and their discoveries opened new areas in antimalarial and anticancer drug development, respectively. In this review, we survey the literature on bioactive alkaloids from these two classes and highlight research achievements prior to the year 2008 (Part I). Over 200 molecules with a broad range of bioactivities, including antitumor, antimalarial, antibacterial and antifungal, antiparasitic and insecticidal, antiviral, antiplatelet, anti‐inflammatory, herbicidal, antioxidant and other activities, were reviewed. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.
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Impaired wound healing and ulcer complications are a leading cause of death in diabetic patients. In this study, we report the design and synthesis of a cyclometalated iridium(III) metal complex 1a ...as a stabilizer of hypoxia-inducible factor-1α (HIF-1α). In vitro biophysical and cellular analyses demonstrate that this compound binds to Von Hippel-Lindau (VHL) and inhibits the VHL-HIF-1α interaction. Furthermore, the compound accumulates HIF-1α levels in cellulo and activates HIF-1α mediated gene expression, including VEGF, GLUT1, and EPO. In in vivo mouse models, the compound significantly accelerates wound closure in both normal and diabetic mice, with a greater effect being observed in the diabetic group. We also demonstrate that HIF-1α driven genes related to wound healing (i.e. HSP-90, VEGFR-1, SDF-1, SCF, and Tie-2) are increased in the wound tissue of 1a-treated diabetic mice (including, db/db, HFD/STZ and STZ models). Our study demonstrates a small molecule stabilizer of HIF-1α as a promising therapeutic agent for wound healing, and, more importantly, validates the feasibility of treating diabetic wounds by blocking the VHL and HIF-1α interaction.
Producing polyesters with high molecular weight (Mn) through ring‐opening copolymerization (ROCOP) of epoxides with cyclic anhydrides remains a major challenge. Herein, we communicate a metal‐free, ...highly active, and high thermoresistance system for the ROCOP of epoxides with cyclic anhydrides to prepare polyesters (13 examples). The organoboron catalysts can endure a reaction temperature as high as 180 °C for the ROCOP of cyclohexane oxide (CHO) with phthalic anhydride (PA) without the observation of any side reactions. The average Mn of the produced poly(CHO‐alt‐PA) climbed to 94.5 kDa with low polydispersity (Ð=1.19). Furthermore, an unprecedented turnover number of 9900, equivalent to an efficiency of 7.4 kg of polyester/g of catalyst, was achieved at a feed ratio of CHO/PA/catalyst=20000:10000:1 at 150 °C. Kinetic studies, crystal structure analysis, 11B NMR spectra, and DFT calculations provided mechanistic justification for the effectiveness of the catalyst system.
Ring‐opening copolymerization of epoxides and cyclic anhydrides by organoboron catalysts is presented. In view of their facile preparation and unprecedented performance (thermostability, reactivity, and productivity), the catalysts provided here hold promise in pushing ROCOP of epoxides with cyclic anhydrides to the industry line.
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This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring‐opening polymerization (ROP) of epoxides under mild conditions. ...The bifunctional catalyst incorporates two 9‐borabicyclo3.3.1nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106 g mol−1). Based on the investigations on crystal structure of catalyst, MALDI‐TOF, and 11B NMR spectroscopy, an intramolecular ammonium cation assisted SN2 mechanism is proposed and verified by DFT calculations.
A new organocatalyst that has unprecedented reactivity for ring‐opening polymerization of epoxides follows a novel intramolecular ammonium cation assisted mechanism. The bifunctional catalyst incorporates two 9‐borabicyclo3.3.1nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site.
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Conspectus Electron-deficient boron-based catalysts with metal-free but metallomimetic characteristics provide a versatile platform for chemical transformations. However, their catalytic performance ...is usually lower than that of the corresponding metal-based catalysts. Furthermore, many elaborate organoboron compounds are produced via time-consuming multistep syntheses with low yields, presenting a formidable challenge for large-scale applications of these catalysts. Given this context, the development of organoboron catalysts with the combined advantages of high efficiency and easy preparation is of critical importance. Therefore, we envisioned that the construction of a dynamic Lewis multicore system (DLMCS) by integrating the Lewis acidic boron center(s) and a Lewis basic ammonium salt in one molecule would be particularly efficient for on-demand applications because of the intramolecular synergistic effect. This Account summarizes our recent efforts in developing modular organoboron catalysts with unprecedented activities for several chemical transformations. A series of mono-, di-, tri-, and tetranuclear organoboron catalysts was readily designed and prepared in nearly quantitative yields over two steps using commercially available feedstocks. Notably, these catalysts can be modularly tailored by fine control over the electrophilic property of the Lewis acidic boron center(s), electronic and steric effects of the electropositive ammonium cation, linker length between the boron center and the ammonium cation, the number of boron centers, and the nucleophilic anion. This modular design allows systematic manipulation of the reactivity and efficacy of the catalysts, thus optimizing suitable catalysts for versatile chemical transformations. These include the coupling of CO2 and epoxides, copolymerization of CO2 and epoxides, ring-opening polymerization (ROP) of epoxides, and ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides. The utilization of mononuclear organoboron catalysts provided a turnover frequency of 11050 h–1 for the CO2/propylene oxide coupling reaction, an unprecedented efficiency of 5.0 kg of polymer/g of catalyst for the copolymerization of CO2 and cyclohexene oxide, and a record-breaking catalytic efficiency of 7.4 kg of polymer/g of catalyst for the ROCOP of epoxides with cyclic anhydrides. A turnover number of 56500 was observed at a catalyst loading of 10 ppm for the ROP of epoxides using the dinuclear catalysts. The tetranuclear organoboron catalysts realized the previously intractable task of the copolymerization of CO2 and epichlorohydrin, producing poly(chloropropylene carbonate) with the highest molecular weight of 36.5 kg/mol reported to date. Furthermore, the study revealed that the interaction between the dynamic Lewis multicore, that is, the intramolecular synergistic effect between the boron center(s) and the quaternary ammonium salt, plays a key role in mediating the catalytic activity and selectivity. This was based on investigations of the crystal structures of the catalysts, key intermediates, reaction kinetics, and density functional theory calculations. The modular tactics for the construction of organoboron catalysts presented in this Account should inspire more advanced catalyst designs.
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IJS, KILJ, NUK, PNG, UL, UM
Thermally sprayed coatings are essentially layered materials and contain large numbers of lamellar pores. It is thus quite necessary to clarify the formation mechanism of lamellar pores which ...significantly influence coating performances. In the present study, to elaborate the formation mechanism of lamellar pores, the yttria-stabilized zirconia (ZrO
2
–7 wt% Y
2
O
3
, 7YSZ) splats, which have high fracture toughness and tetragonal phase stability, were employed. Interestingly, anomalous epitaxial growth occurred for all deposition temperatures in spite of the extremely high cooling rate, which clearly indicated chemical bonding and complete contact at splat/substrate interface before splat cooling. However, transverse spallation substantially occurred for all deposition temperatures in spite of the high fracture toughness of 7YSZ, which revealed that the lamellar pores were from transverse cracking/spallation due to the large stress during splat cooling. Additionally, fracture mechanics analysis was carried out, and it was found that the stress arose from the constraint effect of the shrinkage of the splat by locally heated substrate with the value about 1.97 GPa. This clearly demonstrated that the stress was indeed large enough to drive transverse cracking/spallation forming lamellar pores during splat cooling. All of these contribute to understanding the essential features of lamellar bonding and further tailoring the coating structures and performance.
Construction of well‐defined sulfur‐rich macromolecules in a facile manner is an interesting but challenging topic. Herein, we disclose how to readily construct well‐defined triblock sulfur‐rich ...thermoplastic elastomers via a self‐switchable isothiocyanate/episulfide copolymerization and air‐assisted oxidative coupling strategy. During self‐switchable polymerization, alternating copolymerization of isothiocyanate and episulfide occurs initially due to the lower energy barrier for isothiocyanate insertion with respect to successive episulfide ring‐opening. After exhaustion of isothiocyanate, ring‐opening polymerization of episulfide begins, providing diblock polymers. Subsequent exposure of the reaction to air leads to a transformation of diblock copolymers into triblock thermoplastic elastomers. This protocol can be extended to diverse isothiocyanates and episulfides, allowing fine‐tuning of the performance of the produced sulfur‐rich thermoplastic elastomers.
Episulfide‐involved self‐switchable polymerization to produce well‐defined sulfur‐rich triblock thermoplastic elastomers has been achieved via an ammonium salt mediated copolymerization of episulfide/isothiocyanate together with an air‐assisted oxidative coupling strategy.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Poly(cyclopentene carbonate) (PCPC) produced by copolymerization of CO2 and cyclopentene oxide (CPO) is a promising but challenging chemical recyclable polymer that has high potential in minimizing ...plastic pollution and maximizing CO2 utilization. Currently, problems remain to be solved, include low reactivity of toxic metal catalysts, inevitable byproducts, and especially the ambiguous mechanism understanding. Herein, we present the first metal‐free access to PCPC by using a series of modular dinuclear organoboron catalysts. PCPC was afforded in an unprecedented catalytic efficiency of 1.0 kg of PCPC/g of catalyst; while the depolymerization of PCPC abides by a combination pathway of random chain scission and chain unzipping, returning CPO in near‐quantitative yield (>99 %). The preparation and depolymerization of PCPC along with in depth understanding of related mechanisms would be helpful for further development of advanced catalysts and recyclable plastics.
The first metal‐free access to poly(cyclopentene carbonate) and its chemical recycling to monomer were achieved by using a dinuclear bifunctional organoboron catalyst, enriching the portfolio of the circular plastic economy.
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