Chalcogen bonding (ChB) has emerged as a promising tool in organic synthesis. However, compared with the well‐developed selenium‐ and tellurium‐based salt catalysts, the ChB catalysis of sulfonium ...salts is still unknown. Here, we report a new type of alkynyl‐sulfonium salt ChB catalysis for various ionic transformations, including transfer hydrogenation, bromination, bromolactonization, dimerization of 1,1‐diphenylethylene, nitro‐Michael addition reaction and Ritter reaction. More importantly, the photocapability of ChB was first demonstrated to generate alkynyl radicals for the synthesis of a variety of chalcogenoacetylenes. Mechanistic studies shed light on the mechanism of the photoinduced reactions and confirmed the involvement of alkynyl radicals which are difficult to generate otherwise.
Alkynyl sulfonium salts were employed as chalcogen bonding (ChB) catalysts for the first time. They display superior capability in the generation of alkynyl radicals under blue‐light irradiation.
N‐heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in organic synthesis. In recent years a number of reviews have been published on NHC‐catalyzed transformations involving ...Breslow intermediates, acyl azoliums, α,β‐unsaturated acyl azoliums, homoenolate equivalents, and azolium enolates. However, the azolium dienolate intermediates generated by NHCs have been employed in asymmetric synthesis only very recently, especially in cycloadditions dealing with remote functionalization. This Minireview highlights all the developments and the new advances in NHC‐catalyzed asymmetric cycloaddition reactions involving azolium dienolate intermediates.
An intermediate look: N‐heterocyclic carbene catalysis has emerged as a powerful strategy for enantioselective functionalizations at remote positions, and proceeds via azolium dienolate intermediates that are easily generated from various substrates. This Minireview highlights the development and the new advances of cycloaddition/annulation reactions involving azolium dienolate intermediates.
The sigma (σ)‐hole effect has emerged as a promising tool to construct novel architectures endowed with new properties. A simple yet effective strategy for the generation of monofluoromethyl radicals ...is a continuing challenge within the synthetic community. Fluoromethylphosphonium salts are easily available, air‐ and thermally stable, as well as simple‐to‐handle. Herein, we report the ability of the σ‐hole effect to facilitate the visible‐light‐triggered photolysis of phosphonium iodide salts, a charge‐transfer complex, selectively giving fluoromethyl radicals. The usefulness and versatility of this new protocol are demonstrated through the mono‐, di‐, and trifluoromethylation of a variety of alkenes.
Simple and selective synthesis of fluoromethylated alkenes, heterocycles, enamines and heteroarenes by using the readily available and bench‐stable fluoromethylphosphonium iodide salts is described. Key to this privileged transformation is the formation of a photoactive charge‐transfer complex involving the σ‐hole effect of phosphonium salts.
Micro‐ and nanorobots have shown great potential for applications in various fields, including minimally invasive surgery, targeted therapy, cell manipulation, environmental monitoring, and water ...remediation. Recent progress in the design, fabrication, and operation of these miniaturized devices has greatly enhanced their versatility. In this report, the most recent progress on the manipulation of small‐scale robots based on power sources, such as magnetic fields, light, acoustic waves, electric fields, thermal energy, or combinations of these, is surveyed. The design and propulsion mechanism of micro‐ and nanorobots are the focus of this article. Their fabrication and applications are also briefly discussed.
Externally powered micro‐ and nanorobots are promising candidates for future biomedical applications. Recent progress on externally powered small‐scale robots is summarized based on their power sources. The emphasis is laid on the design and propulsion mechanism of the microrobots. The fabrication and application is briefly discussed as well.
•We propose a DSGE model to examine the impact of the coronavirus outbreak on tourism.•The model is generalizable to any epidemic.•The model supports the policy of providing tourism consumption ...vouchers for residents.
Conspectus In nature, enzymes are a powerful medium for the construction of enantiomerically pure chemicals, which always inspires synthetic chemists to explore new catalysts to imitate the enzyme ...machinery for asymmetric transformations. Vitamin B1, a bifunctional thiazolium N-heterocyclic carbene (NHC) precursor, is the coenzyme for transketolase. In the past two decades, a series of chiral NHCs, including monocyclic, bicyclic, tetracyclic, and even bridged ones, have been synthesized and successfully utilized as efficient organocatalysts for a wide variety of asymmetric organic reactions. The utility of bifunctional catalysts can enhance catalytic activity and improve stereochemical control through their synchronous activation of both reaction partners. However, the NHCs possessing multiple activation sites are far less developed. This Account gives an overview of our research on the design, development, and applications of bifunctional NHCs in organocatalysis. We synthesized a series of l-pyroglutamic acid-derived bifunctional NHCs bearing a free hydroxyl group which can interact with carbonyl or imino groups via hydrogen-bonding. Further studies revealed that these bifunctional catalysts worked well for a variety of reactions. We have developed bifunctional NHC-catalyzed aza-benzoin reactions, 2 + 2, 2 + 3, and 2 + 4 cycloadditions of ketenes, 3 + 2 and 3 + 4 annulations of enals, and aza-MBH and Rauhut–Currier reactions of Michael acceptors. In addition to these reactions via nucleophilic Breslow intermediates, enolates, homoenolates, and zwitterionic azolium intermediates, the bifunctional NHC-catalyzed 3 + 3 annulation via 1,3-biselectrophilic α,β-unsaturated acyl azolium intermediates was also developed. In these reactions, bifunctional NHCs showed amazing effects compared to normal nonbifunctional NHCs. In some cases, the bifunctional NHCs facilitated reactions which did not work under normal NHC catalysis, possibly due to additional activation via H-bonding. More interestingly, the bifunctional NHCs could not only improve but also switch the enantioselectivity to get products with opposite stereochemistry through H-bond controlled stereochemical directing. Furthermore, the reaction mode could be totally changed from 3 + 2 to 3 + 4 annulation to give kinetically favored products when bifunctional NHCs were employed. In future, the applications of bifunctional NHCs in other challenging reactions, such as asymmetric reactions with carbon–carbon unsaturated bonds, and the reactions involving alkyl or heteroatom radicals will be the major focus in our group.
Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme of the salvage pathway of nicotinamide adenine dinucleotide synthesis. NAMPT can also be secreted and functions as a cytokine. We have ...previously shown that in the brain, NAMPT expression and secretion can be induced in microglia upon neuroinflammation and injury. Yet the mechanism for NAMPT secretion remains unclear. Here we show that NAMPT can be actively secreted from microglia upon the treatment of ischemia‐like injury – oxygen‐glucose deprivation and recovery (OGD/R). We confirmed that classical ER‐Golgi pathway is not involved in NAMPT secretion. NAMPT secretion was further enhanced by ATP, and the secretion was mediated by P2X7 receptor and by intracellular Ca2+. Importantly, we found that phospholipase D inhibitor, n‐butanol, phospholipase D siRNA, and wortmannin significantly decreased OGD/R‐induced and ATP‐enhanced release of NAMPT in microglia. After excluding the mechanisms of involving secretory autophagy, endosomes, and secretory lysosome, we have concluded that microglial NAMPT is secreted mainly via exosome. Immune‐electron microscopy identifies NAMPT in extracellular vesicles with the size and morphology characteristic of exosome. With the vesicles harvested by ultra‐centrifugation, exosomal NAMPT is further confirmed by Western blotting analysis. Intriguingly, the amount of NAMPT relative to exosomal protein markers remains unchanged upon the treatment of OGD/R, suggesting a constant load of exosomal NAMPT in microglia. Taken together, we have identified NAMPT is actively secreted via exosome from microglia during neuroinflammation of ischemic injury.
We proposed a cascade for P2X7R‐mediated nicotinamide phosphoribosyltransferase (NAMPT) secretion from microglia through Ca2+‐dependent phospholipase D‐mediated exosomal pathway during cerebral ischemic injury: the activation of P2X7R evokes Ca2+ influx through the ion channel of P2X7R, the increment of intracellular Ca2+ causes the activation of phospholipase D (PLD). The activated PLD (PLD*) catalyzes phosphatidylcholine (PC) to produce phosphatidic acid (PA). PA participates in the release of exosome that contains NAMPT. Our findings provide a new insight into the secretion pathways of NAMPT from microglia.
•An environmentally friendly superhydrophobic film was constructed on mild steel for corrosion protection.•The superhydrophobic film could greatly improve the anti-corrosion performance of the ...substrate in 3.5 wt.% NaCl solution.•The superhydrophobic film exhibited long-term stability even after stored indoor for one year.
In this work, non-particle and fluorine-free superhydrophobic films were constructed on mild steel (MS) for corrosion protection by one-step electrodeposition from dodecyltrimethoxysilane (DTMS)-contained precursor solution. The superhydrophobicity was achieved by the generated micro/nanostructure of hydrophobic DTMS during electrodeposition. The superhydrophobic films exhibited long-term stability to air atmosphere. The protective performance in 3.5 wt. % NaCl solution was estimated by potentiodynamic polarization technique, by electrochemical impedance spectroscopy, by monitoring water contact angle changes and by iron dissolution examination. The results show that the superhydrophobic films exhibit remarkable enhanced anticorrosion performance for MS with a promising inhibition efficiency of 99.74%.
The recent decade has witnessed a new wave of development in the place-based accessibility theory, revolving around the two-step floating catchment area (2SFCA) method. The 2SFCA method, initially ...serving to evaluate the spatial inequity of health care services, has been further applied to other urban planning and facility access issues. Among these applications, different distance decay functions have been incorporated in the thread of model development, but their applicability and limitations have not been thoroughly examined. To this end, the paper has employed a place-based accessibility framework to compare the performance of twenty-four 2SFCA models in a comprehensive manner. Two important conclusions are drawn from this analysis: on a small analysis scale (e.g., community level), the catchment size is the most critical model component; on a large analysis scale (e.g., statewide), the distance decay function is of elevated importance. In sum, this comparative analysis provides the theoretical support necessary to the choice of the catchment size and the distance decay function in the 2SFCA method. Justification of model parameters through empirical evidence (e.g., field surveys about local travel activities) and model validation through sensitivity analysis are needed in future 2SFCA applications for various urban planning, service delivery, and spatial equity scenarios.
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