Nitroarenes are stable, low‐cost, and readily available starting materials. The directly utilize nitroarenes in synthetically valuable C−N bond formation is of great significance, because the ...pre‐reduction step to corresponding amines can be avoided. Previously, phosphines and carbon monoxide (CO) are the most widely used reductants in the reductive cyclization or/and carbonylation of nitroarenes. Currently, much attention has been attracted to organosilanes as new potential reducing agents, not only because they are inexpensive, easy‐to‐handle, and mild reagents, but also various novel reaction models of nitroarenes have been explored. In this review, we mainly summarize the recent progress on the reductive coupling of nitroarenes by using organosilanes as the end reductants. We hope that a deep understanding of the reaction model and underlying working mechanism can provide a timely guideline for researchers who are interested in this fantastic area, leading to further exploration of practical and efficient reductive coupling of nitroarenes for C−N bond formation and N‐heterocycle synthesis.
Radicals are an important class of versatile and highly reactive species. Compared with the wide applications of various C-centred radicals, however, the N-radical species including N-centred ...radicals and radical ions remain largely unexplored due to the lack of convenient methods for their generation. In recent years, visible light photoredox catalysis has emerged as a powerful platform for the generation of various N-radical species and methodology development towards the synthesis of diverse N-containing compounds. In this tutorial review, we highlight recent advances in this rapidly developing area with particular emphases put on the working models and new reaction design.
Visible-light photocatalysis has recently received increasing attention from chemists because of its wide application in organic synthesis and its significance for sustainable chemistry. This ...catalytic strategy enables the generation of various reactive species, frequently without stoichiometric activation reagents under mild reaction conditions. Manipulation of these reactive intermediates can result in numerous synthetically useful bond formations in a controllable manner. In this Account, we describe our recent advances in the rational design and strategic application of photocatalysis in the synthesis of various synthetically and biologically important heterocycles. Our main research efforts toward this goal can be classified into four categories: formal cycloaddition and cyclization reactions, radical-mediated olefin functionalization/cyclization cascades, photocatalytic generation and cyclization of N-centered radicals, and photocatalytic functionalization of heterocycles by visible-light-induced dual catalysis. Inspired by the wide application of tertiary amines as reductive additives in photoredox catalysis, we exploited a series of readily accessible or rationally designed tertiary amines with reactive sites in a range of photocatalytic formal cycloaddition and cyclization reactions, providing efficient access to diverse nitrogen heterocycles. Employing various photogenerated radical species, we further developed a series of radical-mediated olefin functionalization/cyclization cascade reactions to successfully assemble various five- and six-membered heterocycles. We have also achieved for the first time the direct catalytic conversion of recalcitrant N–H bonds into neutral N-centered radicals through a visible-light-photocatalytic oxidative deprotonation electron transfer. Using this generic strategy, we have devised several types of radical cyclizations of unsaturated hydrazones, leading to the construction of diversely functionalized pyrazoline and pyridazine derivatives in good yields and selectivity. Moreover, we have demonstrated that this photocatalysis can serve as a mild and highly selective tool for direct functionalization of heterocycles because of its powerful capability to controllably generate diverse reactive intermediates under mild reaction conditions. Guided by the fundamental principles of photocatalysis and the redox properties of the photocatalysts, we successfully developed an array of dual-catalyst systems by combining the photocatalysts with palladium, nickel, or amine, enabling efficient and selective coupling reactions. An intriguing phototandem catalytic system using a single photocatalyst was also identified for the development of cascade reactions. Notably, some of the newly developed methodologies have also been successfully utilized for late-stage modification of biologically active natural compounds and complex molecules and as key steps for formal synthesis of natural products. This Account presents a panoramic view and the logic of our recent contributions to the design, development, and application of photocatalytic systems and reactions that provide not only methods for the efficient synthesis of heterocycles but also useful insights into the exploration of new photochemical reactions.
Bio-inspired long-based undulating fin propulsion is commonly employed in biological autonomous underwater vehicles (BAUVs), while the hydrodynamic characteristics of various undulating patterns are ...different. To investigate what kind of undulating pattern has outstanding propulsion or braking performance for BAUVs in directional maneuvers, undulations with four basic undulating patterns are numerically examined under the Open-source Field Operation And Manipulation environment at the Reynolds number of 5 × 102, 5 × 103, and 5 × 104, corresponding to viscous, transitional, and inertial flow regimes, respectively. The study is conducted at various non-dimensional phase speeds c (0.5–2.0, normalized by incoming flow speed) at a constant maximum amplitude of 0.08 and a wavelength of 0.5 (both are normalized by the fin cord length) to imitate the long-based fin. The numerical results indicate that the undulating fin motion with the amplitude envelope gradually increasing from the anterior part to the posterior (conical sinusoidal wave) part may be preferable for thrust generation; undulating with the amplitude envelope increasing from the anterior part to the mid part and decreasing toward the posterior (fusiform sinusoidal wave) presents the superior braking performance when the phase speed is low enough. Moreover, the influence of undulating patterns on the wake structure is analyzed. Through further comparative analysis for propulsion and braking performances, the results obtained here may have instructional significance to the propulsion mechanism in bionic design.
Background and Aims
There is growing evidence that single‐stranded, circular RNA (circRNA) plays a key role in the development of certain cancers, including hepatocellular carcinoma (HCC). It is less ...clear, however, what role circRNA plays in HCC metastasis.
Approach and Results
In this study, through circRNA sequencing, we identified a circRNA: circASAP1 (a circRNA derived from exons 2 and 3 of the ASAP1 gene, hsa_circ_0085616), which is associated with pulmonary metastasis after curative resection in patients with HCC. CircASAP1 was overexpressed in HCC cell lines with high metastatic potential and in metastatic HCCs. In vitro, circASAP1 promoted cell proliferation, colony formation, migration, and invasion, and in vivo, it enhanced tumor growth and pulmonary metastasis. Mechanism studies showed that circASAP1 acts as a competing endogenous RNA for microRNA 326 (miR‐326) and microRNA 532‐5p (miR‐532‐5p), both of which are tumor suppressors in HCC. We found that mitogen‐activated protein kinase (MAPK) 1 and colony stimulating factor (CSF)‐1 were direct common targets for microRNA 326 (miR‐326) and microRNA 532‐5p (miR‐532‐5p), which were regulated by circASAP1. CircASAP1 promotes HCC cell proliferation and invasion by regulating miR‐326/miR‐532‐5p‐MAPK1 signaling and, furthermore, mediates tumor‐associated macrophage infiltration by regulating the miR‐326/miR‐532‐5p‐CSF‐1 pathway. Clinical HCC samples exhibited a positive correlation between circASAP1 expression and levels of CSF‐1, MAPK1, and CD68+ tumor‐associated macrophages, all of which were predictive of patient outcomes.
Conclusion
We identified circASAP1 as a key regulator of HCC metastasis that acts on miR‐326/miR‐532‐5p‐MAPK1/CSF‐1 signaling and serves as a prognostic predictor in patients with HCC.
Remote control: New strategies for the activation of remote C(sp3)−H bonds by photoredox‐catalyzed (PC) radical translocation via O‐ and N‐centered radicals have recently been described. These ...methods enable the controlled and site‐selective functionalization of inert C(sp3)−H bonds and provide new opportunities for reaction design (HAT=hydrogen atom transfer).
Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical ...polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm
with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.
Abstract
An interesting result that was recently reported for Mrk 421 is the detection of a significant excess at hard X-ray energies, which could provide useful information to investigate particle ...acceleration and emission mechanisms in the relativistic jet. Considering a two-injection scenario, we develop a self-consistent one-zone leptonic model to understand the origin of the hard X-ray excess in Mrk 421 during the period of extremely low X-ray and very high-energy flux in 2013 January. In the model, two populations of mono-energetic ultra-relativistic electrons are injected into the emission region, which is a magnetized plasmoid propagating along the blazar jet. We numerically calculate the emitting electron energy distribution by solving a kinetic equation that incorporates both shock acceleration and stochastic acceleration processes. Moreover, we infer analytic expressions relating the electrons’ acceleration, cooling, escape, and injection to the observed spectra and variability. In particular, for the injection luminosity, we derive a new approximate analytical expression for the case of continual injection with a mono-energetic distribution. Based on a comparison between the theoretical predictions and the observed SED, we conclude that the hard X-ray excess that was observed in Mrk 421 may be due to the synchrotron radiation emitted by an additional electron population, which is co-spatial with an electron population producing simultaneous optical/UV, soft X-ray, and
γ
-ray emissions. Therefore, stochastic acceleration may play a major role in producing the observed X-ray spectrum.
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