Ynamides are unique alkynes with a carbon-carbon triple bond directly attached to the nitrogen atom bearing an electron-withdrawing group. The alkyne is strongly polarized by the electron-donating ...nitrogen atom, but its high reactivity can be finely tempered by the electron-withdrawing group. Accordingly, ynamides are endowed with both nucleophilic and electrophilic properties and their chemistry has been an active research field. The catalytic intermolecular annulations of ynamides, featuring divergent assembly of structurally important amino-heterocycles in a regioselective manner, have gained much attention over the past decade. This review aims to provide a comprehensive summary of the advances achieved in this area involving transition metal and acid catalysis. Moreover, the intermolecular annulations of ynamide analogs including ynol ethers and thioalkynes are also discussed, which can provide insights into the reactivity difference caused by the heteroatoms.
This review comprehensively summarizes the advances achieved in catalytic intermolecular annulations of ynamides from 2010 to 2020.
The development of precious‐metal alternative electrocatalysts for oxygen reduction reaction (ORR) is highly desired for a variety of fuel cells, and single atom catalysts (SACs) have been envisaged ...to be the promising choice. However, there remains challenges in the synthesis of high metal loading SACs (>5 wt.%), thus limiting their electrocatalytic performance. Herein, a facile self‐sacrificing template strategy is developed for fabricating Co single atoms along with Co atomic clusters co‐anchored on porous‐rich nitrogen‐doped graphene (Co SAs/AC@NG), which is implemented by the pyrolysis of dicyandiamide with the formation of layered g‐C3N4 as sacrificed templates, providing rich anchoring sites to achieve high Co loading up to 14.0 wt.% in Co SAs/AC@NG. Experiments combined with density functional theory calculations reveal that the co‐existence of Co single atoms and clusters with underlying nitrogen doped carbon in the optimized Co40SAs/AC@NG synergistically contributes to the enhanced electrocatalysis for ORR, which outperforms the state‐of‐the‐art Pt/C catalysts with presenting a high half‐wave potential (E1/2 = 0.890 V) and robust long‐term stability. Moreover, the Co40SAs/AC@NG presents excellent performance in Zn–air battery with a high‐peak power density (221 mW cm−2) and strong cycling stability, demonstrating great potential for energy storage applications.
High‐loading Co single atoms and Co atomic clusters co‐anchored on porous‐rich nitrogen‐doped graphene (Co SAs/AC@NG) is constructed via a facile self‐sacrificing template strategy. The Co40SAs/AC@NG catalyst demonstrates remarkable performance with a half‐wave potential of 0.890 V for oxygen reduction reaction and a large power density of 221 mW cm−2 toward Zn–air battery.
This paper introduces “spatial effects” and “dynamic effects” to investigate the influences of economic growth and energy transition on cross‐country CO2 emissions movements within the European Union ...(EU). We apply the fixed‐effects dynamic spatial Durbin error model to empirically gauge the magnitude of the spatial impacts and dynamic impacts for a sample of 26 EU countries throughout 1990–2015. By analyzing the empirical results, we conclude that: (1) Compared with dynamic spatial Durbin error model, the traditional dynamic panel model over‐estimates the parameters because traditional regression methods only capture the direct impacts, and neglect the indirect impacts. (2) A significant positive spatial spillover of CO2 emissions from neighboring countries to the local country is recognized, justifying the use of our spatial model. (3) Economic growth has positive impacts on CO2 emissions, while the spatial effects of economic growth exert negative impacts. Moreover, the total effects of economic growth are positive in both short‐term and long‐term. (4) Although the spatial effects of renewable energy are not significant, renewable energy has negative influences on CO2 emissions. (5) The impacts and spatial effects of natural gas are positive; therefore, its total effects are positive in both short‐run and long‐run. Based on our finding, we provide several policy recommendations, such as the emphasize of cooperation with CO2 reduction policies, the promotion of green economy and renewable energy, and the substitution of natural gas in the future.
In this brief, an adaptive robust finite-time tracking control (ARFTTC) scheme for trajectory tracking of a fully actuated marine surface vehicle with unknown disturbances is proposed. A new ...finite-time disturbance observer is incorporated into the proposed finite-time tracking control (FTTC) structure that facilitates faster convergence and better robustness to disturbances. Hence, in the presence of unknown disturbances, the ARFTTC can cause tracking error to converge to zero in a finite time. Simulation studies and comprehensive comparisons with conventional backstepping technique demonstrate remarkable performance and superiority of the ARFTTC in terms of both tracking accuracy and robustness.
Production of hydrogen by electrochemical water splitting has been hindered by the high cost of precious metal catalysts, such as Pt, for the hydrogen evolution reaction (HER). In this work, novel ...hierarchical β‐Mo2C nanotubes constructed from porous nanosheets have been fabricated and investigated as a high‐performance and low‐cost electrocatalyst for HER. An unusual template‐engaged strategy has been utilized to controllably synthesize Mo‐polydopamine nanotubes, which are further converted into hierarchical β‐Mo2C nanotubes by direct carburization at high temperature. Benefitting from several structural advantages including ultrafine primary nanocrystallites, large exposed surface, fast charge transfer, and unique tubular structure, the as‐prepared hierarchical β‐Mo2C nanotubes exhibit excellent electrocatalytic performance for HER with small overpotential in both acidic and basic conditions, as well as remarkable stability.
From the same sheet: Hierarchical β‐Mo2C nanotubes constructed of ultrathin nanosheets are designed and synthesized. Benefitting from ultra‐small primary nanocrystallites, a large exposed surface, fast charge transfer, and unique tubular structure, the as‐prepared hierarchical β‐Mo2C nanotubes exhibit excellent electrocatalytic performance for the hydrogen evolution reaction.
Development of low‐cost, high‐performance, and bifunctional electrocatalysts for water splitting is essential for renewable and clean energy technologies. Although binary phosphides are inexpensive, ...their performance is not as good as noble metals. Adding a third metal element to binary phosphides (Ni‐P, Co‐P) provides the opportunity to tune their crystalline and electronic structures and thus their electrocatalytic properties. Here, ternary phosphide (NiCoP) films with different nickel to cobalt ratios via an electrodeposition technique are synthesized. The films have a triple‐layered and hierarchical morphology, consisting of nanosheets in the bottom layer, ≈90–120 nm nanospheres in the middle layer, and larger spherical particles on the top layer. The ternary phosphides exhibit versatile activities that are strongly dependent on the Ni/Co ratios and Ni0.51Co0.49P film is found to have the best electrocatalytic activities for both hydrogen evolution reactions and oxygen evolution reactions. The high performance of the ternary phosphide film is attributed to enhanced electric conductivity so that reaction kinetics is accelerated, enlarged surface area due to the hierarchical and three‐layered morphology, and increased local electric dipole so that the energy barrier for the water splitting reaction is lowered.
Bimetallic phosphide (Ni0.51Co0.49P) films with a triple‐layered and hierarchical morphology with superior performance toward overall water splitting are successfully synthesized. The phosphides present versatile activities that are strongly dependent on the Ni/Co ratios. The improvement in performance is mainly ascribed to the alloying effect between Ni and Co atoms.
In this work, a series of methacrylate‐based polymers bearing benzene (poly(benzyl methacrylate)), naphthalene (poly(2‐naphthyl methacrylate)), anthracene (poly(9‐anthracenyl methyl methacrylate), ...PAMA), and pyrene (poly(1‐pyrenemethyl methacrylate)) are blended with conjugated polymer of poly(3‐hexylthiophene) (P3HT) to perform vertical phase separation during spin‐coating. The bilayer structure of the conjugated/insulating polymer blend is driven by their mismatch in surface energy, and the blend films are applied in the phototransistor memory device with the bottom layer of methacrylate‐based polymer as a photoactive electret and the top layer of P3HT as a semiconducting channel. It is found that the vertical phase separation morphology, conjugation, and energy levels of the pendant arene groups in the methacrylate‐based polymers are highly related to the photoresponse, memory retention/endurance of the phototransistor memory. Therefore, the device comprising the polymer blend of P3HT and PAMA successfully produces a high current contrast of 105 to 254 nm light and 104 to 450 nm light over 104 s. This study provides a facile approach to the fabrication of high‐performance phototransistor memory devices.
The polymer blend comprising poly(9‐anthracenyl methyl methacrylate) and poly(3‐hexylthiophene) forms an efficient vertical phase separation during spin‐coating process. The bilayered film is applied as a photoactive electret in a transistor memory device to produce a high current contrast of 105 to 254 nm light and 104 to 450 nm light over 104 s.
Nitrate electrocatalytic reduction (NO3RR) for ammonia production is a promising strategy to close the N‐cycle from nitration contamination, as well as an alternative to the Haber–Bosch process with ...less energy consumption and carbon dioxide release. However, current long‐term stability of NO3RR catalysts is usually tens of hours, far from the requirements for industrialization. Here, symmetry‐broken Cusingle‐atom catalysts are designed, and the catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h−1 cm−2 at an industrial level current density of 366 mA cm−2 is achieved, obtaining a good balance between catalytic activity and long‐term stability. Coordination symmetry breaking is achieved by embedding one Cu atom in graphene nanosheets with two N and two O atoms in the cis‐configuration, effectively lowering the coordination symmetry, rendering the active site more polar, and accumulating more NO3− near the electrocatalyst surface. Additionally, the cis‐coordination splits the Cu 3d orbitals, which generates an orbital‐symmetry‐matched π‐complex of the key intermediate *ONH and reduces the energy barrier, compared with the σ‐complex generated with other catalysts. These results reveal the critical role of coordination symmetry in single‐atom catalysts, prompting the design of more coordination‐symmetry‐broken electrocatalysts toward possible industrialization.
A coordination‐symmetry‐breaking Cusingle‐atom catalyst enables a good balance between catalytic activity and long‐term stability in nitrate electroreduction to ammonia. The catalytic activity is retained after operation for more than 2000 h, while an average ammonia production rate of 27.84 mg h−1 cm−2 at an industrial level current density of 366 mA cm−2 is achieved.
The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium into the basal and the apical (adluminal) compartments. ...Meiosis I and II, spermiogenesis, and spermiation all take place in a specialized microenvironment behind the BTB in the apical compartment, but spermatogonial renewal and differentiation and cell cycle progression up to the preleptotene spermatocyte stage take place outside of the BTB in the basal compartment of the epithelium. However, the BTB is not a static ultrastructure. Instead, it undergoes extensive restructuring during the seminiferous epithelial cycle of spermatogenesis at stage VIII to allow the transit of preleptotene spermatocytes at the BTB. Yet the immunological barrier conferred by the BTB cannot be compromised, even transiently, during the epithelial cycle to avoid the production of antibodies against meiotic and postmeiotic germ cells. Studies have demonstrated that some unlikely partners, namely adhesion protein complexes (e.g., occludin-ZO-1, N-cadherin-β-catenin, claudin-5-ZO-1), steroids (e.g., testosterone, estradiol-17β), nonreceptor protein kinases (e.g., focal adhesion kinase, c-Src, c-Yes), polarity proteins (e.g., PAR6, Cdc42, 14-3-3), endocytic vesicle proteins (e.g., clathrin, caveolin, dynamin 2), and actin regulatory proteins (e.g., Eps8, Arp2/3 complex), are working together, apparently under the overall influence of cytokines (e.g., transforming growth factor-β3, tumor necrosis factor-α, interleukin-1α). In short, a "new" BTB is created behind spermatocytes in transit while the "old" BTB above transiting cells undergoes timely degeneration, so that the immunological barrier can be maintained while spermatocytes are traversing the BTB. We also discuss recent findings regarding the molecular mechanisms by which environmental toxicants (e.g., cadmium, bisphenol A) induce testicular injury via their initial actions at the BTB to elicit subsequent damage to germ-cell adhesion, thereby leading to germ-cell loss, reduced sperm count, and male infertility or subfertility. Moreover, we also critically evaluate findings in the field regarding studies on drug transporters in the testis and discuss how these influx and efflux pumps regulate the entry of potential nonhormonal male contraceptives to the apical compartment to exert their effects. Collectively, these findings illustrate multiple potential targets are present at the BTB for innovative contraceptive development and for better delivery of drugs to alleviate toxicant-induced reproductive dysfunction in men.
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