Structures of Highly Twisted Amides Relevant to Amide N−C Cross‐Coupling: Evidence for Ground‐State Amide Destabilization

Herein, we show that acyclic amides that have recently enabled a series of elusive transition‐metal‐catalyzed N?C activation/cross‐coupling reactions are highly twisted around the N?C(O) axis by a new destabilization mechanism of the amide bond. A unique effect of the N‐glutarimide substituent, leading to uniformly high twist (ca. 90°) irrespective of the steric effect at the carbon side of the amide bond has been found. This represents the first example of a twisted amide that does not bear significant steric hindrance at the α‐carbon atom. The ¹⁵N NMR data show linear correlations between electron density at nitrogen and amide bond twist. This study strongly supports the concept of amide bond ground‐state twist as a blueprint for activation of amides toward N?C bond cleavage. The new mechanism offers considerable opportunities for organic synthesis and biological processes involving non‐planar amide bonds.     

Study of three rotating radio transients with FAST

Rotating radio transients(RRATs) are peculiar astronomical objects whose emission mechanism remains under investigation.In this paper, we present observations of three RRATs, J1538+2345, J1854+0306 and J1913+1330, carried out with the Fivehundred-meter Aperture Spherical radio Telescope(FAST). Specifically, we analyze the mean pulse profiles and temporal flux density evolutions of the RRATs. Owing to the high sensitivity of FAST, the derived burst rates of the three RRATs are higher than those in previous reports. RRAT J1854+0306 exhibited a time-dynamic mean pulse profile, whereas RRAT J1913+1330 showed distinct radiation and nulling segments on its pulse intensity trains. The mean pulse profile variation with frequency is also studied for RRAT J1538+2345 and RRAT J1913+1330, and the profiles at different frequencies could be well fitted with a cone-core model and a conal-beam model, respectively.     

Mono-Heteroatom Substitution for Harnessing Excited-State Structural Planarization of Dihydrodibenzo[a,c]phenazines

With the aim of generalizing the structure–properties relationship of bending heterocyclic molecules that undergo prominent photoinduced structural planarization (PISP), a series of new dihydrodibenzo[ac]phenazine derivatives in which one nitrogen atom is replaced by oxygen ( PNO ), sulfur ( PNS ), selenium ( PNSe ), or dimethylmethanediyl ( PNC ) was strategically designed and synthesized. Compounds PNO , PNS , and PNSe have significantly nonplanar geometries in the ground state, which undergo PISP to give a planarlike conformer and hence a large emission Stokes shift. A combination of femtosecond early relaxation dynamics and computational approaches established an R*→I* (intermediate)→P* sequential kinetic pattern for PNS and PNSe , whereas PNO undergoes R*→P* one-step kinetics. The polarization ability of the substituted heteroatoms, which is in the order O<S<Se, correlates with their increase in π conjugation, and hence the Stokes shift of the emission is in the order PNO < PNS < PNSe . Compound PNSe with the largest PISP barrier was shown to be a highly sensitive viscosity probe. Further evidence for heteroatom-harnessing PISP is given by PNC , in which the dimethylmethanediyl substituent lacks lone pair electrons for π extension, showing the normal emission of the bent structure. The results led to the conclusion that PISP is ubiquitous in dihydrodibenzo[ac]phenazines, for which the driving force is elongation of the π delocalization to gain stabilization in the excited state.     

FeOOH Nanocubes Anchored on Carbon Ribbons for Use in Li/O2 Batteries

A composite of FeOOH nanocubes anchored on carbon ribbons has been synthesized and used as a cathode material for Li/O₂ batteries. Fe²⁺ ion-exchanged resin serves as a precursor for both FeOOH nanocubes and carbon ribbons, which are formed simultaneously. The as-prepared FeOOH cubes are proposed to have a core–shell structure, with FeOOH as the shell and Prussian blue as the core, based on information from XPS, TEM, and EDS mapping. As a cathode material for Li/O₂ batteries, FeOOH delivers a specific capacity of 14816 mA h g⁻¹_cathode with a cycling stability of 67 cycles over 400 h. The high performance is related to the low overpotential of the oxygen reduction/evolution reaction on FeOOH. The cube structure, the supporting carbon ribbons, and the -OOH moieties all contribute to the low overpotential. The discharge product Li₂O₂ can be efficiently decomposed in the FeOOH cathode after a charging process, leading to higher cycling stability. Its high activity and stability make FeOOH a good candidate for use in non-aqueous Li/O₂ batteries.     

Vertically Grown Few-Layer MoS2 Nanosheets on Hierarchical Carbon Nanocages for Pseudocapacitive Lithium Storage with Ultrahigh-Rate Capability and Long-Term Recyclability

Molybdenum disulfide (MoS₂) is an intensively studied anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity, but it is still confronted by severe challenges of unsatisfactory rate capability and cycle life. Herein, few-layer MoS₂ nanosheets, vertically grown on hierarchical carbon nanocages (hCNC) by a facile hydrothermal method, introduce pseudocapacitive lithium storage owing to the highly exposed MoS₂ basal planes, enhanced conductivity, and facilitated electrolyte access arising from good hybridization with hCNC. Thus, the optimized MoS₂/hCNC exhibits reversible capacities of 1670 mAh g⁻¹ at 0.1 A g⁻¹ after 50 cycles, 621 mAh g⁻¹ at 5.0 A g⁻¹ after 500 cycles, and 196 mAh g⁻¹ at 50 A g⁻¹ after 2500 cycles, which are among the best for MoS₂-based anode materials. The specific power and specific energy, which can reach 16.1 kW and 252.8 Wh after 3000 cycles, respectively, indicate great potential in high-power and long-life LIBs. These findings suggest a promising strategy for exploring advanced anode materials with high reversible capacity, high-rate capability, and long-term recyclability.     

High-efficiency α-benzoyloxylation and hydroxylation of β-keto amides by phase transfer catalysis

A facile and efficient protocol for α-benzoyloxylation and α-hydroxylation of β-keto amides by phase-transfer catalysis is presented. This methodology provides mild and practical access to a variety ofα-oxygenated β-keto amides. Furthermore, α-benzoyloxylation products can be easily converted into α-hydroxylation compounds, which are useful synthetic precursors of biological targets.     

Synthesis of fluorine-substituted [2.2]paracyclophane-based carbene precursors for copper-catalyzed enantioselective boration of α,β-unsaturated ketones

Fluorine-substituted [2.2]paracyclophane-based carbene precursors have been successfully synthesized and applied to copper-catalyzed asymmetric β-boration of α,β-unsaturated ketones. Fluorination of the planar chiral carbenes has a beneficial impact on the catalytic performance of the relevant complexes. A variety of chiral β-boryl ketones were obtained in excellent yields (up to 99%) and with high enantioselectivities (up to 99% ee).     

Studies on Carbohydrates X. A New Method for the Preparation of Isopropylidene Saccharides

Cabohydrates reacting with acetone in the presence of molecular sieve and p—toluene sulfonic acid provided a simple, convenient, high yield and good selective process for preparation of isopropylidene carbohydrates.     

A novel efficient medium for chromogenic catalysis of tetramethylbenzidine with horseradish peroxidase

The traditional surfactant sodium dodecyl sulfate (SDS) and ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF₄]) have been combined to create a novel efficient medium for chromogenic catalysis of 3,3',5,5'-tetramethylbenzidine with horseradish peroxidase in presence of H₂O₂. The results have shown the [Emim][BF₄] in the mediums can promote the rate of formation of the blue chromogen, the SDS is responsible for the stabilization of the blue chromogen due to the electrostatic attraction between positively charged blue chromogen and the negatively charged surfactant. The SDS/[Emim][BF₄] combination not only enhance catalytic activity of HRP remarkably but also stabilize the blue chromogen formed in the HRP oxidation of the substrate TMB compared to the conventional medium. Based on the superior combination of SDS and [Emim][BF₄], the colorimetric assay for detecting HRP activity and H₂O₂ concentration was established. This work demonstrates a novel efficient medium for chromogenic catalysis with potential applications in biosensors and clinical diagnosis.