Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible ...from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze 4 + 1-cycloaddition reactions of 1,3-dienes. The C
partner is a vinylidene equivalent generated from the reductive activation of a 1,1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using a
-symmetric chiral ligand that stabilizes a metal-metal bond.
In this study we make use of the closely spaced Swarm A and C spacecraft to determine the main wave parameters of micro‐pulsation in the Pc1 range. Generally, the interpretation of wave events in ...satellite recordings suffers from the spatial/temporal ambiguity of such data. To resolve that problem, we use for the first time in the 0.2–5 Hz apparent frequency range high‐resolution magnetic field data from the Swarm A/C spacecraft pair. Particularly suitable for this analysis is the period of Counter Rotating Orbit Phase in 2021. During that period the along‐track distance between the spacecraft was varied from 2 to 40 s. Surprisingly many of the wavy signals at middle latitudes were identified as small‐scale (order of 10s km) quasi‐static field‐aligned current (FAC) structures. Some of the events turned out to be medium‐scale (100–200 km) waves oscillating at 1 Hz or less. A number of published electromagnetic ion cyclotron (EMIC) waves were checked on their consistency. One characteristic is their long wavelength (∼1,000 km). About half of the cases passed the check, the other did not satisfy the spatial homogeneity. The small‐scale FAC structures we believe to be driven by atmospheric gravity waves. While the medium‐scale waves we prefer to relate to the effects of the ionospheric Alfvén resonator.
Key Points
Resolving for the first time the spatial/temporal ambiguity in satellite wave signals within the Pc1 range by the Swarm constellation
Small‐scale (10s km) quasi‐static current features are frequently detected, also medium‐scale (100s km) waves with less than 1 Hz are found
Electromagnetic ion cyclotron waves exhibit long wavelengths (∼1,000 km). This has to be verified for their identification
By utilizing magnetic field measurements from the Swarm constellation during the years 2014–2019, average characteristics of the height‐integrated ionospheric zonal and meridional currents at middle ...and low latitudes are investigated. We provide for the first time the detailed dependencies of these currents on location, local time, and season. The main results obtained are: (a) Large parts of the ionospheric currents flow in the F‐region, particularly on the nightside and in the winter hemisphere. (b) Clearly outstanding zonal current is the equatorial electrojet (EEJ) around noon, accompanied by currents in opposite direction at middle latitudes. At night, eastward currents are prevailing in the summer hemisphere, and westward in winter. During equinox the nighttime zonal currents show a lot of hemispheric similarity, with westward currents around pre‐midnight and eastward currents post‐midnight at mid latitudes. These features can be attributed to the meridional thermospheric wind effects. (c) The meridional currents are weak at night, exhibiting a preferred direction toward the summer hemisphere. At daytime the meridional currents flow toward equator in the pre‐noon sector and opposite current directions prevail in the afternoon, which is consistent with the closing of the EEJ current circuit. Large hemispheric differences in meridional currents are found during December solstice, suggesting that most of the EEJ current is closed through the winter, northern hemisphere. (d) The zonal and meridional currents at middle latitude exhibit clear signatures of solar tides at daytime. Most prominent are the non‐migrating tidal components DE3 in the zonal currents and SW5 in the meridional.
Key Points
Global distribution of height‐integrated current densities of zonal and meridional ionospheric currents at mid and low latitudes
First comprehensive observational study of combined E‐ and F‐region currents for all local times and seasons
Identification of the primary current closure paths for the equatorial electrojet
Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano‐ to macroscale, which are difficult to mimic ...synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano‐ to submicro‐ to microscale) are spontaneously formed in the bulk material, which are well‐retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications.
Anisotropic hydrogels with perfectly aligned hierarchical fibrous structures are fabricated by a simple method. Drying a physical hydrogel by confining its length direction generates a 1D tensile force that controls polymeric alignment and supramolecular interactions. A tunable structure and mechanical properties are realized in different types of rigid polymeric hydrogels and the properties are comparable with those of natural ligaments.
Dinuclear Ni complexes supported by naphthyridine‐diimine (NDI) ligands catalyze the reductive cyclopropanation of alkenes with CH2Cl2 as the methylene source. The use of mild terminal reductants (Zn ...or Et2Zn) confers significant functional‐group tolerance, and the catalyst accommodates structurally and electronically diverse alkenes. Mononickel catalysts bearing related N chelates afford comparatively low cyclopropane yields (≤20 %). These results constitute an entry into catalytic carbene transformations from oxidized methylene precursors.
Nickel interplay: Dinuclear nickel complexes (see scheme) catalyze the reductive cyclopropanation of alkenes with CH2Cl2 as the methylene source and Zn or Et2Zn as the terminal reductant. Diverse alkenes bearing common functional groups are tolerated under the mildly reducing reaction conditions.
In the recent decade, growing efforts have been devoted to employing elemental selenium as a selenium source in organic synthesis. In contrast to unstable, smelly, and toxic previous selenium ...reagents, elemental selenium is readily available, cheap, bench‐stable, and easy to handle. This review will mainly focus on the strategies for the activation of elemental selenium and the synthesis of organoselenium compounds including monoselenides, diselenides, selenium‐containing heterocycles and so on.
•Pomelo peel is rich in dietary fiber, essential oil, pectin and polyphenols.•Pomelo peels can be directly used to make pickles, jams, tea and food ingredients.•Essential oil, pectin and polyphenols ...were recovered from pomelo peel by diverse ways.•The applied method exerts crucial impacts on the structure and property of extracts.•Economic, effective, eco-friendly ways for using pomelo peel are urgently needed.
Pomelo peel as a by-product from pomelo consumption is rich in various nutrients and functional compounds, while most of the by-product is disposed as wastes. The utilization of pomelo peels could not only result in valued-added products/ingredients, but also reduce the environmental threats. By mainly reviewing the recent articles, pomelo peels could be directly used to produce candied pomelo peel, tea, jams, etc. Additionally, functional components (essential oils, pectin, polyphenols, etc.) could be extracted from pomelo peels and applied in food, pharmaceutical and chemical fields. The extraction methods exerted important influences on the composition, physicochemical properties, bioactivities and structures of the resultant fractions. Furthermore, pomelo peel was exploited to make adsorbents, bioethanol, etc. For the future investigations, the functionality- or bioactivity-oriented regimes to recovery valuable components from pomelo peel should be developed in an economic, effective and eco-friendly way and their applicability in large-scale production should be addressed.
Mucosa is a protective and lubricating barrier in biological tissue, which has a great clinical inspiration because of its slippery, soft, and hydrophilic surface. However, mimicking mucosal traits ...on complex surface remains an enormous challenge. Herein, a novel approach to create mucosa‐like conformal hydrogel coating is developed. A thin conformal hydrogel layer mimicking the epithelial layer is obtained by first absorbing micelles, followed by forming covalent interlinks with the polymer substrate via interface‐initiated hydrogel polymerization. The resulting coating exhibits uniform thickness (≈15 µm), mucosa‐matched compliance (Young's modulus = 1.1 ± 0.1 kPa) and lubrication (coefficients of friction = 0.018 ± 0.003), robust interfacial bonding against peeling (peeling strength = 1218.0 ± 187.9 J m–2), as well as high water absorption capacity. It effectively resists adhesion of proteins and bacteria without compromising biocompatibility. As demonstrated by an in vivo cynomolgus monkey model and clinical trial, applications of the mucosa‐like conformal hydrogel coating on the endotracheal tube significantly reduce intubation‐related complications, such as invasive stimuli, mucosal lesions, laryngeal edema, inflammation, and postoperative pain. This work offers a promising prototype for surface decoration of biomedical devices and holds great prospects for clinical translation to enable interventional operations with minimally invasive impacts.
An ingenious yet feasible method of creating a mucosa‐like conformal hydrogel coating, which is soft, lubricative, hydrophilic, antifouling, biocompatible, and stable, is reported. This coating effectively reduces intubation‐related complications. This work represents a breakthrough to endow interventional medical devices with required surface properties, showing promising prospects for clinical translation.
Black phosphorus (BP) has increasingly attracted scientific attention since its first applications in biomedicine due to its unique properties and excellent biocompatibility. In particular, its ...layer‐dependent bandgap, moderate carrier mobility, large surface‐area‐to‐volume ratio, biodegradability, intrinsic photoacoustic properties, and biocompatibility make it an ideal candidate for use in photothermal therapy, photodynamic therapy, drug delivery, 3D printing, bioimaging, biosensing, and theranostics, which are reviewed here. In addition, the article discusses strategies to overcome challenges related to surface instability due to chemical degradation, a major obstacle for its application. This review not only provides a comprehensive summary on BP preparation and biomedical applications but also summarizes recent research and future possibilities.
2D black phosphorus is extensively used in biomedicine due to its excellent physical and chemical properties. This review focuses on the current progress and future perspectives of 2D black phosphorus–based biomedical applications, including cancer therapy, diagnosis, and theranostics. In addition, the article discusses strategies to overcome challenges related to surface instability, a major obstacle for its application.
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