Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, ...nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C–H or C–C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C–N bond formation via C–H or C–C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C–H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C–H or C–C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out Csp3 –H functionalization on benzylic, allylic, and propargylic C–H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of CC double-bonds and CC triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our synthetic strategy more attractive. Our direct nitrile synthesis methodologies have potential applications in the synthesis of biologically active molecules and drug candidates.
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IJS, KILJ, NUK, PNG, UL, UM
A novel TEMPO-catalyzed aerobic oxygenation and nitrogenation of hydrocarbons via CC double-bond cleavage has been disclosed. The reaction employs molecular oxygen as the terminal oxidant and ...oxygen-atom source by metal-free catalysis under mild conditions. This method can be used for the preparation of industrially and pharmaceutically important N- and O-containing motifs, directly from simple and readily available hydrocarbons.
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IJS, KILJ, NUK, PNG, UL, UM
•The quantity and composition of suspended microplastics are reported for the first time in China.•Microplastics (0.5–5mm) constituted more than 90% of total plastics by number of ...items.•Microplastics concentrations were spatially variable in the Yangtze Estuary.•Large rivers are contributed to the high MP abundances in the adjacent marine environment.•The most abundant plastics were fibres, while plastic spherules were rarely found.
Levels of microplastics (MPs) in China are completely unknown. This study characterizes suspended MPs quantitatively and qualitatively for the Yangtze Estuary and East China Sea. MPs were extracted via a floatation method. MPs were counted and categorized according to shape and size under a stereomicroscope. The MP densities were 4137.3±2461.5 and 0.167±0.138n/m3, respectively, in the estuarine and the sea samples. Plastic abundances varied significantly in the estuary. Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment. Plastic particles (>5mm) were observed with a maximum size of 12.46mm, but MPs (0.5–5mm) constituted more than 90% by number of items. The most frequent geometries were fibres, followed by granules and films. Plastic spherules occurred sparsely. Transparent and coloured plastics comprised the majority of the particles. This study provides clues in understanding the fate and potential sources of MPs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Graphitic-carbon nitride quantum dots (g-C3N4QDs), as a rising star in the carbon nitride family, show great potential in many fields involving bioimaging, fuel cells, and photo(electro)catalysis, ...due to their fascinating optical and electronic properties. Especially, the efficient light capture, tunable photoluminescence and extraordinary up-conversion photoluminescence properties of g-C3N4QDs may offer promising potential for full utilization of the solar spectrum, thus promoting their applications in photocatalytic reactions. Some reviews on g-C3N4 have been presented; while most of them have concentrated on g-C3N4 in 3-dimensional (3D) or 2D structures, few focused on g-C3N4QDs. Therefore, this review aims to summarize the recent advances in g-C3N4QDs regarding their synthesis, optical and electronic properties and photocatalytic applications for degrading organic pollutants. Moreover, crucial issues in g-C3N4QD future application in these flourishing research areas are discussed, with prospects towards the final realization of efficient and long-term stable g-C3N4QD-based photocatalysts.
The 1,000 km‐long Haiyuan fault is the largest strike‐slip fault system in the northeastern Tibetan Plateau, accommodating part of the plateau's eastward extrusion. However, few large earthquakes ...have been instrumentally recorded, hindering our understanding of strain partitioning across the fault system. Here, we use synthetic aperture radar images to investigate fault geometries and slip distributions of the adjacent 2016 Mw5.9 and 2022 Mw6.7 Menyuan earthquakes that occurred 35 km apart along the western Haiyuan fault system. The purely strike and purely thrust slips of the 2022 and 2016 events indicate that strain was released separately on shallow steep fault and low‐angle fault at depth. We propose that such strain partitioning is controlled by the ratio between interseismic shear and normal velocities and the branching fault structure beneath the Lenglongling segment. Seismic hazard due to both focal mechanisms has to be considered along the western Haiyuan fault in northeastern Tibet.
Plain Language Summary
Apart by 35 km, two earthquakes occurred on 20 January 2016 and 7 January 2022 with the moment magnitude of Mw5.9 and Mw6.7 along the western Haiyuan fault system, near Menyuan county, China. They are the largest events on the Lenglongling (LLL) mountain in past decades and also the only ones with clear surface deformation captured by radar imaging geodesy. Here, we use Synthetic aperture radar images to measure the surface deformations caused by these two events and derive their fault geometries and slip distributions. For the 2022 event, our modeling shows that the rupture propagated on both the LLL and the Tuolaishan (TLS) fault, supporting that the Haiyuan fault system may extend westward through LLL to the TLS fault. The purely thrust‐slip and purely strike‐slip mechanisms of the 2016 and 2022 events indicate the strain partitioning that the shear and normal strain can be released by the strike‐slip event and thrust event separately. Such strain partitioning reminds us to consider seismic hazards due to both shallow strike‐slip and deep thrust earthquakes along the western Haiyuan fault system.
Key Points
Slip distributions of the 2016 Mw5.9 and 2022 Mw6.7 Menyuan earthquakes are derived from Sentinel‐1 interferograms and pixel offsets
The 2022 Menyuan earthquake suggests the Tuolaishan fault may as the continuation of the Haiyuan fault west of the Lenglongling fault
Coseismic slip partitioning along the western Haiyuan fault agrees with the interseismic shear‐to‐normal strain ratio and fault geometries
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
By means of the permanent scatterer (PS) technique, repeated spaceborne synthetic aperture radar (SAR) images with relatively low resolution (about 25 m × 5 m for the European Remote Sensing (ERS) ...and Envisat satellites) can be used to estimate the displacement (1-mm precision) and 3-D location (1-m precision) of targets that show an unchanged electromagnetic signature. The main drawback of the PS technique is the limited spatial density of targets that behave coherently during the whole observation span (hundreds of PSs per square kilometer in urban site and up to few points in vegetated areas). In this paper, we describe a new approach for multitemporal analysis of SAR images that also allows extracting information from partially coherent targets. The basic idea is to loosen the restrictive conditions imposed by the PS technique. The results obtained in different test sites allowed to increase significantly the spatial coverage of the estimate of height and deformation trend, particularly in extraurban areas.
High‐resolution interseismic strain mapping is important for studying faulting behavior and for assessing seismic hazards. Interferometric Synthetic Aperture Radar has been widely applied to measure ...interseismic deformation along active strike‐slip faults. However, phase unwrapping errors and over‐smoothing effects limit its ability to map the extremely‐high strain due to shallow creep. Here, without the involvement of ground‐based measurement, we perform phase‐gradient stacking on wrapped Sentinel‐1 interferograms to directly map the shear strain rates along the North Anatolian Fault (NAF) with unprecedented resolution. The derived high‐resolution strain‐rate map reveals five strain‐concentrated segments on the NAF, implying shallow creeps. We find that their spatial distribution coincides with the lower coseismic slip of previous earthquakes that occurred since 1939. The proposed method can be applied to other less‐studied strike‐slip faults to distinguish segments with shallow creep and strong coupling, and thus to better quantify the shallow strain budget and its associated seismic hazards.
Plain Language Summary
Surface deformation measurements along active faults are important for understanding the elastic energy, namely the strain that is accumulated and released during earthquake cycles. Interferometric Synthetic Aperture Radar (InSAR), is an imaging geodetic method that allows mapping millimeter‐scale deformation from phase differences of microwave echoes, has been applied for studying interseismic deformation across active strike‐slip faults worldwide. However, obtaining strain from InSAR‐derived velocity fields is challenged by the high computational burdens and the low resolution. Here, we propose a new phase‐gradient stacking method to obtain high‐resolution shear strain rates along the entire North Anatolian Fault (NAF) in Turkey. Our results show that the presented method can clearly reveal the spatial extents of the creeping segment, indicating the overall non‐uniform strain rate distribution and the close relation with the previous earthquake ruptures along the NAF. We propose to apply the presented phase‐gradient stacking approach to other active strike‐slip faults to better understand their strain budgets and associated seismic hazards.
Key Points
We map the shear strain rates along the North Anatolian Fault (NAF) with an unprecedented resolution by stacking phase gradients of Sentinel‐1 interferograms
Distribution of shear strain rates indicates a tight relation between creeping segments and surface ruptures of NAF earthquakes since 1939
We identify two creeping segments previously undetected along the NAF from the high‐resolution shear strain map
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
AbstractPeridynamic (PD) theory is an integral-type nonlocal continuum mechanics theory that reformulates the equation of motion in local continuum mechanics as an integrodifferential equation. PD ...theory has been used to simulate mechanical responses of various materials with discontinuous structures. During the past two decades, PD theory has been developed to simulate different discontinuous problems and to illustrate various discontinuous phenomena in the diverse fields of engineering and sciences. In this paper, a state-of-the-art review on the investigation of failure processes of geomaterials in a PD framework is performed to illustrate the successful results and potential capability of PD theory in future geotechnical engineering. This review starts with a brief theoretical description of a bond-based peridynamic (BB-PD) model, a state-based peridynamic (SB-PD) model, a hybrid PD–classical continuum mechanics model, and an analytical PD model. Then surveys of PD applications to coupled multiphysical failure problems of geomaterials are conducted, which aim at revealing the associated failure mechanism. The applications of PD theory to simulate real geotechnical engineering are subsequently reported. Finally, some future-oriented research perspectives of PD applications in geotechnical engineering and a brief summary are presented.
The exploration of macromolecular topology provides common ground amongst chemists, material scientists, mathematicians, and artists. Fascinating polymer architectures, ranging from linear to ...branched to cyclic to star, can be constructed from myriad building blocks; their topological-dependent properties merge the beauty of symmetry with the intricacies of polymer physics. Specifically in cyclic macromolecules, the lack of chain ends result in unique physical characteristics (
e.g.
, smaller hydrodynamics volume, lower viscosity, and lack of chain entanglement) compared to their linear counterparts. In this review, developments in the synthesis of cyclic polymers will be addressed, with an emphasis of recent advances in the past five years.
Synthetic methodology to access cyclic macromolecules continues to develop
via
two distinct mechanistic classes: ring-expansion of macrocyclic initiators and ring-closure of functionalized linear polymers.
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