Radical involved transformations are now considered as extremely important processes in modern organic synthetic chemistry. According to the demand by atom-economic and sustainable chemistry, direct ...C(sp(3))-H functionalization through radical oxidative coupling represents an appealing strategy for C-C bond formations. However, the selectivity control of reactive radical intermediates is still a great challenge in these transformations. Here we show a selective radical oxidative C(sp(3))-H/C(sp)-H cross-coupling of unactivated alkanes with terminal alkynes by using a combined Cu/Ni/Ag catalytic system. It provides a new way to access substituted alkynes from readily available materials. Preliminary mechanistic studies suggest that this reaction proceeds through a radical process and the C(sp(3))-H bond cleavage is the rate-limiting step. This study may have significant implications for controlling selective C-C bond formation of reactive radical intermediates by using multimetallic catalytic systems.
Land-use patterns may affect the distribution characteristics of soil microplastics (MPs), but the effects in the agricultural areas of the Qinghai-Tibetan Plateau are still unknown. This study ...investigated the abundance of MPs in facility, farmland, grassland, and orchard soils in the Qaidam basin and Hehuang valley of Qinghai Province and analyzed its shape, size, color, and polymer composition distribution characteristics from 105 sites. The average abundance of MPs in facility, farmland, and grassland soils in the Hehuang valley were 2795.7, 1860.5, and 910.9 items kg−1, which were 1.33, 4.84, and 1.50 times higher than those in the Qaidam basin, respectively. Orchard soils had 1322.2 items kg−1 MPs. Soil MPs abundance in grassland and farmland was positively correlated with precipitation and 0 cm ground temperature; and negatively correlated with average wind speed (p < 0.05). Both the particle size of < 1 mm and pellet-shape MPs abundance showed a positive correlation with SOC (p < 0.05). Land-use patterns had the most significant affecting force (51.35%) on soil MPs abundance (p < 0.0001). Hence, land-use patterns, regional climate, and soil properties influence the distribution characteristics of soil MPs; besides, the land-use patterns were dominant.
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•Land-use pattern has the most significant affecting force (51.35%) on soil MPs.•Soil MP abundance in facility land is 3 times higher than in grassland.•Soil MP abundance in plastic mulching potato and maize was 4.84 times that of wheat.•Soil MP abundance in grassland is significantly decreased with increasing wind speed.•SOC content promotes the fragmentation of MPs and increases their abundance.
The structure and dynamics in SE Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study we determined high-resolution P-wave seismic images in the upper mantle ...and transition zone in SE Tibet by jointly inverting the travel-time residuals of local events and the relative travel-time residuals of teleseismic events recorded by very dense seismic stations. We revealed a high-velocity body in the upper mantle beneath South China that represents the root of the Yangtze Craton. The high-velocity body extends in the entire Yangtze Craton at 300–450 km depths, but it is constrained just beneath the Sichuan Basin and surrounded by extensive low-velocity zones to the southwest at 65–250 km depths. We propose that the Yangtze Craton is destructed laterally by the mantle flow extruded from the Tibetan Plateau. We obtain a low-velocity column in the upper mantle under the Tengchong volcano as well as the visible high-velocity bodies in the upper mantle and transition zone below the low-velocity column. The images suggest that the Tengchong volcano is closely related to the subduction of the Burma plate and caused by the dehydration of the subducted slab. The present study reveals unprecedented details of the mantle structures beneath SE Tibet and provides new insights into the geodynamics of the Tibetan Plateau and its interaction with the stable Yangtze Craton.
•Southeastward mantle flow exists in the upper mantle under SE Tibet.•Yangtze Craton is destructed laterally by the upper-mantle extrusion.•Tengchong volcano is related to the subduction of the Burman plate.
High‐performance covalent organic framework (COF) fibers are demanded for an efficient capturing of blue osmotic power because of their excellent durability, simple integration, and large ...scalability. However, the scalable production of COF fibers is still very challenging due to the poor solubility and fragile structure of COFs. Herein, for the first time, it is reported that COF dispersions can be continuously processed into macroscopic, meter‐long, and pure COF fibers using a wet spinning approach. The two presented COF fibers can be directly used for capturing of osmotic energy, avoiding the production of composite materials that require other additives and face challenges such as phase separation and environmental issues induced by the additives. A COF fiber exhibits power densities of 70.2 and 185.3 W m−2 at 50‐fold and 500‐fold salt gradients, respectively. These values outperform those of most reported systems, which indicate the high potential of COF fibers for capturing of blue osmotic energy.
1D covalent organic framework (COF) fibers obtained by processing of COF dispersions using a wet spinning technique: Dispersions of 2D COFs are continuously processed into flexible solid fibers on a large scale using a wet spinning approach. These COF fibers with excellent tensile properties exhibit good performance for the capture of osmotic energy as ionic conductors.
Neuropathy target esterase (NTE) is a serine hydrolase with phospholipase B activity, which is involved in maintaining the homeostasis of phospholipids. It can be inhibited by aging inhibitors such ...as some organophosphorus (OP) compounds, which leads to delayed neurotoxicity with distal degeneration of axons. However, the detailed binding conformation of aging and non-aging inhibitors with NTE is not known. In this study, new computational models were constructed by using MODELLER 10.3 and AlphaFold2 to further investigate the inhibition mechanism of aging and non-aging compounds using molecular docking. The results show that the non-aging compounds bind the hydrophobic pocket much deeper than aging compounds and form the hydrophobic interaction with Phe1066. Therefore, the unique binding conformation of non-aging compounds may prevent the aging reaction. These important differences of the binding conformations of aging and non-aging inhibitors with NTE may help explain their different inhibition mechanism and the protection of non-aging NTE inhibitors against delayed neuropathy.
This work investigates the interfacial bonding properties between calcium silicate hydrate and fibers at the micro-level.
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•The interfacial shear strength between C-S-H and polymer ...fibers is closely related to the fiber types.•Ca atoms in the interface play an important role in the interfacial bonding interactions.•H bonds provide contribution for enhancing the interfacial bonding strength.
The macroscopic mechanical performance of fiber reinforced concrete (FRC) is determined by the interfacial microstructure and the interfacial bonding properties between hydration products and fibers. This research is dedicated to study the interfacial shear strength, structure and dynamics between calcium-silicate-hydrate (C-S-H) and polymer fibers. To better understand the effects of fiber types on the interfacial shear strength, three kinds of fibers were investigated, including polypropylene (PP), polyvinyl alcohol (PVA) and polyacrylic acid (PAA). The calculation results indicate that the interfacial shear strength is closely related to the fiber types. The interfacial shear strength of fibers restricted in the C-S-H substrate was arranged in the following order PAA fiber > PVA fiber > PP fiber. After measuring the interfacial shear strength, the static molecular structure and dynamics properties, especially at the interface between the fiber and the C-S-H matrix, the cause for the interfacial shear strength discrepancy between different fibers was uncovered. It shown that the Ca atoms in the interface play an important role in the interfacial bonding interactions by the formation of OCSH-Ca-Opolymer connection. The H bonds can be formed between PAA/PVA fibers and C-S-H substrate, also provide some contribution for enhancing the interfacial bonding strength. The chemical bond stability revealed that the interfacial bonding strength of three fibers follows the order of PAA fiber > PVA fiber > PP fiber, which is consistent with the order of interfacial shear strength.
Hypoxia detection is emphasized with attention due to tumor and related diseases diagnosis, which could provide useful methods for exploring the mechanism of hypoxic tumor. Herein, we report two ...unprecedented hypoxia-sensitive probes that specifically switch-on their near-infrared fluorescence signals in the presence of hypoxia up-regulated enzymes (nitroreductase and cytochrome P450 reductase). The probes were designed by featuring the decomposition of IR-780 coupled to hypoxia activatable p-nitrobenzyl or azo moiety, which exhibit near-infrared fluorescence emission, high sensitivity, selectivity, stable photostability, and low cytotoxicity. Besides, the joint use of two probes could differentiate the 4T1 and HepG2 cells lines through fluorescence signals successfully. More importantly, applied to monitor hypoxia in 4T1 tumor-bearing BALB/c mice, the two probes have ideal biodistribution with passive accumulation and fast clearance, and there is negligible organ damage by hematoxylin and eosin staining analysis. To the best of our knowledge, there is no fluorescent probe for hypoxia detection via joint hypoxia regulated enzymes reported so far. This method may be of great potential use in cancer and other relevant diseases diagnosis.
Image restoration is a critical procedure for underwater images, which suffer from serious color deviation and edge blurring. Restoration can be divided into two stages: de-scattering and edge ...enhancement. First, we introduce a multi-scale iterative framework for underwater image de-scattering, where a convolutional neural network is used to estimate the transmission map and is followed by an adaptive bilateral filter to refine the estimated results. Since there is no available dataset to train the network, a dataset which includes 2000 underwater images is collected to obtain the synthetic data. Second, a strategy based on white balance is proposed to remove color casts of underwater images. Finally, images are converted to a special transform domain for denoising and enhancing the edge using the non-subsampled contourlet transform. Experimental results show that the proposed method significantly outperforms state-of-the-art methods both qualitatively and quantitatively.
To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NOx with an ammonia reductant, we employed scanning transmission X‐ray microscopy ...(STXM) to study Cu‐exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000‐mile aging. X‐ray absorption near‐edge structure (XANES) measurements were performed at the Al K‐ and Cu L‐edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi‐factor‐induced catalytic deactivation. In Cu‐exchanged MFI, a transformation of CuII to CuI and CuxOy was observed. We also found a spatial correlation between extra‐framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri‐coordinated Al. By inspecting both Al and Cu in fresh and aged Cu‐exchanged zeolites, we conclude that the importance of the preservation of isolated CuII sites trumps that of Brønsted acid sites for NH3‐SCR activity.
A look at the exhaust: The deactivation of NOx‐reduction catalysts based on Cu‐exchanged SSZ‐13 and ZSM‐5 zeolites was studied by scanning transmissionX‐ray microscopy, which enables a spatial analysis of the local environment of both Al and Cu species at nanoscale resolution. The importance of isolated Cu species was shown and a correlation between zeolite lattice destruction and an inactive Cu phase was established.
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