Radical‐initiated difunctionalization of alkenes is one of the most important methods in organic synthesis and medicinal chemistry, which can be applied to synthesize value complex compounds as well ...as structural motifs that found in bioactive natural products and pharmaceuticals. In recent years, impressive progress have been made in this area with ideal silver catalysis. Here, we summarize recent advances in silver‐mediated radical difunctionalization of alkenes for the formation of diverse bonds, including 1) two‐component radical difunctionalization reactions enabled by an intramolecular cyclization process toward various cyclic compounds and 2) three‐component radical difunctionalization reactions leading to complex linear compounds. These silver‐mediated radical alkene difunctionalization transformations are general initiated by different radicals, such as carbon‐, oxygen‐, sulfur‐, phosphinyl‐, and halogen‐center radicals, followed by terminated with nucleophiles to form two new bonds in a single reaction.
Ag catalysis: Recent advances in the silver‐mediated intermolecular radical 1,2‐difunctionalization of alkenes are summarized. These reaction are classified by the substrate type and radical regents. Two new C−C/C−C bonds, C−C/C−X bonds (X=F, O, S…) and C−X/C−X bonds (X=O, Br, I…) could be constructed in a single reaction.
Abstract
Objectives
To identify a novel plasmid-mediated colistin resistance gene in Klebsiella pneumoniae isolated from chickens in China.
Methods
WGS was used to identify a novel colistin ...resistance gene. The transferability of plasmids carrying mcr-7.1 was investigated by conjugation experiments. The expression of the mcr-7.1 gene was examined using an expression vector.
Results
A novel plasmid-mediated colistin resistance gene mcr-7.1, sharing 70% amino acid identity with the mcr-3 gene, was identified in three K. pneumoniae strains isolated from chickens in China. The mcr-7.1 gene was found in an IncI2-type plasmid (pSC20141012) that co-harboured the blaCTX-M-55 gene in one isolate. pSC20141012 can be transferred from K. pneumoniae SC20141012 to Escherichia coli J53Azr, exhibiting a ≥8-fold increase in colistin MIC compared with the recipient E. coli J53Azr.
Conclusions
We identified a novel plasmid-mediated colistin resistance gene named mcr-7.1 in K. pneumoniae in China. The prevalence of mcr-7.1 in various species of human and animal origin needs to be investigated immediately.
Epigenetic gene silencing is seen in several repeat-expansion diseases. In fragile X syndrome, the most common genetic form of mental retardation, a CGG trinucleotide–repeat expansion adjacent to the ...fragile X mental retardation 1 (FMR1) gene promoter results in its epigenetic silencing. Here, we show that FMR1 silencing is mediated by the FMR1 mRNA. The FMR1 mRNA contains the transcribed CGG-repeat tract as part of the 5′ untranslated region, which hybridizes to the complementary CGG-repeat portion of the FMR1 gene to form an RNA • DNA duplex. Disrupting the interaction of the mRNA with the CGG-repeat portion of the FMR1 gene prevents promoter silencing. Thus, our data link trinucleotide-repeat expansion to a form of RNA-directed gene silencing mediated by direct interactions of the trinucleotide-repeat RNA and DNA.
Fluorinated aromatic polyimide (FAPI) films with rigid polymer backbones have been prepared by chemical imidization approach. The polyimide films exhibited excellent mechanical properties including ...elastic modulus of up to 8.4 GPa and tensile strength of up to 326.7 MPa, and outstanding thermal stability including glass transition temperature (
) of 346.3-351.6 °C and thermal decomposition temperature in air (
) of 544.1-612.3 °C, as well as high colorless transmittance of >81.2% at 500 nm. Moreover, the polyimide films showed stable dielectric constant and low dielectric loss at 10-60 GHz, attributed to the close packing of rigid polymer backbones that limited the deflection of the dipole in the electric field. Molecular dynamics simulation was also established to describe the relationship of molecular structure and dielectric loss.
CXCR4 is expressed on leukaemia cells and haematopoietic stem cells (HSCs), and its ligand stromal‐derived factor 1 (SDF‐1) is produced abundantly by stromal cells in the bone marrow (BM). The ...SDF‐1/CXCR4 axis plays important roles in homing to and retention in the protective BM microenvironment of malignant leukaemia cells and normal HSCs. CXCR4 expression is regulated by multiple mechanisms and the level of CXCR4 expression on leukaemia cells has prognostic indications in patients with acute leukaemia. CXCR4 antagonists can mobilize leukaemia cells from BM to circulation, which render them effectively eradicated by chemotherapeutic agents, small molecular inhibitors or hypomethylating agents. Therefore, such combinational therapies have been tested in clinical trials. However, new evidence emerged that drug‐resistant leukaemia cells were not affected by CXCR4 antagonists, and the migration of certain leukaemia cells to the leukaemia niche was independent of SDF‐1/CXCR4 axis. In this review, we summarize the role of CXCR4 in progression and treatment of acute leukaemia, with a focus on the potential of CXCR4 as a therapeutic target for acute leukaemia. We also discuss the potential value of using CXCR4 antagonists as chemosensitizer for conditioning regimens and immunosensitizer for graft‐vs‐leukaemia effects of allogeneic haematopoietic stem cell transplantation.
CXCR4 is expressed on leukaemia cells and its ligand stromal‐derived factor 1 (SDF‐1) is produced by stromal cells in the bone marrow. The SDF‐1/CXCR4 axis plays an important role in homing to and retention in bone marrow of leukaemia cells. During the last three decades, CXCR4 has been studied as a potential target for treatment of acute leukaemia.
Fine-grained image classification is a challenging task because of the difficulty in identifying discriminant features, it is not easy to find the subtle features that fully represent the object. In ...the fine-grained classification of crop disease, visual disturbances such as light, fog, overlap, and jitter are frequently encountered. To explore the influence of the features of crop leaf images on the classification results, a classification model should focus on the more discriminative regions of the image while improving the classification accuracy of the model in complex scenes. This paper proposes a novel attention mechanism that effectively utilizes the informative regions of an image, and describes the use of transfer learning to quickly construct several fine-grained image classification models of crop disease based on this attention mechanism. This study uses 58,200 crop leaf images as a dataset, including 14 different crops and 37 different categories of healthy/diseased crops. Among them, different diseases of the same crop have strong similarities. The NASNetLarge fine-grained classification model based on the proposed attention mechanism achieves the best classification effect, with an
score of up to 93.05%. The results show that the proposed attention mechanism effectively improves the fine-grained classification of crop disease images.
During HIV-1 infection, antibodies are generated against the region of the viral gp120 envelope glycoprotein that binds CD4, the primary receptor for HIV-1. Among these antibodies, VRC01 achieves ...broad neutralization of diverse viral strains. We determined the crystal structure of VRC01 in complex with a human immunodeficiency virus HIV-1 gp120 core. VRC01 partially mimics CD4 interaction with gp120. A shift from the CD4-defined orientation, however, focuses VRC01 onto the vulnerable site of initial CD4 attachment, allowing it to overcome the glycan and conformational masking that diminishes the neutralization potency of most CD4-binding-site antibodies. To achieve this recognition, VRC01 contacts gp120 mainly through immunoglobulin V-gene regions substantially altered from their genomic precursors. Partial receptor mimicry and extensive affinity maturation thus facilitate neutralization of HIV-1 by natural human antibodies.
•Nitrogen-doped carbon nanoparticle applied in anode to improve MFC performance.•Electrochemical characterization reveals mechanism of improved MFC performance.•Enhanced electron transfer mechanism ...by anode modification was observed in MFCs.
Nitrogen doped carbon nanoparticles (NDCN) were applied to modify the carbon cloth anodes of microbial fuel cells (MFCs) inoculated with Shewanella oneidensis MR-1, one of the most well-studied exoelectrogens. Experimental results demonstrated that the use of NDCN increased anodic absorption of flavins (i.e., the soluble electron mediator secreted by S. oneidensis MR-1), facilitating shuttle-mediated extracellular electron transfer. In addition, we also found that NDCN enabled enhanced contact-based direct electron transfer via outer-membrane c-type cytochromes. Taken together, the performance of MFCs with the NDCN-modified anode was enormously enhanced, delivering a maximum power density 3.5 times’ higher than that of the MFCs without the modification of carbon cloth anodes.
Despite high‐energy density and low cost of the lithium–sulfur (Li–S) batteries, their commercial success is greatly impeded by their severe capacity decay during long‐term cycling caused by ...polysulfide shuttling. Herein, a new phase engineering strategy is demonstrated for making MXene/1T‐2H MoS2‐C nanohybrids for boosting the performance of Li–S batteries in terms of capacity, rate ability, and stability. It is found that the plentiful positively charged S‐vacancy defects created on MXene/1T‐2H MoS2‐C, proved by high‐resolution transmission electron microscopy and electron paramagnetic resonance, can serve as strong adsorption and activation sites for polar polysulfide intermediates, accelerate redox reactions, and prevent the dissolution of polysulfides. As a consequence, the novel MXene/1T‐2H MoS2‐C‐S cathode delivers a high initial capacity of 1194.7 mAh g−1 at 0.1 C, a high level of capacity retention of 799.3 mAh g−1 after 300 cycles at 0.5 C, and reliable operation in soft‐package batteries. The present MXene/1T‐2H MoS2‐C becomes among the best cathode materials for Li–S batteries.
Phase engineered MXene/1T‐2H MoS2‐C with plentiful S‐vacancy defects is highly effective for trapping polysulfide intermediates and accelerating redox kinetics, leading to the enhanced lithium–sulfur batteries.
A novel reduced melon photocatalyst with a bandgap of 2.03 eV developed here has a widened visible light absorption range and suppressed radiative recombination of photo‐excited charge carriers due ...to the homogeneous self‐modification with nitrogen vacancies. As a consequence, the reduced melon shows a much superior photocatalytic activity compared to the pristine melon in generating •OH radicals and degrading the organic pollutant Rhodamine B.
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