The palladium‐catalyzed asymmetric carboamination reaction is one of the most significant transformations in organic chemistry. Herein, we report the first palladium‐catalyzed asymmetric ...alleneamination of β,γ‐unsaturated hydrazones with propargylic acetates. This protocol enables the efficient installation of various multisubstituted allene groups onto dihydropyrazoles in good yields with excellent enantioselectivities. The chiral sulfinamide phosphine ligand Xu‐5 exhibits highly efficient stereoselective control in this protocol. The salient features of this reaction include the readily available starting materials, a broad substrate scope, an easy scale‐up, mild reaction conditions and versatile transformations.
A new robust palladium‐catalyzed enantioselective alleneamination reaction of β,γ‐unsaturated hydrazones with propargylic acetates is described. The salient features of this reaction include general substrate scope, good functional group tolerance, good yields and high enantioselectivities.
A TEMPO promoted oxidative aza‐Diels‐Alder reaction of ketohydrazones with 3‐methyleneoxindoles or 2‐arylidene‐1,3‐indanediones were successfully developed, This reaction provided an efficient ...synthetic protocol for novel functionalized spiroindoline‐3,3′‐pyridazines and spiroindene‐2,3′‐pyridazines. This reaction showed high diastereoselectivity and strict substituent's electron effect, which might be due to the reaction mechanisms process including sequential oxidative generation of 1,2‐diaza‐1,3‐dien and normal electron‐demand aza‐Diels‐Alder reaction.
Spiroindoline‐3,3′‐pyridazine and spiroindene‐2,3′‐pyridazine were efficiently and diastereoselective synthesized from TEMPO‐promoted oxidative aza‐Diels‐Alder reaction of ketohydrazones.
This paper proposes a novel approach to person re-identification, a fundamental task in distributed multi-camera surveillance systems. Although a variety of powerful algorithms have been presented in ...the past few years, most of them usually focus on designing hand-crafted features and learning metrics either individually or sequentially. Different from previous works, we formulate a unified deep ranking framework that jointly tackles both of these key components to maximize their strengths. We start from the principle that the correct match of the probe image should be positioned in the top rank within the whole gallery set. An effective learning-to-rank algorithm is proposed to minimize the cost corresponding to the ranking disorders of the gallery. The ranking model is solved with a deep convolutional neural network (CNN) that builds the relation between input image pairs and their similarity scores through joint representation learning directly from raw image pixels. The proposed framework allows us to get rid of feature engineering and does not rely on any assumption. An extensive comparative evaluation is given, demonstrating that our approach significantly outperforms all the state-of-the-art approaches, including both traditional and CNN-based methods on the challenging VIPeR, CUHK-01, and CAVIAR4REID datasets. In addition, our approach has better ability to generalize across datasets without fine-tuning.
In this work, hydroxyl‐functionalized Mo2C‐based MXene nanosheets are synthesized by facilely removing the Sn layer of Mo2SnC. The hydroxyl‐functionalized surface of Mo2C suppresses the shuttle ...effect of lithium polysulfides (LiPSs) through strong interaction between Mo atoms on the MXenes surface and LiPSs. Carbon nanotubes (CNTs) are further introduced into Mo2C phase to enlarge the specific surface area of the composite, improve its electronic conductivity, and alleviate the volume change during discharging/charging. The strong surface‐bound sulfur in the hierarchical Mo2C‐CNTs host can lead to a superior electrochemical performance in lithium–sulfur batteries. A large reversible capacity of ≈925 mAh g−1 is observed after 250 cycles at a current density of 0.1 C (1 C = 1675 mAh g−1) with good rate capability. Notably, the electrodes with high loading amounts of sulfur can also deliver good electrochemical performances, i.e., initial reversible capacities of ≈1314 mAh g−1 (2.4 mAh cm−2), ≈1068 mAh g−1 (3.7 mAh cm−2), and ≈959 mAh g−1 (5.3 mAh cm−2) at various areal loading amounts of sulfur (1.8, 3.5, and 5.6 mg cm−2) are also observed, respectively.
Mo2C‐based MXene nanosheets composited with carbon nanotubes are synthesized and used as sulfur host in lithium–sulfur (Li–S) batteries. The hydroxyl‐functionalized surface of Mo2C suppresses the shuttle effect of lithium polysulfides (LiPSs) through strong interaction between Mo atoms on the MXenes surface and LiPSs, leading to a superior electrochemical performance in Li–S batteries.
One of the newest fluorine compounds is the enantiopure trifluoromethylated molecule. Information about nantiopure trifluoromethylated molecules is presented.
Although silicon (Si) is ubiquitous in soil and plant, evidence is still lacking that Si is essential for higher plants. However, it has been well documented that Si is beneficial for healthy growth ...of many plant species. Si can promote plant mechanical strength, light interception, as well as resistance to various forms of abiotic and biotic stress, thus improving both yield and quality. Indeed, application of Si fertilizer is a rather common agricultural practice in many countries and regions. As the beneficial effects provided by Si are closely correlated with Si accumulation level in plant, elucidating the possible mechanisms of Si uptake and transport in plants is extremely important to utilize the Si-induced beneficial effects in plants. Recently, rapid progress has been made in unveiling molecular mechanisms of Si uptake and transport in plants. Based on the cooperation of Si influx channels and efflux transporters, a model to decipher Si uptake, transport and distribution system in higher plants has been developed, which involves uptake and radial transport in root, xylem and inter-vascular transport and xylem unloading and deposition in leaf. In this paper, we overviewed the updated knowledge concerning Si uptake, transport and accumulation and its significance for the major crops of agricultural importance and highlighted the further research needs as well.
Whether nonalcoholic fatty liver disease (NAFLD) is associated with an increased risk of mortality remains controversial. The present study aimed to clarify this issue. A systematic search of PubMed ...and Embase was conducted through October 2018. Studies providing risk estimates of NAFLD and mortality were included. A random-effects model was employed to calculate summary risk estimates. Subgroup analyses were performed to identify potential effect modifiers. Fourteen studies, involving 498501 subjects and 24234 deaths, were included. Patients with NAFLD were found to be at an elevated risk of all-cause mortality compared with those without hazard ratio (HR) = 1.34; 95% confidence interval (CI) 1.17-1.54). The significantly positive association between NAFLD and all-cause mortality could not be modified by age, sex, follow-up duration, and adjustment for body mass index, diabetes, smoking or hypertension (all P
> 0.05), and remained in sensitivity analyses. No significant associations of NAFLD with CVD (HR = 1.13; 95% CI 0.92-1.38) and cancer (HR = 1.05; 95% CI 0.89-1.25) mortality were found. In conclusion, NAFLD is a predictor of increased all-cause mortality but not CVD and cancer mortality. These findings have important implications for decision making in public health and clinical practice, and highlight the urgency of developing effective treatments for NAFLD.
Activity‐based E2 conjugating enzyme (E2)‐ubiquitin (Ub) probes have recently emerged as effective tools for studying the molecular mechanism of E3 ligase (E3)‐catalyzed ubiquitination. However, the ...preparation of existing activity‐based E2‐Ub probes depends on recombination technology and bioconjugation chemistry, limiting their structural diversity. Herein we describe an expedient total chemical synthesis of an E2 enzyme variant through a hydrazide‐based native chemical ligation, which enabled the construction of a structurally new activity‐based E2‐Ub probe to covalently capture the catalytic site of Cys‐dependent E3s. Chemical cross‐linking coupled with mass spectrometry (CXMS) demonstrated the utility of this new probe in structural analysis of the intermediates formed during Nedd4 and Parkin‐mediated transthiolation. This study exemplifies the utility of chemical protein synthesis for the development of protein probes for biological studies.
A structurally new activity‐based E2‐Ub probe that closely resembles the native E2∼Ub thioester has been developed and used for structural analysis of Cys‐dependent E3 ligases‐catalyzed transthiolation. This new probe is readily prepared in an expedient total chemical synthesis of atomically‐tailored E2 enzyme variant using hydrazide‐based native chemical ligation.
This paper proposes a split hierarchical cluster analysis algorithm to study the management of political education in colleges and universities. The data mining object of a university is selected, ...and the initial data for the study of ideological and political education and management is obtained by issuing the questionnaire of “quantitative assessment form for counselors”, and the data is optimized by clustering the data with dissimilarity matrices. Based on completing the pre-processing of the research data, the combination of statistical analysis and simulation analysis is used to analyze the example of the management of college civic education in the context of digital intelligence. The results show that when K is equal to 2, both clusters have similar thickness and size, so it is more appropriate to select K=2 to cluster analysis of each crisis group of ideological and political education management, indicating that the split-level cluster analysis algorithm helps to promote the interconnection of the ideological and political education management work. This study can improve the level and overall quality of college students’ ideological and political education in an all-round way, create a high-level management mode of ideological and political education and promote the sustainable development of ideological and political education in colleges and universities.
•Computational simulated models were built for syringe and screw-based 3D printer.•A comparative study was carried out for syringe and screw-based printer based on fluid characteristics.•The ...screw-based printer’s fluid characteristics are more complex than syringe-based one.•Backflows were found at the gap between walls and the filament in the extrusion tube.
Extrusion-based three-dimensional (3D) printing is an emerging technology which has a high application potential in food manufacturing processes. Screw and syringe-based printers are two kinds of extrusion-based 3D printing methods that have been widely studied and reported. The objective of present work was to compare these two different kinds of extrusion-based food 3D printing methods, in fluid flow characteristics and printing profile by computational simulation model and printing experiment. Analysis of simulated model suggested that the screw-based 3D food printer had a complex fluid characteristic, and some backflows were found at the gap between walls and the screw flights in the extrusion tube. Whereas, the syringe-based 3D food printer showed more simple fluid characteristics, which could be easy to adjust. Moreover, the experimental 3D printing suggested that the screw-based 3D food printer were not suitable for extruding the inks with high viscosity. Results in present work provides information for suitable printing method selection, a theoretical base and technical guide for further 3D printing studies and new printer designing.
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