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Palladium-catalyzed enantioselective C(sp3)-H functionalization reactions has attracted considerable attention due to its ability for the synthesis of enantiomerically enriched molecules and stimulation of novel retrosynthetic disconnections. Understanding the reaction mechanism, especially the stereochemical process of the reaction, is crucial for the rational design of more efficient catalytic systems. Previously, we developed a Pd(II)/sulfoxide-2-hydroxypridine (SOHP) catalytic system for asymmetric C(sp3)-H functionalization reactions. In this study, we focused on unraveling the chemistry of chiral palladacycles involved in the Pd(II)-catalyzed enantioselective C(sp3)-H functionalization. We have isolated key palladacycle intermediates involved in the enantioselective ß-C(sp3)-H arylation of carboxylic acids catalyzed by the Pd(II)/SOHP system. These palladacycles, exhibiting ligand-induced chirality, provided a significant opportunity to investigate the stereochemical process and the ligand effect in this asymmetric C-H functionalization. Our investigation provided direct evidence for the C-H palladation step as the enantioselectivity-determining step, which forms diastereomeric palladacycles that exhibited preservation of chirality in the functionalization step. DFT calculations provided insights into the chiral induction in palladacycle formation. This work highlights the value of chiral palladacycle chemistry in offering mechanistic insights into the Pd(II)-catalyzed asymmetric C(sp3)-H functionalization reactions.
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Amide is one of the most widespread functional groups in organic and bioorganic chemistry, and it would be valuable to achieve stereoselective C(sp3 )-H functionalization in amide molecules. Palladium(II) catalysis has been prevalently used in the C-H activation chemistry in the past decades, however, due to the weakly-coordinating feature of simple amides, it is challenging to achieve their direct C(sp3 )-H functionalization with enantiocontrol by PdII catalysis. Our group has developed sulfoxide-2-hydroxypridine (SOHP) ligands, which exhibited remarkable activity in Pd-catalyzed C(sp2 )-H activation. In this work, we demonstrate that chiral SOHP ligands served as an ideal solution to enantioselective C(sp3 )-H activation in simple amides. Herein, we report an efficient asymmetric PdII /SOHP-catalyzed ß-C(sp3 )-H arylation of aliphatic tertiary amides, in which the SOHP ligand plays a key role in the stereoselective C-H deprotonation-metalation step.
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The accurate terrain classification in real time is of great importance to an autonomous robot working in field, because the robot could avoid non-geometric hazards, adjust control scheme, or improve localization accuracy, with the aid of terrain classification. In this paper, we investigate the vibration-based terrain classification (VTC) in a dynamic environment, and propose a novel learning framework, named DyVTC, which tackles online-collected unlabeled data with concept drift. In the DyVTC framework, the exterior disagreement (ex-disagreement) and interior disagreement (in-disagreement) are proposed novely based on the feature diversity and intrinsic temporal correlation, respectively. Such a disagreement mechanism is utilized to design a pseudo-labeling algorithm, which shows its compelling advantages in extracting key samples and labeling; and consequently, the classification accuracy could be retrieved by incremental learning in a changing environment. Since two sets of features are extracted from frequency and time domain to generate disagreements, we also name the proposed method feature-temporal disagreement adaptation (FTDA). The real-world experiment shows that the proposed DyVTC could reach an accuracy of 89.5%, but the traditional time- and frequency-domain terrain classification methods could only reach 48.8% and 71.5%, respectively, in a dynamic environment.
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Pd-catalyzed reactions of azides with CO to access an isocynate intermediate have been developed extensively in recent years. However, the catalytic carbonylation of sensitive acyl azides has not been reported. Herein, we report a simple Pd-catalyzed carbonylation reaction of acyl azides with broad substrate scope, high efficiency, and simple operation under mild conditions, which provides facile access to acyl ureas. In addition, a mechanistic study was carried out by both experiment and DFT calculation. Control experiments and kinetic study revealed that the real active palladium species were Pd(0). The result of kinetic study suggested that palladium catalyst, azide, and CO were all involved in the turnover-limiting step except for amine. Further DFT study suggested that an unprecedented five-membered palladacycle intermediate was the key intermediate in the carbonylation reaction.
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The Pd(II)/sulfoxide-2-hydroxypyridine catalytic system shows promising activity in C-H activation chemistry. In this study, we showcase how this catalytic system solves the problem of native primary amine-directed γ-C(sp3)-H arylation. Primary amines with different complexities are compatible with the established methodology, and the range of applicable substrates can be expanded to include pyridine, oxime ether, and pyridine N-oxide.
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Objectives This study aimed to provide greater insight into the characteristics of severe and extraordinarily severe gas explosion accidents (SESGEAs). Methods. The study analyzed the accident characteristics and causes of SESGEAs. As an example, we conducted a specialized case analysis using the 24Model (fourth edition) on the recent Baoma coal mine gas explosion. Results. SESGEA data are characterized by greater volatility, with significant differences in the geographical distribution, temporal distribution and attributed characteristics of the accidents. From the accident analysis: chaotic ventilation management was the most serious accident cause of SESGEAs; unsafe acts related to ventilation operations accounted for 18.51% of all unsafe acts; coal miners lack professional safety knowledge and have a serious fluke mentality in mining work; enterprises have insufficient enforcement of safety procedure documents, and lack of attention to the allocation of underground human resources and safety training systems; and the importance of safety, the role of the safety department and satisfaction with safety facilities have become the most serious missing items of safety culture. Conclusion. This study can provide important data support and management basis to assist mine operators in developing more targeted accident prevention strategies.
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Minas de Carbón , Explosiones , Humanos , Accidentes de Trabajo/prevención & control , China/epidemiología , Carbón Mineral , AccidentesRESUMEN
A comparative study was conducted to compare the accident cause analysis methods of fault tree analysis (FTA) and 24Model. A major accident - the Xinjia Hotel collapse accident - was selected as the research object, the causes of the accident were reanalysed and accident prevention countermeasures were designed based on 24Model and FTA, respectively, and the systematic characteristics of 24Model were summarized. The research shows that both 24Model and FTA can carry out risk assessment, accident cause analysis and preventive countermeasure design based on their own rules. Different from FTA, 24Model has static and dynamic structures of specific forms, the definition of causes and factors in the model is more comprehensive and the analysis method is more hierarchical and normative. 24Model can analyse the deep-level cultural and system causes, but the analysis process does not use quantitative methods, only qualitative methods. 24Model has eight systematic characteristics, such as integrity, hierarchy and dynamics.
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Prevención de Accidentes , Accidentes , Humanos , Medición de Riesgo/métodosRESUMEN
Anisotropic microstructures resulting from a well-ordered arrangement of filamentous extracellular matrix (ECM) components or cells can be found throughout the human body, including skeletal muscle, corneal stroma, and meniscus, which play a crucial role in carrying out specialized physiological functions. At present, due to the isotropic characteristics of conventional hydrogels, the construction of freeform cell-laden anisotropic structures with high-bioactive hydrogels is still a great challenge. Here, we proposed a method for direct embedded 3D cell-printing of freeform anisotropic structure with shear-oriented bioink (GelMA/PEO). This study focuses on the establishment of an anisotropic embedded 3D bioprinting system, which effectively utilizes the shear stress generated during the extrusion process to create cells encapsulating tissues with distinct anisotropy. In conjunction with the water-solubility of PEO and the in-situ encapsulation effect provided by the carrageenan support bath, high-precise cell-laden bioprinting of intricate anisotropic and porous bionic artificial tissues can be effectively implemented in one-step. Additionally, anisotropic permeable blood vessel has been taken as a representation to validate the effectiveness of the shear-oriented bioink system in fabricating intricate structures with distinct directional characteristics. Lastly, the successful preparation of muscle patches with anisotropic properties and their guiding role for cell cytoskeleton extension have provided a significant research foundation for the application of the anisotropic embedded 3D bioprinting system in the ex-vivo production and in-vivo application of anisotropic artificial tissues.
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Various anisotropic tissue structures exist in organisms, including muscle tissue, skin tissue, and nerve tissue. Replicating anisotropic tissue structuresin vitrohas posed a significant challenge. Three-dimensional (3D) printing technology is often used to fabricate biomimetic structures due to its advantages in manufacturing principle. However, direct 3D printing of freeform anisotropic bioactive structures has not been reported. To tackle this challenge, we developed a ternary F/G/P ink system that integrates the printability of Pluronic F127 (F), the robust bioactivity and photocrosslinking properties of gelatin methacryloyl (G), and the shear-induced alignment functionality of high-molecular-weight polyethylene glycol (P). And through this strategic ternary system combination, freeform anisotropic tissue structures can be 3D printed directly. Moreover, these anisotropic structures exhibit excellent bioactivity, and promote orientational growth of different cells. This advancement holds promise for the repair and replacement of anisotropic tissues within the human body.
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Gelatina , Tinta , Poloxámero , Impresión Tridimensional , Andamios del Tejido , Anisotropía , Gelatina/química , Poloxámero/química , Humanos , Andamios del Tejido/química , Ingeniería de Tejidos , Polietilenglicoles/química , Animales , Materiales Biocompatibles/química , Materiales Biocompatibles/farmacología , Metacrilatos/química , RatonesRESUMEN
The potential of 3D bioprinting in tissue engineering and regenerative medicine is enormous, but its implementation is hindered by the reliance on high-strength materials, which restricts the use of low-viscosity, biocompatible materials. Therefore, a major challenge for incorporating 3D bioprinting into tissue engineering is to develop a novel bioprinting platform that can reversibly provide high biological activity materials with a structural support. This study presents a room temperature printing system based on GelMA combined with carrageenan to address this challenge. By leveraging the wide temperature stability range and lubricating properties of carrageenan the room temperature stability of GelMA could be enhanced, as well as creating a solid ink to improve the performance of solid GelMA. Additionally, by utilizing the solubility of carrageenan at 37 °C, it becomes possible to prepare a porous GelMA structure while mimicking the unique extracellular matrix properties of osteocytes through residual carrageenan content and amplifying BMSCs' osteogenesis potential to some extent. Overall, this study provides an innovative technical platform for incorporating a low-viscosity ink into 3D bioprinting and resolves the long-standing contradiction between material printing performance and biocompatibility in bioprinting technology.
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Bioimpresión , Andamios del Tejido , Andamios del Tejido/química , Carragenina , Impresión Tridimensional , Materiales Biocompatibles/química , Ingeniería de Tejidos , Hidrogeles/química , Gelatina/químicaRESUMEN
We developed a facile, efficient method for synthesizing highly substituted 2-aminopyridines from unstable vinyl carbodiimides generated inâ situ in a one-pot transformation. A series of novel highly substituted 3-functionalized 2-aminopyridines were produced in good yields. Reaction mechanism studies, which included control experiments and density-functional theory (DFT) calculations, demonstrated that Rh and potassium carbonate played key roles in the cyclization step.
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Azidas , Cetonas , Aminopiridinas , CiclizaciónRESUMEN
Efficient control of regioselectivity is a key concern in transition-metal-catalyzed direct C-H functionalization reactions. Various strategies for regiocontrol have been established by tuning the selectivity of the C-H activation step as a common mode. Herein, we present our study on an alternative mode of regiocontrol, in which the selectivity of the C-H activation step is no longer a key concern. We found that, in a reaction where the C-H activation step exhibits a different regio-preference from the subsequent functionalization step, a ligand-enabled switch of the regioselectivity-determining step could provide efficient regiocontrol. This mode has been exemplified by the Pd(ii)-catalyzed aerobic oxidative Heck reaction of indoles, in which a ligand-controlled C3-/C2-selectivity was achieved for the first time by the development of sulfoxide-2-hydroxypyridine (SOHP) ligands.