Ambident Reactivity of Imidazolium Cations as Evidence of the Dynamic Nature of N-Heterocyclic Carbene-Mediated Organocatalysis

This work reveals ambident nucleophilic reactivity of imidazolium cations towards carbonyl compounds at the C2 or C4 carbene centers depending on the steric properties of the substrates and reaction conditions. Such an adaptive behavior indicates the dynamic nature of organocatalysis proceeding via a covalent interaction of imidazolium carbenes with carbonyl substrates and can be explained by generation of the H-bonded ditopic carbanionic carbenes.     

Alkane Shape- and Size-Recognized Selective Vapor Sorption in “Channel-Like” Crystals Based on Thiacalixarene Assemblies

Alkanes composed of C−C and C−H show a low electric polarization, and therefore, there is only very weak interaction between alkanes and adsorbents. Thus, it is difficult to separate a specific alkane from a mixture of alkanes by adsorption. Here, two activated “channel-like” crystals generated from brominated thiacalix[4]arene propyl ethers, which adopt 1,3-alternate and partial cone conformations, recognize specific alkane vapors depending on alkane-shape and -size, sorting in three-type alkane guests such as linear, branched, and cyclic alkanes. Two activated crystals, which are prepared by removal of solvent upon heating under reduced pressure, incorporate branched and/or cyclic alkane vapors by a unique “gate-opening” mechanism via a crystal transformation in the process. Linear alkane vapors do not trigger gate opening and are not taken up by the activated crystals. The shape and size molecular-recognition properties of the activated crystals promises considerable usefulness for the separation of linear, branched, and cyclic alkanes.     

Scalable Total Syntheses and Structure–Activity Relationships of Haouamines A,B, and Their Derivatives as Stable Formate Salts

Haouamines A, B, and their derivatives were synthesized via Suzuki–Miyaura coupling and three key cyclization reactions as follows: the newly developed palladium(0)-catalyzed arylative cyclization of phenylalanine-derived alkyne–aldehydes with 2-bromoarylboronic acid (an “anti-Wacker”-type cyclization); BF₃ ⋅ OEt₂-promoted Friedel–Crafts-type cyclization of symmetrical electron-rich aromatic rings adjacent to a tertiary allylic alcohol leading to the indeno-tetrahydropyridine skeleton; and (cyanomethyl)trimethylphosphonium iodide-mediated macrocyclization of amino alcohols to afford aza-paracyclophane precursors. The palladium-catalyzed reduction of mono- and di-triflate intermediates in the later stages enabled the alteration of both the position and number of hydroxyl groups on the C-ring. The instability of haouamine B was dramatically improved by salt formation with formic acid. An unambiguous evaluation of the cytotoxicity of the prepared haouamine derivative formates with and without hydroxyl groups at different positions on the C-ring indicated that the catechol structure in haouamine B produced weak cytotoxicity.     

不同版本高中化学教科书中学生必做实验的分析与启示——基于“科学探究与创新意识”素养

以人教版、苏教版、鲁科版(2019年版)和沪科版(2020年版)高中化学教科书中的学生必做实验文本为研究对象,基于“科学探究与创新意识”素养构建高中化学教科书中学生必做实验文本的分析框架,分析和比较4个版本教科书中学生必做实验文本“科学探究与创新意识”素养的体现及其异同,为学生必做实验教学提供启示和建议。     

Ru(bpy)32+-Enabled Cell-Surface Photocatalytic Proximity Labeling toward More Efficient Capture of Physically Interacting Cells

Intercellular proximity labeling has emerged as a promising approach to enable the study of cell-cell interactions (CCIs), but the efficiency of current platforms is limited. Here, we use Ru(bpy)₃²⁺ to construct an efficient photocatalytic proximity labeling (PPL) system on the cell surface that allows the highly discriminative CCI detection with spatiotemporal resolution. Through the mechanism study and quantitative characterization on living cells, we demonstrate that the singlet-oxygen (¹O₂) mechanism is more efficient and specific than the single electron transfer (SET) mechanism in Ru-mediated PPL. Ru(bpy)₃²⁺ catalysts with different cell-anchoring moieties are prepared to facilitate the catalyst loading on primary cells. Finally, based on this system, we develop a “live” T cell receptor (TCR) multimer with TCR-T cells that could sensitively identify and discriminate cells presenting antigens of different affinity, providing a powerful tool to better understand the heterogeneity of antigen presenting cells.     

Facile and sustainable synthesis of sodium lignosulfonate derived carbon quantum dots for the detection of total Mn and ascorbic acid

A fluorescent nanoprobe based on sodium lignosulfonate derived carbon quantum dots (SLS-CQDs) was fabricated through a facile and sustainable one-step hydrothermal treatment. The obtained SLS-CQDs had excellent fluorescence properties and were applied to detect total Mn and ascorbic acid (AA). The fluorescence of SLS-CQDs could be effectively quenched by Mn based on a static quenching process and recovered by the addition of AA. An “on–off-on” fluorescent nanoprobe was established to determine total Mn and AA with the detection limits of 6.9 µg/L and 0.65 µM with the corresponding linear ranges of 0.25–2.25, 5–25 mg/L, and 5–110 µM, respectively. This nanoprobe could accurately detect total Mn in surface water and AA in Vitamin C effervescent tablet samples. The proposed method is simple and can be performed easily, indicating that SLS-CQDs might be used in environmental monitoring, food and drug testing.     

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li−S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the “shuttle effect” of lithium polysulfides hinder the commercialization of Li−S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li−S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li−S batteries in the future.     

形状记忆合金作动器的设计及优化

采用Ｂｒｉｓｉｏｎ［１］等提出的ＳＭＡ材料的本构关系，分析了形状记忆合金作动器在三种热交换方式（自然冷却、强制冷却和采用半导体热泵技术）下的动力特性，同时研究了ＳＭＡ丝在恒载和载荷变化时对完成正逆相变所用时间的影响，并简单讨论了影响作动器响应的几个因素和改进方法     

Comparison of the chromatographic fingerprint,multicomponent quantitation and antioxidant activity of Salvia miltiorrhiza Bge. between sweating and nonsweating

Salvia miltiorrhiza Bge. is a traditional Chinese medicine applied in the treatment of various diseases in clinical practice. In the course of its processing, S. miltiorrhiza Bge. is usually processed by sweating. This study employed 10‐component contents determination coupled with high‐performance liquid chromatography (HPLC) fingerprint and antioxidant activity to investigate the effect of sweating on S. miltiorrhiza Bge. so as to evaluate the quality of S. miltiorrhiza Bge. The HPLC method was performed using C₁₈ and 0.05% phosphoric acid aqueous solution–acetonitrile with a gradient elution system. It was validated for linearity, precision, repeatability, stability and recovery. Similarity analysis, principal components analysis and antioxidant activity assays were used to compare sweated S. miltiorrhiza Bge. (SSM) and nonsweated S. miltiorrhiza Bge. (NSSM). SSM and NSSM showed good similarities in HPLC fingerprint (>0.9), but principal components analysis could classify the HPLC fingerprint and 10‐component quantitation analysis. Meanwhile, the antioxidant activity of SSM was significantly higher than that of NSSM (p < 0.01). The results of this study indicated that sweating could alter the content of chemical constituents in S. miltiorrhiza Bge., and could also improve its antioxidant activity. In addition, the method not only affords a viable strategy for comparing SSM and NSSM and assessing the quality of S. miltiorrhiza Bge., but also provides a reference for other herbal medicine that suffers from sweating.     

Synthesis,crystal structure and photo-induced isomerization of [ N,N ′- bis (4-fluorobenzylidene) ethylenediamine]bromo(triphenylphosphine)copper(I) complex

Abstract

The electrochemical behavior of VOQ₂OH or [VOQ₂-OVOQ₂] (Q = 8-hydroxyquinohnate anion) has been investigated by cyclic voltammetry in acetonitnie solutions. Although both species exist simultaneously at every condition analyzed, they can be clearly differentiated by this method. The effect of trace amounts of water on the electrochemical behavior is also discussed.