Catalytic Asymmetric Functionalization of Aromatic CH Bonds by Electrophilic Trapping of Metal‐Carbene‐Induced Zwitterionic Intermediates

Asymmetric functionalization of aromatic C? H bonds of N,N‐disubstituted anilines with diazo compounds and imines is reported for the efficient construction of α,α‐diaryl benzylic quaternary stereocenters in good yields with high diastereoselectivities and excellent enantioselectivities. This Rh^II/chiral phosphoric acid cocatalyzed transformation is proposed to proceed through a metal‐carbene‐induced zwitterionic intermediate which undergoes electrophilic trapping. To the best of our knowledge, this is the first asymmetric example of metal carbene‐induced intermolecular functionalization of aryl C? H bonds.     

An Ylide Transformation of Rhodium(I) Carbene: Enantioselective Three‐Component Reaction through Trapping of Rhodium(I)‐Associated Ammonium Ylides by β‐Nitroacrylates

The chiral Rh^I–diene‐catalyzed asymmetric three‐component reaction of aryldiazoacetates, aromatic amines, and β‐nitroacrylates was achieved to obtain γ‐nitro‐α‐amino‐succinates in good yields and with high diastereo‐ and enantioselectivity. This reaction is proposed to proceed through the enantioselective trapping of Rh^I‐associated ammonium ylides by nitroacrylates. This new transformation represents the first example of Rh^I‐carbene‐induced ylide transformation.     

An E1-Catalyzed Chemoenzymatic Strategy to Isopeptide-N-Ethylated Deubiquitylase-Resistant Ubiquitin Probes

Triazole-based deubiquitylase (DUB)-resistant ubiquitin (Ub) probes have recently emerged as effective tools for the discovery of Ub chain-specific interactors in proteomic studies, but their structural diversity is limited. A new family of DUB-resistant Ub probes is reported based on isopeptide-N-ethylated dimeric or polymeric Ub chains, which can be efficiently prepared by a one-pot, ubiquitin-activating enzyme (E1)-catalyzed condensation reaction of recombinant Ub precursors to give various homotypic and even branched Ub probes at multi-milligram scale. Proteomic studies using label-free quantitative (LFQ) MS indicated that the isopeptide-N-ethylated Ub probes may complement the triazole-based probes in the study of Ub interactome. Our study highlights the utility of modern protein synthetic chemistry to develop structurally and new families of tool molecules needed for proteomic studies.     

Metal–Sulfur Linkages Achieved by Organic Tethering of Ruthenium Nanocrystals for Enhanced Electrochemical Nitrogen Reduction

Inspired by the metal–sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N₂ availability on a catalytic surface, which suppresses the hydrogen evolution reaction (HER) and improves the rate of NH₃ production. Ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11 %) with an improved NH₃ yield (50 μg h⁻¹ mg⁻¹) is achieved at −0.1 V vs. RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N₂ adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst shows excellent stability and recyclability for NH₃ production, as confirmed by rigorous control experiments including ¹⁵N isotope labeling experiments.     

化学教育走进雄安——白洋淀环保主题暑期实践活动

在京津冀一体化、雄安新区建设和"绿水青山就是金山银山"生态文明思想的三大政策背景下,由首都师范大学化学(师范)专业师生组成的京冀科育团队于2019年暑假走进雄安新区,以化学教育为核心、以环境保护为主题、以提升学科核心素养为导向,开展了兼具化学专业特色和教师教育特色的暑期实践活动。     

Determination and comparison of agarwood from different origins by comprehensive two‐dimensional gas chromatography–quadrupole time‐of‐flight mass spectrometry

Agarwood, a species of resinous heartwood, is a precious medicinal plant and a type of rare natural spice, which is widely used in medicine, cosmetics, religious activities, and other fields. In this study, agarwood samples from eight different regions across four countries were analyzed by comprehensive two‐dimensional gas chromatography?quadrupole time‐of‐flight mass spectrometry. A total of 232 species were identified (the match factors of these compounds were above 750). The main compounds of agarwood are oxygenated sesquiterpenes and chromones. The compositions of India1 and Malaysia2 were significantly different from those of other samples, which might be attributed to the different production processes of agarwood. For further investigation, factor analysis was conducted for six agarwood samples. The results showed that the data classification possessed a regional characteristic; according to the retention time and relative content, characteristic compositions were determined by factor scores. Finally, the differences of characteristic compositions were simply analyzed, and the reasons were speculated.     

Hantzsch Ester as a Photosensitizer for the Visible‐Light‐Induced Debromination of Vicinal Dibromo Compounds

The debromination of vicinal dibromo compounds to generate alkenes usually requires harsh reaction conditions and the addition of catalysts. Just recently the visible‐light‐induced debromination of vicinal dibromo compounds emerged as a possible alternative to commonly used methods, but the substrate scope of this reaction is limited and a photocatalyst is necessary for the successful conversion of the starting compounds. A catalyst‐free visible‐light‐induced debromination of vicinal dibromo compounds with a base‐activated Hantzsch ester as photosensitizer is reported. The method has a wide substrate scope and a broad functional‐group compatibility.     

Pressure‐Induced Emission Enhancement of a Series of Dicyanovinyl‐Substituted Aromatics: Pressure Tuning of the Molecular Population with Different Conformations

A series of dicyanovinyl‐substituted aromatic compounds (Ar‐DCV; Ar=9‐anthracenyl, 1‐naphthyl, 1‐pyrenyl) with dual fluorescence are prepared, and their emission properties—when molecularly dispersed in a polymer medium—are investigated under pressure perturbation. The total emission intensity is enhanced drastically from ambient pressure up to 70 kbar. Emission 30–107 times more intense than that at ambient pressure is observed at higher pressure. In dual emission, the enhancement of the local excited state (LE state) is significantly different from that of the intramolecular charge‐transfer state (ICT state). The intensity of the ICT emission increases faster (30–370 times) than that of the LE emission (less than 20 times). In accordance with spectroscopic data, emission dynamics at different pressures, and computational studies on the molecular conformations of these compounds, a kinetic model is proposed to explain the effect of pressure on the emissive properties of the Ar‐DCV compounds from the point of view of pressure‐dependent populations of the species in the ground state.     

园柱壳中环裂纹对弹性波的散射

本文在经典弹性薄壳运动方程基础上,分析了圆柱壳中环向穿透裂纹对扭转波和膨胀波的散射,求得了反射系数及相应的动态应力强度因子。通过检查能量平衡关系验证了所用方法的正确性。     

水滑石负载钯催化剂上的醇无氧脱氢反应

 研究了多种载体负载 Pd 催化剂上苯甲醇无氧脱氢反应. 结果发现, 以兼具较强酸性和碱性的水滑石 (HT) 为载体时, Pd 催化剂具有优异的苯甲醇转化活性和苯甲醛选择性, 当 Pd 含量为 0.32%~0.55% 时催化性能最佳. Pd/HT 催化剂可重复使用, 且对于含推电子取代基的芳香醇、2-噻吩甲醇、α,β-不饱和醇与环状脂肪醇等的直接脱氢反应均具有较好催化性能. HT 表面的 Pd(II) 物种反应后转变为平均粒径为 2.0~2.5 nm 的 Pd 纳米粒子或纳米簇. 具有较高分散度的 Pd(II) 物种易转变为较小的 Pd 纳米粒子, 从而具有较佳的催化性能. 本文推测, 催化剂表面的碱性位可促进苯甲醇 O–H 键的活化, 形成 Pd-苯甲氧基中间体, 该中间体进一步脱氢生成苯甲醛和 Pd-H 物种; 而催化剂表面的质子酸位可与 Pd-H 作用, 促进 H2 的脱除.