Semiconductor SERS on Colourful Substrates with Fabry-Pérot Cavities

Non-metallic materials have emerged as a new family of active substrates for surface-enhanced Raman scattering (SERS), with unique advantages over their metal counterparts. However, owing to their inefficient interaction with the incident wavelength, the Raman enhancement achieved with non-metallic materials is considerably lower with respect to the metallic ones. Herein, we propose colourful semiconductor-based SERS substrates for the first time by utilizing a Fabry-Pérot cavity, which realize a large freedom in manipulating light. Owing to the delicate adjustment of the absorption in terms of both frequency and intensity, resonant absorption can be achieved with a variety of non-metal SERS substrates, with the sensitivity further enhanced by ≈100 times. As a typical example, by introducing a Fabry-Pérot-type substrate fabricated with SiO₂/Si, a rather low detection limit of 10⁻¹⁶ M for the SARS-CoV-2S protein is achieved on SnS₂. This study provides a realistic strategy for increasing SERS sensitivity when semiconductors are employed as SERS substrates.     

Stereodivergent synthesis of enantioenriched azepino[3,4,5-cd]-indoles via cooperative Cu/Ir-catalyzed asymmetric allylic alkylation and intramolecular Friedel–Crafts reaction

The development of enantioselective annulation reactions using readily available substrates for the construction of structurally and stereochemically diverse heterocycles is a compelling topic in diversity-oriented synthesis. Herein, we report efficient catalytic asymmetric formal 1,3-dipolar (3 + 4) cycloadditions of azomethine ylides with 4-indolyl allylic carbonates for the construction of azepino[3,4,5-cd]-indoles fused with a challenging seven-membered N-heterocycle, a frequently occurring tricyclic indole scaffold in bioactive compounds and pharmaceuticals. Through cooperative Cu/Ir-catalyzed asymmetric allylic alkylation followed by intramolecular Friedel–Crafts reaction, an array of azepino[3,4,5-cd]-indoles were obtained in good yields with excellent diastereo-/enantioselective control. More importantly, the full stereodivergence of this transformation was established via synergistic catalysis followed by acid-promoted epimerization, and up to eight stereoisomers of the cycloadducts bearing three stereogenic centers could be predictably achieved from the same set of starting materials for the first time. Quantum mechanical computations established a plausible mechanism for the synergistic Cu/Ir catalysis to stereodivergently introduce two vicinal stereocenters whose stereochemical information is remotely delivered across the fused azepine ring to control the third chiral center. Epimerization of the last center involves protonation-enabled reversal of the thermodynamically controlled relative configuration.

A stereodivergent synthesis of azepino[3,4,5-cd]-indoles bearing three stereogenic centers was established via synergistic dual-metal catalysis followed by acid-promoted epimerization, and up to all eight stereoisomers could be predictably achieved.     

理、化、生不同专业大学生关于能量概念的认识现状研究

能量概念是科学教育的一个核心概念,也是近年来国际科学教育研究的一个热点话题。在柳秀峰、Wilson等人的研究基础上,构建了能量概念的认识模型。基于该模型,并结合国内物理、化学和生物等不同专业的中学、大学教材中涉及的能量相关概念,笔者编制了调查问卷,对北京师范大学物理、化学和生物等不同专业的共280名大学生进行了测查和访谈。通过Rasch模型和SPSS统计分析发现,不同学科背景的学生对能量概念的认识角度和水平存在差异,而且存在一些偏差认识。基于学生的认识现状,笔者最后构建了关于能量概念认识的难度进阶,并对能量概念的教学提出了建议。     

Making JP‐10 Superfuel Affordable with a Lignocellulosic Platform Compound

The synthesis of renewable jet fuel from lignocellulosic platform compounds has drawn a lot of attention in recent years. So far, most work has concentrated on the production of conventional jet fuels. JP‐10 is an advanced jet fuel currently obtained from fossil energy. Due to its excellent properties, JP‐10 has been widely used in military aircraft. However, the high price and low availability limit its application in civil aviation. Here, we report a new strategy for the synthesis of bio‐JP‐10 fuel from furfuryl alcohol that is produced on an industrial scale from agricultural and forestry residues. Under the optimized conditions, bio‐JP‐10 fuel was produced with high overall carbon yields (≈65 %). A preliminary economic analysis indicates that the price of bio‐JP‐10 fuel can be greatly decreased from ≈7091 US$/ton (by fossil route) to less than 5600 US$/ton using our new strategy. This work makes the practical application of bio‐JP‐10 fuel forseeable.     

A Smart Photochromic Semiconductor: Breaking the Intrinsic Positive Relation Between Conductance and Temperature

Breaking the intrinsic rule of semiconductors that conductivity increases with increase of temperature and realizing a dramatic dropping of conductivity at high temperature may arouse new intriguing applications, such as circuit overload or over‐temperature protecting. This goal has now been achieved through T‐type electron‐transfer photochromism of one organic semiconductor assembled by intermolecular cation???π interactions. Conductivity of the viologen‐based model semiconductor (H₂bipy)(Hox)₂ (H₂bipy=4,4′‐bipyridin‐1,1′‐dium; ox=oxalate) increased by 2 orders of magnitude after photoinduced electron transfer (a record for photoswitchable organic semiconductors) and generation of radical cation???π interactions, and fell by approximately 81 % at 100 °C through reverse electron transfer and degeneration of the radical cation???π interactions. The model semiconductor has at least two different electron transfer pathways in the decoloration process.     

痂囊腔菌素A的结构

对实验室生物合成方法制得的痂囊腔菌素A做X射线晶体衍射测定,与文献对照,所属品系及空间群相同,晶胞参数接近,但发现北醌母体外的侧基构型有明显差异,主要表现在两个手性碳原子是R-R型而非S-S型,分别以衍射数据和分子力学优化数据为起始结构,进行STO-3G水平上的结构全优化。计算结果表明所制得的痂囊腔菌素A是一种新的光学活性对映体,由此推测痂囊腔菌素A的高光敏活性可能与手性结构特征有关。     

Highly stereoselective construction of tetrahydroquinolines via cascade aza-Michael-Michael reaction: Formal [4+2] cycloaddition of β,γ-unsaturated α-ketoesters with 2-aminochalcones

An efficient cascade aza-Michael-Michael sequence for the preparation of tetrahydroquinolines has been established. Three contiguous stereogenic centers are created with high levels of enantioselectivities (79–99% ee) and exclusive diastereoselectivities in the presence of a bifunctional squaramide. This approach is compatible with a broad range of β,γ-unsaturated α-ketoesters and 2-aminochalcones. Our protocol indicated that β-site of β,γ-unsaturated α-ketoester is an available pro-nucleophilic site.     

Efficient and Rapid Method for the Oxidation of Electron‐Rich Aromatic Aldehydes to Carboxylic Acids Using Improved Basic Hydrogen Peroxide

An efficient and rapid method for oxidation of electron‐rich aromatic aldehydes to their corresponding carboxylic acids in excellent yields was developed. It is based on the oxidation of methoxy‐substituted benzaldehydes in methanol with an improved aqueous basic hydrogen peroxide system. Benzaldehydes with electron‐withdrawing substituents are oxidized to the corresponding carboxylic acid in excellent yields under mild reaction conditions.