氮自由基启动的1,n-烯炔环化反应

C–N键广泛存在于药物、天然产物和功能材料中,而氮中心自由基在C–N键的构建中起到关键作用.但是,与广泛使用的碳中心自由基相比,氮中心自由基由于缺乏实用简便的产生方法而尚未得到充分研究.因此,发展高效的氮中心自由基引发反应迫在眉睫.在过去的几年里,得益于可信赖且可控制的自由基化学的兴起,可以通过热分解、氧化剂促进、金属盐催化或电催化来产生氮中心自由基.1,n-烯炔环化不仅可以一步反应同时构建形成两个或多个新的化学键,而且可以高选择性引入各种外部官能团,被认为是构建复杂环状化合物必不可少的方法.传统上,通过贵金属(例如Au、Pd、Rh、Ru等)和/或引发剂介导/催化来实现1,n-烯炔环化反应.1985年,Curran和他的同事报道了具有里程碑意义的工作,该方法通过碘代烯炔类化合物的分子内自由基串联环化反应实现了(±)-hirsutene的简洁全合成.受该工作的启发,并伴随着现代合成技术的发展,自由基启动的1,n-烯炔环化由于反应条件温和、具有较高的官能团兼容性、原子利用率高、通常不使用化学计量的金属催化剂和/或有毒引发剂,因而受到化学家们越来越多的关注.在此背景下,化学工作者已经开发了多种氮中心自由基启动的1,n-烯炔类化合物环化反应的方法.然而,据我们所知,目前还没有专门针对该主题的综述,因此本文及时进行总结分析.迄今为止,氮中心自由基启动的1,n-烯炔环化反应大概分为三种途径:(1)氮中心自由基选择性的与1,n-烯炔的C=C键进行加成反应,然后通过分子内环化以生成烯基自由基中间体,最后借助进一步环化反应、氢原子攫取或自由基偶联以得到最终产物;(2)涉及到氮中心自由基与1,n-烯炔的C≡C键的选择性加成反应、分子内环化及氧化脱氢;(3)借助分子内原位生成的氮中心自由基来启动的,随后经过两次分子内环化、单电子转移氧化及脱氢反应转化为最终产物.本文将依据氮中心自由基的类型,分为硝基自由基、叠氮自由基和酰胺自由基进行讨论,并将重点放在生成氮中心自由基的方法及其环化模式、相关反应机理以及存在的挑战上.     

Tunable Linear and Nonlinear Optical Properties from Room Temperature Phosphorescent Cyclic Triimidazole-Pyrene Bio-Probe

Organic materials with multiple emissions tunable by external stimuli represent a great challenge. TTPyr, crystallizing in different polymorphs, shows a very rich photophyisics comprising excitation-dependent fluorescence and phosphorescence at ambient conditions, and mechanochromic and thermochromic behavior. Transformation among the different species has been followed by thermal and X-ray diffraction analyses and the emissive features interpreted through structural results and DFT/TDDFT calculations. Particularly intriguing is the polymorph TTPyr(HT), serendipitously obtained at high temperature but stable also at room temperature, whose non-centrosymmetric structure guarantees an SHG efficiency 10 times higher than that of standard urea. Its crystal packing, where only the TT units are strongly rigidified by π-π stacking interactions while the Pyr moieties possess partial conformational freedom, is responsible for the observed dual fluorescence. The potentialities of TTPyr for bioimaging have been successfully established.     

Improving the sensitivity of cellulose fiber-based lateral flow assay by incorporating a water-dissolvable polyvinyl alcohol dam

Cellulose - Lateral flow assay (LFA) is an important point-of-care (POC) test platform due to the associated portability, on-site testing, and low cost for diagnosis of pathogen infections and...     

苯乙炔配位聚合及光热性能研究——推荐一个绿色高分子化学综合实验

介绍一个绿色高分子化学综合实验.在水相中,苯乙炔通过有机铑配合物催化聚合得到聚苯乙炔,利用红外光谱仪、核磁共振仪、紫外-可见分光光度计、荧光光谱仪和热重分析仪对其结构和光热性能进行研究.本实验难度适中,可以通过溶剂为可变因素展开分析讨论,引导学生主动思考.实验内容涵盖高分子化学、应用波谱学和聚合物仪器分析与表征等知识点.本实验的实施不仅可提升学生的综合运用专业知识能力,还可培养学生系统的科研思维和环保意识.     

Phenoxazine-based supramolecular tetrahedron as biomimetic lectin for glucosamine recognition

The design and synthesis of a phenoxazine-based metal-organic tetrahedro n(Zn_4L_4) as biomimetic lectin for selectively recognition of glucosamine(GlcN) was reported.Different from the free phenoxazinebased ligand(L),Zn_4L_4 displayed the highest fluorescent intensity enhancement efficiency toward GlcN over other related natural mono-and disaccharides.Fluorescence titration demonstrated a 1:1 stoichiometric host-guest complex was formed with an association constant about 4.03 × 10~4 L/mol.~1H NMR spectroscopic studies confirmed this selectivity resulted from the multiple hydrogen bonding interactions formed between GlcN and Zn_4L_4.The present results suggested that rational arrangement of recognition sites in the confined space of metal-organic cage is crucial for the selectivity toward target guests.     

Rapid and label-free classification of pathogens based on light scattering,reduced power spectral features and support vector machine

The rapid identification of pathogens is crucial in controlling the food quality and safety. The proposed system for the rapid and label-free identification of pathogens is based on the principle of laser scattering from the bacterial microbes. The clinical prototype consists of three parts: the laser beam, photodetectors, and the data acquisition system. The bacterial testing sample was mixed with 10 mL distilled water and placed inside the machine chamber. When the bacterial microbes pass by the laser beam, the scattering of light occurs due to variation in size, shape, and morphology. Due to this reason, different types of pathogens show their unique light scattering patterns. The photo-detectors were arranged at the surroundings of the sample at different angles to collect the scattered light. The photodetectors convert the scattered light intensity into a voltage waveform. The waveform features were acquired by using the power spectral characteristics, and the dimensionality of extracted features was reduced by applying minimal-redundancy-maximal-relevance criterion (mRMR). A support vector machine (SVM) classifier was developed by training the selected power spectral features for the classification of three different bacterial microbes. The resulting average identification accuracies of E. faecalis,E. coli and S. aureus were 99%, 87%, and 94%, respectively. The overall experimental results yield a higher accuracy of 93.6%, indicating that the proposed device has the potential for label-free identification of pathogens with simplicity, rapidity, and cost-effectiveness.     

Recent advances in the applications of [1.1.1]propellane in organic synthesis

As a highly strained small molecule, [1.1.1]propellane has been widely used in various synthetic transformations owing to the exceptional reactivity of the central bond between the two bridgehead carbons. Utilizing strain-release approaches, the rapid development of strategies for the construction of bicyclo[1.1.1]pentane (BCP) and cyclobutane derivatives using [1.1.1]propellane as the starting material has been witnessed in the past few years. In this review, we highlight the most recent advances in this field. Accordingly, the reactivity of [1.1.1]propellane can be divided into three pathways, including radical, anionic and transition metal-catalyzed pathways under appropriate conditions.     

Oxidation of aromatic sulfides with molecular oxygen: Controllable synthesis of sulfoxides or sulfones

The recent development of selective oxidation of aromatic sulfides with molecular oxygen was highlighted. The sulfoxides and sulfones could be obtained by simply switching the reaction media, i.e., bis(2-butoxyethyl)ether (BBE) or poly(ethylene glycol)dimethyl ether (PEGDME). The application of the high-boiling-point polyether as an initiator and green media can eliminate the need of large quantities of additives and volatile solvents. This strategy represents an economic and eco-friendly method that could find potential applications.     

全无机卤化铅钙钛矿的结构、热力学稳定性和电子性质

有机-无机杂化卤化铅钙钛矿因具有独特的电子和光学特性,已经成为光电领域最有前途的材料。但是,有机-无机钙钛矿材料及器件稳定性差,限制了其实际应用。与杂化钙钛矿相比,全无机卤化物钙钛矿CsPbX₃(X=Cl,Br,I)显示出更强的热稳定性。全无机卤化物钙钛矿CsPbX₃具有多个晶型,在不同的温度下呈不同相结构。目前,关于CsPbX₃的结构和物理性质仍存在争议。本文我们针对三个晶相α-,β-和γ-CsPbX₃的结构,热力学稳定性和电子性质进行了全面的理论研究。第一性原理计算表明,从高温α相到低温β相,然后再到γ相的相变伴随着PbX₆八面体的畸变。零温形成能计算表明,γ相最稳定,这与实验中γ相为低温稳定相的结论一致。电子性质计算表明,所有CsPbX₃钙钛矿都表现出直接带隙性质,并且带隙值从α相到β相再到γ相逐渐增加。这是由于相变发生时,Pb-X成键强度逐渐减弱,使价带顶能量降低,进而带隙增加。在所有相中,α相结构中较强的Pb-X相互作用,导致了较强的带边色散,使其具有较小的载流子有效质量。     

Self-assembled lamellar nanochannels in polyoxometalate-polymer nanocomposites for proton conduction

The construction of nanostructured ion-transport channels is highly desirable in the design of advanced electrolyte materials,as it can enhance ion conductivity by offering short ion-transport pathways.In this work,we present a supramolecular strategy to fabricate a nanocomposite electrolyte containing highly ordered lamellar proton-conducting nanochannels,by the electrostatic self-assembly of a polyoxometalate H_3 PW_(12)O_(4 O)(PW) and a comb copolymer poly(4-methlstyrene)-graft-poly(N-vinyl pyrrolidone).PW can effectively regulate the self-assembling order of polymer moieties to form a large-ra nge lamellar structure,meanwhile,introducing protons into the nanoscale lamellar domains to build proton transport channels.Moreover,the rigid PW clusters contribute a remarkable mechanical reinforcement to the nanocomposites.The lamellar nanocomposite exhibits a conductivity of 4.3 × 10~(-4) S/cm and a storage modulus of 1.1 × 10~7 Pa at room temperature.This study provides a new strategy to construct nanostructured ion-conductive pathways in electrolyte materials.