基于极课大数据的初中化学组卷及试卷评价

为了提高组卷质量,基于极课大数据建立初中化学校本题库,根据双向细目表,利用该系统的出卷功能进行组卷。采用SPSS软件对试卷难度、区分度、信度和效度进行综合分析和评价,可知基于极课所出试卷各项评价指标较优秀,符合考试要求,试卷质量高。     

高效液相色谱-电感耦合等离子体质谱法测定人尿中硒形态

采用高效液相色谱-电感耦合等离子体质谱法(HPLC-ICP/MS)测定人尿中硒代胱氨酸(SeCys_2)、甲基硒代半胱氨酸(MeSeCys)、亚硒酸盐[Se(Ⅳ)]、硒代蛋氨酸(SeMet)、硒酸盐[Se(Ⅵ)]5种硒形态。样品经超纯水稀释后,采用Hamilton PRP-X100色谱柱(250 mm×4 mm,10μm)分离,以40 mmol/L磷酸氢二铵(含1%甲醇,pH 5)为流动相进行等度洗脱,13 min内可将5种硒形态分离。5种硒形态的线性范围为0～300.0μg/L,相关系数(r)均大于0.999,检出限为0.2～0.5μg/L。除SeCys_2的加标回收率为37.7%～70.4%外,MeSeCys、Se(Ⅳ)、SeMet、Se(Ⅵ)的加标回收率为80.0%～123%;5种硒形态的相对标准偏差(RSD)均不大于7.8%。应用该方法测定实际样品,结果显示人尿中硒形态主要以SeCys_2为主,同时含有少量MeSeCys、SeMet、无机硒及未知含硒化合物。     

ZIF-67 derived carbon wrapped discontinuous CoxP nanotube as anode material in high-performance Li-ion battery

Transition metal phosphides (TMPs) are prospective anode materials for lithium-ion batteries (LIBs) due to their high theoretical capacities and low redox voltages. Herein, we report a template directing method to develop a tube-sheath hybrid composing of cobalt phosphide particles encapsulated in metal organic frameworks (MOFs) derived N-doped carbon sheaths (Co_xP@NC). The utilization of directing template leads to a homogenous distribution of the subsequently formed cobalt phosphide particles, restrains the aggregation of cobalt phosphides, and thus results in the superb rate capability and cyclability. Contributable to the integrated merits of the interior downsized cobalt phosphide particles and the outer ZIF-67 derived porous carbon sheath, the volume expansion during cycling is effectively suppressed. The Co_xP@NC hybrid shows superb electrochemical performance as anode material for LIB, with good reversible capacity of 928 mAh·g^?1 after 100 cycles at 0.1 A g^?1, and high stability of 526 mAh·g^?1 after 600 cycles at 1.0 A g^?1. This work provides a route for rational design of MOF derived carbon-based anode material for LIB, which could also be applied as a promising platform in diverse field.     

Strategy for the Construction of Diverse Poly‐NHC‐Derived Assemblies and Their Photoinduced Transformations

A series of supramolecular assemblies of types [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H₄‐L(PF₆)₄ and Ag^I ions, is described. The assembly type obtained dependends on the N‐wingtip substituents of H₄‐L(PF₆)₄. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either [Ag₄( L )₂](PF₆)₄ or [Ag₈( L )₄](PF₆)₈ stoichiometry. The molecular structures of selected [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄ assemblies were determined by X‐ray diffraction analyses. While H₄‐ L (PF₆)₄ does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.     

An Unexpected Transannular [4+2] Cycloaddition during the Total Synthesis of (+)‐Norcembrene 5

We report a concise and versatile total synthesis of the diterpenoid (+)‐norcembrene 5 from simple building blocks. Ring‐closing metathesis and an auxiliary‐directed 1,4‐addition are the key steps of our synthetic route. During the synthesis, an unprecedented, highly oxidized pentacyclic structural motif was established from a furanocembranoid through transannular [4+2] cycloaddition.     

Trackable Supramolecular Fusion: Cage to Cage Transformation of Tetraphenylethylene‐Based Metalloassemblies

Herein, the trackable supramolecular transformation of a two‐component molecular cage to a three‐component cage through supramolecular fusion with another two‐component molecular square is described. The use of tetraphenylethene (TPE), a chromophore with aggregation‐induced emission (AIE) character, as a component for the molecular cages enables facile fluorescence monitoring of the transformation process: while both cages exhibit fluorescence emission via the restriction of intramolecular motion of the TPE motif, the interactions between TPE and 4,4′‐bipyridine introduced in the supramolecular fusion process result in partial fluorescence quenching and shifts in the emission maximum. This study provides a simple and efficient approach towards complex supramolecular cages with emergent functions and demonstrates that AIE features could provide unique opportunities for the characterization of complex, dynamic supramolecular transformation processes.     

Enhanced Propene/Propane Separation by Directional Decoration of the 12‐Membered Rings of Mordenite with ZIF Fragments

Propene/propane separation is challenging due to the very small difference in molecular sizes, boiling points and condensabilities between these molecules. Herein, we report a strategy of introducing ZIF fragments into traditional mordenite (MOR) zeolite to decorate the 12‐membered ring of MOR. After decoration, the originally ineffective zeolite MOR exhibited high kinetic propene/propane selectivities (139 at 25 °C) and achieved efficient propene/propane separation. The propene/propane separation potentials of the resulting adsorbents were further confirmed by breakthrough experiments with equimolar propene/propane (50/50) mixtures.     

Structure Determination of Alkynyl‐Protected Gold Nanocluster Au22(tBuC≡C)18 and Its Thermochromic Luminescence

An alkynyl‐protected gold nanocluster, Au₂₂(^tBuC≡C)₁₈ ( 1 ), has been synthesized and its structure has been determined by single‐crystal X‐ray diffraction. The molecular structure consists of a Au₁₃ cuboctahedron kernel and three [Au₃(^tBuC≡C)₄] trimeric staples. The cluster 1 has strong luminescence in the solid state with a 15 % quantum yield, and it displays interesting thermochromic luminescence as revealed by temperature‐dependent emission spectra. The enhanced room‐temperature emission is characterized as thermally activated delayed fluorescence.     

Molecular‐Sieving Membrane by Partitioning the Channels in Ultrafiltration Membrane by In Situ Polymerization

Commercial ultrafiltration membranes have proliferated globally for water treatment. However, their pore sizes are too large to sieve gases. Conjugated microporous polymers (CMPs) feature well‐developed microporosity yet are difficult to be fabricated into membranes. Herein, we report a strategy to prepare molecular‐sieving membranes by partitioning the mesoscopic channels in water ultrafiltration membrane (PSU) into ultra‐micropores by space‐confined polymerization of multi‐functionalized rigid building units. Nine CMP@PSU membranes were obtained, and their separation performance for H₂/CO₂, H₂/N₂, and H₂/CH₄ pairs surpass the Robeson upper bound and rival against the best of those reported membranes. Furthermore, highly crosslinked skeletons inside the channels result in the structural robustness and transfer into the excellent aging resistance of the CMP@PSU. This strategy may shed light on the design and fabrication of high‐performance polymeric gas separation membranes.     

Photoinduced Single‐Electron Transfer as an Enabling Principle in the Radical Borylation of Alkenes with NHC–Borane

A photoinduced SET process enables the direct B?H bond activation of NHC–boranes. In contrast to common hydrogen atom transfer (HAT) strategies, this photoinduced reaction simply takes advantage of the beneficial redox potentials of NHC–boranes, thus obviating the need for extra radical initiators. The resulting NHC–boryl radical was used for the borylation of a wide range of α‐trifluoromethylalkenes and alkenes with diverse electronic and structural features, providing facile access to highly functionalized borylated molecules. Labeling and photoquenching experiments provide insight into the mechanism of this photoinduced SET pathway.