温敏性纤维素/聚Ν-异丙基丙烯酰胺复合水凝胶的固体核磁共振表征及动力学研究

利用半互穿网络方法将具有温度响应的高分子聚N-异丙基丙烯酰胺( PNIPAM)与天然纤维素复合得到温敏性水凝胶。通过固体核磁共振的1 H,13 C CP/MAS(交叉极化/魔角旋转)和QCP(定量交叉极化)等实验手段对复合凝胶的结构进行了定性及定量研究,并利用固体静态变温核磁共振实验和偶极滤波-自旋扩散实验研究了复合凝胶中PNIPAM分子链段的动力学行为。     

Solventless Formation of G‐Quartet Complexes Based on Alkali and Alkaline Earth Salts on Au(111)

Template cations have been extensively employed in the formation, stabilization and regulation of structural polymorphism of G‐quadruplex structures in vitro. However, the direct addition of salts onto solid surfaces, especially under ultra‐high‐vacuum (UHV) conditions, to explore the feasibility and universality of the formation of G‐quartet complexes in a solventless environment has not been reported. By combining UHV‐STM imaging and DFT calculations, we have shown that three different G‐quartet‐M (M: Na/K/Ca) complexes can be obtained on Au(111) using alkali and alkaline earth salts as reactants. We have also identified the driving forces (intra‐quartet hydrogen bonding and electrostatic ionic bonding) for the formation of these complexes and quantified the interactions involved. Our results demonstrate a novel route to fabricate G‐quartet‐related complexes on solid surfaces, providing an alternative feasible way to bring metal elements to surfaces for constructing metal–organic systems.     

Determination of three kinds of banned drugs in milk powder by hybrid solid‐phase extraction purification combined with gas chromatography and mass spectrometry

A gradient clean‐up method for the quantification of five kinds of banned drugs (two hormones, two sedatives, and one chloramphenicol) in milk powder was developed. We used the combination of solid‐phase extraction purification with gas chromatography and mass spectrometry. Milk powder was initially hydrolyzed by β‐glucuronidase/arylsulfatase, and then the hydrolyzed solution was concentrated and purified using a C₈ and cation resin solid‐phase extraction column. To isolate hormones and chloramphenicol drugs, products from the previous step were diluted with methanol and further purified using a silica and diatomite solid‐phase extraction column. After derivatization, the drugs were analyzed by gas chromatography with mass spectrometry, and the hydrolyzed solution was diluted with 5% ammoniated methanol to purify sedatives before gas chromatography with mass spectrometry analysis. Results showed that after adding the banned drugs at concentrations of 0.3–10.0 μg/kg, the average recovery range was 78.2–97.3% with relative standard deviations of 5.3–12.5%. The limit of quantification of the banned drugs (S/N ≥ 10) was 0.3–5.0 μg/kg, whereas the limit of detection (S/N ≥ 3) was 0.1–2.0 μg/kg. The solid‐phase extraction gradient purification system was simple, rapid, and accurate, and could satisfy the detection requirements of hormone, sedatives, and chloramphenicol drugs when used together with gas chromatography and mass spectrometry.     

基于主客体竞争模式的凝血酶适配体传感器的研究

基于β-环糊精(β-CD)主客体竞争模式,构建了开关型凝血酶适配体电化学传感器.将末端修饰了二茂铁(Fc)的核酸适配体通过与β-CD的主客体识别固定在金电极表面,当凝血酶存在时,适配体由原来的直立线状构型变为"G-四链体",远离电极表面,适配体探针的氧化还原电流强度减小,即"Signal-off".利用此效应对凝血酶进行了灵敏检测,结果表明,在5.0×10-13~5.0×10-9 mol/L浓度范围内,凝血酶的浓度与电化学响应信号呈良好的线性关系,检出限为2.0×10-13 mol/L(3σ).与其它蛋白分子相比,本方法对凝血酶蛋白的检测具有高特异性.本传感器构建简单,再生性好,为生物血清样本中凝血酶的实时高效检测提供了方法.     

One step synthesis of Fe4.4Ni17.6Se16 coupled NiSe foam as self-supported,highly efficient and durable oxygen evolution electrode

The development of cost-effective, durable and high-efficient oxygen evolution reaction (OER) electrocatalysts is an extremely critical technology for the large-scale industrial water electrolysis. Here, a new strategy is proposed to significantly enhance the electrocatalytic activity by forming a hybrid electrode of NiSe and Fe_4.4Ni_17.6Se₁₆ through direct selenization of porous iron-nickel (FeNi) alloy foam via thermal selenization process. The obtained self-supported Fe_4.4Ni_17.6Se₁₆/NiSe hybrid (FNS/NiSe) foam displays outstanding durability and remarkable catalytic activity in 1.0 M KOH with low overpotentials of 242 and 282 mV to achieve the current densities of 100 and 500 mA cm^?2, respectively. To the best of our knowledge, it exceeds most of the reported OER electrocatalysts in alkaline electrolytes.     

手性高价碘试剂的发展及展望

在过去几十年中，高价碘化学已成为有机化学研究的重要领域.高价碘化合物在多种类型的化学转化中，展现与过渡金属相似的反应性质.而其温和的反应条件、低耗费、环境友好、低毒性等特点，使高价碘化学引起了广泛的研究兴趣，并取得了巨大的进展.手性的高价碘试剂或前体也得以发展并应用于一系列化学计量或催化的不对称反应.近年来，手性高价碘领域研究进展显著，但也存在诸多不足.在本综述中，根据其结构特点以及发展的时间线，对多种类型的手性高价碘试剂和前体做一个总结，这将有助于帮助本领域研究者更好地理解手性高价碘化学的发展以及不足之处.     

指向学习体验的物质及其转化复习的教学实践——以“钠及其化合物”为例

学习体验是学生对学习内容、过程、方法、意义的自我感受和评估,对学生学习志趣、学习素养提升有积极正向作用。以钠及其化合物复习为例,将各类别物质间转化关系的构建、物质制备原理和条件的优选作为学习体验对象,依据学习体验的内在发展历程设计学习任务及活动,引导学生亲身体验学科认知方式、学科思维方法、学科应用价值,评价体验结果,激励学生自主学习发生。     

一系列基于混合配体策略构筑的金属有机骨架的合成、结构及性质

通过简单高效的醛酮缩合反应,合成了碱性配体2,6-二（4-吡啶基亚甲基）环己酮（BPCH）,采用3种芳香羧酸配体：对苯二甲酸（H₂TP）、间苯二甲酸（H₂IP）和均苯三甲酸（H₃TMA）,以混合配体策略制备了7例金属有机骨架（MOFs）。用单晶X射线衍射、红外光谱、粉末X射线衍射和热重分析对其进行表征并分析其拓扑结构。MOFs1、2、3均呈现为多样的三维结构,MOFs4~7表现为同构的二维结构。荧光测试结果显示该类化合物对Fe³⁺有较好的荧光猝灭效应,同时对于染料具有一定的吸附能力。     

Thermodynamically Favourable States in the Reaction of Nitrogenase without Dissociation of any Sulfide Ligand

We have used combined quantum mechanical and molecular mechanical (QM/MM) calculations to study the reaction mechanism of nitrogenase, assuming that none of the sulfide ligands dissociates. To avoid the problem that there is no consensus regarding the structure and protonation of the E₄ state, we start from a state where N₂ is bound to the cluster and is protonated to N₂H₂, after dissociation of H₂. We show that the reaction follows an alternating mechanism with HNNH (possibly protonated to HNNH₂) and H₂NNH₂ as intermediates and the two NH₃ products dissociate at the E₇ and E₈ levels. For all intermediates, coordination to Fe6 is preferred, but for the E₄ and E₈ intermediates, binding to Fe2 is competitive. For the E₄, E₅ and E₇ intermediates we find that the substrate may abstract a proton from the hydroxy group of the homocitrate ligand of the FeMo cluster, thereby forming HNNH₂, H₂NNH₂ and NH₃ intermediates. This may explain why homocitrate is a mandatory component of nitrogenase. All steps in the suggested reaction mechanism are thermodynamically favourable compared to protonation of the nearby His-195 group and in all cases, protonation of the NE2 atom of the latter group is preferred.     

Zeolitic imidazolate framework-8 as a dispersive solid phase extraction sorbent for simultaneous determination of 145 pesticide residues in polyphenol-rich plants

Many plants have a high polyphenol content, which causes the matrix effect and makes the analysis of trace pesticide residues highly challenging. A common approach to improving matrix effects is to purify pesticides through the use of sorbents, but this requires a combination of multiple sorbents and extensive use. Zeolitic imidazolate framework-8 is widely used for pesticide analysis due to its high porosity, large specific surface area, and versatility. Here, we established and validated a modified quick, easy, cheap, effective, rugged, and safe method based on a zeolitic imidazolate framework-8 that was used to test the removal ability for polyphenols. To this end, 145 pesticide residues in peppermint, perilla, fennel, and mulberry leaves were analyzed by the modified method coupled with liquid chromatography with tandem mass spectrometry. The mean recoveries of all pesticide residues were in the range of 74.3–103.7%, with mean relative standard deviations ≤9.1% at spiked concentrations of 1, 10, 50, and 100 μg/kg for mulberry leaves. The limits of quantitation of the method ranged from 1 to 50 μg/kg. This study offers a reliable approach for the accurate quantitative analysis of various trace substances in the polyphenol-rich plants.