Wild-type and molten globular chorismate mutase achieve comparable catalytic rates using very different enthalpy/entropy compensations

The origin of the catalytic power of enzymes with a meta-stable native state,e.g.molten globular state,is an unsolved challenging issue in biochemistry.To help understand the possible differences between this special class of enzymes and the typical ones,we report here computer simulations of the catalysis of both the well-folded wild-type and the molten globular mutant of chorismate mutase.Using the ab initio quantum mechanical/molecular mechanical minimum free-energy path method,we determined the height of reaction barriers that are in good agreement with experimental measurements.Enzyme-substrate interactions were analyzed in detail to identify factors contributing to catalysis.Computed angular order parameters of backbone N–H bonds and side-chain methyl groups suggested site-specific,non-uniform rigidity changes of the enzymes during catalysis.The change of conformational entropy from the ground state to the transition state revealed distinctly contrasting entropy/enthalpy compensations in the dimeric wild-type enzyme and its molten globular monomeric variant.A unique catalytic strategy was suggested for enzymes that are natively molten globules:some may possess large conformational flexibility to provide strong electrostatic interactions to stabilize the transition state of the substrate and compensate for the entropy loss in the transition state.The equilibrium conformational dynamics in the reactant state were analyzed to quantify their contributions to the structural transitions enzymes needed to reach the transition states.The results suggest that large-scale conformational dynamics make important catalytic contributions to sampling conformational regions in favor of binding the transition state of substrate.     

辉光放电质谱技术应用进展

对辉光放电质谱(GDMS)在金属与半导体、非导体、薄层与深度分析、分子信息分析方面的应用和一些新装置、新方法进行了综述.着重介绍了近20年来我国学者在辉光放电质谱方面的成就,并结合国际上的报道对该领域的发展现状进行了总结.     

New Entangled Coordination Networks Based on Charge‐Tunable Keggin‐Type Polyoxometalates

Investigation into a hydrothermal reaction system with transition‐metal (TM) ions, 1,4‐bis(1,2,4‐triazol‐1‐lmethyl)benzene (BBTZ) and various charge‐tunable Keggin‐type polyoxometalates (POMs) led to the preparation of four new entangled coordination networks, [Co^II(HBBTZ)(BBTZ)_2.5][PMo₁₂O₄₀] ( 1 ), [Cu^I(BBTZ)]₅[BW₁₂O₄₀] ? H₂O ( 2 ), [Cu^II(BBTZ)]₃[AsW^V₃W^VI₉O₄₀] ? 10 H₂O ( 3 ), and [Cu^II₅(BBTZ)₇(H₂O)₆][P₂W₂₂Cu₂O₇₇(OH)₂] ? 6 H₂O ( 4 ). All compounds were characterized by using elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. The mixed valence of W centers in compound 3 was further confirmed by using XPS spectroscopy and bond‐valence sum calculations. In the structural analysis, the entangled networks of 1 – 4 demonstrate zipper‐closing packing, 3D polythreading, 3D polycatenation, and 3D self‐penetration, respectively. Moreover, with the enhancement of POM negative charges and the use of different TM types, the number of nodes in the coordination networks of 1 – 4 increased and the basic metal–organic building motifs changed from a 1D zipper‐type chain (in 1 ) to a 2D pseudorotaxane layer (in 2 ) to a 3D diamond‐like framework (in 3 ) and finally to a 3D self‐penetrating framework (in 4 ). The photocatalytic properties of compounds 1 – 4 for the degradation of methylene blue under UV light were also investigated; all compounds showed good catalytic activity and the photocatalytic activity order of Keggin‐type species was initially found to be {XMo₁₂O₄₀}>{XW₁₂O₄₀}>{XW_12?nTM_nO₄₀}.     

A new two‐dimensional manganese(II) coordination polymer based on thiophene‐3,4‐dicarboxylic acid

A novel manganese coordination polymer, poly[(μ₅‐thiophene‐3,4‐dicarboxylato)manganese(II)], [Mn(C₆H₂O₄S)]_n, was synthesized hydrothermally using 3,4‐thiophenedicarboxylate (3,4‐tdc²⁻) as the organic linker. The asymmetric unit of the complex contains an Mn²⁺ cation and one half of a deprotonated 3,4‐tdc²⁻ anion, both residing on a twofold axis. Each Mn²⁺ centre is six‐coordinated by O atoms of bridging/chelating carboxylate groups from five 3,4‐tdc²⁻ anions, forming a slightly distorted octahedron. The Mn²⁺ centres are bridged by 3,4‐tdc²⁻ anions to give an infinite two‐dimensional layer which incorporates one‐dimensional Mn–O gridlike chains, and in which the 3,4‐tdc²⁻ anion adopts a novel hexadentate chelating and μ₅‐bridging coordination mode. The fully deprotonated 3,4‐tdc²⁻ anion exhibits unexpected efficiency as a ligand towards the Mn²⁺ centres, which it coordinates through all of its carboxylate O atoms to provide the novel coordination mode. The IR spectrum of the complex is also reported.     

Phase‐preserved macroscopic visible‐light carpet cloaking beyond two dimensions

Transformation optics, a recent geometrical design strategy of light manipulation with both ray trajectories and optical phase controlled simultaneously, promises an invisibility cloaking device that can render a macroscopic object invisible even to a scientific instrument measuring optical phase. Recent “carpet” cloaks have extended their cloaking capability to broadband frequency ranges and macroscopic scales, but they only demonstrated the recovery of ray trajectories after passing through the cloaks, while whether the optical phase would reveal their existence still remains unverified. In this paper, a phase‐preserved macroscopic visible‐light carpet cloak is demonstrated in a geometrical construction beyond two dimensions. As an extension of previous two‐dimensional (2D) macroscopic carpet cloaks, this almost‐three‐dimensional carpet cloak exhibits three‐dimensional (3D) invisibility for illumination near its center (i.e. with a limited field of view), and its ideal wide‐angle invisibility performance is preserved in multiple 2D planes intersecting in the 3D space. Optical path length is measured with a broadband pulsed‐laser interferometer, which provides unique experimental evidence on the geometrical nature of transformation optics.

     

二维配位聚合物[Tb(1,4⁃bdc)1.5(phen)(H2O)]n的合成、晶体结构及对Fe3+离子的荧光检测

通过溶剂热反应成功合成出一种新型2D配位聚合物[Tb(1,4-bdc)_1.5(phen)(H₂O)]_n(1)(1,4-H₂bdc=对苯二甲酸;phen=菲咯啉)。对其进行了单晶X射线衍射、粉末X射线衍射、红外光谱、元素分析、荧光光谱表征。X射线衍射晶体学分析表明,配合物1结晶于三斜晶系P1空间群,2个相邻的Tb(Ⅲ)离子与4个1,4-bdc^2-通过—O—C—O—桥联成双核单元,并进一步通过1,4-bdc^2-桥联成二维层状结构。荧光实验证明配合物1可以通过荧光猝灭机制检测Fe₃₊,Ksv=8.39×10³ L·mol-1,检测限为0.017μmol·L^-1。     

高中化学优质教学案例中教材分析的现状研究及分析模型建构*

以核心期刊《化学教育》2018-2021年高中化学教学设计及实施类文献为研究对象,在较完备的教材分析视角指引下,采用内容分析法研究优质教学案例中教材分析的现状及特点,在此基础上构建教材分析模型,探索优质教学案例的设计路径。     

利用三维虚拟技术突破物质结构教学*——从演示型工具到探索型工具的转变

针对物质结构教学的抽象性,开发了一套基于三维虚拟技术的物质结构教学软件,可对结构模型进行旋转、平移、缩放、切割、镜像、插入或删除原子(团)及启停预先设置的动画等操作,强大的交互功能不仅能对分子或晶体结构如构造异构、立体异构、晶体的堆积方式、晶胞的划分、配位数、晶体结构中的空隙及空间利用率等问题进行效果极佳的可视化教学,另一方面,通过对B₁₂与C₆₀分子空间构型转变的探究揭示数学构型的重要性,通过对六方晶胞占有原子个数的探究修正晶胞模型,通过对金属晶体的4种基本堆积方式成因的探究提出“半密置层”概念来完善紧密堆积规律等案例,展示出三维虚拟技术在微观结构探索发现方面的巨大潜力。     

计算化学在正丁醚制备实验教学中的应用*

正丁醚的制备是重要的大学有机化学实验,为提高学生对该实验所涉及的反应机理和关键操作要点的深入了解,采用Gaussian计算软件对正丁醇在酸催化下和无催化剂下的反应体系进行了研究,重点考察了酸催化下反应的主、副反应方向的反应机理。结果表明无催化剂下,正丁醇在常压液相下几乎不能发生反应;在酸催化下,正丁醇发生取代反应生成醚的反应路径是优势反应通道;酸催化下正丁醇的取代和消除反应速率常数均随温度增加而迅速增大,但消除反应的反应速率随温度增加更快,温度超过420 K消除反应将变得很明显,综合考虑,制备正丁醚的反应温度应控制在130~140 ℃之间较为合适。利用计算化学以图、表和动图等形式直观、动态、量化地解释了正丁醇成醚和成烯反应的竞争,该结果有助于更好地控制该反应体系,可用作实验教材的补充内容。     

结合PBL课例的无机化学线下对分课堂教学设计与实践*

以原电池一节教学设计为例,探索了将PBL课例融入对分课堂教学模式。教学实践表明,新教学模式激发了学生的学习兴趣,提高了学生学习的积极性和主动性,提升了课程教学效果,达到了课程教学目标。对PBL课例与对分课堂有机融合的全新课堂教学模式的建设与发展进行了展望。