Locating Hydrogen Positions for COF-300 by Cryo-3D Electron Diffraction

Covalent organic frameworks (COFs) have wide-ranging applications, and their host–guest interactions play an essential role in the achievement of COF functions. To investigate these host–guest interactions, it is necessary to locate all atoms, especially hydrogen atoms. However, it is difficult to determine the hydrogen atomic positions in COFs because of the complexities in synthesizing high-quality large single crystals. Three-dimensional electron diffraction (3D ED) has unique advantages for the structural determination of nanocrystals and identification of light atoms. In this study, it was demonstrated for the first time that the hydrogen atoms of a COF, not only on the framework but also on the guest molecule, can be located by 3D ED using continuous precession electron diffraction tomography (cPEDT) under cryogenic conditions. The host–guest interactions were clarified with the location of the hydrogen atoms. These findings provide novel insights into the investigation of COFs.     

X射线晶体学结合电子晶体学在复杂无机晶体结构解析中的应用

自然界中的材料,比如无机材料,有机材料,生物材料等等,均有其独特的物理和化学性质。而材料的性能又与材料的结构息息相关,只有充分了解了材料的结构,才能更加深入的研究材料性质。因此,材料结构的确定在化学、物理、生物等学科中的显得尤为重要。X射线晶体学作为传统的结构解析技术仍然是目前最重要的结构解析手段,但是对于复杂结构,X射线衍射晶体学解析结构也存在一些不足,往往需要其他技术手段相补充才能完成复杂结构的结构解析。电子晶体学虽然起步比X射线晶体学晚,但是,经过近几十年的发展,已经是结构解析领域一个非常重要的手段。本文将主要介绍X射线晶体学结合电子晶体学在复杂无机晶体结构解析中的应用。     

3D Electron Diffraction Unravels the New Zeolite ECNU-23 from the “Pure” Powder Sample of ECNU-21

A novel crystalline high-silica zeolite with 12×8-membered ring (R) channel system is prepared with the aid of the 3D electron diffraction (3D ED) technique. A crystal with the same topology as one of the predicted daughter structures of CIT-13 germanosilicate, named ECNU-23 (East China Normal University 23) was coincidentally detected by the 3D ED investigation during the structure characterization of the “pure” powder sample of existing one-dimension (1D) 10-R ECNU-21. By controlling the alkaline-assisted hydrolysis under moderate conditions, we purified the phase of ECNU-23 by selectively breaking and removing the chemically weak Ge(Si)-O-Ge and metastable Si-O-Si bonds. Its structure was determined based on the 3D ED data, and confirmed by high-resolution TEM images and powder X-ray diffraction (PXRD) data. The aluminosilicate Al-ECNU-23 shows unique catalytic properties in the isomerization/ disproportionation of m-xylene as solid-acid catalyst.     

3D Electron Diffraction Unravels the New Zeolite ECNU‐23 from the “Pure” Powder Sample of ECNU‐21

A novel crystalline high‐silica zeolite with 12×8‐membered ring (R) channel system is prepared with the aid of the 3D electron diffraction (3D ED) technique. A crystal with the same topology as one of the predicted daughter structures of CIT‐13 germanosilicate, named ECNU‐23 (East China Normal University 23) was coincidentally detected by the 3D ED investigation during the structure characterization of the “pure” powder sample of existing one‐dimension (1D) 10‐R ECNU‐21. By controlling the alkaline‐assisted hydrolysis under moderate conditions, we purified the phase of ECNU‐23 by selectively breaking and removing the chemically weak Ge(Si)‐O‐Ge and metastable Si‐O‐Si bonds. Its structure was determined based on the 3D ED data, and confirmed by high‐resolution TEM images and powder X‐ray diffraction (PXRD) data. The aluminosilicate Al‐ECNU‐23 shows unique catalytic properties in the isomerization/ disproportionation of m‐xylene as solid‐acid catalyst.     

Supramolecular Assembly and Chirality of Synthetic Carbohydrate Materials

Hierarchical carbohydrate architectures serve multiple roles in nature. Hardly any correlations between the carbohydrate chemical structures and the material properties are available due to the lack of standards and suitable analytic techniques. Therefore, designer carbohydrate materials remain highly unexplored, as compared to peptides and nucleic acids. A synthetic D -glucose disaccharide, DD , was chosen as a model to explore carbohydrate materials. Microcrystal electron diffraction (MicroED), optimized for oligosaccharides, revealed that DD assembled into highly crystalline left-handed helical fibers. The supramolecular architecture was correlated to the local crystal organization, allowing for the design of the enantiomeric right-handed fibers, based on the L -glucose disaccharide, LL , or flat lamellae, based on the racemic mixture. Tunable morphologies and mechanical properties suggest the potential of carbohydrate materials for nanotechnology applications.     

Image processing and lattice determination for three-dimensional nanocrystals

Three-dimensional nanocrystals can be studied by electron diffraction using transmission cryo-electron microscopy. For molecular structure determination of proteins, such nanosized crystalline samples are out of reach for traditional single-crystal X-ray crystallography. For the study of materials that are not sensitive to the electron beam, software has been developed for determining the crystal lattice and orientation parameters. These methods require radiation-hard materials that survive careful orienting of the crystals and measuring diffraction of one and the same crystal from different, but known directions. However, as such methods can only deal with well-oriented crystalline samples, a problem exists for three-dimensional (3D) crystals of proteins and other radiation sensitive materials that do not survive careful rotational alignment in the electron microscope. Here, we discuss our newly released software AMP that can deal with nonoriented diffraction patterns, and we discuss the progress of our new preprocessing program that uses autocorrelation patterns of diffraction images for lattice determination and indexing of 3D nanocrystals.     

Chemical Preparation,Spectroscopic Study and Crystal Structure of DL 2-Ammoniumbutyric Dihydrogenmonophosphate ({\rm CH_3CH_2CHCOOH)(H_2PO_4)^{\hbox{\bf --}}}\vspace*{-2pt}\break\hspace*{-26pt}|\hspace*{26pt}\break\hspace*{-24pt}{^{\bm +}}{\rm NH_3}\hspace*{24pt}}

Crystals of DL 2-ammoniumbutyric dihydrogenmonophosphate were obtained by evaporating an aqueous solution containing equimolar quantities of DL 2-amino butyric and orthophosphoric acids. IR and NMR spectrometry studies has been investigated and confirmed by X-ray single crystal diffraction results. The title compound is monoclinic, space group P2 1 /c, unit cell dimensions a = 10.5450(3) Å, b = 10.0486(3) Å, c = 8.9526(4) Å, g = 111.769(5);. Using 1,303 reflections with I > 3 (I) measured on CAD4 Mach 3 diffractometer, the crystal structure was solved by direct methods and was refined by least squares full matrix procedures to R = 0.038. The main feature of this structure consists of an alternate stacking of H 2 PO 4 m tetrahedral sheets and NH 3 C 3 H 6 COOH + cation layers. The H 2 PO 4 m groups are associated to form infinite chains [(H 2 PO 4 )n] n m . The crystal structure is stabilized by a three-dimensional network of strong hydrogen bonds.     

Unprecedented zeolite-like framework topology constructed from cages with 3-rings in a barium oxonitridophosphate

A novel oxonitridophosphate, Ba(19)P(36)O(6+x)N(66-x)Cl(8+x) (x ≈ 4.54), has been synthesized by heating a multicomponent reactant mixture consisting of phosphoryl triamide OP(NH(2))(3), thiophosphoryl triamide SP(NH(2))(3), BaS, and NH(4)Cl enclosed in an evacuated and sealed silica glass ampule up to 750 °C. Despite the presence of side phases, the crystal structure was elucidated ab initio from high-resolution synchrotron powder diffraction data (λ = 39.998 pm) applying the charge flipping algorithm supported by independent symmetry information derived from electron diffraction (ED) and scanning transmission electron microscopy (STEM). The compound crystallizes in the cubic space group Fm ?3c (no. 226) with a = 2685.41(3) pm and Z = 8. As confirmed by Rietveld refinement, the structure comprises all-side vertex sharing P(O,N)(4) tetrahedra forming slightly distorted 3(8)4(6)8(12) cages representing a novel composite building unit (CBU). Interlinked through their 4-rings and additional 3-rings, the cages build up a 3D network with a framework density FD = 14.87 T/1000 ?(3) and a 3D 8-ring channel system. Ba(2+) and Cl(-) as extra-framework ions are located within the cages and channels of the framework. The structural model is corroborated by (31)P double-quantum (DQ) /single-quantum (SQ) and triple-quantum (TQ) /single-quantum (SQ) 2D correlation MAS NMR spectroscopy. According to (31)P{(1)H} C-REDOR NMR measurements, the H content is less than one H atom per unit cell.     

The Crystal Structure of Orthocetamol Solved by 3D Electron Diffraction

Orthocetamol is a regioisomer of the well‐known pain medication paracetamol and a promising analgesic and an anti‐arthritic medicament itself. However, orthocetamol cannot be grown as single crystals suitable for X‐ray diffraction, so its crystal structure has remained a mystery for more than a century. Here, we report the ab‐initio structure determination of orthocetamol obtained by 3D electron diffraction, combining a low‐dose acquisition method and a dedicated single‐electron detector for recording the diffracted intensities. The structure is monoclinic, with a pseudo‐tetragonal cell that favors multiple twinning on a scale of a few tens of nanometers. The successful application of 3D electron diffraction to orthocetamol introduces a new gold standard of total structure solution in all cases where X‐ray diffraction and electron‐microscope imaging methods fail.     

Chiral Phosphine Ligands Derived fro m Sugars .14 . Crystal Structure of Diphenyl( m ethyl4’,6’-O-benzylidene-3’-deoxy-α- D-altropyranoside-3-)phosphine Oxide

１　ＩＮＴＲＯＤＵＣＴＩＯＮＣｈｉｒａｌｐｈｏｓｐｈｉｎｅｓａｒｅｕｓｅｆｕｌｌｉｇａｎｄｓｉｎｅｎａｎｔｉｏｓｅｌｅｃｔｉｖｅｃａｔａｌｙｓｉｓｗｉｔｈｔｒａｎｓｉｔｉｏｎｍｅｔａｌｃｏｍｐｌｅｘｅｓ〔１〕，ｓｏｍｅｏｆｔｈｅｍｄｅｒｉｖｅｄｆｒｏｍｓｕｇａｒｓａｒｅａｌｓｏｏｆｐｏｔｅｎｔｉａｌａｐｐｌｉｃａｔｉｏｎｓｉｎｂｉｐｈａｓｉｃｃａｔａｌｙｓｉｓ〔２〕ａｎｄｍｅｄｉｃｉｎｅ〔３〕．Ｂｙｔｈｅｎｕｃｌｅｏｐｈｉｌｉｃｒｅｐｌａｃｅｍｅｎｔｒｅａｃｔｉｏｎ，ｉｔｉｓｄｉｆｆｉｃｕｌ…     

结晶性间同立构1,2-聚丁二烯的单晶结构

近十几年来 ,结晶性间同立构 1 ,2 -聚丁二烯引起人们的广泛关注 ,但绝大多数研究工作集中在聚合物的制备、物理性质和应用方面[1～ 3] ,对于其结晶行为和晶体结构则未见报道 .原因是间同立构 1 ,2 -聚丁二烯分子侧链含有大量的双键 ,在较高温度下很容易交联 ,特别是高间规度的聚合物 ,由于其熔融温度高 (>2 0 0℃ )则更易产生交联 ,这给结晶行为和结构研究带来很大困难 .结晶性间同立构 1 ,2 -聚丁二烯的晶体结构为平面锯齿链正交堆砌 ,Pacm空间群[4 ] .我们曾报道了结晶性间同立构 1 ,2 -聚丁二烯的合成和溶液浇铸膜的板条状结构[5] ,本…     

极性金属间化合物MgIn2的合成、晶体结构及能带特征

在惰性气氛氩气保护下,通过高温固相反应合成得到了一个二元极性金属间化合物MgIn2。经X-射线单晶衍射与元素分析等方法确定了其晶体结构。MgIn2属立方体系,空间群为Fd3m(No.227),晶体学参数a=0.956 13(16)nm,V=0.874 1(3)nm3,Z=8,R1=0.035 3,wR2=0.082 8。MgIn2属于CaAl2结构类型,其结构特征为[In4]四面体通过共用顶点In原子链接而成的三维框架结构,Mg原子填充在三维框架的空隙中。能带结构计算表明MgIn2属于金属性的化合物。     

Chagas Disease: Perspectives on the Past and Present and Challenges in Drug Discovery

Chagas disease still has no effective treatment option for all of its phases despite being discovered more than 100 years ago. The development of commercial drugs has been stagnating since the 1960s, a fact that sheds light on the question of how drug discovery research has progressed and taken advantage of technological advances. Could it be that technological advances have not yet been sufficient to resolve this issue or is there a lack of protocol, validation and standardization of the data generated by different research teams? This work presents an overview of commercial drugs and those that have been evaluated in studies and clinical trials so far. A brief review is made of recent target-based and phenotypic studies based on the search for molecules with anti-Trypanosoma cruzi action. It also discusses how proteochemometric (PCM) modeling and microcrystal electron diffraction (MicroED) can help in the case of the lack of a 3D protein structure; more specifically, Trypanosoma cruzi carbonic anhydrase.     

Crystal structure and fluorescence of supramolecular compound [Cd3Cl6C6N2O8H22]n

A novel trinuclear supramolecular compound of [Cd₃Cl₆C₆N₂O₈H₂₂] _n has been synthesized under alanine with cadmium chloride to the reaction in aqueous solution conditions, and characterized by elemental analyses, FT-IR spectroscopy, X-ray diffraction, DTA-TG. Its crystal structure was determined from single crystal X-ray diffraction. The title compound crystallizes in monoclinic system with space group P2₁/n. The crystal structure of the compound is characterized by forming a trinuclear 3D supramolecular structure with three cadmium(II) ions, six chloride ions, two molecules D, L-alanine in salt, two coordinated water molecules and two crystal water molecules. Cd(1) is distorted octahedrally coordinated with two oxygen atoms (from the adjacent amino acid and water molecule) and four chloride ions; Cd(2) is smaller extent distorted octahedrally coordinated with two oxygen atoms (from the adjacent amino acids) and four chloride ions. Cd(1) and Cd(2) connected by the bridge bonds of μ₂-Cl, μ₃-Cl and the carboxyl oxygen into ID chain structure, which further connected by hydrogen bonds to form 3D supramolecular network. Fluorescence test showed that the compound has a good photoluminescence property, respectively.     

4,4′-联吡啶多钼酸盐的合成、结构与变色性质

通过水热合成法,合成了4,4′-联吡啶多钼酸盐((4,4′-bipyridine)Mo7O22·H2O)单晶超分子化合物.通过元素分析、热重-差热分析(TG-DTA)、粉末X射线衍射(XRD)、单晶X射线衍射、傅里叶变换红外(FTIR)光谱、紫外-可见漫反射光谱(UV-VisDRS)和电子自旋共振(ESR)技术对其组成、热稳定性、结构、光谱和电子特性进行了表征.实验结果表明:该超分子化合物的分子式为C10H12Mo7N2O23,在空气中320℃以下不分解.属于单斜晶系(空间群为P2/n),晶胞参数为a=1.22561(19)nm,b=0.55222(9)nm,c=1.8385(3)nm,β=103.221(2)°,V=1.2113(3)nm3,Z=2和Dc=3.289g·cm-3.基于F2的最终统计:GOF=0.982,R1=0.0228和wR2=0.0557(I2σ(I)).该单晶超分子化合物由质子化的4,4′-联吡啶阳离子和多金属钼酸盐阴离子[Mo7O22]2-及结晶水组成.它们通过氢键、静电引力和分子间作用力结合在一起的,并构成二维网络结构.样品在光照或加热条件下具有光致变色和热致变色性质.XRD和FTIR证明,变色前后,样品的结构除轻微的畸变外几乎没有变化;而ESR结果表明,光致变色与热致变色的机理可能存在差别.该光致和热致变色的超分子化合物能够为变色机理研究提供参考模型,并在传感器和光敏材料等领域具有潜在应用.     

Determination of the Crystal Structure of a New Polymorph of Theophylline

A new approach to crystal structure determination, combining crystal structure prediction and transmission electron microscopy, was used to identify a potential new crystal phase of the pharmaceutical compound theophylline. The crystal structure was determined despite the new polymorph occurring as a minor component in a mixture with Form II of theophylline, at a concentration below the limits of detection of analytical methods routinely used for pharmaceutical characterisation. Detection and characterisation of crystallites of this new form were achieved with transmission electron microscopy, exploiting the combination of high magnification imaging and electron diffraction measurements. A plausible crystal structure was identified by indexing experimental electron‐diffraction patterns from a single crystallite of the new polymorph against a reference set of putative crystal structures of theophylline generated by global lattice energy minimisation calculations.     

Taibaihenryiin C的构型、构象及晶体结构

从太白山产的鄂西香茶菜中分离得到新骨架的二萜类化合物TaibaihenryiinC,对其进行X射线衍射晶体结构分析,确定其分子中各取代基的相对构型、环构象及晶体结构.研究表明,C-3位的羟基和C-11位的乙酰氧基以C-20位的甲基为参考均位于β位;分子中的A环为椅式构象,B,C环接近于船式构象,D环接近于信封式构象.特别是在D环中存在较大的扭转角,使D环中有内应力存在,这表明该化合物具有潜在的生理活性.TaibaihenryiinC的晶体结构属正交晶系,P2₁2₁2₁空间群,晶胞参数a=0.6162(1)nm,b=1.2730(1)nm,c=2.5193(3)nm,Z=4.在晶体中分子间通过C-3位的-OH氢与C-11位的乙酰氧基上的羰基氧形成分子间氢键,使分子在晶体中沿a轴呈螺旋结构排列.     

Isostructural Three‐Dimensional Covalent Organic Frameworks

Herein, we reported the designed synthesis of three isostructural three‐dimensional covalent organic frameworks (3D COFs) with ‐H, ‐Me, or ‐F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9–1.0 Å, enabling the localization of all non‐hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO₂ over N₂. We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.     

Folded chain crystallization of random terpolymer liquid crystal polymers from the nematic state

The morphology of ca. equimolar random terpolymer liquid crystal polymers of an aliphatic segment of 4–7 carbon atoms, oxybenzoate, and dioxyphenyl crystallized from the nematic state in the form of thin films on glycerine by slow cooling and quenching has been characterized by electron microscopy (TEM) and diffraction (ED). In all cases a folded chain, lamellar structure is found. The ED studies suggest adjacent reentry, and despite a large ΔH, indicate no change in lateral molecular packing at the crystal-“liquid crystal” transition with a transformation to the nematic state at a higher temperature “liquid crystal”-liquid crystal transition. The results are interpreted as suggesting similar folded chain, lamellar morphology in the nematic state. © 1992 John Wiley & Sons, Inc.     

Thermal properties and morphology of crystal in nylon 1010 formed isothermally at melting peak temperature

Thermal properties and morphology of crystal in NYLON 1010 formed isothermally at melting peak temperature were studied by using DSC, TEM and ED. It turns out that the crystal on the time scale of the DSC experiment is stable, which is not transformed from the crystal with low melting point. Its electron diffraction pattern shows symmetrical and clear electron diffraction spots of single crystal and is proved to be the electron diffraction pattern of single crystal by means of index with parameters of unit cell of Nylon 1010