CONFORMATION AND CHAIN PACKING STRUCTURES OF POLY (ρ-PHENYLEN BENZOBISTHIAZOLE) BY MOLECULAR SIMULATION*

The conformation, the chain packing stabilization and the unit cell modeling of poly(p-phenylene benzobisthiazole) have been investigated by using molecular simulation techniquein the present work. A coupling behaviour of σ-bond rotations at either side of the pheny-lene ring or the heterocyclic ring was found surely to exceed a length of the repeat unit ofthe polymer chain. For a single chain model, the stable torsion angle of the repeat resultedat 14°. In the crystalline cell minimization, the dihedral angle along the polymer chaincould even be stabilized in various values. It therefore indicates that the intermolecularinteraction does play a considerable role for this polymer forming the conformation. Ac-cording to cohesive energies calculated for these unit cell models, the torsion angle in themost stable crystalline cell is 0°. When the chains packing together, there exist so manyenergy stable wells along the chain axis 0.35--0.36nm apart from neighbouring chains.Most of the unit cells have quite closed cohesive energies. These factors thus cause thedifficulty of forming an unique perfect crystalline structure of the polymer. The presentstudy suggested a number of reasonable unit cells, and the most stable crystalline structurefor this polymer that is monoclinic, non-primitive unit cell.     

Structural Micro-heterogeneities of Crystalline Iβ-cellulose

The crystal structure of the native Iβ-allomorph of cellulose [Nishiyama et al. 2002. J. Am. Chem. Soc. 124: 9074–9082] reveals subtle but significant conformational differences between the two different chains and also a multiplicity of positions of the hydrogen atoms of the HO₂ and HO₆ hydroxyl groups. Two structures differing in the hydrogen bonding networks were then proposed, however, the static or dynamic origin of the observed disorder remains to be specified. Molecular modelling was used to address this question: 18 minicrystal and 2 macrocrystal models of cellulose were generated differing by the initial orientations of the HO₂ and HO₆ hydroxyl groups; among which the two proposed structures (called N1 and N16) together with a random structure which respect the experimental percentage of hydroxyl hydrogen orientations. Results showed that only 10 of the studied combinations were stable, the major structure (N1) defined by crystallographers was estimated viable whereas not the minor one (N16). All the calculated data from the retained crystals, which describe the solid dimensions, the individual chain conformations and the supermolecular organisation, 1/ remained stable at their equilibrium value during the dynamics and 2/ were sensitive to the initial positions of the hydrogen atoms. Analysis of the hydrogen bonds revealed that sheet stacking might be stabilised by unexpected hydrogen bonds in addition to hydrophobic interactions. Our results thus favoured local disorders which involve a limited number of chains; they revealed the structural microheterogeneity of the Iβ-phase of cellulose and a complex disorder of its corresponding hydrogen bonding networks.     

聚苯硫醚及其聚醚砜共混物结晶形态的研究

本文借用偏光显微镜(PLM)、扫描电子显微镜(SEM)、小角激光光散射仪(SALS)及蚀刻的方法,研完了聚苯硫醚及其与聚醚砜共混物的结晶形态和织构,讨论了共混方法及其共混组成对其共混物的结晶形态的影响。结果表明,聚苯硫醚在应力作用下能生成横晶;溶液共混物和粉末机械共混物呈现不同的共混结晶形态;随着聚醚砜组分的增加,共混物的织构从聚苯硫醚为连续相逐渐转变为聚醚砜为连续相,同时,聚醚砜的聚集区域从分散在聚苯硫醚的球晶之间转变为聚集在聚苯硫醚的球晶内,使聚苯硫醚的球晶形态逐渐变得不规整。     

Crystalline degradation products of vancomycin as chiral stationary phase in microcolumn liquid chromatography

The ability of crystalline degradation products (CDPs) of vancomycin as a chiral stationary phase was reported in a previous study for enantioselective separation of drugs, amino acids and agrochemical toxins by conventional LC column (250 x 4.6 mm). In this work, the potential of CDP of vancomycin for the enantiomeric separation in micro-LC (200 x 1 mm) has been studied. The obtained separation results are better than in our previous study with conventional LC columns. The enantiomers of D,L-phenylalanine, D,L-alanine, methyldopa, atropine and propranolol were used for this evaluation. Experiments have been carried out in a stainless steel tube that was packed with chiral silica particles of 3 and 12 microm diameters. Also, three different ratios of 3 and 12 microm silica particles were used for packing material of chiral columns and the effect on aspect ratio and resolving powers was compared.     

Microporous membranes obtained from polypropylene blend films by stretching

Blends of two linear polypropylenes (PP, having different molecular weights) were prepared to develop microporous membranes through melt extrusion followed by stretching. The role of high molecular weight chains on the row-nucleated lamellar crystallization was investigated. The orientation of crystalline and amorphous phases was measured by wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). Long period spacing was obtained using small angle X-ray scattering (SAXS). The effects of annealing temperature and applied elongation during annealing on the crystallinity of the films were studied using differential scanning calorimetry (DSC). It was found that annealing at 140 °C contributed significantly to the perfection of the crystalline phase. Scanning electron microscopy (SEM) images of the membrane surface showed more pore density and uniform pore size as the amount of high molecular weight component increased. The addition of the high M_w PP improved the water vapor transmission rate (WVTR) of the membranes, indicating increased interconnectivity of the pores, which was also confirmed from cross-section SEM micrographs of the membranes. The surface area and pore dimensions of the microporous membranes were measured using the BET nitrogen absorption technique and mercury porosimetry, respectively. The influences of temperature and amount of stretching during cold and hot stretching on WVTR were also explored. Tensile properties in the machine and transverse directions (MD and TD, respectively) as well as puncture resistance in the normal direction (ND) were evaluated. As the high M_w PP was added, a slight reduction in the mechanical properties along MD and TD and no changes in ND were observed.     

Inside Back Cover: Rigid-Flexible Hybrid Porous Molecular Crystals with Guest-Induced Reversible Crystallinity (Angew. Chem. Int. Ed. 13/2023)

A weak CH/O hydrogen-bonded organic framework (HOF) with both rigidity and flexibility that could easily and reversibly switch from a non-crystalline to a crystalline phase was constructed. The specific solvent molecule acts as a “key” to control the crystallinity, while the highly rigid triangle macrocycle as the building block is the “lock”. The introduction and removal of the “key” could influence the local flexibility of the whole framework and lead to switchable crystallinity. Furthermore, the obtained HOF exhibits excellent separation efficiency for benzene and cyclohexane (94.4 %).     

NiMo(O)物相结构与电解水析氢反应活性的关联（英文）

在电催化析氢反应中,Ni Mo(O)催化剂在高电流密度下通常表现为极低的过电位。然而,该优异电催化性能的真正起源尚不明确。一个新的角度,即研究钼镍催化剂结构/性能演变的规律,能够帮助深入理解镍钼催化剂具有高活性的本质原因。基于此,本文详细阐述了含有结晶水的钼酸镍的脱水和氧化过程,在随后的还原处理中,该演变过程也被证实对于衍生不同的催化剂相结构具有重要作用。文中通过热重-差热分析以及程序升温氢气还原的方法探究电催化剂的特征相结构演变过程。同时,借助X射线衍射仪、拉曼光谱和高分辨透射电子显微镜分析确认催化剂物相。原位电化学X射线衍射分析提供了电催化剂在反应过程中的晶相结构。本文合成了具有不同主体相结构的钼镍催化剂：MoNi₄,β-NiMoO₄和α-NiMoO₄,它们的析氢反应活性具有显著差异。其中,β-NiMoO₄作为主体相结构的NiMoO₄-400air-H₂催化剂在碱性水还原反应中显现出最差的析氢性能;与之相比,α-NiMoO₄作为主...     

X-ray diffraction and heterogeneous materials: An adaptive crystallography approach

Cultural heritage materials are often complex and heterogeneous, with a multi-scale architecture. Phases from a variety of crystalline forms co-exist in a wide grain size distribution, with each of these phases keeping in their structural arrangement a memory of the transformations that occurred to the material. Over the last two decades, X-ray diffraction has been applied successfully to the study of cultural heritage materials, with the use of synchrotron facilities offering new possibilities to describe the structural features of such complex materials. The long-range and/or short-range organization of the different crystallographic phases as well as their global position/dispersion in the material are closely related to the properties of the material (optical, mechanical…), its manufacturing process, functionality, or long-term conservation. In this paper, possible diffraction setups and data collection strategies are discussed in order to retrieve adequate data from crystalline and amorphous phases and to take into account single-crystal contributions.     

Room temperature deposition of crystalline indium tin oxide films by cesium-assisted magnetron sputtering

Indium tin oxide (ITO) films were deposited on a Si (1 0 0) substrate at room temperature by cesium-assisted magnetron sputtering. Including plasma characteristics, the structural, electrical, and optical properties of deposited films were investigated as a function of cesium partial vapor pressure controlled by cesium reservoir temperature. We calculated the cesium coverage on the target surface showing maximum formation efficiency of negative ions by means of the theoretical model. Cesium addition promotes the formation efficiency of negative ions, which plays important role in enhancing the crystallinity of ITO films. In particular, the plasma density was linearly increased with cesium concentrations. The resultant decrease in specific resistivity and increase in transmittance (82% in the visible region) at optimum cesium concentration (4.24 × 10⁻⁴ Ω cm at 80 °C of reservoir temperature) may be due to enhanced crystallinity of ITO films. Excess cesium incorporation into ITO films resulted in amorphization of its microstructure leading to degradation of ITO crystallinity. We discuss the cesium effects based on the growth mechanism of ITO films and the plasma density.     

MoVOx催化甘油选择性氧化性能研究

通过添加亮氨酸/谷氨酸制备了MoVOx复合金属氧化物,考察了亮氨酸/谷氨酸添加浓度对MoVOx晶相组成及含量的影响。将制备的MoVOx用于催化甘油选择性氧化性能研究。研究表明,添加亮氨酸/谷氨酸能够抑制产物中V2O5的生成。与谷氨酸相比,添加亮氨酸可以进一步减少产物中MoO3的含量。此外,当添加谷氨酸摩尔比为Mo:V:Glu=1:1:0.5时制备的MoVOx呈现出特殊的多层片状结构,该样品(Mo/V/Glu-0.5)在催化甘油选择性氧化反应中表现出优异的性能,当催化反应温度为340 ℃时,甘油的转化率为98.17%,丙烯醛和丙酮选择性分别为45.96%和34.84%。此时,体系中MoV2O8和MoO3的含量分别为65.56%和34.44%,表明MoVOx催化甘油选择性氧化反应中MoV2O8和MoO3具有明显的协同效应。