Study of liquid crystal space groups using controlled tilting with cryogenic transmission electron microscopy

We developed a method that enables differentiation between liquid crystalline-phase particles corresponding to different space groups. It consists of controlled tilting of the specimen to observe different orientations of the same particle using cryogenic transmission electron microscopy. This leads to the visualization of lattice planes (or reflections) that are present for a given structure and absent for the other one(s) and that give information on liquid crystalline structures and their space groups. In particular, we show that we can unambiguously distinguish among particles having the inverted micellar cubic (space group Fd(3)m, 227), the inverted bicontinuous gyroid (space group Ia(3)d, 230), the inverted bicontinuous diamond (space group Pn(3)m, 224), and the inverted bicontinuous primitive cubic structure (space group Im(3)m, 229).     

Synthesis, structure and properties of intercalation compounds containing perfluoroalkyl groups

Synthesis, structure and properties of various layered materials containing perfluoroalkyl groups in their interlayer space were summarized. They were obtained by ion exchange method for layered materials with ion exchange capacity and by silylation technique for those possessing acidic hydroxyl groups. The orientation of perfluoroalkyl groups greatly changed depending on their contents in the layered materials. The nature of the interlayer space of them changed from hydrophilic to hydrophobic and they were well dispersed in appropriate organic solvents. Some of them formed so called nanosheet solution and film samples were prepared from it. Organic molecules were introduced into the intercalation compounds by co-adsorption or exfoliation-restacking methods. The empty space surrounded by perfluoroalky chains where organic molecules are included showed unique properties. The weak interaction between perfluoroalkyl chains and included organic molecules lead the easy diffusion of them in the interlayer space, which caused the aggregation of them or affected the distribution of isomers obtained by photochemical reaction. The low vibrational C-F bonding in perfluoroalky groups reduced radiational quenching, accordingly enhanced the fluorescence from included organic dyes.     

水煤浆添加剂与煤之间的相互作用规律研究 Ⅰ. 复合煤颗粒间的相互作用对水煤浆流变性的影响

使用12种不同分散剂对14种不同变质程度的煤进行了成浆性实验，分析了182个水煤浆(CWS)样品的流变性。结果表明，低变质程度和高灰煤浆多呈屈服假塑性，煤的性质起主导作用；变质程度高且灰分较低煤浆的流变性，主要依赖于分散剂的结构与性质；分子结构单元立体空间效应大，疏水基团与亲水基团呈立体间隔分布的分散剂，易形成屈服假塑性CWS；分子线度长，亲水基团与疏水基团呈线性间隔分布的分散剂，易形成胀塑性CWS。复合煤粒间的相互作用方式是决定CWS流变特性的关键。     

Fuzzy space periodic symmetries for polyynes and their cyano-compounds

In our previous papers on the molecular fuzzy symmetry, we analyzed the basic characterization in connection with the fuzzy point group symmetry. In this paper, polyynes and their cyano-derivatives are chosen as a prototype of linear molecules to probe the one-dimensional fuzzy space group of parallel translation. It is notable that the space group is an infinite group whereas the point group is a finite group. For the fuzzy point group, we focus on considering the fuzzy characterization introduced due to the difference of atomic types in the monomer through point symmetry transformation in the beginning; and then we consider the difference between the infinity of space group and the finite size of real molecules. The difference between the point group and the space group lies in the translation symmetry transformation. This is the theme of this work. Starting with a simple case, we will only analyze the one-dimensional translation transformation and space fuzzy inversion symmetry transformation in this paper. The theory of the space group is often used in solid state physics; and some of its conclusions will be referred to. More complicated fuzzy space groups will be discussed in our future papers.     

Study of the Chemical Space of Selected Bacteriostatic Sulfonamides from an Information Theory Point of View

The relative structural location of a selected group of 27 sulfonamide‐like molecules in a chemical space defined by three information theory quantities (Shannon entropy, Fisher information, and disequilibrium) is discussed. This group is composed of 15 active bacteriostatic molecules, 11 theoretically designed ones, and para‐aminobenzoic acid. This endeavor allows molecules that share common chemical properties through the molecular backbone, but with significant differences in the identity of the chemical substituents, which might result in bacteriostatic activity, to be structurally classified and characterized. This is performed by quantifying the structural changes on the electron density distribution due to different functional groups and number of electrons. The macroscopic molecular features are described by means of the entropy‐like notions of spatial electronic delocalization, order, and uniformity. Hence, an information theory three‐dimensional space (IT‐3D) emerges that allows molecules with common properties to be gathered. This space witnesses the biological activity of the sulfonamides. Some structural aspects and information theory properties can be associated, as a result of the IT‐3D chemical space, with the bacteriostatic activity of these molecules. Most interesting is that the active bacteriostatic molecules are more similar to para‐aminobenzoic acid than to the theoretically designed analogues.     

Polydispersity and Functional Group Distribution of Dispersant Polymer: Adsorption Properties and Magnetic Paint Dispersion

The quantitative analysis examining the functional group distribution of a dispersant polymer for magnetic paints is conducted by statistical estimation and adsorption experiments. The dispersant polymer contains averagely one or two functional groups on the chain, and has generally large polydispersity. By the calculation based on the random distribution of the functional group and the molecular weight, a typical design of the dispersant polymer is found to contain a significant amount of nonfunctionalized chains and highly functionalized ones. In adsorption experiments, the adsorbed amount of the polymer mass and the functional group are separately measured to determine the functional group distribution. The distribution is also evaluated by a sequential adsorption experiment, in which the chains are fractionated by the adsorption strength. Obtained experimental results agree with the calculated results. A practical method for increasing the effective chains in the paint is to make use of a preferential adsorption of the functionalized chain.     

Determination of the xanthate group distribution on viscose by liquid-state <Superscript>1</Superscript>H NMR spectroscopy

An analytical method for determination of the xanthate group distribution on viscoses based on liquid-state NMR spectroscopy was developed. Sample preparation involves stabilization of the xanthate group by allylation followed by derivatization of the remaining free hydroxyl groups at the glucose unit. The method was applied for studying (1) the γ-value (number of xanthate groups per 100 glucose units) of viscose, (2) the distribution of the xanthate groups on the anhydroglucose unit (AGU), and (3) changes of the xanthate group distribution during ripening. Results of the γ-value determination are well comparable with reference methods. Elucidation of the xanthate group distribution on the AGU gives the percentage at the C-6 position and a cumulative share of the positions C-2 and C-3. During ripening, xanthate groups at C-2 and C-3 degrade first, while xanthates at C-6 decompose at a slower rate.     

用AFM研究DL-缬氨酸晶体的结构及其表面分子的排列

利用原子力显微镜(AFM)成像技术来观察DL-缬氨酸晶体表面分子的规则排列, 研究表明对映体分子在DL-缬氨酸晶体中相互配对排列, 每个晶胞单元中包含两个对映体分子, 属于具有中心对称结构 群, 整个晶体是消旋的. 通过原子力显微镜对DL-缬氨酸晶体表面重复单元的测量结果与X衍射数据对比, 发现用AFM观察到的DL-缬氨酸晶体中分子表面形貌的规整排列的距离, 同X衍射得出的三斜晶系晶胞参数数据基本一致, 由此判定该晶体属于三斜晶系而不是单斜晶系. 探讨了利用纳米技术的研究手段在分子水平研究生命起源中的手性问题, 在确定的晶面上通过分子周期性结构排列规律, 对DL-缬氨酸晶体表面分子进行手性识别.     

Cs[Ag4Zn2(SCN)9]

Caesium tetrasilver dizinc nona­thio­cyanate, Cs[Ag₄Zn₂(SCN)₉], forms a continuous structure, where the Ag atoms and the S atoms of the thio­cyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P, but, if the latter space group is correct, the structure contains a thio­cyanate group disordered across a centre of inversion. The structure is described in space group P, in which the Cs atom also lies on a centre of inversion.     

Clinical efficacy of the liver scintigram--rates of interpretation of physiologically defective activity areas

Liver scintigrams of 406 cases were interpreted by 11 physicians. The ratios of the interpretation of the physiologically decreased activity areas in the liver scintigrams were 27% in the regions of the porta hepatis, 23% in the gall bladder fossa, 20% in the inferior vena cava, 7% in the renal impression, 2% in the portal vein, 2% in the rib impression and 2% in others. The cases having space occupying lesions showed decreased ratio of the interpretation of the physiologically decreased activity areas, as compared with other groups. Cases of the liver cirrhosis showed decreased ratio in the region of inferior vena cava. Cases using Anger camera demonstrated more increased ratio than cases using a scanner. The 11 physicians could be divided for two groups. One group showed high ratios of the interpretation of the physiologically decreased activity areas, and another group showed very low ratio, because of the different interpretation about the physiologically decreased activity areas in the two groups. In our cases, a very few cases showing decreased activity on the liver image were false positive or false negative for diagnosis of space occupying lesions.     

Electrophoresis of a biocolloid covered with a cation-absorptive membrane

The electrophoretic behavior of a biocolloid covered with a charged membrane is theoretically analyzed in the present study. Here, the influences of nonuniformly distributed fixed groups, absorption of cations by fixed original functional groups, variation in dielectric constant in the electrophoretic system, and ionic sizes are considered. The results of numerical simulation suggest that a larger absolute value of the electrophoric mobility of biocolloids could be generated by larger membrane electricity. The absolute value of the electrophoric mobility for the nonlinear distribution of the fixed groups is larger than that for the linear distribution of the fixed groups. The absolute value of the electrophoric mobility increases with (1) the concentration of total fixed groups, (2) the cation-absorption equilibrium constant, (3) the nonuniform feature index for functional-groups distribution, (4) the dielectric constants of the inner uncharged membrane zone for only mobile cationic charge and for both mobile cationic and anionic charge, and (5) the effective size of the cations. An increase in the absolute value of the electrophoric mobility can also be resulted from a decrease in the following parameters: (1) the friction coefficient of the biocolloidal membrane phase, (2) the membrane thickness, (3) the dielectric constant of space for all charge and of outer uncharged membrane zone, (4) the effective sizes of anions and fixed groups, and (5) the number of cations and the fixed original functional groups involved in the formation of a cation-functional group complex.     

Emulsion copolymerization of styrene with acrylic or methacrylic acids – distribution of the carboxylic group

Studies on batch emulsion copolymeization of styrene with acrylic acid (AA) or methacrylic acid (MAA) were carried out. The effect of AA or MAA on the total conversion of the monomers was studied by a gravimetric method. The distribution of the carboxylic group in the copolymer microspheres was investigated by X-ray photoelectron spectroscopy and elemental analysis. The surface content of the carboxylic groups of styrene (St)/AA copolymer microspheres was found to be higher than that of St/MAA copolymer microspheres. The effects of partial neutralization of MAA in emulsifier-free emulsion copolymerization and seeded emulsion copolymerization on the distribution of the carboxylic group was also investigated. Received: 14 December 1999/Accepted: 23 August 2000     

直线群及其在聚合物结构中的应用

对聚合物晶体中各种高分子链的构象进行了研究,找出了它们的三维对称性,并用直线群来表征。在此基础上,讨论了分子链在空间群中排布的规律性,即在空间群中高分子链的对称性与所在位置的对称性相呼应。并利用直线群讨论了有序-无序高分子链所在空间群转变的规律性。     

Influence of microstructure on space charges of polypropylene

The correlation of chemical structure, crystalline morphology, and space charge distribution under a dc electrical field was investigated with three kinds of poly(propylene) (PP) with a different chemical structure, that is, homogeneous PP and block copolymer and random copolymer of PP. The space charge distribution of the samples was prominently affected by their chemical sequence structure and crystalline microstructure. Among samples of different PPs, all isothermally crystallized at 140 °C, the sample of random coPP represents the most well proportional space charge distribution and the smallest number of space charges. The effect of thermal history on the space charge distribution was also investigated by the samples of block coPP. The sample thermally treated at 50 °C clearly represents a better proportional distribution than that at higher temperature of 140 and 100 °C. Subsequent experiments indicate that the better proportional distribution attributes to imperfect and fine sperulites with the fine distribution of the “amorphous” region. The imperfect and fine sperulites originate from the random incorporation of ethylene segments or units into PP chains or from the low annealing temperature, and play an important role in the formation of shallow traps and transportation of space charges. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 365–374, 2002; DOI 10.1002/polb.10100     

Predicted Influence of N-Acetyl Group Content on the Conformational Extension of Chitin and Chitosan Chains

ABSTRACT

Conformational analysis of chitosan molecules has been performed using the MM3(92) force field to investigate the role played by the acetamido groups on the stiffness of these chains. A high dielectric constant value was needed to model an aqueous environment and to reproduce the distribution of the N-acetyl glucosamine group orientation that is observed by NMR. Disaccharidic fragments, differently substituted at C2, were selected as models for chitin and chitosan chains. Their conformational space has been explored by means of adiabatic mapping of the glycosidic Φ,Ψ torsion angles. Although the overall features of all the potential energy surfaces created appear similar, the accessible conformational space of a glycosidic bond is affected by the nature of the substituent at C2 on the non-reducing residue of the disaccharide unit. This is illustrated by the differences in the calculated partition functions together with the predicted average homonuclear and heteronuclear coupling constants. Computed maps were used to predict polymeric unperturbed dimensions, characteristic ratio and persistence length of idealized chitin and chitosan chains, by Monte Carlo methods. Pure chitosan is predicted to be more coiled than pure chitin chains. At low N-acetyl group contents, chain extension appears to be dependent on the degree of substitution. Average chain dimensions increase monotonically for increases in content up to 60% of N-acetyl groups, but show no significant variation at higher contents. For molecules consisting of 50% amino and 50% N-acetylated residues, random, alternate and block patterns of substitution have been investigated. It has also been shown that the spatial extension of the polymer chains is dependent on the primary structure. Comparison with the literature experimental data is difficult because of the extreme diversity of the reported conformationally dependent values. However, such study provides a unique insight into the dependence of these two factors (degree of acetylation and distribution of acetyl groups) on the stiffness and flexibility of different chitin and chitosan chains.     

Hidden histidine radical rearrangements upon electron transfer to gas-phase peptide ions. Experimental evidence and theoretical analysis

Protonated peptides containing histidine or arginine residues and a free carboxyl group (His-Ala-Ile, His-Ala-Leu, Ala-His-Leu, Ala-Ala-His-Ala-Leu, His-Ala-Ala-Ala-Leu, and Arg-Ala-Ile) form stable anions upon collisional double electron transfer from Cs atoms at 50 keV kinetic energies. This unusual behavior is explained by hidden rearrangements occurring in peptide radical intermediates formed by transfer of the first electron. The rearrangements occur on a approximately 120 ns time scale determined by the radical flight time. Analysis of the conformational space for (His-Ala-Ile + H)(+) precursor cations identified two major conformer groups, 1a(+)-1m(+) and 5a(+)-5h(+) , that differed in their H-bonding patterns and were calculated to collectively account for 39% and 60%, respectively, of the gas-phase ions. One-electron reduction in 1a(+) and 5a(+) triggers exothermic hydrogen atom migration from the terminal COOH group onto the His imidazole ring, forming imidazoline radical intermediates. The intermediate from 5a is characterized by its charge and spin distribution as a novel cation radical-COO(-) salt bridge. The intermediate from 1a undergoes spontaneous isomerization by imidazoline N-H migration, re-forming the COOH group and accomplishing exothermic isomerization of the initial (3H)-imidazole radical to a (2H)-imidazole radical. An analogous unimolecular isomerization in simple imidazole and histidine radicals requires activation energies of 150 kJ mol(-1), and its occurrence in 1a and 5a is due to the promoting effect of the proximate COOH group. The rearrangement is substantially reduced in Ala-Leu-His due to an unfavorable spatial orientation of the imidazole and COOH groups and precluded in the absence of a free carboxyl group in His-Ala-Leu amide. In contrast to His-Ala-Ile and Arg-Ala-Ile, protonated Lys-Ala-Ile does not produce stable anions upon double electron transfer. The radical trapping properties of histidine residues are discussed.     

A geometrical approach to the degree of chirality and asymmetry

A new measure of the degree of chirality and asymmetry of a finite number of particles is proposed. To this end a space of configurations of identical particles is defined as the orbit space of the group of all permutations of particles embedded in an Euclidean space. This space is shown to be a metric space and the action of the translation and orthogonal groups is also defined. The results are applied to the study of an algebra of polynomials on the configuration space and its equivalence to the algebra of symmetric Cartesian tensors is demonstrated. An illustrative example is presented. Some general features of chirality are also briefly discussed.