Predicted secondary structure and membrane topology of the scrapie prion protein

The integral membrane sialoglycoprotein PrP^Sc is the only identifiablecomponent of the scrapie prion. Scrapie in animals and Creutzfeldt-Jakobdisease in humans are transmissible, degenerative neurologicaldiseases caused by prions. Standard predictive strategies havebeen used to analyze the secondary structure of the prion proteinin conjunction with Fourier analysis of the primary sequencehydrophobicities to detect potential amphipathic regions. Severalhydrophobic segments, a proline- and glycine-rich repeat regionand putative glycosylation sites are incorporated into a modelfor the integral membrane topology of PrP. The complete aminoacid sequences of the hamster, human and mouse prion proteinsare compared and the effects of residue substitutions upon thepredicted conformation of the polypeptide chain are discussed.While PrP has a unique primary structure, its predicted secondarystructure shares some interesting features with the serum amyloidA proteins. These proteins undergo a post-translational modificationto yield amyloid A, molecules that share with PrP the abilityto polymerize into birefringent filaments. Our analyses mayexplain some experimental observations on PrP, and suggest furtherstudies on the properties of the scrapie and cellular PrP isoforms.     

几种不同来源食用明胶的蛋白二级结构分析及安全性能比较

用傅里叶变换红外光谱仪和圆二色谱仪对四种不同来源食用明胶的蛋白二级结构组成、重金属含量进行了分析。结果表明,四种食用明胶的二级结构均以β-sheet为主,且含有β-turn结构,其中鱼鳞明胶和猪皮明胶还含有大量的310-helix结构,鱼皮明胶和猪皮明胶含有α-helix结构,鱼鳞明胶和牛骨明胶的无序结构含量较高。四个明胶样品的重金属指标均符合国内相关标准,其中牛骨明胶的重金属含量最低,安全性最高。     

The structure and properties of acrylic‐polyurethane hybrid emulsions and comparison with physical blends

Aqueous acrylic‐polyurethane hybrid emulsions were prepared by semibatch emulsion polymerization of a mixture of acrylic monomers (butyl acrylate, methyl methacrylate, and acrylic acid) in the presence of polyurethane dispersion. Equivalent physical blends were prepared by mixing acrylic emulsion and polyurethane dispersion. The weight ratio between acrylic and polyurethane components varied to obtain different emulsion properties, microphase structure, and mechanical film properties of hybrid emulsions and physical blends. Particle size and molecular mass measurements, scanning electron microscopy, glass transition temperature, and rheological measurements performed characterization of the latex system. The mechanical properties were investigated by measuring tensile strength and Koenig hardness of dried films. The experimental results indicate better acrylic‐polyurethane compatibility in hybrid emulsions than in physical blends, resulting in improved chemical and mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 67–80, 2000     

The predicted secondary structure of the G-type glutamineamidotransferase is compatible with TEM-barrel topology

Glutamine amidotransferase (GAT) subunits or domains catalyzean important partial reaction in many complex biosynthetic reactions.The structure of one member of the F-type GATs is known, butthe structure of the unrelated G-type is still unknown. Becausemany protein sequences are available for anthranilate synthasecomponent II (product of the trpG gene), we have predicted itsaverage secondary structure by a joint prediction method [Niermannand Kirschner (1991a) Protein Engng, 4, 359–370]. Thepredicted eight ß-strands and seven -helices followan 8-fold cyclic repetition of a ß-strand-loop--helix-loopmodule with helix 7 missing. This pattern of secondary structuresuggests that the G-type GAT domain has an 8-fold ß-barreltopology, as found first in triose phosphate isomerase (TIM-barrel).This model is supported by the location of known catalyticallyessential residues in loops between (ß-strands and-helices. Evidence from published sequencing and mutationalstudies on selected members of the GAT superfamily (carbamoylphosphate, imidazoleglycerol phosphate, GMP and CTP synthases)support both the secondary structure prediction and the TIM-barreltopology.     

The influence of basecoat pigmentation on chemical structure and surface topology of automotive clearcoats during weathering

The present study aims at elucidating the effect of basecoat pigmentation on the chemical structure and surface topology of its attached clearcoat during weathering exposure. Two extremes of differently behaviored basecoat pigmentations (i.e. silver and black) were chosen. Different analyses such as FTIR, ATR, surface energy measurements and AFM were carried out on such coatings after they were subjected to accelerated weathering conditions. It was found that the black basecoat procured more post-curing reactions to the attached clearcoat at initial weathering times, while the silver basecoat induced higher degrees of photodegradations during the whole time of weathering. Such inductions were attributed to the inherent absorptive or reflective behavior of the black or the silver basecoats toward incident radiation.     

The structure and dynamics of adsorbed molecules in microporous solids; a comparison between experiments and computer simulations

A critical evaluation is made of the results of computer simulations of adsorbed molecules in microporous inorganic materials. Structural, thermochemical and dynamic data are compared with the corresponding experimental findings. The systems examined include inert gases and simple alkanes in zeolites Na-Y and silicalite, benzene and pyridine in Na-Y and K-L, respectively, andp-xylene in silicalite. Future developments in the area are also discussed.     

Strength and deformation of rigid polymers: structure and topology in amorphous polymers

Glassy polymer is formed because the irregular chain architecture prevents crystallisation. Computer simulations allow Voronoi tessellation of atomic groups (for example monomers) to be carried out and measured along the molecular chain, which reveals significant density fluctuations. A Voronoi polyhedron is constructed for each particle according to a unique mathematical procedure [J Reiner Angew Math 134 (1908) 198]. When measured in terms of Voronoi polyhedra, amorphous structures show wide variations in packing density on the atomic/monomer scale, with a characteristic skewed distribution. The Voronoi method can be applied to all polymers; however, in this paper only uncrosslinked amorphous polymers are considered. Constriction points around a chain segment are defined as a locally specific configuration and arrangement of adjacent chains such that the local density within a sphere of radius approximately equal to two monomer diameters comes close to or below the hypothetical crystalline density. The topological theory of molecular structure developed by Bader defines the concepts of atoms and bonds in terms of the topological properties of the observable charge distribution [Rep Prog Phys 44 (1981) 893]. In polymers the high density regions become an even stronger topological feature, and are referred to as the constriction points.     

快速升降模型制品平板硫化机结构设计的改进

传统的平板硫化机液压系统能耗大,柱塞的往复运动依靠缸体导向,磨损后修复困难,经过改造后,增加了快速油缸,改造密封,改进控制系统,使升降平板硫化机的主要技术性能参数较原来的要优化的多、主要执行元件——柱塞的运动速度提高了,液压缸密封导向环的改造使整个液压系统更加完善。     

Surface structure,topology, and liquid wetting behavior in oriented polymers

The structure and the properties of oriented polymer surfaces were studied for three series of uniaxially oriented films of polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET). The surface structure was characterized in terms of relative crystallinity and molecular orientation along with topology and roughness by using FT-IR-ATR dichroism technique, optical microscopy and surface profilometer. In all three polymers, the surface orientation function increases with draw ratio. The relative surface crystallinity and the trans con-former also increases for PP and PET, respectively. In uniaxially drawn PP, the surface becomes rough with increasing draw ratio and the roughness is anisotropic with peaks and valleys elongated along the draw direction. For drawn PP, the equilibrium contact angles for four different liquids all exhibit anisotropy with higher values in perpendicular direction than that in parallel to the draw direction. In contrast, both drawn PET and PS films show smooth surfaces, and the equilibrium contact angles were all isotropic. When roughness is removed from the drawn PP by polishing without altering the molecular orientation, the anisotropy becomes negligible and the contact angles approach the value for undrawn PP. When surface roughness was created deliberately on undrawn PET and PS films, the contact angle anisotropy was clearly observed. Therefore, the anisotropy in surface topology rather than the molecular orientation seems to play a dominant role in developing anisotropic wetting behavior. The equilibrium contact angles for smooth surfaces have been calculated using the experimentally obtained roughness and anisotropic contact angle data from the rough surface. These values are in reasonable agreement with the measured contact angles for smooth surfaces, suggesting that the observed contact angle anisotropy can be attributed entirely to the roughness anisotropy rather than to the molecular orientation.     

Effect of molecular structure and topology on network formation in peroxide crosslinked polyethylene

The present study compared the crosslinking performance of single site linear low density polyethylenes (LLDPE) with high pressure, free radical polymerised, low density polyethylenes (LDPE). The difference in crosslinking performance is not fully explained by different structural parameters such as molar mass distribution (MMD), M_n, MFR₂ value and vinyl groups but is related more to the phenomenon of a long chain branched LDPE macromolecule being smaller in size in the molten state than a macromolecule of a linear LLDPE sample of the same molar mass. The result of the difference in size is that the LDPE will contain a larger number of intramolecular crosslinking points than the LLDPE, which, on the other hand, will contain a larger fraction of intermolecular crosslinking points. The crosslinking points mentioned are of either a physical or chemical nature. From the perspective of the network build-up, the intermolecular crosslinking points are the most efficient. To compensate for the larger fraction of intramolecular crosslinking points in LDPE, more peroxide can be added or vinyl groups can be introduced.     

国外大型液压压砖机主体结构的分析比较

大型液压自动压砖机 (40 0 0ｔ级以上 )是目前我国陶瓷墙地砖自动化生产线中唯一仍要全部引进的关键设备。压砖机的大型化对压砖机的设计及制造技术都提出了新的挑战———以合理的结构、尽可能少的原材料和能耗 ,实现大规格砖坯 (80 0 × 80 0 以上 )的高效率压制成形。目前所知的大型压砖机有萨克米公司的威力系列ＰＨ 42 0 0型、ＰＨ 72 0 0型 ;纳萨蒂公司的ＶＩＳ5 0 0 0型 ;西蒂公司的 72 0 0型 ;莱斯公司的阿尔法 0 5系列 42 0 0型。莱斯公司的新型欧米伽 30 0 0型压砖机虽然在压制吨位上只有 30 0 0ｔ ,但其结构颇具特色。因此笔者…     

Synthesis,structure and properties of two new 3D frameworks with primitive cubic topology

Two new three-dimensional (3D) coordination polymer [Cu₂(tetrazolate)₃(OH)]_n (1) and [Cd₂(tetrazolate)₃Br]_n (2) were synthesized and structurally characterized. By the topology analysis, the complicated architecture of 1 and 2 are all simplified to be the 6-connected pcu-type net. The variable-temperature magnetic susceptibilities (5–300 K) of 1 shows antiferromagnetic interactions of copper(II) ions bridged tetrazolate ligands and/or hydroxide anion.     

Interlaboratory comparison of soybean protein and oil determinations

Iowa State University coordinated an interlaboratory comparison study of Kjeldahl protein and ether oil extraction methods. Blind duplicates of 10 clean, single-variety soybean samples were sent to 30 laboratories grouped in 3 categories of 10 each in public (government and university), commercial and processor facilities. Five of the commercial laboratories were AOCS-certified. Standard deviations among laboratory means across all samples were 3.87 and 1.82 percentage points (dry basis) for protein and oil, respectively (0.48 and 0.27, respectively, for the AOCS-certified laboratories). The average differences between blind duplicates of a sample were 0.71 percentage points for protein and 0.87 percentage points for oil (0.28 and 0.45, respectively, for the certified laboratories). Average standard deviations across laboratories on an individual sample were 2.37 and 1.71 percentage points for protein and oil, respectively (1.87 and 0.99, respectively, for the certified laboratories.     

Liquid li structure and dynamics: A comparison between OFDFT and second nearest‐neighbor embedded‐atom method

The structure and dynamics of liquid lithium are studied using two simulation methods: orbital‐free (OF) first‐principles molecular dynamics (MD), which employs OF density functional theory (DFT), and classical MD utilizing a second nearest‐neighbor embedded‐atom method potential. The properties studied include the dynamic structure factor, the self‐diffusion coefficient, the dispersion relation, the viscosity, and the bond angle distribution function. Simulation results were compared to available experimental data when possible. Each method has distinct advantages and disadvantages. For example, OFDFT gives better agreement with experimental dynamic structure factors, yet is more computationally demanding than classical simulations. Classical simulations can access a broader temperature range and longer time scales. The combination of first‐principles and classical simulations is a powerful tool for studying properties of liquid lithium. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2841–2853, 2015     

Hydrophobic surface modification of FMSS and its application as effective sorbents for oil spill clean‐ups and recovery

Superhydrophobic sponge‐like materials are attracting more attention in recent years as potential sorbent materials for oil spill clean‐up. In this work, the authors report the incorporation of hydrophobic structural features into a superhydrophilic pristine formaldehyde‐melamine‐sodium bisulfite copolymer sponge (FMSS) by N‐acylation with a fatty acid derivative, for use as an oil sorbent in oil spill clean‐ups. This resulted in our ability to transform the surface properties of the sponge skeleton to superhydrophobic with a contact angle of 143°. The acylated FMSS (a‐FMSS) was shown to retain the interconnected porous structure, and was characterized with microscopic and spectroscopic analyses. Sorption experiments with engine oil and chloroform showed that a‐FMSS had a very high oil sorption capacity (amounting to 99 and 168.2 times its own weight respectively) than commercial nonwoven polypropylene sorbent. In this view, a‐FMSS is considered to be a promising oil sorbent for potential applications in large‐scale oil spill clean‐ups. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4090–4102, 2017     

The structure of urea—formaldehyde resins

Fourier transform infrared (FTIR) spectroscopy has been used as a modern analytical tool to elucidate the structure of urea—formaldehyde (UF) resins. Several low molecular weight condensation products of urea and formaldehyde were synthesized and characterized. Structural differences were observed for prepolymers prepared in alkaline and acidic media. Plausible mechanistic routes are proposed to explain the prepolymer structural differences prepared in different experimental conditions. The structural elucidation of the UF resins is considerably increased and improved by using absorbance magnification to further enhance the observed signals.     

The pH,temperature, and protein structure effect on β‐lactoglobulin A and B separation in anion‐exchange chromatography

The effect of pH and temperature on separating a mixture of similar proteins, namely β‐lactoglobulin A (LGA) and β‐lactoglobulin B (LGB) in anion‐exchange chromatography is explored. The proteins carry a slight difference in negative charge at basic pH, providing a separation basis on an Q Sepharose Fast Flow anion‐exchange resin. They were separated at different temperatures and pH values, and the separation factor was evaluated. The experimental results were matched to a theoretical model to compute the equilibrium constant K_A. The data shows that an increase in temperature and pH leads to an increase in the retention time of the proteins. The results were correlated with the net charge of the molecule for the separation so that the elution can be simulated for any condition that was studied. The tertiary structures of LGA and LGB are analyzed to illustrate the structure effect on the separation. © 2018 American Institute of Chemical Engineers AIChE J, 64: 1928–1937, 2018