Design, synthesis, and pharmacological characterization of polyamine toxin derivatives: potent ligands for the pore-forming region of AMPA receptors

Polyamine toxins, such as philanthotoxins, are low-molecular-weight compounds isolated from spiders and wasps, which modulate ligand-gated ion channels in the nervous system. Philanthotoxins bind to the pore-forming region of AMPA receptors, a subtype of glutamate receptors which are important for memory formation and are involved in neurodegenerative diseases. Previous studies have demonstrated that modification of the polyamine moiety of philanthotoxins can lead to very potent and highly selective ligands for the AMPA receptor, as exemplified with philanthotoxin-56. Much less attention has been paid to the importance of the aromatic head group of philanthotoxins, but herein we demonstrate that modification of this moiety leads to a significant improvement in potency relative to philanthotoxin-56 at cloned AMPA receptors. Interestingly, the incorporation of an adamantane moiety is particularly favorable, and the most potent compound has a Ki value of 2 nM, making it the most potent uncompetitive antagonist of AMPA receptors described to date. Such compounds are potentially useful as neuroprotective agents.     

Chemical and biochemical characterization of lignan analogs as novel PAF receptor antagonists

Various derivatives and isosteres of neolignans of the 2,5-diaryl tetrahydrofuran type have been synthesized as antagonists of platelet-activating factor (PAF). A detailed analysis of their structure-activity relationship (SAR) has revealed a clear preference for an asymmetrical molecular configuration with a high degree of stereo and chiral specificity associated with greater potency. Thetrans-2S,5S enantiomers are generally 10–200 times more potentin vitro than their correspondingcis ortrans-2R,5R isomers. A similar stereochemical preference is indicated by the recently reported PAF antagonist MK-287 which has undergone clinical evaluation. An azido derivative L-662,025 has been characterized as a photolabile irreversible antagonist of PAF for the investigation of solubilized and partially purified PAF binding proteins from cell membranes. The biological justification for concomitant inhibition of both PAF receptor and 5-lipoxygenase in inflammation is well recognized. The feasibility of developing such dual-functional agents has been demonstrated by a group of dithiolane analogs of neolignans and several derivatives of futoenone. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

聚烯烃弹性体的结构表征

使用高温核磁共振碳谱、高温凝胶渗透色谱和熔融指数仪等对4种聚烯烃弹性体(P O E)的微观链结构、共聚单体组成及含量、相对分子质量及其分布等进行了分析和表征.结果表明:4种POE的共聚单体均为1-辛烯,共聚单体含量为30.0％～33.2％(w),共聚单体在分子链中分布均匀;4种POE的相对分子质量为7.19×104～1...     

碳纳米管表面结构的分析方法概述

阐述了一系列碳纳米管(CNT)表面结构的分析方法以及他们的优缺点.介绍了各种技术获得的CNT表面化学结构的信息.着重强调了XPS以及XPS谱线模糊时,XPS与化学衍生化方法联合确定CNT表面有机官能团含量的方法.     

Structural and mechanical characterization of platelet graphite nanofibers

Platelet graphite nanofibers have been characterized by scanning electron microscopy, transmission electron microscopy, electron diffraction, X-ray photoemission spectroscopy, and atomic force microscopy. The results show that the graphene sheets are stacked parallel to each other and are perpendicular to the fiber axis; the interlayer spacing is 0.34 nm. A small fraction of carbon atoms are bonded to oxygen. Solid-state nuclear magnetic resonance shows that hydrogenated carbons are under the detection limit (<5%) and that the nanofibers are dominated by sp²-bonded carbons. Mechanical measurements were made on individual nanofibers by nanoindentation.     

Structural characterization of exfoliated graphite nanofibers

Structural characterization of exfoliated graphite nanofibers (EGNFs) with transmission electron microscopy (TEM) and high-angle annular dark-field-scanning TEM (HAADF-STEM) indicates exfoliation has led to structural expansion along the fiber axis, with discrete domains of graphitic nanocones separated by gaps ranging from 50 to 500 Å. Image contrast in HAADF-STEM demonstrates that structural expansion dominates over chemical etching. Raman spectroscopy indicates the EGNF is more graphitic than the precursor, and the disappearance of the characteristic defect (D) peak with multi-wavelength excitation is inconsistent with the presence of amorphous carbon. The highly expanded EGNF structure oxidizes at two distinct rates at 750 °C in CO₂, leading to a highly-disordered graphitic fiber, with apparent collapse of the expanded structure as no gaps or discrete graphitic domains are observed after oxidation. Variation in the heat input per intercalant mass during thermal shock leads to changes in fiber morphology, including the extent of fiber expansion, the number of defects and pores observable within the fiber via TEM, and the surface area measured by nitrogen adsorption.     

Structural characterization of carbonaceous combustion-chamber deposits

The structural properties of combustion-chamber deposits (CCDs) are studied by combining molecular simulation of adsorption in a set of model pores with experimental adsorption measurements, using ethane as the adsorptive. The implemented approach is a modification of the common method used to determine the pore size distribution (PSD) of manufactured carbon adsorbents, changed in order to take into account the higher degree of chemical and physical heterogeneity of CCDs. The realism of the PSD obtained is demonstrated by accurately predicting adsorption under a range of conditions. The general applicability of the method is tested by transferring a characteristic parameter of CCDs (and different from the corresponding parameter in manufactured carbon adsorbents) from one sample to another.     

Structural and molecular recognition studies with acyclic anion receptors

Acyclic molecules containing amides, ureas, and pyrrole groups have proven to be effective and selective anion-binding agents. In this Account, the structural chemistry of isophthalamide anion complexes, ortho-phenylenediamine based bis-ureas, and amidopyrroles, as well as anion-triggered deprotonation processes in neutral anion receptor systems, are discussed.     

PAF receptor and “cache-oreilles” effect. Simple PAF antagonists

Nine simple and structurally flexible PAF antagonists were synthesized and their inhibitory effects on PAF induced platelet aggregation were measured. Compounds with PAF antagonistic activity exhibited a negative electrostatic potential generated by two trimethoxyphenyl groups (isocontour at ?10 Kcal/mole) at various distances between the negative clouds. The optimal distance between the atoms generating the “cache-oreilles” system for exhibiting potent PAF antagonistic activity is estimated to be 11–13 Å. In the flexible molecules studied, the dispersion of the electronic distribution is not necessarily favorable for anti-PAF activity. The data support the simple bipolarized model for the PAF receptor that has been proposed by the authors.     

聚丙烯腈基炭纤维组织结构表征与性能分析

采用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)、激光拉曼光谱(Raman)及化学分析法等测试技术对4种PAN基3K炭纤维(2种国产炭纤维、1种国外原丝国内炭化纤维、一种日本炭纤维)的表面形貌、组织结构及化学组成等方面进行了表征,并分析了材料的微观结构组织与宏观性能的关系。结果表明:相比日本炭纤维,国产炭纤维表面缺陷多、微观结构不完整、R值大、杂质含量多等因素决定了其具有较低的拉伸强度。     

Structural characterization and chemical reactivity of dual doped graphene

Herein, we employed first-principle calculations to study the structure and reactivity of dual-doped graphene. The new materials were derived from graphene by replacing two carbon atoms with one 2p element (B, N or O), and one 3p element (Al, Si, P or S). A total of 12 dual-doped graphenes were used to perform a comparative study and identify the most promising materials for the development of new catalysts and anchoring nanoparticles. The structural analysis indicated that in all cases, except SiB, the dopants prefer to replace a CC bond. Yet, not always the dopants are bonded, presenting an edge-like bonding. As regards chemical reactivity, in general the introduction of two atoms remarkably increases reactivity as compared to graphene. The most prominent examples are Al–O, S–N, P–O and Si–B(para) codoped graphene which present reactivity higher than perfect and monodoped graphenes. This effect was attributed to the strong charge redistribution induced by the dopants. In most cases the heteroatoms are the most reactive sites, but in others the carbon atoms are more reactive, as in Al–O and Si–B codoped graphene. The combination of 2p and 3p dopants offers the possibility of adjusting over a wide range the reactivity of graphene.     

Structural characterization of natural and vulcanized rubber by ozonolysis

A quantitative characterization of natural rubber, both as the raw polymer, and unaccelerated vulcanized samples containing different proportions of sulfur and ranging from soft to hard rubber, is reported. A value of 86% of the chains of natural rubber could be accounted for against 37% as reported by Harries assuming that levulinic acid is the sole degradation product. About 5% of the chain is present as a 3,4 structure which gives rise to formic acid in the degraded product. A small amount of sulfuric acid is present in the degradation product from the vulcanized samples, which decreases with the increases in the percentage of sulfur in the stock as well as the cure time. A chromatographic technique for the separation of levulinic, acetic, and formic acid in the presence of sulfuric acid is reported. It is observed that the total amount of carbon main chain escaping sulfuration decreases and the amount of insoluble fraction increases with increasing proportion of sulfur in the stock.     

Structural characterization and tensile properties of Borassus fruit fibers

The chemical and instrumental analysis of alkali‐treated Borassus fibers is carried out to explore the possibility of their use as reinforcement in green composites. The chemical analysis shows presence of α‐cellulose, hemicellulose, and lignin. This is further confirmed by FTIR and high‐resolution solid‐state ¹³C NMR spectroscopy. The influence of alkali treatment on morphology and mechanical properties is attempted by SEM and UTM techniques, respectively. The wide‐angle X‐ray diffraction analysis of the native and treated fibers shows that alkali treatment influences the crystallinity of the fibers. The efficacy of the Borassus fibers (native and treated) as a component of green composites is discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structural and mechanistic basis of the interaction between a pharmacological chaperone and human phenylalanine hydroxylase

Not without a chaperone: Pharmacological chaperones are designed to bind and ideally stabilise their target protein. Here, we elucidate the molecular mechanism of a potential pharmacological chaperone to treat phenylketonuria. The crystal structure of human phenylalanine hydroxylase with compound IV may help in the rational design of more efficient compounds to treat this disease.     

Structural and tribological characterization of amorphous and crystalline titanium-nickel coatings

The interest in titanium-nickel (TiNi) alloys has increased with the discovery of the versatile properties of these alloys. In this study, the structural, mechanical and tribological properties of amorphous and crystalline TiNi coatings were investigated. The TiNi coatings were deposited with magnetron sputtering system. The crystallization process was conducted in a vacuum heat treatment furnace. The structural properties of the coatings were investigated with XRD, SEM and EDS analyses. Micro-hardness and pin-on-disc wear tests were used to obtain the mechanical and tribological properties of the coatings. AISI D2 steel, AISI 52100 steel, Aluminum 2024 alloy and copper were used as substrate materials, hence the effects of different substrates were also investigated. The highest coating hardness was obtained as 8.5?GPa and the lowest coefficient of friction value was obtained as 0.18. The tribological tests showed that the amorphous and crystalline TiNi coatings have different coefficient of friction and wear rate and using different substrate affects these properties.     

缩氨基硫脲类受体的合成和表征

采用对甲基苯胺和高锰酸钾氧化生成对氨基苯甲酸,后者用磷酸三甲酯N甲基化,生成对二甲氨基苯甲酸,其经酯化、肼解得到对二甲氨基苯甲酰肼（A）。A与异硫氰酸对硝基苯酯反应,制得N-对二甲氨苯甲酰胺基-N’-对硝基苯基硫脲,收率76％;同理,对硝基苯肼与异硫氰酸对甲苯酯反应,得到N-对硝基苯胺基-N’-对甲苯基硫脲,收率41％。通过元素分析,IR,1HNMR对化合物的结构进行了表征。     

硫化胶交联点结构之分析

利用NMR(核磁共振)方法对天然橡胶硫化胶交联点的结构进行了分析,着重阐述了在硫化胶交联点结构分析方面所取得的最新成果。     

Magnesium-doped zircon-type rare-earth orthovanadates: Structural and electrical characterization

Undoped LnVO₄ and magnesium-doped Ln_0.95V_0.95Mg_0.10O_4-δ (Ln = Pr, Sm, Gd, Dy and Er) orthovanadates were synthesized by solid state reaction method and characterized by XRD, SEM/EDS, electrical conductivity measurements in controlled atmospheres, and modified e.m.f. technique for determination of oxygen-ion transference numbers. XRD analysis showed the formation of phase-pure materials with tetragonal zircon-type structure and a decrease in lattice parameters with a decrease of ionic radius of rare-earth cations. Trace amounts of MgO and Mg-V-O phases revealed by SEM/EDS suggest that the solid solubility limit of magnesium cations in LnVO₄ lattice is somewhat lower than the nominal doping level, and that magnesium substitutes preferentially into the vanadium sublattice. LnVO₄ and Ln_0.95V_0.95Mg_0.10O_4-δ orthovanadates show semiconducting behavior under oxidizing conditions at 450–950 °C and are predominantly oxygen-ionic conductors, except PrVO₄ that shows mixed conductivity. In the LnVO₄ series, electrical conductivity is the highest for PrVO₄ and SmVO₄ (~4 × 10^?4 S/cm at 800 °C) and decreases with increasing atomic number of rare-earth cation for the other compositions. Additions of magnesium results in a drop of electrical conductivity, by 1.5–2 times for most of compositions. Interstitial oxygen diffusion is discussed as a prevailing mechanism of ionic transport in undoped LnVO₄, whilst acceptor-type magnesium doping suppresses the formation of interstitial oxygen ions. Humidity has a rather negligible impact on the electrical properties of substituted ceramics, indicating only minor (if any) protonic contribution to the total electrical transport of the studied orthovanadates.     

Structural characterization and thermal behaviour of wool keratin hydrolizates-polypropylene composites

Innovative polypropylene composites were prepared using as a biofiller, wool keratin hydrolizates obtained by a green process with superheated water in a microwave reactor. To promote the affinity between the hydrophobic polymer and the biofiller, maleic anhydride grafted polypropylene was used as a compatibilizer. The composites showed a homogeneous dispersion of the keratin particles in the polymer matrix. The thermal properties and the structure of the composites were investigated in dependence of keratin loading and crystallization conditions. The keratin particles had a heterogeneous nucleating action on polypropylene crystallization that increased the overall crystallization rate. The nucleation density increased as a function of the keratin amount in the composites. The crystallinity, the crystal dimension and the long period of the polypropylene were found to be dependent on the crystallization condition and the composite composition. In the crystallized composites, the keratin component, having dimension in the nano- and micro-scale length, was relegated to the intraspherulitic and/or interspherulitic polypropylene regions.