Study on preparation and properties of polyether polytriazole elastomers

To explore the application of click chemistry in the field of elastomer materials, propargyl-terminated ethylene oxide-tetrahydrofuran copolymer(PTP(E-co-T)) was prepared from hydroxyl-terminated ethylene oxide-tetrahydrofuran copolymer(P(E-co-T)) by end-etherisation modification. FTIR and 13C-NMR results indicate that P(E-co-T)-terminated hydroxyl was etherified thoroughly, yielding the target product PTP(E-co-T), and the content of terminated alkynyl of PTP(E-co-T) was evaluated to be 0.428 mmol·g-1. Using a polyazide compound as a cross-linker, polytriazole elastomers with various functional molar ratio(R) values were prepared from PTP(E-co-T) by virtue of the Cu AAC reaction. Mechanical property tests indicate that with the increase in R, the modulus E and stress σb of the polytriazole elastomers first increase and subsequently decrease, whereas the strain first decreases and later increases. The mechanical properties of the polytriazole elastomers show a parabolic dependence on the R value. Near the stoichiometric ratio, E and σb show maxima and the strain εb shows a minimum. Swelling tests demonstrate that the apparent molecular weight of polytriazole elastomer strands also first decreases and subsequently increases. At the stoichiometric ratio, the network structure possesses strands with a minimum apparent molecular weight and a maximum apparent density. Dynamic mechanical analysis reveals that the polytriazole elastomers presented damping peaks at approximately-64 °C, corresponding to the glass transition of copolyether strands, and the elastomer exhibited the lowest dissipation factor tanδ at the stoichiometric ratio. Thermal analysis suggests that the weight-loss process of the polytriazole elastomer is characteristic of one-step decomposition, and the elastomer begins to decompose from polyether strands, not triazole groups.     

热解二氧化钛/聚苯胺制备高效非贵金属氧还原电催化剂

为了克服传统Pt系催化剂价格昂贵、稳定性差的缺点,采用热解新型Ti O2/聚苯胺(PANI)复合物的方法合成了Ti O2/C催化剂.用扫描电子显微镜、X射线光电子能谱、X射线衍射、傅里叶变换红外光谱、拉曼光谱、透射电子显微镜、循环伏安法和线性扫描伏安法等方法研究了热处理和PANI复合比例对复合物的形貌、成键、晶相组成及氧还原性能的影响.结果表明,PANI与Ti O2间存在相互作用,可以抑制Ti O2的团聚和锐钛矿向金红石的转变.热处理制得Ti O2/C的氧还原活性随着PANI载体含量增加先升高后降低,PANI和Ti O2质量比为35/100时,催化剂的氧还原活性最高.同时,循环伏安和时间-电流曲线测试表明,已制备的复合材料在催化氧还原反应进行时具有较好的稳定性.     

Asymmetric Synthesis of Fully Substituted Cyclopentane‐Oxindoles through an Organocatalytic Triple Michael Domino Reaction

An efficient, highly stereoselective asymmetric synthesis of fully functionalized cyclopentanes bearing an oxindole moiety and several other functional groups in one pot has been developed. Key step is an organocatalytic triple Michael domino reaction forming three C?C bonds and six stereocenters, including a quaternary one. Starting from equimolar amounts of simple substrates, a high molecular complexity can be reached after a Wittig olefination in one pot. The new protocol can easily be scaled up to gram amounts.     

Sr_2CeO_4:Nd~(3+)纳米粒子的合成和近红外发光

采用甘氨酸-硝酸盐燃烧法制备了Sr2CeO4和Sr2CeO4:Nd3+发光纳米粒子。样品的结构及性质采用XRD,TEM,荧光光谱及荧光衰减曲线等进行表征。在1200℃煅烧1h能够得到均匀的类球形Sr2CeO4:Nd3+纳米粒子,其粒径大小为20~40nm,并具有良好的分散性和高效的近红外发光特性。Nd3+合适掺杂浓度为0.15%(摩尔分数)。对Sr2CeO4:Nd3+近红外发光的机制分析表明:通过基质Sr2CeO4吸收紫外光,基团CeO4发生了电荷转移达到激发态,并将激发态能量传递给了Nd3+,从而使Sr2CeO4:Nd3+产生了特征的近红外发射。     

Stereochemical determination of tetrahydropyran-substituted xanthones from fungus Chaetomium murorum

Chaetoxanthone D (1), a new tetrahydropyran-substituted xanthone originated from polyketide pathway, together with the four known natural products chaetoxanthone C (2), alternariol methyl ether (3), alternariol (4) and 2,5-dimethyl-7-hydroxychromone (5) was isolated from a strain of Chaetomium murorum. The structures of these compounds were elucidated based on extensive spectroscopic analyses. The absolute configurations of 1 and 2 were determined by using quantum chemical electronic circular dichroism (ECD) calculations.     

Rational Design of a Humanized Glucagon‐Like Peptide‐1 Receptor Agonist Antibody

Bovine antibody BLV1H12 possesses a unique “stalk–knob” architecture in its ultralong heavy chain CDR3, allowing substitutions of the “knob” domain with protein agonists to generate functional antibody chimeras. We have generated a humanized glucagon‐like peptide‐1 (GLP‐1) receptor agonist antibody by first introducing a coiled‐coil “stalk” into CDR3H of the antibody herceptin. Exendin‐4 (Ex‐4), a GLP‐1 receptor agonist, was then fused to the engineered stalk with flexible linkers, and a Factor Xa cleavage site was inserted immediately in front of Ex‐4 to allow release of the N‐terminus of the fused peptide. The resulting clipped herceptin–Ex‐4 fusion protein is more potent in vitro in activating GLP‐1 receptors than the Ex‐4 peptide. The clipped herceptin–Ex‐4 has an extended plasma half‐life of approximately four days and sustained control of blood glucose levels for more than a week in mice. This work provides a novel approach to the development of human or humanized agonist antibodies as therapeutics.     

Clicked Isoreticular Metal–Organic Frameworks and Their High Performance in the Selective Capture and Separation of Large Organic Molecules

Three highly porous metal–organic frameworks (MOFs) with a uniform rht‐type topological network but hierarchical pores were successfully constructed by the assembly of triazole‐containing dendritic hexacarboxylate ligands with Zn^II ions. These transparent MOF crystals present gradually increasing pore sizes upon extension of the length of the organic backbone, as clearly identified by structural analysis and gas‐adsorption experiments. The inherent accessibility of the pores to large molecules endows these materials with unique properties for the uptake of large guest molecules. The visible selective adsorption of dye molecules makes these MOFs highly promising porous materials for pore‐size‐dependent large‐molecule capture and separation.     

Dynamic compressive strength properties of aluminium foams. Part I—experimental data and observations

This study of the dynamic compressive strength properties of metal foams is in two parts. Part I presents data from an extensive experimental study of closed-cell Hydro/Cymat aluminium foam, which elucidates a number of key issues and phenomena. Part II focuses on modelling issues.The dynamic compressive response of the foam was investigated using a direct-impact technique for a range of velocities from 10 to . Elastic wave dispersion and attenuation in the pressure bar was corrected using a deconvolution technique.A new method of locating the point of densification in the nominal stress-strain curves of the foam is proposed, which provides a consistent framework for the definition of the plateau stress and the densification strain, both essential parameters of the ‘shock’ model in Part II. Data for the uniaxial, plastic collapse and plateau stresses are presented for two different average cell sizes of approximately 4 and 14 mm. They show that the plastic collapse strength of the foam changes significantly with compression rate. This phenomenon is discussed, and the distinctive roles of microinertia and ‘shock’ formation are described. The effects of compression rates on the initiation, development and distribution of cell crushing are also examined. Tests were carried out to examine the effects of density gradient and specimen gauge length at different rates of compression and the results are discussed. The origin of the conflicting conclusions in the literature on the correlation between nominal strain rate (ratio of the impact velocity V_i to the initial gauge length l_o of the specimen) and the dynamic strength of aluminium alloy foams is identified and explained.     

轴向移动系统的参数振动问题研究进展

对近二十年来轴向移动系统(移动弦，移动梁和移动带等)的参数振动研究进展进行了详细的评述，特别关注了轴向张紧力和移动速度随时间改变时轴向移动系统的参数振动特性和稳定性等问题。文章首先讨论了所研究问题的控制方程。然后详细说明了目前研究中人们较为关注的几个重点问题，如参数激励的形式，求解方法和所研究的问题等。接着在其后的两节中，分别评述了在张紧力和移动速度随时间变化时，轴向移动弦和轴向移动梁的振动问题近年来的研究进展，详细、深入讨论了模型的类型、张紧力和轴向移动速度随时间变化的形式以及在研究中使用的解题方法和系统的振动特性(振动响应、固有频率和动态稳定性)等；最后给出了在此领域今后研究中应关注的问题。     

SPATIAL AND SEASONAL DISTRIBUTIONS OF ATMOSPHERIC CARBONACEOUS AEROSOLS IN PEARL RIVER DELTA REGION, CHINA

Concentrations and spatial distributions of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were measured at 8 sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of Pearl River Delta Region (PRDR), China during 2001 winter period and 2002 summer period. PM2.5 (particie diameter smaller than 2.5 um) and PM10 (particie diameter smaller than 10 um) samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed using thermal optical reflectance (TOR) method. The average PM2.5and PM10 Ievel were 60.1 and 93.1 μg·m-3, respectively, with PM2.5 constituting 65.3% of the PM10 mass. The average OC and EC concentrations in PM2.5 were 12.0 and 5.1 μg·m-3, respectively, while those in PM10 were 16.0 and 6.5 μg·m-3, respectively. The carbo-naceous aerosol accounted for 37.2% of the PM2.5 and 32.8% of the PM10. The highest concentrations of OC and EC were observed at Guangzhou city in both vvinter and summer seasons. The average OC/EC ratios were 2.