Micellization and gelation of aqueous solutions of star-shaped PEG-PCL block copolymers consisting of branched 4-arm poly(ethylene glycol) and polycaprolactone blocks

Star-shaped block copolymers consisting of non-toxic poly(ethylene glycol) and biodegradable polycaprolactone ((PEG5K-PCL)₄) were synthesized by ring-opening polymerization of the ε-caprolactone monomer with hydroxyl-terminated 4-armed PEG as initiator. These biodegradable, amphiphilic star block copolymers showed micellization and sol-gel transition behaviors in aqueous solution with varying concentration and temperature. In the dilute aqueous solutions of star block copolymers, micellization behavior occurred over specific concentration. The 1,6-diphenyl-1,3,5-hexatriene (DPH) solubilization method was used to determine the critical micellization concentration (CMC) of star block copolymers. The obtained micelle size increased with increasing hydrophobic PCL block length. In high-concentration solutions, the star block copolymers showed temperature-sensitive sol-gel transition behavior. The morphology of the micelle and gel was investigated by atomic force microscopy (AFM). As a result, the micelles showed a core-corona spherical structure at concentration near CMC, while the gel showed a mountain-chain-like morphology picture. It was proposed that with increasing the micelle concentration the worm-like micelle clusters formed firstly and the gel was constructed by the packing of micelle clusters.     

Immobilized cobalt/rhodium heterobimetallic nanoparticle-catalyzed silylcarbocylization and carbonylative silylcarbocyclization of 1,6-enynes

Reaction of 1,6-enynes with a hydrosilane in the presence of immobilized cobalt/rhodium bimetallic nanoparticles gives 2-methyl-1-silylmethylidene-2-cyclopentanes in the absence of carbon monoxide and 2-formylmethyl-1-silylmethylidene-2-cyclopentanes under 1 atm of carbon monoxide, respectively. [reaction: see text]     

Fabrication of lead titanate single crystalline nanowires by hydrothermal method and their characterization

Single crystalline nanowires of lead titanate (PbTiO₃) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure and optical properties of PbTiO₃ nanowires were investigated. The PbTiO₃ nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO₃ with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm. The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies are responsible for the light emission of PbTiO₃ nanowires.     

溶胶-凝胶法制备高取向Bi4Ti3O12/SrTiO3(100)薄膜

Bi4Ti3O12具有良好的铁电、电光等性能山、特别是Bi4Ti3O12薄膜很适合作永久性存储材料，也可用于电光器件问．在微电子学、光电子学、集成光学、集成铁电学等领域均有广泛开发和应用前景，国外已用溅射法、激光沉积法制备出c轴取向Bi。Ti3Ol。薄膜【’，＼山东大学用MOCVD法制     

聚乙二醇、聚丙二醇和环氧乙烷-环氧丙烷嵌段共聚物在固液界面上的吸附——Ⅰ.活性炭/水界面

测定了25℃时活性炭自水溶液中吸附五种聚乙二醇(PEG)、一种聚丙二醇(PPG)和三种环氧乙烷(EO)-环氧丙烷(PO)嵌段共聚物的吸附等温线。结果表明,各等温线均为Langmuir型的,且在较低浓度时即可达极限吸附。当以g.g~(-1)表示吸附量时,各聚合物的极限吸附量相近。对于PEG系列和EO-PO嵌段共聚物系列,极限吸附时每个分子占据的面积与分子中所含EO数的关系为两条斜率相同的直线。由直线斜率和后一直线的截距可求得每个EO和PO所占的面积分别为26和2.9 nm~2。这些结果支持了分子以其EO和PO链节都平躺在表面上的吸附模型。     

The complex of a bivalent derivative of galanthamine with torpedo acetylcholinesterase displays drastic deformation of the active-site gorge: implications for structure-based drug design

Bifunctional derivatives of the alkaloid galanthamine, designed to interact with both the active site of the enzyme acetylcholinesterase (AChE) and its peripheral cation binding site, have been assayed with Torpedo californica AChE (TcAChE), and the three-dimensional structures of their complexes with the enzyme have been solved by X-ray crystallography. Differences were noted between the IC(50) values obtained for TcAChE and those for Electrophorus electricus AChE. These differences are ascribed to sequence differences in one or two residues lining the active-site gorge of the enzyme. The binding of one of the inhibitors disrupts the native conformation of one wall of the gorge, formed by the loop Trp279-Phe290. It is proposed that flexibility of this loop may permit the binding of inhibitors such as galanthamine, which are too bulky to penetrate the narrow neck of the gorge formed by Tyr121 and Phe330 as seen in the crystal structure.     

Synthesis and electrochemical properties of nanostructured LiCoO2 fibers as cathode materials for lithium-ion batteries

Nanostructured LiCoO2 fibers were prepared by the sol-gel related electrospinning technique using metal acetate and citric acid as starting materials. The transformation from the xerogel fibers to the LiCoO2 fibers and the nanostructure of LiCoO2 fibers have been investigated in detail. The LiCoO2 fibers with 500 nm to 2 mum in diameter were composed of polycrystalline nanoparticles in sizes of 20-35 nm. Cyclic voltammetry and charge-discharge experiments were applied to characterize the electrochemical properties of the fibers as cathode materials for lithium-ion batteries. The cyclic voltammogram curves indicated faster diffusion and migration of Li+ cations in the nanostructured LiCoO2 fiber electrode. In the first charge-discharge process, the LiCoO2 fibers showed the initial charge and discharge capacities of 216 and 182 (mA.h)/g, respectively. After the 20th cycle, the discharge capacity decreased to 123 (mA.h)/g. The X-ray diffraction and high-resolution transmission electron microscopy analyses indicated that the large loss of capacity of fiber electrode during the charge-discharge process might mainly result from the dissolution of cobalt and lithium cations escaping from LiCoO2 to form the crystalline Li2CO3 and CoF2 impurities.     

用旋转园盘-园环电极研究碘酸盐阴极还原反应的机理

本文研究了低浓度的碘酸盐在硫酸介质中, 在铂电报上的电化学还原。用旋转盘环电极检测到了碘酸盐阴极还原的中间产物I_2及最终产物I~-。测定了电化学反应的动力学参数。最后提出了磺酸盐阴极反应的机理。     

荧光探针法研究PEO-PPO嵌段共聚物胶束的特性

利用十六烷基罗丹明Ｂ作为主要荧光探针，研究了水溶性嵌段共聚物Ｐｌｕｒｏｎｉｃ Ｆ－６８在水溶液中的胶束化行为，研究表明，Ｐｌｕｒｏｎｉｃ－Ｆ－６８形成胶束的监界胶束浓度与温度有极大关系，随温度的升高，其ＣＭＣ值急剧下降，并且温度对胶束的性质也有很大，影响温度升高可导致胶束的微观粘度增大，表现出很强的负粘－温效应，并发现引起这种负粘－温效应的主要原因是Ｐｌｕｒｏｎｉｃ Ｆ－６８分子中聚环氧乙烷（ＰＥ