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.     

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     

Determination of lead by selective chelatometric titration with HEDTA after separation as its sulphate by an improved method of precipitation

A selective titrimetric determination of Pb after separation by a modified method of precipitation as its sulphate is proposed. Pb(II), present as the perchlorate, is precipitated by gentle boiling in 3.6M H(2)SO(4) presaturated with PbSO(4) and free from any extraneous anions. The customary time-consuming evaporation to fumes of sulphuric acid is dispensed with. The precipitate is collected, and dissolved in excess of HEDTA, the surplus of which is back-titrated with Zn(II) at pH 5.0-5.5. Use of Catechol Violet and Xylenol Orange as a mixed indicator gives a sharper end-point. The standard deviation of the proposed method for 60 mg of lead is 0.35 mg. The method has been successfully used to determine Pb in non-ferrous alloys.     

褐煤超临界流体抽提产物中脂肪烃组成结构的特征

用硅胶-氧化铝柱色谱预分离和色谱-质谱分析研究了两种褐煤超临界流体抽提物中脂肪烃馏分组成结构特征。结果表明,除主要成份正构烷烃(C_(13)～C_(33))外,尚有少量的类异戊二烯烃(姥鲛烷、植烷等)和萜烷。其中萜烷以五环三萜为主(C_(27)、C_(29)～C_(32)藿烷类化合物),并有一定量的C_(27)、C_(29)和C_(30)藿烯,倍半萜和三环二萜烷含量很少。未检出甾烷。此外,还检出一完整系列的烯烃。试验结果表明,超临界流体抽提条件对褐煤抽出物各组分、含量及其分布有一定的影响。     

富勒烯化聚环氧丙基咔唑的合成与表征

通过Ｆｒｉｅｄｅｌ－Ｃｒｒａｆｔｓ反应制备了富勒烯化的聚环氧丙基咔唑，聚合物中Ｃ６０的含量最高可达７．６ｗｔ％。通过凝胶渗透色谱法测定了聚合物分子量，并采用＾上Ｈ和＾１３Ｃ－ＮＭＲ，ＩＲ，热分析及光谱等手段对其结构进行了分析与表征。     

CO(υ)高振动激发态向C2H2的振动传能研究

用时间分辨富里叶红外发射谱研究了高振动激发态ＣＯ向Ｃ２Ｈ２的传能，得到了ＣＯ（ｖ＝１－３）各振动态布居及其随时间的变化。利用微分法解出弛豫微分方程组，获得ＣＯ（ｖ＝１－３）向Ｃ２Ｈ２的传能速率常数分别为：２．０±０．１，６．０±０．２和９．４±０．８（１０＾－１３ｃｍ＾３·ｍｏｌｅｃｕｌｅ＾－１·ｓ＾－１）。传能速率随着振动量子数的增加而迅速增加。ＣＯ的振动能应向Ｃ２Ｈ２的对称伸缩模ｖ２近共振Ｖ－