Mixed micellar medium for the spectrophotometric determination of molybdenum in molybdenum/tungsten mixtures

Effects of cetyltrimethylammonium bromide (CTAB) and/or nonylphenoxypolyethoxyethanol (OP) on the absorption spectra of the complexes of molybdenum and tungsten with bromopyrogallol red (BPR) were studied. Based on these effects, a mixture of CTAB and OP was thus selected as a medium for the selective and sensitive determination of Mo in Mo/W binary mixtures. Under the optimum conditions, Beer's law was obeyed over the range 0.06-0.8 mug ml(-1) Mo with molar absorptivity being 1.3x10(5) l mol(-1) cm(-1) and detection limit 0.025 mug ml(-1). For 1.0 mug Mo, at least 20 mug W did not interfere in the determination of Mo with average recovery and relative standard deviation being 99.5% and <2%, respectively. The method developed maintained the features of simplicity and rapidity and, moreover, its selectivity and sensitivity enhanced greatly due to the use of CTAB/OP mixed micellar medium. When coupled with a compatible concentration method, the proposed method could be used for the determination of trace Mo in natural waters.     

Improved enzyme immobilization for enhanced bioelectrocatalytic activity of porous electrodes

Porous electrodes with increased surface area have been prepared using a template route via colloidal crystals. The ordered porous structure and the interconnections between the pores have been quantitatively characterized by Focused Ion Beam Tomography. The internal surfaces of the electrodes have been biofunctionalized with two enzymatic systems for glucose oxidation. In order to increase significantly the stability, the biocatalysts have been immobilized either by crosslinking or by incorporation in an electrodeposition paint. The modified porous electrodes show an increased overall signal and therefore a better detection limit and a higher sensitivity when used as sensors, and a potentially higher power output when employed in biofuel cells.     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

Study on the interaction between nucleic acids and cationic surfactants

The interactions of nucleic acids and cationic surfactants (cetylpyridine bromide (CPB) and cetyltrimethylammonium bromide (CTMAB)) in aqueous solution have been studied using the techniques of resonance light scattering (RLS) spectroscopy, the absorption spectroscopy, zeta potential assay and NMR assignment measurement. It is considered that CPB or CTMAB can assemble on the surface of nucleic acid via electrostatic and hydrophobic forces, which results in the formation of large associate of nucleic acid-cationic surfactant and RLS enhancement of nucleic acid. Besides these forces, the pi-pi stacking force between CPB and nucleic acid also exists in the associate. In comparison with CTMAB, CPB has larger enhancement on RLS of nucleic acid, which is attributed to that the enhancement of the former is only due to the absorption of the bases of nucleic acid, while the enhancement of the latter is own to the synergetic resonance caused by the absorption of both bases of nucleic acid and the pyridyl in CPB. These results have important implication for understanding the influence of surfactants on nucleic acid functionality in life science.     

亚烷基卡宾与甲醛环加成反应机理的理论研究

用二阶微扰理论研究了单重态亚烷基卡宾与甲醛发生的三种环加成反应的机理 ，采用MP2/6－31G~*方法计算了势能面上各驻点的构型参数、振动频率和能量。根 据能量数据可以预言环加成反应（1）的a途径将是单重态亚烷基卡宾与甲醛环加成 反应的主要反应通道，该反应由两步组成：（I）亚烷基卡宾与甲醛生成了一富能 中间体（INT1a），是一无势垒的放热反应，（II）中间体异构化为产物亚烷基环 乙烷，其势垒为24.1 kJ·mol~(-1)(MP2/6-31G~*)。     

Characterization and separation of Al13 species using gel-filtration chromatography

A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic strength and pH on separation of Al₁₃ were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of Al₁₃ but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible to produce pure Al₁₃ species using a gel column chromatographic technique.     

Characterization and separation of Al13 species using gel-filtration chromatography

A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic strength and pH on separation of Al₁₃ were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of Al₁₃ but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible to produce pure Al₁₃ species using a gel column chromatographic technique.     

1－芳酰基－4－芳基氨基脲类化合物的合成及表征

利用N－取代三氯乙酰胺与芳基酰肼反应，合成了6个新的1－芳酰基－4－芳基 氨基脲类化合物，其结构经IR，^1H NMR和元素分析证实。初步生物活性测试表明 ，具有一定的除草活性。     

小角X射线散射表征AOT/水层状溶致液晶的有序性

用小角X射线散射研究了AOT/水层状溶致液晶的有序性. 通过对散射曲线的解析, 讨论了表面活性剂浓度、温度和助表面活性剂等三个方面对溶致液晶层状相结构有序性的影响. 在一定的范围内, 提高温度, 改变表面活性剂浓度和加入少量助表面活性剂可使碳氢链排列由稀疏转变为密实, 层状相也相应地由“柔性双层”过渡到更加有序化的“平面双层”. 基于形状因子和体系内分子间作用力, 提出了层状相形成与有序化的机理, 同时采用分子模拟的方法展现了不同浓度下的液晶结构.     

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.