Theoretical investigation of novel silsesquioxane-supported Phillips-type catalyst by density functional theory (DFT) method

In spite of great commercial importance of the Phillips CrO_x/SiO₂ catalyst and long term research efforts, the precise physicochemical nature of active sites and polymerization mechanisms still remains unclear. The difficulties in a clear mechanistic understanding of this catalyst mainly come from the complexity of the surface chemistry of the amorphous silica gel support. In this work, novel silsesquioxane-supported Phillips Cr catalysts are utilized as realistic models of the industrial catalyst for theoretical investigation using the density functional theory (DFT) method in order to elucidate the effects of surface chemistry of silica gel in terms of supporting of chromium compounds and fluorination of the silica surface on the catalytic properties of the Phillips catalyst. Both qualitative and quantitative aspects with respect to various electronic properties and thermodynamic characteristics of the model catalysts were achieved. The future prospects of a state-of-the-art catalyst design and mechanistic approaches for the heterogeneous SiO₂-supported Phillips catalyst has been demonstrated. The text was submitted by the authors in English.     

Self-assembled biotinylated disulfide derivative monolayer on gold electrode for immobilizing enzymes

Based on self-assembled biotinylated disulfide derivative monolayer on gold electrode, the sensors immobilized monolayer or multilayer membranes composed of avidin and biotinlabeled glucose oxidase (B.GOD) or of avidin-B.GOD complex (ABC) and B.COD were prepared. The present technique may be useful for controlling the enzyme content of the sensors in molecular level by repeating the deposition of enzyme layers. The sensors have the characteristics of shorter response time, higher sensitivity. The linear range is from 6.0 x 10(-6) - 5.0 x 10(-3) M. The sensor can be used for more than 1 month and can be reactivated. The sensor was used to determine glucose in human blood serum, and the results are satisfactory.     

Boomerang‐Type Substitution Reaction: Reactivity of Fullerene Epoxides and a Halofullerenol

The C_s‐symmetric fullerene chlorohydrin C₆₀(Cl)(OH)(OOtBu)₄ reacts with 4‐dimethylaminopyridine (DMAP) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) to yield two isomers with the formula C₆₀(O)(OOtBu)₄ in good yields. These isomers differ with respect to the location of the epoxy functionality. The one from DMAP is C_s symmetric, whereas that from DABCO is C₁ symmetric with the epoxy group on the central pentagon. Two different mechanisms are proposed to explain the chemoselectivity of these reactions. The reaction with DMAP involves single‐electron transfer as the key step; DMAP acts as the electron donor. A combination of an oxygen‐atom shift and S_N2′′ processes (boomerang substitution) are responsible for the formation of isomer with DACBO. Various related reactions support the proposed mechanisms. The structures of new fullerene derivatives were determined by spectroscopy, single‐crystal X‐ray analysis, and chemical correlation experiments.     

Solvent effects on infrared spectra of methyl 4-hydroxybenzoate in pure organic solvents and in ethanol/CCl4 binary solvents

Infrared spectroscopy studies of methyl 4-hydroxybenzoate (MHB) in 17 different organic solvents and in ethanol/CCl4 binary solvent were undertaken to investigate the solvent-solute interactions. The frequencies of carbonyl stretching vibration nu(C=O) of MHB in single solvents were correlated with the solvent acceptor number (AN) and the linear solvation energy relationships (LSER). The assignments of the two bands of nu(C=O) of MHB in alcohols and the single one of that in non-alcoholic solvents were discussed. The shifts of nu(C=O) of MHB in ethanol/CCl4 binary solvents showed that several kinds of solute-solvent hydrogen bonding interactions coexisted in the mixture solvents, with a change in the mole fraction of ethanol in the binary solvents.     

非晶态Co-B的局域电子结构的X_α原子簇计算

金属玻璃TM-Met(TM为过渡金属原子,Met为类金属原子,如硼、磷等)由于其优异性能已成为非晶态研究的重要课题之一。实验研究表明,类金属原子与过渡金属原子构成非晶态合金(即金属玻璃)后,平均原子磁矩随Met的含量在一定范围内的变化呈线性下降关系.相当多的文献用“电荷转移刚性能带”模型来解释.认为金属玻璃的能带是     

硒芳香杂环化合物的光谱和电化学性质

用紫外光谱，荧光光谱和循环伏安法研究了含硒芳香杂环化合物（苤硒脑）在不同溶剂中的谱学和电化学性质，对不同分子结构或取代基的苤硒脑化合物的性质进行了比较，并初步探讨了溶剂对苤硒脑化合物谱学性质的影响规律。     

The influence of cetyltrimethyl ammonium bromide on electrochemical properties of thyroxine reduction at carbon nanotubes modified electrode

The effect of cetyltrimethyl ammonium bromide (CTAB) on the electrochemical behaviors of thyroxine at a glassy carbon electrode (GCE) modified with single-walled carbon nanotubes (SWNTs) was investigated. At the SWNTs film-coated GCE, a well-defined oxidation peak of thyroxine at 0.78 V was obtained, but the reduction peak of thyroxine was indiscernible. When trace CTAB was added to the working solution, the reduction current could be greatly enhanced and the oxidation current remained stable. The reaction mechanisms for the reduction of thyroxine were explored by chronocoulometry. Thyroxine might form particular ion complex with CTAB via the interaction between iodine atoms on thyroxine and bromide ions in CTAB, which made the concentration of thyroxine at the surface of the modified electrode increased and the electron transfer rate enhanced. The proper mechanisms for the enhanced reduction of thyroxine in the present of CTAB were explored by several electrochemical techniques including cycle voltammetry linear sweep voltammetry and others. It was concluded that the special interactions between the thyroxine CTAB and SWNTs resulted in the increase of the reduction peak current. All results indicated that two iodine atoms on the thyroxine and four electrons were involved the reduction process which was irreversible and two iodine ions produced. In this system, the sensitive reduction peak of thyroxine at 0.3 V was employed to determine thyroxine and a low detection limit of 2x10(-8) mol/L was obtained for 2 min accumulation at 0.9 V. The SWNTs coated GCE had good stability and reproducibility.     

Highly Regioselective Sequential 1,1‐Dihydrosilylation of Terminal Aliphatic Alkynes with Primary Silanes

A regioselective double 1,1‐hydrosilylation of terminal aliphatic alkynes with primary silanes catalyzed by one cobalt catalyst has been developed. gem‐Bis(dihydrosilyl)alkanes containing four silicon‐hydrogen bonds are efficiently constructed in an atom‐economical manner. Tolerated substrates include simplest alkyne‐ethyne, a complicated drug derivative and various functionalized terminal aliphatic alkynes. Asymmetric approach using two catalysts is achieved with excellent enantioselectivities to access corresponding chiral products. The transformations of Si—H bonds into Si—C, Si—O, and Si—F bonds and the synthesis of enantioriched α‐hydroxysilane show synthetic utility.     

速差动力学分析及其应用进展

速差动力学分析是不经分离同时或连续测定混合物中性质密切相关的多组份的重要方法。本文综述了该法在１９８９－１９９２年间国内外新进展，尤着重其在有机，生物混合物中多组份分析的应用及新的计算方法，化学计量学的引入。引用最新文献６７篇。