过渡金属大环配合物的研究Ⅲ 4-硝基-苯并15冠-5与钴(Ⅱ)、铜(Ⅱ)和银(Ⅰ)配合物的合成及性质

有关冠醚配体与碱金属,碱土金属和稀土离子形成配合物的特性研究,国内外均有报导,但冠醚与d-过渡金属离子配合物的研究工作,则开展较晚,文献报导亦甚少。本文为探讨4-硝基-苯并15冠-5(No_2·B15C15)与过渡金属离子的配位能力,合成了Co(Ⅱ),Cu(Ⅱ),和Ag(Ⅰ)与4-硝基-苯并15冠-5配合物。并进行了元素分析,X-射线衍射,红外光谱,摩尔电导,激光拉曼光谱及差热-热失重分析的研究。     

On the ab initio evaluation of the solvent shift of electronic absorption spectra

Solvent shift in water of π → π^* transitions of the carbonyl group is evaluated making use of a recently proposed computdtional procedure for the continuum solvent model. Comparisons with the discrete model and with composite discrete-continuum procedures are performed.     

Solid Phase Extraction and Flame Atomic Absorption Spectrometric Determination of Trace Amounts of Zinc and Cobalt Ions in Water Samples

A simple and rapid method for the preconcentration of Co²⁺ and Zn²⁺ as their 2-guanidino-benzimidazole chelates is proposed using an octadecyl silica cartridge. The retained analytes were recovered with a mixture of 5mL of 0.01M HNO₃ and 5mL of methanol. The metal ions in the effluent were determined by flame atomic absorption spectrometry. The effect of different parameters, such as sample matrix, amount of ligand, type of eluent for elution of ions from cartridge, flow rates of sample solution and eluent, breakthrough volume, and limit of detection, were evaluated. The effects of various cationic and anionic interferences on the percent recovery of Co²⁺ and Zn²⁺ were also studied. Quantitative extraction efficiencies were obtained by elution of the cartridge with a minimal amount of solvent. Hence, with a typical preconcentration factor of 50, the limits of detections of the proposed method are 0.26 and 1.62ngmL^–1 for Zn²⁺ and Co²⁺, respectively. The method was applied to the determination of zinc and cobalt ions in different water samples.     

2D F/F NOESY for the assignment of NMR spectra of fluorochemicals

Two-dimensional (2D) NMR is an invaluable technique for the complete analysis and assignment of chemical structures. Although ¹⁹F/¹⁹F COSY experiments are routinely used for assignments in perfluorochemicals, interpretation can be difficult because four-bond (⁴J_FF) coupling constants are typically 5-10-fold larger than vicinal (³J_FF) coupling constants. Furthermore, the dependence of long range coupling constants on stereochemistry is not always known. Fluorine-fluorine NOESY correlations represent an enhancement in the arsenal of 2D ¹⁹F NMR experiments. The NOESY and COSY spectra of 2,2,3,3,4,4,4-heptafluorobutanol and a telomeric perfluorochemical iodide show that COSY identifies the 1,4-fluorine interactions whereas NOESY identifies the vicinal fluorine atoms. The combined experiments have been used to unambiguously assign all of the fluorines in a mixture of cis- and trans-perfluoro-1,3-dimethylcyclohexane and in a substituted perfluorotetrahydrofuran.     

Dipyrrolo[1,2-a;2':,1'-c]pyrazines. 7. Electrophilic Substitution of Dipyrrolo[1,2-a;2',1'-c]pyrazines and 5,6-Dihydrodipyrrolo[1,2-a;2',1'-c]pyrazines via Formylation of Dipyrrolo[1,2-a;2':,1'-c]pyrazines

A series of previously unreported aldehydes has been prepared by the formylation reaction of dipyrrolo[1,2-a;2':,1'-c]pyrazines and their 5,6-dihydro analogs by DMF and phosphorus oxychloride.     

Determination of the valence distribution of vanadium in polyolefin catalysts prepared from vanadium trichloride

An electrochemical method has been developed for determining the relative amounts of V(II) and V(III) in polyolefin catalysts prepared using aluminum alkyls and vanadium trichloride. The catalyst, usually obtained as a slurry in n-heptane, is titrated potentiometrically with ceric sulfate using a platinum indicator electrode. Under proper experimental conditions, 2 breaks are obtained, corresponding to the reactions V(II) →V(III) + e and V(III) →V(IV) + e. Interferences from other components of the catalyst are negligible. The method is useful for the analysis of both laboratory catalysts and grab samples taken from pilot plant reactors.     

Analysis of Early Medieval Glass Beads – The Raw Materials to Produce Green, Orange and Brown Colours

 Monochrome coloured glass beads of the Merovingians (5^th–7^th cent. AD) have been examined by different analytical methods. The elemental composition of a large number of mostly unprepared beads have been measured non-destructively by X-ray fluorescence analysis. After subtracting the content of the colouring oxides of the glass beads and normalising the residual values to 100% an identical soda-lime-glass matrix was obtained. X-ray diffraction was used for the identification of the crystalline colouring and opacifying pigments (SnO₂, Cu, Cu₂O, PbSnO₃), and scanning electron microscopy as well as electron probe microanalysis were applied to study the microstructure and the composition of white, brown, green, orange and yellow coloured glass beads. Oxidised metals, alloys (lead, copper, bronze, brass and mixtures of them) and iron smelting slag have been identified as raw materials to colour the soda-lime-glass.     

Contracted polarization functions for B to Ar

Using optimal exponents for B through Ne given by Dunning and those for Al through Ar by Woon and Dunning, d-type contracted polarization functions (2d/1d), (3d/1d), and (3d/2d) are generated from natural orbitals of atomic single and double excitation configuration interaction (SDCI) calculations, where the numbers before and after the slash are those of the primitive and contracted Gaussian type functions. The resulting contracted functions are tested on N₂ and P₂ molecules by self-consistent field and SDCI calculations, which clarify characteristics of the present polarization functions. Received: 5 June 1997 / Accepted: 20 August 1997     

Determination of trace rhodium by supramolecular catalytic kinetic spectrofluorimetry of β-CD-rhodium-KBrO3-vanillin salicylhydrazone

A sensitive catalytic kinetic spectrofluorimetric approach for determining ng mL⁻¹ levels of rhodium is presented, and the possible mechanism of the catalytic reaction was investigated. The determination is based on the catalytic property of rhodium to enhance the reaction of o-vanillin salicylhydrazone (OVSH) with potassium bromate in a water-ethanol medium at pH 4.80 and 45 °C. The presence of β-cyclodextrin (β-CD) obviously sensitized the assay due to its high inclusion ability towards OVSH. Under optimized experimental conditions, fluorescence measurements of the β-CD-rhodium-KBrO₃-OVSH catalytic kinetic reaction system were carried out in its fluorescent band centered at λ_ex = 333 nm and λ_em = 476 nm, respectively. The calibration graph was linear over the concentration range of 0.47–100 ng mL⁻¹ with a detection limit of 0.14 ng mL⁻¹. The effect of interferences was discussed, and the results show that the extraction method can be used to separate rhodium from interference species such as iridium. The proposed method, applied to several synthetic mixtures containing rhodium mixed with varying amounts of metal salts, produced satisfactory results.     

Purification and characterization of an extracellular α-l-arabinofuranosidase from Fusarium oxysporum

An α-l-arabinofuranosidase from Fusarium oxysporum F3 was purified to homogeneity by a two-step ion exchange intercalated by a gel filtration chromatography. The enzyme had a molecular mass of 66 kDa and was optimally active at pH 6.0 and 60°C. It hydrolyzed aryl α-l-arabinofuranosides and cleaved arabinosyl side chains from arabinoxylan and arabinan. There was a marked synergistic effect between the α-l-arabinofuranosidase and an endo-(1 →4)-β-d-xylanase produced by F. oxysporum in the extensive hydrolysis of arabinoxylan.