An efficient synthesis of [1,1]ferrocenophane via 1,1′-bis(6-fulvenyl)ferrocene

[1,1]Ferrocenophane can be prepared by reduction of 1,1′-bis(6-fulvenyl)ferrocene with complex borohydrides to give the dianion of 1,1′-bis(cyclopentadienylmethyl)ferrocene. Reaction of this dianion with ferrous chloride produces the ferrocenophane in good yield.     

Impact of adsorption isotherm parameters on the performance of enantioseparation using simulated moving bed chromatography

Often there are several chromatographic systems, i.e., combinations of mobile and stationary phases, available to solve a certain separation problem. Essential differences of these chromatographic systems are the separation factors and the efficiencies. For preparative applications in addition also the column saturation capacities and solubility limits are of importance. The impact of all these parameters appears to be rather well understood for conventional overloaded elution chromatography using a single column. In the last years the continuous simulated moving bed (SMB) process was increasingly used as a powerful alternative to batch elution since increased productivities and reduced solvent consumptions could be realised. However, the selection of suitable chromatographic systems is more sophisticated for this process. In this paper five different chromatographic systems capable of separating the enantiomers of mandelic acid are compared based on the achievable productivities using SMB chromatography. For these five systems the adsorption isotherms have been determined experimentally. Subsequently, an analysis of the SMB process was performed numerically using a well-established model.     

Quantitative depth profiling in glow discharge spectroscopies – A new deconvolution technique to separate effects of an uneven erosion crater shape

An algorithm is presented as a concept for the quantification in direct current and radiofrequency glow discharge (GD) modes for GD optical emission spectroscopy. The algorithm is divided into excitation and sputtering part and thus it is possible to distinguish between the different excitation processes and to consider equivalent sputtering crater formations in both modes. Intensity-time profiles are affected corresponding to the method by several effects. One important effect is that sputtering occurs at a single time in different depths because of curved crater bottoms, this is usually called crater effect. The main purpose is to introduce an iterative deconvolution technique which for the quantification numerically takes into account the curved sputtering crater bottom. Input data for the deconvolution technique are the calibrated mass-time profile, the partial densities of the sample constituents and the measured final shape of the sputtering crater. Using a relatively simple model for ion sputtering the deconvolution technique improves iteratively the calculated layer structure by means of information on crater formation. The mathematical handling is illustrated for the quantification of a depth profile of a multilayer sample of ten 100 nm layers. The resulting concentration-depth profile reflects excellently the real elemental distribution of the multilayer system.     

Photochemistry of condensed isoxazolines

Summary The condensed bridged isoxazolines4 are rearranged on irradiation with a low-pressure mercury lamp exclusively into condensed derivatives of tetrahydropyridine5. The selectivity of the rearrangement is due to a stabilization of the biradical8 by the overlap of the radical-electrons with -electrons of the C=C double bond and the heterocyclic ring. Quantum yields of the photorearrangement, established from the consumption of the starting materials4, were determined.

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Photochemie kondensierter Isoxazoline

Zusammenfassung Die kondensierten überbrückten Isoxazoline4 werden durch Bestrahlen mit einer Niederdruckquecksilberlampe ausschließlich zu kondensierten Tetrahydropyridinderivaten (5) umgelagert. Die Selektivität der Umlagerung beruht auf der Stabilisierung des Diradikals8 durch Überlappung der ungepaarten Elektronen mit -Elektronen der C=C-Doppelbindung und des Heterocyclus. Aus dem Verbrauch an Ausgangsmaterial (4) wurden Quantenausbeuten der Photoumlagerung bestimmt.

     

Determination of Low Contents of Fenpiverine Bromide by Extraction Spectrophotometry

An ion-pair extraction spectrophotometry method was developed for the determination of fenpiverine bromide in tablets. To determine this substance it was necessary to find experimental conditions that would allow eliminating the influence of other components of the tablets. Attention was paid to the fact that a suitable pH of water phase was necessary to achieve high selectivity.Received December 11, 2002; accepted April 24, 2003 Published online July 28, 2003     

Shortcut method for evaluation and design of a hybrid process for enantioseparations

Hybrid processes for enantioseparations have a considerable potential for reducing investment and operational costs. An example is the combination of simulated moving bed (SMB) chromatography and selective crystallisation. However, the design of integrated processes is a difficult task. A shortcut method is presented that can serve as a tool for design and estimation of the potential of such processes. The approach requires only limited experimental data and thus allows for systematic parameter studies. The method is based on the determination of the purity-performance characteristic of the SMB process and rigorous application of mass balances. The use of relative mass fluxes allows derivation of simple algebraic expressions for essential process parameters. The significant potential of combining SMB and crystallisation is demonstrated for the example of the separation of mandelic acid enantiomers.     

Radiochemische und elektrochemische untersuchung der adsorption von cytochrom c an der phasengrenze elektrolyt/quecksilber

The surface area of an adsorbed cytochrome-c molecule was calculated both from the radiochemically determined surface concentration and from the adsorption kinetics. The value thus obtained is 2000±200 Ų. This accordance shows that the Koryta equation holds for the adsorption kinetics of proteins. The comparison with the cross-section of the molecule in crystalline state allows us to conclude that cytochrome c is unfolded at the electrode. While at low concentrations the molecules are strongly adsorbed, at high concentrations an exchange of adsorbed molecules with molecules in the bulk occurs. The mechanism of charge transfer is proposed to be a superposition of electron transport through adsorbed molecules and exchange of already reduced molecules.     

Substoichiometric determination of heavy rare earths by isotopic dilution analysis

A substoichiometric method for the determination of heavy rare earths (holmium, thulium) has been developed. After the addition of a substoichiometric amount of EDTA to the test sample of rare earth labelled with its radioactive isotopes, the negatively charged complex formed was separated by passage through a column of Dowex 50 x 8. Interfering metals can be removed by preliminary cupferron and diethylammonium diethyldithiocarbamate extraction. Concentrations of rare earth down to 4 x 10(-7)g 5 ml have been determined.