Zur regioselektiven nucleophilen Addition an 2,3-Dihydrobilatriene-abc

Donors are added regioselectively to position 10 of 2,3-dihydrobilatrienes-abc in a reversible reaction, which is complicated in case of strongly basic donors due to the easy deprotonation of the partially saturated ring. Compared to the bilatrienes-abc the addition equilibrium is retarded by about two orders of magnitude.

     

Synthese von (±)-Porantherilidin

The synthesis of the title compound is described in detail.

     

Novel unexpected examples of 5JHH long range couplings in carbohydrates.

⁵J_HH Couplings proceeding through a HCCCCH - fragment rather than a HCOCCH - path in certain L-idofuranose derivatives are described. The probable mechanism is discussed.     

Elaboration of a programmed,semi-automated radiochemical processing system for neutron activation analysis of some volatile elements

Based on the method of SAMSAHL a programmed, semi-automated processing system has been developed and tested for the neutron activation analysis of the following elements: As, Se, Sb, Br, Sn and Te. The main characteristics of the procedure are the following: wet ashing of the sample (by means of digestion in a mixture of concentrated sulphuric acid and hydrogen peroxide), bromination, and chlorination. The procedure is controlled via the appropriate dosage of the reagents and a carefully managed thermal balance. The chemical yield and its reproducibility were determined by tracer techniques using exactly the same parameters as for the active runs. According to the results the method can be used for the routine determination of the given elements except antimony. Presented at the 4th Symposium on the Recent Developments in Neutron Activation Analysis, 1975, Cambridge.     

On the behaviour of styrene-acrylonitrile copolymers in solution—VI. Presentation of light-scattering results according to excluded-volume theory

A new procedure for the evaluation of the excluded-volume parameter and the unperturbed dimensions from light-scattering data is described. The treatment is based upon a test recommended by Yamakawa. The principal feature is the fitting of an appropriate theoretical master-curve to the experimental points by shifting along the logarithmic x axis. The advantages are the graphical representation, the possibility of checking the chosen co-ordination of experimental and theoretical data by means of the known relation between expansion factor and molar mass, and the relatively small amount of protracted computation needed. The method is applied to azeotropic styrene/acrylonitrile copolymers and to azeotropic α-methylstyrene/acrylonitrile copolymers.     

Synthese von Trimethyl- und Triphenylsulfonium-Cyanometallaten

Two cyano complexes of the type [R ₃S]₂ [Pd(CN)₄] (R ₃S⁺=Me ₃S⁺,Ph ₃S⁺ cations) were prepared. The identity of the obtained samples was verified by chemical analysis and investigated by IR-spectroscopy. Thev _CN stretching frequencies of the complexes were compared with similar frequencies of the corresponding alkaline cyano complex. The thermal decomposition of the compounds was examined.     

AB initio SCF LCAO MO Calculations on styrene

Minimal basis set ab initio SCF LCAO MO calculations with gaussian-type have been performed for different conformations of the styrene molecule. The computations show the molecule to be planar and the rotational barrier of the vinyl group is estimated to 3.9 kcal/mole.     

Comparability of retention indices of polar substances at elevated temperatures

Summary The non-linear dependency of the retention indices of drugs on temperature is demonstrated hence an indication of the actual working temperature is essential. Fixed temperatures for the determination of retention indices of drugs are proposed. Interlaboratory comparisons of the retention indices of 14 drugs frequently encountered in analytical practice are made for the first time on two stationary phases in three laboratories and on four GC apparatus. The data show that, in comparison with literature values, the interlaboratory deviation is reduced by 1/3 to 1/2 if same temperatures are used. Standardization of the temperature of determination of the retention indices of drugs and unknown substances in biological specimens on OV-1 and OV-17 is proposed.     

Considerations on the planned use of a scientific balance on Mars

The balance is the most widely used complex measuring instrument in science and techniques. To install a balance on Mars is a challenge for numerous aspects of in situ measurements in the next decade. By means of a balance useful parameters could be determined and a variety of investigations could be carried out there. Possible applications of a balance on Mars are reviewed. Choice of type and demands on the balance with regard to the conditions on Mars are discussed. The first step is to test a load cell with strain gauge deflection sensor.     

Morphology and oxygen sensor response of luminescent Ir-labeled poly(dimethylsiloxane)/polystyrene polymer blend films

Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir-PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir-PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir-PDMS in PS (ca. 10 wt %), the Ir-PDMS exists as circular domains, with diameters ranging from 2 to 5 mum, surrounded by the majority PS phase. For larger weight fractions of Ir-PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern-Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 mum. The results of this investigation show that the micrometer-sized Ir-PMDS domains display a 2-3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed.