Zur Kenntnis der thermischen Zersetzung von Ammoniumhexafluoroscandat,-titanat,-vanadat und-chromat

Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described.     

PAMAM Dendrimers as Anchors for the Preparation of Electrocatalytically Active Ultrathin Metallic Films

This paper describes the formation of catalytically active thin films of Pt, Pt/Au, and Pt/Ru on gold substrates stabilized by amine‐terminated polyamidoamine (PAMAM) dendrimers. A monolayer of dendrimer is initially self‐assembled on the gold substrate, which serves as a template for the growth of catalytically active thin films. As dendrimers contain tens to hundreds of functional groups at the periphery, the aggregate strength of the multidentate interactions with the gold substrate leads to the formation of robust films. The films were found to exhibit high catalytic activity for the oxidation of small hydrocarbons such as methanol. Such films offer versatility and scope for the design of effective electrocatalysts, especially in the context of microfuel cells and “dendrichips”; hence, they could find applications in the fields of sensors, fuel cells, and waste‐water treatment.     

Untersuchungen zur 3-Phononenabsorption in partiell kristallinen Polymeren

Zusammenfassung In dieser Arbeit wird die Dreiphononenabsorption in Polymeren, die den Hauptanteil an den dielektrischen Verlusten im Millimeterwellengebiet stellt, theoretisch und experimentell untersucht. Aus der Störungsrechnung bis zur 2. Ordnung wird die Temperaturabhängigkeit der Absorption abgeschätzt. Damit ist eine befriedigende Deutung des gesamten Temperaturverlaufs der dielektrischen Verlust-Kurven möglich. Im Hochtemperaturbereich läßt sich die Mehrphononenabsorption eindeutig gegenüber restlichen Relaxationsprozessen abgrenzen. Im Tieftemperaturgebiet konnte erstmals auch für das Millimeterwellengebiet ein temperaturunabhängiger Bestandteil fehlordnungsinduzierter Einphononenabsorption nachgewiesen werden. Im Übergangsbereich durchlaufen die Absorptionskurven einen Wendepunkt bei einer charakteristischen TemperaturT ₀, die dem Schwerpunkt der am Absorptionsprozeß beteiligten Phononenfrequenzen entspricht. Daraus konnten in Übereinstimmung mit dem Experiment die Frequenzen der niedrigsten optisch aktiven Phononen für die verschiedenen Polymeren abgeschätzt werden.

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Summary The 3-phonon absorption in polymers, which gives the main contribution to their dielectric loss in the microwave region, is theoretically and experimentally investigated. Perturbation theory up to the second order is used for the evaluation of its temperature dependence. The theoretical results allow an interpretation of the total absorption-temperature-curves: In the high temperature region 3-phonon absorption can be distinguished from residual relaxation losses (above the glass temperature). In the low temperature region the existence of a low frequency tail of temperature independent disorderinduced one-phonon absorption became evident. At intermediate temperatures (50–150°K) the curves show an inflexion point or plateau at a characteristic temperatureT ₀, which according toT ₀= ⁰, corresponds to the frequencies of those phonons, that mainly contribute to the multiphonon absorption. The plateau gives, in good agreement with the experiment, the frequencies of the lowest optically active phonons in the various polymers.

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Mit 6 Abbildungen in 8 Einzeldarstellungen

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung 1970 des Regionalverbandes Hessen-Mittelrhein-Saar der Deutschen Physikalischen Gesellschaft in Darmstadt, 10.–13. März 1970.     

Structure des savons alcalins

Summary This is a systematic X-ray diffraction study of the structure of the mesomorphic phases occurring with potassium soaps ranging from C₈ to C₂₂.Four types of structure have been identified. The first is lamellar with both polar groups and paraffin chains in the crystalline state. The second is also lamellar, but with both polar groups and paraffin chains in the liquid state. The third corresponds to the localization of indefinitely long ribbons on a two-dimensional oblique lattice; polar groups are crystalline and paraffin chains desorganized. The fourth corresponds to the localization of discs on a three-dimensionnalB-faces centered orthorhombic lattice; polar groups are crystalline and paraffin chains disorganized.The structural parameters and the polymorphism of the polar groups have been discussed.

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Zusammenfassung Wir beschreiben hier eine systematische Röntgenstrahlendiffraktionsforschung der Struktur der mesomorphen Phasen von Kalium Seifen von C₈ bis C₂₂.Vier Strukturtypen wurden gefunden. Die erste Struktur ist lamellar; beides, die polaren Gruppen und die Paraffinketten sind kristallisiert. Die zweite Struktur ist auch lamellar; aber in diesem Falle sind beides, die polaren Gruppen und Paraffinketten geschmolzen. Die dritte Struktur entspricht einer Lokalisation von Seifenbändern in einem zweidimensionalen monoklinen Gitter; die polaren Gruppen sind kristallisiert und die Paraffinketten geschmolzen. Die vierte Struktur entspricht einer Lokalisation von Seifenscheiben in einemB-flächenzentrierten orthorhombischen Raumgitter; die Polargruppen sind kristallisiert und die Paraffinketten geschmolzen.Wir haben aus den experimentellen Resultaten einige Schlußfolgerungen gezogen.

     

Mathematical model for the analytical signal of an herbicide sensor based on the reaction centre of Rhodobacter sphaeroides

This paper introduces a mathematical model which makes it possible both to determine the concentration of photosynthetic herbicides and to obtain a quantitative parameter in order to compare their activity using a previously described sensing system. The working principle involves the changes in absorption properties at 860 nm of the reaction centre (RC) isolated from the bacteria Rhodobacter sphaeroides when photosynthetic herbicides are present. The method has been used for the determination and activity comparison of five photosynthetic herbicides: diuron, atrazine, terbutryn, terbuthylazine and simazine. Detection limits obtained were 2.2, 0.75, 0.046, 0.25, and 1.4 μM, respectively. The resulting order for the different herbicides according to their action on RC was: terbutryn > terbuthylazine > atrazine > simazine > diuron.     

U-4C-3CR versus U-5C-4CR and stereochemical outcomes using suitable bicyclic β-amino acid derivatives as bifunctional components in the Ugi reaction

Intramolecular Ugi reactions with bicyclic β-amino acids have been performed and the effects of the configuration and N-alkylation have been studied. We have proven that preferential ring contraction or nucleophilic attack by the solvent depend not only on the presence of N-alkylation but also on the relative disposition of the carboxyl group and the amine. Excellent results in terms of stereoselectivity have been obtained in the case of N-alkyl-3-exo-amino-7-oxabicyclo[2.2.1]-2-endo-carboxylic acids.     

Solid state extrusion of thermoplastic elastomers 4

A solid state extrusion technique is applied as to produce oriented block copoly(ether ester) under various physical conditions. The morphology of the extruded samples is characterized in relation to the extrusion parameters and hard segment compositions of the polymer, using thermal analysis and X-ray methods. The lateral dimensions of the crystalline domains are found to be approximately 150 Å depending on the extrusion conditions. The statistics of the long range periodicity of the structure along the extrusion direction is in agreement with a one-dimensional two phase model, the crystalline portion of which does not vary much in thickness (35 – 45 Å). The unexpected increase in the long period and the thermal shrinkage suggest the existence of strained interlamellar amorphous chains (tie molecules). The observed variations in tensile properties are interpreted under the assumption that both the number of such tie molecules and their fully extended lengths are determined by the hard segment composition and the extrusion conditions. It is also argued that the increase in the glass transition temperature is not only a function of the composition of hard segments in the amorphous phase but also of the number of strained tie molecules.Herrn Dr. Dr. h. c. H. Hellmann zum 70. Geburtstag gewidmet.Part 3 cf. lit [11]     

Determination of gamma-hydroxybutyric acid in human urine by capillary electrophoresis with indirect UV detection and confirmation with electrospray ionization ion-trap mass spectrometry

γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ.     

Carbocyclische Verbindungen aus Monosacchariden. I. Umsetzungen in der glucosereihe

Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose Series A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23 , see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 and 24 , see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62 . The configuration of the cyclization products were established by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).