Optically active oligomer units in aggregates of a highly unsaturated, optically inactive carotenoid phospholipid

Enantiomers of glycerophospholipids show low or no optical activity. Accordingly, optical activity was not observed with the R enantiomer of a highly unsaturated carotenoyl lysophospholipid in solution. In spite of this, strong Cotton effects are detected in water. The amphiphilic carotenoid-phospholipid monomers associate to form aggregates, whose optical activity is attributed to oligomeric entities. These small helical assemblies cannot exist independently. Yet, the calculated octamer represents the simplest repeating primary unit that sufficiently expresses the absorption properties and supramolecular optical activity.     

Photoproduction of neutral pions at backward angles in the resonance region and the η-cusp

At the Bonn 2.5 GeV electron synchrotron we have measured the differential cross section of the reaction γp→π⁰ p at a pion CM angle of 170° and at photon energiesK _γ between 0.6 and 1.8 GeV. In comparison to previous measurements the accuracy of the data was improved substantially. For the first time in neutral pion photoproduction a cusp structure at the η-threshold has been confirmed [1].     

Analysis of complex thermoanalytical curves: The thermodynamic and kinetic parameters of isopropylammonium nitrate

A method is presented to determine thermodynamic and kinetic parameters from complex thermoanalytical curves. Such curves are obtained when thermoanalytical events like phase transition and chemical decomposition overlap.Isopropylammonium nitrate was taken as an example to demonstrate how these parameters were determined from non-isothermal TG and DSC curves by constructing DSC-DTG sum curves.

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Zusammenfassung Es wird ein Verfahren zur Bestimmung thermodynamischer und kinetischer Parameter von komplexen thermoanalytischen Kurven beschrieben. Kurven dieser Art entstehen bei der Überlappung thermoanalytischer Ereignisse wie z.B. Phasenumwandlungen und chenliche Zersetzungen.Am Beispiel von Isopropylammoniumnitrat wird demonstriert, wie die einzelnen Parameter der nicht-isothermen TG und DSC Kurven durch Konstruktion von DSC-DTG-Summenkurven ermittelt werden.

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Die papierchromatographische Trennung von Kreatin und Kreatinin und die quantitative Bestimmung von Gesamtkreatinin in Lebensmitteln

Zusammenfassung Es wird ein Verfahren zur papierchromatographischen Trennung von Kreatin und Kreatinin angegeben. Bei der papierchromatographischen Bestimmung des Gesamtkreatinins in Lebensmitteln wird vorhandenes Kreatin durch Eindampfen mit Salzsäure zuerst in Kreatinin umgewandelt. Störende Stoffe, die ebenfalls die Jaffésche Reaktion geben, lassen sich ebenso wie die Eigenfärbungen gut abtrennen. Die quantitative Bestimmung erfolgt durch Photometrie der mit Pikrinsäure in alkalischer Lösung erhaltenen Färbung. In Erzeugnissen mit niedrigem Kreatiningehalt wird das Kreatinin vorher durch Ausziehen mit Alkohol angereichert.     

Beitrag zur Bestimmung des Gesamtkreatinins in Lebensmitteln

Zusammenfassung Es wird über die Sichtbarmachung papierchromatographisch isolierten Kreatinins mit Hilfe einer Quecksilberlampe, welche bevorzugt kurzwelliges Ultraviolett ausstrahlt, berichtet. Die Erfassungsgrenze liegt bei 3–5 g Kreatinin. Der molare Extinktionskoeffizient wird im Maximum der Kreatininbande bei 235 m zu =6448 bestimmt. Es wird über eine Abänderung des Arbeitsverfahrens von L. Acker, W. Diemair, D. Pfeil u. G. Schiffner ¹ berichtet.     

A portable absorption-fluorometer for detection of organic substances in fluids

Using the method of multipath-saturation fluorescence, which considers both fluorescent as well as nonfluorescent substances, the total absorption coefficient can be determined with high sensitivity. This new fluorescence method is appropriate, e.g. for in-situ applications. Thus a portable absorption-fluorometer has been constructed. The main part of the device is a multireflection cell based on a design of Herriott with a 1 cm quartz-cuvette. Two pairs of spherical dielectric mirrors are used to realize the multireflection of the excitation radiation in the UV and blue spectral range. The combination of a cylindrical and a convace mirror leads to a long pathway of the excitation radiation and, thus, to a full absorption by the fluid. A first experiment has been performed with drinking water samples defined polluted by non-fluorescent p-nitrophenol and 2-nitroaniline. Based on the method of multipath-saturation fluorescence a good correlation to the substance concentration was achieved, whereas the conventional absorption failed.     

Construction, operation and output characteristics of a small, long-life, cataphoretic HeSe laser

The properties and main design features of a small, cataphoretic HeSe⁺ laser are described. By improving both the He buffer gas containment and the Se vapour deposition, laser life can be increased considerably to several thousand hours. The length of the active laser region can be reduced to 100 mm without appreciable loss in single pass gain by reduction of the capillary diameter to 1 mm. Up to 3 mW laser power in six blue-green and green Sell lines can be extracted from this small active volume. By synchronizing the spontaneous discharge striations in the He-Se vapour mixture, laser noise is reduced to less than 3% r m s. A few potential applications for this type of laser are listed to encourage commercial interest.     

Conformation and Circular Dichroism of β,β-Carotene Derivatives with Nitrogen-, Sulfur-, and Selenium-Containing Substituents

The CD spectra of several 3-substituted azido-, amino-, thio-, phenylseleno- and (phosphonoseleno)-β,β-carotene derivatives with one or two stereogenic centers are discussed with respect to conformational changes of the cyclohexene end group. N- and S-Substituents (N₃, NH₂, SH) have no influence on the conformer equilibrium compared to O-substituents, whereas Se-substituents (SePh, SePO(OC₃H₇)₂) slightly destabilize the preferred conformer of the β-end group.     

Formation of DMSO and DMF radicals with minute amounts of base

So far overlooked DMSO and DMF form long-lived radicals in the presence of small amounts of bases, DMF radicals being less stable than DMSO radicals. In solvent mixtures, the presence of DMSO prolonged the lifetime of DMF radicals. The occurrence of radicals may explain previously reported unexpected outcomes of reactions performed in these solvents. The commonly accepted inertness of these solvents towards minor quantities of alkali seems not to be warranted.