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- Birch-Reduction (1)
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- Cyclohexadien (1)
- Cyclohexadienderivate ; Chemische Synthese ; Birch-Reduktion ; Decarbonylierung | Cyclohexadienderivate ; Photooxidation ; Stereoselektive Reaktion ; (1)
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Research on monolayers of amphiphilic lipids on aqueous solution is of basic importance in surface science. Due to the applicability of a variety of surface sensitive techniques, floating insoluble monolayers are very suitable model systems for the study of order, structure formation and material transport in two dimensions or the interactions of molecules at the interface with ions or molecules in the bulk (headword 'molecular recognition'). From the behavior of monolayers conclusions can be drawn on the properties of lipid layers on solid substrates or in biological membranes. This work deals with specific and fundamental interactions in monolayers both on the molecular and on the microscopic scale and with their relation to the lattice structure, morphology and thermodynamic behavior of monolayers at the air-water interface. As model system especially monolayers of long chain fatty acids are used, since there the molecular interactions can be gradually adjusted by varying the degree of dissociation by means of the suphase pH value. For manipulating the molecular interactions besides the subphase composition also temperature and monolayer composition are systematically varied. The change in the monolayer properties as a function of an external parameter is analyzed by means of isotherm and surface potential measurements, Brewster-angle microscopy, X-ray diffraction at grazing incidence and polarization modulated infrared reflection absorption spectroscopy. For this a quantitative measure for the molecular interactions and for the chain conformational order is derived from the X-ray data. The most interesting results of this work are the elucidation of the origin of regular polygonal and dendritic domain shapes, the various effects of cholesterol on molecular packing and lattice order of long chain amphiphiles, as well as the detection of an abrupt change in the head group bonding interactions, the chain conformational order and the phase transition pressure between tilted phases in fatty acid monolayers near pH 9. For the interpretation of the latter point a model of the head group bonding structure in fatty acid monolayers as a function of the pH value is developed.
Einfache Decarbonylierungen und stereoselektive Oxidationen von Cyclohexadienen und Cyclohexenen
(2001)
Zusammenfassend konnte im Rahmen dieser Arbeit das Synthesepotential von Cyclohexadienen und Cyclohexenen deutlich erweitert werden. Die Darstellung der 1-Alkylcyclohexa-2,5-dien-1-carbonsäuren erfolgte mittels Birch-Reduktion in flüssigem Ammoniak und anschließender Umsetzung der intermediär entstehenden Dianionen mit Alkylhalogeniden. So konnte ausgehend von verschiedenen Benzoesäurederivaten eine Reihe interessanter Cyclohexadiene in sehr guten Ausbeuten synthetisiert werden. Erstmals gelangen säurekatalysierte Decarbonylierungen von Cyclohexadiencarbonsäuren, was die einfache Synthese substituierter Aromaten in ausgezeichneten Ausbeuten ermöglichte. In dieser Arbeit wird der Reaktionsmechanismus vorgestellt, welcher durch den Nachweis von Kohlenmonoxid in der Gasphase der Reaktionslösung durch IR-Spektroskopie untermauert wird. Bei der säurekatalysierten Umsetzung von 3-alkylsubstituierten Cyclohexadien-carbonsäuren entstanden neben den erwarteten Aromaten Lactone in ca. 50% Ausbeute. Schließlich zeigen die untersuchten Singulettsauerstoff-En-Reaktionen, der im ersten Teil dargestellten Cyclohexadiene und Lactone, durchweg hohe Regioselektivitäten und lieferten durch elektrostatische Wechselwirkungen und konformative Effekte zum Teil sehr gute Diastereoselektivitäten. Die auxiliarkontrollierte Photooxygenierungen von Cyclohexenon welches mit verschiedenen Weinsäureestern ketalisiert wurde, zeigten jedoch keine bevorzugte p-Facialität des Singulettsauerstoffs.
Electronic intensity and frequency modulation of diode lasers enables new perspectives for highly sensitive analytical in-situ techniques. For analyis of "heterogeneous" media, which may consist of coexisting gaseous, liquid, and solid phases and often show multiple light scattering, non-invasive techniques with outstanding performance characteristics can be developed. Analysis of photon density waves launched by intensity-modulated lasers provide an elegant way for the determination of absorption and scattering coefficients of multiple scattering media. The absorption coefficient can be used for qualitative and quantitative analysis of chemical constituents (which absorb in the range of the laser wavelengths). The scattering coefficient allows characterization of physical and morphological properties of the sample. In the current work, applicability of appropriate radiation transport models was investigated with simple light scattering solutions and compared with results obtained from the treatment according to the theory of Kubelka and Munk. Measurements of human blood samples are discussed. A new method for determination of water vapor partial pressure in a polyurethane foam with a frequency-modulated external cavity diode laser is discussed.
Based on a study of the German Ministry of Research and Technology in 1990 every year about 2.5 t of heavy metals are released per hectare of landfill by aqueous leaching. This leachate contains approximately 2000 t of heavy metals per year. Their decontaminations in accordance with the legal requirements represent an enormous potential for easing the burden on the environment. On the other hand, this potential opens new possibilities in the production and recycling of selected compounds. The composition of a given model solution corresponds to a landfill leachate resulting from a municipal dump leachate produced by an average German city. Actually, in most cases, a decontamination of such solutions occurs by the transfer of the problematic cations into insoluble compounds usually done by precipitation. The result of the procedure is an unspecific separation of all liquid components - and the "cycle of waste" (landfill- leaching-deposition) begins anew, certainly on a higher level. The objective of our work is the simultaneous separation of heavy metals from alkaline earth metals and iron in order to obtain a leachate which we can lead back to the landfill. The reactive extraction as a separation process offers the possibility of a selective separation of cations that is the separation of toxic - from unproblematic components and includes also the possibility of electrolysis or further winning processes to obtain the wished metals. For the realisation of extraction processes, several commercial extractants and technical equipments are available. Apart from iron, LIX 54 could be used advantageously for an extraction process - unfortunately without any considerable extraction of cadmium. But it is favourable to separate non toxic alkaline earth metals from problematic heavy metals. Such a complex task as the separation of cations from natural solutions cannot be solved easily in a one-step-extraction process. Better results should be obtained by the combination of different procedures, e.g. extraction, ion-exchange and precipitation.