Stohrer, Wolf-Dieter
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Stohrer, Wolf-Dieter
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Stohrer, Wolf-Dieter
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Stohrer, W.-D.
GND
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Item type:Publication, Porphyrin- und Porphyrin-Fulleren-Derivate - Synthese und Immobilisierung auf GoldoberflächenPrimary object of this work was the derivatisation of porphyrins and fullerenes for enabling them to adsorb and co-adsorb on gold surfaces, respectively. The adsorbates were designed according to a tool box concept. Starting from the red blood pigment heme, partial synthetic routes easily lead to desired products. Commercially available hemin was first converted to deuteroporphyrin dimethylester, which served as starting material. Metalloporphyrins and fullerenes were both functionalised by bis-lipoic acid anchors. A fullerene SAM could be postmodified by Diels-Alder reaction without cleaving the gold-sulphur bond yielding a Zn(II) porphyrin fullerene dyad. Due to strong surface attachment it should be possible to generate a photocurrent using said donor-acceptor pair. Immobilised species were electrochemically and morphologically characterised by state-of-the-art techniques. Surface coverages of modified gold electrodes were calculated after reductive desorption in strong alkaline solution. Nanostructured surfaces exposing different chemical functionalities were tested regarding sensor and catalytic activities.doctoral thesis294 473 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Identification of the Molecular Mechanisms underlying the Gastrointestinal Toxicity of the Immunosuppressants Mycophenolate Mofetil and Enteric-coated Mycophenolate Sodium using a Proteo-Metabolomic Approach(2013-06-11); ; ; Mycophenolic acid (MPA) is the cornerstone of most immunosuppressive drug regimens after organ transplantation. However, gastrointestinal side effects diminish MPA's otherwise outstanding safety and efficiency. Using a unique cell culture model featuring the human colon cancer cell line LS180 and a combination of molecular biology methods and a non-targeted proteo-metabolomic strategy based on high-performance liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy, we were able to identify impairment of LS180 cell lipid metabolism as well as effects on structural proteins and nucleotide-dependent processes as main mediators of the negative effects of MPA on gastrointestinal barrier function.doctoral thesis283 163 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Untersuchungen des Flüssig-Flüssig Phasenübergangs von Lösungen Ionischer Flüssigkeiten mit dem Trifluormethylsulfonat-AnionPhase separations of solutions of ionic liquids of the type Alkylmethylimidazolium Trifluoromethylsulfonate (Cnmimtfo) with different lengths of alkyl side chains (n=4,5,6,7,8) were investigated in various solvents. Phase diagrams were analysed for solutions in water, dioxane and weakly polar arene-halides using a function that presumes Ising critical behavior and takes the asymmetry of the phase diagrams into account. The phase diagrams are in agreement with the theorem of corresponding states. Comparison with the model system of charged hard spheres in a dielectric continuum (restricted primitive model; RPM) is made. The RPM critical temperatures depend linearly on the dielectric constant of the solvents. Two systems were selected (C6mimtfo-Chlorobenzene and C8mimtfo-4Chlortoluol) for studies of the critical behavior with mK-accuracy of viscosity, refractive index, static and dynamic light scattering and theoretical analysis. The measurements prove Ising behavior with deviations indicating normal crossover to mean-field criticality.doctoral thesis331 261 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, NMR Spektroskopische Untersuchungen von Körperflüssigkeiten (Kinderurin)(2007-10-17); ; ; Urine is an information-rich biofluid that can provide insights into the metabolic state of an organism. While urine is easy to gain, the investigation is difficult since every metabolite needs a single analysis. NMR offers several advantages for metabolomic investigations. It requires minimal or no sample preparation and small sample volume. It is non-destructive and allows the observation of a large number of metabolites simultaneously and without preselection. A goal of this study was the assignment of resonances of recent metabolites in the one- and two-dimensional NMR spectra of human urine since the inherent complexity of urine NMR spectra is a common barrier to apply targeted investigations. The identification of recent metabolites was assisted by using SPE and HPLC.Changes in metabolic profiles resulting from diet may be difficult to differentiate from normal or pathological physiologic variation. Thus another aim was the definition of dietary influence on the composition of urine. We examined the effect of eating banana, pecans and oranges on the composition of urine. The metabolites were quantified on the basis of peak heights and were expressed in terms of Creatinine, which can provide an internal standard.doctoral thesis279 233 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Methodological developments towards quantitative short TE in vivo :sup:1:/sup:H NMR spectroscopy without water suppression(2002-08-15); ; ; Water suppression (WS) has been used exclusively as a routine for almost two decades in the in vivo 1H NMR spectroscopy to avoid the experimental and postprocessing difficulties caused by the dominant water signal, which is 3 to 5 orders magnitude larger than the signals of metabolites of interest. However, WS has some disadvantages as compared to the spectroscopy without WS. This thesis is devoted to methodological developments towards short echo time (TE) in vivo proton NMR spectroscopy without WS. The methodology developed in this thesis integrates experimental and software approaches for the optimization of the spectroscopic techniques, which concerns the two major parts, namely, the spectral measurements and spectral quantification. An experimental method was developed to eliminate frequency modulation sidebands induced by gradient pulses, a major obstacle of in vivo 1H NMR spectroscopy without WS. First order phase errors were eliminated by radio frequency pulse sequence optimization. The dominant water signal was modeled and extracted with a scheme developed on the basis of the Matrix Pencil Method, The extracted water signal was used as a reference for the lineshape correction. With these approaches the imperfections of the spectra were removed. Spectral quantification scheme was developed by combining the baseline characterization by a wavelet transform based technique and the time domain spectral fitting using full prior knowledge of the metabolite model spectra. The model spectra were obtained by spectral simulation instead of in vitro measurements. The performance of the methodology was tested and verified by Monte Carlo studies, phantom measurements and in vivo measurements on rat brain, and compared with existing methods. More than 10 metabolites can be quantified from spectra measured on a 4.7 T NMR imaging system. The estimated concentrations of major metabolites are in good agreement with literature values.doctoral thesis228 266 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Metabolische Veränderungen bei cerebralen Erkrankungen unter Einfluss therapeutischer Maßnahmen.(2014-11-19); ; ; The liver synthesizes a lot of essential substances and works as a detoxification organ by biotransforming toxic compounds, like ammonia. Ammonia is mainly produced by the metabolism of proteins and amino acids. Considering the numerous hepatic functions, chronic and acute liver failure can lead to metabolic disorders. The toxic Ammonia cannot be degraded any longer by the urea cycle and causes high concentrations in blood. This is called hyperammonaemia (HA) and leads to hepatic encephalopathy (HE), which is a neuropsychiatric disorder. The aim of this study was to investigate the effect of L-carnitine (L-C) on primary brain cell cultures under HA conditions. The results showed that, for example, the glutamine-glutamate-cycle, which plays an important role for the ammonia detoxification, was altered under hyperammonamic conditions. L-C normalises the alterations of the metabolic pathways and the syntheses of their metabolites under HA/HE. Thus, L-C as a potential therapeutic agent is of high interest in the context of acute and chronic HE. Further research is necessary to clarify the procedures of the mechanisms of L-C precisely.doctoral thesis283 134 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Selektive Totalsynthese von Chlorinen mit annellierten Chinonen zur Untersuchung des Symmetrieeinflusses auf den Lichtinduzierten Elektronentransfer(1998-02-27); ; ; Um den Einfluss von Symmetrieeffekten auf den lichtinduzierten Elektronentransfer zu untersuchen, wurden zwei unterschiedlich mit Chinonstrukturen annellierte Chlorine als Donor-Akzeptor-Modellsysteme synthetisiert. Das Chinon ist entweder entlang der x-Achse orientiert, welche den gesaettigten und den diesem gegenueberliegenden Ring durschschneidet oder entlang der y-Achse, so dass das Chinon benachbart zum gesaettigten Ring lokalisiert ist, Im Rahmen dieser Dissertation konnte ein totalsynthetischer Zugang zu den angestrebten Chlorin-Chinon-Diaden in 12 bzw.17 Reaktionsschritten erarbeitet werden. Die zur Untersuchung von Symmetrieeinfluessen auf den lichtinduzierten Elektronentransfer notwendigen Substitutionsmuster beider Diaden wurden im Verlauf der Synthese durch den Einbau der entsprechenden, bereits die Chinonuntereinheit tragenden Pyrrolbausteine erhalten.Letztere konnten ausgehend von Naphthochinon aus einfachen Grundchemikalien aufgebaut werden.In order to investigate the effect of the molecular symmetry on the light induced electron transfer in chlorin-quinone dyades two chlorin-quinone donor-acceptor model systems were synthesized. The quinone is either be orientated along the x-axis, by which the chlorin is intersected at the reduced ring and the opposite ring or along the y-axis, so that the quinone ist located adjacent to the reduced ring. The target donor-acceptor systems could be obtained according to a general synthetic approach which was developed for the synthesis of chlorins and corrins. The concept of this ynthesis requires altogether four monocyclic building blocks. A new synthetic pathway was developed for the preparation of the pyrrole rings bearing the quinone moieties.doctoral thesis267 113 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Synthese von Chlorinen mit annellierten Lactamringen als Untereinheiten für künstliche Photosynthese-Modellsysteme(1998-03-11); ; ; The dissertation subsumes to the actual photosynthetic research, which is engaged in discussions about details of biological photosynthetic processes. At the present time the synthesis of artificial modelsystems is aimed to abstract functional and structural aspects of natural photosynthetic-reaction center. These modelsystems allow investigations of processes under defined conditions. The dissertation describes the synthesis of chlorines with annellated lactame rings from cyclohept-4-enone and pyrrolic building blocks, which should be used as potential subunits for artificial photosynthtetic-reactioncenters. On attemps to synthesize differrent pyrrolic chlorin prebuilding blocks the synthesis of 5-formyl-2-cyanopyrrole was evolved. After linkage of this pyrrolic building block with an ABC-tricycle the cyclisation to chlorins containing an annellated ring were successful. After cleavage of a protecting group the chlorines underwent Beckmann-rearrangement which delivers chlorines with annellated lactame rings as potential subunits for photosynthetic-modelsystems.doctoral thesis421 122 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Selektive Synthese von neuartigen Chlorinen für die Photodynamische Therapie(1998-08-13); ; ; From Deuteroporphyrin through partial synthesis derived chlorins were taken in this work as starting products for the synthesis of regioisomeric formylchlorins, crown ether- and estron-chlorin adducts. The cis- trans- stereoisomeric chlorins can be through appropriate protonating conditions interconverted. The difference in the bathochromic shift of the UV/Vis bands of the formylchlorins were investigated and qualitatively interpreted on the basis of similar in the literature described phenomena. The binding through esterification of an enantiomeric estron derivative to the propionic side chains of a racemic chlorin yields two through open column chromatography separable optical active diastereomers which can be deployed as fluorescence pigments and photosensibilisators for the tumor detection and/or destruction. The binding through amidation of crown ether to the propionic side chains of a chlorin produce derivatives which could be of interest for a variety of host-guest relations concerning molecular recognition and catalysis. The last part of the work deals with the novel enzymatic and catalytic oxidation of deuteroporphyrin to chlorins and oxochlorins which should carry significant consequences for the biosynthesis and synthesis of similar natural hydroporphyrins.doctoral thesis342 86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Verwendung einer neuartigen Ringschlussreaktion zur Totalsynthese von Chlorin-Fulleren- und Chlorin-Chinon-Dyaden als Modellsysteme fuer die Photosynthese(2000-02-18); ; ; The aim of this dissertation was the total synthesis of model compounds for an elementary step of photosynthesis, the light induced charge separation. In contrast to many known model systems in literature, in which porphyrins have been used as electron donors, the donor used in this case was the chromophore of the naturally photosynthetic pigments, a chlorin derivative (dihydroporphyrine). As an electron acceptor a fullerene C60 has been used, which is known to be an excellent electron and energy acceptor since a few years. Another acceptor, which has been used was a quinone, which serves also as an acceptor in the naturally photosynthetic systems. Based on a model synthesis a total synthetic approach to a chlorin derivative with an anellated sulfolene ring could be achieved. This chlorin derivative, which is a precursor for a dimethylene chlorin (heterocyclic o-quinodimethane), could be used for many functionalisations by Diels-Alder reactions. Further a new ring closure method has been developed which has some advantages in preparative use. This new ring closure method involves a thermic cyclization of a carboethoxy-substituted hydrobiline derivative to the corresponding chlorin macrocycle. The cyclization is part of a cascade of reactions during which also the dienophile like fullerene C60 or quinone is covalently linked to the chlorin framework by a Diels-Alder reaction. This led to the desired dyads, in which the luminescence is quenched, which indicates an intramolecular transfer of electrons or energy from the chlorin moiety to the acceptor moiety.doctoral thesis341 94