Simultaneous measurement of cross sections for pion production in pp recations at beam momenta of 805.2 MeV/c and 796.0 MeV/c with the TOF spectrometer at the COSY accelerator. / Simultane Bestimmung der Wirkungsquerschnitte von pionenproduzierenden pp-Reaktionen bei Strahlimpulsen von 805,2 MeV/c und 796,0 MeV/c mit dem TOF-Spektrometer am Beschleuniger COSY.

Simultaneous measurement of cross sections for pion production in pp recations at beam momenta of 805.2 MeV/c and 796.0 MeV/c with the TOF spectrometer at the COSY accelerator. / Simultane Bestimmung der Wirkungsquerschnitte von pionenproduzierenden pp-Reaktionen bei Strahlimpulsen von 805,2 MeV/c und 796,0 MeV/c mit dem TOF-Spektrometer am Beschleuniger COSY.

Techn. Universiẗat, Diss., 2003--Dresden.

No description available.

La spectroscopie RMN 2D du deutérium en abondance naturelle (DAN) en utilisant les cristaux liquides chiraux comme solvant de RMN est une méthodologie efficace pour deux raisons: i) l’interaction quadrupolaire (interaction RMN sensible à l’ordre orientationnel des molécules et spécifique aux noyaux de spin I>1/2) n’est plus nulle en moyenne comme dans les liquides; ii) la chiralité du milieu permet de discriminer spectralement des énantiomères (molécule chirale) ou des directions énantiotopes (molécule prochirale). L'objectif principal de ce travail de Thèse était d'explorer le potentiel analytique de cette technique pour analyser le fractionnement isotopique naturel deutérium dans le cas d’ester d’acides gras saturés (AGS) et (poly)insaturés (AGI). Le but ultime de ce travail est de fournir de nouvelles informations (de nature stéréochimique) pour améliorer la compréhension de certains mécanismes enzymatiques impliqués au cours de leur biosynthèse. Dans ce contexte, nous avons montré que l'utilisation de solutions organiques orientées de polypeptides (mésophases chirales) utilisant des co-solvants polaires comme le DMF ou la pyridine (Py) fournissait les meilleurs résultats en termes d’(énantio)discrimination spectrale (nombre de sites et amplitude) sur la base des déplacements chimiques et des éclatements quadrupolaires du deutérium. Ainsi, la mésophase chirale (PBLG/Py) a été utilisée avec succès pour analyser les AGI comme le linoléate de méthyle (C18), pour lequel nous avons pu mesurer l'excès énantio-isotopomèrique (eei) au niveau de chaque site méthylène de la molécule. Pour la première fois, d'importantes informations relatives à la stéréochimie des mécanismes enzymatiques, inaccessibles par la méthode conventionnelle SNIF-NMR®, ont été déterminées. La même méthodologie impliquant la mésophase achirale (PBG/Py) et chirale (PBLG/Py) s’est révélée également être un excellent outil pour l'analyse des SAFA sous leur forme libre (C14 à C18) ou sous leur forme de triglycérides (3*C4 et 3*C14). L'attribution des doublets 2H détectés sur les spectres RMN 2D anisotropes des SAFA a été confirmée par l'élaboration d'un modèle théorique capable de prédire le comportement orientationnel de ces molécules flexibles. Comme exemple illustratif, la méthode a été appliquée pour étudier les mécanismes enzymatiques convertissant le linoléate en vernoléate dans deux plantes différentes. Enfin, pour améliorer la compréhension des interactions «soluté-polypeptide» impliquées dans les mécanismes d'orientation et d’énantio-discrimination, nous avons étudié par RMN 2D DAN, l'évolution des paramètres d'ordre (matrice de Saupe) de deux molécules prochirales, rigides et apolaires dissoutes dans une mésophase chirale préparée en mélangeant deux polypeptides de même stéréochimie (L), mais dont la nature chimique des chaînes latérales est différente, en fonction de leur proportion massique respective. / Natural abundance deuterium (NAD) 2D-NMR spectroscopy using (a)chiral liquid crystals as NMR solvent is a powerful method for two reasons: i) the quadrupolar interaction (an order-sensitive NMR interaction specific to spins I > ½) is not averaged to zero anymore as in liquids; ii) the chirality of medium allows enantiomers (chiral molecule) or enantiotopic directions (prochiral molecule) to be spectrally discriminated. The main objective of this Thesis work was to explore the analytical potential of this technique to analyze the natural distribution of deuterium in the case of esters of saturated fatty acids (SAFA) and (poly)unsaturated fatty acids (PUFA). The ultimate goal of this research is to collect new (stereochemical) information to improve the understanding of some enzymatic mechanisms involved during their biosynthesis. In this context, we have shown that the use of oriented solutions of polypeptide (chiral mesophases) using polar co-solvents such as DMF or pyridine (py) provided better results in terms of spectral (enantio)discrimination (number of sites and magnitude) on the the basis of chemical shifts and deuterium quadrupole splittings. Thus, the chiral mesophase (PBLG/py) has been applied successfully to analyse PUFA’s like the methyl linoleate (C18) for which we could measure the enantio-isotopomeric excess (eie) at each methylen site of the molecule. For the first time, important information related to the stereochemistry of enzymatic mechanisms, inaccessible by the conventional method SNIF-NMR®, have been determined. The same methodology using achiral (PBG / py) and chiral (PBG / py) mesophases, revealed also to be an excellent tool for analysing SAFA in their free form (C14 to C18), or in triglyceride forms (3*C4 and 3*C14). The assignment of 2H doublets detected on 2D-NMR spectra of SAFA’s was confirmed by developing a theoretical model predicting the orientational ordering behavior of these flexible molecules. As illustrative exemple, the method was applied for investigating the enzymatic mechanisms converting the linoleate into vernoleate in two different plants. Finally, to improve the understanding of “solute/polypeptide" interactions involved in the orientation and enantiodiscrimination mechanisms, we have investigated by NAD 2D-NMR the evolution of the order parameters (Saupe matrix) of two apolar, rigid prochiral molecules dissolved in a chiral mesophase made by mixing two polypeptides having the same stereochemistry (L) but different type of side chains, versus their respective mass proportion.

Bile is a biofluid synthesized by liver and concentrated in the gallbladder. Interference with the bile flow may cause cholestasis. Primary sclerosing cholangitis (PSC) is an inflammatory cholestatic disorder which eventually may result in liver cirrhosis and failure. The management of PSC is controversial. The only effective treatment for end stage disease is orthotopic liver transplantation (OLT). However, cholangiocarcinoma (CC), which is the major complication of this long-lasting disease, is an absolute contraindication for the surgery. Therefore, early diagnosis of the disease can not only improve the outcome of PSC, but also facilitate the allocation of donated livers to those who can benefit from transplantation. Unfortunately, the diagnosis of CC is challenging. Endoscopic retrograde cholangiopancreatography (ERCP), the gold standard technique, is highly invasive. Non-invasive alternatives such as magnetic resonance cholangiopancreatography (MRCP) have lower accuracy. Therefore, it is essential to develop more accurate and less invasive diagnostic techniques. Magnetic resonance spectroscopy (MRS) is an evolving technique with potential to detect disease-related metabolic changes. In vitro studies have proven the capacity of MRS in the early detection of hepatopancreatobiliary (HPB) disorders based on the metabolic analysis of bile obtained invasively. An in vivo alternative has been attempted by others on human bile within the gallbladder. However, due to the poor quality of the acquired spectra, quantification of most major bile metabolites was not possible, except for choline-containing phospholipids (chol-PLs). In the current study, the quality of the in vivo 1D spectra has been greatly improved, and we have obtained the first 2D L-COSY spectra from bile within the gallbladder. Spectral data from healthy controls and PSC patients were compared. Statistically significant differences in the concentrations of chol-PLs, and glycine- and taurine-conjugated bile acids were revealed in the 1D analysis. Our 2D spectra also demonstrated potential for the detection of metabolic differences between the two groups. The success of these studies indicates a strong potential of in vivo bile MRS techniques to characterize and diagnose a wide variety of HPB disorders. / May 2014

Since the development of the ruthenium containing precatalysts Grubbs 1 (1) and Grubbs 2 (2), there was an increase in the development of new precatalysts. The NMR characterization could not cope with this. The NMR characterization mainly consists of 1H, 31P, COSY and rarely 13C. Due to the high natural abundance of 1H and 31P (99.98% and 100%), these experiments could be carried out quickly and easily. The only change that had to be made was to the spectral width, to accommodate the carbene signal (Ru=CH) between δ 20.02 and δ 17.32 ppm. The lack of 13C characterization is attributed to the low natural abundance of these nuclei that is only 1.10% and the lack of published parameters. Furthermore, the broad spectral width of 300 ppm increases the difficulty because the number of scans has to be increased to increase the sensitivity of the spectra and obtain useful data. In this study the precatalyst 1 was used to learn the NMR technique as well as to acquire the NMR parameters. 2 and two other commercial Grubbs-type precatalysts 3 and 4 underwent NMR characterization so that acquired values could be compared with the literature. Six other non-commercial Grubbs-type precatalysts 5-10 were synthesized and characterized. Due to the instability of the precatalysts and taking into account the duration of these experiments, the characterization was done over three steps. The first step was to do the following experiments: 1H, COSY, HSQC and HMBC, which took four hours. The next step was the DEPT135 experiment of three hours, and finally the 13C experiment of seven hours. The maximum amount of information could be obtained in this way. The combined NMR parameters for this study was obtained and used to characterize the Grubbs-type precatalysts 5-10 partially. Due to the large amount of overlapping peaks in the aromatic and alkane areas the resolution was not sufficient for full characterization. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Since the development of the ruthenium containing precatalysts Grubbs 1 (1) and Grubbs 2 (2), there was an increase in the development of new precatalysts. The NMR characterization could not cope with this. The NMR characterization mainly consists of 1H, 31P, COSY and rarely 13C. Due to the high natural abundance of 1H and 31P (99.98% and 100%), these experiments could be carried out quickly and easily. The only change that had to be made was to the spectral width, to accommodate the carbene signal (Ru=CH) between δ 20.02 and δ 17.32 ppm. The lack of 13C characterization is attributed to the low natural abundance of these nuclei that is only 1.10% and the lack of published parameters. Furthermore, the broad spectral width of 300 ppm increases the difficulty because the number of scans has to be increased to increase the sensitivity of the spectra and obtain useful data. In this study the precatalyst 1 was used to learn the NMR technique as well as to acquire the NMR parameters. 2 and two other commercial Grubbs-type precatalysts 3 and 4 underwent NMR characterization so that acquired values could be compared with the literature. Six other non-commercial Grubbs-type precatalysts 5-10 were synthesized and characterized. Due to the instability of the precatalysts and taking into account the duration of these experiments, the characterization was done over three steps. The first step was to do the following experiments: 1H, COSY, HSQC and HMBC, which took four hours. The next step was the DEPT135 experiment of three hours, and finally the 13C experiment of seven hours. The maximum amount of information could be obtained in this way. The combined NMR parameters for this study was obtained and used to characterize the Grubbs-type precatalysts 5-10 partially. Due to the large amount of overlapping peaks in the aromatic and alkane areas the resolution was not sufficient for full characterization. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

No description available.

Homopolymers and copolymers produced from aromatic based methacrylates, acrylates, and dimethacrylates are excellent materials with many applications in dentistry, microelectronics, and optics, including optical eye wear, fiber optics, and non-linear optics, such as holography. Carbazole based polymers have demonstrated good optical, photo-refractive, and charge-transporting properties, combined with ease of processing. The objective of this research was to design, synthesize, and characterize high refractive index polymers and copolymers for use in optical spectacle lenses of eyeglasses. Additionally, other interesting attributes were observed for selected carbazole based polymers, such as high thermal stability and birefringence, which could lend these materials to other uses, such as non-linear optics and electronic data storage. A family of novel, high refractive index homopolymers and copolymers were synthesized by incorporating carbazole, along with other aromatic substituents, into methacrylates, acrylates, and dimethacrylates. Subsequent free radical polymerizations provided for high refractive index materials well suited for lightweight optical spectacles and other applications. The refractive index of materials can be increased by increasing the polarizability of substituent groups. By incorporating oxygen, sulfur, or sulfoxide groups into polymers, high refractive index polymers have been attained. By reacting the phenol, aromatic diols, or aromatic thiols with 9-(2,3-epoxypropyl)-carbazole, the refractive index of the final polymer can be increased further. The reaction of the carbazole based intermediate with methacryloyl chloride or methacrylic anhydride eliminated any hydroxyl groups in the final methacrylate or dimethacrylate. Hydroxyl groups undergo intermolecular hydrogen bonding, which increases viscosity. The absence of hydrogen bonding in the final methacrylated monomers reduces viscosity, which is desirable for processing. Novel carbazole based monomers and polymers were characterized in terms of molecular composition and molecular weight, thermal properties, such as melting point, glass transition temperature, and decomposition, and in terms of optical properties, such as refractive index. The AIBN initiated carbazole-phenoxy based methacrylate polymerization was followed using in-situ FTIR, which showed the reaction to be completed within 40 minutes in DMAC at 90°C. Photo-DSC was used to determine the heat of polymerization (DHp) for the carbazole-phenoxy based methacrylate, which was found to be -39.4 kJ/mole. One and two dimensional 1H NMR was used to characterize the molecular structure of the carbazole-phenoxy based methacrylate monomer. The carbazole-phenoxy based methacrylate homopolymer had a surprisingly high decomposition temperature. 13C NMR spectroscopy experiments and molecular modeling were employed to explore the configuration of the polymerized carbazole-phenoxy based methacrylate. The lack of head-to-head linkages due to steric considerations could explain the higher thermal stability observed for the carbazole-phenoxy based methacrylate polymer. Refractive indices of these carbazole based methacrylates, acrylates, and dimethacrylate polymers ranged from 1.53 to 1.63. Statistical copolymers of carbazole based methacrylates with methyl methacrylate were also produced by solution polymerization in DMAC, and characterized. Using free radical polymerization techniques, homopolymers and copolymers of the carbazole functionalized methacrylates, acrylates, and dimethacrylates were readily obtained. This research demonstrated a variety of carbazole based chemistries which could produce controlled linear and cross-linked materials with high refractive index values and other interesting features. / Ph. D.