Hundertneunundzwanzig Xe NMR for investigations of complex and dynamic systems

In this work, the remarkable versatility and usefulness of applications of Xe-129 NMR experiments is further extended. The application of Xe-129 NMR spectroscopy to very different system is studied, including dynamic and static, solid and liquid, porous and non-porous systems. Using the large non-equilibrium polarization created by hyperpolarization of Xe-129, time-resolved NMR measurements can be used for the online-monitoring of dynamic systems. In the first part of this work, several improvements for medical applications of hyperpolarized Xe-129 are achieved and their feasibility shown experimentally. A large gain in speed and reproducibility of the accumulation process of Xe-129 as ice and an enhancement of the usable polarization in any experiment requiring prior accumulation are achieved. An enhancement of the longitudinal relaxation time of Xe-129 is realized by admixture of a buffer gas during the storage of hyperpolarized Xe-129. Pursuing the efforts of simplifying the accumulation process and enhancing the storage time of hyperpolarized Xe-129 will allow for a wider use of the hyperpolarized gas in (medical) MRI experiments. Concerning the use of hyperpolarized Xe-129 in MRI, the influence of the diffusion coefficient of the gas on parameters of the image contrast is experimentally demonstrated here by admixture of a buffer gas and thus changing the diffusion coefficient. In the second part of this work, a polymer system with unique features is probed by Xe-129 NMR spectroscopy, proving the method to be a valuable tool for the characterization of the anisotropic properties of semicrystalline, syndiotactic polystyrene films. The polymer films contain hollow cavities or channels with sizes in the sub-nanometer range, allowing for adsorption of Xe-129 and subsequent NMR measurements. Despite the use of a ’real-world’ system, the transfer of the anisotropic properties from the material to adsorbed Xe-129 atoms is shown, which was previously only known for fully crystalline materials. The anisotropic behavior towards atomar guests inside the polymer films is proven here for the first time for one of the phases. For the polymer phase containing nanochannels, the dominance of interactions between Xe-129 atoms in the channels compared to interactions between Xe atoms and the channel walls are proven by measurements of a powder sample of the polymer material and experiments including the rotation of the films in the external magnetic field as well as temperature-dependent measurements. The characterization of ’real-world’ systems showing very high degrees of anisotropy by Xe-129 are deemed to be very valuable in future applications. In the last part of this work, a new method for the online monitoring of chemical reactions has been proposed and its feasibility and validity are experimentally proven. The chemical shift dependence of dissolved Xe-129 on the composition of a reaction mixture is used for the online monitoring of free-radical miniemulsion polymerization reactions. Xe-129 NMR spectroscopy provides an excellent method for the online monitoring of polymerization reactions, due to the simplicity of the Xe-129 NMR spectra and the simple relationship between the Xe-129 chemical shift and the reaction conversion. The results of the time-resolved Xe-129 NMR measurements are compared to those from calorimetric measurements, showing a good qualitative agreement. The applicability of the new method to reactions other than polymerization reactions is investigated by the online monitoring of an enzymatic reaction in a miniemulsion. The successful combination of the large sensitivity of Xe-129, the NMR signal enhancements due to hyperpolarization, and the solubility of Xe-129 gives access to the large new field of investigations of chemical reaction kinetics in dynamic and complex systems like miniemulsions.

Spectroscopic investigations of functional bulk and thin film Heusler alloys

Functional and smart materials have gained large scientific and practical interest in current research and development. The Heusler alloys form an important class of functional materials used in spintronics, thermoelectrics, and for shape memory alloy applications. An important aspect of functional materials is the adaptability of their physical properties. In this work functional polycrystalline bulk and epitaxial thin film Heusler alloys are characterized by means of spectroscopic investigation methods, X-ray magnetic circular dichroism (XMCD) and energy dispersive X-ray analysis (EDX). With EDX the homogeneity of the samples is studied extensively. For some cases of quaternary compounds, for example Co2(MnxTi1−x)Sn and Co2(Mn0.5Dy0.5)Sn, an interesting phase separation in two nearly pure ternary Heusler phases occurs. For these samples the phase separation leads to an improvement of thermoelectric properties. XMCD as the main investigation method was used to study Co2TiZ (Z = Si, Sn, and Sb), Co2(MnxTi1−x)Si, Co2(MnxTi1−x)Ge, Co2Mn(Ga1−xGex), Co2FeAl, Mn2VAl, and Ni2MnGa Heusler compounds. The element-specific magnetic moments are calculated. Also, the spin-resolved unoccupied density of states is determined, for example giving hints for half-metallic ferromagnetism for some Co-based compounds. The systematic change of the magnetic moments and the shift of the Fermi energy is a proof that Heusler alloys are suitable for a controlled tailoring of physical properties. The comparison of the experimental results with theoretical predictions improves the understanding of complex materials needed to optimize functional Heusler alloys.

Investigations on asymptotic safety of metric, tetrad and Einstein-Cartan gravity

Among the different approaches for a construction of a fundamental quantum theory of gravity the Asymptotic Safety scenario conjectures that quantum gravity can be defined within the framework of conventional quantum field theory, but only non-perturbatively. In this case its high energy behavior is controlled by a non-Gaussian fixed point of the renormalization group flow, such that its infinite cutoff limit can be taken in a well defined way. A theory of this kind is referred to as non-perturbatively renormalizable. In the last decade a considerable amount of evidence has been collected that in four dimensional metric gravity such a fixed point, suitable for the Asymptotic Safety construction, indeed exists. This thesis extends the Asymptotic Safety program of quantum gravity by three independent studies that differ in the fundamental field variables the investigated quantum theory is based on, but all exhibit a gauge group of equivalent semi-direct product structure. It allows for the first time for a direct comparison of three asymptotically safe theories of gravity constructed from different field variables. The first study investigates metric gravity coupled to SU(N) Yang-Mills theory. In particular the gravitational effects to the running of the gauge coupling are analyzed and its implications for QED and the Standard Model are discussed. The second analysis amounts to the first investigation on an asymptotically safe theory of gravity in a pure tetrad formulation. Its renormalization group flow is compared to the corresponding approximation of the metric theory and the influence of its enlarged gauge group on the UV behavior of the theory is analyzed. The third study explores Asymptotic Safety of gravity in the Einstein-Cartan setting. Here, besides the tetrad, the spin connection is considered a second fundamental field. The larger number of independent field components and the enlarged gauge group render any RG analysis of this system much more difficult than the analog metric analysis. In order to reduce the complexity of this task a novel functional renormalization group equation is proposed, that allows for an evaluation of the flow in a purely algebraic manner. As a first example of its suitability it is applied to a three dimensional truncation of the form of the Holst action, with the Newton constant, the cosmological constant and the Immirzi parameter as its running couplings. A detailed comparison of the resulting renormalization group flow to a previous study of the same system demonstrates the reliability of the new equation and suggests its use for future studies of extended truncations in this framework.

Investigations into the effect of nucleoside modifications on the physicochemical properties and biological function of DNA and RNA

This thesis explores the effect of chemical nucleoside modification on the physicochemical and biological properties of nucleic acids. Positional alteration on the Watson-Crick edge of purines and pyrimidines, the “C-H” edge of pyrimidines, as well as both the Hoogsteen and sugar edges of purines were attempted by means of copper catalyzed azide-alkyne cycloaddition. For this purpose, nucleic acid building blocks carrying terminal alkynes were synthesized and introduced into oligonucleotides by solid-phase oligonucleotide chemistry. rnOf particular interest was the effect of nucleoside modification on hydrogen bond formation with complementary nucleosides. The attachment of propargyl functionalities onto the N2 of guanosine and the N4 of 5-methylcytosine, respectively, followed by incorporation of the modified analogs into oligonucleotides, was successfully achieved. Temperature dependent UV-absorption melting measurements with duplexes formed between modified oligonucleotides and a variety of complementary strands resulted in melting temperatures for the respective duplexes. As a result, the effect that both the nature and the site of nucleoside modification have on base pairing properties could thus be assisted. rnTo further explore the enzymatic recognition of chemically modified nucleosides, the oligonucleotide containing the N2-modified guanosine derivative on the 5’-end, which was clicked to a fluorescent dye, was subjected to knockdown analyses of the eGFP reporter gene in the presence of increasing concentrations of siRNA duplexes. From these dose-dependent experiments, a clear effect of 5’-labeling on the knockdown efficiency could be seen. In contrast, 3’-labeling was found to be relatively insignificant.rn

Bio-inspired polymer-supported nitrido molybdenum(VI) complexes for ammonia synthesis − reactivity towards protons and electrons : EPR investigations on paramagnetic molybdenum(V) and copper(II) complexes

Die biologische Stickstofffixierung durch Molybdän-haltige Nitrogenasen sowie die Erforschung des zugrundeliegenden komplexen Mechanismus (N2-Aktivierung an Metall-Zentren, 6-fache Protonierung und Reduktion, N–N Bindungsspaltung unter Bildung von Ammoniak) ist von erheblichem Interesse. Insbesondere Molybdän-Komplexe wurden bereits erfolgreich als Modellverbindungen für die Untersuchung elementarer Einzelschritte der N2-Aktivierung eingesetzt. Durch die Verwendung von Triamidoamin-Liganden ist es Schrock et al. sogar gelungen mehrere Katalysezyklen zu durchlaufen und einen Mechanismus zu formulieren. Trotz der sterisch anspruchsvollen Substituenten in den Schrock-Komplexen ist die Umsatzrate dieses homogenen Katalysators, aufgrund Komplex-Deaktivierung infolge intermolekularer Reaktionen wie Dimerisierung und Disproportionierung, limitiert. In der vorliegenden Arbeit wurden einige dieser Herausforderungen angegangen und die aktiven Spezies auf einer Festphase immobilisiert, um intermolekulare Reaktionen durch räumliche Isolierung der Komplexe zu unterdrücken.rnEin Polymer-verankertes Analogon des Schrock Nitrido-Molybdän(VI)-Komplexes wurde auf einem neuen Reaktionsweg synthetisiert. Dieser beinhaltet nur einen einzigen Reaktionsschritt, um die funktionelle Gruppe „MoN“ einzuführen. Protonierung des immobilisierten Nitrido-Molybdän(VI)-Komplexes LMoVIN (L = Polymer-verankerter Triamidoamin-Ligand) mit 2,6-Lutidinium liefert den entsprechenden Imido-Molybdän(VI)-Komplex. Durch anschließende Ein-Elektronen-Reduktion mit Cobaltocen wird der Polymer-angebundene Imido-Molybdän(V)-Komplex erhalten, bewiesen durch EPR-Spektroskopie (g1,2,3 = 1.989, 1.929, 1.902). Durch die Immobilisierung und die effektive räumliche Separation der Reaktionszentren auf der Festphase werden bimolekulare Nebenreaktionen, die oft in homogenen Systemen auftreten, unterdrückt. Dies ermöglicht zum ersten Mal die Darstellung des Imido-Molybdän(V)-Intermediates des Schrock-Zyklus.rnEPR-Spektren des als Spin-Label eingeführten immobilisierten Nitrato-Kupfer(II)-Komplexes wurden unter verschiedenen Bedingungen (Lösungsmittel, Temperatur) aufgenommen, wobei sich eine starke Abhängigkeit zwischen der Zugänglichkeit und Reaktivität der immobilisierten Reaktionszentren und der Art des Lösungsmittels zeigte. Somit wurde die Reaktivität von LMoVIN gegenüber Protonen und Elektronen, welches zur Bildung von NH3 führt, unter Verwendung verschiedener Lösungsmittel untersucht und optimiert. Innerhalb des kugelförmigen Polymers verläuft die Protonierung und Reduktion von LMoVIN stufenweise. Aktive Zentren, die sich an der „äußeren Schale“ des Polymers befinden, sind gut zugänglich und reagieren schnell nach H+/e− Zugabe. Aktive Zentren im „Inneren des Polymers“ hingegen sind schlechter zugänglich und zeigen langsame diffusions-kontrollierte Reaktionen, wobei drei H+/e− Schritte gefolgt von einer Ligandenaustausch-Reaktion erforderlich sind, um NH3 freizusetzen: LMoVIN  LMoVNH  LMoIVNH2  LMoIIINH3 und anschließender Ligandenaustausch führt zur Freisetzung von NH3.rnIn einem weiteren Projekt wurde der Bis(ddpd)-Kupfer(II)-Komplex EPR-spektroskopisch in Hinblick auf Jahn−Teller-Verzerrung und -Dynamik untersucht. Dabei wurden die EPR-Spektren bei variabler Temperatur (70−293 K) aufgenommen. Im Festkörperspektrum bei T < 100 K erscheint der Kupfer(II)-Komplex als gestreckter Oktaeder, wohingegen das EPR-Spektrum bei höheren Temperaturen g-Werte aufzeigt, die einer pseudo-gestauchten oktaedrischen Kupfer(II)-Spezies zuzuordnen sind. Diese Tatsache wird einem intramolekularen dynamischen Jahn−Teller Phänomen zugeschrieben, welcher bei 100 K eingefroren wird.

Understanding of stuck fermentations : investigations on the relationship between the microbial diversity and chemical composition of must

Das Ziel dieser Arbeit war es, mehr Informationen über unkonventionelle Gründe für Gärstockungen zu gewinnen und neue Wege zu finden, diese zu überwinden. Mikrobielle Sukzession und die chemische Zusammensetzung bei der Gärung wurden in zwei aufeinander folgenden Jahren in einem Weingut von der oberen Mosel in Deutschland studiert. Es gab keinen Hinweis darauf, dass die isolierten Bakterienspezies oder chemischen Komponenten von Most und Jungwein an schleppenden oder stockenden Gärungen beteiligt waren. Ferner konnte während dieser Arbeit gezeigt werden, dass Saccharomyces bayanus die dominierende Weinhefe in diesem Weingut war statt der klassischen und bekannten Weinhefe Saccharomyces cerevisiae. Während der Gärstockung konnte ein Dreifach-Hybrid Saccharomyces cerevisiae x Saccharomyces kudriavzevii x Saccharomyces bayanus wachsen, Saccharomyces bayanus ersetzen und die Gärung beenden. Beide isolierten Hefestämme Saccharomyces bayanus Stamm HL 77 und der Dreifach-Hybrid Saccharomyces cerevisiae x Saccharomyces kudriavzevii x Saccharomyces bayanus Stamm HL 78 konnten Glucose und Fructose von Anfang an verwerten und konnten bei niedrigen Temperaturen von 15 °C und in der Abwesenheit von Hefe-verwertbarem Stickstoff in Form von Ammonium wachsen, solange Aminosäuren im Medium vorhanden waren, im Gegensatz zu einer kommerziellen Saccharomyces cerevisiae-Starterkultur. Chemische Untersuchungen ergaben, dass Hefe-verwertbarer Stickstoff in dem kooperierenden Weingut mit einem Maximum von 160 mg/l zu Beginn der Gärung vorhanden war und auf 40 mg/L verringert war nach zwei Wochen. Aus diesem Grund sind beide isolierten Hefestämme interessant als Starterkulturen in diesem Weingut und dies kann neben der niedrigen Temperatur im Keller auch ein Grund sein, warum Saccharomyces cerevisiae nicht die dominierende Weinhefe in diesem Fall ist. Der Dreifach-Hybrid Saccharomyces cerevisiae x Saccharomyces kudriavzevii x Saccharomyces bayanus Stamm HL 78 ist in der Lage, Fructose noch effizienter zu nutzen als Saccharomyces bayanus Stamm HL 77 und ist weniger abhängig von der Aminosäurekonzentration. Dieser Stamm wurde bereits erfolgreich bei diesem Projekt eingesetzt, um eine Gärstockung in dem kooperierenden Weingut zu beheben. Es ist bekannt, dass Saccharomyces-Hybride in der Weinherstellung vorkommen aber ihre Rolle bei der Überwindung von Gärstockungen wurde bisher noch nicht beschrieben. Diese Ergebnisse sind nützlich, um Gärstockungen zu vermeiden oder zu überwinden mit der selektiven Verwendung dieser Hefestämme in verschiedenen Stadien der Gärung. Das kooperierende Weingut, welches im oberen Qualitätssegment platziert ist, hatte jedes Jahr Probleme mit Gärstockungen. Daher ist die Anwendung der Dreifach-Hybriden Saccharomyces cerevisiae x Saccharomyces kudriavzevii x Saccharomyces bayanus Stamm HL 78 eine große Chance, Gärstockungen und finanzielle Verluste ohne kommerzielle Starterkulturen oder andere übliche Praktiken, die zu einer Veränderung des Aromaprofils führen können, zu vermeiden. Die beschriebenen Untersuchungen stellen ein Modell dar, um Gärstockungen auch in anderen Weingütern, die Spontangärungen anwenden, zu überwinden.

Investigations on DNA methylation by Dnmt2 and impact of tRNA modifications on TLR7 stimulation

The incorporation of modified nucleotides into ribonucleic acids (RNAs) is important for their structure and proper function. These modifications are inserted by distinct catalytic macromolecules one of them being Dnmt2. It methylates the Cytidine (C) at position 38 in tRNA to 5-methylcytidine (m5C). Dnmt2 has been a paradigm in this respect, because all of its nearest neighbors in evolution are DNA-cytosine C5-methyltransferases and methylate DNA, while its (own) DNA methyltransferase activity is the subject of controversial reports with rates varying between zero and very weak. This work determines whether the biochemical potential for DNA methylation is present in the enzyme. It was discovered that DNA fragments, when presented as covalent RNA:DNA hybrids in the structural context of a tRNA, can be more efficiently methylated than the corresponding natural tRNA substrate. Additional minor deviations from a native tRNA structure that were seen to be tolerated by Dnmt2 were used for a stepwise development of a composite system of guide RNAs that enable the enzyme to perform cytidine methylation on single stranded DNA in vitro. Furthermore, a proof-of-principle is presented for utilizing the S-adenosyl methionine-analog cofactor SeAdoYn with Dnmt2 to search for new possible substrates in a SELEX-like approach.rnIn innate immunity, nucleic acids can function as pathogen associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRRs). The modification pattern of RNA is the discriminating factor for toll-like receptor 7 (TLR7) to distinguish between self and non-self RNA of invading pathogens. It was found that a 2'-O-methylated guanosine (Gm) at position18, naturally occurring at this position in some tRNAs, antagonizes recognition by TLR7. In the second part of this work it is pointed out, that recognition extends to the next downstream nucleotide and the effectively recognized molecular detail is actually a methylated dinucleotide. The immune silencing effect of the ribose methylation is most pronounced if the dinucleotide motif is composed of purin nucleobases whereas pyrimidines diminish the effect. Similar results were obtained when the Gm modification was transposed into other tRNA domains. Point mutations abolishing base pairings important for a proper tertiary structure had no effect on the immune stimulatory potential of a Gm modified tRNA. Taken together these results suggest a processive type of RNA inspection by TLR7.rn

[Thyroid nodules: which further investigations should be done]

Thyroid nodules are a very common clinical finding with an age-related increase in prevalence. The clinical detection of thyroid nodules is outnumbered by the ultrasonographic assessment of thyroid nodules. The clinical challenge is to exclude thyroid cancer and clinical or subclinical hyperthyroidism. Ultrasonography is the first imaging study in all patients with palpable nodules; their size and TSH determine further diagnostic evaluations. Fine-needle aspiration (cytology) is recommended in euthyroid patients of nodules measuring more than 1-1.5 cm in diameter. Nodules more than 4 cm in diameter have to be removed surgically without preceding cytological examination. Without risk factors thyroid nodules are followed by clinical examination and ultrasonography every 6-12 months, in case of symptoms or rapid growth a follow-up assessment should be done earlier.

Laboratory based investigations for diagnosing gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) still remains the most common out- GI-related condition in the out-patient setting. While primary care physicians often use empiric trials with proton pump inhibitors (PPI trial) to diagnose GERD, often specialised tests are required to confirm or exclude gastroesophageal reflux causing esophageal or extraesophageal symptoms. The most commonly used procedures to diagnose GERD include: conventional (catheter based) pH monitoring, wireless esophageal pH monitoring (Bravo), bilirubin monitoring (Bilitec), and combined multichannel intraluminal impedance-pH monitoring (MII-pH). Each technique has strengths and limitations of which clinicians and investigators should be aware when deciding which one to choose.

Agricultural Policymaking: Interest Groups and Access to Governmental Officials

Conservation agriculture that focuses on soil recovery is both economically and environmentally sustainable. This lies in contrast with many of the current agricultural practices, which push for high production, which, in turn lead to over-depletion of the soil. Agricultural interest groups play a role in crafting farming policies with governmental officials. Therefore, my study examined three interest group types agribusinesses, farmer organizations, and environmental NGOs that seek to influence agricultural policy, specifically focusing on the federal farm bill, due to its large impact throughout the nation. The research in which data wasgathered through subject interviews, a literature review, and databases found that access to governmental officials affects the amount of influence a group can have. Access is contingent upon: 1) the number of networks (social, professional, and political), 2) amount of money spent through campaign contributions and lobbying expenditures, and 3) extent of business enterprises and subsidiaries. The evidence shows that there is a correlation between these variables and the extent of access. My research concludes that agribusiness interest groups have the most access to government officials, and thus have the greatest influence on agricultural policies. Because agribusinesses support subsidies of commodity-crops this indirectly impacts conservation agriculture, as the two programs compete in a zero-sum game for funding in the farm bills.

Epizootiologic Investigations of Selected Abortive Agents in Free-Ranging Alpine Ibex (Capra Ibex Ibex) in Switzerland

In the early 2000s, several colonies of Alpine ibex (Capra ibex ibex) in Switzerland ceased growing or began to decrease. Reproductive problems clue to infections with abortive agents might have negatively affected recruitment. We assessed the presence of selected agents of abortion in Alpine ibex by serologic, molecular, and culture techniques and evaluated whether infection with these agents might have affected population densities. Blood and fecal samples were collected from 651 ibex in 14 colonies throughout the Swiss Alps between 2006 and 2008. All samples were negative for Salmonella. spp., Neospora caninum, and Bovine Herpesvirus-1. Antibodies to Coxiella burnetii, Leptospira spp., Chlamydophila abortus, Toxoplasma gondii, and Bovine Viral Diarrhea virus were detected in at least one ibex. Positive serologic results for Brucella spp. likely were false. Overall, 73 samples (11.2%) were antibody-positive for at least one abortive agent. Prevalence was highest for Leptospira spp. (7.9%, 95% CI=5.0-11.7). The low prevalences and the absence of significant differences between colonies with opposite population trends suggest these pathogens do not play a significant role in the population dynamics of Swiss ibex. Alpine ibex do not seem to be a reservoir for these abortive agents or an important source of infection for domestic livestock in Switzerland. Finally, although interactions on summer pastures occur frequently, spillover from infected livestock to free-ranging ibex apparently is uncommon.