Global simulated soil biogenic nitric oxide (NO) emissions: Impact, improvement and innovation

rnNitric oxide (NO) is important for several chemical processes in the atmosphere. Together with nitrogen dioxide (NO2 ) it is better known as nitrogen oxide (NOx ). NOx is crucial for the production and destruction of ozone. In several reactions it catalyzes the oxidation of methane and volatile organic compounds (VOCs) and in this context it is involved in the cycling of the hydroxyl radical (OH). OH is a reactive radical, capable of oxidizing most organic species. Therefore, OH is also called the “detergent” of the atmosphere. Nitric oxide originates from several sources: fossil fuel combustion, biomass burning, lightning and soils. Fossil fuel combustion is the largest source. The others are, depending on the reviewed literature, generally comparable to each other. The individual sources show a different temporal and spatial pattern in their magnitude of emission. Fossil fuel combustion is important in densely populated places, where NO from other sources is less important. In contrast NO emissions from soils (hereafter SNOx) or biomass burning are the dominant source of NOx in remote regions.rnBy applying an atmospheric chemistry global climate model (AC-GCM) I demonstrate that SNOx is responsible for a significant part of NOx in the atmosphere. Furthermore, it increases the O3 and OH mixing ratio substantially, leading to a ∼10% increase in the oxidizing efficiency of the atmosphere. Interestingly, through reduced O3 and OH mixing ratios in simulations without SNOx, the lifetime of NOx increases in regions with other dominating sources of NOx

Hyperbranched polyglycerols as building blocks for complex amphiphilic structures: synthesis, characterization and applications

Among hyperbranched polymers, polyglycerol is one of the most promising and commonly used macromolecules due to its biocompatibility and versatility. However, the synthesis of high molecular weight polyglycerols still involves many intricacies and has only been understood to a limited extent. Furthermore, only few complex structures like star or block copolymers incorporating polyglycerol have been realized so far. Particularly biocompatible block copolymers are considered promising candidates for biomedical applications.rnThe scope of this thesis was the enhancement of the synthetic process leading to polyglycerol derivatives which implies improved molecular weight control for a broad molecular weight range as well as the assembly of more complex structures like amphiphilic block copolymers. Further insight into the relation between reaction solvent, degree of deprotonation during the ring-opening multibranching polymerization of glycidol and the characteristics of the obtained polymers were achieved within the scope of this work. Based on these results, a novel concept for the preparation of hyperbranched polyglycerols with molecular weights up to 20,000 g/mol was developed, applying a two step synthesis pathway. Starting from a partially deprotonated TMP core, low molecular weight hb-PGs were prepared using the known synthetic protocol that has been established since the late 1990ies. In a subsequent reaction sequence, these well defined polymers were used as hyperbranched macroinitiator cores in order to obtain high molecular weight hb-PGs with remarkably low polydispersity (Mw/Mn < 1.8). Molecular weight control was shown to be excellent and undesired low molecular weight side products were absent. Furthermore, the technique of continuous spin fractionation has been discovered as an efficient method for polyglycerol work-up to remove quantitatively residual monomer- and oligomer traces from hb-PG compositions to result in samples with significantly reduced polydispersities. Based on these results the synthesis of amphiphilic block copolymers containing hydrophilic hyperbranched polyglycerol blocks and linear, apolar poly(propylene oxide) blocks has been significantly improved and augmented to hb-PG-b-l-PPO-b-hb-PG ABA block copolymers. The influence of different polyglycerol-based amphiphiles on the fibril formation was studied by Thioflavin T Fluorescence showing remarkable increasing lag times which is promising in order to enhance the stability of this protein. In addition the first synthesis of poly(glyceryl glycerols) (PGG), introducing a new solketyl glycidyl ether monomer (IGG) was shown. It was furthermore demonstrated that core-functional carbosilane wedges allow application in block copolymer synthesis. Bisglycidolized amine functional polymers were successfully employed as macroinitiators for glycidol polymerization. This resulted in the first example of amphiphilic hyperbranched-hyperbranched polymer structures. Finally, it has been shown that the previously reported synthetic pathway to carboxylated hyperbranched polyglycerol polyelectrolytes can also be applied for the amphiphilic linear-hyperbranched block copolymers. These novel biocompatible and highly amphiphilic polyelectrolytes offer great potential for further investigations. rnrn

EPR spectroscopy as a tool for the elucidation of non-covalent structuring principles in complex soft matter

This thesis aims at connecting structural and functional changes of complex soft matter systems due to external stimuli with non-covalent molecular interaction profiles. It addresses the problem of elucidating non-covalent forces as structuring principle of mainly polymer-based systems in solution. The structuring principles of a wide variety of complex soft matter types are analyzed. In many cases this is done by exploring conformational changes upon the exertion of external stimuli. The central question throughout this thesis is how a certain non-covalent interaction profile leads to solution condition-dependent structuring of a polymeric system.rnTo answer this question, electron paramagnetic resonance (EPR) spectroscopy is chosen as the main experimental method for the investigation of the structure principles of polymers. With EPR one detects only the local surroundings or environments of molecules that carry an unpaired electron. Non-covalent forces are normally effective on length scales of a few nanometers and below. Thus, EPR is excellently suited for their investigations. It allows for detection of interactions on length scales ranging from approx. 0.1 nm up to 10 nm. However, restriction to only one experimental technique likely leads to only incomplete pictures of complex systems. Therefore, the presented studies are frequently augmented with further experimental and computational methods in order to yield more comprehensive descriptions of the systems chosen for investigation.rnElectrostatic correlation effects in non-covalent interaction profiles as structuring principles in colloid-like ionic clusters and DNA condensation are investigated first. Building on this it is shown how electrostatic structuring principles can be combined with hydrophobic ones, at the example of host-guest interactions in so-called dendronized polymers (denpols).rnSubsequently, the focus is shifted from electrostatics in dendronized polymers to thermoresponsive alkylene oxide-based materials, whose structuring principles are based on hydrogen bonds and counteracting hydrophobic interactions. The collapse mechanism in dependence of hydrophilic-hydrophobic balance and topology of these polymers is elucidated. Complementarily the temperature-dependent phase behavior of elastin-like polypeptides (ELPs) is investigated. ELPs are the first (and so far only) class of compounds that is shown to feature a first-order inverse phase transition on nanoscopic length scales.rnFinally, this thesis addresses complex biological systems, namely intrinsically disordered proteins (IDPs). It is shown that the conformational space of the IDPs Osteopontin (OPN), a cytokine involved in metastasis of several kinds of cancer, and BASP1 (brain acid soluble protein one), a protein associated with neurite outgrowth, is governed by a subtle interplay between electrostatic forces, hydrophobic interaction, system entropy and hydrogen bonds. Such, IDPs can even sample cooperatively folded structures, which have so far only been associated with globular proteins.