Untersuchung von Gastdiffusion in porösen Materialien mittels kernmagnetischer Resonanzspektroskopie unter Einsatz gepulster Feldgradienten (PFG-NMR) und Konformationsstudien von N,O-substituierten Hydroxamaten mittels dynamischer 1D- und 2D-NMR Methoden

Thoma, Roland (2017) Untersuchung von Gastdiffusion in porösen Materialien mittels kernmagnetischer Resonanzspektroskopie unter Einsatz gepulster Feldgradienten (PFG-NMR) und Konformationsstudien von N,O-substituierten Hydroxamaten mittels dynamischer 1D- und 2D-NMR Methoden. Heinrich-Heine-University Duesseldorf, Doctoral Thesis, 199pp.

Abstract

The main topics of this thesis are, on one hand, conformational studies using 1D-as well as 2D-NMR methods, and on the other hand, PFG-NMR experiments on guest diffusion in porous host materials. Additionally, parts of a ”home-built” PFG-NMR spectrometer-system were installed, moreover, pulse programs in the programming language Python were created.The conducted conformational studies were done using a N,O-substituted hydroxamic acid, as well as the tetra- and hexameric form. The secondary structure of the oligomers could not be revealed by Proton NOESY data.Low temperature NMR measurements of the N,O-substituted hydroxamic acid monomer showed the existence of chemical exchange. The cause of this exchange process was investigated by dynamic 1H-NMR and low-temperature 2D-NOESY spectra, yielding the activation parameters of the exchange process, as well as their spatial arrangement. This data collection hints to a chemical exchange based on a hindered rotation around the NO bond.The used porous host materials for guest diffusion studies were polyacrylamide hydrogels, as well as metal-organic frameworks (MOFs).Diffusion studies on swollen hydrogels were conducted using aminodextrans with successively increasing molecular weights as diffusive tracer molecules inside thegel, as well as in solution. These results supported the findings of FCS- and MTI generated data, performed in the workgroups of Prof. Seidel and Prof. Egelhaaf .Guest diffusion in MOFs was accomplished by using the MOF MIL-53-NH2(Al)and DMSO at 5°C as guest molecule, as well as the installed ”home-built” spectrometer system. The MOF sample consisted of irregularely formed crystal agglomerates with a broad diameter distribution. A diffusion model for this situation was formulated, yielding two diffusing regimes with different propagation pat-terns. Whereas one regime is located in agglomerates with diameters greater than 20μm, showing anomal diffusion behavior, and the second regime, located in agglomerates with diameters less than 20μm, shows indications for restricted diffusion. The latter regime was successfully simulated numerically in Matlab.

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