The secondary structure of DNA is variable and depends on the sequence of nu- cleotides in a strand. While DNA can form duplexes, formations of three, four, or even a single strand have been observed in vivo and in vitro as well. In this thesis, we study the effect of small changes of oligonucleotide sequences on the stability of hairpins formed by DNA heptamers by 1 H nuclear magnetic resonance (NMR) spectroscopy. Suitable DNA sequences were selected based on symmetry rules and stability prediction by near- est neighbor model. Two-dimensional 1 H -1 H NOESY spectra were used to assign the 1 H resonances of aromatic hydrogens. Variable-temperature 1D spectra served for ob- taining melting curves, from which the thermodynamic properties of the hairpins were determined. The presence of hairpins in the solutions was confirmed by the character of the NOESY spectra, independence of melting temperature on oligonucleotide concen- tration, and comparison of competing melting-curve models of duplex and hairpin. Our results point out the importance of the order of the stem base pairs and contribute to the description of the extraordinary stability of DNA mini-hairpins. 1

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This body of work is tackling some of the challenges in the field of lithium-ion batteries (LIBs) for electric vehicles through in situ nuclear magnetic resonance (NMR). In situ NMR allows for the simultaneous monitoring of both liquid and solid components (electrolyte, cathode, anode, separator) and provides timely data acquisition making it a great method to extract real-time information about structural changes, degradation products and failure mechanisms in batteries. A combined in situ 7Li NMR and ex situ 29Si magic-angle spinning (MAS) NMR study on silicon and silicon monoxide was used to compare structural differences in these anode materials using a custom-made in situ cell. Some key differences between the two materials were obtained, highlighting the importance of in situ NMR to be used for identifying phases, which are not present under ex situ conditions. In addition, fast charging of silicon anodes was investigated to gain a better understanding of their performance at high current rates. Magnetic resonance imaging was also implemented to localize lithium metal deposition under these conditions, which was made possible by a unique in situ parallel-plate resonator setup. Finally, the successful development of a novel in situ MAS NMR technique is introduced, which for the first time allows for an in situ analysis of a LIB under MAS. This strategy paves the way toward acquisition of valuable in situ data on the formation and transformations of metastable states within the active materials of both electrodes; data that is difficult to obtain from static in situ NMR experiments alone. / Thesis / Doctor of Philosophy (PhD)

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