Interrupted NMR pulse sequences

NMR (Nuclear Magnetic Resonance) spectroscopy is arguably the most-often used technique for the structural analysis of small and medium-sized molecules. It allows the analysis of magnetic properties of atomic nuclei. The absorption of specific wavelength of radiofrequency pulsed irradiation is monitored and provides information about the chemical environment of the individual atoms in a molecule and their connectivities. It provides not only the structure of the molecule but also information about its dynamical behavior, like molecular rearrangements. Due to their superior sensitivity most often hydrogen atoms are investigated. Each hydrogen nucleus results in a signal in the NMR spectrum which shows a splitting due to interactions with other hydrogen nuclei in the molecule. These splittings result in signal overlaps. We have recently introduced a technique (pure shift NMR) to completely remove the splittings and thereby significantly increase the resolution of hydrogen NMR spectra. However, this removal only works when the interacting atoms have absorption frequencies which are not too similar. As part of this project we will extend pure shift NMR to work also for interacting signals with similar frequencies. A related technique can be used to study fast chemical reactions between a major compound and a minor compound, which can be even invisible in the NMR spectrum. While NMR is often used for following slow chemical reactions (which last minutes or hours), it is much more difficult to study reactions on a time scale of seconds or faster by NMR. Within the project we will also establish two new NMR techniques where the actual NMR experiment is interrupted in order to study such very fast reactions. The presented methods would allow not only the monitoring of chemical reactions, but should also enable the study of for example conformational rearrangements in intrinsically disordered proteins.

I was interviewed by our university journal (UniZeit) about research work associated with this project, which resulted in a two page article on recent NMR developments at the University of Graz. I was also invited a couple of times to hold teaching and tutorial workshops on pure shift NMR for general chemistry or NMR audiences. Since a few years I am also annually holding NMR talks for Chemistry students at the University of Zagreb, Croatia. Together with Sebastian Tassoti, who was employed by this project we are developing hands-on NMR experiments for high-school students in order to possibly attract future chemistry students.