Electron-nuclear double resonance (ENDOR) and dynamic nuclear polarization (DNP) are two techniques based on polarization transfer between electron and nuclear spins. Despite differences in the experimental realization, their similarities rely on the detailed mechanism of hyperfine interactions. The lecture will give an overview of our recent developments in these two methods in solids (ENDOR) and solution (Overhauser DNP) to study biological systems. To this end, design and implementation of coupled EPR/NMR experiments at various microwave frequencies, particularly in the high-frequency/high-field EPR regime, has been in focus.
We have recently implemented a spectrometer to perform routine ENDOR spectroscopy at 263 GHz/9.4 Tesla. Spectrometer design, performance as well as the demonstration of unprecedented spectral resolution in ENDOR for studies of protein radicals is presented. Moreover, we illustrate that high frequency ENDOR in combination with a new 19F/nitroxide labelling strategy can be used to measure interspin distances in the range 0.5 – 1.5 nm. Finally, expansion of 13C dynamic nuclear polarization in the liquid state towards high magnetic fields is discussed. We could recently measure 13C NMR signal enhancements on small molecules up to fields of 9.4 Tesla.