High-Field Pulsed Dynamic Nuclear Polarization – HFPulsedDNP

This research proposal aims to achieve a breakthrough in nuclear magnetic resonance (NMR) applications by advancing dynamic nuclear polarization (DNP)–a powerful sensitivity enhancement method–to high magnetic fields and at near ambient temperatures. NMR is a non-invasive technique that can provide atomic-resolution structures of biological molecules and inorganic materials. Despite its inherently poor sensitivity, the NMR signal can be boosted by many orders of magnitude using DNP. However, the enhancement factors obtained with continuous-wave (CW) DNP technology decrease dramatically as the magnetic field increases. In other words, the NMR peaks are separated farther apart (higher resolution) but have lower intensities (poor DNP performances) in high-field magnets. This has limited its access to high-resolution NMR offered by high field magnets. To surmount this hurdle, we introduce Electron-Nuclear Magnetic Resonance (ENMR) spectroscopy that facilitates a time domain or pulsed DNP technique with a field-independent DNP performance, hyperfine recoupling that correlates nuclei separated by long distances up to 2 nm, and electron decoupling that yields high-resolution NMR spectra in paramagnetic systems. We expect the pulsed DNP technique to allow biomolecules or inorganic materials to be characterized at near ambient temperatures—in a real-world environment where the catalytic materials or biomolecules are functional. This would be a ground-breaking achievement because the main limitation of CW DNP technology is that the experiments are primarily performed at cryogenic temperatures, which obviously do not provide a native environment for biological molecules and catalysts; It also risks destroying the samples.
Despite the promising prospect conferred by the pulsed DNP technique, the stringent microwave power requirements have prevented its use at high fields, where high-power pulsed microwave sources are not readily available. To circumvent these issues, we propose building a 9.4 T/ 263 GHz pulsed DNP spectrometer that is well beyond the state-of-the-art, i.e., we will incorporate an arbitrary waveform generator (AWG), a high-power microwave source, and a high-Q resonator into a single setup. Besides, we plan to build a basic high-frequency gyrotron-based electron paramagnetic resonance (GyroEPR) instrument to characterize the DNP polarizing agents at DNP-relevant conditions, i.e., at high field (18.8 T / 527 GHz) and under magic angle spinning (MAS). GyroEPR can provide crucial information on the radicals’ EPR and relaxation properties, which could help guide the design of the best DNP polarizing agents.
These cutting-edge instruments will be employed to shed light on the structures of metal nanoparticles grafted on metal-organic frameworks (MOFs), which may then be optimized to improve the catalytic conversion of CO2 to alcohols. Beyond this demonstration, we expect HFPulsedDNP to open new avenues for studying material science, biological molecules, medical imaging, and drug screening techniques, i.e., all fields where magnetic resonance can provide valuable insight into matters at an atomic level. We will build the world’s first highest-frequency (263 GHz) pulsed DNP spectrometer and the first 18.8 T gyrotron-based MAS EPR setup at ENS.