Topical Developments in High-Field Dynamic Nuclear Polarization

We report our recent efforts directed at improving high-field dynamic nuclear polarization (DNP) experiments. We investigated a series of thiourea nitroxide radicals and the associated DNP enhancements ranging from epsilon=25 to 82, which demonstrate the impact of molecular structure on performance. We directly polarized low-gamma nuclei, including C-13, H-2, and O-17, by the cross effect mechanism using trityl radicals as a polarization agent. We discuss a variety of sample preparation techniques for DNP with emphasis on the benefits of methods that do not use a glass-forming cryoprotecting matrix. Lastly, we describe a corrugated waveguide for use in a 700MHz/460GHz DNP system that improves microwave delivery and increases enhancements up to 50%.