Dynamic Nuclear Polarization Methods Development for Achieving High Nuclear Magnetic Resonance Signal Sensitivity

Solid-state nuclear magnetic resonance (NMR) is an essential tool for the study of biological solids, catalysts, and other functional materials. However, NMR has intrinsically low signal sensitivity and dynamic nuclear polarization (DNP) is one of the most effective approaches to enhance NMR sensitivity. DNP enhances NMR signal sensitivity through transferring the high polarization of electron spins to nuclear spins using microwave (mw) irradiation as a perturbation via different DNP mechanisms. As current DNP efficiency is still far from the theoretical limit (660 for 1H NMR), a major focus in DNP research is to develop methods that can maximize DNP enhancements at conditions germane to solid-state NMR, at high magnetic fields, with fast magic angle spinning (MAS), and under variable temperatures. There are many aspects involved in DNP methods development, including the DNP mechanisms clarification and improvement, instrumentation development, better samples preparation methods, and new data processing techniques.DNP mechanisms development is one of the most important aspects in the DNP methods development area. Current diagnostics of DNP mostly rely on the analysis of the nuclear spin dynamics as a function of mw irradiation parameters which provides incomplete (sometimes even misleading) insights into the mechanism diagnosis process. With the help of continuous wave and pulsed electron paramagnetic resonance (EPR) spectrometers at various fields (from 0.35 to 7 Tesla) as well as quantum mechanical simulations, I have developed and standardized a workflow to diagnose DNP mechanisms and improve their efficiencies. Using the developed workflow, I have improved the existing Cross Effect (CE) DNP efficiency significantly by rationally tuning the the EPR spectral density of mixed broad (TEMPO) and narrow (Trityl)-line radicals, suggesting a novel polarizing agent design of one Trityl tethered to at least two TEMPO moieties. With the help of this novel workflow, a new t