Rational Design of Dinitroxide Polarizing Agents for Dynamic Nuclear Polarization to Enhance Overall NMR Sensitivity

We evaluate the overall sensitivity gains provided by a series of eighteen nitroxide biradicals for dynamic nuclear polarization (DNP) solid-state NMR at 9.4 T and 100 K, including eight new biradicals. We find that in the best performing group the factors contributing to the overall sensitivity gains, namely the DNP enhancement, the build-up time, and the contribution factor, often compete with each other leading to very similar overall sensitivity across a range of biradicals. NaphPol and HydroPol are found to provide the best overall sensitivity factors, in organic and aqueous solvents respectively. One of the new biradicals, AMUPolCbm, provides high sensitivity for all three solvent formulations measured here, and can be considered to be a "universal" polarizing agent.|Eighteen nitroxide biradicals for DNP-enhanced solid-state NMR are compared at 9.4 T and 100 K, including eight new biradicals. Among the best performing radicals, the factors contributing to the overall sensitivity gains often compete with each other leading to very similar overall performance across a range of biradicals. One of the new biradicals, AMUPolCbm, works well in both organic and aqueous solvents, making it a "universal" polarizing agent.image