Hosted By: Dr. Aaron Rossini 

Title: Pathways for Better Dynamic Nuclear Polarization NMR Polarizing Agents

Abstract: Dynamic nuclear polarization (DNP) is a powerful approach to enhance the sensitivity of solid-state NMR spectroscopy. However, the overall efficiency of DNP largely depends on the optimal choice of polarizing agent and impregnating solvent, and the properties of the material. DNP is widely enabled by biradical polarizing agents using the cross effect mechanism. However, even the currently best biradical polarizing agents show signal enhancements less than half the theoretical maximum. We will first describe strategies to improve the efficiency of DNP biradical polarizing agents including the identification of biradical design criteria, and the systematic evaluation of biradical performance.^1,2 The identification of these criteria has allowed us to recently develop improved polarizing agents that offer increased NMR sensitivity factors at high magnetic fields.³

As an alternative to biradicals, monoradicals and Gd(III) complexes that utilize the solid effect mechanism are also promising DNP polarizing agents.⁴ We show unprecedented DNP enhancements using monoradicals, and the application of Gd(III) complexes for DNP in-cells. The enhanced NMR sensitivity obtained using DNP is demonstrated with MgAl layered double hydroxides, which are promising sorbents for recovery of phosphate from wastewater.