Tan, Kong Ooi, Luming Yang, Michael Mardini, Choon Boon Cheong, Benoit Driesschaert, Mircea Dincă, and Robert G. Griffin. “Observing Nearby Nuclei on Paramagnetic Trityls and MOFs via DNP and Electron Decoupling.” Chemistry – A European Journal, October 11, 2022.
https://doi.org/10.1002/chem.202202556.
Dynamic nuclear polarization (DNP) is an NMR sensitivity enhancement technique that mediates polarization transfer from unpaired electrons toNMR-active nuclei. Despite its success in elucidating important structural information on biological and inorganic materials, the detailed polarization-transfer pathway from the electrons to the nearby and then the bulk solvent nuclei, and finally to the molecules of interest-remains unclear. In particular, the nuclei in the paramagnetic polarizing agent play significant roles in relaying the enhanced NMR polarizations to more remote nuclei. Despite their importance, the direct NMR observation of these nuclei is challenging because of poor sensitivity. Here, we show that a combined DNP and electron decoupling approach can facilitate direct NMRdetection of these nuclei. We achieved an ~80% improvement in NMR intensity via electron decoupling at 0.35T and 80K on trityl radicals. Moreover, we recorded aDNPenhancement factor of e ~90 and ~11% higher NMR intensity using electron decoupling on paramagnetic metal-organic framework, magnesium hexaoxytriphenylene (MgHOTP MOF).