Methyl-Driven Overhauser Dynamic Nuclear Polarization

The Overhauser effect is unique among DNP mechanisms in that it requiresthe modulation of the electron-nuclear hyperfine interactions. While it dominates DNP inliquids and metals, where unpaired electrons are highly mobile, Overhauser DNP is possiblein insulating solids if rapid structural modulations are linked to a modulation in hyperfinecoupling. Herein, we report that Overhauser DNP can be triggered by the strategic additionof a methyl group, demonstrated here in a Blatter's radical. The rotation of the methyl groupleads to a modulation of the hyperfine coupling to its protons, which in turn facilitateselectron-nuclear cross-relaxation. Removal of the methyl protons, through deuteration,quenches the process, as does the reduction of the hyperfine coupling strength. This resultsuggests the possibility for the design of tailor-made Overhauser DNP polarizing agents forhigh-field MAS-DNP

Automated summary

The Overhauser effect, which requires the modulation of electron-nuclear hyperfine interactions, dominates dynamic nuclear polarization (DNP) in liquids and metals. This effect can also occur in insulating solids through rapid structural modulations linked to a modulation in hyperfine coupling. In this study, the addition of a methyl group to Blatter's radical was found to trigger Overhauser DNP. The rotation of the methyl group leads to a modulation of the hyperfine coupling to its protons, facilitating electron-nuclear cross-relaxation. The findings suggest the possibility of designing tailor-made Overhauser DNP polarizing agents for high-field MAS-DNP.