B. Corzilius et al., High-Field Dynamic Nuclear Polarization with High-Spin Transition Metal Ions, 2011, JACS
http://dx.doi.org/10.1021/ja1109002
We report the dynamic nuclear polarization of 1H spins in magic-angle-spinning spectra recorded at 5 T and 84 K via the solid effect using Mn2+ and Gd3+ complexes as polarizing agents. We show that the magnitude of the enhancements can be directly related to the effective line width of the central (mS = -1/2, 1/2) EPR transition. Using a Gd3+ complex with a narrow central transition EPR line width of 29 MHz, we observed amaximum enhancement of ∼13, which is comparable to previous results on the narrow-line-width trityl radical.