High-Field Dynamic Nuclear Polarization with High-Spin Transition Metal Ions

We report the dynamic nuclear polarization of H-1 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 (m(s) = -1/2 -> +1/2) EPR transition. Using a Gd3+ complex with a narrow central transition EPR line width of 29 MHz, we observed a maximum enhancement of similar to 13, which is comparable to previous results on the narrow-line-width trityl radical.