High-field (13)c dynamic nuclear polarization with a radical mixture.

We report direct (13)C dynamic nuclear polarization at 5 T under magic-angle spinning (MAS) at 82 K using a mixture of monoradicals with narrow EPR linewidths. We show the importance of optimizing both EPR linewidth and electron relaxation times by studying direct DNP of (13)C using SA-BDPA and trityl radical, and achieve (13)C enhancements above 600. This new approach may be best suited for dissolution DNP and for studies of (1)H depleted biological and other nonprotonated solids.