Liquid State DNP on Metabolites at 260 GHz EPR/400 MHz NMR Frequency

We have performed liquid state (Overhauser) dynamic nuclear polarization (DNP) experiments at high magnetic field (9.2 T, corresponding to 260 GHz EPR and 400 MHz H-1-NMR resonance frequency) on solutions of pyruvate, lactate and alanine in water with TEMPOL nitroxide radicals as polarizing agent. We present experimental results showing DNP enhancement on metabolite methyl protons, varying for the different target metabolites. It is shown that the enhancements are achieved through direct coupling between the radicals and the target metabolites in solution, i.e., the effect is not mediated by the solvent water protons. The coupling factors between the TEMPOL radicals and the metabolites observed are a factor of 3-5 smaller compared to direct polarization transfer from TEMPOL to water protons.