TEMPOL, because of its broad EPR resonance line typical of nitroxides, efficiently polarizes nuclear spins with large gyromagnetic ratios, such as 1 H, and was therefore used as the polarizing agent. All the experiments were performed on fully protonated compounds and with large volume (800µL) samples containing a mixture of 250µL H 2 O, 400µL unlabelled Glycerol, and 50 mM of the TEMPOL radical obtained from a 150µL stock solution. The absence of deuteration of the compounds is unusual for DNP experiments, but turned out to be necessary to obtain sufficient sample magnetization in our setup, therefore significant radiation feedback. This can be explained by the moderate quality factor Q ≈ 127 of the probe used for NMR signal detection at 1.2K. (full width at -3 dB was 2.23 MHz, measured at 285.325 MHz), as well as the limited power of the µw source used for these experiments (≈ 32 mW) In all experiments performed in this study, nuclear spins were polarized negatively, and read pulses for polarization buildup monitoring, as well as pulses used to trigger maser experiments used flip angles ≤ 1 o .