First DNP Results from a Liquid Water-TEMPOL Sample at 400 MHz and 260 GHz
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Using a newly designed liquid-state dynamic nuclear polarization (DNP) spectrometer operating at a magnetic field of 9.2 T, a DNP enhancement of −4.0(1) was achieved for protons in a liquid water-TEMPOL sample. The DNP mechanism was observed to be the Overhauser effect, where the polarization was transfered via electron–proton dipolar relaxation. At full microwave power, the sample was heated by 17 K above room temperature, causing a significant increase in the DNP enhancement. These first results from the Frankfurt liquid-state DNP spectrometer represent a significant step towards the application of DNP to large biomolecules in the liquid state.