(1)H and (13)C dynamic nuclear polarization in aqueous solution with a two-field (0.35 T/14 T) shuttle DNP spectrometer.

Dynamic nuclear polarization (DNP) permits increasing the NMR signal of nuclei by pumping the electronic spin transitions of paramagnetic centers nearby. This method is emerging as a powerful tool to increase the inherent sensitivity of NMR in structural biology aiming at detection of macromolecules. In aqueous solution, additional technical issues associated with the penetration of microwaves in water and heating effects aggravate the performance of the experiment. To examine the feasibility of low-field (9.7 GHz/0.35 T) DNP in high resolution NMR, we have constructed the prototype of a two-field shuttle DNP spectrometer that polarizes nuclei at 9.7 GHz/0.35 T and detects the NMR spectrum at 14 T. We report our first (1)H and (13)C DNP enhancements with this spectrometer. Effective enhancements up to 15 were observed for small molecules at (1)H 600 MHz/14 T as compared to the Boltzmann signal. The results provide a proof of principle for the feasibility of a shuttle DNP experiment and open up perspectives for the application potential of this method in solution NMR.