Benchtop DNP on Varying 1H Spins Quantities Towards Broad Range Sample Hyperpolarization

Hyperpolarization by Dynamic Nuclear Polarization (DNP) at 1 Tesla and 77 Kelvin in a benchtop polarizer was recently demonstrated [1], achieving a sensitivity boost of two orders of magnitude on ¹H and ¹³C spins. The development of such compact instrumentation lies within the HypFlow approach aiming to hyperpolarize various native frozen solutions without sample contamination nor dilution. It employs porous hyperpolarizing matrices (HYPSOs) [2] covalently supporting radicals in which the solution is flowed, frozen and hyperpolarized.

The polarizer performances were initially evaluated using partially deuterated samples with fixed ¹H and ¹³C spin quantities, however, it is crucial to assess the DNP efficiency across a wider range of spins concentrations, especially for the analysis of native samples. In this study, we assessed the solid-state DNP performance in H2O:D2O and 13C-urea solutions impregnated in HYPSOs, varying the urea concentration and water ratios. We show a DNP enhancement of 50 for proton spins of a non-deuterated water solution (100% H₂O) with urea. The high ¹H polarization is subsequently transferred to ¹³C spins by ¹H→¹³C cross-polarization (CP) which efficiency was also evaluated.

The study also highlights that the build-up time of polarization accelerates with increasing proton concentration, consistent with MAS-DNP observations [3]. Using a conventional frozen solution with varying proton concentrations, we applied the approach by Prisco et al. [3] to investigate hyperpolarization spreading across the spin diffusion barrier. Results show that up to 50 M of protons, polarization remains limited by spin diffusion, with restricted spin exchange preventing the polarization from transferring back to the lattice. Beyond that concentration, the bulk polarization decreases due to rapid spin relaxation, with a minimum observed enhancement of 80.

Hyperpolarization with non-deuterated samples may significantly expand DNP applications through the HypFlow approach across various domains where samples need to be analyzed in their natural state. Our simple benchtop polarizer combined in the future with sample melting, may enable replenishable hyperpolarization, opening new avenues for integrating hyperpolarization with multi-dimensional liquid-state NMR.

[1]   Bocquelet, C. et al. Science Advances. 10 (2024)

[2]   Cavailles, M. et al. Angewandte Chemie. 130, 7575-7579 (2018).

[3]   Prisco, N. A., et al. Phys. Chem. Chem. Phys. 23, 1006-1020, (2021)

We acknowledge Bruker BioSpin for providing the prototype benchtop DNP polarizer and particularly R. Melzi, and J. Kempf, Laurent Martinache and Olivier Gonella for scientific and technical support. We additionally acknowledge C. Jose and C. Pages for use of the ISA Prototype Service, and S. Martinez of the UCBL mechanical workshop for machining parts of the experimental apparatus. This research was supported by Lyon 1 University, the Doctoral School of Chemistry of Lyon (ED 206), ENS Lyon, the French CNRS, the European Research Council under the European Union research and innovation program (ERC Grant Agreements No. 101044726 / HypFlow) and the French National Research Agency (project 'HyMag' ANR 18-CE09-0013).