Paul, Subhradip, Eric Bouleau, Quentin Reynard-Feytis, Jean-Pierre Arnaud, Florian Bancel, Bertrand Rollet, Pierre Dalban-Moreynas, et al. “Sustainable and Cost-Effective MAS DNP-NMR at 30 K with Cryogenic Sample Exchange.” Journal of Magnetic Resonance 356 (November 2023): 107561.
https://doi.org/10.1016/j.jmr.2023.107561.
We report here instrumental developments to achieve sustainable, cost-effective cryogenic Helium sample spinning in order to conduct dynamic nuclear polarisation (DNP) and solid-state NMR (ssNMR) at ultra-low temperatures (< 30 K). More specifically, we describe an efficient closed-loop helium system composed of a powerful heat exchanger (95% efficient), a single cryocooler and a single helium compressor to power the sample spinning and cooling. The system is integrated with a newly designed triple-channel NMR probe that minimizes thermal losses without compromising the RF performance and spinning stability (+/- 0.05%). The probe is equipped with an innovative cryogenic sample exchange system that allows swapping samples in minutes without introducing impurities in the close-loop system. We report that significant gain in sensitivity can be obtained at 30-40 K on large micro-crystalline molecules, with unfavorable relaxation timescales, making them difficult or impossible to polarize at 100 K. We also report rotor-synchronized 2D experiments to demonstrate the stability of the system.