Sustainable and cost-effective MAS DNP-NMR at 30 K with cryogenic sample exchange

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Cryogenics and Low-Temperature Physics
• Materials Science

Background:

• Dynamic nuclear polarization (DNP) and solid-state NMR (ssNMR) are powerful techniques for molecular structure determination.
• Achieving high sensitivity in ssNMR, especially for large molecules with poor relaxation properties, remains a challenge.
• Current methods often require higher temperatures (e.g., 100 K), limiting their applicability to certain sample types.

Purpose of the Study:

• To develop and validate a sustainable and cost-effective cryogenic helium sample spinning system for DNP-ssNMR at ultra-low temperatures (<30 K).
• To enhance sensitivity for challenging samples that are difficult to polarize at higher temperatures.
• To demonstrate the stability and performance of the developed system for advanced NMR experiments.

Main Methods:

• Implementation of an efficient closed-loop helium system with a high-efficiency heat exchanger, a single cryocooler, and a single helium compressor.
• Integration of a newly designed triple-channel NMR probe minimizing thermal losses and ensuring spinning stability (±0.05%).
• Development of an innovative cryogenic sample exchange system for rapid sample swapping without system contamination.

Main Results:

• Demonstrated successful operation of the cryogenic helium system at ultra-low temperatures (<30 K).
• Achieved significant sensitivity gains at 30-40 K for large micro-crystalline molecules with unfavorable relaxation timescales.
• Validated system stability through rotor-synchronized 2D experiments.

Conclusions:

• The developed cryogenic helium system offers a sustainable and cost-effective solution for DNP-ssNMR at ultra-low temperatures.
• This advancement significantly improves the sensitivity and applicability of DNP-ssNMR for a wider range of challenging molecules.
• The system's stability and efficiency open new avenues for low-temperature solid-state NMR research.