Maximizing Relayed ¹H Hyperpolarization Transfer by Slow-Fast MAS NMR Spectroscopy

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Advanced materials characterization
• Biomolecular structure determination

Background:

• ¹H-detected dynamic nuclear polarization (DNP)-enhanced fast magic angle spinning (MAS) NMR offers high sensitivity for studying complex systems.
• Sensitivity in relayed DNP experiments decreases at higher MAS rates due to reduced ¹H-¹H spin diffusion.
• This limitation hinders detailed structural and dynamic investigations of advanced materials and biomolecules.

Purpose of the Study:

• To develop a novel DNP-enhanced NMR strategy to overcome sensitivity loss at fast MAS rates.
• To enhance the sensitivity of ¹H NMR experiments at high MAS frequencies.
• To enable more effective structural and dynamic analysis of challenging samples.

Main Methods:

• Implementation of a two-stage MAS approach: polarization at a slow MAS rate followed by signal acquisition at a fast MAS rate.
• Utilizing relayed DNP for efficient polarization build-up.
• Performing experiments on l-histidine·HCl·H₂O using a 0.7 mm DNP probe at 18.8 T and 100 K.
• Employing MAS rates up to 65 kHz.

Main Results:

• Achieved a 35% improvement in sensitivity by combining polarization at 20 kHz MAS with acquisition at 60 kHz MAS.
• Demonstrated the effectiveness of the proposed method in enhancing signal detection.
• Successfully applied the technique to a model compound (l-histidine·HCl·H₂O).

Conclusions:

• The proposed combined slow-MAS polarization and fast-MAS acquisition strategy significantly improves sensitivity in DNP-enhanced NMR.
• This method effectively addresses the challenge of reduced sensitivity at high MAS rates.
• The findings pave the way for more sensitive NMR studies of structure and dynamics in challenging materials and biological systems.