Cryogenic-compatible spherical rotors and stators for magic angle spinning dynamic nuclear polarization

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP) Enhancement Techniques
• Cryogenic Engineering for Spectroscopic Applications

Background:

• Magic Angle Spinning (MAS) is crucial for solid-state NMR, with cryogenic temperatures enhancing sensitivity.
• Dynamic Nuclear Polarization (DNP) significantly boosts NMR signal, but often requires small sample volumes.
• Advancements in MAS technology, particularly spherical rotors, offer potential for larger sample capacities.

Purpose of the Study:

• To optimize and implement a stator for cryogenic MAS using 9.5 mm diameter spherical rotors.
• To enable DNP experiments on significantly larger sample volumes than previously feasible.
• To achieve high DNP enhancements with improved spinning stability at cryogenic temperatures.

Main Methods:

• Design and construction of a novel stator for cryogenic MAS accommodating 9.5 mm spherical rotors.
• Integration of sample insert/eject mechanisms for user convenience.
• Characterization of spinning stability and DNP performance at 7 Tesla and 105-107 K.

Main Results:

• Demonstrated temperature-independent spinning stability of $$ * Hz* is negligible.
• DNP enhancements of 223 and 200 were achieved for 124 and 223 µL sample volumes, respectively.
• Experiments utilized 4 M ¹³C, ¹⁵N-labeled urea and 20 mM AMUPol in a glycerol-water matrix at 105-107 K and 7 T.

Conclusions:

• The developed cryogenic MAS stator effectively supports DNP experiments on large sample volumes.
• The system demonstrates high DNP enhancements, making it suitable for sensitive solid-state NMR studies.
• This advancement facilitates the study of larger, more dilute, or less sensitive samples in solid-state NMR.