Solid-state dynamic nuclear polarization at 263 GHz: spectrometer design and experimental results

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Spectroscopic Instrumentation

Background:

• Dynamic Nuclear Polarization (DNP) enhances nuclear magnetic resonance (NMR) sensitivity by transferring electron spin polarization to nuclear spins.
• Magic Angle Spinning (MAS) is crucial for high-resolution NMR, and integrating it with DNP presents unique technical challenges.

Purpose of the Study:

• To design and test a novel spectrometer for MAS DNP experiments at a 263 GHz microwave frequency.
• To evaluate the performance and stability of the DNP spectrometer under various experimental conditions.

Main Methods:

• Development of a DNP spectrometer utilizing a continuous-wave gyrotron for microwave generation at 263 GHz.
• Integration of microwave transmission lines and a specialized NMR probe for irradiating a 3.2 mm rotor during MAS.
• System characterization through analysis of magnetic field, temperature, microwave power, and spinning frequency dependencies.

Main Results:

• Achieved DNP signal enhancements of up to 80 at 95 K using TOTAPOL polarizing agent on urea and proline in water-glycerol.
• Detailed characterization of experimental parameters influencing DNP efficiency, including sample heating effects.
• Demonstrated stable system operation and DNP performance over a 36-hour period.

Conclusions:

• The developed MAS DNP spectrometer is effective for significantly enhancing NMR sensitivity.
• The system's performance is well-characterized, providing a reliable platform for advanced NMR studies.
• This work contributes to the advancement of high-sensitivity solid-state NMR spectroscopy.