¹H Detected Relayed Dynamic Nuclear Polarization

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Physical Chemistry

Background:

• Mesoscale structure determination in complex materials using NMR is challenging due to low sensitivity.
• Previous methods relied on indirect detection of proton (¹H) polarization, limiting experimental efficiency.

Purpose of the Study:

• To improve sensitivity and reduce experiment times for NMR-based mesoscale structure determination.
• To enable direct detection of proton hyperpolarization dynamics.

Main Methods:

• Combination of relayed-dynamic nuclear polarization (R-DNP) with fast magic angle spinning (MAS) at high magnetic field (21.2 T).
• Utilized 0.7 mm rotors for MAS frequencies up to 60 kHz, enabling direct ¹H detection.
• Modulated ¹H spin diffusion rates by varying MAS frequency to obtain independent R-DNP curves.

Main Results:

• Achieved a 16-fold acceleration in experiment times through direct ¹H detection.
• Successfully determined a Weibull distribution of particle sizes in microcrystalline l-histidine·HCl·H₂O.
• Established a mean particle radius of 440 ± 20 nm with an order parameter k = 2.2.

Conclusions:

• The combined R-DNP and fast MAS approach significantly enhances sensitivity and speed for mesoscale structure analysis.
• Direct proton detection coupled with variable MAS rates provides accurate domain size determination.
• This technique offers a powerful tool for characterizing complex materials.