Dynamic nuclear polarization at 40 kHz magic angle spinning.

Area of Science:

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

Background:

• Dynamic Nuclear Polarization (DNP) enhanced solid-state NMR spectroscopy is a powerful technique for analyzing solid materials, offering significant sensitivity gains.
• Previous DNP MAS NMR applications were primarily demonstrated at moderate spinning frequencies (up to 14 kHz) using 3.2 mm rotors.

Purpose of the Study:

• To investigate the impact of smaller rotor volumes and higher magic angle spinning (MAS) frequencies on DNP-enhanced solid-state NMR sensitivity.
• To evaluate signal amplification factors and coherence lifetimes at very fast MAS rates.
• To assess the contribution of quenching effects to sensitivity gains at high MAS frequencies.

Main Methods:

• Utilized a 1.3 mm MAS DNP probe operating at a high magnetic field (18.8 T) and low temperature (∼100 K).
• Performed experiments with sample spinning rates ranging from 10 to 40 kHz.
• Investigated signal amplification factors, (29)Si coherence lifetimes, and quenching effects.

Main Results:

• Achieved signal amplification factors up to two times higher with 1.3 mm rotors compared to 3.2 mm rotors.
• Reported DNP enhancements of approximately 60 over a range of MAS rates from 10 to 40 kHz.
• Demonstrated a threefold increase in (29)Si coherence lifetimes at 40 kHz MAS compared to 10 kHz MAS, enhancing sensitivity in CPMG experiments.

Conclusions:

• Employing smaller rotors and very fast MAS in DNP-enhanced solid-state NMR significantly increases sensitivity and improves coherence properties.
• This advancement enables more effective structural investigations of solid materials, including functionalized mesostructured organic-inorganic materials.