High-Field Magic Angle Spinning Dynamic Nuclear Polarization Using Radicals Created by γ-Irradiation

Area of Science:

• Solid-state chemistry
• Nuclear magnetic resonance spectroscopy
• Materials science

Background:

• High-field magic angle spinning dynamic nuclear polarization (MAS DNP) significantly boosts sensitivity in solid-state NMR.
• This technique relies on transferring spin polarization from electron spins to nuclear spins.
• Generating stable radicals is crucial for efficient MAS DNP.

Purpose of the Study:

• To investigate gamma irradiation as a method for generating stable radicals in diverse solid materials.
• To assess the suitability of these radiation-induced radicals for high-field MAS DNP experiments.
• To explore the potential of ionizing radiation for enhancing NMR sensitivity.

Main Methods:

• Gamma irradiation of inorganic solids (fused quartz, borosilicate glasses) and organic solids (glucose, cellulose, urea/polyethylene polymer).
• Utilizing the generated stable radicals to polarize 29Si or 1H nuclear spins.
• Measuring dynamic nuclear polarization enhancements (ε) using high-field MAS DNP.

Main Results:

• Stable radicals were successfully induced by gamma irradiation in both inorganic and organic solids.
• Significant MAS DNP enhancements (ε > 400 for fused quartz, ε > 30 for glucose) were achieved.
• Negligible enhancements were observed in some samples, attributed to low radical concentrations or interfering quadrupolar spins.

Conclusions:

• Ionizing radiation, specifically gamma irradiation, is an effective method for generating stable radicals in solids.
• These radiation-induced radicals are suitable for high-field MAS DNP, offering a promising alternative for sensitivity enhancement.
• The study highlights a novel approach for preparing materials for advanced solid-state NMR applications.