Characterization of dielectric properties and their impact on MAS-DNP NMR applications

• Published in: Journal of magnetic resonance (1997) 2024-08, Vol.365, p.107742, Article 107742
• Main Authors: Scott, Faith J., Dubroca, Thierry, Schurko, Robert W., Hill, Stephen, Long, Joanna R., Mentink-Vigier, Frédéric
• Format: Article
• Language: English
• Subjects: Ceramics; Dielectric Properties; Electron Paramagnetic Resonance; Instrumentation; Microwaves; Sample preparation; Terahertz
• ISSN: 1090-7807; 1096-0856; 1096-0856
• DOI: 10.1016/j.jmr.2024.107742

[Display omitted] •Dielectric properties of common materials used in high field DNP and EPR.•Characterization with quasi-optical bench between 70–960 GHz.•Design of microwave efficient MAS rotors for DNP.•Quantitative DNP simulations explain the field dependence of the Cross-Effect. The dielectric properties of materials play a crucial role in the propagation and absorption of microwave beams employed in Magic Angle Spinning − Dynamic Nuclear Polarization (MAS-DNP) NMR experiments. Despite ongoing optimization efforts in sample preparation, routine MAS-DNP NMR applications often fall short of theoretical sensitivity limits. Offering a different perspective, we report the refractive indices and extinction coefficients of diverse materials used in MAS-DNP NMR experiments, spanning a frequency range from 70 to 960 GHz. Knowledge of their dielectric properties enables the accurate simulation of electron nutation frequencies, thereby guiding the design of more efficient hardware and sample preparation of biological or material samples. This is illustrated experimentally for four different rotor materials (sapphire, yttria-stabilized zirconia (YSZ), aluminum nitride (AlN), and SiAlON ceramics) used for DNP at 395 GHz/1H 600 MHz. Finally, electromagnetic simulations and state-of-the-art MAS-DNP numerical simulations provide a rational explanation for the observed magnetic field dependence of the enhancement when using nitroxide biradicals, offering insights that will improve MAS-DNP NMR at high magnetic fields.