Four millimeter spherical rotors spinning at 28 kHz with double-saddle coils for cross polarization NMR.

Autor: Gao C; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Judge PT; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Biochemistry, Biophysics & Structural Biology, Washington University in St. Louis, St. Louis, MO 63110, USA., Sesti EL; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Price LE; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Alaniva N; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Saliba EP; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Albert BJ; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Soper NJ; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA., Chen PH; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA., Barnes AB; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA. Electronic address: barnesab@wustl.edu.
Jazyk: angličtina
Zdroj: Journal of magnetic resonance (San Diego, Calif. : 1997) [J Magn Reson] 2019 Jun; Vol. 303, pp. 1-6. Date of Electronic Publication: 2019 Apr 01.
DOI: 10.1016/j.jmr.2019.03.006
Abstrakt: Spherical rotors in magic angle spinning (MAS) experiments have significant advantages over traditional cylindrical rotors including simplified spinning implementation, easy sample exchange, more efficient microwave coupling for dynamic nuclear polarization (DNP), and feasibility of downscaling to access higher spinning frequencies. Here, we implement spherical rotors with 4 mm outside diameter (o.d.) and demonstrate spinning >28 kHz using a single aperture for spinning gas. We show a modified stator geometry to improve fiber optic detection, increase NMR filling factor, and improve alignment for sample exchange and microwave irradiation. Higher NMR Rabi frequencies were obtained using smaller radiofrequency (RF) coils on small-diameter spherical rotors, compared to our previous implementation of MAS spheres with an o.d. of 9.5 mm. We report nutation fields of 110 kHz on 13 C with 820 W of input power and 100 kHz on 1 H with 800 W of input power. Proton decoupling fields of 78 kHz were applied over 20 ms of signal acquisition without any sign of arcing. Compared to our initial demonstration of a split coil for 9.5 mm spheres, this current implementation of a double-saddle coil inductor for 4 mm spheres not only intensifies the RF fields, but also improves RF homogeneity. We achieve an 810°/90° nutation intensity ratio of 0.84 at 300.197 MHz ( 1 H). We also show electromagnetic simulations predicting a nearly 3-fold improvement in electron Rabi frequency of 0.99 MHz (with 4 mm spheres) compared to 0.38 MHz (with 3.2 mm cylinders), with 5 W of incident microwave power. Further improvements in magnetic resonance spin control are expected as RF inductors and microwave coupling are optimized for spherical rotors and scaled down to the micron scale.
(Copyright © 2019. Published by Elsevier Inc.)
Databáze: MEDLINE
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