Research ArticleAPPLIED PHYSICS

Magic angle spinning spheres

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Science Advances  21 Sep 2018:
Vol. 4, no. 9, eaau1540
DOI: 10.1126/sciadv.aau1540
  • Fig. 1 Rotors for MAS NMR.

    (A) Cylindrical rotor (3.2 mm) with 36-μl sample volume. Spherical rotors (9.5 mm) include equatorial turbine grooves cut into the surface to generate angular momentum. Two sample chambers have been machined: (B) 36 μl and (C) 161 μl. All linear dimensions are in millimeters. The first-order sidebands in 79Br spectra of KBr were used to analyze NMR sensitivity of (D) 3.2-mm cylindrical rotors, (E) 36-μl spherical rotors, and (F) 161-μl spherical rotors. Each spectrum is an average of 256 transients.

  • Fig. 2 A selection of the four 3D printed stators for spherical rotors.

    (A) Enclosed design with multiple gas streams for spinning. (B) Open-face design with a single gas stream and a pathway to guide exhaust gas. (C) Design complete with single gas stream, exhaust pathway, and pivots for adjustment of the magic angle. (D) In comparison to (C), a vertical extrusion of 2 mm is added above the cup of the stator, and blind holes have been added to accept fiber optics for spinning frequency detection.

  • Fig. 3 Our current stator design with a single gas stream.

    (A) The gas introduced under the sphere 35.3° off of B0 suspends the sphere and aligns its spinning axis with the magic angle. (B) A section view from (A) shows the gas inlet path and how the gas is directed into the drive cup by a tangent plane. (C and D) Overall flow path of the spinning gas from two separate isometric views.

  • Fig. 4 Implementation of rotating spheres into a transmission line probe previously used in cryogenic MAS-DNP.

    (A) The pivots of the 3D printed stator serve as the gas inlet and as the pivot point for the magic angle adjustment. The complete NMR probe head includes fiber optics for spinning frequency detection, magic angle adjustment via a threaded adjustment assembly, waveguide to transmit microwaves to the sample for DNP, tube for sample exchange, and a 3D printed post for connection of the stator to the gas supply. An isometric view (B) and a section view (C) show the path for the introduction of microwaves to the sample for DNP. RF, radio frequency.

  • Fig. 5 Magic angle adjustment and spinning stability regulation of MAS with spherical rotors.

    79Br magnetic resonance of MAS spheres packed with KBr. (A) Free induction decay of 64 transients with rotational echoes observed out to 10 ms. (B) Spinning sidebands in the frequency domain indicate spinning of 4.3 kHz stably at the magic angle. (C) Optimization of the magic angle at a spinning frequency of 2.5 kHz. The height ratio (R) of the center band peak relative to the second sideband decreases as the angle of rotation approaches 54.7° from B0 (36). (D) Spinning frequency stability over 22 min with and without spinning regulation controlled through a resistive heating element circuit. (E) Expansion of spinning frequency shows moderate excursion in spinning frequency of less than 20 Hz without regulation and improved frequency stability with regulation. (F) Histogram of spinning frequencies showing the rotor spinning at 4560 ± 1 Hz for 98% of the 22 min observed. a.u., arbitrary units.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/9/eaau1540/DC1

    Section S1. Rapid prototyping by 3D printing

    Section S2. MAS test station for 3D printed stators

    Section S3. MAS (10.6 kHz) with helium gas

    Section S4. Spinning frequency reproducibility

    Section S5. Correlation between temperature and spinning frequency

    Fig. S1. 3D printed stators for spherical rotors.

    Fig. S2. Spinning test station for spherical rotors in 3D-printed stators.

    Fig. S3. Spherical rotor spun at 10.6 kHz with helium gas.

    Fig. S4. Correlation between temperature and spinning frequency of spherical rotor.

    Table S1. Spinning test with same stator and different spherical rotors.

    Table S2. Spinning test with same spherical rotor and different stator copies.

    Movie S1. Spherical rotor (9.5 mm) spins stably at magic angle in 3D-printed stator.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Rapid prototyping by 3D printing
    • Section S2. MAS test station for 3D printed stators
    • Section S3. MAS (10.6 kHz) with helium gas
    • Section S4. Spinning frequency reproducibility
    • Section S5. Correlation between temperature and spinning frequency
    • Fig. S1. 3D printed stators for spherical rotors.
    • Fig. S2. Spinning test station for spherical rotors in 3D-printed stators.
    • Fig. S3. Spherical rotor spun at 10.6 kHz with helium gas.
    • Fig. S4. Correlation between temperature and spinning frequency of spherical rotor.
    • Table S1. Spinning test with same stator and different spherical rotors.
    • Table S2. Spinning test with same spherical rotor and different stator copies.

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mov format). Spherical rotor (9.5 mm) spins stably at magic angle in 3D-printed stator.

    Files in this Data Supplement:

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