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600 MHz 1H/15N probe
shown w/o VT chamber
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1. PURPOSE
The work is underway to enhance facility at NHMFL that studies membrane protein samples.
A double-tuned 1H/15N static NMR probe with VT capability has been built and tested to take advantage of our
600 MHz wide bore magnet,
while similar probe for 400 MHz is currently under construction.
The probe is designed to work in tandem with console-programmable upper VT stack, which was also built
in-house to free up valuable physical space inside the probe for high-voltage components.
In general, principal challenges in building probes for solid state NMR of membrane proteins are:
- Relatively large sample size with RF coils exceeding 1/4 wavelength
- High B1 homogeneity requirement for proton channel
- High efficiency of both channels, especially of 15N channel
- Accoustic ringing at 15N frequency
- Sample preparation and packaging that optimises filling factor while maintaining hydration for long time
- High power handling capability on both channels
- Sample heating resulting from high power decoupling pulse
2. PROBE FEATURES
- Sample coil ID: 8 mm x 6 mm, 4 turns
- Balanced proton RF channel for improved homogeneity
- Temperature range: -40°C...+100°C
- Temperature regime delivered by upper VT stack
- Circuit efficiency, calibrated with single NAV crystal:
- p90° = 5.6 us at 75 W for 1H
- p90° = 4.2 us at 670 W for 15N
- Maximum input power:
- 1H: 360 W
- 15N: not tested (> 710 W)
- Acoustic ringing time for 15N is less than 15 us.
3. EXAMPLE
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15N-1H 2D PISEMA spectrum of 15N-Ala5-gA in DMPC (20/70mg)
Coil ID: 8mm x 6mm
Sample size: 6mm x 4mm x 12mm
Stacked glass plates, lossy sample
Temperature regime: 37°C
Matching condition:
p90° = 6.5 us at 80 W for 1H
p90° = 6.5 us at 335 W for 15N
Decoupling power = 10 ms at 60 W
(This was older probe version)
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