Feb 17, 2025
Version 2
Direct Polarization Spin Diffusion V.2
This protocol is a draft, published without a DOI.
- Alexander L. Paterson1
- 1National Magnetic Resonance Facility at Madison (NMRFAM), University of Wisconsin-Madison, Madison, WI, United States
Protocol Citation: Alexander L. Paterson 2025. Direct Polarization Spin Diffusion. protocols.io https://protocols.io/view/direct-polarization-spin-diffusion-dzx777rnVersion created by NMRFAM Facility
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: In development
We are still developing and optimizing this protocol, but it should be functional. We hope to solicit feedback primarily on clarity and usability. We intend to publish it in June 2025.
Created: June 14, 2024
Last Modified: February 17, 2025
Protocol Integer ID: 120543
Keywords: Materials Spin Diffusion
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To obtain 2D spin diffusion spectra in highly correlated protonated systems.
Scope
This protocol describes a very basic implementation of a spin diffusion experiment. It is focused on the case of 1H spin diffusion, i.e., Proton Spin Diffusion (PSD) under fast MAS. This is very straightforward to set up, but provides no mechanism for 1H resolution enhancement via homonuclear decoupling.
Guidelines
This experiment can also be used for the Proton-Driven Spin Diffusion (PDSD) case, for use with X nuclei in protonated systems. The implementation in this sequence is a direct polarization case, and should only be used when direct polarization is preferred over cross polarization. Bruker implements a cross polarization-based experiment in the default cpspindiff sequence available in TopSpin.
While labelled as a “spin diffusion” experiment, the spindiffusion.nmrfam pulse sequence (and any simple PSD experiment) can also be used to probe chemical exchange dynamics in the same way as an EXSY experiment.
Measuring a PSD build-up curve requires running multiple experiments with different diffusion periods. Interpreting a build-up curve is beyond the scope of this protocol, and for that the user is directed to the literature.
Materials
Definitions:
- MAS: Magic-Angle Spinning
- PSD: Proton Spin Diffusion
- PDSD: Proton-Driven Spin Diffusion
Appendix:
Note that while fast and ultra-fast MAS may be required for sufficient peak resolution in 1H spin diffusion spectra, fast MAS also reduces the rate of spin diffusion. Choose the values of d21 after careful consideration.
Safety warnings
If proton decoupling is used, user must ensure that the total high-power decoupling time is less than 50 ms or the limit of the probe, whichever is less. This time includes the spin diffusion period.
Before start
User should be familiar with the power, duty cycle, and decoupling limits of the probe.
If proton decoupling is used, user must ensure that the total high-power decoupling time is less than 50 ms or the limit of the probe, whichever is less. This time includes the spin diffusion period.
Expected amount of time SOP will use: 1 to 2 days, depending on sensitivity.
Procedure
Procedure
Load the spindiffusion.nmrfam pulse program. Set the following flags and parameters:
d1: Set to 1.3 × previously measured T1, or 5 × previously measured T1 for quantitation.
ns: 16*n for full phase cycle; 8*n often suffices.
p1: Previously optimized 90° pulse, using power level plw1.
plw1: Previously optimized 90° pulse power, for pulse length pl1.
d21: Set to desired spin diffusion time. This will vary from microseconds to seconds depending on the spin system under investigation.
Note
In 1H spin diffusion, this is typically on the order of milliseconds. For an initial default value for testing with 1H, set to 1 ms.
If presaturation is desired:
- Add the -Dpresat flag to zgoptns.
- Set d20, the presaturation comb delay, to a previously optimized value.
- Set l20, the presaturation comb loop counter, to a previously optimized value.
If heteronuclear decoupling is desired for X-detect PDSD:
- Add the -Dpdsd flag to zgoptns.
- Set cpdprg2 to spinal64 or equivalent.
- Set pcpd2 and plw2 to previously optimized decoupling parameters.
Safety information
Ensure that the acquisition time is below the high-power limit of the probe.
Acquire an initial 1D spectrum. Ensure that all expected peaks are present, and that none overlap with the transmitter frequency.
Convert to a 2D experiment. Set the following additional parameters:
FnMODE: States-TPPI
1 td: a small value, e.g., 16.
1 swh: sufficiently wide to capture all exchange peaks. This can typically be safely set to the same value as 2 swh, but can often be much smaller.
Safety information
Decoupling runs through both 2aq, and 1 aq. If -Dpdsd is set, ensure that the sum of these values is within the high-power decoupling limit of the probe.
Acquire an initial 2D spectrum with a minimal number of scans. Ensure that the F1 spectral width is as wide as desired, and that the transmitter is not overlapping with any regions of interest.
Adjust 1 td to ensure sufficient digitization in F1.
Adjust ns to make best use of available instrument time.
Acquire the 2D experiment. If spin diffusion build-up curves are required, repeat with different values of d21.
Protocol references
L. Emsley, Spin diffusion in crystalline solids, in: NMR Crystallography, John Wiley & Sons Ltd., 2009.
Bruker Solid State NMR User Manual Z4D10641B, Section 11