Feb 17, 2025
Version 1
MQMAS Using Split-t1 Acquisition V.1
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. MQMAS Using Split-t1 Acquisition. protocols.io https://protocols.io/view/mqmas-using-split-t1-acquisition-dzuu76wwVersion 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 15, 2024
Last Modified: February 17, 2025
Protocol Integer ID: 120436
Keywords: Materials 3QMAS with Split-t1 Acquisition: 23Na
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
Acquisition of a multiple quantum MAS experiment with a 3Q coherence pathway and split-t1 acquisition.
Scope
This protocol is intended for use on a sample of interest after completing SOP Materials Central-Transition-Selective Pulse Width Optimization and SOP Materials Spin Echo. MQMAS should only be performed when a) the 1D spectrum has insufficient resolution for adequate deconvolution, and b) all peaks are in the fast-spinning limit.
Materials
Definitions:
- MQMAS: Multiple-quantum magic angle spinning
- 3QMAS: Triple-quantum magic angle spinning
- CT: Central transition
- rf: Radiofrequency
- υrf: Radiofrequency amplitude
- CQ: Quadrupolar coupling constant
Appendix:
If the phasing in F2 requires adjustment, transform F2 using the command xf2 and correct the phasing on the first row.
Before start
User should be familiar with the power limitations and duty cycle of the probe being used.
Expected amount of time: 24 hours.
Procedure
Procedure
Begin with an optimized 90° pulse using the highest safe rf power allowed by probe. Note the duration and power level.
Safety information
If you are not sure what the highest safe rf power of the probe is, check with your local facility manager. Using a lower power will primarily affect the sensitivity of the experiment, so when in doubt use a power that is known to be safe.
Optimize a weak CT-selective 180° pulse. Note the duration and power level.
Note
This pulse will usually be on the order of 10-20 μs long.
Using a Hahn echo with whole-echo acquisition, test to see if full echo acquisition is possible.
Set the parameter l20 to ensure that there is no residual FID and a full echo is acquired.
Load the 3QMAS pulse sequence mp3q.
Set initial values for later optimization:
The triple-quantum excitation pulse p1 and power level pl11 should be set to the 90° pulse optimized in Step 1.
The conversion pulse p2 should be set to p1/3.
The selective pulse p4 and power level pl12 should be set to the CT-selective 180° pulse values optimized in Step 2.
The relaxation delay d1 should be set to 1.3 ×T1, where T1 is the largest value in the sample.
l20 should be set to the value optimized in Step 3.1.
cnst31 should be set to the MAS frequency.
ns should be set to 96.
- If the experimental time with ns=96 is too long to allow for optimization, using ns=48 should allow for adequate optimization of p1 and p2.
Using popt, optimize p2, followed by p1.
Both will have maxima at somewhat greater than 90°; optimizing over a range from 70° to 140° should find an appropriate maximum.
Consider all resonances when optimizing these pulses. The optimal length depends on the CQ of the resonance, so in systems with a wide range of CQ values there may not be an universally optimal pulse length. Choose a value which provides adequate sensitivity for all resonances.
Once p1 and p2 are optimized, create a new experiment and convert it to 2D acquisition.
Set the following parameters for 2D acquisition:
FnMode QF
MC2 QF
F1 NUC1 to match the nucleus being acquired. Note that this must be set in the eda panel and cannot be set from the command line.
Note
The default value is often 1H, which interferes with the ability to set the F1 sweep width.
1 td 64
Note
The optimal value of 1 TD depends on the desired resolution in F1, the T2 of the environments in the sample, and the available spectrometer time. Too few 1 TD points could lead to truncation artifacts, while too many wastes time.
Note
1 td 64 will likely be acceptable or even excessive for amorphous samples, but too short for crystalline samples with long T2; even if too short, 64 can be an adequate starting point.
1 swh to the MAS rate in Hz.
Note
Be sure 1 NUC1 is set appropriately before setting 1 swh.
Note
If this is too small to observe all of the resonances in the sample without folding, half-rotor synchronization (where 1 swh is twice the MAS rate) is permissible but will lead to spinning sidebands being observed in the spectrum.
in0 to one rotor period
in10 to the following value depending on nuclear spin:
- For I = 3/2, in0 × 7/9
- For I > 3/2, 0
in11 to the following value depending on nuclear spin:
- For I = 3/2, 0
- For I = 5/2, in0 × 19/12
- For I = 7/2, in0 × 101/45
Adjust both ns (in multiples of 96) and 1 td to make best use of available experimental time.
Acquire the spectrum.
As this is a split-t1 acquisition, no special post-processing is required.
Protocol references
Amoureux, J.-P. and Pruski, M. (2008). MQMAS NMR: Experimental Strategies and Applications. In eMagRes (eds R.K. Harris and R.L. Wasylishen).
Yannick Millot, Pascal P Man, Procedures for Labeling the High-Resolution Axis of Two-Dimensional MQ-MAS NMR Spectra of Half-Integer Quadrupole Spins, Solid State Nuclear Magnetic Resonance, Volume 21, Issues 1–2, 2002, Pages 21-43,
Protocol
NAME
Saturation Recovery for Quadrupolar Nuclei
CREATED BY
NMRFAM Facility
Protocol
NAME
Spin Echo with Whole-Echo Acquisition
CREATED BY
NMRFAM Facility
Protocol
NAME
Quadrupole Non-Selective Pulse Width Optimization
CREATED BY
NMRFAM Facility
Protocol
NAME
Quadrupole CT-Selective Pulse Width Optimization
CREATED BY
NMRFAM Facility