Feb 17, 2025
Version 1
Direct Detect D-HMQC 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. Direct Detect D-HMQC. protocols.io https://protocols.io/view/direct-detect-d-hmqc-dfpu3mnw
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: 101844
Keywords: Materials Quadrupolar Direct-Detect D-HMQC
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To observe through-space correlations between quadrupolar nuclei and spin-1/2 nuclei.
Scope
The dipolar heteronuclear multiple-quantum coherence (D-HMQC) experiment reveals through-space proximities between two nuclei, facilitating spectral assignments. This implementation is a robust choice for nuclei that are significantly averaged at moderate MAS rates, e.g., 20 kHz. Examples of nuclei pairs which benefit from this experiment are 27Al{1H}, 23Na{31P}, and 11B{29Si}. The indirect-detect, or proton-detect, version of D-HMQC benefits from alternate implementations.
Attachments
Guidelines
As this implementation of D-HMQC places the dipolar recoupling pulses on the indirect channel, the quadrupolar nucleus should be the one that is detected.
This pulse sequence should not be used for observing the correlations between two quadrupolar nuclei.
This protocol uses the SR412 recoupling scheme.
Materials
Definitions:
- D-HMQC: Dipolar Heteronuclear Multiple-Quantum Coherence
- MAS: Magic angle spinning
- νr: Magic angle spinning speed
- νrf: Radiofrequency power
- X: Direct nucleus
- Y: Indirect nucleus
- CT: Central transition
Appendix:
While the SR412 recoupling sequence is robust against minor rf imperfections and MAS instability, in dilute systems this sequence can suffer from t1 noise. Reducing the d1 to a very short value (e.g., 0.2 × T1) can mitigate this noise. If doing so, ensure that the overall probe duty cycle is respected.
Before start
Operator should be familiar with acquisition of 2D NMR spectra.
Operator must be familiar with both the MAS spinning limitations of the probe and the RF power limitations of the probe, particularly on the indirect channel.
Operator must be familiar with the duty cycle of the probe.
Expected amount of time SOP will use: 24 hours.
Procedure
Procedure
Identify an appropriate MAS rate, νr, for the sample under investigation.
Note that the Y rf power, νrf, will need to be set such that vrf = 2vr.
Safety information
Ensure that this is within the safe limits of the probe.
Note
A MAS speed which returns a rotor period which is an integer number of microseconds can aid in rotor synchronization. E.g., νr = 13333.3 Hz, 25000 Hz.
Optimize a CT-selective 90° pulse length and power for the X nucleus.
Note
Overly long pulse lengths can cause issues with rotor synchronization.
Optimize a Y nucleus 90° pulse width and power that vrf = 2vr.
Note
For example, an MAS rate of 25 kHz would require vrf = 50 kHz, i.e., a 5 µs pulse.
Load the dp_d-hmqc_indirect_rec.nmrfam pulse sequence and set the following parameters:
cnst31: MAS rate in Hz
p3: X channel CT-selective 90° pulse length
plw21: X channel CT-selective 90° pulse power
p1: Y channel 90° pulse length.
Note
This does not have to be the same as in Step 3.
plw3: Y channel 90° pulse power.
Note
This does not have to be the same as in Step 3.
plw23: Y channel 90° pulse power for SR412 recoupling, optimized in Step 3.
Note
This must be the same as in Step 3.
p16: Initial SR412 recoupling time, in µs. 700 µs is a reasonable starting point.
d1: 1.3 × T1.
Acquire an initial 1D spectrum. Repeat with increased ns until the signal-to-noise is high enough to allow for optimization.
Optimize the value of plw23 to maximize the signal intensity. This will likely be within 1 or 2 W of the previously optimized value.
Optimize the value of p16 to maximize the signal intensity.
Safety information
The total time used for SR412 recoupling is reported in p17 in µs. Ensure that this time is short enough to respect the probe duty cycle and maximum sustained high-power pulse limit.
Copy the parameters to a new dataset. Convert this dataset to a 2D experiment.
Set the following 2D parameters:
FnMODE: States-TPPI
F1 TD: 64, or as appropriate to allow for adequate F1 resolution.
F1 SWH: MAS rate in Hz.
Note
If this spectral window is too narrow, F1 SWH can be set to an integer multiple of the MAS rate in Hz.
Acquire the 2D spectrum.
Protocol references
Tricot, G.; Trébosc, J.; Pourpoint, F.; Gauvin, R.; Delevoye, L. The D-HMQC MAS-NMR Technique. Annual Reports on NMR Spectroscopy, 2014; pp 145-184. DOI: 10.1016/B978-0-12-800185-1.00004-8
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Quadrupole CT-Selective Pulse Width Optimization
CREATED BY
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Quadrupole Non-Selective Pulse Width Optimization
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Saturation Recovery for Quadrupolar Nuclei
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