Feb 17, 2025
Version 2
REDOR 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. REDOR. protocols.io https://protocols.io/view/redor-dzyf77tnVersion 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: 120551
Keywords: Materials REDOR
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To probe internuclear distances between either two spin-1/2 nuclei, or a spin-1/2 nucleus and a quadrupolar nucleus with a small quadrupolar coupling constant.
Scope
The Resonance Echo DOuble Resonance (REDOR) experiment is an effective means of probing through-space internuclear distances between nuclei. It is limited to systems where both nuclei are spin-1/2, or where one nucleus is spin-1/2 and the other is a half-integer-spin quadrupole where you can obtain good spectra via magic angle spinning (e.g., 11B, 23Na, 27Al). For systems where the quadrupole is integer spin (e.g., 14N), or has a large quadrupole coupling constant (e.g., 139La), or where both nuclei are quadrupoles, the Resonance Echo Saturation Pulse DOuble Resonance (RESPDOR) experiment is preferred.
Guidelines
When considering target X{Y} pairs of nuclei, the preference should be that the Y nucleus has the higher fractional abundance in the sample to allow for more dynamic range in the REDOR curve. If both abundances are similar, the direct nucleus should be the one with more favourable spectral properties, particularly sensitivity per unit time and peak resolution. Note that in cases where the Y nucleus is sparsely abundant, REDOR dephasing will be challenging to observe.
In protonated systems, heteronuclear decoupling should be applied during both evolution and acquisition periods. Care must be taken to ensure that the total decoupling time and power does not exceed probe limits.
When a quadrupole is the indirect nucleus, it is important to minimize the number of pulses on the indirect channel. The appropriate flag must be set when the quadrupole is the indirect nucleus.
The pulse program REDOR.HXY.i.nmrfam is written for pseudo-2D acquisition, to allow for better compatibility with queuing experiments and multizg. It has flags to adjust between 1D acquisition and pseudo-2D acquisition, to avoid the need to change between different pulse programs during setup.
Materials
Definitions:
- REDOR: Resonance Echo DOuble Resonance
Appendix:
If the zgoptns flags -Dsetup_norec or -Dsetup_rec are not set, the experiment will expect to be run in pseudo-2D mode and will throw the error “td1 symbol not found” if loaded into a 1D experiment. This is normal and can be removed by either setting the above flags, or by changing to a 2D experiment.
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 REDOR evolution 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 REDOR evolution period.
Expected amount of time SOP will use: 1 to 4 days, depending on sample sensitivity.
Procedure
Procedure
Load the REDOR.HXY.i.nmrfam pulse program as a 1D experiment. Set the following flags and parameters:
zgoptns: -Dsetup_norec.
NUC1: Direct/observed nucleus.
cnst31: MAS rate in Hz.
d1: Set to 1.3 * previously measured T1.
ns: 64*n for full phase cycle; 4*n for optimization if sensitivity permits.
l5: Set to 1.
l10: Number of REDOR pulse pairs per recoupling block.
Note
Set to 4 for xy-8 phase cycling; set to 1 for the shortest possible recoupling block.
p1: Previously optimized excitation X pulse, using power level plw1.
p2: Previously optimized 180° X pulse, using power level plw11.
Note
If the X nucleus is a quadrupole, this should be a central-transition-selective 180° pulse.
plw1: Previously optimized X pulse power for excitation pulse p1.
plw11: Previously optimized X pulse power for 180° X pulse p2.
If the indirect nucleus is quadrupolar, add the -DI_quad flag to zgoptns and set the following additional parameters:
CPDPRG1: redor.nmrfam
pcpd1: Set to a previously optimized direct nucleus 180° pulse length, using power level plw10.
plw10: Set to a previously optimized direct nucleus 180° pulse power.
NUC3: Indirect quadrupolar nucleus.
o3. Ensure that the indirect nucleus frequency is set such that the resonances of interest will be irradiated.
If heteronuclear decoupling is desired, add -Ddec to zgoptns. Set the following additional parameters:
NUC2: Heteronuclear decoupling nucleus, typically 1H.
Set cpdprg2 to an appropriate decoupling sequence, e.g., spinal64.
Set pcpd2 and plw12 to previously optimized decoupling pulse length and power.
Safety information
Ensure that the total decoupling time does not exceed the high-power decoupling limit of the probe, typically 50 ms. Decoupling is active during both d10 periods, both d18 periods, d16, d19, and aq.
If presaturation of the direct nucleus is desired, add -Dpresat to zgoptns. Set the following additional parameters:
Set d20 to a previously optimized presaturation comb delay.
Set l20 to a previously optimized presaturation comb loop count.
Acquire an initial 1D spectrum. Ensure that all expected peaks are present. Save this spectrum, either with wrp or by moving to a new experiment.
Change zgoptns from -Dsetup_norec to -Dsetup_rec. This enables the REDOR recoupling.
If the indirect nucleus is spin-1/2 and the -DI_quad flag is not active, set the following additional parameters:
NUC3: Indirect spin-1/2 nucleus.
Set cpdprg1 to redor.nmrfam.
Set p3 to a previously optimized indirect nucleus 180° pulse length, using power level plw10.
Set plw10 to a previously optimized indirect nucleus 180° pulse power.
o3. Ensure that the indirect nucleus frequency is set such that the resonances of interest will be irradiated.
If the indirect nucleus is quadrupolar and the -DI_quad flag is active, set the following additional parameter:
Set plw11 to the power for a previously optimized CT-selective 180° pulse; this is the power level for p3 for a quadrupole.
The REDOR recoupling is now active. Acquire a spectrum and compare with the spectrum acquired without the recoupling (Step 5). Some dephasing should be observed in the peaks from environments
closest to NUC3 atoms.
If no dephasing is observed, the recoupling block counter l5 can be increased to a larger value to increase the dephasing. If l5 is increased, an additional spectrum with the flag -Dsetup_norec must also be acquired to ensure an accurate comparison is made.
It is important to ensure that some dephasing can be observed before proceeding with the protocol. If dephasing is not observed with an increased l5, double-check all parameters, but particularly 180° pulse lengths, cnst31, and o3.
Once dephasing has been confirmed, create a new experiment and set it to 2D acquisition mode. Set the following parameters:
The 2D acquisition mode FnMODE must be set to QF.
Set l5 to 1.
Set 1 td appropriately to sample a sufficiently long recoupling time.
Note
The recoupling time can be calculated as d10 × (1 td) when l5 is set to 1.
Note
This is inherently a sample-dependent quantity.
Remove the -Dsetup_rec and -Dsetup_norec flags from zgoptns.
Adjust ns to best use available experiment time.
Note
Remember that the data at longer recoupling times will have lower S/N ratios. The number of scans should be set to ensure sufficient S/N at the later points.
Ensure l5 is set to start sampling at the desired portion of the recoupling curve.
Note
To sample at the beginning of the recoupling curve, set l5 to 1.
Acquire the pseudo-2D experiment. The data will be stored in alternating rows, first with no recoupling, then with recoupling.
Process the REDOR curve.
Protocol references
Gullion, T.; Schaefer, J. Rotational-echo double-resonance NMR. J. Magn. Reson. (1969) 1989, 81 (1), 196-200. DOI: 10.1016/0022-2364(89)90280-1.
Chan, J. C.; Eckert, H. Dipolar coupling information in multispin systems: application of a compensated REDOR NMR approach to inorganic phosphates. Rotational echo double resonance. J. Magn. Reson. 2000,
147 (2), 170-178. DOI: 10.1006/jmre.2000.2191
Protocol
NAME
Quadrupole CT-Selective Pulse Width Optimization
CREATED BY
Nmrfam Facility
Protocol
NAME
Saturation Recovery
CREATED BY
Nmrfam Facility