Feb 17, 2025
RESPDOR
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. RESPDOR. protocols.io https://protocols.io/view/respdor-dfpt3mnn
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: 101843
Keywords: Materials CP-PM-RESPDOR
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose
To probe internuclear distances between a spin-1/2 and spin >1/2 spin pair in a highly protonated system.
Scope
The Resonance Echo Saturation Pulse DOuble Resonance experiment with a phase-modulated saturation pulse (PM-RESPDOR) is an effective means of probing through-space internuclear distances between a spin-1/2 nucleus and a quadrupolar nucleus. By using a phase-modulated saturation pulse, it effectively recouples the heteronuclear dipolar interaction over a wide frequency range, and can be used for both integer-spin and half-integer-spin nuclei.
Guidelines
RESPDOR can be used either with direct polarization or, if protons are present, cross polarization. If protons are present, proton decoupling should be applied during both evolution and acquisition. In either case, when considering an X{Y} pair, the preference should be that the Y nucleus has the higher fractional abundance in the sample.
In protonated systems, it can be convenient to calibrate the saturation pulse using a 1H{X} experiment. In this case, SR412 recoupling is preferred over REDOR recoupling.
The phase modulated pulse can result in significant amounts of reflected power. Care should be taken to avoid excessive reflections.
This protocol is written for the context of highly protonated systems. The procedure for non-protonated systems is broadly similar.
The pulse program PM-RESPDOR.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.
Materials
Definitions:
- RESPDOR: Resonance Echo Saturation Pulse DOuble Resonance
- PM: Phase modulated
- CP: Cross polarization
- rf: radiofrequency
Appendix:
If the zgoptns flags -Dsetup_nosat or -Dsetup_sat 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.
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.
Expected amount of time SOP will use: 1 to 3 days, depending on sensitivity.
Procedure
Procedure
Load the PM-RESPDOR.HXY.i.nmrfam pulse program. Set the following flags and parameters:
zgoptns: -Dsetup_nosat, -DSR421
cnst31: MAS rate in Hz.
NUC1: 1H
d1: Set to 1.3 * previously measured T1.
ns: 64*n for full phase cycle; 4*n for optimization if sensitivity permits.
CPDPRG1: SR421.nmrfam
p1: Previously optimized 90° 1H pulse length, using power level plw1.
p2: Previously optimized 180° 1H pulse length, using power level plw1.
plw1: Previously optimized 1H pulse power for p1 and p2.
pcpd1: Set to a previously optimized 180° 1H at a rf power of 2×cnst31
Note
This corresponds to a 180° pulse length of 1/(0.25×cnst31) if plw10 is set appropriately.
plw10: Set to a previously optimized power level to produce a rf power of 2×cnst31
l10: Set to 3 for full SR412 supercycling.
l5: Set to 1.
l22: Set to 1
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_nosat to -Dsetup_sat. Set the following additional parameters:
NUC3: Target nucleus for saturation.
CPDPRG3: modLAREDORphase.nmrfam
plw22: 50 W.
The saturation pulse is now active. Acquire a spectrum and compare with the spectrum acquired without the saturation pulse. Some dephasing should be observed in the peaks from environments closest to NUC3 atoms.
Note
If there are no protons directly bound to the nucleus of interest, the recoupling block counter l5 can be increased to a larger value to emphasize the dephasing.
Optimize plw22 for maximum dephasing. The dephasing should at first increase with applied power, then reach a plateau.
Safety information
Pay careful attention to probe power limits: the rapidly changing phase of the saturation pulse can lead to power transients.
If necessary, adjust the saturation pulse length by increasing l22 by steps of 1.
Note
l22 does not generally need to be greater than 2. Use caution when increasing beyond that length.
Create a new experiment and load the pulse sequence cp.PM-RESPDOR.HXY.i.nmrfam. Load the following parameters:
Adjust the channel routing using edasp so that NUC1 is the detect nucleus, NUC2 is 1H, and NUC3 is the indirect nucleus.
zgoptns: remove the -DSR421 flag
Set cpdprg1 to redor.nmrfam.
Set p2 and plw1 to a detect nucleus 180° pulse.
Set pcpd1 and plw10 to a detect nucleus 180° pulse. This can be the same parameters as above.
Set l10 to 4.
Note
This sets the the number of REDOR pairs per recoupling increment; 4 implements xy-8 cycling. A lower value of l10 can be used if the dipolar coupling is very large.
Set p15 and plw15 to previously optimized CP contact time and X power.
Set cpdprg2 to an appropriate decoupling sequence, e.g., spinal64.
Set pcpd2 and plw12 as appropriate for the optimized decoupling sequence.
Set p1 and plw2 to a proton 90° pulse.
Set spnam0 and spw0 to a previously optimized CP shape and proton power.
Acquire an initial pair of spectra, one with and one without the saturation pulse, by using the flags -Dsetup_nosat and -Dsetup_sat.
Note
If necessary, the recoupling block counter l5 can be increased to a larger value to emphasize the dephasing.
Create a new experiment and set it to 2D acquisition mode.
The 2D acquisition mode FnMODE must be set to QF.
Remove the -Dsetup_nosat and/or -Dsetup_sat flags.
Set 1 td appropriately to sample a sufficiently long recoupling time.
Note
This is inherently a sample-dependent quantity.
Note
The recoupling time can be calculated as d10 × (1 td) when l5 is set to 1.
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 saturation, then with saturation.
Process the RESPDOR curve.
Protocol references
Dorn, R. W.; Wall, B. J.; Ference, S. B.; Norris, S. R.; Lubach, J. W.; Rossini, A. J.; VanVeller, B. Attached Nitrogen Test by 13C-14N Solid-State NMR Spectroscopy for the Structure Determination of Heterocyclic Isomers. Org Lett 2022, 24 (31), 5635-5640. DOI: 10.1021/acs.orglett.2c01576
Nimerovsky, E.; Gupta, R.; Yehl, J.; Li, M.; Polenova, T.; Goldbourt, A. Phase-modulated LA-REDOR: a robust, accurate and efficient solid-state NMR technique for distance measurements between a spin-1/2 and a quadrupole spin. J Magn Reson 2014, 244, 107-113. DOI: 10.1016/j.jmr.2014.03.003
Protocol
NAME
CPMAS
CREATED BY
NMRFAM Facility