Feb 17, 2025

Public workspaceCP-Based Saturation Recovery

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
NMRFAM Facility
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Protocol Citation: Alexander L. Paterson 2025. CP-Based Saturation Recovery. protocols.io https://protocols.io/view/cp-based-saturation-recovery-dfpj3mkn
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: 101835
Keywords: Measuring 1H T1 via Cross-Polarization Enhanced Saturation Recovery
Funders Acknowledgements:
National Science Foundation
Grant ID: 1946970
Abstract
Purpose 
To measure the longitudinal relaxation time, T1, of 1H present in the sample, while observing non-1H spin-1/2 nuclei. 

Scope 
This SOP should be completed after an initial 1D cross-polarization (CP) experiment has been completed, but before further experiments are performed. Upon completion of this SOP, the user will be able to set recycle delays appropriate for the purpose of later experiments, either to maximize signal per unit time, or to ensure quantitative intensities. 
Guidelines
This SOP does not require a well-optimized CP condition. Once an initial CP signal is observed, this SOP can be completed prior to further CP optimization, especially if a very fine CP condition optimization is to be completed. 

If acquisition of a 1D spectrum requires substantial signal averaging, this SOP may not be appropriate. 

This SOP is written for acquisition using a Bruker console and TopSpin 3.6.2. It may be adapted to other TopSpin versions where appropriate. 

This SOP is intended for a beginning user who has been trained on basic spectrometer safety and principles. 
Materials
Definitions:
  1. T1: Longitudinal relaxation time
  2. l20: Number of saturation pulse loops
  3. d20: Presaturation loop delay
  4. CP: Cross polarization

Appendix:

If the presaturation train is not completely effective, the recovery curve might initially decrease, and then follow the expected exponential curve. This is common behaviour and can be dealt with by discarding the initial points of the curve.

The values of the variable delay list T1_standard_array range from 0.25 to 128 s, increasing by a factor of two for each increment. This should provide adequate spacing to accurately determine T1 values between 1 s and 64 s. If necessary, adjust the list for shorter or longer values of T1.


Figure 1.Example of a successful 7Li saturation recovery experiment performed on a lithium silicate glass. The T1 of this environment was found to be 3.4 s.

Safety warnings
CP-based experiments are assumed to use high-power decoupling. Therefore, d1 should be about 20 times as long as the acquisition period aq, typically on the order of 1 s. A long acquisition (50 ms) protection limit is set. This protection limit should not be disabled while high-power decoupling is in use. 
Before start
User is responsible for knowing the duty cycle of the probe and instrument being used.

User is responsible for knowing the maximum power limits of the probe.

Expected time to completion: 1 hour or less
Procedure
Procedure
Prepare the experimental environment.
Create a new experiment window.
Load the cphsatrect1 pulse program.
Set the 1H excitation pulse length, p3, and pulse power, plw12, to previously optimized 1H powers.
Set the 1H contact pulse power, spw0, and the X contact pulse power, plw1, to previously optimized values.
Set the CP contact time, p15, appropriate to the sample. If the optimum value is not known, set a value of 1 ms.
Set the CP ramp shape, spnam0, to ramp70100.100.
Set the 1H decoupling program, CPDPRG2, pulse length, PCPD2, and pulse power, plw12, to previously optimized values
aq: Set to 50 ms or less. This is required for the safety of the probe.
Set the recycle delay, d1, to a relatively long value, e.g., 10 s.
Set the number of saturation pulse loops, l20, to 0.
Set the variable delay list, vdlist, to T1_standard_array.
Acquire an initial experiment. The number of scans should be as small as practicable to allow for adequate signal, ideally as low as 2.
Ensure that all expected resonances are visible. If some are not visible, either reduce the pulse length or increase d1, as appropriate.
Set the number of saturation pulse loops, l20, to an initial value of 10. Set the presaturation loop delay, d20, to an initial value of 100 µs.
Acquire a spectrum. There should be no signal present.
If signal is still present, increase l20, up to a maximum of 100, and reacquire the spectrum.
If increasing l20 does not result in a null signal, reduce the number of loops and retry with longer presaturation loop delays d20.
If increasing d20 does not result in a null signal, retry with shorter presaturation loop delays d20.
Convert the experiment to a 2D experiment window.
Move to the acqupars window via the command eda.
Click on the button titled “Change acquisition dimension of current data set” and change the dimension to 2D.
Set the following parameters:
  1. F1 TD: 12
  2. FnMODE: QF
  3. F1 SI: 16
  4. d1: A minimal value that respects the probe duty cycle, see Appendix.
Critical
Acquire the 2D experiment via the command zg.
Process the 2D experiment.
Transform the data using the command xf2.
Correct the F2 phasing of the slice with the longest delay period.

Note
Do not transform or phase the F1 axis.

To process the data, launch the TopSpin utility t1guide and follow the workflow in the utility.
Extract the slice with the longest variable delay, i.e., the most recently acquired slice.
Integrate each resonance. Save using the option “Export Regions to Relaxation Module and .ret”.

Note
  1. If resonances are not resolved, attempt to select the regions of least overlap.
  2. If resonances cannot be reasonably separated, integrating over all of the peaks will allow for the determination of the longest T1 component.

Enter the relaxation window and set the Fitting Function Function Type to uxnmrt1.
Calculate fit for all peaks. If successful, the fitting window should resemble the example in the appendix.
Record the T1 for each site. Use the longest value of T1 for determining the recycle delay of future experiments.
Protocol references
Bruker Solid State NMR User Manual Z4D10641B, Section 16.2.4

Y. Nishiyama and N. T. Duong, “Practical guides for 1H detected solid-state NMR under fast MAS for small molecules,” Journal of Magnetic Resonance Open, vol. 10-11, p. 100062, Jun. 2022. https://doi.org/10.1016/j.jmro.2022.100062
Protocol
CPMAS
NAME

CPMAS

CREATED BY
NMRFAM Facility