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Pseudo rotary resonance relaxation dispersion effects in isotropic samples
Evgeny Nimerovsky1, Jonas Mehrens1, Loren B Andreas1
1Department of NMR-based Structural Biology, Max Planck Institute for Multidisciplinary Sciences, Am Faßberg 11, Göttingen, Germany.
Magnetic Resonance (Gottingen, Germany)
|July 14, 2025
Summary
Researchers observed unexpected signal decay in rotating liquids under magic-angle spinning (MAS) conditions. This pseudo rotary resonance relaxation dispersion (pseudo-RRD) effect is linked to RF field inhomogeneity and impacts MAS experiments.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
- Materials Science
- Physical Chemistry
Background:
- Magic-angle spinning (MAS) is crucial for studying anisotropic solid samples, inducing enhanced transverse relaxation near rotary resonance.
- Anisotropic interactions in solids are typically averaged out at much faster timescales than the spinning frequency in rotating liquids.
Purpose of the Study:
- To investigate the surprising observation of transverse signal decay in rotating liquids under rotary resonance conditions.
- To characterize the phenomenon of pseudo rotary resonance relaxation dispersion (pseudo-RRD) in liquid samples during MAS.
- To understand the influence of instrumental imperfections on MAS experiments.
Main Methods:
- Measurements of Carbon-13 (13C) and Proton-1 (1H) signal intensities under spin lock for spinning liquid samples.
- Utilizing samples including polybutadiene rubber, polyethylene glycol solution, and deuterated water (D2O).
- Performing simulations to qualitatively describe the pseudo-RRD phenomenon.
Main Results:
- A significant reduction in spin-lock signal intensities was observed when the spin-lock frequency matched 1 or 2 times the MAS rate.
- Oscillations in the signal were detected, indicating a coherent origin for the observed effect (pseudo-RRD).
- Simulations qualitatively explained pseudo-RRD by time dependence due to sample rotation and inhomogeneous radio frequency (RF) fields.
Conclusions:
- Transverse signal decay near rotary resonance conditions, termed pseudo-RRD, occurs in rotating liquids, contrary to expectations.
- This effect is attributed to time dependence from sample rotation and instrumental RF field inhomogeneity.
- Understanding pseudo-RRD is vital for MAS experiments utilizing rotary resonance and necessitates improved RF field homogeneity in MAS coils.
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