NMR relaxation in multipolar AMX systems under spin-locking conditions

Area of Science:

• Magnetic Resonance Spectroscopy
• Biophysical Chemistry
• Nuclear Magnetic Resonance (NMR)

Background:

• Multipolar AMX systems are relevant for studying proteins with fractional deuterium (2H) enrichment.
• Understanding relaxation processes is crucial for interpreting NMR data in complex biological systems.

Purpose of the Study:

• To calculate the relaxation network for multipolar AMX systems under a spin-locking radiofrequency (RF) field.
• To investigate the impact of RF fields on relaxation pathways and spectral densities.

Main Methods:

• Development and application of a relaxation network model for multipolar AMX systems.
• Inclusion of all auto- and cross-correlation terms for dipolar, quadrupolar, and chemical shift anisotropy (CSA) interactions.
• Analysis of spectral densities at zero frequency under spin-locking conditions.

Main Results:

• Identified non-vanishing spectral densities at zero frequency for interactions involving locked nuclei, even without fast molecular motion.
• Demonstrated that the spin-locking field effectively blocks specific cross-correlation interactions.
• Showcased a significant simplification of the relaxation network due to the applied RF field.

Conclusions:

• The spin-locking RF field simplifies the relaxation network in multipolar AMX systems.
• The presence of non-vanishing zero-frequency spectral densities has implications for NMR studies of proteins.
• This approach offers a more tractable model for analyzing relaxation in deuterium-enriched proteins.