CSA-enabled spin diffusion leads to MAS rate-dependent T1's at high field.

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Biophysical chemistry
• Macromolecular structure determination

Background:

• Nuclear Magnetic Resonance (NMR) T(1) relaxation times are crucial for understanding molecular dynamics and structure.
• Magic Angle Spinning (MAS) is a technique used to improve spectral resolution in solid-state NMR.
• Spin diffusion is a process by which nuclear spin polarization is transferred between spins.

Purpose of the Study:

• To investigate the spin rate dependence of (15)N and (13)C NMR T(1) times in solid peptides.
• To elucidate the underlying mechanism responsible for the observed spin rate dependence.
• To explore the potential application of this phenomenon in macromolecular structural analysis.

Main Methods:

• Solid-state NMR experiments were performed on isotopically labeled peptides.
• Magic Angle Spinning (MAS) conditions were varied to study spin rate dependence.
• Nuclear spin relaxation (T(1)) measurements were conducted for (15)N and (13)C nuclei.
• Analysis focused on the role of chemical shift anisotropy (CSA) and spin diffusion.

Main Results:

• A surprisingly strong dependence of (15)N and (13)C NMR T(1) times on the magic angle spinning rate was observed.
• This spin rate dependence was attributed to chemical shift anisotropy (CSA)-mediated spin diffusion.
• The effect was confirmed using various isotopomers, validating the proposed mechanism.

Conclusions:

• The spin rate dependence of NMR T(1) times in solid peptides is a significant phenomenon driven by CSA-mediated spin diffusion.
• This effect provides a novel and powerful tool for measuring long-range distance constraints in complex macromolecular systems.
• The findings open new avenues for structural studies of peptides and proteins using solid-state NMR.