Correlating fast and slow chemical shift spinning sideband patterns in solid-state NMR

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Chemical Physics

Background:

• Accurate measurement of chemical shift anisotropy (CSA) tensors is crucial for understanding molecular structure and dynamics in solid materials.
• Fast magic-angle spinning (MAS) is a key technique for high-resolution solid-state NMR, but measuring small CSA values can be challenging.

Purpose of the Study:

• To develop and demonstrate a novel 2D NMR experiment for precise measurement of small chemical shift anisotropy (CSA) tensors.
• To enable CSA determination under fast magic-angle spinning (MAS) conditions with enhanced accuracy and efficiency.

Main Methods:

• A new 2D NMR experiment utilizing rotor-synchronized pi-pulses to scale spinning sideband intensities.
• The experiment employs a fixed-length pulse sequence with efficient sampling, avoiding quadrature detection and storage periods.
• Demonstrated using 31P NMR of sodium phosphate and 13C NMR of fumaric acid monoethyl ester.

Main Results:

• The experiment successfully measures small CSA tensors by scaling sideband intensities in the directly observed dimension.
• The scaling factor (N) can be adjusted by modifying the number and timing of pi-pulses, allowing for flexible experimental design.
• Demonstrated a scaling factor of N=10.2 for specific phosphorus-31 and carbon-13 NMR measurements.

Conclusions:

• The presented NMR experiment offers a robust method for quantifying small chemical shift anisotropy tensors in solid-state samples.
• The technique simplifies CSA measurement by effectively scaling sideband intensities, improving spectral analysis.
• This approach enhances the capabilities of solid-state NMR for detailed structural and dynamic investigations.