3D relaxation-assisted separation of wideline solid-state NMR patterns for achieving site resolution

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Materials Science
• Analytical Chemistry

Background:

• Ultra-wideline (UW) solid-state NMR spectra under static conditions lack methods for resolving overlapping powder patterns from distinct nuclei.
• Existing techniques for spin-1/2 or half-integer quadrupolar nuclei under magic-angle spinning (MAS) are not directly applicable to UW spectra.
• Relaxation Assisted Separation (RAS) shows promise but is sensitive to noise and requires large differences in relaxation rates.

Purpose of the Study:

• To develop and validate advanced methods for resolving overlapping UW solid-state NMR powder patterns.
• To enhance the signal-to-noise ratio and stability of RAS routines for broader applicability.
• To improve the resolution of complex NMR spectra from organic and biological compounds.

Main Methods:

• Implementation of Principal Component Analysis (PCA) for denoising relaxation datasets.
• Stabilization of RAS routines using truncated singular value decomposition (TSVD) and elastic net (EN) regularization.
• Extension of RAS to 3D frequency-R₁-R₂ correlation spectra for enhanced pattern resolution.

Main Results:

• PCA denoising significantly increased signal-to-noise ratios in relaxation datasets.
• TSVD and EN regularization stabilized RAS, allowing resolution of overlapped patterns with smaller differences in relaxation rates.
• 3D RAS demonstrated superior resolution compared to regularized 2D RAS for synthetic and experimental datasets (³⁵Cl, ²H, ¹⁴N NMR).

Conclusions:

• The developed methods, including PCA denoising and regularized RAS (2D and 3D), effectively resolve overlapping UW solid-state NMR powder patterns.
• 3D RAS offers improved spectral resolution, expanding the applicability of relaxation-based separation techniques.
• These advancements hold significant potential for analyzing complex materials and biological systems under both static and MAS conditions.