t₁-Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy

Area of Science:

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

Background:

• Heteronuclear correlation (HETCOR) spectroscopy is crucial for determining proximities between nuclei in solid-state NMR.
• Dipolar heteronuclear multiple-quantum coherence (D-HMQC) enables 1H-detected 2D HETCOR spectra but suffers from t1-noise.
• t1-noise reduces sensitivity and complicates spectral interpretation in conventional D-HMQC experiments.

Purpose of the Study:

• To develop novel pulse sequences that minimize t1-noise in 1H-detected D-HMQC solid-state NMR.
• To improve spectral sensitivity and resolution compared to existing D-HMQC methods.
• To demonstrate the broad applicability of the new technique across different NMR-active nuclei and materials.

Main Methods:

• Development of t1-noise eliminated (TONE) D-HMQC pulse sequences.
• Utilizing 1H π-pulses to refocus 1H chemical shift anisotropy (CSA) and improve stability against MAS frequency fluctuations.
• Employing flip-back or spin-lock trim pulses to suppress uncorrelated signals.
• Monte-Carlo and numerical simulations to understand t1-noise origins.

Main Results:

• TONE D-HMQC sequences effectively minimize t1-noise, leading to higher sensitivity and resolution.
• Successful acquisition of 1H-detected 2D HETCOR spectra for 1H{35Cl}, 1H{13C}, 1H{17O}, and 1H{25Mg} nuclei.
• Demonstrated application to histidine·HCl·H2O, fmoc-alanine, magnesium hydroxide, and Mg-Al layered double hydroxides.
• Confirmed Mg and Al even mixing in layered double hydroxides using 1H-25Mg and 1H-27Al proximities.

Conclusions:

• TONE D-HMQC is a superior alternative to conventional D-HMQC for solid-state NMR HETCOR experiments.
• The technique offers enhanced spectral quality and broader applicability for structural and compositional analysis.
• This method advances the capability of solid-state NMR for probing nuclear proximities in diverse materials.