Dipolar-order-based broadband adiabatic inversion as cross- polarization alternative in solid state Wideline NMR

Area of Science:

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

Background:

• Solid-state NMR is crucial for atomic-level structural analysis across the periodic table.
• Low sensitivity and ultra-wideline spectra from unreceptive nuclei in powdered samples pose significant challenges.
• Enhancing signal detection is key to unlocking NMR's full potential for diverse materials.

Purpose of the Study:

• To develop and validate a novel NMR experiment for sensitivity enhancement of unreceptive nuclei in static samples.
• To investigate the transfer of dipolar order from protons to improve signal detection.
• To analyze the performance of the new technique for both spin-½ and quadrupolar nuclei.

Main Methods:

• Introduction of the Dipolar-Order-based BRoadband Adiabatic INversion Cross-Polarization (DOBRAIN-CP) experiment.
• Utilizing a Freeman-Kupče broadband inversion WURST pulse for cross-polarization.
• Analytical, numerical, and experimental studies on spin-dynamics for various nuclear spins (spin-½, integer, and half-integer quadrupolar).

Main Results:

• DOBRAIN-CP demonstrates broadband excitation and sensitivity enhancement compared to direct excitation methods.
• The technique successfully transfers dipolar order from surrounding protons.
• Sensitivity enhancement of DOBRAIN-CP was found to be comparable to, but not exceeding, the BRAIN-CP variant using Hartmann-Hahn matching.

Conclusions:

• DOBRAIN-CP offers a low-power method for enhancing NMR signals from challenging nuclei.
• The technique's effectiveness is dependent on long dipolar-order lifetimes (T1D) for sufficient build-up.
• Further optimization may be needed to surpass existing sensitivity enhancement methods like BRAIN-CP.