Electron decoupling with cross polarization and dynamic nuclear polarization below 6 K

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP)

Background:

• Dynamic nuclear polarization (DNP) significantly boosts NMR sensitivity.
• Hyperfine couplings from polarizing agents can broaden nuclear resonances, limiting sensitivity.

Purpose of the Study:

• To implement cross-polarization with electron decoupling to mitigate hyperfine couplings.
• To demonstrate magic angle spinning (MAS) DNP at sub-Kelvin temperatures for enhanced polarization.

Main Methods:

• Cross-polarization experiments with electron decoupling.
• Magic angle spinning (MAS) DNP experiments conducted below 6 Kelvin.
• Measurement of proton polarization build-up times (T1DNP, 1H) for urea using trityl and AMUPol radicals.

Main Results:

• Electron decoupling effectively attenuates detrimental hyperfine couplings.
• Successful demonstration of MAS DNP below 6 K, achieving high nuclear spin polarization.
• Collected 13C correlation spectra using MAS DNP below 6 K for the first time.
• Measured short polarization build-up times (T1DNP, 1H) of 1.3 µs with AMUPol.

Conclusions:

• MAS DNP below 6 K with electron decoupling is a powerful strategy for increasing NMR signal-to-noise ratios.
• This approach allows for shorter polarization periods while maintaining high sensitivity.
• Enables unprecedented nuclear spin polarization in rotating solids.