Direct observation of hyperpolarization breaking through the spin diffusion barrier

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Dynamic nuclear polarization (DNP) enhances nuclear magnetic resonance (NMR) sensitivity but is limited by the spin diffusion barrier.
• The spin diffusion barrier impedes efficient polarization transfer from paramagnetic centers to bulk nuclei.
• Lack of methods to study nuclear polarization flow near paramagnetic centers has hindered quantitative assessment.

Purpose of the Study:

• To introduce a general experimental method for studying nuclear polarization flow.
• To quantitatively assess the spin diffusion barrier in dynamic nuclear polarization.
• To investigate the temperature dependence of polarization flow.

Main Methods:

• Development and implementation of microwave gating experiments.
• Experiments conducted at temperatures between 1.2 and 4.2 K in static mode.
• Experiments performed at 100 K under magic angle spinning (MAS) conditions.

Main Results:

• Successfully demonstrated a general method for studying nuclear polarization flow.
• Directly observed the dependence of polarization flow on temperature.
• Validated the approach under conditions relevant to dissolution DNP and MAS-DNP.

Conclusions:

• The developed microwave gating technique effectively probes nuclear polarization flow.
• Temperature significantly influences polarization flow, impacting DNP efficiency.
• This method provides a quantitative tool to overcome the spin diffusion barrier in DNP.