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Electron-driven spin diffusion supports crossing the diffusion barrier in MAS DNP
Johannes J Wittmann1, Michael Eckardt, Wolfgang Harneit
1Institute of Physical and Theoretical Chemistry, Institute of Biophysical Chemistry, and Biomolecular Magnetic Resonance Center (BMRZ), Goethe University Frankfurt, Max-von-Laue-Str. 7-9, 60438 Frankfurt, Germany. corzilius@em.uni-frankfurt.de.
Physical Chemistry Chemical Physics : PCCP
|April 13, 2018
Summary
Dynamic nuclear polarization (DNP) enhances NMR sensitivity. A new mechanism, electron-driven spin diffusion (EDSD), explains polarization transfer near electron spins under magic-angle spinning conditions.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
- Quantum mechanics and spin physics
Background:
- Dynamic nuclear polarization (DNP) significantly boosts NMR sensitivity through microwave-driven spin transfer from electrons to nuclei.
- The large-scale spin dynamics in DNP, involving numerous nuclear spins per electron, lack a complete consensus.
- Efficient nuclear spin diffusion is traditionally considered crucial for hyperpolarization, moving polarization from strongly interacting nuclei to the observable bulk.
Purpose of the Study:
- To investigate the spin-dynamics in Dynamic Nuclear Polarization (DNP) under magic-angle spinning (MAS) conditions.
- To explore the role of the spin-diffusion barrier in nuclear hyperpolarization.
- To introduce and explain a novel mechanism for nuclear polarization transfer.
Main Methods:
- Experimental studies using endohedral fullerene N@C60 as a polarizing agent diluted in C60.
- Analysis of nuclear spin dynamics and polarization transfer mechanisms.
- Theoretical considerations under magic-angle spinning (MAS) conditions.
Main Results:
- Experimental evidence on N@C60 suggests a spin-diffusion barrier affecting hyperpolarization.
- A novel mechanism, electron-driven spin diffusion (EDSD), is proposed for nuclear polarization transfer.
- EDSD is particularly relevant for nuclei in close proximity to electron spins under MAS DNP.
Conclusions:
- The traditional view of spin diffusion as the sole mechanism for bulk hyperpolarization in DNP may be incomplete.
- Electron-driven spin diffusion (EDSD) offers an alternative pathway for polarization transfer, especially near electron spins.
- Understanding EDSD is crucial for optimizing DNP experiments and maximizing NMR sensitivity, particularly under MAS conditions.
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