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Tuning nuclear depolarization under MAS by electron T
Alicia Lund1, Asif Equbal, Songi Han
1Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106-9510, USA. songi@chem.ucsb.edu.
Physical Chemistry Chemical Physics : PCCP
|September 14, 2018
Summary
Electron spin relaxation rates (T1e) significantly impact Nuclear Magnetic Resonance (NMR) signal depolarization during Magic Angle Spinning (MAS) Dynamic Nuclear Polarization (DNP). Experiments confirm T1e is the primary factor modulating this depolarization effect.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
- Dynamic Nuclear Polarization (DNP)
Background:
- The Cross-Effect (CE) mechanism in DNP under Magic Angle Spinning (MAS) can lead to Nuclear Magnetic Resonance (NMR) signal depolarization.
- Understanding the factors influencing this depolarization is crucial for optimizing DNP experiments.
Purpose of the Study:
- To experimentally investigate the role of electron spin relaxation time (T1e) in nuclear depolarization under MAS.
- To determine if T1e is the primary modulator of depolarization, independent of other spin parameters.
Main Methods:
- Systematic variation of electron spin concentration using mono-, bi-, and tri-radicals.
- Doping a tri-radical system with GdCl3 to selectively tune T1e rates.
- Quantum mechanics-based numerical simulations to corroborate experimental findings.
Main Results:
- Depolarization effects correlated with T1e rates across different radical systems.
- Tuning T1e rates by doping confirmed their direct impact on the depolarization factor.
- Simulations highlighted the importance of T1e and spin-pair orientations in depolarization.
Conclusions:
- Electron spin relaxation time (T1e) is the major factor modulating nuclear depolarization in CE-DNP/MAS.
- While spin-pair orientation influences depolarization, T1e remains the dominant parameter in the studied nitroxide systems.
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