A spin-thermodynamic approach to characterize spin dynamics in TEMPO-based samples for dissolution DNP at 7 T field

[Display omitted] •Spin-dynamics of DNP in TEMPO-based samples is investigated at 7 T field.•At all radical concentrations the spin dynamics can be described by a spin-temperature based model.•Differences and similarities of spin dynamics at 3.4 T are discussed.•The spin-temperature model can be use...

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Veröffentlicht in:Journal of magnetic resonance (1997) 2019-06, Vol.303, p.91-104
Hauptverfasser: Jähnig, Fabian, Himmler, Aaron, Kwiatkowski, Grzegorz, Däpp, Alexander, Hunkeler, Andreas, Kozerke, Sebastian, Ernst, Matthias
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Sprache:eng
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Zusammenfassung:[Display omitted] •Spin-dynamics of DNP in TEMPO-based samples is investigated at 7 T field.•At all radical concentrations the spin dynamics can be described by a spin-temperature based model.•Differences and similarities of spin dynamics at 3.4 T are discussed.•The spin-temperature model can be used for prediction of enhancement. The spin dynamics of dissolution DNP samples consisting of 4.5 M [13C]urea in a mixture of (1/1)Vol glycerol/water using 4-Oxo-TEMPO as a radical was investigated. We analyzed the DNP dynamics as function of radical concentration at 7 T and 3.4 T static magnetic field as well as function of deuteration of the solvent matrix at the high field. The spin dynamics could be reproduced in all cases, at least qualitatively, by a thermodynamic model based on spin temperatures of the nuclear Zeeman baths and an electron non-Zeeman (dipolar) bath. We find, however, that at high field (7 T) and low radical concentrations (25 mM) the nuclear spins do not reach the same spin temperature indicating a weak coupling of the two baths. At higher radical concentrations, as well as for all radical concentrations at low field (3.4 T), the two nuclear Zeeman baths reach the same spin temperature within experimental errors. Additionally, the spin system was prepared with different initial conditions. For these cases, the thermodynamic model was able to predict the time evolution of the system well. While the DNP profiles do not give clear indications to a specific polarization transfer mechanism, at high field (7 T) increased coupling is seen. The EPR line shapes cannot clarify this in absence of ELDOR type experiments, nevertheless DNP profiles and dynamics under frequency-modulated microwave irradiation illustrate the expected increase in coupling between electrons with increasing radical concentration.
ISSN:1090-7807
1096-0856
DOI:10.1016/j.jmr.2019.04.012