Dynamic nuclear polarization with trityl radicals
Name
nihms-2093803.pdf
Description
Accepted version
Size
1.38 MB
Format
Adobe PDF
Checksum (MD5)
d4078ee3e940d8eabe7f1be4383b30cb
Author(s)
Shankar Palani, Ravi
Mardini, Michael
Quan, Yifan
Griffin, Robert G
Date Issued
April 2023
Journal
Journal of Magnetic Resonance
Publisher
Elsevier BV
Version
Author's final manuscript
Abstract
Despite the expanding applications of dynamic nuclear polarization (DNP) to problems in biological and materials science, there remain unresolved questions concerning DNP mechanisms. In this paper, we investigate the Zeeman DNP frequency profiles obtained with trityl radicals, OX063 and its partially deuterated analog OX071, in two commonly used glassing matrices based on glycerol and dimethyl sulfoxide (DMSO). When microwave irradiation is applied in the neighborhood of the narrow EPR transition, we observe a dispersive shape in the 1H Zeeman field and the effects are larger in DMSO than in glycerol. With the help of direct DNP observations on 13C and 2H nuclei, we investigate the origin of this dispersive field profile. In particular, we observe a weak nuclear Overhauser effect between 1H and 13C in the sample, which, when irradiating at the positive 1H solid effect (SE) condition, results in a negative enhancement of 13C spins. This observation is not consistent with thermal mixing (TM) being the mechanism responsible for the dispersive shape in the 1H DNP Zeeman frequency profile. Instead, we propose a new mechanism, resonant mixing, involving mixing of nuclear and electron spin states in a simple two-spin system without invoking electron–electron dipolar interactions.
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Creative Commons Attribution-NonCommercial-NoDerivatives
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DOI of Published Version
https://doi.org/10.1016/j.jmr.2023.107411
