Radical-induced hetero-nuclear mixing and low-field 13C relaxation in solid pyruvic acid

Hana Kouřilová; Michael Jurkutat; David Peat; Karel Kouřil; Alixander S. Khan; Anthony J. Horsewill; James F. MacDonald; John Owers-Bradley; Benno Meier

doi:10.1039/D2CP04535D

Radical-induced hetero-nuclear mixing and low-field ¹³C relaxation in solid pyruvic acid†

Hana Kouřilová,*^a Michael Jurkutat,

*^a David Peat,^b Karel Kouřil,

^a Alixander S. Khan,^b Anthony J. Horsewill,

^b James F. MacDonald,^b John Owers-Bradley^b and Benno Meier

*^ac

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* Corresponding authors

^a Institute of Biological Interfaces 4, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany
E-mail: hana.kourilova@kit.edu, michael.jurkutat@kit.edu, benno.meier@kit.edu

^b School of Physics and Astronomy, University of Nottingham, Nottingham, UK

^c Institute of Physical Chemistry, Karlsruhe Institute of Technology, Karlsruhe, Germany

Abstract

Radicals serve as a source of polarization in dynamic nuclear polarization, but may also act as polarization sink, in particular at low field. Additionally, if the couplings between the electron spins and different nuclear reservoirs are stronger than any of the reservoirs’ couplings to the lattice, radicals can mediate hetero-nuclear polarization transfer. Here, we report radical-enhanced ¹³C relaxation in pyruvic acid doped with trityl. Up to 40 K, we find a linear carbon T₁ field dependence between 5 mT and 2 T. We model the dependence quantitatively, and find that the presence of trityl accelerates direct hetero-nuclear polarization transfer at low fields, while at higher fields ¹³C relaxation is diffusion limited. Measurements of hetero-nuclear polarization transfer up to 600 mT confirm the predicted radical-mediated proton–carbon mixing.

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DOI: https://doi.org/10.1039/D2CP04535D
Article type: Paper
Submitted: 28 Sep 2022
Accepted: 09 Nov 2022
First published: 14 Nov 2022
This article is Open Access

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Phys. Chem. Chem. Phys., 2022,24, 28242-28249

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Radical-induced hetero-nuclear mixing and low-field ¹³C relaxation in solid pyruvic acid

H. Kouřilová, M. Jurkutat, D. Peat, K. Kouřil, A. S. Khan, A. J. Horsewill, J. F. MacDonald, J. Owers-Bradley and B. Meier, Phys. Chem. Chem. Phys., 2022, 24, 28242 DOI: 10.1039/D2CP04535D

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Physical Chemistry Chemical Physics

Radical-induced hetero-nuclear mixing and low-field ¹³C relaxation in solid pyruvic acid†

Abstract

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Radical-induced hetero-nuclear mixing and low-field ¹³C relaxation in solid pyruvic acid

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Physical Chemistry Chemical Physics