Tailoring of Polarizing Agents in the bTurea Series for Cross‐Effect Dynamic Nuclear Polarization in Aqueous Media |
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| Authors: | Claire Sauvée Dr. Gilles Casano Dr. Sébastien Abel Prof. Antal Rockenbauer Dr. Dimitry Akhmetzyanov Dr. Hakim Karoui Prof. Didier Siri Dr. Fabien Aussenac Dr. Werner Maas Dr. Ralph T. Weber Prof. Thomas Prisner Dr. Mélanie Rosay Prof. Paul Tordo Dr. Olivier Ouari |
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| Affiliation: | 1. Aix-Marseille Université, CNRS, ICR UMR 7273, Marseille cedex 20, France;2. Institute of Materials and Environmental Chemistry, Hungarian Academy of Sciences, Department of Physics, Budapest University of Technology and Economics and MTA-BME Condensed Matter Research Group, Budapest, Hungary;3. Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Frankfurt-am-Main, Germany;4. Bruker BioSpin S.A.S., Wissembourg, France;5. Bruker BioSpin Corporation, Billerica, Massachusetts, USA |
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| Abstract: | A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ? (1H) in cross‐effect dynamic nuclear polarization (CE DNP) NMR experiments at 9.4 and 14.1 T and 100 K in a DNP‐optimized glycerol/water matrix (“DNP juice”) have been studied. We observe that ? (1H) is strongly correlated with the substituents on the polarizing agents, and its trend is discussed in terms of different molecular parameters: solubility, average e–e distance, relative orientation of the nitroxide moieties, and electron spin relaxation times. We show that too short an e–e distance or too long a T1e can dramatically limit ? (1H). Our study also shows that the molecular structure of AMUPol is not optimal and its ? (1H) could be further improved through stronger interaction with the glassy matrix and a better orientation of the TEMPO moieties. A new AMUPol derivative introduced here provides a better ? (1H) than AMUPol itself (by a factor of ca. 1.2). |
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| Keywords: | dinitroxides molecular dynamics organic synthesis polarizing agents solvent effects |
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