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Tailoring of Polarizing Agents in the bTurea Series for Cross‐Effect Dynamic Nuclear Polarization in Aqueous Media
Author(s) -
Sauvée Claire,
Casano Gilles,
Abel Sébastien,
Rockenbauer Antal,
Akhmetzyanov Dimitry,
Karoui Hakim,
Siri Didier,
Aussenac Fabien,
Maas Werner,
Weber Ralph T.,
Prisner Thomas,
Rosay Mélanie,
Tordo Paul,
Ouari Olivier
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201504693
Subject(s) - nitroxide mediated radical polymerization , polarization (electrochemistry) , aqueous medium , aqueous solution , relaxation (psychology) , chemistry , molecule , electron , materials science , analytical chemistry (journal) , chemical physics , polymer , nuclear magnetic resonance , organic chemistry , physics , copolymer , quantum mechanics , psychology , social psychology , radical polymerization
A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ɛ ( 1 H) 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 ɛ ( 1 H) 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 T 1e can dramatically limit ɛ ( 1 H). Our study also shows that the molecular structure of AMUPol is not optimal and its ɛ ( 1 H) 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 ɛ ( 1 H) than AMUPol itself (by a factor of ca. 1.2).