Tailoring of Polarizing Agents in the bTurea Series for Cross-Effect Dynamic Nuclear Polarization in Aqueous Media

Claire Sauvée (1) , Gilles Casano (1) , Sébastien Abel (1) , Antal Rockenbauer (2) , Dimitry Akhmetzyanov (3) , Hakim Karoui (1) , Didier Siri (1) , Fabien Aussenac (4) , Werner Maas (5) , Ralph T. Weber (5) , Thomas Prisner (3) , Mélanie Rosay (5) , Paul Tordo (1) , Olivier Ouari (1)

1 ICR - Institut de Chimie Radicalaire
2 Institute of Materials and Environmental Chemistry, Hungarian Academyof Sciences
3 Goethe-University Frankfurt am Main
4 Bruker Biospin SA
5 Bruker BioSpin [Billerica, MA]

A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ɛ (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 ɛ (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 ɛ (1H). Our study also shows that the molecular structure of AMUPol is not optimal and its ɛ (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 ɛ (1H) than AMUPol itself (by a factor of ca. 1.2).

Keywords: dinitroxides · molecular dynamics · organic synthesis · polarizing agents · solvent effects

Domains: Chemical Sciences

Claire Sauvée, Gilles Casano, Sébastien Abel, Antal Rockenbauer, Dimitry Akhmetzyanov, et al.. Tailoring of Polarizing Agents in the bTurea Series for Cross-Effect Dynamic Nuclear Polarization in Aqueous Media. Chemistry - A European Journal, 2016, 22 (16), pp.5598 - 5606. ⟨10.1002/chem.201504693⟩. ⟨hal-01400659⟩