title: Tailoring of Polarizing Agents in the bTurea Series for Cross-Effect Dynamic Nuclear Polarization in Aqueous Media.
abstract: 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 T1e 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).
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Sauvée
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Casano
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Abel
authors.affiliation: 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, Budafoki ut 8, 1111, Budapest, Hungary.
authors.forename: Antal
authors.initials: A
authors.lastname: Rockenbauer
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue Str. 7, 60438, Frankfurt-am-Main, Germany.
authors.forename: Dimitry
authors.initials: D
authors.lastname: Akhmetzyanov
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
authors.forename: Hakim
authors.initials: H
authors.lastname: Karoui
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France.
authors.forename: Didier
authors.initials: D
authors.lastname: Siri
authors.affiliation: Bruker BioSpin S.A.S., 34 rue de l'industrie, 67166, Wissembourg, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Aussenac
authors.affiliation: Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA.
authors.forename: Werner
authors.initials: W
authors.lastname: Maas
authors.affiliation: Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA.
authors.forename: Ralph T
authors.initials: RT
authors.lastname: Weber
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue Str. 7, 60438, Frankfurt-am-Main, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Prisner
authors.affiliation: Bruker BioSpin Corporation, 15 Fortune Drive, Billerica, Massachusetts, 01821, USA.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Rosay
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France. paul.tordo@univ-amu.fr.
authors.forename: Paul
authors.identifier: http://orcid.org/0000-0002-4968-8841
authors.initials: P
authors.lastname: Tordo
authors.affiliation: Aix-Marseille Université, CNRS, ICR UMR 7273, 13397, Marseille cedex 20, France. olivier.ouari@univ-amu.fr.
authors.forename: Olivier
authors.initials: O
authors.lastname: Ouari
keywords: dinitroxides; molecular dynamics; organic synthesis; polarizing agents; solvent effects