Nuclear magnetic resonance studies of DNP-ready trehalose obtained by solid state mechanochemical amorphization.
(1)H nuclear spin-lattice relaxation and Dynamic Nuclear Polarization (DNP) have been studied in amorphous samples of trehalose sugar doped with TEMPO radicals by means of mechanical milling, in the 1.6-4.2 K temperature range. The radical concentration was varied between 0.34 and 0.81%. The highest polarization of 15% at 1.6 K, observed in the sample with concentration 0.50%, is of the same order of magnitude of that reported in standard frozen solutions with TEMPO. The temperature and concentration dependence of the spin-lattice relaxation rate 1/T1, dominated by the coupling with the electron spins, were found to follow power laws with an exponent close to 3 in all samples. The observed proportionality between 1/T1 and the polarization rate 1/Tpol, with a coefficient related to the electron polarization, is consistent with the presence of Thermal Mixing (TM) and a good contact between the nuclear and the electron spins. At high electron concentration additional relaxation channels causing a decrease in the nuclear polarization must be considered. These results provide further support for a more extensive use of amorphous DNP-ready samples, obtained by means of comilling, in dissolution DNP experiments and possibly for in vivo metabolic imaging.
Department of Physics, University of Pavia-CNISM, Via Bassi 6, 27100 Pavia, Italy. marta.filibian@unipv.it.
M
M
Filibian
Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via Giorgieri 1, 34127 Trieste, Italy and UMET, Unité Matériaux et Transformations, CNRS, Univ. Lille, F-59000 Lille, France.
E
E
Elisei
Bracco Research Center, Bracco Imaging S.p.A., Via, Ribes 5, 10010 Colleretto Giacosa (TO), Italy.
S
S
Colombo Serra
Laboratoire de Physique Théorique et Modèles Statistiques (UMR CNRS 8626), Université Paris-Sud, Bât. 100, 15 rue Georges Clémenceau, 91405 Orsay Cedex, France.
A
A
Rosso
Bracco Research Center, Bracco Imaging S.p.A., Via, Ribes 5, 10010 Colleretto Giacosa (TO), Italy.
F
F
Tedoldi
Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via Giorgieri 1, 34127 Trieste, Italy and Elettra Sincrotrone Trieste, Area Science Park, I-34149 Trieste, Italy.
A
A
Cesàro
Department of Physics, University of Pavia-CNISM, Via Bassi 6, 27100 Pavia, Italy. marta.filibian@unipv.it.
P
P
Carretta