Dynamic Nuclear Polarization of β-Cyclodextrin Macromolecules.

H dynamic nuclear polarization and nuclear spin-lattice relaxation rates have been studied in amorphous complexes of β-cyclodextrins doped with different concentrations of the TEMPO radical. Nuclear polarization increased up to 10% in the optimal case, with a behavior of the buildup rate (1/T) and of the nuclear spin-lattice relaxation rate (1/T) consistent with a thermal mixing regime. The temperature dependence of 1/T and its increase with the radical concentration indicate a relaxation process arising from the modulation of the electron-nucleus coupling by the glassy dynamics. The high-temperature relaxation is driven by molecular motions, and 1/T was studied at room temperature in liquid solutions for dilution levels close to the ones typically used for in vivo studies.