Molecular Dynamics and Hyperpolarization Performance of Deuterated β-Cyclodextrins

We discuss the temperature dependence of the ¹H and ¹³C nuclear spin-lattice relaxation rate 1/ T₁ and dynamic nuclear polarization (DNP) performance in β-cyclodextrins with deuterated methyl groups. It is shown that ¹³C DNP-enhanced polarization is raised up to 10%. The temperature dependence of the buildup rate for nuclear spin polarization and of 1/ T₁, below 4.2 K, is analyzed in the framework of the thermal mixing regime and the origin of the deviations from the theoretical behavior discussed. ¹³C 1/ T₁ is determined at low temperature by the glassy dynamics and at high temperature by the rotational molecular motions of the deuterated methyl groups. Thanks to deuteration, relaxation times approaching 30 s are achieved at room temperature, making this material interesting for molecular imaging applications. The effect of molecular dynamics on the line width of the NMR spectra is also discussed.