Proton and Carbon-13 Dynamic Nuclear Polarization of Methylated β-Cyclodextrins

H-1 and C-13 dynamic nuclear polarizations have been studied in C-13-enriched beta-cyclodextrins doped with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl free radical. H-1 and C-13 polarizations raised above 7.5 and 7%, respectively, and for both nuclear species, the transfer of polarization from the electron spins appears to be consistent with a thermal mixing scenario for a concentration of 9 C-13 nuclei per molecule. When the concentration is increased to 21 C-13 nuclei per molecule, a decrease in the spin-lattice relaxation and polarization buildup rates is observed. This reduction is associated with the bottleneck effect induced by the decrease in the number of electron spins per nucleus when both the nuclear spin-lattice relaxation and the polarization occur through the electron non-Zeeman reservoir. C-13 nuclear spin-lattice relaxation has been studied in the 1.8-340 K range, and the effects of internal molecular motions and of the free radicals on the relaxation are discussed. C-13 hyperpolarization performances and room-temperature spin-lattice relaxation times show that these are promising materials for future biomedical applications.