DYNAMICS OF BETA-CYCLODEXTRIN HYDRATE - SOLID-STATE H-2 NMR-STUDIES

The H-2 NMR spectra and spin-lattice relaxation times of powder sample s of C-deuterated beta-cyclodextrin (CD) hydrate beta-CD-2,3,6,6-d(28) . 11H(2)O) 1 and O-deuterated beta-CD hydrate (beta-CDd(21). 11H(2)O-d (22))2 were measured in the temperature range from 160 to 295 K at 46 MHz. Information about the degree and time scales of dynamic disorder processes was obtained by comparing the powder patterns with computer simulations and analyzing the multi-exponential recovery curves. The d ata on 1 provide evidence for small-angle reorientations of the C-D gr oups with a correlation times tau(c) similar or equal to 10(-7) s at 2 95 < and suggest that the beta-CD macrocycles do not move as a rigid e ntity. The NMR responses of 2 at 295 K show two components and are con sistent with the hydroxyl O-D groups undergoing 2-fold reorientational jumps with tau similar or equal to 10(-8) s and with the water molecu les exchanging between all sites and a significant fraction performing reorientational jumps with .(c) similar or equal to 10(-8) s. Below 2 35 K, at least three components are evident: two were associated with slow reorientations (tau(c) similar or equal to 10(-4) s at 60 K) of h ydroxyl and water O-D groups, and the third with a small number of wat er molecules for which rapid reorientations (tau(c) < 10(-7) s) persis t at 160 K. These dynamic features are considered in terms of the know n structure and the findings of other techniques. These results sugges t that the reorientation jumps of the hydroxyls and water molecules ar e lower than previously thought.