NMR relaxation interference effects and internal dynamics in gamma-cyclodextrin.

Multiple-magnetic field (9.4, 14.1 and 21.1 T) measurements of (13)C spin-lattice and spin-spin relaxation rates, the heteronuclear Overhauser enhancement and cross-correlated relaxation rates (CCRRs) in the methylene groups are reported for gamma-cyclodextrin in water/dimethylsulfoxide solution at 323 and 343K. The CCRRs are obtained from differences in the initial relaxation rates of the components of the CH(2) triplet in the (13)C spectra. The relaxation data are analyzed using the Lipari-Szabo approach and a novel modification of the two-site jump model. According to the latter model, inclusion of the dipolar (CH,CH(')) cross-correlated longitudinal and transverse relaxation is important for estimating the rate of the conformational jumps in the hydroxymethyl group. Using the dynamic information from the jump model, we have also used the differences in the initial relaxation rates for the triplet components to estimate the anisotropy of the chemical shielding tensor.