Solid-state deuterium NMR and molecular modeling studies of conformationaldynamics in carbohydrates

We report a deuterium nuclear magnetic resonance (NMR) investigation of oct a-O-decanoylthio-beta,beta-trehalose (TTH-10) in the solid state. For the i nterpretation of deuterium NMR line shapes and spin-lattice relaxation rate s, a two-site exchange model was invoked. The motional amplitude for the C- D vector in TTH-10 molecule was estimated to 72 degrees, while the relative populations of the two sites were assumed to be temperature dependent. Fro m the longitudinal deuterium relaxation rates, correlation times for the dy namic process were derived. We found these to be approximately 50 ns at 20 degrees C and 30 ns at 90 degrees C. In addition to NMR experiments, molecu lar dynamics (MD) computer simulations of octa-O-acetylthio-beta,beta-treha lose (TTH-2) and an oxygen analogue, octa-O-acetyl-beta,beta-trehalose (TH- 2), were performed. The analysis of the two torsion angles relevant for the glycosidic linkage indicates that the conformations of the TTH-2 molecule essentially correspond to two states. This observation gives strong support for our assumption about the two-site exchange model used for interpretati on of deuterium solid-state experiments.