Effect of Clathrate Hydrate Formation and Decomposition on NMR Parameters in THF-D2O Solution

The NMR spin-lattice relaxation time (T-1), spin spin relaxation time (T-2) and the diffusion coefficient D were measured for H-1 in a 1:17 mol % solution of tetrahydrofuran (THF) in D2O. The aim of the work was to clarify some earlier points raised regarding the utility of these measurements to convey structural information on hydrate formation and reformation. A number of irregularities in T-1 and T-2 measurements during hydrate processes reported earlier are explained in terms of the presence of interfaces and possible temperature gradients. We observe that T-1 and T-2 in solution are exactly the same before and after hydrate formation, thus confirming that the solution is isotropic. This is inconsistent with the presence of memory effects, at least those that may affect the dynamics to which T-1 and T-2 are sensitive. The measurement of the diffusion coefficient for a number of hours in the subcooled solution before nucleation proved invariant with time, again suggesting that the solution remains isotropic without affecting the guest dynamics and diffusion.