2002 年 12 巻 1 号 p. 22-27
The guest-host interactions and the rotational dynamics in the clathrate hydrates of acetone and THF are discussed in comparison with those in the supercooled aqueous solutions by measuring the 13C NMR chemical shift and the 2D spin-lattice relaxation time as functions of the temperature. When the temperature is decreased, the guest-water hydrogen bond is discontinuously reduced upon the clathrate cage formation. Due to the reduced friction with surrounding waters, the guest molecule reorients much faster in the clathrate cage than in the aqueous solution. On the other hand, the remaining guest-water interaction fluctuates the reorientational motion of the cage water. We also review the structural similarity between the clathrate hydrate and the aqueous solution.