COUPLING OF MOLECULAR MOTIONS THROUGH NONBONDING INTERACTIONS - C-13 NMR SPIN-LATTICE RELAXATION STUDIES OF A HOST-GUEST COMPLEX

C-13 NMR spin-lattice relaxation and C-13-{H-1} nuclear Overhauser mea surements were performed on the encapsulation complex between [2.2]par acyclophane and a dimeric capsule known as the hydroxy 'softball.' The data were analyzed using the formalism for an isotropically diffusing sphere. The binding constant for the complex is (3.5 +/- 0.5) x 10(3) l mol(-1) in CDCl3 at 295 K. The average dipole-dipole relaxation tim e is 0.45 +/- 0.04 s for the CH vectors of the encapsulated [2.2]parac yclophane and 0.30 +/- 0.03 s for the skeleton of the hydroxy 'softbal l.' The correlation time for the skeleton of the hydroxy 'softball' is 2.7 x 10(-10) s. The corresponding correlation time for the encapsula ted [2.2]paracyclophane is calculated to be 1.2 x 10(-10) s. This resu lts in an average dynamic coupling constant, chi, of 0.47, indicating shape complementarity and correlated motion between the hydroxy 'softb all' and the [2.2]paracyclophane. (C) 1998 John Wiley & Son Ltd.