Molecular Dynamics of Novel a-Cyclodextrin Adducts Studied by 13C-NMR Relaxation

In the presence of poly(ethylene glycol) (PEG), cyclodextrin forms a molecular adduct called “molecular necklace” that belongs to the class of polyrotaxanes. The condensation of cyclodextrin with epichlorohydrin results in the formation of the so-called “molecular tube” (MT), a rodlike rigid molecule with an empty hydrophobic cavity that can behave as a host for ions or small organic molecules. MT has been obtained from PEG, considerably longer than the chain used in previous works. This paper reports an NMR investigation of the dynamic properties, via carbon spin-lattice relaxation technique, of cyclodextrin, the molecular necklace, and the molecular tube. The results show that the molecular tube is really formed by a linear thread of condensed R-cyclodextrin molecules and that MT possesses a faster reorientational motion than all the other compounds. UV spectroscopy shows that the molecular tube forms a host-guest system with iodine in aqueous solution.