Dynamic and kinetic properties of molecular necklaces and molecular tubes from alpha-cyclodextrin/polyethylene glycol inclusion compounds in water solution.

We synthesized a new polyethylene glycol/α-cyclodextrin (PEG/α-CY) molecular adduct where α-CY molecules are threaded around a single PEG (MW=3,350) chain. The condensation of α-CY with epichlorohydrin results in the formation of the so-called “molecular tube”, a rod-like rigid molecule with an empty hydrophobic cavity that can host ions or small organic molecules. The kinetic of the threading process has been studied as a function of temperature and solvent composition. The dynamic properties of the α-CY molecular necklace (MN) and molecular tube (MT) have been studied by 13C-NMR spin lattice relaxation. The results show that MT is formed by a linear thread of cross-linked α-CY moieties, and that MT possesses a faster orientational motion than α-CY and MN.