Self-Threading and Dethreading Dynamics of Poly(ethylene glycol)-Substituted Cyclodextrins with Different Chain Lengths

Poly(ethylene glycol) (PEG)-substituted cyclodextrins (CDs) with different chain lengths have been synthesized. PEG-substituted CDs formed self-threading complexes in aqueous solutions. The conformation of PEG-substituted CDs changed from a self-threading form to a dethreading form in the presence of an equal molar amount of 1-adamantanecarboxylic acid (AdCA) as a competitive guest and exchanged between a self-threading form and a dethreading form in the presence of a half molar amount of AdCA. The conformational exchange dynamics of PEG-substituted CDs were studied by means of variable-temperature NMR and 2D EXSY NMR experiments, and it was revealed that the conformational exchange rates decreased exponentially with the PEG chain length of the substituent.