Formation of chiral supramolecular polymer based on modified Cyclodextrin by host-guest interactions

Abstract

Recently, much attention has been focused on molecular design and construction of supramolecular structures by controlling self-assembly processes. The continuous intermolecular inclusion complexation of substituted cyclodextrins (CDs) gives in the formation of supramolecular polymers. Now we here prepared two cinnamamide modified cyclodextrins, 3-CiNH-α-CD and 3- (p-tBocCiNH)-α-CD, bearing cinnamamide and p-tert-butoxycarbonylaminocinnamamide on the 3-position of CDs. These modified CDs formed intermolecular complexes to give supramolecular polymers. The degree of polymerization of the supramolecular polymer is higher than 15 at 20 mM, as proved by VPO (vapor pressure osmometry) measurements and turbo ion spray TOF MS measurements. 3-(p-t3BocCiNH)-α-CD formed much more stable and larger supramolecular polymers in comparison with 3-CiNH-α-CD. The existence of substitution/substitution interactions between adjacent monomers of the supramolecular polymer have been confirmed by the observation of positive and negative Cotton bands in circular dichroism spectra. The mechanism for the induction of the chirality was confirmed using model compounds. The substituents were found to exist as a left-handed anti configuration in supramolecular polymers. The supramolecular polymer was found to take a helical structure. The structure of the supramolecular polymer was observed by STM measurements. This is the first example of the formation of a cyclodextrin-based helical supramolecular polymer.