Preparation of inclusion complexes of poly(ethylene glycol)-bearing artificial lipids with α-cyclodextrin and of a poly(rotaxane) based on the complex

We synthesized eight different α-amino-terminated poly(ethylene glycol)-bearing double-chain or triple-chain artificial lipids (PEG-lipids) with the molecular weight (Mw) of the poly(ethylene glycol) (PEG) moiety being 700, 1,000 or 1,600. The mixing of the aqueous bilayers of these lipids with α-cyclodextrin gradually formed crystalline inclusion complexes that were characterized by ¹H NMR and FTIR spectroscopies, differential scanning calorimetry (DSC), and X-ray analysis. A large induced circular dichroism spectra was observed for an achiral bilayer of a chromophore-containing PEG-lipid during the initial stage of the complex formation process. The ¹H NMR spectra revealed that the stoichiometry number of the α-CyD/ethylene glycol unit in the inclusion complexes was 1.8-2.2, suggesting that only the poly(ethylene glycol) moiety in the lipids interacted with α-CyD. The bilayer of a triple-chain PEG-lipid with Mw = 700 of the PEG moiety and of a phenyl-containing triple chain PEG-lipid with Mw = 1,600 of the PEG moiety maintained the bilayer phase transition even after the complex formation with α-CyD. On the contrary, the phase transition was lost via the complex formation of the bilayers of the double-chain PEG-lipids with Mw = 700, 1,000 or 1,600, as well as of triple-chain lipids with Mw = 1,000 or 1,600 of the PEG moiety. The FTIR spectral data for the complexes suggested that the difference in the phase transition behavior would come from the change in the molecular cross-sectional area (top view) of the double-chain and triple-chain in the lipids, as well as in the chain length of the PEG moiety. Lastly, we describe the synthesis of a poly(rotaxane) of α-CyD based on the inclusion complex.