Polyrotaxanes based on PEG-amine with cucurbit[7]uril, α-cyclodextrin and its tris-O-methylated derivative

Cucurbit[7]uril (CB7), native α-cyclodextrin (αCD) and its tris-O-methylated derivative (TMαCD) as macrocyclic host molecules and amine-terminated poly(ethylene glycol) (PEG) as neutral guest were used for the synthesis of 3-CB7, 3-αCD and 3-TMαCD polyrotaxanes. The binding affinities of the neutral PEG guest into the CB7, αCD and TMαCD cavities were evaluated by isothermal titration calorimetry. The high value of the stability constant (1 × 104 M−1) indicates that PEG provides a preferential binding to CB7 over αCD. The polyrotaxane structure was confirmed by FT-IR and 1H NMR spectroscopy. The coverage ratio of the PEG with CB7, αCD and TMαCD macrocycles, were 63%, 71%, and 30%, respectively. The polyrotaxanes 3-CB7 and 3-αCD exhibit an enhancement in thermal stability compared with the non-rotaxane 3 counterpart. In addition, polyrotaxane 3-CB7 shows blue-shifted absorption by more than 20 nm and enhanced water solubility.