Complex formation of cyclodextrins with poly(propylene glycol) derivatives

The complex formation between cyclodextrins (CDs) and poly(propylene glycol) (PPG) derivatives is described. β-CD and γ-CD formed complexes with PPG derivatives such as 1-naphthyl (1NA), 2-naphthyl (2NA), 3,5-dinitrobenzoyl, and 2,4-dinitrophenyl PPG. α-CD did not form complexes with these PPG derivatives. Although γ-CD gave complexes with 9-anthryl PPG (PPG9An), β-CD did not efficiently form complexes with PPG9An. β-CD did not form complexes with trityl PPG, demonstrating that trityl groups were too bulky to thread a (3-CD cavity. The emission spectra of the complexes showed that β-CD bound a single 2NA moiety in its cavity and that γ-CD included two 2NA moieties. In contrast, γ-CD bound a single 1NA moiety in the cavity. X-ray diffraction studies and 1 H NMR analysis showed that the CD molecules were stacked along a PPG chain to form a channel structure. The inclusion modes are discussed.