Formation of cyclodextrin nanotube induced by POPOP molecule

The interaction between 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) and cyclodextrins (CDs) was investigated using UV-Vis absorption, steady-state fluorescence, and dynamic light scattering (DLS). The results indicated that POPOP could form the 1:2 (guest:host) inclusion complex with β-CD at lower concentrations, which could further form the extended nanotube at higher concentrations. POPOP could also induce the formation of the nanotube of γ-CD. The fluorescence emission of POPOP in aqueous solution of γ-CD showed obvious red shift accompanied by the disappearance of fine structure compared with that in aqueous solution of β-CD, which could be attributed to the formation of the excimer of POPOP in the larger cavity of γ-CD. It was found that at pH greater than 12, the hydrogen bond between the neighboring CDs was destroyed, which led to the collapse of the nanotubular structure. The results also showed that the nanotube structure was not stable at temperatures above 331 K.