Regulation of pseudo-polyrotaxane formation between alpha-cyclodextrins and azobenzene-terminated poly(ethylene glycol)

Regulation of pseudo-polyrotaxane formation between alpha-cyclodextrins (al pha-CDs) and azobenzene(Az)-terminated poly(ethylene glycol) (PEG) was stud ied in terms of the photoisomerization of the terminal Az groups. pseudo-Po lyrotaxane formation was analyzed by a change in the transmittance at 550 n m in water. It was found that the rate of transmittance change was decrease d with an increase in the cis isomer content in Az-PEG. The cis-isomerizati on effect was quantitatively evaluated, assuming that Az-PEG having two cis -isomerized Az groups does not participate in the pseudo-polyrotaxane forma tion. From this analysis, it is suggested that pseudo-polyrotaxane formatio n between alpha-CDs and PEG was hindered when the both terminal Az groups w ere isomerized to cis isomer. The content of Az-PEG in the pseudo-polyrotax ane aggregate and the content of cis-isomerized Az-PEG in the supernatant w ere measured by H-1 NMR and UV-Vis absorption spectrum, respectively, and t he obtained results supported our suggestion. It is concluded that the term inal Az groups act as a gate to regulate the pseudo-polyrotaxane formation.