Photoresponsive Hydrogel System Using Molecular Recognition of α-Cyclodextrin

Abstract

Using molecular recognition of α-cyclodextrin (α-CD), we have successfully constructed a photoresponsive hydrogel system by combination of simple components, α-CD, dodecyl (C12)-modified poly(acrylic acid) (p(AA/C12)), and a photoresponsive competitive guest, 4,4‘-azodibenzoic acid (ADA). An aqueous solution of p(AA/C12) exhibited a gel-like behavior because polymer chains form a network structure via hydrophobic associations of C12 side chains. When α-CD was added to the gel-like aqueous solution, the gel was converted to a sol mixture because hydrophobic interactions of C12 side chains were dissociated by the formation of inclusion complexes of α-CD with C12 side chains. Upon addition of ADA to a binary sol mixture of p(AA/C12) and α-CD, α-CD interacted predominantly with ADA, and then hydrophobic associations of C12 side chains were restored, resulting in a sol-to-gel transition. When a ternary gel mixture of p(AA/C12), α-CD, and ADA was irradiated with UV light, ADA was isomerized from trans to cis, a...