title: Construction of chemical-responsive supramolecular hydrogels from guest-modified cyclodextrins.
abstract: A methodology for preparing supramolecular hydrogels from guest-modified cyclodextrins (CDs) based on the host-guest and hydrogen-bonding interactions of CDs is presented. Four types of modified CDs were synthesized to understand better the gelation mechanism. The 2D ROESY NMR spectrum of beta-CD-AmTNB (Am=amino, TNB=trinitrobenzene) reveals that the TNB group was included in the beta-CD cavity. Pulsed field gradient NMR (PFG NMR) spectroscopy and AFM show that beta-CD-AmTNB formed a supramolecular polymer in aqueous solution through head-to-tail stacking. Although beta-CD-AmTNB did not produce a hydrogel due to insufficient growth of supramolecular polymers, beta-CD-CiAmTNB (Ci=cinnamoyl) formed supramolecular fibrils through host-guest interactions. Hydrogen bonds between the cross-linked fibrils resulted in the hydrogel, which displayed excellent chemical-responsive properties. Gel-to-sol transitions occurred by adding 1-adamantane carboxylic acid (AdCA) or urea. (1)H NMR and induced circular dichroism (ICD) spectra reveal that AdCA released the guest parts from the CD cavity and that urea acts as a denaturing agent to break the hydrogen bonds between CDs. The hydrogel was also destroyed by adding beta-CD, which acts as the competitive host to reduce the fibrils. Furthermore, the gel changed to a sol by adding methyl orange (MO) as a guest compound, but the gel reappeared upon addition of alpha-CD, which is a stronger host for MO.
authors.affiliation: Department of Macromolecular Science, Graduate School of Science, Osaka University, Machikaneyama, Toyonaka, Osaka, 560-0043, Japan.
authors.forename: Wei
authors.initials: W
authors.lastname: Deng
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Takashima
authors.forename: Akira
authors.initials: A
authors.lastname: Harada
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry; D003505:Cyclodextrins / Q000737:chemistry*; D020100:Hydrogels / Q000138:chemical synthesis*; D008958:Models, Molecular; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D003505:Cyclodextrins; D020100:Hydrogels; D011108:Polymers