pH-Responsive Shrinkage/Swelling of a Supramolecular Hydrogel Composed of Two Small Amphiphilic Molecules

• Published in: Chemistry : a European journal Vol. 11; no. 4; pp. 1130 - 1136
• Main Authors: Zhou, Shan-Lai, Matsumoto, Shinji, Tian, Huai-Dong, Yamane, Hiroki, Ojida, Akio, Kiyonaka, Shigeki, Hamachi, Itaru
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 04.02.2005; WILEY‐VCH Verlag; Wiley
• Subjects: carboxylic acids; Chemistry; Chemistry, Multidisciplinary; copolymerization; gels; pH response; Physical Sciences; Science & Technology; supramolecular chemistry; copolymerization; GELATION PROCESS; pH response; MEMORY; gels; carboxylic acids; PHASE-TRANSITION; DESIGNED PEPTIDE; WEIGHT HYDROGELATORS; CHIRALITY; supramolecular chemistry; REVERSIBLE HYDROGELS; DERIVATIVES; POLYMER GELS; GLYCOSYLATED AMINO-ACID
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200400677

A pH‐responsive volume‐change function was successfully introduced into a supramolecular hydrogel that contained GalNAc‐appended (GalNAc=N‐acetylgalactosamine) glutamate ester 1 by the simple mixing of it with an appropriate amount of 2 a or 2 b amphiphilic carboxylic acid. In the 1:1 mixture (1:2), the hydrogel swelled under neutral pH conditions, but shrank to almost half of its original volume under acidic pH conditions. The structure and pH response of the mixed hydrogel were characterized by using X‐ray diffraction (XRD), confocal laser scanning microscopy (CLSM), transmission or scanning electron microscopy (TEM, SEM), and Fourier transform IR (FTIR) spectroscopy. Well‐developed fibers formed a stable hydrogel by self‐assembly, and under acidic conditions the charge of the carboxylic acid terminal (from the carboxylate anion) was neutralized and then these fibers became densely packed. This macroscopic pH response was also applied to the pH‐triggered release of bioactive substances. In this mixed supramolecular hydrogel, the hydrogelator 1 provides a stable hydrogel structure and the additive 2 acts as a commander that is sensitive to an environmental pH signal. The present supramolecular copolymerization strategy should be useful for the construction of novel, stimuli‐responsive, soft materials. Swell gels! A pH‐responsive volume‐change function was successfully introduced into a supramolecular hydrogel by the simple mixing of a hydrogelator with an appropriate amount of amphiphilic carboxylic acid. By using this hydrogel prepared by supramolecular copolymerization, the controlled release of bioactive substances in response to pH was achieved.