pH-Responsive Phase Transition of Supramolecular Hydrogel Consisting of Glycosylated Amino Acetate and Carboxylic Acid Derivative

Abstract

By addition of a carboxylated amino acetate (2) to a low-molecular-weight hydrogel (1) which has a unique thermally induced volume-phase transition character, a macroscopic pH-responsive feature is newly conferred on the supramolecular hydrogel. The direct observation of temperature-dependent behavior of the mixed hydrogel clearly showed that the thermally induced swelling-shrinkage type of the volume phase transition at pH 4 is shifted to the gel–sol transition at pH 7 by 10 mol% addition of 2 to the hydrogel 1. On the basis of the measurements by TEM, SEM, XRD and FT-IR, it is conceivable that incorporation of the anionic carboxylate of 2 slightly disturbs the packing of the hydrogen bond belt of the mixed hydrogel. Such a slight disturbance greatly leads to the sol–gel transition by elevating temperature, instead of the volume-phase transition. Introduction of dynamic characteristics to supramolecular systems in a macroscopic level may extend the potential of these materials in various fields.

Keywords:

• Hydrogel
• Glycosylated amino acid
• pH response
• Supramolecular materials

Notes

The Future of Supramolecular ChemistryOne future for supramolecular chemistry lies in biology- and biomolecular science-oriented research, such as new artificial receptors, modulators for bio-macromolecules and novel matrices or materials which can regulate living cells. Application of supramolecular approaches to these topics is being actively pursued in the Hamachi group. This paper discusses a pH-responsive feature of the supramolecular copolymer hydrogel consisting of a glycosylated amino acetate and a structurally related carboxylic acid. This is important because we have demonstrated that the supramolecular concept provides a great synthetic accessibility to the intelligent materials. These macroscopic responses towards physiological environments such as pH, temperature and biological substances should extend the potential of supramolecular biomaterials.Professor Itaru Hamachi obtained a PhD from Kyoto University, Japan in 1988 and was engaged as an assistant professor in Kyushu University (emeritus Professor Kunitake's group) at the same time. In 1992, he moved to Professor Shinkai's group as an associate professor and then was promoted to a full professor in IFOC, Kyushu University in 2001. He is also now a PRESTO investigator (JST). His research interests are in the range of bio-organic and bio-inorganic chemistry, protein engineering, chemical biology and supramolecular chemistry.