Are there impacts of zwitterions to the pH and sugar responsiveness of boronic acids? Are there unique properties in the pH and sugar responsiveness of polymeric micelles of block copolymers composed of a zwitterionic polymer and boronic acid-containing polymers?
Molecular assemblies that transform in response to pH and saccharide concentration are promising nanomaterials in the field of biomedicine, and polymeric micelles of amphiphilic polymers with phenylboronic acids have been studied. We explored the impact of zwitterions on the acidity constant for the collapse and the glucose sensitivity of a polymeric micelle produced from a diblock copolymer comprising polyacrylamides with phenylboronic acid and zwitterionic carboxybetaine. The diblock copolymer produced micellar aggregates in aqueous solutions at a neutral pH and the polymeric micelles collapsed at a pH of 11.0 because the phenylboronic acid transformed into a hydroxyboronate anion, while the pKa decreased in the presence of glucose owing to the boronate ester formation. The zwitterionic polymer chains significantly increased the pH at which the molecular assemblies dissociated probably because the pKa of boronic acid increased through the dipolar interaction of zwitterions, and/or the zwitterionic polymer corona is valid for screening of PBA ionization and electrostatic repulsion of boronate anions. This study on the modulation of the pKa through zwitterionic interaction can facilitate the molecular design of pH- and saccharide-responsive biomaterials.
Saya Maeda was in charge of this project. She had sincerely conducted our new research project handling phenylboronic acid/sugar chemistry. We have faced and overcome many challenges. The research project was urged to change the direction frequently; however, she tackled her research with a positive attitude, sometimes hesitating. She was attentive to the overall laboratory management and worked very hard to mentor the younger students. I am grateful to her for her dedication, which enabled the members of the laboratory to be as active as they wanted to be. I wish her every success and good health.
This is the collaboration work with Prof. Yoshiko Miura in Kyushu University, with support from the JSPS KAKENHI. We sincerely appreciate her support and advice on this research.
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