title: Stability of (1→3)-β-polyglucuronic acid under various pH and temperature conditions.
abstract: Regioselective oxidation of C6 primary hydroxyls to carboxyls was applied to curdlan, to prepare a water-soluble (1→3)-β-polyglucuronic acid Na salt [(1,3)-β-PGluA], using a 4-acetamido-TEMPO/NaClO/NaClO₂ oxidation system at pH 4.7. Changes in the chemical structure and degree of polymerization of (1,3)-β-PGluA treated in water at various temperatures and pHs were studied to evaluate the stability of (1,3)-β-PGluA to these treatments. This polyuronic acid was found to be stable, without any depolymerization, to treatment in water at pHs 1-9 and room temperature for up to 128 h; slight depolymerization was observed at pHs 11 and 13. When heated in water at pH 1 and high temperatures (1,3)-β-PGluA molecules were randomly depolymerized by hydrolysis, primarily forming glucuronic acid. In contrast, dicarboxylic-acid-type monomers containing ethylene carbons were formed from the C1-carboxyl or C1 reducing ends of (1,3)-β-PGluA molecules by treatment under alkaline conditions; this was initiated by β-alkoxy elimination, similar to the peeling-off reaction of cellulose.
authors.affiliation: Department of Biomaterial Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Erika
authors.initials: E
authors.lastname: Watanabe
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Tamura
authors.forename: Shuji
authors.initials: S
authors.lastname: Fujisawa
authors.forename: Tsuguyuki
authors.initials: T
authors.lastname: Saito
authors.forename: Naoto
authors.initials: N
authors.lastname: Habu
authors.forename: Akira
authors.initials: A
authors.lastname: Isogai
keywords: (1→3)-β-Polyglucuronic acid; Curdlan; SEC-MALLS; Stability; TEMPO; β-Elimination