title: A pH-responsive carboxylic β-1,3-glucan polysaccharide for complexation with polymeric guests.
abstract: The helix-forming nature of β-1,3-glucan polysaccharides is a characteristic that has potential for producing gene carriers, bio-nanomaterials and other chiral nanowires. Herein, carboxylic curdlan (CurCOOH) bearing the β-1,3-polyglucuronic acid structure was successfully prepared from β-1,3-glucan polysaccharide curdlan (Cur) by one-step oxidation using a 4-acetamido-TEMPO/NaClO/NaClO(2) system as the oxidant. The resulting high-molecular-weight CurCOOH was proved to bear the 6-COOH group in 100% purity. The optical rotatory dispersion (ORD) spectra indicated that the obtained CurCOOH behaves as a water-soluble single-strand in various pH aqueous media. This advantage has allowed us to use CurCOOH as a polymeric host to form various macromolecular complexes. For example, complexation of CurCOOH with single-walled carbon nanotubes (SWNTs) resulted in a water-soluble one-dimensional architecture, which formed a dispersion in aqueous solution that was stable for several months, and much more stable than SWNTs complexes of the similar negatively-charged polyacrylic acid (PAA) and polymethacrylic acid (PMAA). It was shown that in the complex, SWNTs are effectively wrapped by a small amount of CurCOOH, enabling them to avoid electrostatic repulsion. This pH-responsive CurCOOH formed a very stable complex with cationic water-soluble polythiophenes (PT-1), which was stabilized not only by the hydrophobic interaction but also by the electrostatic attraction between trimethylammonium cations in PT-1 and dissociated anionic COO(-) groups in CurCOOH. The included PT-1 became CD-active only in the neutral to basic pH region, and the positive Cotton effect suggested that the conjugated main chain is twisted in the right-handed direction. We also found that CurCOOH can interact with polycytidylic acid (poly(C)) only under high NaCl concentrations, the binding and release of which could be controlled by a change in the salt concentration. We believe, therefore, that CurCOOH bearing a dissociable COOH group can act as a new potential polymeric host to construct novel polymeric complexes applicable for gene carriers, biosensors, chiral polymer assemblies, etc.
authors.affiliation: Department of Applied Chemistry, Faculty of Engineering, Kyushu University, Nishi-ku, Moto-oka 744, Fukuoka, 819-0395, Japan.
authors.forename: Le Thi Ngoc
authors.initials: le TN
authors.lastname: Lien
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shiraki
authors.forename: Arnab
authors.initials: A
authors.lastname: Dawn
authors.forename: Youichi
authors.initials: Y
authors.lastname: Tsuchiya
authors.forename: Daisuke
authors.initials: D
authors.lastname: Tokunaga
authors.forename: Shun-ichi
authors.initials: S
authors.lastname: Tamaru
authors.forename: Naoya
authors.initials: N
authors.lastname: Enomoto
authors.forename: Junichi
authors.initials: J
authors.lastname: Hojo
authors.forename: Seiji
authors.initials: S
authors.lastname: Shinkai
mesh_terms: D002264:Carboxylic Acids / Q000138:chemical synthesis / Q000737:chemistry*; D005965:Glucuronates / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010316:Particle Size; D013499:Surface Properties; D047071:beta-Glucans / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D005965:Glucuronates; D047071:beta-Glucans