title: NMR study on hydroxy protons of κ- and κ/μ-hybrid carrageenan oligosaccharides: experimental evidence of hydrogen bonding and chemical exchange interactions in κ/μ oligosaccharides.
abstract: The hydroxy protons of κ- and κ/μ-hybrid carrageenan oligosaccharides have been studied by NMR spectroscopy in 85% H(2)O/15% acetone-d(6). Hydration and hydrogen bonding interactions in di- (κ), tetra- (κκ), hexa (κκκ), and octa- (κκκκ) κ-oligosaccharides and hexa- (κμκ), octa- (κμμκ), and deca- (κμμμκ) κ/μ-oligosaccharides have been investigated by measuring the chemical shifts, temperature coefficients, and chemical exchange of the hydroxy protons. These NMR parameters indicate that no strong and persistent intramolecular hydrogen bonds involving hydroxy protons stabilize the structure of κ-carrageenan oligosaccharides in aqueous solution. In the κ/μ-oligosaccharides, the presence of chemical exchange between OH3 of α-d-Gal-6-sulfate (D6S) and OH2 of β-d-Gal-4-sulfate (G4S) across the β-d-Gal-4-S-(1→4)-α-d-Gal-6-S linkage reveals the existence of a weak hydrogen bond interaction between the two hydroxyl groups. The smaller temperature coefficients of OH2_D6S and OH3_D6S indicate reduced hydration, interpreted as spatial proximity to the 4-sulfate group and O5 ring oxygen of the neighboring G4S residues, respectively. These first experimental results on the conformation of κ/μ-carrageenan oligosaccharides shine light on the potential role of "kinks" in the properties of the three-dimensional carrageenan gel network.
authors.affiliation: Department of Chemistry, Swedish University of Agricultural Sciences, P.O. Box 7015, SE-750 07 Uppsala, Sweden.
authors.forename: Eric Morssing
authors.initials: EM
authors.lastname: Vilén
authors.forename: Lena C E
authors.initials: LC
authors.lastname: Lundqvist
authors.forename: Diane
authors.initials: D
authors.lastname: Jouanneau
authors.forename: William
authors.initials: W
authors.lastname: Helbert
authors.forename: Corine
authors.initials: C
authors.lastname: Sandström
mesh_terms: D002236:Carbohydrate Conformation; D002351:Carrageenan / Q000737:chemistry*; D005782:Gels; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D005782:Gels; D012996:Solutions; D014867:Water; D002351:Carrageenan