title: Rb+ and Na+ spin relaxation in aqueous gellan solutions and implication of selective site binding of alkali metal ions.
abstract: 87Rb NMR was applied to investigate the site binding of Rb+ ions in gellan gum gels. The temperature dependence of the transverse and longitudinal relaxation NMR relaxation rates of 87Rb+ ion and 23Na+ ion have been compared in aqueous 5% (w/v) rubidium-type and sodium-type gellan. In each sample, the relaxation rates were sensitive to the conformation (helix or random coil). In rubidium-type gellan, significant line-broadening effects (losses in intensity) were found, which is due to the presence of cation-binding sites in the ordered conformation. In sodium-type gellan, such an enhancement of the relaxation was not observed. These results indicated that gellan gum produced highly selective binding sites for alkali metal ions, in which Rb+ ion bound more strongly than Na+ ion. The 87Rb NMR line shift suggested selective site binding of ions to form the cross-linking domains in gellan gels.
authors.affiliation: Department of Materials Technology, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi, Chiba 263-8522, Japan. annaka@galaxy.tc.chiba-u.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Annaka
authors.forename: R
authors.initials: R
authors.lastname: Takahashi
authors.forename: T
authors.initials: T
authors.lastname: Nakahira
authors.forename: M
authors.initials: M
authors.lastname: Tokita
authors.forename: T
authors.initials: T
authors.lastname: Matsuura
mesh_terms: D001665:Binding Sites; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005782:Gels; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D012413:Rubidium; D012964:Sodium; D012996:Solutions; D013816:Thermodynamics; D014867:Water
chemical_list: D005782:Gels; D011135:Polysaccharides, Bacterial; D012996:Solutions; D014867:Water; C048288:gellan gum; D012964:Sodium; D012413:Rubidium