Solution Properties of Gellan Gum:  Change in Chain Stiffness between Single- and Double-Stranded Chains

Abstract

Nine samples of gellan gum in the sodium form, ranging in weight-average molar mass from 3.47 x 10(4) to 1.15 x 10(5) at 40 degrees C, were investigated by static and dynamic light scattering and viscometry in 25 mM aqueous NaCl both at 40 and at 25 degrees C. The ratios of the molar mass at 25 degrees C (in the ordered state) to that at 40 degrees C (in the disordered state) were in the range of 1.99 to 2.07, supporting the scheme of the conformational transition of gellan gum between a disassociated single chain and an associated chain composed of two molecules. Focusing on the effects of polydispersity, the intrinsic viscosities, radii of gyration, and hydrodynamic radii were analyzed on the basis of unperturbed wormlike chain models. The persistence lengths were evaluated as 9.4 nm at 40 degrees C and 98 nm at 25 degrees C.

Unassociated Molecular Chains in Physically Crosslinked Gellan Gels

“…In the case of sodium-type gellan, the value was determined to be 1.3 at 25 C in the 25 mmol kg À1 NaCl aqueous solution. 30 The ratio of the molecular weight of unreleased and released gellan chains was evaluated to be ca. 3.5 assuming that ¼ 1:3 and that the value is independent of the type of counter ion and salt concentration added.…”

Thermally induced coil‐to‐helix transition of sodium gellan gum with different molar masses in aqueous salt solutions

“…The weight average molar masses (M w ) for the Nagellan samples obtained in this study are shown in 32 reported that the molar mass dependence of intrinsic viscosity of Na-gellan in aqueous solutions with 25 mM NaCl at 408C was described by the Yamakawa-Fujii-Yoshizaki (YFY) theory 38,39 for an unperturbed wormlike chain using the values of persistence length q ¼ 9.4 nm, molar mass per unit contour length of the chain M L ¼ 355 nm…”

“…The value of persistence length for the Na-gellan chain was 9.4 nm and the Na-gellan chain behaves as a semiflexible chain at 408C. 32,40 It is considered that the substantial stiffness of the single-stranded Na-gellan chain facilitates the coil-to-double-helix transition in the allor-none type. In this study, even at the highest polymer concentration (c p ¼ 1.0 wt %), the Na-gellan solution did not form gels due to an insufficient number of helices to form a three-dimensional network.…”

“…Nevertheless, only a few studies concerning the effects of molar mass on the double-helix formation have been carried out, partly due to the difficulty of sample preparation. Takahashi et al 32 studied the conforma- tional change of sodium-type gellan gums in 25 mM aqueous NaCl solutions from LS and viscosity measurements. The molar mass dependence of the intrinsic viscosities, radii of gyration, and hydrodynamic radii in both the disordered and ordered states were analyzed on the basis of a wormlike chain model.…”

“…The persistence length of the Na-gellan (q ¼ 9.4 nm) was close to the values of sodium hyaluronate (q ¼ 4.2 nm) 41 and nitrocellulose (q ¼ 17 nm), 38 suggesting that at 408C the Na-gellan chain in aqueous solutions with 25 mM NaCl behaved as a semiflexible chain. 32,40 The ratios of M w obtained at 25 40 , which suggests that on lowering the temperature, the aggregation of double helices occurred for G1 and G2, and the amount of double helices increased for G4 and G5 with the progress of the double-helix formation. M w 15 /M w 40 for G2 was larger than that of G1.…”