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

Using 5 samples of well‐purified Na‐gellans (Na‐gellans G1–G5, weight‐average molar mass M w = 120 × 10 3 −32 × 10 3 at 40°C), the effects of molar mass on the coil‐to‐double‐helix transition in aqueous solutions with 25 mM NaCl were studied by light scattering and circular dichroism (CD) measurements, viscometry, and differential scanning calorimetry (DSC). From the temperature dependence of M w , molar ellipticity at 201nm [θ] 201 , intrinsic viscosity [η], and DSC exothermic curves, it was found that the coil‐to‐double‐helix transitions for G1–G5 samples took place at almost the same temperature. The [η] and M w obtained in the temperature range from 40 to 25°C can be explained by a simple coil/double‐helix equilibrium model using the double‐helix contents determined from CD data. The van't Hoff's transition enthalpy Δ H vH of Na‐gellans depended on M w . It is concluded that the coil‐to‐double‐helix transitions of Na‐gellans are all‐or‐none type transitions, and are accelerated with increasing M w . © 2005 Wiley Periodicals, Inc. Biopolymers 79: 207–217, 2005 This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com