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<p>The dimension and the flexibility of a biopolymer sodium alginate have been investigated in methanol-water binaries to explore the effects of medium, ionic strength, and temperature on the solution behavior of this polymer from viscosity measurement. In particular, several mixtures of methanol and water with varying dielectric constants were used as the media, and the ionic strength of the sodium alginate solutions was adjusted by adding an external salt (NaCl). A phenomenological approach was applied for the determination of the intrinsic viscosities of the polymer solutions. There has been a drastic reduction in the polyion coil size as manifested by the generalized intrinsic viscosity as well as by the root mean square radii of gyration values when the concentration of the added salt is increased. With respect to the maximally stretched conformation in salt-free solutions, the radius of gyration under <i>θ</i>-condition (obtained from the base values of the sigmoidal fits of the intrinsic viscosity vs. the logarithmic concentration of the added salt plots) decreases by nearly 65% and 63% at 298.15 and 308.15&#xa0;K respectively, which is quite large compared to that in the aqueous phase (47% and 51% respectively). The alginate chains have been found to remain stiff over a length of about 6–7 monomers at the temperatures investigated, indicating a semi-flexible nature of this carbohydrate polymer in methanol-water media. The electrostatic contributions to the persistence length in the solution with the lowest amount of the added salt (0.1 mmol·L<sup>−1</sup>) shoot up to ca. 80–90 times the intrinsic persistence length indicating an appreciable chain extension in low-salt solutions. The variation of the chain dimensions with the composition of the mixed solvent media has been interpreted considering the formation and disruption of internal rings involving two monomeric units on the chain and solvent molecules. This study also assessed critically the relative contributions of the dielectric constant, counterion desolvation and dissociation to the temperature-dependence of the chain dimension.</p>

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Dimension and flexibility of sodium alginate in solution

  • 期刊论文

  • 发表日期：

    2025年8月22日

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  • Arnab Banerjee,
  • Bidyut Debnath,
  • Bijan Das

摘要

The dimension and the flexibility of a biopolymer sodium alginate have been investigated in methanol-water binaries to explore the effects of medium, ionic strength, and temperature on the solution behavior of this polymer from viscosity measurement. In particular, several mixtures of methanol and water with varying dielectric constants were used as the media, and the ionic strength of the sodium alginate solutions was adjusted by adding an external salt (NaCl). A phenomenological approach was applied for the determination of the intrinsic viscosities of the polymer solutions. There has been a drastic reduction in the polyion coil size as manifested by the generalized intrinsic viscosity as well as by the root mean square radii of gyration values when the concentration of the added salt is increased. With respect to the maximally stretched conformation in salt-free solutions, the radius of gyration under θ-condition (obtained from the base values of the sigmoidal fits of the intrinsic viscosity vs. the logarithmic concentration of the added salt plots) decreases by nearly 65% and 63% at 298.15 and 308.15 K respectively, which is quite large compared to that in the aqueous phase (47% and 51% respectively). The alginate chains have been found to remain stiff over a length of about 6–7 monomers at the temperatures investigated, indicating a semi-flexible nature of this carbohydrate polymer in methanol-water media. The electrostatic contributions to the persistence length in the solution with the lowest amount of the added salt (0.1 mmol·L−1) shoot up to ca. 80–90 times the intrinsic persistence length indicating an appreciable chain extension in low-salt solutions. The variation of the chain dimensions with the composition of the mixed solvent media has been interpreted considering the formation and disruption of internal rings involving two monomeric units on the chain and solvent molecules. This study also assessed critically the relative contributions of the dielectric constant, counterion desolvation and dissociation to the temperature-dependence of the chain dimension.