Double-Stranded Helix of Xanthan in Dilute Solution: Further Evidence

Abstract

Viscosity measurements were made on ten samples of a bacterial polysaccharide xanthan in 0.1 M aqueous NaCl and cadoxen (at 25°C); the polymer dissolves as dimers in the former and as monomers in the latter. Intrinsic viscosities [η] as a function of molecular weight in 0.1 M aqueous NaCl fitted to Yamakawa–Yoshizaki’s theory for the Kratky–Porod wormlike chain with a linear mass density ML of 1940 nm−1, a persistence length of 120 nm, and a chain diameter of 2.0—2.5 nm. This ML corresponds to the 0.47 nm pitch (per main chain glucose residue) of the 51 double-stranded helix proposed for the crystalline structure of xanthan, and is consistent with the previous conclusion from light scattering that the xanthan dimer in 0.1 M aqueous NaCl has this helical structure. On the other hand, the values of [η] in cadoxen showed that the single chain of xanthan in this solvent is essentially flexible. Those in mixtures of cadoxen and water decreased sharply with an increase in cadoxen composition in a range from 60 to 70wt% cadoxen. The double-helical xanthan dimer was not restored once dissociated into single chains in pure cadoxen at 25°C or in pure water at 95°C.

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Sato, T., Kojima, S., Norisuye, T. et al. Double-Stranded Helix of Xanthan in Dilute Solution: Further Evidence. Polym J 16, 423–429 (1984). https://doi.org/10.1295/polymj.16.423

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Keywords

  • Xanthan
  • Polysaccharide
  • β-1,4-D-Glucan
  • Double Helix
  • Persistence Length
  • Semiflexible Chain
  • Intrinsic Viscosity

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