A sodium salt xanthan sample dissolved directly in mixtures of water and cadoxen was investigated by elastic light scattering and viscometry at 25°C. With the increase in weight fraction wcad of cadoxen in the mixed solvent, the weight-average molecular weight, z-average radius of gyration ‹S2›z1/2, and intrinsic viscosity [η] of the sample fairly sharply decreased from the values for the double-helical dimer (in 0.1 M aqueous NaCl) to those for the single random coil (in pure cadoxen) in a range of wcad from 0.3 to 0.8. It was found that these data can be explained if it is assumed that only these two species coexist in the mixed solvent and if care is taken of the fact, found from measurements on cadoxen solutions diluted with water, that ‹S2›z and [η] of the single chain species markedly increase with decreasing wcad from 1.0 to 0.6. Thus, it was concluded that xanthan double helices in water-cadoxen mixtures dissociate into single chains directly, i.e., without passing through their partial melting. The expansion of the single chain species was attributed to the formation of intramolecular hydrogen bonds.
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Sato, T., Norisuye, T. & Fujita, H. Double-Stranded Helix of Xanthan: Dissociation Behavior in Mixtures of Water and Cadoxen. Polym J 17, 729–735 (1985). https://doi.org/10.1295/polymj.17.729
- Double Helix
- Radius of Gyration
- Intrinsic Viscosity
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