Order–Disorder conformation change of xanthan in 0.01M aqueous sodium chloride: Dimensional behavior

✍ Scribed by Wei Liu; Takashi Norisuye

• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 731 KB
• Volume: 27
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360271009

✦ Synopsis

Weight-average molecular weights M,, second virial coefficients, and z-average radii of gyration (S2):/2 were determined by light scattering as a function of temperature T for four sodium salt samples of xanthan in 0.01M aqueous NaCI, in which the polysaccharide undergoes an order-disorder conformation change with increasing T. The data for (S2):/' and 44, at 25 and 80"C, the lowest and highest temperatures studied, confirmed the previous conclusion that the predominant conformation at the former T, i.e., in the ordered state, is a double helix, while that at the latter T, i.e., in the disordered state, is a dimerized coil expanded by electrostatic repulsions between charged groups of the polymer. As T was increased from 25 to W C , (SZ):/' sigmoidally decreased or increased depending on the dimer's molecular weight. This temperature dependence of (S2):/2 and that determined elsewhere for a high molecular weight sample were found to be described almost quantitatively by a simple dimer model in which the double helix melts from both ends, when the double-helical fraction in the dimer at a given T estimated previously from optical rotation data was used.