ISSN:
0006-3525
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Weight-average molecular weights Mw, second virial coefficients, and z-average radii of gyration 〈S2〉1/2z were determined by light scattering as a function of temperature T for four sodium salt samples of xanthan in 0.01M aqueous NaCl, in which the polysaccharide undergoes an order-disorder conformation change with increasing T. The data for 〈S2〉1/2z and Mw 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 80°C, 〈S2〉1/2z sigmoidally decreased or increased depending on the dimer's molecular weight. This temperature dependence of 〈S2〉1/2z 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.
Zusätzliches Material:
7 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/bip.360271009
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