Viscosity and sedimentation studies on amylose in aqueous solution—further evidence for non-helical character
✍ Scribed by W. Banks; C.T. Greenwood
- Publisher
- Elsevier Science
- Year
- 1969
- Tongue
- English
- Weight
- 502 KB
- Volume
- 5
- Category
- Article
- ISSN
- 0014-3057
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✦ Synopsis
Viscosity and sedimentation measurements have been carried out on sub fractions of native amylose dissolved in a thermodynamically ideal solvent (0" 33 M KCI) and a good solvent (0"2 M KOH). The relations:
[r~lzct = 1"12 × 10-1~,,°~°;
[~]zoH = 6"92 × 10-3~I,°'7s;
(So)Kcl = 1"1l × 10-1~t~Iw°5°; (So)KoH = 2"73 × 10-tSlVl, °''.I, were obtained. The divergence of the exponents from a value of 0" 50 for the measurements in KOH is shown to be due to expansion of the molecule through solvent-polymer interaction rather than to partial free-draining character. The unperturbed dimensions of amylose were found to be the same in both solvents, on the basis of the Burchard-Stockmayer-Fixman and the Cowie-Bywater treatments. Measures of 'molecular stiffness' were obtained (Kuhn-Kuhn and Hearst-Stockmayer theories) on the basis of different molecular models including that of the 'interrupted helix'. The latter model appears to be incorrect: analysis of the hydrodynamic data shows that the amylose molecule in aqueous solution is best regarded as a fairly flexible coil.
* This is Part 47 in the series Physicochemical Studies on Starches. The authors dedicate this paper to Professor Husemann on the occasion of her Sixtieth birthday, in recognition of her outstanding contributions to the physical chemistry of polysaccharides.
1In this respect, it is of interest that amylose can be regarded as an isotactic glucan in contrast to the syndiotactic cellulose polymer. 649