Conformational analysis of polysaccharides. III. The relation between stereochemistry and properties of some natural polysaccharide sulfates (1)

Abstract

The sol → gel → sol transformation of aqueous K‐carrageenan occurs with complex changes in optical rotation which may be explained qualitatively in terms of the double helix model for junction zones. Evidence is given that the double helices in the gel are normally aggregated but can be kept separate within a narrow temperature range, and that gelation is a kinetic rather than an equilibrium process. An attempt has been made to predict the preferred conformations of irregular carrageenans by joining segments of simpler polysaccharides; the effect of certain structural variations on gel properties may then be explained. Model building in the computer does not exclude the possibility of double helices for the following polysaccharides which are structurally related to K‐ and i‐carrageenan: hyaluronic acid, chondroitin, chondroitin 4‐sulfate, chondroitin 6‐sulfate, dermatan sulfate, keratan sulfate, agarose, porphyran, μ‐carrageenan and furcellaran.

Investigation of particle dynamics in gels involving casein micelles: A diffusing wave spectroscopy and rheology approach

“…At high temperature (above 50 1C), the k-carrageenan molecules exist in an unordered form, but as they cool, they first adopt a helical conformation and then form gels. Experimental evidence shows that the ordered conformation of kcarrageenan in solution and gels is that of a double helix formation (Rees, Steele, & Williamson, 1969). k-carrageenan aggregates consist of ''bundles'' of aligned helices (Piculell, Hakansson, & Nilsson, 1987).…”

Activity coefficients of counterions and conformation in kappa‐carrageenan systems

“…that (2) In this work, the dependence of the activity coefficient y and of the conductance coefficient f are discussed as a function of temperature and of the nature of the counterions, assuming that the value o f f is independent of the counterions in the same conformation. exchanger.…”

Formation and Viscoelastic Properties of Cellulose Gels in Aqueous Alkali

“…We suspect this tran sition occurs from the fact that when the cellulose-aqueous NaOH solution system is heated the radius of gyration of the chain decreases abruptly at 40°C. For the aggregated structure in the gel of naturally occurring polysaccharides, several models have been proposed, e.g., the egg-box type for polyelectrolytes such as poly-L-guluronate (alginate) and its optical iso mer, in water containing alkali metal ions (8), and the double helical form for carrageenan and agarose in water (9). However, with respect to cel lulose gel, cellulose chains must not aggregate in any regular form, such as egg-box or helix, because cellulose chains in the solution or in the solid state have never been reported to be conformed in helical strands.…”