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

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.