Structure and Gelling Properties of Carrageenan Family Studied by Scattering Techniques

Abstract

A series of regio-selectively sulfated carrageenans was prepared by sulfation and subsequent desulfation at specific positions. Prepared carrageenans were molecularly characterized by means of static/dynamic light scattering and small-angle X-ray scattering. The results have indicated that the shape of overall carrageenan chains depends on the position of sulfate groups as represented by a rod-like molecule, a random coil or a compact particle-like molecule, although the local chain behaves rod-like in any carrageenan. When a carrageenan has a rod-like shape as a whole, its aqueous solution forms gel at lower temperatures. The sulfate groups on C2 of (1→3)- linked β-D-galactose break a helical conformation, while the sulfate groups on C4 of (1→3)- linked β-D-galactose stabilize it as confirmed by the model energy calculation for hypothetical carrageenan single or double helices. The helical conformation of a certain length seems to be prerequisite for gelation.