Chain conformations in the sol–gel transitions for poly-saccharide systems, and their characterisation by spectroscopic methods

Abstract

The sol-gel transition has been studied for two polysaccharide systems, which form gels by the noncovalent association of chain segments in ordered conformations, but which differ in the geometry of these conformations. For ι-carrageenan they are double helices, the formation and melting of which is monitored by [¹³C]-n.m.r. and by optical rotation. For alginate, the associations involve the site-binding of Ca²⁺ ions in an egg-box or sandwich-like geometry, the formation of which is monitored and related to similar structures in solid films using circular dichroism spectroscopy. Despite the low concentration of dispersed polysaccharide (of the order of 1 %), each gel network is a very highly associated structure in which almost all sequences of sugar residues having the appropriate covalent structure to permit the ordered binding, are actually involved in binding to other chains.