Polysaccharide shapes and their interactions - some recent advances

Abstract

Recent improvements in methods for the investigation of ordered polysaccharide states in the hydrated environment have led to a number of new insights. For example, the spectroscopic origin of the conformation sensitivity of the optical rotation of polysaccharides now seems to be better understood, opening up wider possibilities for application. Fast reaction kinetic studies with stopped-flow polarimetry have been helpful for determination of the number of strands in the activated complex between ordered and disordered states, and point to two-stranded conformations (most likely double helices) for agarose, kappa-carrageenan and iota-carrageenan, and a single-stranded conformation (most likely with stabilizing interactions between the main chain and side chains) for xanthan. Site-binding of cations can be important for the stability of ordered conformations of polysaccharide polyelectrolytes and the counter-ion selectivity in a number of such instances, seems to be explicable in terms of sandwiching of arrays of cations; this may involve Group II cations between two-fold buckled ribbons in polyguluronate and polygalacturonate (i.e. alginate and pectin respectively), or Group I cations between carrageenan double helices. Ordered states are usually stabilized by interchain interaction, and the pairwise association of chains can often be recognised as a distinct event even when larger aggregates form eventually. © IUPAC