STRUCTURE AND CONFORMATION OF ACETAN POLYSACCHARIDE

Acetan is an anionic bacterial polysaccharide. The chemical repeat uni t consists of a cellobiose unit solubilised by attachment of a charged pentasaccharide sidechain to one of the glucose residues. The repeat unit contains two sites of acetylation. H-1 and C-13 NMR studies, coup led with both basic-methylation and mild-methylation studies, have sho wn that acetylation occurs at C6 on the (1,2)D-Man and the (1,34)D-Glc residues. A variety of techniques including NMR, optical rotation, ci rcular dichroism and DSC show evidence for a thermoreversible conforma tional order (helix)-disorder (coil) transition for acetan in aqueous solution. The studies suggest that acetylation of the backbone does no t prevent helix formation.