POLYSACCHARIDES AS AMPHIPHILES

Polysaccharide chains are usually considered to be highly hydrophilic, since they contain no obvious apolar moieties but a large number of hydroxyl groups. However, it is possible even for these chains to display hydrophobic character, arising out of stereochemical constraints on the chain. We present experimental and theoretical evidence which show that the alpha-1a,4e-D-glucopyranose chains, namely linear dextrin, display amphiphilic properties, since all the hydroxyl groups are disposed on one side or face of the chain and the hydrogens disposed on the other. As a result, dextrin solubilizes lipophilic compounds in water, retards organic reactions that are hydrophobically accelerated in water, destabilizes globular protein chains, and binds to a fluorescent probe dye and enhances its emission. In contrast, the beta-1,4-linked glucoside cellulose and the alpha-1,6-linked dextran chains exhibit only hydrophilicity. Several other oligosaccharide chains are also predicted to display amphiphilic properties. This is expected to be relevant to intermolecular recognition on cell surfaces, lectin-sugar binding, antigen-antibody interactions, and the like.