Homopolysaccharides conformations

Unperturbed dimensions are calculated for several 1,3- and 1,4-linked homopolysaccharides. The characteristic ratio depends strongly on the bonding geometry and on the degree of rotational freedom about the glycosidic bonds. It appears that unperturbed dimensions can be predicted qualitatively from a knowledge of the regular conformations of the polysaccharide. 

Cellulose is a linear homopolysaccharides which consists of glucose (D-gluco-pyranose) linked by glycosidic p (1-4). In this connection, the hydroxyl at C-1 (anomeric carbon) of one molecule of glucose is in the p conformation and reacts with the hydroxyl at C-4 of the second molecule. 

Chitin (Figure 5.5C) is an abundant natural polysaccharide found in the cell walls of fungi, the exoskeletons of insects and arthropods, the radulae of molluscs and the beaks and internal shells of cephalopods [213,214]. Chitin is a linear homopolysaccharide consisting of (1 4)-linked units of 2-acetamido-2-deoxy-(3-deoxy-D-glucopyranose (A Units) with an extended chain conformation. Chitosan (Figure 5.5D) is derived... 

The majority of native starches are mixtures of amylose and amylopectin, two homopolysaccharides composed of a-D-gluco-pyranose molecules in Cj conformation. Amylose and amylopectin usually occur in a weight ratio of 1 3. In some varieties of cereals (maize, barley and rice) and other plants (potatoes), either amylose (starches of high amylose content or amylostarches) or amylopectin (starches high in amylopectin or waxy starches) predominate. 

For the configuration-conformational properties of simple carbohydrates, as well as their reactivities, comprehensive treatises should be consulted (Pigman and Horton, 1972). It has to be mentioned on closing, that recent achievements in macromolecular science have established the ways to the synthesis of linear homopolysaccharides and copolysaccharides (normally by cationic polymerization) of different suitably protected anhydrosugars (Schuerch, 1981). These syntheses open the route to the availability for our studies of a variety of tailor made carbohydrate polymers. A few synthetic polysaccharides have in fact already been used to investigate immunological and allergic reactions in experimental animals and the interaction of plant lectins with carbohydrates (Schuerch, 1981). 

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