Acidic and Ester Polysaccharides

A whole class of fascinating, acidic and ester polysaccharides of biological significance awaits exploration by x-ray diffraction. Typical of these compounds are the pneumococcal polysaccharides, whose structures are highly specific, albeit they contain a wide variety of carbohydrate moieties, of which D-glucuronic acid is a common one. Occasionally, a phosphoric ester link between moieties is an integral part of the complex, repeating 

It is clear that the quality of the fiber diagrams so far achieved for sodium pectate leaves much to be desired, and that x-ray study of this important polysaccharide should be conducted on well-characterized samples. A single-crystal study on a model oligosaccharide would be most helpful. 

X-Ray Spacing8,° in of Powders of the Two Major Components in Alginic Acid in an Atmosphere having 98 per cent Relative Humidity, and the Prominent Spacings of Cellulose (All from Himanthalia elongata ) 

The x-ray structure of oriented fibers from the carrageenan fractions, k and X, was examined by Bayley over a decade ago. The fractions differ in the sulfate substitution. The level of order in his stretched fibers appears to have been of the paracrystalline type, but an ordered conformation along the backbone was clearly present. He drew the important conclusion that the x-ray pattern from the whole carrageenan does not represent the sum of those from the separate k and X components, and that, therefore, the two components must exist in a unique structural relationship with respect to one another. Only continued, intensive efforts on the native and pure components will permit a full appreciation of this complex structure. The same comment applies to all of the acidic and ester polysaccharide studies mentioned in this Section. A review of chemical work on carrageenans mentions that Bayley interpreted his diagrams in terms of incorrect structures for both components. 

Pyrolysis Products from Starch-like Materials. 496 

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