Schardinger dextrins, structure

Prior to 1939, however, it was not known whether the cyclodextrins were products of the synthetic metabolism of Bacillus macerans, and therefore, perhaps, quite different from the components of starch, or whether they were formed by a single enzyme and therefore closely related to the starch structure. Then, Tilden and Hudson announced the discovery of a cell-free enzyme preparation from cultures of Bacillus macerans which had the ability to convert starch into the Schardinger dextrins without the production of maltose, glucose, or any other reducing sugars. They thus concluded that the Schardinger dextrins were either the true components of starch or closely related to such true components. 

While the enzymic approach must be refined and rationalized, present evidence is completely in accord with the concept of linear and branched structures for the two starch components. The theory has been advanced that the individual alpha and beta Schardinger dextrins originate from specific starch fractions, but this appears to be untenable. No satisfactory mechanism has been proposed to account for the production of the several crystalline dextrins. 

A second major structural method applied to the Schardinger dextrins was methylation analysis. This method was fraught with experimental difficulties, and in a few cases it had led to rather embarrassing errors in assigning of structure. ... 

Fia. 28.—Crystal structure of the a-dextrin-iodine complex formed in the absence of iodide. The outlines of the Schardinger dextrin molecules have been chosen on the basis of possible packing arrangements the iodine atoms have been located by x-ray crystal structure analysis. In this tan-brown complex, there is little or no interaction between the iodine molecules such as occurs in the highly-colored blue or black canal compounds. 

Structure and stoichiometry. Cyclodextrins (CyDs) were discovered over 100 years ago by Villiers.23 They are formed by Bacillus macerans, which is a type of bacteria that degrades starch,24 using the enzyme cyclomaltodextrin gluconotransferase, or CyD glycosyl transferase.25 CyDs were often called Schardinger dextrins because they were first popularized by Schardinger.26... 

In this connection the unusual stability of cyclic structures should be mentioned. In the case of carbohydrates this was clearly demonstrated by Swanson and Cori (1948) and by Myrback (1949), who showed that the cyclic Schardinger dextrins are considerably more stable than corresponding open chain polysaccharides. Similarly Consden et al. (1947b) found the cyclopeptide gramicidin S to be unusually... 

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