Dextrin cyclic

Cyclodoxtrins (cycloamyloses, cycloglucans after their discoverer also Schardinger dextrins). Cyclic dextrins are formed on degradation of starch by Bacillus macerans or B. circulans under the action of cyclodextrin glycosyltransferase. The C. consist of 6,7,... 

Note. The cyclic oligosaccharides arising from enzymic transglycosylation of starch have been referred to as Schardinger dextrins. These names (and those of the cyclohexaamylose type) are not recommended, but the abbreviation CD is tolerated. 

Pacsu4 5 has suggested a structure for starch involving a small number of non-cyclic hemiacetal linkages, the number being presumably sufficient to account for the number of endgroups determined by the methylation method. Halsall, Hirst and Jones6 have commented on this structure, however, and have shown it to be incompatible with the results of periodate-oxidation studies. In addition, these authors pointed out that it would be difficult to explain enzymic hydrolysis and dextrin formation on the basis of such a structure. 

Although Schardinger did not propose a structure for his crystalline dextrins, he made several observations that can now be attributed to their cyclic structure. For example, he discovered their ability to engage in complex-formation "With various substances, the crystalline dextrins form loose complexes which, like those produced with alcohol, ether, and chloroform, are indeed partly decomposed by water, while the iodine complexes are more stable toward water. He also found, as previously mentioned, that the crystalline dextrins were nonreducing toward copper salts and nonfermentable by yeast. This last observation he considered was "... the most essential thing that I was able to mention concerning the formation of crystalline dextrins by microbes. Both of these observations can be explained by the lack of a chain termination. 

Schardinger brought his work on the crystalline dextrins to a close in 1911. He ended his work with the statement I realise that still very many questions remain unsolved. The answer to these I must leave to another, who, owing to more favorable external conditions, can deal with the subject more intensively. It was to be another twenty-five years before the cyclic nature of Schardinger s dextrins was recognized. 

Freudenberg later concurred with French s results, after studying the X-ray measurements of Borchert and also his and Cramer s optical rotation data. He also proposed that the gamma dextrin consisted of eight d-glucosyl residues joined by a linkages in a cyclic structure, as in the case of the alpha and beta dextrins. 

Finally, French and Mclntire studied the periodate oxidation of alpha, beta, and gamma dextrin, found that neither formic acid nor formaldehyde was produced, and concluded that all three have a cyclic structure, as earlier proposed by Freudenberg. Also supported was the gamma dextrin structure proposed by Freudenberg, on the basis of acid... 

Figure 17.7. Cyclic dextrin from amylopectin by branching enzyme.

Takata, H., Ohdan, K., Takaha, T., Kuriki, T., and Okada, S. 2003. Properties of branching enzyme from hyperthermophihc bacterium, Aquifex aeolicus, and its potential for production of highly-branched cyclic dextrin. J. Appl. Glycosci., 50, 15-20. 

Fig. 18.7a-e. Cyclic and chain-like hydrogen-bonding patterns O-H- -O observed in a a-cyclo-dextrin-6H20, form I b a-cyclodextrin 6 H20, form II , intramolecular c,d,e a-cyclodextrin-7.57 H20. Infinite homodromic chains are marked chain, and cycles are indicated by round arrows with one (homodromic) and two (antidromic) heads. Only atoms of water molecules and of hydroxyl groups are drawn, the former denoted by W and the latter by the nomenclature described in Fig. 18.1. Each of the pictures a to e shows only a section of the respective crystal structure [78, 109, 575]...

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