13C-n.m.r. study of the conformation of helical complexes of amylodextrin and of amylose in solution

✍ Scribed by Jay-lin Jane; John F. Robyt; Dee-Hua Huang

• Publisher: Elsevier Science
• Year: 1985
• Tongue: English
• Weight: 977 KB
• Volume: 140
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(85)85046-1

✦ Synopsis

Amylose (average d.p. 1000) and amylodextrin (average d.p. 25) have identical 13C-n.m.r. spectra, except for some minor signals from the small amount of (u-1+6 branch linkages present in amylodextrin. Amylodextrin can be obtained as stable solutions in much higher concentrations than amylose and so requires only 11100th as many scans to obtain a spectrum comparable to that of amylose. 13C-N.m.r. spectroscopy has been used to study the formation of amylodextrin complexes with organic complexing agents in aqueous solution. A control study using dextran, which does not form helical complexes, showed that, when complexing agents are added, the signals from all of the carbons show a slight downfield shift due to a general solvent effect. In the case of amylodextrin, the addition of increasing concentrations of complexing agent also produced a downfield shift of the signals of all the carbons, but there was a greater shift of the signals for carbons 1 and 4 than for carbons 2,3, and 6, indicating that something more than a solvent effect was occurring. The cycloamyloses (cyclic a-1-4 linked D-glucose oligosaccharides which may be considered as model for an amylose helix) in water have chemical shifts for carbons 1 and 4 that are comparable to those shown by the amylodextrin complexes. It is thus proposed that the formation of a helical complex with amylodextrin results in a change in the conformation of the glycosidic linkage, which is reflected by greater downfield shifts of the signals for carbons 1 and 4, relative to those for carbons 2,3, and 6. It was observed that differences in the ratio of the downfield shifts of C-l and C-4 of the different amylodextrin complexes indicate differences in the degree of compactness of the helical structures. A comparison of the 13C chemical shifts of methyl a-D-glucoside and methyl cr-mal-