ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The 1H NMR parameters (chemical shift and coupling constant) of ß(1→4)-linked polysaccharides xylan, cellulose, and chitin are compared in solutions of aprotic solvents. The following NMR parameters are analyzed: (1) Chemical shifts of labile protons, (2) their variation with temperature, (3) coupling constants through the H—C—O—H moiety - for monomers, dimers, and the corresponding polymers. It is observed that the OH-3 hydroxyl group for cellulose and chitin oligomers and polymers present a particular behaviour, which is in agreement with the existence of an intramolecular hydrogen bond between this hydroxyl of one monomeric unit, and the heterocyclic oxygen atom of the adjacent monomeric unit. This kind of intramolecular hydrogen bond is not observed in case of the xylan series. It can be concluded that substitution of an equatorial hydrogen atom at the C-5 position of the sugar ring by a CH2OH group - when passing from xylan to cellulose and chitin - induces a rotation restriction around the glycosidic bond. This places the OH-3 hydroxyl group in a favourable position to be hydrogen-bonded. The consequent implication on the respective conformations of the chains in solution is discussed.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1988.021890115
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