Zusammenfassung
Two chitosans with widely different chemical composition (fraction
of N-acetylated units (F-A)<0.001 and F-A= 0.59), were degraded by
nitrous acid, to obtain the reactive 2,5-anhydro-D-mannose- (M-)
unit at the new reducing end. The fully N-acetylated and fully N-deacetylated
oligomers were separated by size-exclusion chromatography. Both the
chemical structure and purity were studied by one- and two-dimensional
H-1 and C-13 NMR methods. The fully N-acetylated oligomers were found
to be stable, whereas the N-deacetylated oligomers reacted intermolecularly
by a Schiff base reaction between the 2-amino group on the N-deacetylated
units and the M-units, facilitating the cleavage of the glycosidic
bond next to the M-unit and the formation of 5-hydroxymethylfurfural
(HMF). (C) 2001 Elsevier Science Ltd. All rights reserved.
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