ABSTRACT
Chitosans with chemical composition ranging from a fraction of N-acetylated units (F(A)) of 0.01 to 0.61 were used to prepare fluorescence labelled chitosans by reductive amination with 9-anthraldehyde. Fluorescent chitosans with a low theoretical degree of substitution (DS, 0.001-1%) were prepared, and the actual DS of the products were determined by UV and (1)H NMR spectroscopy. The fluorescence excitation and emission spectra of the chitosan with F(A) of 0.09 and DS 1% showed an excitation maximum at 254 nm and an emission maximum at 413 nm. The intrinsic viscosities ([eta]) of the fluorescent chitosans were compared to those of the original chitosans, showing that the derivatisation procedure lead only to a negligible decrease in [eta]. The conformation of these fluorescent chitosans with very low DS-values is not altered and they can conveniently be directly quantified by UV or fluorescence spectroscopy.
Subject(s)
Anthracenes/chemistry , Chitin/chemical synthesis , Fluorescent Dyes/chemical synthesis , Acetylation , Calibration , Chitin/analogs & derivatives , Chitin/chemistry , Chitosan , Fluorescent Dyes/chemistry , Magnetic Resonance Spectroscopy , Spectrometry, Fluorescence , Spectrophotometry, Ultraviolet , Spectrum Analysis , ViscosityABSTRACT
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 1H and 13C 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).
Subject(s)
Chitin/chemistry , Nitrous Acid/chemistry , Oligosaccharides/chemistry , Acetylation , Carbohydrate Sequence , Chitin/analogs & derivatives , Chitin/metabolism , Chitosan , Chromatography/methods , Magnetic Resonance Spectroscopy , Molecular Sequence Data , Molecular Structure , Oligosaccharides/metabolismABSTRACT
Electrostatic properties of three chitosans with fractions of N-acetylated units (F(A)) of 0.01, 0.13 and 0.49 were examined by electrophoretic light-scattering technique (ELS) and (1)H NMR spectroscopy. From the dependency of mean electrophoretic mobilities on pH, the pK(a) values were calculated. Despite their large differences in chemical composition, all chitosans had similar pK(a) values of 6.5-6.6. All chitosans also showed the same polyelectrolyte behavior when apparent pK(a) values were calculated according to Katchalsky and plotted as a function of the degree of ionization alpha. The intrinsic pK(a) values (pK(0)) extrapolated to zero charge were about 9. The results derived from an independent (1)H NMR study of the same chitosan samples showed no effect of F(A) on titration behavior of chitosan, confirming the results obtained by ELS.
