Preparation and characterisation of fluorescent chitosans using 9-anthraldehyde as fluorophore

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 H-1 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. (C) 2001 Elsevier Science Ltd. All rights reserved.