Synthesis of a fluorescent chitosan derivative and its application for the study of chitosan-mucin interactions

Fluorescein isothiocyanate-labeled chitosan was synthesized as a macromolecular fluorophore to investigate the molecular mechanism of interactions between chitosan and mucin by the fluorescence polarization method. The percent change in polarization upon chitosan-mucin association was measured as a function of the molecular weight of chitosan, and the pH and ionic strength of the medium. Dextran sulfate and albumin were used as positive and negative controls of polyelectrolyte complexation, respectively. The degree of polarization increased significantly with increasing mucin/chitosan (molecular weight, 750 000 daltons) molar ratio in 0.10 M acetic acid to suggest that there was multivalent binding between the two polymers. In contrast, only one dextran sulfate molecule was able to bind with the chitosan molecule. Albumin, having a net positive charge at a pH of 2.9, did not bind with chitosan. There was a possibility of multivalent association between high molecular weight chitosan and mucin as compared to univalent association with low molecular weight chitosan. The results of pH and ionic strength studies suggest that, in addition to electrostatic interactions between D-glucosamine residue of chitosan and the sialic acid residue of mucin, there could be other attractive forces involved in chitosan-mucin binding such as hydrogen bonding and/or hydrophobic interaction. (C) 1999 Elsevier Science Ltd. All rights reserved.