Selective Adsorption of Dibenzothiophene Sulfone by an Imprinted and Stimuli-Responsive Chitosan Hydrogel

A DBTS-imprinted chitosan hydrogel (IHDBTS) was synthesized by cross-linking of chitosan with glutaraldehyde in the presence of dibenzothiophene sulfone (DBTS) as the template. An increase in cross-linker induced a major adsorption of DBTS until a plateau was reached at a ratio of 2.0 mol of glutaraldehyde per mole of glucosamine. The IHDBTS was found to be stimuli-responsive with temperature and showed a LCST between the swollen and the collapsed phases at 50 °C. The major specific adsorption of DBTS by the hydrogel occurred at such transition and was due to the stronger ligand−gel interactions as demonstrated by the fluorometric studies where DBTS served as ligand and fluorescent probe. The fluorescence results showed that the DBTS presented a hydrophobic environment with predominance of intermolecular DBTS complexes (dimers) in the presence of the IHDBTS. In contrast, the soluble chitosan promoted a higher hydrophobicity around DBTS and also favored the presence of monomeric DBTS as temperature increased. The steady-state fluorometry was found to be a useful technique to identify the molecular recognition conformation based on the ligands and not the polymers, to reveal the general interaction between ligands and MIP, and to give information concerning the nature of the environment around the ligands in the presence of MIPs.