Physicochemical study of modified dextrans with a β-cyclodextrin polymer

Abstract

The aim of this work was the design of a pH-sensitive system consisting of an amphiphilic polymer and a β-cyclodextrin coepichlorhydrin water-soluble polymer (pβCD/EP). Different modified dextrans were synthesized from reaction of dextran (M _w =40,000) with phthalic anhydride, 2-phenylglutaric anhydride and 1,2-cyclohexane dicarboxylic anhydride with grafting ratio around 2%. The viscometric study of modified dextrans with pendant cyclohexane carboxylic acid groups mixed with pβCD/EP was performed at pH 1 and 7 and showed a small increase of reduced viscosity compared to mixtures of dextran and pβCD/EP. The phase diagram shows association phase-separation at low pH, whereas monophasic mixtures were obtained at pH higher than the pK _a . Furthermore this phase-separation is reversible according to the pH. The use of 8-anilinonaphtalene-1-sulfonic acid, as a fluorescent probe, allowed us to determine the inclusion constants of the modified dextrans. Complexation constants higher by 1 order of magnitude for the most hydrophobically modified dextrans were obtained at pH 2.5 compared to pH 7.