Associative pH sensitive system

New associative pH sensitive systems composed of a modified dextran bearing 2-carboxycyclohexyl carboxyl groups and neutral (p betaCD) or positively charged (p betaCDN(+))beta-cyclodextrin-co-epichlorhydrin copolymers have been synthesized and their properties were investigated as a function of pH by phase diagrams and viscosimetry. The affinity between the CD cavities and the hydrophobic guests (2-carboxycyclohexyl carboxyl groups) has been studied as a function of pH. The system with the neutral p betaCD shows a pH dependent behavior due to the lowest affinity of the guest at pH above 5 for the cavity. Associative phase separation is produced at low pH whereas soluble complexes occur at higher pH. The opposite trend is observed with the system containing the cationic p betaCDN(+). This behavior is due to the combination of electrostatic and inclusion complex interactions in this system. Addition of salt, by screening the electrostatic interactions, also strongly influences the response of the system.