Bile acids covalently bound to polysaccharides 2. Dextran with pendant cholic acid groups

摘要

New anionic amphiphilic polymers were synthesized by chemical modification of dextran' with cholic acid derivatives. The hydroxyl groups of dextran were reacted with the free carboxyl group of 3-(succinoyloxy)cholic acid trichloroethyl ester in the presence of N, N-dicyclohexylcarbodiimide as a coupling agent and 4-(N, N-dimethyla-mino)pyridine as a catalyst. The trichloroethyl ester groups of the pendant cholic acid moieties were transformed to free carboxylic groups through a selective elimination reaction, which did not affect the other ester groups in the molecule. The degree of substitution of dextran was influenced by the molar ratio of the reagents and the solvent used. The steady-state fluorescence measurements in the presence of N-phenyl-1-naphthylamine indicated a strong aggregation of synthesized polymers due to hydrophobic interactions between the steroid side groups. Viscometric measurements of the polymers in COONa form showed a preponderance of hydrophobic interactions towards electrostatic repulsion between pendant groups. Electrostatic repulsion between carboxylate groups has an increasing contribution to the conformation of the polymer chains with increasing degree of substitution, but it never overcomes the hydrophobic interactions.