STUDIES ON INTERACTION BETWEEN WATER-SOLUBLE POLYMER AND DYES .3. COOPERATIVE BINDING OF PARA-AMINOAZOBENZENE AND ITS DERIVATIVE TO SODIUM POLY(STYRENESULFONATE) STUDIED BY DYNAMIC DIALYSIS

The binding isotherms of p-aminoassobenzene or p-[bis(2-hydroxyethyI)amino]azobenzene to sodium poly(styrenesulfonate) having various degrees of sulfonation have been determined in acetate buffer at pH 5.65 and 25°C using the dynamic dialysis technique. The apparent binding constant, calculated on the basis of free residue of the polymer and free and bound dye, was dependent on the dye concentration in all cases examined. The positive cooperativity in the dye binding was suggested by sigmoidal increases (Fig. 5 and Fig. 8) of the binding density, the molar ratio of bound dye to polymer residue, with rise of free dye concentration and by the concave upward shape of the Scatchard plots (Fig. 7 and Fig. 9). Application of the McGhee and von Hippel's theory to the present results gave the following values : the number of consecutive residues covered by a bound dye, n=75~90; the intrinsic binding constant, K =25~55 in liter/residue mol of the polymer; and the cooperativity parameter, ω=120~300 (Table 2). A speculative model of the interaction was presented in terms of the three parameters. © 1979, The Chemical Society of Japan. All rights reserved.