INTRINSIC BINDING EFFECTS IN MIXED COUNTERIONIC POLYELECTROLYTE SYSTEMS - EXTENSION OF CONDENSATION THEORY AND COMPARISON WITH VOLTAMMETRICDATA

Voltammetric speciation data for the potassium/zinc/polymethacrylate s ystem, recently obtained for various charge densities of the polyelect rolyte (Diaz-Cruz et al., Anal. Chim. Acta, 264 (1992) 163) and for di fferent concentrations of monovalent counterions (van den Hoop and van Leeuwen, Anal. Chim. Acta, 273 (1993) 275), are compared with theoret ical predictions computed according to a new thermodynamic model devel oped by Paoletti et al. (Biophys. Chem., 41 (1991) 73) and recently ex tended by Benegas and Paoletti (in preparation). The model allows: (i) the simultaneous condensation of both monovalent and divalent counter ions and (ii) can account for a certain specific affinity of the polye lectrolyte for one type of the counterion over the other. For various charge densities of the polyelectrolyte, experimentally obtained speci ation data for the K/Zn/PMA system agree well with theoretical predict ions by considering an extra reduced molar affinity energy of -4RT for the Zn2+ polyelectrolyte binding. The agreement between experimental and theoretical values for the distribution of Zn2+ ions over the free and bound state becomes less perfect for relatively high concentratio ns of monovalent counterions.