SELECTIVE COUNTERION BINDING TO LINEAR POLYELECTROLYTES IN AQUEOUS-SOLUTIONS

The selective counterion condensation induced by a charged cylindrical polyelectrolyte in aqueous solution containing different mono- and di-valent ions was investigated by means of the numerical solutions of the non linearized cylindrical Poisson-Boltzmann equation. The critical charge fraction f(c), above which the condensation predicted by the Manning theory occurs, has been evaluated in some selected cases of relevance in biopolyelectrolyte systems and a selective binding of counterions has been shown to occur. To take into account the effects of different types of mono- and di-valent salts, an extension of the Manning theory recently proposed by Paoletti et al. and based on Gibbs free energy minimization, was considered. Discrepancies between the charge distribution of bound ions calculated by means of numerical solutions of Poisson-Boltzmann equation and those predicted by the extended Manning theory, were found.