Influence of the hydrophobic groups and the nature of counterions on ion-binding in aliphatic ionene solutions

Transport and binding capabilities in aqueous solutions of 3,3-, 6,6-, and 6,9-ionene fluorides and bromides at 25 °C were explored through the experimentally determined values for transport numbers of counterions and polyion constituents, along with the data for electrical conductivity in these solutions. Within the association theory, the fractions of free counterions and the effective linear charge densities of polyions were calculated. Experimental data were compared with the predictions of the Manning theory of polyelectrolyte solutions. It was determined that binding of the counterions to the polyion critically depends (i) on charge density of the polyion and (ii) on the chemical nature of the counterion in question. The effects of the charge density are the strongest in solutions of ionene bromides. Differences in the behavior of solutions of ionene fluorides and bromides are the consequence of different hydration capabilities of these ions. The effective linear charge density was found to be much lower than the one predicted from structural parameters of ionenes. The study addresses questions important to the biomedical field, in particular that of binding of ligands to charged macromolecules.

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► Transport properties in the solutions studied have weak concentration dependence.
► The nature of the counterions has a strong influence on the behavior of the solutions.
► The charge density of the polyion is drastically reduced due to counterion binding.
► The ion specific effects are determining the effective charge density of the polyion.