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

Counter-ion binding and mobility in the presence of hydrophobic polyions – combining molecular dynamics simulations and NMR

“…ii) Experimental 22,23 and MD simulation data concerning the strength of counter-ion binding to the ionene oligoion arrive at the following sequence for the halide ions: F − (weakest binding) < Cl − < Br − < I − (strongest binding). [26][27][28][29] The situation recently encountered with the hydrophobic 12, 12-ionenes seems to differ from the above.…”

“…17,[26][27][28][29] The experimental results mentioned above indicate strong deviations from theoretical predictions based on the classical theories of polyelectrolyte solutions. 16,18,19,21,22,25 We mention now in more detail the enthalpies of dilution and mixing, notice that both quantities provide similar physical information, but they carry an opposite sign. For example, the enthalpy of dilution ∆H dil is on the basis of the electrostatic theory 30 expected to be exothermic but experiments prove that ∆H dil can also be positive.…”

“…17): ∆H m is mostly negative and decreases in the order F − > Cl − > Br − > I − . Similarly to the above sequence, the counter-ion trends concerning the strength of counter-ion binding to the ionene oligoion, observed in experimental 22,23 and MD simulation data, 17,[26][27][28][29] were: F − (weakest binding) < Cl − < Br − < I − (strongest binding). Very interestingly, the calorimetric (∆H m and ∆H dil ) data for 12, 12-ionenes, presented in our recent study 21 did not follow the above trends.…”

“…For the ionene solutions neutralized by a single counter-ion species the fractions of "free" counter-ions were measured by Rodič et al 22 They applied a combination of conductivity and transport number measurements to determine this quantity in solutions of 3, 3-, 6, 6-and 6, 9-ionenes. The solutions with F − and Br − counter-ions were probed at 298 K. It was found that binding of counter-ions to the polyion, in addition to the charge density of the latter, depends also on the chemical nature of the counter-ion in question.…”

“…Experimental studies have been performed for x, y equal to 3,3-, 4,5-, 6,6-, and 6,9-to 12,12-ionenes, that is for increasingly more hydrophobic polyelectrolytes. [16][17][18][19][20][21][22][23] Among physico-chemical properties we measured enthalpies of dilution and mixing, osmotic coefficients, dielectric relaxation, conductivities and transport numbers. These solutions have also been examined using NMR, X-ray and neutron scattering methods.…”