Donnan Potential Caused by Polyelectrolyte Monolayers

The Donnan potential is successfully isolated from ion pair potential on a ferrocene labelled polyelectrolyte (DNA) monolayer. The isolated Donnan potential shifts negatively upon the increase of NaClO4 concentration with a slope of -58.8 mV/decade. With the salt concentration grow up to 1 M, the stretched DNA chains in low salt concentration are found experienced a gradual conformation relaxing process. At salt concentrations higher than 2 M, Donnan breakdown occurs where only the ion pair effect modulates the apparent potential. The apparent formal potential also shows strong dependence on solution pH, which reveals that the charge density in the polyelectrolyte monolayer plays an important role on the establishment of Donnan equilibrium.