Predicting the maximum oxidation potential shift in redox-active pH-responsive molecules in their electrostatic interaction with substrates

Potentiometric and electrochemical studies have been carried out in THF-H2O (60:40 v/v) and H2O on several ferrocene-containing pH-responsive molecules and the acidity constants of the reduced species (K-m), the 'oxidised' species (K-m(n)) and the maximum oxidation potential shift due to the binding process of L with protons (Delta E) have been determined. From these values, and Delta E data in MeCN, MeCN-H2O (80:20 v/v), THF-H2O (80:20 v/v) and H2O, an empirical equation based on a Coulomb charge model, is obtained which accounts for the maximum oxidation potential shift as a function of the charge of the oxidised electroactive framework, the charge of the substrate, the number of electrons involved in the electrochemical process, the number of redox-active units, the distance between the redox-active groups and the substrate and the macroscopic relative permittivity of the medium.