The coupling among electron transfer, deformation, screening and binding in electrochemically active macromolecules

Experimental data are presented demonstrating that electrochemically active macromolecules show a coupling among electron transfer, deformation, screening and binding. The work includes dependence of the redox potential of synthetic and natural electrochemically active polymers on the electrolyte pH (electron transfer-binding coupling), the changes in volume during the redox switching of synthetic electrochemically active polymers (deformation-electron transfer coupling) and the changes in the macromolecular conformation during the acid–base titration of polyelectrolytes and proteins (deformation-binding coupling). A simple equilibrium statistical thermodynamic model is presented that allows explaining these couplings effects. The model is based on the assumption that a macromolecule is composed of segments of different length that may bind species present in the external solution and that also contain redox centers that may be oxidized and reduced. The partition function of the system is obtained, and from it the expressions for the redox potentials, the total length and the chemical potential of the bound species are obtained. Simple calculations shows that the model satisfactorily explains the qualitative behavior of the experimental results.