The Coupling Between Electron Transfer, Deformation and Binding during the Redox Switching of Electroactive Macromolecules. A Simple Model

D. POSADAS; M. I. FLORIT; W. A. MARMISOLLÉ; G. YBARRA

Sevilla, España

Conferencia; 59th Annual Meeting of the International Society of Electrochemistry; 2008

International Society of Electrochemistry

Many electroactive macromolecules, both natural and synthetic, show a coupling between the redox potential, its state of tension (deformation) and its state of binding, that is the extension in which a determined species (usually protons in electroactive proteins) binds to a particular site in the macromolecule. This phenomenon manifests itself as a change in the redox potential with the concentration of the binding species in solu tion or as a change in the concentration of the binding species in solution as the macromolecule is oxidized or reduced. To describe these systems we employ a very simple statistical mechanic model in which the polymer chains are composed of two classes of segments: short and long ones. A short segment contains a reduced redox center that when it is oxidized converts the segment into a long one. Thus, oxidizing the polymer results in a different state of tension of the chain. Moreover both kinds of segments are capable of binding a species present in solution in a way that also changes the state of tension of the polymer. The solution of the model provide an expression for the potential that shows how it depends on the fraction of oxidized centers, the fraction of long segments and the fraction of bound species on each kind of segments. Calculations based on this model provide a simple insight on how these systems work. The change of the redox potential of an electroactive polymer, such as the Os bipyridile polyvinylpyridile, with the pH provides an example that qualitatively agrees with the model. Another example is the pH change produced during the redox titration of human hemoglobine.