Redox Polyelectrolyte Monolayers

A large number of examples of redox polyelectrolyte monolayers have been reported [42[. Anson described the adsorption of poly(acrylic acid) onto glassy carbon with electrostatic binding of Ru(NH3)6 and Co(NH3)6 ions from solution [43]. Finklea [44] adsorbed poly(4-vinyl-I-methyl-pyridinium methylsulfate) on self-assembled mercapto-undecanoic self-assembled monolayer (SAM) on gold electrodes to 

In both cases the top layer of these layered polyelectrolyte films contains many ion sites that can bind redox ions by ion exchange vdth the electrolyte solution. Homo polypeptides such as poly(L-lysine) and poly(L-glutamic add) have been employed to form layered polyelectrolyte films with Fe(CN)6 electrostatically adsorbed onto ammonium sites in poly(lysine) [45]. Modified electrodes with polyelectrolytes mono-layers have also been deposited using the Langmuir-Blodgett technique [46-48]. 

Recently, pH-responsive redox bmshes have been described by Katz and Minko [61], It has been shown that the electrochemical response of PVP-Os grafted to ITO completely disappears when going from pH 4 to pH 6, which was attributed to film collapse due to deprotonation of pyridine units. The same effect was not observed for randomly adsorbed polyelectrolytes. 

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Another consequence of the anionic nature of the DNA films is the restricted transfer of ions across the monolayer-solution interface. The resulting interfacial Donnan potentials are expected to shift the apparent formal potentials of redox molecules bound within the film, by analogy to polyelectrolyte film coatings.In the general case of an -electron, m-proton redox couple (Equation 5-3), the apparent formal potential shifts as a function of both pH and cation concentration according to 5-4. 

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