Controlling catalytic activity of a polyion scaffold on an electrode via microemulsion composition

Electrochemical and catalytic properties of vitamin Bit hexacarboxylate-pol ylysine films covalently immobilized onto pyrolytic graphite electrodes wer e controlled by microemulsion composition. Sodium dodecyl sulfate (SDS) in microemulsions and micellar solutions is incorporated to form micelles with in the cationic films. This changes the net film charge from positive, char acteristic of the protonated lysines, to negative, characteristic of SDS mi celles. Micelle formation was supported by voltammetry and quartz crystal m icrobalance results, which also suggested that cationic surfactants do not enter the film. Catalytic turnover rates for the reduction of dibromocycloh exane to cyclohexene mediated by the film in SDS microemulsions were contro lled by the difference between the reduction potential of the reactant and the catalyst E-o' in the film. Thus, reaction rate in these systems is cont rolled by the intrinsic activation free energy. For a given reactant, catal yst E-o', and consequently activation free energy, can be controlled by mic roemulsion composition via interactions of surfactant and salt with the pol ymer network. Fast catalyst turnover was also facilitated by high conductiv ity and low viscosity of the bulk microemulsion.