(i) Electrostatic adsorption of Cyt c at mercaptoundecanoic acid (MUA) modified gold electrodes:

The values of surface concentration Γ, rate constant k_s and formal potential E^o were chosen according to the literature [1] and reflect a quasi-reversible electron exchange of a monolayer.

(ii)   Coverage of the SAM with a poly-scopoletin layer: 

The electropolymerization takes place at the MUA coated gold electrode at potentials between 0 V and 1 V versus Ag/AgCl in presence of the water-soluble scopoletin (7-hydroxy-6-methoxycoumarin). The polymer growth is self-limited by the isolating character of the polymer film. Furthermore, the polymer film is thin, highly hydrophilic and non-conducting. Incubation of the MUA-poly-scopoletin covered gold electrode in a Cyt c containing solution leads to electroactive surface concentrations below a complete monolayer. The values for k_s and the peak separation indicate that the Cyt c is converted at the MUA layer.

(iii) Enhancement of Cyt c adsorption by SDS:

The electrostatic binding of Cyt c to the poly-Scopoletin modified Au-Electrodes (with Q = 0.37 ± 0.02 mC) was enhanced by loading the weakly positive charged polymer layer with  negatively charged Sodium Dodecyl Sulfate (SDS). Characterization of this Cyt c coated electrodes showed a formal potential of (-13.48 ± 11) mV vs. Ag/AgCl with a peak separation of 36 mV and a heterogeneous electron transfer constant of 9.75 ± 2 s^-1.

The value of the formal potential is in agreement with that for native Cyt c, whilst denaturation would shift the potential into cathodic direction [2]. The electroactive surface concentration of Cyt c is (6.73 ± 2.96) pmol cm^-2 which is almost 2 times higher than the value of electroactive protein on MUA modified electrodes. These values suggest the participation of more than one layer of Cyt c in the electrode process.

Conclusions

Coverage of the MUA-modified gold electrode by electropolymerized scopoletin leads to an effective architecture for the direct electron transfer of Cyt c. This system will be applied for surface imprinting and sensor development.

References

[1]        B. Ge, F. Lisdat “Superoxide sensor based on cytochrome c immobilized on mixed-thiol SAM with a new calibration method” Analytica Chimica Acta 454 (2002) 53-64

[2]        A. V. Krylov, W. Pfeil, F. Lisdat “Denaturation and renaturation of cytochrome c immobilized on gold electrodes in DMSO-containing buffers” Journal of Electroanalytical Chemistry 569 (2004) 225-231

The authors gratefully acknowledge the financial support of BMBF (0311993) Germany. This work is a part of UniCat, the Cluster of Excellence in the field of catalysis coordinated by TU Berlin and financially supported by Deutsche Forschunsgemeinschaft (DFG) within the framework of the German Excellence Initiative (EXC 314).

1. POSTER: Electrochemical behaviour of Cytochrome c immobilised in a poly-scopoletin layer, PDF document, version 1.2, 0MB

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