ELECTROCHEMICAL CHARACTERIZATION OF PROPYL PROPIONYL VIOLOGEN ATTACHED TO A POLYPEPTIDIC MATRIX

An electroactive polymer (PPV-BSA) has been prepared by covalent attachment of propyl propionyl viologen (PPV) to free amine residues of the protein bovine serum albumin (BSA). The electrochemical behaviour of PPV linked to the protein was compared with that of soluble PPV and benzyl viologen (BV). Immobilization of PPV onto BSA altered its electrochemistry and also the optical visible spectrum of its semiquinone radical. We have observed a shift of the peak potentials of PPV-BSA towards more positive values compared to those of the monomer PPV, and a decrease of the stability of the cation radical. Reduced PPV showed the typical visible spectrum of viologens with short side chains, e.g. methyl viologen. In contrast, the visible spectrum of the reduced PPV-BSA was much more similar to that of reduced benzyl viologen, with a shift of the absorbance maximum towards shorter wavelengths and a strong dependence on the degree of grafting. It is proposed that these changes are due to local increases in viologen concentration at the surface of the protein which enhance the interactions amongst reduced viologen molecules. © 1990.