Figure 5: Galvanostatic or Cu(II)-induced generation of tyrosyl radicals in peptide film.
From: Tyrosine-mediated two-dimensional peptide assembly and its role as a bio-inspired catalytic scaffold
(a) Cyclic voltammetry (CV) polarization curve for the YYACAYY film on FTO glass in 0.1 M NaCl electrolyte. Electrochemical oxidation of tyrosine (Tyr→Tyr·) resulted in a broad peak (*), with the maximum current at 0.9 V (versus NHE). (b) The current density profiles of the YYACAYY peptide film (red) and tyrosine monomer (blue) deposited in FTO substrates during bulk electrolysis at 0.9 V in 0.1 M NaCl containing 50 mM pyrrole. After 30 min of electrolysis, remarkably different kinetics in polypyrrole formation could be confirmed by the colour change on the substrate (inset). (c) Photograph of the polypyrrole/peptide film suspended stably in neutral water. The peptide film assembled on the surface of water containing 4 mM CuCl2 was able to induce the polymerization of pyrrole. (d) The schematics of the proposed mechanism involving Cu(II) reduction, tyrosyl radical generation and pyrrole oxidation. The Cu(II) reduction in distilled water spontaneously induced the formation of tyrosyl radical (Tyr·) without any additional oxidant or applied potential. Thereafter, the Tyr· initiates pyrrole polymerization.
