Photo-active and electro-active protein films prepared by reconstitution with metalloporphyrins self-assembled on gold

Long-chain thiol derivatives of metalloporphyrins (M-protoporphyrinate IX di[12-sulfanyldodecyl] ester; M = Fe3+, Zn2+) were synthesized and self-assembled onto a gold substrate. X-Ray photoelectron spectroscopy (XPS), fluorescence spectroscopy and electrochemistry were employed to characterize the surface-immobilized species. XP spectra of the Fe-porphyrin showed the characteristic core level signals for C 1s, O 1s, S 2p, N 1s and, in particular, Fe 2p. The compound also displayed chemically reversible and stable electrochemical reactivity in an aqueous electrolyte, and its voltammetric response was manipulated by co-adsorbing with a diluent component, sulfanylpropionic acid. Fluorescence excitation and emission spectra of the Zn derivative adsorbed on Au closely resembled those of Zn-protoporphyrins in solution. After immersion in a dilute solution of apomyoglobin, significant changes in the voltammetric response of the adsorbed Fe-porphyrin and fluorescence excitation spectra of the Zn derivative were observed, and were attributed to the formation of the respective Fe- and Zn-myoglobin protein at the interface. A control experiment using native myoglobin instead of the apoprotein in the reaction ruled out the possibility of non-specific protein binding as the cause for the observed changes.