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

Abstract

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.