Redox and conformational equilibria of cytochrome c₅₅₂ from Thermus thermophilus adsorbed on a chemically modified silver electrode probed by surface‐enhanced resonance Raman spectroscopy

Surface‐enhanced resonance Raman spectroscopy (SERRS) was employed to study the potential‐dependent processes of the electron transferring heme protein cytochrome c 552 (Cyt‐ c 522 ) from Thermus thermophilus . Cyt‐ c 552 was adsorbed on Ag electrodes coated with functionalized self‐assembled monolayers (SAMs) of alkanethiols, regarded as a model of its redox partner ba 3 ‐oxidase. By a quantitative analysis of the SERR spectra recorded at different potentials, the redox potential of Cyt‐ c 552 and the number of transferred electrons were determined. On pure hydrophobic alkanethiols, the Cyt‐ c 552 heme structure is greatly modified in a non‐electroactive way with the appearance of a 5cHS species. When Cyt‐ c 552 is adsorbed on mixed surfaces of hydroxyl‐ and methyl‐terminated alkanethiols, the electron transfer is effective ( n = 1) and the structure of the heme is not modified, as is assumed when Cyt‐ c 552 interacts with its natural redox partner ba 3 ‐oxidase. When the chain length of the mixed SAMs is increased, the defects on the surface are decreased and the electron transfer becomes less efficient. The presence of defects in the organization of the short chain of five carbons seems to be relevant for having a good surface model of the redox partner.