[A non-resonance surface-enhanced Raman spectroscopic study of hemin on a roughened silver electrode]

The non-resonance Raman spectra of hemin were studied with the excitation of a 632.8 nm laser. The results indicated that the spectra of oxidized and reduced hemin are dominated by B1g vibration modes. The SERS spectral feature demonstrates that the porphyrin plane is perpendicular to the electrode surface. Moreover, the enhancement of the bands related to propionic acid substituents indicates that hemin is attached to the electrode surface via propionic acid substituents. The dependence of the SERS spectra on the electrode potential was examined. One of the B1g modes, nu 15, was found to be highly sensitive to the oxidation state of the central iron in heme group, and thereby exclusively assigned to be the oxidation state marker band for heme iron.