Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin

Surface-enhanced resonance Raman scattering (SERRS) spectra of myoglobin (Mb) with various ligands were measured. In the resonance Raman scattering (RRS) spectra, peaks at around 1610 and 1640 cm(-1) have so far been used to discriminate between the heme iron in a high or low spin state. In the SERRS spectra, however, the spin state cannot be distinguished by the corresponding peaks. Alternatively, the intensity ratio of the SERRS peak at 1560 cm(-1) to that at 1620 cm(-1) was applied to detect the spin states sensitively (1.5 x 10(5) times compared with the RRS): namely, a high ratio was obtained from met-Mb in the high spin state at pH <= 7 except for in a strong acid solution. The different marker bands between the SERRS and RRS spectra may be due to the enhancement order from the surface selection rule.