Multimode analysis of depolarization ratio dispersion and excitation profiles of seven Raman fundamentals from the haeme group in ferrocytochrome c

Abstract

Experimental data for depolarization ratio dispersion (DPD) and resonance excitation profiles (REPs) with high spectral resolution (20 cm-I) are provided for seven Raman fundamentals in the region between 1150 and 1650 cm-' of the haeme spectrum from ferrocytochrome c. They cover the resonant region of the Q-band and the preresonant region of the &band. A self-consistent analysis of the depolarization ratio dispersion (DPD) and resonance excitation profiles (REPs) of these Raman lines is carried out by explicit consideration of multimode mixing. This is achieved by first formulating the Raman tensor in Loudon's formulation to fifth order for each mode, thus restricting the contribution of the fifth-order term to the vibration itself and omitting multimode contributions. By fitting this expression to the DPDs and REPs of each Raman mode, one obtains coupling parameters which in the next step are inserted into the fifth-order term of each mode. Thus one takes account of their contributions to multimode mixing. To account for contributions of lower frequency modes, an effective 'helping rest mode' was added to the multimode contributions. This procedure yields satisfactory fits to all data sets. The respective fits to the D P D and REP of the oxidation marker line at 1363 cm-' reproduce also the corresponding R E P and DPD in the resonant region of the B-band reported by Champion and Albrecht with a high degree of accuracy. The vibronic coupling parameters obtained are consistent with the weak coupling limit. Further, they confirm the validity of Gouterman's four-orbital model for ferrocytochrome c.

Cytochrome c: A Multifunctional Protein Combining Conformational Rigidity with Flexibility

“…Shelnutt as well as Zgierski and Pawlikowski explained these dispersions in terms of electronic and vibronic perturbations, which will be explained below [55,56]. A systematic investigation of Raman depolarization ratio dispersions and resonance excitation profiles of various heme proteins was subsequently in our research group at the University of Bremen [57][58][59][60]. For ferrocytochrome c, we reported dispersion and excitation data over a rather broad range of excitation wavelengths that encompasses the entire -band region [60].…”

“…A systematic investigation of Raman depolarization ratio dispersions and resonance excitation profiles of various heme proteins was subsequently in our research group at the University of Bremen [57][58][59][60]. For ferrocytochrome c, we reported dispersion and excitation data over a rather broad range of excitation wavelengths that encompasses the entire -band region [60]. As an example, Figure 5 shows the depolarization dispersion and resonance excitation profile of the oxidation marker ] 4 .…”

“…If this was the case, the band would be practically undetectable in the entire preresonance and resonance regions of the Q-band, contrary to what the excitation profile in Figure 5 suggests. In reality, the ] 4 -band gains considerable Raman activity from Herzberg-Teller coupling [19,60,62,63].…”

“…The solid line results from a multimode fitting procedure described by Schweitzer-Stenner et al [60], from where the figure was taken with permission. The data in the Soret band region of the resonance excitation profile have been measured earlier by Champion and Albrecht [49].…”

“…This mixing of symmetries changes the depolarization ratio of the Raman mode. Combined with some interference between Franck-Condon, Jahn-Teller, and Herzberg-Teller coupling, this causes a dispersion of the depolarization ratio, as shown in Figure 5 for the 1 -mode ] 4 [60].…”