The B-band excited resonance Raman (RR) spectra (100-1700 cm-1) of the bacterial cytochrome bc1 complex purified from Rhodospirillum rubrum are reported. Four redox states, i.e., the persulfate-oxidized, "as prepared", and ascorbate- and dithionite-reduced states of the complex, were investigated with the laser excitations at 406.7, 413.1, and 441.6 nm. Following the different absorption properties of the b- and c-type hemes and the different resonance enhancements of the vibrational modes of oxidized and reduced hemes, RR contributions from the b- and c-type hemes were characterized. For the nu2, nu10, and nu8 porphyrin vibrational modes, individual contributions of hemes c1, bH, and bL were determined. The data show that the macrocycle conformation of the three hemes of the cytochrome bc1 complex is different. In particular, the frequencies assigned to ferrous heme bL (1580, 1610, and 352 cm-1, respectively) reveal that its porphyrin is more strongly distorted than that of ferrous heme bH (1584, 1614, and 344 cm-1, respectively). The frequencies of the nu11 modes (1543, 1536, and 1526 cm-1 for ferrous heme c1, heme bH, and heme bL, respectively) confirm that the axial histidylimidazole ligands of heme bL have a marked anionic character. Strong differences in the peripheral interactions of the three hemes with the proteins were also detected through the frequency differences of the nu5, nu13, nu14, and nu42 modes. Considering that hemes bH and bL are inserted into a four-helice bundle, the RR data are interpreted in the frame of a strong protein constraint on heme bL.

The absorption and resonance Raman (RR) spectra of the bis-N-methylimidazole, bis-1,5-dicyclohexylimidazole, and bis-pyridine complexes of the meso-alphaalphabetabeta and meso-alphabetaalphabeta atropisomers of Fe(II)-tetrakis(o-pivalamidophenyl)porphyrins (Fe(II)TpivPP) were obtained in methylene chloride. The different spatial arrangements of the o-pivalamide pickets in these two Fe(II)TpivPP compounds are expected to control the absolute and relative positions of the axial ligand rings with respect to the Fe-N(pyrrole) bonds. In particular, the spectroscopic data obtained for the bis-N-methylimidazole and bis-dicyclohexylimidazole complexes of the Fe(II)[alphabetaalphabeta-TpivPP] derivative showed the most important differences. Redshifts of the B and Q absorption bands (+ 4-5 nm) as well as an upshift of the low frequency nu(8) RR mode (+ 5 cm(-)(1)) were observed. No shift of the skeletal high frequency modes was detected. These spectral effects were associated with a change in relative position of the axial imidazole rings from nearly parallel in the bis-N-methylimidazole complex to nearly perpendicular in the bis-dicyclohexylimidazole complex. On the basis of stereochemical considerations as well as previous spectroscopic investigations, the data were interpreted in terms of change in porphyrin structure from planar to saddled. Complementing to a parallel study on bis-base Fe(II) "basket handle" porphyrin complexes, this spectroscopic investigation provides an additional means to distinguish planar, ruffled, and saddled conformations for ferrous hemes included in proteins.

Electronic absorption, electron paramagnetic resonance (EPR), and Soret-excited resonance Raman (RR) spectra are reported for bis(N-alkylimidazole) complexes of various iron(III)-"basket-handle" (Fe(III)BHP(+)) and "picket-fence" (Fe(III)PFP(+)) porphyrins in methylene chloride. The Fe(III)BHP(+) derivatives consist of four cross-trans (CT) and two adjacent-cis (AC) -linked in which the composition and the length of the handles are variable (CT Fe(III)[(C(11)Im)(2)(+)], CT and AC Fe(III)[((C(4))(2)phi)(2)](+), CT Fe(III)[((C(3))(2)phi)(C(12))](+), CT and AC Fe(III)[((C(3))(2)phi)(2)](+)). The meso-alphaalpha betabeta and meso-alphabeta alphabeta atropisomers of Fe(III)-tetrakis(o-pivalamidophenyl)-porphyrins represents the Fe(III)PFP(+) derivatives (Fe(III)alphaalpha betabeta-T(piv)PP(+) and Fe(III)alphabeta alphabeta-T(piv)PP(+), respectively). The absorption and RR data obtained for these ferric compounds were compared to those previously published for the homologous ferrous complexes (Picaud, T., Le Moigne, C., Loock, B., Momenteau, M. and Desbois, A. J. Am. Chem. Soc. 2003, 125, 11616 and Le Moigne, C., Picaud, T., Boussac, A., Loock, B., Momenteau, M. and Desbois, A. Inorg. Chem. 2003, 42, 6081). The Soret band position of the eight investigated ferric compounds is observed between 417 and 424 nm, indicating that none of the complexes possesses a planar heme. The EPR spectra show that most of the Fe(III)BHP(+) complexes and all the Fe(III)PFP(+) complexes are rhombic B-type hemichromes (g(max) = 2.86-2.96). Notable exceptions concern the bis(N-methylimidazole) complexes of two CT Fe(III)BHP(+). The Fe(III)BHP(+) with the shortest handles (Fe(III)[((C(3))(2)phi)(2)](+)) exhibits a g value at 2.80. When the handles are lengthened by two methylene units (Fe(III)[((C(3))(2)phi)(2)](+)), the EPR spectrum corresponds to a mixture of two "highly anisotropic low-spin " or "large g(max)" type I EPR signals, a major species at g = 3.17 and a minor species at g = 3.77. All these EPR data were converted in terms of dihedral angle formed by the rings of the axial ligands. The RR spectra of the Fe(III)BHP(+) and Fe(III)PFP(+) complexes exhibited variable frequencies for the structure-sensitive nu(2) and nu(8) lines (1558-1563 cm(-1) and 386-401 cm(-1), respectively). In considering the ability of the different superstructures to stabilize particular out-of-plane distortions, this vibrational information was analyzed in terms of heme structure through changes in core size and Fe-N(pyrrole) bond length, in relation to changes in coordination geometry. The bis(N-methylimidazole) complex of Fe(III)[((C(3))(2)phi)(2)](+) was found to be the most distorted with a strongly ruffled tetrapyrrole. Because of a handle asymmetry, the heme conformation of the bis(N-methylimidazole) complex of Fe(III)[((C(3))(2)phi)(C(12))](+) was deduced to be a composition of ruffled and domed structures. The heme structure of the other complexes is a mixture of ruffled and saddled or ruffled and waved conformations. Taking into account our previous ...