Differences in iron-fluoride bonding between the isolated subunits of human methemoglobin fluoride and sperm whale metmyoglobin fluoride as measured by resonance Raman spectroscopy

Abstract

The heme geometries of the isolated alpha and beta subunits of human methemoglobin fluoride (HbIIIF) and sperm whale metmyoglobin fluoride (MbIIIF) have been examined by exciting their Raman spectra within their ca. 6000-A charge-transfer absorption bands. The Fe-F stretching vibration at 471 cm-1 in the beta subunits shifts to 466 cm-1 in the alpha subunits and to 461 cm-1 in MbIIIF. The Fe-F bond is estimated to elongate by 0.02 A in the alpha subunits and 0.03 AZ in MbIIIF compared with that in the beta subunits. This bond elongation is interpreted to result from an increased iron displacement toward the proximal histidine side of the heme in the series MbIIIF greater than alpha greater than beta. A comparison of the isolated subunit spectra with that of tetrameric HbIIIF indicates little change occurs in isolated subunit heme geometry upon association into tetrameric HbIIIF. A correlation is found between the gamma max of the 600-A charge-transfer absorption band and the Fe-F bond length. Elongation of the Fe-F bond is associated with a shift of the absorption spectral maximum to a longer wavelength. However, the absorption spectral shift induced by the inositsol hexaphosphate induced R leads to T conversion does not result from a change in the Fe-F stretching frequency (+/- 0.5 cm-1). In contrast, frequency shifts are observed for heme macrocyclic vibrational modes. The data are interpreted to indicate that the effect of the R leads to T conversion in HbIIIF is to perturb heme macrocycle conformation without altering the heme out-of-plane iron distance or the Fe-F bond length.

Active Sites of O2-Evolving Chlorite Dismutases Probed by Halides and Hydroxides and New Iron–Ligand Vibrational Correlations

“…Assignment of the ν­(Fe–F) bands at 385, 390, and 393 cm –1 for the Kp Cld–F, Da Cld–F, and Da Cld­(W227F)–F complexes, respectively, was facilitated by Raman excitation within both the Soret and CT2 transitions using 406.7 and 441.6 nm light, respectively. Resonance enhancement of scattering by the z -polarized ν­(Fe–F) modes of heme fluorides has been reported with excitation at the frequency of the x , y -polarized CT1 transition, where scattering by ν­(Fe–F) gains resonance enhancement in hemes exhibiting equilibrium out-of-plane distortion . More recently, scattering by the ν­(Fe–F) modes has been achieved via excitation within the z -polarized CT2 transition, whose energy lies between those of the B and Q­(0,1) transitions (Figure , insets) .…”

“…As ν(Fe−F) modes have been shown to be isolated (i.e. they behave as diatomic oscillators 45 ), the compositions of the other normal heme modes are sufficiently unperurbed by F − binding that they are easily correlated between the spectra recorded in the absence and presence of F − . Finally, by moving the exciting wavelength away from the B band and toward or within the z -polarized CT2 absorbance band, the z -polarized ν(Fe−F) band gains resonance enhancement while the relative intensities of the in-plane polarized heme bands are diminished.…”

“…Resonance enhancement of scattering by the z-polarized ν(Fe−F) modes of heme fluorides has been reported with excitation at the frequency of the x,y-polarized CT1 transition, where scattering by ν(Fe−F) gains resonance enhancement in hemes exhibiting equilibrium out-of-plane distortion. 45 More recently, scattering by the ν(Fe−F) modes has been achieved via excitation within the z-polarized CT2 transition, whose energy lies between those of the B and Q(0,1) transitions (Figure 5, insets). 43 There are two advantages to this approach.…”

A study of the mechanism of fluoride adsorption from aqueous solutions onto Fe-impregnated chitosan

“…44 The peaks centered at 375 and 580 cm À1 were assigned to Fe-Cl and Fe-N 45 vibrations, respectively. The appearance of two new peaks after adsorption at 485 and 533.5 cm À1 associated with Fe-F vibrations 46 indicated that complexation between Fe and F ions occurred. However, observation of any notable change in the intensity of the Fe-Cl peak was difficult possibly because only a small amount of Cl and F ions was exchanged in the 10 mg L À1 fluoride solution.…”

Coherent infrared emission from myoglobin crystals: An electric field measurement

“…Band 5 as well as band 7 arise from vibrational modes closely associated with the core of the heme (see Table 1) and they have been shown to be markers for the heme macrocycle structure. Asher and Schuster (30) found a correlation between a frequency shift from 1,232 to 1,217 cm Ϫ1 and a decreased heme core size as well as an out-of-plane movement of the iron toward the proximal histidine, for the hemes of ␣ and ␤ hemoglobin subunits in Raman measurements. Berthomieu et al (32) showed that upon oxidation a band shift from 1,237 to 1,223 cm Ϫ1 occurred in IR-absorption spectra of double-coordinated Fe-protoporphyrin IX.…”