Iron complex, absorption spectrum

Figure 4. The calculated spectrum of the complex after a Lorentzian band convolution. Region I is dominated by bridging-sulfur-to-iron CT transitions, while region II is mostly due to organic-sulfur-to-iron electron transitions. Regions I and II are explained in a MO diagram. The vertical lines correspond to the experimental bands observed in the absorption spectrum of the [Fe2 (J. - S2) P o - CqH4S) ) ] complex, from Reference 1.

The core of the iron storage protein ferritin consists of a hydrated ferric oxide-phosphate complex. Various models have been proposed which feature Fe111 06 oct., Fe111 O4 tet. or Fe111 O4 tet. Fe111 06 oct. complexing the first listed is preferred by Gray (99) on the basis of the electronic absorption spectrum. The protein very closely related to ferritin which occurs in the mold Phycomyces blakesleeanus contains... 

Figure 18-7 Visible absorption spectrum of the complex (ferrazine)3Fe(ll) used in the colorimetric analysis of iron.

Knowing that carbon monoxide complexes of hemes are dissociated by light, Warburg and Negelein, in 1928, determined the photochemical action spectrum (see Chapter 23) for reversal of the carbon monoxide inhibition of respiration of the yeast Torula utilis. The spectrum closely resembled the absorption spectrum of known heme derivatives (Fig. 16-7). Thus, it was proposed that 02, as well as CO, combines with the iron of the heme group in the Atmungsferment. 

Mossbauer spectroscopy of the 57Fe nucleus has been extensively used to investigate aspects of spin equilibria in the solid state and in frozen solutions. A rigid medium is of course required in order to achieve the Mossbauer effect. The dynamics of spin equilibria can be investigated by the Mossbauer experiment because the lifetime of the excited state of the 57Fe nucleus which is involved in the emission and absorption of the y radiation is 1 x 10 7 second. This is just of the order of the lifetimes of the spin states of iron complexes involved in spin equilibria. Furthermore, the Mossbauer spectra of high-spin and low-spin complexes are characterized by different isomer shifts and quad-rupole coupling constants. Consequently, the Mossbauer spectrum can be used to classify the dynamic properties of a spin-equilibrium iron complex. 

Fia. 8. Absorption spectrum of the soluble iron-sulfur protein (4 mg/ml) isolated from complex I. Dashed line, after treatment with dithionite dotted line, after treatment with sodium mersalyl to destroy the iron-sulfur chromophore. From Hatefi et al. (Si),... 

The resolved complex is composed of two fractions, a soluble part, which comprises about 15% of complex I proteins, and a water-insoluble part consisting of the rest of the protein and the bulk of complex I lipids. The soluble fraction is easily separated from the insoluble material by centrifugation. Upon fractionation with ammonium sulfate, it yields a soluble flavoprotein containing iron and labile sulfide and a dark brown protein, which contains large amounts of iron and labile sulfide but no flavin. The latter appears to be an iron-sulfur protein and exhibits an EPR signal which is characteristic of iron-sulfur center 2 of intact complex I (46). Its absorption spectrum is shown in Fig. 8. The insoluble fraction also contains equimolar amounts of iron and labile sulfide and little or no flavin. 

During irradiation of sensitized epoxide matrices, the absorption spectrum is altered and colourless coatings are obtained. Iron arene complexes are thermally stable up to 300 °C. 

Reactions of NO were also studied with the synthetic heme protein discussed earlier, namely the recombinant human serum albumin (rHSA) with eight incorporated TPPFe derivatives bearing a covalently linked axial base, were also investigated. The UV-vis absorption spectrum of the phosphate buffer solution at physiological pH showed absorption band maxima at 425 and 546 nm upon the addition of NO to form the nitrosyl species, which was also formed when the six-coordinate CO-adducts were reacted with NO gas. EPR spectroscopy revealed that the albumin-incorporated iron(II) porphyrin formed six-coordinate nitrosyl complexes. It was observed that the proximal imidazole moiety does not dissociate from the central iron when NO binds to the trans position. The NO-binding affinity P1 /2no was 1.7 X 10 torr at pH 7.3 and 298 K, significantly lower than that of the porphyrin complex itself, and was interpreted as arising from the decreased association rate constant (kon(NO), 8.9 x 10 M s" -1.5 x 10 M s ). Since NO-association is diffusion controlled, incorporation of the synthetic heme into the albumin matrix appears to restrict NO access to the central iron(II). ... 

Also shown in Figure 8 is the absorption spectrum of the iron-citrate complex obtained by preparing 0.1 mM Fe + in the presence of 10 mM citrate. Figure 8 thus provides a rationale for why the UV and visible ICH stressing conditions will both lead to the observed photodegradation as Fe can be photoreduced to Fe + in the presence of citrate by either lamp output. 

Figure 8 Solid lines) Spectral outputs for International Conference on Harmonization (ICH) visible and ultraviolet lamps with Hg emission lines removed dotted line) absorption spectrum for the iron-citrate complex dashed line) transmission profile for the yellow light filters used in this study and common to many manufacturing areas. Note the spectral overlap of both ICH lamps with iron-citrate complex absorption.

Tris(bipyridyl)iron(0) does not dissociate into ions despite the fact that the absorption spectrum of the complex is similar to that of... 

The conclusion that the cobalt and iron complexes 2.182 and 2.183 are formally TT-radical species is supported by a wealth of spectroscopic evidence. For instance, the H NMR spectrum of the cobalt complex 2.182 indicated the presence of a paramagnetic system with resonances that are consistent with the proposed cobalt(III) formulation (as opposed to a low-spin, paramagnetic cobalt(IV) corrole). Further, the UV-vis absorption spectrum recorded for complex 2.182 was found to be remarkably similar to those of porphyrin 7r-radicals. In the case of the iron complex 2.183, Mdssbauer spectroscopy was used to confirm the assignment of the complex as having a formally tetravalent metal and a vr-radical carbon skeleton. Here, measurements at 120 K revealed that the formal removal of one electron from the neutral species 2.177 had very little effect on the Mdssbauer spectrum. This was interpreted as an indication that oxidation had occurred at the corrole ligand, and not at the metal center. Had metal oxidation occurred, more dramatic differences in the Mdssbauer spectrum would have been observed. 

The reactive intermediates leading to the (charge-transfer) photodecomposition of the 6w(arene)iron(II) acceptor are revealed by picosecond time-resolved spectroscopy. For example, photoexcitation of the CT absorption band of the ferro-cene-(HMB)2Fe complex (HMB = hexamethylbenzene) with the second harmonic output (at 532 nm) of a mode-locked Nd YAG laser (25-ps pulse width) generates a transient spectrum with an absorption maximum at 580 nm (see Figure 11 A). Careful deconvolution of this absorption spectrum reveals the superposition of the absorption bands of ferrocenium (Imax = 620 nm, e = 360 cm [162]) and (HMB)2Fe+ (2 ,ax = 580 nm, = 604 M" cm" [163]). 

Mossbauer parameters of iron containing components in solid-state phthalocianinato-iron complexes (IS isomer shift, related to metallic a-iron, mm/s QS quadrupole splitting, mm/s, Rl relative contribution to the the spectrum, % A spectral absorption, intensity/base line, % A77/A30Q ratios of absorptions obtained from 77 K and 300 K spectra)... 

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