Iron porphyrins spectra

After this first step, where some samples are eliminated because they are not suited to the protocol, the positive ion mode is used to investigate haem, an iron porphyrin which is a blood marker. Spectra taken of the haem reference show that it can be detected due to [M]+ and [M+H]+ ions (respectively, at m/z 616.2 and 617.2), and also due to a large distribution of fragment peaks between m/z 350 and m/z 550 (Figure 15.12a). The same spectrum has also been obtained for haemoglobin leading to the conclusion that the presence of protein does not disturb the detection of haem. 

The electronic spectrum of Fe—O2 in a hemerythrin derivative has been reported. Further references to reactions of iron porphyrins with dioxygen species appear in Section 5.4.3.7.2. 

Iron Porphyrins. Porphyrins (15—17) are aromatic cyclic compounds that consist of four pyrrole units linked at the OC-positions by methine carbons. The extended 71-systems of these compounds give rise to intense absorption bands in the uv/vis region of the spectrum. The most intense absorption, which is called the Soret band, falls near 400 nm and has eM 105. The 71-system is also responsible for the notable ring current effect observed in/H-nmr spectra, the preference for planar conformations, the prevalence of electrophilic substitution reactions, and the redox chemistry of these compounds. Porphyrins obtained from natural sources have a variety of peripheral substituents and substitution patterns. Two important types of synthetic porphyrins are the meso-tetraaryl porphyrins, such as 5,10,15,20-tetraphenylporphine [917-23-7] (H2(TPP)) (7) and (3-octaalkylporphyrins, such as 2,3,7,8,12,13,17,18-octaethylporphine [2683-82-1] (H2(OEP)) (8). Both types can be prepared by condensation of pyrroles and aldehydes (qv). 

The preparation of the iron porphyrin TPPFeCl-d20 (21), where the phenyl groups are completely deuterated, has allowed the further characterization of the bis-cyano Fe(II) and Fe(III) porphyrins. In the spectrum of TPPFeIII(CN)21" in DMSO, the resonance at +15.45 ppm upfield from TMS is verified as the pyrrole H. Comparing the spectrum of TPPFe11 (CN),2 and TPPFe11 (CN)22--d20 shows the peak at -7.82 ppm from TMS to be the pyrrole H, and integration indicates that the... 

Other Systems. Alkyl Thiols. The reduction of hemin with ethane-thiol has been suggested to occur by a free radical mechanism on the basis of product analysis (II). The reaction of n-hexanethiol with TPPFeCl in DMSO carried out in the ESR cavity gives rise to the signal illustrated in Figure 7. These are preliminary results, and the spectrum is of poor quality and probably reflects some saturation from the low steady-state concentration of the radical. Nevertheless the signal only appears during the autoreduction of the iron porphyrin and again indicates that the autoreduction occurs by a free radical pathway. 

Recently synthesized iron porphyrin-carbene complexes (136) may be considered as carbon analogues of the oxo-iron(IV) porphyrin (HRP-II and CAT-II) species.476 The one-electron oxidation of [Fe(TPP)(C=CR2)] (R = aryl) by CuCl2 affords the stable complex [Fe(TPP)(C=CR2)] Cl (TPP = wieso-tetra-p-tolyl porphyrin and R = p-ClC6H4) which has a visible spectrum very similar to that of CAT-I. X-Ray analysis of this complex has revealed a structure (137) in which the vinylidene moiety has inserted between the iron atom and one pyrrole ring of the porphyrin and it is suggested that this may constitute a model, i.e. structure (138), for the active site of CAT-I as an alternative to the Fe117 cation radical model.477... 

Fig. 14. Examples of experimental NFS time patterns with corresponding schematic conventional Mossbauer spectra (a) stainless steel 221), (b) iron porphyrin complex [Fe(CH3COO)(TPpivP] (spectrum taken at 30K in a 4T field) (222), and (c) a-Fe 221).

The most prominent features in NRVS spectra are the strong set of peaks in the middle portion of the spectrum, which are principally from the in-plane motion of iron. At this time, a complete general analysis ofthe in-plane modes is notpossible. However this is probably not a frnal state. A relationship between the frequencies of the in-plane modes, iron spin state, and coordination state can be reasonably expected and is qualitatively observed. The increasing database of NRVS measurements on oriented single crystals of iron porphyrins... 

Thus in all cases where an electronic spectrum of an iron porphyrin or of any other metalloporphyrin is not normal , it is connected with an unsymmetrical axial coordination of the central ion and/or a non-planar coordination sphere of the metal ion in the porphyrin plane. 

---