Iron with imidazole

Killday etal. (1988) also provided evidence for internal autoreduction of ferric nitrosyl heme complexes, as previously proposed by Giddings (1977). Heating of chlorohemin( iron-III) dimethyl ester in dimethyl sulfoxide solution with imidazole and NO produced a product with an infrared spectra identical to that of nitrosyl iron(ll) protoporphyrin dimethyl ester prepared by dithionite reduction. Both spectra clearly showed the characteristic nitrosyl stretch at 1663 and 1665 cm. They thus proposed a mechanism for formation of cured meat pigment which includes internal autoreduction of NOMMb via globin imidazole residues. A second mole of nitrite is proposed to bind to the heat-denatured protein, possibly at a charged histidine residue generated in the previous autoreduction step. 

The coordination of indazolium ligands, as present in KP1019, appears beneficial for transferrin binding, compared to analogous complexes with imidazole or triazole ligands [102], as these ligands are better accommodated into the iron binding sites [97]. 

The hyperfine-shifted proton resonance of metmyoglobin and methemoglobin complexes with imidazoles, in particular, 4-nitroimidazole, was studied in order to obtain an insight into the structural features of the iron-bound imidazole [352], The structure of l-(l,3-dihydroxy-2-propyl)-4-nitroimidazoles, so called acyclic nucleosides, has been established by II and 13C NMR [327],... 

The [Fe2S2] + core, (2) (Figure 2), appears in plant-type (chloroplast) ferredoxins (Fd) and in Rieske proteins. In ferredoxins, the [Fe2S2] + core is ligated with thiolate from Cys residues, while in Rieske proteins, the thiolates ligating one of the iron atoms are substituted with imidazole ligands from His residues. 

Iron(III) porphyrins with imidazole anion(s) as ligands have been synthesized in non-aqueous media"" , and are potential models for heme-containing enzymatic species. Metalloporphyrin vr-cation radicals generated electrochemically (but never from iron porphyrins) are models for compound I or horseradish peroxidase " (see 14.8.5.3.2). 

Figure 3.20. Ligand-induced conformational changes in CYP119. Compared to the phenylimidazole complex (dark shading), the C-terminal end of the F-helix in the imidazole complex unfolds which lengthens the F/G loop thus allowing the F/G loop to dip into the active site and interact with the iron-linked imidazole. Since phenylimidazole is larger than imidazole, the F/G loop cannot remain positioned in the active site complex. Therefore, the F/G helical region and loop shapes itself around the ligand bound in the active site.

Schejter and Aviram studied the reaction of cytochrome c with imidazole and observed spectral changes which led them to suggest that the path followed by the electron in its transfer to the iron atom in ferricyctochrome c is different from that followed in its transfer from the iron atom in ferrocytochrome c. 

Iron(u), Rhodium(i), and Iridium(i).— Arguably iron(n) is square-planar in ferrous phthalocyanine in DMSO solution (c/. [PtClJ - in water ). The reaction of this compound with imidazole has been much studied, but kinetic ambiguities have prevented the unequivocal assignment of mechanism. Now the kinetic pattern for the analogous reactions with A-methylimidazole and with iV-n-butylimidazole, where there is no possibility of proton removal from nitrogen, has been shown to be very similar to that with imidazole. It is therefore now reasonable to rule out reaction of ferrous phthalocyanine with the deprotonated imidazole anion as a plausible pathway. ... 

The reaction of five-coordinate high-spin iron(III) porphyrin chlorides, Fe(Por)Cl, with imidazoles, Rim, to produce six-coordinate low-spin complexes according to reaction (1) has recently received attention [1-7]. The monoimidazole... 

Of these B, which is the only one with significant acid properties, is almost wholly suppressed, and this accountsfor thefact that the free imidazolium ion is a monobasic acid. Bonding with the iron occurs only with the dissociated form and in acid solution leads to the displacement of a proton. We may therefore represent the covalent linkage of the ferrous iron and imidazole group of histidine by means of the three resonating structures ... 

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