Hydroxylation heme iron complex

With regard to the biomimetic non-heme iron complexes, the work devoted to develop catalysts that perform catalytic alkane hydroxylation has resulted in a large number of iron complexes, which generate Fe =0 iron-oxo species characterized by different spectroscopic techniques. There is now direct evidence that the involvement of high-valent iron-oxo species leads to stereospecific alkane hydroxylation, while hydroxyl radicals contribute to non-selective oxidations. The impressive work performed by Que and co-workers has demonstrated that olefin epoxidation and cis-dihydroxylation are different facets of the reactivity of a common Fe -OOH intermediate, whose spin state can be modulated by the electronic and steric properties of... 

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

A component of the ribotide reductase complex of enzymes, protein Ba, has been shown to contain two non-heme iron atoms per mole (77). This enzyme plays a vital, albeit indirect, role in the synthesis of DNA. Curiously, the lactic acid bacteria do not employ iron for the reduction of the 2 hydroxyl group of ribonucleotides. In these organisms this role has been assumed by the cobalt-containing vitamin Bi2 coenzyme (18). The mechanism of the reaction has been studied and has been shown to procede with retention of configuration (19). 

Several diverse metal centres are involved in the catalysis of monooxygenation or hydroxylation reactions. The most important of these is cytochrome P-450, a hemoprotein with a cysteine residue as an axial ligand. Tyrosinase involves a coupled binuclear copper site, while dopamine jS-hydroxylase is also a copper protein but probably involves four binuclear copper sites, which are different from the tyrosinase sites. Putidamonooxin involves an iron-sulfur protein and a non-heme iron. In all cases a peroxo complex appears to be the active species. 

Iron-sulfur proteins contain non-heme iron and inorganic (acid-labile) sulfur in their active centers as 4Fe-4S or 2Fe-2S or, in the case of rubredoxin, as one iron alone. The iron is always bonded to cysteine sulfur. They catalyze redox reactions between +350 and —600 mV (hydrogen electrode = —420 mV). They are usually of low molecular weight (6000-15,000 Daltons) but can form complex enzymes with molybdenum and flavin. They occur as soluble or membrane-bound proteins and catalyze key reactions in photosynthesis, oxidative phosphorylation, nitrogen fixation, H2 metabolism, steroid hydroxylation, carbon and sulfur metabolism, etc. They occur in all organisms so far investigated and may... 

Since the discovery of cytochrome P450 hemes, many questions have been resolved using iron porphyrin model systems. The first question concerns the nature of the iron complexes involved as intermediates in the catalytic cycle of dioxygen activation and substrate hydroxylation or epoxidation. The understanding of the mechanisms by which cytochrome P450 hemes act during the... 

In the 2.1 A resolution diclofenac complex, the ligand electron density was unambiguously interpreted as a single binding mode with the 4 -hydroxylation site of diclofenac 4.7 A from the heme iron (Fig. 2.4). The carboxylate group of diclofenac makes... 

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