Ferryl complexes

A comparison of anisotropic Fe HFCs with the experimental results shows good agreement between theory and experiment for the ferryl complexes and reasonable agreement for ferrous and ferric complexes. Inspection reveals that the ZORA corrections are mostly small ( 0.1 MHz) but can approach 2 MHz and improve the agreement with the experiment. The SOC contributions are distinctly larger than the scalar-relativistic corrections for the majority of the investigated iron complexes. They can easily exceed 20%. 

Finally, attack of the ferryl complex on another heme results in the formation of hematic ... 

We have recently shown that the peroxynitrite-mediated oxidation of oxyMb and oxyHb proceeds via intermediate oxoiron(iv) (ferryl) complexes, which, in a second step, react further with peroxynitrite to yield metMb and metHb, respec-... 

Although several studies indicate that HO is formed in Fenton systems according to Eq. 37 and it is responsible for the efficiency of degradative reactions, it is presently believed that other Fe(IV) or Fe(V) species like Fe03+ and ferryl complexes, are also active agents in the processes [53— 55,58, 112]. For example, Kremer [112] identified a mixed valence binuclear species, FeOFe 5+, and proposed a new mechanism for the Fenton reaction, in which Fe02+ acts as the key intermediate. 

Cleavage of the first species to the transient ferryl complex and a ferric hydroxo monomeric complex can explain the near 50% yield of the ferryl compound. The ferric monomer subsequently dimerizes to the paramagnetic dimer, 32, responsible for the 65% of the Mossbauer signal. The dimer formed after the oxidation is proposed to be similar to the starting material, based on comparisons of its Mossbauer spectrum with that of 31. 

The low temperature spectroscopic observation of the FeIV ferryl complex (134) [P = TPP, B = py, pip or jV-Me-im] formed via reaction (31) has been followed by the demonstration by the same group of its role in oxygen atom transfer reactions. Thus, it was found446 that PFe11 catalyzes... 

Lawrence Que Synthesis of a nonheme ferryl complex, an analogue of nonheme iron oxygenase active intermediates... 

The alkyl peroxide then can decompose to give PFe OH and 0=CR2, or, if a tertiary alkyl group, Acyl complexes such as PFe C(0)C4H9 react with dioxygen to yield only PFe carboxylate complexes and the fi-oxo dimer, PFe -0-Fe -P, with no evidence of ferryl complexes being formed. 

Five types of Fe porphyrin complexes have beenreported, all of which have spin state 5=1 (l)the deep red, five-coordinate ferryl, (Fe =0) +, complexes and the six-coordinate adducts of these ferryl complexes, the (B)(Fe = 0) + complexes (2) the Fe phenyl complex (3) iron(fV) carbene complexes (4) iron(fV) hydrazine complexes and (5) the six-coordinate d complex [TPPFe(OMe)2] mentioned briefly in Section 7 above. The ferryl and Fe - phenyl cases have direct appheation to active states of heme proteins, particularly the cytochromes P450, peroxidases, catalases, and related enzymes. 

Cleavage of the peroxo complex results in two molecules of a ferryl complex with the iron in the +4 formal oxidation state ... 

From 2, it was concluded that the ferryl complex is the catalytically active species. Observation 1 suggested that 80% of the epoxide product in the aerobic reaction is derived from a carbon-based radical, which is quenched by O2 (autoxidation), and this is known to produce epoxide in reactions with cyclooc-tene (325). Methanol (observation 3) is known to quench radicals. The fact that the diols formed are a mixture of cis and trans products (observation 1 this is very unusual in iron-catalyzed olefin oxidations) suggested that the diol results from the capture of OH radicals by the putative carbon-based radical. 

Filatov, M., N. Harris, and S. Shaik (1999). A theoretical study of electronic factors affecting hydroxylation by model ferryl complexes of cytochrome P-450 and horseradish peroxidase. J. Chem. Soc. Perkin Trans. 2, 399-410. 

Ferryl complexes have been implicated in the reaction mechanisms of peroxidases and cytochromes P450. 38,1596 Pqj. horseradish peroxidase, two intermediates are spectroscopically detectable. Compound I, formed upon addition of peroxide to the resting Fe form of the enzyme, is a green species that is formally two oxidation levels higher than the resting state, and is widely believed to consist of an (Fe =0) + unit complexed by a porphyrin jt-cation radical. The [(P" ) Fe =0]+ complexes are discussed in Section 9. Compound II, which is red, and is obtained upon one-electron reduction of Compound I, also possesses a (Fe =0) + unit, in this case complexed by a normal porphyrin dianion, PFe =0. The fifth ligand, provided by the protein in the various enzymes, is a cysteine thiolate for the cytochromes nitric oxide synthases... 

Importantly, differences in the metal-Ugand bonding to the two tertiary amine donors have been shown to be of importance for the tuning of the spin state of the ferryl complexes (see Section 6.4) [13g] and the redox potentials and catalytic activities of Cu couples [21] the bispidine-derived geometry is particularly well suited for the Jahn-Teller active Cu" ion and has led to a rich Cu coordination chemistry [22] with interesting applications in bioinorganic model chemistry (hemocyanin [23], catecholase[24]), catalytic aziridination [21a,... 

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