Ferryl

If a dilute solution of hydrogen peroxide in dry acetonitrile is added to a solution of a sulphoxide and an iron(II) salt in dry acetonitrile then the sulphone is produced in quantitative yield34. This latter reaction works equally well for aliphatic and aromatic sulphoxides and is thought to involve oxygen transfer by the reaction of a ferryl ion with the sulphoxide, as shown in equation (12). 

The less specific binding of flavonoids to ferrylmyoglobin is in agreement with establishment of LFERs, linear free energy relationships, i.e. Ink(ferryl) depends linearly on E , for reduction of MbFe(IV)=0 by flavonoids within series of flavonons and ftavonols (Jorgensen and Skibsted, 1998). The relevance of such LFERs, as demonstrated for MbFe(IV)=0 and plant phenols, draws further support from the observation that the same sequence, i.e. chlorogenic caffeic > ferulic > coumaric acid, is seen for reaction of the phenols with... 

Dee, G., Rice-Evans, C., Obeyesekera, S., Meraji, S., Jacobs, M. and Bruckdorfer, K.R. (1991). The modulation of ferryl myoglobin formation and its oxidative effects on low density liproprotein by nitric oxide. FEBS Lett. 294, 38-42. 

In order to understand the potential for haem proteins to mediate the oxidative modification of LDLs, the interaction between ruptured erythrocytes (Paganga et al., 1992) and ruptured myocytes (Bourne etal., 1994) with LDL has been explored. Previous studies from this group have demonstrated that ferryl myoglobin radicals and ruptured cardiac myocytes, which generate ferryl myoglobin species on activation (Turner et al., 1990,... 

The time-scale of this haem conversion is related to the antioxidant status of the LDL and that of the erythrocyte lysate. The incorporation of lipid-soluble antioxidants, such as tocopherol and butylated hydroxy-toluene (BHT) at specific time points during the LDL-erythrocyte interaction, prolongs the lag phase to oxidation, eliminates the oxy to ferryl conversion of the haemoglobin and delays the oxidative modification of the LDL. 

The findings here surest that, after an initial slow phase corresponding to the antioxidant capacity of the LDL, hydroperoxides can interact with haemoglobin in a similar manner to hydrogen peroxide, forming ferryl haemoglobin, which is then rapidly reduced to mixtures consisting mainly of oxy- and met- forms, possibly by the synproportionation reaction, as proposed in the studies... 

Giulivi, C. and Davies, K. (1990). A novel antioxidant role for haemoglobin. The comproportionation of ferryl haemoglobin with oxyhaemoglobin. J. Biol. Chem. 265, 19453-19460. 

Compound 1 (Fig. 18.18) reversibly forms an analogous ferric-superoxo/Cu adduct at 60 °C, as demonstrated by resonance Raman spectroscopy. However, warming the sample to 40 °C results in a rapid four-electron reduction of the bound O2 ligand, generating a ferryl/Cu /phenoxyl radical derivative (Fig. 18.18) [Collman et al., 2007a]. 

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%. 

Numerous studies have shown that oxidation of a wide range of AH2 by HRP in the presence of H202 is characterized by a loss of enzyme activity. It is now well established that HRP is inactivated by H202.32 Because the final step (Equation 17.4), during which the oxidized ferryl intermediate is... 

Catalases and peroxidases both promote H2O2 reduction by mechanisms that involve ferryl intermediates. Catalases differ from peroxidases by their ability to use H2O2 both as an electron acceptor and as donor, thus catalysing the disproportionation reaction (catalatic activity) (equation 1) ... 

Then the ferryl ion either reacts with water to form the hydroxyl radical, or oxidizes another Fe2+ ion [14,16],... 

Thus, two routes of transformation are possible for the Fe2+(H202) complex one-electron transfer to form the hydroxyl radical and two-electron transfer to form the ferryl ion. It is difficult to prove experimentally the formation of the ferryl ions because they are very reactive, so that this route of interaction of H202 with Fe2+ remains hypothetical to a great extent. Another change in the mechanism of H202 decomposition with increasing pH is related to the acidic dissociation of H02 (pKa = 4.4)... 

This mode of superoxide-dependent free radical-mediated damaging activity remains an important one although the nature of the generated reactive species (free hydroxyl radicals or perferryl, or ferryl ions) is still obscure. However, after the discovery of the fact that many cells produce nitric oxide in relatively large amounts (see below), it became clear that there is another and possibly a more portent mechanism of superoxide-induced free radical damage, namely, the formation of highly reactive peroxynitrite. 

Peroxynitrite reacts with heme proteins such as prostacycline synthase (PGI2), microperoxidase, and the heme thiolate protein P450 to form a ferryl nitrogen dioxide complex as an intermediate [120]. Peroxynitrite also reacts with acetaldehyde with the rate constant of 680 1 mol 1 s" 1 forming a hypothetical adduct, which is decomposed into acetate, formate, and methyl radicals [121]. The oxidation of NADH and NADPH by peroxynitrite most certainly occurs by free radical mechanism [122,123], Kirsch and de Groot [122] concluded that peroxynitrite oxidized NADH by a one-electron transfer mechanism to form NAD and superoxide ... 

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