Superoxide complexes

The rhodium(II) compound is a diamagnetic dimer with oxygen it forms a paramagnetic monomeric 02 adduct, probably a superoxide complex represented as (porph)Rh3+02. 

Subrahmanyam VV, Kolachana P, Smith MT. 1991. Hydroxylation of phenol to hydroquinone catalyzed by a human myeloperoxidase-superoxide complex Possible implications in benzene-induced myelotoxicity. Free Radic Res Comms 15 285-296. 

Fig. 9. Possible electron transfer mechanism for NOS utilizing a pterin radical. The oxy-complex in 2 is shown as the ferric (Fe +)-superoxide complex. The role of the pterin then is to donate an electron to the iron, thus giving the peroxy dianion in 3. The dianion is a potent base that abstracts a proton from the substrate, giving 4. The system is now set up for a peroxidase-like heterolytic cleavage of the 0-0 bond to give the active hydroxylating intermediate in 5 and, finally, the first product in 6.

While the ultimate product of the reaction is the product of an O2 insertion into the Cr - C bond (Sect. 3.1), the first identifiable sfep is the binding of O2 to chromium. At - 45 °C, a color change of the solution from the brilliant blue of Tp Cr-Ph to a dark red indicated the formation of a new compound, which is stable at this low temperature. Monitoring the reaction by in-situ IR spectroscopy revealed the appearance of a new band at 1027 cm which shifted to 969 cm when 02 was used. These vibrational data are consistent with the formation of a chromium(lll) superoxide complex, namely Tp u.MeQy(Q2)pj (Scheme 3, top). 

Bielski, B. H. J. Discussion. Formation of copper-superoxide complexes. In Ciba Foundation Symp. 65 Oxygen Free Radicals and Tissue Damage, Amsterdam-Oxford-New York, Excerpta Medica, 1979, pp. 52-53... 

MoO(TPP)Br] can be chemically reduced by superoxide to give [MoO(TPP)], via Mov and Mo superoxide complexes, which are stable at low temperatures.114 In the presence of superoxide, the substitution reaction of [MoO(TPP)Br] with MeOH to give [MoO(TPP)(OMe)] proceeds via an Mo species rather than via [MoO(TPP)(MeOH)]+, which is the pathway in the absence of superoxide.277 Photochemical reduction of [MoO(TPP)(OMe)] yields [MoO(TPP)], which reacts with 02 in MeOH to re-form [MoO(TPP)(OMe)j and produce H202, thus giving a catalytic route for the photoassisted reduction of molecular oxygen to hydrogen peroxide.278... 

An electron delivered from the reductase then reduces the iron to the Fe(II) state (Eq. 18-57, step b). Then 02 combines with the iron, the initial oxygenated complex formed in step c being converted to an Fe(III)-superoxide complex (Eq. 18-57, step d). Subsequent events are less certain.4973 Most often a second electron is transferred in from the reductase (Eq. 18-57,... 

Step b of Eq. 18-65 is an unusual three-electron oxidation, which requires only one electron to be delivered from NADPH by the reductase domain. Hydrogen peroxide can replace 02 in this step.536 A good possibility is that a peroxo or superoxide complex of the heme in the Fe(III) state adds to the hydroxyguanidine group. For example, the following structure could arise from addition of Fe(III)-O-C) ... 

Isildar M, Schuchmann MN, Schulte-Frohlinde D, von Sonntag C (1982) Oxygen uptake in the radiolysis of aqueous solutions of nucleic acids and their constituents. Int J Radiat Biol 41 525-533 Jacobsen F, Flolcman J, Sehested K (1997) Manganese(ll)-superoxide complex in aqueous solution. J Phys Chem A 101 1324-1328... 

Superoxide is also implicated in the conversion of 9.20 to 9.21. The first step of the reaction involves the formation of a nickel(m)-superoxide complex, which then undergoes the intramolecular oxygen atom transfer reaction. In this case, the superoxide is... 

A lanthanide superoxide complex, [HB(3,5-Me2pz)3]2Sm(7j2-02), has recently been reported.15 It is simply made by the reaction of the pyrazolylborato compound of Sm11 with 02. 

Figure 12 shows a generally accepted reaction sequence for these enzymes. O2 can bind trans to any of the facial triad residues forming an adduct that may be described as an iron(III)-superoxide complex as shown in Figure 12d. This superoxide then attacks the electrophilic carbonyl carbon of 2-OG to form iron(IV)-peroxo adduct Figure 12e, which in turn undergoes C-C bond cleavage and subsequent O bond...

Huang X, Zhai HJ, Waters T, Li J, Wang LS (2006) Experimental and theoretical characterization of superoxide complexes [W O iO " )] and [WjO,(O W)] Models for the interaction of O with reduced W sites on tungsten oxide surfaces. Angew Chem Int Ed 45 657... 

The mechanistic sequence for adsorption of Mn + on the surface and then oxidation proposed by Davies and Morgan (1989) is illustrated in Fig. 9.8. After Mn + adsorption there is adsorption of O2 molecules on the surface (Fig. 9.8b) and then an electron transfer between adsorbed O2 and Mn + (Fig. 9.8c). The mechanism is completed by reaction of the adsorbed Mn(III)-superoxide complex (Fig. 9.8d). If the rate-limiting step is the reaction of the adsorbed Mn(III)-superoxide complex to products, then the rate for the elementary reaction is... 

The superoxide complexes typically bind end-on r/1 though this is not always the case, as in TpCon02 (Tp = hydridotris(3-tert-butyl-5-methylpyrazolyl)borate) (3),12 in which the superoxo species was found to bind rj1. Interestingly this compound had an O—O stretching frequency between superoxo and peroxo species of 961 cm-1, though the crystal structure showed the O—O bond to be 1.262 A, identifying it as a superoxo species. 

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