Peroxide disproportionation

Generation of superoxide radical under physiological conditions ultimately leads to the production of hydroxyl radical through a cascade of redox reactions. Initially, sn-peroxide disproportionates to generate hydrogen peroxide (Eq. 3, Scheme 8.36) Superoxide radical exists in equilibrium with its protonated form (H02, = 5). 

Arginase, 46 306-307 binuclearity, 46 325-327 EPR spectroscopy, 46 389 hydrogen peroxide disproportionation, 46 326-327... 

The favored peroxide disproportionation pathway requires two two-electron steps, with an optimal two-electron reduction potential of +0.86 V [5],... 

A study of the kinetics and mechanism of peroxide disproportionation by the complexes of L3 (Figure 12) probed anion inhibition pathways [96], The disproportionation in water was found, as expected, to proceed by two consecutive two-electron steps ascribed to the MnnMnn MninMnm redox changes. 

Nuclearity 2, redox chemistry of peroxide disproportionation (2 electrons)... 

We have seen a quantum leap in progress in the coordination chemistry of copper-dioxygen interactions, resulting in a complete change in thinking about Cu202 structure and related protein chemistry. The problems of copper ion lability, peroxide disproportionation and air/moisture sensitivity have been overcome, and it has been proved that low-molecular-weight Cu 02 or Cu (0)2 complexes can be prepared, and that several different structural types exist. It is apparent that u-r 2 r 2-peroxo coordination is present in oxy-Hc and oxy-Tyr. 

Figure 2. The four-step mechanism for hydrogen peroxide disproportionation by the Mn catalse proposed by Penner-Hahn (22) is shown above the solid line. Our proposed mechanism for the inactivation of the Mn catalase by hydroxylamine in the presence of hydrogen peroxide is shown below the solid line.

Figure 11. (A) Rate of hydrogen peroxide disproportionation vs. hydrogen...

Figure 12. Plot of the hydrogen peroxide disproportionation rate vs. the concentration of Na2[Mn2(2-OH-(5-Cl-sal)pn)]2 in acetonitrile.

Fig. 10.4. Peroxidase catalytic cycle. Four pathways are shown for the return of Compound I to the resting state (1) oxidative dehydrogenation, where RH is the substrate (2) oxidative halogenation, where X" is a halogen ion and RH is the substrate (3) peroxide disproportionation, and (4) oxygen transfer, where R is the substrate.

Reduction of peroxidase Compound I back to the resting state can occur by one of four pathways, depending on the reaction catalyzed oxidative dehydrogenation (pathway (1) in Fig. 10.4), oxidative halogenation (2), peroxide disproportionation (3) or oxygen transfer (4) [60]. 

Iron(III) is then reduced back to iron(II), a peroxide radical and a proton by the same hydrogen peroxide (disproportionation). 

Scheme 3 Possible mechanism for Mn catalase peroxide disproportionation...

Scheme 19. Proposed mechanism of hydrogen peroxide disproportionation by Mn"(2-OHbenzimpn)(/n-OAc) 22 . [Reproduced with permission from (439). Copyright 1994 the American Chemical Society.]...

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