Mechanism of oxygen transfer

The mechanism of oxygen transfer is believed to involve nucleophilic opening of the oxaziridine, followed by collapse of the resulting X-sulfonylcarbinolamine.252... 

Thus, the isotope effect for the allylic oxidation of cyclohexene by cytochrome P 450 is about 5 and is the same for the reconstituted, NADPH-dependent and the peroxide-dependent paths. This similarity suggests that although product ratios may change from one oxygen donor to another, the mechanism of oxygen transfer may be invariant. Efforts to develop a clearer understanding of the relationships between the 02-dependent and peroxide-dependent pathways for oxygen transfer catalyzed by cytochrome P 450 are currently underway. 

Significant characteristics of the porphyrin iron monoxide are seen in the chemical reactivity. Naphthalene is converted initially to the corresponding arene oxide on treatment with P 450 (19), consistent with a molecular mechanism of oxygen transfer from an iron monoxide to the aromatic nucleus. Retention of stereochemistry in the P-450 catalyzed hydroxylation of d ethylbenzene also supports the molecular mechanism. The unusually large kinetic isotope effect observed for the P-450 oxidation of dideutero 1,3-diphenylpropane, kJkD = 11, demonstrates that C—H cleavage is involved in the rate determining step (20), probably in a very unusual environment, not incompatible with a molecular mechanism. 

Doerge DR, Cooray NM, Brewster ME (1991) Peroxidase-catalyzed S-oxygenation mechanism of oxygen transfer for lactoperoxidase. Biochemistry 30 8960-8964... 

Preparation of Oxomanganese(V)-Salen Complexes The Mechanism of Oxygen Transfer... 

The mechanism of oxygen transfer from the peroxide (29) to the substrate still remains a matter of controversy. Current opinions favor the formation of a high-valent FeO (or Fe =0 or Fe —0-) (30) active species, which acts as a homolytic hydrogen abstractor from the substrate. An alternative mechanism considers the Fe -peroxide complex as the actual hydroxylating reagent, by analogy with the reactivity of vanadium(V)-peroxo and -alkylperoxo complexes and that of chromium(Vl)-peroxo complexes (see below). ... 

As an extension of our earlier work, studies of new transition metal and noble metal oxide systems have been undertaken. The systems selected for study are widely used as both catalysts and catalytic supports in industrial processes. Particular emphasis has been on establishing structure reactivity relationships and elucidating the molecular level mechanisms of oxygen transfer reactions that are not well understood. A discussion of several of our most recent studies follows. A detailed review of our earlier work may be found in the literature [41]. 

The mechanism of oxygen transfer from oxaziridines to nucleophiles is believed to involve an Sn2 type reaction and this assumption is supported by theoretical and experimental studies. When sulfides are oxidized to the corresponding sulfoxides and sulfones, the molecular recognition is steric in origin, and it is determined by the substituents on both the substrate and the oxaziridine. For the oxidation of enolates, the molecular recognition is explained with an Sn2 mechanism as well as by an open (non-chelated) transition state where the nonbonded interactions are minimized. The mechanism of oxygen transfer to an enolate to form the corresponding acyloin is shown below. ... 

Bach, R. D., Wolber, G. J. Mechanism of oxygen transfer from oxaziridine to ethylene the consequences of HOMO-HOMO interactions on frontier orbital narrowing. J. Am. Chem. Soc. 1984,106,1410-1415. 

D. V. Deubel, G. Frenking, P. Gisdakis, W. A. Herrmann, N. Rosch, J. Sundermeyer, Olefin epoxidation with inorganic peroxides, solutions to four long-standing controversies on the mechanism of oxygen transfer, Acc. Chem. Res. Zl (2004) 645. 

Scheme 9. Mechanism of oxygen transfer by intact dioxirane (A) and dioxyl diradical (B)...

Kazakov DV, Barzilova AB, Kazakov V.P. A novel chemiluminescence from the reaction of dioxiranes with alkanes. Proposed mechanism of oxygen-transfer chemiluminescence. Chem Commun 2001 191-2. 

In this review, we will focus on the mechanistic aspects of the oxygen activation and reactions of the P-450 systems involving metalloporphyrins. For this purpose, we will briefly outline some of the chemistry of P-450 and examine in detail the mechanisms of oxygen transfer by comparing the enzymic system to the model studies. At this time, applications of these model systems in synthetic chemistry have not been extensively pursued. 

The mechanism of oxygen transfer from the peroxide (29) to the substrate still remains a matter of controversy. Current opinions favor the formation of a high-valent FeO (or Fe =0 or... 

The kinetics and mechanism of oxygen transfer in the reaction of p-cyano-N,N-dimethylaniline N-oxide with the manganese(III) complex of the me50-tetrakis(2,6-dimethylphenyl)porphinato dianion have been investigated in the presence of imidazole.From the dependence of the pseudo first-order rate constants upon [ImH], and a knowledge of the equilibrium constants for imidazole ligation, second-order rate constants of = 3.3 x 10 s 2 = 5.53 s and —... 

The porphyrin complexes of iron were found in the excrements of reptiles, the so-called coprolites, several tenths of millions years old, suggesting that the mechanism of oxygen transfer did not basically change during this vast period of time up to our days. 

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