The reaction of 5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphinatoiron(III) hydrate with alkyl and acyl hydroperoxides. The dynamics of reaction of water-soluble and non .mu.-oxo dimer forming iron(III) porphyrins in aqueous solution. 7

Abstract

Kinetic and product studies (30 °C, µ = 0.20 with NaN03, between pH 1.0 and 12.35) are reported for the reaction in water of an iron(III) octa-o-chloro-substituted tetraphenylporphyrin [5,10,15,20-tetrakis(2,6-dichloro-3-sulfonatophenyl)porphinatoiron(III) hydrate ((2)Fem(H20)2 ^(2)Fenl(H0)(H20) + H+ -(2)Fe,n(OH)2 + 2H+) with a number of acyl and alkyl hydroperoxides (r-BuOOH, Ph(CH3)2COOH, Ph2(C02CH3)C00H, Ph2(CN)COOH, zm-C1C6H4C03H, p-N02C6H4C03H, and PhCH2C03H). All reactions are first-order in the hydroperoxide and in (2)Fem(X)2 (where X = H20, HO"). The rates are (1) insensitive to the presence or absence of 02 and (2) not subject to specific-acid, general-acid, nor general-base catalysis at any pH. For the reaction with r-BuOOH, characteristics of the pH dependence of the second-order rate constant (fc|y) are as follows; (1) < pH 3.5, kly is pH independent; (2) from pH 3.5 to 9.5, k]y increases and then decreases ("bell-shape curve"); (3) above pH 10, k]y again increases and then decreases (second "bell-shape curve"). These results are explained if one assumes that three steady-state intermediates [( 2)Feln(H20)(Z-Bu00H), ( 2)Fem(HO")(Z-BuOOH) *=* (2)Fem(H20)(f-Bu00"), and (2)Fe,1I(HO')(i-BuOO")] break down in the commitment step and are in acid-base equilibria. From product analysis, reactions with r-BuOOH provide 90% yield of (CH3)2CO and >50% yield of CH3OH. Neither CH4, C2H6, 02, or (Z-BuO)2 could be detected. In the presence of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) trap, (CH3)2CO is formed in 10-20% yield, and the main product (80-90%) is z-BuOH. With Ph(CH3)2COOH, Ph(CH3)C=0 was formed in ~70% yield at pH 7.25. Neither PhOH nor (CH3)2C=0 could be detected. These findings uniquely identify R(CH3)2CO* intermediates and allow the mechanism (2)Feln(H20)(X) + R(CH3)2COOH -/(2)Fe,v(0)(X) + R(CH3)2C0'/ -(2)Fe,v(0)(X) + R(CH3)2CO* followed by fragmentation of R(CH3)2CO" (within the /intimate pair/ and after solvent separation) to provide R(CH,)C=0 + CH3'. Reaction of CH3* with (2)Fe!II(H20)(X) or (2)Fe,v(0)(X) leads to CH3OH plus (2)Feu(H20) and (2)Fe"'(H20)(X), respectively. The putative (2)FeM(H20) species was trapped (20% yield) with CO as (2)Fe"(CO). The difference in product yields in the presence and absence of ABTS may be explained by the inability of ABTS to trap the components of the initially formed solvent caged pair, /(2)Fe(l) **IV(0)(X) + R(CH3)2CO"/, but essentially complete trapping of the solvent-separated (2)Felv(0)(X) and R(CH3)2CO" species. The reaction of (2)Fe*n(X)2 with r-BuOOH, and the other alkyl and acyl hydroperoxides investigated, gives rise to an observable iron(IV)-oxo porphyrin intermediate between pH 2.0 and 12. The formation of (2)Fe,v(0)(X) with z-BuOOH or Ph(CH3)2COOH requires the presence of 02. This is consistent with the formation of (2)Felv(0)(X) from the reaction of (2)Fe"(H20) with 02. Once generated, the spectra of the (2)Felv(0)(X) species persist for an extended time [70 h (pH 4.87), 100 h (pH 6.3), 80 h (pH 7.25), 50 h (pH 10.37), and 24 h (pH 11.6...

Mechanistic Insight into Peroxo‐Shunt Formation of Biomimetic Models for Compound II, Their Reactivity toward Organic Substrates, and the Influence of N‐Methylimidazole Axial Ligation

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New approach to the activation of anti-cancer pro-drugs by metalloporphyrin-based cytochrome P450 mimics in all-aqueous biologically relevant system

“…The cytochromes P450 biomimetic models have been intensively studied [12,[50][51][52][53][54][55][56][57][58][59][60][61], particularly with intention of elucidating the mechanism of O-O-cleavage. Our data are best accommodated by the studies of Almarsson and Bruice [50], Murata et al [51] and Panicucci and Bruice [52]. The initial oxygen binding to the ascorbate-reduced Fe II porphyrin center generates O ÅÀ 2 -Fe III P, which is further reduced to Fe(III) hydroperoxo species similar to cytochrome P450 [12].…”

Effect of distal histidines on hydrogen peroxide activation by manganese reconstituted myoglobin

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