Oxygen transfer involving nonheme iron: the influence of leaving group ability on the rate constant for oxygen transfer to (EDTA)Fe(III) from peroxycarboxylic acids and hydroperoxides.

Abstract

Ethylenediaminetetraacetato iron (III) [ ( and zero-order reactions with the help of a computer program written for this purpose using a Hewlett-Packard Model 9825A computer. In the case of the alkyl hydroperoxide reactions, the oxygen transfer reactions were inconveniently slow and, therefore, the method of initial rates was employed to determine the rate constant from the absorbance vs. time kinetic trace for the oxygen transfer reactions as given (8, 9). Further, it should be noted that, since each equivalent of alkyl hydroperoxide results in the oxidation of two equivalents of TBPH, the rate constant obtained by the method of initial rates is 2-fold greater than the absolute rate constant for the oxygen transfer reaction and the necessary adjustment was made for the alkyl hydroperoxide reactions. RESULTSThe plots of A400 vs. time for the reaction of (EDTA)Fe (III) with peroxycarboxylic acids are biphasic, as reported (6) for MCPBA. The initial 90% of the appearance of TBP-follows the first-order rate law, and this is followed by a very slow zero-order component of TBPh radical formation. It has been established (3), using MCPBA, that the pseudo-first-order component of TBP-radical formation corresponds to the oxygen transfer reaction from peroxycarboxylic acids to (EDTA)Fe(III), and the slow zero-order component is due to the breakdown of a peroxidic component (ODH; 1,3,5-tri-tbutyl-4-oxycyclohexa-2,5-dienyl-hydroperoxide) formed during the oxidation reaction (10-12). Therefore, all the plots of A400 vs. time for ODH '0-0-Y the reaction of the various peroxycarboxylic acids with (EDTA)Fe(III) were analyzed as a combination of sequential first-order and zero-order reactions. A complete kinetic analysis that accounts for the percentage yields of product and the rates of their formation has been reported (6). In the present study our only concern is with the second-order rate constants for oxygen transfer to (EDTA)Fe(III) so that we have restricted the kinetic analysis to the major pseudo-firstorder component of the TBP-radical formation. For the reaction of the most reactive alkyl hydroperoxides, diphenylhydroperoxyacetonitrile and methyl diphenylhydroperoxyacetate, pseudo-first-order rate constants were determined Abbreviations: TBPH, 2,4,6-tri-t-butylphenol; TBP, 2,4,6-tri-t-butylphenoxyl radical; MCPBA, m-chloroperoxybenzoic acid; ODH, 1,3,5-tri-t-butyl-4-oxycyclohexa-2,5-dienyl-hydroperoxide; TPP, meso-tetrakis(tetraphenyl)porphinato; [(EDTA)Fe(III)]i, initial concentration of (EDTA)Fe(III); YOOH, either alkyl hydroperoxide or peroxycarboxylic acid; ROOH, alkyl hydroperoxide only. 1734The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Pterin-Dependent Amino Acid Hydroxylases

“…Bruice's group has shown how the reactivity of [Fe 3+ (EDTA)(Sol)] -can be modulated by the identity of the "leaving group" of the oxygen atom donor. 784 A related phenomenon has also been observed with heme compounds, which catalyze oxygen transfer from OIC 6 F 5 faster than from OIPh. 772 Recently, the ability of a carboxylate-rich environment to support oxygen atom transfer chemistry in model systems was demonstrated.…”

“…In the wake of the crystal structure of the binuclear non-heme iron hydroxylase component of methane monooxygenase, which has a carboxylate-rich primary coordination sphere, the coordination chemistry of anionic ligands has returned to prominence in the modeling field. Bruice's group has shown how the reactivity of [Fe 3+ (EDTA)(Sol)] - can be modulated by the identity of the “leaving group” of the oxygen atom donor . A related phenomenon has also been observed with heme compounds, which catalyze oxygen transfer from OIC 6 F 5 faster than from OIPh …”

Peroxidase-Type Reactions Suggest a Heterolytic/Nucleophilic O–O Joining Mechanism in the Heme-Dependent Chlorite Dismutase

“…Linear free energy relationship (LFER) analyses have given insight into the kinetics and mechanisms of bond cleavage by oxidation catalysts. These analyses have shown that rate constants for RO–O(H) bond heterolysis ( k RO–O(H) ) depend linearly on the p K a of the leaving group (RO – + H + ⇆ ROH). , Leaving groups that are stronger acids (and hence relatively stable anions) are associated with faster heterolytic bond scission. As leaving group p K a ’s increase, however, the downward linear trend in k RO–O(H) values abruptly ceases and the plot becomes horizontal.…”

Detailed Spectroscopic and Theoretical Studies on [Fe(EDTA)(O2)]3-: Electronic Structure of the Side-on Ferric−Peroxide Bond and Its Relevance to Reactivity

“…As an alternative to radical chain reactions in ferric−peroxide systems, metal-based active oxygen species have been postulated (Scheme b). 1e,17e,,90b,c,− In relation to the well-studied heme systems, , one could reasonably assume that such a species would be highly reactive toward organic substrates. However, a key question related to the existence of a high-valent iron-oxo intermediate in a mononuclear non-heme environment is the source of its stability.…”