Reactions of Dioxygen and Its Reduced Forms with Heme Proteins and Model Porphyrin Complexes

Traylor, Teddy G.; Traylor, Patricia S.

doi:10.1007/978-94-011-0609-2_3

Cited by 39 publications

(40 citation statements)

References 376 publications

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“…Thus, the rate of formation of [Mn V (O)(TAML)] − was given by the following equation: d[Mn V (O)]/d t = k 2 ([Mn III ] 0 – [Mn V (O)])[cyclohexene][O 2 ]. Because the rate exhibited first-order dependence with respect to concentration of the Mn III complex, no bimetallic species (e.g., Mn IV –O 2 –Mn IV ) are involved in the formation of the Mn V –oxo complex. Products formed in the O 2 -activation reactions by [Mn III (TAML)] − with cyclohexene were analyzed by GC and GC–MS, showing that cyclohex-2-enol and cyclohex-2-enone were obtained as products with the yields of 21(3)% and 32(3)%, respectively (Figure S7).…”

Section: Resultsmentioning

confidence: 99%

A Manganese(V)–Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion

Lee²,

et al. 2016

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A mononuclear non-heme manganese(V)-oxo complex, [Mn(V)(O)(TAML)](-) (1), was synthesized by activating dioxygen in the presence of olefins with weak allylic C-H bonds and characterized structurally and spectroscopically. In mechanistic studies, the formation rate of 1 was found to depend on the allylic C-H bond dissociation energies (BDEs) of olefins, and a kinetic isotope effect (KIE) value of 16 was obtained in the reactions of cyclohexene and cyclohexene-d10. These results suggest that a hydrogen atom abstraction from the allylic C-H bonds of olefins by a putative Mn(IV)-superoxo species, which is formed by binding O2 by a high-spin (S = 2) [Mn(III)(TAML)](-) complex, is the rate-determining step. A Mn(V)-oxo complex binding Sc(3+) ion, [Mn(V)(O)(TAML)](-)-(Sc(3+)) (2), was also synthesized in the reaction of 1 with Sc(3+) ion and then characterized using various spectroscopic techniques. The binding site of the Sc(3+) ion was proposed to be the TAML ligand, not the Mn-O moiety, probably due to the low basicity of the oxo group compared to the basicity of the amide carbonyl group in the TAML ligand. Reactivity studies of the Mn(V)-oxo intermediates, 1 and 2, in oxygen atom transfer and electron-transfer reactions revealed that the binding of Sc(3+) ion at the TAML ligand of Mn(V)-oxo enhanced its oxidizing power with a positively shifted one-electron reduction potential (ΔEred = 0.70 V). This study reports the first example of tuning the second coordination sphere of high-valent metal-oxo species by binding a redox-inactive metal ion at the supporting ligand site, thereby modulating their electron-transfer properties as well as their reactivities in oxidation reactions.

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Section: Resultsmentioning

confidence: 99%

A Manganese(V)–Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion

Lee²,

et al. 2016

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“…407,456 This is intriguing given that the CO affinity for free heme centers are ≈20000 times greater than that for dioxygen. 457 This remarkable change in affinity is brought about by suppressing back-bonding interactions that stabilize heme-carbonyl adducts, while exerting stability-enhancing hydrogen-bonding interactions on heme-dioxygen moieties (see Figure 28). 453,458…”

Section: Heme/dioxygen Interactions: From Biology To Model Systemsmentioning

confidence: 99%

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

et al. 2018

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Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e− reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper–O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme–Cu models, evaluating experimental and computational results, which highlight important fundamental structure–function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.

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“…Activation of O 2 or H 2 O 2 by heme often leads to the generation of high-valent iron-oxo (ferryl) intermediates. 1 In reactions catalyzed by heme peroxidases, donation of two electrons from the Fe(III)-porphyrin complex results in heterolytic cleavage of the HOOH bond. The resulting compound I intermediate carries one oxidizing equivalent on the iron and the other in the porphyrin π system, and is consequently described as Fe(IV) =O coupled to a porphyrin radical cation (por •+ ): 2,3…”

Section: ■ Introductionmentioning

confidence: 99%

“…Activation of O 2 or H 2 O 2 by heme often leads to the generation of high-valent iron-oxo (ferryl) intermediates . In reactions catalyzed by heme peroxidases, donation of two electrons from the Fe(III)-porphyrin complex results in heterolytic cleavage of the HOOH bond.…”

Section: Introductionmentioning

confidence: 99%

Structure-Based Mechanism for Oxidative Decarboxylation Reactions Mediated by Amino Acids and Heme Propionates in Coproheme Decarboxylase (HemQ)

et al. 2017

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Coproheme decarboxylase catalyzes two sequential oxidative decarboxylations with H2O2 as the oxidant, coproheme III as substrate and cofactor, and heme b as the product. Each reaction breaks a C-C bond and results in net loss of hydride, via steps that are not clear. Solution and solid-state structural characterization of the protein in complex with a substrate analog revealed a highly unconventional H2O2-activating distal environment with the reactive propionic acids (2 and 4) on the opposite side of the porphyrin plane. This suggested that, in contrast to direct C-H bond cleavage catalyzed by a high-valent iron intermediate, the coproheme oxidations must occur through mediating amino acid residues. A tyrosine that hydrogen bonds to propionate 2 in a position analogous to the substrate in ascorbate peroxidase is essential for both decarboxylations, while a lysine that salt bridges to propionate 4 is required solely for the second. A mechanism is proposed in which propionate 2 relays an oxidizing equivalent from a coproheme compound I intermediate to the reactive deprotonated tyrosine, forming Tyr■. This residue then abstracts a net hydrogen atom (H■) from propionate 2, followed by migration of the unpaired propionyl electron to the coproheme iron to yield the ferric harderoheme and CO2 products. A similar pathway is proposed for decarboxylation of propionate 4, but with a lysine residue as an essential proton shuttle. The proposed reaction suggests an extended relay of heme-mediated e−/H+ transfers and a novel route for the conversion of carboxylic acids to alkenes.

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Reactions of Dioxygen and Its Reduced Forms with Heme Proteins and Model Porphyrin Complexes

Cited by 39 publications

References 376 publications

A Manganese(V)–Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion

A Manganese(V)–Oxo Complex: Synthesis by Dioxygen Activation and Enhancement of Its Oxidizing Power by Binding Scandium Ion

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

Structure-Based Mechanism for Oxidative Decarboxylation Reactions Mediated by Amino Acids and Heme Propionates in Coproheme Decarboxylase (HemQ)

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