Oxygen Activation and Radical Transformations in Heme Proteins and Metalloporphyrins

Abstract

As a result of the adaptation of life to an aerobic environment, nature has evolved a panoply of metalloproteins for oxidative metabolism and protection against reactive oxygen species. Despite the diverse structures and functions of these proteins, they share common mechanistic grounds. An open-shell transition metal like iron or copper is employed to interact with O2 and its derived intermediates such as hydrogen peroxide to afford a variety of metal–oxygen intermediates. These reactive intermediates, including metal-superoxo, -(hydro)peroxo, and high-valent metal–oxo species, are the basis for the various biological functions of O2-utilizing metalloproteins. Collectively, these processes are called oxygen activation. Much of our understanding of the reactivity of these reactive intermediates has come from the study of heme-containing proteins and related metalloporphyrin compounds. These studies not only have deepened our understanding of various functions of heme proteins, such as O2 storage and transport, degradation of reactive oxygen species, redox signaling, and biological oxygenation, etc., but also have driven the development of bioinorganic chemistry and biomimetic catalysis. In this review, we survey the range of O2 activation processes mediated by heme proteins and model compounds with a focus on recent progress in the characterization and reactivity of important iron–oxygen intermediates. Representative reactions initiated by these reactive intermediates as well as some context from prior decades will also be presented. We will discuss the fundamental mechanistic features of these transformations and delineate the underlying structural and electronic factors that contribute to the spectrum of reactivities that has been observed in nature as well as those that have been invented using these paradigms. Given the recent developments in biocatalysis for non-natural chemistries and the renaissance of radical chemistry in organic synthesis, we envision that new enzymatic and synthetic transformations will emerge based on the radical processes mediated by metalloproteins and their synthetic analogs.

Hybrid Metalloporphyrin Magnetic Nanoparticles as Catalysts for Sequential Transformation of Alkenes and CO2 into Cyclic Carbonates

“…Moreover,n os ignificant effects of the porphyrin meso-aryl substituents were observed in the catalytic activity.I nc ontrast, as trong influence of the central metal was identified, as chromium(III)-porphyrinc atalysts 2Cr, 7Cr,a nd 9Cr were found to be significantly less active and selectivet owardse poxide,w ith formation of benzaldehydei nu pt o3 0% yield, as previouslyo bserved [96] ( Table 1, entries 5-7). [52,97] Our study corroborates previous observations, in which the use of molecular oxygen as an oxygen donor requires, in general, the presence of an electron source. [52,97] Our study corroborates previous observations, in which the use of molecular oxygen as an oxygen donor requires, in general, the presence of an electron source.…”

Photocatalytic Oxygenation Reactions Using Water and Dioxygen

“…[15] However,O 2 has at riplet ground spin state and, therefore, direct reaction of O 2 with singlet organic substrates is spin-forbidden. [24][25][26][27][28][29][30][31][32][33][34] In such cases, oxygen in the high-valent metal-oxo species comes from O 2 ,w hich is the oxygen source in oxygenated products. [24][25][26][27][28][29][30][31][32][33][34] In such cases, oxygen in the high-valent metal-oxo species comes from O 2 ,w hich is the oxygen source in oxygenated products.…”

“…[15] Thus,t ransitionm etal catalysts are utilized for the catalytic oxidation of organic substrates by O 2 , [16][17][18][19][20][21][22][23] wherebyh igh-valent metal-oxo species are generated as reactive intermediates from the oxidation of metal complexes by O 2 with reductants. [24][25][26][27][28][29][30][31][32][33][34] High-valent metal-oxo speciesc an also be generated by the oxidation of metal complexesw ith H 2 O, when the oxygen atom in highvalent metal-oxo speciesc omes from H 2 O, as does that in the oxygenated products. [24][25][26][27][28][29][30][31][32][33][34] High-valent metal-oxo speciesc an also be generated by the oxidation of metal complexesw ith H 2 O, when the oxygen atom in highvalent metal-oxo speciesc omes from H 2 O, as does that in the oxygenated products.…”

Highly Active Catalysis of Cobalt Tetrakis(pentafluorophenyl)porphyrin Promoted by Chitosan for Cyclohexane Oxidation in Response‐Surface‐Methodology‐Optimized Reaction Conditions

“…Cytochrome P450 enzyme has a special structure with an important acid group, a key axial cysteine ligand and a natural cavity. This natural structure makes the enzyme, its related artificial enzyme and biomimetic catalyst having excellent functionality and becoming an important catalyst used for substrate oxidation . Duplication of the core structure and part functions of the enzyme using immobilized metalloporphyrin systems is of tremendous interest in order to improve the performance (activity and reusability) of metalloporphyrins .…”