Download or read book Activation of Dioxygen by a Mononuclear Nonheme Iron Complex Via Sequential Peroxo Oxo and Hydroxo Intermediates written by David Philip Goldberg and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The activation of dioxygen by nonheme iron centers is of fundamental importance to biological and synthetic oxidation reactivity. Dioxygen activation by nonheme iron is often proposed to follow a sequence of steps involving initial O2 binding, reduction of O2 to form a peroxo species, and Ou2013O bond cleavage to produce a reactive high-valent FeIV(O) intermediate. Individual intermediates involved in these steps have been observed in both synthetic and enzymatic systems; however, the observation of multiple, sequentially formed Fe/oxygen intermediates is extremely rare. This presentation will discuss the reactivity of a dithiolate-ligated nonheme iron complex, FeII(Me3TACN)(S2SiMe2), with dioxygen to produce a peroxo(diiron) species, FeIII2(O2)(Me3TACN)2(S2SiMe2)2, which was characterized by UV-vis, Mu00f6ssbauer, resonance Raman (RR), and X-ray absorption spectroscopies. This peroxo(diiron) complex undergoes photochemically or thermally induced Ou2013O bond cleavage to generate an FeIV(O) complex, FeIV(O)(Me3TACN)(S2SiMe2), exhibiting a highly activated FeIV=O bond, as seen by RR and X-ray absorption spectroscopy. The FeIV(O) reacts with H-atom donors to produce an FeIII(OH) complex, FeIII(OH)(Me3TACN)(S2SiMe2), which could also be synthesized independently by addition of a one-electron oxidant followed by a hydroxide source to the FeII complex. The generation, stability, and spectroscopic characterization of each of these species will be discussed.

Download or read book Oxygen Activation by Mononuclear Non heme Iron Enzymes written by Jeffrey T Babicz and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Non-heme iron (NHFe) enzymes are in critical in Nature, playing significant roles in bioremediation, the biosynthesis of natural products, DNA repair and human health. These metalloenzymes utilize an Fe cofactor to activate dioxygen for reaction with organic substrates in a wide variety of chemical transformations including: H-atom abstraction, hydroxylation, halogentation, aromatic ring cleavage, aliphatic ring expansion/formation, electrophilic aromatic substitution and sulfur oxygenation/oxidation. Elucidating the mechanisms of these diverse catalysts requires defining the geometric and electronic structure of key Fe-O2 intermediates along the reaction cycle. An ideal tool for the interrogation of these Fe-O2 intermediates is nuclear resonance vibrational spectroscopy (NRVS), a synchrotron-based technique that observes the vibrational side-bands of the Fe-57 Mossbauer transition, making it a site-selective probe of all normal modes containing Fe displacement. Interpretation and analysis of NRVS spectra by correlation to quantum mechanical simulations (via density functional theory), allows for assignment of Fe vibrations and crucially geometric structure. In this thesis, NRVS is applied to the Fe-O2 intermediates in the extradiol dioxygenase, homoprotocatechuate 2,3-dioxygenase (HPCD-HPCA-Int-1) and the intradiol dioxygenase, protocatechuate 3,4-dioxygenase (PCD-4FC-Int-1), the pre-Fe(IV)=O intermediate in the pterin-dependent hydroxylase, tryptophan hydroxylase, and intermediate Q in methane monooxygenase (included in the appendix), while the ETHE1 sulfur oxidase versus oxygenase and the alpha-KG-dependent DAOCS concerted versus sequential DAOCS mechanistic studies utilize a combination of spectroscopic methods.

Download or read book Catalytic Activation of Dioxygen by Metal Complexes written by László I. Simándi and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 407 pages. Available in PDF, EPUB and Kindle. Book excerpt: The activation of dioxygen by metal ions has both synthetic potential and biological relevance. Dioxygen is the cleanest oxidant for use in emission-free technologies to minimize pollution of the environment. The book gives a survey of those catalyst systems based on metal complexes which have been discovered and studied in the last decade. They activate molecular oxygen and effect the oxidation of various organic compounds under mild conditions. Much of the recent progress is due to a search for biomimetic catalysts that would duplicate the action of metalloenzymes. Mechanistic aspects are emphasized throughout the book. An introductonary chapter reviews the chemistry of transition metal dioxygen complexes, which are usually the active intermediates in the catalytic reactions discussed. Separate chapters are devoted to oxidation of saturated, unsaturated and aromatic hydrocarbons, phenols, catechols, oxo-compounds, phosphorus, sulfur and nitrogen compounds.

Download or read book High valent Oxygen Intermediates of Mononuclear Non heme Iron Enzymes written by Shaun Di Hang Wong and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear non-heme iron (NHFe) enzymes catalyze a wide variety of biologically-important reactions such as hydroxylation, halogenation, desaturation, ring closure, and electrophilic aromatic substitution. The key intermediate in the catalytic cycle is the S = 2 Fe(IV)=O species, capable of abstracting an H-atom from inert C--H bonds as strong as 106 kcal/mol. The Fe(IV)=O intermediate in enzymes is transient and difficult to trap; as such, stable synthetic analogs have proven invaluable for spectroscopic elucidation of the geometric/electronic structure of the Fe(IV)=O unit and how it is activated for reactivity. Such biomimetic Fe(IV)=O model complexes can be either intermediate-spin (S = 1) or high-spin (S = 2) in contrast to the S = 2 ground state of enzyme intermediates. For an S = 1 Fe(IV)=O species, the Fe--oxo [beta] [pi]*-frontier molecular orbital (FMO) [from the combination of Fe d(xz/yz) and oxo p(x/y)] is involved in H-atom abstraction, and this FMO requires a side-on approach ([pi]-attack) to achieve maximum overlap with the substrate C--H bond. Through magnetic circular dichroism (MCD) and nuclear vibrational resonance spectroscopy (NRVS) studies, the reactivity of the S = 1 Fe(IV)=O unit has been shown to be affected by the oxo contribution in the [pi]*-FMO, where a larger oxo contribution results in greater orbital overlap (with the substrate C--H) and higher reactivity; also, the [pi]-attack pathway results in steric clashes between substrate and ligand, giving a significant steric contribution to the energy of the reaction barrier. For an S = 2 Fe(IV)=O species, the Fe--oxo [alpha] [sigma]*-FMO [Fe d(z2) and oxo p(z)] is spin-polarized (exchange-stabilized) to an energy level comparable with its [pi]*-FMO, making it accessible as a second pathway ([sigma]-attack) for reactivity. In the S = 2 Fe(IV)=O model complex ligated by TMG3tren, this [sigma]*-FMO is active but is axially hindered by the ligand, again giving a large steric contribution to the reaction barrier; however, the intrinsic electronic reaction barriers of the S = 2 [sigma]*-FMO and the S = 1 [pi]*-FMO are comparable, suggesting they are similarly active in H-atom abstraction. Furthermore, MCD excited-state spectroscopy in combination with multiconfigurational calculations on the S = 2 model reveal two different [pi]-pathways for reactivity involving Fe(III)--oxyl[p(x), [pi]] character, in addition to the [sigma]-pathway involving Fe(III)--oxyl[p(z), [sigma]] character, showing that the S = 2 Fe(IV)=O unit is activated for both [pi] and [sigma] H-atom abstraction reactivities. Finally, the S = 2 enzyme intermediate for the halogenase SyrB2 was trapped and structurally characterized by NRVS, revealing two possible 5-coordinate trigonal bipyramidal candidates with the Fe--oxo vector oriented either perpendicular or parallel to the substrate C--H bond. Importantly, this difference in orientation leads to Fe(III)--OH products oriented efficiently for different rebound reactivities -- native halogenation in the case of perpendicular orientation and non-native hydroxylation in the case of parallel orientation.

Download or read book The Activation of Dioxygen and Homogeneous Catalytic Oxidation written by D.H.R. Barton and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 503 pages. Available in PDF, EPUB and Kindle. Book excerpt: This monograph consists of the proceedings of the Fifth International Symposium on the Activation of Dioxygen and Homogeneous Catalytic Oxidation, held in College Station, Texas, March 14-19, 1993. It contains an introductory chapter authored by Professors D. H. R. Barton and D. T. Sawyer, and twenty-nine chapters describing presentations by the plenary lecturers and invited speakers. One of the invited speakers, who could not submit a manuscript for reasons beyond his control, is represented by an abstract of his lecture. Also included are abstracts of forty-seven posters contributed by participants in the symposium. Readers who may wish to know more about the subjects presented in abstract form are invited to communicate directly with the authors of the abstracts. This is the fifth international symposium that has been held on this subject. The first was hosted by the CNRS, May 21-29, 1979, in Bendor, France (on the Island of Bandol). The second meeting was organized as a NATO workshop in Padova, Italy, June 24-27, 1984. This was followed by a meeting in Tsukuba, Japan, July 12-16, 1987. The fourth symposium was held at Balatonfured, Hungary, September 10-14, 1990. The sixth meeting is scheduled to take place in Delft, The Netherlands (late Spring, 1996); the organizer and host will be Professor R. A. Sheldon.

Download or read book Oxygen Activation in Mononuclear Non heme Iron Enzymes written by Serra Goudarzi and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear non-heme iron (NHFe) enzymes catalyze a variety of reactions that are of pharmaceutical, industrial and environmental importance. A large number of these enzymes use a ferrous site to activate O2 for reaction with organic substrates, often requiring additional electrons from an outside source. These O2-activating NHFe enzymes can be divided into subclasses based on the cofactors used to supply these additional electrons. NHFe(II) enzymes generally possess a 2-His/1-(Asp/Glu) facial triad ligand set for binding of Fe(II), and they have been shown to utilize a general mechanistic strategy (GMS) for reaction with O2. The resting active sites of these enzymes (only Fe(II) bound) are six coordinate (6C) with the three protein derived ligands of the facial triad and three waters. When both cofactor and substrate are bound, the Fe(II) site loses a water ligand to become five coordinate (5C), opening a position for O2 to bind for reaction. NHFe(II) enzymes have d-d ligand field transitions in the near-IR region that are difficult to study because of their low absorption intensity and overlapping water and protein derived vibrations. A ferrous methodology using circular dichroism (CD), magnetic CD (MCD) and variable-temperature, variable-field (VTVH) MCD allows for determination of the active site geometric and electronic structures of these enzymes for development of functional insights. To extend these studies to the initial O2 binding step, NO is used as an unreactive analog of O2. The resulting {FeNO}7 (S = 3/2) complexes can be studied with absorbance, CD, MCD, VTVH MCD and electron paramagnetic resonance (EPR) to define the substrate interaction with the Fe(III) center that results from NO binding. These effects are used to gain insight into the experimentally inaccessible {FeO2}8 complexes with density functional theory calculations that are used to study the initial O2 activation steps. A major study of this thesis involves oxygen activation in deacetoxycephalosporin C synthase (DAOCS), a NHFe(II) enzyme that uses an alpha-ketoglutarate (aKG) cofactor to supply two electrons for its ring expansion of various penicillin substrates. A crystallographic study of DAOCS that did not observe simultaneous aKG and penicillin G (penG) binding to the same Fe(II) center led researchers to suggest a new sequential reaction for this enzyme, where reaction with aKG cofactor and O2 precedes substrate binding. Spectroscopic studies of the DAOCS Fe(II) site and its interaction with aKG and penG showed simultaneous binding of both is possible in solution. They further showed that the complex with aKG only was a mixture of 5C and 6C sites. A mixture of sites has not been observed in other enzymes of this class, which have been shown to remain as a single 6C site when aKG binds. This open coordination site allows for reaction with O2 in the absence of substrate, and this reaction was studied. Kinetic analysis of this reaction excludes the sequential reaction as a mechanistic possibility, because substrate binding cannot outpace the rapid decay of the intermediate that initiates the ring expansion. Comparison to the concerted reaction of the GMS, where both aKG and penG are bound before reaction with O2, shows that substrate binding activates the Fe site for a more kinetically efficient reaction with O2. This confirms the requirement for the general mechanistic strategy. The second major study of this thesis is on ETHE1, a member of a growing subclass of NHFe(II) enzymes that transforms sulfur containing substrates without a cofactor. ETHE1 dioxygenates glutathione persulfide (GSSH) to glutathione (GSH) and sulfite in a reaction that is similar to that of cysteine dioxygenase (CDO), but with monodentate (vs. bidentate in CDO) substrate coordination and a 2-His/1-Asp (vs. 3-His in CDO) ligand field. From MCD, GSS- binds directly to the iron active site causing coordination unsaturation to prime the site for O2 activation. {FeNO}7 complexes without and with GSSH were generated and spectroscopically characterized, and the new spectral features from persulfide binding to the Fe(III) were identified. Time-dependent density functional theory calculations were used to simulate the experimental absorbance spectra to determine the persulfide orientation in the active site (not known from crystallography). Comparison of these spectral features to those from monodentate cysteine binding in another enzyme of this subclass, isopenicillin N synthase (IPNS), shows that persulfide is a poorer donor than thiolate, but still results in an equivalent frontier molecular orbital (FMO) for reactivity. In IPNS, this reaction is an oxidative ring closure without incorporation of O2 atoms into the product. The persulfide dioxygenation reaction coordinate of ETHE1 was calculated, and while the initial steps are similar to the sulfur dioxygenation reaction coordinate of CDO, an additional hydrolysis step is required in ETHE1 to break the persulfide S-S bond. Unlike ETHE1 and CDO, which both oxygenate sulfur, IPNS oxidizes sulfur through an initial H-atom abstraction. Thus, the factors that control oxygenase vs. oxidase activity were evaluated. In general, sulfur oxygenation is thermodynamically favored and has a lower barrier for reactivity. However, in IPNS, second sphere residues in the active site pocket constrain the substrate raising the barrier for sulfur oxygenation relative to oxidation via H-atom abstraction.

Download or read book Coordination Chemistry of Mononuclear Non heme Iron Oxygenase Enzymes written by Paul C. Tarves and published by . This book was released on 2013 with total page 468 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Mononuclear non-heme iron oxygenase (MNO) enzymes utilize ferrous iron and dioxygen to perform a variety of thermodynamically challenging reactions at standard temperatures and pressures. The potent oxidizing power of these enzymatic systems has led to increased interest from the bioinorganic and synthetic organic communities. Presented herein is the preparation and characterization of an a-keto acid dependent synthetic system that closely models the active site electronic and dioxygen reactivity properties of the Fe II/a-ketoglutarate dependent class of MNH iron oxygenase enzymes. The ferrous complex utilized possesses a facially coordinating N,N,O- donor ligand reminiscent of a common active site motif observed for MNO iron enzymes. The labile coordination sites opposite the ligand framework allow for the ligation of exogenous a-keto acid cofactor as well as the binding and activation of dioxygen. The coordination of exogenous a-keto acid cofactor has been shown to greatly enhance the rate of dioxygen reactivity of the ferrous complex and lead to the catalytic decarboxylation of the cofactor. The enhancement in rate is attributed to the coupling of the dioxygen reduction step to the oxidative decarboxylation of the bound cofactor, which is a thermodynamically favorable process. The oxidative decarboxylation pathway suggests the formation of a high valent iron-oxo intermediate, which has been further supported by the concentration dependence of solvent oxidation during catalysis. The mechanism of dioxygen reactivity was further probed by Hammett analysis using substituted aromatic a-keto acid cofactors. The data presented suggest that the model system prepared proceeds via a biomimetic mechanism capable of catalytic dioxygen activation and substrate oxidation under ambient conditions. Investigation of differential carboxylate and phenolate ligation as it pertains to MNO iron enzymes is also reported. The synthesis and characterization of both ferrous and ferric compounds containing ligands with similar ethylene diamine backbones and either one or two phenolate moities: 2-(((2-(dimethylamino)ethyl)(methyl)amino)-methyl)phenol (N2O1-Ph) and 2,2'-((ethane-1,2-diylbis(methylazanediyl))bis-(methylene))diphenol (N2O2-Ph). The replacement of carboxylate moiety with a phenolate led to a significant decrease in reduction potential and subsequent enhancement in dioxygen sensitivity. This observation may provide insight into the reactivity of other iron containing enzymes with coordinated tyrosine residues, such as intradiol catechol dioxygenases.

Download or read book 2 Oxoglutarate Dependent Oxygenases written by Christopher J Schofield and published by Royal Society of Chemistry. This book was released on 2015-05-06 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the discovery of the first examples of 2-oxoglutarate-dependent oxygenase-catalysed reactions in the 1960s, a remarkably broad diversity of alternate reactions and substrates has been revealed, and extensive advances have been achieved in our understanding of the structures and catalytic mechanisms. These enzymes are important agrochemical targets and are being pursued as therapeutic targets for a wide range of diseases including cancer and anemia. This book provides a central source of information that summarizes the key features of the essential group of 2-oxoglutarate-dependent dioxygenases and related enzymes. Given the numerous recent advances and biomedical interest in the field, this book aims to unite the latest research for those already working in the field as well as to provide an introduction for those newly approaching the topic, and for those interested in translating the basic science into medicinal and agricultural benefits. The book begins with four broad chapters that highlight critical aspects, including an overview of possible catalytic reactions, structures and mechanisms. The following seventeen chapters focus on carefully selected topics, each written by leading experts in the area. Readers will find explanations of rapidly evolving research, from the chemistry of isopenicillin N synthase to the oxidation mechanism of 5-methylcytosine in DNA by ten-eleven-translocase oxygenases.

Download or read book Insights Into Dioxygen Bond Activation and Formation by Small Biomimetic Complexes written by Maksym A. Dedushko and published by . This book was released on 2020 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: Formation of an O-O bond is a crucial step in the biological oxidation of water to produce molecular O2. Its microscopic reverse, namely the activation of an O-O bond, is an essential step in key oxidative transformations during metabolism. Both of the reactions are employed by Nature to garner energy, synthesize, and degrade biomolecules in order to sustain life. A common feature of these two seemingly opposite, yet intimately interlinked, reactions in biological systems is that they are catalyzed by first-row transition metals such as manganese, iron, and copper. Both types of reactions are proposed to proceed through several reactive intermediates. Among them, metal-(hydro)peroxo and high-valent metal-oxo are common to both an O-O bond activation and formation step. Iron-containing metalloenzymes that utilize O2 as an oxidant perform a wide variety of biologically important chemical transformations. Cysteine-ligated iron metalloenzymes are of particular interest due to the unique properties that thiolates impart on transition metal ions. Thiolate (RS−) ligands form highly-covalent metal-ligand bonds, lower the activation energy barrier to O2 binding and one-electron reduction, facilitate an O-O bond activation. This dissertation describes a cis-thiolate ligated [FeII(SMeN4(tren))]+ complex that reacts with O2 to afford a series of metastable intermediates such as Fe111-superoxo, Mu-peroxo Fe111 dimer, Fe1v-oxo, and Fe111-hydroxo at low temperature, (Chapters 2 - 3). Remarkably, addition of oxo-atom donors (OAD) to [Fe11(SMeN4(tren))]+ affords an identical metastable Mu-peroxo Fe111 dimeric species, suggesting that a reversible O-O bond formation can occur, (Chapter 4). Chapter 5 describes the structure and properties of a O2-derived thiolate-ligated, Mu-peroxo-bridged CoIII dimer and provides a comparison with structurally analogous Mu-peroxo-bridged Mn111 dimers. And lastly, Chapter 6 provides a detailed description of a successfully developed, versatile synthetic procedure to the Schiff-based precursors en route to heterobimetallic Robson-type target complexes. Moreover, a heterobimetallic NaMn3O4 cubane complex relevant to the oxygen-evolving complex (OEC) has been synthesized and crystallographically characterized.

Download or read book Structure function Correlations in Oxygen and Substrate Activating Mononuclear Non heme Iron Enzymes written by Michael Lee Neidig and published by . This book was released on 2007 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Catalytic Activation of Dioxygen by Metal Complexes written by L. I. Simándi and published by Taylor & Francis US. This book was released on 2003-01-31 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: The catalytic activation of dioxygen continues to attract interest both due to its biological importance and synthetic potential. Metalloenzymes play crucial roles in metabolism by living organisms. The modelling of metalloenzymes by biomimetic metal complexes helps the search for useful oxidation catalysts and the understanding of their mechanisms of operation. Dioxygen is also the oxidant of choice in emission-free technologies aimed at minimising pollution of the environment, in line with the green chemistry requirements. This volume is devoted to recent progress in the field of catalytic oxidations using ruthenium, copper, iron, gold, cobalt and other complexes. Products and mechanistic aspects are given special emphasis throughout the book.

Download or read book Iron containing Enzymes written by Sam P. De Visser and published by Royal Society of Chemistry. This book was released on 2011 with total page 463 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear iron containing enzymes are important intermediates in bioprocesses and have potential in the industrial biosynthesis of specific products. This book features topical review chapters by leaders in this field and its various sub-disciplines.

Download or read book Characterization and Mechanistic Study of Oxygen iron Intermediates in Mononuclear Nonheme Model Systems written by Michael R. Bukowski and published by . This book was released on 2005 with total page 494 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthetic Models of Dioxygen Activation by Mononuclear Copper Enzymes written by Anne Michelle Reynolds and published by . This book was released on 2005 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Oxygen Complexes and Oxygen Activation by Transition Metals written by Arthur Martell and published by . This book was released on 1988-03-01 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physical Methods in Bioinorganic Chemistry written by Lawrence Que and published by Sterling Publishing Company. This book was released on 2000 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text provides detailed coverage of physical methods used in bioinorganic chemistry. By integrating theory with experimentation, and providing a more biological orientation, the book aims to serve as a major textbook for students of bioinorganic chemistry.

Download or read book Dioxygen Activation by Thiolate Ligated Complexes with Tunable Pi acceptor N heterocyclic Ligands written by Chaau Yan Poon and published by . This book was released on 2021 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dioxygen reduction and water oxidation are critical processes for aerobic life. Developing a better understanding of O-O bond activation and formation mechanisms mediated by metalloenzymes involving first-row transition metals such as Fe and Mn, would provide valuable insights for catalyst and drug development. While synthetic iron and copper oxo species generated from O2 have been extensively studied, the process of manganese dioxygen activation and its intermediates is comparatively unexplored. This dissertation focuses on the synthesis, characterization, and dioxygen reactivity of structurally analogous Mn- and Fe-thiolate complexes with tunable N-heterocyclic amine ligands. Chapter one provides an introduction to oxygen-evolving and oxygen-dependent metalloenzymes containing Mn and Fe metallocofactors. Chapter two highlights how metal ion Lewis acidity and steric properties influence the kinetics and thermodynamics of O2 activation by a series of structurally analogous Mn-thiolate complexes. A total of four high-valent Mn-oxo intermediates were observed along the O2 activation pathway, including MnIIIMnIV(m-oxo)(m-OH) intermediates. Chapter three covers the hydrogen atom transfer activity by the MnIIIMnIV(mu-oxo)(mu-OH) intermediate characterized in chapter two. Chapter four focuses on the synthesis, characterization, and preliminary O2 reactivity of Fe-thiolate complexes that possess a tunable N-heterocyclic amine, wherein a less Lewis acidic FeII species within the structurally analogous series led to the observation of a new O2 activation intermediate. Chapter five discusses the comparison between the structures and reactivities of alkoxide- and thiolate-ligated Mn alkylperoxo species with otherwise identical ligand frameworks, which demonstrates key insight into how the primary coordination sphere of active sites could alter their reactivity.