Download or read book Physical Characterization of Diiron dioxygen Complexes and Resonance Raman Studies of Mononuclear Non heme Iron Proteins written by Bridget Anne Brennan and published by . This book was released on 1991 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Dissertation Abstracts International written by and published by . This book was released on 1992 with total page 760 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Structural and Mechanistic Studies of Oxygen Activating Mononuclear and Dinuclear Nonheme Iron Enzymes and Their Models written by Kevin Douglas Koehntop and published by . This book was released on 2005 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Models for Mononuclear Nonheme Iron Proteins written by Yu-Min Catherine Chiou and published by . This book was released on 1994 with total page 534 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bioinorganic Spectroscopy Structure function Correlations in Binuclear Non heme Iron Enzymes and Developing Nuclear Resonance Vibrational Spectroscopy for Characterization of Enzyme Intermediates written by Caleb Branson Bell and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The foci of this dissertation are: 1) combined use of spectroscopies for mechanistic understanding of the oxygen reactions of various non-heme iron enzymes and related model complexes, and 2) the development of the recently described nuclear vibrational resonance spectroscopy (NRVS) coupled with density functional calculations (DFT) for characterization of non-heme iron enzyme intermediates. Binuclear non-heme iron enzymes are involved in many medically and industrially important processes such as DNA synthesis by ribonucleotide reductase (RNR), conversion of methane to methanol by methane monooxygenase (MMO), fatty acid desaturation by [Delta]9 desaturase, iron storage and homeostasis by ferritins, degradation of aromatic compounds by various bacterial monooxygenases (ToMO, T4MO, etc.) and antibiotic biogenesis by p-aminobenzoate N-oxygenase (AurF), etc. Interestingly, these diverse reactions typically begin with O2 reacting with a biferrous active site, coordinated by highly conserved protein ligands (ExxH motifs) in four [Alpha]-helix bundles. Moreover, spectroscopically and chemically similar intermediates can be detected in many of the enzyme systems. The best studied in this family are RNRs, where biferric peroxo intermediates (P and P'), and the high-valent Fe(III)Fe(IV) intermediate X have been stabilized and spectroscopically characterized in wt and numerous variants. De novo designed four [Alpha]-helix bundles have been synthesized (the ~140 amino acid dui ferri (DF) peptide family) and are good models for binuclear non-heme iron enzymes. These systems provide a protein environment and can be viewed as a bridge between inorganic model complexes and native proteins. The pseudo-symmetric single chain version (DFsc) coordinates two ferrous ions by two His and four Glu amino acid residues. Circular dichroism (CD), magnetic CD (MCD) and variable-temperature variable-field MCD (VTVH MCD) show that this "active site" in DFsc has a 4-coordinate and 5-coordinate (4C+5C) geometry that is weakly antiferromagnetically coupled (J [approximately equal to] --2 cm-1) indicative of [Mu]1,3 carboxylate bridges, highly similar to RNR biferrous structures. Extended x-ray absorption fine structure (EXAFS) data are consistent with this assignment and show that one terminal carboxylate residue coordinates in a bidentate fashion. Changes in the CD/MCD/VTVH MCD and EXAFS spectra in the Y51L and E11D variants show that the 4C site is proximal to (but not bound by) Y51 and the bidentate carboxylate is coordinated to the 5C iron. Open coordination positions on both irons allow for dioxygen to react rapidly with the biferrous site. The reaction of biferrous DFsc with dioxygen yields a 520 nm ([Epsilon] = [weak approximation to]1200 M-1cm-1) species with a formation rate of 2 s-1, again similar to RNR (the Class Ia RNR from Escherichia coli has a dioxygen reaction rate of ~1 s-1, however the first species formed (intermediate P) has [Lambda]max = 700 nm). The resonance Raman (rR) spectrum obtained by excitation into the 520 nm feature in DFsc (and the E11D variant) proves this chromophore arises from a Tyr to ferric charge transfer (CT) transition. The 520 nm feature is lost by substitution of Y51 but not Y18, thus Y51 binds to the site after reaction with dioxygen. Subsequent binding of Y51 functions as an internal spectral probe of the dioxygen reaction and as a proton source that would promote loss of hydrogen peroxide. Coordination by a ligand that functions as a proton source could be a structural mechanism used by natural binuclear iron enzymes to drive their reactions past peroxo biferric level intermediates. RNR's can be divided into 3 major classes based on the radical generating machinery. Class I RNR's utilize a dimetal cofactor that reacts with dioxygen and can be subdivided into Classes Ia, Ib and Ic based on sequence homology and metal dependency. Class Ia enzymes are the best studied an present in higher organisms including human (host) while Class Ib enzymes are typically found in pathogens. CD, MCD and VTVH MCD data on biferrous loaded Class Ib RNR from Bacillus cereus allow assignment of the active site as 4C+5C in solution, resolving discrepancies from available crystal structures. Differences in the zero-field splitting parameters (D and E) and magnetic coupling extracted from fits to the VTVH MCD data can be ascribed to differences in the bridging carboxylate conformations. FeII loading, monitored by CD, shows cooperative binding with Kd 100 mM, significantly stronger that the metal binding in Class Ia. This provides the pathogen a competitive advantage relative to host in physiological, iron-limited environments Returning to Class Ia, the recently discovered intermediate P' notably lacks structural definition. This is mainly due to the lack of spectroscopic handles from which to obtain the needed experimental data. What is know, however, is that this species directly forms intermediate X and is directly derived from the well-defined intermediate P. Spectroscopically, P' has Mössbauer isomer shifts ([lowercase Delta] = 0.52 and 0.45 mm/s) that are significantly lower than the cis-[Mu]1,2 peroxo P ([lowercase Delta] = 0.63 mm/s) and lacks the ~700 nm peroxo to ferric CT suggesting some change in coordination mode or protonation may be involved in P -- P'. Comparisons of the reduced and oxidized crystal structures show differences in carboxylate coordination modes and water binding that must occur at some stage along the reaction coordinate. All of these potential structural perturbations were systematically incorporated into computational models of the intermediate site and correlated with experimental data using density functional theory (DFT). Two potential reaction pathways consistent with available experimental data were found. The first involves water addition to Fe1 of the cis-[Mu]-1,2 peroxo intermediate P causing opening of a bridging carboxylate to form intermediate P' which has an increased electron affinity and is activated for proton-coupled electron transfer to form the Fe(III)Fe(IV) intermediate X. While the second, more energetically favorable pathway, involves addition of a proton to a terminal carboxylate ligand in the site which increases the electron affinity and triggers electron transfer to form X. Vibrational characterization could, in principle, distinguish these pathways. However, the lack of a reasonably intense chromophore precludes rR experiments. The recently available method of nuclear vibrational resonance spectroscopy (NRVS) does not have these chromophoric constraints and can provide the needed vibrational data for P'--and many other "spectroscopically challenged" intermediates in non-heme iron biochemistry. The vibrations enhanced in NRVS are typically lower in energy and differ from those observed in rR, thus studies on well defined model complexes are needed prior to intermediate studies. A series of mononuclear Fe(IV)=O have been characterized by NRVS coupled with DFT calculations to define NRVS spectral assignments and set a foundation for vibrational characterization of non-heme iron enzyme intermediates. These studies show that the NRVS spectrum is rich in structural information. Of the four Fe(IV)=O models, supported by the 1, 4, 8, 11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMC); N, N-bis(2-pyridylmethyl)-N-bis(2-pyridyl) methylamine (N4Py); N-benzyl-N, N', N'-tris(2-pyridylmethyl)-1,2-diaminoethane (BnTPEN); and 1,1,1-tris{2-[N(2)-(1,1,3,3-tetramethylguanidino)]ethyl}amine (TMG3tren) ligand sets, only the trigional bipyramidal geometry (relative to the 6C approximatly C4v geometry of TMC, N4Py and BnTPEN) enforced by the TMG3tren ligand affords a high-spin species. Isotope sensitive Fe-O stretches are observed for all complexes at 820 to 831 cm-1. However, at lower energy (
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 American Doctoral Dissertations written by and published by . This book was released on 1991 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Graduate School Commencement written by University of Minnesota. Graduate School and published by . This book was released on 1992 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ACS Directory of Graduate Research 1993 written by American Chemical Society. Committee on Professional Training and published by . This book was released on 1993 with total page 1700 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Iron oxo Complexes written by Cheryl A. Christmas and published by . This book was released on 1993 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Structure and Reactivity of Non heme Iron III Proteins and Model Complexes written by Bruce Prentiss Murch and published by . This book was released on 1987 with total page 534 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Spectroscopic and Computational Studies of Mononuclear Nonheme Iron Enzymes written by Kenneth M. Light and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear nonheme iron enzymes (NH Fe enzymes) catalyze a variety of biological reactions. A large group of NH Fe enzymes use a ferrous active site to activate dioxygen towards reaction with substrate, and require an additional cofactor as a source of electrons necessary for catalysis. The main part of this thesis involves the application of a circular dichroism (CD), magnetic circular dichroism (MCD) and variable temperature, variable-field MCD (VTVH MCD) spectroscopic methodology to a series of alpha-ketoglurate-dependent (alpha-KG-dependent) enzymes for the purpose of understanding how this enzyme family and the NH Ferrous enzymes in general induce the dissociation the generation of a 5C site for dioxgyen reactivity, as well as how dioxygen binding is oriented for proper catalysis. In addition to catalyzing oxidation of organic substrates, NH Fe enzymes are also involved in the catalytic hydrolysis and hydration of substrates. A prominent example of this is nitrile hydratases (NHases), unusual low-spin (LS) Ferric or Cobaltic enzymes that catalyze the conversion of nitriles to amides in soil bacteria. Another part of this thesis involves the spectroscopic characterization of a ferric NHase for the determination of its active site geometric and electronic structure, which are used to calibrate a computational model which is extended to explore the NHase catalytic mechanism.
Download or read book Magnetic Circular Dichroism Spectroscopic Studies of Mononuclear Non heme Iron Sites written by Elizabeth Gottlieb Pavel and published by . This book was released on 1997 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Spectroscopic and Theoretical Studies of Mononuclear Non heme Iron Enzymes written by Adrienne Renee Diebold and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Mononuclear non-heme iron enzymes are an important class with a wide range of medical, pharmaceutical and environmental applications. Within this class, the oxygen activating enzymes use Fe(II) to activate O2 for reaction with the substrate. The focus of this thesis is on understanding two major themes of the oxygen activating enzymes - the role of the (2His/1 carboxylate) facial triad and the initial O2 reaction steps of alpha-keto acid-dependent dioxygenases - using a combination of spectroscopic techniques and DFT calculations. For ferrous systems, abs/CD/MCD/VTVH MCD studies define the geometric and electronic structure of the ferrous site. In combination with DFT calculations, a structure/function picture of the ferrous sites is developed. To extend these studies to the initial steps of O2 binding, studies with NO as an O2 analogue ({FeNO}7/{FeO2}8) utilize EPR/abs/CD/MCD/VTVH MCD spectroscopy with DFT calculations to elucidate important effects of the substrate on the {FeNO}7 bond. These effects are used in the computational extension to the experimentally inaccessible O2 bound complexes giving insight into the initial steps of O2 binding and activation. Taken together, these studies shed light on the rational for facial triad ligation at the Fe(II) site in the oxygen activating enzymes and how the Fe(II) ligand set tunes the specific reactivity of these enzymes.
Download or read book Spectroscopic and Reactivity Studies of Mononuclear and Binuclear Non heme Iron Complexes written by Bala Sundari T. Kasibhatla and published by . This book was released on 1998 with total page 478 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.
