Use of Sterically Hindered Carboxylate Ligands to Model Structural and Functional Features of Dioxygen-activating Centers in Non-heme Diiron Enzymes PDF Download
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Author: Dongwhan Lee
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Category :
Languages : en
Pages : 888
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(Cont.) By using sterically hindered carboxylate ligands, 2,6-di(p-tolyl)benzoate (ArTolCO2- ) and 2,6-di(4-tert-butylphenyl)benzoate (Ar4-tBPhCO2- ), series of four-, five-, and six-coordinate iron(II) complexes were synthesized. The compounds are [Fe(O2CArTol)2(1-BnIm)2] (3), [Fe(O2CArTol)2(1-MeBzIm)2] (4), [Fe(02C-Ar4-tBuPh)2(2,2'-bipy)2] (5), [Fe(O2CArTol)2(TMEDA)] (6), and [Fe(O2CArTol)2(BPTA)] (7). Structural analyses of 3-7 revealed that the overall stereochemistry of the [Fe(O2CAr')2Ln] units is dictated by electronic and steric factors of the N-donor ligands (L), as well as by the flexible coordination of the carboxylate ligands. Distinctive MOss-Bauer parameters obtained for these and related compounds facilitated the spectral assignment of a diiron(II) complex having asymmetric metal sites, [Fe2(p-02CArTol)3(2CArTol)(2,6-lutidine)] (2). Well-defined mononuclear iron carboxylate complexes thus may serve as subsite models for higher nuclearity species in both synthetic and biological systems. Chapter III. Functional Mimic of Dioxygen-Activating Centers in Non-Heme Diiron Enzymes: Mechanistic Implications of Paramagnetic Intermediates in the Reactions between Diiron(II) Complexes and Dioxygen Tetracarboxylate diiron(II) complexes, [Fe2( -O02CArTOl)2(02CArToll)2(C5H5N)2] (la) and [Fe2(Pl-02CArTol)4(4-tBuC5H4N)2] (2a), where ArTloCO2- = 2,6-di(p-tolyl)benzoate, react with 02 in CH2C12 at -78 C to afford deep green intermediates ...
Author: Dongwhan Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 888
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(Cont.) By using sterically hindered carboxylate ligands, 2,6-di(p-tolyl)benzoate (ArTolCO2- ) and 2,6-di(4-tert-butylphenyl)benzoate (Ar4-tBPhCO2- ), series of four-, five-, and six-coordinate iron(II) complexes were synthesized. The compounds are [Fe(O2CArTol)2(1-BnIm)2] (3), [Fe(O2CArTol)2(1-MeBzIm)2] (4), [Fe(02C-Ar4-tBuPh)2(2,2'-bipy)2] (5), [Fe(O2CArTol)2(TMEDA)] (6), and [Fe(O2CArTol)2(BPTA)] (7). Structural analyses of 3-7 revealed that the overall stereochemistry of the [Fe(O2CAr')2Ln] units is dictated by electronic and steric factors of the N-donor ligands (L), as well as by the flexible coordination of the carboxylate ligands. Distinctive MOss-Bauer parameters obtained for these and related compounds facilitated the spectral assignment of a diiron(II) complex having asymmetric metal sites, [Fe2(p-02CArTol)3(2CArTol)(2,6-lutidine)] (2). Well-defined mononuclear iron carboxylate complexes thus may serve as subsite models for higher nuclearity species in both synthetic and biological systems. Chapter III. Functional Mimic of Dioxygen-Activating Centers in Non-Heme Diiron Enzymes: Mechanistic Implications of Paramagnetic Intermediates in the Reactions between Diiron(II) Complexes and Dioxygen Tetracarboxylate diiron(II) complexes, [Fe2( -O02CArTOl)2(02CArToll)2(C5H5N)2] (la) and [Fe2(Pl-02CArTol)4(4-tBuC5H4N)2] (2a), where ArTloCO2- = 2,6-di(p-tolyl)benzoate, react with 02 in CH2C12 at -78 C to afford deep green intermediates ...
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Category : Dissertations, Academic
Languages : en
Pages : 846
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Author: Loi Hung Do
Publisher:
ISBN:
Category :
Languages : en
Pages : 244
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Chapter 1 A comprehensive review of diiron modeling in the Lippard group over the past thirty years is presented. This account describes the different strategies employed to prepare biomimetic complexes of non-heme diiron protein active sites, highlighting the accomplishments of the past as well as the challenges for the future. Studies of various model systems have led to a more profound understanding of the fundamental properties of carboxylate-bridged diiron units and their reactivity toward molecular oxygen and organic substrates. The key principles and lessons that have emerged from these studies have been an inspiration for the original work presented in this thesis. Chapter 2 A series of phenoxylpyridyl and phenoxylimine ligands, H2LR,R' (compounds derived from bis(phenoxylpyridyl)diethynylbenzene, where R = H, Me, or t-Bu, and R' = H, or Ph) and H2BIPSMe,Ph (bis((phenylphenoxyl)iminephenyl)sulfone) were synthesized as platforms for non-heme diiron(II) protein (III) core and molecular oxygen as the source of the bridging oxo group. The [LMe,Ph]2- ligand is robust toward oxidative decomposition and does not display any reversible redox activity. Chapter 3 A dinucleating macrocycle, H2PIM, containing phenoxylimine metal-binding units has been prepared. Reaction of H2PIM with [Fe2(Mes)4] (Mes = 2,4,6-trimethylphenyl) and sterically hindered carboxylic acids, Ph3CCO2H or ArTolCO2H (2,6-bis(p-tolyl)benzoic acid), afforded complexes [Fe2(PIM)(Ph3CCO2)2] (1) and [Fe2(PIM)(ArTolCO2)2] (2), respectively. X-ray diffraction studies revealed that these diiron(II) complexes closely mimic the active site structures of the hydroxylase components of bacterial multi-component monooxygenases (BMMs), particularly the syn disposition of the nitrogen donor atoms and the bridging [mu]--n1n2 and [mu]-n1n1 modes of the carboxylate ligands at the diiron(II) centers. Cyclic voltammograms of 1 and 2 displayed quasi-reversible redox couples at +16 and +108 mV vs. ferrocene/ferrocenium, respectively, assigned to metal-centered oxidations. Treatment of 2 with silver perchlorate afforded a silver(I)/diiron(III) heterotrimetallic complex, [Fe2([mu]-OH)2(CIO4)2(PIM)(ArTolCO2)Ag] (3), which was structurally and spectroscopically characterized. Complexes 1 and 2 both react rapidly with dioxygen. Oxygenation of 1 afforded a ([mu]-hydroxo)diiron(III) complex [Fe2([mu]- OH)(PIM)(Ph3CCO2)3] (4), a hexa([mu]-hydroxo)tetrairon(III) complex [Fe4([mu]- OH)6(PIM)2(Ph3CCO2)2] (5), and an unidentified iron(III) species. Oxygenation of 2 exclusively formed di(carboxylato)diiron(III) products. X-ray crystallographic and 57Fe Mössbauer spectroscopic investigations indicated that 2 reacts with dioxygen to give a mixture of ([mu]- oxo)diiron(III) [Fe2([mu]-O)(PIM)(ArTolCO2)2] (6) and di([mu]-hydroxo)diiron(III) [Fe2([mu]- OH)2(PIM)(ArTolCO2)2] (7) complexes in the same crystal lattice. Compounds 6 and 7 spontaneously convert to a tetrairon(III) complex, [Fe4([mu]-OH)6(PIM)2(ArTolCO2)2] (8), when treated with excess H2O. The possible biological implications of these findings are discussed. Chapter 4 To investigate how protons may be involved in the dioxygen activation pathway of non-heme diiron enzymes, the reaction of H+ with a synthetic ([mu]-1,2-peroxo)(carboxylato)diiron(III) complex was explored. Addition of an H+ donor to [Fe2(O2)(N-EtHPTB)(PhCO2)]2+ (1.O2, where N-EtHPTB = anion of N,N,N' ,N' -tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane) resulted in protonation of the carboxylate rather than the peroxo ligand. Mössbauer and resonance Raman spectroscopic measurements indicate that the Fe2(O2) core of the protonated complex [1.O2]H+ is identical to that of 1.O2. In contrast, the benzoate ligand of [1.O2]H+ displays significantly different IR and NMR spectral features relative to those of the starting complex. The [1.O2]H+ species can be converted back to 1.O2 upon treatment with base, indicating that protonation of the carboxylate is reversible. These findings suggest that in the reaction cycle of soluble methane monooxygenases and related diiron proteins, protons may 6 induce a carboxylate shift to enable substrate access to the diiron core and/or increase the electrophilicity of the oxygenated complex. Chapter 5 To explore additional methods to interrogate the properties of diiron protein intermediates, studies of the vibrational profiles of ([mu]-1,2-peroxo)diiron(III) species were pursued using nuclear resonance vibrational spectroscopy (NRVS). Comparison of the NRVS of [Fe2(O2)(NEtHPTB)(PhCO2)]2+ (1.O2) to that of the diiron(II) starting material [Fe2(N-EtHPTB)(PhCO2)]2+ (1) revealed that the oxygenated complex displays new frequencies above 350 cm-1, which are attributed to the Fe-O-O-Fe core vibrations based on 18O2/16O2 isotopic labeling studies. The peak at 338 cm-1 has not been previously observed by resonance Raman spectroscopy. Empirical normal mode analysis provides a qualitative description of these isotopic sensitive modes. The NRVS of [Fe2([mu]-O2)(HB(iPrpz)3)2(PhCH2CO2)2] (4.O2, where HB(iPrpz)3 = tris(3,5-diisopropylpyrazoyl) hydroborate) was also measured and shows several Fe2(O2) modes between 350-500 cm-1. Appendix A Attempts to prepare a diiron(IV) complex described in the literature led to several unexpected discoveries. Reaction of tris((3,5-dimethyl-4-methoxy)pyridyl-2-methyl)amine (R3TPA) with iron(III) perchlorate decahydrate and sodium hydroxide afforded a ([mu]-oxo)([mu]-hydroxo)diiron(III) [Fe2([mu]-O)([mu]-OH)(R3TPA)2](ClO4)3 complex (1), rather than [Fe2([mu]-O)(OH)(H2O)-(R3TPA)2](ClO4)3 (B) as previously reported. The putative diiron(III) starting material B is formed only at low temperature when excess water is present. Compound 1 hydrolyzes acetonitrile to acetate under ambient conditions. The acetate-bridged diiron compound, [Fe2([mu]- O)([mu]-CH3CO2)(R3TPA)2](ClO4)3 (4A), was characterized by X-ray crystallography as well as various spectroscopic methods and elemental analysis. The identity of the acetate bridged complex was confirmed by comparing the structural and spectroscopic characteristics of 4A to those of an independently prepared sample of [Fe2([mu]-O)([mu]-CH3CO2)(R3TPA)2](ClO4)3.
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Category : Medicine
Languages : en
Pages : 1684
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Vols. for 1963- include as pt. 2 of the Jan. issue: Medical subject headings.
Author: Heinz-Bernhard Kraatz
Publisher: Wiley-VCH
ISBN:
Category : Science
Languages : en
Pages : 480
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Destined to set the standard, this book meets the need for a didactic textbook focusing on the role of model systems in bioinorganic chemistry. The first part features concepts in bioinorganic chemistry such as electron transfer, medicinal inorganic chemistry, bioorganometallics and metal DNA complexes, while the second part presents inorganic model chemistry on metallo-enzymes, organized by metal ion. Experts in the pertinent fields provide a didactically well-organized background on relevant biological systems, as well as on their structural, functional and spectroscopic properties. All chapters are similarly structured, each one beginning with a timeline featuring the most important historical facts on the subject, followed by a table of the most significant enzymes. The authors also summarize key developments and open questions within the respective model systems. This book is aimed at senior undergraduate and graduate students in chemistry, biochemistry, life science and related fields.
Author: Simone Friedle
Publisher:
ISBN:
Category :
Languages : en
Pages : 233
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(Cont.) These Mossbauer parameters are comparable to those observed for a peroxo intermediate formed in the reaction of reduced toluene/o-xylene monooxygenase hydroxylase (ToMOH) with dioxygen. Resonance Raman studies reveal an unusually low-energy 0-0 stretching mode in the peroxo intermediate that is consistent with a short diiron distance. Although peroxodiiron(lll) intermediates generated from 6, 7, and 8 are poor O-atom transfer catalysts, they display highly efficient catalase activity, with turnover numbers up to 10,000. In contrast to hydrogen peroxide reactions of diiron(Ill) complexes that lack a dinucleating ligand, the intermediates generated here could be reformed in significant quantities after a second addition of H20 2, as observed spectroscopically and by mass spectrometry. Appendix 1. Supporting Tables and Figures for Chapter 2 Appendix 2. Supporting Information for Chapter 4 Appendix 3. Synthesis of Triptycene Carboxylate-Bridged Dimetallic Complexes with First Row Transition Metals The synthesis and structural characterization of dimetallic complexes of the type [M2(1t-02CTrp) 4(THF)2] (M = Mn, Co, Ni, Cu, Zn) supported by triptycenecarboxylate ligands ( -O2CTrp) is described. Appendix 4. Synthesis and Structure of a Molecular Ferrous Wheel, [Fe(0 2CH)(O 2CArPro)(1,4-dioxane)]6 The structural characterization of a novel, hexanuclear iron(ll) compound with the carboxylate ArPrOCO2- is described.
Author: 岡崎国立共同研究機構分子科学研究所
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ISBN:
Category : Chemical bonds
Languages : en
Pages : 314
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Author: Mikael Antoine Minier
Publisher:
ISBN:
Category :
Languages : en
Pages : 276
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Chapter 1: Understanding the Utility of Hydrogen Bonding Donors in the Secondary Coordination Sphere of Non-heme Metal Complexes Chapter 1 is a mini-review that covers systematic studies on the effect of hydrogen bonding donors on the properties of metal complexes. Generalizing across different metals studied in biomimetic chemistry, the review allows for the comparison between different systems and generalizations are drawn about the effects of secondary coordination sphere hydrogen bond donors. Chapter 2: 19F NMR Study of Ligand Dynamics in Carboxylate-Bridged Diiron(II) Complexes Supported by a Macrocyclic Ligand A series of asymmetrically carboxylate-bridged diiron(II) complexes featuring fluorine atoms as NMR spectroscopic probes, [chemical formula ...] (10), [chemical formula ...] (11), and [chemical formula ...] (12) were prepared and characterized by X-ray crystallography, M6ssbauer spectroscopy, and VT 19F NMR spectroscopy. These complexes are part of a rare family of syn-N diiron(II) complexes, [chemical formula ...], that are structurally very similar to the active site of MMOHred. Solution characterization of these complexes demonstrates that they undergo intramolecular carboxylate rearrangements, or carboxylate shifts, a dynamic feature relevant to the reactivity of the diiron centers in bacterial multicomponent monooxygenases. Chapter 3: Structural Characterization of Carboxylate-Bridged and Hydroxo-Bridged Dizinc(II) Complexes Supported by a Macrocyclic Ligand Using a syn-N dinucleating macrocyclic ligand, H2PIM, a doubly carboxylate-bridged dizinc(II) complex, [chemical formula ...] (6) was prepared. In crystallizations of 6, two pseudoisomorphs of [chemical formula ...] (7) were discovered. On route to the synthesis of 6, a zinc complex, [chemical formula ...] (4) was prepared and the product upon reaction with air, [chemical formula ...] (5), was crystallized. Chapter 4: Secondary Coordination Sphere Modulation of Redox Potentials in Azide-Bridged Diiron(II) Complexes Observation that the H2PIM macrocyclic ligand provides an extra binding site for the binding of small molecules adjacent to corresponding diiron(II) complexes inspired the appendage of a secondary coordination sphere hydroxyl group to the ligand. The new ligand, H3PIM2, models not only the primary coordination sphere of the diiron sites of methane monooxygenase and toluene/o-xylene monooxygenase, but also that of a local threonine in the secondary coordination sphere. This chapter explores the differences between the PIM system and PIM2 system through the electrochemistry of the azido diiron(II) derviatives. Chapter 5: Synthesis and Characterization of a Linear Dinitrosyl-Triiron Complex Nitric oxide is released during the immune response by the host during bacterial infection. To counteract this response, bacteria have evolved nitric oxide reductases to convert NO to N2O. Some of these nitric oxide reductases contain a flavodiiron active site that have bridging carboxylates and hydroxides. Only a handful of synthetic complexes currently exist as models for the protein reactivity. Here we report the reaction of [chemical formula ...] (4) with NO(g) and Ph3CSNO to prepare the dinitrosyl-triiron complex [chemical formula ...] (5). The reaction was monitored by U V-Vis and ReactIR spectroscopy and compound 5 was characterized by X-ray crystallography, 5 7Fe M6ssbauer spectroscopy, Evans' method, and FTIR spectroscopy. The IR spectrum of compound 5 compares favorably to experimental spectroscopic data obtained for the proposed mononitrosylated intermediate of the protein. Chapter 6: Doubly and Triply Carboxylate Bridged Bis(ethylzinc) Complexes and Formation of the ([mu]-Oxo)tetrazinc Carboxylate [chemical formula ...] Ethylzinc 2,6-bis(p-tolyl)benzoate converts between two forms in solution. Through NMR spectroscopic techniques and X-ray crystallography, the species in equilibrium were identified as [chemical formula ...] (1), [chemical formula ...] (2), and diethyl zinc [chemical formula ...]. The equilibrium provides a model for understanding the speciation between doubly and triply m-terphenylcarboxylate-bridged diiron(II) and mononuclear iron(II) complexes. Evidence is presented for the occurrence of coordinatively unsaturated trigonal zinc species in solution. Both 1 and 2 decompose in air to form the T-symmetric oxozinc carboxylate, [chemical formula ...] (3). Appendix A: Synthesis and Characterization of Mononuclear, Pseudotetrahedral Cobalt(III) Compounds The preparation and characterization of two mononuclear cobalt(III) tropocoronand complexes, [chemical formula ...] and [chemical formula ...], are reported. The cobalt(III) centers exist in rare pseudotetrahedral conformations, with twist angles of 65° and 74° for the [Co(TC-5,5]+ and [Co(TC-6,6)]+ species, respectively. Structural and electrochemical characteristics are compared with those of newly synthesized [chemical formula ...] and [chemical formula ...] analogs. The spin state of the pseudotetrahedral [chemical formula ...] was determined to be S = 2, a change in spin state from the value of S = 1 that occurs in the square-planar and distorted square-planar complexes, [chemical formula ...] and [chemical formula ...], respectively. Appendix B: Synthetic Strategies toward Sterically Demanding Macrocyclic Ligands In order to prevent the formation of iron complexes of nuclearity higher than 2, a picket-fence macrocyclic ligand, H2tipp4PIM was designed. This chapter discusses the progress towards the synthesis of this ligand as well as design strategies.
Author: Albrecht Messerschmidt
Publisher: Wiley
ISBN: 9780471627432
Category : Science
Languages : en
Pages : 1500
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"it is a pleasure just to read this handsome and carefully produced work" Angewandte Chemie 2002 "...the Handbook of Metalloproteins is highly recommended as a resource for bioinorganic chemistry. It will have lasting value for researchers in the field..." The Alchemist - Chemweb In recent years, the analysis and classification of metalloproteins at the interface between chemistry and biology has accelerated. Many developments and initiatives have taken place and this two-volume handbook provides a comprehensive, yet focussed, collection of 105 major metalloproteins. Content is presented in both a large format and full colour and covers the most relevant transition metals such as Iron, Nickel, Copper, Cobalt, Molybdenum, Manganese Tungsten and Vanadium. This is the first Handbook of Metalloproteins ever published and is comprised of articles written by renowned experts in the field. It draws together contributions from over two hundred internationally renowned researchers that include: Douglas Rees and Charles Stout as well as Nobel Prize winner Robert Huber. Each contribution is presented in a similar format and shows a ribbon plot of the overall 3D Structure on their first page, a representation of the metal active site and numerous other figures and tables underpinning the remarks. Comparative information is provided on different proteins and every entry has been extensively referenced to current literature. * First comprehensive handbook to cover the major metalloproteins * Presents structural and functional data in an organised manner * Incorporates full-colour representation of molecular structures throughout * Unifies information from molecular biology, enzymology, spectroscopy, biochemistry, chemistry, biophysics, macromolecular crystallography and structural biology * Includes comprehensive sections that cover: Functional Class, Occurrence, Amino Acid Sequence Information, Protein Production, Purification and Molecular Characterisation, Metal Content and Cofactors, Activity Test, Spectroscopy, 3D Structure, Functional Aspects.
Author: D.H.R. Barton
Publisher: Springer Science & Business Media
ISBN: 1461530008
Category : Science
Languages : en
Pages : 503
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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.
