Modeling the Active Sites of Diiron and Dicopper Metalloproteins with Napthyridine-, Phthalazine-, and Diethynylbenzene-based Ligands PDF Download
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Author: Jane Kuzelka
Publisher:
ISBN:
Category :
Languages : en
Pages : 212
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Book Description
Chapter 1. Bio-Inspired Reactions of Diiron Centers with Dioxygen A variety of biological systems employ carboxylate-bridged diiron centers to achieve substrate oxidation using dioxygen, and numerous small molecule model compounds have been synthesized in order to mimic this chemistry in the absence of a protein scaffold. In this introductory chapter, a brief overview is presented of ligand systems that have been used to prepare diiron complexes, and the subsequent oxidation chemistry of these systems is outlined. Chapter 2. Carboxylate, Phosphodiester, and Hydroxide-Bridged Diiron(II) Complexes with a Sterically Hindered Phthalazine Ligand The synthesis and crystallographic characterization of a series of diiron(II) complexes with a sterically hindered bridging phthalazine ligand are presented. The compounds [Fe2(Ph4bdptz)([mu]-O2CR)2]2+ (R = CH3 (3); C2H5 (4); CH2Ph (5); t-C4H9 (6)), [Fe2(Ph4bdptz)([mu]-O2P(OPh)2)2]2+ (7), and [Fe2(Ph4bdptz) ([mu]-OH)(MeCN)2]3+ (8) were prepared as small molecule models of the catalytic sites in non-heme carboxylate-bridged diiron enzymes. The phenyl rings of Ph4bdptz form a hydrophobic size-constrained pocket in which additional ligands can be accommodated, and they block the possible formation of tetranuclear species. As the steric bulk of the ancillary ligands is increased, the carboxylates shift from a syn, anti to a syn, syn coordination mode, and the Mossbauer spectra of the diiron(II) compounds clearly reflect the symmetry of the iron coordination environment. The oxidation chemistry of the diiron(II) compounds is presented.
Author: Jane Kuzelka
Publisher:
ISBN:
Category :
Languages : en
Pages : 212
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Book Description
Chapter 1. Bio-Inspired Reactions of Diiron Centers with Dioxygen A variety of biological systems employ carboxylate-bridged diiron centers to achieve substrate oxidation using dioxygen, and numerous small molecule model compounds have been synthesized in order to mimic this chemistry in the absence of a protein scaffold. In this introductory chapter, a brief overview is presented of ligand systems that have been used to prepare diiron complexes, and the subsequent oxidation chemistry of these systems is outlined. Chapter 2. Carboxylate, Phosphodiester, and Hydroxide-Bridged Diiron(II) Complexes with a Sterically Hindered Phthalazine Ligand The synthesis and crystallographic characterization of a series of diiron(II) complexes with a sterically hindered bridging phthalazine ligand are presented. The compounds [Fe2(Ph4bdptz)([mu]-O2CR)2]2+ (R = CH3 (3); C2H5 (4); CH2Ph (5); t-C4H9 (6)), [Fe2(Ph4bdptz)([mu]-O2P(OPh)2)2]2+ (7), and [Fe2(Ph4bdptz) ([mu]-OH)(MeCN)2]3+ (8) were prepared as small molecule models of the catalytic sites in non-heme carboxylate-bridged diiron enzymes. The phenyl rings of Ph4bdptz form a hydrophobic size-constrained pocket in which additional ligands can be accommodated, and they block the possible formation of tetranuclear species. As the steric bulk of the ancillary ligands is increased, the carboxylates shift from a syn, anti to a syn, syn coordination mode, and the Mossbauer spectra of the diiron(II) compounds clearly reflect the symmetry of the iron coordination environment. The oxidation chemistry of the diiron(II) compounds is presented.
Author:
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Category : Dissertations, Academic
Languages : en
Pages : 858
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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: American Chemical Society. Committee on Professional Training
Publisher:
ISBN:
Category : Biochemistry
Languages : en
Pages : 1932
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Faculties, publications and doctoral theses in departments or divisions of chemistry, chemical engineering, biochemistry and pharmaceutical and/or medicinal chemistry at universities in the United States and Canada.
Author: Sungho Yoon
Publisher:
ISBN:
Category :
Languages : en
Pages : 301
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Book Description
(Cont.) tetrairon(II) cubane complex was identified and structurally characterized. Chapter 4: Synthesis and Characterization of [Fe2 ... CR)]3 and [Fe2 ... CR)]3+ Complexes with Carboxylate-Rich Metal Coordination Environment as Models for Diiron Centers in Oxygen-Dependent Non-Heme Enzymes. Utilizing hydrogen bonding interactions and sterically bulky carboxylates, synthetic routes were developed to prepare the mononuclear iron(II) complexes with the vacant coordination sites for O2 binding. Reactions of such complexes with O2 resulted in rare asymmetric complexes having an [Fe2 ... CR)]3+ or [Fe2 ... CR)]3+ unit. These diiron(III) complexes with carboxylate-rich metal coordination environments reproduce the diiron(III) cores housed in four-helix bundles found in nature. Compound 3, which replicates the [Fe2 ... CR)] core of sMMOH[ox], shares several physical properties with the enzyme, electronic transitions, Mossbauer spectra, and magnetic exchange interactions. On the other hand, the structure of 4, ([mu]-oxo)([mu]-carboxylato)diiron(III) complex, mimics the diiron(III) sites of RNR-R2. The electronic and Mbssbauer spectral transitions of 4 are typical of diiron(III) complexes with an Fe-O-Fe moiety. Magnetic exchange coupling interaction between the two iron atoms is within the expected range for oxo-bridged diiron(III) sites. These results demonstrate how the diiron(III) structures in different metalloproteins, namely, the [mu]-oxo cores of RNR-R2 and the [mu]-dihydroxo unit in MMOH, can be replicated by subtle changes in ligand composition ...
Author: Loi Hung Do
Publisher:
ISBN:
Category :
Languages : en
Pages : 244
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Book Description
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.
Author: Michael K. Johnson
Publisher: John Wiley & Sons
ISBN: 1119159857
Category : Science
Languages : en
Pages : 941
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Book Description
Summarizes the essential biosynthetic pathways for assembly of metal cofactor sites in functional metalloproteins Metalloprotein Active Site Assembly focuses on the processes that have evolved to orchestrate the assembly of metal cofactor sites in functional metalloproteins. It goes beyond the simple incorporation of single metal ions in a protein framework, and includes metal cluster assembly, metal-cofactor biosynthesis and insertion, and metal-based post-translational modifications of the protein environments that are necessary for function. Several examples of each of these areas have now been identified and studied; the current volume provides the current state-of-the-art understanding of the processes involved. An excellent companion to the earlier book in this series Metals in Cells—which discussed both the positive and negative effects of cellular interactions with metals—this comprehensive book provides a diverse sampling of what is known about metalloprotein active site assembly processes. It covers all major biological transition metal components (Mn, Fe, Co, Ni, Mo), as well as the other inorganic components, metal-binding organic cofactors (e.g., heme, siroheme, cobalamin, molybdopterin), and post-translationally modified metal binding sites that make up the patchwork of evolved biological catalytic sites. The book compares and contrasts the biosynthetic assembly of active sites involving all biological metals. This has never been done before since it is a relatively new, fast-developing area of research. Metalloprotein Active Site Assembly is an ideal text for practitioners of inorganic biochemistry who are studying the biosynthetic pathways and gene clusters involved in active site assembly, and for inorganic chemists who want to apply the concepts learned to potential synthetic pathways to active site mimics.
Author: Emily Carrig Carson
Publisher:
ISBN:
Category :
Languages : en
Pages : 231
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Book Description
(Cont.) 2-, 3-, or 4-Diphenylphosphino moieties incorporated into a pyridine ligand (2-, 3-, or 4-Ph2Ppy) were allowed to react with the preassembled diiron(II) complex ..., where ... is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). Triply-, doubly-, and tetrabridged compounds ... (1) ... (2) ... (3) ... (4) resulted and were characterized crystallographically. Exposure of 1 - 4 to dioxygen revealed both stoichiometric and catalytic phosphine oxidation. Oxidation of 4 in CH2C12 affords ... (6), which contains the biologically relevant [Fe2([mu]-OH)2([mu]-O2CR)] 3 core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analog 1 yielded a hexanuclear species, 5, upon oxidation.
Author: C. W. Hahn
Publisher:
ISBN:
Category :
Languages : en
Pages : 244
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Author: Jeffrey W. Kelly
Publisher: Springer Science & Business Media
ISBN: 1475792352
Category : Science
Languages : en
Pages : 312
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Book Description
The Industry-University Cooperative Chemistry Program (IUCCP) has sponsored eight previous international symposia covering a range of topics of interest to industrial and academic chemists. The ninth IUCCP Symposium, held March 18-21, 1991 at Texas A&M University was the second in a two part series focusing on Biotechnology. The title for this Symposium "Applications of Enzyme Biotechnology" was by design a rather all encompassing title, similar in some respects to the discipline. Biotechnology refers to the application of biochemistry for the development of a commercial product. Persons employed in or interested in biotechnology may be chemists, molecular biologists, biophysicists, or physicians. The breadth of biotech research projects requires close collaboration between scientists of a variety of backgrounds, prejudices, and interests. Biotechnology is a comparatively new discipline closely tied to new developments in the fields of chemistry, biochemistry, molecular biology and medicine. The primary function of Texas A&M University is to educate students who will be appropriately trained to carry out the mission of biotechnology. The IUCCP Symposium serves as an important forum for fostering closer ties between academia and industry and exchanging ideas so important to this evolving area.
