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Peter C E Moody, Emma L Raven
Aerobic organisms have evolved to activate oxygen from the atmosphere, which allows them to catalyze the oxidation of different kinds of substrates. This activation of oxygen is achieved by a metal center (usually iron or copper) buried within a metalloprotein. In the case of iron-containing heme enzymes, the activation of oxygen is achieved by formation of transient iron-oxo (ferryl) intermediates; these intermediates are called Compound I and Compound II. The Compound I and II intermediates were first discovered in the 1930s in horseradish peroxidase, and it is now known that these same species are used across the family of heme enzymes, which include all of the peroxidases, the heme catalases, the P450s, cytochrome c oxidase, and NO synthase...
January 12, 2018: Accounts of Chemical Research
Hirokazu Masai, Toshiaki Ina, Shun Okumura, Ko Mibu
X-ray absorption near edge structure (XANES) measurement is one of the most powerful tools for the evaluation of a cation valence state. XANES measurement is sometimes the only available technique for the evaluation of the valence state of a dopant cation, which often occurs in phosphor materials. The validity of the core excitation process should be examined as a basis for understanding the applicability of this technique. Here, we demonstrate the validity of valence estimation of tin in oxide glasses, using Sn K-edge and L-edge XANES spectra, and compare the results with 119Sn Mössbauer analysis...
January 11, 2018: Scientific Reports
Johan Cedervall, Elise Nonnet, Daniel Hedlund, Lennart Häggström, Tore Ericsson, Mirosław Werwiński, Alexander Edström, Ján Rusz, Peter Svedlindh, Klas Gunnarsson, Martin Sahlberg
The substitutional effects of cobalt in (Fe1-xCox)5PB2 have been studied with respect to crystalline structure and chemical order with X-ray diffraction and Mössbauer spectroscopy. The magnetic properties have been determined from magnetic measurements, and density functional theory calculations have been performed for the magnetic properties of both the end compounds, as well as the chemically disordered intermediate compounds. The crystal structure of (Fe1-xCox)5PB2 is tetragonal (space group I4/mcm) with two different metal sites, with a preference for cobalt atoms in the M(2) position (4c) at higher cobalt contents...
January 3, 2018: Inorganic Chemistry
P R Pansara, P Y Raval, N H Vasoya, S N Dolia, K B Modi
This communication presents a detailed study on a Fe3+ modified CaCu3Ti4O12 cubic perovskite system (CaCu3-xTi4-xFe2xO12 with x = 0.0-0.7) by performing X-ray powder diffractometry, DC SQUID magnetization and 57Fe Mössbauer spectroscopy. The first ever Mössbauer studies on the system supported the reported peculiarity of the structure. Mössbauer analysis for the compositions x = 0.1, 0.3, and 0.5 suggest Fe3+ ions in two different environments. The site with larger quadrupole splitting corresponds to Fe3+ in the octahedral symmetry, while the site with lower chemical shift and quadrupole splitting belongs to Fe3+ in the square-planar (A'-) configuration...
January 3, 2018: Physical Chemistry Chemical Physics: PCCP
J Y Zhao, W Bi, S Sinogeikin, M Y Hu, E E Alp, X C Wang, C Q Jin, J F Lin
A new miniature panoramic diamond anvil cell (mini-pDAC) as well as a unique gas membrane-driven mechanism is developed and implemented to measure electronic, magnetic, vibrational, and thermodynamic properties of materials using the nuclear resonant inelastic X-ray scattering (NRIXS) and the synchrotron Mössbauer spectroscopy (SMS) simultaneously at high pressure (over Mbar) and low temperature (T < 10 K). The gas membrane system allows in situ pressure tuning of the mini-pDAC at low temperature. The mini-pDAC fits into a specially designed compact liquid helium flow cryostat system to achieve low temperatures, where liquid helium flows through the holder of the mini-pDAC to cool the sample more efficiently...
December 2017: Review of Scientific Instruments
Chuanjiang Hu, Bruce C Noll, Charles E Schulz, W Robert Scheidt
The influence of hydrogen binding to the N-H group of coordinated imidazole in high-spin iron(II) porphyrinates has been studied. The preparation and characterization of new complexes based on [Fe(TPP)(2-MeHIm)] (TPP is the dianion of tetraphenylporphyrin) are reported. The hydrogen bond acceptors are ethanol, tetramethylene sulfoxide, and 2-methylimidazole. The last acceptor, 2-MeHIm, was found in a crystalline complex with two [Fe(TPP)(2-MeHIm)] sites, only one of which has the 2-methylimidazole hydrogen bond acceptor...
December 27, 2017: Inorganic Chemistry
Yunping Fei, Muhammad Iqbal, Seong D Kong, Zheng Xue, Charles P Mcfadden, Jesse L Guillet, Linda H Doerrer, Esen E Alp, Wenli Bi, Yi Lu, Chola Bhargava Dandamudi, Prashant Ranganath, Kevin J Javier, Mohsen Ahmadian, Christopher J Ellison, Keith P Johnston
Superparamagnetic nanoparticles with a high initial magnetic susceptibility χo are of great interest in a wide variety of chemical, biomedical, electronic and subsurface energy applications. In order to achieve the theoretically predicted increase in χo with the cube of the magnetic diameter, new synthetic techniques are needed to control the crystal structure, particularly for magnetite nanoparticles larger than 10 nm. Aqueous magnetite dispersions (Fe3O4) with a χo of 3.3 (dimensionless SI units) at 1...
December 20, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Anthony Cavaillé, Nathalie Saffon-Merceron, Noel Nebra, Marie Fustier-Boutignon, Nicolas Mézailles
Reduction of the FeII complex [(PhPP2Cy)FeCl2] (2) generates an electron rich and unsaturated Fe0 which is reacted with white phosphorus. The new complex obtained, [(PhPP2Cy)Fe(η4-P4)] (3), is the first iron cyclo-P4 complex and the only known stable end deck cyclo-P4 complex outside of group V. Complex 3 bears a FeII center as shown by Mössbauer spectroscopy, associated to a P42- fragment. Analysis of the molecular orbitals rationalizes the distinct reactivity of complex 3. Reaction of complex 3 with H+ affords the unstable complex [(PhPP2Cy)Fe(η4-P4)(H)]+ (4), whereas with CuCl and BCF the complexes [(PhPP2Cy)Fe(η4:η1-P4)(μ-CuCl)]2 (5) and [(PhPP2Cy)Fe(η4:η1-P4)B(C6F5)3] (6) are formed...
December 15, 2017: Angewandte Chemie
Zeba Haque, Gohil Singh Thakur, Ganesan Kalai Selvan, Theresa Block, Oliver Janka, Rainer Pöttgen, Amish G Joshi, Rangasamy Parthasarathy, Sonachalam Arumugam, Laxmi Chand Gupta, Ashok Kumar Ganguli
Recently, we reported the synthesis and investigations of EuSr2Bi2S4F4 and Eu2SrBi2S4F4. We have now been able to induce superconductivity in EuSr2Bi2S4F4 by Se substitution at the S site (isovalent substitution) with Tc = 2.9 K in EuSr2Bi2S2Se2F4. The other compound, Eu2SrBi2S4F4, shows a significant enhancement of Tc. In Se-substituted Eu2SrBi2S4-xSexF4, we find Tc = 2.6 K for x = 1.5 and Tc = 2.8 K for x = 2, whereas Tc = 0.4 K in the Se-free sample. In addition to superconductivity, an important effect associated with Se substitution is that it gives rise to remarkable changes in the Eu valence...
December 13, 2017: Inorganic Chemistry
N S Genz, D Baabe, T Ressler
Iron oxide catalysts supported on nanostructured silica SBA-15 were synthesized with various iron loadings using two different precursors. Structural characterization of the as-prepared Fe x O y /SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, DR-UV-Vis spectroscopy, and Mössbauer spectroscopy. An increasing size of the resulting iron species correlated with an increasing iron loading. Significantly smaller iron species were obtained from (Fe(III), NH4)-citrate precursors compared to Fe(III)-nitrate precursors...
2017: Journal of Analytical Methods in Chemistry
I Vieira, J Klemm-Toole, E Buchner, D L Williamson, K O Findley, E De Moor
A new approach for non-isothermal tempering analysis utilizing dilatometry is proposed and was carried out on a medium carbon steel with high silicon and additions of Mo and V for secondary hardening. The method includes a second non-isothermal step performed with the same heating rate (2 °C/min) used for the first step in order to create a baseline for analysis. The results were correlated with several other characterization techniques. Mössbauer spectroscopy confirmed the formation of transition carbides by auto-tempering as well as the presence of retained austenite decomposition (stage II) and cementite precipitation (stage III), which demonstrated significant overlap...
December 11, 2017: Scientific Reports
Michael J Moore, Joshua Wofford, Andrew Dancis, Paul Alan Lindahl
Mrs3 and Mrs4 are mitochondrial inner membrane proteins that deliver an unidentified cytosolic iron species into the matrix for use in iron-sulfur-cluster (ISC) and heme biosynthesis. The Mrs3/4 double-deletion strain (ΔΔ) grew slowly in iron-deficient glycerol/ethanol medium but recovered to WT rates in iron-sufficient medium. ΔΔ cells grown under both iron-deficient and iron-sufficient respiring conditions accumulated large amounts of iron relative to WT cells, indicating iron homeostatic dysregulation regardless of nutrient iron status...
December 11, 2017: Biochemistry
Natsaran Saichana, Katsuyuki Tanizawa, Hiroshi Ueno, Jiří Pechoušek, Petr Novák, Jitka Frébortová
PqqE is a radical S-adenosyl-l-methionine (SAM) enzyme that catalyzes the initial reaction of pyrroloquinoline quinone (PQQ) biosynthesis. PqqE belongs to the SPASM (subtilosin/PQQ/anaerobic sulfatase/mycofactocin maturating enzymes) subfamily of the radical SAM superfamily and contains multiple Fe-S clusters. To characterize the Fe-S clusters in PqqE from Methylobacterium extorquens AM1, Cys residues conserved in the N-terminal signature motif (CX 3 CX 2C) and the C-terminal seven-cysteine motif (CX 9-15 GX 4 CX n CX 2 CX 5 CX 3 CX n C; n = an unspecified number) were individually or simultaneously mutated into Ser...
December 2017: FEBS Open Bio
Jerzy A Sawicki
The abundance of 57Fe isotope in nuclear reactor core materials can be considerably enriched by neutron-capture 56Fe(n,γ) reactions. This is demonstrated using the sections of Zr-2.5 wt.%Nb pressure tubes removed from two CANDU* reactors. The tubes contained 0.11 and 0.04wt% Fe and were irradiated for about 10 effective full power years (EFPY) up to ~1026n/m2 fast neutron (E > 1MeV) fluencies. The Mössbauer spectra of 57Fe in irradiated samples indicated up to 10 times larger areas than unirradiated off-cuts from the same pressure tubes...
November 17, 2017: Applied Radiation and Isotopes
Olivier Toulemonde, Alexis Devoti, Patrick Rosa, Philippe Guionneau, Mathieu Duttine, Alain Wattiaux, Eric Lebraud, Nicolas Penin, Rodolphe Decourt, Alexandre Fargues, Sonia Buffière, Alain Demourgues, Manuel Gaudon
The synthesis of a Co-doped or Fe-doped La(Ga,Al)O3 perovskite via the Pechini process aimed to achieve a color change induced by temperature and associated with spin crossover (SCO). In Fe-doped samples, iron was shown to be in the high-spin state, whereas SCO from the low-spin to the high-spin configuration was detected in Co-doped compounds when the temperature increased. Fe-doped compounds clearly adopted the high-spin configuration even down to 4 K on the basis of Mössbauer spectroscopic analysis. The original SCO phenomenon in the Co-doped compounds LaGa1-xCoxO3 (0 < x < 0...
December 8, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Michael V Schaefer, Robert M Handler, Michelle M Scherer
Iron (Fe) and manganese (Mn) are the two most common redox-active elements in the Earth's crust and are well known to influence mineral formation and dissolution, trace metal sequestration, and contaminant transformations in soils and sediments. Here, we characterized the reaction of aqueous Fe(II) with pyrolusite (β-MnO2) using electron microscopy, X-ray diffraction, aqueous Fe and Mn analyses, and 57Fe Mössbauer spectroscopy. We reacted pyrolusite solids repeatedly with 3 mM Fe(II) at pH 7.5 to evaluate whether electron transfer occurs and to track the evolving reactivity of the Mn/Fe solids...
December 5, 2017: Geochemical Transactions
Natalia Kulikova, Alexander Yu Polyakov, Vasily A Lebedev, Dmitry Abroskin, Dmitry S Volkov, Denis Pankratov, Olga Klein, Svetlana V Senik, Tatiana Sorkina, Alexey V Garshev, Alexey A Veligzhanin, Jose Garcia Mina, Irina V Perminova
Availability of Fe in soil to plants is closely related to the presence of humic substances (HS). Still, the systematic data on applicability of iron-based nanomaterials stabilized with HS as a source for plant nutrition are missing. The goal of our study was to establish a connection between properties of iron-based materials stabilized by HS and their bioavailability to plants. We have prepared two samples of leonardite HS-stabilized iron-based materials with substantially different properties using the reported protocols, and studied their physical chemical state in relation to iron uptake and other biological effects...
December 5, 2017: Journal of Agricultural and Food Chemistry
Guangbo Chen, Rui Gao, Yufei Zhao, Zhenhua Li, Geoffrey I N Waterhouse, Run Shi, Jiaqing Zhao, Mengtao Zhang, Lu Shang, Guiyang Sheng, Xiangping Zhang, Xiaodong Wen, Li-Zhu Wu, Chen-Ho Tung, Tierui Zhang
A series of novel CoFe-based catalysts are successfully fabricated by hydrogen reduction of CoFeAl layered-double-hydroxide (LDH) nanosheets at 300-700 °C. The chemical composition and morphology of the reaction products (denoted herein as CoFe-x) are highly dependent on the reduction temperature (x). CO2 hydrogenation experiments are conducted on the CoFe-x catalysts under UV-vis excitation. With increasing LDH-nanosheet reduction temperature, the CoFe-x catalysts show a progressive selectivity shift from CO to CH4 , and eventually to high-value hydrocarbons (C2+ )...
December 5, 2017: Advanced Materials
V Funari, L Mantovani, L Vigliotti, M Tribaudino, E Dinelli, R Braga
During their production, management, and landfilling, bottom (BA) and fly (FA) ashes from municipal solid waste incineration may liberate Fe-bearing, ultrafine particles and easily enter different environmental sinks of the biosphere. We aim to explore a collection of BA and FA samples from Italian incinerators to probe magnetic mineralogy and the fraction of harmful superparamagnetic (SP) nanoparticles (d<30nm). X-ray diffraction, electron microscopy observation, temperature- and frequency-dependent magnetometry, and Mossbauer analysis are performed...
November 29, 2017: Science of the Total Environment
Anna Maria Miłaczewska, Ewa Kot, José A Amaya, Thomas M Makris, Marcin Zając, Józef Korecki, Aleksandr Chumakov, Bartosz Trzewik, Sylwia Kędracka-Krok, Władek Minor, Maksymilian Chruszcz, Tomasz Maciej Borowski
Acireductone dioxygenase (ARD) is an intriguing enzyme from the methionine salvage pathway capable of catalyzing two different oxidation reactions with the same substrate, depending on the type of the metal ion in the active site. To date, the structural information regarding ARD-acireductone complex is limited and the reaction mechanisms are still under debate. In this contribution we report results of joint experimental and computational studies undertaken to advance our knowledge about ARD. We have determined a structure of ARD from Homo sapiens with selenomethionine...
November 28, 2017: Chemistry: a European Journal
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