Elucidating nano and meso-structures of lignin carbon composites: A comprehensive study of feedstock and temperature dependence
Abstract not provided
García-Negrón, Valerie↗
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Comprehensive Structural and Biochemical Analysis of the Terminal Myxalamid Reductase Domain for the Engineered Production of Primary Alcohols
Here, the terminal reductase (R) domain from the non-ribosomal peptide synthetase (NRPS) module MxaA in Stigmatella aurantiaca Sga15 catalyzes a non-processive four-electron reduction to produce the myxalamide family of secondary metabolites. Despite widespread use in nature, a lack of structural and mechanistic information concerning reductive release from polyketide synthase (PKS) and NRPS assembly lines principally limits our ability to redesign R domains with altered or improved activity. We report crystal structures for MxaA R, both in the absence and, for the first time, in the presence of the NADPH cofactor. Molecular dynamics simulations were employed to provide a deeper understanding of this domain and further identify residues critical for structural integrity, substrate binding, and catalysis. Aggregate computational and structural findings provided a basis for mechanistic investigations and, in the process, delivered a rationally altered variant with improved activity toward highly reduced substrates.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cryo-based Structural Characterization and Growth Model of Salt Film on Metal
Metal salt films play a critical role in high rate dissolution processes such as within an active pit. However, structural and compositional characterization of salt films is challenging owing to the dynamic nature of the dissolving interface. Here, the salt film formed on SS304 one-dimensional artificial pit surface was directly characterized using flash freezing and cryo-based focused ion beam/scanning electron microscopy. The salt film exhibits a porous structure. Ni is co-located with Fe in the salt film, indicating the formation of co-precipitated salt containing Fe2+ and Ni2+. Additionally, a salt film growth model is presented based on ion transport.
Salt film, Pitting corrosion, Cryogenic, Cryo-FIB/↗
Characterization of ferredoxins involved in electron transfer pathways for nitrogen fixation implicates differences in electronic structure in tuning 2[4Fe 4S] Fd activity
Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation. This pathway involves a variant of the primary Fd of nitrogen fixation in R. palustris, Fer1, in which threonine at position 11 is substituted for isoleucine (Fer1 T11I ). To understand why this substitution in Fer1 enables more efficient electron transfer, we used in vivo and in vitro methods to characterize Fer1 and Fer1 T11I . Electrochemical characterization revealed both Fer1 and Fer1 T11I have similar redox transitions (–480 mV and – 550 mV), indicating the reduction potential was unaffected despite the proximity of T11 to an iron-sulfur (Fe—S) cluster of Fer1. Additionally, disruption of hydrogen bonding around an Fe—S cluster in Fer1 by substituting threonine with alanine (T11A) or valine (T11V) did not increase nitrogenase activity, indicating that disruption of hydrogen bonding does not explain the difference in activity observed for Fer1 T11I . Electron paramagnetic resonance spectroscopy studies revealed key differences in the electronic structure of Fer1 and Fer1 T11I , which indicate changes to the high spin states and/or spin-spin coupling between the Fe—S clusters of Fer1. Finally, our data implicates these electronic structure differences in facilitating electron flow and sets a foundation for further investigations to understand the connection between these properties and intermolecular electron transfer.
59 BASIC BIOLOGICAL SCIENCES↗
Structures of Vanadium-Containing Silicate and Borosilicate Glasses: Vanadium Potential Development and MD Simulations
Vanadium-containing multi-component glasses have been found with widely interests in various applications. However, the complex compositions, thus structures, lead to the challenges in experiments to understand the structural origin of the property change of these glasses. In this work, we developed compatible vanadium-related parameters for a widely used pair wise potential set to enable the simulations of the vanadium-containing multi-component glasses. Various crystal structures and glass compositions (with vanadium in different oxidation states) have been tested using the newly developed parameters, and structural information of cell parameters, pair distribution function, estimated bond distance, and coordination number have been obtained. The results are in good agreement with available experimental data, which indicates the new vanadium parameters can be used to simulate the vanadium-containing multi-component glasses and thus help study those applications with wide interests.
Deng, Lu↗
Iron phosphate glasses: Bulk properties and atomic scale structure
Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.
36 MATERIALS SCIENCE↗
Structural, magnetic, and oxygen storage properties of hexagonal Dy{sub 1−x}Y{sub x}MnO{sub 3+δ}
Single-phase polycrystalline samples of hexagonal Dy{sub 1−x}Y{sub x}MnO{sub 3+δ} were synthesized over the full solubility range under reducing oxygen partial pressure conditions. Rietveld refinements using neutron powder diffraction data (NPD) confirmed the persistence of the parent hexagonal P6{sub 3}cm (Space group #185) structure for all the stoichiometric (δ=0) samples. The (Mn–O) bond lengths derived from NPD data were found to be consistent with non-degenerate Mn{sup +3} high-spin state e“{sup 2}e′{sup 2} in trigonal–bipyramidal coordination. Detailed thermogravimetric measurements show large reversible oxygen storage/release capabilities (within the range of oxygen content 3.0–3.3) at unusually low temperatures of 200–400 °C in air or oxygen atmospheres. A phase transition to a new hexagonal phase (Hex1) was observed to take place around δ∼0.29 for the oxygen-loaded Dy-rich samples (x<0.5). Analysis of x-ray and neutron diffraction data using Rietveld refinements demonstrate that the superstructure is formed by tripling the c-axis of the original P6{sub 3}cm unit cell. Modeling of the Hex1 superstructure converged to a structural symmetry consistent with the noncentrosymmetric space group R3c (#161). In magnetization measurements, a ferrimagnetic order for DyMnO{sub 3.0} was observed below 8 K. The dilution of Dy magnetism with nonmagnetic yttrium results in reducing both the transition temperature and the effective paramagnetic moment. - Graphical abstract: Superstructure of the (R3c) Dy{sub 0.7}Y{sub 0.3}MnO{sub 3.29} in the lattice range c=0.27611–0.42829 (left panel) along with its low-temperature oxygen absorption/desorption capability in pure O{sub 2} (right panel). - Highlights: • Polycrystalline samples of Dy{sub 1−x}Y{sub x}MnO{sub 3+δ} were synthesized in the hexagonal phase. • They exhibit large oxygen storage/release capabilities at low oxidation temperatures. • A phase transition to the R3c superstructure was observed around δ=0.29. • Both the Tc and effective paramagnetic moment were reduced with the Dy substitution.
36 MATERIALS SCIENCE↗
Mild hydrothermal crystal growth of new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}: Structures, optical and magnetic properties
Two new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} (1) and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} (2), were synthesized through an in situ mild hydrothermal route, and were structurally characterized by single crystal X-ray diffraction. The compounds exhibit complex crystal structures composed of corner- or edge-shared UF{sub 9} and MF{sub 6} (M=Mg, Mn) polyhedra, forming hexagonal channels in the three-dimensional framework, in which ordered or disordered divalent metal and sodium atoms reside. The large hexagonal voids contain the nearly regular M(II)F{sub 6} octahedra and sodium ions, whereas the small hexagonal cavities include M(II) and sodium ions on a mixed-occupied site. Magnetic susceptibility measurements yielded effective magnetic moments of 8.36 and 11.6 µ{sub B} for 1 and 2, respectively, confirming the presence and oxidation states of U(IV) and Mn(II). The large negative Weiss constants indicate the spin gap between a triplet and a singlet state in the U(IV). Magnetization data as a function of applied fields revealed that 2 exhibits paramagnetic behavior due to the nonmagnetic singlet ground state of U(IV) at low temperature. UV–vis diffuse reflectance and X-ray photoelectron spectroscopy data were also analyzed. - Graphical abstract: Two new quaternary U(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}, were crystallized via an in situ reduction step of U(VI) to U(IV) under mild hydrothermal conditions. The compounds show complex crystal structures based on the 3-D building block of U{sub 6}F{sub 30}. Magnetic property measurements revealed that the U(IV) exhibits a nonmagnetic singlet ground state at low temperature with a spin gap. - Highlights: • Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} have been synthesized and characterized. • The U(IV) fluorides exhibit complex three-dimensional crystal structures. • The optical properties were investigated. • Magnetic susceptibility data were collected.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Metal-ion exchange induced structural transformation as a way of forming novel Ni(II)− and Cu(II)−salicylaldimine structures
A Zn(II)−salicylaldimine complex [Zn(L{sup salpyca})(H{sub 2}O)]{sub n} (1, where H{sub 2}L{sup salpyca}=4-hydroxy-3-(((pyridin-2-yl)methylimino)methyl)benzoic acid), with a one-dimensional (1D) chain structure, has been successfully converted to a discrete Ni(II)−salicylaldimine complex [Ni(L{sup salpyca})(H{sub 2}O){sub 3}] (2) and an infinite Cu(II)−salicylaldimine complex ([Cu(L{sup salpyca})]·3H{sub 2}O){sub n} (3) through a metal-ion exchange induced structural transformation process. However, such processes do not worked by Mn(II) and Co(II) ions. Solid-state structure analyses reveal that complexes 1–3 form comparable coordinative or supramolecular zigzag chains running along the crystallographic [201] direction. In addition, replacing Zn(II) ion by Ni(II) and Cu(II) ions caused changes in coordination environment and sphere of metal centers, from a 5-coordinate intermediate geometry of square pyramidal and trigonal bipyramidal in 1 to a 6-coordinate octahedral geometry in 2, and to a 4-coordiante square planar geometry in 3. This study shows that metal-ion exchange serves as a very efficient way of forming new coordination complexes that may not be obtained through direct synthesis. - Graphical abstract: A Zn(II)−salicylaldimine zigzag chain has been successfully converted to a Ni(II)−salicylaldimine supramolecular zigzag chain and a Cu(II)−salicylaldimine coordinative zigzag chain through metal-ion exchange induced structural transformations, which is not achieved by Mn(II) and Co(II) ions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Syntheses, crystal structures, and optical properties of CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl and CsBa{sub 2}Cl{sub 5}
The mixed-cation compounds CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl and CsBa{sub 2}Cl{sub 5} were synthesized in the same solid-state reaction at 1173 K. CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl adopts the Cs{sub 3}CoCl{sub 5} structure type in the tetragonal crystal system whereas CsBa{sub 2}Cl{sub 5} crystallizes in the PbU{sub 2}Se{sub 5} structure type in the monoclinic crystal system. The CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl structure displays both Cs/Ba and Se/Cl disorder. From optical absorption measurements CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl is an indirect wide-gap semiconductor. From theoretical calculations CsBa{sub 2}Cl{sub 5} has a large band gap of 6.4 eV. - Graphical abstract: General view of the crystal structure of CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl. Display Omitted - Highlights: • CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl is an indirect wide-gap semiconductor. • Red crystals of CsBa{sub 5}Ti{sub 2}Se{sub 9}Cl show an absorption transition at 2.00(2) eV. • As expected, DFT calculations indicate CsBa{sub 2}Cl{sub 5} has a large band gap of 6.4 eV. • Unexpectedly, crystals of CsBa{sub 2}Cl{sub 5} are pink, perhaps from minimal Ti impurities.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Magnetic structure of CaSrFeCoO6–δ: Correlations with structural order
Highlights: • Neutron diffraction shows that CaSrFeCoO{sub 6–δ} has G-type antiferromagnetic order at 10 K. • Magnetic moments are along the shortest axis at 10 K, contrary to the Ca{sub 2}-analogue, Ca{sub 2}FeCoO{sub 6–δ}. • CaSrFeCoO{sub 6–δ} retains the same orientation of moments up to 300 K, contrary to Ca{sub 2}FeCoO{sub 6–δ}. • CaSrFeCoO{sub 6–δ} has the optimum composition for G-type order and retention of the moment orientation. - Abstract: With the aid of neutron diffraction, the magnetic structure of CaSrFeCoO{sub 6–δ} is determined at 10 K and 300 K. The vacancies, created due to oxygen-deficiency, are ordered in this material. In addition to structural order, neutron diffraction shows a long-range G-type antiferromagnetic order, where each magnetic moment is aligned antiparallel to all nearest neighbors. The orientation of moments is along the shortest unit cell axis at 10 K. The magnetic structure and orientation of moments remain unchanged up to room temperature. This is in contrast to the Ca{sub 2}-analogue, Ca{sub 2}FeCoO{sub 6–δ}, where the magnetic moments at 10 K are parallel to the longest axis and change their orientation when temperature is raised to room temperature. These differences highlight the ability to control the magnetic properties by tuning the structural parameters. Comparisons to similar materials show that CaSrFeCoO{sub 6–δ} has the optimum composition for G-type magnetic order and the retention of the moment orientation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Crystal Structures of the E. coli Transcription Initiation Complexes with a Complete Bubble
During transcription initiation, RNA polymerase binds to promoter DNA to form an initiation complex containing a DNA bubble and enters into abortive cycles of RNA synthesis before escaping the promoter to transit into the elongation phase for processive RNA synthesis. Here we present the crystal structures of E. coli transcription initiation complexes containing a complete transcription bubble and de novo synthesized RNA oligonucleotides at about 6-Å resolution. The structures show how RNA polymerase recognizes DNA promoters that contain spacers of different lengths and reveal a bridging interaction between the 5'-triphosphate of the nascent RNA and the σ factor that may function to stabilize the short RNA-DNA hybrids during the early stage of transcription initiation. The conformation of the RNA oligonucleotides and the paths of the DNA strands in the complete initiation complexes provide insights into the mechanism that controls both the abortive and productive RNA synthesis.
59 BASIC BIOLOGICAL SCIENCES↗
Yolk-shell structured Sb@C anodes for high energy Na-ion batteries
Despite great advances in sodium-ion battery developments, the search for high energy and stable anode materials remains a challenge. Alloy or conversion-typed anode materials are attractive candidates of high specific capacity and low voltage potential, yet their applications are hampered by the large volume expansion and hence poor electrochemical reversibility and fast capacity fade. Here, we use antimony (Sb) as an example to demonstrate the use of yolk-shell structured anodes for high energy Na-ion batteries. The Sb@C yolk-shell structure prepared by controlled reduction and selective removal of Sb2O3 from carbon coated Sb2O3 nanoparticles can accommodate the Sb swelling upon sodiation and improve the structural/electrical integrity against pulverization. It delivers a high specific capacity of ~554 mAh•g-1, good rate capability (315 mhA•g-1 at 10C rate) and long cyclability (92% capacity retention over 200 cycles). Full-cells of O3-Na0.9[Cu0.22Fe0.30Mn0.48]O2 cathodes and Sb@C-hard carbon composite anodes demonstrate a high specific energy of ~130 Wh•kg-1 (based on the total mass of cathode and anode) in the voltage range of 2.0-4.0 V, ~1.5 times energy of full-cells with similar design using hard carbon anodes.
Song, Junhua↗
Fundamental understanding and rational design of high energy structural microbatteries
Microbatteries play a critical role in determining the lifetime of downsized sensors, wearable devices and medical applications, etc. More often, structural batteries are required from the perspective of aesthetics and space utilization, which is however rarely explored. Herein, we discuss the fundamental issues associated with the rational design of practically usable high energy microbatteries. The tubular shape of the cell further allows the flexible integration of microelectronics. A functioning acoustic micro-transmitter continuously powered by this tubular battery has been successfully demonstrated. Multiple design features adopted to accommodate large mechanical stress during the rolling process are discussed providing new insights in designing the structural microbatteries for emerging technologies.
25 ENERGY STORAGE↗