I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[13284, 18786]
Abstract: Sr2CrO2Cr2As2 and Ba2CrO2Cr2As2 with Cr2+ ions in CrO2 sheets and in CrAs layers crystallize with the Sr2Mn3Sb2O2 structure (space group I4/mmm, Z = 2) and lattice parameters a = 4.00800(2) Å, c = 18.8214(1) Å (Sr2CrO2Cr2As2) and a = 4.05506(2) Å, c = 20.5637(1) Å (Ba2CrO2Cr2As2) at room temperature. Powder neutron diffraction reveals checkerboard-type antiferromagnetic ordering of the Cr2+ ions in the arsenide layers below TN1_Sr, of 600(10) K (Sr2CrO2Cr2As2) and TN1_Ba 465(5) K (Ba2CrO2Cr2As2) with the moments initially directed perpendicular to the layers in both compounds. Checkerboard-type antiferromagnetic ordering of the Cr2+ ions in the oxide layer below 230(5) K for Ba2CrO2Cr2As2 occurs with these moments also perpendicular to the layers, consistent with the orientation preferences of d4 moments in the two layers. In contrast, below 330(5) K in Sr2CrO2Cr2As2, the oxide layer Cr2+ moments are initially oriented in the CrO2 plane; but on further cooling, these moments rotate to become perpendicular to the CrO2 planes, while the moments in the arsenide layers rotate by 90° with the moments on the two sublattices remaining orthogonal throughout [behavior recently reported independently by Liu et al. [Liu et al. Phys. Rev. B 2018, 98, 134416]]. In Sr2CrO2Cr2As2, electron diffraction and high resolution powder X-ray diffraction data show no evidence for a structural distortion that would allow the two Cr2+ sublattices to couple, but high resolution neutron powder diffraction data suggest a small incommensurability between the magnetic structure and the crystal structure, which may account for the coupling of the two sublattices and the observed spin reorientation. The saturation values of the Cr2+ moments in the CrO2 layers (3.34(1) μB (for Sr2CrO2Cr2As2) and 3.30(1) μB (for Ba2CrO2Cr2As2)) are larger than those in the CrAs layers (2.68(1) μB for Sr2CrO2Cr2As2 and 2.298(8) μB for Ba2CrO2Cr2As2) reflecting greater covalency in the arsenide layers.
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Oct 2020
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I04-Macromolecular Crystallography
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Žiga
Skok
,
Michaela
Barančoková
,
Ondřej
Benek
,
Cristina
Durante Cruz
,
Päivi
Tammela
,
Tihomir
Tomašič
,
Nace
Zidar
,
Lucija Peterlin
Mašič
,
Anamarija
Zega
,
Clare E. M.
Stevenson
,
Julia E. A.
Mundy
,
David M.
Lawson
,
Anthony
Maxwell
,
Danijel
Kikelj
,
Janez
Ilaš
Diamond Proposal Number(s):
[18565]
Abstract: We designed and synthesized a series of inhibitors of the bacterial enzymes DNA gyrase and DNA topoisomerase IV, based on our recently published benzothiazole-based inhibitor bearing an oxalyl moiety. To improve the antibacterial activity and retain potent enzymatic activity, we systematically explored the chemical space. Several strategies of modification were followed: varying substituents on the pyrrole carboxamide moiety, alteration of the central scaffold, including variation of substitution position and, most importantly, modification of the oxalyl moiety. Compounds with acidic, basic, and neutral properties were synthesized. To understand the mechanism of action and binding mode, we have obtained a crystal structure of compound 16a, bearing a primary amino group, in complex with the N-terminal domain of E. coli gyrase B (24 kDa) (PDB: 6YD9). Compound 15a, with a low molecular weight of 383 Da, potent inhibitory activity on E. coli gyrase (IC50 = 9.5 nM), potent antibacterial activity on E. faecalis (MIC = 3.13 μM), and efflux impaired E. coli strain (MIC = 0.78 μM), is an important contribution for the development of novel gyrase and topoisomerase IV inhibitors in Gram-negative bacteria.
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Oct 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151, 18431]
Open Access
Abstract: The technique of inelastic neutron scattering (INS) is used to investigate how hydrogen is partitioned within a series of Na and S promoted iron-based Fischer-Tropsch-to-olefin catalysts. Two reaction test regimes are examined. First, reaction testing at elevated temperature and pressure demonstrate how Na/S additions enhance short chain olefin selectivity and reduce methane formation under industrially relevant reaction conditions. For a fixed level of Na incorporation (2000 ppm), sulfur concentrations of ≤ 100 ppm result in only a modest improvement in olefin selectivity. However, for sulfur values of ≥ 100 ppm there is a noticeable and systematic increase in C2-C4 olefin selectivity; rising from ∼30.0 % to 35.2% at 250 ppm. Second, using ambient pressure CO hydrogenation as a test reaction in INS and micro-reactor configurations, catalyst samples are further analysed by TPR, TPO, XRD and S K-edge XANES. INS shows the formation of a hydrocarbonaceous overlayer to be significantly attenuated by the presence of the promoters, with increasing S levels significantly reducing the intensity of the sp2 and sp3 hybridised ν(C-H) modes of the overlayer, albeit to differing degrees. A probable role for how this combination of promoters is perturbing the form of the hydrocarbonaceous overlayer to subsequently moderate the product distribution is considered.
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Oct 2020
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B18-Core EXAFS
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B.
Venezia
,
E.
Cao
,
Santhosh K.
Matam
,
C.
Waldron
,
G.
Cibin
,
E. K.
Gibson
,
S.
Golunski
,
P. P.
Wells
,
I.
Silverwood
,
C. R. A.
Catlow
,
G.
Sankar
,
A.
Gavriilidis
Diamond Proposal Number(s):
[19359]
Open Access
Abstract: Operando X-ray absorption spectroscopy (XAS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectrometry (MS) provide complementary information on the catalyst structure, surface reaction mechanisms and activity relationships. The powerful combination of the techniques has been the driving force to design and engineer suitable spectroscopic operando reactors that can mitigate limitations inherent to conventional reaction cells and facilitate experiments under kinetic regimes. Microreactors have recently emerged as effective spectroscopic operando cells due to their plug-flow type operation with no dead volume and negligible mass and heat transfer resistances. Here we present a novel microfabricated reactor that can be used for both operando XAS and DRIFTS studies. The reactor has a glass–silicon–glass sandwich-like structure with a reaction channel (3000 μm × 600 μm; width × depth) packed with a catalyst bed (ca. 25 mg) and placed sideways to the X-ray beam, while the infrared beam illuminates the catalyst bed from the top. The outlet of the reactor is connected to MS for continuous monitoring of the reactor effluent. The feasibility of the microreactor is demonstrated by conducting two reactions: i) combustion of methane over 2 wt% Pd/Al2O3 studied by operando XAS at the Pd K-edge and ii) CO oxidation over 1 wt% Pt/Al2O3 catalyst studied by operando DRIFTS. The former shows that palladium is in an oxidised state at all studied temperatures, 250, 300, 350, 400 °C and the latter shows the presence of linearly adsorbed CO on the platinum surface. Furthermore, temperature-resolved reduction of palladium catalyst with methane and CO oxidation over platinum catalyst are also studied. Based on these results, the catalyst structure and surface reaction dynamics are discussed, which demonstrate not only the applicability and versatility of the microreactor for combined operando XAS and DRIFTS studies, but also illustrate the unique advantages of the microreactor for high space velocity and transient response experiments.
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Oct 2020
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B18-Core EXAFS
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Wolfgang
Bensch
,
Jonas
Van Dinter
,
Kevin
Synnatschke
,
Tobias
Engesser
,
Sylvio
Indris
,
Niklas
Wolff
,
Ole
Gronenberg
,
Martin
Etter
,
Giannantonio
Cibin
,
Lorenz
Kienle
,
Claudia
Backes
Diamond Proposal Number(s):
[20060]
Abstract: The layered compound Ni2P2S6 was electrochemically characterized for application as anode material in sodium-ion batteries (SIBs). A high reversible capacity of 621 mAh g 1 at 1 A g 1 was achieved after 190 cycles. The investigation of the complex reaction mechanism of the conversion reaction was performed applying complementary techniques including X-ray powder diffraction, pair distribution function analyses, X-ray absorption spectroscopy, 19F/23Na/31P MAS NMR, TEM and nano-EDX. The results highlight that Na uptake for up to 5 Na/formula unit (f.u.) led to reduction of Ni2+ to metallic Ni nanoparticles and concomitant formation of an intermediate compound Na4P2S6. Increasing the Na content to 12 Na/f.u. generates nanocrystalline Na2S, which is accompanied by loss of the long-range order of the pristine sample. In the completely discharged state elemental Ni and Na2S are present, but in contrast to literature reports, no evidence for the formation of NaxP phases was found. During the charge process, Ni3S2 is formed upon the release of ~11.7 Na/f.u. A very high specific capacity of 621 mAh g 1 at 1.0 A g 1 is obtained after 190 cycles, and Coulombic efficiencies reach nearly 100% after the 3rd cycle.
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Oct 2020
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[25819]
Abstract: Menisporopsin A is a fungal bioactive macrocyclic polylactone, the biosynthesis of which requires only reducing (R) and non‐reducing (NR) polyketide synthases (PKSs) to guide a series of esterification and cyclolactonization reactions. There is no structural information pertaining to these PKSs. Here, we report the solution characterization of singlet and doublet acyl carrier protein (ACP2 and ACP1‐ACP2)–thioesterase (TE) domains from NR‐PKS involved in menisporopsin A biosynthesis. Small angle X‐ray scattering (SAXS) studies in combination with homology modelling reveal that these polypeptides adopt a distinctive Beads‐on‐a‐String configuration, characterized by the presence of highly flexible interdomain linkers. These models provide a platform for studying domain organization and interdomain interactions in fungal NR‐PKSs, which may be of value in directing the design of functionally optimised polyketide scaffolds.
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Oct 2020
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[21717]
Abstract: Corrosion research related to CO2-containing environments has focused over the past few decades on siderite formation (FeCO3) as a main corrosion product on carbon steel, yet the influence of Ca and other ions on its chemical and structural characteristics is not fully understood. Metal-localized corrosion is the biggest industrial challenge because of the unknown and unpredictable character of this phenomenon that frequently leads to failure. We report here the role of Ca and formation of iron-calcium carbonate (FexCayCO3) through a spiral growth model as in the calcite system and quantify the replacement of Fe2+ by Ca2+ ions in the structure of FeCO3 to form FexCayCO3. The incorporation of Ca2+ inhibits the completion of spiral segments on the growth of the rhombohedral crystals of FeCO3, promoting an enlargement of its structure along the c-axis. This leads to distortions in the chemical structure and morphology affecting the chemical and mechanical properties. Under flow conditions over time in an undersaturated environment, Ca is leached out from the expanded structure of FexCayCO3 increasing the solubility of the crystals, weakening the mechanical properties of the resulting corrosion films and stimulating localized corrosion.
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Oct 2020
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M.
Dendebera
,
Y.
Chornodolskyy
,
R.
Gamernyk
,
O.
Antonyak
,
I.
Pashuk
,
S.
Myagkota
,
I.
Gnilitskyi
,
V.
Pankratov
,
V.
Vistovskyy
,
V.
Mykhaylyk
,
M.
Grinberg
,
A.
Voloshinovskii
Abstract: The work reports the results of spectroscopic and luminescence-kinetic studies of CsPbBr3 single crystal over 14–300 K temperature range. It is shown that at low temperatures the luminescence spectrum contains three narrow bands at 534, 537, and 541.5 nm exhibiting a fast decay and a broad emission band at ca. 560 nm with long decay. The evolution of the luminescence bands and their temporal characteristics with temperature are discussed from the viewpoint of possible emission mechanisms. The origin of the luminescence bands is discussed in relation with the observed features of their temporal characteristics. The mechanism of luminescence quenching for different emission band is suggested.
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Sep 2020
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[11204]
Abstract: The fracture resistance of load-bearing trabecular bone is adversely affected by diseases such as osteoporosis. However, there are few published measurements of trabecular bone fracture toughness due to the difficulty of conducting reliable tests in small specimens of this highly porous material. A new approach is demonstrated that uses digital volume correlation of X-ray computed tomographs to measure 3D displacement fields in which the crack shape and size can be objectively identified using a phase congruency analysis. The criteria for crack propagation, i.e. fracture toughness, can then be derived by finite element simulation, with knowledge of the elastic properties.
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Sep 2020
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21742]
Open Access
Abstract: Amorphous tin-gallium oxide (a-SGO) grown with atomic layer deposition was evaluated as a buffer layer in (Ag,Cu)(In,Ga)Se2 thin-film solar cells in search for a new material that is compatible with a variety of absorber band gaps. Hard and soft X-ray photoelectron spectroscopy on absorber/a-SGO stacks combined with J–V characterization of solar cells that were fabricated, showed that the conduction band alignment at the absorber/a-SGO interface can be tuned by varying the cation composition and/or growth temperature. Here, the surface band gap was 1.1 eV for the absorber. However, optical band gap data for a-SGO indicate that a suitable conduction band alignment can most likely be achieved even for wider absorber band gaps relevant for tandem top cells. A best efficiency of 17.0% was achieved for (Ag,Cu)(In,Ga)Se2/a-SGO devices, compared to η = 18.6% for the best corresponding CdS reference. Lower fill factor and open-circuit voltage values were responsible for lower cell efficiencies. The reduced fill factor is explained by a larger series resistance, seemingly related to interface properties, which are yet to be optimized. Some layer constellations resulted in degradation in fill factor during light soaking as well. This may partly be explained by light-induced changes in the electrical properties of a-SGO, according to analysis of Al/SGO/n-Si metal-oxide-semiconductor capacitors that were fabricated and characterized with J–V and C–V. Moreover, the introduction of a 1 nm thick Ga2O3 interlayer between the absorber and a-SGO improved the open-circuit voltage, which further indicates that the absorber/a-SGO interface can be improved.
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Sep 2020
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