I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[15899, 18191]
Abstract: The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K2TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K2TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K2TCNQ and Cs2TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.
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Nov 2020
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B18-Core EXAFS
I18-Microfocus Spectroscopy
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Eitaro
Kurihara
,
Masato
Takehara
,
Mizuki
Suetake
,
Ryohei
Ikehara
,
Tatsuki
Komiya
,
Kazuya
Morooka
,
Ryu
Takami
,
Shinya
Yamasaki
,
Toshihiko
Ohnuki
,
Kenji
Horie
,
Mami
Takehara
,
Gareth T. W.
Law
,
William
Bower
,
J. Frederick W.
Mosselmans
,
Peter
Warnicke
,
Bernd
Grambow
,
Rodney C.
Ewing
,
Satoshi
Utsunomiya
Diamond Proposal Number(s):
[21211]
Abstract: Traces of Pu have been detected in material released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March of 2011; however, to date the physical and chemical form of the Pu have remained unknown. Here we report the discovery of particulate Pu associated with cesium-rich microparticles (CsMPs) that formed in and were released from the reactors during the FDNPP meltdowns. The Cs-pollucite-based CsMP contained discrete U(IV)O2 nanoparticles, <~10 nm, one of which is enriched in Pu adjacent to fragments of Zr-cladding. The isotope ratios, 235U/238U, 240Pu/239Pu, and 242Pu/239Pu, of the CsMPs were determined to be ~0.0193, ~0.347, and ~0.065, respectively, which are consistent with the calculated isotopic ratios of irradiated-fuel fragments. Thus, considering the regional distribution of CsMPs, the long-distance dispersion of Pu from FNDPP is attributed to the transport by CsMPs that have incorporated nanoscale fuel fragments prior to their dispersion up to 230 km away from the Fukushima Daiichi reactor site.
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Nov 2020
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I13-2-Diamond Manchester Imaging
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Open Access
Abstract: Hypothesis: We define contact angles, h, during displacement of three fluid phases in a porous medium using energy balance, extending previous work on two-phase flow. We test if this theory can be applied to quantify the three contact angles and wettability order in pore-scale images of three-phase displacement. Theory: For three phases labelled 1, 2 and 3, and solid, s, using conservation of energy ignoring viscous dissipation ðDa1s cos h12 Da12 /j12 DS1 Þr12 1⁄4 ðDa3s cos h23 þ Da23 /j23 DS3 Þr23 þ Da13 r13 , where / is the porosity, r is the interfacial tension, a is the specific interfacial area, S is the saturation, and j is the fluid–fluid interfacial curvature. D represents the change during a displacement. The third contact angle, h13 can be found using the Bartell-Osterhof relationship. The energy balance is also extended to an arbitrary number of phases.
Findings: X-ray imaging of porous media and the fluids within them, at pore-scale resolution, allows the difference terms in the energy balance equation to be measured. This enables wettability, the contact angles, to be determined for complex displacements, to characterize the behaviour, and for input into pore-scale models. Two synchrotron imaging datasets are used to illustrate the approach, comparing the flow of oil, water and gas in a water-wet and an altered-wettability limestone rock sample. We show that in the water-wet case, as expected, water (phase 1) is the most wetting phase, oil (phase 2) is inter- mediate wet, while gas (phase 3) is most non-wetting with effective contact angles of h12 % 48 and h13 % 44, while h23 1⁄4 0 since oil is always present in spreading layers. In contrast, for the altered-wettability case, oil is most wetting, gas is intermediate-wet, while water is most non-wetting with con- tact angles of h12 1⁄4 134 $ 10;h13 1⁄4 119 $ 10, and h23 1⁄4 66 $ 10.
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Sep 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Open Access
Abstract: The activation of C–H bonds for carbon–carbon coupling reactions remains a challenge in organic synthesis. Visible light photocatalysis offers a unique opportunity to sustainably perform these reactions in a single-step, without the need for caustic reagents, and under ambient operating conditions. We utilize non-noble metals in the form of hybrid cobalt-based zeolitic imidazole frameworks, for the first time, to explore the structure–property correlations leading to the photocatalytic formation of C–C bonds. Combining in situ spectroscopy and theoretical simulations we can rationalize the photocatalytic efficacy of different frameworks. This led to an improved understanding of the nature of the photocatalytic active sites and associated reaction pathway.
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Sep 2020
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[19013]
Open Access
Abstract: Surfactant-mediated chemical routes allow one to synthesize highly engineered shape- and size-controlled nanocrystals. However, the occurrence of capping agents on the surface of the nanocrystals is undesirable for selected applications. Here, a novel approach to the production of shape-controlled nanocrystals which exhibit high thermal stability is demonstrated. Ceria nanocubes obtained by surfactant-mediated synthesis are embedded inside a highly porous silica aerogel and thermally treated to remove the capping agent. Powder X-ray Diffraction and Scanning Transmission Electron Microscopy show the homogeneous dispersion of the nanocubes within the aerogel matrix. Remarkably, both the size and the shape of the ceria nanocubes are retained not only throughout the aerogel syntheses but also upon thermal treatments up to 900 °C, while avoiding their agglomeration. The reactivity of ceria is measured by in situ High-Energy Resolution Fluorescence Detected - X-ray Absorption Near Edge Spectroscopy at the Ce L3 edge, and shows the reversibility of redox cycles of ceria nanocubes when they are embedded in the aerogel. This demonstrates that the enhanced reactivity due to their prominent {100} crystal facets is preserved. In contrast, unsupported ceria nanocubes begin to agglomerate as soon as the capping agent decomposes, leading to a degradation of their reactivity already at 275 °C.
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Sep 2020
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I15-Extreme Conditions
I22-Small angle scattering & Diffraction
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Danilo
Di Genova
,
Richard A.
Brooker
,
Heidy M.
Mader
,
James W. E.
Drewitt
,
Alessandro
Longo
,
Joachim
Deubener
,
Daniel R.
Neuville
,
Sara
Fanara
,
Olga
Shebanova
,
Simon
Anzellini
,
Fabio
Arzilli
,
Emily C.
Bamber
,
Louis
Hennet
,
Giuseppe
La Spina
,
Nobuyoshi
Miyajima
Diamond Proposal Number(s):
[17615, 20447]
Open Access
Abstract: Although gas exsolution is a major driving force behind explosive volcanic eruptions, viscosity is critical in controlling the escape of bubbles and switching between explosive and effusive behavior. Temperature and composition control melt viscosity, but crystallization above a critical volume (>30 volume %) can lock up the magma, triggering an explosion. Here, we present an alternative to this well-established paradigm by showing how an unexpectedly small volume of nano-sized crystals can cause a disproportionate increase in magma viscosity. Our in situ observations on a basaltic melt, rheological measurements in an analog system, and modeling demonstrate how just a few volume % of nanolites results in a marked increase in viscosity above the critical value needed for explosive fragmentation, even for a low-viscosity melt. Images of nanolites from low-viscosity explosive eruptions and an experimentally produced basaltic pumice show syn-eruptive growth, possibly nucleating a high bubble number density.
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Sep 2020
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B21-High Throughput SAXS
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[16258]
Open Access
Abstract: Cellular cross-talk between ubiquitination and other posttranslational modifications contributes to the regulation of numerous processes. One example is ADP-ribosylation of the carboxyl terminus of ubiquitin by the E3 DTX3L/ADP-ribosyltransferase PARP9 heterodimer, but the mechanism remains elusive. Here, we show that independently of PARP9, the conserved carboxyl-terminal RING and DTC (Deltex carboxyl-terminal) domains of DTX3L and other human Deltex proteins (DTX1 to DTX4) catalyze ADP-ribosylation of ubiquitin’s Gly76. Structural studies reveal a hitherto unknown function of the DTC domain in binding NAD+. Deltex RING domain recruits E2 thioesterified with ubiquitin and juxtaposes it with NAD+ bound to the DTC domain to facilitate ADP-ribosylation of ubiquitin. This ubiquitin modification prevents its activation but is reversed by the linkage nonspecific deubiquitinases. Our study provides mechanistic insights into ADP-ribosylation of ubiquitin by Deltex E3s and will enable future studies directed at understanding the increasingly complex network of ubiquitin cross-talk.
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Sep 2020
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Wout
Oosterheert
,
Katerina T.
Xenaki
,
Viviana
Neviani
,
Wouter
Pos
,
Sofia
Doulkeridou
,
Jip
Manshande
,
Nicholas M.
Pearce
,
Loes M. J.
Kroon-batenburg
,
Martin
Lutz
,
Paul M. P.
Van Bergen En Henegouwen
,
Piet
Gros
Diamond Proposal Number(s):
[19800]
Open Access
Abstract: Tetraspanins are eukaryotic membrane proteins that contribute to a variety of signaling processes by organizing partner-receptor molecules in the plasma membrane. How tetraspanins bind and cluster partner receptors into tetraspanin-enriched microdomains is unknown. Here, we present crystal structures of the large extracellular loop of CD9 bound to nanobodies 4C8 and 4E8 and, the cryo-EM structure of 4C8-bound CD9 in complex with its partner EWI-F. CD9–EWI-F displays a tetrameric arrangement with two central EWI-F molecules, dimerized through their ectodomains, and two CD9 molecules, one bound to each EWI-F transmembrane helix through CD9-helices h3 and h4. In the crystal structures, nanobodies 4C8 and 4E8 bind CD9 at loops C and D, which is in agreement with the 4C8 conformation in the CD9–EWI-F complex. The complex varies from nearly twofold symmetric (with the two CD9 copies nearly anti-parallel) to ca. 50° bent arrangements. This flexible arrangement of CD9–EWI-F with potential CD9 homo-dimerization at either end provides a “concatenation model” for forming short linear or circular assemblies, which may explain the occurrence of tetraspanin-enriched microdomains.
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Sep 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[13704, 18197]
Open Access
Abstract: The torsional performance of bi-axially braided carbon fibre reinforced polymer (CFRP) tubes as a function of braid architecture is investigated. It is found that for a given braid pattern, the 45° braided CFRP tubes have higher shear moduli and lower shear strength than the 35° braids. In general, 2/2 (regular) braided CFRP tubes exhibit both higher shear strength and higher shear modulus than 1/1 (diamond) braids. However, beyond the peak load, the shear strength of 2/2 braided CFRPs exhibits sudden, steep drops, resulting in a lower remnant shear strength than 1/1 structures after the shear strain exceeds 4.5%. Moreover, the damage evolution is monitored in-situ by synchrotron X-ray computed tomography during torsional straining. It showed that for a 2/2 structure, inter-tow debonded regions are vertically interconnected allowing rapid crack propagation and strength drops, whereas for the 1/1 braid they are distributed in a chequer board causing more gradual loss of strength. The fibre/matrix interfacial strength and tow cross-over density play key roles in the torsional failure of 1/1 and 2/2 braided CFRP tubes, as the former controls damage initiation and the latter controls damage propagation.
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Sep 2020
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[21776]
Open Access
Abstract: Small-angle X-ray scattering (SAXS) is used to characterize the in situ formation of diblock copolymer spheres, worms and vesicles during reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate at 70 °C using a poly(glycerol monomethacrylate) steric stabilizer. 1H NMR spectroscopy indicates more than 99% HPMA conversion within 80 min, while transmission electron microscopy and dynamic light scattering studies are consistent with the final morphology being pure vesicles. Analysis of time-resolved SAXS patterns for this prototypical polymerization-induced self-assembly (PISA) formulation enables the evolution in copolymer morphology, particle diameter, mean aggregation number, solvent volume fraction, surface density of copolymer chains and their mean inter-chain separation distance at the nanoparticle surface to be monitored. Furthermore, the change in vesicle diameter and membrane thickness during the final stages of polymerization supports an ‘inward growth’ mechanism.
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Sep 2020
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