I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[18215]
Abstract: The addition of nano-fillers has been widely proposed as a method to enhance the dielectric properties of high voltage polymeric insulation, though there are mixed reports in the literature. Here the potential of silica nano-particles to extend the time to failure specifically through resistance to electrical tree growth in epoxy resin is determined. The benefit of silane treating the nano-particles before compounding is clearly established with regard to slowing tree growth and subsequent time to failure. The growth of trees in needle-plane samples is measured in the laboratory with loadings of 1, 3 and 5 wt% nano-filler. In all cases the average times to failure are extended, but silane treatment of the nano-particles prior to compounding yields much superior results. The emergence of a pronounced inception time before tree growth is also noted for the higher-filled, silane-treated cases. The average time to failure of silane-treated 5 wt% filled material was 28 times that of the unfilled resin. The improvement in performance between the nanocomposites with untreated and treated fillers is attributed to fewer agglomerations and improved dispersion of the filler in the treated cases. Measurements of Partial Discharge (PD) indicated significant differences in PD patterns during the growth of trees in the treated and untreated cases. This distinction may provide a quality control method for monitoring materials. In particular, long periods in which PDs were not measured were observed in the silane-treated cases. Visual imaging of tree growth in the unfilled material allowed the changing nature of the tree from fine to tree to dark tree to be observed as it grew. Corresponding PD measurements suggest the dark tree is gradually becoming conductive, and that growth of maximum PD measured is dependent on the relative rates of the growth of the tree and its carbonization. X-ray computer tomography identified significant differences in average tree channel diameters (a reduction from 2.8 ”m to 2.0 ”m for 1 wt% and 3 wt% cases). This implies that in addition to tree length changes, evaporated tree volumes also change and may explain the change in partial discharge characteristics observed.
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Jul 2021
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[13440]
Open Access
Abstract: The activity-regulated cytoskeleton-associated protein (Arc) is important for synaptic plasticity and the normal function of the brain. Arc interacts with neuronal postsynaptic proteins, but the mechanistic details of its function have not been fully established. The C-terminal domain of Arc consists of tandem domains, termed the N- and C-lobe. The N-lobe harbours a peptide binding site, able to bind multiple targets. By measuring the affinity of human Arc towards various peptides from stargazin and guanylate kinase-associated protein (GKAP), we have refined its specificity determinants. We found two sites in the GKAP repeat region that bind to Arc and confirmed these interactions by X-ray crystallography. Phosphorylation of the stargazin peptide did not affect binding affinity but caused changes in thermodynamic parameters. Comparison of the crystal structures of three high-resolution human Arc-peptide complexes identifies three conserved CâHâŠÏ interactions at the binding cavity, explaining the sequence specificity of short linear motif binding by Arc. We further characterise central residues of the Arc lobe fold, show the effects of peptide binding on protein dynamics, and identify acyl carrier proteins as structures similar to the Arc lobes. We hypothesise that Arc may affect protein-protein interactions and phase separation at the postsynaptic density, affecting protein turnover and re-modelling of the synapse. The present data on Arc structure and ligand binding will help in further deciphering these processes.
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Jul 2021
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[8395, 10006]
Abstract: Neutron or proton irradiation induced dislocation loops in Zr and its alloys are usually characterized by electron microscopy methods. In plastically deformed materials X-ray line profile analysis (XLPA) is now a well-established tool to determine dislocation densities (DDs) with excellent agreement between XLPA and TEM analysis. In irradiated zirconium alloys, however, XLPA determined DDs are often considerably larger than those obtained by TEM. In ion irradiated Cu and W it was shown that X-ray diffraction or MD simulations give significantly larger dislocation loop densities than conventional TEM analysis, which suggests that the smallest loops remain undetected by TEM. Based on these results we developed a new methodology to determine power-law size-distributions of irradiation-induced dislocation loops. We assume that only loops larger than a certain threshold are fully counted in TEM micrographs, whereas XLPA detects all the loops in the entire size range. This new analysis procedure shows that in neutron irradiated Zircaloy-2 in the channel-box materials the total DD is larger than in the cladding materials, even though TEM counting shows the opposite. We also found that there is a correlation between the reciprocal square-root of loop DDs and the diameter of loops. Our work shows that irradiation induced loop-formation and irradiation-damage in general can be better determined when we combine TEM investigations with XLPA.
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Jul 2021
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[19354]
Open Access
Abstract: Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO2, under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features (> 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO2, using a NIR beam.
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Jun 2021
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[9893, 11806, 12483]
Abstract: Metabolic bone diseases have an impact on the multi-scale structure of bone and its mechanical properties. This study aims to conduct quantitative analysis of the link between specific material-level changes and mechanical alterations of bone tissue. We combine several scanning probe methods with an analytical multiscale model to investigate these links in a mouse model (đ¶đhâ120â+) with endogenous steroid production. Experimental results from our prior study are used, which showed significant changes in spatial maps of nano-scale orientation, mineralization, and microporosity in đ¶đhâ120â+ mice bone. An analytical composite/continuum mechanical model is incorporated with these experimental parameters to predict the progressive reduction in elastic moduli. The largest fractional reduction in elastic modulus is found to arise from incorporation of microscale porosity, followed by the reduced nanoscale degree of orientation. Our work provides both insights into the altered structure-performance relations and a systematic analytical framework for linking scanning micro- and nanoprobe experimental data on hierarchical structural materials to macroscopic biomechanical outcomes.
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Jun 2021
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I03-Macromolecular Crystallography
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Igor M.
Ferreira
,
José Edwin N.
Quesñay
,
Alliny C. S.
Bastos
,
Camila T.
Rodrigues
,
Melanie
Vollmar
,
Tobias
Krojer
,
Claire
Strain-Damerell
,
Nicola A.
Burgess-Brown
,
Frank
Von Delft
,
Wyatt W.
Yue
,
Sandra M G.
Dias
,
Andre L. B.
Ambrosio
Diamond Proposal Number(s):
[8421]
Open Access
Abstract: Cancer cells exhibit an altered metabolic phenotype, consuming higher levels of the amino acid glutamine. This metabolic reprogramming depends on increased mitochondrial glutaminase activity to convert glutamine to glutamate, an essential precursor for bioenergetic and biosynthetic processes in cells. Mammals encode the kidney-type (GLS) and liver-type (GLS2) glutaminase isozymes. GLS is overexpressed in cancer and associated with enhanced malignancy. On the other hand, GLS2 is either a tumor suppressor or an oncogene, depending on the tumor type. The GLS structure and activation mechanism are well known, while the structural determinants for GLS2 activation remain elusive. Here, we describe the structure of the human glutaminase domain of GLS2, followed by the functional characterization of the residues critical for its activity. Increasing concentrations of GLS2 lead to tetramer stabilization, a process enhanced by phosphate. In GLS2, the so-called âlid loopâ is in a rigid open conformation, which may be related to its higher affinity for phosphate and lower affinity for glutamine; hence, it has lower glutaminase activity than GLS. The lower affinity of GLS2 for glutamine is also related to its less electropositive catalytic site than GLS, as indicated by a Thr225Lys substitution within the catalytic site decreasing the GLS2 glutamine concentration corresponding to half-maximal velocity (K0.5). Finally, we show that the Lys253Ala substitution (corresponding to the Lys320Ala in the GLS âactivationâ loop, formerly known as the âgatingâ loop) renders a highly active protein in stable tetrameric form. We conclude that the âactivationâ loop, a known target for GLS inhibition, may also be a drug target for GLS2.
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Jun 2021
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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John
Liddle
,
Andrew C.
Pearce
,
Christopher
Arico-Muendel
,
Svetlana
Belyanskaya
,
Andrew
Brewster
,
Murray
Brown
,
Chun-Wa
Chung
,
Alexis
Denis
,
Nerina
Dodic
,
Anthony
Dossang
,
Peter
Eddershaw
,
Diana
Klimaszewska
,
Imran
Haq
,
Duncan S.
Holmes
,
Alistair
Jagger
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Toral
Jakhria
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Emilie
Jigorel
,
Ken
Lind
,
Jeff
Messer
,
Margaret
Neu
,
Allison
Olszewski
,
Riccardo
Ronzoni
,
James
Rowedder
,
Martin
RĂŒdiger
,
Steve
Skinner
,
Kathrine J.
Smith
,
Lionel
Trottet
,
Iain
Uings
,
Zhengrong
Zhu
,
James A.
Irving
,
David A.
Lomas
Diamond Proposal Number(s):
[23853, 17201]
Abstract: α1-antitrypsin deficiency is characterised by the misfolding and intracellular polymerisation of mutant α1-antitrypsin protein within the endoplasmic reticulum (ER) of hepatocytes. Small molecules that bind and stabilise Z α1-antitrypsin were identified via a DNA-encoded library screen. A subsequent structure based optimisation led to a series of highly potent, selective and cellular active α1-antitrypsin correctors.
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Jun 2021
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[22299]
Open Access
Abstract: As a result of the synthesis protocol polyoxyethylene sorbitan monooleate (polysorbate 80, PS80) is a highly complex mixture of compounds. PS80 was therefore separated into its main constituents, e.g. polyoxyethylene isosorbide esters and polyoxyethylene esters, as well as mono- di- and polyesters using preparative high-performance liquid chromatography. In this comprehensive study the individual components and their ethoxylation level were verified by matrix assisted laser desorption/ionization time-of-flight and their thermotropic behavior was analyzed using differential scanning calorimetry and X-ray diffraction. A distinct correlation was found between the average length of the ethylene oxide (EO) chains in the headgroup and the individual compoundsâ ability to crystallize. Importantly, a critical number of EO units required for crystallization of the headgroup was determined (6 EO units per chain or 24 per molecule). The investigation also revealed that the hydrocarbon tails only crystallize for polyoxyethylene sorbitan esters if saturated. PS80 is synthesized by reacting with approximately 20 mol of EO per mole of sorbitol, however, the number of EO units in the sorbitan ester in commercial PS80 products is higher than the expected 20 (5 EO units per chain). The complex behavior of all tested compounds revealed that if the amount of several of the linear by-products is reduced, the number of EO units in the chains will stay below the critical number and the product will not be able to crystallize by the EO chains.
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Jun 2021
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I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[22176]
Abstract: Hypothesis: Despite the widespread industrial usage of erucamide as a slip additive to modify polymer surface properties, a controversy appears to have persisted regarding the nanostructure of erucamide surface layers, particularly the molecular orientation at the outermost layer. The erucamide nanostructure and molecular orientation, along with its surface coverage, hydrophobicity, and adhesive response, can be tuned by simply varying the erucamide concentration in the solution from which the spin coated layer is prepared. Experiments: Synchrotron X-ray reflectivity (XRR) allowed a comprehensive characterisation of the out-of-plane structural parameters (e.g. molecular packing and thickness) of the erucamide layers prepared via spin coating from nonaqueous solution on silica. Complementary Atomic Force Microscopy (AFM) imaging with high lateral resolution revealed localised in-plane structures. Contact angle measurements provided information on the wettability of erucamide-coated surfaces. Peak Force Quantitative Nanomechanical Mapping (QNM) allowed a correlation between the erucamide nanostructure with the surface nanomechanical properties (i.e. adhesive response). Findings: Our results reveal erucamide surface nanostructures on silica as patchy monolayers, isolated circular bilayers/rounded rectangle-like aggregates and overlapping plate-like multilayers as the erucamide concentration in the spin coating solution was varied. In all the cases, XRR and AFM results were consistent with the picture that the erucamide tails were oriented outwards. The QNM adhesion force mapping of all the observed morphologies also supported this molecular orientation at the outermost erucamide monolayer. The wettability study further confirmed this conclusion with the observed increase in the surface hydrophobicity and coverage upon increasing erucamide concentration, with the macroscopic water contact angle Ξ = 92.9° ± 2.9° at the highest erucamide concentration of 2 wt%.
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May 2021
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[24717]
Open Access
Abstract: This structural and biophysical study exploited a method of perdeuterating hen egg-white lysozyme based on the expression of insoluble protein in Escherichia coli followed by in-column chemical refolding. This allowed detailed comparisons with perdeuterated lysozyme produced in the yeast Pichia pastoris, as well as with unlabelled lysozyme. Both perdeuterated variants exhibit reduced thermal stability and enzymatic activity in comparison with hydrogenated lysozyme. The thermal stability of refolded perdeuterated lysozyme is 4.9°C lower than that of the perdeuterated variant expressed and secreted in yeast and 6.8°C lower than that of the hydrogenated Gallus gallus protein. However, both perdeuterated variants exhibit a comparable activity. Atomic resolution X-ray crystallographic analyses show that the differences in thermal stability and enzymatic function are correlated with refolding and deuteration effects. The hydrogen/deuterium isotope effect causes a decrease in the stability and activity of the perdeuterated analogues; this is believed to occur through a combination of changes to hydrophobicity and protein dynamics. The lower level of thermal stability of the refolded perdeuterated lysozyme is caused by the unrestrained Asn103 peptide-plane flip during the unfolded state, leading to a significant increase in disorder of the Lys97âGly104 region following subsequent refolding. An ancillary outcome of this study has been the development of an efficient and financially viable protocol that allows stable and active perdeuterated lysozyme to be more easily available for scientific applications.
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May 2021
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