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Andi
Di
,
Julien
Schmitt
,
Kun
Ma
,
Marcelo A.
Da Silva
,
Naomi S.
Elstone
,
Najet
Mahmoudi
,
Peixun
Li
,
Adam
Washington
,
Zi
Wang
,
R. John
Errington
,
Karen J.
Edler
Abstract: Hypothesis: Polyoxometalates (POMs) are metal oxygen clusters with a range of interesting magnetic and catalytic properties. POMs with attached hydrocarbon chains show amphiphilic behaviour so we hypothesised that mixtures of a non-ionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, but which would differ in size and shape from micelles formed by the individual surfactants. Due to the high charge and large size of the POM, we suggested that these would be nonideal mixtures due to the complex interactions between the two types of surfactants. The nonideality and the micellar composition may be quantified using regular solution theory. With supplementary information provided by small-angle neutron scattering, an understanding of this unusual binary surfactant system can be established. Experiments: A systematic study was performed on mixed surfactant systems containing polyoxometalate-headed amphiphiles (K10[P2W17O61OSi2(CnH2n+1)2], abbreviated as P2W17-2Cn, where n = 12, 14 or 16) and hexaethylene glycol monododecyl ether (C12EO6). Critical micelle concentrations (CMCs) of these mixtures were measured and used to calculate the interaction parameters based on regular solution theory, enabling prediction of micellar composition. Predictions were compared to micelle structures obtained from small angle neutron scattering (SANS). A phase diagram was also established. Findings: The CMCs of these mixtures suggest unusual unfavourable interactions between the two species, despite formation of mixed micelles. Micellar compositions obtained from SANS concurred with those calculated using the averaged interaction parameters for P2W17-2Cn/C12EO6 (n = 12 and 14). We attribute the unfavourable interactions to a combination of different phenomena: counterion-mediated interactions between P2W17 units and the unfolding of the ethylene oxide headgroups of the nonionic surfactant, yet micelles still form in these systems due to the hydrophobic interactions between surfactant tails.
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Jun 2020
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I15-1-X-ray Pair Distribution Function (XPDF)
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Abstract: The crystal structure of the organic pigment 2-monomethyl-quinacridone (Pigment Red 192, C21H14N2O2) was solved from X-ray powder diffraction data. The resulting average structure is described in space group [P\overline 1], Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head-to-tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice-energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long-range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice-energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [0[\bar 1]1] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering.
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Jun 2020
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[9157]
Abstract: To advance the scientific understanding of bacteria-driven mercury (Hg) transformation processes in natural environments, thermodynamics and kinetics of divalent mercury Hg(II) chemical speciation need to be understood. Based on Hg LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopic information, combined with competitive ligand exchange (CLE) experiments, we determined Hg(II) structures and thermodynamic constants for Hg(II) complexes formed with thiol functional groups in bacterial cell-membranes of two extensively studied Hg(II) methylating bacteria: Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. The Hg EXAFS data suggest 5% of the total number of membrane thiol functionalities (Mem-RStot = 380 ± 50 µmol g−1 C) are situated closely enough to be involved in a 2-coordinated Hg(Mem-RS)2 structure in Geobacter. The remaining 95% of Mem-RSH are involved in mixed-ligation Hg(II)-complexes, either with low molecular mass (LMM) thiols like Cys, Hg(Cys)(Mem-RS) or with neighboring O/N membrane functionalities, Hg(Mem-RSRO). We report log K values for the formation of the structures Hg(Mem-RS)2, Hg(Cys)(Mem-RS), and Hg(Mem-RSRO) to be 39.1 ± 0.2 , 38.1 ± 0.1 and 25.6 ± 0.1, respectively, for Geobacter; and 39.2 ± 0.2 , 38.2 ± 0.1 and 25.7 ± 0.1, respectively for ND132. Combined with results obtained from previous studies using the same methodology to determine chemical speciation of Hg(II) in presence of natural organic matter (Suwannee River DOM) and 15 LMM thiols, an internally consistent thermodynamic data set is created, which we recommend to be used in studies of Hg transformation processes in Bacterium–NOM–LMM thiols systems.
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Jun 2020
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I03-Macromolecular Crystallography
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Ganesh Kumar
Mothukuri
,
Sangram S
Kale
,
Carl Leonard
Stenbratt
,
Alessandro
Zorzi
,
Jonathan
Vesin
,
Julien
Bortoli Chapalay
,
Kaycie
Deyle
,
Gerardo
Turcatti
,
Laura
Cendron
,
Alessandro
Angelini
,
Christian
Heinis
Diamond Proposal Number(s):
[21741]
Open Access
Abstract: Macrocycles provide an attractive modality for drug development, but generating ligands for new targets is hampered by the limited availability of large macrocycle libraries. We have established a solution-phase macrocycle synthesis strategy in which three building blocks are coupled sequentially in efficient alkylation reactions that eliminate the need for product purification. We demonstrate the power of the approach by combinatorially reacting 15 bromoacetamide-activated tripeptides, 42 amines, and 6 bis-electrophile cyclization linkers to generate a 3,780-compound library with minimal effort. Screening against thrombin yielded a potent and selective inhibitor (Ki = 4.2 ± 0.8 nM) that efficiently blocked blood coagulation in human plasma. Structure-activity relationship and X-ray crystallography analysis revealed that two of the three building blocks acted synergistically and underscored the importance of combinatorial screening in macrocycle development. The three-component library synthesis approach is general and offers a promising avenue to generate macrocycle ligands to other targets.
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Jun 2020
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B18-Core EXAFS
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Camila
Rivera-cárcamo
,
Faqiang
Leng
,
Iann C.
Gerber
,
Iker
Del Rosal
,
Romuald
Poteau
,
Vincent
Collière
,
Pierre
Lecante
,
Divya
Nechiyil
,
Wolfgang
Bacsa
,
Anna
Corrias
,
M. Rosa
Axet
,
Philippe
Serp
Diamond Proposal Number(s):
[14239]
Abstract: We report a procedure for preparing ulta-high metal loading (10-20 % w/w Ru) Ru@C60 nanostructured catalysts comprising exclusively Ru single atoms. We show that by changing the Ru/C60 ratio and the nature of the solvent used during the synthesis, it is possible to increase the Ru loading up to 50% w/w, and to produce hetero-structures containing subnanometric Ru nanoparticles. Several techniques such as high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy – high angle annular dark field (STEM-HAADF), Raman spectroscopy, wide-angle X-ray scattering (WAXS), extended X-ray absorption fine structure (EXAFS) and X-ray photoelectron spectroscopy (XPS) together with theoretical calculations were used to characterize these materials. At such high metal loading, the distinction between Ru single atoms and clusters is not trivial, even with this combination of techniques. We evaluated the catalytic properties of these materials for the hydrogenation of nitrobenzene and 2,3-dimethyl-2-butene. The catalysts containing only Ru single atoms are much less active for these reactions than the ones containing clusters. For nitrobenzene hydrogenation, this is because electro-deficient Ru single atoms and few atom Run clusters are not performant for H2 activation compared to larger clusters (n ≥ 13), as shown by density functional theory (DFT) calculations. For the more crowded substrate 2,3-dimethyl-2-butene, DFT calculations have shown that this is due to steric hindrance. These simple tests can thus been used to distinguish samples containing metallic sub-nanometer nanoparticles. These novel catalysts are also extremely active for the hydrogenation of -substituted 2,3-dimethyl-2-butene.
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Jun 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[18165]
Abstract: Environment Induced Cracking (EIC) has been observed in three dimensions (3D) at high spatial and temporal resolution for AA5083 H131 alloy using in situ synchrotron X-ray CT. The initiation of EIC cracks occurred in humid air at ∼0.5σy and started from corrosion sites associated with intermetallic particle clusters. Time-resolved monitoring of the crack growth confirmed cracks grow below threshold KIEIC and are susceptible to arrest under fixed displacement conditions. Even when the cracks exceed threshold KIEIC and enter sustained propagation they exhibit very uneven growth rates. Failure occurs when the K of the largest crack exceeds the fracture toughness KIC.
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Jun 2020
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B16-Test Beamline
Detectors
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Abstract: One of the major limitations of XAS experiment at synchrotron facilities is the performance of the detectors. In order to be able to measure more challenging samples and to cope with the very high photon flux of the current and future (diffraction limited) sources technological developments of detectors are necessary. This paper reports on the construction and characterization of a monolithic nineteen channel germanium detector demonstrator fitted with CMOS preamplifiers. The detector was characterized in the lab with radioactive sources and with the X-ray synchrotron beam. Characteristics such as energy resolution, linearity, counting rate capabilities, and stability of the detector were thoroughly evaluated. In addition, it was proved that by using an advanced pulse processor such as Xspress4 it was possible to improve the performance of the detector system by eliminating the cross talk among channels and by suppressing the charge shared events. This work could pave the way to enhanced germanium fluorescence detectors for high throughput X-ray spectroscopy.
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Jun 2020
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Abstract: Hypothesis: Extracellular Vesicles (EVs) are natural nanosized lipid vesicles involved in most intercellular communication pathways. Given their nature, they represent natural cell membrane models, with intermediate complexity between real and synthetic lipid membranes. Here we compare EVs-derived (EVSLB) and synthetic Supported Lipid Bilayers (SLBs) in the interaction with cationic superparamagnetic iron oxide nanoparticles (SPIONs). The aim is twofold: (i) exploit SPIONs as nanometric probes to investigate the features of EVSLBs as novel biogenic platforms; (ii) contribute at improving the knowledge on the behavior of SPIONs with biological interfaces. Experiments: Quartz Crystal Microbalance, X-ray Reflectivity, Grazing-incidence Small-angle X-ray Scattering, Atomic Force Microscopy, Confocal Microscopy data on SPIONs-EVSLB were systematically compared to those on SPIONs challenging synthetic SLBs, taken as references. Findings: The ensemble of experimental results highlights the much stronger interaction of SPIONs with EVSLBs with respect to synthetic SLBs. This evidence strongly supports the hypotheses on the peculiar structure of EVSLBs, with cushioned non-flat areas and extended exposed surface; in addition, it suggests that these features are relevant in the response of biogenic membranes to nano-objects. These findings contribute to the fundamental knowledge on EVSLBs, key for their development both as biomimetic membranes, or as platforms for biomedical applications.
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Jun 2020
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B18-Core EXAFS
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Grazia
Malta
,
Simon A.
Kondrat
,
Simon J.
Freakley
,
David J.
Morgan
,
Emma K.
Gibson
,
Peter P.
Wells
,
Matteo
Aramini
,
Diego
Gianolio
,
Paul B. J.
Thompson
,
Peter
Johnston
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[15214]
Open Access
Abstract: The replacement of HgCl2/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl−, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C2H2 alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.
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Jun 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
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Thien D.
Duong
,
Sergey A.
Sapchenko
,
Ivan
Da Silva
,
Harry G. W.
Godfrey
,
Yongqiang
Cheng
,
Luke L.
Daemen
,
Pascal
Manuel
,
Mark D.
Frogley
,
Gianfelice
Cinque
,
Anibal J.
Ramirez-cuesta
,
Sihai
Yang
,
Martin
Schroeder
Diamond Proposal Number(s):
[14938]
Open Access
Abstract: Metal–organic frameworks (MOFs) functionalised with amine, amide and hydroxyl groups show great promise for CO2 binding due to their ability to form hydrogen bonds to CO2. Herein we report the adsorption and selectivity of CO2 in four iso-reticular MOFs adopting the NbO topology. Functionalisation of the parent MOF, MFM-102, with –NO2, –NH2 and alkyl groups leads to an enhancement of CO2 adsorption of up to 36% for the NO2-decorated MOF and with raised selectivity. MFM-102-NO2 shows the highest adsorption capacity for CO2 (184 cm3 g−1 at 273 K and 1.0 bar) within this series, comparable to the best-behaving iso-reticular MOFs. At 298 K and 1.0 bar, MFM-102-NO2 shows a CO2/CH4 selectivity of 5.0. In situ inelastic neutron scattering and synchrotron FT-IR micro-spectroscopy were employed to elucidate the host–guest interaction dynamics within CO2-loaded MFM-102-NO2. Neutron powder diffraction enabled the direct observation of the preferred binding domains in MFM-102-NO2, and, to the best of our knowledge, we report the first example of CO2 binding to a –NO2 group in a porous MOF. Synergistic effects between the –NO2 group and the open metal sites lead to optimal binding of CO2 molecules within MFM-102-NO2 via hydrogen bonding to C–H groups.
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May 2020
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