I18-Microfocus Spectroscopy
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Abstract: The impact of long-lived radionuclides on human health depends on their behaviour in near-surface soils and sediments and the LORISE project aims to define the key controlling physical, chemical and biological processes at a number of ‘natural laboratories’ around the UK. Within this PhD project, the role of natural organic matter (NOM) is of especial importance because NOM can potentially facilitate the transport or attenuation of radiologically significant elements such as U and radiocarbon (14C). Peaty soils in the vicinity of natural uranium mineralisations are often highly enriched in U with concentrations of up to 3000 mg kg-1, 4000 mg kg-1 and 2500 mg kg-1 having been found in the US (Owen and Otten, 1995), Switzerland (Regenspurg et al., 2010), and the UK (Xu, 2013), respectively. The NOM within these soils has been implicated in U retention but the controlling processes and the nature of interactions are poorly characterised. The Needle’s Eye natural mineralisation, SW Scotland, provides a rare opportunity within the UK to investigate long-term U-NOM interactions. Similarly, the well characterised inputs of radiocarbon into the Irish Sea from the Sellafield nuclear reprocessing facility since the mid-1960s present an opportunity to investigate the transfer of anthropogenic 14C between environmental pools and trace its incorporation into coastal sediments. While the enrichment of sediment organic matter with anthropogenic 14C has been identified, (MacKenzie et al., 2004), the chemical and physical characteristics of NOM enriched with 14C have not been investigated. Currently, there is not a good understanding of which NOM components govern U binding or incorporate 14C, and therefore the implications of the influence of NOM on radionuclide mobilisation or immobilisation are hard to assess. In this study, the characteristics of organic matter from the Needle’s Eye natural analogue site have been examined and the relationship with the geochemical properties of the site and U binding have been investigated. Further to this, NOM extracted from the Needle’s Eye peat bog and from sediments of the Solway coast at the Southwick Merse has been fractionated and characterised using a range of spectroscopic techniques to identify the components of NOM which are responsible for binding U and those which incorporate anthropogenic 14C.
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Jul 2019
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I18-Microfocus Spectroscopy
I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[10311]
Open Access
Abstract: Structural and associated biomechanical gradients within biological tissues are important for tissue functionality and preventing damaging interfacial stress concentrations. Articular cartilage possesses an inhomogeneous structure throughout its thickness, driving the associated variation in the biomechanical strain profile within the tissue under physiological compressive loading. However, little is known experimentally about the nanostructural mechanical role of the collagen fibrils and how this varies with depth. Utilising a high-brilliance synchrotron X-ray source, we have measured the depth-wise nanostructural parameters of the collagen network in terms of the periodic fibrillar banding (D-period) and associated parameters. We show that there is a depth dependent variation in D-period reflecting the pre-strain and concurrent with changes in the level of intrafibrillar order. Further, prolonged static compression leads to fibrillar changes mirroring those caused by removal of extrafibrillar proteoglycans (as may occur in aging or disease). We suggest that fibrillar D-period is a sensitive indicator of localised changes to the mechanical environment at the nanoscale in soft connective tissues.
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Jul 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[14747]
Abstract: Prostatic zinc content is a known biomarker for discriminating normal healthy tissue from benign prostatic hyperplasia (BPH) and prostate cancer (PCa). Given that zinc content is not readily measured without a tissue biopsy, we have been exploring noninvasive imaging methods to detect these diagnostic differences using a zinc-responsive MRI contrast agent. During imaging studies in mice, we observed that a bolus of glucose stimulates secretion of zinc from the prostate of fasted mice. This discovery allowed the use of a Gd-based zinc sensor to detect differential zinc secretion in regions of healthy versus malignant prostate tissue in a transgenic adenocarcinoma mouse model of PCa. Here, we used a zinc-responsive MRI agent to detect zinc release across the prostate during development of malignancy and confirm the loss of total tissue zinc by synchrotron radiation X-ray fluorescence (μSR-XRF). Quantitative μSR-XRF results show that the lateral lobe of the mouse prostate uniquely accumulates high concentrations of zinc, 1.06 ± 0.08 mM, and that the known loss of zinc content in the prostate is only observed in the lateral lobe during development of PCa. Additionally, we confirm that lesions identified by a loss of zinc secretion indeed represent malignant neoplasia and that the relative zinc concentration in the lesion is reduced to 0.370 ± 0.001 mM. The μSR-XRF data also provided insights into the mechanism of zinc secretion by showing that glucose promotes movement of zinc pools (∼1 mM) from the glandular lumen of the lateral lobe of the mouse prostate into the stromal/smooth muscle surrounding the glands. Co-localization of zinc and gadolinium in the stromal/smooth muscle areas as detected by μSR-XRF confirm that glucose initiates secretion of zinc from intracellular compartments into the extracellular spaces of the gland where it binds to the Gd-based agent and albumin promoting MR image enhancement.
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Jul 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15771]
Abstract: This research aimed to find the best phenotype of the brown algae Fucus vesiculosus (kelp) which has the greater potential to become a sorption byproduct for Zn removal from contaminated waters. Thus, the Zn uptake capacity and sorption mechanisms of the kelp collected from the Baltic Sea shore was, for the first time, investigated under various conditions, and compared to the phenotype habiting on the Irish Sea shore. Sorption studies were performed investigating the effect of algal dosage, Zn sources as well as algal harvesting time of the year on Zn uptake capacity. The results suggested that the Baltic algae is a better biosorbent for Zn uptake. Sorption mechanisms were studied by employing various indirect and direct approaches, more importantly, including high resolution synchrotron X-Ray Fluorescence and X-Ray Absorption Spectroscopy (XAS) and molecular modelling (MM). The results revealed that alginate and cellulose are among the main polysaccharide bonding Zn at algal surface, via coordination with O atoms from carboxyl and hydroxyl groups. XAS results giving direct measurements of Zn bonding environment on algal surface are supported by MM outputs and suggested that Zn is surrounded by ca. 5 O atoms at interatomic distances varying from 1.94 to 2.02 Å. The results contribute to understanding sorption mechanisms which can further lead to finding the best eluent for Zn desorption from the used biomass, bio sorbent reconditioning and reuse in multiple sorption desorption cycles as well as process optimization before industrial scaling up.
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Aug 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[14793, 15903]
Abstract: Eudialyte group minerals (EGM) attract global interest as potential resources for High Field
Strength Elements (HFSE, e.g. Zr, Nb, Ta, and Rare Earth Elements, REE), i.e. critical
materials for modern technologies. They are particularly valued for their relative enrichment
in the most critical lanthanides, i.e. Nd and heavy REE (Gd-Lu). However, REE substitution
mechanisms into the EGM structure are still poorly understood. Light and heavy REE may
occupy different sites and there may be ordering and/or defect clustering in the structure. This
study uses X-ray Absorption Spectroscopy (XAS) to determine the structural state of REE in
EGM from prospective eudialyte-bearing complexes. Yttrium K-edge and Nd L3-edge spectra
were collected as proxies for heavy and light REE, respectively, and compared to natural and
synthetic REE-bearing standards. Extended X-ray Absorption Fine Structure (EXAFS) data
yield best fits for Y in six-fold coordination with Y-O distances of 2.24-2.32 Å, and a second
coordination sphere comprising Fe, Na, Ca, Si and O at radial distances of 3.6-3.8 Å. These
findings are consistent with dominant Y3+ substitution for Ca2+ on the octahedral M1 site in
all samples studied, and exclude preferential substitution of Y3+ onto the smaller octahedral Z
site or the large low-symmetry N4 site. Using lattice strain theory, we constructed relative partitioning models to predict site
preferences of lanthanides we have not directly measured. The models predict that all REE
are favoured on the Ca-dominant M1 site and that preferential partitioning of heavy over light
REE increases in EGM containing significant Mn in the M1-octahedral rings (oneillite
3
subgroup). Thus, the flat REE profiles that make EGM such attractive exploration targets are
not due to preferential partitioning of light and heavy REE onto different sites. Instead, local
ordering of Mn- and Ca-occupied M1 sites may influence the capacity of EGM to
accommodate heavy REE.
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Aug 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15854, 19779]
Open Access
Abstract: Transition metals have essential roles in brain structure and function, and are associated with pathological processes in neurodegenerative disorders classed as proteinopathies. Synchrotron x-ray techniques, coupled with ultrahigh-resolution mass spectrometry, have been applied to study iron and copper interactions with amyloid β (1–42) or α-synuclein. Ex vivo tissue and in vitro systems were investigated, showing the capability to identify metal oxidation states, probe local chemical environments, and localize metal-peptide binding sites. Synchrotron experiments showed that the chemical reduction of ferric (Fe3+) iron and cupric (Cu2+) copper can occur in vitro after incubating each metal in the presence of Aβ for one week, and to a lesser extent for ferric iron incubated with α-syn. Nanoscale chemical speciation mapping of Aβ-Fe complexes revealed a spatial heterogeneity in chemical reduction of iron within individual aggregates. Mass spectrometry allowed the determination of the highest-affinity binding region in all four metal-biomolecule complexes. Iron and copper were coordinated by the same N-terminal region of Aβ, likely through histidine residues. Fe3+ bound to a C-terminal region of α-syn, rich in aspartic and glutamic acid residues, and Cu2+ to the N-terminal region of α-syn. Elucidating the biochemistry of these metal-biomolecule complexes and identifying drivers of chemical reduction processes for which there is evidence ex-vivo, are critical to the advanced understanding of disease aetiology.
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Oct 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[15971, 17888]
Abstract: Rhizosphere soil has distinct physical and chemical properties from bulk soil. However, besides root induced physical changes, chemical changes have not been extensively measured in situ on the pore scale.
In this study we couple structural information, previously obtained using synchrotron X‐ray computed tomography (XCT), with synchrotron X‐ray Fluorescence (SR‐XRF) microscopy and X‐ray Absorption Near‐Edge Structure (XANES) to unravel chemical changes induced by plant roots.
Our results suggest that iron (Fe) and sulfur (S) increase notably in the direct vicinity of the root via solubilization and microbial activity. XANES further shows that Fe is slightly reduced, S is increasingly transformed into sulfate (SO42‐) and that phosphorus (P) is increasable adsorbed to humic substances in this enrichment zone. In addition, the ferrihydrite fraction decreases drastically suggesting the preferential dissolution and the formation of more stable Fe‐oxides. Additionally, the increased transformation of organic S to sulfate indicates that the microbial activity in this zone is increased. These changes in soil chemistry correspond to the soil compaction zone as previously measured via X‐ray CT.
The fact that these changes are co‐located near the root and the compaction zone suggests that decreased permeability due to soil structural changes acts as a barrier creating a zone with increased rhizosphere chemical interactions via surface mediated processes, microbial activity and acidification.
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Oct 2019
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I18-Microfocus Spectroscopy
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Abstract: Determining the oxidation state of Fe through parameterization of X-ray absorption near-edge structure (XANES) spectral features is highly dependent on accurate and repeatable energy calibration between spectra. Small errors in energy calibration can lead to vastly different interpretations. While simultaneous measurement of a reference foil is often undertaken on X-ray spectroscopy beamlines, other beamlines measure XANES spectra without a reference foil and therefore lack a method for correcting energy drift. Here a method is proposed that combines two measures of Fe oxidation state taken from different parts of the spectrum to iteratively correct for an unknown energy offset between spectra, showing successful iterative self-calibration not only during individual beam time but also across different beamlines.
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Nov 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[17250]
Abstract: From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxygen fugacity with depth may be disrupted by the accumulation of oxidised crustal material in the deep lower mantle, entrained there as a result of subduction. While hotspot volcanoes are fed by regions of the mantle likely to have incorporated such recycled material, the oxygen fugacity of erupted hotspot basalts had long been considered comparable to or slightly more oxidised than that of mid-ocean ridge basalt (MORB) and more reduced than subduction zone basalts. Here we report measurements of the redox state of glassy crystal-hosted melt inclusions from tephra and quenched lava samples from the Canary and Cape Verde Islands, that we can independently show were entrapped prior to extensive sulphur degassing. We find high ferric iron to total iron ratios (Fe3+/∑Fe) of up to 0.27–0.30, indicating that mantle plume primary melts are significantly more oxidised than those associated with mid-ocean ridges and even subduction zone. These results, together with previous investigations from the Erebus, Hawaiian and Icelandic hotspots, confirm that mantle upwelling provides a return flow from the deep Earth for components of oxidised subducted lithosphere and suggest that highly oxidised material accumulates or is generated in the lower mantle. The oxidation state of the Earth's interior must therefore be highly heterogeneous and potentially locally inversely stratified.
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Dec 2019
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[9446, 9456]
Abstract: Mantle oxygen fugacity (fO2) governs the physico-chemical evolution of the Earth, however current estimates from commonly used basalt redox proxies are often in disagreement. In this study we compare three different potential basalt fO2 proxies: Fe3+/Fetot, V/Sc and V isotopes, determined on the same submarine lavas from a 700 km section of the Reykjanes Ridge, near Iceland. These samples provide a valuable test of the sensitivities of fO2 proxies to basalt petrogenesis, as they formed at different melting conditions and from a mantle that towards Iceland exhibits increasing long-term enrichment of incompatible elements. New trace element data were determined for 63 basalts with known Fe3+/Fetot. A subset of 19 lavas, covering the geographical spread of the ridge transect, was selected for vanadium isotope analyses.
Vanadium is a multi-valence element whose isotopic fractionation is theoretically susceptible to redox conditions. Yet, the
δ51
VAA composition of basaltic glasses along the Reykjanes Ridge covers only a narrow range (
δ51
VAA = −1.09 to −0.86‰; 1SD = 0.02–0.09) and does not co-vary with fractionation-corrected Fe3+/Fetot (0.134–0.151; 1SD = 0.005) or V/Sc (6.6–8.5; 1SD = 0.1-1.3) ratios. However, on a global scale, basaltic
δ51
VAA may be controlled by the extent of melting. The V/Sc compositions of primitive (MgO > 7.5 wt%) basalts show no systematic change along the entire length of the Reykjanes Ridge. Typical peridotite melting models in which source Fe3+/Fetot is constant at 5% and that account for the increased mantle potential temperature nearer the plume center and the fO2 dependent partitioning of V, can reproduce the V/Sc data. However, while these melting models predict that basalt Fe3+/Fetot ratios should decrease with increasing mantle potential temperature towards Iceland, fractionation-corrected Fe3+/Fetot of Reykjanes Ridge lavas remain nearly constant over the ridge length. This discrepancy is explained by source heterogeneity, where an oxidized mantle pyroxenite component contributes to melting with increasing proximity to Iceland.
Comparison of observed and modeled Fe3+/Fetot indicate that source variation in fO2 is present under the Reykjanes Ridge, with higher Fe3+/Fetot closer to Iceland. This source variability in fO2 cannot be resolved by V isotopes and redox-sensitive trace element ratios, which instead appear to record magmatic processes.
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Dec 2019
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