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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.

Open Access

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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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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.

Open Access

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Abstract: Biometals such as iron, copper, potassium, and zinc are essential regulatory elements of several biological processes. The homeostasis of biometals is often affected in age-related pathologies. Notably, impaired iron metabolism has been linked to several neurodegenerative disorders. Autophagy, an intracellular degradative process dependent on the lysosomes, is involved in the regulation of ferritin and iron levels. Impaired autophagy has been associated with normal pathological aging, and neurodegeneration. Non-mammalian model organisms such as Drosophila have proven to be appropriate for the investigation of age-related pathologies. Here, we show that ferritin is expressed in adult Drosophila brain and that iron and holoferritin accumulate with aging. At whole-brain level we found no direct relationship between the accumulation of holoferritin and a deficit in autophagy in aged Drosophila brain. However, synchrotron X-ray spectromicroscopy revealed an additional spectral feature in the iron-richest region of autophagy-deficient fly brains, consistent with iron–sulfur. This potentially arises from iron–sulfur clusters associated with altered mitochondrial iron homeostasis.

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Abstract: It is well established that oxygen fugacity, fO₂ , is one of the key parameters that needs to be quantified in order to understand igneous processes, model the geophysical behaviour of the core and mantle, to understand the exchange of C-O-H-S gases between the atmosphere and the interior of the Earth, and to further our understanding of other terrestrial planets. Despite this it remains one of the most poorly constrained geochemical variables, limiting our understanding of terrestrial systems. Recent work has focused on using accessory minerals for determining magmatic fO₂ , as a probe to constraining conditions in planetary interiors. Accessory minerals are already important petrological tools for providing insight into magmatic conditions. These minerals may concentrate a variety of trace elements, and hence are crucial in understanding the elemental budget of magmas. Accessory minerals such as zircon and apatite are also some of the hardier minerals found in igneous rocks and are, therefore, less likely to be altered by processes such as chemical weathering, metasomatism or crustal anatexis. Furthermore, study of detrital accessory minerals in ancient sedimentary rocks could provide much needed insight into the evolution of the oxidation state of the early Earth. This work aims to assess how the compositions and structures of two accessory minerals, spinel and apatite, respond to variations in magmatic fO₂ and to determine whether these minerals could act as probes of fO₂ in planetary interiors. Focus has been concentrated on the element manganese, as (1) it is a relatively abundant trace element, (2) it can exist in valence states from Mn²⁺ to Mn⁵⁺ in nature, and (3) recent work has suggested that Mn may become preferentially concentrated in apatite under reduced conditions. In an initial investigation, large single crystals of Mn-rich spinel were synthesised under a variety of fO₂ conditions. X-ray absorption near edge structure (XANES) spectroscopy and structural refinements of single crystal X-ray diffraction data were used to determine Mn valence state and coordination. Results show that Mn is present in spinel as both Mn²⁺ and Mn³⁺, distributed over both octahedral and tetrahedral cation sites. However, in contrast to the Fe⁺²/Fe³⁺ ratio, little variation in Mn valence as a function of fO₂ was observed. Results were, however, useful in testing and refining protocols for modelling Mn XANES data in a simple, model system. In contrast to results from spinel, previous studies have indicated that Mn valence may change significantly in the accessory mineral apatite due to variations in magmatic fO₂ .