Nanoscale Anatomy of Iron-Silica Self-Organized Membranes: Implications for Prebiotic Chemistry

Iron-silica self-organized membranes, so-called chemical gardens, behave as fuel cells and catalyze the formation of amino/carboxylic acids and RNA nucleobases from organics that were available on early Earth. Despite their relevance for prebiotic chemistry, little is known about their structure and mineralogy at the nanoscale. Studied here are focused ion beam milled sections of iron-silica membranes, grown from synthetic and natural, alkaline, serpentinization-derived fluids thought to be widespread on early Earth. Electron microscopy shows they comprise amorphous silica and iron nanoparticles of large surface areas and inter/intraparticle porosities. Their construction resembles that of a heterogeneous catalyst, but they can also exhibit a bilayer structure. Surface-area measurements suggest that membranes grown from natural waters have even higher catalytic potential. Considering their geochemically plausible precipitation in the early hydrothermal systems where abiotic organics were produced, iron-silica membranes might have assisted the generation and organization of the first biologically relevant organics

A geochemical approach to fossilization processes in Miocene vertebrate bones from Sahabi, NE Libya

In the present paper a multi-technique approach was followed in order to study the diagenetic alterations of fifteen fossil bones derived from the Miocene site of Sahabi in NE Libya. Specifically, X-ray Diffraction (XRD) supplemented by the Rietveld method, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), Electron Probe Microanalysis (EPMA) and Fourier Transform Infrared Spectroscopy in the Mid-IR (FTIR, Mid-IR), were performed on fossilized bone fragments belonging mainly to artiodactyl mammals. From the qualitative observation of bone histology by means of SEM, a moderate preservation of the internal bone morphology and limited microbial attack were inferred. The high percentage (wt.%) of F concentration that the EPMA analyses yielded, combined: (a) with the absorbance bands of carbonate anions in the FTIR spectra and (b) the structural parameters calculated by the Rietveld method, revealed the partial substitution of F− for OH− and CO3 2− for PO4 3− in the apatite structure. As a result, one of the basic diagenetic trends was the preservation of the inorganic part of the studied samples as carbonate fluorapatite. Additionally, according to our infrared spectra, CO3 2− substituted for OH− and a carbonate species known to be labile was also present. Apart from F, EPMA also detected S and Fe. Sulfur speciation was studied by micro-XANES, that confirmed the presence of S6+ (sulfates). Iron speciation was investigated with Mössbauer spectroscopy, which indicated the possible presence of goethite-type (FeOOH) submicroscopic inclusions. In nearly all specimens, quartz and gypsum were identified as the main secondary phases. © 2018 Elsevier Lt

A geochemical approach to fossilization processes in Miocene vertebrate bones from Sahabi, NE Libya

In the present paper a multi-technique approach was followed in order to study the diagenetic alterations of fifteen fossil bones derived from the Miocene site of Sahabi in NE Libya. Specifically, X-ray Diffraction (XRD) supplemented by the Rietveld method, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), Electron Probe Microanalysis (EPMA) and Fourier Transform Infrared Spectroscopy in the Mid-IR (FTIR, Mid-IR), were performed on fossilized bone fragments belonging mainly to artiodactyl mammals. From the qualitative observation of bone histology by means of SEM, a moderate preservation of the internal bone morphology and limited microbial attack were inferred. The high percentage (wt.%) of F concentration that the EPMAanalysesyielded,combined:(a)withtheabsorbancebandsofcarbonateanionsintheFTIRspectraand(b) the structural parameters calculated by the Rietveldmethod, revealed the partial substitution ofF− forOH− and CO32− for PO43− in the apatite structure. As a result, one of the basic diagenetic trends was the preservation of the inorganic part of the studied samples as carbonate fluorapatite. Additionally, according to our infrared spectra, CO32− substituted for OH− and a carbonate species known to be labile was also present. Apart from F, EPMA alsodetected Sand Fe.Sulfur speciation was studied by micro-XANES, thatconfirmed the presence ofS6+ (sulfates). Iron speciation was investigated with Mössbauer spectroscopy, which indicated the possible presence of goethite-type (FeOOH) submicroscopic inclusions. In nearly all specimens, quartz and gypsum were identified as the main secondary phases

Trans fatty acid intake increases likelihood of dyslipidemia especially among individuals with higher saturated fat consumption

Background: Evidence points to adverse effects of trans fatty acids (TFA) on health. The aim of this study was to estimate total TFA intake, evaluate major food contributors and its effect on dyslipidemia. Methods: A total of 3537 adults (48.3% males) were included. Total TFA intake was assessed using two 24-hour dietary recalls. Foods were categorized into specific food groups. Adjusted Logistic Regression analysis was performed to assess the likelihood of dyslipidemia by tertile of TFA aand Saturated Fatty Acid (SFA) level. Results: Median TFA intake was 0.53% of energy (from 0.34 to 0.81) ranging from 0.27 (Q1) to 0.95 (Q3) (p < 0.001, for trend), and 16% of individuals consumed TFA above 1% of their total energy. Cheese was the main contributor to TFA intake, with processed/refined grains and fried fish following. The latter was the main contributor in older adults (51+ years). Adjusted logistic regression analysis showed that individuals at the highest tertile of trans consumption were 30% more likely to have dyslipidemia compared to the lowest (OR(Q3−Q1): 1.3; 95% CI: 1.02–1.66 and OR(Q2−Q1): 1.3; 95% CI:1.01–1.66, respectively). This increased by 10% when stratified by SFA intake (OR: 1.4; 95% CI: 1.061–1.942) and remained significant only in individuals at the highest tertile and with higher than recommended SFA intake. Conclusions: A high intake of TFA combined with high SFA intakes further increase the likelihood of dyslipidemia and should be accounted for in public health prevention programs. Monitoring and evaluation of the recent EU legislative measures on TFA levels in foods is also necessary. © 2022 The Author(s

A crystallographic study of crystalline casts and pseudomorphs from the 3.5 Ga Dresser Formation, Pilbara Craton (Australia)

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Metastable Iron (Mono)sulfides in the Shallow-Sea Hydrothermal Sediments of Milos, Greece

Metastable iron sulfides are involved in a series of biotic and abiotic processes in the marine environment, including the mineralization of organic matter. However, naturally occurring metastable iron (mono)sulfide minerals are rarely reported in marine sediments, and current information about their formation and characteristics comes from synthetic sulfides. Here, we studied sulfur speciation and mineralogy in a submarine surface core (0-22 cm depth) from an active, shallow-sea hydrothermal system (Milos, Greece) that is dominated by sulfur-metabolizing microorganisms. Geochemical analysis results showed S-Fe-As enrichment in the bottom layers of the core, which were further characterized using a suite of techniques. Powder X-ray diffraction and Synchrotron-based μ-X-ray diffraction did not show crystalline Fe-S compounds whereas scanning electron microscopy and Synchrotron-based X-ray fluorescence mapping indicated the presence of Fe-S(-As) phases and sulfur particles. Sulfur microspeciation by X-ray absorption near-edge structure spectroscopy showed a mixture of oxidation states, including organic sulfur species, indicative of active sulfur biogeochemical cycling. Ultimately, transmission electron microscopy was used for the identification of the Fe-S mineral assemblage in the samples that included arsenic-bearing pyrite and the metastable mackinawite, monoclinic pyrrhotite and greigite, alongside elemental sulfur nanoparticles. Previous studies on the mineralogy of Milos hydrothermal sediments omitted the presence of metastable iron sulfides, that were up to now known to form in marine sediments from estuaries and anoxic/euxinic basins. Our results highlight that the use of standard microscopic, spectroscopic and diffraction techniques may overlook the presence of metastable iron sulfides in natural samples. Considering that metastable iron sulfides are implicated in critical biogeochemical processes for the marine ecosystems, their role in sulfur, iron, and carbon cycling in modern and ancient marine sediments might be underrated. © 2022 American Chemical Society. All rights reserved