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This study explores the delivery of phosphorus to the upper atmospheres of Earth, Mars, and Venus via the ablation of cosmic dust particles. Micron-size meteoritic particles were flash heated to temperatures as high as 2900 ​K in a Meteor Ablation Simulator (MASI), and the ablation of PO and Ca recorded simultaneously by laser induced fluorescence. Apatite grains were also ablated as a reference. The speciation of P in anhydrous chondritic porous Interplanetary Dust Particles was made by K-edge X-ray absorption near edge structure (XANES) spectroscopy, demonstrating that P mainly occurs in phosphate-like domains. A thermodynamic model of P in a silicate melt was then developed for inclusion in the Leeds Chemical Ablation Model (CABMOD). A Regular Solution model used to describe the distribution of P between molten stainless steel and a multicomponent slag is shown to provide the most accurate solution for a chondritic-composition, and reproduces satisfactorily the PO ablation profiles observed in the MASI. Meteoritic P is moderately volatile and ablates before refractory metals such as Ca; its ablation efficiency in the upper atmosphere is similar to Ni and Fe. The speciation of evaporated P depends significantly on the oxygen fugacity, and P should mainly be injected into planetary upper atmospheres as PO2, which will then likely undergo dissociation to PO (and possibly P) through hyperthermal collisions with air molecules. The global P ablation rates are estimated to be 0.017 ​t ​d−1 (tonnes per Earth day), 1.15 ​× ​10−3 ​t ​d−1 and 0.024 ​t ​d−1 for Earth, Mars and Venus, respectively.

Titanium, Cr, and V valences were determined by applying micro-X-ray Absorption Near Edge Structure (micro-XANES) spectroscopy methods to individual grains of olivine and pyroxene in the ungrouped achondrite NWA 7325 and ureilite Y-791538, as well as to plagioclase in NWA 7325. The advantages of applying multiple, multivalent-element-based oxybarometers to individual grains are (1) the ability to cover the entire oxygen fugacity (fO2) range encountered in nature, and (2) the increased reliability from consistent results for semi-independent fO2 proxies. fO2 values were inferred from each mineral valence determination after correcting with available laboratory-experiment-derived, valence-specific partition coefficients to obtain melt valences and then calibrating with the fO2 values of the relevant equal species proportions points suggested for igneous (primarily basaltic) systems. The resulting olivine and pyroxene valences are highly reduced and similar in the two meteorites with substantial fractions of Cr2+, Ti3+ and V2+. The exception is Cr in NWA 7325 pyroxene which is much more oxidized than the Cr in its olivine. Chromium and Ti in plagioclase in NWA 7325 is relatively oxidized (V valence not determined). The anomalously oxidized Cr in NWA 7325 pyroxene may be due to a secondary reheating event that oxidized Cr in the pyroxene without similarly oxidizing Ti and V. Such a separation of the redox couples may be an effect of re-equilibration kinetics, where the valence of Cr would be more rapidly modified. These valences yielded similar mean fO2s for the two meteorites; IW-3.1 ± 0.2 for NWA 7325 and IW-2.8 ± 0.2 for Y-791538, consistent with an origin of NWA 7325 in either Mercury or an asteroid that experienced redox conditions similar to those on the ureilite parent body.

Miller Range (MIL) 090340 and MIL 090206 are olivine-rich achondrites originally classified as ureilites. We investigate their petrography, mineral compositions, olivine Cr valences, equilibration temperatures, and (for MIL 090340) oxygen isotope compositions, and compare them with ureilites and other olivine-rich achondrites. We conclude that they are brachinite-like achondrites that provide new insights into the petrogenesis of brachinite clan meteorites. MIL 090340,6 has a granoblastic texture and consists of ~97 modal % by area olivine (Fo = molar Mg/[Mg+Fe] = 71.3 ± 0.6). It also contains minor to trace augite, chromite, chlorapatite, orthopyroxene, metal, troilite, and terrestrial Fe-oxides. Approximately 80% by area of MIL 090206,5 has a granoblastic texture of olivine (Fo 72.3 ± 0.1) plus minor augite and chromite, similar to MIL 090340 but also containing minor plagioclase. The rest of the section consists of a single crystal of orthopyroxene (~11 × 3 mm), poikilitically enclosing rounded grains of olivine (Fo = 76.1 ± 0.6), augite, chromite, metal, and sulfide. Equilibration temperatures for MIL 090340 and MIL 090206, calculated from olivine-spinel, olivine-augite, and two-pyroxene thermometry range from ~800 to 930 °C. In both samples, symplectic intergrowths of Ca-poor orthopyroxene + opaque phases (Fe-oxides, sulfide, metal) occur as rims on and veins/patches within olivine. Before terrestrial weathering, the opaques were probably mostly sulfide, with minor metal. All petrologic properties of MIL 090340 and MIL 090206 are consistent with those of brachinite clan meteorites, and largely distinct from those of ureilites. Oxygen isotope compositions of olivine in MIL 090340 (δ18O = 5.08 ± 0.30‰, δ17O = 2.44 ± 0.21‰, and Δ17O = −0.20 ± 0.12‰) are also within the range of brachinite clan meteorites, and well distinguished from ureilites. Olivine Cr valences in MIL 090340 and the granoblastic area of MIL 090206 are 2.57 ± 0.06 and 2.59 ± 0.07, respectively, similar to those of three brachinites also analyzed here (Brachina, Hughes 026, Nova 003). They are higher than those of olivine in ureilites, even those containing chromite. The valence systematics of MIL 090340, MIL 090206, and the three analyzed brachinites (lower Fo = more oxidized Cr) are consistent with previous evidence that brachinite-like parent bodies were inherently more oxidized than the ureilite parent body. The symplectic orthopyroxene + sulfide/metal assemblages in MIL 090340, MIL 090206, and many brachinite clan meteorites have superficial similarities to characteristic “reduction rims” in ureilites. However, they differ significantly in detail. They likely formed by reaction of olivine with S-rich fluids, with only minor reduction. MIL 090340 and the granoblastic area of MIL 090206 are similar in modal mineralogy and texture to most brachinites, but have higher Fo values typical of brachinite-like achondrites. The poikilitic pyroxene area of MIL 090206 is more typical of brachinite-like achondrites. The majority of their properties suggest that MIL 090340 and MIL 090206 are residues of low-degree partial melting. The poikilitic area of MIL 090206 could be a result of limited melt migration, with trapping and recrystallization of a small volume of melt in the residual matrix. These two samples are so similar in mineral compositions, Cr valence, and cosmic ray exposure ages that they could be derived from the same lithologic unit on a common parent body.

Objectives Alkaline extracts from soils generate operationally-defined isolates that are referred to as “humic substances” but may not relate to a distinct molecular structure within the soil organic matter (SOM) matrix. This study examines whether alkaline extracts from black carbon (BC) rich soils can be identified on a fine spatial scale. Methods We related the functional group composition of alkaline extracts derived from BC-rich soils using Scanning Transmission X-ray Microscopy (STXM) coupled with near-edge X-ray absorption fine- structure (NEXAFS) spectroscopy to the spatial composition of a BC-rich soil microaggregate at a scale of Results Using principal component analysis, we were unable to obtain a good fit (RMS Conclusions Our results suggest that a distinct component class similar to alkaline extracted materials, often referred to as “black humic substances”, is not present in SOM on a fine spatial scale. Rather, alkaline extracts of BC-rich soils reflect the mixture of various materials at different stages of decomposition.

NASA has an ongoing program of collecting interplanetary dust particles (IDPs) in the stratosphere using high altitude research aircraft. The collected IDPs are derived from asteroids and comets and here we report studies of a subset of hydrated IDPs rich in carbonaceous matter that are proposed to have a cometary origin. Our studies are aimed at understanding the evolution of oxygen reservoirs in the Solar System and their interaction with cometary minerals and organic matter. The small size (

Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ∼74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75–76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4–92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1σ) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200–1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW−1.9 to IW−2.8 (assuming basaltic melt composition), consistent with fO2 values obtained by assuming olivine-silica-iron metal (OSI) equilibrium. For the primary chromite-bearing-ureilites, the corresponding fO2 were estimated (again, assuming basaltic melt composition) to be ∼IW to IW+1.0, i.e., several orders of magnitude more oxidizing than the conditions estimated for the chromite-free ureilites. In terms of Fo and Cr valence properties, ureilites appear to form two groups rather than a single “Cr-valence (or fO2) vs. Fo” trend. The chromite-bearing ureilites show little variation in Fo (∼74–76) but significant variation in Cr valence, while the non-chromite-bearing ureilites show significant variation in Fo (∼77–95) and little variation in Cr valence. These groups are unrelated to petrologic type (i.e., olivine–pigeonite, olivine–orthopyroxene, or augite-bearing). The chromite-bearing ureilites also have lower contents of Cr in olivine than most non-chromite-bearing ureilites, consistent with predictions based on Cr olivine/melt partitioning in spinel saturated vs. non-spinel-saturated systems. Under the assumption that at magmatic temperatures graphite–gas equilibria controlled fO2 at all depths on the ureilite parent body, we conclude: (1) that ureilite precursor materials having the Fo and Cr valence properties now observed in ureilites are unlikely to have been preserved during planetary processing; and (2) that the Fo and Cr valence properties now observed in ureilites are consistent with having been established by high-temperature carbon redox control over a range of depths on a plausible-sized ureilite parent body. The apparent limit on ureilite Fo values around 74–76 suggests that the precursor material(s) had bulk mg# ⩾ that of LL chondrites.

Soil represents the largest reservoir of terrestrial organic C, and plays a critical role in global C cycling. In light of predicted climate change and a more unified approach to mitigate greenhouse gas emissions, the soil's ability to sequester C, and thus to act as a sink or a source for atmospheric CO2 has received growing interest. Organomineral assemblages are a unique niche in C cycling, with large capacity for storing anthropogenic C. However, the underlying biogeochemical mechanisms for C sequestration through organomineral associations are not yet well understood. One of the major challenges to study C sequestration in organomineral assemblages is lack of non-invasive analytical tools with a potential to obtain molecular-level information about the interactions between C and mineral components in submicron geochemical environments. In the present study, we have effectively employed synchrotron-based STXM–NEXAFS spectroscopy to access the K- and L-edges of biogeochemically relevant elements (C, N, Ca, Fe, Al, Si) to identify and image micro- and nano-C sequestration environments, and conduct submicron-level investigation of the compositional chemistry and other interactive features of C and minerals present in these hotspots using ultrathin section of intact organomineral assemblage. The C K-edge NEXAFS spectromicroscopy micrographs clearly demonstrated the existence of spatially distinct seemingly terminal micro- and nano-C repository zones, where organic C was sequestered in apparent agglomeration in the investigated organomineral assemblage. These submicron-C repository environments were only a few micrometers apart from each other; yet they were considerably different compositionally from each other. The organic C in the first repository environment was pyrogenic in origin, largely composed of quinone, phenols, ketones and aromatic ring structures. However, the second hotspot was dominated by filament-like structure, with striking similarity to the C 1s NEXAFS spectral signatures of organic C isolated from soil fungal and bacteria, and dominated by resonances from aliphatic-C and CN bonds of imidazol structures, carboxyl/carbonyl-C, amide- and O-alkyl-C functionalities. The composition of organic C in the organomineral interface around the strand-like structure was highly complex and composed of polysaccharides, amino sugars, amino acids, nucleic acids, and phospholipid fatty acid structures with polar and non-polar termini. The chemistry of mineral matter in the organomineral interface was also equally complex, ranging from Ca, Fe and Al ions, Fe and Al oxides, hydroxides and oxyhydroxides to phyllosilicates, which could provide a variety of polyvalent cations, hydroxyl surface functional groups and edge sites that can attract and bind microbial biomolecules. Based on the enormous complexity of the organic C functionalities and the coexistence of various inorganic components in the organomineral interface, it is possible to suggest that no single binding mechanism could be accountable for the organic C stored in the investigated submicron-C repository environment. Our results seem to suggest that the apparent C sequestration in the micro- and nano-C repository environment appear to be the cumulative result of physical protection and heterogeneous binding mechanisms ranging from ion exchange, hydrogen bonding, and hydrophobic bonding on silicate clay–organic complexes to adsorption on external and internal surfaces of clay minerals.

Black C is an essential component of the terrestrial C pool and its formation is often credited as a CO2 sink by transferring the fast-cycling C from the atmosphere–biosphere system into slower cycling C in the geosphere. This study is the first multi-element K- (C, N, Ca, Fe, Al and Si) soft-X-ray STXM–NEXAFS investigation conducted at a submicron-scale spatial resolution specifically targeting black C and its interaction with the mineral and non-black C organic matter in the organomineral assemblage. The STXM–NEXAFS micrographs and spectra demonstrated that pyrogenic C was dominated by quinoide, aromatic, phenol, ketone, alcohol, carboxylic and hydroxylated- and ether-linked C species. There was also evidence for the presence of pyridinic, pyridonic, pyrrolic, amine and nitril N functionalities. The non-black C organic matter contained amino acids, amino sugars, nucleic acids and polysaccharides known to exhibit negatively charged carboxylic, phenolic, enolic, thiolate and phosphate functionalities highly reactive towards metal ions and black C. The metal-rich mineral matrix was composed of phyllosilicate clay minerals, Fe and Al hydroxypolycations, oxides, hydroxides and oxyhydroxide that can attract and bind organic biopolymers. STXM–NEXAFS provided evidence for interactive association between pyrogenic C, non-black C organic matter and the mineral oxide and oxyhydroxide communities in the organomineral interface. These intimate associations occurred through a “two-way” direct linkage between black C and the mineral or non-black C organic matter or via a “three-way” indirect association where non-black C organic matter could serve as a molecular cross-linking agent binding black C with the mineral matrix or vice versa where inorganic oxides, hydroxides and polycations could act as a bridge to bind black C with non-black C organic matter. The binding and sequestration of black C in the investigated micro- and nano-C repository environments seem to be the combined action of physical entrapment in seemingly terminal biotic exclusion zone through the action of metal oxides and organic matter induced microaggregation and through molecular-level association ranging from ligand exchange, polyvalent cation bridging to weak hydrophobic interactions including van der Waals and H-bonding.

To improve the understanding of the effect of carbon nanotubes (CNTs) on the environment, the characterization of CNTs and their interaction with soils needs to be assessed. Here, we demonstrate an analysis of pristine and modified CNTs, in dry and wet state using soft X-ray spectromicroscopy with energies around the C 1s K-shell edge (280 eV–300 eV). Apart from that, suspensions of the CNTs and the colloidal fraction as well as the extracted humic substances of a chernozem soil sample were studied. The effect of the different sample environments on the CNTs were observable both in the microscopic images and the spectral data, e.g., in aqueous environment the CNTs built clusters. Since CNTs are mainly analyzed under sterile laboratory conditions, this study intends to show how to investigate CNTs and their interaction with other substances under ambient conditions. One of the major objectives was, whether differences between CNTs and organic soil particles are distinguishable at all, and subsequently, how to describe the observed interactions.

Summary Although focused ion beam (FIB) microscopy has been used successfully for milling patterns and creating ultra-thin electron and soft X-ray transparent sections of polymers and other soft materials, little has been documented regarding FIB-induced damage of these materials beyond qualitative evaluations of microstructure. In this study, we sought to identify steps in the FIB preparation process that can cause changes in chemical composition and bonding in soft materials. The impact of various parameters in the FIB-scanning electron microscope (SEM) sample preparation process, such as final milling voltage, temperature, ion beam overlap and mechanical stability of soft samples, was evaluated using two test-case materials systems: polyacrylamide, a low melting-point polymer, and Wyodak lignite coal, a refractory organic material. We evaluated changes in carbon bonding in the samples using X-ray absorption near-edge structure spectroscopy (XANES) at the carbon K edge and compared these samples with thin sections that had been prepared mechanically using ultramicrotomy. Minor chemical changes were induced in the coal samples during FIB-SEM preparation, and little effect was observed by changing ion-beam parameters. However, polyacrylamide was particularly sensitive to irradiation by the electron beam, which drastically altered the chemistry of the sample, with the primary damage occurring as an increase in the amount of aromatic carbon bonding (C=C). Changes in temperature, final milling voltage and beam overlap led to small improvements in the quality of the specimens. We outline a series of best practices for preparing electron and soft X-ray transparent samples, with respect to preserving chemical structure and mechanical stability of soft materials using the FIB.

Preliminary examination (PE) of samples returned from Comet 81P/Wild 2 by the NASA Stardust mission revealed a wide variety of carbonaceous samples [e.g. 1]. Carbonaceous matter is present as inclusions, rinds, and films in polyminerallic terminal particles [2-4], as carbon-rich particles along track walls [2, 5, 6], and as organic matter in aerogel around tracks [7, 8]. The organic chemistry of these samples ranges from purely aliphatic hydrocarbons to highly-aromatic material, often modified by various organic functional groups [2, 4, 5, 9-11]. Difficulty arises when interpreting the genesis of these carbonaceous samples, since contaminants could be introduced from the spacecraft [12], aerogel [1, 8], or during sample preparation. In addition, hypervelocity capture into aerogel may have heated cometary material in excess of 1000 C, which could have significantly altered the structure and chemistry of carbonaceous matter. Fortunately, much of this contamination or alteration can be identified through correlated microanalysis with transmission electron microscopy (TEM), scanning-transmission X-ray microscopy (STXM), and nanoscale secondary ion mass spectroscopy (SIMS).

Numerous potential sources of organic contaminants could have greatly complicated the interpretation of the organic portions of the samples returned from comet 81P/Wild 2 by the Stardust spacecraft. Measures were taken to control and assess potential organic (and other) contaminants during the design, construction, and flight of the spacecraft, and during and after recovery of the sample return capsule. Studies of controls and the returned samples suggest that many of these potential sources did not contribute any significant material to the collectors. In particular, contamination from soils at the recovery site and materials associated with the ablation of the heatshield do not appear to be significant problems. The largest source of concern is associated with the C present in the original aerogel. The relative abundance of this carbon can vary between aerogel tiles and even within individual tiles. This C was fortunately not distributed among a complex mixture of organics, but was instead largely present in a few simple forms (mostly as Si-CH{sub 3} groups). In most cases, the signature of returned cometary organics can be readily distinguished from contaminants through their different compositions, nonterrestrial isotopic ratios, and/or association with other cometary materials. However, some conversion of the carbon indigenousmore » to the flight aerogel appears to have happened during particle impact, and some open issues remain regarding how this C may be processed into new forms during the hypervelocity impact collection of the comet dust.« less

The extracellular matrix (ECM) is composed of mixed protein fibers whose precise composition affects biomineralization. New methods are needed to probe the interactions of these proteins with calcium phosphate mineral and with each other. Here we follow calcium phosphate mineralization on protein fibers self-assembled in vitro from solutions of fibronectin, elastin and their mixture. We probe the surface morphology and mechanical properties of the protein fibers during the early stages. The development of mineral crystals on the protein matrices is also investigated. In physiological mineralization solution, the elastic modulus of the fibers in the fibronectin-elastin mixture increases to a greater extent than that of the fibers from either pure protein. In the presence of fibronectin, longer exposure in the mineral solution leads to the formation of amorphous calcium phosphate particles templated along the self-assembled fibers, while elastin fibers only collect calcium without any mineral observed during early stage. TEM images confirm that small needle-shape crystals are confined inside elastin fibers which suppress the release of mineral outside the fibers during late stage, while hydroxyapatite crystals form when fibronectin is present. These results demonstrate complementary actions of the two ECM proteins fibronectin and elastin to collect cations and template mineral, respectively.

Carbonaceous microbe-like features preserved within a local chert unit of the 3.5 Ga old Apex Basalt in Western Australia may represent some of the oldest evidence of life on Earth. However, the biogenicity of these putative microfossils has been called into question, primarily because the sample collection locality is a black, carbon-rich, brecciated chert dike representing an Archean submarine hydrothermal spring, suggesting a formation via an abiotic organic synthesis mechanism. Here we describe the macromolecular hydrocarbon structure, carbon bonding, functional group chemistry, and biotic element abundance of carbonaceous matter associated with these filamentous features. These characteristics are similar to those of biogenic kerogen from the ca. 1.9 Ga old Gunflint Formation. Although an abiotic origin cannot be entirely ruled out, it is unlikely that known abiotic synthesis mechanisms could recreate both the structural and compositional complexity of this ancient carbonaceous matter. Thus, we find that a biogenic origin for this material is more likely, implying that the Apex microbe-like features represent authentic biogenic organic matter.

Carbon K-edge soft X-ray spectromicroscopy was used to obtain information on the orientation, purity and chemical composition of graphite within natural samples. Highly crystalline natural graphite had spectra indistinguishable from highly ordered pyrolytic graphite, but contained a wide variety of internal structures in the 100–500 nm size range. These structures were both physical (domains with differing sheet orientations) and chemical in nature. Graphite sheet orientations could vary from normal to the X-ray beam to nearly perpendicular within a few hundred nanometers. Chemical compositions ranged from pure crystalline material to nearly amorphous carbon. Little evidence for significant addition of O- or N-bearing groups was observed in these samples, although this may have been a result of the extraction techniques used. The range of carbon types found in the environment may provide clues to the types of thermal alteration and source mechanisms behind graphitic kerogen fractions.

At nanometre scales, organic matter forms in soil are spatially, rather than chemically, complex, according to X-ray spectromicroscopy studies of thin sections of entire and intact free microaggregates. Organic matter forms detected at this spatial scale have no similarity to organic carbon forms of total soil. Organic matter in soil has been suggested to be composed of a complex mixture of identifiable biopolymers1 rather than a chemically complex humic material2. Despite the importance of the spatial arrangement of organic matter forms in soil3, its characterization has been hampered by the lack of a method for analysis at fine scales. X-ray spectromicroscopy has enabled the identification of spatial variability of organic matter forms, but was limited to extracted soil particles4 and individual micropores within aggregates5,6. Here, we use synchrotron-based near-edge X-ray spectromicroscopy7 of thin sections of entire and intact free microaggregates6 to demonstrate that on spatial scales below 50 nm resolution, highly variable yet identifiable organic matter forms, such as plant or microbial biopolymers, can be found in soils at distinct locations of the mineral assemblage. Organic carbon forms detected at this spatial scale had no similarity to organic carbon forms of total soil. In contrast, we find that organic carbon forms of total soil were remarkably similar between soils from several temperate and tropical forests with very distinct vegetation composition and soil mineralogy. Spatial information on soil organic matter forms at the scale provided here could help to identify processes of organic matter cycling in soil, such as carbon stability or sequestration and responses to a changing climate.

Anhydrous interplanetary dust particles (IDPs), which are the most mineralogically primitive extraterrestrial materials available for laboratory analysis, contain several percent organic matter. The high O:C and N:C ratios suggest the organic matter in the anhydrous IDPs is significantly less altered by thermal processing than the organic matter in meteorites. X-ray Absorption Near-Edge Structure (XANES) spectroscopy and infrared spectroscopy demonstrate the presence of C=C, most likely as C-rings, C=O, and aliphatic C-H2and C-H3in all the IDPs examined. A D-rich spot, containing material that is believed to have formed in a cold molecular cloud, has C-XANES and infrared spectra very similar to the organic matter in the anhydrous IDPs, possibly indicating a common formation mechanism. However the primitive organic matter in the IDPs differs from the interstellar/circumstellar organic matter characterized by astronomical infrared spectroscopy in the relative strengths of the asymmetric aliphatic C-H2and C-H3absorptions, with the IDP organic having a longer mean chain length. If both types of organic matter originated by the same process, this may indicate the interstellar organic matter has experienced more severe radiation processing than the organic matter in the primitive IDPs.

In this work we present the results of a sy stematic search for cometary organics in 14 Stardust particles (particles from comet 81P/Wild 2, captured by NASAs Stardust mission) by TEM and multidisciplinary studies (XANES and NanoSIMS) of Febo and Ada, two of the organic-bearing particles identified. The combination of the three analytical techniques has established the presence of organic, cometary C in both particles. Using energy-filtered and high-resolution imaging it was shown that the C is amorphous and rare, given that it is found in grains ≤200 nm in size that are not abundant throughout the particles. The XANES maps and spectra of the carbonaceous areas identified with the TEM have shown that the carbonaceous material is organic due to the presence of carbonyl (C=O) functional groups and the overlapping of C and N on the same grains. In addition, several different C-XANES spectra were obtained from the same particle, suggesting that there is diversity in the types of carbonaceous phases present in these particles, as well as a heterogeneous distribution of the carbonaceous phases within these particles. The C-XANES spectra obtained are different from C-XANES spectra of carbonaceous chondrites and IDPs. In the particle Febo we found five spots showing a pronounced enrichment in the isotope 15N (δ15N from 420 to 639 ± 20 to 70‰, 1σ) that were clearly associated with the C-rich regions. The carbonaceous material has approximately solar C and D/H isotopic compositions, and the bulk O isotopic composition was found to be δ17 O = −18 ± 13‰ and δ18 O = −37 ± 12‰ (1σ ). In the particle Ada we found a C-rich phase with enrichments in the isotope 15N (δ15 N = 550 ± 70 ‰, 1σ ) and the isotope D (δD = 610 ± 254‰, 1σ The C isotopic composition at this phase is solar (δ13 C = −4 ± 29‰, 1σ ).. The bulk O isotopic composition of Ada was found to be δ17 O = 9 ± 14.6‰ and δ18 O = −7.3 ± 8.1‰ (2σ).

Methodological constraints limit the extent to which existing soil aggregationmodels explaincarbon(C) stabilization insoil. Wehypothesize that the physical infrastructure of microaggregates plays a major role in determining the chemistry of the occluded C and intimate associations between particulate C, chemically stabilized C and the soil mineral matrix. We employed synchrotron-based scanning transmission X-ray microscopy (STXM) coupled with near-edge X-ray absorption fine structure (C 1s-NEXAFS) spectroscopy to investigate the nanoscale physical assemblage and C chemistry of 150-mm microaggregates from a Kenyan Oxisol. Ultra-thin sections were obtained after embedding microaggregates in a sulfur block and sectioning on a cryo-microtome at 255C. Principal component and cluster analyses revealed four spatially distinct features: pore surfaces, mineral matter, organic matter, and their mixtures. The occurrence of these features did not vary between exterior and interior locations; however, the degree of oxidation decreased while the complexity and occurrence of aliphatic C forms increased from exterior to interior regions of the microaggregate. At both locations, compositional mapping rendered a nanoscale distribution of oxidized C clogging pores and coating pore cavities on mineral surface. Hydrophobic organic matter of aromatic and aliphatic nature, representing particulate C forms appeared physically occluded in 2- to 5-mm pore spaces. Our findings demonstrate that organic matter in microaggregates may be found as either oxidized C associated with mineral surfaces or aromatic and aliphatic C in particulate form. Using STXM and C 1s-NEXAFS we are for the first time able to resolve the nanoscale biogeocomplexity of unaltered soil microaggregates.

The chemical composition of the graphitic black carbon (GBC) fraction of marine organic matter was explored in several marine and freshwater sedimentary environments along the west coast of North America and the Pacific Ocean. Analysis by carbon X-ray absorption near-edge structure spectroscopy and scanning transmission X-ray microscopy shows the GBC fraction of Stillaguamish River surface sediments to be dominated by more highly ordered and impure forms of graphite, together forming about 80% of the GBC, with a smaller percent of an aliphatic carbon component. Eel River Margin surface sediments had very little highly ordered graphite, and were instead dominated by amorphous carbon and to a lesser extent, impure graphite. However, the GBC of surface sediments from the Washington State Slope and the Mexico Margin was composed almost solely of amorphous carbon. Pre-anthropogenic, highly oxidized deep-sea sediments from the open Equatorial Pacific Ocean contained over half their GBC in different forms of graphite as well as highly aliphatic carbon, low aromatic/highly acidic aliphatic carbon, low aromatic/highly aliphatic carbon, and amorphous forms of carbon. Our results clearly show the impact of graphite and amorphous C phases in the BC fraction in modern riverine sediments and nearby marine shelf deposits. The pre-anthropogenic Equatorial Pacific GBC fraction is remarkable in the existence of highly ordered graphite.

The Gorleben aquifer system, overlaying a Permian salt dome, has been under investigation for more than two decades for the potential to host a nuclear waste repository. Groundwater in the system shows a range of compositions, especially with respect to salt content and dissolved organic carbon (DOC) concentration. An uncertainty for safety analysis is the mobility of metal-complexing dissolved organic acids. Hence, isotopic data and carbon/sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy have been used in order to determine the mobility of fulvic acids (FAs). Isotopic data (13C, 14C, 3H) show that FAs from the recharge zone are mobile over the entire depth, including into the salt dome influenced brines.14C and δ 34S (up to 34‰) analysis shows furthermore that enhanced DOC (mainly humic and fulvic acids) concentrations originate from microbiologically mediated turnover of lignite intercalations in sandy Miocene sediments (“in situ generation”). XANES revealed that these in situ generated FAs have a high Carom/Caliph ratio (∼2.8), a decreased carboxyl/carbonyl content (less hydrophilic), a red shift in the Carom = Carom peak at 285.2eV, indicating heteroatom substitution and aromatic ring distortion, and feature a high reduced S content (∼69%). Shallow recharge groundwater and deep brine derived FAs exhibit a similar Carom/Caliph ratio (1.1–1.4), indicating invariance in the backbone structure against higher residence times and variation in geochemical conditions. XANES data also suggest that only heteroatom-substituted, destabilized aromatic ring structures of the FAs are stable in the brines and revealed 43% reduced S in recharge FAs and high (61%) reduced S with higher sulfate content in the channel brine FAs. Sulfur redox speciation therefore reflects geochemical conditions/reactions and shows a high stability of reduced sulfur species in more aerobic channel brine environments. The application of carbon and sulfur XANES shows that key structural information can be obtained from small sample amounts. The high mobility of FAs over a range of groundwater conditions and residence times verifies the potential for dissolved humic substances to enhance radionuclide transport.

The research presented herein is the first attempt to probe the chemical nature of lignocellulosic samples by the application of carbon near edge X-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft X-ray technique that principally provides selective interrogation of discrete atomic moieties using photoelectrons of variable energies. The X1A beam line of the National Synchrotron Light Source was employed for the specific purpose of observing carboxylic acid moieties that display a signature absorption band centered at 289 eV. This study caps a larger effort to support the mechanistic basis for lignocellulosic fiber chemical degradation induced by the disproportionation of hydrogen peroxiduring fiber bleaching trials. It is shown that fibers that have been bleached with a hydrogen peroxide phase without removal of resident pendant metals (Mn, Cu, Fe) sustain significant macroscopic damage likely via classical Fenton-type radical reactions, as evidenced by a tensile reduction by over 30%. We present X-ray absorption spectra obtained using a scanning transmission X-ray microscope (STXM) at the end of a 2.5 GeV electron synchrotron that provided 1s → π* contrast-enhanced micrographs illustrating a random distribution of acid functionalities that were principally located on fiber surfaces. Control studies using non-bleached fibers demonstrated that very little signature carboxylic acid absorption patterns were present in the fibers, suggesting that these groups are an incriminating fingerprint for macroscopic fiber strength damage during non-radical suppressed bleaching trials.

Diesel soot was investigated with electron energy loss spectroscopy (EELS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The EELS spectra were obtained in connection with transmission electron microscopy studies, whereas the NEXAFS were obtained from a scanning transmission X-ray microscope (STXM) and from a conventional NEXAFS beamline at two synchrotron facilities. The X-ray absorption spectra show molecular species, aliphatics, such as carboxyl, and C–H bonds, which are not visible in EELS spectra of the same material. In particular, EELS fails to detect surface-functional groups, which can be detected with NEXAFS. Since numerous works on molecular carbon structure determined with TEM-EELS have been published, it is possible that these results have to be reassessed.

Marine sinking particulate organic matter (POM) represents the link between surface primary production and burial of organic matter in marine sediments. As such, the nature of this material has been the subject of numerous studies attempting to characterize its composition. The results of these studies have shown that a significant proportion of POM is not recognizable as known compounds, and that the proportion of uncharacterized material increases with age/depth/diagenesis. However, few studies have examined the spatial heterogeneity of this material. This study uses a new tool, scanning transmission X-ray microscopy (STXM), together with carbon X-ray absorption near edge structure (C-XANES), to examine POM collected from sediment traps deployed at one location in the Arabian Sea as part of the JGOFS program. The results indicate that POM is composed primarily of four distinct phases: protein, an aliphatic rich phase, a carboxylic-acid-rich phase, and a phase with complex unsaturated and quinone character. This last phase may be a condensation product between carbohydrates and proteins, or from degraded plant pigments. Many particles consisted of a single chemical phase; however, in particles with mixed compositions, individual domains retained distinctive chemical signatures at the instrument's resolution limit (50 nm). All major chemical phases were observed in sediment trap particles from 531 to 3369 m depth, supporting the hypothesis that non-selective degradation dominates particle remineralization, and that overall particle compositions are determined by near surface processes. Only one particle, out of more than 60 examined, exhibited soot-like composition. The lack of a significant black carbon/soot component may be attributable to sampling during the winter monsoon period.

Eight interplanetary dust particles (IDPs) exhibiting a wide range of H and N isotopic anomalies have been studied by transmission electron microscopy, x-ray absorption near-edge structure spectroscopy, and Fourier-transform infrared spectroscopy. These anomalies are believed to have originated during chemical reactions in a cold molecular cloud that was the precursor to the Solar System. The chemical and mineralogical studies reported here thus constitute direct studies of preserved molecular cloud materials. The H and N isotopic anomalies are hosted by different hydrocarbons that reside in the abundant carbonaceous matrix of the IDPs. Infrared measurements constrain the major deuterium (D) host in the D-enriched IDPs to thermally labile aliphatic hydrocarbon groups attached to macromolecular material. Much of the large variation observed in D/H in this suite of IDPs reflects the variable loss of this labile component during atmospheric entry heating. IDPs with elevated 15N/14N ratios contain N in the form of amine (-NH2) functional groups that are likely attached to other molecules such as aromatic hydrocarbons. The host of the N isotopic anomalies is not as readily lost during entry heating as the D-rich material. Infrared analysis shows that while the organic matter in primitive anhydrous IDPs is similar to that observed in acid residues of primitive chondritic meteorites, the measured aromatic:aliphatic ratio is markedly lower in the IDPs.

Carbonaceous particulate matter from diesel fuel combustion was studied with Scanning Transmission X-ray Microspectroscopy, a novel synchrotron radiation-based technique, which combines X-ray absorption spectroscopy and microscopy. Single soot particles were chemically identified with a spatial resolution of better than 100 nm. Near-edge X-ray Absorption Fine Structure spectra from the carbon K-absorption edge could be assigned to specific particle regions, making it possible to distinguish graphitic carbon in the soot particles from hydrocarbons, such as residual lubricating oil and diesel fuel and their reaction products.

A continuous, planet-wide rain of about 30,000 tons/year of interplanetary dust accretes onto the Earth. The mass-frequency distribution of this dust is sharply peaked at about 400 lm, but the larger particles are most severely heated during atmospheric deceleration, with many of them vaporizing as meteors. Modeling of the peak temperature distribution experienced during atmospheric entry indicates that particles near 10 lm in size contribute the bulk of the mass that is not heated above 600 � C, which is believed to be the mean pyrolysis temperature of extraterrestrial organic matter. We have used infrared spectroscopy and X-ray absorption near-edge structure spectroscopy to characterize the types and abundance of organic matter in 10 lm interplanetary dust particles collected from the Earths stratosphere. These particles contain high abundance, from a few to over 90 vol%, of carbon, including percent-levels of both carbonyl (C@O) and aliphatic hydrocarbons (C–H3 and C–H2). We estimate that, in the current era interplanetary dust contributes 15 tons/year of unpyrolized organic matter to the surface of the Earth. During the first 0.6 billion years of Earths history, this contribution is likely to have been much greater. � 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

The detailed examination of meteorites and interplanetary dust particles provides an opportunity to infer the origin of the organic matter found in primitive Solar System materials. If this organic matter were produced by aqueous alteration of elemental (graphitic or amorphous) carbon on an asteroid, then we would expect to see the organic matter occurring preferentially in interplanetary materials that exhibit evidence of aqueous activity, such as the presence of hydrated silicates. On the other hand, if the organic matter were produced either during the nebula phase of Solar System evolution or in the interstellar medium, we might expect this organic matter to be incorporated into the dust as it formed. In that case pre-biotic organic matter would be present in both the anhydrous and the hydrated interplanetary materials. We have performed carbon X-ray absorption near-edge structure spectroscopy and infrared spectroscopy on primitive anhydrous and hydrated interplanetary dust particles (IDPs) collected by NASA from the Earth's stratosphere. We find that organic matter is present in similar types and abundances in both the anhydrous and the hydrated IDPs, and, in the anhydrous IDPs some of this organic matter is the “glue” that holds grains together. These measurements provide the first direct, experimental evidence from the comparison of extraterrestrial samples that the bulk of the pre-biotic organic matter occurs in similar types and abundances in both hydrated and anhydrous samples. This indicates that the bulk of the pre-biotic organic matter in the Solar System did not form by aqueous processing, but, instead, had already formed at the time that primitive, anhydrous dust was being assembled. Thus, the bulk of the pre-biotic organic matter in the Solar System was formed by non-aqueous processing, occurring in either the Solar nebula or in an interstellar environment. Aqueous processing on asteroids may have altered this pre-existing organic matter, but such processing did not affect in any substantial way the C=O content of the organic matter, the aliphatic C-H abundance, or the mean aliphatic chain length.

Interplanetary dust particles (IDPs), fragments from asteroids and comets, contain important clues to the conditions in the solar nebula when dust was forming, provide evidence of the chemical and physical properties of their parent bodies, and may have been an important source of pre-biotic organic matter on the early Earth. We mapped the spatial distributions in IDPs of C, O, K, and Ca using a scanning transmission x-ray microscope and of Fe, Ni, Zn, Sr and Br using fluorescence microtomography. In addition, we obtained carbon and oxygen x-ray absorption near-edge structure (XANES) Spectra of the C-rich regions, identifying the C-ring and C=O functional groups, and Fourier Transform InfraRed (FTIR.) spectra, identifying the aliphatic C-H 2 and C-H 3 functional groups. The C-mapping indicates that IDPs contain anywhere from a few wt-% up to 90 wt-% carbon, much more carbon than is found in the most carbon-rich meteorites, and C- and O-XANES demonstrate that a significant fraction of this carbon is organic. The Ca, K, Fe, Ni, Zn, Sr, and Br maps allow inference of the host phases of these elements and place constraints on surface contamination.

Soft X-ray microscopy allows one to study nanoscale heterogeneities in dry and wet environmental science, biological, polymer, and geochemical specimens. Recent advances in instrumentation at the X-1A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory are described. Spectromicroscopy data analysis methods including component mapping and principal component analysis (PCA) are then discussed.

The X1A soft X-ray undulator beamline at the NSLS has been rebuilt to serve two microscopy stations operating simultaneously. Separate spherical-grating monochromators provide the resolving power required for XANES spectroscopy at the C, N and O absorption edges. The exit slits are fixed and define the coherent source for the experiments. The optical design and the operational performance are described.

The phenomenon of luminescence alteration has been shown to correlate with the thermal maturity of Type III kerogens (vitrinites). In order to establish a chemical structural basis for this correlation, carbon near edge X-ray absorption fine structure (C-NEXAFS) spectroscopy is used to monitor the gain and loss of organic functionality in ultra-thin sections of vitrinite following time incremental exposure to blue light (390–490 nm) irradiation in air. These data are compared with luminescence alteration behavior measured at 600 nm. Three samples are studied; low maturity (% R 0 =0.29), medium maturity (% R 0 =0.73), and high maturity (% R 0 =1.35) vitrinite. These exhibit “positive”, “dual”, and “negative” luminescence alteration, respectively. It has been previously established that the luminescence alteration of vitrinites is the result of photo–oxidation. C-NEXAFS data are used to identify the types of reactions and correlate the chemical structural changes with luminescence alteration behavior. The unaltered C-NEXAFS spectrum of each vitrinite is significantly different, reflecting the broad range in vitrinite maturity. The dominant reaction is the formation of COOH groups, through the attack of singlet oxygen on, predominantly, benzylic carbon. Carbonyl substituted aromatics are the dominant photo–oxidation product of the most mature vitrinite. The photo–chemical oxidation pathways and kinetics vary significantly between the three samples. Virtually all of the major spectral trends (excluding the formation of COOH groups) reverse, moving from low to high maturity, i.e. gains in absorption at a given energy at one maturity level are observed to be losses at a different maturity level. The spectral changes reveal that in the lower maturity samples aromatic acids, aliphatic ketones, and hydroxylated aromatic compounds are formed; aliphatic and aldehydic carbon are lost. In the more mature vitrinite, aryl–ketones and aromatic acids are formed, whereas polycyclic aromatic compounds are lost. Strong correlations exist between the development of “positive” alteration and the formation of COOH functionality. No obvious correlation could be made between the C-NEXAFS data and the “negative” luminescence alteration, suggesting that the lumophor participating in this reaction is below the detection limit of C-NEXAFS spectroscopy. The maturity of a given vitrinite sample, hence its molecular structure, strongly controls the specific reaction pathways as well as the total extent of reaction.

Spectromicroscopy combines spectral data with microscopy, where typical datasets consist of a stack of images taken across a range of energies over a microscopic region of the sample. Manual analysis of these complex datasets can be time-consuming, and can miss the important traits in the data. With this in mind we have developedMANTiS, an open-source tool developed in Python for spectromicroscopy data analysis. The backbone of the package involves principal component analysis and cluster analysis, classifying pixels according to spectral similarity. Our goal is to provide a data analysis tool which is comprehensive, yet intuitive and easy to use.MANTiSis designed to lead the user through the analysis using story boards that describe each step in detail so that both experienced users and beginners are able to analyze their own data independently. These capabilities are illustrated through analysis of hard X-ray imaging of iron in Roman ceramics, and soft X-ray imaging of a malaria-infected red blood cell.

The Scanning Transmission Soft X‐ray Microscope at the NSLS has been instrumented for the following new forms of imaging: (1) XANES microscopy for the mapping of chemical constituents and for absorption spectroscopy of small specimen areas; (2) luminescence microscopy for locating visible light emitting labels at the resolution determined by the size of the x‐ray microprobe; and (3) dichroism microscopy for mapping the alignment of molecules whose absorption spectra are polarization dependent. Since the instrument is used mostly for the imaging of biological and other radiation sensitive materials, a cryostage is being planned to accommodate frozen hydrated specimens.

We used the model organisms Nicotiana tabacum L. cv Xanthi (tobacco) and Triticum aestivum (wheat) to investigate plant uptake of 10-, 30-, and 50-nm diameter Au manufactured nanomaterials (MNMs) coated with either tannate (T-MNMs) or citrate (C-MNMs). Primary particle size, hydrodynamic size, and zeta potential were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), and electrophoretic mobility measurements, respectively. Plants were exposed to NPs hydroponically for 3 or 7 days for wheat and tobacco, respectively. Volume averaged Au concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS). Spatial distribution of Au in tissue samples was determined using laser ablation ICP-MS (LA-ICP-MS) and scanning X-ray fluorescence microscopy (μXRF). Both C-MNMs and T-MNMs of each size treatment bioaccumulated in tobacco, but no bioaccumulation of MNMs was observed for any treatment in wheat. These results indicate that MNMs of a wide range of size and with different surface chemistries are bioavailable to plants, provide mechanistic information regarding the role of cell wall pores in plant uptake of MNMs, and raise questions about the importance of plant species to MNM bioaccumulation.

The scanning transmission X-ray microscope on the X1A undulator beam line, at the National Synchrotron Light Source, has been used for imaging various biological as well as polymer samples at 55 nm Rayleigh resolution. The microscope is operated mainly in direct imaging mode, where X-rays of fixed energy are diffractively focussed to a microprobe and the sample is scanned in two dimensions. However, by varying the X-ray energy while keeping the beam focussed to one spot on the sample we can also determine the localized chemical composition of the sample from the carbon X-ray absorption near edge spectra in an area smaller than 0.2 μm by 0.2 μm. The spatial distribution of the chemical constituents can be obtained by imaging at absorption maxima of specific chemical bonds, while retaining the 0.05 μm spatial resolution of the microscope. The chemical sensitivity of X-ray-absorption near-edge spectroscopy provides a powerful contrast mechanism for imaging organic systems. The well-known differences in energy among π resonances of different chemical bonds have been used to distinguish different polymer phases and have been applied to biological systems.

Inner shell processes in the light elements provide the contrast mechanisms for soft X-ray microscopy. Bright X-ray sources and precision focusing elements have led to the development of high resolution instruments. Our efforts in scanning microscopy, holography and diffraction at the National Synchrotron Light Source are aimed at the development of microimaging techniques mostly for biological specimens.

International audience; Clay-rich low-organic carbon formations (e.g., Callovo-Oxfordian argillite in France and Opalinus Clay in Switzerland) are considered as host rocks for radioactive waste disposal. The clay-organic carbon has a strong impact on the chemical stability of the clays. For this reason, the nature of the clay-organic carbon, the release of hydrophilic organic compounds, namely, humic (HA) and fulvic acids (FA) and the radiation sensitivity of the undisturbed host rock organics was investigated. The clay sample originates from Oxfordian argillite (447 m depth, borehole EST 104). HA and FA were extracted following the standard International Humic Substance Society (IHSS) isolation procedure. Synchrotron based (C-, K-, Ca-, O- and Fe-edge XANES) scanning transmission X-ray microscopy (STXM) and FT-IR microspectroscopy was used to identify under high spatial resolution the distribution of clay-organic matter with different functionality using principal component and cluster analysis. The results show that in this old (Jurassic) geological formation, small parts of the organic inventory (1–5%) keeps the structure/functionality and can be mobilized as hydrophilic humic substance type material (HA and FA). Target spectra analysis shows best correlation for isolated humic acids with organics found in smectite-rich regions, whereas the extractable FA has better spectral similarities with the illite mixed layer minerals (MLM) regions. After radiation of 1.7 GGy under helium atmosphere the same rock sample area was investigated for radiation damage. Radiation damage in the smectite and illite–MLM associated organic matter is comparably low with 20–30% total oxygen mass loss and 13–18% total carbon mass loss. A critical dose dc of 2.5 GGy and a optical density after infinite radiation (OD∝) of 54% was calculated under room temperature conditions. C(1s) XANES show a clear increase in CC bonds especially in the illite–MLM associated organics. This results suggests a combination of the formation of CC bond due to crosslinking via polymerization and mass loss due to bond breaking (scissioning) in the main chain or in side groups of the organic macromolecules upon irradiation.

Black carbon (BC) may play an important role in the global C budget, due to its potential to act as a significant sink of atmospheric CO2. In order to fully evaluate the influence of BC on the global C cycle, an understanding of the stability of BC is required. The biochemical stability of BC was assessed in a chronosequence of high-BC-containing Anthrosols from the central Amazon, Brazil, using a range of spectroscopic and biological methods. Results revealed that the Anthrosols had 61–80% lower (P 0.05) difference in CO2 respiration per unit C was observed between Anthrosols with contrasting ages of BC (600–8700 years BP) and soil textures (0.3–36% clay). Similarly, the molecular composition of the core regions of micrometer-sized BC particles quantified by synchrotron-based Near-Edge X-ray Fine Structure (NEXAFS) spectroscopy coupled to Scanning Transmission X-ray Microscopy (STXM) remained similar regardless of their ages and closely resembled the spectral characteristics of fresh BC. BC decomposed extremely slowly to an extent that it was not possible to detect chemical changes between youngest and oldest samples, as also confirmed by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of NEXAFS spectra revealed greater oxidation on the surfaces of BC particles with little penetration into the core of the particles. The similar C mineralization between different BC-rich soils regardless of soil texture underpins the importance of chemical recalcitrance for the stability of BC, in contrast to adjacent soils which showed the highest mineralization in the sandiest soil. However, the BC-rich Anthrosols had higher proportions (72–90%) of C in the more stable organo-mineral fraction than BC-poor adjacent soils (2–70%), suggesting some degree of physical stabilization.

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.

Melanosomes are specialized intracellular membrane bound organelles that produce and store melanin pigment. The composition of melanin and distribution of melanosomes determine the color of many mammalian tissues, including the hair, skin, and iris. However, the presence of melanosomes within a tissue carries potentially detrimental risks related to the cytotoxic indole–quinone intermediates produced during melanin synthesis. In order to study melanosomal molecules, including melanin and melanin-related intermediates, we have refined methods allowing spectromicroscopic analysis of purified melanosomes using scanning transmission X-ray microscopy. Here, we present for the first time absorption data for melanosomes at the carbon absorption edge ranging from 284 to 290 eV. High-resolution images of melanosomes at discrete energies demonstrate that fully melanized mature melanosomes are internally non-homogeneous, suggesting the presence of an organized internal sub-structure. Spectra of purified melanosomes are complex, partially described by a predominating absorption band at 288.4 eV with additional contributions from several minor bands. Differences in these spectra were detectable between samples from two strains of inbred mice known to harbor genetically determined melanosomal differences, DBA/2J and C57BL/6J, and are likely to represent signatures arising from biologically relevant and tractable phenomena.

著者人数: 75名, 資料番号: SA1003700000

Received 17 December 2004; accepted 3 January 2005; published 16 February 2005. [1] Small-scale heterogeneity of organic carbon (C) forms in soils is poorly quantified since appropriate analytical techniques were not available up to now. Specifically, tools for the identification of functional groups on the surface of micrometer-sized black C particles were not available up to now. Scanning Transmission X-ray Microscopy (STXM) using synchrotron radiation was used in conjunction with Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to investigate nano-scale distribution (50-nm resolution) of C forms in black C particles and compared to synchrotron-based FTIR spectroscopy. A new embedding technique was developed that did not build on a C-based embedding medium and did not pose the risk of heat damage to the sample. Elemental sulfur (S) was melted to 220� C until it polymerized and quenched with liquid N2 to obtain a very viscous plastic S in which the black C could be embedded until it hardened to a noncrystalline state and was ultrasectioned. Principal component and cluster analysis followed by singular value decomposition was able to resolve distinct areas in a black carbon particle. The core of the studied biomass-derived black C particles was highly aromatic even after thousands of years of exposure in soil and resembled the spectral characteristics of fresh charcoal. Surrounding this core and on the surface of the black C particle, however, much larger proportions of carboxylic and phenolic C forms were identified that were spatially and structurally distinct from the core of the particle. Cluster analysis provided evidence for both oxidation of the black C particle itself as well as adsorption of non-black C. NEXAFS spectroscopy has great potential to allow new insight into black C properties with important implications for biogeochemical cycles such as mineralization of black C in soils and sediments, and adsorption of C, nutrients, and pollutants as well as transport in the geosphere, hydrosphere, and atmosphere.