The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to delta D = 3500% in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (dD > 95000%). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (dD = 600-3500%) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk dD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and dD, and increasing aromaticity. (C) 2021 Elsevier Ltd. All rights reserved.

The large variations in hydrogen isotope ratios found in insoluble organic matter (IOM) in chondritic meteorites may be attributed to hydrogen isotopic exchange between IOM and water during aqueous alteration. We conducted D-H exchange experiments (1) during synthesis of IOM simulant (hereafter called chondritic organic analog, COA) from formaldehyde, glycolaldehyde, and ammonia with water, and (2) with the synthesized COA with a secondary reservoir of water. The changes in the D/H ratios obtained by infrared spectra of the COA suggest that most of the hydrogen in the COA is derived from water during synthesis. We further investigated the kinetics of D-H exchange between D-rich COA and D-poor water, as well as the opposite case, D-poor COA and D-rich water. To help assess understanding exchange kinetics, two-dimensional isotope imaging obtained using isotope microscope revealed that no gradient D-H exchange profiles were present in the COA grains, indicating that the rate-limiting step for D-H exchange is not diffusion. Thus, the changes in D/(D + H) ratios were fit by the first-order reaction rate law. Apparent kinetic parameters-the rate constants, the activation energies, and the frequency factors-were obtained with the Arrhenius equation. Using these kinetic expressions, hydrogen isotopic exchange profiles were estimated for time and temperature behavior. The D-H exchange between organic matter and water is apparently relatively fast and this implies that the aqueous alteration temperatures should have been very low, likely close to 0 degrees C to maintain hydrogen isotopic disequilibrium between organic matter and liquid water for millions of years.

The large variations in hydrogen isotope ratios found in insoluble organic matter (IOM) in chondritic meteorites may be attributed to hydrogen isotopic exchange between IOM and water during aqueous alteration. We conducted D-H exchange experiments (1) during synthesis of IOM simulant (hereafter called chondritic organic analog, COA) from formaldehyde, glycolaldehyde, and ammonia with water, and (2) with the synthesized COA with a secondary reservoir of water. The changes in the D/H ratios obtained by infrared spectra of the COA suggest that most of the hydrogen in the COA is derived from water during synthesis. We further investigated the kinetics of D-H exchange between D-rich COA and D-poor water, as well as the opposite case, D-poor COA and D-rich water. To help assess understanding exchange kinetics, two-dimensional isotope imaging obtained using isotope microscope revealed that no gradient D-H exchange profiles were present in the COA grains, indicating that the rate-limiting step for D-H exchange is not diffusion. Thus, the changes in D/(D + H) ratios were fit by the first-order reaction rate law. Apparent kinetic parameters-the rate constants, the activation energies, and the frequency factors-were obtained with the Arrhenius equation. Using these kinetic expressions, hydrogen isotopic exchange profiles were estimated for time and temperature behavior. The D-H exchange between organic matter and water is apparently relatively fast and this implies that the aqueous alteration temperatures should have been very low, likely close to 0 degrees C to maintain hydrogen isotopic disequilibrium between organic matter and liquid water for millions of years.

Here we report the elemental and isotopic compositions of the insoluble organic material (TOM) isolated from several previously unanalyzed meteorites, as well as the reanalyses of H isotopic compositions of some previously measured samples (Alexander et al., 2007). The IOM in ordinary chondrites (OCs) has very large D enrichments that increase with increasing metamorphism and decreasing H/C, the most extreme delta D value measured being almost 12,000 parts per thousand. We propose that such large isotopic fractionations could be produced in the OC parent bodies through the loss of isotopically very light 112 generated when Fe was oxidized by water at low temperatures (<200 degrees C). We suggest that similar isotopic fractionations were not generated in the IOM of CV and CO chondrites with similar metamorphic grades and IOM H/C ratios because proportionately less water was consumed during metamorphism, and the remaining water buffered the H isotopic composition of the TOM even a H was being lost from it.

Insight into the chemical history of an ungrouped type 2 carbonaceous chondrite meteorite, Wisconsin Range (WIS) 91600, is gained through molecular analyses of insoluble organic matter (IOM) using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, X-ray absorption near edge structure spectroscopy (XANES), and pyrolysis-gas chromatography coupled with mass spectrometry (pyr-GC/MS), and our previous bulk elemental and isotopic data. The IOM from WIS 91600 exhibits similarities in its abundance and bulk delta 15N value with IOM from another ungrouped carbonaceous chondrite Tagish Lake, while it exhibits H/C, delta 13C, and delta D values that are more similar to IOM from the heated CM, Pecora Escarpment (PCA) 91008. The 13C NMR spectra of IOM of WIS 91600 and Tagish Lake are similar, except for a greater abundance of CH(x)O species in the latter and sharper carbonyl absorption in the former. Unusual cross-polarization (CP) dynamics is observed for WIS 91600 that indicate the presence of two physically distinct organic domains, in which the degrees of aromatic condensation are distinctly different. The presence of two different organic domains in WIS 91600 is consistent with its brecciated nature. The formation of more condensed aromatics is the likely result of short duration thermal excursions during impacts. The fact that both WIS 91600 and PCA 91008 were subjected to short duration heating that is distinct from the thermal history of type 3 chondrites is confirmed by Carbon-XANES. Finally, after being briefly heated (400 degrees C for 10 s), the pyrolysis behavior of Tagish Lake IOM is similar to that of WIS 91600 and PCA 91008. We conclude that WIS 91600 experienced very moderate, short duration heating at low temperatures (< 500 degrees C) after an episode of aqueous alteration under conditions that were similar to those experienced by Tagish Lake.

Because all known Eoarchean (>3.65 Ga) volcano-sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation, the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate. To determine the biogenicity of carbon in graphite in such rocks, carbonaceous material must be demonstrably indigenous and its composition should be consistent with thermally altered biogenic carbon as well as inconsistent with abiogenic carbon. Here we report the petrological and spectroscopic characteristics of carbonaceous material, typically associated with individual apatite grains, but also with various other minerals including calcite, in a >3.83 Ga granulite-facies ferruginous quartz-pyroxene unit (Qp rock) from the island of Akilia in southern West Greenland. In thin sections of the fine-grained parts of Akilia Qp rock sample G91-26, mapped apatites were found to be associated with graphite in about 20% of the occurrences. Raman spectra of this carbonaceous material had strong G-band and small D-band absorptions indicative of crystalline graphite. Three apatite-associated graphites were found to contain curled graphite structures, identified by an anomalously intense second-order D-band (or 2D-band) Raman mode. These structures are similar to graphite whiskers or cones documented to form at high temperatures. Raman spectra of apatite-associated graphite were consistent with formation at temperatures calculated to be between 635 and 830 degrees C, which are consistent with granulite-facies metamorphic conditions. Three graphite targets extracted by focused ion beam (FIB) methods contained thin graphite coatings on apatite grains rather than inclusions sensu stricto as inferred from transmitted light microscopy and Raman spectroscopy. TEM analyses of graphite in these FIB sections showed a (0 0 0 2) interplanar spacing between 3.41 and 3.64 angstrom for apatite-associated graphite, which is larger than the spacing of pure graphite (3.35 angstrom) and may be caused by the presence of non-carbon heteroatoms in inter-layer sites. Samples analyzed by synchrotron-based scanning transmission X-ray microscopy (STXM) also confirmed the presence of crystalline graphite, but abundances of N and O heteroatoms were below detection limit for this method. Graphite in the Akilia Qp rock was also found to occur in complex polyphase mineral assemblages of hornblende +/- calcite +/- sulfides +/- magnetite that point to high-temperature precipitation from carbon-bearing fluids. These complex mineral assemblages may represent another generation of graphitization that could have occurred during the amphibolite-facies metamorphic event at 2.7 Ga. Several observations point to graphitization from high-temperature fluid-deposition for some of the Akilia graphite and our results do not exclude a biogenic source of carbon in graphite associated with apatite, but ambiguities remain for the origin of this carbon. (C) 2010 Elsevier Ltd. All rights reserved.

Model compound chitin and invertebrate cuticles were analysed using pyrolysis-gas chromatography-mass spectrometry, (13) C NMR and C-, N-, and O-Xray Absorption Near Edge Structure (XANES) spectral imaging using Scanning Transmission X-ray Microscopy (STXM) to detect spectra that are characteristic of chitin. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones appear to be characteristic pyrolysis products for chitin. Pyrolysis products with ions of m/z 70, 154, 168, 194 likely derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. The C-13 NMR spectra of chitin reveals that amidyl methyl group resonates at 23 ppm, amidyl linked glyocosyl carbon resonates at 56 ppm, glucosyl secondary alcohols resonate between 62 and 84 ppm, and glycosidic carbon absorption is evident at similar to 105 ppm. The presence of protein in the arthropod cuticles is evident by resonance intensity associated with sp(2) bonded carbon associated in unsaturated amino acids (e.g. phenyl alanine, tyrosine, and histidine) occurring at 116, 129, and 137 ppm. Additionally, the protein back bone methine carbon atoms are indicated by resonance intensity at 43 ppm. Additional broad resonance intensity in the 20-30 ppm range is derived both from aliphatic aminoacids (e.g. valine and leucine) as well as the fatty acids associated with the waxy cuticulin layer of the cuticle. High energy resolution C-, N-, and O-XANES spectra provide further functional group level characterization of the biomacromolecular assemblages at spatial scales on the order of 100's of nm. Combining the power of Solid state C-13 NMR, pyrolysis with the micro-analytical capabilities of C-, N-, and O-XANES yields a formidable analytical approach towards detecting and quantitating the presence of chitin in complex biomacromolecular assemblages.

The conventional geochemical view holds that the chitin and structural protein are not preserved in ancient fossils because they are readily degradable through microbial chitinolysis and proteolysis. Here we show a molecular signature of a relict chitin-protein complex preserved in a Pennsylvanian (310 Ma) scorpion cuticle and a Silurian (417 Ma) eurypterid cuticle via analysis with carbon, nitrogen, and oxygen X-ray absorption near edge structure (XANES) spectro-microscopy. High-resolution X-ray microscopy reveals the complex laminar variation in major biomolecule concentration across modern cuticle; XANES spectra highlight the presence of the characteristic functional groups of the chitin-protein complex. Modification of this complex is evident via changes in organic functional groups. Both fossil cuticles contain considerable aliphatic carbon relative to modern cuticle. However, the concentration of vestigial chitin-protein complex is high, 59% and 53% in the fossil scorpion and eurypterid, respectively. Preservation of a high-nitrogen-content chitin-protein residue in organic arthropod cuticle likely depends on condensation of cuticle-derived fatty acids onto a structurally modified chitin-protein molecular scaffold, thus preserving the remnant chitin-protein complex and cuticle from degradation by microorganisms.