Organic residues formed in the laboratory from the ultraviolet (UV) photo-irradiation or ion bombardment of astrophysical ice analogs have been extensively studied for the last 15 years with a broad suite of techniques, including infrared (IR) and UV spectroscopies, as well as mass spectrometry. Analyses of these materials show that they consist of complex mixtures of organic compounds stable at room temperature, mostly soluble, that have not been fully characterized. However, the hydrolysis products of these residues have been partly identified using chromatography techniques, which indicate that they contain molecular precursors of prebiotic interest such as amino acids, nitrile-bearing compounds, and amphiphilic compounds. In this study, we present the first X-ray absorption near-edge structure (XANES) spectroscopy measurements of three organic residues made from the UV irradiation of ices having different starting compositions. XANES spectra confirm the presence of different chemical functions in these residues, and indicate that they are rich in nitrogen- and oxygen-bearing species. These data can be compared with XANES measurements of extraterrestrial materials. Finally, this study also shows how soft X rays can alter the chemical composition of samples. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

The adsorption configuration of organic molecules on mineral surfaces is of great interest because it can provide fundamental information for both engineered and natural systems. Here we have conducted surface-enhanced Raman spectroscopy (SERS) measurements to probe the attachment configurations of DOPA on nanorutile particles under different pH and surface coverage conditions. The Raman signal enhancement arises when a charge transfer (CT) complex forms between the nanopartides and adsorbed DOPA This Raman signal is exdusively from the surface-bound complexes with great sensitivity to the binding and orientation of the DOPA attached to the TiO2 surface. Our SERS spectra show peaks that progressively change with pH and surface coverage, indicating changing surface speciation. At low pH and surface coverage, DOPA adsorbs on the surface lying down, with probably three points of attachment, whereas at higher pH and surface coverage DOPA stands up on the surface as a species involving two attachment points via the two phenolic oxygens. Our results demonstrate experimentally the varying proportions of the two surface species as a function of environmental conditions consistent with published surface complexation modeling. This observation opens up the possibility to manipulate organic molecule attachment in engineered systems such as biodetection devices. Furthermore, it provides a perspective on the possible role of mineral surfaces in the chemical evolution of biomolecules on the early Earth. Adsorbed biomolecules on mineral surface in certain configurations may have had an advantage for subsequent condensation reactions, facilitating the formation of peptides.

Recent studies reveal substantial variability in biosynthetic H-2/H-1 fractionation between lipids and water, which highlights the effect of central metabolic pathways on the H isotopic composition of the end products. Using multi-nuclear (H-1, H-2 and C-13) solid state nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS), we were able to track the incorporation of H-1 and H-2 metabolic fluxes into different cellular components of Escherichia coli during growth on two sets of media: (i) 10% deuterated water and non-deuterated glucose, and (ii) non-deuterated water and 10% deuterated glucose. In the 10% H-2 water experiment, the H-2 abundance of the bulk cell was 4.5%; the H-2 uptake by membrane lipids, aliphatic H in proteins, and all the non-aliphatic H positions (including nucleic acids and sugars) was 6.2%, 2.3% and 6.2%, respectively. In the 10% H-2 glucose experiment, the corresponding H-2 uptake was 2.0%, 1.4% and 2.5%, respectively, and 1.9% for the bulk cell. The net fractionation of fatty acids (FAs) relative to water and glucose was consistent with that in studies employing natural H-2 abundance, suggesting the 10% deuterated environment does not alter isotope fractionation during FA biosynthesis. Aliphatic H in proteins was significantly depleted in H-2 relative to FAs by 290-640 parts per thousand. This depletion is likely related to the dynamic regulation of central metabolic pathways that gradually builds up H-2 in tricarboxylic acid (TCA) cycle intermediates though continuous interaction with water, leading to the rapid synthesis of isotopically light amino acids early in the cell cycle and the production of isotopically enriched FAs late in the cell cycle. Besides, enzyme malfunctioning caused by H-2 substitution is likely to promote proteolysis, which could also contribute to the H-2 depletion in proteins. Non-aliphatic H positions as a whole exhibited similar net fractionation factors to the lipids. The study provides an overview of H isotope distribution in the major molecular constituents of intact bacterial cells, offering insight into the mechanisms underlying the metabolic control on the H isotopic composition of biomarker precursors. (c) 2013 Elsevier Ltd. All rights reserved.

Polymerization of interstellar formaldehyde, first through the formose reaction and then through subsequent condensation reactions, provides a plausible explanation for how abundant and highly chemically complex organic solids may have come to exist in primitive solar system objects. In order to gain better insight on the reaction, a systematic study of the relationship of synthesis temperature with resultant molecular structure was performed. In addition, the effect of the presence of ammonia on the reaction rate and molecular structure of the product was studied. The synthesized formaldehyde polymer is directly compared to chondritic insoluble organic matter (IOM) isolated from primitive meteorites using solid-state C-13 nuclear magnetic resonance, Fourier transform infrared, and X-ray absorption near edge structure spectroscopy. The molecular structure of the formaldehyde polymer is shown to exhibit considerable similarity at the functional group level with primitive chondritic IOM. The addition of ammonia to the solution enhances the rate of polymerization reaction at lower temperatures and results in substantial incorporation of nitrogen into the polymer. Morphologically, the formaldehyde polymer exists as submicron to micron-sized spheroidal particles and spheroidal particle aggregates that bare considerable similarity to the organic nanoglobules commonly observed in chondritic IOM. These spectroscopic and morphological data support the hypothesis that IOM in chondrites and refractory organic carbon in comets may have formed through the polymerization of interstellar formaldehyde after planetesimal accretion, in the presence of liquid water, early in the history of the solar system.

Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) analysis of Neolithic (4900-3800 BC) archeological rice grains (husked rice fruit) from the Tianluoshan site (Zhejiang Province, eastern China) revealed no polysaccharide products from starch present in the original rice fruit; however, benzene, toluene, dimethyl benzene, phenol, dimethyl phenol and n-alkanes > C-30 were detected, indicating their aromatic nature, plus some aliphatic components. On the contrary, polysaccharides were observed in husk material but in significantly lower concentration than in the modern equivalent. The molecular composition was supported by C-13 nuclear magnetic resonance spectroscopy (NMR) data. Variation in preservation quality was also detected in persimmon seeds, oak acorns and amanranthaceous seeds from the site. This variation in molecular preservation, which could also be observed at the micro-morphological level, was tracked with scanning electron microscopy (SEM). Variation in bulk tissue carbon isotopic values (delta C-13) was apparent among archeological samples, a net 1-2 parts per thousand positive shift in bulk tissue delta C-13 being found in most of the Tianloushan plant remains. Our data suggest the importance of post-excavation storage conditions and illustrate the power of the application of multiple analytical methods for the study of archeological plant remains. (c) 2013 Elsevier Ltd. All rights reserved.

Purple sulfur bacteria (PSB) are important photoautotrophs inhabiting chemoclines in euxinic and meromictic lakes. These organisms are the only producers of the carotenoid, okenone, a compound that has been targeted as a biomarker for photic zone euxinia, particularly in ancient sedimentary environments. Although the natural occurrence and geochemistry of this compound has been studied previously, this is the first systematic and comprehensive report on the microbial physiology of okenone production in pure cultures. Four strains/species: Marichromatium purpuratum DSMZ 1591, Marichromatium purpuratum DSMZ 1711, Thiocapsa marina DSMZ 5653, and FGL21 (isolated from Fayetteville Green Lake, New York) were chosen because they produce okenone and Bacteriochlorophyll a (Bchl a). We developed a new, in vivo technique for the quantification of okenone allowing for more rapid and accurate quantification. The ratio of okenone to Bchl a differs among species and strains of PSB, varying from 0.463 +/- 0.002 to 0.864 +/- 0.002. Photoheterotrophically grown PSB have statistically significant, lowered okenone:Bchl a ratios, decreasing from 0.784 +/- 0.009 under autotrophic metabolism to 0.681 +/- 0.002, which we interpret to indicate a decreased requirement for okenone when PSB are provided with a complex (> C1) carbon source. The variation in okenone production raises the question on whether okenone expression is constitutive or inducible. The broader implication is that concentrations of okenone in sediments are dependent on metabolism and species composition, and not solely on PSB cell density.

The mechanism leading to the formation of aliphatic components in sedimentary rocks and petroleum products has been the subject of debate. Recent research has concluded that algaenan is not as widespread ecologically or phylogenetically, so may contribute less to the resistant aliphatic content of kerogens where such algae are source organisms. We conducted experiments with the non-algaenan producing alga, Chlamydomonas reinhardtii, at 260 and 350 degrees C and 700 bar to simulate fossilization of the microorganism under confined pyrolysis conditions. Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) analysis revealed that the unheated alga consisted of biopolymers primarily related to proteins and lipids, including C-16 and C-18 fatty acids (FAs). However, heating at 260 and 350 degrees C resulted in macromolecules with a significant aliphatic component similar to high hydrogen content kerogen, derived from lipids in the alga, primarily from saturated and unsaturated C-16 and C-18 FAs, as determined from experiments with model compounds. The presence of amides, nitriles and oximes in the heated alga was likely due to the reaction of the lipids with the abundant N-containing proteinaceous compounds. Py-GC-MS of the residue of Scenedesmus quadricauda at 350 degrees C (a green alga containing algaenan as a control) demonstrated survival of algaenan at that temperature. The solvent insoluble residue of a cyanobacterium (Oscillatoria sp.) and a purple non S containing bacterium Rhodopseudomonas palustris subjected to similar high temperature and pressure, resulted in a residue with significant aliphatic content. The results reveal that algaenan survived the P/T conditions of the experiments, which additionally suggest an alternative mechanism that may lead to aliphatic geopolymers. Since this mechanism seems to be valid for organisms that are phylogenetically wide apart, it may be valid for organism cells in general. Thus, bacterial biomass may also contribute to the insoluble organic inventory of ancient sediments. (C) 2013 Elsevier Ltd. All rights reserved.

Organic nanoglobules are microscopic spherical carbon-rich objects present in chondritic meteorites and other astromaterials. We performed a survey of the morphology, organic functional chemistry, and isotopic composition of 184 nanoglobules in insoluble organic matter (IOM) residues from seven primitive carbonaceous chondrites. Hollow and solid nanoglobules occur in each IOM residue, as well as globules with unusual shapes and structures. Most nanoglobules have an organic functional chemistry similar to, but slightly more carboxyl-rich than, the surrounding IOM, while a subset of nanoglobules have a distinct, highly aromatic functionality. The range of nanoglobule N isotopic compositions was similar to that of nonglobular 15N-rich hotspots in each IOM residue, but nanoglobules account for only about one third of the total 15N-rich hotspots in each sample. Furthermore, many nanoglobules in each residue contained no 15N enrichment above that of bulk IOM. No morphological indicators were found to robustly distinguish the highly aromatic nanoglobules from those that have a more IOM-like functional chemistry, or to distinguish 15N-rich nanoglobules from those that are isotopically normal. The relative abundance of aromatic nanoglobules was lower, and nanoglobule diameters were greater, in more altered meteorites, suggesting the creation/modification of IOM-like nanoglobules during parent-body processing. However, 15N-rich nanoglobules, including many with highly aromatic functional chemistry, likely reflect preaccretionary isotopic fractionation in cold molecular cloud or protostellar environments. These data indicate that no single formation mechanism can explain all of the observed characteristics of nanoglobules, and their properties are likely a result of multiple processes occurring in a variety of environments.