Organic compounds in carbonaceous meteorites

Sephton, Mark A.

doi:10.1039/b103775g

Cited by 610 publications

(561 citation statements)

References 168 publications

(253 reference statements)

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“…Life is not just a process of reorganizing existing components that are close to equilibrium into something that looks like a cell, life is an exergonic chemical reaction, a continuous far from equilibrium process (Sousa et al 2013b). Second, the kind of substrates that heterotrophic origins supporters have in mind, namely organics from space delivered to earth by comets or meteorites (Chyba et al 1990), tend to show what is called complete structural diversity (Sephton 2002), meaning that for a given chemical formula detected, a very large number of isomers are found, all in very minute quantities (Sephton 2002). For any cell to be able to access such a mixture as a growth substrate, it would have to ( pre-)possess a very large enzymatic repertoire of specific isomerases and mutases, which is not a viable proposition.…”

Section: Hot Debates Ii: Carbon Metabolismmentioning

confidence: 99%

Early Microbial Evolution: The Age of Anaerobes

Martin

Sousa

2015

Cold Spring Harb Perspect Biol

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In this article, the term "early microbial evolution" refers to the phase of biological history from the emergence of life to the diversification of the first microbial lineages. In the modern era (since we knew about archaea), three debates have emerged on the subject that deserve discussion: (1) thermophilic origins versus mesophilic origins, (2) autotrophic origins versus heterotrophic origins, and (3) how do eukaryotes figure into early evolution. Here, we revisit those debates from the standpoint of newer data. We also consider the perhaps more pressing issue that molecular phylogenies need to recover anaerobic lineages at the base of prokaryotic trees, because O 2 is a product of biological evolution; hence, the first microbes had to be anaerobes. If molecular phylogenies do not recover anaerobes basal, something is wrong. Among the anaerobes, hydrogen-dependent autotrophs-acetogens and methanogenslook like good candidates for the ancestral state of physiology in the bacteria and archaea, respectively. New trees tend to indicate that eukaryote cytosolic ribosomes branch within their archaeal homologs, not as sisters to them and, furthermore tend to root archaea within the methanogens. These are major changes in the tree of life, and open up new avenues of thought. Geochemical methane synthesis occurs as a spontaneous, abiotic exergonic reaction at hydrothermal vents. The overall similarity between that reaction and biological methanogenesis fits well with the concept of a methanogenic root for archaea and an autotrophic origin of microbial physiology.

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Section: Hot Debates Ii: Carbon Metabolismmentioning

confidence: 99%

Early Microbial Evolution: The Age of Anaerobes

Martin

Sousa

2015

Cold Spring Harb Perspect Biol

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“…They have been found in great quantities (to form up to a few percent of the organic carbon; for a review see e.g. Sephton 2002) in several meteorites, specifically in those believed to be the most primitive ones, i.e. the carbonaceous chondrites.…”

Section: Introductionmentioning

confidence: 99%

About the detectability of glycine in the interstellar medium

Lattelais

Pauzat

Pilmé

et al. 2011

A&A

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Context. Glycine, the simplest of aminoacids, has been found in several carbonaceous meteorites. It remains unclear, however, wether glycine is formed in the interstellar medium (ISM) and therefore available everywhere in the Universe. For this reason, radioastronomers have searched for many years unsuccessfully to detect glycine in the ISM. Aims. We provide possible guidelines to optimize the return of these searches. Since, for most of the species observed so far in the ISM, the most abundant isomer of a given generic chemical formula is the most stable one (minimum energy principle (MEP)), we assess whether neutral glycine is the best molecule to search for or whether one of its isomers/conformers or ionic, protonated, or zwitterionic derivatives would have a higher probability of being detected. Methods. The question of the relative stability of these different species is addressed by means of quantum density functional theory (DFT) simulations within the hybrid B3LYP formalism. Each fully optimized structure is verified as a stationary point by means of a vibrational analysis. A comprehensive screening of 32 isomers/conformers of the C 2 H 5 O 2 N chemical formula (neutral, negative, and positive ions together with the corresponding protonated species and the possible zwitterionic structures) is carried out. In the sensitive case of the neutral compounds, more accurate relative energies were obtained by means of high level post Hartree-Fock coupled cluster calculations with large basis sets (CCSD(T)/cc-pVQZ). Results. We find that neutral glycine is not the most stable isomer and, therefore, probably not the most abundant one, which might explain why it has escaped detection so far. We find instead that N-methyl carbamic acid and methyl carbamate are the two most stable isomers and, therefore, probably the two most abundant ones. Among the non-neutral forms, we found that glycine is the most stable isomer only if protonated or zwitterionic if present in interstellar ices. Conclusions. Assuming that MEP can be applied to optimize our search for glycine, our conclusion is that this search will remain extremely difficult with the present instruments and we propose searching instead for other examples among the most stable isomers.

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“…PAHs are composed of aromatic rings and characterized by high stability against radiation, in particular when in peri-condensed (compact) form. The insoluble carbon fraction of carbonaceous meteorites contains predominantly solid aromatic carbon networks; soluble PAHs are also found in concentrations of *50 ppm (Sephton 2002). The abundance and stability of PAHs and their ubiquitous presence in space environment make them interesting target molecules.…”

Section: Searching For Organic Materials On Marsmentioning

confidence: 99%

Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota

Ehrenfreund

Röling²,

Thiel

et al. 2011

International Journal of Astrobiology

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Several robotic exploration missions will travel to Mars during this decade to investigate habitability and the possible presence of life. Field research at Mars analogue sites such as desert environments can provide important constraints for instrument calibration, landing site strategies and expected life detection targets. We have characterized the mineralogy, organic chemistry and microbiology of ten selected sample sites from the Utah desert in close vicinity to the Mars Desert Research Station (MDRS) during the EuroGeoMars 2009 campaign (organized by International Lunar Exploration Working Group (ILEWG), NASA Ames and ESA ESTEC). Compared with extremely arid deserts (such as the Atacama), organic and biological materials can be identified in a larger number of samples and subsequently be used to perform correlation studies. Among the important findings of this field research campaign are the diversity in the mineralogical composition of soil samples even when collected in close proximity, the low abundances of detectable polycyclic aromatic hydrocarbons (PAHs) and amino acids and the presence of biota of all three domains of life with significant heterogeneity. An extraordinary variety of putative extremophiles, mainly Bacteria and also Archaea and Eukarya was observed. The dominant factor in measurable bacterial abundance seems to be soil porosity and lower small (clay-sized) particle content. However, correlations between many measured parameters are difficult to establish. Field research conducted during the EuroGeoMars 2009 campaign shows that the geological history and depositional environment of the region, as well as the mineralogy influence the ability to detect compounds such as amino acids and DNA. Clays are known to strongly absorb and bind organic molecules often preventing extraction by even sophisticated laboratory methods. Our results indicate the need for further development and optimization of extraction procedures that release biological compounds from host matrices to enable the effective detection of biomarkers during future sampling campaigns on Earth and Mars.

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Organic compounds in carbonaceous meteorites

Cited by 610 publications

References 168 publications

Early Microbial Evolution: The Age of Anaerobes

Early Microbial Evolution: The Age of Anaerobes

About the detectability of glycine in the interstellar medium

Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota

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