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  • 1
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    Organic chemistry of Murchison meteorite: Carbon isotopic fractionation (1986)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.
    Keywords: ASTROPHYSICS
    Type: NASA, Washington Second Symposium on Chemical Evolution and the Origin and Evolution of Life; p 40
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  • 2
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    The possible role of solid surface area in condensation reactions during chemical evolution - Reevaluation (1976)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Using surface concentration and reaction rate as the main criteria for the feasibility of condensation reactions, four types of prebiotic environments were analyzed: (1) an ocean-sediment system, (2) a dehydrated lagoon bed produced by evaporation, (3) the surface of a frozen sediment, and (4) a fluctuating system where hydration (rainstorms, tidal variations, flooding) and dehydration (evaporation) take place in a cyclic manner. With the possible exception of nucleotides, low adsorption of organomonomers on sediment surfaces of a prebiotic ocean (pH 8) is expected, and significant condensation is considered unlikely. In dehydrated and frozen systems, high surface concentrations are probable and condensation is more likely. In fluctuating environments, condensation rates will be enhanced and the size distribution of the oligomers formed during dehydration may be influenced by a 'redistribution mechanism' in which adsorbed oligomers and monomers are desorbed and redistributed on the solid surface during the next hydration-dehydration cycle.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 8; 4, 19; 1976
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  • 3
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    Laser microprobe characterization of C species in Interplanetary Dust Particles (IDP) (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Preliminary results of a study whose aim is the characterization of carbon (C) species in microvolumes of materials by means of laser ionization mass spectrometry (LIMS) are presented. The LIMS instrument employs a pulsed UV laser to produce nearly instantaneous vaporization and ionization of materials, followed by acceleration and time-of-flight analysis of the ions produced. LIMS provides a survey technique with nearly simultaneous acquisition of mass spectra covering the entire elemental range. The main limitation of the LIMS technique at present is its limited ability to perform quantitative analysis, due in part to insufficient knowledge of the mechanism of laser-solid interaction. However, considerable effort is now being directed at making LIMS a more quantitative technique. A variety of different C samples, both natural and man made were analyzed to establish the ability of LIMS to differentiate among the various C phases. The results of preliminary analyses performed on meteoritical and interplanetary dust samples are also presented. The C standards selected for the LIMS characterization range from essentially amorphous soot to diamond, which exhibits the highest degree of ordering.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst. Trajectory Determinations and Collection of Micrometeoroids on the Space Station; p 77-79
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  • 4
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    The carbon chemistry of meteorites: Relationships to comets (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Workshop on Analysis of Returned Comet Nucleus Samples; p 13-14
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  • 5
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    Adsorption and recombination of hydrogen atoms on a model graphite surface (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The adsorption and recombination of atomic hydrogen on a model graphite grain have been examined in a series of calculations in which a modified, iterative, extended Hueckel program was used. The hydrogen atom is found to be chemisorbed at a site with a zero-point binding energy of 0.7 eV and at an equilibrium distance of 2.25 A above the site. Despite a barrier of about 0.4 eV between adjacent sites, calculations suggest that at temperatures as low as 10 K, an H atom will tunnel through to adjacent sites in less than one nanosecond. However, a potential barrier to the recombination of two hydrogen atoms has been found which displays high sensitivity to the mutual arrangement of the two hydrogen atoms with respect to the graphite surface. Results show that at very low temperatures, recombinations can occur only by tunneling. Consistent with experiment, the region in which H2 begins to form exhibits a repulsive potential with respect to possible chemisorption of the incipient H2 entity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 243-250
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  • 6
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    Evaluation of the Strecker synthesis as a source of amino acids on carbonaceous chondrites (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The Strecker synthesis (SS) has been proposed as the source of amino acids (AA) formed during aqueous alteration of carbonaceous chondrites. It is postulated that the aldehyde and ketone precursors of the meteoritic AA originated in interstellar syntheses and accreted on the meteorite parent body along with other reactant species in cometesimal ices. The SS has been run with formaldehyde, acetyldehyde, propionaldehyde, acetone, and methyl ketone as starting materials. To study the effect of minerals on the reaction, the SS was run in the presence and absence of dust from the Allende meteorite using deuterated aldehydes and ketones as starting materials. The products were studied by GC/MS. With the exception of glycine, the retention of deuterium in the AA was greater than 90 pct. Some D exchange with water does occur, however, and determination of the rate of exchange as a function of pH and temperature may allow some bounds to be placed on the duration of parent body aqueous alteration. The retention of D by the AA under conditions studied thus far is consistent with the model that a SS starting from interstellar aldehydes and ketones led to the production of meteoritic AA.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Abstracts for the 54th Annual Meeting of the Meteoritical Society; p 132
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  • 7
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    Origin of life (1985)
    In:  CASI
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    Publication Date: 2016-06-07
    Description: The pathways of organic chemical synthesis, the chemical evolution on the early Earth leading to life was constrained by the development of the planet by accretion and core formation. The accretion and differentiation into the core-mantle-crust-atmosphere system strongly influenced the temperature and composition of the atmosphere, surface, and interior; but large gaps persist in our understanding of these processes. The time-span over which Earth acquired its volatiles, the composition of these volatiles, and the conditions under which outgassing of volatiles occurred to form the atmosphere, are unknown. Uncertainties in existing models for Earth accretion and early planetary development allows a wide range of possible prebiotic atmospheric compositions at the time and temperature when liquid water appeared and thermally-labile organic compounds could survive. These compositions range from strongly reducing atmospheres to mildly reducing ones.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: NASA, Washington The Global Sulfur Cycle; p 11-13
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  • 8
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    The Strecker synthesis from interstellar precursors as a source of amino acids in carbonaceous chondrites: Deuterium retention during synthesis (1994)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Amino acids in the Murchison carbonaceous chondrite are anomalously enriched in deuterium. Synthesis in Strecker reactions from D-enriched interstellar precursors during low temperature aqueous alteration of the parent body has been proposed by Cronin et al. (1988) to account for the isotopic observations. To test this hypothesis, we have measured the retention of deuterium in the glycine, alanine, and alpha-amino isobutyric acid produced, respectively, by reactions of formaldehyde-D2, acetaldehyde-D4, and acetone-D6 with HCN and NH3 in water.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Origins of Life and Evolution of the Biosphere (ISSN 0169-6149); 24; 2-4; p. 113-114
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  • 9
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    Carbon in Comet Halley dust particles (1994)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Comets are small bodies of the solar system containing primarily a mixture of frozen gases and carbonaceous and mineral grains. They are likely to preserve volatile mineral from cold regions of the protosolar nebula and remnants of interstellar dust and gas. More than 2500 mass spectra of cometary grains with masses in the range 5 x 10 exp -17 to 5 x 10 exp -12 g were measured in situ by PUMA1 and PUMA2 mass spectrometers on board the VEGA spacecraft during flyby missions to Comet Halley. In this paper, we discuss different organic and inorganic C-containing components discovered so far in Comet Halley dust particles, the nature and abundance of which provide information about possible astrophysical sources of C and constrain models of interstellar grains.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Workshop on the Analysis of Interplanetary Dust Particles; p 22-24
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  • 10
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    Mass and spatial distribution of carbonaceous component in Comet Halley (1993)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Cometary grains containing large amounts of carbon and/or organic matter were discovered by in situ measurements of cometary dust composition during VEGA and GIOTTO fly-by missions. In accordance with the classification for the data of PUMA-1 and PUMA-2 mass-spectrometers on board the VEGA spacecraft, particles with a ratio of C to any rock-forming element (Mg, Si, Fe, Ca etc.) greater than 10, were categorized as CHON. There are 464 such particles in PUMA-1 data and 51 in PUMA-2 data. Application of cluster analysis to these grains revealed several distinct compositional classes, namely: (H,C,N,O), (H,C,N), (H,C), (H,C,O), (C,N), (C,O), (C,N,O), and (C). Similar classes were identified among particles analyzed by PIA. Also, about a third of all particles fell into groups (H) and (O) characterized by abundances of these elements beyond chemically reasonable limits.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 501-502
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