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John R. Cronin - One of the best experts on this subject based on the ideXlab platform.
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Alanine enantiomers in the Murchison Meteorite
Nature, 1998Co-Authors: Sandra Pizzarello, John R. CroninAbstract:Engel and Macko 1 have reported that alanine indigenous to the Murchison Meteorite has an l-enantiomer excess of about 33%. Furthermore, they reported very similar δ15nitrogen values for l-alanine and d-alanine; these values are quite high in comparison with those of terrestrial amino acids. On this basis, they argued that contamination of the Meteorite by terrestrial l-alanine can be ruled out because, if it contributed to the l-enantiomer excess, the lower 15N content of terrestrial l-alanine would significantly lower the δ15N value that they observed for l-alanine.
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Characteristics and formation of amino acids and hydroxy acids of the Murchison Meteorite.
Advances in Space Research, 1995Co-Authors: John R. Cronin, G.w Cooper, Sandra PizzarelloAbstract:Abstract Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison Meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the α-amino acids and α-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the Meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.
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linear and cyclic aliphatic carboxamides of the Murchison Meteorite hydrolyzable derivatives of amino acids and other carboxylic acids
Geochimica et Cosmochimica Acta, 1995Co-Authors: George Cooper, John R. CroninAbstract:Abstract Analyses of fractionated aqueous extracts of the Murchison Meteorite by gas chromatographymass spectrometry after silylation with N-methyl-N ( tert -butyldimethylsilyl) trifluoroacetamide have revealed an extensive series of linear and cyclic aliphatic amides. These include monocarboxylic acid amides, dicarboxylic acid monoamides, hydroxy acid amides, lactams, carboxy lactams, lactims, N-acetyl amino acids, and substituted hydantoins. Numerous isomers and homologues through at least C 8 were observed in all cases, except for the N-acetyl amino acids and hydantoins. Carboxy lactams, lactams, hydantoins, and N-acetyl amino acids are converted to amino acids by acid hydrolysis, thus, these compounds qualitatively account for the earlier observation of acid-labile amino acid precursors in meteoritic extracts. Laboratory studies of the spontaneous decomposition of N-carbamyl-α-amino acids and their dehydration products, the 5-substituted hydantoins, have led to the recognition of a series of aqueous phase reactions by which amino acids and cyanic acid/cyanate ion in the primitive parent body might have given rise to several of the observed classes of amides, as well as to monocarboxylic acids, dicarboxylic acids, and hydroxy acids. A previously undescribed reaction of 5-substituted hydantoins with cyanic acid/cyanate ion to give carboxamides of the 5-substituent groups was observed in the course of these studies. The presence of an extensive suite of amides in a CM chondrite appears to be consistent with the interstellar-parent body formation hypothesis for the organic compounds of these Meteorites. The presence of carboxy lactams and lactams along with free amino acids suggests the possibility of further chemical evolution of Meteorite amino acids by thermal polymerization. The cyclic amides, given their potential for hydrogen-bonded pair formation, might be considered candidate bases for a primitive sequence coding system.
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isotopic analyses of nitrogenous compounds from the Murchison Meteorite ammonia amines amino acids and polar hydrocarbons
Geochimica et Cosmochimica Acta, 1994Co-Authors: Sandra Pizzarello, Samuel Epstein, Xiahong Feng, John R. CroninAbstract:The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison Meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 Meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D 93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.
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Molecular and isotopic analyses of the hydroxy acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1993Co-Authors: John R. Cronin, Sandra Pizzarello, Samuel Epstein, R. V. KrishnamurthyAbstract:The hydroxymonocarboxylic acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite were analyzed as their tert-butyldimethylsilyl derivatives using combined gas chromatography-mass spectrometry. The hydroxydicarboxylic acids have not been found previously in Meteorites. Each class of compounds is numerous with carbon chains up to C_8 or C_9 and many, if not all, chain and substitution position isomers represented at each carbon number. The α-hydroxycarboxylic acids and α-hydroxydicarboxylic acids correspond structurally to many of the known meteoritic α-aminocarboxylic acids and α-aminodicarboxylic acids, a fact that supports the proposal that a Strecker synthesis was involved in the formation of both classes of compounds. Isotopic analyses show these acids to be D-rich relative to terrestrial organic compounds as expected; however, the hydroxy acids appear to be isotopically lighter than the amino acids with respect to both carbon and hydrogen. The latter finding would not be expected if both classes of compounds came exclusively from common precursors as would have been the case for a Strecker synthesis.
Sandra Pizzarello - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Cyanide in the Murchison Meteorite
The Astrophysical Journal, 2012Co-Authors: Sandra PizzarelloAbstract:Carbonaceous chondrites are Meteorites that may contain abundant organic materials, including soluble compounds as diverse as amino acids and hydrocarbons. We report here the finding of hydrogen cyanide in the Murchison Meteorite in amounts ≤ 10 ppm. HCN was never searched for in Meteorites and its detection in sizeable amount is surprising in view of the extensive water phase that is recorded by the petrology of this type of Meteorites and could have exhausted their HCN content through multiple reactions. The finding adds to the inventory of simple volatile molecules found in both comets and Meteorites.
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nonracemic isovaline in the Murchison Meteorite chiral distribution and mineral association
Geochimica et Cosmochimica Acta, 2003Co-Authors: Sandra Pizzarello, M E Zolensky, Kendra A TurkAbstract:Abstract The enantiomeric and carbon-isotopic composition of the amino acid isovaline have been analyzed in several samples of the Murchison Meteorite and one sample of the Murray Meteorite. l -Enantiomeric excesses of the amino acid were found to range from 0 to 15.2%, varying significantly both between Meteorite stones and at short distances within a single stone. The upper limit of this range is the largest enantiomeric excess measured to date for a biologically rare meteoritic amino acid and raises doubts that circularly polarized light irradiation could have been the sole cause of amino acids chiral asymmetry in Meteorites. Individual d - and l- isovaline δ13C values ware found to be about +18‰, with no significant differences between the two enantiomers to suggest terrestrial contamination. The amino acid relative abundance also varied between samples, with isovaline/alanine ratios of 0.5 to 6.5. X-ray diffraction analyses of contiguous Meteorite fragments suggest a possible correlation between isovaline and hydrous silicates abundances.
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Alanine enantiomers in the Murchison Meteorite
Nature, 1998Co-Authors: Sandra Pizzarello, John R. CroninAbstract:Engel and Macko 1 have reported that alanine indigenous to the Murchison Meteorite has an l-enantiomer excess of about 33%. Furthermore, they reported very similar δ15nitrogen values for l-alanine and d-alanine; these values are quite high in comparison with those of terrestrial amino acids. On this basis, they argued that contamination of the Meteorite by terrestrial l-alanine can be ruled out because, if it contributed to the l-enantiomer excess, the lower 15N content of terrestrial l-alanine would significantly lower the δ15N value that they observed for l-alanine.
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Characteristics and formation of amino acids and hydroxy acids of the Murchison Meteorite.
Advances in Space Research, 1995Co-Authors: John R. Cronin, G.w Cooper, Sandra PizzarelloAbstract:Abstract Eight characteristics of the unique suite of amino acids and hydroxy acids found in the Murchison Meteorite can be recognized on the basis of detailed molecular and isotopic analyses. The marked structural correspondence between the α-amino acids and α-hydroxy acids and the high deuterium/hydrogen ratio argue persuasively for their formation by aqueous phase Strecker reactions in the Meteorite parent body from presolar, i.e., interstellar, aldehydes, ketones, ammonia, and hydrogen cyanide. The characteristics of the meteoritic suite of amino acids and hydroxy acids are briefly enumerated and discussed with regard to their consonance with this interstellar-parent body formation hypothesis. The hypothesis has interesting implications for the organic composition of both the primitive parent body and the presolar nebula.
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isotopic analyses of nitrogenous compounds from the Murchison Meteorite ammonia amines amino acids and polar hydrocarbons
Geochimica et Cosmochimica Acta, 1994Co-Authors: Sandra Pizzarello, Samuel Epstein, Xiahong Feng, John R. CroninAbstract:The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison Meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 Meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D 93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.
Hiroshi Naraoka - One of the best experts on this subject based on the ideXlab platform.
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bulk chemical characteristics of soluble polar organic molecules formed through condensation of formaldehyde comparison with soluble organic molecules in Murchison Meteorite
Geochemical Journal, 2019Co-Authors: Yuki Isono, S Tachibana, Hiroshi Naraoka, F R Orthousdaunay, Laurette Piani, Yoko KebukawaAbstract:Carbonaceous chondrites contain up to 2 wt% organic carbon, which is present as acid and solvent insoluble solid organic matter (IOM) and solvent soluble organic matter (SOM). The extraterrestrial organic matter should record chemical processes occurred in different environments in the early history of the Solar System, and the role of parent body aqueous alteration in the synthesis or subsequent modification of IOM and SOM still requires accurate constraints. We conducted hydrothermal experiments to simulate the synthesis of organic molecules during aqueous alteration on small bodies. Bulk chemical characteristics of soluble organic matter synthesized from formaldehyde in aqueous solutions were studied to compare them with that of chondritic SOM. We found that the redox state of synthesized organic molecules depends on temperature; the molecules become richer in hydrogen at higher temperatures. This can be explained by a cross-disproportionation reaction between organic molecules and formic acid, which occurs as a side reaction of the aldol condensation and works more effectively at higher temperatures. Comparison of the bulk chemical characteristics between the synthesized molecules and SOM extracted from the Murchison Meteorite with methanol shows that the soluble organic molecules in Murchison are more reduced than the synthesized molecules. Considering the temperature condition for aqueous alteration on the CM parent body that is lower than or equivalent to the experimental temperatures, the reduced nature of Murchison organic molecules requires a reducing environment for them to be formed during hydrothermal alteration or imply that processes other than hydrothermal alteration were responsible for their synthesis. In case of hydrothermal synthesis, reducing conditions might be established by the interaction between water and iron-bearing silicates or metals on the parent body.
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Molecular Evolution of N-Containing Cyclic Compounds in the Parent Body of the Murchison Meteorite
ACS Earth and Space Chemistry, 2017Co-Authors: Hiroshi Naraoka, Yohei Yamashita, Mihoko Yamaguchi, François-régis Orthous-daunayAbstract:Primitive Meteorites contain various classes of organic compounds. Because the molecular distribution in these Meteorites is not fully clarified, we do not yet understand the comprehensive formation mechanism(s) of extraterrestrial organic compounds. In this study, diverse and abundant alkylated homologues of N-containing cyclic compounds were identified in the methanol extract of the Murchison Meteorite by electrospray ionization using high-performance liquid chromatography/ultrahigh-resolution mass spectrometry. More than 600 positive ions were assigned to CnHmN+ and CnHmN2+, in which saturated and unsaturated alkylated pyridines and alkylimidazoles are predominant. Both can be synthesized from aldehydes and ammonia through aldol condensation and imine formation under an alkaline environment. Further redox reactions could have proceeded to make these molecules evolve to various CHN compounds, including alkylpiperidines and pyridine carboxylic acids. This study indicates that aldol condensation and formo...
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a new family of extraterrestrial amino acids in the Murchison Meteorite
Scientific Reports, 2017Co-Authors: Toshiki Koga, Hiroshi NaraokaAbstract:The occurrence of extraterrestrial organic compounds is a key for understanding prebiotic organic synthesis in the universe. In particular, amino acids have been studied in carbonaceous Meteorites for almost 50 years. Here we report ten new amino acids identified in the Murchison Meteorite, including a new family of nine hydroxy amino acids. The discovery of mostly C3 and C4 structural isomers of hydroxy amino acids provides insight into the mechanisms of extraterrestrial synthesis of organic compounds. A complementary experiment suggests that these compounds could be produced from aldehydes and ammonia on the Meteorite parent body. This study indicates that the meteoritic amino acids could be synthesized by mechanisms in addition to the Strecker reaction, which has been proposed to be the main synthetic pathway to produce amino acids.
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Molecular Evolution of N‑Containing Cyclic Compounds in the Parent Body of the Murchison Meteorite
2017Co-Authors: Hiroshi Naraoka, Yohei Yamashita, Mihoko Yamaguchi, François-régis Orthous-daunayAbstract:Primitive Meteorites contain various classes of organic compounds. Because the molecular distribution in these Meteorites is not fully clarified, we do not yet understand the comprehensive formation mechanism(s) of extraterrestrial organic compounds. In this study, diverse and abundant alkylated homologues of N-containing cyclic compounds were identified in the methanol extract of the Murchison Meteorite by electrospray ionization using high-performance liquid chromatography/ultrahigh-resolution mass spectrometry. More than 600 positive ions were assigned to CnHmN+ and CnHmN2+, in which saturated and unsaturated alkylated pyridines and alkylimidazoles are predominant. Both can be synthesized from aldehydes and ammonia through aldol condensation and imine formation under an alkaline environment. Further redox reactions could have proceeded to make these molecules evolve to various CHN compounds, including alkylpiperidines and pyridine carboxylic acids. This study indicates that aldol condensation and formose reaction with ammonia are an important mechanism for the molecular evolution of N-containing compounds in the asteroid
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two homologous series of alkylpyridines in the Murchison Meteorite
Geochemical Journal, 2014Co-Authors: Yohei Yamashita, Hiroshi NaraokaAbstract:Copyright © 2014 by The Geochemical Society of Japan. extract (Krishnamurthy et al., 1992). The heavy isotope enrichments suggest that the more primitive organic compounds may have originated partly from an interstellar environment. However, the less polar solvent extracts of CCs have rarely been studied, despite their relatively high content of organic compounds. Recently, ultrahighresolution mass spectral analysis on various solvent extracts of the Murchison Meteorite (CM2) was performed by electrospray ionization (ESI) using Fourier transformion cyclotron resonance/mass spectrometry (FT-ICR/MS) to reveal significant chemical diversity with tens of thousands of different mass peaks having CHO, CHOS, CHNO and CHNOS elemental compositions (Schmitt-Kopplin et al., 2010). However, without any chromatographic separation, the detailed chemical structures of the individual compounds present cannot be determined. In particular, the organic compounds with their elemental compositions of CH and CHN were not investigated in spite of their potential importance as primitive organic components because the CH and CHN compounds may have escaped chemical oxidation during parent-body aqueous alteration. In this study, we performed high-performance liquid chromatography/high-resolution mass spectrometry (HPLC/HRMS) analysis of polar solvent extracts of the Murchison Meteorite in order to characterize the more primitive organic compounds.
Samuel Epstein - One of the best experts on this subject based on the ideXlab platform.
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shock induced devolatilization and isotopic fractionation of h and c from Murchison Meteorite some implications for planetary accretion
Earth and Planetary Science Letters, 2001Co-Authors: James A Tyburczy, Thomas J Ahrens, Samuel EpsteinAbstract:Incipient shock-induced devolatilization of Murchison Meteorite occurs upon subjecting samples to a minimum shock stress, or pressure, of about 5 GPa. This pressure is similar to that required to initiate devolatilization of 20% porous serpentine. Upon low velocity impact (61.5 km/s) the solid shocked products were combusted and isotopic analysis of the resulting H_2O and CO_2 was performed. H and ^(13)C are partitioned preferentially over D and ^(12)C, respectively, into the released gas suggesting that the inorganic (mineral) portion of Murchison is devolatilized preferentially over the organic (kerogen) fraction (which is relatively enriched in D and ^(12)C) at the shock pressures studied. These results are combined with previous results on serpentine devolatilization to derive an empirical H fractionation versus devolatilization relation that is used to evaluate the extent of impact-induced isotopic fractionation during planetary accretion. During accretion of the Earth, impact-induced devolatilization and formation of the early primitive atmosphere would have begun at a point where the `growing' Earth achieved a radius in the 480-800 km range. The present experimental results suggest that the Earth's early atmosphere would have been enriched in hydrogen (relative to D) compared to the residual solid, with a fractionation factor of -18 to -23‰. Assuming that current planetary atmospheres have resulted from degassing of planetary interiors after loss of the earliest H-enriched atmosphere, the above degree of isotopic fractionation is not sufficient by itself to explain the large positive δD values of the present Martian and Venusian atmospheres. However, this mechanism in conjunction with tectonic recycling over geologic time could contribute to preferential H loss for Earth and Mars.
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isotopic analyses of nitrogenous compounds from the Murchison Meteorite ammonia amines amino acids and polar hydrocarbons
Geochimica et Cosmochimica Acta, 1994Co-Authors: Sandra Pizzarello, Samuel Epstein, Xiahong Feng, John R. CroninAbstract:The combined volatile bases (ammonia, aliphatic amines, and possibly other bases), ammonia, amino acids, and polar hydrocarbons were prepared from the Murchison Meteorite for isotopic analyses. The volatile bases were obtained by cryogenic transfer after acid-hydrolysis of a hot-water extract and analyzed by combined gas chromatography-mass spectrometry of pentafluoropropionyl derivatives. The aliphatic amines present in this preparation comprise a mixture that includes both primary and secondary isomers through C5 at a total concentration of > or = 100 nmoles g-1. As commonly observed for meteoritic organic compounds, almost all isomers through C5 are present, and the concentrations within homologous series decrease with increasing chain length. Ammonia was chromatographically separated from the other volatile bases and found at a concentration of 1.1-1.3 micromoles g-1 Meteorite. The ammonia analyzed includes contributions from ammonium salts and the hydrolysis of extractable organic compounds, e.g., carboxamides. Stable isotope analyses showed the volatile bases to be substantially enriched in the heavier isotopes, relative to comparable terrestrial compounds delta D 93%) can be inferred for the other bases, which include the amines. Solvent-extractable polar hydrocarbons obtained separately were found to be enriched in 15N (delta 15N = +104%). Total amino acids, prepared from a hydrolyzed hot-water extract by cation exchange chromatography, gave a delta 15N of +94%, a value in good agreement with that obtained previously. Nitrogen isotopic data are also given for amino acid fractions separated chromatographically. The delta 15N values of the Murchison soluble organic compounds analyzed to date fall within a rather narrow range (delta 15N = +94 +/- 8%), an observation consistent with their formation, or formation of their precursors, by interstellar chemistry.
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Molecular and isotopic analyses of the hydroxy acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1993Co-Authors: John R. Cronin, Sandra Pizzarello, Samuel Epstein, R. V. KrishnamurthyAbstract:The hydroxymonocarboxylic acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite were analyzed as their tert-butyldimethylsilyl derivatives using combined gas chromatography-mass spectrometry. The hydroxydicarboxylic acids have not been found previously in Meteorites. Each class of compounds is numerous with carbon chains up to C_8 or C_9 and many, if not all, chain and substitution position isomers represented at each carbon number. The α-hydroxycarboxylic acids and α-hydroxydicarboxylic acids correspond structurally to many of the known meteoritic α-aminocarboxylic acids and α-aminodicarboxylic acids, a fact that supports the proposal that a Strecker synthesis was involved in the formation of both classes of compounds. Isotopic analyses show these acids to be D-rich relative to terrestrial organic compounds as expected; however, the hydroxy acids appear to be isotopically lighter than the amino acids with respect to both carbon and hydrogen. The latter finding would not be expected if both classes of compounds came exclusively from common precursors as would have been the case for a Strecker synthesis.
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isotopic and molecular analyses of hydrocarbons and monocarboxylic acids of the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1992Co-Authors: R. V. Krishnamurthy, Sandra Pizzarello, John R. Cronin, Samuel Epstein, George U YuenAbstract:The monocarboxylic acids and hydrocarbons of the Murchison Meteorite (CM2) were isolated for isotopic analysis. The nonvolatile hydrocarbons were analyzed as crude methanol and benzene-methanol extracts and also after separation by silica gel chromatography into predominantly aliphatic, aromatic, and polar hydrocarbon fractions. The volatile hydrocarbons were obtained after progressive decomposition of the Meteorite matrix by freeze-thaw, hot water, and acid treatment. Molecular analyses of the aromatic hydrocarbons showed them to comprise a complex suite of compounds in which pyrene, fluoranthene, phenanthrene, and acenaphthene were the most abundant components, a result similar to earlier analyses. The polar hydrocarbons also comprise a very complex mixture in which aromatic ketones, nitrogen, and sulfur heterocycles were identified. Both δ^(13)C and δD values were obtained for all preparations. The monocarboxylic acids, aliphatic, aromatic, and polar hydrocarbons, and the indigenous volatile hydrocarbons were found to be D-rich with δD values ranging from about +100 to +1000. The δ^(13)C values ranged overall from −13 to +17. The deuterium enrichment observed in these compounds is suggestive of a relationship to interstellar organic compounds. In two separate analyses, the δD values of the nonvolatile hydrocarbons were observed to increase in the following order: aliphatic < aromatic < polar. This finding is consistent with an early solar system or parent body conversion of aromatic to aliphatic compounds as well as the earlier suggestion of pyrolytic formation of aromatic from aliphatic compounds.
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isotopic analyses of amino acids from the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1991Co-Authors: Sandra Pizzarello, Samuel Epstein, R. V. Krishnamurthy, John R. CroninAbstract:Previous isotopic analyses of the total amino acids of the Murchison Meteorite showed these compounds to be substantially enriched in ^2H, ^(13)C, and ^(15)N relative to terrestrial organic matter. These analyses have been repeated (^2H, ^(13)C) with inclusion of an ultrafiltration step to exclude the possibility that a fine paniculate contaminant carried the isotopic excesses observed in the previous work. In addition, the Meteorite amino acids were chromatographically separated to rule out the possibility that the isotopic enrichment of the Meteorite extract could reside in basic compounds other than amino acids. The results indicate that the Murchison amino acids are truly isotopically unusual, that the isotopic excesses reside in at least several different amino acids, and that the isotopic contents of some of these amino acids reach values of about +40%. (δ^(13)C) and +2500%. (δD). If it is assumed that the high deuterium content of the Meteorite ɑ - amino acids is a result of the synthesis of their molecular precursors by low temperature ion-molecule reactions in an interstellar cloud, their formation by aqueous phase Strecker reactions in the parent body is consistent with their general characteristics and with known parent body processes.
R. V. Krishnamurthy - One of the best experts on this subject based on the ideXlab platform.
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Molecular and isotopic analyses of the hydroxy acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1993Co-Authors: John R. Cronin, Sandra Pizzarello, Samuel Epstein, R. V. KrishnamurthyAbstract:The hydroxymonocarboxylic acids, dicarboxylic acids, and hydroxydicarboxylic acids of the Murchison Meteorite were analyzed as their tert-butyldimethylsilyl derivatives using combined gas chromatography-mass spectrometry. The hydroxydicarboxylic acids have not been found previously in Meteorites. Each class of compounds is numerous with carbon chains up to C_8 or C_9 and many, if not all, chain and substitution position isomers represented at each carbon number. The α-hydroxycarboxylic acids and α-hydroxydicarboxylic acids correspond structurally to many of the known meteoritic α-aminocarboxylic acids and α-aminodicarboxylic acids, a fact that supports the proposal that a Strecker synthesis was involved in the formation of both classes of compounds. Isotopic analyses show these acids to be D-rich relative to terrestrial organic compounds as expected; however, the hydroxy acids appear to be isotopically lighter than the amino acids with respect to both carbon and hydrogen. The latter finding would not be expected if both classes of compounds came exclusively from common precursors as would have been the case for a Strecker synthesis.
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isotopic and molecular analyses of hydrocarbons and monocarboxylic acids of the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1992Co-Authors: R. V. Krishnamurthy, Sandra Pizzarello, John R. Cronin, Samuel Epstein, George U YuenAbstract:The monocarboxylic acids and hydrocarbons of the Murchison Meteorite (CM2) were isolated for isotopic analysis. The nonvolatile hydrocarbons were analyzed as crude methanol and benzene-methanol extracts and also after separation by silica gel chromatography into predominantly aliphatic, aromatic, and polar hydrocarbon fractions. The volatile hydrocarbons were obtained after progressive decomposition of the Meteorite matrix by freeze-thaw, hot water, and acid treatment. Molecular analyses of the aromatic hydrocarbons showed them to comprise a complex suite of compounds in which pyrene, fluoranthene, phenanthrene, and acenaphthene were the most abundant components, a result similar to earlier analyses. The polar hydrocarbons also comprise a very complex mixture in which aromatic ketones, nitrogen, and sulfur heterocycles were identified. Both δ^(13)C and δD values were obtained for all preparations. The monocarboxylic acids, aliphatic, aromatic, and polar hydrocarbons, and the indigenous volatile hydrocarbons were found to be D-rich with δD values ranging from about +100 to +1000. The δ^(13)C values ranged overall from −13 to +17. The deuterium enrichment observed in these compounds is suggestive of a relationship to interstellar organic compounds. In two separate analyses, the δD values of the nonvolatile hydrocarbons were observed to increase in the following order: aliphatic < aromatic < polar. This finding is consistent with an early solar system or parent body conversion of aromatic to aliphatic compounds as well as the earlier suggestion of pyrolytic formation of aromatic from aliphatic compounds.
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isotopic analyses of amino acids from the Murchison Meteorite
Geochimica et Cosmochimica Acta, 1991Co-Authors: Sandra Pizzarello, Samuel Epstein, R. V. Krishnamurthy, John R. CroninAbstract:Previous isotopic analyses of the total amino acids of the Murchison Meteorite showed these compounds to be substantially enriched in ^2H, ^(13)C, and ^(15)N relative to terrestrial organic matter. These analyses have been repeated (^2H, ^(13)C) with inclusion of an ultrafiltration step to exclude the possibility that a fine paniculate contaminant carried the isotopic excesses observed in the previous work. In addition, the Meteorite amino acids were chromatographically separated to rule out the possibility that the isotopic enrichment of the Meteorite extract could reside in basic compounds other than amino acids. The results indicate that the Murchison amino acids are truly isotopically unusual, that the isotopic excesses reside in at least several different amino acids, and that the isotopic contents of some of these amino acids reach values of about +40%. (δ^(13)C) and +2500%. (δD). If it is assumed that the high deuterium content of the Meteorite ɑ - amino acids is a result of the synthesis of their molecular precursors by low temperature ion-molecule reactions in an interstellar cloud, their formation by aqueous phase Strecker reactions in the parent body is consistent with their general characteristics and with known parent body processes.
