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  • 1
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    A kinetic estimate of the free aldehyde content of aldoses (2000)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The relative free aldehyde content of eight hexoses and four pentoses has been estimated within about 10% from the rate constants for their reaction with urazole (1,2,4-triazole-3,5-dione). These values of the percent free aldehyde are in agreement with those estimated from CD measurements, but are more accurate. The relative free aldehyde contents for the aldoses were then correlated to various literature NMR measurements to obtain the absolute values. This procedure was also done for three deoxyaldoses, which react much more rapidly than can be accounted for by the free aldehyde content. This difference in reactivity between aldoses and deoxyaldoses is due to the inductive effect of the H versus the OH on C-2'. This may help explain why deoxyribonucleosides hydrolyze much more rapidly than ribonucleosides.
    Keywords: Exobiology
    Type: Carbohydrate research (ISSN 0008-6215); Volume 329; 2; 359-65
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  • 2
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    Alternative bases in the RNA world: the prebiotic synthesis of urazole and its ribosides (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Urazole is a five-membered heterocyclic compound which is isosteric with uracil's hydrogen-bonding segment. Urazole reacts spontaneoulsy with ribose (and other aldoses) to give a mixture of four ribosides: alpha and beta pyranosides and furanosides. This reaction occurs in aqueous solution at mild temperatures. Thermodynamic and kinetic parameters for the reaction of urazole with ribose were determined. In contrast, uracil is completely unreactive with ribose under these conditions. Urazole's unusual reactivity is ascribed to the hydrazine portion of the molecule. Urazole can be synthesized from biuret and hydrazine under prebiotic conditions. The prebiotic synthesis of guanazole, which is isosteric in part to diaminopyrimidine and cytosine, is accomplished from dicyandiamide and hydrazine. Kinetic parameters for both prebiotic reactions were measured. Urazole and guanazole are transparent in the UV, which would be a favorable property in the absence of an ozone layer on the early Earth. Urazole makes hydrogen bonds with adenine in DMSO similar to those of uracil, as established by H NMR. All of these properties make urazole an attractive potential precursor to uracil and guanazole a potential precursor to cytosine in the RNA or pre-RNA world.
    Keywords: Exobiology
    Type: Journal of molecular evolution (ISSN 0022-2844); Volume 38; 549-57
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  • 3
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    Attempted prebiotic synthesis of pseudouridine (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Pseudouridine is a modified base found in all tRNA and rRNA. Hence, it is reasonable to think that pseudouridine was important in the early evolution, if not the origin, of life. Since uracil reacts rapidly with formaldehyde and other aldehydes at the C-5 position, it is plausible that pseudouridine could be synthesized in a similar way by the reaction of the C-5 of uracil with the C-1 of ribose. The determining factor is whether the ribose could react with the uracil faster than ribose decomposes. However, both rates are determined by the amount of free aldehyde in the ribose. Various plausible prebiotic reactions were investigated and none showed pseudouridine above the detection limit (〈0.01%). Only unreacted uracil and ribose decomposition products could be observed. Thus the rate of addition of ribose to uracil is much slower than the decomposition of ribose under any reasonable prebiotic conditions. Unless efficient non-biological catalysts for any of these reactions exist, pseudouridine would not have been synthesized to any significant extent without the use of biologically produced enzymes.
    Keywords: Exobiology
    Type: Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life (ISSN 0169-6149); Volume 27; 4; 345-55
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  • 4
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    Amino Acid Analyses of Acid Hydrolysates in Desert Varnish (2001)
    In:  CASI
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    Publication Date: 2005-08-02
    Description: There has long been a debate as to whether rock varnish deposits are microbially mediated or are deposited by inorganic processes. Varnished rocks are found throughout the world primarily in arid and semi-arid regions. The varnish coats are typically up to 200 microns thick and are composed of clays and alternating layers enriched in manganese and iron oxides. The individual layers range in thickness from 1 micron to greater than 10 microns and may continue laterally for more than a 100 microns. Overlapping botryoidal structures are visible in thin section and scanning electron micrographs. The coatings also include small amounts of organic mater and detrital grains. Amino-acid hydrolysates offer a means of assessing the organic composition of rock varnish collected from the Sonoran Desert, near Phoenix, AZ. Chromatographic analyses of hydrolysates from powdered samples of rock varnish suggest that the interior of rock varnish is relatively enriched in amino acids and specifically in d-alanine and glutamic acid. Peptidoglycan (murein) is the main structural component of gram-positive bacterial cell walls. The d-enantiomer of alanine and glutamic acid are specific to peptidoglycan and are consequently an indicator for the presence of bacteria. D-alanine is also found in teichoic acid which is only found in gram-positive bacteria. Several researchers have cultured bacteria from the surface of rock varnish and most have been gram-positive, suggesting that gram-positive bacteria are intimately associated with varnish coatings and may play a role in the formation of varnish coatings.
    Keywords: Exobiology
    Type: General Meeting of the NASA Astrobiology Insititute; 125
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  • 5
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    Organic Synthesis in Simulated Interstellar Ice Analogs (2001)
    In:  CASI
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    Publication Date: 2005-08-02
    Description: Comets and carbonaceous micrometeorites may have been significant sources of organic compounds on the early Earth. Ices on grains in interstellar dense molecular clouds contain a variety of simple molecules as well as aromatic molecules of various sizes. While in these clouds the icy grains are processed by ultraviolet light and cosmic radiation which produces more complex organic molecules. We have run laboratory simulations to identify the types of molecules which could have been generated photolytically in pre-cometary ices. Experiments were conducted by forming various realistic interstellar mixed-molecular ices with and without polycyclic aromatic hydrocarbons (PAHs) at approx. 10 K under high vacuum irradiated with UV light from a hydrogen plasma lamp. The residue that remained after warming to room temperature was analyzed by HPLC, and by laser desorption mass spectrometry. The residue contains several classes of compounds which may be of prebiotic significance.
    Keywords: Exobiology
    Type: General Meeting of the NASA Astrobiology Insititute; 7-8
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  • 6
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    The Origin of Primitive Cells, Nutrient Intake, and Non-Enzymatic Elongation of Encapsulated Nucleotides (2009)
    In:  CASI
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    Publication Date: 2018-06-06
    Description: Fatty acids and fatty alcohols are commonly found in experiments simulating the prebiotic 'soup'. These amphiphiles can be synthesized under prebiotic conditions, at least as long as the molecules are chemically relatively simple and do not need to be enantiomerically pure. In the context of topical origin-of-life theories, two distinct formation pathways for amphiphiles have been described; one related to geophysical sites, such as marine hydrothermal systems, and another to extraterrestrial sources, such as the proto-solar nebula, which was fed by interplanetary and interstellar nebulae. The chemical analysis of each provides individual characteristic challenges.
    Keywords: Exobiology
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  • 7
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    Amino Acids in the Antarctic Martian Meteorite MIL03346 (2005)
    In:  CASI
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    Publication Date: 2017-10-02
    Description: The report by McKay et al. that the Martian meteorite ALH84001 contains evidence for life on Mars remains controversial. Of central importance is whether ALH84001 and other Antarctic Martian meteorites contain endogenous organic compounds. In any investigation of organic compounds possibly derived from Mars it is important to focus on compounds that play an essential role in biochemistry as we know it and that have properties such as chirality which can be used to distinguish between biotic versus abiotic origins. Amino acids are one of the few compounds that fulfill these requirements. Previous analyses of the Antarctic Martian meteorites ALH84001 and EETA79001 have shown that these meteorites contain low levels of terrestrial amino acid contamination derived from Antarctic ice meltwater. Here we report preliminary amino acid investigations of a third Antarctic Martian meteorite MIL03346 which was discovered in Antarctica during the 2003-04 ANSMET season. Additional information is included in the original extended abstract
    Keywords: Exobiology
    Type: Lunar and Planetary Science XXXVI, Part 7; LPI-Contrib-1234-Pt-7
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  • 8
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    The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices (2002)
    In:  CASI
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    Publication Date: 2018-06-06
    Description: Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids.
    Keywords: Astrophysics
    Type: Proceedings of the NASA Laboratory Astrophysics Workshop; 198-200; NASA/CP-2002-211863
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  • 9
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    Distinct Distribution of Purines in CM and CR Carbonaceous Chondrites (2010)
    In:  Other Sources
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    Publication Date: 2018-06-06
    Description: Carbonaceous meteorites contain a diverse suite of organic molecules and delivered pre biotic organic compounds, including purines and pyrimidines, to the early Earth (and other planetary bodies), seeding it with the ingredients likely required for the first genetic material. We have investigated the distribution of nucleobases in six different CM and CR type carbonaceous chondrites, including fivc Antarctic meteorites never before analyzed for nucleobases. We employed a traditional formic acid extraction protocol and a recently developed solid phase extraction method to isolate nucleobases. We analyzed these extracts by high performance liquid chromatography with UV absorbance detection and tandem mass spectrometry (HPLC-UV -MS/MS) targeting the five canonical RNAIDNA bases and hypoxanthine and xanthine. We detected parts-per-billion levels of nucleobases in both CM and CR meteorites. The relative abundances of the purines found in Antarctic CM and CR meteorites were clearly distinct from each other suggesting that these compounds are not terrestrial contaminants. One likely source of these purines is formation by HCN oligomerization (with other small molecules) during aqueous alteration inside the meteorite parent body. The detection of the purines adenine (A), guanine (0), hypoxanthine (HX), and xanthine (X) in carbonaceous meteorites indicates that these compounds should have been available on the early Earth prior to the origin of the first genetic material.
    Keywords: Exobiology
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  • 10
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    The Interstellar Production of Biologically Important Organics (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: One of the primary tasks of the Astrochemistry Laboratory at Ames Research Center is to use laboratory simulations to study the chemical processes that occur in dense interstellar clouds. Since new stars are formed in these clouds, their materials may be responsible for the delivery of organics to new habitable planets and may play important roles in the origin of life. These clouds are extremely cold (less than 50 kelvin), and most of the volatiles in these clouds are condensed onto dust grains as thin ice mantles. These ices are exposed to cosmic rays and ultraviolet (UV) photons that break chemical bonds and result in the production of complex molecules when the ices are warmed (as they would be when incorporated into a star-forming region). Using cryovacuum systems and UV lamps, this study simulates the conditions of these clouds and studies the resulting chemistry. Some of the areas of progress made in 1999 are described below. It shows some of the types of molecules that may be formed in the interstellar medium. Laboratory simulations have already confirmed that many of these compounds are made under these conditions.
    Keywords: Astrophysics
    Type: Research and Technology 1999; 116-117; NASA/TM-2000-209618
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