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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 412 (2001), S. 61-64 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Nitrogen is an essential element for life and is often the limiting nutrient for terrestrial ecosystems. As most nitrogen is locked in the kinetically stable form, N2, in the Earth's atmosphere, processes that can fix N2 into biologically available forms—such as ...
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 45 (2000), S. 419-424 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Bisphenol-A polycarbonate (PC) was γ-irradiated under vacuum at doses from 125 to 1000 kGy. Gases formed were analyzed by gas chromatography - mass spectrometry, and their radiation-chemical yields (G) were calculated. The total G value of gases was equal to 1.00 molec/100 eV, and main products of PC radiolysis were carbon monoxide and hydrogen, their G = 0.87 and 0.08, respectively. Traces of methane, carbon dioxide, acetaldehyde and acetone were detected at doses above 300 kGy. It has been found that acetaldehyde and acetone were produced practically by radiolysis of carbon monoxide - hydrogen mixture evolved from the irradiated PC. Mechanism of gaseous products formation by the PC irradiation has been discussed.
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  • 3
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a computer model calculation for the racemization of a possible excess of amino acids in the icy fraction of comet nuclei bring about by ionizing radiation released during the decay of26Al,40K,235U,238U and232Th. The model takes into account a total of 110 chemical reactions, of which 91 are needed to explain the radiation chemical processing of the major constituents of comet nuclei (Navarro-Gonzálezet al., 1992) and 19 are necessary to simulate the radiolysis of glycine/alanine mixtures in aqueous solutions (Navarro-Gonzálezet al., 1994 and 1996). It is predicted that an enantiomeric excess of alanine would not be destroyed by radioracemization during the decay of embedded radionuclides. Nevertheless, this enantiomeric excess could be attenuated by the formation of racemic amino acids in the interior of comet nuclei as a result of the radiation-induced polymerization of HCN.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 236 (1996), S. 61-75 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The available literature on sources, chemical composition, and importance of dust particles for the origins of life is analyzed. The most abundant sources of dust on the early terrestrial planets are sedimentation of interplanetary dust, meteoritic/cometary impacts, and volcanic eruptions. Interplanetary dust can originate directly from interstellar space, from evaporation of cometary bodies, from collisional destruction of asteroidal and meteoritic bodies, and nucleation in sunspots. Many rather complex organic species, including those of prebiotic interest, have been identified in the interstellar medium and cometary dust. Some of them are believed to formvia catalytic processes on the surfaces of dust particles. However, the mechanisms are not known, and even simulating experiments are difficult to perform due to insufficient knowledge of physical conditions in the space media and of chemical composition and properties of the dust. Besides the catalytic roles, cometary dust is believed to be the best delivery vehicle for organic matter of space origin to the atmospheres of terrestrial planets. Abundant sources of catalytically active fine dust can be volcanoes. Various organic and biological compounds have been found in terrestrial volcanic gases and ash, which are assumed to formvia the catalytic Fischer-Tropsch reactions. At present the eruptions on the Earth provide a unique opportunity to observein situ the formation of organic matter, and knowledge of the ash composition and local conditions allows to perform simulating experiments.
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  • 5
    ISSN: 1573-0689
    Keywords: Alanine ; Amino acids ; Chirality ; Glycine ; Ionizing radiation ; Kinetics ; Primitive hydrosphere ; Racemization ; Radiolysis ; Radioracemization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Akaboshi et al. (1990) has found an unexpected protection of the achiral amino acid, glycine, towards ionizing radiation at the expense of the selective destruction of the chiral amino acids, alanine and aspartic acid. The present work examines the mechanism of this protection for the case of alanine. We have developed a computer model for the radiolysis of glycine, alanine and glycine-alanine mixtures in aqueous solution. It is established that this protection is due in part to the reaction of the α-radical of glycine with alanine to regenerate a more stable α-radical, according to the following reaction, $$ \cdot CH(NH_3^ + )CO_2^ - + CH_3 CH(NH_3^ + )CO_2^ - \to CH_2 (NH_3^ + )CO_2^ - + CH_3 \dot C(NH_3^ + )CO_2^ -$$ The rate constant of this reaction was estimated to be ≤104M-1s-1. The implications for this selective protection of glycine are considered for a hypothetical case in which there would be an enrichment of about 10% ofL-alanine in the primitive ocean and taking the glycine/alanine ratios obtained in CH4-and CO2- dominated atmospheres using electric discharge experiments. It is predicted that alanine would be rapidly destroyed and radioracemized in spite of the fact that the concentration of alanine is equal or significantly lower than that of glycine. Assuming that chiral amino acids were a prerequisite for the origin of life, it can be deduced that life could have appeared in a relatively short period of time unless there was a constant supply of optical amino acids from extraterrestrial sources.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 26 (1996), S. 363-364 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 26 (1996), S. 534-535 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 28 (1998), S. 105-108 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 28 (1998), S. 167-193 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract To evaluate the types of amino acid thermal transformations caused by silicate materials, we studied the volatilization products of Aib, L-Ala, L-Val and L-Leu under temperatures of up to 270 °C in the presence of silica gel as a model catalyst and pulverized basaltic lava samples. It was found that silica gel catalyzes nearly quantitative condensation of amino acids, where piperazinediones are the major products, whereas lava samples have much lower catalytic efficiency. In addition bicyclic and tricyclic amidines and several products of their subsequent thermal decomposition have been identified using the coupled technique of GC-FTIR-MS and HPLC-PB-MS, with auxiliary computer simulation of IR spectra and NMR spectroscopy. The decomposition is due to dehydrogenation, elimination of the alkyl substituents and dehydration as well as cleavage of the bicyclic ring system. The imidazole ring appears to be more resistant to thermal decomposition as compared to the pyperazine moiety, giving rise to the formation of different substituted imidazolones. The amidines were found to hydrolyze under treatment with concentrated HCl, releasing the starting amino acids and thus behaving as amino acid anhydrides. The thermal transformations cause significant racemization of amino acid residues. Based on our observations, the formation of amidine-type products is suggested to be rather common in the high-temperature experiments on amino acid condensation.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Origins of life and evolution of the biospheres 28 (1998), S. 131-153 
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract An accurate and precise knowledge of the amount of energy introduced into prebiotic discharge experiments is important to understand the relative roles of different energy sources in the synthesis of organic compounds in the primitive Earth's atmosphere and other planetary atmospheres. Two methods widely used to determine the power of spark discharges were evaluated, namely calorimetric and oscilloscopic, using a chemically inert gas. The power dissipated by the spark in argon at 500 Torr was determined to be 2.4 (+12%/_17%) J s_1 by calorimetry and 5.3 (± 15%) J s_1 by the oscilloscope. The difference between the two methods was attributed to (1) an incomplete conversion of the electric energy into heat, and (2) heat loss from the spark channel to the connecting cables through the electrodes. The latter contribution leads to an unwanted effect in the spark channel by lowering the spark product yields as the spark channel cools by mixing with surrounding air and by losing heat to the electrodes. Once the concentrations of the spark products have frozen at the freeze-out temperature, any additional loss of heat from the spark channel to the electrodes has no consequence in product yields. Therefore, neither methods accurately determines the net energy transferred to the system. With a lack of a quantitative knowledge of the amount of heat loss from the spark channel during the interval from ignition of the spark to when the freeze-out temperature is reached, it is recommended to derive the energy yields of the spark products from the mean value of the two methods with the uncertainty being their standard deviation. For the case of argon at 500 Torr, this would be 3.8 (±50%) J s_1.
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