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  • 1
    ISSN: 1432-1432
    Keywords: Chiral selection in chemical systems ; Parity nonconservation in weak interactions ; Origin of prebiotic asymmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The decarboxylations of sublimated solidd- andl-leucine by nonpolarized γ-rays give quite different quantum yields, indicating significant selection. The G(CO2) value for thed-isomer is higher than that for thel-isomer by a factor of 2 within a dose range of 103–105 rads. The G value for thedl-racemate is close to that of thed-isomer. The effect vanishes if instead of sublimation, crystallization from aqueous solution is the last preparation step. Our results on sublimated leucine agree well with those reported for γ-induced decarboxylation of solid β-phenylalanine prepared similarly by sublimation. The asymmetry increases with longer cooling periods after irradiation. An intrinsic energy difference due to parity nonconservation between enantiomers is discussed as a possible stereoselective mechanism, with special reference to the prebiotic origin of asymmetry in living matter. Other possible sources of the observed effects are also discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 11 (1978), S. 313-332 
    ISSN: 1432-1432
    Keywords: Evolution ; Optical activity ; Photolysis ; Circularly ; polarized radiation ; Selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Stereoselective physical phenomena and their possible importance for the prevalence of D-sugars and L-aminoacids in living matter are reviewed. A classification is presented according to which a selective force provides a microscopic or macroscopic selection depending on its generality when taken over a macrosystem (a ‘unitary biosphere’ such as the Earth). The microscopic ‘selections’ are not genuine selections because the final sense of asymmetry is here determined by chance, in other words the initial choice is ‘random’, while it is ‘directed’ in the macroscopic selection. Two macroscopic selections appear possible: 1. selection due to an intrinsic energy difference between enantiomorph configurations, 2. selection accomplished by elliptically polarised radiation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine semiempirische SCF-MO-Methode, die PEEL-Methode, wurde zur Untersuchung der Elektronenstruktur sowie von angeregten Zuständen der beiden Eisenverbindungen [Fe(II)-(GMI)3]++ und [Fe(II)-(bipy)3]++ angewendet. Die elektronischen Absorptionsspektren wurden aufgenommen. Die Berechnungen zeigen, daß die trigonale Verzerrung und die Kovalenz berücksichtigt werden müssen, um die Spektren quantitativ zu erklären. Mössbauer-Messungen wurden ebenfalls durchgeführt. Die berechnete Elektronenverteilung am Eisenatom ist in Übereinstimmung mit den Daten der Isomerenverschiebung der Mössbauer-Messungen, wodurch gezeigt wird, daß mit der PEEL-Methode eine realistische Elektronen-Verteilung erhalten wurde.
    Abstract: Résumé Une méthode SCF-MO semi-empirique, la méthode PEEL, a été appliquée à une étude de la structure électronique et des états excités de deux composés ferreux: [Fe(II)-(bipy)3]++ et [Fe(II)-(GMI)3]++. Les spectres d'absorption électronique ont été enregistrés. Les calculs montrent qu'il est nécessaire de rendre compte de la distorsion trigonale et de la covalence pour expliquer ces spectres quantitativement. Des mesures de l'effet Mössbauer ont aussi été effectuées. La population électronique calculée du fer est en bon accord avec les données sur le déplacement isomérique de Mössbauer, ce qui indique que la méthode PEEL fournit une distribution électronique réaliste.
    Notes: Abstract A semi-empirical SCF-MO method, the PEEL method, has been applied in an investigation of the electronic structure and excited states of two iron compounds, [Fe(II)-(GMI)3]++ and [Fe(II)-(bipy)3]++. The electronic absorption spectra have been recorded. The calculations show that it is necessary to account for the trigonal distortion and the covalency in order to explain these spectra quantitatively. Mössbauer measurements have also been performed. The calculated electronic population of the iron is in accord with Mössbauer isomer shift data, indicating that a realistic electron distribution has been obtained by the PEEL method.
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  • 4
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Attempts to characterize nucleic acid-silver interactions raise questions about how the free nucleic acid bases interact with silver ions in dilute aqueous solution. Studies of ultraviolet and infrared dichroism lead to the conclusion that with silver(I) ions in dilute solution adenine forms linear polymers, whereas 1-methyladenine forms dimers. The composition and structure of the complexes are further discussed against the background of the spectroscopic results.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical crystallography 16 (1986), S. 217-226 
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The linear dichroism of the complexes of thymine and cytosine with silver(I) ions dispersed in stretched polyvinylalcohol films was measured in the infrared and in the near ultraviolet regions of the spectrum. The infrared results were helpful in establishing the orientation of the complexes in the films; they also confirmed that the site of silver binding in the case of cytosine involves the carbonyl oxygen. The ultraviolet spectra were deconvoluted into separate electronic transitions and the corresponding transition moments of silver complexes were determined.
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  • 6
  • 7
    Publication Date: 2010-06-10
    Description: There is a need to reduce the amount of fossil energy used for transport, both because of the easily available fossil fuel is becoming sparser and because of climate concerns. In this article, the concept of “peak oil” is briefly presented. Second, a practical approach to reduction of fossil fuel use for transport elaborated by two British commissions is presented. A key feature is the introduction of electric cars. This raises the third issue covered in this article: namely, how battery technology is going to meet the increasing needs posed by the transport sector. ©2010 Royal Swedish Academy of Sciences
    Print ISSN: 0044-7447
    Electronic ISSN: 1654-7209
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Springer on behalf of Royal Swedish Academy of Sciences.
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