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  • 1
    Electronic Resource
    Electronic Resource
    β-decay, Bremsstrahlen, and the origin of molecular chirality (1984)
    Springer
    Journal of molecular evolution 21 (1984), S. 84-89 
    Details
    ISSN: 1432-1432
    Keywords: Parity violation ; β-Decay ; Asymmetric radiolysis ; Optical activity ; Vester-Ulbricht hypothesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A brief review is presented of the Vester-Ulbricht β-decay Bremsstrahlen hypothesis for the origin of optical activity, and of subsequent experiments designed to test it. Certain of our experiments along these lines, begun in 1974 and involving the irradiation of racemic and optically active amino acids in a 61.7 KCi90Sr−90Y Bremsstrahlen source, have now been completed and are described. After 10.89 years of irradiation with a total Bremsstrahlen dose of 2.5×109 rads, crystallinedl-leucine, norleucine, and norvaline suffered 47.2, 33.6, and 27.4% radiolysis, respectively, but showed no evidence whatsoever of asymmetric degradation.d- andl-Leucine underwent about 48% radiolysis and showed 2.4–2.9% radioracemization. Other samples in solution were too severely degraded to analyze. Probable intrinsic reasons for the failure of the Vester-Ulbricht mechanism to afford asymmetric radiolysis in the present and related experiments involving β-decay Bremsstrahlen are enumerated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02100632
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  • 2
    Electronic Resource
    Electronic Resource
    The radiolysis of tryptophan and leucine with32Pβ-radiation (1980)
    Springer
    Journal of molecular evolution 15 (1980), S. 21-28 
    Details
    ISSN: 1432-1432
    Keywords: β-radiolysis ; Asymmetric radiolysis ; Vester-Ulbricht Hypothesis ; Origin of optical activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have extended earlier experiments on the radiolysis of DL-tryptophan using32Pβ-radiation to longer reaction times, observing complete destruction of the tryptophan by secondary, non-radiolytic processes. We have also undertaken the irradiation of DL-leucine with32Pβ's at -196°, achieving radiolyses to the extents of ca. 20–30%, but observing no concomittant asymmetric bias. The implications of these observations are discussed with regard to the Vester-Ulbricht mechanism for the origin of optical activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01732580
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  • 3
    Electronic Resource
    Electronic Resource
    Experiments of the amplification of optical activity (1980)
    Springer
    Origins of life and evolution of the biospheres 10 (1980), S. 255-263 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract By way of investigating possible mechanisms for the abiotic amplification of small enantiomeric excesses (e.e.'s) in almost racemic mixtures of amino acid enantiomers, we have undertaken a quantitative study of the base-initiated partial polymerization of leucine and valineN-carboxy-anhydride (NCA) enantiomer mixtures containing known excesses of both theR- andS-forms. Polymerization to the extent ofca. 50% of leucine NCA having an 8–70% e.e. of either theR- orS-enantiomer led to an e.e. enhancement in the polymer, which contained a 12–84% e.e. of that enantiomer which predominated in the original monomer NCA. A corresponding decrease in the e.e. of the initially predominant enantiomer was noted in the unpolymerized residue from each reaction. Polymerization to the extent of 25–50% of mixtures of valine NCA enantiomers containing a 12–13% e.e. of eitherR- orS-isomer led to polymers showing a 7–8%decrease in the e.e. of the initially predominant enantiomer, and to an increase of its e.e. in the unpolymerized residue. These divergent results, the latter of which is quite novel, are compared with earlier qualitative results in the literature and are discussed briefly from the viewpoint of both mechanism and the amplification of optical activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00928403
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  • 4
    Electronic Resource
    Electronic Resource
    Experiments on the abiotic amplification of optical activity (1981)
    Springer
    Origins of life and evolution of the biospheres 11 (1981), S. 119-134 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Our earlier experiments are briefly reviewed, involving the abiotic generation of optical activity by exposure of DL-amino acids to various “chiral” physical forces. The enantiomeric enrichments so obtained were low, however, and additional experiments were undertaken with the objective of abiotically enhancing such small enantiomeric excesses. D≠L Mixtures of leucine N-carboxy anhydride gave enantiomerically enriched polymers on partial polymerization, while valine NCA mixtures behaved oppositely. Leucine polymers were also found to hydrolyze stereoselectively, providing for additional enantiomenic enhancement. A repetitive sequence of partial polymerization-hydrolysis steps is suggested as a possible mechanism for the abiotic genesis of optically enriched polypeptides on the primitive Earth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00928003
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  • 5
    Electronic Resource
    Electronic Resource
    The radiolysis and racemization of leucine on proton irradiation (1982)
    Springer
    Origins of life and evolution of the biospheres 12 (1982), S. 51-54 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract D- and L-Leucine have been subjected to 39–55 percent radiolysis using 0–11 MeV protons, both with the proton beam passing through the sample or being absorbed by it, and with quenching the sample immediately on completion of irradiation or after a 21-day interval. Racemization was small (1.1–1.7 percent) and comparable in all cases, suggesting that radioracemization and secondary degradative effects were not important factors in our recent unsuccessful attempts to induce optical activity in DL-leucine by partial radiolysis using 0–11 MeV longitudinally polarized protons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00926911
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  • 6
    Electronic Resource
    Electronic Resource
    The radiolysis and radioracemization of amino acids on silica surfaces (1981)
    Springer
    Origins of life and evolution of the biospheres 11 (1981), S. 321-330 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract L-Leucine, deposited on both 1-quartz powder and on a commercial amorphous silica preparation (Syloid 63), has been subjected to irradiation in a60Co γ-ray source, and the ensuing radiolysis and radioracemization have been determined gas chromatographically. The radiolysis and radioracemization observed for leucine on 1-quartz were rather similar to those noted for a crystalline L-leucine control. L-Leucine on Syloid 63, however, was vastly more susceptible to radiolysis as compared to the L-leucine control, and radioracemization was also markedly enhanced—each increasing with larger radiation dosage. L-Isovaline showed a similar, but diminished, enhancement of radiolysis sensitivity when adsorbed on the Syloid surface, but underwent no radioracemization whatsoever. The divergent results of the control and quartz-leucine irradiationsversus the Syloid-leucine and Syloid-isovaline irradiations are interpreted qualitatively in terms of the surface area parameters of the two silica adsorbents and the amino acid adsorbates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00931486
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  • 7
    Electronic Resource
    Electronic Resource
    A model for the enantiomeric enrichment of polypeptides on the primitive Earth (1981)
    Springer
    Origins of life and evolution of the biospheres 11 (1981), S. 331-335 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A mixture of D- and L-leucine N-Carboxyanhydride (NCA) having an enantiomeric composition of 65.6% L- and 34.4% D-isomer (i.e. 31.2% enantiomeric excess (e.e.)) was polymerized to the extent of 52% with sodium methoxide initiator to yield a polyleucine product the enantiomeric composition of which was 72.7% L- and 27.3% D-leucine (45.4% e.e.). This polymer was in turn partially hydrolyzed by acid, whereupon the unhydrolyzed polyleucine residue was found to have an enantiomeric composition of 77.5% L- and 22.5% D-leucine (55.0% e.e.). Thus the e.e. increase in the partial polymerization step (14.2%) and the partial hydrolysis step (9.6%) combined to total 23.8% for the overall polymerization-hydrolysis sequence. On the basis of these model experiments it is proposed that repetitive partial polymerization hydrolysis reactions, driven by environmental dry-wet cycles, might have been operative on the primitive Earth to engender the abiotic evolution of optically enriched polypeptides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00931487
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental evidence for β-decay as a source of chirality by enantiomer analysis (1984)
    Springer
    Origins of life and evolution of the biospheres 14 (1984), S. 383-390 
    Details
    ISSN: 1573-0875
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Earlier experiments testing the Vester-Ulbricht β-decay hypothesis for the origin of molecular chirality are reviewed, followed by descriptions of our own experiments involving attempted asymmetric radiolysis of DL-amino acids using quantitative gas chromotography as a probe for optical activity. Our radiation sources included90Sr−90Y,14C and32P Bremsstrahlen, longitudinally polarized electrons from a linear accelerator and longitudinally polarized protons from a cyclotron. With the possible exception of the linear accelerator irradiations, these experiments failed to produce g. c.-detectable enantiomeric excesses, even at 50–70% gross radiolysis. We thus find no unambigous support for the Vester-Ulbricht hypothesis in any of the attempted asymmetric radiolyses performed to date. Radioracemization, a possible reason for these failures, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00933681
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