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"Boyd, Richard N"
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Amino Acid Chiral Selection Via Weak Interactions in Stellar Environments: Implications for the Origin of Life
Magnetochiral phenomena may be responsible for the selection of chiral states of biomolecules in meteoric environments. For example, the Supernova Amino Acid Processing (SNAAP) Model was proposed previously as a possible mode of magnetochiral selection of amino acids by way of the weak interaction in strong magnetic fields. In earlier work, this model was shown to produce an enantiomeric excess (ee) as high as 0.014% for alanine. In this paper we present the results of molecular quantum chemistry calculations from which ees are determined for the α-amino acids plus isovaline and norvaline, which were found to have positive ees in meteorites. Calculations are performed for both isolated and aqueous states. In some cases, the aqueous state was found to produce larger ees reaching values as high as a few percent under plausible conditions.
Journal Article
Supernovae, neutrinos and the chirality of amino acids
A mechanism for creating an enantioenrichment in the amino acids, the building blocks of the proteins, that involves global selection of one handedness by interactions between the amino acids and neutrinos from core-collapse supernovae is defined. The chiral selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the (14)N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. It also requires an asymmetric distribution of neutrinos emitted from the supernova. The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species. The resulting amino acids could either be the source thereof on Earth, or could have triggered the chirality that was ultimately achieved for Earth's proteinaceous amino acids.
Journal Article
Implementing the r-process in metal-poor stars via black hole collapse and relevance to the light element enhancement
Recent data compilations of abundances of Strontium and Barium in Extremely Metal Poor Stars show that large fluctuations exist in the ratio of the abundances of those elements. Two models exist for explaining those fluctuations, as well as the apparent truncation of data for those elements for stars having metallicity of [Fe/H] < −3.5. We study the factors that place upper limits on the logarithmic ratio [Sr/Ba] in the two models. A model has been developed in which the collapse of type II supernovae may produce a pronounced [Sr/Ba] enhancement in single-site r-process enriched stars. This model is consistent with galactic chemical constraints of light-element enrichment in metal-poor stars.
Journal Article
The Illogical Basis of Phylogenetic Nomenclature
The current advocacy for the so-called PhyloCode has a history rooted in twentieth-century arguments among biologists and philosophers regarding a putative distinction between classes and individuals. From this seemingly simple and innocuous discussion have come supposed distinctions between definitions and diagnosis, classification and systematization, and now Linnaean and “phylogenetic” nomenclature. Nevertheless, the metaphysical dichotomy of class versus individual, insofar as its standard applications to the issue of biological taxonomy are concerned, is an outdated remnant of early logical positivist thinking. Current views on natural kinds and their definitions under a scientific realist perspective provide grounds for rejecting the class versus individual dichotomy altogether insofar as biological entities are concerned. We review the role of natural kinds in scientific practice and the nature of definitions and scientific classifications. Although inherent instabilities of the PhyloCode are clearly sufficient to argue against the general application of this nominally phylogenetic system, our goal here is to address serious and fundamental flaws in its very foundation by exposing the unsubstantiated philosophical assumptions preceding and subtending it.
Journal Article
Kinds, Complexity and Multiple realization
According to Millikan the theory of natural kinds is essentially concerned with issues of objective projectibility. [...]I do not intend to always explain the possibility of imperfect homeostasis by appealing to spatio-temporal variability in underlying HPCs. Eternal Kinds and Intrinsic DefinitionsI suspect that one reason Professor Millikan associates HPC kinds with historical kinds both in the sense of kinds necessarily limited to an historical region and in the sense of kinds defined in the first instance by historical relations between members is that she contrasts eternal natural kinds, defined by central intrinsic properties, say from an inner structure common to all members of the kind, with historical kinds in the senses just mentioned, apparently taking this classificatory scheme to be exhaustive. Since biological species and lots of other HPC kinds are defined partly by extrinsic properties, they will all then appear to be historical in both senses.If by an eternal natural kind one means a natural kind which is historical in neither of the senses just mentioned, then many meteorological kinds and perhaps some astronomical kinds as well may turn out to be partly extrinsically defined but still eternal kinds. [...]this is important it is because these processes operate in ping pong balls (and, thus, because they exhibit the associated levels of multiple realizability) that they have the stable macroscopic properties (like shape and coefficient of restitution) which makes them fall under the non-accidental generalizations of Newtonian mechanics.
Journal Article
Chiral Selection, Isotopic Abundance Shifts, and Autocatalysis of Meteoritic Amino Acids
The discovery of amino acids in meteorites has presented two clues to the origin of their processing subsequent to their formation: a slight preference for left-handedness in some of them, and isotopic anomalies in some of their constituent atoms. In this article we present theoretical results from the Supernova Neutrino Amino Acid Processing (SNAAP) model, which uses electron anti-neutrinos and the magnetic fields from source objects such as supernovae or colliding neutron stars to selectively destroy one amino acid chirality and to create isotopic abundance shifts. For plausible magnetic fields and electron anti-neutrino fluxes, non-zero, positive enantiomeric excesses, \\(ee\\)s, defined to be the relative left/right asymmetry in an amino acid population, are reviewed for two amino acids, and conditions are suggested that would produce \\(ee>0\\) for all of the \\(\\alpha\\)-amino acids. The relatively high energy anti-neutrinos that produce the \\(ee\\)s would inevitably also produce isotopic anomalies. A nuclear reaction network was developed to describe the reactions resulting from them and the nuclides in the meteorites. At similar anti-neutrino fluxes, assumed recombination of the detritus from the anti-neutrino interactions is shown to produce appreciable isotopic anomalies in qualitative agreement with those observed for D/\\(^1\\)H and \\(^{15}\\)N/\\(^{14}\\)N. The isotopic anomalies for \\(^{13}\\)C/\\(^{12}\\)C are predicted to be small, as are also observed. Autocatalysis may be necessary for any model to produce the largest \\(ee\\)s observed in meteorites. This allows the constraints of the original SNAAP model to be relaxed, increasing the probability of meteoroid survival in sites where amino acid processing is possible. These results have obvious implications for the origin of life on Earth.
Paper