Special Issue "Possible Scenarios for Homochirality on Earth"

A special issue of Symmetry (ISSN 2073-8994).

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editor

Guest Editor
Prof. Michiya Fujiki Website E-Mail
Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology (NAIST) 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
Phone: 81-743-72-6040
Fax: 81-743-72-6049
Interests: symmetry breaking; polarized light; helix; photoexcited state; weak neutral current; Hund’s paradox

Special Issue Information

Dear Colleagues,

As evidenced in several Myths, humankind has long been thinking of life: Where did our life come from? And where will our life go? A more apt question is whether life exists only on Earth. In 1903, Svante Arrhenius proposed the radio-panspermia hypothesis as the origin of life; that is, certain seeds of life in the size of 200–300 nm travelled slowly by solar radiation pressure and landed on the Earth. This scenario led to the litho-panspermia and ballistic panspermia hypotheses. In 1978, Fred Hoyle proposed that interstellar comets carrying several viruses landed on the Earth to ensure these panspermia hypotheses. With respect to our life, the origin of homochirality on the Earth has been the greatest mystery because our life cannot exist without molecular asymmetry. Living organisms on the Earth are always tempo-spatial and metastable as a consequence of a far-from-equilibrium open system. Life can survive only under open flows of energy and chemical sources because life eats low-entropy foods and/or harvests solar/thermal energy.

In recent years, several discoveries led by modern spacecrafts and telescopes have brought new horizons on the origins of life and chirality. For example, Hubble space telescope (NASA) captured geysers of liquid water from Europa, one of Jupiter’s moons. Rosetta (ESA) detected prebiotic constituents and water on the comet, 67P/Churyumov-Gerasimenko, that is one of the Jupiter family. Using a quadrupole gravity measurement system, Cassini (NASA) discovered water under the surface of Enkelados, one of Saturn’s moons. The Jet Propulsion Laboratory (NASA) showed that Titan, the largest Saturnian moon, has water comprising inorganic salts. Kepler (NASA) discovered over two thousand Earth-like exoplanets, located in habitable zones. More recently, in 2016, radio telescope astronomers detected chiral propylene oxide in a giant molecular cloud, called SagittariusB2 in the Milky Way Galaxy, by analyzing absorption bands in mm wavelength, although the L-D preference is yet to be characterized.

Thus far, many scientists have proposed several possible hypotheses to answer this long-standing L-D question. Previously, Martin Gardner raised the question about mirror symmetry and broken mirror symmetry in terms of the homochirality question in his monographs (1964 and 1990). Possible scenarios for the L-D issue can be categorized into (i) Earth and exoterrestrial origins, (ii) by-chance and necessity mechanisms, and (iii) mirror-symmetrical and non-mirror-symmetrical forces as physical and chemical origins. These scenarios should involve further great amplification mechanisms, enabling pure L- or D-world. Recent studies have demonstrated that even nearly racemic substances as low as 10–5 % ee can be significantly amplified to nearly 100 % ee.

The present Special Issue encourages researchers from a broad range of disciplines to publish original papers, account papers, and reviews, which describe possible scenarios of bimolecular handedness, followed by the L-D amplification on the Earth, and also a possible life under the exoterrestrial cosmological environments.

Prof. Michiya Fujiki
Guest Editor

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Keywords

  • symmetry breaking
  • polarized light
  • helix
  • photoexcited state
  • weak neutral current
  • Hund’s paradox

Published Papers (16 papers)

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Research

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Open AccessArticle
Symmetry Breaking in Self-Assembled Nanoassemblies
Symmetry 2019, 11(8), 950; https://doi.org/10.3390/sym11080950 - 25 Jul 2019
Abstract
The origin of biological homochirality, e.g., life selects the L-amino acids and D-sugar as molecular component, still remains a big mystery. It is suggested that mirror symmetry breaking plays an important role. Recent researches show that symmetry breaking can also occur [...] Read more.
The origin of biological homochirality, e.g., life selects the L-amino acids and D-sugar as molecular component, still remains a big mystery. It is suggested that mirror symmetry breaking plays an important role. Recent researches show that symmetry breaking can also occur at a supramolecular level, where the non-covalent bond was crucial. In these systems, equal or unequal amount of the enantiomeric nanoassemblies could be formed from achiral molecules. In this paper, we presented a brief overview regarding the symmetry breaking from dispersed system to gels, solids, and at interfaces. Then we discuss the rational manipulation of supramolecular chirality on how to induce and control the homochirality in the self-assembly system. Those physical control methods, such as Viedma ripening, hydrodynamic macro- and micro-vortex, superchiral light, and the combination of these technologies, are specifically discussed. It is hoped that the symmetry breaking at a supramolecular level could provide useful insights into the understanding of natural homochirality and further designing as well as controlling of functional chiral materials. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessArticle
A General Phenomenon of Spontaneous Amplification of Optical Purity under Achiral Chromatographic Conditions
Symmetry 2019, 11(5), 680; https://doi.org/10.3390/sym11050680 - 17 May 2019
Abstract
This work explores the behavior of chiral compound mixtures enriched in one of the enantiomers whilst a typical chromatography on the achiral stationary phase is employed. The influence of several factors, such as the eluent composition, ratio of the compound to the stationary [...] Read more.
This work explores the behavior of chiral compound mixtures enriched in one of the enantiomers whilst a typical chromatography on the achiral stationary phase is employed. The influence of several factors, such as the eluent composition, ratio of the compound to the stationary phase, and the initial enatiomeric purity of the compound used on the distribution of the enantiomers in the collected chromatographic fraction, was studied. The obtained results indicate that the phenomenon of Self Disproportionation of Enantiomer (SDE) occurred in all cases, and some of the collected fractions got higher optical purities than the initial one. Thus, achiral column chromatography could be applied in some cases as the simplest approach for chiral purification. Based on the experimental results and DFT calculations, an alternative concept explaining the SDE phenomenon was proposed. Due to its generality and simplicity, SDE may also be responsible for the formation of the first chiral non-racemic compounds on the early Earth. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessArticle
Homochirality: A Perspective from Fundamental Physics
Symmetry 2019, 11(5), 661; https://doi.org/10.3390/sym11050661 - 11 May 2019
Abstract
In this brief review, possible mechanisms which could lead to complete biological homochirality are discussed from the viewpoint of fundamental physics. In particular, the role played by electroweak parity violation, including neutrino-induced homochirality, and contributions from the gravitational interaction, will be emphasized. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
Open AccessFeature PaperArticle
Characterization of Hidden Chirality: Two-Fold Helicity in β-Strands
Symmetry 2019, 11(4), 499; https://doi.org/10.3390/sym11040499 - 05 Apr 2019
Abstract
A β-strand is a component of a β-sheet and is an important structural motif in biomolecules. An α-helix has clear helicity, while chirality of a β-strand had been discussed on the basis of molecular twists generated by forming hydrogen bonds in parallel or [...] Read more.
A β-strand is a component of a β-sheet and is an important structural motif in biomolecules. An α-helix has clear helicity, while chirality of a β-strand had been discussed on the basis of molecular twists generated by forming hydrogen bonds in parallel or non-parallel β-sheets. Herein we describe handedness determination of two-fold helicity in a zig-zag β-strand structure. Left- (M) and right-handedness (P) of the two-fold helicity was defined by application of two concepts: tilt-chirality and multi-point approximation. We call the two-fold helicity in a β-strand, whose handedness has been unrecognized and unclarified, as hidden chirality. Such hidden chirality enables us to clarify precise chiral characteristics of biopolymers. It is also noteworthy that characterization of chirality of high dimensional structures like a β-strand and α-helix, referred to as high dimensional chirality (HDC) in the present study, will contribute to elucidation of the possible origins of chirality and homochirality in nature because such HDC originates from not only asymmetric centers but also conformations in a polypeptide chain. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessArticle
Questions of Mirror Symmetry at the Photoexcited and Ground States of Non-Rigid Luminophores Raised by Circularly Polarized Luminescence and Circular Dichroism Spectroscopy. Part 2: Perylenes, BODIPYs, Molecular Scintillators, Coumarins, Rhodamine B, and DCM
Symmetry 2019, 11(3), 363; https://doi.org/10.3390/sym11030363 - 11 Mar 2019
Abstract
We investigated whether semi-rigid and non-rigid π-conjugated fluorophores in the photoexcited (S1) and ground (S0) states exhibited mirror symmetry by circularly polarized luminescence (CPL) and circular dichroism (CD) spectroscopy using a range of compounds dissolved in achiral liquids. The [...] Read more.
We investigated whether semi-rigid and non-rigid π-conjugated fluorophores in the photoexcited (S1) and ground (S0) states exhibited mirror symmetry by circularly polarized luminescence (CPL) and circular dichroism (CD) spectroscopy using a range of compounds dissolved in achiral liquids. The fluorophores tested were six perylenes, six scintillators, 11 coumarins, two pyrromethene difluoroborates (BODIPYs), rhodamine B (RhB), and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM). All the fluorophores showed negative-sign CPL signals in the ultraviolet (UV)–visible region, suggesting energetically non-equivalent and non-mirror image structures in the S1 state. The dissymmetry ratio of the CPL (glum) increased discontinuously from approximately −0.2 × 10−3 to −2.0 × 10−3, as the viscosity of the liquids increased. Among these liquids, C2-symmetrical stilbene 420 showed glum ≈ −0.5 × 10−3 at 408 nm in H2O and D2O, while, in a viscous alkanediol, the signal was amplified to glum ≈ −2.0 × 10−3. Moreover, BODIPYs, RhB, and DCM in the S0 states revealed weak (−)-sign CD signals with dissymmetry ratios (gabs) ≈ −1.4 × 10−5 at λmax/λext. The origin of the (−)-sign CPL and the (−)-sign CD signals may arise from an electroweak charge at the polyatomic level. Our CPL and CD spectral analysis could be a possible answer to the molecular parity violation hypothesis based on a weak neutral current of Z0 boson origin that could connect to the origin of biomolecular handedness. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessFeature PaperArticle
Astrophysical Sites that Can Produce Enantiomeric Amino Acids
Symmetry 2019, 11(1), 23; https://doi.org/10.3390/sym11010023 - 28 Dec 2018
Abstract
Recent work has produced theoretical evidence for two sites, colliding neutron stars and neutron-star–Wolf–Rayet binary systems, which might produce amino acids with the left-handed chirality preference found in meteorites. The Supernova Neutrino Amino Acid Processing (SNAAP) model uses electron antineutrinos and the magnetic [...] Read more.
Recent work has produced theoretical evidence for two sites, colliding neutron stars and neutron-star–Wolf–Rayet binary systems, which might produce amino acids with the left-handed chirality preference found in meteorites. The Supernova Neutrino Amino Acid Processing (SNAAP) model uses electron antineutrinos and the magnetic field from source objects such as neutron stars to preferentially destroy one enantiomer over another. Large enantiomeric excesses are predicted for isovaline and alanine; although based on an earlier study, similar results are expected for the others. Isotopic abundances of 13 C and 15 O in meteorites provide a new test of the SNAAP model. This presents implications for the origins of life. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessArticle
Chiral Proportions of Nepheline Originating from Low-Viscosity Alkaline Melts. A Pilot Study
Symmetry 2018, 10(9), 410; https://doi.org/10.3390/sym10090410 - 18 Sep 2018
Abstract
Chromatographic interaction between infiltrating solutions of racemic mixtures of enantiomers and enantiomorphic minerals with chiral excess has been proposed as a scenario for the emergence of biomolecular homochirality. Enantiomer separation is supposed to be produced by different partition coefficients of both enantiomers with [...] Read more.
Chromatographic interaction between infiltrating solutions of racemic mixtures of enantiomers and enantiomorphic minerals with chiral excess has been proposed as a scenario for the emergence of biomolecular homochirality. Enantiomer separation is supposed to be produced by different partition coefficients of both enantiomers with regard to crystal faces or walls of capillary tubes in the enantiomorphic mineral. Besides quartz, nepheline is the only common magmatic mineral with enantiomorphic symmetry. It crystallizes from SiO2-undersaturated melts with low viscosity and is a promising candidate for chiral enrichment by autocatalytic secondary nucleation. Under liquidus conditions, the dynamic viscosity of silicate melts is mainly a function of polymerization. Melts with low concentrations of SiO2 (<55 wt%) and rather high concentrations of Na2O (>7 wt%) are only slightly polymerized and hence are characterized by low viscosities. Such melts can ascend, intrude or extrude by turbulent flow. Fourteen volcanic and subvolcanic samples from alkaline provinces in Africa and Sweden were chemically analyzed. Polished thin sections containing fresh nepheline phenocrysts were etched with 1% hydrofluoric acid at 20 °C for 15 to 25 min. Nepheline crystals suitable for a statistical evaluation of their etch figures were found in four samples. Crystals with chiral etch figures are mainly not twinned. Their chiral proportions in grain percentages of single crystals are close to parity in three samples. Only one sample shows a slight chiral excess (41.67% L-type vs. 58.33% D-type) but at a low level of significance (15 vs. 21 crystals, respectively). Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Review

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Open AccessReview
Possible Roles of Amphiphilic Molecules in the Origin of Biological Homochirality
Symmetry 2019, 11(8), 966; https://doi.org/10.3390/sym11080966 - 01 Aug 2019
Abstract
A review. The question of homochirality is an intriguing problem in the field of chemistry, and is deeply related to the origin of life. Though amphiphiles and their supramolecular assembly have attracted less attention compared to biomacromolecules such as RNA and proteins, the [...] Read more.
A review. The question of homochirality is an intriguing problem in the field of chemistry, and is deeply related to the origin of life. Though amphiphiles and their supramolecular assembly have attracted less attention compared to biomacromolecules such as RNA and proteins, the lipid world hypothesis sheds new light on the origin of life. This review describes how amphiphilic molecules are possibly involved in the scenario of homochirality. Some prebiotic conditions relevant to amphiphilic molecules will also be described. It could be said that the chiral properties of amphiphilic molecules have various interesting features such as compositional information, spontaneous formation, the ability to exchange components, fission and fusion, adsorption, and permeation. This review aims to clarify the roles of amphiphiles regarding homochirality, and to determine what kinds of physical properties of amphiphilic molecules could have played a role in the scenario of homochirality. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessFeature PaperReview
Origin of Terrestrial Bioorganic Homochirality and Symmetry Breaking in the Universe
Symmetry 2019, 11(7), 919; https://doi.org/10.3390/sym11070919 - 15 Jul 2019
Abstract
The origin of terrestrial bioorganic homochirality is one of the most important and unresolved problems in the study of chemical evolution prior to the origin of terrestrial life. One hypothesis advocated in the context of astrobiology is that polarized quantum radiation in space, [...] Read more.
The origin of terrestrial bioorganic homochirality is one of the most important and unresolved problems in the study of chemical evolution prior to the origin of terrestrial life. One hypothesis advocated in the context of astrobiology is that polarized quantum radiation in space, such as circularly polarized photons or spin-polarized leptons, induced asymmetric chemical and physical conditions in the primitive interstellar media (the cosmic scenario). Another advocated hypothesis in the context of symmetry breaking in the universe is that the bioorganic asymmetry is intrinsically derived from the chiral asymmetric properties of elementary particles, that is, parity violation in the weak interaction (the intrinsic scenario). In this paper, the features of these two scenarios are discussed and approaches to validate them are reviewed. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
Open AccessFeature PaperReview
Role of Asymmetric Autocatalysis in the Elucidation of Origins of Homochirality of Organic Compounds
Symmetry 2019, 11(5), 694; https://doi.org/10.3390/sym11050694 - 20 May 2019
Abstract
Pyrimidyl alkanol and related compounds were found to be asymmetric autocatalysts in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde and related aldehydes. In the asymmetric autocatalysis with amplification of enantiomeric excess (ee), the very low ee (ca. 0.00005%) of 2-alkynyl-5-pyrimidyl alkanol was significantly [...] Read more.
Pyrimidyl alkanol and related compounds were found to be asymmetric autocatalysts in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde and related aldehydes. In the asymmetric autocatalysis with amplification of enantiomeric excess (ee), the very low ee (ca. 0.00005%) of 2-alkynyl-5-pyrimidyl alkanol was significantly amplified to >99.5% ee with an increase in the amount. By using asymmetric autocatalysis with amplification of ee, several origins of homochirality have been examined. Circularly polarized light, chiral quartz, and chiral crystals formed from achiral organic compounds such as glycine and carbon (13C/12C), nitrogen (15N/14N), oxygen (18O/16O), and hydrogen (D/H) chiral isotopomers were found to act as the origin of chirality in asymmetric autocatalysis. And the spontaneous absolute asymmetric synthesis was also realized without the intervention of any chiral factor. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessReview
Overview of Low-Temperature Heat Capacity Data for Zn2(C8H4O4)2.C6H12N2 and the Salam Hypothesis
Symmetry 2019, 11(5), 657; https://doi.org/10.3390/sym11050657 - 11 May 2019
Abstract
The review presents the progress in the analysis of low-temperature heat capacity of the metal-organic framework Zn2(C8H4O4)2.C6H12N2 (Zn-DMOF). In Zn-DMOF, left-twisted D3(S) and right-twisted D [...] Read more.
The review presents the progress in the analysis of low-temperature heat capacity of the metal-organic framework Zn2(C8H4O4)2.C6H12N2 (Zn-DMOF). In Zn-DMOF, left-twisted D3(S) and right-twisted D3(R) DABCO molecules (C6H12N2) can transform into each other by tunneling to form a racemate. Termination of tunneling leads to a phase transition in the subsystem of twisted molecules. It is suggested that Zn-DMOF may be considered a model system to study the mechanisms of phase transitions belonging to the same type as hypothetical Salam phase transitions. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessFeature PaperReview
Сhiral and Racemic Fields Concept for Understanding of the Homochirality Origin, Asymmetric Catalysis, Chiral Superstructure Formation from Achiral Molecules, and B-Z DNA Conformational Transition
Symmetry 2019, 11(5), 649; https://doi.org/10.3390/sym11050649 - 08 May 2019
Abstract
The four most important and well-studied phenomena of mirror symmetry breaking of molecules were analyzed for the first time in terms of available common features and regularities. Mirror symmetry breaking of the primary origin of biological homochirality requires the involvement of an external [...] Read more.
The four most important and well-studied phenomena of mirror symmetry breaking of molecules were analyzed for the first time in terms of available common features and regularities. Mirror symmetry breaking of the primary origin of biological homochirality requires the involvement of an external chiral inductor (environmental chirality). All reviewed mirror symmetry breaking phenomena were considered from that standpoint. A concept of chiral and racemic fields was highly helpful in this analysis. A chiral gravitational field in combination with a static magnetic field (Earth’s environmental conditions) may be regarded as a hypothetical long-term chiral inductor. Experimental evidences suggest a possible effect of the environmental chiral inductor as a chiral trigger on the mirror symmetry breaking effect. Also, this effect explains a conformational transition of the right-handed double DNA helix to the left-handed double DNA helix (B-Z DNA transition) as possible DNA damage. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessReview
Electrochirogenesis: The Possible Role of Low-Energy Spin-Polarized Electrons in Creating Homochirality
Symmetry 2019, 11(4), 528; https://doi.org/10.3390/sym11040528 - 11 Apr 2019
Abstract
Electrochirogenesis deals with the induction of chirality by polarized electrons of which those with low energy (<15 eV) are seen to be the most effective. Possible sources of such electrons in the prebiotic universe are discussed and several examples where chiral induction by [...] Read more.
Electrochirogenesis deals with the induction of chirality by polarized electrons of which those with low energy (<15 eV) are seen to be the most effective. Possible sources of such electrons in the prebiotic universe are discussed and several examples where chiral induction by these electrons have been demonstrated are given. Finally, some possible scenarios where electrochirogenesis could have played a role in forming a chiral imbalance in a prebiotic setting have been speculated on and some possible future areas of research proposed. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessReview
The Chirality Induction and Modulation of Polymers by Circularly Polarized Light
Symmetry 2019, 11(4), 474; https://doi.org/10.3390/sym11040474 - 03 Apr 2019
Cited by 2
Abstract
Chirality is a natural attribute nature of living matter and plays an important role in maintaining the metabolism, evolution and functional activities of living organisms. Asymmetric conformation represents the chiral structure of biomacromolecules in living organisms on earth, such as the L-amino acids [...] Read more.
Chirality is a natural attribute nature of living matter and plays an important role in maintaining the metabolism, evolution and functional activities of living organisms. Asymmetric conformation represents the chiral structure of biomacromolecules in living organisms on earth, such as the L-amino acids of proteins and enzymes, and the D-sugars of DNA or RNA, which exist preferentially as one enantiomer. Circularly polarized light (CPL), observed in the formation regions of the Orion constellation, has long been proposed as one of the origins of single chirality. Herein, the CPL triggered asymmetric polymerization, photo-modulation of chirality based on polymers are described. The mechanisms between CPL and polymers (including polydiacetylene, azobenzene polymers, chiral coordination polymers, and polyfluorene) are described in detail. This minireview provides a promising flexible asymmetric synthesis method for the fabrication of chiral polymer via CPL irradiation, with the hope of obtaining a better understanding of the origin of homochirality on earth. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Open AccessReview
Biological Homochirality on the Earth, or in the Universe? A Selective Review
Symmetry 2018, 10(12), 749; https://doi.org/10.3390/sym10120749 - 13 Dec 2018
Cited by 2
Abstract
The discovery of meteoritic alpha-amino acids with significant enantiomeric excesses of the L-form has suggested that some cosmic factors could serve as the initial source for chiral imbalance of organic compounds delivered to the early Earth. The paper reviews major hypothesis considering the [...] Read more.
The discovery of meteoritic alpha-amino acids with significant enantiomeric excesses of the L-form has suggested that some cosmic factors could serve as the initial source for chiral imbalance of organic compounds delivered to the early Earth. The paper reviews major hypothesis considering the influence of chiral irradiation and chiral combinations of physical fields on the possible ways asymmetric synthesis and transformations of organics could take place within the solar system. They could result in a small enantiomeric imbalance of some groups of compounds. More attention is paid to the hypothesis on parity violation of weak interaction that was supposed to cause homochirality of all primary particles and a more significant homochirality of compounds directly synthesized from the latter in a plasma reactor. The first experiment with material synthesized in a plasma torch resulting from a super-high-velocity impact showed formation of alanine with the excess of L-form between 7 and 25%. The supposed conclusion is that L-amino acids could serve as a starting homochiral biomolecular pool for life to emerge all over the Universe. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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Other

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Open AccessConcept Paper
Chemical Basis of Biological Homochirality during the Abiotic Evolution Stages on Earth
Symmetry 2019, 11(6), 814; https://doi.org/10.3390/sym11060814 - 20 Jun 2019
Abstract
Spontaneous mirror symmetry breaking (SMSB), a phenomenon leading to non-equilibrium stationary states (NESS) that exhibits biases away from the racemic composition is discussed here in the framework of dissipative reaction networks. Such networks may lead to a metastable racemic non-equilibrium stationary state that [...] Read more.
Spontaneous mirror symmetry breaking (SMSB), a phenomenon leading to non-equilibrium stationary states (NESS) that exhibits biases away from the racemic composition is discussed here in the framework of dissipative reaction networks. Such networks may lead to a metastable racemic non-equilibrium stationary state that transforms into one of two degenerate but stable enantiomeric NESSs. In such a bifurcation scenario, the type of the reaction network, as well the boundary conditions, are similar to those characterizing the currently accepted stages of emergence of replicators and autocatalytic systems. Simple asymmetric inductions by physical chiral forces during previous stages of chemical evolution, for example in astrophysical scenarios, must involve unavoidable racemization processes during the time scales associated with the different stages of chemical evolution. However, residual enantiomeric excesses of such asymmetric inductions suffice to drive the SMSB stochastic distribution of chiral signs into a deterministic distribution. According to these features, we propose that a basic model of the chiral machinery of proto-life would emerge during the formation of proto-cell systems by the convergence of the former enantioselective scenarios. Full article
(This article belongs to the Special Issue Possible Scenarios for Homochirality on Earth)
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