Origin Of Homochirality In Life Research Articles

The Formation of Supramolecular Chiral Materials from Achiral Molecules Using a Liquid-Crystallin System: Symmetry Breaking, Amplification, and Transfer

Recently, the formation of chiral materials by the self-organization of achiral small molecules has attracted much attention. How can we obtain chirality without a chiral source? Interesting approaches, such as mechanical rotation, circularly polarized light, and asymmetric reaction fields, have been used. We describe recent research developments in supramolecular chirality in liquid crystals, focusing primarily on our group’s experimental results. We present the following concepts in this review. Spontaneous mirror symmetry breaking in self-assembled achiral trimers induces supramolecular chirality in the soft crystalline phase. Two kinds of domains with opposite handedness exist in non-equal populations. The dominant domain is amplified to produce a homochiral state. Chirality is transferred to a polymer film during the polymerization of achiral monomers by using the homochiral state as a template. Finally, we discuss how the concepts obtained from this liquid crystal research relate to the origin of homochirality in life.

Spontaneous Resolution of Racemic Cage-Catenanes via Diastereomeric Enrichment at the Molecular Level and Subsequent Narcissistic Self-Sorting at the Supramolecular Level.

The spontaneous resolution of racemates, from natural compounds to artificial structures, has long been pursued to shed light on the origin of homochirality in life. Even though diverse synthetic systems have been elegantly devised to elaborate the underlying principles of spontaneous symmetry breaking, their complexity is still unparalleled to the natural masterpieces including DNA helix and proteins, which convey remarkable coalescence at both molecular and supramolecular levels. Here, we report on the spontaneous resolution of a pair of homochiral entities from a racemic mixture of a triply interlocked cage-catenane comprising 720 possible stereoisomers. This cage-catenane comprises six methyldithiane ring-containing linkers (denoted rac-2). As each methyldithiane ring has two chiral centers, it exhibits four possible diastereomers. These otherwise equimolar diastereomers are preferentially differentiated with the equatorial conformers over their axial analogues, leading to the dominant formation of (S, R)-2 and (R, S)-2, i.e., diastereomeric enrichment at the molecular level. This diastereomeric enrichment is unbiasedly transferred from precursor rac-2 to cage-catenane rac-4, from which a pair of homochirals (S, R)6-4 and (R, S)6-4 is narcissistically self-sorted upon crystallization. This powerful symmetry breaking is attributed to a supramolecular synergy of directional π-π stacking with the multivalency of erstwhile weak S···S contacts (with an unusual distance of 3.09 Å) that are cooperatively arranged in a helical fashion. This work highlights the attainability of complex homochiral entities by resorting to coalesced covalent and noncovalent contributions and therefore provides additional clues to the symmetry breaking of sophisticated yet well-defined architectures.

Formation of homochiral helical nanostructures in diblock copolymers under the confinement of nanopores.

The control of the homochirality of helical structures formed in achiral systems is of great interest as it is helpful for understanding the origin of homochirality in life. In this work, we introduce a spiral arrangement of patches into the inner surface of a nanopore to guide the self-assembly of a cylinder-forming AB diblock copolymer melt into a homochiral single helix. We calculate the free energy of the single-helical structures with different handedness using self-consistent field theory (SCFT). Moreover, we simulate the self-assembly process using an iterative process of SCFT solution starting from a disordered state, and count the formation probability of different helical structures. We find that the formation probability of the homochiral helix with favorable free energy increases rapidly, leading to the conclusion that a minuscule difference of 0.5-1.0 × 10-4kBT per chain is enough to obtain the homochiral helix by suppressing its counterpart of a higher free energy. However, for a stronger chiral guiding field, other homochiral helical structures with unfavorable handedness and thus increasingly higher free energy become more likely to be formed. Morphological snapshots during the self-assembly process reveal that the formation of these metastable helical structures is induced by their kinetic pathways, which are altered to be favorable by the strong chiral field of the patch pattern. Therefore, our work suggests that both thermodynamics and kinetics are important for controlling the chirality of helical structures.

Control over the emerging chirality in supramolecular gels and solutions by chiral microvortices in milliseconds

The origin of homochirality in life is a fundamental mystery. Symmetry breaking and subsequent amplification of chiral bias are regarded as one of the underlying mechanisms. However, the selection and control of initial chiral bias in a spontaneous mirror symmetry breaking process remains a great challenge. Here we show experimental evidences that laminar chiral microvortices generated within asymmetric microchambers can lead to a hydrodynamic selection of initial chiral bias of supramolecular systems composed of exclusively achiral molecules within milliseconds. The self-assembled nuclei with the chirality sign affected by the shear force of enantiomorphic microvortices are subsequently amplified into almost absolutely chirality-controlled supramolecular gels or nanotubes. In contrast, turbulent vortices in stirring cuvettes fail to select the chirality of supramolecular gels. This study reveals that a laminar chiral microflow can induce enantioselection far from equilibrium, and provides an insight on the origin of natural homochirality.

Transfer of chiral information from a chiral solvent to a two-dimensional network.

Chiral induction in self-assembled monolayers has garnered considerable attention in the recent past, not only due to its importance in chiral resolution and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. Here, we demonstrate the emergence of homochirality in a supramolecular low-density network formed by achiral molecules at the interface of a chiral solvent and an atomically-flat achiral substrate. We focus on the impact of structure and functionality of the adsorbate and the chiral solvent on the chiral induction efficiency in self-assembled physisorbed monolayers, as revealed by scanning tunneling microscopy. Different induction mechanisms are proposed and evaluated, with the assistance of advanced molecular modeling simulations.

Chirality in adsorption on solid surfaces.

In the present review we survey the main advances made in recent years on the understanding of chemical chirality at solid surfaces. Chirality is an important topic, made particularly relevant by the homochiral nature of the biochemistry of life on Earth, and many chiral chemical reactions involve solid surfaces. Here we start our discussion with a description of surface chirality and of the different ways that chirality can be bestowed on solid surfaces. We then expand on the studies carried out to date to understand the adsorption of chiral compounds at a molecular level. We summarize the work published on the adsorption of pure enantiomers, of enantiomeric mixtures, and of prochiral molecules on chiral and achiral model surfaces, especially on well-defined metal single crystals but also on other flat substrates such as highly ordered pyrolytic graphite. Several phenomena are identified, including surface reconstruction and chiral imprinting upon adsorption of chiral agents, and the enhancement or suppression of enantioselectivity seen in some cases upon adsorption of enantiomixtures of chiral compounds. The possibility of enhancing the enantiopurity of adsorbed layers upon the addition of chiral seeds and the so-called "sergeants and soldiers" phenomenon are presented. Examples are provided where the chiral behavior has been associated with either thermodynamic or kinetic driving forces. Two main approaches to the creation of enantioselective surface sites are discussed, namely, via the formation of supramolecular chiral ensembles made out of small chiral adsorbates, and by adsorption of more complex chiral molecules capable of providing suitable chiral environments for reactants by themselves, via the formation of individual adsorbate:modifier adducts on the surface. Finally, a discussion is offered on the additional effects generated by the presence of the liquid phase often required in practical applications such as enantioselective crystallization, chiral chromatography, and enantioselective catalysis.

Chiral selection of single helix formed by diblock copolymers confined in nanopores.

Chiral selection has attracted tremendous attention from the scientific communities, especially from biologists, due to the mysterious origin of homochirality in life. The self-assembly of achiral block copolymers confined in nanopores offers a simple but useful model of forming helical structures, where the helical structures possess random chirality selection, i.e. equal probability of left-handedness and right-handedness. Based on this model, we study the stimulus-response of chiral selection to external conditions by introducing a designed chiral pattern onto the inner surface of a nanopore, aiming to obtain a defect-free helix with controllable homochirality. A cell dynamics simulation based on the time-dependent Ginzburg-Landau theory is carried out to demonstrate the tuning effect of the patterned surface on the chiral selection. Our results illustrate that the chirality of the helix can be successfully controlled to be consistent with that of the tailored surface patterns. This work provides a successful example for the stimulus response of the chiral selection of self-assembled morphologies from achiral macromolecules to external conditions, and hence sheds light on the understanding of the mechanism of the stimulus response.

Solvent-Induced Homochirality in Surface-Confined Low-Density Nanoporous Molecular Networks

Induction of chirality in achiral monolayers has garnered considerable attention in the recent past not only due to its importance in chiral resolutions and enantioselective heterogeneous catalysis but also because of its relevance to the origin of homochirality in life. In this contribution, we demonstrate the emergence of macroscopic chirality in multicomponent supramolecular networks formed by achiral molecules at the interface of a chiral solvent and an achiral substrate. The solvent-mediated chiral induction provides a simple, efficient, and versatile approach for the fabrication of homochiral surfaces using achiral building blocks.

ChemInform Abstract: Understanding Prebiotic Chemistry Through the Analysis of Extraterrestrial Amino Acids and Nucleobases in Meteorites

AbstractReview: 66 refs.

Understanding prebiotic chemistry through the analysis of extraterrestrial amino acids and nucleobases in meteorites

The discoveries of amino acids of extraterrestrial origin in many meteorites over the last 50 years have revolutionized the Astrobiology field. A variety of non-terrestrial amino acids similar to those found in life on Earth have been detected in meteorites. A few amino acids have even been found with chiral excesses, suggesting that meteorites could have contributed to the origin of homochirality in life on Earth. In addition to amino acids, which have been productively studied for years, sugar-like molecules, activated phosphates, and nucleobases have also been determined to be indigenous to numerous meteorites. Because these molecules are essential for life as we know it, and meteorites have been delivering them to the Earth since accretion, it is plausible that the origin(s) of life on Earth were aided by extraterrestrially-synthesized molecules. Understanding the origins of life on Earth guides our search for life elsewhere, helping to answer the question of whether biology is unique to Earth. This tutorial review focuses on meteoritic amino acids and nucleobases, exploring modern analytical methods and possible formation mechanisms. We will also discuss the unique window that meteorites provide into the chemistry that preceded life on Earth, a chemical record we do not have access to on Earth due to geologic recycling of rocks and the pervasiveness of biology across the planet. Finally, we will address the future of meteorite research, including asteroid sample return missions.

Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life

first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessReview Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life by David B. Cline Astrophysics Division, UCLA Physics & Astronomy Department, 405 Hilgard Avenue, Los Angeles, California 90095, USA Symmetry 2010, 2(3), 1450-1460; https://doi.org/10.3390/sym2031450 Received: 2 February 2010 / Revised: 8 May 2010 / Accepted: 21 June 2010 / Published: 9 July 2010 (This article belongs to the Special Issue Symmetry of Life and Homochirality) Download Download PDF Download PDF with Cover Download XML Download Epub Browse Figures Versions Notes Abstract: The origin of homochirality in life remains a mystery that some believe is essential for life, and which may result from chiral symmetry breaking interactions with galactic organic material. Keywords: homochirality; symmetry-breaking; biomolecules 1. IntroductionFor more than a century, there has been evidence for the chiral nature of life forms on Earth. Pasteur was among the first to point this out (1848–1880), and the universal nature of chiral symmetry breaking in DNA and RNA is now very well established for all life forms. Figure 1 and Figure 2 show how the homochirality is manifest at the molecular level. We note that amino acids are L and DNA is largely D handed.With the discovery of parity violation within charged current reactions in 1956, and of the weak neutral currents (WNCs) in 1973, two universal symmetry-breaking processes (WNC and β-decay) were uncovered that could have determined the handedness of DNA and RNA. The main problem is the extremely small symmetry-breaking effects (ΔE/kB T ~ 10-17). However there are plausible non-linear mechanisms that could have amplified this small, symmetry-breaking phase transition up to the full symmetry-breaking level observed in life forms [1,2,3,4,5,6,7,8,9,10,11].For many years, there have been several issues associated with the homochiral structure of biomolecules, as first observed by Pasteur in 1848:(a)Is a homochiral structure necessary for life as we know it?(b)Did homochirality precede the formation of life (homochiral prebiotic medium hypothesis)?(c)Is there any reasonable physical mechanism that could have produced the large chiral symmetry breaking in the prebiotic medium or in the observed homochiral structure?(d)Is the homochiral structure an accident that occurred in biological systems, which was later amplified?(e)Can the homochirality be used as a signature for existing, or previous, living systems in the solar system or other parts of our galaxy?(f)Are there any experiments that can be carried out now to clarify the origin of homochirality?(g)Work on the RNA world and the homochirality of biomolecules is promising. See, for example, Reference [39,40,41].Recently, there has been increasing interest in the chiral nature or handedness of biomolecules. In fact, there are some who claim that the complex biomolecular structure of life must have arisen from a “chiral pure” medium [12,13]. This may be a precondition for the emergence of self-replicating biomolecular systems. Table 1 lists some of these ideas, which have been put forward largely by W. Bonner and V. Goldanskii [12,13]. We also point out a recent review in Reference [14]; see also Reference [15] for more recent details. Life on Earth is likely to have originated between 3.8 and 3.5 billion years ago. This estimate of time, along with the previous concept of the prebiotic medium, leaves a small window of 300 million years or less for life to have emerged from that prebiotic medium. Indeed, some speculate that the time could be less than 10 million years. Recently, some evidence has been obtained for an excess of L amino acids in the Murchison meteorite [37]. This and other observations may point to an extraterrestrial origin of homochirality [37].We now turn to the experiments that study possible asymmetry processes. Over a period of 20 years, many experiments have been carried out (see Reference [12] for a nearly complete list). However, it appears that nearly every positive effect that was observed has turned out to be incorrect. In Table 2, we list some experimental results that are not yet refuted or are in direct conflict with previous null effects. The observation that circularly polarized light destroys L and D isomers selectively (entry 1 in Table 2) is now well established.The other experiment to which we will refer is that of entry 2 (also in Table 2), the study of Cherenkov light in L or D material with chiral e- (β-decay) [20]. The authors claim an effect of perhaps 10-2 magnitude. This is, in our belief, far too large an effect, but a future study of Cherenkov radiation from L or D materials with polarized e- beams could be promising.In Figure 3, we show the current limits or observations of asymmetry. The e+ measurement of Gridley et al. [18] is a very nice experiment. See also references [16] and [17]. Our conclusion is that no present experiment has reached the level of sensitivity needed to observe an effect. Therefore, it is premature to count out the weak force as a determining factor in the origin of homochirality in life. 2. Organic Molecules in Space and the Possible Role of Nearby Supernovae and Neutron StarsOne of the main themes of recent attempts to understand life on Earth is the likelihood that most of the early organic material on Earth was brought in by comets and asteroids. Reference [15] gives a nice introduction, from different points of view, to this concept. There are some interesting “large numbers” to consider in this regard:(1)The estimated amount of dust matter in the galaxy is ~10-4 mG, or ≤ 107 solar masses, largely in the form of dust grains. A fraction of that material is in the form of organic materials [26].(2)It has not been possible to measure the amount of interstellar dust that has accumulated on the Earth (some of this dust would have brought organic material) [27,28].(3)In a molecular cloud with a density of 104 M/cm3 and a radius of 1 parsec, there could be a complex of organic matter equal to 100 solar masses.(4)The Earth revolves around the galaxy every ~250 million years, and it likely encounters several dense layers of molecular clouds in this trajectory.(5)It is likely that large quantities of organic material were deposited in the Earth in the first billion years.The above information is obtained by observing the infrared scattering of dust in the galaxy and by modeling various UV-driven processes here on Earth [26]. Ultraviolet photo processing plays an important role in the organic chemistry of the dust particles [27]; see also Reference [28]. Figure 4 shows the nature of a dust grain with prebiotic molecules inside [29].We discuss here two scenarios where chiral interactions in the ISM could have led to a preponderance of homochiral molecules. These two concepts are outlined in Table 3, with Figure 5 giving a fairly complete description of the hypothesis. The second hypothesis is illustrated in Figure 6, where the possibility of the relative survival of the e± polarization deep within the cloud is also illustrated. Of course, during this time, the effect of the WNC can be driving the system towards a homochiral state.Let us consider the rate of these three effects: (1)For ν e ¯ absorption and a supernova 1 parsec away (or inside a 1-parsec dense cloud), the number of interactions will be ~10-3 /kg of material for 100 MO of organic material (which would be 1012 g of organic matter that is active), therefore the positron from the ν e ¯ interactions would lose energy at a rate of 10-19 MeV/cm, and thus travel over a parsec. ( ν e ¯ is an antielectron neutrino).(2)For the coherent vx + N → vx + N, and for the carbon in the hydrocarbons, we would have ~102 more or ~1014 grams of active material. Note that νx stands for all types of neutrinos. This effect could be very important in light of the small energy difference that separates L and D molecules, and the possibility of large coherent effects.(3)For the Al26 over the half-life, there would be ~1050 decays producing ~1050 positrons that lose energy at the rate of 10-19 MeV/cm; for MeV positrons, the range would be on the order of a parsec (ignoring possible magnetic-field effects). 2.1. Direct Interaction of the Supernova II NeutrinoConsider the example where 0.001 MO of Al26 is produced and assume (MO is the mass of the sun), for simplicity, that the energy of the e+ is 1 MeV and is contained in the gas cloud. Assume that the cloud has a density of 104 atoms/cm3 and that 10-3 of the atoms are organic. The stopping power for e+ would then be d E / d x ~ M e V g − 1 c m − 3 and for a density of ρ = 104 atoms/cm3 ~ 10-17 g/cm3, we find d x ~ ( M e V / ρ ) d E ~ 10 19 c m ( ~ 3 p a r sec ) and for an average energy exchange of 10 eV, we have 10 e 5 c o l l i s i o n s / A l 26 d e c a y For 0.001 MO of Al26 and a 10-3 organic fraction, we obtain a total of ~1050 collisions of polarized positrons, with organic materials in the cloud, assuming all of the e+ stop in the cloud (we assume that only one of the collisions can result in spin exchange). There will also be the same order of polarized photons from the e+e- → γγ annihilation. It is estimated in [17] and [24] that the asymmetry due to the weak interaction would be of order 10-11 to 10-6, depending on the positron energy {it scales like α2[α/(ν/c)]2}. Thus, it takes N ~1022 interactions for the asymmetric to become statistically important. In this example there are far more interactions.More recently we have considered the main effects of a SN II explosion in a hydrocarbon cloud. We estimate that the larger anti-neutrino interaction rate would cause a chirality breaking effect and estimate this effect in Table 4. See Reference [34].It appears that supernova neutrinos could include a chiral symmetry breaking in the ISM that could be transferred to the biomolecules of life. I wish to thank Goldanskii for some very useful conversations while he was a Regents Lecturer at UCLA and I regret his passing; please see Reference [5]. 3. Other Calculations of Chiral Symmetry BreakingThe process shown in Figure 6 could come about in similar ways. Here are two examples: (a)Effects of cosmological neutrinos on the discrimination between the two enantiomers of a chiral molecule [35]. This concept is similar in spirit to that of Cline and the authors reference that work [34]. The basic concept in this work is that cosmological neutrinos and antineutrinos interact with the electrons in organic materials in the galaxy. This results in a split in the energy of the different chiral systems. This energy split is enhanced by the contributions if all the electrons in the molecules, and other mechanisms, up to the point of a larger chiral symmetry breaking.(b)A relativistic neutron fireball from a supernova explosion is a possible source of chiral influence [36]. This concept is also similar to the one by Cline [34]. However, in this case, it is the decay of neutrons n → p + e − + ν e ¯ that leads to polarized electrons that destroy organic material differently for L and D enantiomers. This is shown in Figure 3 and explained in the text. This work studies the effect of neutrinos from the supernova fireball with a Lorentz factor of one hundred. The relativistic electron-proton plasma (from the neutron decays) is slowed down by collective effect. 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We also include some recent measurements of the limits on such an asymmetry. Figure 3. Most recently published calculations of the expected asymmetry for the scattering of e* from chiral molecules. We also include some recent measurements of the limits on such an asymmetry. Figure 4. The structure of grains, when they initially accrete, is inferred from laboratory simulations, in which mixtures of water, methane, ammonia, and other simple molecules are subjected to UV irradiation at 10 K. (a) Each grain begins as a silicate core that condensed in the atmosphere of a cool giant star. Around this core, a mantle of ice forms. Ultraviolet radiation breaks some of the mantle molecules into radicals or reactive molecular fragments. (b) The radicals can then recombine in new ways. (c) Over a longer period, the continued UV irradiation of the grain can give rise to ever more complex mixtures of molecules and radicals. Data from Reference 29, which was used in the talk of Greenburg M. at the Homochiralty Symp., Santa Monica, CA, USA, 1995. Figure 4. The structure of grains, when they initially accrete, is inferred from laboratory simulations, in which mixtures of water, methane, ammonia, and other simple molecules are subjected to UV irradiation at 10 K. (a) Each grain begins as a silicate core that condensed in the atmosphere of a cool giant star. Around this core, a mantle of ice forms. Ultraviolet radiation breaks some of the mantle molecules into radicals or reactive molecular fragments. (b) The radicals can then recombine in new ways. (c) Over a longer period, the continued UV irradiation of the grain can give rise to ever more complex mixtures of molecules and radicals. Data from Reference 29, which was used in the talk of Greenburg M. at the Homochiralty Symp., Santa Monica, CA, USA, 1995. Figure 5. Possible extraterrestrial origin of terrestrial homochiralty. Figure 5. Possible extraterrestrial origin of terrestrial homochiralty. Figure 6. (a) Schematic representation of the effect of a supernova II on the organic molecules in a dense molecular cloud. (b) Estimated polarization of the β* decay particles as the energy decreases, by ionization, in H2O and in the dense molecular cloud. An observation of polarized e+ is made by the Michigan group in Figure 6. Figure 6. (a) Schematic representation of the effect of a supernova II on the organic molecules in a dense molecular cloud. (b) Estimated polarization of the β* decay particles as the energy decreases, by ionization, in H2O and in the dense molecular cloud. An observation of polarized e+ is made by the Michigan group in Figure 6. Table 1. Trends in life origins. Table 1. Trends in life origins. 1DNA: Self replication would not work with heterochiral systems (50% L and 50% D).2Errors in DNA Replication: Without a pure chiral structure, the error rate in replication would be unacceptable for long-lived systems (higher animal forms, trees, etc.).3In a prebiotic medium, homochirality must have been either (a) or (b) (a) Established in a very short time on Earth (≤ 100 Million years) (b) Existed in Interstellar Medium (ISM) organic materials near the solar system Table 2. Experiments where a chiral effect has been observed (and not refuted). Table 2. Experiments where a chiral effect has been observed (and not refuted). ExperimentBeam/SourceTargetDetectionCommentsReference1CPL on L/D/ photo absorptionUV/keV radiationDC tartaric acid, DL alanine, DL glutamicObserve destructive difference in one chiralityTo be expected from optical activityNorden [19]2e- target → Č lightp32 source and Ca137 (no chiral electrons)R- or S-PBAObserve different Č light intensity due to chiral electronsEffect too large to be due to Č radiation from spin effectsGaray et al. [20]3Co60 → γ + (L,D)Co60 γsD or L alanineObserve different amounts of L,D after irradiationOther experiments did not produce this effectAkabosh et al. [21]4Introduction of L/D/ chiral particlesSr90, Y90 β-decayY90 D or L alanineDetects effects by electron spin resonance techniqueThe electron spin resonance may be sensitive to spin dependenceConte et al. [22]5Low-energy polarized e- beamGaAs polarized source 5 eVCamphor L,DObserve different electron polarization and beam attenuation in L/DAt such low energy, asymmetry may be too largeCampbell et al. [23] Table 3. Possible sources of CPL (UV/keV) radiation in dense molecular clouds. Table 3. Possible sources of CPL (UV/keV) radiation in dense molecular clouds. Primordial Soup – Molecular Clouds (ISM)1Synchronotron radiation from neutron stars ([12,26]) CPL helicity depends on position (i.e., above or below star) In principle, this mechanism works. However, on the 250-Myr orbit around the galaxy, this effect is expected to average out.2Radiation from weak interaction processes [30]-injection into molecular cloud Processes: supernova II ν e ¯ interaction, Al26 from nearby supernovas, etc.; Because of grain structure, dE/dx will be very different from that of solids, gases, or liquids; Always gives the same chiral symmetry breaking; An act as a chiral impulse along with WNC. Table 4. Estimated rate of νe interactions in the dense presolar cloud. Table 4. Estimated rate of νe interactions in the dense presolar cloud. Estimated rate of ν e ¯ Interactions in the Dense Presolar Cloud [ N v ¯ ~ 10 57 f r o m S N I I ] [ A s s u m e S N I p a r sec f r o m c l o u d ] Assume: Cloud density 104 protons/cm3 [fraction of organic material] 10-3-- Range of e+ 1 parsec; Number of ν interactions ~ 1035 = Number of e+ for interaction with organics in cloud > 1030We estimate that only 1022 interactions are necessary to produce asymmetry. From this, it is clear a much larger asymmetry is produced. © 2010 by the authors; licensee MDPI, Basel, Switzerland. This article is an Open Access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/). Share and Cite MDPI and ACS Style Cline, D.B. Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life. Symmetry 2010, 2, 1450-1460. https://doi.org/10.3390/sym2031450 AMA Style Cline DB. Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life. Symmetry. 2010; 2(3):1450-1460. https://doi.org/10.3390/sym2031450 Chicago/Turabian Style Cline, David B. 2010. "Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life" Symmetry 2, no. 3: 1450-1460. https://doi.org/10.3390/sym2031450 Find Other Styles Article Metrics No No Article Access Statistics For more information on the journal statistics, click here. Multiple requests from the same IP address are counted as one view.

Homochirality in life: two equal runners, one tripped.

Strong arguments can be found in the literature addressed to the question of the origin of homochirality in life, supporting the hypothesis that primordial life could have evolved in both homochiral forms and that early on when life was still rarely found, random events led to the survival of only one of these living mirror images. This proposal is an alternative to the generally accepted view that small enantiomeric excesses of biologically important molecules were amplified to homochirality prior to life's origin. Acceptance of the possibility of "two equal runners" leads to the importance of research investigations on routes to formation of ensembles of racemic mixtures of isotactic biologically interesting polymers, supramolecular entities and aggregates.