Origin Of Biomolecular Homochirality Research Articles

Connections Between Nuclear Physics and the Origin of Life - Examining the Origin of Biomolecular Chirality

The discovery of bio-molecules in meteorites with an excess of one chiral state has created one of the biggest questions in astrobiology today. That is, what is the origin of bio-molecular homochirality? Studies of this question are highly interdisciplinary, and while several phenomenological models exist, we examine the relationship between fundamental symmetries at the particle level and the macroscopic formation of bio-molecules. A model has been developed which couples fundamental interactions with the formation of molecular chirality. In this magneto-chiral model atomic nuclei bound in amino acids interact via the weak interaction in stellar environments. Nuclei are coupled to the molecular geometry (chirality) via the shielding tensor, the same interaction responsible for NMR identification. Associated with this is the fact that isotopic abundances vary from solar system values. Interactions with leptons can selectively destroy one chiral state over the other while changing isotopic values. Possible sites are proposed in which this model may exist.

ChemInform Abstract: Enantioselective Gas Chromatography in Search of the Origin of Biomolecular Asymmetry in Outer Space

AbstractReview: [67 refs.

Enantioselective Gas Chromatography in Search of the Origin of Biomolecular Asymmetry in Outer Space

AbstractSince the pioneering work of Emanuel Gil‐Av and his associates at the Weizmann Institute of Science the direct gas chromatographic resolution of enantiomers has found its application in different fields of natural sciences, even expanding to space research and astrobiology. In these domains the resolution of chiral molecules of prebiotic relevance is of particular interest, since the determination of ratios between l‐ and d‐enantiomers within non‐terrestrial samples is assumed to shed light on the origin of biomolecular homochirality and the beginnings of life itself. According to an astrophysical scenario, the first molecular symmetry breaking event occurred upon irradiation of chiral organic molecules with circularly polarized light present in the interstellar medium. To examine this hypothesis, among others, chiral gas chromatographic stationary phases have been widely used to provide the differentiation of enantiomers in extracts of meteorites, samples of simulated interstellar ices and Mars soil analogues. Moreover several chiral capillary columns have been selected for in situ analyses of extraterrestrial organic matter by Mars missions and the cometary Rosetta mission. This review will highlight current advances of enantioselective gas chromatography applied to space science.

Spontaneous symmetry breaking on ordered, racemic monolayers of achiral theophylline: formation of unichiral stripes on Au(111).

We report the observation of spontaneous chiral symmetry breaking within ordered, racemic monolayers of theophylline, manifesting itself as extended, nanoscale unichiral stripes at the interface between molecular domains. Theophylline is a xanthine derivative playing an important role in several biochemical processes. Molecular chirality is induced by adsorption on the Au(111) surface, resulting in extended domains with two different racemic, ordered structures, coexisting with a disordered phase. By combining low-temperature scanning tunneling microscopy (LT-STM) and ab initio density functional theory calculations, we first provide a detailed picture of the interactions within the ordered assemblies, and we uncover the origin of the distinct contrast features in STM images. Secondly, experiments reveal the existence of nanoscale stripes of unichiral molecules separating racemic domains of one of the two ordered phases, giving rise to a local enantiomeric imbalance. Systematic theoretical investigation of their structure and chiral composition confirm their unichirality, with the specific handedness related to the registry between the two ordered domains facing the stripes. These findings can open the way to new insights into the elusive mechanisms leading to local chiral imbalances in racemic systems, possibly at the origin of biomolecular homochirality, as well as suggest novel approaches for stereoselective heterogeneous catalysis.

Life's chirality from prebiotic environments

AbstractA key open question in the study of life is the origin of biomolecular homochirality: almost every life-form on Earth has exclusively levorotary amino acids and dextrorotary sugars. Will the same handedness be preferred if life is found elsewhere? We review some of the pertinent literature and discuss recent results suggesting that life's homochirality resulted from sequential chiral symmetry breaking triggered by environmental events. In one scenario, autocatalytic prebiotic reactions undergo stochastic fluctuations due to environmental disturbances, in a mechanism reminiscent of evolutionary punctuated equilibrium: short-lived destructive events may lead to long-term enantiomeric excess. In another, chiral-selective polymerization reaction rates influenced by environmental effects lead to substantial chiral excess even in the absence of autocatalysis. Applying these arguments to other potentially life-bearing platforms has implications to the search for extraterrestrial life: we predict that a statistically representative sampling of extraterrestrial stereochemistry will be racemic (chirally neutral) on average.

Chiroptical Signatures of Life and Fundamental Physics

This paper aims to inspire experimentalists to carry out proposed new chiroptical experiments springing from the theoretical study of the role of parity violation in the origin of biomolecular homochirality and to provide a brief update on the current status of calculations of the electroweak parity-violating energy difference (PVED) between enantiomers. If the PVED did select life's handedness, we would expect to find life on other planets consistently using the same hand as terrestrial biochemistry. Much more importantly, even finding the "wrong" hand (rather than a racemic mixture) on another planet could be the homochiral signature of life, and we discuss our proposal for chiroptical detection of life on extra-solar planets. The PVED may also have an exciting future as a "molecular footprint" of fundamental physics: comparison of calculated PVEDs with measured values could one day allow chemists to do "table-top particle physics" more cheaply with improved chiroptical techniques instead of ever larger particle accelerators. We discuss our proposed chiroptical method to measure the PVED by using molecular beams. To our knowledge, optical rotation has not yet been measured in molecular beams, but the rewards of doing so include a host of other "first ever" results in addition to measurement of the PVED.

Theoretical investigations into the enantiomeric and racemic forms of α-(trifluoromethyl)lactic acid

There are many different hypotheses on the origin of biomolecular homochirality. One possible scenario concerns the enantiomeric enrichment of a nearly racemic solid via self-disproportionation of enantiomers. In particular, in a recent paper Soloshonok and co-workers showed a first example of optical self-purification of α-(trifluoromethyl)lactic acid by sublimation [V. A. Soloshonok et al., J. Am. Chem. Soc. 2007, 129, 12112]. Here we present detailed theoretical studies of α-(trifluoromethyl)lactic acid in the solid state as well as in the gas-phase dimeric form. The calculations of energy differences between dimers show that in the solid state the enantiomeric pure compound is energetically preferred, while in the gas phase the equilibrium shifts towards the racemic mixture although thermodynamic corrections cannot be neglected, thus providing a detailed microscopic explanation for the enantio-purification process for the first time.

Evolução biomolecular homoquiral: a origem e a amplificação da quiralidade nas moléculas da vida

The fact that biologically relevant molecules exist only as one of the two enantiomers is a fascinating example of complete symmetry breaking of chirality and has long intrigued our curiosity. The origin of this selective chirality has remained a fundamental enigma with regard to the origin of life since the time of Pasteur, 160 years ago. The symmetry breaking processes, which include autocatalytic crystallization, asymmetric autocatalysis, spontaneous crystallization, adsorption and polymerization of amino acids on mineral surfaces, provide new insights into the origin of biomolecular homochirality.

Earth’s Orbital Chirality and Its Possible Role in Biomolecular Evolution

This essay pointed out and described the natural Earth’s orbital chirality (EOC) and its force field. According to the 2nd law of thermodynamics, it was suggested that the EOC force field could be a natural driving force to result in the origin of biomolecular homochirality, the evolution of biomolecular order and complexity, the origin of “Junk DNA” and the origin of biological information, as well as the origin of biomolecular rhythms, and so on.

Dendritic crystal growth, differential circular scattering, and the origin of biomolecular homochirality

Phthalic acid rapidly crystallizing in thin aqueous films is deposited radially and rhythmically as dendritic banded spherulites that have heterochiral meso-textures in hemi-circles. The chiral fields differentially scatter left and right circularly polarized light. A scenario for chiral amplification and the origin of biomolecular homochirality is thus proposed that combines the influences of crystals and light.

Asymmetric photoreactions as the origin of biomolecular homochirality: a critical review.

The role of asymmetric photoreactions (occurring in space or on the primitive Earth) in the origin of biomolecular homochirality is critically reviewed. A general description of the various possible ways for light to interact with chiral molecules is first presented on the basis of a series expansion of the dielectric constant: natural, magnetic and magnetochiral circular dichroism are identified with the first three terms in this development. Natural and magnetochiral circular dichroism may cause, through asymmetric photolysis, an enantiomeric excess in a racemic mixture of chiral molecules irradiated, respectively, by circularly polarized ultraviolet light, or by unpolarized ultraviolet light in the presence of a magnetic field non-perpendicular to the light beam. Terrestrial and extraterrestrial sites matching these conditions are then critically reviewed. Finally, we stress the possibility to arrive at the homochirality of amino acids through a path involving D-ribose during RNA world as an alternative to the usual scenarios operating directly on amino acids.

Origin of organic molecules and biomolecular homochirality.

Theories about the origin of biomolecular homochirality, which seems to be a prerequisite for the creation of life, are discussed. First, possible terrestrial and extraterrestrial sources of organic molecules are outlined. Then, mechanisms for the formation of enantiomerically enriched compounds and for the amplification of their chirality are described.

ChemInform Abstract: Chiral Autocatalysis: Where Stereochemistry Meets the Origin of Life

This article summarizes a series of recent and simple experiments to produce optically active substances from achiral precursors. These symmetry-breaking processes include either autocatalytic crystallization or asymmetric autocatalysis, and provide new insights into the origin of biomolecular homochirality. In addition, support from an extraterrestrial origin of chiral molecules has also come from recent findings.

Effect of chiral helical force field on molecular helical enantiomers and possible origin of biomolecular homochirality

Biomolecular homochirality means that the amino acids in proteins, and sugars in nucleic acids, occur in one form: amino acids in L-form and sugars in D-form. So far, the reason why these molecules have such uniform chirality is not known. In this paper, it is suggested that a net natural chiral right-handed helical force field, produced by the Earth's orbital chirality (EOC), could affect the stability of molecular helical enantiomers and make the right-handed helical enantiomers more stable than their left-handed enantiomers, so terrestrial biological systems must select both right-handed helical nucleic acids based on D-sugars, and proteins based on L-amino acids. In given conditions, the maximum energy difference between biomolecular helical enantiomers ( ΔE max ⋎E left − E right ∥ ) caused by the EOC may be calculated theoretically to be in the order: B-DNA > A-RNA > A-DNA ⪢ α-protein > β-protein. Our experimental results strongly supported the hypothesis that the EOC could cause the spontaneous selection and amplification of right-handed helical enantiomers and could be the origin of homochirality on the Earth.

Parity-violating energy differences and the origin of biomolecular homochirality

The violation of parity by the weak interactions ensures that enantiomeric chiral molecules have inequivalent energies. These parity-violating energy differences have been calculated, using ab initio methods, for the series of α -amino acids glycine, alanine, valine, serine and aspartic acid, and for a set of polypeptide/protein fragments in both the α -helix and β -sheet secondary structures. In each case the energy differences are found to favour the existence of the natural left-handed l -enantiomers over their unnatural mirror-image right-handed d -enantiomers. The variation of the parity-violating energy difference along a prebiotic reaction path leading to the formation of a possible precursor of alanine has also been determined. Under equilibrium conditions the energy difference is found to preferentially select the stereochemical reaction channel corresponding to the eventual formation of l -alanine rather than that for its unnatural d -enantiomer. The significance of these results in accounting for the prebiotic origins of the terrestrial biomolecular homochirality are discussed.

Parity-violating energy differences of chiral minerals and the origin of biomolecular homochirality

The biochemistry of terrestrial organisms is based on chiral (handed) molecules, with one of the two possible series of enantiomers (mirror-image isomers) being predominant. Specifically, terrestrial biochemistry is homochirally supported by L-α-amino acids and D-sugars to the almost complete exclusion of the enantiomeric D-α-amino acids and L-sugars. This particular homochiral selection may be a result of very small differences between the electronic energies of enantiomeric prebiotic molecules due to the parity-violating weak interactions. The energy differences are, however, so small for simple chiral molecules, that the propagation of homochirality would require a dissymmetry amplification mechanism involving both large quantities of reactants and a long reaction time. An alternative theory, presented here, considering the effects of the parity-violating weak interactions in crystalline enantio-selective prebiotic catalysts, such as the clay silicates, may require considerably less amplification.