Asymmetric Autocatalysis Research Articles

Asymmetric Autocatalysis Initiated by Finite Single-Wall Carbon Nanotube Molecules with Helical Chirality

An asymmetric autocatalysis reaction was initiated by a finite single-wall carbon nanotube molecule with helical chirality. The asymmetric induction was initiated by the chiral environment arising from the planar chirality of the tubular polyaromatic hydrocarbons.

Enantiodivergent formation of a chiral cytosine crystal by removal of crystal water from an achiral monohydrate crystal under reduced pressure

An achiral nucleobase cytosine forms an achiral monohydrate crystal (space group: P21/c) by crystallization from a water solution. It was found that the removal of crystal water under reduced pressure at room temperature afforded a chiral crystal of anhydrous cytosine (P212121). The crystal chirality of anhydrous cytosine corresponds to the enantiotopic crystal face of the achiral monohydrate; therefore, when the enantiotopic b1-face is exposed to the reduced pressure, dehydration occurred in the direction from the b1-face to provide [CD(+)310KBr]-cytosine crystal. In contrast, dehydration from the b2-face gave the opposite enantiomorphous [CD(−)310KBr]-cytosine crystal. The correlation between enantiotopic faces and the formed crystal chirality is opposite to that from dehydration by heating. The formed chiral cytosine crystals act as a chiral trigger for asymmetric autocatalysis with enantioenrichment amplification of pyrimidylalkanol.

Asymmetric Autocatalysis Induced by Cinnabar: Observation of the Enantioselective Adsorption of a 5‐Pyrimidyl Alkanol on the Crystal Surface

Asymmetric Autocatalysis Induced by Cinnabar: Observation of the Enantioselective Adsorption of a 5‐Pyrimidyl Alkanol on the Crystal Surface

Asymmetric Autocatalysis Induced by Cinnabar: Observation of the Enantioselective Adsorption of a 5‐Pyrimidyl Alkanol on the Crystal Surface

Das chirale Mineral Zinnober bewirkt die Bildung von enantiomerenangereichertem 5-Pyrimidylalkanol in einer asymmetrischen Autokatalyse. Die Strukturen dabei auftretender adsorbierter Verbindungen wurden rasterkraftmikroskopisch untersucht. Die enantioselektive Adsorption des asymmetrischen Autokatalysators führte zur Ablagerung von Mikrokristallen auf der chiralen Oberfläche des Zinnobers.

Enantioselective Synthesis Induced by the Helical Molecular Arrangement in the Chiral Crystal of Achiral Tris(2-hydroxyethyl) 1,3,5-Benzenetricarboxylate in Conjunction with Asymmetric Autocatalysis

Abstract 5-Pyrimidyl alkanol with an enantiomeric excess of up to >99.5% was formed using chiral crystals of achiral tris(2-hydroxyethyl) 1,3,5-benzenetricarboxylate as a chiral initiator. In the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, the helicity of the molecular arrangement of achiral tricarboxylate in the crystalline state could be successfully used as a source of chirality to afford enantioenriched alkanol in conjunction with asymmetric autocatalysis with amplification of enantiomeric excess.

ChemInform Abstract: Asymmetric Autocatalysis Triggered by Chiral Crystals Formed from Achiral Compounds and Chiral Isotopomers

AbstractReview: 77 refs.

Creation and Persistence of Chiral Asymmetry in a Microscopically Reversible Molecular Model

Of the numerous mechanisms that have been postulated to explain the origin of biological homochirality, asymmetric autocatalysis coupled with mutual inhibition is often cited as a plausible route to abiotic symmetry breaking. However, in a system closed to mass flow, the constraint of microscopic reversibility ensures that this far-from-equilibrium phenomenon can at best provide a temporary excursion from racemic equilibrium. Comparatively little attention has been paid in the literature to the manner in which such a closed system approaches equilibrium, examining the mechanisms and time scales involved in its transit. We use an elementary lattice model with molecular degrees of freedom, and satisfying microscopic reversibility, to investigate the temporal evolution of stochastic symmetry breaking in a closed system. Numerical investigation of the model's behavior identified conditions under which the system's evolution toward racemic equilibrium becomes extremely slow, allowing for long-time persistence of a symmetry-broken state. Strong mutual inhibition between enantiomers facilitates a "monomer purification" mechanism, in which molecules of the minor enantiomer are rapidly sequestered and a nearly homochiral state persists for long times, even in the presence of significant reverse reaction rates. Simple order of magnitude estimates show that with reasonable physical parameters a symmetry-broken state could persist over geologically relevant time scales.

Asymmetric autocatalysis triggered by oxygen isotopically chiral glycerin

Chiral (S)- and (R)-(18)O-glycerin induces enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde, and the subsequent asymmetric autocatalysis affords (R)- and (S)-pyrimidyl alkanol with high enantiomeric excess, respectively.

不斉の起源解明への有機合成化学的アプローチ—不斉増幅する不斉自己触媒反応—

不斉の起源解明への有機合成化学的アプローチ—不斉増幅する不斉自己触媒反応—

Observation of a Transient Intermediate in Soai’s Asymmetric Autocatalysis: Insights from 1H NMR Turnover in Real Time

Observation of a Transient Intermediate in Soai’s Asymmetric Autocatalysis: Insights from ¹H NMR Turnover in Real Time

Observation of a Transient Intermediate in Soai’s Asymmetric Autocatalysis: Insights from 1H NMR Turnover in Real Time

Observation of a Transient Intermediate in Soai’s Asymmetric Autocatalysis: Insights from 1H NMR Turnover in Real Time

Autocatalytic Replication and Homochirality in Biopolymers: Is Homochirality a Requirement of Life or a Result of It?

A key step in the origin of life is the establishment of autocatalytic cycles controlled by biopolymer catalysts. These catalysts (either ribozymes or proteins) are composed of homochiral monomers. Homochirality in living systems is maintained because biopolymers are asymmetric in their catalysis and synthesize molecules of their own handedness. Asymmetric autocatalysis is also possible with small molecules, as demonstrated by the Soai reaction, but it is rare. As far as we know, single nucleotides and amino acids are not autocatalytic. The observation that organic molecules in meteorites can have an enantiomeric excess of a few percent suggests that the prebiotic mixture may have had a partial chiral bias that was caused by external physical influences. Here, we consider the way that such a partial prebiotic bias would influence the origin of ribozymes in an RNA world scenario. We have previously shown how a transition to a living state can occur in a model for RNA polymerization. Here, we add chirality to the problem by considering simultaneous synthesis and polymerization of left- and right-handed monomers. The two chemical synthesis rates may be equal or unequal, due to physical or chemical effects prior to the origin of life. We determine the stationary states of this reaction system. The nonliving state is racemic, or slightly biased. There are two living states that are almost completely homochiral, whether or not the nonliving state is biased. It is a feature of our model that, for some regions of parameter space, living and nonliving states are both found to be stable under the same conditions. The origin of life therefore involves a stochastic transition between the nonliving and living states. Our model extends previous theories by treating the origin of life and the origin of chirality as aspects of the same model.

Asymmetric Autocatalysis Triggered by Chiral Crystals Formed from Achiral Compounds and Chiral Isotopomers

AbstractAsymmetric autocatalysis with amplification of enantiomeric excess is found in the enantioselective addition of diisopropylzinc to pyrimidine‐5‐carbaldehyde using pyrimidyl alkanol as an asymmetric autocatalyst. Asymmetric autocatalysis has been employed as a method for clarifying the origin of homochirality. Circularly polarized light, inorganic chiral crystals and statistical fluctuation of enantiomeric imbalance act as chiral initiators in asymmetric autocatalysis to afford highly enantioenriched products. We have investigated asymmetric autocatalysis using chiral crystals formed from achiral and racemic compounds as an origin of chirality. Absolute control of the crystal chirality of cytosine was achieved by the removal of crystal water. Enantioselective carbon‐carbon bond formation at the enantiotopic crystal face of aldehydes was established using diisopropylzinc vapor. In addition, asymmetric autocatalysis triggered by chiral compounds arising from H, C and O isotope substitution has been achieved.

Reversal in enantioselectivity induced by achiral alcohols in asymmetric autocatalysis in the presence of a chiral diol as a chiral initiator

A reversal in enantioselectivity was observed by the combination of a chiral diol and achiral alcohols as a chiral initiator in the asymmetric alkylation of a pyrimidine-5-carbaldehyde using diisopropylzinc. (2S,3S)-Butane-2,3-diol alone induced (R)-pyrimidyl alkanol, while a mixture of the chiral diol and phenol derivatives induced (S)-pyrimidyl alkanol. The effect of achiral alcohols is also discussed.

Amplification of enantiomeric excess, mirror-image symmetry breaking and kinetic proofreading in Soai reaction models with different oligomeric orders

A comprehensive kinetic analysis of three prototypical autocatalytic cycle models based on the absolute asymmetric Soai reaction is presented. The three models, which can give rise to amplification of enantiomeric excess and mirror-image symmetry breaking, vary by their monomeric, dimeric or trimeric order of the assumed catalytic species. Our numerical approach considered the entire chiral combinatorics of the diastereomeric interactions in the models as well as the multiplicity of coupled reversible reactions without applying fast equilibration or quasi-steady state approximations. For the simplest monomeric model, an extensive range of parameters was explored employing a random grid parameter scanning method that revealed the influence of the parameter values on the product distribution, the reaction-time, the attenuation or amplification of enantiomeric excess as well as on the presence or absence of mirror-image symmetry breaking. A symmetry breaking test was imposed on the three models showing that an increase in the catalytic oligomer size from one to three leads to a higher tolerance to poorer chiral recognition between the diastereoisomers and identifies the greater impact of the diastereoisomeric energy difference over an imperfect stereoselectivity in the catalytic step. This robustness is understood as a particular case of so-called kinetic proofreading in asymmetric autocatalysis.

Asymmetric autocatalysis initiated by achiral nucleic acid base adenine: implications on the origin of homochirality of biomolecules

Enantiomorphous crystals of adeninium dinitrate acted as the source of chirality in asymmetric autocatalysis producing highly enantioenriched (S)- and (R)-5-pyrimidyl alkanols, with the absolute configurations corresponding to that of crystals.

ChemInform Abstract: Asymmetric Induction Arising from Enantiomerically Enriched Carbon‐13 Isotopomers and Highly Sensitive Chiral Discrimination by Asymmetric Autocatalysis

AbstractReview: 50 refs.

Asymmetric Induction Arising from Enantiomerically Enriched Carbon-13 Isotopomers and Highly Sensitive Chiral Discrimination by Asymmetric Autocatalysis

Abstract Carbon-isotope chirality generated only by the substitution of carbon-13/carbon-12 can be amplified to enantioenriched 5-pyrimidyl alkanol by asymmetric autocatalysis, in which an extremely low enantiomeric excess (ca. 0.00005% ee) can automultiply during three consecutive reactions to >99.5% ee. Chiral carbon-isotopomers can act as a chiral trigger in the reaction between pyrimidine-5-carbaldehyde and diisopropylzinc to induce a small enantioselectivity in the resulting asymmetric autocatalyst, whose enantiomeric excess can be enhanced significantly by the subsequent asymmetric autocatalysis. Asymmetric autocatalysis has the enormous power to recognize the isotope chirality arising from the small difference between carbon (13C/12C) and hydrogen (D/H) isotopes. The tiny chiral influence in the hydrogen isotopically chiral amino acids such as glycine can be recognized and amplified by asymmetric autocatalysis. Furthermore, asymmetric autocatalysis can be applied to the highly sensitive chiral discrimination of cryptochiral compounds such as saturated quaternary hydrocarbon and isotactic polystyrene. Circularly polarized light, which is considered a possible candidate for the origin of chirality, acts as the chiral initiator in asymmetric autocatalysis, affording highly enantioenriched products with the absolute configuration correlated to the helicity of CPL. In addition, chiral crystals formed from achiral organic compounds can act as chiral initiators of asymmetric autocatalytic amplification of ee to afford enantioenriched (S)- and (R)-5-pyrimidyl alkanols corresponding to the solid-state chirality in chiral crystals.

ChemInform Abstract: Enantioselective Synthesis Induced by Compounds with Chirality Arising from Partially Deuterated Methyl Groups in Conjunction with Asymmetric Autocatalysis.

AbstractThe use of less amounts of the catalyst leads to moderate enantiomeric excess of the product.

Asymmetric Autocatalysis: Triggered by Chiral Isotopomer Arising from Oxygen Isotope Substitution

Trigger happy: chiral oxygen isotopomers of hydrobenzoin ([(18)O](R)-1 and [(18)O](S)-1) acted as chiral triggers to induce the enantioselective addition of iPr(2)Zn to pyrimidine-5-carbaldehyde. An extremely small chiral influence arising from the presence of the oxygen isotope ((18)O) is amplified through asymmetric autocatalysis to enantioenrich the 5-pyrimidyl alkanol product.