Origins of Asymmetric Amplification in Autocatalytic Alkylzinc Additions

Blackmond, Donna G.; McMillan, Christopher R.; Ramdeehul, Shailesh; Schorm, and Andrea; Brown, John M.

doi:10.1021/ja0165133

Cited by 223 publications

(163 citation statements)

References 16 publications

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“…The extracted rate parameters again confirm the higher stability of the heterochiral dimers and simultaneously gave rise to mirror-symmetry breaking that has been also observed experimentally in this specific system. A variation in only one of the fitted parameters in the monomeric mechanism (model 2) leads to a qualitative reproduction of the kinetic results of Blackmond et al (20). Hence arguments that have been previously promoted to exclude monomer catalysis (18,20,22,23) have to be reassessed.…”

Section: Resultsmentioning

confidence: 71%

“…A variation in only one of the fitted parameters in the monomeric mechanism (model 2) leads to a qualitative reproduction of the kinetic results of Blackmond et al (20). Hence arguments that have been previously promoted to exclude monomer catalysis (18,20,22,23) have to be reassessed. In fact, our simulations give slight indication for a monomeric instead of a dimeric catalytic pathway because of the better agreement of model 2 with the experimental kinetic data reported by Gridnev et al (16).…”

Section: Resultsmentioning

confidence: 71%

“…Blackmond and coworkers (20) conducted a series of calorimetrically monitored kinetic studies from which it was first concluded that the catalyst is dimeric, and then later that it is tetrameric (23) or even multimeric. In these experiments no mirror-symmetry breaking has been mentioned.…”

Section: Resultsmentioning

confidence: 99%

“…From the various attempts of kinetic modeling (19)(20)(21)(22)(23), it appears that autocatalysis and mutual inhibition are the necessary ingredients for the Soai reaction to describe the observed chiral amplification. However, reports using these approaches have not discussed the origin of the experimentally observed mirror-symmetry breaking so far.…”

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confidence: 99%

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Mirror-symmetry breaking in the Soai reaction: A kinetic understanding

Islas

Lavabre

Grévy

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

127

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Kinetic modeling using nonlinear differential equations is proposed to analyze the spontaneous generation of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction). Our approach reproduces experimentally observed giant chiral amplification from an initial enantiomeric excess of <10 ؊6 % to >60%, high sensitivity and positive response to the presence of minute amounts of chiral initiator at concentrations <10 ؊14 M, and spontaneous absolute asymmetric synthesis from achiral starting conditions. From our numerical simulations using kinetic schemes derived from the Frank model, including stereospecific autocatalysis and mutual inhibition, we have shown that it is possible to reproduce the mirror-symmetry-breaking behavior of the Soai reaction under batch conditions leading to a bimodal enantiomeric product distribution. Mirror-symmetry breaking was found to be resistant to a loss of stereoselectivity up to 30%. While the mutual inhibition between enantiomers seems to originate from the presence of dimerization equilibria, the exact nature of the autocatalytic stereoselective process still remains to be revealed. From the kinetic viewpoint, simple autocatalysis involving monomers as the catalytic species is consistent with all reported experimental effects of the Soai reaction.alkylzinc addition ͉ autocatalysis ͉ chirality A symmetric synthesis usually requires the intervention of chiral chemical reagents or catalysts. Few examples are known in which the generation of enantiomerically enriched products occurs from achiral precursors without the involvement of such auxiliaries. These cases, known as absolute asymmetric synthesis (1, 2), have been mostly observed in the combination of spontaneous resolution and enantioselective catalysis (3) as well as by the influence of external chiral factors such as circularly polarized light (4) or vortex motion (5). Some cases were reported in which no obvious chiral inductor was used and, nevertheless, high enantiomeric excess (ee) has been obtained systematically. These examples display the signature of mirrorsymmetry breaking (6), i.e., a process in which a small random ee is greatly amplified, whereas the chirality sign remains unpredictable for each individual experiment. The generation of small random ee occurs practically in any chiral system for statistical reasons alone in which the ee is inversely proportional to the square root of the number of molecules, ee ϰ n Ϫ1/2 (7). However, this value remains negligible as long as a large number of molecules is involved, so an amplification mechanism is needed to increase such minute ee to a macroscopic level.Mirror-symmetry breaking in chemical systems is typically associated to autocatalytic kinetics, i.e., a feedback mechanism in which one or several reaction products directly increase the overall rate of the chemical reaction. Hence in the specific case of chiral autocatalysis, the enantiomeric product could act as an asymmetric catalyst of its proper forma...

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Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Mirror-symmetry breaking in the Soai reaction: A kinetic understanding

Islas

Lavabre

Grévy

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

127

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“…14 and in Fig. 3 of this work, when not coupled to a mutual heterochiral interaction reaction between enantiomers, as in the case of Frank-like systems 9,28,29 and LES models, 5,6 most likely cannot play a role in spontaneous mirror symmetry breaking and the abiotic emergence of chirality. …”

Section: Discussionmentioning

confidence: 70%

Necessary conditions for the emergence of homochirality via autocatalytic self-replication

Stich

Ribó

Blackmond

et al. 2016

The Journal of Chemical Physics

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We analyze a recent proposal for spontaneous mirror symmetry breaking based on the coupling of first-order enantioselective autocatalysis and direct production of the enantiomers that invokes a critical role for intrinsic reaction noise. For isolated systems, the racemic state is the unique stable outcome for both stochastic and deterministic dynamics when the system is in compliance with the constraints dictated by the thermodynamics of chemical reaction processes. In open systems, the racemic outcome also results for both stochastic and deterministic dynamics when driving the autocatalysis unidirectionally by external reagents. Nonracemic states can result in the latter only if the reverse reactions are strictly zero: these are kinetically controlled outcomes for small populations and volumes, and can be simulated by stochastic dynamics. However, the stability of the thermodynamic limit proves that the racemic outcome is the unique stable state for strictly irreversible externally driven autocatalysis. These findings contradict the suggestion that the inhibition requirement of the Frank autocatalytic model for the emergence of homochirality may be relaxed in a noise-induced mechanism. Published by AIP Publishing. [http://dx

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Description of the Condition for Asymmetric Amplification in Autocatalytic Reactions

Blackmond

2002

Advanced Synthesis & Catalyis

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Origins of Asymmetric Amplification in Autocatalytic Alkylzinc Additions

Cited by 223 publications

References 16 publications

Mirror-symmetry breaking in the Soai reaction: A kinetic understanding

Mirror-symmetry breaking in the Soai reaction: A kinetic understanding

Necessary conditions for the emergence of homochirality via autocatalytic self-replication

Description of the Condition for Asymmetric Amplification in Autocatalytic Reactions

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