Titelbild: Asymmetric Induction by a Nitrogen ¹⁴N/¹⁵N Isotopomer in Conjunction with Asymmetric Autocatalysis (Angew. Chem. 49/2016)

Abstract

Chiralität durch Isotopensubstitution , namentlich mit schwereren Atomen als Wasserstoffisotopen, wird generell nicht als Chiralitätsquelle für chemische Reaktionen angesehen. In der Zuschrift auf S. 15472 ff. nutzen A. Matsumoto, K. Soai et al. ein 14N/15N‐isotopenchirales Diamin, N2,N2,N3,N3‐Tetramethyl‐2,3‐butandiamin, als Initiator für eine asymmetrische Autokatalyse. Dabei gelingt erstmals eine enantioselektive Chiralitätsinduktion ausschließlich auf Grundlage von Stickstoff(14N/15N)‐Isotopensubstitution.

Chemical Mechanisms of Prebiotic Chirality Amplification

“…Summarizing the discussion above, we would like to point out that only the models of chirality amplification based on DNLEs, i.e., on asymmetric autocatalysis and asymmetric autoamplification/dynamic chirality control [33,34,42,47], stand close to the expected conditions for mimicking natural selection in chemical systems [55]. The DNLE-based models, dealing with far-from-equilibrium chemical systems, operate by analogy with competition-based biological processes (which are fundamentally irreversible) [48,55,56], while the models exploiting crystallization-assisted chiral amplification [53,54] or "hyperpositive" nonlinear effects [49] lack this similarity.…”

“…It is thus compatible with the hypothesis of extraterrestrial introduction of organic matter with initial small enantiomeric imbalance ( Figure 2). It is important to notice that the asymmetric bias could be introduced to the Soai reaction not only by nonracemic chiral produc-t/autocatalyst but also by extraneous chiral additives, such as quartz, chiral inorganic crystals, helical silica gel, small chiral (including isotopically chiral) organic molecules [20,[32][33][34], and the abiogenous chiral amino acids obtained from the Murchison meteorite [35], simulating the "chiral triggers" of extraterrestrial origin.…”

Energy Threshold for Chiral Symmetry Breaking in Molecular Self-Replication

“…22,23 Intriguingly, Soai has demonstrated that enantiomers of isotopically chiral initiators -molecules exhibiting chirality only by virtue of an isotope such as 12 C/ 13 C or D/H -are able to direct the reaction faithfully towards opposite enantiomers of the reaction product. [24][25][26][27][28] Figure 1. Left: the Soai autocatalytic reaction.…”

Energy Threshold for Chiral Symmetry Breaking in Molecular Self-Replication

“…22,23 Intriguingly, Soai has demonstrated that enantiomers of isotopically chiral initiators -molecules exhibiting chirality only by virtue of an isotope such as 12 C/ 13 C or D/H -are able to direct the reaction faithfully towards opposite enantiomers of the reaction product. [24][25][26][27][28] We recently reported mechanistic studies to probe the role of isotopically chiral molecule 3 added as an initiator in lieu of the reaction product in the Soai reaction of Scheme 1 to direct stereochemistry in this reaction network. 29 Surprisingly, our studies revealed that the initiator in fact acts as an inhibitor of the autocatalytic pathway.…”