Homochirality mirror symmetry breaking

A closer exploration of the parameter space showed that symmetry breaking is sensitive to the thermodynamic stabilities of the dimers but also to the rate of their formation, predicting that the heterochiral dimers are formed faster and are more stable than the homochiral ones [69]. The fitting of the experimentally obtained data (Fig. 5) resulted in rate parameters that confirm these conclusions and that simultaneously give rise to mirror-symmetry breaking. 

We have given kinetic insight into a number of experimental features of the Soai reaction. It was shown that chiral amplification and mirror-symmetry breaking are driven by a reaction network that contains enantioselective autocatalysis and mutual inhibition as the essential ingredients. In this sense, the Soai reaction moves the early concepts of Frank forward into experimental reality. Taking into account the formation of isopropylzinc alkoxide dimers, an evaluation of the parameter space in which amplification and symmetrybreaking are observed indicates that the heterochiral dimers display a higher thermodynamic stability and have to be formed faster than the homochiral ones. The necessity of such sensitive interplay may explain why such reactions systems are so scarce. 

Chiral surfaces Enantiomorphous crystals Homochiral peptides Mirror symmetry breaking Non-linear kinetics Self-replication of peptides... 

The above examples demonstrate that mirror symmetry breaking by self-assembly of non-chiral molecules into chiral architectures is indeed a feasible process. However, in order to preserve the handedness and amplify the stochastically-generated chirality, it is imperative to couple such chance events with efficient sequential autocatalytic processes. We refer now to several experimental systems that illustrate the occurrence of such scenarios. We shall allude in particular to systems undergoing amplification via non-linear asymmetric catalysis processes, via the formation of 2-D and 3-D crystalline systems and amplification of homochiral bio-like polymers in general and oligopeptides in particular. 

The asymmetric polymerization in crystalline architectures provides an excellent environment to conduct the absolute asymmetric synthesis of polymers, and also provides an effident route for the ampHfication of chirality. Mirror-symmetry breaking might occur either through total asymmetric transformations, either in enantiomorphous crystals that have self-assembled from achiral molecules, or within racemic crystalline architectures which are delineated by chiral rims or surfaces when one of the chiral faces is blocked by an interface. The self-assembly of nonracemic mixtures into a mixture comprising eutectic compositions of a racemic compound and an enantiomorphous assembly, followed by asymmetric transformation, provides a series of thermodynamically controlled, alternative routes for the effident ampHfication of homochirality. 

Such a capability of an oligonucleotide system deserves special attention in the context of the problem of the origin of biomolecular homochirality breaking molecular mirror symmetry by de-racemization is an intrinsic property of such a system whenever the constitutional complexity of the products of co-oligomerization exceeds a critical level. 

One of the most recent observations in supramolecular surface chirality is the induction of homochirality on surfaces via cooperatively amplified interactions in molecular monolayers. As discussed in Sect. 2, adsorption-induced chirality leads to both mirror motifs. However, in the presence of additional chiral bias, lattice homo chirality can be installed in the entire molecular layer. Such bias comes from a chiral dopant, small ee or physical fields in combination with symmetry breaking of the surface. 

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