Chiral Symmetry Breaking in Sodium Chlorate Crystallization
16 Nov 1990-Science (American Association for the Advancement of Science)-Vol. 250, Iss: 4983, pp 975-976
TL;DR: This result represents an experimental demonstration of chiral symmetry breaking or total spontaneous resolution on a macroscopic level brought about by autocatalysis and competition between L- and D-crystals.
Abstract: Sodium chlorate (NaClO3) crystals are optically active although the molecules of the compound are not chiral. When crystallized from an aqueous solution while the solution is not stirred, statistically equal numbers of levo (L) and dextro (D) NaClO3 crystals were found. When the solution was stirred, however, almost all of the NaClO3 crystals (99.7 percent) in a particular sample had the same chirality, either levo or dextro. This result represents an experimental demonstration of chiral symmetry breaking or total spontaneous resolution on a macroscopic level brought about by autocatalysis and competition between L- and D-crystals.
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TL;DR: In this paper, it was shown that autocatalysis in a chemical reaction can indeed enhance a small initial enantiomeric excess of a chiral molecule, and that the resulting chirality imbalance can become overwhelming.
Abstract: THE homochirality of natural amino acids and sugars remains a puzzle for theories of the chemical origin of life1–18. In 1953 Frank7 proposed a reaction scheme by which a combination of autocatalysis and inhibition in a system of replicating chiral molecules can allow small random fluctuations in an initially racemic mixture to tip the balance to yield almost exclusively one enantiomer. Here we show experimentally that autocatalysis in a chemical reaction can indeed enhance a small initial enantiomeric excess of a chiral molecule. When a 5-pyrimidyl alkanol with a small (2%) enantiomeric excess is treated with diisopropylzinc and pyrimidine-5-car-boxaldehyde, it undergoes an autocatalytic reaction to generate more of the alkanol. Because the reaction involves a chiral catalyst generated from the initial alkanol, and because the catalytic step is enantioselective, the enantiomeric excess of the product is enhanced. This process provides a mechanism by which a small initial imbalance in chirality can become overwhelming.
861 citations
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Abstract: Over the past thirty years, a new systemic conception of life has emerged at the forefront of science. New emphasis has been given to complexity, networks, and patterns of organisation, leading to a novel kind of 'systemic' thinking. This volume integrates the ideas, models, and theories underlying the systems view of life into a single coherent framework. Taking a broad sweep through history and across scientific disciplines, the authors examine the appearance of key concepts such as autopoiesis, dissipative structures, social networks, and a systemic understanding of evolution. The implications of the systems view of life for health care, management, and our global ecological and economic crises are also discussed. Written primarily for undergraduates, it is also essential reading for graduate students and researchers interested in understanding the new systemic conception of life and its implications for a broad range of professions - from economics and politics to medicine, psychology and law.
835 citations
TL;DR: This paper presents a probabilistic analysis of the stationary phase replacement of Na6(CO3)(SO4)/ Na2SO4 in horseshoe clusters and shows clear trends in the number of stationary phases and in the stationary phases of Na2CO3.
Abstract: Kepa Ruiz-Mirazo,†,∥ Carlos Briones,‡,∥ and Andreś de la Escosura* †Biophysics Unit (CSIC-UPV/EHU), Leioa, and Department of Logic and Philosophy of Science, University of the Basque Country, Avenida de Tolosa 70, 20080 Donostia−San Sebastiań, Spain ‡Department of Molecular Evolution, Centro de Astrobiología (CSIC−INTA, associated to the NASA Astrobiology Institute), Carretera de Ajalvir, Km 4, 28850 Torrejoń de Ardoz, Madrid, Spain Organic Chemistry Department, Universidad Autońoma de Madrid, Cantoblanco, 28049 Madrid, Spain
616 citations
TL;DR: System Chemistry has arisen in recent years as a new discipline that aims to investigate complex mixtures of interacting molecules and can give rise to outstanding emergent properties as a result of the interaction of the individual components and cannot be ascribed to any of their components acting in isolation.
Abstract: Nature successfully manages under extremely adverse conditions to accomplish intricate functions responsible for the regulation and control of the vast majority of biological processes that eventually sustain life on our planet. Biological molecules are required to carry out selective functions while often being hindered by surrounding agents which are simultaneously competing to bind the same targets. This high degree of selectivity in nature ultimately depends on the “molecular instructions” encoded in the chemical structure of the interacting species responsible for every single recognition or discrimination event. The formation of the DNA double helix, for instance, requires the base-pairing (sorting) of complementary nitrogenous bases (adenine thymine (A T) and cytosine guanine (C G)). These high-fidelity recognition processes are crucial in the storage of genetic information used in the development and functioning of all known living organisms and some viruses. Other sophisticated superstructures such as microtubules, are built upon polymerization of dimers of two different globular proteins (Rand β-globulin), giving rise to cylindrical micrometric arrangements. The formation of heterodimers composed of two different proteins requires the self-discrimination of equals, and the simultaneous recognition of complementary units. In the final instance, the small molecules of life (e.g., sugars, amino acids and fatty acids) are able to assemble not only to form such abovementioned macromolecules, but also to self-sort in one of the most efficient and complex processes known in nature to build the functional basic unit of life: a cell. In a cell, multiple levels of compartmentalization arising from the self-sorting of their molecular components allow the coexistence of different functional architectures acting independently. This exceptional selectivity in nature makes possible the existence of life on our planet. Unlike the high complexity of natural or biological architectures, the majority of artificial self-assembled systems reported so far have been investigated in isolation. This has been mainly due to the lack of suitable characterization methods and technical or economic constraints, which far exceed the resources of most research institutes. However, the remarkable development of analytical tools is increasingly enabling scientists to pinpoint intractable problems associated to multicomponent mixtures. In this context, Systems Chemistry has arisen in recent years as a new discipline that aims to investigate complex mixtures of interacting molecules. 17 These mixtures can give rise to outstanding emergent properties as a result of the interaction of the individual components and cannot be ascribed to any of their components acting in isolation. Although this emerging discipline is still in its infancy, ongoing research advances are enabling current (supramolecular) chemists to unravel the behavior of individual molecules in multicomponent mixtures and to anticipate the reasons that lead artificial molecules to bind or ignore a specific partner in a complex multicomponent environment. In this review, wewill discuss the external variables and intrinsic factors (molecular codes) that influence the recognition or discrimination of supramolecularly interacting chemical species in solution. The comprehension of this “molecular programming” in artificial systems will define the variables that control self-sorting processes, and may ultimately contribute to a better understanding of the self-assembly pathways in natural systems. By restricting ourselves to noncovalent bonds and self-sorting in solution we will not cover self-assembly processes on solid surfaces and self-sorting phenomena based on reversible covalent bonds.However, excellent reviews have recently become available by De Feyter and Otto, which cover these topics.
595 citations
TL;DR: The unexpected result is that the chirality sign of these homoassociates can be selected by vortex motion during the aggregation process and this result is confirmed by means of circular dichroism spectra.
Abstract: Achiral diprotonated porphyrins, forming homoassociates in aqueous solution, lead to spontaneous chiral symmetry breaking. The unexpected result is that the chirality sign of these homoassociates can be selected by vortex motion during the aggregation process. This result is confirmed by means of circular dichroism spectra. These experimental findings are rationalized in terms of the asymmetric influence of macroscopic forces on bifurcation scenarios and by considering the specific binding characteristics of the porphyrin units to form the homoassociates.
581 citations
References
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TL;DR: This work has shown that the parity-violating weak neutral current interaction gives rise to an energy difference between a chiral molecule and its mirror-image isomer, resulting in a small stabilization of the L-amino acids and theL-peptides in the α-helix and the β-sheet conformation relative to the corresponding enantiomer.
Abstract: Classical mechanisms proposed for the transition from racemic geochemistry to homochiral biochemistry in terrestrial evolution generally ascribe to chance the particular handed choice of the L-amino acids and the D-sugars by self-replicating systems. The parity-violating weak neutral current interaction gives rise to an energy difference between a chiral molecule and its mirror-image isomer, resulting in a small stabilization of the L-amino acids and the L-peptides in the alpha-helix and the beta-sheet conformation relative to the corresponding enantiomer. The energy difference suffices to break the chiral symmetry of autocatalytic racemic reaction sequences in an open non-equilibrium system.
366 citations
284 citations
TL;DR: These results demonstrate the possibility of the spontaneous generation of optically active material starting from an inactive, closed system without interference of any directing, dissymmetric agency.
181 citations
TL;DR: I think that organisms acquired optical activity, not as a gift from the inorganic world, but through processes of selection out of originally racemic mixtures, and the nature of such processes is outlined.
Abstract: No other chemical characteristic is as distinctive of living organisms as is optical activity. Outside of organisms, all syntheses of disymmetric molecules produce equal numbers of optical antipodes (racemic mixtures) unless deliberate means are employed to bias the result by the use of asymmetric reagents or forces. Inside living organisms, however, all syntheses and degradations of such molecules involve one enantiomorph alone. Only the fact that chemistry is learned from the plane surfaces of paper and blackboard makes such selectivity seem strange. We tend to think of optical isomers as very much alike, but in fact they represent profound differences in shape; and, in the types of reaction upon which life depends, involving the ceaseless, intimate fitting together of molecular surfaces, shape is all-important. Organisms made the choice between optical antipodes long ago. To tamper with that choice now would be like trying to draw a left glove on a right hand. A start in either direction might be self perpetuating, but how was the original choice made? I n the past I think discussions of this problem have been misdirected, in the sense that an attempt was made to propose ways in which inorganic devices might have produced populations of organic molecules of predominantly one configuration or the other which, on their later incorporation into living organisms, conferred their optical activity on the latter. It is enormously more probable, of course, that all geochemical syntheses of organic molecules produced racemic mixtures. I think that organisms acquired optical activity, not as a gift from the inorganic world, but through processes of selection out of originally racemic mixtures. In what follows I shall try to outline the nature of such processes. How was this choice made initially?
167 citations