No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Origins of Biomolecular Handedness
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.
... There was a considerable amount of speculation in relation to the early findings of the stabilization of L-amino acids and D-sugars by parity violation. [7][8][9][10][11] These results were, however, refuted by recent theory." [12][13][14][15][16][17][18][19][20][21][22][23][24][25] Three-dimensional structure is a minimum prerequisite for protein functions. ...
... We use other work published by Brack to illustrate. Asp side chains are more effective than Glu in forming β-sheets, 71 and (Asp-Leu) 5 , (Asp-Leu) 10 , and (Asp-Leu) 15 in water did not produce β-sheets at all. Cationic metal ions can interact with acidic side chains to inhibit charge repulsions, but no β-sheets were observed even if NH 4 Cl, CaCl 2 , or MgCl2 were added to (Asp-Leu) 5 and (Asp-Leu) 12 . ...
Three-dimensional structure is a minimum prerequisite for protein functions. I show that even for optimized amino acid sequences under ideal laboratory conditions only 5–10% randomly distributed D-amino acids would prevent polypeptides composed of L-amino acids from forming a stable structure in water. Parity violation and selective degradation of one amino acid enantiomer by circularly polarized light could not have produced the necessary L-amino acid excess. Carefully
designed experiments to amplify an initial enantiomeric excess using partial sublimation, crystallization separation techniques, isolation of eutectic mixtures, chiral minerals, and chiral auxiliaries are not plausible naturalistic solutions
for the origin of large enantiopure peptides.
... In 1898, Frederic S. Kipping and William J. Pope were possibly the first to use statistical analysis to account for MSB of chiral d-or l-NaClO 3 cubic crystal (space group P2 1 3) obtained from water solutions of achiral NaClO 3 in the absence and in the presence of D-glucitol under stagnant conditions as to whether the chance or necessity mechanism is valid regarding the origin of biological chirality [124]; whether MSB is merely as a result of by-chance mechanism, obeying a mirror-symmetrical gaussian function, or a handed MSB (HMSB) is determined by the necessity due to unresolved factors, obeying a non-mirror-symmetrical gaussian function [125,126]. Note that MSB does not mean P-violation in chemistry, while, possibly, an HMSB means P-violation in chemistry. ...
... Re-use and distribution is strictly not permitted, except for Open Access articles. molecules, that possess rotational freedom along with single bonds such as C-C, C-O, C-N, and O-O [126,166,167]. ...
The present comprehensive chapter would stimulate to overview historical backgrounds and recent topics, regarding C(charge conjugation), P(parity), T(time reversal), CP(charge-parity), PT(parity-time), and CT(charge-time) violations in the framework of CPT(charge-parity-time) invariance in cosmology, elementary particle physics, subatomic and atomic physics, chemistry (inorganic and organic small molecules, supramolecules, macromolecules, and polymeric materials), biochemistry, and life science. In my view with a deep understanding, and cumulative knowledge of four fundamental forces in physics, involving P-violating weak force and P-conserving gravitational, electromagnetic, and strong forces, it is possible to state that they are no longer segregated, and are likely to intimately connect to each other.
... The constituents participating in supramolecular architecture should possess more than two complementary sites in terms of strong and directional hydrogen bonds 5 . Nature sets a beautiful example of maintaining integrity in bio-molecular structures by exploiting 6 the complementarities between hydrogen bonded systems 6,7 . Appropriate programming of complementarities between molecular species resulted in linear as well as non-linear arrays in supramolecular architectures. ...
... The constituents participating in supramolecular architecture should possess more than two complementary sites in terms of strong and directional hydrogen bonds 5 . Nature sets a beautiful example of maintaining integrity in bio-molecular structures by exploiting 6 the complementarities between hydrogen bonded systems 6,7 . Appropriate programming of complementarities between molecular species resulted in linear as well as non-linear arrays in supramolecular architectures. ...
The present manuscript describes an in-depth analysis of various interactions present in the crystal structure of formyl coumarins using Crystal explorer 17.0. Element based interactions were quantified by the decomposition of generated 3D surfaces into 2D fingerprint regions. DFT methods were used to explore electrostatic parameters, global and local reactivity descriptors. Electrophilicity based charge transfer (ECT) analysis was done to explore the probability of charge transfer between formyl coumarins and DNA base pairs. The reactivity and selectivity of different formyl coumarins have been accessed using Fukui functions in their reduced form. Non-bonding orbital (NBO) analysis revealed the presence of various hyperconjugative interactions and their stabilization energy in formyl coumarins. Non-linear optical properties are presented in terms of first order hyperpolarizibility (β0), where maximum β0 is observed for C4 (1.64 × 10-30esu.) which is found to be 2 times greater than that of p-nitroaniline. Molecular electrostatic potential (MEP) plots are mapped in terms of electron density.
... The chirality, or handedness, introduced by Lord Kelvin in 1894, is defined as a fundamental asymmetry property describing systems, distinguishable from their mirror images. The concept of chirality provides a remarkable addition to the foundational pillars of our world that applies to a wide multiplicity of sciences ranging from particle physics and life science to the structure of the universe (Hegstrom and Kondepudi, 1990;Mason, 1984;Monastyrsky, 2007;Wagnière, 2008). The chirality of the materials has become one of the focuses of modern material science, focusing on the materials manifesting exceptional optical, plasmonic, biochemical, and pharmaceutic properties. ...
Chirality, an inherent property of most objects of the universe, is a dynamic research topic in material science, physics, chemistry, and biology. The fundamental appeal of this extensive study is supported by the technological quest to manufacture materials with configurable chiralities for emerging applications ranging from optoelectronics and photonics to pharmaceutics and medicine. Recent advances put forth ferroelectrics as a host of chiral topological states in the form of Bloch domain walls, skyrmions, merons, and Hopfions, offering thus a unique ground for making chirality switchable and tunable. Here we review current developments, milestones achieved, and future routes of chiral ferroelectric materials. We focus on insights into the topological origin of the chirality in the nanostructured ferroelectrics, bringing new controllable functionalities. We pay special attention to novel developments enabling tunability and manipulating the chiroptical response and enantioselectivity, leading to new applications in nano-optoelectronics, plasmonics, pharmaceutics, and bio-medical industries.
... However, these PVEDs are extremely small, orders of magnitude smaller than statistical fluctuations. The biggest result for this theory has been that the PVED between two enantiomers was shown to almost systematically favor the populations of "natural" enantiomers (L-amino acid, D-sugars and their polymers) over their "unnatural" mirror image to the extent of about 1 part in 10 17 (Mason 1984;Mason, Tranter 1985). This means that the biological versions of chiral monomers and polymers are ever so slightly more stable than their nonbiological counterparts, due to the asymmetry of the weak interactions. ...
... e., spin polarized) substrates. The driving force for this search comes mainly from chemical and biological applications: since all living beings accept only one of the two stereoisomers, 3 there is a strong drive from the chemical and pharmaceutical industries to find ways to selectively produce the desired enantiomer 4 or at least to efficiently separate the two forms contained in a racemic mixture. The former goal could be achieved, for instance, thanks to the use of enantioselective heterogeneous catalysts based on magnetic materials that selectively adsorb the desired reactant, or else that only catalyze the formation of a specific enantiomer through spinselective charge transfer. ...
The recent demonstration of the existence of an intimate relationship between the chiral structure of some materials and the spin polarization of electrons transmitted through them, what has been called the chirality-induced spin selectivity (CISS) effect, is sparking interest in many related phenomena. One of the most notorious is the possibility of using magnetic materials to apply enantioselective interactions on chiral molecules and chemical reactions involving them. In this work, x-ray photoelectron spectroscopy has been used to characterize the adsorption and growth kinetics of enantiopure organic molecules on magnetic (Co) and non-magnetic (Cu) substrates. While on these latter, no significant enantiosensitive effects are found, on spin-polarized, in-plane magnetized Co surfaces, the two enantiomers have been found to deposit differently. The observed effects have been interpreted as the result of one of the enantiomers being adsorbed in a transient, weakly bound physisorbed-like state with higher mobility due to limited, spin-selective charge transfer between it and the substrate. The study of these phenomena can provide insight into the fundamental mechanisms responsible for the CISS effect.
... However, it may seem as if forces are negligible to favour a form over its mirror image. There is hardly any difference in energy between two enantiomers when in a test tube [1][2][3][4][5] or between a particle and its antiparticle when in a cloud chamber [6,7]. Thus, under these reduced experimental conditions, the dissymmetry in abundance between left-and right-handed forms seems inexplicable indeed [8,9]. ...
The prevalence of chirally pure biological polymers is often assumed to stem from some slight preference for one chiral form at the origin of life. Likewise, the predominance of matter over antimatter is presumed to follow from some subtle bias for matter at the dawn of the universe. However, rather than being imposed from the start, handedness standards in societies emerged to make things work. Since work is the universal measure of transferred energy, it is reasoned that standards at all scales and scopes emerge to consume free energy. Free energy minimization, equal to entropy maximization, turns out to be the second law of thermodynamics when derived from statistical physics of open systems. This many-body theory is based on the atomistic axiom that everything comprises the same fundamental elements known as quanta of action; hence, everything follows the same law. According to the thermodynamic principle, the flows of energy naturally select standard structures over less-fit functional forms to consume free energy in the least time. Thermodynamics making no distinction between animate and inanimate renders the question of life’s handedness meaningless and deems the search for an intrinsic difference between matter and antimatter pointless.
... Chiral molecules such as L-amino acids and D-sugars are utilized in many biological and bio-inspired systems to execute essential biological functions and control of chirality is essential for crystal engineering, chiroptical, pharmaceutical and biomedical applications. [5][6][7][8][9][10][11][12] Beyond singlemolecule chirality based on differences in the single-molecular structure, supramolecular chirality is also observed in materials composed of periodic asymmetric assemblies of molecules (typically, helical and spiral geometry) packed via non-covalent interactions. These include electrostatic binding forces, principally hydrogen bonds (H-bonds), and weaker van der Waals forces which are mainly London dispersion forces between transient dipoles. ...
Supramolecular helical structures formed by the assembly of biological and bio-inspired building blocks (typically amino acids, peptides and proteins) are an intriguing class of materials with prospective applications in sustainable...
... Homochirality is a signature of life, whose most important constituents, including amino acids, sugars and nucleotides, are almost exclusively homochiral; [1,2] while compounds that can crystallize in either chiral or racemic crystal predominantly prefer the latter. [3] This seemly paradox raises an intriguing question: How single-handed molecules are selfsorted/enriched in biological and abiotic systems? ...
Without chiral induction the emergence of homochirality from achiral molecules is rather serendipitous, as the rationale is somewhat ambiguous. We herein provide a plausible solution. From achiral precursors are formed a pair of interconverting cage conformers that exhibit a C3‐axis as the only symmetry element. When their interconversion is impeded with intramolecular H‐bonding, each conformer self‐sorts into a homochiral crystal, which is driven by a helical network of multivalent intermolecular interactions during the self‐assembly of homochiral cage conformers. As no chiral induction is involved throughout, we believe our study could enlighten the rational design for the emergence of homochirality with several criteria: 1) formation of a molecule without inversion center or mirror plane; 2) suppression of the enantiomeric interconversion, and introduction of multivalent interactions along the helical trajectory of screw symmetry within the resulting superstructure.
... While proteins are made mostly of L-amino acids, nucleic acids often contain D-ribose sugars. [1][2] Many of the hypothesis that address this predominance stems from the theories of the origin of life. [3][4][5] One such hypothesis states that in the RNA world, preceding the modern "protein world," chiral amino acids worked as chaperons for RNA folding and functions. ...
One of the possible hypotheses for the homochirality of amino acids in the context of the origin of life is that only a particular stereoisomer provides preferential stability to RNA folding by acting as a chemical chaperon. This study probes into the molecular understanding of such preferential stability for a small GAAA RNA tetraloop in the presence of chiral arginine amino acids using a combination of umbrella sampling and parallel bias metadynamics involving five collective variables to tackle the multi-dimensional free energy landscape for faster, better, and more efficient estimation with controlled sampling. Our results show that the free energetic stability of RNA differs significantly in the presence of D- and L- arginine, giving rise to different un-folding rates. Interestingly, the folding rates are not altered. We show that the origin of the chirality difference in RNA folding–unfolding dynamics is due to the differences in configurational diversity of RNA by adopting different unnatural conformations accompanied by different binding modes of D-arginine and L-arginine towards the given RNA motif.
... The spatial arrangements of atoms and functional groups in a molecule are critical to its chemical and biological applications, as isomers can often demonstrate distinctly different chemical reactivity modes, or biological functions [1][2][3][4][5][6] . The development of methods to create, conserve and modify the stereochemistry of organic compounds is a major research focus in modern organic and medical chemistry [7][8][9] . ...
Creating, conserving and modifying the stereochemistry of organic compounds has been the subject of significant research efforts in synthetic chemistry. Most synthetic routes are designed according to the stereoselectivity-determining step. Stereochemical editing is an alternative strategy, wherein the chiral-defining or geometry-defining steps are independent of the construction of the major scaffold or complexity. It enables late-stage alterations of stereochemistry and can generate isomers from a single compound. However, in many instances, stereochemical editing processes are contra-thermodynamic, meaning the transformation is unfavourable. To overcome this barrier, photocatalysis uses photogenerated radical species and introduces thermochemical biases. A range of synthetically valuable contra-thermodynamic stereochemical editing processes have been invented, including deracemization of chiral molecules, positional alkene isomerization and dynamic epimerization of sugars and diols. In this Review, we highlight the fundamental mechanisms of visible-light photocatalysis and the general reactivity modes of the photogenerated radical intermediates towards contra-thermodynamic stereochemical editing processes. Stereochemical editing is a strategy to access three-dimensional skeletons, where the stereochemistry-defining steps are decoupled from the major connectivity-forming reactions. This Review highlights recent advances in the area of light-driven contra-thermodynamic stereochemical editing.
... Although chirality has been recognized as a key factor for life, it remains a big mystery how the homochirality in nature emerged in essential biomolecules; for example, lives mainly select L-amino acids and D-sugar as molecular components. 3,4 Especially, from the developmental point of view, it has a profound effect across a spectrum of disciplines in both academic and industrial research studies to understand how chirality can be generated from the achiral environment and transferred from the molecular level to supramolecular and even higher hierarchical levels. Moreover, spontaneous mirror symmetry breaking in exclusively achiral systems is a fascinating phenomenon, which may enlighten understanding of the origin of chirality and the biomolecular homochirality during the evolution of life and provide important methods toward constructing functional chiral materials from achiral building blocks. ...
... The fundamental components that build biological macromolecules have a specific chirality that is essential for their function [1,2]. A chiral molecule cannot be superimposed on its mirror image and thus attains two forms (L-and D-), referred to as enantiomers. ...
Homochirality of biomacromolecules is a prerequisite for their proper functioning and hence essential for all life forms. This underscores the role of cellular chiral checkpoints in enforcing homochirality during protein biosynthesis. D‐aminoacyl‐tRNA deacylase (DTD) is an enzyme that performs ‘Chirality‐based proofreading’ to remove D‐amino acids mistakenly attached to tRNAs, thus recycling them for further rounds of translation. Paradoxically, owing to its L‐chiral rejection mode of action, DTD can remove glycine as well, which is an achiral amino acid. However, this activity is modulated by discriminator base (N73) in tRNA, a unique element that protects the cognate Gly‐tRNAGly. Here, we review our recent work showing various aspects of DTD and tRNAGly co‐evolution and its key role in maintaining proper translation surveillance in both bacteria and eukaryotes. Moreover, we also discuss two major optimization events on DTD and tRNA that resolved compatibility issues among the archaeal and the bacterial translation apparatuses. Importantly, such optimizations are necessary for the emergence of mitochondria and successful eukaryogenesis. Here, we summarize various aspects of DTD and tRNAGly co‐evolution and their key role in maintaining proper translation surveillance in both bacteria and eukaryotes. We also discuss two major optimization events on DTD and tRNA resulting from incompatibility issues among the archaeal and bacterial translation apparatuses for the emergence of mitochondria and successful eukaryogenesis.
... Chirality is one of interesting properties found in nature, and its various hierarchical levels can be observed everywhere, from atomic to galaxial scales [1][2][3][4] . Understanding how chiral matter is generated in nature and accumulated in biological systems such as DNA and the helices of proteins, has been considered a key to nding the origin of life [5][6][7] . Among the many levels of chirality, one of the most interesting and signi cant subjects is chirality at the supramolecular level. ...
We report the self-assembly of achiral triphenylamine molecules with different numbers of hydrogen bonding sites. The supramolecular chirality was controlled by the symmetry breaking effect of circularly polarized light (CPL) occurring in the nucleation step. As the number of hydrogen bonding sites increased, the stability of supramolecular helices increased, and reversible transformation of the right- and left-handed helices by CPL became feasible only with aid of ultra-sonication. In contrast, triphenylamine molecules without hydrogen bonding sites did not undergo light-induced self-assembly.
... Most biologically active compounds (amino acids, sugars, peptides, proteins, etc.) and modern drugs are chiral. [1][2][3][4] Although enantiomers have similar physicochemical properties, they exhibit completely different physiological effects in terms of biological activity, toxicity, and pharmacological actions. 5 A characteristic example of enantiomers is 3,4-dihydroxyphenylalanine (DOPA). ...
Chiral differentiation is an important topic in diverse fields ranging from pharmaceutics to chiral synthesis. The improvement of sensitivity and the elucidation of the mechanism of chiral recognition are still the two main challenges. Herein, a plasmon-free semiconductive surface-enhanced Raman spectroscopy (SERS) substrate with sensitive chiral recognition ability is proposed for the discrimination of enantiomers. A homochiral environment is constructed by typical π-π stacking between l-tryptophan (l-Trp) and phenyl rings on well-aligned TiO2 nanotubes (TiO2 NTs). Using 3,4-dihydroxyphenylalanine (DOPA) enantiomers as the targets and the chelating interaction of Fe3+-DOPA for the onsite growth of Prussian blue (PB), the enantioselectivity difference between l-DOPA and d-DOPA on the homochiral substrate can be directly monitored from PB signals in the Raman-silent region. By combining the experimental results with molecular dynamic (MD) simulations, it is found that satisfactory enantioselective identification not only requires a homochiral surface but also largely depends on the chiral center environment-differentiated hydrogen-bond formation availability.
... Other than some interesting exceptions (2), biological systems are almost perfectly homochiral. The benefits that homochirality might offer for biological organisms and biochemical processes remain an open issue (see, for example, 29). More fundamentally, one might wonder why chirality, as such, is preserved so persistently through evolution. ...
Chirality in life has been preserved throughout evolution. It has been assumed that the main function of chirality is its contribution to structural properties. In the past two decades, however, it has been established that chiral molecules possess unique electronic properties. Electrons that pass through chiral molecules, or even charge displacements within a chiral molecule, do so in a manner that depends on the electron's spin and the molecule's enantiomeric form. This effect, referred to as chiral induced spin selectivity (CISS), has several important implications for the properties of biosystems. Among these implications, CISS facilitates long-range electron transfer, enhances bio-affinities and enantioselectivity, and enables efficient and selective multi-electron redox processes. In this article, we review the CISS effect and some of its manifestations in biological systems. We argue that chirality is preserved so persistently in biology not only because of its structural effect, but also because of its important function in spin polarizing electrons.
Expected final online publication date for the Annual Review of Biophysics, Volume 51 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
The ability to accurately monitor chiral biological molecules is of great significance for their potential applications in disease diagnosis and virus detection. As the existing chiral detection technologies are mainly relying on an optical method by using left/right circularly polarized light, the universality is low and the operation is complicated. Moreover, large quantity of chiral molecules is required, causing low detection efficiency. Here, a self-assembled monolayer of polypeptides has been fabricated to realize trace detection of chirality based on spin selectivity of photon–electron interaction. We have utilized Kerr technique to detect the rotation angle by the molecular monolayer, which indicates the chirality of polypeptides. The chiral structure of a biological molecule could result in spin-selectivity of electrons and thus influence the interaction between electron spin and light polarization. A Kerr rotation angle of ∼3° has been obviously observed, equivalent to the magneto-optic Kerr effect without magnetic material or magnetic field. Furthermore, we have provided a novel solution to achieve chirality discrimination and amplification simultaneously through an optical fiber. The proposed design is applicable for chiral detection via increasing their differential output signal, which clearly demonstrates a useful strategy toward chirality characterization of biological molecules.
This work shows that electron spin polarization and stereoisomeric effects make comparable contributions to the enantioselective binding of amino acids. Magneto-electrochemical quartz crystal microbalance methods are used to study the adsorption of chiral amino acids onto a monolayer film of chiral molecules that are spin polarized by an underlying ferromagnetic substrate. The direction of the electron spin polarization affects both the kinetics and thermodynamics of the enantiospecific adsorption of the amino acids. Comparison of these data with the circular dichroism (CD) spectra of the amino acid adsorbates shows that the CD spectrum of the interacting group provides a good figure-of-merit for predicting the contributions of electron spin to the intermolecular interaction. These findings demonstrate the importance of electron spin in enantioselective intermolecular interactions between chiral amino acids and represent a paradigm shift for how selectivity should be viewed in biorecognition.
Synthesizing biomimetic systems with stereospecific architectures and advanced bioactivity remains an enormous challenge in modern science. To fundamentally eliminate biosafety issues of natural oncolytic viruses, the development of synthetic virus-inspired particles with high oncolytic activity is urgently needed for clinical antitumor treatments. Here, we describe the design and synthesis of enantiomeric virus-inspired particles for efficient oncolytic therapy from homochiral building blocks to stereospecific supramolecular constructions. The L-virus-inspired oncolytic particles (L-VOPs) and D-VOPs possess similar biomimetic nanostructures but mirror-imaged enantiomeric forms. It is important that both L-VOPs and D-VOPs successfully mimic the pharmacological activity of oncolytic viruses, including direct tumor lysis and antitumor immune activation. D-VOPs provide quite better oncolytic efficacy than that of clinical-grade oncolytic agents (LTX-315, IC50 = 53.00 μg mL-1) with more than 5-fold decrease in IC50 value (10.93 μg mL-1) and close to 100% tumor suppression (98.79%) against 4T1 tumor-bearing mice, attributed to the chirality-dependent tumor recognition, interaction, antidegradation, and immunotherapy. This work provides a strategy for the synthesis of stereospecific biomimetic material systems as well as develops an advanced candidate for biomimetic oncolytic agents without biosafety risks.
Although numerous chiral small molecules have been discovered and synthesized, the investigation on their enantioselective immunological effects remains limited. In this study, we designed and synthesized a pair of small molecule enantiomers ( R / S ‐ResP) by covalently bonding two immunostimulators (resiquimod/Res) onto a planar chiral framework (paracyclophane/P). Notably, we found that S ‐ResP exhibits a 4.05‐fold higher affinity for toll‐like receptor 7 (TLR7) than R ‐ResP, thereby more effectively enhancing the functions of dendritic cells and macrophages in cytokine secretion and antigen internalization. Furthermore, we observed that S ‐ResP significantly enhances RBD antigen‐induced cross‐neutralization against various SARS‐CoV‐2 strains compared to R ‐ResP. These findings demonstrate the enantioselective effects of small molecules on regulating vaccine‐induced immune responses and emphasize the significance of chirality in designing small molecular adjuvants.
Although numerous chiral small molecules have been discovered and synthesized, the investigation on their enantioselective immunological effects remains limited. In this study, we designed and synthesized a pair of small molecule enantiomers (R/S‐ResP) by covalently bonding two immunostimulators (resiquimod/Res) onto a planar chiral framework (paracyclophane/P). Notably, we found that S‐ResP exhibits a 4.05‐fold higher affinity for toll‐like receptor 7 (TLR7) than R‐ResP, thereby more effectively enhancing the functions of dendritic cells and macrophages in cytokine secretion and antigen internalization. Furthermore, we observed that S‐ResP significantly enhances RBD antigen‐induced cross‐neutralization against various SARS‐CoV‐2 strains compared to R‐ResP. These findings demonstrate the enantioselective effects of small molecules on regulating vaccine‐induced immune responses and emphasize the significance of chirality in designing small molecular adjuvants.
One of the hypotheses for the homochirality of amino acids in the context of the origin of life is that only a particular stereoisomer provides preferential stability to RNA folding by acting as a chemical chaperon. However, the effect at the molecular level is not well understood. This study provides a molecular understanding of such preferential stability for a small GAAA RNA tetraloop in the presence of chiral arginine through a multidimensional free energy landscape constructed using a combination of umbrella sampling and parallel bias metadynamics (PBMetaD) simulations. We show that the origin of the chirality difference in RNA folding-unfolding dynamics is due to differences in the configurational diversity of RNA in adopting various non-natural conformations that accompany the diverse binding modes of D-arginine and L-arginine. We show that while D-arginine stabilizes the native folded state of RNA, L-arginine destabilizes it. Furthermore, free energy calculations on the binding of D- and L-arginine reveal a specific geometric constraint that helps D-arginine to stack with the terminal base pairs of RNA and pushes L-arginine for groove binding.
Chiral materials with the same atomic compositions exhibit different chemical, physical, and biological properties because of their distinct spatial structures. Herein, a chiral strategy was proposed to develop poly(lactic acid) (PLA) nanoparticle as an efficient nanoadjuvant to activate adaptive anticancer immunity. Two chiral nanovaccines were prepared by directly mixing amino-terminated PLA (PLLA-NH2 or PDLA-NH2) with the model protein antigen ovalbumin (OVA). After being injected into mice subcutaneously, both nanovaccines efficiently migrated to the lymph nodes to initiate the sequential anticancer immune responses. Compared with the PLLA nanovaccine (PLLA-OVA), the PDLA one (PDLA-OVA) contributed to more robust dendritic cell (DC) maturation, antigen presentation, and T lymphocyte activation. In addition to the activation of cellular immunity, PDLA-OVA also triggered a more vigorous activation of humoral immunity, which induced the production of more anti-OVA immunoglobulin G (IgG) than PLLA-OVA. When used as prophylactic or therapeutic nanovaccine toward murine melanoma models, PDLA-OVA triggered more potent adaptive anticancer immune responses that more effectively inhibited the cancer genesis and progression, indicating the significant potential of immunologically effective PDLA nanoadjuvant in cancer immunotherapy.
Without chiral induction the emergence of homochirality from achiral molecules is rather serendipitous, as the rationale is somewhat ambiguous. We herein provide a plausible solution. From achiral precursors are formed a pair of interconverting cage conformers that exhibit a C3‐axis as the only symmetry element. When their interconversion is impeded with intramolecular H‐bonding, each conformer self‐sorts into a homochiral crystal, which is driven by a helical network of multivalent intermolecular interactions during the self‐assembly of homochiral cage conformers. As no chiral induction is involved throughout, we believe our study could enlighten the rational design for the emergence of homochirality with several criteria: 1) formation of a molecule without inversion center or mirror plane; 2) suppression of the enantiomeric interconversion, and introduction of multivalent interactions along the helical trajectory of screw symmetry within the resulting superstructure.
Here we describe the self‐assembly of an achiral molecule into macroscopic helicity as well as the emergent chirality selective spin filtering effect. It was found that benzene‐1,3,5‐tricarboxamide (BTA) motif with an aminopyridine group in each arm could coordinate with Ag(I) and self‐assemble into nanospheres. Upon sonication symmetry breaking occurred and the nanospheres transfer into helical nanofibers with strong CD signals. Although the sign of the CD signals appeared randomly, it could be controlled by using the as‐made chiral assemblies as a seed. Furthermore, it was found that the charge transport of the helical nanofibers was highly selective with a spin‐polarization transport of up to 45% although the chiral nanofibers are composed exclusively from achiral building blocks. The work demonstrated a new example of the symmetry breaking under sonication and the chirality selective spin filtering effect.
Herein we describe the self‐assembly of an achiral molecule into macroscopic helicity as well as the emergent chiral‐selective spin‐filtering effect. It was found that a benzene‐1,3,5‐tricarboxamide (BTA) motif with an aminopyridine group in each arm could coordinate with AgI and self‐assemble into nanospheres. Upon sonication, symmetry breaking occurred and the nanospheres transferred into helical nanofibers with strong CD signals. Although the sign of the CD signals appeared randomly, it could be controlled by using the as‐made chiral assemblies as a seed. Furthermore, it was found that the charge transport of the helical nanofibers was highly selective with a spin‐polarization transport of up to 45 %, although the chiral nanofibers are composed exclusively from achiral building blocks. This work demonstrates symmetry breaking under sonication and the chiral‐selective spin‐filtering effect.
Chirality is a fundamental chemical property that can be found in almost all aspects of life. Generally, in nature chirality exists in only one of the possible enantiomeric forms. Bitter experience showed that chiral drugs having the same chemical composition but opposite chirality may have extremely different biological effects. It is therefore that detecting and quantifying chirality is important in multiple fields ranging from analytical and biological chemistry to pharmacology, biotechnology, and fundamental physics. To date, the most widely used analytical methods for chiral detection, remain the traditional approaches of measuring circular dichroism and optical rotation. However, these methods suffer from low signal‐to‐noise due to large time‐dependent backgrounds and require complicated optical setups. Recent works associate circular dichroism measurements with the Chiral Induced Spin Selectivity (CISS) spin current measurements. The CISS effect relates the probability of electron spin transmission through chiral molecules to chirality. Depending on the handedness of the molecule, electrons of a certain spin can traverse the molecule more easily in one direction than in the other. It is therefore that the CISS effect could be utilized to electronically measure chirality using spin currents and spin induced dipoles. The review summarizes the different approaches for utilizing the CISS effect for electrical measurements of chirality. Starting with a Hall device that can measure the chirality of the lowest energetic CD band of a monolayer in dry or wet systems. Presenting an enhancement of the effect as well as achieving a wider CD spectrum using electrical gating. Going down to 100 molecules limit with full spectrum response utilizing electro‐optical nano floret devices.
D-Histidine (D-His), L-Histidine (L-His), and their racemic compound DL-Histidine (DL-His) have different stereo chirality, making them intrinsic diverse functionalities to the living system. Identifying the configuration and crystal structures of enantiomers and the racemic compound is always the foremost requirement in processing protein foods. Although these features can be analyzed by spectroscopic technologies individually, it remains challenging to incorporate these complex methods into a facile analytical strategy. Herein, we propose a terahertz spectroscopy with solid-state density functional theory to both distinguish the configurational difference and quantify the crystal transformation from L-His and D-His to DL-His. By comparison with X-ray diffraction analysis, the validity of the crystal transformation evaluation based on terahertz spectroscopy is verified. A normalized fitting line regarding the terahertz absorption frequency and intensity is calculated to quantitatively elucidate the crystal transformation from enantiomers to DL-His. Our findings provide a new analytical approach to the research on food chemistry.
The concept of chiral interactions has been intensively studied in various fields involving diverse scales of objects, e.g., nucleons, amino acids, and liquid crystals. One of the key problems is how chiral interactions induce synchronization effects among initially uncorrelated objects. In this study, we propose a model of chirality-selective synchronized fluorescence (superfluorescence) that involves spirally configured quantum emitters at the center of a spirally stacked metal nanostructure. The emitters mutually develop the correlation in time by repeatedly exchanging the radiated photons, which experience the chirality of their environment. We numerically show that the peak fluorescent intensity strongly depends on whether or not the chiralities of the emitters and the metals match, even though the localized surface plasmon decays sufficiently at the positions of the emitters. Our model of chirality-selective superfluorescence will provide an alternative tool for analyzing chiral interactions in synchronization processes.
The generation and regulation of chirality are closely related to the origin of life. Using achiral precursors to spontaneously build chiral MOFs remains a major challenge. Here, a method to synthesize chiral MOFs from achiral precursors by utilizing chiral fragments was achieved. The transformation from chiral fragments of 1 to chiral frameworks of 2 and 3 was realized by modifying the substituents, and the enantiomer resolution of 3-P41212 and 3-P43212 was achieved by d/l camphoric acid. 3 was then further studied in applications.
We present a theory-experiment investigation of the helically chiral compounds Ru(acac)3 and Os(acac)3 as candidates for next-generation experiments for detection of molecular parity violation (PV) in vibrational spectra. We used relativistic density functional theory calculations to identify optimal vibrational modes with expected PV effects exceeding by up to 2 orders of magnitude the projected instrumental sensitivity of the ultrahigh resolution experiment under construction at the Laboratoire de Physique des Lasers in Paris. Preliminary measurements of the vibrational spectrum of Ru(acac)3 carried out as the first steps toward the planned experiment are presented.
Creating, preserving, and manipulating the stereochemistry of organic compounds has long been a cornerstone of modern organic synthetic chemistry, and the synthetic routes are typically designed according to stereoselectivity-determining step that is known as stereochemical logic. As an alternative strategic platform, stereochemical editing, wherein the chiral- or geometry-defining events are decupled from the main scaffold or complexity-forming steps, has the potential for late-stage flexibility in generating isomers from a single compound. However, under many instances, the desired stereochemical editing processes are contra-thermodynamic on ground states and thus unfavorable. Recent research has begun to leverage photocatalysis to yield many potentially generalizable concepts to empower contra-thermodynamic stereochemical editing by providing approach to irreversible elementary steps via excited electronic states and/or by introducing thermochemical biases. A broad range of synthetically valuable contra-thermodynamic stereochemical editing processes were thus invented, including deracemization of racemic chiral molecules, positional alkene isomerization, and dynamic epimerization of sugars and diols. In this review, we highlight how an understanding of the mechanisms of visible-light photocatalysis and of the general reactivity patterns of the photogenerated radical intermediates has been engineered to develop these concepts.
Synthesizing many-body interaction Hamiltonians is a central task in quantum simulation. However, it is challenging to synthesize Hamiltonians that have more than two spins in a single term. Here we synthesize m-body spin-exchange Hamiltonians with m up to 5 in a superconducting quantum circuit by simultaneously exciting multiple independent qubits with time-energy correlated photons generated from a qudit. The dynamic evolution of the m-body interaction is governed by the Rabi oscillation between two m-spin states, in which the states of each spin are different. We demonstrate the scalability of our approach by comparing the influence of noises on the three-, four- and five-body interaction and building a many-body Mach-Zehnder interferometer which potentially has a Heisenberg-limit sensitivity. This study paves a way for quantum simulation involving many-body interaction Hamiltonians such as lattice gauge theories in quantum circuits.
The single chirality of biological molecules in terrestrial biology raises more questions than certitudes about its origin. The emergence of biological homochirality (BH) and its connection with the appearance of life have elicited a large number of theories related to the generation, amplification and preservation of a chiral bias in molecules of life under prebiotically relevant conditions. However, a global scenario is still lacking. Here, the possibility of inducing a significant chiral bias "from scratch", i.e. in the absence of pre-existing enantiomerically-enriched chemical species, will be considered first. It includes phenomena that are inherent to the nature of matter itself, such as the infinitesimal energy difference between enantiomers as a result of violation of parity in certain fundamental interactions, and physicochemical processes related to interactions between chiral organic molecules and physical fields, polarized particles, polarized spins and chiral surfaces. The spontaneous emergence of chirality in the absence of detectable chiral physical and chemical sources has recently undergone significant advances thanks to the deracemization of conglomerates through Viedma ripening and asymmetric auto-catalysis with the Soai reaction. All these phenomena are commonly discussed as plausible sources of asymmetry under prebiotic conditions and are potentially accountable for the primeval chiral bias in molecules of life. Then, several scenarios will be discussed that are aimed to reflect the different debates about the emergence of BH: extra-terrestrial or terrestrial origin (where?), nature of the mechanisms leading to the propagation and enhancement of the primeval chiral bias (how?) and temporal sequence between chemical homochirality, BH and life emergence (when?). Intense and ongoing theories regarding the emergence of optically pure molecules at different moments of the evolution process towards life, i.e. at the levels of building blocks of Life, of the instructed or functional polymers, or even later at the stage of more elaborated chemical systems, will be critically discussed. The underlying principles and the experimental evidence will be commented for each scenario with particular attention on those leading to the induction and enhancement of enantiomeric excesses in proteinogenic amino acids, natural sugars, and their intermediates or derivatives. The aim of this review is to propose an updated and timely synopsis in order to stimulate new efforts in this interdisciplinary field.
The work is devoted to computer studies of the structural and physical properties of such self-organizing structures as peptide nanotubes (PNT) based on diphenylalanine (FF) dipeptide with different initial isomers of the left (L-FF) and right (D-FF) chiralities of these dipeptides. The structures under study are considered both with empty anhydrous and with internal cavities filled with water molecules. Molecular models of both chiralities are investigated using quantum-chemical DFT and semi-empirical methods, which are in consistent with the known experimental data. To study the effect of nano-sized clusters of water molecules embedded in the inner hydrophilic cavity on the properties of nanotubes (including the changes in their dipole moments and polarizations), as well as the changes in the structure and properties of water clusters themselves (their own dipole moments and polarizations), the surfaces of internal cavities of nanotubes and outer surfaces of water cluster structures for both types of chirality are analyzed. A specially developed method of visual differential analysis of structural features of (bio)macromolecular structures is applied for these studies. The results obtained of a number of physical properties (interacting energies, dipole moments, polarization values) are given for various cases and analyzed in comparison with the known data. These data are necessary for analyzing the interactions of water molecules with hydrophilic parts of nanotube molecules based on FF, such as COO- and NH3 + , since they determine many properties of the structures under study. The data obtained are useful for further analysis of the possible adhesion and capture of medical molecular components by active layers of FF-based PNT, which can be designed for creating capsules for targeted delivery of pharmaceuticals and drugs on their basis.
We developed a chiral symmetry breaking method for monoacylated meso diols. The X‐ray crystal structure analysis of monoacylated 1,4‐anhydroerythritols, meso cyclic diols with a cis configuration, revealed that the O‐(p‐anisoyl) derivative crystallized as a racemic conglomerate of the P212121 crystal system. It was confirmed that the substrate racemized by intramolecular transfer of the acyl group in the presence of a catalytic amount of base. Evaporating the solvent gradually from the solution or Viedma ripening to promote crystallization‐induced deracemization efficiently led to enantiomer crystals. These results provide the first successful example of asymmetric expression and amplification by deracemization of sugar derivatives without an external chemical chiral source. Furthermore, we applied this methodology to acyclic meso‐1,2‐diols. Three O‐monoacylated substrates were successfully deracemized to 99 % ee by Viedma ripening. We also developed asymmetric desymmetrization of meso‐1,2‐diols by combining acylation and crystallization‐induced deracemization.
We developed a chiral symmetry breaking method for monoacylated meso diols. The X‐ray crystal structure analysis of monoacylated 1,4‐anhydroerythritols, meso cyclic diols with a cis configuration, revealed that the O‐(4‐anisoyl) derivative crystallized as a racemic conglomerate of the P 2 1 2 1 2 1 crystal system. It was confirmed that the substrate racemized by intramolecular transfer of the acyl group in the presence of a catalytic amount of base. Evaporating the solvent gradually from the solution or Viedma ripening to promote crystallization‐induced deracemization efficiently led to enantiomer crystals. These results provide the first successful example of asymmetric expression and amplification by deracemization of sugar derivatives without an external chemical chiral source. Furthermore, we applied this methodology to acyclic meso ‐1,2‐diols. Three O‐monoacylated substrates were successfully deracemized to 99% ee by Viedma ripening. We also developed asymmetric desymmetrization of meso ‐1,2‐diols by combining acylation and crystallization‐induced deracemization.
The synthesis of crystalline homochiral MOF materials is very important for their potential application in enantioselective processes and asymmetric catalysis. In this paper, four novel zinc based chiral boron imidazolate frameworks (BIFs), Zn2[BH(2-eim)3](BA)2(OH) (BIF-132-BA, 2-eim = 2-ethylimidazolate, BA = benzoate), Zn[HBH(2-ipim)3](OHBA)(Ac) (BIF-133-OHBA, 2-ipim = 2-isopropylimidazolate, OHBA = o-hydroxybenzoate, Ac = acetate), Zn[HBH(2-ipim)3](PHBA)(Ac) (BIF-133-PHBA, PHBA = p-hydroxybenzoate), and Zn[HBH(2-ipim)3](DHBA)(Ac) (BIF-133-DHBA, DHBA = 2,4-dihydroxybenzoate) were prepared via solvothermal synthesis. Single-crystal X-ray diffraction demonstrated that the existence of hydrogen bonds between adjacent chains results in two different structure features of BIF-131: a chiral ladder-like 1D chain (BIF-133-OHBA) and two supramolecular 2D layers (BIF-133-PHBA and BIF-133-DHBA). Then, the optical activities of as-synthesied crystals were preliminarily studied by circular dichroism (CD) spectroscopy. In addition, because they crystallized in noncentrosymmetric space groups, the powder second-harmonic generation (SHG) measurements were carried out and the SHG response of BIF-133-PHBA was almost comparable to potassium dihydrogen phosphate (KDP).
A photochemical deracemization of 5-substituted 3-phenylimidazolidine-2,4-diones (hydantoins) is reported (27 examples, 69%-quant., 80-99% ee). The reaction is catalyzed by a chiral diarylketone which displays a two-point hydrogen bonding site. Mechanistic evidence (DFT calculations, radical clock experiments, H/D labeling) suggests the reaction to occur by selective hydrogen atom transfer (HAT). Upon hydrogen binding, one substrate enantiomer displays the hydrogen atom at the stereogenic center to the photoexcited catalyst allowing for a HAT from the substrate and eventually for its conversion into the product enantiomer. The product enantiomer is not processed by the catalyst and is thus enriched in the photostationary state.
Chiroptical inversion of amyloid fibrils is a novel phenomenon and is of fundamental importance; however, the underlying structural basis remains poorly understood. Here, the co‐assembly of Thioflavin T (ThT) with T1 amyloid fibril and the induced supramolecular chirality is investigated by induced circular dichroism (ICD) and circularly polarized luminescence (CPL), followed by direct morphological helicity observation of the fibril by an atomic force microscope (AFM). ThT exhibits negative ICD and CPL when assembled on the left‐handed T1 fibril. Interestingly, when ThT dynamically interacts with the T1 fibril, the left‐handed fibril partially converts into right‐handed, accompanied with the inversion of CD and CPL signals. These results indicate that the morphological helicity of template fibril cannot be arbitrarily distinguished by the sign of chiroptical spectra of the dye/peptide assemblies.
The theory of energy shifts in mirror‐image molecules arising from parity nonconserving weak neutral currents is developed. Its connection with the theory of optical activity is discussed. In order to demonstrate the existence of the energy shift, which produces an energy difference between an optically active molecule and its mirror image, an exact calculation is performed for a simple one‐electron model (the Condon model). Then approximate LCAO‐MO calculations are performed on two specific molecules, twisted ethylene and A‐nor‐2‐thiacholestane, in order to obtain more reliable order‐of‐magnitude estimates of the energy shifts than available previously. According to our calculations, the former molecule has an energy shift two orders of magnitude larger than the latter, but both molecules have energy shifts which are appreciably smaller than the previous estimates.
This chapter reviews diverse experimental and theoretical programs engaged in the study of parity nonconservation in atoms. The existence of parity nonconservation in atoms is now reasonably well established by experiment. Four different laboratories have performed parity nonconservation (PNC)optical rotation experiments on bismuth. Although there is strong evidence for an effect of the sign and order of magnitude expected from the Weinberg–Salam theory, the various experiments are not consistent among themselves. The atomic calculations are judged to be reliable to about 30%. This chapter starts with a discussion on the neutral current interaction in atoms. In the absence of HPNC, the states of the atom have definite parity. Electric dipole (E1) transitions, which normally dominate atomic spectroscopy, are forbidden between states of like parity. However, HPNC mixes s and p states and causes, in some cases, small E1 transition amplitude to appear and to interfere with transitions (M1, E2) normally present but weak between states of like panty, giving rise to an observable PNC effect. For instance, when HPNC couples E1 amplitude into an M1 transition, the transition rate acquires a dependence on the sense of circular polarization of incident radiation. The optical rotation experiments utilize this effect. This chapter ends with a view of experiments on cesium and thallium, and atomic hydrogen.
The search for parity nonconservation in heavy elements has been extended to the 1.28-$\mu${}m $^{3}P_{0}$\rightarrow${}^{3}P_{1}$ magnetic dipole transition in atomic lead. The experimental result, $R=\mathrm{Im}(\frac{E1}{M1})=($-${}9.9\ifmmode\pm\else\textpm\fi{}2.5)\ifmmode\times\else\texttimes\fi{}{10}^{$-${}8}$, agrees, within the present uncertainties in experiment and atomic theory, with the prediction, $R=$-${}13\ifmmode\times\else\texttimes\fi{}{10}^{$-${}8}$, derived from the Weinberg-Salam-Glashow theory of weak neutral-current interactions.
A number of polymers derived from D-, L- and DL-leucine were subjected to partial hydrolysis under comparable conditions, with the finding that the polymers from DL-leucine were hydrolyzed more extensively than those from D- or L-leucine. Leucine polymers containing an excess of one enantiomer were partially hydrolyzed, resulting in an enhancement of the enantiomeric excess in the residual unhydrolyzed polymer and a depletion of the enantiomeric excess in the recovered monomer. These stereoselective hydrolyses are discussed from the viewpoint of the abiotic enhancement of optical activity on the primitive Earth.
Ab initio (STO-nG) computations of ordinary and rotatory intensities of low-lying electronic transitions are presented for twisted ethylene and twisted trans-2-butene in the random-phase approximation (RPA). The intensities are computed in both dipole length and dipole velocity forms, as well as the mixed form for the oscillator strength, and the convergence of these formally equivalent results is examined in the RPA and several other methods for constructing the electronic excitation: the virtual orbital, or single-transition, approximation (STA), the monoexcited configuration-interaction, or Tamm-Dancoff, approximation (TDA), and one version of the higher RPA (HRPA). We show that the RPA has consistent advantages over the TDA for calculation of CD as well as ordinary intensities. Our computations confirm that a localized, ethylenic chromophore is indeed adequate to account for the low-lying CD spectrum in mono-olefins. Further, even with minimal valence-shell basis sets, our RPA rotatory strengths agree essentially completely in both sign and magnitude with the experimental results of Mason and Schnepp on trans-cyclooctene.
Sensitivity of a nonequilibrium chemical system to small symmetry-breaking influences is analyzed in the context of chiral-symmetry breaking. For a hypothetical model system, with realistic kinetic constants, a reaction energy barrier difference of $\frac{$\Delta${}E}{\mathrm{kt}}={10}^{$-${}17}$-${}{10}^{$-${}15}$ is shown to be sufficient to have a strong chiral selectivity. This is in the range of the estimated energy differences between right- and left-handed molecules due to weak neutral currents.
L-Alanine and L-peptides in the α-helix and β-sheet conformation are stabilized relative to the corresponding enantiomer by the weak parity-violating interaction.
The asymmetric adsorption of the racemic alanine by the optically active quartz from ethanol solution at 8 °C was studied by the 14C-tracer method and the newly developed 14C-tracer·ninhydrin-colorimetry combination method. The preferential adsorption of L-alanine by levorotatory quartz (l-quartz) and D-alanine by dextrorotatory quartz (d-quartz) was confirmed. The asymmetric adsorptivity (As) falls in the range of 1.1–1.3, which is comparable with the value determined at −80 °C in the previous paper. The effects of water content in the ethanol solution and of the adsorption temperature upon the adsorption affinity of alanine to quartz were also measured. The cause for the asymmetric adsorption is discussed from the crystallographic point of view.
A model is presented to show that a minute difference ΔE in the activation energies of L and D isomers of biomolecules is sufficient to achieve optical stereoselection in biochemical evolution. The limits on ΔE imposed by thermodynamic fluctuations are discussed.
“Helicene” is the name introduced by Newman in 1955, to describe the benzologues of phenanthrene in which the extra ortho-condensed rings give rise to a (regular) cylindrical helix. The pioneer work of Newman in this field cannot be overemphasized; his brillant synthesis and resolution of [6]helicene, achieved eighteen years ago, will remain as a landmark, for it opened the way to the study of a fascinating class of synthetic molecules. In the following review, an attempt is made to summarize the present state of our knowledge in this rapidly expanding field.
The reactions induced by circularly polarized light are reviewed and a general discussion of the induction of optical activity by circularly polarized light is presented. It is concluded that three different mechanisms, or their combinations, can cause asymmetric induction. In each case the optical yield is dependent on the optical anisotropy factor g, the ratio between the circular dichroism (Δϵ) and the extinction coefficient (ϵ). The results are discussed in terms of the presumed mechanisms, and particular attention is paid to the asymmetric synthesis of helicenes. It is concluded that this kind of photochemistry may have analytical importance.
The question of parity conservation in β decays and in hyperon and meson decays is examined. Possible experiments are suggested which might test parity conservation in these interactions.
CERN now seems confident that it has observed five examples of the Z0 particle, a kind of heavy photon. What is there left to do?
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
The rôle of time reversal symmetry in natural and magnetic optical activity is discussed. Natural optical rotation is shown to be generated by an anti-hermitian odd parity time-even operator and magnetic optical rotation by an anti-hermitian even parity time-odd operator. This shows that lack of time reversal invariance is not the source of natural optical rotation and that free atoms can show natural optical rotation without violating reversality, which leads to a fundamental distinction between the conditions necessary for natural optical rotation and a permanent space-fixed electric dipole moment. General transition optical activity and polarizability tensors between components of degenerate states are discussed with reference to possible new Raman experiments and new contributions to discriminating intermolecular forces between chiral molecules. Time reversal symmetry also leads to a new criterion for chiral objects and to the concept that natural optical activity provides an example of spontaneous symmetry breaking with respect to CP.
LINEAR polarization of clear daytime sky and twilight is produced by molecular (Rayleigh) scattering and aerosol (Mie) scattering, which predominates in the infrared. Incident linearly polarized light scattered by aerosols is in general elliptically polarized, whereas no ellipticity can arise from the molecular component1. The principal component of clear daytime sky arises from single scattering of unpolarized sunlight and is not elliptically polarized. However, whenever multiple scattering by the aerosol component is important, the strong linear polarization produced on the first scattering will lead to elliptical polarization from the second and subsequent scatterings. Although in the daytime sky this mechanism should give only a small ellipticity2 (10−5–10−3) the possibility of a substantially larger effect at twilight arises because there is no direct illumination. We report here observations of circular polarization of twilight of order 10−3.
Kinetic data have been obtained for the strong base initiated polymerization of γ-benzyl-L-glutamate-N-carboxyanhydride under a variety of experimental conditions using both the previously described infrared absorption and carbon dioxide evolution methods. Strong base initiated polymerizations show a first-order rate following an initial autocatalytic period. Strong base initiated polymerizations thus differ from amine initiated polymerizations (which exhibit two successive pseudo-first-order rates) in the shape of the rate curve, in the rate, which is at least 100 times faster, and also in the production of much higher molecular weight polypeptides. Polymers isolated after the first 30% reaction show a nonproportional increase in molecular weight with increased extent of monomer conversion. Addition of monomer to a completed polymerization solution produces more polymer, and its molecular weight is the same as the original polymer. The solvent in which polymerization is performed affects the rate; thirty-fold differences in rate constant have been observed. Determination of activation energy by varying the temperature of the polymerization was inconclusive. The presence of small amounts of the optical isomer of an amino acid-N-carboxyanhydride markedly decreases its polymerization rate and lowers the molecular weight of the polypeptide formed. By using triphenylmethylsodium as an initiator for the polymerization in a proton-free solution, it has been shown that protons are not required for the production of high molecular weight polypeptide. The more electro-positive the cation of the strong base, the shorter is the autocatalytic period of the polymerization. It is suggested that the low molecular weight reaction product of strong base and amino acid-N-carboxyanhydrides are the effective initiators of the polymerization.
Recent attempts to achieve asymmetric synthesis from achiral reactants contained in a rapidly rotating vessel are examined theoretically. It is concluded that such attempts must fail.
Apparently simple chemical systems and reaction mechanisms involving a small number of components may give rise to a remarkable variety of dynamical phenomena if the systems are maintained sufficiently far from equilibrium. These include multiple stationary states, simple and complex periodic oscillation, aperiodic oscillation (chaos), and the growth of traveling waves and spatial structures in initially homogeneous media. Examples of these phenomena are described, both in mathematical models and in experimental chemical systems. The mechanistic treatment of such behavior is progressing rapidly, and several cases are cited. The relationship between studies of exotic dynamical behavior in chemical systems and related investigations in mathematics, physics, and biology is discussed briefly.
An upper limit of relative energy difference between L- and D-molecules due to the contribution of parity violating effects has been estimated as 10-10. The theoretical value is 10-13. The estimate has been based on crystallization of NaNH4 tartrate molecules.
Es wird versucht, aus der Form der Schrdingerschen Differentialgleichung einige strukturelle Eigenschaften der Spektren abzuleiten. Es wird die Aufspaltung im elektrischen und magnetischen Feld, das Aufbauprinzip der Serienspektren und einiges Verwandte behandelt. Es ergibt sich — soweit das rotierende Elektron nicht in Betracht zu ziehen ist — bereinstimmung mit der Erfahrung.
The importance of optical purity, which was stressed in an earlier review, is reassessed in the light of recent evidence concerning the optical configuration of amino acids in biological systems. The most significant fact to emerge in recent years that bears on the origin of optical asymmetry is the experimental evidence for the Salam-Weinberg theory. However, the problem remains: is the effect of PNC-interactions too small to be detectable, and if it is so small, can it be of any significance? In view of the contradictory and confusing nature of the evidence on the induction of optical activity, it is suggested that the Bremen Symposium should agree on some experimental protocols.
Our earlier experiments are briefly reviewed, involving the abiotic generation of optical activity by exposure of DL-amino acids to various chiral physical forces. The enantiomeric enrichments so obtained were low, however, and additional experiments were undertaken with the objective of abiotically enhancing such small enantiomeric excesses. DL Mixtures of leucine N-carboxy anhydride gave enantiomerically enriched polymers on partial polymerization, while valine NCA mixtures behaved oppositely. Leucine polymers were also found to hydrolyze stereoselectively, providing for additional enantiomenic enhancement. A repetitive sequence of partial polymerization-hydrolysis steps is suggested as a possible mechanism for the abiotic genesis of optically enriched polypeptides on the primitive Earth.
DOI:https://doi.org/10.1103/PhysRev.105.1413
Full details are given of a recent time-of-flight neutron diffraction experiment in which partial pair correlation functions for liquid water are extracted by isotope substitution. Measurements of differential cross sections of mixtures of heavy and light water are made, and by performing the experiment at the high neutron energies available at a pulsed neutron source (Los Alamos) the magnitude of dynamic corrections to the data is reduced. The problematic hydrogen incoherent scattering is removed by a subtraction technique which avoids reference to dynamic models of the liquid. The results, although they show good agreement with computer simulations, show serious qualitative differences with other neutron experiments on water, and it is suggested these discrepancies are a result of lack of attention to the unusual properties of hydrogen as a scatterer of neutrons.
We point out that weak neutral and charged currents may lead to observable effects in molecular spectra. We also indicate a possible connection between weak interactions and biological isomerism.
The adsorption by quartz of alanine derivatives blocked at the COOH group by esterification (2), at the NH2 group by acylation (3), and at both groups (4) was studied to see which group was primarily responsible for the adsorption. It was found that the NH2 (or NH3+) group had to be free for effective adsorption to occur. The comparative adsorption of a number of amino n-butyl ester hydrochlorides was investigated to see what type of esterified amino acid was most strongly adsorbed. Basic amino esters were adsorbed most effectively, hydroxylic and neutral amino esters next, and esters of acidic amino acids least. The adsorption of n-butyl ester hydrochlorides of each type of amino acid varied inversely with molecular weight. The adsorption of alanine isopropyl ester hydrochloride (2) by quartz was most pronounced from nonpolar solvents, and decreased as the polarity of the solvent increased. The adsorption of 2 from chloroform solution was studied as a function of concentration, and the resulting adsorption isotherm was found to be clearly of the Langmuir type. Finally, the asymmetric adsorption of (R,S)-2 by d- and l-quartz was studied by fractional elution, using gas chromatography for the analytical estimation of enantiomeric enrichment. l-Quartz preferentially adsorbed (R)-2 and d-quartz (S)-2, the extent of enantiomeric enrichment among the various fractions varying between 1.5 and 12.4%.
Summary The paper presents some experiments which were aimed at the demonstration of enrichment of enantiomer substances by precipitation from saturated racemic solutions. As a working hypothesis we searched for a possible very small “asymmetry effect” that might by observable during precipitation if the solubilities of enantiomer components were affected. Crystallization of a small fraction out of a bulk of racemate would lead to an amplification of an elementary effect which by itself would have escaped any direct experimental verification. We chose DL-asparagine-monohydrate in aqueous solution as the system to be investigated. — Of particular interest is the result that below 7.5 °C the yield of D-asparagine seems to exceed that of L-asparagine in the precipitate, while above 8 °C the opposite is true. This qualitative result is confirmed by extrapolation of experimental data gained from precipitation of non-racemic asparagine solutions — at least for a crystallization temperature of 0 °C.
Differences in the free energy of enantiomers may have two principal reasons: 1. the result of a special arrangement of external fields, or 2. asymmetric interaction due to parity-non-conservation. The effects, in general, will be very small so that an amplification is necessary in order to make them measurable. In doing so, the main problem is not to find a process of high amplification potential, but a reliable one where the obtained enantiomeric resolution is really due to differences in their properties and not an artifact caused by uncontrolled experimental parameters. Well-known cascading processes have been examined under this aspect, and two new types of amplifying processes involving solid phases and especially designed for this purpose, are described.
Bioids are the simplest chemical open systems capable of Darwinian evolution by mutation from one steady state into a more stable one (Decker & Speidel, 1972). In the case of exactly equal fitness as with a racemic (Decker, 1973b) or a prochiral (Seelig, 1971a; Decker, 1973a) substrate and with stereospecific autocatalysts, the addition of an aggressive reaction, i.e. a reciprocal inhibition of the autocatalysts, causes the spontaneous generation of asymmetric products throughbistability. This also can occur in nonaggressive systems with hypercompetitive, i.e. more than 2nd order competitive kinetics (Decker, in press). Such systems can exist in up to 7 steady states depending on several threshold values. They could be realizable by stereospecific catalysis on twodentated ligands in an octahedral coordination sphere. In a new type of kinetics, where in a complex MeA1A2A2 or MeA1A1A2 with a racemic substrate, A1,A2, a preferential reactivity of the odd ligand may cause resolution by bistability. Evolution in bioids involves acquisition and amplification of different kinds of in-formation, depending on the physical nature of its channel. Autocatalysis requires a molecule which does not always arise spontaneously but can survive and spread as a material channel independet of energy supply. In contrast, dissipative structures like kinetic asymmetry arise spontaneously as acausal macroscopic quantum events but vanish through relaxation without energy supply. Useful general theorems follow from a representation of bioids as a topology on the set of systems of differential equations.
Summary The role of the parity violating weak interaction in atomic and molecular physics is pursued. Parity violating forces do in fact distinguish between molecular configurations which are identical up to a space reflection as is assumed to be the case for optical isomers. The corrections to the binding energies of such molecules are, however, tiny. In conventional weak interaction theory this is due to the gauge invariance of the photon mediating electromagnetic forces between electrons and electrons and between electrons and nucleons. The constraint of gauge invariance does not allow for long range parity violating forces of first order in the weak coupling constant G. This implies that parity violating effects in atoms or molecules are suppressed not only by a factor of ? 10-5 due to the smallness of the weak coupling constant but also by the ratio of the range of parity violating forces divided by the average extension of the electron cloud which is in addition at most of order ? 10-5. Therefore no appreciable energy difference between optical isomers is expected within the framework of conventional weak interaction.
A system of two autocatalysts competing for one common substrate would allow one extinct and two reacting states, being stable or metastable depending on the presence of the respective autocatalysts (representing a kind of information11) and environmental conditions7-9. In the presence of both autocatalysts, inequality of the respective reaction constants would cause the ratio of the products of the competing reactions to shift until one of them dies out, a process representing a selection of the “fittest” autocatalyst, its selective value12 being a function of the ratio of the reaction constants.Thus physical generalizations of the familiar biological concepts of “species” (as steady states), “mutation” and “evolution by mutation and selection” (as competition between autocatalytic systems) can be derived as general properties of the class of open systems which can exist in several steady states. Biological systems represent the most prominent subclass of that class.
Optical activity of natural compounds is a characteristic of our living world which is based on the asymmetry of the molecular set-up. It is hard to realize a biological cell which would be constructed from racemic compounds alone. Yet it seems attractive to ask why nature preferred onlyone of two possible enantiomers, e.g. the L-amino-acids and D-sugars. Was there or is there a chance for an antipodic biosphere constructed on the basis of the ‘unnatural’ enantiomers like D-amino-acids and L-sugars on Earth or elsewhere?-The paper presents in its first part a review about hypotheses that would be able to explain the apparent discrepancy between the expectation from laboratory experience and the observation that biological matter consists of extremely asymmetric molecules. The speculations found in literature are divided mainly into two categories: The first one interprets the appearance of optical activity by a chance process and its amplification by suitable means, the second one postulates a cogency leading to the chirality of the biosphere observed today. The discovery of the non-conservation of parity in nuclear physics stimulated a search for related ‘asymmetry effects’ in chemistry. Experiments were undertaken by some workers to construct possible laboratory models for the evolution of optical activity, but many of them failed due to different causes. On the other hand a number of papers has been published that were not directed specifically to the problem discussed, but could be interpreted on the basis of the various hypotheses. It is particularly interesting in this context to look into papers describing the crystallisation of racemates from solutions, that were published as early as 70 yr ago. —In its second part the paper deals with the study of the polymerization of racemic amino-acids as a model that would possibly allow a decision between the hypotheses for the origin of optical activity, — mere chance or a physical driving force determining the chirality of evolution. Since great care was taken to eliminate all sources of systematical errors, one expected-form the classical standpoint-racemic poly-peptides of absolute zero optical activity. — The monomer amino-acids (a-alanine, a-amino-butyric acid, and lysine) were racemized before the polymerization in order to guarantee ‘ideally racemic’ substrates. Polymerization was achieved via the N-carboxyanhydrides of the amino-acids. Reaction vessels and measuring cells were thoroughly cleaned with boiling chromic sulfuric acid and kept sealed from the laboratory atmosphere to prevent any contamination. The optical activity was determined in a Cary 60 spectropolarimeter calibrated to detect angles of rotations in the range of 0.5 mdeg with a maximum error of ±50%. All the poly-amino-acids investigated showed negative angles of rotation at 310 nm between 0.25 and 0.84 mdeg that would correspond to an hypothetical asymmetry effect-i.e. the relative difference of the polymerization constants of L-and D-amino-acids-in the order of 8×10-6. We believe that this result emphasises the existence of a physical force that enables a slight accumulation of the L-amino-acids within the high molecular weight polymers in excess to the D-amino-acids and could be of significance for the evolution of the biomass. At this point the experiments do not allow any conclusion about the nature of the observed ‘asymmetry effect’.