False Chirality Research Articles

True and False Chirality in Chiral Magnetic Nanoparticles.

Determining the true or false chirality of a system is essential for the design of advanced chiral materials and for improving their applications. Typically, a magnetic field would cause false optical activity in the chiral material system, thus confusing the true chirality's influence. Here, we provide a simple way to uncover the true and false chirality in chiral ferrimagnetic nanoparticles (FNPs) by using the gel as a rigid frame. The remnant local magnetic field of the FNP gel can be easily adjusted by an external magnetic field or by controlling the concentration of the FNPs. Moreover, the potential application of the FNP gel is detected by induced magnetic circularly polarized luminescence. This work provides deep insight into the true and false chirality in magnetic nanosystems and offers a strategy to construct new optic elements with an adjustable local magnetic field.

Symmetry and Chirality: Where Physics Shakes Hands with Chemistry and Biology

AbstractIn reflecting the author's personal perspective, this review demonstrates how chirality is a unifying theme in modern science. Using the discrete symmetries of parity P, time reversal T and charge conjugation C to characterize chiral systems, the concepts of true and false chirality that emerge provide an extension of Lord Kelvin's definition to dynamic situations This clarifies the nature of physical influences able to induce absolute enantioselection, emphasizing the distinct behaviour of processes under thermodynamic and kinetic control. Parity violation and CP violation are suggested to be manifestations of true and false cosmic chirality, respectively, with possible roles in abiotic enantioselection. Truly chiral systems support time‐even pseudoscalar observables which endows chiroptical spectroscopies with a special sensitivity to absolute stereochemistry, exemplified by the application of vibrational Raman optical activity to small chiral organic molecules and intact viruses.

Molecular Chirality in Classical Spacetime: Solving the Controversy about the Spinning Cone Model of Rotating Molecules.

The spinning cone is a model of rotating molecules used by Barron in 1986 in relation to asymmetric synthesis and to parity violation. He considered that the non-translating cone spinning about its symmetry axis has false chirality (i.e., it is not chiral), whereas Mislow concluded in 1999 that it is indeed chiral and severely criticized the true versus false chirality nomenclature introduced by Barron, who still disagreed in 2013 with the conclusion of Mislow. Here, it is shown that this controversy comes from an ambiguity in the spinning cone model and that in fact both authors were right. Light is thrown on the true chirality versus false chirality controversy with a very recently published result, which was thus unavailable to both authors: this is a new definition of chirality that encompasses the one introduced by Lord Kelvin at the end of the 19th century.

False Chirality, Absolute Enantioselection and CP Violation: Pierre Curie’s Legacy

The 1884 suggestion of Pierre Curie (1859–1906) that the type of dissymmetry shown by collinear electric and magnetic fields may induce an enantiomeric excess, in a chemical reaction that would otherwise produce a racemic mixture, is explored in the context of fundamental symmetry arguments. Curie’s arrangement exhibits false chirality (time-noninvariant enantiomorphism), and so it may not induce absolute enantioselection (ae) in a process that has reached thermodynamic equilibrium, since it does not lift the degeneracy of chiral enantiomers. However, it may do so in far-from-equilibrium processes via a breakdown in microscopic reversibility analogous to that observed in elementary particle processes under the influence of CP violation, the associated force possessing false chirality with respect to CP enantiomorphism. In contrast, an influence like circularly polarized light exhibiting true chirality (time-invariant enantiomorphism) lifts the degeneracy of enantiomers, and so may induce ae in all circumstances. Although to date, ae has not been observed under the influence of Curie’s arrangement of collinear electric and magnetic fields, it is argued that two different experiments have now demonstrated ae under a falsely chiral influence in systems far from equilibrium, namely in a spinning sample under a gravitational field, and in the separation of enantiomers at a ferromagnetic surface.

Artificial Neural Network based Modelling and Simulation to Identify new candidates for hosting Skyrmions

Abstract The premise of this work is to identify new candidates for hosting exotic topological excitations known as skyrmions. The tool used in this research is artificial neural network. The strategy is the statistical analysis of chiral structures contained in the ICSD database, with the additional information about the group number of constituent elements in the periodic table. The model described in this study predicts ideal chiral crystal and proposes a new chiral crystal design direction. Skyrmions are topologically protected materials with an unusual spin composition that are structurally asymmetric. This research introduces a deep learning method for L1 and L2 regularization with solution to a loss minimization problem for identifying the chiral crystals in skyrmion material of thin films. This paper introduces an approach to building a probabilistic classifier and an Artificial Neural Network(ANN) from a true or false chirality dataset consisting of chiral and achiral compounds with elements of the type ‘A’ and ‘B’. A quantitative indicator is demonstrated for the accuracy of chiral crystal formation. Through contrasting with probabilistic classifier method, the viability of the ANN approach is checked comprehensively. We present deep learning algorithm with Artificial Neural Network(ANN)modeling and simulations. Through out the manuscript we employ statistical techniques as well as deep learning strategies to identify chirality property for chiral crystal design. This research work opens the way to build sophisticated crystal design software methodology.

Logistic Regression Analysis for the Material Design of Chiral Crystals

Crystal design is one of the biggest dreams of scientists. Currently, statistical methods and artificial intelligence (AI) technology are rapidly developing and suitable for material design. Large scale crystallographic databases like ICSD are also gathered. Here we demonstrate to design chiral crystals by logistic regression analysis. 689 chiral compounds and 1000 achiral AxBy type compounds (A and B are elements) were used with a true or false chirality dataset. When logistic regression model analysis was applied to all data, it became clear that crystals containing Group 14 or 16 element elements in the crystal become chiral crystals with high probability. These results are consistent with the bonding modes of the elements. Elements in groups 7 (Mn group), 8 (Fe group), 10 (Ni group) and 12 (Zn group) also tended to grow chiral crystals, consistent with the composition of a new chiral magnetic material (Mn–Co–Zn alloy) that has been recently reported (see text). This result implies that logistic regres...

Chirality and gravitational parity violation.

In this review, parity-violating gravitational potentials are presented as possible sources of both true and false chirality. In particular, whereas phenomenological long-range spin-dependent gravitational potentials contain both truly and falsely chiral terms, it is shown that there are models that extend general relativity including also coupling of fermionic degrees of freedom to gravity in the presence of torsion, which give place to short-range truly chiral interactions similar to that usually considered in molecular physics. Physical mechanisms which give place to gravitational parity violation together with the expected size of the effects and their experimental constraints are discussed. Finally, the possible role of parity-violating gravity in the origin of homochirality and a road map for future research works in quantum chemistry is presented.

Eight types of symmetrically distinct vectorlike physical quantities.

The Letter draws the attention to the spatiotemporal symmetry of various vectorlike physical quantities. The symmetry is specified by their invariance under the action of symmetry operations of the nonrelativistic space-time rotation group O(3)×(1,1') = O'(3), where 1' is a time-reversal operation, the symbol × stands for the group direct product, and O(3) is a group of proper and improper rotations. It is argued that along with the canonical polar vector, there are another seven symmetrically distinct classes of stationary physical quantities, which can be--and often are--denoted as standard three-component vectors, even though they do not transform as a static polar vector under all operations of O'(3). The octet of symmetrically distinct "directional quantities" can be exemplified by two kinds of polar vectors (electric dipole moment P and magnetic toroidal moment T), two kinds of axial vectors (magnetization M and electric toroidal moment G), two kinds of chiral "bidirectors" C and F (associated with the so-called true and false chirality, respectively) and still another two bidirectors N and L, achiral ones, transforming as the nematic liquid crystal order parameter and as the antiferromagnetic order parameter of the hematite crystal α-Fe(2)O(3), respectively.

True and false chirality and absolute enantioselection

The discrete symmetries of parity P, time reversal T, and charge conjugation C are used to characterize the properties of chiral systems. The concepts of true chirality (time-invariant enantiomorphism) and false chirality (time-noninvariant enantiomorphism) that emerge provide an extension of Lord Kelvin’s original definition of chirality to situations where motion is an essential ingredient thereby clarifying, inter alia, the nature of physical influences able to induce absolute enantioselection. Only a truly chiral influence lifts the degeneracy of chiral enantiomers and so may induce absolute enantioselection in all circumstances. Chiral enantiomers remain strictly degenerate under a falsely chiral influence, which may therefore not induce absolute enantioselection in a process that has reached thermodynamic equilibrium, but may do so in far-from-equilibrium processes via a breakdown in microscopic reversibility analogous to that observed in elementary particle processes under the influence of CP violation. Parity violation and CP violation are suggested to be manifestations of true and false cosmic chirality, respectively, and their possible roles in abiotic enantioselection discussed.

Cosmic Chirality both True and False

The discrete symmetries of parity P, time reversal T, and charge conjugation C may be used to characterize the properties of chiral systems. It is well known that parity violation infiltrates into ordinary matter via an interaction between the nucleons and electrons, mediated by the Z(0) particle, that lifts the degeneracy of the mirror-image enantiomers of a chiral molecule. Being odd under P but even under T, this P-violating interaction exhibits true chirality and so may induce absolute enantioselection under all circumstances. It has been suggested that CP violation may also infiltrate into ordinary matter via a P-odd, T-odd interaction mediated by the (as yet undetected) axion. This CP-violating interaction exhibits false chirality and so may induce absolute enantioselection in processes far from equilibrium. Both true and false cosmic chirality should be considered together as possible sources of homochirality in the molecules of life.

From Cosmic Chirality to Protein Structure: Lord Kelvin's Legacy

A selection of my work on chirality is sketched in two distinct parts of this lecture. Symmetry and Chirality explains how the discrete symmetries of parity P, time reversal T, and charge conjugation C may be used to characterize the properties of chiral systems. The concepts of true chirality (time-invariant enantiomorphism) and false chirality (time-noninvariant enantiomorphism) that emerge provide an extension of Lord Kelvin's original definition of chirality to situations where motion is an essential ingredient thereby clarifying, inter alia, the nature of physical influences able to induce absolute enantioselection. Consideration of symmetry violations reveals that strict enantiomers (exactly degenerate) are interconverted by the combined CP operation. Raman optical activity surveys work, from first observation to current applications, on a new chiroptical spectroscopy that measures vibrational optical activity via Raman scattering of circularly polarized light. Raman optical activity provides incisive information ranging from absolute configuration and complete solution structure of smaller chiral molecules and oligomers to protein and nucleic acid structure of intact viruses.

False chirality, CP violation and the breakdown of microscopic reversibility in chiral molecular and elementary particle processes

False chirality, CP violation and the breakdown of microscopic reversibility in chiral molecular and elementary particle processes

CP violation and molecular physics

The proof that a particle and its antiparticle have identical rest mass, which is based on the CPT invariance of the Hamiltonian, can be adapted to show that the CP enantiomers of a chiral molecule remain degenerate even in the presence of CP violation. This reinforces an earlier suggestion that the force responsible for CP violation exhibits false chirality with respect to CP enantiomorphism and leads naturally to the idea that the CP violation observed in the neutral K-meson system is analogous to a special type of chemical catalysis since it affects the rates of certain particle—antiparticle interconversion pathways (via a break-down in microscopic reversibility) without affecting the initial and final particle energies and hence the equilibrium thermodynamics. CP violation of this type is unlikely to have any direct manifestations in molecular physics.

Fundamental symmetry aspects of chirality

Physical systems which exhibit distinguishable enantiomers under space inversion are not necessarily chiral. A new definition of chirality is proposed that enables true and false chirality to be distinguished. Although spatial enantiomorphism is sufficient to guarantee chirality in a stationary object, enantiomorphous systems are not necessarily chiral when motion is involved. Only a truly chiral influence can induce absolute asymmetric synthesis in a reaction mixture at thermodynamic equilibrium, but false chirality might suffice if equilibrium is not attained. Parity violation lifts only the degeneracy of enantiomers of truly chiral systems, the true enantiomers (i.e. strictly degenerate) being interconverted by space inversion together with charge conjugation. The time-independence of optical activity arising from parity violation is contrasted with the time-dependence of that arising from spontaneous parity breaking.

True and false chirality and absolute asymmetric synthesis

True and false chirality and absolute asymmetric synthesis

True and false chirality and parity violation

Systems that exhibit distinguishable enantiomers under space inversion are not necessarily chiral. A new definition of chirality is proposed that enables true and false chirality to be distinguished. This definition is reinforced by a consideration of parity violation, which lifts only the degeneracy of the space-inverted enantiomers of truly chiral systems.