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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Chemistry: Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 42704

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Special Issue Editor

Prof. Dr. Rui Tamura

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Graduate School of Human and Environmental Studies, Kyoto University, Kyoto 6068501, Japan
Interests: complexity phenomena; chiral symmetry breaking; spin symmetry breaking; chiral resolution; liquid crystals; organic crystals; magnetism
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Special Issue Information

Dear colleagues,

The ‘complexity theory’, which has developed rapidly since the 1970s, is regarded as one of the paradigm shifts or epoch-making revolutions of natural science in the twentieth century, together with the birth and establishment of ‘quantum mechanics’ and ‘Einsteinian general theory of relativity’ at the beginning of the same century. Today, a concept of the nonlinear complexity theory is recognized to govern a variety of dynamic behaviors observed in both natural and social sciences. In the ‘non-equilibrium (or out-of-equilibrium) complexity system’, symmetry-breaking occurs easily in concert with a phase transition of a chaotic or dissipative state to another one. In other words, fluctuation in a non-equilibrium state induces a phase transition to trigger the symmetry-breaking, and eventually, the nonlinear amplification of fluctuation leads to dissymmetric circumstances. A typical example is the birth of the universe by the cosmic inflation followed by big bang starting from a quantum fluctuation. Other familiar and important examples include many-body interactions of multiple elements responsible for the nonlinearity. Intermolecular interactions can give non-equilibrium objects, such as cells, bubbles, and metastable crystals, which may have strong links to the origin of the selected chirality of life. Thus, symmetry-breaking has been playing a primordial role in physics, chemistry and life science.

This Special Issue is devoted to investigations on the various chemical phenomena which originate from the symmetry-breaking induced by a phase transition in the condensed phases, such as metastable crystals, liquid crystals, amorphous solids, and polymer materials under non-equilibrium conditions, including other mysterious or strange chemical phenomena, which need elucidation of their mechanism in the near future, and theoretical calculations, such as determination of anisotropic organic crystal structures by computer simulations using various algorithm, etc.

You are cordially invited to contribute a short or long review article or full paper on such subjects to this Special Issue. We are particularly excited about the potential for the collected manuscripts to be further published in a book entitled “Chemical Symmetry Breaking” from MDPI.

Prof. Dr. Rui Tamura
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Polymorphic transition of an achiral crystal to a chiral one and vice versa
Hydration/dehydration polymorphic transition mechanism in organic crystals
Photoinduced mechanical motion of photochromic organic crystals
Mechanochromism of organometallic crystals
Chirality control of circularly polarized light (CPL) by cocrystals
Chirality control of the helical structure of polymers
Chiral discrimination in the conglomerate crystals
Chiral resolution of racemic mixed crystals by simple recrystallization
Chiral resolution and absolute asymmetric synthesis using crystallization of achiral molecules
Crystal structure determination by direct space approach
Chiral symmetry-breaking in liquids and liquid crystals
Superparamagnetic behavior observed in magnetic organic nanocrystals and liquid crystals

Published Papers (12 papers)

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Research

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20 pages, 695 KiB

Open AccessArticle

Off-Shell Quantum Fields to Connect Dressed Photons with Cosmology

by Hirofumi Sakuma, Izumi Ojima, Motoichi Ohtsu and Hiroyuki Ochiai

Symmetry 2020, 12(8), 1244; https://doi.org/10.3390/sym12081244 - 28 Jul 2020

Cited by 5 | Viewed by 2503

Abstract

The anomalous nanoscale electromagnetic field arising from light–matter interactions in a nanometric space is called a dressed photon. While the generic technology realized by utilizing dressed photons has demolished the conventional wisdom of optics, for example, the unexpectedly high-power light emission from indirect-transition type semiconductors, dressed photons are still considered to be too elusive to justify because conventional optical theory has never explained the mechanism causing them. The situation seems to be quite similar to that of the dark energy/matter issue in cosmology. Regarding these riddles in different disciplines, we find a common important clue for their resolution in the form of the relevance of space-like momentum support, without which quantum fields cannot interact with each other according to a mathematical result of axiomatic quantum field theory. Here, we show that a dressed photon, as well as dark energy, can be explained in terms of newly identified space-like momenta of the electromagnetic field and dark matter can be explained as the off-shell energy of the Weyl tensor field. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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15 pages, 2197 KiB

Open AccessFeature PaperArticle

Absolute Asymmetric Synthesis Involving Chiral Symmetry Breaking in Diels–Alder Reaction

by Naohiro Uemura, Seiya Toyoda, Waku Shimizu, Yasushi Yoshida, Takashi Mino and Masami Sakamoto

Symmetry 2020, 12(6), 910; https://doi.org/10.3390/sym12060910 - 01 Jun 2020

Cited by 19 | Viewed by 3796

Abstract

Efficient generation and amplification of chirality from prochiral substrates in the Diels–Alder reaction (DA reaction) followed by dynamic crystallization were achieved without using an external chiral source. Since the DA reaction of 2-methylfuran and various maleimides proceeds reversibly, an exo-adduct was obtained as the main product as the reaction proceeded. From single crystal X-ray structure analysis, it was found that five of ten exo-adducts gave conglomerates. When 2-methylfuran and various maleimides with a catalytic amount of TFA were reacted in a sealed tube, the exo-DA adducts were precipitated from the solution, while the reaction mixtures were continuously ground and stirred using glass beads. Deracemization occurred and chiral amplification was observed for four of the substrates. Each final enantiomeric purity was influenced by the crystal structure, and when enantiomers were included in the disorder, they reached an enantiomeric purity reflecting the ratio of the disorder. The final ee value of the 3,5-dimethylphenyl derivative after chiral amplification was 98% ee. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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Review

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51 pages, 11892 KiB

Open AccessReview

Resonance in Chirogenesis and Photochirogenesis: Colloidal Polymers Meet Chiral Optofluidics

by Michiya Fujiki

Symmetry 2021, 13(2), 199; https://doi.org/10.3390/sym13020199 - 26 Jan 2021

Cited by 4 | Viewed by 3727

Abstract

Metastable colloids made of crystalline and/or non-crystalline matters render abilities of photonic resonators susceptible to chiral chemical and circularly polarized light sources. By assuming that μm-size colloids and co-colloids consisting of π- and/or σ-conjugated polymers dispersed into an optofluidic medium are artificial models of open-flow, non-equilibrium coacervates, we showcase experimentally resonance effects in chirogenesis and photochirogenesis, revealed by gigantic boosted chiroptical signals as circular dichroism (CD), optical rotation dispersion, circularly polarized luminescence (CPL), and CPL excitation (CPLE) spectral datasets. The resonance in chirogenesis occurs at very specific refractive indices (RIs) of the surrounding medium. The chirogenesis is susceptible to the nature of the optically active optofluidic medium. Moreover, upon an excitation-wavelength-dependent circularly polarized (CP) light source, a fully controlled absolute photochirogenesis, which includes all chiroptical generation, inversion, erase, switching, and short-/long-lived memories, is possible when the colloidal non-photochromic and photochromic polymers are dispersed in an achiral optofluidic medium with a tuned RI. The hand of the CP light source is not a determining factor for the product chirality. These results are associated with my experience concerning amphiphilic polymerizable colloids, in which, four decades ago, allowed proposing a perspective that colloids are connectable to light, polymers, helix, coacervates, and panspermia hypotheses, nuclear physics, biology, radioisotopes, homochirality question, first life, and cosmology. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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20 pages, 6777 KiB

Open AccessEditor’s ChoiceReview

Elastic Organic Crystals of π-Conjugated Molecules: New Concept for Materials Chemistry

by Shotaro Hayashi

Symmetry 2020, 12(12), 2022; https://doi.org/10.3390/sym12122022 - 07 Dec 2020

Cited by 18 | Viewed by 6575

Abstract

It is generally believed that organic single crystals composed of a densely packed arrangement of anisotropic, organic small molecules are less useful as functional materials due to their mechanically inflexible and brittle nature, compared to polymers bearing flexible chains and thereby exhibiting viscoelasticity. Nevertheless, organic crystals have attracted much attention because of their tunable optoelectronic properties and a variety of elegant crystal habits and unique ordered or disordered molecular packings arising from the anisotropic molecular structures. However, the recent emergence of flexible organic crystal materials showing plasticity and elasticity has considerably changed the concept of organic single crystals. In this review, the author summarizes the state-of-the-art development of flexible organic crystal materials, especially functional elastic organic crystals which are expected to provide a foothold for the next generation of organic crystal materials. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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29 pages, 10024 KiB

Open AccessFeature PaperReview

Spin Symmetry Breaking: Superparamagnetic and Spin Glass-Like Behavior Observed in Rod-Like Liquid Crystalline Organic Compounds Contacting Nitroxide Radical Spins

by Shuichi Sato, Yoshiaki Uchida and Rui Tamura

Symmetry 2020, 12(11), 1910; https://doi.org/10.3390/sym12111910 - 20 Nov 2020

Cited by 5 | Viewed by 4460

Abstract

Liquid crystalline (LC) organic radicals were expected to show a novel non-linear magnetic response to external magnetic and electric fields due to their coherent collective molecular motion. We have found that a series of chiral and achiral all-organic LC radicals having one or two five-membered cyclic nitroxide radical (PROXYL) units in the core position and, thereby, with a negative dielectric anisotropy exhibit spin glass (SG)-like superparamagnetic features, such as a magnetic hysteresis (referred to as ‘positive magneto-LC effect’), and thermal and impurity effects during a heating and cooling cycle in weak magnetic fields. Furthermore, for the first time, a nonlinear magneto-electric (ME) effect has been detected with respect to one of the LC radicals showing a ferroelectric (chiral Smectic C) phase. The mechanism of the positive magneto-LC effect is proposed and discussed by comparison of our experimental results with the well-known magnetic properties of SG materials and on the basis of the experimental results of a nonlinear ME effect. A recent theoretical study by means of molecular dynamic simulation and density functional theory calculations suggesting the high possibility of conservation of the memory of spin-spin interactions between magnetic moments owing to the ceaseless molecular contacts in the LC and isotropic states is briefly mentioned as well. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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12 pages, 3688 KiB

Open AccessFeature PaperReview

Vapochromism of Organic Crystals Based on Macrocyclic Compounds and Inclusion Complexes

by Toshikazu Ono and Yoshio Hisaeda

Symmetry 2020, 12(11), 1903; https://doi.org/10.3390/sym12111903 - 19 Nov 2020

Cited by 14 | Viewed by 3196

Abstract

Vapochromic materials, which change color and luminescence when exposed to specific vapors and gases, have attracted considerable attention in recent years owing to their potential applications in a wide range of fields such as chemical sensors and environmental monitors. Although the mechanism of vapochromism is still unclear, several studies have elucidated it from the viewpoint of crystal engineering. In this mini-review, we investigate recent advances in the vapochromism of organic crystals. Among them, macrocyclic molecules and inclusion complexes, which have apparent host–guest interactions with analyte molecules (specific vapors and gases), are described. When the host compound is properly designed, its cavity size and symmetry change in response to guest molecules, influencing the optical properties by changing the molecular inclusion and recognition abilities. This information highlights the importance of structure–property relationships resulting from the molecular recognition at the solid–vapor interface. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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15 pages, 4205 KiB

Open AccessReview

Chiral Symmetry Breaking in Liquid Crystals: Appearance of Ferroelectricity and Antiferroelectricity

by Yoichi Takanishi

Symmetry 2020, 12(11), 1900; https://doi.org/10.3390/sym12111900 - 19 Nov 2020

Cited by 2 | Viewed by 2295

Abstract

The study of chiral symmetry breaking in liquid crystals and the consequent emergence of ferroelectric and antiferroelectric phases is described. Furthermore, we show that the frustration between two phases induces a variety of structural phases called subphases and that resonant X-ray scattering is a powerful tool for the structural analysis of these complicated subphases. Finally, we discuss the future prospects for clarifying the origin of such successive phase transition. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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17 pages, 7012 KiB

Open AccessReview

Spontaneous and Controlled Macroscopic Chiral Symmetry Breaking by Means of Crystallization

by Gérard Coquerel and Marine Hoquante

Symmetry 2020, 12(11), 1796; https://doi.org/10.3390/sym12111796 - 30 Oct 2020

Cited by 9 | Viewed by 2434

Abstract

In this paper, macroscopic chiral symmetry breaking refers to as the process in which a mixture of enantiomers departs from 50–50 symmetry to favor one chirality, resulting in either a scalemic mixture or a pure enantiomer. In this domain, crystallization offers various possibilities, from the classical Viedma ripening or Temperature Cycle-Induced Deracemization to the famous Kondepudi experiment and then to so-called Preferential Enrichment. These processes, together with some variants, will be depicted in terms of thermodynamic pathways, departure from equilibrium and operating conditions. Influential parameters on the final state will be reviewed as well as the impact of kinetics of the R ⇔ S equilibrium in solution on chiral symmetry breaking. How one can control the outcome of symmetry breaking is examined. Several open questions are detailed and different interpretations are discussed. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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13 pages, 2676 KiB

Open AccessReview

Generation of Circularly Polarized Luminescence by Symmetry Breaking

by Yoshitane Imai

Symmetry 2020, 12(11), 1786; https://doi.org/10.3390/sym12111786 - 28 Oct 2020

Cited by 22 | Viewed by 4158

Abstract

Circularly polarized luminescence (CPL) has attracted significant attention in the fields of chiral photonic science and optoelectronic materials science. In a CPL-emitting system, a chiral luminophore derived from chiral molecules is usually essential. In this review, three non-classical CPL (NC-CPL) systems that do not use enantiomerically pure molecules are reported: (i) supramolecular organic luminophores composed of achiral organic molecules that can emit CPL without the use of any chiral auxiliaries, (ii) achiral or racemic luminophores that can emit magnetic CPL (MCPL) by applying an external magnetic field of 1.6 T, and (iii) circular dichroism-silent organic luminophores that can emit CPL in the photoexcited state as a cryptochiral CPL system. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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13 pages, 3476 KiB

Open AccessReview

Photochemical Methods for the Real-Time Observation of Phase Transition Processes upon Crystallization

by Fuyuki Ito

Symmetry 2020, 12(10), 1726; https://doi.org/10.3390/sym12101726 - 19 Oct 2020

Cited by 4 | Viewed by 2017

Abstract

We have used the fluorescence detection of phase transformation dynamics of organic compounds by photochemical methods to observe a real-time symmetry breaking process. The organic fluorescent molecules vary the fluorescence spectra depending on molecular aggregated states, implying fluorescence spectroscopy can be applied to probe the evolution of the molecular-assembling process. As an example, the amorphous-to-crystal phase transformation and crystallization with symmetry breaking at droplet during the solvent evaporation of mechanofluorochromic molecules are represented in this review. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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15 pages, 3152 KiB

Open AccessReview

Robust Dynamics of Synthetic Molecular Systems as a Consequence of Broken Symmetry

by Yoshiyuki Kageyama

Symmetry 2020, 12(10), 1688; https://doi.org/10.3390/sym12101688 - 14 Oct 2020

Cited by 2 | Viewed by 3117

Abstract

The construction of molecular robot-like objects that imitate living things is an important challenge for current chemists. Such molecular devices are expected to perform their duties robustly to carry out mechanical motion, process information, and make independent decisions. Dissipative self-organization plays an essential role in meeting these purposes. To produce a micro-robot that can perform the above tasks autonomously as a single entity, a function generator is required. Although many elegant review articles featuring chemical devices that mimic biological mechanical functions have been published recently, the dissipative structure, which is the minimum requirement for mimicking these functions, has not been sufficiently discussed. This article aims to show clearly that dissipative self-organization is a phenomenon involving autonomy, robustness, mechanical functions, and energy transformation. Moreover, it reports the results of recent experiments with an autonomous light-driven molecular device that achieves all of these features. In addition, a chemical model of cell-amplification is also discussed to focus on the generation of hierarchical movement by dissipative self-organization. By reviewing this research, it may be perceived that mainstream approaches to synthetic chemistry have not always been appropriate. In summary, the author proposes that the integration of catalytic functions is a key issue for the creation of autonomous microarchitecture. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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16 pages, 8666 KiB

Open AccessReview

Symmetry Breaking and Photomechanical Behavior of Photochromic Organic Crystals

by Daichi Kitagawa, Christopher J. Bardeen and Seiya Kobatake

Symmetry 2020, 12(9), 1478; https://doi.org/10.3390/sym12091478 - 09 Sep 2020

Cited by 9 | Viewed by 3259

Abstract

Photomechanical materials exhibit mechanical motion in response to light as an external stimulus. They have attracted much attention because they can convert light energy directly to mechanical energy, and their motions can be controlled without any physical contact. This review paper introduces the photomechanical motions of photoresponsive molecular crystals, especially bending and twisting behaviors, from the viewpoint of symmetry breaking. The bending (right–left symmetry breaking) and twisting (chiral symmetry breaking) of photomechanical crystals are based on both intrinsic and extrinsic factors like molecular orientation in the crystal and illumination conditions. The ability to design and control this symmetry breaking will be vital for generating new science and new technological applications for organic crystalline materials. Full article

(This article belongs to the Special Issue Chemical Symmetry Breaking)

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