Feature Papers in Chemistry

A topical collection in Symmetry (ISSN 2073-8994). This collection belongs to the section "Chemistry: Symmetry/Asymmetry".

Viewed by 79786

Editor

Topical Collection Information

All kinds of symmetry-related problems in chemistry may be the subject of papers submitted to Symmetry. One of the most relevant fields includes optical activity that is the consequence of a kind of chirality center, such as an asymmetric C atom or a heteroatom like P. Discussion of problems associated with a stereogenic center or centers, such as separation of racemates, enantiomer enrichment or separation, chiral induction, diastereomeric transition states, diastereomers or intermediates, asymmetric syntheses, or any kind of selective synthesis, is welcome. New transition metal complex catalysts comprising optically active ligands and the asymmetric reactions they allow are also of interest.

X-ray crystallography is another exciting field that produces results within the scope of Symmetry. These days, single-crystal X-ray analysis is a routine method that not only allows the elucidation of the stereostructures of individual molecules but also gives insights regarding the hidden symmetry/asymmetry issues of the crystal structure.

Prof. Dr. György Keglevich
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 collection 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.

Published Papers (36 papers)

2024

Jump to: 2023, 2022, 2021, 2020

26 pages, 1183 KiB  
Article
New Insights into Aromaticity through Novel Delta Polynomials and Delta Aromatic Indices
by Krishnan Balasubramanian
Symmetry 2024, 16(4), 391; https://doi.org/10.3390/sym16040391 - 27 Mar 2024
Viewed by 1017
Abstract
We have developed novel polynomials called delta polynomials, which are, in turn, derived from the characteristic and matching polynomials of graphs associated with polycyclic aromatic compounds. Natural logarithmic aromatic indices are derived from these delta polynomials, which are shown to provide new insights [...] Read more.
We have developed novel polynomials called delta polynomials, which are, in turn, derived from the characteristic and matching polynomials of graphs associated with polycyclic aromatic compounds. Natural logarithmic aromatic indices are derived from these delta polynomials, which are shown to provide new insights into the aromaticity of polycyclic aromatic compounds, including the highly symmetric C60 buckminsterfullerene, several other fullerenes, graphene, kekulene series and other cycloarenes, such as polycyclic circumcoronaphenes and coronoids. The newly developed aromatic index yields a value of 6.77 for graphene, 6.516865 for buckminsterfullerene C60(Ih), 5.914023 for kekulene (D6h symmetry), 6.064420 for coronene (D6h), 6.137828 for circumcoronene (D6h), 6.069668 for dicronylene and so forth. Hence, the novel scaled logarithmic aromatic delta indices developed here appear to provide good quantitative measures of aromaticity, especially when they are used in conjunction with other aromatic indicators. Full article
Show Figures

Figure 1

26 pages, 15538 KiB  
Review
Stereoselective Syntheses of Organophosphorus Compounds
by Oleg I. Kolodiazhnyi and Anastasy O. Kolodiazhna
Symmetry 2024, 16(3), 342; https://doi.org/10.3390/sym16030342 - 12 Mar 2024
Viewed by 698
Abstract
The review is devoted to the theoretical and synthetic aspects of the stereochemistry of organophosphorus compounds. Organophosphorus compounds are not only widely exist in biologically active pharmaceuticals and agrochemicals, but also have widespread applications in material science and organic synthesis as ligands for [...] Read more.
The review is devoted to the theoretical and synthetic aspects of the stereochemistry of organophosphorus compounds. Organophosphorus compounds are not only widely exist in biologically active pharmaceuticals and agrochemicals, but also have widespread applications in material science and organic synthesis as ligands for transition metal complexes. One of the mainstreams for the development in this field is the creation of biologically active organophosphorus compounds that are searched and used as drugs or plant-protecting agents, which leads to the elaboration of advanced methods and monitoring, yielding up-to-date approaches to perform synthesis in an environmentally friendly manner. The review consists of two parts. The first part presents methods for the asymmetric synthesis of organophosphorus compounds using asymmetric organocatalysis and metal complex catalysis. In the review is described the nature of the chirality generation in the prebiotic period, the mechanisms of asymmetric induction, and double stereodifferentiation are discussed. The use of these methods for the preparation of chiral phosphorus analogs of natural compounds (phosphono-isonorstatin, phosphono-GABOB, phosphacarnitine, bis-phosphonates, and others) is described. Some data concerning of λ5-phosphanediones as metaphosphate anion analogues are also reported. The second part of the presented review shows examples of the use of these methods for the synthesis of phosphorus analogues of natural compounds—chiral phosphonoamino acids and hydroxyphosphonates: phosphonoaspartic acid, phosphonoglutamic acid, phosphonohomoproline, chiral bis-phosphonates. The reaction of dehydration aromatization with the formation of pho sphono isoindolinones, including isoindolinone bis-phosphonates, has been studied. Some of the synthesized compounds showed biological activity as protein tyrosine phosphatase inhibitors. A phosphonic analogue of iso-norstatine was synthesized. A stereoselective method for the synthesis of tetradecapentaenoic acid derivatives was developed. Full article
Show Figures

Figure 1

15 pages, 3848 KiB  
Article
Unsymmetrical and C3-Symmetrical Partially Fluorinated Hexaarylbenzenes: Effect of Terminal Alkoxy Chain Length on Photophysical and Thermophysical Behavior
by Yizhou Wang, Shigeyuki Yamada, Motohiro Yasui and Tsutomu Konno
Symmetry 2024, 16(3), 314; https://doi.org/10.3390/sym16030314 - 06 Mar 2024
Viewed by 717
Abstract
Solution-state photoluminescence (PL) is affected by the electronic state; however, solid-state PL varies widely depending on the aggregated state. Although the synthesis and photophysical properties of unsymmetrical and C3-symmetrical hexaarylbenzenes (HABs) have been reported, the influence of their terminal alkoxy chains [...] Read more.
Solution-state photoluminescence (PL) is affected by the electronic state; however, solid-state PL varies widely depending on the aggregated state. Although the synthesis and photophysical properties of unsymmetrical and C3-symmetrical hexaarylbenzenes (HABs) have been reported, the influence of their terminal alkoxy chains on their physical properties remains unclear. Therefore, we synthesized a series of unsymmetrical and C3-symmetrical partially fluorinated HABs with different alkoxy chains and investigated the effects of alkoxy chain length on the thermophysical and photophysical properties. While investigating phase transition behavior, the ethoxy-substituted unsymmetrical derivative revealed a columnar liquid-crystalline phase, whereas the other derivatives only exhibited a phase transition between crystalline and isotropic phases. While evaluating PL behavior, both the unsymmetrical and C3-symmetrical analogs exhibited relatively strong blue PL, independent of the alkoxy chain length. Through-space π-conjugation caused the PL spectra of C3-symmetrical derivatives to redshift compared to those of unsymmetrical derivatives. Partially fluorinated HABs exhibited relatively strong fluorescence, even in the crystalline state, depending on the alkoxy chain length, owing to the formation of various aggregated structures. Crystalline fluorinated HABs exhibited photochromism, resulting in the appearance of long-wavelength PL bands when exposed to ultraviolet (UV) irradiation, making them promising candidates for PL sensing materials for UV detection. Full article
Show Figures

Figure 1

13 pages, 17568 KiB  
Review
Organocatalytic Conjugate Hydroazidation and Hydrocyanation: A Metal-Free Approach to Synthetically Versatile Chiral Building Blocks
by Rosaria Schettini and Giorgio Della Sala
Symmetry 2024, 16(2), 199; https://doi.org/10.3390/sym16020199 - 08 Feb 2024
Viewed by 569
Abstract
Chiral β-azido- and β-cyanocarbonyl compounds are extremely useful building blocks in asymmetric synthesis, thanks to the manyfold reactivity of their functional groups. The enantioselective synthesis of such compounds, until the beginning of the 21st century, has been mostly achieved using transition-metal chiral catalysts. [...] Read more.
Chiral β-azido- and β-cyanocarbonyl compounds are extremely useful building blocks in asymmetric synthesis, thanks to the manyfold reactivity of their functional groups. The enantioselective synthesis of such compounds, until the beginning of the 21st century, has been mostly achieved using transition-metal chiral catalysts. The explosion of enantioselective organocatalysis, however, has enabled the development of efficient metal-free methodologies with significant benefits in terms of costs and environmental safety. An overview of the advances made in recent years in this field is herein presented. Full article
Show Figures

Figure 1

11 pages, 1801 KiB  
Article
Synthesis of 2,6-Diaminotriptycene Conjugates with Chiral Auxiliaries: Towards the Scalable Resolution of Crucial Triptycene Intermediates
by Giovanni Preda, Emanuele Casali, Alessio Porta and Dario Pasini
Symmetry 2024, 16(1), 116; https://doi.org/10.3390/sym16010116 - 18 Jan 2024
Cited by 1 | Viewed by 659
Abstract
Triptycenes are tridimensional molecular scaffolds with interesting properties for applications in materials science: molecular rigidity and preorganization, tailorable chromophores, and, with an appropriate substitution pattern, chirality. The separation of the two enantiomers of chiral triptycenes has been the subject of increasing interest in [...] Read more.
Triptycenes are tridimensional molecular scaffolds with interesting properties for applications in materials science: molecular rigidity and preorganization, tailorable chromophores, and, with an appropriate substitution pattern, chirality. The separation of the two enantiomers of chiral triptycenes has been the subject of increasing interest in recent years, with limited success. Here, we report the synthesis and characterization of a series of new organic compounds, in which a chiral triptycene scaffold, derivatized in the 2 and 6 positions with amino groups, has been functionalized with different enantiopure chiral auxiliaries, forming diastereoisomeric couples. The properties of such compounds, in terms of the optimization of their chromatographic separation, are elucidated with the aid of computational calculations of preferred conformations and molecular polarities. Full article
Show Figures

Figure 1

18 pages, 4133 KiB  
Article
Synthesis and Structural Elucidation of P-stereogenic Coumarins
by Kamil F. Dziuba, Sławomir Frynas, Anna E. Kozioł and Katarzyna Szwaczko
Symmetry 2024, 16(1), 73; https://doi.org/10.3390/sym16010073 - 05 Jan 2024
Viewed by 764
Abstract
This paper presents the general synthesis of a comprehensive group of P-chiral phosphinyl derivatives with a natural coumarin-type motif. A chiral substituent was attached at the third position of the coumarin molecule via the Knoevenagel procedure using readily available P-chiral phoshinylacetic acid esters [...] Read more.
This paper presents the general synthesis of a comprehensive group of P-chiral phosphinyl derivatives with a natural coumarin-type motif. A chiral substituent was attached at the third position of the coumarin molecule via the Knoevenagel procedure using readily available P-chiral phoshinylacetic acid esters without loss of enantiomeric purity. The application of salicylaldehyde-based derivatives allowed the incorporation of substituents of different electron character into the backbone of these coumarins making them suitable for subsequent chemical modifications. As a result, we gained access to six achiral (2a–g) and a large number ((Sp)-4a–f, (Sp)-6a–e and (Rp)-8a) of new potential chiral ligand precursors, pharmaceuticals, etc. with an imbedded phosphinyl group with evidenced biological activity based on the natural coumarin backbone. The molecular structure, including absolute configuration, was determined for seven compounds. Full article
Show Figures

Figure 1

2023

Jump to: 2024, 2022, 2021, 2020

13 pages, 3131 KiB  
Article
Stereoselectivity in Butadiene Polymerization Promoted by Using Ziegler–Natta Catalysts Based on (Anilidomethyl)pyridine Group (IV) Complexes
by Stefano Milione and Stefania Pragliola
Symmetry 2024, 16(1), 18; https://doi.org/10.3390/sym16010018 - 22 Dec 2023
Viewed by 626
Abstract
The stereoselective polymerization of conjugated dienes promoted by using transition metal complexes has attracted much interest in both industrial and academic environments for the relevance of polydienes as synthetic rubbers and for the challenging reaction mechanisms. Among the different transition metal complexes, those [...] Read more.
The stereoselective polymerization of conjugated dienes promoted by using transition metal complexes has attracted much interest in both industrial and academic environments for the relevance of polydienes as synthetic rubbers and for the challenging reaction mechanisms. Among the different transition metal complexes, those based on group IV have been demonstrated to be versatile and efficient catalysts. Titanium complexes are generally more active than zirconium complexes. A rare exception to this trend is represented by a series of Zr(IV) complexes supported by (anilidomethyl)pyridine ligands that, after activation by using Al(iBu2H)/MAO, were found to be highly active affording exclusively cis-1,4-polybutadiene. To rationalize this unexpected trend and to obtain more insights into the parameters that control the reactivity of group IV complexes, a theoretical investigation of the entire polymerization mechanism, employing density functional methods, was undertaken. In the framework of the widely accepted polymerization scheme, the different intermediates featuring h4 (both cis and trans) coordination of the monomer and h1 or h3 (syn or anti)allyl coordination of the growing chain were scrutinized. Subsequently, the effects of the metal center on the free-energy profiles of the elementary steps involved in the reaction were examined. The results presented herein aim to achieve a better knowledge of the influence of the metal on the polymerization rates and on the stereoselectivity of the reaction. Full article
Show Figures

Figure 1

12 pages, 2651 KiB  
Article
Chiral Separation of Vildagliptin by Capillary Electrophoresis—The Study of Enantiomeric Complexation
by Lajos Attila Papp, Gabriel Hancu, Zoltán István Szabó, Blanka Székely-Szentmiklósi, Tamás Gáti, Béla Fiser, Márta Kraszni and Gergő Tóth
Symmetry 2024, 16(1), 17; https://doi.org/10.3390/sym16010017 - 22 Dec 2023
Viewed by 779
Abstract
Vildagliptin (VIL) is a dipeptidyl peptidase-4 inhibitor used in the treatment of type 2 diabetes mellitus; in therapy, it is available as the enantiomerically pure S-VIL, the other enantiomer R-VIL being considered as an enantiomeric impurity. A systematic screening of 16 [...] Read more.
Vildagliptin (VIL) is a dipeptidyl peptidase-4 inhibitor used in the treatment of type 2 diabetes mellitus; in therapy, it is available as the enantiomerically pure S-VIL, the other enantiomer R-VIL being considered as an enantiomeric impurity. A systematic screening of 16 cyclodextrin (CD) derivatives as chiral selectors was performed at three pH levels using phosphate (pH 2.5, pH 7.0) and acetate (pH 4.5) buffers. Method optimization employed an experimental design approach, systematically investigating the effect of buffer and CD concentration, buffer pH, capillary temperature, and applied voltage on the chiral resolution and analysis time. The method’s analytical performance was thoroughly assessed and subsequently employed for determining the enantiomeric purity of VIL in a pharmaceutical formulation. The properties of the inclusion complexes, such as stoichiometry and atomic level intermolecular host–guest interactions were studied by NMR measurements and molecular modeling. Native α-CD at acidic pH has demonstrated its exceptional suitability for the separation of VIL enantiomers with a favorable migration order (R-VIL followed by S-VIL). The optimized analytical conditions (75 mM acetate buffer, pH 4.5, containing 50 mM α-CD, 18 kV applied voltage, and 15 °C capillary temperature) provided a baseline separation of VIL enantiomers within 9 min. The developed method represents a cost-effective alternative to the enantiomeric impurity control of VIL. Symmetry is often a fundamental aspect of molecular structures and interactions, and our detailed analysis of the chiral recognition process contributes to the understanding of symmetry-related aspects in molecular systems. This developed method not only offers a cost-effective alternative for the enantiomeric impurity control of VIL but also provides valuable information regarding the mechanism of the chiral recognition process, aligning with the broader themes of symmetry in molecular sciences. Full article
Show Figures

Figure 1

16 pages, 9021 KiB  
Article
Asymmetry of Structural and Electrophysical Properties of Symmetrical Titania Nanotubes as a Result of Modification with Barium Titanate
by Elizaveta Konstantinova, Vladimir Zaitsev, Ekaterina Kytina, Mikhail Martyshov, Timofey Savchuk, Danil Butmanov, Daria Dronova, Daria Krupanova, Lidiya Volkova and Andrey Tarasov
Symmetry 2023, 15(12), 2141; https://doi.org/10.3390/sym15122141 - 01 Dec 2023
Viewed by 819
Abstract
Anodic titania nanotubes (TiO2-NT) are very promising for use in photocatalysis and photovoltaics due to their developed surface, symmetrical structure and conductive properties, which, moreover, makes them a convenient matrix for creating various nanocomposites. Herein we propose a new facile way [...] Read more.
Anodic titania nanotubes (TiO2-NT) are very promising for use in photocatalysis and photovoltaics due to their developed surface, symmetrical structure and conductive properties, which, moreover, makes them a convenient matrix for creating various nanocomposites. Herein we propose a new facile way of synthesizing symmetrical TiO2-NT followed by a modification with barium titanate (BaTiO3) nanoparticles, combining the advantages of electrochemical oxidation and hydrothermal synthesis. The electrophysical and optoelectronic properties of the formed nanocomposites have been studied. An asymmetry of the current–voltage characteristics was revealed. It is shown that during the barium titanate deposition, a symmetry-breaking nanoheterojunction TiO2/BaTiO3 is formed. Using EPR spectroscopy, paramagnetic defects (titanium, barium and oxygen vacancies) in the samples were determined. It was observed for the first time that upon illumination of titania nanotubes modified with BaTiO3, the asymmetrical separation of photoexcited charge carriers (electrons and holes) between TiO2-NT and BaTiO3 occurs, followed by the capture of electrons and holes by defects. As a result, the photoinduced charge accumulates on the defects. Full article
Show Figures

Figure 1

19 pages, 1199 KiB  
Review
Alloy Quasicrystals: Perspectives and Some Open Questions at Forty Years
by Enrique Maciá
Symmetry 2023, 15(12), 2139; https://doi.org/10.3390/sym15122139 - 01 Dec 2023
Cited by 2 | Viewed by 793
Abstract
Four decades have elapsed since the first quasiperiodic crystal was discovered in the Al–Mn alloy system, and much progress has been made during this time on the science of quasicrystals (QCs). Notwithstanding this, a significant number of open questions still remain regarding both [...] Read more.
Four decades have elapsed since the first quasiperiodic crystal was discovered in the Al–Mn alloy system, and much progress has been made during this time on the science of quasicrystals (QCs). Notwithstanding this, a significant number of open questions still remain regarding both fundamental and technological aspects. For instance: What are QCs good for? How can we improve the current provisional QC definition? What is the role of the underlying quasiperiodic order and the characteristic inflation symmetry of these compounds in the emergence of their unusual physicochemical properties? What is the nature of chemical bonding in QCs formed in different sorts of materials such as alloys, oxides, or organic polymers? Herein these and other closely related issues are discussed from an interdisciplinary perspective as well as prospective future work in the field in the years to come. Full article
Show Figures

Figure 1

21 pages, 3555 KiB  
Article
Molecular Descriptors—Spectral Property Relations for Characterizing Molecular Interactions in Binary and Ternary Solutions, Excited State Dipole Moment Estimation
by Dana Ortansa Dorohoi, Steluta Gosav, Ana Cezarina Moroșanu, Dan Gheorghe Dimitriu, Gabriela Apreotesei and Teodora Gosav
Symmetry 2023, 15(11), 2075; https://doi.org/10.3390/sym15112075 - 15 Nov 2023
Viewed by 672
Abstract
The nature and strength of the molecular interactions were established by solvatochromic studies of 22 binary and 42 ternary diluted solutions of pyridinium–carbethoxy–anilidomethylid (PCAnM). The visible absorption band of PCAnM, due to an intramolecular charge transfer (ICT) from the carbanion towards the heterocycle, [...] Read more.
The nature and strength of the molecular interactions were established by solvatochromic studies of 22 binary and 42 ternary diluted solutions of pyridinium–carbethoxy–anilidomethylid (PCAnM). The visible absorption band of PCAnM, due to an intramolecular charge transfer (ICT) from the carbanion towards the heterocycle, shows a great sensitivity to the solvent nature. The spectral data are analysed by linear energy relationship (LERS) and the contribution of each type of interaction to the total spectral shift is estimated. The results from the solvatochromic study and those obtained by quantum mechanical computations were correlated in order to estimate the excited state dipole moment of the studied methylid. The decrease of the dipole moment by excitation emphasized in this study corresponds to the ICT nature of the visible absorption band of the solute. The ternary solutions of PCAnM achieved in mixtures of water with primary alcohols (ethanol and methanol) show the dependence of the visible band on the molar fraction of water and give the difference between the interaction energies in molecular pairs of the type water–methylid and alcohol–methylid, computed based on the statistical cell model of ternary solutions. The decrease in strength of the hydrogen bond between PCAnM and the protic solvent molecules was estimated in the following order: water > methanol > ethanol. The results from this study can be utilized in Organic Chemistry to generate knowledge of the interactions with solvents when cycloimmonium methylids are used as precursors to obtain new heterocycles and also in Quantum Chemistry to obtain a better description of their excited electronic states. Full article
Show Figures

Figure 1

11 pages, 8539 KiB  
Article
Synthesis and Structure of a New Iodate Cs5[Sc2(IO3)9](IO3)2 with a Complex Framework Based on the Condensation of [Sc(IO3)6] Building Blocks
by Olga V. Reutova, Elena L. Belokoneva, Anatoly S. Volkov and Olga V. Dimitrova
Symmetry 2023, 15(9), 1777; https://doi.org/10.3390/sym15091777 - 17 Sep 2023
Viewed by 783
Abstract
Transparent single crystals of a new iodate Cs5[Sc2(IO3)9](IO3)2 were synthesized under mild hydrothermal conditions. X-ray diffraction of single crystal was used to determine the large crystal structure with 52 independent atoms, sp. [...] Read more.
Transparent single crystals of a new iodate Cs5[Sc2(IO3)9](IO3)2 were synthesized under mild hydrothermal conditions. X-ray diffraction of single crystal was used to determine the large crystal structure with 52 independent atoms, sp. gr. P21/c. The building blocks [Sc(IO3)6]3− of Sc octahedra and six (IO3) groups are condensed into a framework; the structure contains additional isolated (IO3) groups. Large Cs cations occupy holes and form an intercrossing framework. Similar building blocks [M(IO3)6] are known for many iodates; however, most are isolated. Their topology and symmetry differ and determine the properties of the compounds. Full article
Show Figures

Figure 1

48 pages, 1811 KiB  
Article
Recursive Symmetries: Chemically Induced Combinatorics of Colorings of Hyperplanes of an 8-Cube for All Irreducible Representations
by Krishnan Balasubramanian
Symmetry 2023, 15(5), 1031; https://doi.org/10.3390/sym15051031 - 06 May 2023
Viewed by 1509
Abstract
We outline symmetry-based combinatorial and computational techniques to enumerate the colorings of all the hyperplanes (q = 1–8) of the 8-dimensional hypercube (8-cube) and for all 185 irreducible representations (IRs) of the 8-dimensional hyperoctahedral group, which contains 10,321,920 symmetry operations. The combinatorial techniques [...] Read more.
We outline symmetry-based combinatorial and computational techniques to enumerate the colorings of all the hyperplanes (q = 1–8) of the 8-dimensional hypercube (8-cube) and for all 185 irreducible representations (IRs) of the 8-dimensional hyperoctahedral group, which contains 10,321,920 symmetry operations. The combinatorial techniques invoke the Möbius inversion method in conjunction with the generalized character cycle indices for all 185 IRs to obtain the generating functions for the colorings of eight kinds of hyperplanes of the 8-cube, such as vertices, edges, faces, cells, tesseracts, and hepteracts. We provide the computed tables for the colorings of all the hyperplanes of the 8-cube. We also show that the developed techniques have a number of chemical, biological, chiral, and other applications that make use of such recursive symmetries. Full article
Show Figures

Figure 1

16 pages, 2144 KiB  
Article
Intermolecular Interactions in Binary and Ternary Solutions of a Zwitterionic Compound Studied by Solvatochromism
by Dana Ortansa Dorohoi, Dorina Emilia Creanga and Dan Gheorghe Dimitriu
Symmetry 2023, 15(2), 563; https://doi.org/10.3390/sym15020563 - 20 Feb 2023
Viewed by 1139
Abstract
The 1-dithiocarboxy-2-ethoxy-1-(isoquinolin-2-yl)-2-oxoethan-1-ylid (iQTCY) zwitterionic molecule has been studied by computational and spectral means in order to establish some of its structural parameters in the ground electronic state as well as the nature and the strength of its universal and specific interactions with different [...] Read more.
The 1-dithiocarboxy-2-ethoxy-1-(isoquinolin-2-yl)-2-oxoethan-1-ylid (iQTCY) zwitterionic molecule has been studied by computational and spectral means in order to establish some of its structural parameters in the ground electronic state as well as the nature and the strength of its universal and specific interactions with different solvents. The prevalence of the orientation–induction interactions in the diluted solutions of iQTCY in aprotic solvents and the additional specific interactions by hydrogen bonds (HB) in the protic solvents were demonstrated. Three theoretical models were comparatively used to estimate the composition of the first solvation shell of the iQTCY molecule in ternary solutions. The difference between the interaction energies in molecular pairs solute–solvent was computed based on the statistical cell model of ternary solutions of iQTCY in mixtures of water–ethanol and water–methanol. Using the electro-optical parameters computed by the quantum-mechanical technique and the results of the solvatochromic study, the excited state dipole moment of iQTCY was estimated within the limit of the variational method applicable to molecules that show only an absorption electronic spectrum. Full article
Show Figures

Figure 1

20 pages, 1789 KiB  
Article
Topological Indices, Graph Spectra, Entropies, Laplacians, and Matching Polynomials of n-Dimensional Hypercubes
by Krishnan Balasubramanian
Symmetry 2023, 15(2), 557; https://doi.org/10.3390/sym15020557 - 20 Feb 2023
Cited by 8 | Viewed by 4313
Abstract
We obtain a large number of degree and distance-based topological indices, graph and Laplacian spectra and the corresponding polynomials, entropies and matching polynomials of n-dimensional hypercubes through the use of Hadamard symmetry and recursive dynamic computational techniques. Moreover, computations are used to provide [...] Read more.
We obtain a large number of degree and distance-based topological indices, graph and Laplacian spectra and the corresponding polynomials, entropies and matching polynomials of n-dimensional hypercubes through the use of Hadamard symmetry and recursive dynamic computational techniques. Moreover, computations are used to provide independent numerical values for the topological indices of the 11- and 12-cubes. We invoke symmetry-based recursive Hadamard transforms to obtain the graph and Laplacian spectra of nD-hypercubes and the computed numerical results are constructed for up to 23-dimensional hypercubes. The symmetries of these hypercubes constitute the hyperoctahedral wreath product groups which also pave the way for the symmetry-based elegant computations. These results are used to independently validate the exact analytical expressions that we have obtained for the topological indices as well as graph, Laplacian spectra and their polynomials. We invoke a robust dynamic programming technique to handle the computationally intensive generation of matching polynomials of hypercubes and compute all matching polynomials up to the 6-cube. The distance degree sequence vectors have been obtained numerically for up to 108-dimensional cubes and their frequencies are found to be in binomial distributions akin to the spectra of n-cubes. Full article
Show Figures

Figure 1

8 pages, 7487 KiB  
Article
Se⋯π Chalcogen Bonding in 1,2,4-Selenodiazolium Tetraphenylborate Complexes
by Alexander A. Sapronov, Alexey S. Kubasov, Victor N. Khrustalev, Alexey A. Artemjev, Gleb M. Burkin, Evgeny A. Dukhnovsky, Alexander O. Chizhov, Andreii S. Kritchenkov, Rosa M. Gomila, Antonio Frontera and Alexander G. Tskhovrebov
Symmetry 2023, 15(1), 212; https://doi.org/10.3390/sym15010212 - 11 Jan 2023
Cited by 8 | Viewed by 1602
Abstract
The series of substituted 1,2,4-selenodiazolium tetraphenylborate complexes were synthesized via cyclization between 2-pyridylselenylchloride, followed by the anion metathesis, and fully characterized. The utilization of tetraphenylborate anion, a strong π-electron donor via its phenyl rings, promoted the formation of assemblies exhibiting selenium–π interactions. The [...] Read more.
The series of substituted 1,2,4-selenodiazolium tetraphenylborate complexes were synthesized via cyclization between 2-pyridylselenylchloride, followed by the anion metathesis, and fully characterized. The utilization of tetraphenylborate anion, a strong π-electron donor via its phenyl rings, promoted the formation of assemblies exhibiting selenium–π interactions. The chalcogen bonding (ChB) interactions involving the π-systems of the tetraphenylborate anion were studied using density functional theory (DFT) calculations, where “mutated” anions were used to estimate the strength of the Se···π chalcogen bonds. Moreover, molecular electrostatic potential (MEP) surfaces were used to investigate the electron-rich and poor regions of the ion pairs. The quantum theory of atoms-in-molecules (QTAIM) and the noncovalent interaction (NCI) plot methods based on the topology of the electron density were used and combined to characterize the ChBs. The investigation reported herein disclosed that the formation of symmetrical dimers can be broken by the introduction of a stronger π-acceptor and, consequently, forming stronger Se···π contacts with selenodiazolium cations. Full article
Show Figures

Figure 1

11 pages, 3560 KiB  
Article
Synthesis, Crystal Packing Aspects and Pseudosymmetry in Coordination Compounds with a Phosphorylamide Ligand
by Taisiya S. Sukhikh, Radmir M. Khisamov and Sergey N. Konchenko
Symmetry 2023, 15(1), 157; https://doi.org/10.3390/sym15010157 - 05 Jan 2023
Cited by 3 | Viewed by 1393
Abstract
This work reports the synthesis and crystal structure of new closely related coordination compounds, [ML2nTHF, where M is Zn or Mn; L is a phosphorylmethylamide derivative of benzothiadiazole; n = 1 (M = Zn) and 1, 2 (M = [...] Read more.
This work reports the synthesis and crystal structure of new closely related coordination compounds, [ML2nTHF, where M is Zn or Mn; L is a phosphorylmethylamide derivative of benzothiadiazole; n = 1 (M = Zn) and 1, 2 (M = Mn); and THF is tetrahydrofuran. The zinc compound, 1·THF, crystallizes in a high-symmetry space group, I41/a, that is relatively rare for compounds with organic ligands. The corresponding manganese congener, 2·THF, with a similar crystal packing, features a pseudosymmetrical structure P21/c of the doubled volume of the unit cell as compared to 1·THF. The main difference between the structures lies in a different arrangement of solvate THF molecules, which likely modulates the crystal packing of the complexes. Another manganese solvatomorph, 2·2THF, reveals a fundamentally different crystal packing while exhibiting a similar geometry of the complex. We consider the problem of localization of solvate THF molecules and the types of their disorder by the example of compounds 12. Full article
Show Figures

Figure 1

2022

Jump to: 2024, 2023, 2021, 2020

14 pages, 11463 KiB  
Review
New Modification of Polar Nonlinear Optical Iodate Fluoride PbF(IO3), the Family MX(IO3), M = Bi, Ba, Pb, X = O, F, (OH) Related to Aurivillius Phases and Similar Iodates
by Elena Belokoneva, Olga Reutova, Anatoly Volkov, Olga Dimitrova and Sergey Stefanovich
Symmetry 2023, 15(1), 100; https://doi.org/10.3390/sym15010100 - 30 Dec 2022
Cited by 2 | Viewed by 1389
Abstract
A new modification of PbF(IO3) has been obtained as single crystals from hydrothermal synthesis, alongside the known centrosymmetric, Pb(IO3)2, as a second phase. Measured with the Kurtz-Perry SHG method, the new crystals are phase-matchable for YAG:Nd laser [...] Read more.
A new modification of PbF(IO3) has been obtained as single crystals from hydrothermal synthesis, alongside the known centrosymmetric, Pb(IO3)2, as a second phase. Measured with the Kurtz-Perry SHG method, the new crystals are phase-matchable for YAG:Nd laser radiation and demonstrate strong SHG output. According to an X-ray diffraction analysis conducted on a single crystal at low temperature, the new crystals appear monoclinic, of space group Pn, as opposed to the known orthorhombic modification of the PbF(IO3), of space group Iba2. The new crystals were also measured at room temperature, showing an orthorhombic disordered variant of the new phase (space group C2ma, standard Abm2). This variant presents an “average structure” with the mirror plane in the group. The low-temperature X-ray single-crystal experiment allowed us to find the correct structural model, where the mirror plane was found as a twin element in the real monoclinic Pn structure. A careful crystal chemical analysis led to a whole family of nonlinear optical crystals with a common formula, AX(IO3), A = Bi, Ba, Pb, X = O, F, (OH), currently counting six representatives, including the well-known BiO(IO3). All of them possess common central cationic layers similar to those known in Aurivillius-type phases, with anionic iodate layers attached above and below these layers instead of the perovskite-like, or halogens. The structure–property relationships are discussed with respect to the important role of the large cations: Pb2+, Bi3+ or Ba2+. A number of iodates with similar structures are also analyzed. Full article
Show Figures

Figure 1

13 pages, 3622 KiB  
Article
Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion
by Timofey Savchuk, Ilya Gavrilin, Andrey Savitskiy, Alexey Dronov, Daria Dronova, Svetlana Pereverzeva, Andrey Tarhanov, Tomasz Maniecki, Sergey Gavrilov and Elizaveta Konstantinova
Symmetry 2022, 14(12), 2678; https://doi.org/10.3390/sym14122678 - 18 Dec 2022
Cited by 2 | Viewed by 1798
Abstract
Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of [...] Read more.
Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2. Full article
Show Figures

Figure 1

10 pages, 1751 KiB  
Article
Chemical Models for Understanding the Emergence of Homo-Chirality of Phospholipids for Origin of Life Studies
by Fryni Skorda, Carolina Chieffo and Michele Fiore
Symmetry 2022, 14(10), 2109; https://doi.org/10.3390/sym14102109 - 11 Oct 2022
Cited by 1 | Viewed by 1635
Abstract
In the prebiotic world, the chemical assembly of biotic building blocks led to racemic mixtures; however, homo-chirality emerged in the racemic prebiotic soup. Polymers and other molecules assembled from mixtures of enantiomers rather than racemic ones. Understanding how symmetry breaking happens is one [...] Read more.
In the prebiotic world, the chemical assembly of biotic building blocks led to racemic mixtures; however, homo-chirality emerged in the racemic prebiotic soup. Polymers and other molecules assembled from mixtures of enantiomers rather than racemic ones. Understanding how symmetry breaking happens is one of the most challenging fields of research in origin of life studies. With this article, we aim to shed light on one of the problems: in the absence of physical examples for use in a laboratory scale, what are the best models to use to simulate the conditions and lead to homo-chiral symmetry breaking? In this perspective, we suggest looking to chemical models that can represent a poorly studied class of prebiotic compounds in the context of symmetry breaking: the phospholipids. Full article
Show Figures

Figure 1

26 pages, 18774 KiB  
Review
Lamellar Tetragonal Symmetry of Amphiphilic Thermotropic Ionic Liquid Crystals in the Framework of Other Closely Related Highly Ordered Structures
by Michael Arkas, Marilina Douloudi, Michail Vardavoulias and Theodora Katsika
Symmetry 2022, 14(2), 394; https://doi.org/10.3390/sym14020394 - 16 Feb 2022
Cited by 4 | Viewed by 2866
Abstract
An overview of the chemical compounds forming the rare smectic T phases is presented with references to the historical context. Thermodynamics (transition temperatures, enthalpies) along with the factors (stereochemical constraints, electrostatic interactions, aliphatic chain stacking, intermolecular forces) contributing to the adoption of tetragonal [...] Read more.
An overview of the chemical compounds forming the rare smectic T phases is presented with references to the historical context. Thermodynamics (transition temperatures, enthalpies) along with the factors (stereochemical constraints, electrostatic interactions, aliphatic chain stacking, intermolecular forces) contributing to the adoption of tetragonal scaffolds are also discussed. Characteristic optical microscopy textures and X-ray diffraction patterns are presented. In parallel, a comparison of the geometrical parameters such as distances between atoms, molecular areas, volumes, and lattice parameters with the closest two-dimensional and three-dimensional organizations, is performed. Full article
Show Figures

Figure 1

23 pages, 5621 KiB  
Review
Dancing with Azulene
by Alexandru C. Razus
Symmetry 2022, 14(2), 297; https://doi.org/10.3390/sym14020297 - 01 Feb 2022
Cited by 4 | Viewed by 2556
Abstract
It seems interesting to adopt the idea of dance in the context of the arrangement of molecular blocks in the building of molecular systems. Just as various dances can create various feelings, the nature and arrangement of molecular blocks in the generated molecular [...] Read more.
It seems interesting to adopt the idea of dance in the context of the arrangement of molecular blocks in the building of molecular systems. Just as various dances can create various feelings, the nature and arrangement of molecular blocks in the generated molecular system can induce different properties. We consider obtaining such “dancing” systems in which the still little-known azulene moieties are involved. The dark blue nonbenzenoid aromatic azulene has one less axis of symmetry relative to the two axes of its isomer, i.e., the fully benzenoid naphthalene, acquiring valuable properties as a result that can be used successfully in technical applications. In a dancing system, the azulene moieties can be connected directly, or a more or less complex spacer can be inserted between them. Several azulene moieties can form a linear oligomer or a polymer and the involvement of azulene moieties in nonlinear molecules, such as crown ethers, calixarenes, azuliporphyrins, or azulenophane, is a relatively new and intensely studied topic. Some aspects are covered in this review, which are mainly related to obtaining the mentioned azulene compounds and less to their characterization or physico-chemical properties. Full article
Show Figures

Scheme 1

18 pages, 4783 KiB  
Review
Sweet Boron: Boron-Containing Sugar Derivatives as Potential Agents for Boron Neutron Capture Therapy
by Daniela Imperio and Luigi Panza
Symmetry 2022, 14(2), 182; https://doi.org/10.3390/sym14020182 - 18 Jan 2022
Cited by 20 | Viewed by 3420
Abstract
Boron neutron capture therapy (BNCT) is a binary type of radiotherapy for the treatment of cancer. Due to recent developments of neutron accelerators and their installation in some hospitals, BNCT is on the rise worldwide and is expected to have a significant impact [...] Read more.
Boron neutron capture therapy (BNCT) is a binary type of radiotherapy for the treatment of cancer. Due to recent developments of neutron accelerators and their installation in some hospitals, BNCT is on the rise worldwide and is expected to have a significant impact on patient treatments. Therefore, there is an increasing need for improved boron delivery agents. Among the many small molecules and delivery systems developed, a significant amount of recent research focused on the synthesis of boron-containing sugar and amino acid derivatives to exploit specific transport proteins, as d-glucose transporter 1 (GLUT1) and large neutral amino acid transporter (LAT1), overexpressed by tumor cells. This review will discuss the last year’s achievements in the synthesis and some biological evaluation of boronated sugars derivatives. The compounds described in this review are intrinsically asymmetric due to the presence of chiral sugar moieties, often joined to boron clusters, which are structural elements with high symmetry. Full article
Show Figures

Figure 1

2021

Jump to: 2024, 2023, 2022, 2020

46 pages, 20885 KiB  
Review
Advances in the Development of Trifluoromethoxylation Reagents
by Qian Wang, Xin Zhang, Alexander E. Sorochinsky, Greg Butler, Jianlin Han and Vadim A. Soloshonok
Symmetry 2021, 13(12), 2380; https://doi.org/10.3390/sym13122380 - 10 Dec 2021
Cited by 15 | Viewed by 6203
Abstract
This review provides a short summary of the traditional methods for synthesis of CF3-O-containing compounds, followed by a critical overview of known trifluoromethoxylating reagents, focusing on their preparation, synthetic generality and limitations. Full article
Show Figures

Figure 1

13 pages, 3463 KiB  
Article
Unsymmetrical Hexafluorocyclopentene-Linked Twisted π-Conjugated Molecules as Dual-State Emissive Luminophores
by Shigeyuki Yamada, Akito Nishizawa, Kazuki Kobayashi, Keigo Yoshida, Masato Morita, Tomohiro Agou, Takaaki Hosoya, Hiroki Fukumoto and Tsutomu Konno
Symmetry 2021, 13(10), 1885; https://doi.org/10.3390/sym13101885 - 06 Oct 2021
Cited by 3 | Viewed by 1905
Abstract
Dual-state emissive (DSE) luminophores, which can luminesce both in solution and in solid states, have recently attracted significant attention because of their broad applications. However, their development is difficult due to the difference in molecular design between solution- and solid-state luminophores. In this [...] Read more.
Dual-state emissive (DSE) luminophores, which can luminesce both in solution and in solid states, have recently attracted significant attention because of their broad applications. However, their development is difficult due to the difference in molecular design between solution- and solid-state luminophores. In this study, DSE luminophores based on unsymmetrical hexafluorocyclopentene-linked twisted π-conjugated structures carrying various substituents to tune the electron-density were designed and synthesized in a single-step reaction from heptafluorocyclopentene or perfluoro-1,2-diphenylcyclopentene derivatives. The twisted π-conjugated luminophores exhibited absorption in the UV region at approximately 330 nm, along with several signals in the high-energy region. Upon irradiating the luminophore solution (wavelength 330 nm), light-green to yellow photoluminescence (PL) was observed in the range of 422–471 nm with high PL efficiency. Theoretical calculations revealed that excitation from ground to excited states altered the structural shape of the luminophores from twisted to planar, leading to red-shifted PL and high PL efficiency (ΦPL). The intense blue PL exhibited by the luminophores in the crystalline state was attributed to their twisted molecular structures that suppressed non-radiative deactivation via the effective blocking of π/π stacking interactions. Full article
Show Figures

Figure 1

29 pages, 28569 KiB  
Article
An Application of the Eigenproblem for Biochemical Similarity
by Dan-Marian Joiţa, Mihaela Aurelia Tomescu, Donatella Bàlint and Lorentz Jäntschi
Symmetry 2021, 13(10), 1849; https://doi.org/10.3390/sym13101849 - 02 Oct 2021
Cited by 9 | Viewed by 1782
Abstract
Protein alignment finds its application in refining results of sequence alignment and understanding protein function. A previous study aligned single molecules, making use of the minimization of sums of the squares of eigenvalues, obtained for the antisymmetric Cartesian coordinate distance matrices Dx [...] Read more.
Protein alignment finds its application in refining results of sequence alignment and understanding protein function. A previous study aligned single molecules, making use of the minimization of sums of the squares of eigenvalues, obtained for the antisymmetric Cartesian coordinate distance matrices Dx and Dy. This is used in our program to search for similarities between amino acids by comparing the sums of the squares of eigenvalues associated with the Dx, Dy, and Dz distance matrices. These matrices are obtained by removing atoms that could lead to low similarity. Candidates are aligned, and trilateration is used to attach all previously striped atoms. A TM-score is the scoring function that chooses the best alignment from supplied candidates. Twenty essential amino acids that take many forms in nature are selected for comparison. The correct alignment is taken into account most of the time by the alignment algorithm. It was numerically detected by the TM-score 70% of the time, on average, and 15% more cases with close scores can be easily distinguished by human observation. Full article
Show Figures

Figure 1

24 pages, 26290 KiB  
Review
Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update
by Michał Rachwalski, Aleksandra Buchcic-Szychowska and Stanisław Leśniak
Symmetry 2021, 13(10), 1762; https://doi.org/10.3390/sym13101762 - 22 Sep 2021
Cited by 2 | Viewed by 2867
Abstract
The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications [...] Read more.
The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications in various fields. Among an extremely wide variety of asymmetric reactions catalyzed by chiral systems, we are interested in: asymmetric cyclopropanation, Friedel–Crafts reaction, Mannich and Michael reaction, and other stereoselective processes conducted in the presence of zinc ions. This paper describes the achievements of the above-mentioned asymmetric transformations in the last three years. The choice of reactions is related to the research that has been carried out in our laboratory for many years. Full article
Show Figures

Figure 1

14 pages, 2147 KiB  
Article
The Kinetic Model of Diffusion and Reactions in Powder Catalysts during Temperature Programmed Oxygen Isotopic Exchange Process
by Arvaidas Galdikas, Muhammad Usman and Matas Galdikas
Symmetry 2021, 13(8), 1526; https://doi.org/10.3390/sym13081526 - 19 Aug 2021
Viewed by 2129
Abstract
The mathematical model of diffusion in powder oxide catalysts during the process of temperature programmed oxygen isotopic exchange is proposed. The diffusion is considered together with the homogeneous and heterogeneous oxygen isotopic exchange processes. The matrix forms of exchange rate equations of simple [...] Read more.
The mathematical model of diffusion in powder oxide catalysts during the process of temperature programmed oxygen isotopic exchange is proposed. The diffusion is considered together with the homogeneous and heterogeneous oxygen isotopic exchange processes. The matrix forms of exchange rate equations of simple and complex heteroexchange, and homoexchange reactions which obtain symmetrical forms are analyzed. The quantitative values of model parameters are found from the fitting of experimental data taken from literature of temperature programmed oxygen isotopic exchange process in catalysts ZrO2 and CeO2. The fittings show a good matching of model results with experimental data. The shapes of kinetic curves registered during temperature programmed oxygen isotopic exchange process are analyzed and the influence of various process parameters such as activation energies of simple and complex heteroexchange, oxygen surface concentration of catalyst, ratio of catalysts surface and volume of reactor, diffusion activation energy is considered. The depth profiles of diffusing oxygen species in oxide catalysts powder are calculated. Full article
Show Figures

Figure 1

9 pages, 1474 KiB  
Article
Possibilities of Exploiting Kinetic Control in the Continuous Fractional Crystallization of Diastereomeric Mixtures
by Dorottya Fruzsina Bánhegyi, Elemér Fogassy and Emese Pálovics
Symmetry 2021, 13(8), 1516; https://doi.org/10.3390/sym13081516 - 18 Aug 2021
Cited by 2 | Viewed by 1991
Abstract
For rapid and kinetic control-influenced resolutions, it is advisable to choose a resolving agent with the highest possible eutectic composition (eeEuResAg). It may also be advantageous to add the crystalline resolving agent directly to the solution of the racemic compound. In [...] Read more.
For rapid and kinetic control-influenced resolutions, it is advisable to choose a resolving agent with the highest possible eutectic composition (eeEuResAg). It may also be advantageous to add the crystalline resolving agent directly to the solution of the racemic compound. In addition, the use of a quasi-racemic resolving agent or amphoteric resolving agent can provide kinetic resolution. In some cases, the continuous fractional crystallization of diastereomeric salts requires the salt of the resolving agent (Ca2+, Na+, etc.) or other achiral additives (thiourea) that cause rapid crystallization and provide high diastereomeric purity. A further advantage may be the sequential use of the same resolving agent that is capable of forming crystalline diastereomers with both enantiomers when using kinetic control (tandem resolution). Full article
Show Figures

Figure 1

13 pages, 2652 KiB  
Review
Towards New Chiroptical Transitions Based on Thought Experiments and Hypothesis
by Takashiro Akitsu, Sanyobi Kim and Daisuke Nakane
Symmetry 2021, 13(6), 1103; https://doi.org/10.3390/sym13061103 - 21 Jun 2021
Cited by 1 | Viewed by 2278
Abstract
We studied supramolecular chirality induced by circularly polarized light. Photoresponsive azopolymers form a helical intermolecular network. Furthermore, studies on photochemical materials using optical vortex light will also attract attention in the future. In contrast to circularly polarized light carrying spin angular momentum, an [...] Read more.
We studied supramolecular chirality induced by circularly polarized light. Photoresponsive azopolymers form a helical intermolecular network. Furthermore, studies on photochemical materials using optical vortex light will also attract attention in the future. In contrast to circularly polarized light carrying spin angular momentum, an optical vortex with a spiral wave front and carrying orbital angular momentum may impart torque upon irradiated materials. In this review, we summarize a few examples, and then theoretically and computationally deduce the differences in spin angular momentum and orbital angular momentum depending on molecular orientation not on, but in, polymer films. UV-vis absorption and circular dichroism (CD) spectra are consequences of electric dipole transition and magnetic dipole transition, respectively. However, the basic effect of vortex light is postulated to originate from quadrupole transition. Therefore, we explored the simulated CD spectra of azo dyes with the aid of conventional density functional theory (DFT) calculations and preliminary theoretical discussions of the transition of CD. Either linearly or circularly polarized UV light causes the trans–cis photoisomerization of azo dyes, leading to anisotropic and/or helically organized methyl orange, respectively, which may be detectable by CD spectroscopy after some technical treatments. Our preliminary theoretical results may be useful for future experiments on the irradiation of UV light under vortex. Full article
Show Figures

Figure 1

52 pages, 4723 KiB  
Review
Phosphorus Compounds of Natural Origin: Prebiotic, Stereochemistry, Application
by Oleg I. Kolodiazhnyi
Symmetry 2021, 13(5), 889; https://doi.org/10.3390/sym13050889 - 17 May 2021
Cited by 23 | Viewed by 9833
Abstract
Organophosphorus compounds play a vital role as nucleic acids, nucleotide coenzymes, metabolic intermediates and are involved in many biochemical processes. They are part of DNA, RNA, ATP and a number of important biological elements of living organisms. Synthetic compounds of this class have [...] Read more.
Organophosphorus compounds play a vital role as nucleic acids, nucleotide coenzymes, metabolic intermediates and are involved in many biochemical processes. They are part of DNA, RNA, ATP and a number of important biological elements of living organisms. Synthetic compounds of this class have found practical application as agrochemicals, pharmaceuticals, bioregulators, and othrs. In recent years, a large number of phosphorus compounds containing P-O, P-N, P-C bonds have been isolated from natural sources. Many of them have shown interesting biological properties and have become the objects of intensive scientific research. Most of these compounds contain asymmetric centers, the absolute configurations of which have a significant effect on the biological properties of the products of their transformations. This area of research on natural phosphorus compounds is still little-studied, that prompted us to analyze and discuss it in our review. Moreover natural organophosphorus compounds represent interesting models for the development of new biologically active compounds, and a number of promising drugs and agrochemicals have already been obtained on their basis. The review also discusses the history of the development of ideas about the role of organophosphorus compounds and stereochemistry in the origin of life on Earth, starting from the prebiotic period, that allows us in a new way to consider this most important problem of fundamental science. Full article
Show Figures

Graphical abstract

12 pages, 9350 KiB  
Article
The Stoichiometry, Structure and Possible Formation of Crystalline Diastereomeric Salts
by Dorottya Fruzsina Bánhegyi and Emese Pálovics
Symmetry 2021, 13(4), 667; https://doi.org/10.3390/sym13040667 - 13 Apr 2021
Cited by 5 | Viewed by 2759
Abstract
Knowing the eutectic composition of the binary melting point phase diagrams of the diastereomeric salts formed during the given resolution, the achievable F (F = eeDia*Y) value can be calculated. The same value can also be calculated and predicted by knowing [...] Read more.
Knowing the eutectic composition of the binary melting point phase diagrams of the diastereomeric salts formed during the given resolution, the achievable F (F = eeDia*Y) value can be calculated. The same value can also be calculated and predicted by knowing the eutectic compositions of the binary melting point phase diagrams of enantiomeric mixtures of the racemic compound or the resolving agent. An explanation was sought as to why and how the crystalline precipitated diastereomeric salt—formed in the solution between a racemic compound and the corresponding resolving agent—may be formed. According to our idea, the self-disproportionation of enantiomers (SDE) has a decisive role when the enantiomers form two nonequal ratios of conformers in solution. The self-organized enantiomers form supramolecular associations having M and P helicity, and double helices are formed. Between these double spirals, with the formation of new double spirals, a dynamic equilibrium is achieved and the salt crystallizes. During this process between acids and bases, chelate structures may also be formed. Acids appear to have a crucial impact on these structures. It is assumed that the behavior of each chiral molecule is determined by its own code. This code validates the combined effect of constituent atoms, bonds, spatial structure, charge distribution, flexibility and complementarity. Full article
Show Figures

Figure 1

20 pages, 6853 KiB  
Article
Partitioning Pattern of Natural Products Based on Molecular Properties Descriptors Representing Drug-Likeness
by Miroslava Nedyalkova and Vasil Simeonov
Symmetry 2021, 13(4), 546; https://doi.org/10.3390/sym13040546 - 26 Mar 2021
Cited by 6 | Viewed by 3468
Abstract
A cheminformatics procedure for a partitioning model based on 135 natural compounds including Flavonoids, Saponins, Alkaloids, Terpenes and Triterpenes with drug-like features based on a descriptors pool was developed. The knowledge about the applicability of natural products as a unique source for the [...] Read more.
A cheminformatics procedure for a partitioning model based on 135 natural compounds including Flavonoids, Saponins, Alkaloids, Terpenes and Triterpenes with drug-like features based on a descriptors pool was developed. The knowledge about the applicability of natural products as a unique source for the development of new candidates towards deadly infectious disease is a contemporary challenge for drug discovery. We propose a partitioning scheme for unveiling drug-likeness candidates with properties that are important for a prompt and efficient drug discovery process. In the present study, the vantage point is about the matching of descriptors to build the partitioning model applied to natural compounds with diversity in structures and complexity of action towards the severe diseases, as the actual SARS-CoV-2 virus. In the times of the de novo design techniques, such tools based on a chemometric and symmetrical effect by the implied descriptors represent another noticeable sign for the power and level of the descriptors applicability in drug discovery in establishing activity and target prediction pipeline for unknown drugs properties. Full article
Show Figures

Figure 1

16 pages, 2146 KiB  
Article
Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions
by Péter Kisszékelyi, Zsuzsanna Fehér, Sándor Nagy, Péter Bagi, Petra Kozma, Zsófia Garádi, Miklós Dékány, Péter Huszthy, Béla Mátravölgyi and József Kupai
Symmetry 2021, 13(3), 521; https://doi.org/10.3390/sym13030521 - 23 Mar 2021
Cited by 4 | Viewed by 3286
Abstract
In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonstrated to obtain size-enlarged organocatalysts. By modifying the cinchona skeleton in different positions, we prepared four C3-symmetric size-enlarged cinchona derivatives (hub-cinchonas), which were tested as organocatalysts and their [...] Read more.
In this work, anchoring of cinchona derivatives to trifunctional cores (hub approach) was demonstrated to obtain size-enlarged organocatalysts. By modifying the cinchona skeleton in different positions, we prepared four C3-symmetric size-enlarged cinchona derivatives (hub-cinchonas), which were tested as organocatalysts and their catalytic activities were compared with the parent cinchona (hydroquinine) catalyst. We showed that in the hydroxyalkylation reaction of indole, hydroquinine provides good enantioselectivities (up to 73% ee), while the four new size-enlarged derivatives resulted in significantly lower values (up to 29% ee) in this reaction. Anchoring cinchonas to trifunctional cores was found to facilitate nanofiltration-supported catalyst recovery using the PolarClean alternative solvent. The C3-symmetric size-enlarged organocatalysts were completely rejected by all the applied membranes, whereas the separation of hydroquinine was found to be insufficient when using organic solvent nanofiltration. Furthermore, the asymmetric catalysis was successfully demonstrated in the case of the Michael reaction of 1,3-diketones and trans-β-nitrostyrene using Hub3-cinchona (up to 96% ee) as a result of the positive effect of the C3-symmetric structure using a bulkier substrate. This equates to an increased selectivity of the catalyst in comparison to hydroquinine in the latter Michael reaction. Full article
Show Figures

Graphical abstract

2020

Jump to: 2024, 2023, 2022, 2021

12 pages, 1505 KiB  
Article
Push or Pull for a Better Selectivity? A Study on the Electronic Effects of Substituents of the Pyridine Ring on the Enantiomeric Recognition of Chiral Pyridino-18-Crown-6 Ethers
by Balázs Szemenyei, Balázs Novotny, Sarolta Zsolnai, Zsombor Miskolczy, László Biczók, Attila Takács, László Kollár, László Drahos, Ildikó Móczár and Péter Huszthy
Symmetry 2020, 12(11), 1795; https://doi.org/10.3390/sym12111795 - 30 Oct 2020
Cited by 2 | Viewed by 2389
Abstract
Seven dimethyl-substituted optically active pyridino-18-crown-6 ethers containing various substituents at position 4 of the pyridine ring were studied with regards to the electron-donating and -withdrawing effects of substituents on enantiomeric recognition. In order to compile this set of compounds, we prepared four novel [...] Read more.
Seven dimethyl-substituted optically active pyridino-18-crown-6 ethers containing various substituents at position 4 of the pyridine ring were studied with regards to the electron-donating and -withdrawing effects of substituents on enantiomeric recognition. In order to compile this set of compounds, we prepared four novel pyridino-18-crown-6 ethers, including an intermediate of a new synthetic route for a formerly reported crown ether. The discriminating ability of these pyridino-crown ethers with C2-symmetry toward the enantiomers of protonated primary amines was examined by isothermal titration calorimetry. Full article
Show Figures

Graphical abstract

23 pages, 6444 KiB  
Article
Supramolecular Diversity of Oxabicyclo[2.2.2]octenes Formed between Substituted 2H-Pyran-2-ones and Vinyl-Moiety-Containing Dienophiles
by Krištof Kranjc, Amadej Juranovič, Marijan Kočevar and Franc Perdih
Symmetry 2020, 12(10), 1714; https://doi.org/10.3390/sym12101714 - 17 Oct 2020
Cited by 2 | Viewed by 2928
Abstract
In Diels–Alder reactions, 2H-pyran-2-ones as dienes can yield a large variety of cycloadducts with up to four contiguous carbon stereogenic centers. Some of the potentially most useful, however difficult to prepare due to their low thermal stability, are the primary CO [...] Read more.
In Diels–Alder reactions, 2H-pyran-2-ones as dienes can yield a large variety of cycloadducts with up to four contiguous carbon stereogenic centers. Some of the potentially most useful, however difficult to prepare due to their low thermal stability, are the primary CO2-containing oxabicyclo[2.2.2]octenes, which could be formed as eight distinctive isomers (two sets of regioisomers, each of these composed of four different stereoisomers). A high-pressure synthesis of such products was recently described in a few cases where vinyl-moiety-containing dienophiles were used as synthetic equivalents of acetylene. However, structures of the primary products have been so far only rarely investigated in detail. Herein, we present seven novel single-crystal X-ray diffraction structures of such cycloadducts of both stereoisomeric forms, i.e., endo and exo. Additionally, we present a single-crystal structure of a rare case of a cyclohexadiene system stable at room temperature, obtained as a secondary product upon the retro-hetero-Diels–Alder elimination of CO2 under thermal conditions (microwave irradiation), during this elimination the symmetry is increased and out of eight initially possible isomers of the reactant, this number in the product is decreased to four. In oxabicyclo[2.2.2]octene compounds, centrosymmetric hydrogen bonding was found to be the predominant motif and diverse supramolecular patterns were observed due to rich variety of C–H⋯O and C–H⋯π interactions. Full article
Show Figures

Figure 1

Back to TopTop