Topical Collection "Feature Papers in Chemistry"
Share This Topical Collection
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 2000 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 (24 papers)
Open AccessArticle
Recursive Symmetries: Chemically Induced Combinatorics of Colorings of Hyperplanes of an 8-Cube for All Irreducible Representations
Viewed by 589
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
Open AccessArticle
Intermolecular Interactions in Binary and Ternary Solutions of a Zwitterionic Compound Studied by Solvatochromism
Viewed by 557
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
Open AccessArticle
Topological Indices, Graph Spectra, Entropies, Laplacians, and Matching Polynomials of n-Dimensional Hypercubes
Cited by 3 | Viewed by 1449
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
Open AccessArticle
Se⋯π Chalcogen Bonding in 1,2,4-Selenodiazolium Tetraphenylborate Complexes
Cited by 2 | Viewed by 822
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
Open AccessArticle
Synthesis, Crystal Packing Aspects and Pseudosymmetry in Coordination Compounds with a Phosphorylamide Ligand
Viewed by 670
Abstract
This work reports the synthesis and crystal structure of new closely related coordination compounds, [ML
2]·
nTHF, 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, [ML
2]·
nTHF, 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,
I4
1/
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
P2
1/
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
1–
2.
Full article
►▼
Show Figures
Open AccessReview
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
Viewed by 653
Abstract
A new modification of PbF(IO
3) has been obtained as single crystals from hydrothermal synthesis, alongside the known centrosymmetric, Pb(IO
3)
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(IO
3) has been obtained as single crystals from hydrothermal synthesis, alongside the known centrosymmetric, Pb(IO
3)
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(IO
3), of space group
Iba2. The new crystals were also measured at room temperature, showing an orthorhombic disordered variant of the new phase (space group
C2
ma, 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(IO
3), A = Bi, Ba, Pb, X = O, F, (OH), currently counting six representatives, including the well-known BiO(IO
3). 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: Pb
2+, Bi
3+ or Ba
2+. A number of iodates with similar structures are also analyzed.
Full article
►▼
Show Figures
Open AccessArticle
Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion
Viewed by 1002
Abstract
Symmetric titania nanotube arrays (TiO
2 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 TiO
2 nanotubes in argon was used to change the carbon content of
[...] Read more.
Symmetric titania nanotube arrays (TiO
2 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 TiO
2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO
2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO
2 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 CO
2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO
2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO
2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO
2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO
2 NTs arrays for the photocatalytic conversion of CO
2.
Full article
►▼
Show Figures
Open AccessArticle
Chemical Models for Understanding the Emergence of Homo-Chirality of Phospholipids for Origin of Life Studies
Viewed by 973
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
Open AccessEditor’s ChoiceReview
Lamellar Tetragonal Symmetry of Amphiphilic Thermotropic Ionic Liquid Crystals in the Framework of Other Closely Related Highly Ordered Structures
Cited by 1 | Viewed by 1806
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
Open AccessReview
Dancing with Azulene
Cited by 2 | Viewed by 1739
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
Open AccessReview
Sweet Boron: Boron-Containing Sugar Derivatives as Potential Agents for Boron Neutron Capture Therapy
Cited by 12 | Viewed by 2132
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
Open AccessReview
Advances in the Development of Trifluoromethoxylation Reagents
Cited by 9 | Viewed by 4230
Abstract
This review provides a short summary of the traditional methods for synthesis of CF
3-O-containing compounds, followed by a critical overview of known trifluoromethoxylating reagents, focusing on their preparation, synthetic generality and limitations.
Full article
►▼
Show Figures
Open AccessArticle
Unsymmetrical Hexafluorocyclopentene-Linked Twisted π-Conjugated Molecules as Dual-State Emissive Luminophores
Cited by 3 | Viewed by 1396
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
Open AccessArticle
An Application of the Eigenproblem for Biochemical Similarity
Cited by 7 | Viewed by 1175
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 D
x
[...] 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 D
x and D
y. 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 D
x, D
y, and D
z 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
Open AccessReview
Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update
Cited by 1 | Viewed by 1994
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
Open AccessArticle
The Kinetic Model of Diffusion and Reactions in Powder Catalysts during Temperature Programmed Oxygen Isotopic Exchange Process
Viewed by 1506
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 ZrO
2 and CeO
2. 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
Open AccessArticle
Possibilities of Exploiting Kinetic Control in the Continuous Fractional Crystallization of Diastereomeric Mixtures
Cited by 1 | Viewed by 1318
Abstract
For rapid and kinetic control-influenced resolutions, it is advisable to choose a resolving agent with the highest possible eutectic composition (ee
EuResAg). 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 (ee
EuResAg). 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 (Ca
2+, 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
Open AccessReview
Towards New Chiroptical Transitions Based on Thought Experiments and Hypothesis
Cited by 1 | Viewed by 1637
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
Open AccessEditor’s ChoiceReview
Phosphorus Compounds of Natural Origin: Prebiotic, Stereochemistry, Application
Cited by 14 | Viewed by 5816
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
Open AccessArticle
The Stoichiometry, Structure and Possible Formation of Crystalline Diastereomeric Salts
Cited by 5 | Viewed by 1926
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 = ee
Dia*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 = ee
Dia*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
Open AccessArticle
Partitioning Pattern of Natural Products Based on Molecular Properties Descriptors Representing Drug-Likeness
Cited by 5 | Viewed by 2843
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
Open AccessArticle
Synthesis of C3-Symmetric Cinchona-Based Organocatalysts and Their Applications in Asymmetric Michael and Friedel–Crafts Reactions
Cited by 1 | Viewed by 2367
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 C
3-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 C
3-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 C
3-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 C
3-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
Open AccessArticle
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
Cited by 2 | Viewed by 1826
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
Open AccessFeature PaperArticle
Supramolecular Diversity of Oxabicyclo[2.2.2]octenes Formed between Substituted 2H-Pyran-2-ones and Vinyl-Moiety-Containing Dienophiles
Cited by 1 | Viewed by 2154
Abstract
In Diels–Alder reactions, 2
H-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, 2
H-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
2-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 CO
2 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
Planned Papers
The below list represents only planned manuscripts. Some of these
manuscripts have not been received by the Editorial Office yet. Papers
submitted to MDPI journals are subject to peer-review.
Title: Chemoselectivity in butadiene polymerization promoted by Zieger-Natta catalysts based on (Anilidomethyl)pyridine group (IV) complexes
Authors: Stefano Milione and Stefania Pragliola
Affiliation: Department of Chemistry and Biology, University of Salerno, via Giovanni Paolo II, 132 Fisciano I-84084, Salerno, Italy
Abstract: The stereoselective polymerization of conjugated dienes promoted by 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 mechanism. 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 the 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 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 h2 or 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 effect 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 chemioselectivity of the reaction.
Title: Organocatalytic Conjugate Hydroazidation and Hydrocyanation: A Metal-free Approach to Synthetically Versatile Chiral Building Blocks
Authors: Rosaria Schettini, and Giorgio Della Sala
Affiliation: Department of Chemistry and Biology “A. Zambelli”, University of Salerno, Fisciano, SA 84084, Italy
Abstract: Chiral β-azido- and β-cianocarbonyl 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 XXI century, have been mostly achieved by 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.
.jpg)
