Chemistry: Symmetry/Asymmetry—Feature Papers and Reviews

Symmetry and asymmetry are fascinating topics in chemistry. “Chemistry: Symmetry/Asymmetry. Feature Papers and Reviews” is a Special Issue that covers a wide range of topics related to symmetry or asymmetry in chemistry. Papers submitted to Symmetry may include all types of symmetry-related problems in chemistry. All organic chemists, theoretical chemists, and crystal chemists are invited to submit papers focusing on, but not limited to, the following emerging research topics in related areas: molecular symmetry, asymmetric carbon, stereocenter, chirality, racemates, optical resolution, enantiomers, optically active compounds, asymmetric synthesis, stereoselective synthesis, chiral ligands diastereomers, homochirality in chemistry and biochemistry, homochirality in the origin of life, symmetry elements, mirror plane, X-ray crystallography, X-ray structures, crystal structures, symmetry and spectroscopy, symmetry and isomerism, and chirogenesis.

M. Fiore, in his review “Homochirality Emergence: A Scientific Enigma with Profound Implications in Origins of Life Studies”, discusses homochirality—the ubiquitous preference of larger biological molecules, such as proteins and carbohydrates/nucleic acids comprising L-amino acid and D-sugars, respectively—and phospholipids, which are fundamental characteristics of life. This consistent bias across the biosphere is not merely a biochemical peculiarity, but a crucial aspect of life’s molecular architecture. However, the origin of this homochirality remains one of the most compelling and unresolved mysteries. In this study this question is considered [1].

G. Hancu et al. wrote a review titled “Analyzing the Chiral Purity of Pharmaceuticals: The Application of Cyclodextrin-Based Chiral Selectors in Capillary Electrophoresis”. The article provides a focused analysis of the application of capillary electrophoresis (CE) techniques to determine the chiral purity of pharmaceuticals, with a specific emphasis on cyclodextrin-based chiral selectors highlighting advancements, methodologies, and trends in this area, as reported in studies published from 2010 to 2024. This review paper outlines future research and developments, underlining the importance of the optimization of CE methodologies for pharmaceutical applications [2].

The review titled “Medicinally Significant Enantiopure Compounds from Garcinia Acid Isolated from Garcinia gummi-gutta”, written by S. Haleema and P. L. Polavarapu et al., highlights the major bioactive compounds present in the tree Garcinia gummi-gutta, with particular emphasis on (2S, 3S)-tetrahydro-3-hydroxy-5-oxo-2,3-furan dicarboxylic acid, commonly referred to as garcinia acid, which is used in the treatment of obesity. The synthetic transformations of garcinia acid into biologically potent and functionally useful enantiopure compounds are also explored. The syntheses of chiral 3-substituted and 3,4-disubstituted pyrrolidine-2,5-diones, analogs of a chiral enolic-γ-lactone; the concave bislactone skeletons of fungal metabolites (+)-avenaciolide and (−)-canadensolide; the structural skeletons of the furo [2,3-b]furanol, which is used in the anti-HIV drug Darunavir; (−)-tetrahydropyrrolo [2,1-a]isoquinolinones, an analog of (−)-crispine A; (−)-hexahydroindolizino [8,7-b]indolones, an analog of the naturally occurring (−)-harmicine; and furo [2,3-b]pyrroles are presented here [3].

The aim of the review “A Century of Azulene Chemistry: A Brief Look at Azulenes Building” by A. C. Razus is to encourage researchers in the field, especially those who wish to uncover information on the synthesis pathways of azulenes. The properties of the azulene system are very different from those of its isomer, naphthalene. The processing of the information from the literature on azulene synthesis starts with the raw materials on which the procedures are based. In many cases, instead of descriptions of reaction pathways, presentation in the form of schemes was preferred, in which the steps and reaction conditions chosen, as well as the yields, were highlighted [4].

B. L. Pham and C. Humbert et al. surveyed the “Sum-Frequency Generation Spectroscopy at Aqueous Electrochemical Interfaces” phenomenon. The electrochemical interface (EI) is the determining factor in the yield and mechanism of sustainable energy storage and conversion systems due to its intrinsic functionality as a dynamic junction, which breaks the symmetry of molecular arrangements in the complex reaction fields of mass transport and heterogeneous electron transfer. Based on the non-centrosymmetry of the interfaces’ electronic properties, sum-frequency generation (SFG) spectroscopy was shown to be specifically well suited for probing the EI with detailed and comprehensive characteristics of adsorbates’ chemical structures and electrochemical events. In this review, the authors holistically engage in a methodical and scrupulous assessment of the fundamental electrical double layer models and navigate towards the connection of the renowned Stark effect and the potential dependence of SFG spectra at heterogeneous electrode–electrolyte interfaces. The development, advantages, and available geometrical configurations of in situ SFG spectroscopy were dissected for the harnessing of the EI. A broad spectrum of applications for unraveling water orientations and rationalizing the convoluted mechanism of fuel-generated electrocatalytic reactions with particular encumbrances and potential resolutions is underscored through the use of SFG spectroscopy [5].

As part of a series of original research papers, M. Fujiki et al. include a work titled “Nuclear-Spin-Dependent Chirogenesis: Hidden Symmetry Breaking of Poly(di-n-butylsilane) in n-Alkanes”, where they report the dual mirror-symmetry-breaking and second-order phase transition characteristics of mirror-symmetric 7₃-helical poly(di-n-butylsilane) in n-alkanes under static (non-stirring) conditions [6].

A. Raczyńska and E. Żymańczyk-Duda et al., in their paper “Fungal Biocatalysis in Stereoselective Oxidation of 2-Phenylethanol”, described biosynthesis. Three fungal strains (Beauveria bassiana DSM 1344, Beauveria brongniartii DSM 6651, and Rhizopus arrhizus DSM 1185) were employed for the stereoselective oxidation of the cheap and commercially available substrate 2-phenylethanol, which resulted in chiral building blocks, e.g., 1-phenylethane-1,2-diol [7].

The second article of the Polish scholars M. Serafin-Lewańczuk and E. Żymańczyk-Duda et al. “Complete Epoxy Phosphonate Conversion to Dimethyl (1E)-3-Hydroxyprop-1-Enylphosphonate with Photobiocatalysts’ Assistance” is on photobiocatalysts employed in the bioconversion of epoxymethyl dimethyl phosphonate (EMDP), which are able to convert EMDP into a pure geometric isomer of the unsaturated product, dimethyl (1E)-3-hydroxyprop-1-enylphosphonate, a rare and expensive compound of high added value. Six different strains were screened towards dimethyl epoxy phosphonate, and in the case of Synechococcus bigranulatus, a conversion of over 99% was achieved [8].

The aim of the article “On the Solvatochromism of Fluorescein Sodium” by D. G. Dimitriu et al. is to determine certain parameters of the fluorescein sodium molecule in terms of the quantum-mechanical modeling and experimental solvatochromism in both binary and ternary solutions. For data analysis, several theoretical models were applied. The results highlight the intermolecular interactions involved in the spectral shift in the electronic absorption band of fluorescein sodium, when dissolved in different solvents or binary solvents. The results are useful for a better understanding of the behavior of fluorescein sodium, when dissolved in different solvents or combinations of solvents, to develop new practical applications [9].

In another paper, the Romanian team of D-G. Dimitriu et al. published their results on “Solvatochromic Analysis of Triton X-100 in Binary Mixtures”. Binary solvent mixtures of the non-ionic surfactant Triton X-100 with water, methanol, ethanol, and 1-propanol, respectively, were investigated by solvatochromic studies. The absorption spectral bands of methyl red dye, used as a solvatochromic probe, were recorded in ternary solutions prepared with different mole ratios between Triton X-100 and water/alcohols. Different models were used during this experimental study [10].

The study by P. Snopiński et al., titled “The Influence of Grain Structure on Mechanical Properties of LPBF AlSi10Mg Alloy Obtained via Conventional and KOBO Extrusion Process”, compares the microstructures and mechanical properties of the AlSi10Mg alloy processed by laser powder bed fusion (LPBF) after undergoing different post-processing techniques. These techniques include conventional extrusion at 350 °C (CE-350) and KOBO extrusion at both room temperature (KOBO-RT) and at 350 °C (KOBO-350). The extrusion processes, regardless of the method used, effectively densified the alloy, fragmented the primary silicon network, and refined the grain structure [11].

The next article, “Bi-Symmetric Polyhedral Cages with Nearly Maximally Connected Faces and Small Holes” by B. Piette, discusses polyhedral cages (p-cages) providing a good description of the geometry of some families of artificial protein cages. p-cages made out of two families of equivalent polygonal faces/protein rings were identified, where each face has at least four neighbors, and where the holes are contributed by at most four faces [12].

In the paper “Symmetries of Confined H₂⁺ Molecule” by S. Longo et al., the symmetries of a H₂⁺ molecule confined within potential energy wells of various shapes were highlighted. This system has been long regarded as a model for small molecules trapped in crystalline cavities and molecular cages. In this context, the role of symmetry assumes significant importance [13].

The article “Quantum-Chemical Investigations on the Structure and Stability of Mixed Trimers Containing HC₃N in Combination with H₂C₂ and/or HCN Analyzed by QTAIM, NBO and SAPT Methods”, written by A. P. Charmet et al., deals with the computational study of HC₃N⋅⋅HCN⋅⋅H₂C₂-, (HC₃N)₂⋅⋅H₂C₂-, and HC₃N⋅⋅(H₂C₂)₂-mixed trimers. The different equilibrium structures of the different low-lying minima on the corresponding potential energy surface were accurately determined, and the relative stabilities were computed by extrapolation procedures to the complete basis set limit. The results can be used to assist further theoretical investigations and experimental studies on the formation of larger molecules potentially relevant in astrochemistry [14].

Last but not least, the study by K. Balasubramanian, titled “Enumeration of n-Dimensional Hypercubes, Icosahedra, Rubik’s Cube Dice, Colorings, Chirality, and Encryptions Based on Their Symmetries” is a kind of real delicate. The whimsical Las Vegas/Monte Carlo cubic dice are generalized to construct the combinatorial problem of enumerating all n-dimensional hypercube dice and dice of other shapes that exhibit cubic, icosahedral, and higher symmetries. By utilizing powerful generating function techniques for various irreducible representations, the authors derived the combinatorial enumerations of all possible dice in n-dimensional space with hyperoctahedral symmetries. It was shown that all enumerated dice are chiral, and the authors provided counts of chiral pairs of dice in the n-dimensional space. Applications for the nonlinear n-dimensional hypercube and other dicey encryptions are exemplified with romantic, clandestine messages: “I love U” and “V Elope at 2” [15].