Search Results (225)

In this study, the applicability of achiral column chromatography—including both medium-pressure liquid chromatography (MPLC) and classical gravity-driven techniques—was evaluated as a laboratory method for enantiomeric enrichment of scalemic (non-racemic) samples of axially chiral compounds. As model substrates, 3-(ortho-substituted-phenyl)quinazolin-4-one derivatives were employed. The results confirmed that self-disproportionation of enantiomers (SDE), occurring during column chromatography (SDEvCC), enabled the efficient isolation of enantiomerically pure fractions, with MPLC demonstrating particularly high effectiveness. Additionally, the parameters governing gravity-driven column chromatography were systematically optimized, with particular attention to variables such as eluent type and concentration, stationary phase composition, sample preparation protocol, and solvent purity. Furthermore, leveraging known crystallographic data and quantum chemical calculations based on Density Functional Theory (DFT), a molecular association mechanism was proposed to elucidate the physicochemical basis of the SDE phenomenon. Full article

The two-dimensional chiral self-assembly and chiral separation of achiral Ext-TEB molecules on a Bi(111) surface were investigated using low-temperature scanning tunneling microscopy (LT-STM). At low coverage, the molecules self-assembled into chiral clusters. As the coverage increased, a monolayer film with a non-edge-sharing honeycomb structure was formed. This supramolecular structure exhibited organizational chirality, accompanied by chiral separation. Upon annealing, part of the non-edge-sharing honeycomb structure transformed into a close-packed structure, while retaining the organizational chirality, supramolecular chirality, and pronounced chiral separation. Furthermore, applying a higher bias was found to induce a transition in the electronic state of the non-edge-sharing honeycomb structure, converting it into an edge-sharing honeycomb configuration. This study reveals that the chirality of 1,3,5-tris(4-ethynylphenyl) benzene (Ext-TEB) arises from the rotation of the side-chain phenyl rings, which is induced by the rotation of the molecular axis relative to the substrate lattice. This work presents a strategy for the preparation of chiral nanostructures from achiral molecules due to the spontaneous chiral symmetry generation. Full article

Background/Objectives/Methods: A bioassay-informed investigation of the Australian pasture soil-derived Streptomyces sp. S4S-00193A39 yielded the anthelmintic principals as three new spiroketal polyketide alkaloids, goondoxazoles A–C (1–3), with structures assigned by detailed spectroscopic analysis. Results: A structure–activity relationship based on the ability to inhibit the motility of Dirofilaria immitis microfilariae (mf) revealed a positive correlation for the benzoxazole moiety present in 2 and 3 (EC₅₀ 55–85 nM) versus the ring-opened aminobenzoic acid moiety evident in 1 (EC₅₀ 1.38 µM). This hypothesis was strengthened by extension of the SAR assessment to the known benzoxazole natural products A-33583 (12), UK-1 (13) and nataxazole (14), and the new analogue 5-hydroxynataxazole (15), which were isolated in our lab from three additional Australian pasture soil-derived Streptomyces spp. Of note, while the benzoxazole methyl esters 13–15 exhibited approximately 9- to 65-fold lower potency against D. immitis mf compared with 2 and 3, the carboxylic acid substituted benzoxazole 12 displayed comparable activity (EC₅₀ 72 nM) against D. immitis mf, and >5-fold improved potency against D. immitis L4 larvae (EC₅₀ 0.43 µM). Conclusions: These observations reveal the promising anthelmintic potential (against D. immitis) for the new structurally complex and chiral goondoxazoles (e.g., 2 and 3), and demonstrate that this effect can be replicated, even improved, by simpler, achiral benzoxazole microbial natural products (e.g., 12). Full article

Fungicide contamination is an increasing global environmental concern, due to the harm they may pose to non-target organisms, their contribution to antimicrobial resistance, and the potential risks to human health when drinking water (DW) sources are impacted. Many fungicides used in agriculture are chiral and may exist as racemates, or a combination of diastereoisomers and/or enantiomers. Since enantiomers can differ in environmental fate, distribution, and toxicity, enantioselective analysis of chiral fungicides is crucial. The aim of this study was to develop and validate an analytical method for the determination of azole chiral and achiral fungicides in DW using solid-phase extraction followed by liquid chromatography-tandem mass spectrometry (SPE-LC-MS/MS). Chromatographic separation of one achiral fungicide and five chiral fungicides was achieved using a polysaccharide chromatographic column under reverse elution mode. The validated method demonstrated high sensitivity with method detection limits (MDL) below 0.86 ng L⁻¹ and was successfully applied to 13 DW samples collected from various supply networks across Portugal. Seven out of the 15 targeted analytes were found at trace concentrations (>MDL). Fluconazole was the most frequently detected (~87% of the samples). The hazard quotients (HQs) for individual compounds for each individual fungicide (sum of the enantiomers for those chiral) and the hazard index (HI, sum of the individual HQ values) were calculated in each DW sample, indicating no significant health risks to consumers, since it is well below 0.1 for all compounds. Full article

Chiral and racemic forms of a pyridyl ligand (R-L and rac-L, respectively), containing urea groups at their core and synthesised by the condensation of 3-aminopyridine and α-methylbenzylisocyante, were incorporated into silver complexes. The resulting species depend on the enantiopurity of the ligand alongside an influence from the counter-anion. The enantiopure ligand generated isomorphous, one-dimensional polymeric compounds [Ag(R-L)X] (where X = NO₃, CF₃SO₃) or [Ag(R-L)]X (where X = BF₄, PF₆). The polymeric chains, connected by N and O coordination of the ligands, have outwards facing urea groups that form hydrogen bonds to the counter-anions, which play little role in determining the overall structure. Despite all syntheses containing an excess of Ag(I) salt, the racemic ligand formed only discrete complexes of [Ag(rac-L)₂]⁺ in the presence of each of the above anions. Three of these complexes contain ligands of the same chirality (i.e., complexes with R,R and S,S ligand pairs within the centrosymmetric structures) with only the PF₆-containing compound being different. The anions play a role in dictating the structure of hydrogen-bonded chains, although PF₆⁻ is unique with urea···urea interactions present between complexes. Overall, this system highlights the nuances associated with predicting the structure, and even speciation, of related chiral/achiral systems in addition to influences of counter-anions on structural motifs. Full article

Many organic fungicides are chiral and are used in diverse application areas, including pharmaceuticals, personal care products, agrochemicals, and industry. Fungicides have valuable effects such as preventing fungal infestations and the treatment of diseases, but their generalized use resulted in their occurrence in diverse environmental compartments which is an increasing environmental concern with negative impact on non-target organisms and human health risks. Besides, enantiomers of chiral fungicides may exhibit distinct bioactivity including toxicity and degradation profiles. Therefore, monitoring their enantioselective occurrence in the environment is essential to accurately assess enantioselective (eco)toxicity and establish environmental quality standard levels. This review provides the first comprehensive and critically interpretative assessment of enantioselective chromatographic methods for the determination of fungicides, with a primary focus on azole compounds, in complex environmental matrices (e.g., soil, sediment, plants, earthworms, sewage sludge, water, wastewater) due to their regulatory relevance in the EU Watch Lists, frequent occurrence in environmental matrices, and specific analytical challenges associated with their chiral nature. Other fungicide classes are also included, since other fungicides (either chiral or achiral) reported in the articles retrieved by the literature search, were also evaluated, integrating methodological, analytical and regulatory dimensions. Liquid chromatography was identified as the predominant analytical technique, with polysaccharide-based chiral stationary phases being the most frequently used, while sample preparation was mainly based on solid-phase extraction and QuEChERS-based approaches for complex environmental matrices. Analytical performance parameters were compared to highlight strengths and limitations of reported methods, while environmental monitoring data were reviewed, identifying soil and water as matrices with the highest reported chiral fungicide levels. The urgent need to develop robust enantioselective analytical methods to recognize the distinctive biological and toxicological properties of individual enantiomers are critically discussed. By revealing persistent gaps in enantioselective workflows and regulatory differentiation between enantiomers, it highlights the need for robust analytical approaches and reliable monitoring strategies to contribute for future enantiomer-specific environmental risk assessment frameworks. Full article

For those who did not follow the invention and development of enantioselective catalysis, this review introduces pertinent historical aspects of the field and presents the scientific concepts of asymmetric bio- and organocatalysis. They are powerful technologies applied in organic laboratories and industry. They realize chiral amplification by converting inexpensive achiral substrates and reagents into enantiomerically enriched products using readily recoverable solvents, if any are used. Racemic substrates can also be deracemized catalytically. More sustainable fabrications are now available that require neither toxic metallic species nor costly reaction conditions in terms of energy, atmosphere control, product purification, and safety. Nature has been the source of the first asymmetric catalysts (microorganisms, enzymes, alkaloids, amino acids, peptides, terpenoids, sugars, and their derivatives). They act as temporary chiral auxiliaries and lower the activation free energy of the reaction by altering the reaction mechanism. Reductions, oxidations, carbon-carbon and carbon-heteroatom bond-forming reactions are part of the process panoply. Asymmetric catalyzed multicomponent and domino reactions are becoming common. Typical modes of activation are proton transfers, hydrogen bonded complex formation, charged or uncharged acid/base pairing (e.g., σ-hole catalysts), formation of equilibria between achiral aldehydes and ketones with their chiral iminium salt or/and enamine intermediates, umpolung of aldehydes and ketones by reaction with N-heterocyclic carbenes (NHCs), phase transfer catalysis (PTC), etc. Often, the best enantioselectivities are observed with polyfunctional catalysts derived from natural compounds, but not always. They may combine to form chiral structures containing nitrogen, phosphorus, sulfur, selenium, and iodine functional moieties. Today, man-made enantiomerically enriched catalysts, if not enantiomerically pure, are available in both enantiomeric forms. Being robust, they are recovered and reused readily. Full article

The detection of chiral properties is crucial for pharmacology and biochemistry, yet standard circular dichroism spectroscopy suffers from low sensitivity when probing minute sample volumes. While complex asymmetric chiral nanostructures can enhance these Circular Dichroic (CD) signals, their fabrication is intricate and costly. In this work, we analyzed an alternative based on extrinsic chirality in achiral square arrays of plasmonic circular NHAs realized via Displacement Talbot Lithography (DTL), thus exploring the chiroptical response arising from symmetry breaking induced by oblique illumination. Unlike isolated nanoparticles, nanohole arrays (NHAs) support propagating Surface Plasmon Polaritons (SPPs), allowing for unique light confinement capabilities essential for high-throughput sensing. A careful characterization in terms of Stokes parameters has been performed over a selected range of different optical angles of incidence and sample orientation to disentangle extrinsic chiral contribution from spurious effects related to sample imperfections. By optimizing such extrinsic chiral contributions, enhanced chiroptical response could be engineered by significantly amplifying the interaction between light and chiral biomolecules trapped within the holes. This methodology establishes DTL-fabricated achiral NHAs as an ultrasensitive, cost-effective platform for the detection and discrimination of enantiomers in biosensing applications. Full article

The chirality transfer from chiral domains to achiral molecules is an important theoretical and applicative issue. In this work, we have investigated the interaction between two anionic chiral surfactants bearing a proline residue as hydrophilic head and the cationic, achiral porphyrin Zn(II) [5-{4-(3-trimethylammonium)propyloxyphenyl}-10,15,20-triphenylporphyrinyl]chloride to assess the effects of the structural variations in both units on the chirality transfer efficiency and amplification. We showed that the efficiency of transferring molecular information depends on the surfactant’s features, namely the chiral configuration of the polar head, the length of the aliphatic chain, and the aggregation state. At the same time, the presence of a coordinated metal and the peripheral charged group on the porphyrin macrocycle are key factors. In detail, the study of the hetero-aggregates formed at a surfactant concentration below the critical micellar concentration (cmc) indicates that the chirality depends on the synergy of hydrophobic effect, coordination interaction, and electrostatic forces. If the surfactant concentration is higher than the cmc, at a low concentration, porphyrins are included in micelles as monomers. Under these conditions, no chirality transfer is evident. When the porphyrin is in excess with respect to the micelles, an efficient asymmetry induction is again observed, transmitted from the chiral polar head to the porphyrin oligomers included in the micelle, through the polar heads and the hydrocarbon chains of the surfactants. Full article

Hydrogen atom transfer (HAT) is a fundamental class of radical transformations that enables the direct generation of open-shell radical intermediates from R–H bonds (R = C, N, etc.), offering unique opportunities for green and sustainable synthesis. Significant progress has been made not only in identifying diverse molecular scaffolds capable of mediating HAT but also in developing synthetic methodologies to achieve precise stereocontrol in these processes. In this context, this review highlights recent advances in the use of sugar-derived compounds, cysteine-containing peptides, and chiral/achiral thiols/thiophenols as catalysts for stereoselective HAT, emphasizing their potential to expand the synthetic utility of HAT in organic transformations. Full article

This paper comprehensively reports experimental proof of parity violation in the ground and photoexcited states of three mirror-symmetric Si–Si bond polymers in homogeneous solutions of achiral molecules under non-stirring conditions by analyzing 370 chiroptical datasets relating to multiple second-order helix–helix transitions in the circular dichroism (CD) of poly(di-i-butylsilane) (iBS), poly(di-i-pentylsilane) (iPS), and poly(di-i-hexylsilane) (iHS) in achiral alkanols and p-dioxane-h₈/-d₈. Particularly large (–)-CD of g_abs = −3.1 × 10⁻² at 290 nm was found for iBS in i-pentanol at 25 °C. Notably, iPS in n-propanol at −5 °C generated (–)-CD with g_abs = −0.48 × 10⁻² at 300 nm, but (+)-circularly polarized luminescence (CPL) with g_lum = +0.84 × 10⁻² at 326 nm. In contrast, iHS in n-octanol at 0 °C showed only very weak (–)-CD of g_abs ~−0.03 × 10⁻² at 310 nm. The H/D isotopes of p-dioxane-h₈/-d₈ weakly affected the helix–helix transition characteristics of iBS. (–)-Sign vibrational CD signals assigned to the handed symmetric and asymmetric bending modes of the CH₃ and CH₂ groups of the solvents and other achiral molecules were observed. We assumed (i) three ¹H nuclear-spin-1/2 induced handed motions of CH₃ rotors at i-alkyl side chains and achiral alkanols, and (ii) helical main-chain Si atoms (δ⁺) coordinated by handed lone pairs at oxygen (δ⁻) in gauche-containing n- and i-alkanols induced by the CH₃ rotors. A possible origin of biomolecular handedness is proposed based on the first observation of far-UV CD and UV spectra of zwitterionic glycine bearing H₃N⁺ rotor in neutral H₂O. Full article

Structural symmetry preservation and breaking play important roles in optical manipulation at subwavelength scales. By precisely engineering the symmetry of the nanostructures, metasurfaces can effectively realize various optical functions such as polarization control, wavefront shaping, and on-chip optical integration, with promising applications in information photonics, bio-detection, and flexible devices. In this article, we review the recent advances in chiral and achiral metasurfaces based on symmetry manipulation. We first introduce the fundamental principles of chiral and achiral metasurfaces, including methods for characterizing chirality and mechanisms for phase modulation. Then, we review the research on chiral metasurfaces based on material type and structural dimensions and related applications in high-sensitivity chiral sensing, reconfigurable chiral modulation, and polarization-selective imaging. We then describe the developments in the application of achiral metasurfaces, particularly in polarization-multiplexed holography, phase-gradient imaging, and polarization-insensitive metalenses. Finally, we provide an outlook on the future development of chiral and achiral metasurfaces. Full article

Helical ladder polymers attract attention because of their well-defined, one-handed helical ladder structures and unique properties, which differ from precursor polymers that have random-coil conformations. However, the synthesis of helical ladder polymers is difficult and inhibits their functions and applications. In this study, we reported the synthesis of amphiphilic optically active 2,2′-tethered binaphthyl-embedded helical ladder polymers carrying hydrophilic oligo (ethylene glycol) (OEG) as side chains through quantitative and chemoselective acid-promoted intramolecular cyclization of random-coil precursor polymers. The obtained helical ladder polymers exhibited dramatic circular dichroism (CD) and circularly polarized luminescence (CPL) enhancement. Moreover, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the helical ladder polymers work as a donor, emitting circularly polarized fluorescence to excite an achiral fluorophore (coumarin-6) as the acceptor, producing green CPL with luminescence dissymmetry factor (2.5 × 10⁻⁴). Full article

Intense circularly polarized luminescence is crucial for high-performance electroluminescent, optoelectronic, and photonic devices. This study investigates the magneto-chiral characteristics of two achiral soluble diamagnetic perovskite-type PbQDs. Magnetic fields of 158 and 198 mT are applied using an electromagnet in a toluene solution at 25 °C. Both PbQDs show a magnetic circularly polarized luminescence magnitude of approximately 10⁻³ within the (480 to 580) nm wavelength range. The strength of the magnetic circularly polarized luminescence increases with the intensity of the applied magnetic field. Furthermore, the study demonstrates rapid and reversible switching of the rotation direction of the magnetic circularly polarized luminescence when the magnetic poles are rapidly changed. These results suggest that the direction (right- and left-rotating light) and circular polarization of circularly polarized luminescence (CPL) from circularly polarized perovskites can be alternately and freely controlled by applying an external magnetic field with an appropriate direction and strength. Full article

Broccoli, a highly valued Brassica vegetable, is renowned for its rich content of bioactive substances, including glucosinolates, phenolic compounds, vitamins, and essential minerals. Glucosinolates (GSLs), secondary plant metabolites, are particularly abundant in broccoli. The global consumption of broccoli has increased due to its high nutritional value. This review examines the essential bioactive compounds in broccoli and their biological properties. Numerous in vitro and in vivo studies have demonstrated that broccoli exhibits various biological activities, including antioxidant, anticancer, antimicrobial, anti-inflammatory, anti-obesity and antidiabetic effects. This review analyzes several aspects of the chemical and biological activity of GSLs and their hydrolysis products, isothiocyanates such as sulforaphane, as well as phenolic compounds. Particular emphasis is placed on sulforaphane’s chemical structure, the reactivity of its isothiocyanate fraction (-NCS), and given the different behavior of SFN enantiomers, a wide and detailed review of the chemical synthesis methods described, by microbial oxidation, or using a chiral ruthenium catalyst and more widely using chiral auxiliaries for synthesizing sulforaphane enantiomers. In addition, the methods of chiral resolution of racemates by HPLC are reviewed, explaining the different chiral fillers used for this resolution and a third section on resolution using the formation of diastereomeric complexes and subsequent separation on achiral columns. Additionally, this review highlights the presence of antimicrobial peptides in broccoli, which have shown potential applications in food preservation and as natural alternatives to synthetic antibiotics. The antimicrobial peptides (AMPs) derived from broccoli target bacterial membranes, enzymes, oxidative stress pathways and inflammatory mediators, contributing to their effectiveness against a wide range of pathogens and with potential therapeutic applications. Full article