Search Results (431)

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

The manipulation of vector beams (VBs) with longitudinally variant polarization states is an important research topic and has potential applications in classical and quantum fields. In this study, we propose a half-wave plate dielectric metasurface composed of two interleaved sub-metasurfaces to generate longitudinally separated dual-channel vectorial structured light fields. The propagation and Pancharatnam–Berry phases are employed to construct hyperbolic, helical, and opposite gradient phases for focusing wavefronts, generating circularly polarized (CP) vortices, and deflecting CP vortices with the same chirality in opposite directions. Consequently, dual-channel higher-order or hybrid-order Poincaré (HOP or HyOP) beams are generated along the optical axis under elliptically polarized illumination, and their polarization states evolve along an arbitrary pair of antipodal meridians on the HOP or HyOP sphere by varying the ellipticity of the incident light, the propagation-phase topological charge, and the rotation order of the meta-atom. The consistency between the theoretical and simulated results demonstrates the feasibility and practicability of the proposed method. This study is significant for compact, integrated, and multifunctional optical devices, and provides an innovative strategy to extend optical field manipulation from two-dimensional to three-dimensional space. Full article

This paper reports the chiral separation of menthol enantiomers using the VARICOL process to improve productivity. Amylose 3,5-dimethylphenylcarbamate coated on silica gel was employed as the chiral stationary phase, and n-hexane/2-propanol (95/5, v/v) was used as the eluent. To design and optimize the VARICOL process, a linear driving-force model was developed to predict the separation performance. Separation regions of the conventional simulated moving bed (SMB) and VARICOL processes were evaluated and compared. It was found that, under an outlet purity requirement of 95.0%, the five-column VARICOL process has a separation region comparable to that of the six-column conventional SMB process. As an illustrative example, a five-column VARICOL unit and a six-column conventional SMB unit, both operating under the same conditions, were employed to resolve the menthol racemate. Purities for both the extract and raffinate were above 95.0%, and a productivity of 0.400 g_racemate/(L_CSP∙min) and a solvent consumption of 0.355 L/g_racemate were achieved in the VARICOL process. Productivity increased by 20% while solvent consumption maintained relative to the conventional SMB process, though product purities decreased slightly. 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

Lindera sericea var. sericea (Japanese common name: “Kekuromoji”) is a deciduous shrub belonging to the Lauraceae family. Mainly distributed in Japan and Korea, L. sericea has been traditionally used as a source of essential oils and has not been characterized as a medicinal plant. In this study, we aimed to isolate and identify compounds that activate Takeda G protein-coupled receptor 5 (TGR5) and peroxisome proliferator-activated receptor-γ (PPARγ). Bioactivities were evaluated using a dual-color real-time bioluminescence monitoring system. The methanolic extract of L. sericea showed significant dose-dependent TGR5 activation and modest PPARγ activation. Spectroscopic analysis identified rac-pinocembrin (rac-1) and rac-pinostrobin (rac-2) as the major bioactive compounds in the methanolic extract. Reporter assays revealed that rac-2 is a TGR5 activator, whereas both rac-1 and rac-2 are modest PPARγ activators. We then separated the enantiomers of pinocembrin (1) and pinostrobin (2) using chiral column chromatography. Both enantiomers of 2 contributed comparably to TGR5 activation, whereas each pair of enantiomers (1 and 2) exhibited similar activity within the same compound toward PPARγ. These findings suggest that L. sericea is a promising source of bioactive compounds with potential metabolic regulatory activity. 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

l-menthol is one of the most popular flavors in the world. The separation of menthol enantiomers is crucial because of the unpleasant taste of d-menthol. This work presents the chiral separation of racemic menthol by simulated moving bed chromatography for the first time. Six preparative columns packed with amylose 3,5-dimethylphenylcarbamate coated on silica gel were used for separation, and a mixture of n-hexane/isopropanol was selected as the mobile phase. The hydrodynamic properties of the SMB columns were studied to minimize the packing asymmetry in the SMB experiment. The binary adsorption isotherm of menthol enantiomers was measured by the adsorption–desorption method. Fixed-bed batch chromatography was carried out to evaluate the adsorption kinetic behavior. Mathematical models, considering the mass transfer resistance and axial dispersion, were applied to describe the dynamics of the chromatographic separation process. The SMB process for chiral separation of racemic menthol was designed by evaluating the separation region using simulations. Reasonable agreements were achieved between the predicted results and the experimental results. Purities for both the extract and raffinate were above 99.0%, and a productivity of 0.267 g_racemate/(L_CSP∙min) and a solvent consumption of 0.431 L/g_racemate were achieved. Full article

This study contains a combination of a review and a related individual case study, which discusses the possibility of predicting the success of enantiomers’ optical separation using fractional crystallization of diastereomeric salts. The key idea is to use relatively simple and rapid experimental methods, such as differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD), to construct ternary melting diagrams. These diagrams can be used for visualization and predicting compositional conditions favorable for successful separation. The main limitations are also mentioned, such as the ideal eutectic behavior of components and the need to identify all crystalline phases in the system. For demonstration, three novel studies, attempts in ternary resolution systems of racemic o- and p-chloromandelic acids with chiral 1-cyclohexylethylamine or pregabalin, resulting in either declined or promising aspects for a successful resolution, were completed, and the corresponding individual ternary phase diagrams have been compiled and presented, as well. In addition, indexing and modeling of one of the diastereomeric salts’ unit cells have been successfully carried out by means of powder X-ray diffraction, using the DASH software package. Full article

Essential oils from species of the genus Varronia (Boraginaceae) are recognized for their chemical diversity and biological potential; however, phytochemical information on Varronia crenata Ruiz & Pav. remains scarce, despite its wide distribution in the Andean region. The aim of this study was to provide the first chemical and enantioselective characterization of the essential oil obtained from the leaves of V. crenata growing in Ecuador. Qualitative and quantitative analyses were carried out by GC–MS and GC–FID, respectively, using two columns with stationary phases of contrasting polarity. Compounds were identified by matching linear retention indices and mass spectra to literature references and quantified by external calibration using relative response factors (RRFs) calculated for each compound based on its combustion enthalpy. The most abundant constituents (≥3.0% on average between the two columns) of the essential oil of V. crenata, both in the nonpolar and polar stationary phases, were germacrene D (18.4%), (E)-β-caryophyllene (13.3%), α-copaene (10.4%), tricyclene (9.3%), δ-cadinene (8.9%), and α-pinene (8.3%). The volatile fraction was dominated by sesquiterpenes (60.2%) and monoterpenes (22.1%), while other chemical families were present in minor proportions. The enantioselective analysis was performed on two different columns, coated with stationary phases based on β-cyclodextrins: 2,3-diacetyl-6-tert-butyl-dimethylsilyl-β-cyclodextrin and 2,3-diethyl-6-tert-butyl-dimethylsilyl-β-cyclodextrin. Nine chiral compounds were analyzed; among them, (1R,5R)-(+)-α-pinene, (1R,5R)-(+)-sabinene, and (S)-(+)-β-phellandrene were detected as enantiomerically pure, while the other metabolites presented scalemic mixtures. Overall, the high content of bioactive sesquiterpenes and the observed stereochemical complexity highlight the potential pharmaceutical and agricultural relevance of V. crenata essential oil, while also providing novel chemotaxonomic information for the genus. Full article

The giant atom paradigm, where a single quantum emitter couples to a continuum at multiple discrete points, has enabled unprecedented control over light-matter interactions, including decoherence-free subspaces and chiral emission. However, realizing these non-local effects beyond the microwave regime remains a significant challenge due to the diffraction limit. Here, we theoretically propose a photonic analog of giant atoms operating at optical frequencies, utilizing a quantum emitter resonantly coupled to a pair of spatially separated single-mode cavities interacting with a common 1D photonic continuum. By rigorously deriving the effective non-Hermitian Hamiltonian and integrating out the bath degrees of freedom, we demonstrate that the interference between cavity-mediated emission pathways leads to the formation of robust Bound States in the Continuum (BICs). These interference-induced dark states allow for the infinite trapping of excitation within the emitter-cavity subsystem, effectively shielding it from radiative decay. Our results extend the giant atom toolbox to the optical domain, offering a scalable architecture for integrated quantum photonics and quantum interconnects. Full article

We present a numerical study comparing light scattering by small clusters composed of helices, capsules, and spheres. Using the discrete-dipole approximation (DDA), we compute orientation-averaged Mueller-matrix elements M₁₁, M₁₂, and M₁₄ for clusters with varying number of monomers (N = 5–45) and mean center-to-center separation (1–10 particle diameters). Our analysis isolates the influence of particle morphology on angular scattering intensity, linear polarization, and circular intensity differential scattering (CIDS), providing a direct comparison of symmetric and chiral shapes. Helices display persistent angular fine structure in M₁₁ and deep, side-scattering maxima in M₁₂, while spheres and capsules converge to smoother polarization curves with increasing separation. CIDS from symmetric monomers manifests as small oscillations around zero that decay rapidly with monomer separation and number. In contrast, helices produce a stable backward CIDS slope that is largely separation-independent but gradually flattens with increasing number of monomers. These trends confirm that morphology alone can influence key polarization characteristics and provide insights for interpreting scattering from complex-shaped particles. Such morphology-related features may help in the interpretation of polarization data in aerosol and planetary remote sensing and justify the refinement of the design of optical setups for studying irregular or chiral particles in controlled environments. Full article

A cone calix[4]arene having one tert-butyl group and three amino groups at the wide rim was bis-N-protected stepwise using sulfonylation with 4-nitrobenzylsulfonyl chloride, followed by acylation with di-tert-butyl dicarbonate. The selective sulfonylation was shown to prefer the amino group located in the proximal calixarene aromatic unit relative to the tert-butylated moiety, resulting in the formation of an inherently chiral calix[4]arene with a wide-rim substitution pattern of AABC type. Further acylation of one of the two remaining amino groups also proceeded selectively. It involved the calixarene aromatic unit adjacent to the sulfonylated moiety, as clearly demonstrated by 2D NMR data for the ABCD-substituted reaction product, which was obtained as a mixture of enantiomers. The mixture was acylated with (R)-mandelic acid succinimide ester, and the resulting diastereomers were separated by conventional column chromatography, thus demonstrating the applicability of the stepwise protection strategy for the further preparation of enantiopure calix[4]arene cores possessing inherent chirality due to four different substituents at their wide rims. Full article

Four new porous homochiral metal–organic frameworks (MOFs), [M₂(camph)₂(bpa)]∙Solv (M = Co(II), Ni(II), Cu(II) and Zn(II)), based on (+)-camphoric acid (H₂camph) and 1,2-bis(4-pyridyl)ethane (bpa) were synthesized and characterized. The crystal structures of [Ni₂(camph)₂(bpa)] and [Zn₂(camph)₂(bpa)] were established by single-crystal X-ray diffraction analysis. Powder X-ray data prove the phase purity and isostructural nature of all four compounds. The thermal stability of [M₂(camph)₂(bpa)] was found to depend on the electronic configuration, as well as on the redox properties of the metal cation, and varied from 225 °C (M = Zn²⁺) to 375 °C (M = Ni²⁺). The reversible, solvent-induced sponge-like dynamics of the coordination frameworks was thoroughly investigated. Changes in the positions of reflexes, related to the length of the flexible bpa linker, were observed by powder XRD, pointing to transitions between an open-framework phase and a squeezed, non-porous phase in a crystal-to-crystal manner, while the integrity and connectivity of the coordination network were maintained. Size-selective adsorption from a benzene–cyclohexane 1:1 mixture on [Zn₂(camph)₂(bpa)] was studied by ¹H NMR analysis. The benzene-favorable composition of guest molecules (C₆H₆:C₆H₁₂ = 5:1) occluded within the host crystalline sponge revealed a preferable adsorption affinity towards smaller benzene compared with larger cyclohexane. High framework stability in various solvents, as well as successful molecular separation in the liquid state, validates the potential utilization of chiral porous metal(II) camphorate MOFs in important stereoselective applications. Full article

Chirality remains the most neglected axis of pesticide residue science. Many active ingredients are sold as racemates although their enantiomers differ in potency, persistence, transport, and toxicology; as a result, total concentration is a poor surrogate for risk. This review synthesizes green and enantioselective strategies spanning the full analytical–remediation continuum. We survey solvent-minimized sample preparation approaches (SPME/TF-SPME, FPSE, µSPE, DLLME with DES/NADES), MS-compatible chiral separations (immobilized polysaccharide CSPs in LC and SFC, cyclodextrin-based selectors in GC, CE/CEC), and HRMS-enabled confirmation and suspect screening. Complex matrices (e.g., fermented beverages such as wine and high-sugar products) are critically discussed, together with practical matrix-tolerant workflows and the complementary role of chiral GC for hydrophobic residues. We then examine emerging enantioselective materials—MIPs, MOFs/COFs, and cyclodextrin-based sorbents—for extraction and preconcentration and evaluate stereoselective removal via adsorption, biodegradation, and chiral photocatalysis. Finally, we propose toxicity-weighted enantiomeric fraction (EF) metrics for decision-making, outline EF-aware green treatment strategies, and identify metrological and regulatory priorities (CRMs, ring trial protocols, FAIR data). Our thesis is simple: to reduce hazards efficiently and sustainably, laboratories and practitioners must measure—and manage—pesticide residues in the chiral dimension. Full article

Four new methionine sulfoxide-containing diketopiperazines, (+)-dysidmetsulfoxide A [(+)-1], (+)-dysidmetsulfoxide B [(+)-2], (+)-dysidmetsulfoxide C [(+)-3] and (−)-dysidmetsulfoxide C [(−)-3], were isolated from the South China Sea sponge Dysidea sp. These compounds represented the first example of diketopiperazines possessing the unit of methionine sulfoxide (MetO) isolated from marine sponges. As it was difficult to determine the configuration of chiral sulfur atom in the thionyl group, the structures with absolute configurations of these compounds were elucidated by spectroscopic analyses and total synthesis. It was noteworthy that the purchased synthetic precursors, Fmoc-L- and Fmoc-D-MetO, were mixtures of epimers, respectively, due to the stereogenic sulfur atom in MetO, which were separated to prepare the optically pure isomers via the method of supercritical fluid chromatography (SFC). In addition, the other four optical isomers [(−)-1, (−)-2, (+)-4 and (−)-4] were also synthesized. Furthermore, (+)-1, (−)-1, (+)-3, (+)-4 and (−)-4 showed potential anti-Parkinson’s disease activities in an in vivo zebrafish model. Full article