Explore the vast range of titles available.

Chiral 2-substituted chromanes are important substructures in organic synthesis and appear in numerous natural products. Herein, the correlation between specific optical rotations (SORs) and the stereochemistry at C2 of chiral 2-substituted chromanes was investigated through data mining, quantum-chemical calculations using density functional theory (DFT), and mechanistic analyses. For 2-aliphatic (including acyloxy and alkenyl) chromanes, the P-helicity of the dihydropyran ring usually corresponds to a positive SOR; however, 2-aryl chromanes with P-helicity tend to exhibit negative SORs. 2-Carboxyl (including alkoxycarbonyl and carbonyl) chromanes often display small experimental SORs, and theoretical calculations for them are prone to error because of the fluctuating conformational distribution with computational parameters. Several typical compounds were discussed, including detailed descriptions of the asymmetric synthesis, absolute configuration (AC) assignment methods, and systematic conformational analysis. We hope this work will enrich the knowledge of the stereochemistry of chiral 2-substituted chromanes.

Besides the well-known hallucinogenic ketamine, various novel ketamine derivatives are available on the illicit drug market, sold as designer drugs. Minor chemical changes to the parent compound aim to circumvent existing narcotic drug laws while mimicking the effects of the original substance. Ketamine and some of its derivatives possess a chiral centre and therefore exist as two enantiomers. While differences in the effects of S- and R-ketamine are well studied, this is not the case for ketamine derivatives. Therefore, the development and adaptation of suitable enantioseparation methods for those compounds is important to face the problems of the constantly changing drug market. In this study, different chiral separation methods for capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) were tested on 11 ketamine derivatives. Some of them were enantioseparated for the first time due to their novelty. All compounds were at least partially separated on both instruments. HPLC separations were conducted using four different polysaccharide-based chiral stationary phases. Furthermore, an optical rotation detector coupled to the HPLC enabled the determination of the enantiomer elution order. In CE analysis, enantioseparation was achieved using 2% (w/v) acetyl-β-cyclodextrin or carboxymethyl- β-cyclodextrin in 10 mM di-sodium hydrogen phosphate as the background electrolyte in capillary electrophoresis.

The concept of chirality dates back to 1848, when Pasteur manually separated left-handed from right-handed sodium ammonium tartrate crystals 1 . Crystallization is still an important means for separating chiral molecules into their two different mirror-image isomers (enantiomers) 2 , yet remains poorly understood 3 . For example, there are no firm rules to predict whether a particular pair of chiral partners will follow the behaviour of the vast majority of chiral molecules and crystallize together as racemic crystals 4 , or as separate enantiomers. A somewhat simpler and more tractable version of this phenomenon is crystallization in two dimensions, such as the formation of surface structures by adsorbed molecules. The relatively simple spatial molecular arrangement of these systems makes it easier to study the effects of specific chiral interactions 5 ; moreover, chiral assembly and recognition processes can be observed directly and with molecular resolution using scanning tunnelling microscopy 6 , 7 , 8 , 9 . The enantioseparation of chiral molecules in two dimensions is expected to occur more readily because planar confinement excludes some bulk crystal symmetry elements and enhances chiral interactions 10 , 11 ; however, many surface structures have been found to be racemic 12 , 13 , 14 , 15 , 16 , 17 , 18 . Here we show that the chiral hydrocarbon heptahelicene on a Cu(111) surface does not undergo two-dimensional spontaneous resolution into enantiomers 19 , but still shows enantiomorphism on a mesoscopic length scale that is readily amplified. That is, we observe formation of racemic heptahelicene domains with non-superimposable mirror-like lattice structures, with a small excess of one of the heptahelicene enantiomers suppressing the formation of one domain type. Similar to the induction of homochirality in achiral enantiomorphous monolayers 20 by a chiral modifier, a small enantiomeric excess suffices to ensure that the entire molecular monolayer consists of domains having only one of two possible, non-superimposable, mirror-like lattice structures.

A one-pot synthesis of stereomer cross-linked copolymers of l -malic acid with tuned properties is reported. The β-cyclodextrin, as co-monomer with several OH groups, was applied to promote the polyester formation with higher, pre-defined molecular weight. The importance of the experimental conditions for preparation of polymers with tailor-made, optically active compositions is described, and their structures are characterized by different techniques such as thermogravimetry–differential scanning calorimetry−mass spectrometric evolved gas analysis, infrared spectroscopy and specific rotation. To our knowledge, first time was used the specific optical rotation for characterization of retention of the optical activity in the course of the synthesis.

Here, we report the synthesis of polyesters of l-malic acid, β-cyclodextrin, and two other comonomers, resorcinol and salicylic acid that, involved in the polyester chain by direct polycondensation, could improve the antibacterial activity. The copolymers were characterized by thermal analysis, infrared spectroscopy as well as by specific optical rotation values. The thermogravimetric and differential scanning calorimetry (TG–DSC) measurement results showed the influence of the comonomers on the thermal stability of the copolymers, which was higher when ZnO was present in the reaction mixture. The FTIR spectra confirmed the presence of the comonomers in the polyesters and the influence of the ZnO on the products. The specific optical rotation values showed similar tendency, and the results were in accordance with those got by TG–DSC and FTIR techniques. In short, the zinc oxide helped not only in ester formation but improved the polyester stability. Results allowed elaboration of reproducible polyester synthesis with tailor-made characteristic.

The effects of honey type (X 1 ), liquefaction temperature (X 2 ) and timing (X 3 ), prefiltering (X 4 ), sample weight (X 5 ), dilution volume (X 6 ), Carrez I (X 7 ) and Carrez II volume (X 8 ), final filtering (X 9 ), polarimeter tube length (X 10 ) and reading system (X 11 ) on the determination of the specific optical rotation (SOR, R 1 ) determination were investigated using the fractional experimental design . X 1 and X 11 showed strong influence as key factors. Although X 1 differentiate blossom from honeydew honey, X 11 can mistake the determination of this parameter and thus the classification of honeys. This study sets an uncertain interval (−5º to +5º) of overlapping between the SOR of blossom and honeydew honeys. Automatic polarimeter system showed lower variability than manual. Factors affecting pH (R 2 ) and electrical conductivity (EC, R 3 ) of working solutions were identified as X 4 , X 6 , X 8 , X 11; and X 4 , X 7 , X 8 , X 11 , respectively.

Kagome metals AV 3 Sb 5 (A = K, Cs, Rb) provide a rich platform for intertwined orders, where evidence for time-reversal symmetry breaking, likely due to the long-sought loop currents, has emerged in STM and muon spin relaxation experiments. An isotropic component in the spontaneous optical rotation has also been reported and was interpreted as the magneto-optic Kerr effect. Intriguingly, the observed rotations differ by five orders of magnitude between different wavelengths and samples, suggesting more intricate physics. Here we report optical rotation and polar Kerr measurements in CsV 3 Sb 5 crystals at the same wavelength. We observe large isotropic components of 1 milliradian in the optical rotation that do not respond to applied magnetic fields, while the spontaneous Kerr signal is less than 20 nanoradians. Our results prove unambiguously that the reported isotropic rotation is not from time-reversal symmetry breaking but represents the long-sought specular optical rotation and indicates a new intertwined order. Kagome materials, such as CsV3Sb5, a rich array of correlated phase, including a time-reversal symmetry breaking phase, which could possibly be the result of loop currents. Attempts to verify this with magneto-optical measurements have yielded mixed results. Here, Farhang et al show that the magneto-optical signals are due to specular optical rotation. ‘

Chirally sensitive measurement techniques have generally been restricted to bulk samples. Here, we report the observation of fluorescence-detected circular dichroism (FDCD) from single (bridgedtriarylamine) helicene molecules by using an excitation wavelength (457 nanometers) in the vicinity of an electronic transition that shows circular dichroism in bulk samples. The distributions of dissymmetry (g) parameters by analysis of signals from pure M- and P-type diastereomers are almost perfect mirror images of one another, each spanning a range of both positive and negative values. In addition, we observe a well-defined structure in the histogram of dissymmetry parameters suggestive of specific molecular orientations at the polymer interface. These single-molecule results highlight strong intrinsic circular dichroism responses that can be obscured by cancellation effects in ensemble measurements of a randomly oriented bulk sample.

The magnetic skyrmion is a spin-swirling topological object characterized by its nontrivial winding number, holding potential for next-generation spintronic devices. While optical readout has become increasingly important towards the high integration and ultrafast operation of those devices, the optical response of skyrmions has remained elusive. Here, we show the magneto-optical Kerr effect (MOKE) induced by the skyrmion formation, i.e., topological MOKE, in Gd 2 PdSi 3 . The significantly enhanced optical rotation found in the skyrmion phase demonstrates the emergence of topological MOKE, exemplifying the light-skyrmion interaction arising from the emergent gauge field. This gauge field in momentum space causes a dramatic reconstruction of the electronic band structure, giving rise to magneto-optical activity ranging up to the sub-eV region. The present findings pave a way for photonic technology based on skyrmionics. In the magneto-optical Kerr effect, light incident on a magnetic material is reflected with a shifted polarization, the size of the shift characterized by the Kerr angle. Here, Kato et al introduce a topological magneto-optical Kerr effect, where the presence of skyrmions, a type of topological spin texture, leads to a significant enhancement of the Kerr signal.

Ferroaxial materials that exhibit spontaneous ordering of a rotational structural distortion with an axial vector symmetry have gained growing interest, motivated by recent extensive studies on ferroic materials. As in conventional ferroics (e.g., ferroelectrics and ferromagnetics), domain states will be present in the ferroaxial materials. However, the observation of ferroaxial domains is non-trivial due to the nature of the order parameter, which is invariant under both time-reversal and space-inversion operations. Here we propose that NiTiO 3 is an order-disorder type ferroaxial material, and spatially resolve its ferroaxial domains by using linear electrogyration effect: optical rotation in proportion to an applied electric field. To detect small signals of electrogyration (order of 10 −5  deg V −1 ), we adopt a recently developed difference image-sensing technique. Furthermore, the ferroaxial domains are confirmed on nano-scale spatial resolution with a combined use of scanning transmission electron microscopy and convergent-beam electron diffraction. Our success of the domain visualization will promote the study of ferroaxial materials as a new ferroic state of matter. The presence of ferroaxial domain states is recently experimentally demonstrated by a nonlinear optical technique, which lacks high spatial resolution to visualize ferroaxial domains. Here, the authors visualize spatial distributions of ferroaxial domains in NiTiO 3 showing an order-disorder type ferroaxial transition.