Showing papers on "Circular dichroism published in 2022"
TL;DR: In this article , the authors examined the inducement of an interaction between two carrier proteins, human serum albumin (HSA) and human holo transferrin (HTF) within the presence of cyanidinin the form of binary and ternary systems, which was conducted by different spectroscopic, isothermal titration calorimetric (ITC), and molecular dynamics simulation techniques.
59 citations
TL;DR: A guest-driven self-assembly and chiral induction approach for the construction of otherwise inaccessible Ln4L4-type (Ln = lanthanide ions, i.e., EuIII, TbIII; L = ligand) tetrahedral hosts is reported, revealing remarkable guest-adaptive cavity breathing on the Tetrahedral cages, reflecting the advantage of the variation tolerance on coordination geometry of the f-elements.
Abstract: Chiral luminescent lanthanide-organic cages have many potential applications in enantioselective recognition, sensing, and asymmetric catalysis. However, due to the paucity of structures and their limited cavities, host-guest chemistry with lanthanide-organic cages has remained elusive so far. Herein, we report a guest-driven self-assembly and chiral induction approach for the construction of otherwise inaccessible Ln4L4-type (Ln = lanthanide ions, i.e., EuIII, TbIII; L = ligand) tetrahedral hosts. Single crystal analyses on a series of host-guest complexes reveal remarkable guest-adaptive cavity breathing on the tetrahedral cages, reflecting the advantage of the variation tolerance on coordination geometry of the f-elements. Meanwhile, noncovalent confinement of pyrene within the lanthanide cage not only leads to diminishment of its excimer emission but also facilitates guest to host energy transfer, opening up a new sensitization window for the lanthanide luminescence on the cage. Moreover, stereoselective self-assembly of either Λ4- or Δ4- type Eu4L4 cages has been realized via chiral induction with R/S-BINOL or R/S-SPOL templates, as confirmed by NMR, circular dichroism (CD), and circularly polarized luminescence (CPL) with high dissymmetry factors (glum) up to ±0.125.
51 citations
TL;DR: In this article , the symmetry-reduced meta-atoms with high birefringence supporting winding elliptical eigenstate polarizations with opposite helicity were employed to achieve the maximal planar chirality tuned by either breaking inplane structure symmetry or changing illumination angle.
Abstract: Abstract Optical metasurfaces with high quality factors (Q-factors) of chiral resonances can boost substantially light-matter interaction for various applications of chiral response in ultrathin, active, and nonlinear metadevices. However, current approaches lack the flexibility to enhance and tune the chirality and Q-factor simultaneously. Here, we suggest a design of chiral metasurface supporting bound state in the continuum (BIC) and demonstrate experimentally chiroptical responses with ultra-high Q-factors and near-perfect circular dichroism (CD = 0.93) at optical frequencies. We employ the symmetry-reduced meta-atoms with high birefringence supporting winding elliptical eigenstate polarizations with opposite helicity. It provides a convenient way for achieving the maximal planar chirality tuned by either breaking in-plane structure symmetry or changing illumination angle. Beyond linear CD, we also achieved strong near-field enhancement CD and near-unitary nonlinear CD in the same planar chiral metasurface design with circular eigen-polarization. Sharply resonant chirality realized in planar metasurfaces promises various practical applications including chiral lasers and chiral nonlinear filters.
43 citations
TL;DR: In this paper , the Möbius carbon nanobelts (MCNBs) with a twist moiety were synthesized and the topological chirality of the MCNB was confirmed using chiral HPLC separation and circular dichroism spectroscopy.
Abstract: Abstract Technologies for the creation of topological carbon nanostructures have greatly advanced synthetic organic chemistry and materials science. Although simple molecular nanocarbons with a belt topology have been constructed, analogous carbon nanobelts with a twist—more specifically, Möbius carbon nanobelts (MCNBs)—have not yet been synthesized owing to their high intrinsic strain. Here we report the synthesis, isolation and characterization of a MCNB. Calculations of strain energies suggest that large MCNBs are synthetically accessible. Designing a macrocyclic precursor with an odd number of repeat units led to a successful synthetic route via Z -selective Wittig reactions and nickel-mediated intramolecular homocoupling reactions, which yielded (25,25)MCNB over 14 steps. NMR spectroscopy and theoretical calculations reveal that the twist moiety of the Möbius band moves quickly around the MCNB molecule in solution. The topological chirality that originates from the Möbius structure was confirmed experimentally using chiral HPLC separation and circular dichroism spectroscopy.
41 citations
TL;DR: A comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials can be found in this article , where the fundamental design principles and bottom-up synthesis strategies are discussed.
Abstract: Abstract Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.
40 citations
TL;DR: The Beta Structure Selection (BeStSel) method is developed, which can handle the spectral diversity of β-structured proteins, and overperforms any available method in accuracy and information content.
Abstract: Abstract Circular dichroism (CD) spectroscopy is widely used to characterize the secondary structure composition of proteins. To derive accurate and detailed structural information from the CD spectra, we have developed the Beta Structure Selection (BeStSel) method (PNAS, 112, E3095), which can handle the spectral diversity of β-structured proteins. The BeStSel webserver provides this method with useful accessories to the community with the main goal to analyze single or multiple protein CD spectra. Uniquely, BeStSel provides information on eight secondary structure components including parallel β-structure and antiparallel β-sheets with three different groups of twist. It overperforms any available method in accuracy and information content, moreover, it is capable of predicting the protein fold down to the topology/homology level of the CATH classification. A new module of the webserver helps to distinguish intrinsically disordered proteins by their CD spectrum. Secondary structure calculation for uploaded PDB files will help the experimental verification of protein MD and in silico modelling using CD spectroscopy. The server also calculates extinction coefficients from the primary sequence for CD users to determine the accurate protein concentrations which is a prerequisite for reliable secondary structure determination. The BeStSel server can be freely accessed at https://bestsel.elte.hu.
38 citations
TL;DR: A comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials can be found in this paper , where the fundamental design principles and bottom-up synthesis strategies are discussed.
Abstract: Abstract Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.
37 citations
TL;DR: The first chiral Au10 nanoclusters stabilized by chiral bis N-heterocyclic carbene (bisNHC) ligands were reported in this paper , where the chiral core adopts a linear edge-shared tetrahedral geometry with a prolate shape.
Abstract: Herein we report the first chiral Au10 nanoclusters stabilized by chiral bis N-heterocyclic carbene (bisNHC) ligands. ESI-MS and single-crystal X-ray crystallography confirmed the molecular formula to be [Au10(bisNHC)4Br2](O2CCF3)2. The chiral Au10 nanocluster adopts a linear edge-shared tetrahedral geometry with a prolate shape. DFT calculations provide insight into the electronic structure, optical absorption, and circular dichroism (CD) characteristics of this unique Au10 nanocluster. CD spectra demonstrate chirality transfer from the chiral bisNHC ligand to the inner Au10 nanocluster core. Examination of ESI-MS and UV-vis spectra show that cluster [Au9(bisNHC)4Br]Br2 is formed initially and then transformed into the Au10 nanocluster in solution.
33 citations
TL;DR: In this article , several γ-cyclodextrin derivatives mono- or di-substituted by pyrenes at the primary rim of CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into g-CD cavities.
Abstract: Abstract: Several γ-cyclodextrin (CD) derivatives mono- or di-substituted by pyrenes at the primary rim of CD were demonstrated to aggregate into nano-strips in aqueous solutions, with the pyrene moieties interpenetrating into g-CD cavities. The hydrophobic complexation-induced aggregation provides a rigid chiral environment for the pyrenes and leads to significant ECD and CPL activities, giving unprecedently high g abs and g lum values up to 4.3 × 10 -2 and 5.3 × 10 - 2 , respectively. The aggregates lead to excimer emission with high quantum yields and show B CPL and B i CPL up to 338. 6 M -1 cm - 1 and 169.3 M -1 cm - 1 , respectively.
30 citations
TL;DR: In this article , a double π-helix based on a cyclooctatetraene-embedded perylene diimide dimer was proposed for chirality with molecular entanglement and high barriers for racemization.
Abstract: Design challenges in the development of circularly polarized luminescence (CPL) materials are focused on balancing the luminescence dissymmetry factor (glum) and photoluminescence quantum yield (ΦPL) by regulating the electric (μ) and magnetic (m) transition dipole moment vectors. Aiming at designing efficient CPL emitters and clarifying the chiroptical variation mechanism, herein, we present a double π-helix based on a cyclooctatetraene-embedded perylene diimide dimer that combines chirality with molecular entanglement and very high barriers for racemization. Through finely regulating the magnitudes of μ and m, the maximal dissymmetry factors |gabs| and |glum| can be boosted to 0.035 and 0.030, respectively, as revealed by circular dichroism (CD) and CPL spectra. The results indicate a 3-fold improvement of g values and a modulated ΦPL from 1a, 4, to 5 by nitrogen heteroannulation at the bay region. The CPL brightness (BCPL) of 5 reaches a recorded value of up to 573.4 M-1 cm-1, among the highest values of chiral small molecules reported so far. This work has provided a comprehensive insight into a new class of chiral materials with high CPL activities, further laying molecular fundamentals for chiral optoelectronics.
30 citations
TL;DR: In this article , the authors adopt a planar nanostructure design to realize all-dielectric perovskite metasurfaces with giant superstructural chirality, and tune the electric and magnetic multipole moments of the resonant chiral metamolecules to obtain large anisotropy factor of 0.49 and circular dichroism of 6350 mdeg.
Abstract: Recent attempts to synthesize hybrid perovskites with large chirality have been hampered by large size mismatch and weak interaction between their structure and the wavelength of light. Here we adopt a planar nanostructure design to overcome these limitations and realize all-dielectric perovskite metasurfaces with giant superstructural chirality. We identify a direct spectral correspondence between the near- and the far- field chirality, and tune the electric and magnetic multipole moments of the resonant chiral metamolecules to obtain large anisotropy factor of 0.49 and circular dichroism of 6350 mdeg. Simulations show that larger area metasurfaces could yield even higher optical activity, approaching the theoretical limits. Our results clearly demonstrate the advantages of nanostructrure engineering for the implementation of perovskite chiral photonic, optoelectronic, and spintronic devices.
TL;DR: Results reveal that magneto-chiral Co(OH)2 NPs exhibit a remarkable ability to quantify ROS levels in living organisms, and could therefore provide new tools for exploring chiral nanomaterials as a potential biosensor to investigate biological events.
Abstract: Biological application of chiral nanoparticles (NPs) has aroused enormous levels of attention over recent years. Here, we synthesized magneto-chiral cobalt hydroxide (Co(OH)2) NPs that exhibited strong chiroptical and unique magnetic properties and applied these NPs to detect and monitor reactive oxygen species (ROS) in living cells and in vivo. Circular dichroism (CD) and magnetic resonance imaging (MRI) signals of the magneto-chiral Co(OH)2 NPs exhibited a wide intracellular ROS detection range from 0.673 to 612.971 pmol/106 cells with corresponding limits of detection (LOD) at 0.087 and 0.179 pmol/106 cells, far below that of currently available probes; the LOD for d-aspartic acid coated Co(OH)2 NPs (d-Co(OH)2 NPs) was 5.7 times lower than that for l-aspartic acid coated Co(OH)2 NPs (l-Co(OH)2 NPs) based on the CD signals. In addition, d-Co(OH)2 NPs also exhibited dynamic ROS monitoring ability. The high levels of selectivity and sensitivity to ROS in complex biological environments can be attributed to the Co2+ oxidation reaction on the surface of the NPs. Furthermore, magneto-chiral Co(OH)2 NPs were able to quantify the levels of ROS in living mice by fluorescence and MRI signals. Collectively, these results reveal that magneto-chiral Co(OH)2 NPs exhibit a remarkable ability to quantify ROS levels in living organisms, and could therefore provide new tools for exploring chiral nanomaterials as a potential biosensor to investigate biological events.
TL;DR: This work provides insights into regulating the optical activity and anisotropic SHG effect of lead-free chiral HMHs and confirms the feasibility of SHG-CD spectroscopy as a promising tool for characterizing the intrinsic optical activity of chiral materials.
Abstract: Structural engineering permits the introduction of chirality into organic-inorganic hybrid metal halides (HMHs), which creates a promising and exclusive material for applications in various optoelectronics. However, the optical activity regulation of chiral HMHs remains largely unexplored. In this work, we have synthesized two pairs of lead-free chiral HMHs with a zero-dimensional tetrahedral arrangement, i.e., (R- and S-1-(1-naphthyl)ethylammonium)2CuCl4 and (R- and S-1-(2-naphthyl)ethylammonium)2CuCl4. The magnitude of optical activity in these HMHs can be efficiently modulated as a result of the different magnetic transition dipole moments. Furthermore, these HMHs exhibited effective second-harmonic generation (SHG) and distinct SHG-circular dichroism (CD), with (R-1-(1-naphthyl)ethylammonium)2CuCl4 having an anisotropy factor (gSHG-CD) of up to 0.41. This work not only provides insights into regulating the optical activity and anisotropic SHG effect of lead-free chiral HMHs but also confirms the feasibility of SHG-CD spectroscopy as a promising tool for characterizing the intrinsic optical activity of chiral materials.
TL;DR: In this paper , the authors employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursor, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan.
Abstract: Carbon dots (CDs) are light-emitting nanoparticles that show great promise for applications in biology and medicine due to the ease of fabrication, biocompatibility, and attractive optical properties. Optical chirality, on the other hand, is an intrinsic feature inherent in many objects in nature, and it can play an important role in the formation of artificial complexes based on CDs that are implemented for enantiomer recognition, site-specific bonding, etc. We employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursors, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan. The resulting CDs consisted of O,N-doped (and also S-doped, in some cases) carbonized cores with surfaces rich in amide and hydroxyl groups; they exhibited high photoluminescence quantum yields reaching 57%, chiral optical signals in the UV and visible spectral regions, and two-photon absorption. Chiral signals of CDs were rather complex and originated from a combination of the chiral precursors attached to the CD surface, hybridization of lower-energy levels of chiral chromophores formed within CDs, and intrinsic chirality of the CD cores. Using DFT analysis, we showed how incorporation of the chiral precursors at the optical centers induced a strong response in their circular dichroism spectra. The optical characteristics of these CDs, which can easily be dispersed in solvents of different polarities, remained stable during pH changes in the environment and after UV exposure for more than 400 min, which opens a wide range of bio-applications.
TL;DR: In this article, the authors investigated the effect of pH-shifting on myofibrillar proteins (MPs) extracted from pale, soft and exudative (PSE)-like chicken.
TL;DR: In this paper, the authors used dielectric barrier discharge (DBD) plasma to modify soy protein isolate (SPI) and investigate the effects of this treatment on the protein's structural and physicochemical properties.
TL;DR: An injectable pH-responsive OE peptide hydrogel as a carrier material for the antitumor drugs gemcitabine (GEM) and paclitaxel (PTX) that can release drugs at the tumor site simultaneously to achieve the antitUMor effect is designed.
Abstract: Conventional antitumor chemotherapeutics generally have shortcomings in terms of dissolubility, selectivity and drug action time, and it has been difficult to achieve high antitumor efficacy with single-drug therapy. At present, combination therapy with two or more drugs is widely used in the treatment of cancer, but a shortcoming is that the drugs do not reach the target at the same time, resulting in a reduction in efficacy. Therefore, it is necessary to design a carrier that can release two drugs at the same site. We designed an injectable pH-responsive OE peptide hydrogel as a carrier material for the antitumor drugs gemcitabine (GEM) and paclitaxel (PTX) that can release drugs at the tumor site simultaneously to achieve the antitumor effect. After determining the optimal gelation concentration of the OE polypeptide, we conducted an in vitro release study to prove its pH sensitivity. The release of PTX from the OE hydrogel in the medium at pH 5.8 and pH 7.4 was 96.90% and 38.98% in 7 days. The release of GEM from the OE hydrogel in media with pH of 5.8 and 7.4 was 99.99% and 99.63% in 3 days. Transmission electron microscopy (TEM) and circular dichroism (CD) experiments were used to observe the microstructure of the peptides. The circular dichroism of OE showed a single negative peak shape when under neutral conditions, indicating a β-folded structure, while under acidic conditions, it presented characteristics of a random coil. Rheological experiments were used to investigate the mechanical strength of this peptide hydrogel. Furthermore, the treatment effect of the drug-loaded peptide hydrogel was demonstrated through in vitro and in vivo experiments. The results show that the peptide hydrogels have different structures at different pH values and are highly sensitive to pH. They can reach the tumor site by injection and are induced by the tumor microenvironment to release antitumor drugs slowly and continuously. This biologically functional material has a promising future in drug delivery for combination drugs.
TL;DR: In this paper , the authors reported the experimental realization of true/intrinsic chiral response with resonant metasurfaces in which the engineered slant geometry breaks both in-plane and out-of-plane symmetries.
Abstract: Photons with spin angular momentum possess intrinsic chirality, which underpins many phenomena including nonlinear optics1, quantum optics2, topological photonics3 and chiroptics4. Intrinsic chirality is weak in natural materials, and recent theoretical proposals5-7 aimed to enlarge circular dichroism by resonant metasurfaces supporting bound states in the continuum that enhance substantially chiral light-matter interactions. Those insightful works resort to three-dimensional sophisticated geometries, which are too challenging to be realized for optical frequencies8. Therefore, most of the experimental attempts9-11 showing strong circular dichroism rely on false/extrinsic chirality by using either oblique incidence9,10 or structural anisotropy11. Here we report on the experimental realization of true/intrinsic chiral response with resonant metasurfaces in which the engineered slant geometry breaks both in-plane and out-of-plane symmetries. Our result marks, to our knowledge, the first observation of intrinsic chiral bound states in the continuum with near-unity circular dichroism of 0.93 and a high quality factor exceeding 2,663 for visible frequencies. Our chiral metasurfaces may lead to a plethora of applications in chiral light sources and detectors, chiral sensing, valleytronics and asymmetric photocatalysis.
TL;DR: In this article , the authors investigated the effect of pH-shifting on myofibrillar proteins (MPs) extracted from pale, soft and exudative (PSE)-like chicken.
TL;DR: In this paper , a single-crystal structure of Rac - Ag 70 was reported, which contains enantiomeric pairs of 70-nuclearity silver clusters with 20 free valence electrons (Ag 70 ), and each of these clusters is a doubly truncated tetrahedron with pseudo-T symmetry.
Abstract: Abstract The origins of the chiroptical activities of inorganic nanostructures have perplexed scientists, and deracemization of high-nuclearity metal nanoclusters (NCs) remains challenging. Here, we report a single-crystal structure of Rac - Ag 70 that contains enantiomeric pairs of 70-nuclearity silver clusters with 20 free valence electrons ( Ag 70 ), and each of these clusters is a doubly truncated tetrahedron with pseudo- T symmetry. A deracemization method using a chiral metal precursor not only stabilizes Ag 70 in solution but also enables monitoring of the gradual enlargement of the electronic circular dichroism (CD) responses and anisotropy factor g abs . The chiral crystals of R/S - Ag 70 in space group P 2 1 containing a pseudo- T -symmetric enantiomeric NC show significant kernel-based and shell-based CD responses. The small symmetry breaking of T d symmetry arising from local distortion of Ag−S motifs and rotation of the apical Ag 3 trigons results in large chiroptical responses. This work opens an avenue to construct chiral medium/large-sized NCs and nanoparticles, which are promising for asymmetric catalysis, nonlinear optics, chiral sensing, and biomedicine.
TL;DR: In this paper , the authors employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursor, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan.
Abstract: Carbon dots (CDs) are light-emitting nanoparticles that show great promise for applications in biology and medicine due to the ease of fabrication, biocompatibility, and attractive optical properties. Optical chirality, on the other hand, is an intrinsic feature inherent in many objects in nature, and it can play an important role in the formation of artificial complexes based on CDs that are implemented for enantiomer recognition, site-specific bonding, etc. We employed a one-step hydrothermal synthesis to produce chiral CDs from the commonly used precursors citric acid and ethylenediamine together with a set of different chiral precursors, namely, L-isomers of cysteine, glutathione, phenylglycine, and tryptophan. The resulting CDs consisted of O,N-doped (and also S-doped, in some cases) carbonized cores with surfaces rich in amide and hydroxyl groups; they exhibited high photoluminescence quantum yields reaching 57%, chiral optical signals in the UV and visible spectral regions, and two-photon absorption. Chiral signals of CDs were rather complex and originated from a combination of the chiral precursors attached to the CD surface, hybridization of lower-energy levels of chiral chromophores formed within CDs, and intrinsic chirality of the CD cores. Using DFT analysis, we showed how incorporation of the chiral precursors at the optical centers induced a strong response in their circular dichroism spectra. The optical characteristics of these CDs, which can easily be dispersed in solvents of different polarities, remained stable during pH changes in the environment and after UV exposure for more than 400 min, which opens a wide range of bio-applications.
TL;DR: In this article, a multi-spectroscopic approach was used to study supramolecular structures (SS) formation upon ovalbumin (OVA) and chitosan (CHS) interaction in HCl solution, at pH 4.0 or 6.0.
TL;DR: In this paper , the authors used dielectric barrier discharge (DBD) plasma and investigated the effects of this treatment on the protein's structural and physicochemical properties, including solubility, water holding capacity, emulsifying activity and emulsion stability, foaming capacity and foam stability, total and reactive sulfhydryl, free carbonyl, FTIR, electrophoretic patterns, as well as protein structures were evaluated.
TL;DR: In this paper , a single-crystal structure of Rac - Ag 70 was reported, which contains enantiomeric pairs of 70-nuclearity silver clusters with 20 free valence electrons (Ag 70 ), and each of these clusters is a doubly truncated tetrahedron with pseudo-T symmetry.
Abstract: Abstract The origins of the chiroptical activities of inorganic nanostructures have perplexed scientists, and deracemization of high-nuclearity metal nanoclusters (NCs) remains challenging. Here, we report a single-crystal structure of Rac - Ag 70 that contains enantiomeric pairs of 70-nuclearity silver clusters with 20 free valence electrons ( Ag 70 ), and each of these clusters is a doubly truncated tetrahedron with pseudo- T symmetry. A deracemization method using a chiral metal precursor not only stabilizes Ag 70 in solution but also enables monitoring of the gradual enlargement of the electronic circular dichroism (CD) responses and anisotropy factor g abs . The chiral crystals of R/S - Ag 70 in space group P 2 1 containing a pseudo- T -symmetric enantiomeric NC show significant kernel-based and shell-based CD responses. The small symmetry breaking of T d symmetry arising from local distortion of Ag−S motifs and rotation of the apical Ag 3 trigons results in large chiroptical responses. This work opens an avenue to construct chiral medium/large-sized NCs and nanoparticles, which are promising for asymmetric catalysis, nonlinear optics, chiral sensing, and biomedicine.
TL;DR: In this article , two quaterrylene bisimides with either one or twofold-twisted π-backbones enabled by the steric congestion of a fourfold bay arylation leading to an end-to-end twist of up to 76° were reported.
Abstract: Graphene nanoribbons (GNRs) have the potential for next-generation functional devices. So far, GNRs with defined stereochemistry are rarely reported in literature and their optical response is usually bound to the ultraviolet or visible spectral region, while covering the near-infrared (NIR) regime is still challenging. Herein, we report two novel quaterrylene bisimides with either one- or twofold-twisted π-backbones enabled by the steric congestion of a fourfold bay arylation leading to an end-to-end twist of up to 76°. The strong interlocking effect of the π-stacked aryl substituents introduces a rigidification of the chromophore unambiguously proven by single-crystal X-ray analysis. This leads to unexpectedly strong NIR emissions at 862 and 903 nm with quantum yields of 1.5 and 0.9%, respectively, further ensuring high solubility as well as resolvable and highly stable atropo-enantiomers. Circular dichroism spectroscopy of these enantiopure chiral compounds reveals a strong Cotton effect Δε of up to 67 M-1 cm-1 centered far in the NIR region at 849 nm.
TL;DR: In this paper , the authors used hard X-rays with spiral Fresnel zone, which can induce an orbital angular momentum (OAM) of light, to probe molecular chirality on disordered samples and showed that the asymmetry ratios for the HD spectra are within one to five percent for OAM beams with topological charges of one and three.
Abstract: Chirality is a structural property of molecules lacking mirror symmetry that has strong implications in diverse fields, ranging from life to materials sciences. Established spectroscopic methods that are sensitive to chirality, such as circular dichroism (CD), exhibit weak signal contributions on an achiral background. Helical dichroism (HD), which is based on the orbital angular momentum (OAM) of light, offers a new approach to probe molecular chirality, but it has never been demonstrated on disordered samples. Furthermore, in the optical domain the challenge lies in the need to transfer the OAM of the photon to an electron that is localized on an {\AA}-size orbital. Here, we overcome this challenge using hard X-rays with spiral Fresnel zone, which can induce an OAM. We present the first HD spectra of a disordered powder sample of enantiopure molecular complexes of [Fe(4,4'-diMebpy)3]2+ at the iron K-edge (7.1 keV) with OAM-carrying beams. The HD spectra exhibit the expected inversions of signs switching from a left to a right helical wave front or from an enantiomer to the other. The asymmetry ratios for the HD spectra are within one to five percent for OAM beams with topological charges of one and three. These results open a new window into the studies of molecular chirality and its interaction with the orbital angular momentum of light.
TL;DR: In this paper , higher-order G-quadruplex structures were obtained by an iterative integrated structural biology approach using quantitative biophysical tools (analytical ultracentrifugation, small-angle X-ray scattering, and circular dichroism spectroscopy) combined with modeling and molecular dynamics simulations.
Abstract: We report on higher-order G-quadruplex structures adopted by long promoter sequences obtained by an iterative integrated structural biology approach. Our approach uses quantitative biophysical tools (analytical ultracentrifugation, small-angle X-ray scattering, and circular dichroism spectroscopy) combined with modeling and molecular dynamics simulations, to derive self-consistent structural models. The formal resolution of our approach is 18 angstroms, but in some cases structural features of only a few nucleotides can be discerned. We report here five structures of long (34-70 nt) wild-type sequences selected from three cancer-related promoters: c-Myc, c-Kit and k-Ras. Each sequence studied has a unique structure. Three sequences form structures with two contiguous, stacked, G-quadruplex units. One longer sequence from c-Myc forms a structure with three contiguous stacked quadruplexes. A longer c-Kit sequence forms a quadruplex-hairpin structure. Each structure exhibits interfacial regions between stacked quadruplexes or novel loop geometries that are possible druggable targets. We also report methodological advances in our integrated structural biology approach, which now includes quantitative CD for counting stacked G-tetrads, DNaseI cleavage for hairpin detection and SAXS model refinement. Our results suggest that higher-order quadruplex assemblies may be a common feature within the genome, rather than simple single quadruplex structures.
TL;DR: A novel self-reporting activated ester-amine reaction that can provide multi-channel visual detection of organic amines that exhibits an outstanding enantioselectivity towards various chiral amines and can be applied to determine enantiomeric composition.
Abstract: Chiral recognition is of pivotal importance not only in living systems but also in estimating the optical purity of enantiomeric drugs and fabricating advanced materials. Herein we report a novel self-reporting activated ester-amine reaction that can provide multi-channel visual detection of organic amines. It relies on the reaction extent dependent cis-transoid to cis-cisoid helical transition of polyphenylacetylene backbone and thus triggered fluorescence. Owing to the high selectivity, this visual process can recognize structurally diverse achiral amines and quantitatively checkout the impurity content. Moreover, it also exhibits an outstanding enantioselectivity towards various chiral amines and can be applied to determine enantiomeric composition. The multiple responses in absorption, circular dichromism, photoluminescence, and circularly polarized luminescence make the helical transition of polymer backbone potential as a novel detection mode for high throughput screening of chiral chemicals.
20 Jul 2022
TL;DR: In this article , the first helicene carbon nano-ohop that integrates a [6]helicene into [7]cycloparaphenylene was presented, which has chiroptical properties and configurational stability typical for higher helicenes.
Abstract: Abstract We present the first helicene carbon nanoohop that integrates a [6]helicene into [7]cycloparaphenylene. The [6]helicene endows the helicene carbon nanohoop with chiroptical properties and configurational stability typical for higher helicenes, while the radially conjugated seven para‐phenylenes largely determine the optoelectronic properties. The structure of the helicene carbon nanoohop was unambiguously characterized by NMR, MS and X‐ray analysis that revealed that it possesses a topology of a Möbius strip in the solid state and in solution. The chirality transfers from the [6]helicene to the para‐phenylenes and leads to a pronounced circular dichroism and bright circularly polarized luminescence, which is affected by the structural topology of the nanohoop.