Pure Chiral Research Articles

An efficient approach toward production of near-zigzag single-chirality carbon nanotubes.

Synthesizing single-walled carbon nanotubes (SWCNTs) with a narrow chirality distribution is essential for obtaining pure chirality materials through postgrowth sorting techniques. Using carbon monoxide chemical vapor deposition, we devise a ruthenium (Ru) catalyst supported by silica for the bulk production of SWCNTs containing only a few (n, m) species. The result is attributed to the limited carbon dissociation on the supported Ru clusters, favoring the growth of only small-diameter SWCNTs at comparable growth rates. The resulting materials expedite high-purity single chirality separation using gel chromatography, leading to unprecedented yields of 3.5% for (9, 1) and 5.2% for (9, 2) nanotubes, which surpass those separated from HiPco SWCNTs by two orders of magnitude. This work sheds light on the large-quantity synthesis of SWCNTs with enriched species beyond near-armchair ones for their high-yield separation.

A wideband low‐profile dual‐circularly polarized reflectarray with decoupled LHCP/RHCP beams

AbstractThis letter presents the design principle and experimental verification of a Ku‐band wideband low‐profile dual‐circularly polarized (dual‐CP) reflectarray (RA) with independent control of left‐/right‐handed circularly polarized (LHCP/RHCP) beams. Both the dynamic phase (DP) and Berry phase (BP) compensating methods are employed in the design of the unit cell, achieving independent LHCP/RHCP phase modulation based on the single‐functional‐layer concept. A single‐layer unit cell is designed, offering a ‐bit dual‐CP phase shift which facilitates the independent control of LHCP/RHCP beams. A prototype with asymmetrical dual‐CP beams is fabricated and tested. For LHCP and RHCP excitation, beam directions of () and () are realized, respectively, with sidelobe levels and cross‐polarizations both under −15 dB. The prototype exhibits a wide axial ratio (AR) bandwidth of over 36% with AR dB. The overlapped 1‐dB gain and AR dB bandwidth is 19.5% under LHCP input and 12.2% under RHCP input, with maximum aperture efficiency of 41.3% and 34.6%, respectively. The proposed dual‐CP RA exhibits broad band, pure chirality, high gain, low profile and independent polarization control, with single‐layer construction which is of low cost and easy processing.

Pure Chiral Polar Vortex Phase in PbTiO3/SrTiO3 Superlattices with Tunable Circular Dichroism.

Nontrivial polarization textures have been demonstrated in ferroelectric/dielectric superlattices, where the electrostatic, elastic, and different gradient energies compete in a delicate balance. When PbTiO3/SrTiO3 superlattices are grown on DyScO3, the coexistence of ferroelectric domains and vortex structure is observed for n = 12-20 unit cells. Here, we report an approach to achieve single-phase vortex structures in superlattices by controlling the epitaxial strain using Sr1.04Al0.12Ga0.35Ta0.50O3 substrates. The domain width follows Kittel's law with the thickness of the ferroelectric PbTiO3 layers. A phase transition from vortex to a disordered phase with temperature is characterized by the correlation length. Resonant soft X-ray diffraction circular dichroism at the titanium L-edge reveals enhanced chirality with the thickness of the ferroelectric layer. These results are supported by second-principles simulations, which demonstrate that the integrated helicity increases with n. The stabilization of chiral single-phase polar vortices in ferroelectric/dielectric superlattices can enable novel optoelectronic devices with enhanced ferroelectric-light interaction.

Anomalous Josephson effect and quantum anomaly in inversion asymmetric Weyl semimetals

We study a Josephson junction involving an inversion-asymmetric Weyl semimetal in presence of time-reversal symmetric (TRS) or time-reversal symmetry broken tilt in the Weyl spectra. We reveal that both types of tilts in the Weyl nodes lead to a Josephson $0$-$\pi$ transition and a zero bias valley/chiral supercurrent. Strikingly, the TRS tilt gives rise to a pure valley Josephson current (VJC) and TRS broken tilt induces a pure chirality Josephson current (CJC) in this system. The VJC and CJC are the manifestation of valley symmetry broken and $\mathbb{Z}_2$ symmetry broken by the respective tilt. We obtain the reversal of a pure VJC and pure CJC even in the zero bias condition controllable by the junction length. Our analysis of controllability of valley and chirality dependent transport in an inversion asymmetric Weyl semimetal junction could allow applications in valleytronics and chiralitytronics, respectively. The tilt induced Josephson effect provides an alternative route for supercurrent $0$-$\pi$ transition, different from the conventional ferromagnetism Josephson junctions where the spin polarization is essential. In the long junction and zero temperature limit, VJC and CJC are associated with a quantum anomaly which is manifested through a discontinuous jump in the current in absence of TRS and TRS breaking tilts, respectively.

(Invited) 20 Years of Carbon Nanotube Evolution

From the advent of individualized carbon nanotubes nearly 20 years ago to the current ability to control their properties at multiple levels, the world of CNTs has changed tremendously. Through the lens of my group’s efforts, I will provide a retrospective on how our understanding of CNTs has changed through this period. An overview will be given of our efforts on Raman and photoluminescence (PL) spectroscopy to identify and characterize fundamental CNT properties. While spectroscopic separation enabled many revelations on CNT photophysics, the limitations imposed by mixed-chirality samples ultimately were overcome with the advent of effective and efficient methods for chirality enrichment. Examples will be given of advances in photophysics established through Raman performed on pure chirality samples. New separations techniques presented new questions on nanotube surface chemistry, ultimately leading to studies of surface chemistry, surface structure, and defects, at the ensemble and single tube levels. Most recently, development of functionalization methods to introduce optically active defect states has opened an exciting new direction in nanotube studies. An overview of the new photophyics and quantum light emission enabled by defects will be given, along with some perspective on future outlook.

Chemical vapor deposition growth of single-walled carbon nanotubes with controlled structures for nanodevice applications.

Single-walled carbon nanotubes (SWNTs), a promising substitute to engineer prospective nanoelectronics, have attracted much attention because of their superb structures and physical properties. The unique properties of SWNTs rely sensitively on their specific chiral structures, including the diameters, chiral angles, and handedness. Furthermore, high-performance and integrated circuits essentially require SWNT samples with well-aligned arrays, of single conductive type and of pure chirality. Although much effort has been devoted to chemical vapor deposition (CVD) growth of SWNTs, their structure control, growth mechanism, and structural characterizations are still the primary obstacles for the fabrication and application of SWNT-based nanodevices. In this Account, we focus on our established CVD growth methodology to fulfill the requirements of nanodevice applications. A rational strategy was successfully exploited to construct complex architectures, selectively enrich semiconducting (s) or metallic (m) SWNTs, and control chirality. First, well-aligned and highly dense SWNT arrays are beneficial for nanodevice integration. For the directed growth mode, anisotropic interactions between the SWNTs and the crystallographic structure of substrate are crucial for their growth orientation. Just as crystals possess various symmetries, SWNTs with controlled geometries have the corresponding turning angles. Their complex architectures come from the synergetic effect of lattice and gas flow directed modes. Especially, the aligned orientations of SWNTs on graphite are chirality-selective, and their chiral angles, handedness, and (n,m) index have been conveniently and accurately determined. Second, UV irradiation and sodium dodecyl sulfate (SDS) washing-off methods have been explored to selectively remove m-SWNTs, leaving only s-SWNT arrays on the surface. Moreover, the UV-assisted technique takes the advantages of low cost and high efficiency and it directly produces a high ratio of s-SWNT arrays. We also designed a smart scotch tape to sort out the s-SWNTs and m-SWNTs from the as-grown mixture with 3-aminopropyl-triethoxysilane and triethoxyphenylsilane as glues, respectively. This is analogous to the mechanical exfoliation of a graphene sheet. Third, the obtained SWNT intramolecular junctions obtained by temperature-mediated CVD indicate that temperature can seriously affect the SWNT's chirality during its growth. Importantly, the cloning method can validate the chirality-controlled growth of SWNTs, and the cloning efficiency is significantly improved on a quartz surface. Well-aligned SWNT arrays with a high density and controlled structures are highly desirable for carbon nanoelectronics. We hope that the advanced methodology used here will promote their controlled preparation and provide insights into the growth mechanism of SWNTs.

Biocatalytic Approaches to the Synthesis of Enantiomerically Pure Chiral Amines

Enantiomerically pure chiral amines are valuable building blocks for the synthesis of pharmaceutical drugs and agrochemicals. Indeed it is estimated that currently 40 % of pharmaceuticals contain a chiral amine component in their structure. Chiral amines are also widely used as resolving agents for diastereomeric salt crystallization. One of the challenges of preparing chiral amines in enantiomerically pure form is the development of cost-effective and sustainable catalytic methods that are able to address the requirement for the entire range of primary, secondary and tertiary amines. In this review we highlight various biocatalytic strategies that have been developed, particularly those based upon asymmetric synthesis or their equivalent therefore (i.e. dynamic kinetic resolution, deracemisation) in which yields and enantiomeric excesses approaching 100 % can be attained. Particular attention is given to the use of monoamine oxidase (MAO-N) from Aspergillus niger which has been engineered by directed evolution to provide a tool-box of variants which can generate enantiomerically pure primary, secondary and tertiary amines. These MAO-N variants are combined with non-selective chemical reducing agents in deracemisation processes.

Colloquium: Homochirality: Symmetry breaking in systems driven far from equilibrium

Subsequent to the discovery of chirality of organic molecules by Pasteur, living organisms have been found to utilize biomolecules of only one handedness. The origin of this homochirality in life still remains unknown. It is believed that homochirality is attained in two stages: the initial creation of a chirality bias and its subsequent amplification to pure chirality. In the last two decades, two novel experiments have established the second stage in different fields: Soai and co-workers achieved the amplification of enantiomeric excess in the production of chiral organic molecules, and Viedma obtained homochirality in the solution growth of sodium chlorate crystals. These experiments are explained by a theory with a nonlinear evolution equation for the chiral order parameter; nonlinear processes in reactions or in crystal growth induce enantiomeric excess amplification, and the recycling of achiral elements ensures homochirality. Recycling drives the system to a state far from equilibrium with a free energy higher than that of the equilibrium state.

Design and Synthesis of Enantiomerically Pure Chiral Sandwichlike Lamellar Structure: New Explorations from Molecular Building Blocks to Three-Dimensional Morphology

This article reports a pair of novel chiral sandwichlike complexes for the first time. In the two complexes, lanthanide Eu3+ ions and Na+ ions are sandwiched between Schiff base ligands, resulting in a two-dimensional plane. For both of the complexes, the intraplane and interplane interactions are utterly different. The adjacent planes are held together by weak van der Waals forces, while the single plane is formed by covalently bonded intraplane N–Eu–O, O–Eu–O, and O–Na–O atoms. On the basis of this characteristic information derived from their molecular building blocks, we studied three-dimensional morphology which has good agreement with expected lamellar morphology. Furthermore, to examine the chiroptical and stable activities, the CD spectra were investigated in the solution of methanol and five different solid forms.

Raman Scattering at Pure Graphene Zigzag Edges

Theory has predicted rich and very distinct physics for graphene devices with boundaries that follow either the armchair or the zigzag crystallographic directions. A prerequisite to disclose this physics in experiment is to be able to produce devices with boundaries of pure chirality. Exfoliated flakes frequently exhibit corners with an odd multiple of 30°, which raised expectations that their boundaries follow pure zigzag and armchair directions. The predicted Raman behavior at such crystallographic edges however failed to confirm pure edge chirality. Here, we perform confocal Raman spectroscopy on hexagonal holes obtained after the anisotropic etching of prepatterned pits using carbothermal decomposition of SiO(2). The boundaries of the hexagonal holes are aligned along the zigzag crystallographic direction and leave hardly any signature in the Raman map indicating unprecedented purity of the edge chirality. This work offers the first opportunity to experimentally confirm the validity of the Raman theory for graphene edges.

ChemInform Abstract: Enzymatic Synthesis of Enantiomerically Pure Chiral Synthons: Lipase- Catalyzed Resolution of (R/S,4D)-2-Methyl-4-hexen-1-ol.

ChemInform Abstract: Enzymatic Synthesis of Enantiomerically Pure Chiral Synthons: Lipase- Catalyzed Resolution of (R/S,4D)-2-Methyl-4-hexen-1-ol.

ChemInform Abstract: The Biocatalytic Approach to the Preparation of Enantiomerically Pure Chiral Building Blocks

ChemInform Abstract: The Biocatalytic Approach to the Preparation of Enantiomerically Pure Chiral Building Blocks

ChemInform Abstract: Optically Pure Chiral Sulfoxides Using Ephedrine as a Chiral Auxiliary.

Abstract Optically pure chiral sulfoxides can be formed in good to excellent yields by sequential displacement reactions of organometallic reagents on the 1,2,3-oxathiazolidine-S-oxide formed from ephedrine and thionyl chloride, a modification of the Wudl and Lee procedure.

Efficient Production of Enantiomerically Pure Chiral Amines at Concentrations of 50 g/L Using Transaminases

Two methods for the efficient (50 g/L) production of optically pure amines from their corresponding ketones using transaminases have been developed. The first method utilizes an ion-exchange resin for in situ product removal allowing the reaction to be carried out a substrate concentration of 50 g/L. The second approach relies upon conversion of the initially formed amine, via spontaneous cyclisation, to a noninhibitory product. Both methods have been demonstrated at 50 mL scale. (R)- and (S)-methylbenzylamine, and (R)- and (S)-6-methyl-2-piperidone have been produced in >90% isolated yield and >99% ee.

Optical Resolution of Chiral Molecules by Stretching Hydrogen-Bonding Helical Polymers

The effect of stretching polymer chains bearing helical segments induced by hydrogen-bonded chiral molecules in the mixtures of chiral molecules is theoretically studied. The end-to-end distance R of a polymer with induced helical sequences and the chiral order parameter ψ (difference in the content of left- and right-handed helices on a chain) are calculated as functions of the external tension given at the chain ends. The chiral order parameter is shown to be sensitive to chain extension and drastically enhanced by stretching. With the slightest enantiomer excess, therefore, a mixture of chiral molecules in a solution can be separated into assemblies of pure chirality by repeating the operation of stretching polymers and washing the adsorbed chiral molecules. The possibility of optical resolution of racemic solutions by stretching polymeric gels consisting of such hydrogen-bonded helical subchains is discussed.

Enantiomerically pure chiral coordination polymers: synthesis, spectroscopy, and electrochemistry in solution and on surfaces.

The two enantiomerically pure bridging ligands (+/-)-[ctpy-x-ctpy] have been prepared employing a two-fold stereospecific alkylation reaction of the enantiomerically pure, chiral terpyridyl-type ligands (+/-)-ctpy. The reaction of each of the enantiomerically pure bridging ligands with Fe(2+) gives rise to chiral coordination polymers whose formation and stoichiometry were followed spectrophotometrically. An assignment of the absolute configuration of the formed helical polymeric structures was carried out on the basis of circular dichroism studies. Highly ordered domains (as determined from STM imaging) of the enantiomerically pure chiral redox polymers could be prepared via the interfacial reaction, over an HOPG substrate, of the bridging ligand in CH(2)Cl(2) and FeSO(4) in water. The degree of polymerization was estimated to be up to 60 from analysis of the STM images of the highly ordered domains on HOPG. The helicality of the domains was compared to the configuration obtained from the circular dichroism studies. The electrochemical properties of the polymers were investigated using cyclic voltammetry and the results compared to those of the respective monomeric complexes. The redox behavior of the iron centers in the polymer was comparable to that of the monomeric complex [Fe((-)-ctpy)(2)](PF(6))(2) as well as to that of [Fe(tpy)(2)](PF(6))(2). The polymeric materials undergo electrodeposition following the two-electron reduction of each bridging ligand unit (one electron per terpyridine group). No ligand-mediated metal-metal interactions were evident from the cyclic voltammetric measurements, suggesting that the metal centers act independently. Moreover, oxidation of the metal centers within the polymeric materials did not give rise to electrodeposition.

M and P double helical complexes of copper(I) with bis-imino bis-quinoline enantiomerically pure chiral ligands.

The enantiomerically pure bis-imino bis-quinoline ligands R,R-ImQ and S,S-ImQ have been prepared by Schiff condensation of 2-quinoline carboxyaldehyde with the pure R,R and S,S enantiomers of trans-1,2-diaminocyclohexane. Both ligands form 2:2 helical complexes with CuI perchlorate, and the crystal and molecular structure of [Cu2(R,R-ImQ)2]ClO4.H2O have been determined by X-ray diffraction methods: the [Cu2(R,R-ImQ)2]2+ molecular cation is a chiral double helix of M handedness, in which the two ligands are entertwined in such an arrangement that half of each ligand is not equivalent to the other half of the same ligand. Coupled circular dichroism and 1H NMR studies reveal that in CH3CN solution a rearrangement takes place toward a more symmetric helical structure (in which the two halves of the same ligand become equivalent), which maintains the same handedness found in the solid state and is a pure M isomer. Solid state and CH3CN solution CD experiments confirm that [Cu2(S,S-ImQ)2]ClO4.H2O, both in solution and in the solid state, is a pure double helix of P handedness, i.e., the enantiomer of the species containing the R,R ligand.

ChemInform Abstract: The First Stable Enantiomerically Pure Chiral N-H Oxaziridines: Synthesis and Reactivity.

ChemInform Abstract: The First Stable Enantiomerically Pure Chiral N-H Oxaziridines: Synthesis and Reactivity.

The first stable enantiomerically pure chiral N-H oxaziridines: synthesis and reactivity

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTThe First Stable Enantiomerically Pure Chiral N−H Oxaziridines: Synthesis and ReactivityPhilip C. Bulman Page, Victor L. Murrell, Corinne Limousin, David D. P. Laffan, Donald Bethell, Alexandra M. Z. Slawin, and Timothy A. D. SmithView Author Information Department of Chemistry, Loughborough University, Loughborough, Leicestershire, LE11 3TU, England, Astra Zeneca Pharmaceuticals, Silk Road Business Park, Macclesfield, Cheshire, SK10 2NA, U.K., Robert Robinson Laboratories, Department of Chemistry, University of Liverpool, Oxford Street, Liverpool L69 3BX, U.K. Cite this: J. Org. Chem. 2000, 65, 13, 4204–4207Publication Date (Web):June 6, 2000Publication History Received8 February 2000Published online6 June 2000Published inissue 1 June 2000https://doi.org/10.1021/jo000176jCopyright © 2000 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2172Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (46 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Anions,Mixtures,Molecular structure,Nitrogen,Oxidation Get e-Alerts

ChemInform Abstract: Enantiomerically Pure Chiral Phenazino‐crown Ethers: Synthesis, Preliminary Circular Dichroism Spectroscopic Studies and Complexes with the Enantiomers of 1‐Arethyl Ammonium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.