Optimization of chiral lattice based metastructures for broadband vibration suppression using genetic algorithms

NASA Astrophysics Data System (ADS)

Abdeljaber, Osama; Avci, Onur; Inman, Daniel J.

2016-05-01

One of the major challenges in civil, mechanical, and aerospace engineering is to develop vibration suppression systems with high efficiency and low cost. Recent studies have shown that high damping performance at broadband frequencies can be achieved by incorporating periodic inserts with tunable dynamic properties as internal resonators in structural systems. Structures featuring these kinds of inserts are referred to as metamaterials inspired structures or metastructures. Chiral lattice inserts exhibit unique characteristics such as frequency bandgaps which can be tuned by varying the parameters that define the lattice topology. Recent analytical and experimental investigations have shown that broadband vibration attenuation can be achieved by including chiral lattices as internal resonators in beam-like structures. However, these studies have suggested that the performance of chiral lattice inserts can be maximized by utilizing an efficient optimization technique to obtain the optimal topology of the inserted lattice. In this study, an automated optimization procedure based on a genetic algorithm is applied to obtain the optimal set of parameters that will result in chiral lattice inserts tuned properly to reduce the global vibration levels of a finite-sized beam. Genetic algorithms are considered in this study due to their capability of dealing with complex and insufficiently understood optimization problems. In the optimization process, the basic parameters that govern the geometry of periodic chiral lattices including the number of circular nodes, the thickness of the ligaments, and the characteristic angle are considered. Additionally, a new set of parameters is introduced to enable the optimization process to explore non-periodic chiral designs. Numerical simulations are carried out to demonstrate the efficiency of the optimization process.

Development of a temperature gradient focusing method for in situ extraterrestrial biomarker analysis.

PubMed

Danger, Grégoire; Ross, David

2008-08-01

Scanning temperature gradient focusing (TGF) is a recently described technique for the simultaneous concentration and separation of charged analytes. It allows for high analyte peak capacities and low LODs in microcolumn electrophoretic separations. In this paper, we present the application of scanning TGF for chiral separations of amino acids. Using a mixture of seven carboxyfluorescein succinimidyl ester-labeled amino acids (including five chiral amino acids) which constitute the Mars7 standard, we show that scanning TGF is a very simple and efficient method for chiral separations. The modulation of TGF separation parameters (temperature window, pressure scan rate, temperature range, and chiral selector concentration) allows optimization of peak efficiencies and analyte resolutions. The use of hydroxypropyl-beta-CD at low concentration (1-5 mmol/L) as a chiral selector, with an appropriate pressure scan rate ( -0.25 Pa/s) and with a low temperature range (3-25 degrees C over 1 cm) provided high resolution between enantiomers (Rs >1.5 for each pair of enantiomers) using a short, 4 cm long capillary. With these new results, the scanning TGF method appears to be a viable method for in situ trace biomarker analysis for future missions to Mars or other solar system bodies.

Application of Δ- and λ-isomerism of octahedral metal complexes for inducing chiral nematic phases.

PubMed

Sato, Hisako; Yamagishi, Akihiko

2009-11-20

The Delta- and Lambda-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(beta-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C(2) symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described.

Application of Δ- and Λ-Isomerism of Octahedral Metal Complexes for Inducing Chiral Nematic Phases

PubMed Central

Sato, Hisako; Yamagishi, Akihiko

2009-01-01

The Δ- and Λ-isomerism of octahedral metal complexes is employed as a source of chirality for inducing chiral nematic phases. By applying a wide range of chiral metal complexes as a dopant, it has been found that tris(β-diketonato)metal(III) complexes exhibit an extremely high value of helical twisting power. The mechanism of induction of the chiral nematic phase is postulated on the basis of a surface chirality model. The strategy for designing an efficient dopant is described, together with the results using a number of examples of Co(III), Cr(III) and Ru(III) complexes with C2 symmetry. The development of photo-responsive dopants to achieve the photo-induced structural change of liquid crystal by use of photo-isomerization of chiral metal complexes is also described. PMID:20057959

Quantum memory and gates using a Λ -type quantum emitter coupled to a chiral waveguide

NASA Astrophysics Data System (ADS)

Li, Tao; Miranowicz, Adam; Hu, Xuedong; Xia, Keyu; Nori, Franco

2018-06-01

By coupling a Λ -type quantum emitter to a chiral waveguide, in which the polarization of a photon is locked to its propagation direction, we propose a controllable photon-emitter interface for quantum networks. We show that this chiral system enables the swap gate and a hybrid-entangling gate between the emitter and a flying single photon. It also allows deterministic storage and retrieval of single-photon states with high fidelities and efficiencies. In short, this chirally coupled emitter-photon interface can be a critical building block toward a large-scale quantum network.

Metal-Ion-Mediated Supramolecular Chirality of l-Phenylalanine Based Hydrogels.

PubMed

Wang, Fang; Feng, Chuan-Liang

2018-05-14

For chiral hydrogels and related applications, one of the critical issues is how to control the chirality of supramolecular systems in an efficient way, including easy operation, efficient transfer of chirality, and so on. Herein, supramolecular chirality of l-phenylalanine based hydrogels can be effectively controlled by using a broad range of metal ions. The degree of twisting (twist pitch) and the diameter of the chiral nanostructures can also be efficiently regulated. These are ascribed to the synergic effect of hydrogen bonding and metal ion coordination. This study may develop a method to design a new class of electronically, optically, and biologically active materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of Ar-BINMOL-Derived Atropisomeric Ligands with Matched Axial and sp(3) Central Chirality for Catalytic Asymmetric Transformations.

PubMed

Xu, Zheng; Xu, Li-Wen

2015-10-01

Recently, academic chemists have renewed their interest in the development of 1,1'-binaphthalene-2,2'-diol (BINOL)-derived chiral ligands. Six years ago, a working hypothesis, that the chirality matching of hybrid chirality on a ligand could probably lead to high levels of stereoselective induction, prompted us to use the axial chirality of BINOL derivatives to generate new stereogenic centers within the same molecule with high stereoselectivity, obtaining as a result sterically favorable ligands for applications in asymmetric catalysis. This Personal Account describes our laboratory's efforts toward the development of a novel class of BINOL-derived atropisomers bearing both axial and sp(3) central chirality, the so-called Ar-BINMOLs, for asymmetric synthesis. Furthermore, on the basis of the successful application of Ar-BINMOLs and their derivatives in asymmetric catalysis, the search for highly efficient and enantioselective processes also compelled us to give special attention to the BINOL-derived multifunctional ligands with multiple stereogenic centers for use in catalytic asymmetric reactions. Copyright © 2015 The Chemical Society of Japan and Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Broadband and chiral binary dielectric meta-holograms.

PubMed

Khorasaninejad, Mohammadreza; Ambrosio, Antonio; Kanhaiya, Pritpal; Capasso, Federico

2016-05-01

Subwavelength structured surfaces, known as meta-surfaces, hold promise for future compact and optically thin devices with versatile functionalities. By revisiting the concept of detour phase, we demonstrate high-efficiency holograms with broadband and chiral imaging functionalities. In our devices, the apertures of binary holograms are replaced by subwavelength structured microgratings. We achieve broadband operation from the visible to the near infrared and efficiency as high as 75% in the 1.0 to 1.4 μm range by compensating for the inherent dispersion of the detour phase with that of the subwavelength structure. In addition, we demonstrate chiral holograms that project different images depending on the handedness of the reference beam by incorporating a geometric phase. Our devices' compactness, lightness, and ability to produce images even at large angles have significant potential for important emerging applications such as wearable optics.

Broadband and chiral binary dielectric meta-holograms

PubMed Central

Khorasaninejad, Mohammadreza; Ambrosio, Antonio; Kanhaiya, Pritpal; Capasso, Federico

2016-01-01

Subwavelength structured surfaces, known as meta-surfaces, hold promise for future compact and optically thin devices with versatile functionalities. By revisiting the concept of detour phase, we demonstrate high-efficiency holograms with broadband and chiral imaging functionalities. In our devices, the apertures of binary holograms are replaced by subwavelength structured microgratings. We achieve broadband operation from the visible to the near infrared and efficiency as high as 75% in the 1.0 to 1.4 μm range by compensating for the inherent dispersion of the detour phase with that of the subwavelength structure. In addition, we demonstrate chiral holograms that project different images depending on the handedness of the reference beam by incorporating a geometric phase. Our devices’ compactness, lightness, and ability to produce images even at large angles have significant potential for important emerging applications such as wearable optics. PMID:27386518

Asymmetric Functional Organozinc Additions to Aldehydes Catalyzed by 1,1′-Bi-2-naphthols (BINOLs)†

PubMed Central

2015-01-01

Conspectus Chiral alcohols are ubiquitous in organic structures. One efficient method to generate chiral alcohols is the catalytic asymmetric addition of a carbon nucleophile to a carbonyl compound since this process produces a C–C bond and a chiral center simultaneously. In comparison with the carbon nucleophiles such as an organolithium or a Grignard reagent, an organozinc reagent possesses the advantages of functional group tolerance and more mild reaction conditions. Catalytic asymmetric reactions of aldehydes with arylzincs, vinylzincs, and alkynylzincs to generate functional chiral alcohols are discussed in this Account. Our laboratory has developed a series of 1,1′-bi-2-naphthol (BINOL)-based chiral catalysts for the asymmetric organozinc addition to aldehydes. It is found that the 3,3′-dianisyl-substituted BINOLs are not only highly enantioselective for the alkylzinc addition to aldehydes, but also highly enantioselective for the diphenylzinc addition to aldehydes. A one-step synthesis has been achieved to incorporate Lewis basic amine groups into the 3,3′-positions of the partially hydrogenated H8BINOL. These H8BINOL–amine compounds have become more generally enantioselective and efficient catalysts for the diphenylzinc addition to aldehydes to produce various types of chiral benzylic alcohols. The application of the H8BINOL–amine catalysts is expanded by using in situ generated diarylzinc reagents from the reaction of aryl iodides with ZnEt2, which still gives high enantioselectivity and good catalytic activity. Such a H8BINOL–amine compound is further found to catalyze the highly enantioselective addition of vinylzincs, in situ generated from the treatment of vinyl iodides with ZnEt2, to aldehydes to give the synthetically very useful chiral allylic alcohols. We have discovered that the unfunctionalized BINOL in combination with ZnEt2 and Ti(OiPr)4 can catalyze the terminal alkyne addition to aldehydes to produce chiral propargylic alcohols of high synthetic utility. The reaction was conducted by first heating an alkyne with ZnEt2 in refluxing toluene to generate an alkynylzinc reagent, which can then add to a broad range of aldehydes at room temperature in the presence of BINOL and Ti(OiPr)4 with high enantioselectivity. It was then found that the addition of a catalytic amount of dicyclohexylamine (Cy2NH) allows the entire process to be conducted at room temperature without the need to generate the alkynylzincs at elevated temperature. This BINOL–ZnEt2–Ti(OiPr)4–Cy2NH catalyst system can be used to catalyze the reaction of structurally diverse alkynes with a broad range of aldehydes at room temperature with high enantioselectivity and good catalytic activity. The work described in this Account demonstrates that BINOL and its derivatives can be used to develop highly enantioselective catalysts for the asymmetric organozinc addition to aldehydes. These processes have allowed the efficient synthesis of many functional chiral alcohols that are useful in organic synthesis. PMID:24738985

Asymmetric functional organozinc additions to aldehydes catalyzed by 1,1'-bi-2-naphthols (BINOLs).

PubMed

Pu, Lin

2014-05-20

Chiral alcohols are ubiquitous in organic structures. One efficient method to generate chiral alcohols is the catalytic asymmetric addition of a carbon nucleophile to a carbonyl compound since this process produces a C-C bond and a chiral center simultaneously. In comparison with the carbon nucleophiles such as an organolithium or a Grignard reagent, an organozinc reagent possesses the advantages of functional group tolerance and more mild reaction conditions. Catalytic asymmetric reactions of aldehydes with arylzincs, vinylzincs, and alkynylzincs to generate functional chiral alcohols are discussed in this Account. Our laboratory has developed a series of 1,1'-bi-2-naphthol (BINOL)-based chiral catalysts for the asymmetric organozinc addition to aldehydes. It is found that the 3,3'-dianisyl-substituted BINOLs are not only highly enantioselective for the alkylzinc addition to aldehydes, but also highly enantioselective for the diphenylzinc addition to aldehydes. A one-step synthesis has been achieved to incorporate Lewis basic amine groups into the 3,3'-positions of the partially hydrogenated H8BINOL. These H8BINOL-amine compounds have become more generally enantioselective and efficient catalysts for the diphenylzinc addition to aldehydes to produce various types of chiral benzylic alcohols. The application of the H8BINOL-amine catalysts is expanded by using in situ generated diarylzinc reagents from the reaction of aryl iodides with ZnEt2, which still gives high enantioselectivity and good catalytic activity. Such a H8BINOL-amine compound is further found to catalyze the highly enantioselective addition of vinylzincs, in situ generated from the treatment of vinyl iodides with ZnEt2, to aldehydes to give the synthetically very useful chiral allylic alcohols. We have discovered that the unfunctionalized BINOL in combination with ZnEt2 and Ti(O(i)Pr)4 can catalyze the terminal alkyne addition to aldehydes to produce chiral propargylic alcohols of high synthetic utility. The reaction was conducted by first heating an alkyne with ZnEt2 in refluxing toluene to generate an alkynylzinc reagent, which can then add to a broad range of aldehydes at room temperature in the presence of BINOL and Ti(O(i)Pr)4 with high enantioselectivity. It was then found that the addition of a catalytic amount of dicyclohexylamine (Cy2NH) allows the entire process to be conducted at room temperature without the need to generate the alkynylzincs at elevated temperature. This BINOL-ZnEt2-Ti(O(i)Pr)4-Cy2NH catalyst system can be used to catalyze the reaction of structurally diverse alkynes with a broad range of aldehydes at room temperature with high enantioselectivity and good catalytic activity. The work described in this Account demonstrates that BINOL and its derivatives can be used to develop highly enantioselective catalysts for the asymmetric organozinc addition to aldehydes. These processes have allowed the efficient synthesis of many functional chiral alcohols that are useful in organic synthesis.

Enantioselective ultra high performance liquid and supercritical fluid chromatography: The race to the shortest chromatogram.

PubMed

Ciogli, Alessia; Ismail, Omar H; Mazzoccanti, Giulia; Villani, Claudio; Gasparrini, Francesco

2018-03-01

The ever-increasing need for enantiomerically pure chiral compounds has greatly expanded the number of enantioselective separation methods available for the precise and accurate measurements of the enantiomeric purity. The introduction of chiral stationary phases for liquid chromatography in the last decades has revolutionized the routine methods to determine enantiomeric purity of chiral drugs, agrochemicals, fragrances, and in general of organic and organometallic compounds. In recent years, additional efforts have been placed on faster, enantioselective analytical methods capable to fulfill the high throughput requirements of modern screening procedures. Efforts in this field, capitalizing on improved chromatographic particle technology and dedicated instrumentation, have led to highly efficient separations that are routinely completed on the seconds time scale. An overview of the recent achievements in the field of ultra-high-resolution chromatography on column packed with chiral stationary phases, both based on sub-2 μm fully porous and sub-3 μm superficially porous particles, will be given, with an emphasis on very recent studies on ultrafast chiral separations. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rational design of cyclopropane-based chiral PHOX ligands for intermolecular asymmetric Heck reaction

PubMed Central

Rubina, Marina; Sherrill, William M; Barkov, Alexey Yu

2014-01-01

Summary A novel class of chiral phosphanyl-oxazoline (PHOX) ligands with a conformationally rigid cyclopropyl backbone was synthesized and tested in the intermolecular asymmetric Heck reaction. Mechanistic modelling and crystallographic studies were used to predict the optimal ligand structure and helped to design a very efficient and highly selective catalytic system. Employment of the optimized ligands in the asymmetric arylation of cyclic olefins allowed for achieving high enantioselectivities and significantly suppressing product isomerization. Factors affecting the selectivity and the rate of the isomerization were identified. It was shown that the nature of this isomerization is different from that demonstrated previously using chiral diphosphine ligands. PMID:25161709

Mirror Symmetry Breaking by Chirality Synchronisation in Liquids and Liquid Crystals of Achiral Molecules.

PubMed

Tschierske, Carsten; Ungar, Goran

2016-01-04

Spontaneous mirror symmetry breaking is an efficient way to obtain homogeneously chiral agents, pharmaceutical ingredients and materials. It is also in the focus of the discussion around the emergence of uniform chirality in biological systems. Tremendous progress has been made by symmetry breaking during crystallisation from supercooled melts or supersaturates solutions and by self-assembly on solid surfaces and in other highly ordered structures. However, recent observations of spontaneous mirror symmetry breaking in liquids and liquid crystals indicate that it is not limited to the well-ordered solid state. Herein, progress in the understanding of a new dynamic mode of symmetry breaking, based on chirality synchronisation of transiently chiral molecules in isotropic liquids and in bicontinuous cubic, columnar, smectic and nematic liquid crystalline phases is discussed. This process leads to spontaneous deracemisation in the liquid state under thermodynamic control, giving rise to long-term stable symmetry-broken fluids, even at high temperatures. These fluids form conglomerates that are capable of extraordinary strong chirality amplification, eventually leading to homochirality and providing a new view on the discussion of emergence of uniform chirality in prebiotic systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoexcitation circular dichroism in chiral molecules

NASA Astrophysics Data System (ADS)

Beaulieu, S.; Comby, A.; Descamps, D.; Fabre, B.; Garcia, G. A.; Géneaux, R.; Harvey, A. G.; Légaré, F.; Mašín, Z.; Nahon, L.; Ordonez, A. F.; Petit, S.; Pons, B.; Mairesse, Y.; Smirnova, O.; Blanchet, V.

2018-05-01

Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.

Dynamic Covalent Chemistry within Biphenyl Scaffolds: Reversible Covalent Bonding, Control of Selectivity, and Chirality Sensing with a Single System.

PubMed

Ni, Cailing; Zha, Daijun; Ye, Hebo; Hai, Yu; Zhou, Yuntao; Anslyn, Eric V; You, Lei

2018-01-26

Axial chirality is a prevalent and important phenomenon in chemistry. Herein we report a combination of dynamic covalent chemistry and axial chirality for the development of a versatile platform for the binding and chirality sensing of multiple classes of mononucleophiles. An equilibrium between an open aldehyde and its cyclic hemiaminal within biphenyl derivatives enabled the dynamic incorporation of a broad range of alcohols, thiols, primary amines, and secondary amines with high efficiency. Selectivity toward different classes of nucleophiles was also achieved by regulating the distinct reactivity of the system with external stimuli. Through induced helicity as a result of central-to-axial chirality transfer, the handedness and ee values of chiral monoalcohol and monoamine analytes were reported by circular dichroism. The strategies introduced herein should find application in many contexts, including assembly, sensing, and labeling. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Construction of quaternary stereocenters: asymmetric α-amination of branched aldehydes catalyzed by monoimide substituted cyclohexane-1,2-diamines.

PubMed

Fu, Ji-Ya; Wang, Qi-Lin; Peng, Lin; Gui, Yong-Yuan; Xu, Xiao-Ying; Wang, Li-Xin

2013-10-01

A highly efficient enantioselective α-amination of branched aldehydes catalyzed by chiral imide monosubstituted 1,2-diamine derivatives was reported to afford the quaternary stereogenic centers in excellent yields (up to 99%) and enantioselectivities (up to 97% ee). Chirality 25:668-672, 2013. © 2013 Wiley Periodicals, Inc. © 2013 Wiley Periodicals, Inc.

Application of Carbon Nanotubes in Chiral and Achiral Separations of Pharmaceuticals, Biologics and Chemicals

PubMed Central

Hemasa, Ayman L.; Maher, William A.; Ghanem, Ashraf

2017-01-01

Carbon nanotubes (CNTs) possess unique mechanical, physical, electrical and absorbability properties coupled with their nanometer dimensional scale that renders them extremely valuable for applications in many fields including nanotechnology and chromatographic separation. The aim of this review is to provide an updated overview about the applications of CNTs in chiral and achiral separations of pharmaceuticals, biologics and chemicals. Chiral single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) have been directly applied for the enantioseparation of pharmaceuticals and biologicals by using them as stationary or pseudostationary phases in chromatographic separation techniques such as high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and gas chromatography (GC). Achiral MWCNTs have been used for achiral separations as efficient sorbent objects in solid-phase extraction techniques of biochemicals and drugs. Achiral SWCNTs have been applied in achiral separation of biological samples. Achiral SWCNTs and MWCNTs have been also successfully used to separate achiral mixtures of pharmaceuticals and chemicals. Collectively, functionalized CNTs have been indirectly applied in separation science by enhancing the enantioseparation of different chiral selectors whereas non-functionalized CNTs have shown efficient capabilities for chiral separations by using techniques such as encapsulation or immobilization in polymer monolithic columns. PMID:28718832

Visualization of Stereoselective Supramolecular Polymers by Chirality-Controlled Energy Transfer.

PubMed

Sarkar, Aritra; Dhiman, Shikha; Chalishazar, Aditya; George, Subi J

2017-10-23

Chirality-driven self-sorting is envisaged to efficiently control functional properties in supramolecular materials. However, the challenge arises because of a lack of analytical methods to directly monitor the enantioselectivity of the resulting supramolecular assemblies. Presented herein are two fluorescent core-substituted naphthalene-diimide-based donor and acceptor molecules with minimal structural mismatch and they comprise strong self-recognizing chiral motifs to determine the self-sorting process. As a consequence, stereoselective supramolecular polymerization with an unprecedented chirality control over energy transfer has been achieved. This chirality-controlled energy transfer has been further exploited as an efficient probe to visualize microscopically the chirality driven self-sorting. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Brønsted acid-catalysed enantioselective construction of axially chiral arylquinazolinones

NASA Astrophysics Data System (ADS)

Wang, Yong-Bin; Zheng, Sheng-Cai; Hu, Yu-Mei; Tan, Bin

2017-05-01

The axially chiral arylquinazolinone acts as a privileged structural scaffold, which is present in a large number of natural products and biologically active compounds as well as in chiral ligands. However, a direct catalytic enantioselective approach to access optically pure arylquinazolinones has been underexplored. Here we show a general and efficient approach to access enantiomerically pure arylquinazolinones in one-pot fashion catalysed by chiral phosphoric acids. A variety of axially chiral arylquinazolinones were obtained in high yields with good to excellent enantioselectivities under mild condition. Furthermore, we disclosed a method for atroposelective synthesis of alkyl-substituted arylquinazolinones involving Brønsted acid-catalysed carbon-carbon bond cleavage strategy. Finally, the asymmetric total synthesis of eupolyphagin bearing a cyclic arylquinazolinone skeleton was accomplished with an overall yield of 32% in six steps by utilizing the aforementioned methodology.

Preliminary kinetic evaluation of an immobilized polysaccharide sub-2μm column using a low dispersion supercritical fluid chromatograph.

PubMed

Berger, Terry A

2017-08-11

The performance of a 3×50mm, 1.6μm d p column with an immobilized polysaccharide stationary phase (ChiralPak IA-U) was evaluated for efficiency, and pressure drop, with respect to flow rate and modifier concentration using supercritical fluid chromatography (SFC). This appears to be the first such report using such a column in SFC. A unique low dispersion (ultra-high performance) SFC was used for the evaluation. The minimum reduced plate height of 2.78, indicates that the maximum efficiency was similar to or better than coated polysaccharide columns. Selectivity was different from ChiralPak AD, with the same chiral selector, as reported by many others. At high flows and high methanol concentrations, pump pressures sometimes approached 600bar. With 5% methanol, pressure vs. flow rate was non-linear suggesting turbulent flow in the connector tubing. The optimum flow rate (F opt ) at 40% methanol was ≈0.8mL/min, where the column efficiency was highest. At 5% methanol, F opt increased to ≈1.6mL/min, but efficiency degraded noticeably. The differences in F opt suggests that the solute diffusion coefficients are a strong function of modifier concentration. Several sub-1min separations, including a 7.5s separation, are presented. Copyright © 2017 Elsevier B.V. All rights reserved.

Enantioselective decarboxylative chlorination of β-ketocarboxylic acids

PubMed Central

Shibatomi, Kazutaka; Kitahara, Kazumasa; Sasaki, Nozomi; Kawasaki, Yohei; Fujisawa, Ikuhide; Iwasa, Seiji

2017-01-01

Stereoselective halogenation is a highly useful organic transformation for multistep syntheses because the resulting chiral organohalides can serve as precursors for various medicinally relevant derivatives. Even though decarboxylative halogenation of aliphatic carboxylic acids is a useful and fundamental synthetic method for the preparation of a variety of organohalides, an enantioselective version of this reaction has not been reported. Here we report a highly enantioselective decarboxylative chlorination of β-ketocarboxylic acids to obtain α-chloroketones under mild organocatalytic conditions. The present method is also applicable for the enantioselective synthesis of tertiary α-chloroketones. The conversions of the resulting α-chloroketones into α-aminoketones and α-thio-substituted ketones via SN2 reactions at the tertiary carbon centres are also demonstrated. These results constitute an efficient approach for the synthesis of chiral organohalides and are expected to enhance the availability of enantiomerically enriched chiral compounds with heteroatom-substituted chiral stereogenic centres. PMID:28580951

Enantioselective decarboxylative chlorination of β-ketocarboxylic acids

NASA Astrophysics Data System (ADS)

Shibatomi, Kazutaka; Kitahara, Kazumasa; Sasaki, Nozomi; Kawasaki, Yohei; Fujisawa, Ikuhide; Iwasa, Seiji

2017-06-01

Stereoselective halogenation is a highly useful organic transformation for multistep syntheses because the resulting chiral organohalides can serve as precursors for various medicinally relevant derivatives. Even though decarboxylative halogenation of aliphatic carboxylic acids is a useful and fundamental synthetic method for the preparation of a variety of organohalides, an enantioselective version of this reaction has not been reported. Here we report a highly enantioselective decarboxylative chlorination of β-ketocarboxylic acids to obtain α-chloroketones under mild organocatalytic conditions. The present method is also applicable for the enantioselective synthesis of tertiary α-chloroketones. The conversions of the resulting α-chloroketones into α-aminoketones and α-thio-substituted ketones via SN2 reactions at the tertiary carbon centres are also demonstrated. These results constitute an efficient approach for the synthesis of chiral organohalides and are expected to enhance the availability of enantiomerically enriched chiral compounds with heteroatom-substituted chiral stereogenic centres.

Immobilized polysaccharide derivatives: chiral packing materials for efficient HPLC resolution.

PubMed

Ikai, Tomoyuki; Yamamoto, Chiyo; Kamigaito, Masami; Okamoto, Yoshio

2007-01-01

Polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography have frequently been used not only to determine the enantiomeric excess of chiral compounds but also to preparatively resolve a wide range of racemates. However, these CPMs can be used with only a limited number of solvents as mobile phases because some organic solvents, such as tetrahydrofuran, chloroform, and so on, dissolve or swell the polysaccharide derivatives coated on a support, e.g., silica gel, and destroy their packed columns. The limitation of mobile phase selection is sometimes a serious problem for the efficient analytical and preparative resolution of enantiomers. This defect can be resolved by the immobilization of the polysaccharide derivatives onto silica gel. Efficient immobilizations have been attained through the radical copolymerization of the polysaccharide derivatives bearing small amounts of polymerizable residues and also through the polycondensation of the polysaccharide derivatives containing a few percent of 3-(triethoxysilyl)propyl residue. (c) 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.

Compound analysis via graph kernels incorporating chirality.

PubMed

Brown, J B; Urata, Takashi; Tamura, Takeyuki; Arai, Midori A; Kawabata, Takeo; Akutsu, Tatsuya

2010-12-01

High accuracy is paramount when predicting biochemical characteristics using Quantitative Structural-Property Relationships (QSPRs). Although existing graph-theoretic kernel methods combined with machine learning techniques are efficient for QSPR model construction, they cannot distinguish topologically identical chiral compounds which often exhibit different biological characteristics. In this paper, we propose a new method that extends the recently developed tree pattern graph kernel to accommodate stereoisomers. We show that Support Vector Regression (SVR) with a chiral graph kernel is useful for target property prediction by demonstrating its application to a set of human vitamin D receptor ligands currently under consideration for their potential anti-cancer effects.

Five chiral Cd(II) complexes with dual chiral components: Effect of positional isomerism, luminescence and SHG response

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Lin, E-mail: lcheng@seu.edu.cn; Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, Southeast University, Nanjing 211189; Wang, Jun

2015-01-15

Five chiral Cd(II) complexes with dual chiral components have been synthesized by using a series of (1R,2R)–N{sup 1},N{sup 2}-bis(pyridinylmethyl)cyclohexane-1,2-diamine ligands with different N-positions of pyridyl rings and Cd(NO{sub 3}){sub 2}. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements confirmed that they are of structural chirality in the bulk samples. The luminescent properties indicated that they may have potential applications as optical materials. The formation of discrete mononuclear and binuclear complexes, and one-dimensional chains may be attributed to positional isomerism of the ligands. - Graphical abstract: Five chiral Cd(II) complexes with dual chiral components have been synthesized bymore » using a series of chiral ligands with different N-positions of pyridyl rings. - Highlights: • Five chiral Cd(II) complexes with dual chiral components have been synthesized. • CD spectra and SHG efficiency of the bulk samples have been measured. • The complexes display luminescent properties.« less

Highly enantioselective asymmetric direct aldol reaction promoted by aziridine amides constructed on chiral terpene scaffold.

PubMed

Wujkowska, Zuzanna; Strojewska, Aleksandra; Pieczonka, Adam M; Leśniak, Stanisław; Rachwalski, Michał

2017-05-01

Optically pure, diastereomeric aziridine amides built on the chiral skeletons of camphor, fenchone, and menthone have proven to be highly efficient ligands for enantioselective asymmetric direct aldol reaction in the presence of water and zinc triflate. Desired products were formed in moderate to high chemical yields (up to 95%) and with enantiomeric excess up to 99%. The influence of the stereogenic centers located at the aziridine subunit on the stereochemical course of the reaction is discussed. © 2017 Wiley Periodicals, Inc.

Bioinspired Mesoporous Chiral Nematic Graphitic Carbon Nitride Photocatalysts modulated by Polarized Light.

PubMed

Lin, Wensheng; Hong, Wei; Sun, Lu; Yu, Di; Yu, Dingshan; Chen, Xudong

2018-01-10

Endowing materials with chirality and exploring the responses of the material under circularly polarized light (CPL) can enable further insight into the physical and chemical properties of the semiconductors to be gained, thus expanding on optoelectronic applications. Herein a bioinspired mesoporous chiral nematic graphitic carbon nitride (g-C 3 N 4 ) for efficient hydrogen evolution with polarized light modulation based on chiral nematic cellulose nanocrystal films prepared through silica templating is described. The mesoporous nematic chiral g-C 3 N 4 exhibits an ultrahigh hydrogen evolution rate of 219.9 μmol h -1 (for 20 mg catalyst), corresponding to a high enhancement factor of 55 when compared to the bulk g-C 3 N 4 under λ>420 nm irradiation. Furthermore, the chiral g-C 3 N 4 material exhibits unique photocatalytic activity modulated by CPL within the absorption region. This CPL-assisted photocatalytic regulation strategy holds great promise for a wide range of applications including optical devices, asymmetric photocatalysis, and chiral recognition/separation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-catalyzed asymmetric hydrogenation of tetrasubstituted β-acetoxy-α-enamido esters and efficient synthesis of droxidopa.

PubMed

Guan, Yu-Qing; Gao, Min; Deng, Xu; Lv, Hui; Zhang, Xumu

2017-07-18

A rhodium-catalyzed asymmetric hydrogenation of challenging tetrasubstituted β-acetoxy-α-enamido esters was developed, giving chiral β-acetoxy-α-amido esters in high yields with excellent enantioselectivities (up to >99% ee). The products could be easily transformed to β-hydroxy-α-amino acid derivatives which are valuable chiral building blocks and a novel route for the synthesis of droxidopa was also developed.

A relativistic neutron fireball from a supernova explosion as a possible source of chiral influence.

PubMed

Gusev, G A; Saito, T; Tsarev, V A; Uryson, A V

2007-06-01

We elaborate on a previously proposed idea that polarized electrons produced from neutrons, released in a supernova (SN) explosion, can cause chiral dissymmetry of molecules in interstellar gas-dust clouds. A specific physical mechanism of a relativistic neutron fireball with Lorentz factor of the order of 100 is assumed for propelling a great number of free neutrons outside the dense SN shell. A relativistic chiral electron-proton plasma, produced from neutron decays, is slowed down owing to collective effects in the interstellar plasma. As collective effects do not involve the particle spin, the electrons can carry their helicities to the cloud. The estimates show high chiral efficiency of such electrons. In addition to this mechanism, production of circularly polarized ultraviolet photons through polarized-electron bremsstrahlung at an early stage of the fireball evolution is considered. It is shown that these photons can escape from the fireball plasma. However, for an average density of neutrals in the interstellar medium of the order of 0.2 cm(-3) and at distances of the order of 10 pc from the SN, these photons will be absorbed with a factor of about 10(-7) due to the photoeffect. In this case, their chiral efficiency will be about five orders of magnitude less than that for polarized electrons.

Catalytic enantioselective addition of Grignard reagents to aromatic silyl ketimines

NASA Astrophysics Data System (ADS)

Rong, Jiawei; Collados, Juan F.; Ortiz, Pablo; Jumde, Ravindra P.; Otten, Edwin; Harutyunyan, Syuzanna R.

2016-12-01

α-Chiral amines are of significant importance in medicinal chemistry, asymmetric synthesis and material science, but methods for their efficient synthesis are scarce. In particular, the synthesis of α-chiral amines with the challenging tetrasubstituted carbon stereocentre is a long-standing problem and catalytic asymmetric additions of organometallic reagents to ketimines that would give direct access to these molecules are underdeveloped. Here we report a highly enantioselective catalytic synthesis of N-sulfonyl protected α-chiral silyl amines via the addition of inexpensive, easy to handle and readily available Grignard reagents to silyl ketimines. The key to this success was our ability to suppress any unselective background addition reactions and side reduction pathway, through the identification of an inexpensive, chiral Cu-complex as the catalytically active structure.

Readily Available Chiral Benzimidazoles-Derived Guanidines as Organocatalysts in the Asymmetric α-Amination of 1,3-Dicarbonyl Compounds.

PubMed

Benavent, Llorenç; Puccetti, Francesco; Baeza, Alejandro; Gómez-Martínez, Melania

2017-08-11

The synthesis and the evaluation as organocatalysts of new chiral guanidines derived from benzimidazoles in the enantioselective α-amination of 1,3-dicarbonyl compounds using di- t -butylazodicarboxylate as aminating agent is herein disclosed. The catalysts are readily synthesized through the reaction of 2-chlorobezimidazole and a chiral amine in moderate-to-good yields. Among all of them, those derived from ( R )-1-phenylethan-1-amine ( 1 ) and ( S )-1-(2-naphthyl)ethan-1-amine ( 3 ) turned out to be the most efficient for such asymmetric transformation, rendering good-to-high yields and moderate-to-good enantioselectivities for the amination products.

Relative quantification of enantiomers of chiral amines by high-throughput LC-ESI-MS/MS using isotopic variants of light and heavy L-pyroglutamic acids as the derivatization reagents.

PubMed

Mochizuki, Toshiki; Taniguchi, Sayuri; Tsutsui, Haruhito; Min, Jun Zhe; Inoue, Koichi; Todoroki, Kenichiro; Toyo'oka, Toshimasa

2013-04-22

L-Pyroglutamic acid (L-PGA) was evaluated as a chiral labeling reagent for the enantioseparation of chiral amines in terms of separation efficiency by reversed-phase chromatography and detection sensitivity by ESI-MS/MS. Several amines and amino acid methyl esters were used as typical representatives of the chiral amines. Both enantiomers of the chiral amines were easily labeled with L-PGAS at room temperature for 60 min in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and 1-hydroxy-1H-benzotriazole as the activation reagents. The resulting diastereomers were completely separated by reversed-phase chromatography using the small particle (1.7 μm) ODS column (Rs=1.6-6.8). A highly sensitive detection at a low-fmol level (1-4 fmol) was also obtained from the multiple reaction monitoring (MRM) chromatograms. Therefore, a high-throughput determination was achieved by the present UPLC-ESI-MS/MS method. An isotope labeling strategy using light and heavy L-PGAs for the differential analysis of chiral amines in different sample groups was also proposed in this paper. As a model study, the differential analysis of the R and S ratio of 1-phenylethylamine (PEA) was performed according to the proposed procedure using light and heavy reagents, i.e., L-PGA and L-PGA-d5. The R/S ratio of PEA, spiked at the different concentrations in rat plasma, was almost similar to the theoretical values. Consequently, the proposed strategy using light and heavy chiral labeling reagents seems to be applicable for the differential analysis of chiral amine enantiomers in different sample groups, such as healthy persons and disease patients. Copyright © 2013 Elsevier B.V. All rights reserved.

Significant Enhancement of the Chiral Correlation Length in Nematic Liquid Crystals by Gold Nanoparticle Surfaces Featuring Axially Chiral Binaphthyl Ligands.

PubMed

Mori, Taizo; Sharma, Anshul; Hegmann, Torsten

2016-01-26

Chirality is a fundamental scientific concept best described by the absence of mirror symmetry and the inability to superimpose an object onto its mirror image by translation and rotation. Chirality is expressed at almost all molecular levels, from single molecules to supramolecular systems, and present virtually everywhere in nature. Here, to explore how chirality propagates from a chiral nanoscale surface, we study gold nanoparticles functionalized with axially chiral binaphthyl molecules. In particular, we synthesized three enantiomeric pairs of chiral ligand-capped gold nanoparticles differing in size, curvature, and ligand density to tune the chirality transfer from nanoscale solid surfaces to a bulk anisotropic liquid crystal medium. Ultimately, we are examining how far the chirality from a nanoparticle surface reaches into a bulk material. Circular dichroism spectra of the gold nanoparticles decorated with binaphthyl thiols confirmed that the binaphthyl moieties form a cisoid conformation in isotropic organic solvents. In the chiral nematic liquid crystal phase, induced by dispersing the gold nanoparticles into an achiral anisotropic nematic liquid crystal solvent, the binaphthyl moieties on the nanoparticle surface form a transoid conformation as determined by imaging the helical twist direction of the induced cholesteric phase. This suggests that the ligand density on the nanoscale metal surfaces provides a dynamic space to alter and adjust the helicity of binaphthyl derivatives in response to the ordering of the surrounding medium. The helical pitch values of the induced chiral nematic phase were determined, and the helical twisting power (HTP) of the chiral gold nanoparticles calculated to elucidate the chirality transfer efficiency of the binaphthyl ligand capped gold nanoparticles. Remarkably, the HTP increases with increasing diameter of the particles, that is, the efficiency of the chirality transfer of the binaphthyl units bound to the nanoparticle surface is diminished as the size of the particle is reduced. However, in comparison to the free ligands, per chiral molecule all tested gold nanoparticles induce helical distortions in a 10- to 50-fold larger number of liquid crystal host molecules surrounding each particle, indicating a significantly enhanced chiral correlation length. We propose that both the helicity and the chirality transfer efficiency of axially chiral binaphthyl derivatives can be controlled at metal nanoparticle surfaces by adjusting the particle size and curvature as well as the number and density of the chiral ligands to ultimately measure and tune the chiral correlation length.

Enantio-Relay Catalysis Constructs Chiral Biaryl Alcohols over Cascade Suzuki Cross-Coupling-Asymmetric Transfer Hydrogenation

NASA Astrophysics Data System (ADS)

Zhang, Dacheng; Gao, Xiaoshuang; Cheng, Tanyu; Liu, Guohua

2014-05-01

The construction of chiral biaryl alcohols using enantio-relay catalysis is a particularly attractive synthetic method in organic synthesis. However, overcoming the intrinsic incompatibility of distinct organometallic complexes and the reaction conditions used are significant challenges in asymmetric catalysis. To overcome these barriers, we have taken advantage of an enantio-relay catalysis strategy and a combined dual-immobilization approach. We report the use of an imidazolium-based organopalladium-functionalized organic-inorganic hybrid silica and ethylene-coated chiral organoruthenium-functionalized magnetic nanoparticles to catalyze a cascade Suzuki cross-coupling-asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols in a two-step, one-pot process. As expected, the site-isolated active species, salient imidazolium phase-transfer character and high ethylene-coated hydrophobicity can synergistically boost the catalytic performance. Furthermore, enantio-relay catalysis has the potential to efficiently prepare a variety of chiral biaryl alcohols. Our synthetic strategy is a general method that shows the potential of developing enantio-relay catalysis towards environmentally benign and sustainable organic synthesis.

Controlled synthesis and chiral recognition of immobilized cellulose and amylose tris(cyclohexylcarbamate)s/3-(triethoxysilyl)propylcarbamates as chiral packing materials for high-performance liquid chromatography.

PubMed

Shen, Jun; Liu, Shuangyan; Li, Pengfei; Shen, Xiande; Okamoto, Yoshio

2012-07-13

The cyclohexylcarbamates of cellulose and amylose bearing a controlled amount of 3-(triethoxysilyl)propyl residue were synthesized by a one-pot process and efficiently immobilized onto silica gel through the intermolecular polycondensation of triethoxysilyl group. Their chiral recognition abilities were evaluated as chiral packing materials (CPMs) for high-performance liquid chromatography (HPLC). The immobilized CPMs exhibited comparable or higher recognition abilities than the conventional coated-type CPMs. The universal solvent compatibility of the immobilized CPMs clearly contributes to the improvement of chiral recognition for most racemates used in the present study. Interestingly, a significantly improved resolution for racemic trans-stilbene oxide (α=2.23) could be attained on the immobilized CPM using the eluent containing 30 vol.% chloroform in hexane, which cannot be used for the conventional coated-type CPMs. On the CPMs, almost no resolution of trans-stilbene oxide was attained by a typical eluent, hexane-2-propanol mixture (90/10, v/v). The novel immobilized CPM can also be used in thin-layer chromatography (TLC) due to the absence of an aromatic group. Copyright © 2012 Elsevier B.V. All rights reserved.

An excellent fluorescent dye with a twistable aromatic chain and its axially chiral crystals.

PubMed

Ma, Yan; Hao, Rui; Shao, Guangsheng; Wang, Yuan

2009-04-30

A new organic fluorescent dye, 2,4-dichloro-6-[p-(N,N-diethylamino)biphenylyl]-1,3,5-triazine (DBQ), with an electron withdrawing-donating pair bridged by a twistable aromatic chain has been synthesized. DBQ exhibits high fluorescence quantum yields (0.96 in hexane and 0.71 in THF), high extinction coefficients, and an excitation window extending up to approximately 480 nm. Due to the strong intramolecular charge transfer character, DBQ shows obviously solvent-dependent Stokes shifts with a value as high as 6360 cm(-1) in THF and controllable fluorescence emission in the visible region from "blue" to "orange". The axially chiral structures of DBQ crystals were clearly revealed by the X-ray analyses and CD spectroscopy measurements. Two enantiomers of DBQ were obtained by spontaneous resolution upon crystallization without any chiral auxiliary. The low rotation barriers around the interannular bonds in DBQ molecules resulted in an efficient and selective multiplication of each of the chiral structures when DBQ crystallized in THF at room temperature in the presence of an enantiopure crystal seed, leaving racemized DBQ molecules in the solution. The special crystalline properties of DBQ provided a new approach to the design and synthesis of organic chiral crystals. The photophysical properties of DBQ make it promising in the preparation of new fluorescent probes with high sensitivity.

Construction of a hydrazone-linked chiral covalent organic framework-silica composite as the stationary phase for high performance liquid chromatography.

PubMed

Zhang, Kai; Cai, Song-Liang; Yan, Yi-Lun; He, Zi-Hao; Lin, Hui-Mei; Huang, Xiao-Ling; Zheng, Sheng-Run; Fan, Jun; Zhang, Wei-Guang

2017-10-13

Covalent organic frameworks (COFs), as an emerging class of crystalline porous organic polymers, have great potential for applications in chromatographic separation owning to their fascinating crystalline structures and outstanding properties. However, development of COF materials as novel stationary phases in high performance liquid chromatography (HPLC) is just in its infancy. Herein, we report the design and construction of a new hydrazone-linked chiral COF, termed BtaMth COF, from a chiral hydrazide building block (Mth) and present a one-pot synthetic method for the fabrication of BtaMth@SiO 2 composite for HPLC separation of isomers. The as-synthesized BtaMth chiral COF displays good crystallinity, high porosity, as well as excellent chemical stability. Meanwhile, the fabricated HPLC column by using BtaMth@SiO 2 composite as the new stationary phase exhibits high resolution performances for the separation of positional isomers including nitrotoluene and nitrochlorobenzene, as well as cis-trans isomers including beta-cypermethrin and metconazole. Additionally, some effects such as the composition of the mobile phase and column temperature for HPLC separations on the BtaMth@SiO 2 packed column also have been studied in detail. The successful applications indicate the great potentials of hydrazone-linked chiral COF-silica composite as novel stationary phase for the efficient HPLC separation. Copyright © 2017 Elsevier B.V. All rights reserved.

Design and Stereoselective Preparation of a New Class of Chiral Olefin Metathesis Catalysts and Application to Enantioselective Synthesis of Quebrachamine: Catalyst Development Inspired by Natural Product Synthesis

PubMed Central

Sattely, Elizabeth S.; Meek, Simon J.; Malcolmson, Steven J.; Schrock, Richard R.; Hoveyda, Amir H.

2010-01-01

A total synthesis of the Aspidosperma alkaloid quebrachamine in racemic form is first described. A key catalytic ring-closing metathesis of an achiral triene is used to establish the all-carbon quaternary stereogenic center and the tetracyclic structure of the natural product; the catalytic transformation proceeds with reasonable efficiency through the use of existing achiral Ru or Mo catalysts. Ru- or Mo-based chiral olefin metathesis catalysts have proven to be inefficient and entirely nonselective in cases where the desired product is observed. In the present study, the synthesis route thus serves as a platform for the discovery of new olefin metathesis catalysts that allow for efficient completion of an enantioselective synthesis of quebrachamine. Accordingly, on the basis of mechanistic principles, stereogenic-at-Mo complexes bearing only monodentate ligands have been designed. The new catalysts provide significantly higher levels of activity than observed with the previously reported Ru- or Mo-based complexes. Enantiomerically enriched chiral alkylidenes are generated through diastereoselective reactions involving achiral Mo-based bispyrrolides and enantiomerically pure silyl-protected binaphthols. Such chiral catalysts initiate the key enantioselective ring-closing metathesis step in the total synthesis of quebrachamine efficiently (1 mol % loading, 22 °C, 1 h, >98% conversion, 84% yield) and with high selectivity (98:2 er, 96% ee). PMID:19113867

D-Glucosamine as a novel chiral auxiliary for the stereoselective synthesis of P-stereogenic phosphine oxides.

PubMed

D'Onofrio, A; Copey, L; Jean-Gérard, L; Goux-Henry, C; Pilet, G; Andrioletti, B; Framery, E

2015-09-14

D-Glucosamine was successfully employed as a chiral auxiliary for the enantioselective synthesis of phosphine oxides. The influence of the anomeric position was also investigated and revealed the excellent ability of the α-anomer to perform this transformation in a highly selective fashion. The methodology employed consisted of three steps: diastereoselective formation of the oxazaphospholidine followed by subsequent selective cleavage of P-N and P-O bonds by reaction with two Grignard reagents. P-epimers oxazaphospholidines were prepared switching from a P(v) to a P(III) precursor, thus allowing for the synthesis of enantiomeric phosphine oxides. In addition, the chiral auxiliary could be recovered and efficiently recycled.

Catalytic Enantioselective and Diastereoselective Allylic Alkylation with Fluoroenolates: Efficient Access to C3-Fluorinated and All-Carbon Quaternary Oxindoles

PubMed Central

Balaraman, Kaluvu; Wolf, Christian

2017-01-01

Synthetically versatile 3,3-disubstituted fluorooxindoles exhibiting vicinal chirality centers were obtained in high yields and with excellent enantio-, diastereo- and regioselectivity by catalytic asymmetric fluoroenolate alkylation with allylic acetates. The reaction proceeds under mild conditions and can be upscaled without compromising the asymmetric induction. The unique synthetic usefulness of the products is highlighted with the incorporation of additional functionalities and the formation of 3-fluorinated oxindoles exhibiting an array of four adjacent chirality centers. A new C-F bond functionalization path that provides unprecedented means for stereoselective generation of a chiral quaternary carbon center in the alkaloid scaffold is introduced. PMID:28026079

Recent progress of chiral stationary phases for separation of enantiomers in gas chromatography.

PubMed

Xie, Sheng-Ming; Yuan, Li-Ming

2017-01-01

Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal-organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Separation mechanism of chiral impurities, ephedrine and pseudoephedrine, found in amphetamine-type substances using achiral modifiers in the gas phase.

PubMed

Holness, Howard K; Jamal, Adeel; Mebel, Alexander; Almirall, José R

2012-11-01

A new mechanism is proposed that describes the gas-phase separation of chiral molecules found in amphetamine-type substances (ATS) by the use of high-resolution ion mobility spectrometry (IMS). Straight-chain achiral alcohols of increasing carbon chain length, from methanol to n-octanol, are used as drift gas modifiers in IMS to highlight the mechanism proposed for gas-phase separations of these chiral molecules. The results suggest the possibility of using these achiral modifiers to separate the chiral molecules (R,S) and (S,R)-ephedrine and (S,S) and (R,R)-pseudoephedrine which contain an internal hydroxyl group at the first chiral center and an amino group at the other chiral center. Ionization was achieved with an electrospray source, the ions were introduced into an IMS with a resolving power of 80, and the resulting ion clusters were characterized with a coupled quadrupole mass spectrometer detector. A complementary computational study conducted at the density functional B3LYP/6-31g level of theory for the electronic structure of the analyte-modifier clusters was also performed, and showed either "bridged" or "independent" binding. The combined experimental and simulation data support the proposed mechanism for gas-phase chiral separations using achiral modifiers in the gas phase, thus enhancing the potential to conduct fast chiral separations with relative ease and efficiency.

Synthesis of cellulose-2,3-bis(3,5-dimethylphenylcarbamate) in an ionic liquid and its chiral separation efficiency as stationary phase.

PubMed

Liu, Runqiang; Zhang, Yijun; Bai, Lianyang; Huang, Mingxian; Chen, Jun; Zhang, Yuping

2014-04-11

A chiral selector of cellulose-2,3-bis(3,5-dimethylphenylcarbamate) (CBDMPC) was synthesized by reacting 3,5-dimethylphenyl isocyanate with microcrystalline cellulose dissolved in an ionic liquid of 1-allyl-3-methyl-imidazolium chloride (AMIMCl). The obtained chiral selector was effectively characterized by infrared spectroscopy, elemental analysis and 1H NMR. The selector was reacted with 3-aminopropylsilanized silica gel and the CBDMPC bonded chiral stationary phase (CSP) was obtained. Chromatographic evaluation of the prepared CSPs was conducted by high performance liquid chromatographic (HPLC) and baseline separation of three typical fungicides including hexaconazole, metalaxyl and myclobutanil was achieved using n-hexane/isopropanol as the mobile phase with a flow rate 1.0 mL/min. Experimental results also showed that AMIMCl could be recycled easily and reused in the preparation of CSPs as an effective reaction media.

Synthesis of Cellulose-2,3-bis(3,5-dimethylphenylcarbamate) in an Ionic Liquid and Its Chiral Separation Efficiency as Stationary Phase

PubMed Central

Liu, Runqiang; Zhang, Yijun; Bai, Lianyang; Huang, Mingxian; Chen, Jun; Zhang, Yuping

2014-01-01

A chiral selector of cellulose-2,3-bis(3,5-dimethylphenylcarbamate) (CBDMPC) was synthesized by reacting 3,5-dimethylphenyl isocyanate with microcrystalline cellulose dissolved in an ionic liquid of 1-allyl-3-methyl-imidazolium chloride (AMIMCl). The obtained chiral selector was effectively characterized by infrared spectroscopy, elemental analysis and 1H NMR. The selector was reacted with 3-aminopropylsilanized silica gel and the CBDMPC bonded chiral stationary phase (CSP) was obtained. Chromatographic evaluation of the prepared CSPs was conducted by high performance liquid chromatographic (HPLC) and baseline separation of three typical fungicides including hexaconazole, metalaxyl and myclobutanil was achieved using n-hexane/isopropanol as the mobile phase with a flow rate 1.0 mL/min. Experimental results also showed that AMIMCl could be recycled easily and reused in the preparation of CSPs as an effective reaction media. PMID:24733066

Asymmetric synthesis of diacceptor cyclopropylphosphonates catalyzed by chiral Ru(II)-Pheox complexes

NASA Astrophysics Data System (ADS)

Chi, Le Thi Loan; Chanthamath, Soda; Shibatomi, Kazutaka; Iwasa, Seiji

2018-04-01

The first Ru(II)-catalyzed asymmetric cyclopropanation of diacceptor diazophosphonates with olefins is reported. The Ru(II)-Pheox complex 7e was found to be an efficient catalyst for the asymmetric cyclopropanation of α-cyano diazophosp honate with styrene under mild conditions to give the corresponding chiral diacceptor cyclopropylphosphonate products in high yields (up to 99%) with excellent diastereoselectivities (up to 99/1 dr). However, the enantioselectivity was difficult to control by the C1-symmetric catalyst (up to 68% ee).

Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature.

PubMed

Liao, Wei-Chun; Liao, Shu-Wei; Chen, Kuo-Ju; Hsiao, Yu-Hao; Chang, Shu-Wei; Kuo, Hao-Chung; Shih, Min-Hsiung

2016-05-25

Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and -1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations.

Gold-catalyzed and N-iodosuccinimide-mediated cyclization of gamma-substituted allenamides.

PubMed

Hyland, Christopher J T; Hegedus, Louis S

2006-10-27

Chiral gamma-substituted allenamides have been shown to undergo efficient gold-catalyzed and N-iodosuccinimide-mediated cyclization to highly functionalized dihydrofurans. These reactions proceed rapidly and without loss of stereochemistry.

Asymmetric photoredox transition-metal catalysis activated by visible light.

PubMed

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-06

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules.

Asymmetric photoredox transition-metal catalysis activated by visible light

NASA Astrophysics Data System (ADS)

Huo, Haohua; Shen, Xiaodong; Wang, Chuanyong; Zhang, Lilu; Röse, Philipp; Chen, Liang-An; Harms, Klaus; Marsch, Michael; Hilt, Gerhard; Meggers, Eric

2014-11-01

Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the `green' synthesis of non-racemic chiral molecules.

Highly Efficient Chirality Transfer from Diamines Encapsulated within a Self-Assembled Calixarene-Salen Host.

PubMed

Martínez-Rodríguez, Luis; Bandeira, Nuno A G; Bo, Carles; Kleij, Arjan W

2015-05-04

A calix[4]arene host equipped with two bis-[Zn(salphen)] complexes self-assembles into a capsular complex in the presence of a chiral diamine guest with an unexpected 2:1 ratio between the host and the guest. Effective chirality transfer from the diamine to the calix-salen hybrid host is observed by circular dichroism (CD) spectroscopy, and a high stability constant K2,1 of 1.59×10(11)  M(-2) for the assembled host-guest ensemble has been determined with a substantial cooperativity factor α of 6.4. Density functional calculations are used to investigate the origin of the stability of the host-guest system and the experimental CD spectrum compared with those calculated for both possible diastereoisomers showing that the M,M isomer is the one that is preferentially formed. The current system holds promise for the chirality determination of diamines, as evidenced by the investigated substrate scope and the linear relationship between the ee of the diamine and the amplitude of the observed Cotton effects. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures

PubMed Central

Tian, Xiaorui; Fang, Yurui; Sun, Mengtao

2015-01-01

Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule. PMID:26621558

Computationally Aided Absolute Stereochemical Determination of Enantioenriched Amines.

PubMed

Zhang, Jun; Gholami, Hadi; Ding, Xinliang; Chun, Minji; Vasileiou, Chrysoula; Nehira, Tatsuo; Borhan, Babak

2017-03-17

A simple and efficient protocol for sensing the absolute stereochemistry and enantiomeric excess of chiral monoamines is reported. Preparation of the sample requires a single-step reaction of the 1,1'-(bromomethylene)dinaphthalene (BDN) with the chiral amine. Analysis of the exciton coupled circular dichroism generated from the BDN-derivatized chiral amine sample, along with comparison to conformational analysis performed computationally, yields the absolute stereochemistry of the parent chiral monoamine.

A chiral-based magnetic memory device without a permanent magnet

PubMed Central

Dor, Oren Ben; Yochelis, Shira; Mathew, Shinto P.; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices. PMID:23922081

A chiral-based magnetic memory device without a permanent magnet.

PubMed

Ben Dor, Oren; Yochelis, Shira; Mathew, Shinto P; Naaman, Ron; Paltiel, Yossi

2013-01-01

Several technologies are currently in use for computer memory devices. However, there is a need for a universal memory device that has high density, high speed and low power requirements. To this end, various types of magnetic-based technologies with a permanent magnet have been proposed. Recent charge-transfer studies indicate that chiral molecules act as an efficient spin filter. Here we utilize this effect to achieve a proof of concept for a new type of chiral-based magnetic-based Si-compatible universal memory device without a permanent magnet. More specifically, we use spin-selective charge transfer through a self-assembled monolayer of polyalanine to magnetize a Ni layer. This magnitude of magnetization corresponds to applying an external magnetic field of 0.4 T to the Ni layer. The readout is achieved using low currents. The presented technology has the potential to overcome the limitations of other magnetic-based memory technologies to allow fabricating inexpensive, high-density universal memory-on-chip devices.

[Topological models of retention index of thin-layer chromatogram for chiral organic acids].

PubMed

Li, Mingjian; Wang, Yuxiao; Feng, Hui; Feng, Changjun

2014-03-01

On the basis of Kier's molecular connectivity indices and conjugated matrix, novel molecular connectivity indices ((m) G(t)(v)) were defined and calculated for 18 chiral hydroxyl acids and amino acids. The chiral connectivity indices ((m)C(t)(v)) were introduced by extending (m)G(t)(v): (m)C(t)(v) = (m)G(t)(v) x w(j), where w(j) is the chiral index. The quantitative structure-retention index relationship (QSRR) between the retention index (R(M)) of thin-layer chromatogram for the chiral organic acids and (m)C(t)(v) was studied by multivariate statistical regression. By leaps-and-bounds regression analysis, the best four-parameter QSRR model was set up, and the traditional correlation coefficient (R2) and the cross-validation correlation coefficient (Q2) of leave-one-out (LOO) were 0.973 and 0.950, respectively. The results demonstrated that the model was highly reliable and had good predictive ability from the point of view of statistics. From the four parameters (0C(p)(v), 2C(p)(v), C(ch),(v), 5C(p)(v)) of the model, it is known that the dominant influence factors of the retention index were the molecular structure characteristics of two-dimensional and the space factors: the chiral characteristics, the flexibility and the puckered degree of molecules for the chiral organic acids. The results showed that the new parameter mC(t)(v) had good rationality and efficiency for the retention indices of the chiral organic acids. Therefore, an effective method was provided to predict the retention indices of the chiral organic acids.

Highly efficient chiral resolution of DL-arginine by cocrystal formation followed by recrystallization under preferential-enrichment conditions.

PubMed

Iwama, Sekai; Kuyama, Kazunori; Mori, Yuko; Manoj, Kochunnoonny; Gonnade, Rajesh G; Suzuki, Katsuaki; Hughes, Colan E; Williams, P Andrew; Harris, Kenneth D M; Veesler, Stéphane; Takahashi, Hiroki; Tsue, Hirohito; Tamura, Rui

2014-08-11

An excellent chiral symmetry-breaking spontaneous enantiomeric resolution phenomenon, denoted preferential enrichment, was observed on recrystallization of the 1:1 cocrystal of dl-arginine and fumaric acid, which is classified as a racemic compound crystal with a high eutectic ee value (>95 %), under non-equilibrium crystallization conditions. On the basis of temperature-controlled video microscopy and in situ time-resolved solid-state (13) C NMR spectroscopic studies on the crystallization process, a new mechanism of phase transition that can induce preferential enrichment is proposed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A chiral aluminum solvating agent (CASA) for 1H NMR chiral analysis of alcohols at low temperature.

PubMed

Seo, Min-Seob; Jang, Sumin; Kim, Hyunwoo

2018-03-16

A chiral aluminum solvating agent (CASA) was demonstrated to be a general and efficient reagent for 1H NMR chiral analysis of alcohols. The sodium salt of the CASA (CASA-Na) showed a complete baseline peak separation of the hydroxyl group for various chiral alcohols including primary, secondary, and tertiary alcohols with alkyl and aryl substituents in CD3CN. Due to the weak intermolecular interaction, 1H NMR measurement at low temperature (-40 to 10 °C) was required.

Lewis Acid Catalyzed Asymmetric Three-Component Coupling Reaction: Facile Synthesis of α-Fluoromethylated Tertiary Alcohols.

PubMed

Aikawa, Kohsuke; Kondo, Daisuke; Honda, Kazuya; Mikami, Koichi

2015-12-01

A chiral dicationic palladium complex is found to be an efficient Lewis acid catalyst for the synthesis of α-fluoromethyl-substituted tertiary alcohols using a three-component coupling reaction. The reaction transforms three simple and readily available components (terminal alkyne, arene, and fluoromethylpyruvate) to valuable chiral organofluorine compounds. This strategy is completely atom-economical and results in perfect regioselectivities and high enantioselectivities of the corresponding tertiary allylic alcohols in good to excellent yields. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Robust flow of light in three-dimensional dielectric photonic crystals.

PubMed

Chen, Wen-Jie; Jiang, Shao-Ji; Dong, Jian-Wen

2013-09-01

Chiral defect waveguides and waveguide bend geometry were designed in diamond photonic crystal to mold the flow of light in three dimensions. Propagations of electromagnetic waves in chiral waveguides are robust against isotropic obstacles, which would suppress backscattering in waveguides or integrated devices. Finite-difference time-domain simulations demonstrate that high coupling efficiency through the bend corner is preserved in the polarization gap, as it provides an additional constraint on the polarization state of the backscattered wave. Transport robustness is also demonstrated by inserting two metallic slabs into the waveguide bend.

Proline catalyzed sequential α-aminooxylation or -amination/reductive cyclization of o-nitrohydrocinnamaldehydes: a high yield synthesis of chiral 3-substituted tetrahydroquinolines.

PubMed

Rawat, Varun; Kumar, B Senthil; Sudalai, Arumugam

2013-06-14

A new sequential organocatalytic method for the synthesis of chiral 3-substituted (X = OH, NH2) tetrahydroquinoline derivatives (THQs) [ee up to 99%, yield up to 87%] based on α-aminooxylation or -amination followed by reductive cyclization of o-nitrohydrocinnamaldehydes has been described. This methodology has been efficiently demonstrated in the synthesis of two important bioactive molecules namely (-)-sumanirole (96% ee) and 1-[(S)-3-(dimethylamino)-3,4-dihydro-6,7-dimethoxy-quinolin-1(2H)-yl]propanone (92% ee).

Diaminophosphine oxide ligand enabled asymmetric nickel-catalyzed hydrocarbamoylations of alkenes.

PubMed

Donets, Pavel A; Cramer, Nicolai

2013-08-14

Chiral trivalent phosphorus species are the dominant class of ligands and the key controlling element in asymmetric homogeneous transition-metal catalysis. Here, novel chiral diaminophosphine oxide ligands are described. The arising catalyst system with nickel(0) and trimethylaluminum efficiently activates formamide C-H bonds under mild conditions providing pyrrolidones via intramolecular hydrocarbamoylation in a highly enantioselective manner with as little as 0.25% mol catalyst loading. Mechanistically, the secondary phosphine oxides behave as bridging ligands for the nickel center and the Lewis acidic organoaluminum center to give a heterobimetallic catalyst with superior reactivity.

Enantioselective Copper-Catalyzed Carboetherification of Unactivated Alkenes**

PubMed Central

Bovino, Michael T.; Liwosz, Timothy W.; Kendel, Nicole E.; Miller, Yan; Tyminska, Nina

2014-01-01

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein is reported a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols that terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition state calculations support a cis-oxycupration stereochemistry-determining step. PMID:24798697

Templated Synthesis of Single-Walled Carbon Nanotubes with Specific Structure.

PubMed

Yang, Feng; Wang, Xiao; Li, Meihui; Liu, Xiyan; Zhao, Xiulan; Zhang, Daqi; Zhang, Yan; Yang, Juan; Li, Yan

2016-04-19

Single-walled carbon nanotubes (SWNTs) have shown great potential in various applications attributed to their unique structure-dependent properties. Therefore, the controlled preparation of chemically and structurally pristine SWNTs is a crucial issue for their advanced applications (e.g., nanoelectronics) and has been a great challenge for two decades. Epitaxial growth from well-defined seeds has been shown to be a promising strategy to control the structure of SWNTs. Segments of carbon nanotubes, including short pipes from cutting of preformed nanotubes and caps from opening of fullerenes or cyclodehydrogenation of polycyclic hydrocarbon precursors, have been used as the seeds to grow SWNTs. Single-chirality SWNTs were obtained with both presorted chirality-pure SWNT segments and end caps obtained from polycyclic hydrocarbon molecules with designed structure. The main challenges of nanocarbon-segment-seeded processes are the stability of the seeds, yield, and efficiency. Catalyst-mediated SWNT growth is believed to be more efficient. The composition and morphology of the catalyst nanoparticles have been widely reported to affect the chirality distribution of SWNTs. However, chirality-specific SWNT growth is hard to achieve by alternating catalysts. The specificity of enzyme-catalyzed reactions brings us an awareness of the essentiality of a unique catalyst structure for the chirality-selective growth of SWNTs. Only catalysts with the desired atomic arrangements in their crystal planes can act as structural templates for chirality-specific growth of SWNTs. We have developed a new family of catalysts, tungsten-based intermetallic compounds, which have high melting points and very special crystal structures, to facilitate the growth of SWNTs with designed chirality. By the use of W6Co7 catalysts, (12,6) SWNTs were directly grown with purity higher than 92%. Both high-resolution transmission electron microscopy measurements and density functional theory simulations show that the selective growth of (12,6) tubes is due to a good structural match between the carbon atom arrangement around the nanotube circumference and the metal atom arrangement of (0 0 12) planes in the catalyst. Similarly, (16,0) SWNTs exhibit a good structural match to the (116) planes of the W6Co7 catalyst. By optimization of the chemical vapor deposition (CVD) conditions, zigzag (16,0) SWNTs, which are generally known as a kinetically unfavorable species in CVD growth, were obtained with a purity of ∼80%. Generally speaking, the chirality-specific growth of SWNTs is realized by the cooperation of two factors: the structural match between SWNTs and the catalysts makes the growth of SWNTs with specific chirality thermodynamically favorable, and further manipulation of the CVD conditions results in optimized growth kinetics for SWNTs with this designed chirality. We expect that this advanced epitaxial growth strategy will pave the way for the ultimate goal of chirality-specified growth of SWNTs and will also be applicable in the controlled preparation of other nanomaterials.

Chromatographic enantioseparation by poly(biphenylylacetylene) derivatives with memory of both axial chirality and macromolecular helicity.

PubMed

Ishidate, Ryoma; Ikai, Tomoyuki; Kanoh, Shigeyoshi; Yashima, Eiji; Maeda, Katsuhiro

2017-03-01

Novel poly(biphenylylacetylene) derivatives bearing two acetyloxy groups at the 2- and 2'-positions and an alkoxycarbonyl group at the 4'-position of the biphenyl pendants (poly-Ac's) were synthesized by the polymerization of the corresponding biphenylylacetylenes using a rhodium catalyst. The obtained stereoregular (cis-transoidal) poly-Ac's folded into a predominantly one-handed helical conformation accompanied by a preferred-handed axially twisted conformation of the biphenyl pendants through noncovalent interactions with a chiral alcohol and both the induced main-chain helicity and the pendant axial chirality were maintained, that is, memorized, after complete removal of the chiral alcohol. The stability of the helicity memory of the poly-Ac's in a solution was lower than that of the analogous poly(biphenylylacetylene)s bearing two methoxymethoxy groups at the 2- and 2'-positions of the biphenyl pendants (poly-MOM's). In the solid state, however, the helicity memory of the poly-Ac's was much more stable and showed a better chiral recognition ability toward several racemates than that of the previously reported poly-MOM when used as a chiral stationary phase for high-performance liquid chromatography. In particular, the poly-Ac-based CSP with a helicity memory efficiently separated racemic benzoin derivatives into enantiomers. © 2017 Wiley Periodicals, Inc.

Effective construction of quaternary stereocenters by highly enantioselective α-amination of branched aldehydes.

PubMed

Fu, Ji-Ya; Xu, Xiao-Ying; Li, Yan-Chun; Huang, Qing-Chun; Wang, Li-Xin

2010-10-21

A highly efficient enantioselective α-amination of branched aldehydes with azadicarboxylates promoted by chiral proline-derived amide thiourea bifunctional catalysts was developed for the first time, affording the adducts bearing quaternary stereogenic centers with excellent yields (up to 99%) and enantioselectivities (up to 97% ee).

Local light-induced magnetization using nanodots and chiral molecules.

PubMed

Dor, Oren Ben; Morali, Noam; Yochelis, Shira; Baczewski, Lech Tomasz; Paltiel, Yossi

2014-11-12

With the increasing demand for miniaturization, nanostructures are likely to become the primary components of future integrated circuits. Different approaches are being pursued toward achieving efficient electronics, among which are spin electronics devices (spintronics). In principle, the application of spintronics should result in reducing the power consumption of electronic devices. Recently a new, promising, effective approach for spintronics has emerged, using spin selectivity in electron transport through chiral molecules. In this work, using chiral molecules and nanocrystals, we achieve local spin-based magnetization generated optically at ambient temperatures. Through the chiral layer, a spin torque can be transferred without permanent charge transfer from the nanocrystals to a thin ferromagnetic layer, creating local perpendicular magnetization. We used Hall sensor configuration and atomic force microscopy (AFM) to measure the induced local magnetization. At low temperatures, anomalous spin Hall effects were measured using a thin Ni layer. The results may lead to optically controlled spintronics logic devices that will enable low power consumption, high density, and cheap fabrication.

High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism

NASA Astrophysics Data System (ADS)

Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

2016-09-01

Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg2+-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C-O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface.

High-effective approach from amino acid esters to chiral amino alcohols over Cu/ZnO/Al2O3 catalyst and its catalytic reaction mechanism

PubMed Central

Zhang, Shuangshuang; Yu, Jun; Li, Huiying; Mao, Dongsen; Lu, Guanzhong

2016-01-01

Developing the high-efficient and green synthetic method for chiral amino alcohols is an intriguing target. We have developed the Mg2+-doped Cu/ZnO/Al2O3 catalyst for hydrogenation of L-phenylalanine methyl ester to chiral L-phenylalaninol without racemization. The effect of different L-phenylalanine esters on this title reaction was studied, verifying that Cu/ZnO/Al2O3 is an excellent catalyst for the hydrogenation of amino acid esters to chiral amino alcohols. DFT calculation was used to study the adsorption of substrate on the catalyst, and showed that the substrate adsorbs on the surface active sites mainly by amino group (-NH2) absorbed on Al2O3, and carbonyl (C=O) and alkoxy (RO-) group oxygen absorbed on the boundary of Cu and Al2O3. This catalytic hydrogenation undergoes the formation of a hemiacetal intermediate and the cleavage of the C–O bond (rate-determining step) by reacting with dissociated H to obtain amino aldehyde and methanol ad-species. The former is further hydrogenated to amino alcohols, and the latter desorbs from the catalyst surface. PMID:27619990

Observation of chiral phonons

NASA Astrophysics Data System (ADS)

Zhu, Hanyu; Yi, Jun; Li, Ming-Yang; Xiao, Jun; Zhang, Lifa; Yang, Chih-Wen; Kaindl, Robert A.; Li, Lain-Jong; Wang, Yuan; Zhang, Xiang

2018-02-01

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

Coupled Chiral Structure in Graphene-Based Film for Ultrahigh Thermal Conductivity in Both In-Plane and Through-Plane Directions.

PubMed

Meng, Xin; Pan, Hui; Zhu, Chengling; Chen, Zhixin; Lu, Tao; Xu, Da; Li, Yao; Zhu, Shenmin

2018-06-21

The development of high-performance thermal management materials to dissipate excessive heat both in plane and through plane is of special interest to maintain efficient operation and prolong the life of electronic devices. Herein, we designed and constructed a graphene-based composite film, which contains chiral liquid crystals (cellulose nanocrystals, CNCs) inside graphene oxide (GO). The composite film was prepared by annealing and compacting of self-assembled GO-CNC, which contains chiral smectic liquid crystal structures. The helical arranged nanorods of carbonized CNC act as in-plane connections, which bridge neighboring graphene sheets. More interestingly, the chiral structures also act as through-plane connections, which bridge the upper and lower graphene layers. As a result, the graphene-based composite film shows extraordinary thermal conductivity, in both in-plane (1820.4 W m -1 K -1 ) and through-plane (4.596 W m -1 K -1 ) directions. As a thermal management material, the heat dissipation and transportation behaviors of the composite film were investigated using a self-heating system and the results showed that the real-time temperature of the heater covered with the film was 44.5 °C lower than a naked heater. The prepared film shows a much higher efficiency of heat transportation than the commonly used thermal conductive Cu foil. Additionally, this graphene-based composite film exhibits excellent mechanical strength of 31.6 MPa and an electrical conductivity of 667.4 S cm -1 . The strategy reported here may open a new avenue to the development of high-performance thermal management films.

Studies towards asymmetric synthesis of 4(S)-11-dihydroxydocosahexaenoic acid (diHDHA) featuring cross-coupling of chiral stannane under mild conditions.

PubMed

Wang, Rui; He, Anyu; Ramu, Errabelli; Falck, John R

2015-02-14

An efficient and asymmetric synthetic approach towards one of the biologically interesting 4(S)-11-diHDHA derivatives was developed. This process mainly relied on two reactions, one is the copper-catalyzed mild cross-coupling that allows for the efficient construction of a chiral α-alkynyl α-hydroxy motif and another is the synthesis of chiral α-hydroxy α-stannanes that has previously been developed by our group featuring the asymmetric stannylation using the well-established tributyltin hydride/diethyl zinc system from an aldehyde.

Chiral Amine Synthesis Using ω-Transaminases: An Amine Donor that Displaces Equilibria and Enables High-Throughput Screening**

PubMed Central

Green, Anthony P; Turner, Nicholas J; O'Reilly, Elaine

2014-01-01

The widespread application of ω-transaminases as biocatalysts for chiral amine synthesis has been hampered by fundamental challenges, including unfavorable equilibrium positions and product inhibition. Herein, an efficient process that allows reactions to proceed in high conversion in the absence of by-product removal using only one equivalent of a diamine donor (ortho-xylylenediamine) is reported. This operationally simple method is compatible with the most widely used (R)- and (S)-selective ω-TAs and is particularly suitable for the conversion of substrates with unfavorable equilibrium positions (e.g., 1-indanone). Significantly, spontaneous polymerization of the isoindole by-product generates colored derivatives, providing a high-throughput screening platform to identify desired ω-TA activity. PMID:25138082

Nonlinear optical and multiphoton processes for in situ manipulation and conversion of photons: applications to energy and healthcare (Conference Presentation)

NASA Astrophysics Data System (ADS)

Prasad, Paras N.

2017-02-01

Chiral control of nonlinear optical functions holds a great promise for a wide range of applications including optical signal processing, bio-sensing and chiral bio-imaging. In chiral polyfluorene thin films, we demonstrated extremely large chiral nonlinearity. The physics of manipulating excitation dynamics for photon transformation will be discussed, along with nanochemistry control of upconversion in hierarchically built organic chromophore coupled-core-multiple shell nanostructures which enable introduce new, organic-inorganic energy transfer routes for broadband light harvesting and increased upconversion efficiency via multistep cascaded energy transfer. We are pursuing the applications of photon conversion technology in IR harvesting for photovoltaics, high contrast bioimaging, photoacoustic imaging, photodynamic therapy, and optogenetics. An important application is in Brain research and Neurophotonics for functional mapping and modulation of brain activities. Another new direction pursued is magnetic field control of light in in a chiral polymer nanocomposite to achieve large magneto-optic coefficient which can enable sensing of extremely weak magnetic field due to brain waves. Finally, we will consider the thought provoking concept of utilizing photons to quantify, through magneto-optics, and augment - through nanoptogenetics, the cognitive states, thus paving the path way to a quantified human paradigm.

Regular scanning tunneling microscope tips can be intrinsically chiral.

PubMed

Tierney, Heather L; Murphy, Colin J; Sykes, E Charles H

2011-01-07

We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

Regular Scanning Tunneling Microscope Tips can be Intrinsically Chiral

NASA Astrophysics Data System (ADS)

Tierney, Heather L.; Murphy, Colin J.; Sykes, E. Charles H.

2011-01-01

We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

Highly efficient induction of chirality in intramolecular

PubMed

Cossio; Arrieta; Lecea; Alajarin; Vidal; Tovar

2000-06-16

Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between ketenimines and imines leading to 1,2-dihydroazeto[2, 1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent either to the iminic carbon or nitrogen atom. In the first case, the stereocontrol stems from the preference for the axial conformer in the first transition structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma orbital corresponding to the polar C-X bond, X being an electronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.

Room temperature high circular dichroism ultraviolet lasing from planar spiral metal-GaN nanowire cavity (Conference Presentation)

NASA Astrophysics Data System (ADS)

Shih, Min-Hsiung

2016-09-01

Circularly polarized light and chiroptical effect have received considerable attention in advanced photonic and electronic technologies including optical spintronics, quantum-based optical information processing and communication, and high-efficiency liquid crystal display backlights. Moreover, the development of circularly polarized photon sources has played a major role in circular dichroism (CD) spectroscopy, which is important for analyses of optically active molecules, chiral synthesis in biology and chemistry, and ultrafast magnetization control. However, the conventional collocation of light-emitting devices and additional circular-polarization converters that produce circularly polarized beams makes the setup bulky and hardly compatible with nanophotonic devices in ultrasmall scales. In fact, the direct generation of circularly polarized photons may simplify the system integration, compact the setup, lower the cost of external components, and perhaps enhance the power efficiency. In this work, with the spiral-type metal-gallium nitride (GaN) nanowire cavity, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and -1.6 (2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with decently high degrees of circular polarizations.

Acylation of Chiral Alcohols: A Simple Procedure for Chiral GC Analysis.

PubMed

Oromí-Farrús, Mireia; Torres, Mercè; Canela, Ramon

2012-01-01

The use of iodine as a catalyst and either acetic or trifluoroacetic acid as a derivatizing reagent for determining the enantiomeric composition of acyclic and cyclic aliphatic chiral alcohols was investigated. Optimal conditions were selected according to the molar ratio of alcohol to acid, the reaction time, and the reaction temperature. Afterwards, chiral stability of chiral carbons was studied. Although no isomerization was observed when acetic acid was used, partial isomerization was detected with the trifluoroacetic acid. A series of chiral alcohols of a widely varying structural type were then derivatized with acetic acid using the optimal conditions. The resolution of the enantiomeric esters and the free chiral alcohols was measured using a capillary gas chromatograph equipped with a CP Chirasil-DEX CB column. The best resolutions were obtained with 2-pentyl acetates (α = 3.00) and 2-hexyl acetates (α = 1.95). This method provides a very simple and efficient experimental workup procedure for analyzing chiral alcohols by chiral-phase GC.

P-chiral 1-phosphanorbornenes: from asymmetric phospha-Diels-Alder reactions towards ligand design and functionalisation.

PubMed

Möller, Tobias; Wonneberger, Peter; Sárosi, Menyhárt B; Coburger, Peter; Hey-Hawkins, Evamarie

2016-02-07

The principle of stereotopic face differentiation was successfully applied to 2H-phospholes which undergo a very efficient and highly stereoselective Diels-Alder reaction giving phosphorus-chiral 1-phosphanorbornenes with up to 87% yield. The observed reaction pathway has been supported by theoretical calculations showing that the cycloaddition reaction between 2H-phosphole 3a and the dienophile (5R)-(-)-menthyloxy-2(5H)-furanone (8) is of normal electron demand. Optically pure phosphanes were obtained by separation of the single diastereomers and subsequent desulfurisation of the sulfur-protected phosphorus atom. Finally, divergent ligand synthesis is feasible by reduction of the chiral auxiliary, subsequent stereospecific intramolecular Michael addition, and various functionalisations of the obtained key compound 13a. Furthermore, the unique structural properties of phospanorbornenes are presented and compared to those of phosphanorbornanes.

Enantioselective copper-catalyzed carboetherification of unactivated alkenes.

PubMed

Bovino, Michael T; Liwosz, Timothy W; Kendel, Nicole E; Miller, Yan; Tyminska, Nina; Zurek, Eva; Chemler, Sherry R

2014-06-16

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols which terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-catalyzed asymmetric tandem cyclization for efficient and rapid access to underexplored heterocyclic tertiary allylic alcohols containing a tetrasubstituted olefin.

PubMed

Li, Yi; Xu, Ming-Hua

2014-05-16

The first Rh-catalyzed asymmetric tandem cyclization of nitrogen- or oxygen-bridged 5-alkynones with arylboronic acids was achieved. The simple catalytic system involving a rhodium(I) complex with readily available chiral BINAP ligand promotes the reaction to proceed in a highly stereocontrolled manner. This protocol provides a very reliable and practical access to a variety of chiral heterocyclic tertiary allylic alcohols possessing a tetrasubstituted carbon stereocenter and an all-carbon tetrasubstituted olefin functionality in good yields with great enantioselectivities up to 99% ee.

Recent Advances in Dynamic Kinetic Resolution by Chiral Bifunctional (Thio)urea- and Squaramide-Based Organocatalysts.

PubMed

Li, Pan; Hu, Xinquan; Dong, Xiu-Qin; Zhang, Xumu

2016-10-14

The organocatalysis-based dynamic kinetic resolution (DKR) process has proved to be a powerful strategy for the construction of chiral compounds. In this feature review, we summarized recent progress on the DKR process, which was promoted by chiral bifunctional (thio)urea and squaramide catalysis via hydrogen-bonding interactions between substrates and catalysts. A wide range of asymmetric reactions involving DKR, such as asymmetric alcoholysis of azlactones, asymmetric Michael-Michael cascade reaction, and enantioselective selenocyclization, are reviewed and demonstrate the efficiency of this strategy. The (thio)urea and squaramide catalysts with dual activation would be efficient for more unmet challenges in dynamic kinetic resolution.

All-dielectric planar chiral metasurface with gradient geometric phase.

PubMed

Ma, Zhijie; Li, Yi; Li, Yang; Gong, Yandong; Maier, Stefan A; Hong, Minghui

2018-03-05

Planar optical chirality of a metasurface measures its differential response between left and right circularly polarized (CP) lights and governs the asymmetric transmission of CP lights. In 2D ultra-thin plasmonic structures the circular dichroism is limited to 25% in theory and it requires high absorption loss. Here we propose and numerically demonstrate a planar chiral all-dielectric metasurface that exhibits giant circular dichroism and transmission asymmetry over 0.8 for circularly polarized lights with negligible loss, without bringing in bianisotropy or violating reciprocity. The metasurface consists of arrays of high refractive index germanium Z-shape resonators that break the in-plane mirror symmetry and induce cross-polarization conversion. Furthermore, at the transmission peak of one handedness, the transmitted light is efficiently converted into the opposite circular polarization state, with a designated geometric phase depending on the orientation angle of the optical element. In this way, the optical component sets before and after the metasurface to filter the light of certain circular polarization states are not needed and the metasurface can function under any linear polarization, in contrast to the conventional setup for geometry phase based metasurfaces. Anomalous transmission and two-dimensional holography based on the geometric phase chiral metasurface are numerically demonstrate as proofs of concept.

Self-organized chiral colloidal crystals of Brownian square crosses.

PubMed

Zhao, Kun; Mason, Thomas G

2014-04-16

We study aqueous Brownian dispersions of microscale, hard, monodisperse platelets, shaped as achiral square crosses, in two dimensions (2D). When slowly concentrated while experiencing thermal excitations, the crosses self-organize into fluctuating 2D colloidal crystals. As the particle area fraction φA is raised, an achiral rhombic crystal phase forms at φA ≈ 0.52. Above φA ≈ 0.56, the rhombic crystal gives way to a square crystal phase that exhibits long-range chiral symmetry breaking (CSB) via a crystal-crystal phase transition; the observed chirality in a particular square crystallite has either a positive or a negative enantiomeric sense. By contrast to triangles and rhombs, which exhibit weak CSB as a result of total entropy maximization, square crosses display robust long-range CSB that is primarily dictated by how they tile space at high densities. We measure the thermal distribution of orientation angles γ of the crosses' arms relative to the diagonal bisector of the local square crystal lattice as a function of φA, and the average measured γ (φA) agrees with a re-scaled model involving efficient packing of rotated cross shapes. Our findings imply that a variety of hard achiral shapes can be designed to form equilibrium chiral phases by considering their tiling at high densities.

Enantioselective Synthesis of Chiral α-Azido and α-Aryloxy Quaternary Stereogenic Centers via the Phase-Transfer-Catalyzed α-Alkylation of α-Bromomalonates, Followed by SN2 Substitution.

PubMed

Kim, Doyoung; Ha, Min Woo; Hong, Suckchang; Park, Cheonhyoung; Kim, Byungsoo; Yang, Jewon; Park, Hyeung-Geun

2017-05-05

A new efficient synthetic method for chiral α-azido-α-alkylmalonates and α-aryloxy-α-alkylmalonates was developed. The enantioselective α-alkylation of diphenylmethyl tert-butyl α-bromomalonate under phase-transfer catalytic conditions [(S,S)-3,4,5-trifluorophenyl-NAS bromide, 50% KOH, toluene, and -40 °C) provided the corresponding α-bromo-α-alkylmalonates in high chemical yields (≤98%) and high optical yields (≤99% ee). The resulting α-alkylated products were converted to α-azido-α-alkylmalonates (≤96%, ≤97% ee) and α-aryloxy-α-alkylmalonates (≤79%, ≤93% ee) by S N 2 substitution with sodium azide and aryloxides, respectively.

Diastereoselective addition of anisoles to N-tert-butanesulfinyl imines via four-membered lithium cycles.

PubMed

Reddy, Leleti Rajender; Kotturi, Sharadsrikar; Waman, Yogesh; Patel, Chirag; Patwa, Aditya; Shenoy, Rajesh

2018-06-06

A highly regio- and diastereo-selective ortho-lithiation/addition of anisoles to N-tert-butanesulfinyl imines resulting in the selective formation of chiral α-branched amines is described. This method is also efficient for highly regioselective benzylic lithiation of o-methylanisoles, followed by diastereoselective addition to N-tert-butanesulfinyl imines.

Efficient and highly enantioselective construction of trifluoromethylated quaternary stereogenic centers via high-pressure mediated organocatalytic conjugate addition of nitromethane to β,β-disubstituted enones.

PubMed

Kwiatkowski, Piotr; Cholewiak, Agnieszka; Kasztelan, Adrian

2014-11-21

A very effective high-pressure-induced acceleration of asymmetric organocatalytic conjugate addition of nitromethane to sterically congested β,β-disubstituted β-CF3 enones has been developed. A combination of pressure (8-10 kbar) and noncovalent catalysis with low-loading of chiral tertiary amine-thioureas (0.5-3 mol %) is shown to provide very efficient access to a wide range of γ-nitroketones containing trifluoromethylated all-carbon quaternary stereogenic centers in the β-position (80-97%, 92-98% ee).

DEVELOPMENT OF AN AFFINITY SILICA MONOLITH CONTAINING HUMAN SERUM ALBUMIN FOR CHIRAL SEPARATIONS

PubMed Central

Mallik, Rangan; Hage, David S.

2008-01-01

An affinity monolith based on silica and containing immobilized human serum albumin (HSA) was developed and evaluated in terms of its binding, efficiency and selectivity in chiral separations. The results were compared with data obtained for the same protein when used as a chiral stationary phase with HPLC-grade silica particles or a monolith based on a copolymer of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA). The surface coverage of HSA in the silica monolith was similar to values obtained with silica particles and a GMA/EDMA monolith. However, the higher surface area of the silica monolith gave a material that contained 1.3- to 2.2-times more immobilized HSA per unit volume when compared to silica particles or a GMA/EDMA monolith. The retention, efficiency and resolving power of the HSA silica monolith were evaluated using two chiral analytes: D/L-tryptophan and R/S-warfarin. The separation of R- and S-ibuprofen was also considered. The HSA silica monolith gave higher retention and higher or comparable resolution and efficiency when compared with HSA columns that contained silica particles or a GMA/EDMA monolith. The silica monolith also gave lower back pressures and separation impedances than these other materials. It was concluded that silica monoliths can be valuable alternatives to silica particles or GMA/EDMA monoliths when used with immobilized HSA as a chiral stationary phase. PMID:17475436

Hydroacylation of 2-vinyl benzaldehyde systems: an efficient method for the synthesis of chiral 3-substituted indanones.

PubMed

Kundu, Kousik; McCullagh, James V; Morehead, Andrew T

2005-11-23

Asymmetric rhodium-catalyzed hydroacylation has been utilized in the synthesis of 3-substituted indanones with high conversions and enantioselectivity. The hydroacylation reaction of 2-vinyl benzaldehyde had been previously reported to give a low yield of indanone and an unidentified product. We have identified this compound as a dimer of the starting material. Substitution at the alpha-position of the 2-vinyl benzaldehyde substrates blocks the competitive dimerization reaction and allows the reaction to proceed with yields generally greater than 90%. Utilization of BINAP as a chiral ligand results in good chemical yields and enantioselectivity greater than 95% in most cases.

Observation of chiral phonons.

PubMed

Zhu, Hanyu; Yi, Jun; Li, Ming-Yang; Xiao, Jun; Zhang, Lifa; Yang, Chih-Wen; Kaindl, Robert A; Li, Lain-Jong; Wang, Yuan; Zhang, Xiang

2018-02-02

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Multigram Synthesis of a Chiral Substituted Indoline Via Copper-Catalyzed Alkene Aminooxygenation.

PubMed

Sequeira, Fatima C; Bovino, Michael T; Chipre, Anthony J; Chemler, Sherry R

2012-05-01

(S)-5-Fluoro-2-(2,2,6,6-tetramethylpiperidin-1-yloxymethyl)-1-tosylindoline, a 2-methyleneoxy-substituted chiral indoline, was synthesized on multigram scale using an efficient copper-catalyzed enantioselective intramolecular alkene aminooxygenation. The synthesis is accomplished in four steps and the indoline is obtained in 89% ee (>98% after one recrystallization). Other highlights include efficient gram-scale synthesis of the (4R,5S)-di-Ph-box ligand and efficient separation of a monoallylaniline from its bis(allyl)aniline by-product by distillation under reduced pressure.

Multigram Synthesis of a Chiral Substituted Indoline Via Copper-Catalyzed Alkene Aminooxygenation

PubMed Central

Sequeira, Fatima C.; Bovino, Michael T.; Chipre, Anthony J.

2012-01-01

(S)-5-Fluoro-2-(2,2,6,6-tetramethylpiperidin-1-yloxymethyl)-1-tosylindoline, a 2-methyleneoxy-substituted chiral indoline, was synthesized on multigram scale using an efficient copper-catalyzed enantioselective intramolecular alkene aminooxygenation. The synthesis is accomplished in four steps and the indoline is obtained in 89% ee (>98% after one recrystallization). Other highlights include efficient gram-scale synthesis of the (4R,5S)-di-Ph-box ligand and efficient separation of a monoallylaniline from its bis(allyl)aniline by-product by distillation under reduced pressure. PMID:22639473

Impact of molecular flexibility on binding strength and self-sorting of chiral π-surfaces.

PubMed

Safont-Sempere, Marina M; Osswald, Peter; Stolte, Matthias; Grüne, Matthias; Renz, Manuel; Kaupp, Martin; Radacki, Krzysztof; Braunschweig, Holger; Würthner, Frank

2011-06-22

In this work, we have explored for the first time the influence of conformational flexibility of π-core on chiral self-sorting properties of perylene bisimides (PBIs) that are currently one of the most prominent classes of functional dyes. For this purpose, two series of chiral macrocyclic PBIs 3a-c and 4a-c comprising oligoethylene glycol bridges of different lengths at the 1,7 bay positions were synthesized and their atropo-enantiomers (P and M enantiomers) were resolved. Single crystal analysis of atropo-enantiomerically pure (P)-3a not only confirmed the structural integrity of the ethylene glycol bridged macrocycle but also illustrated the formation of π-stacked dimers with left-handed supramolecular helicity. Our detailed studies with the series of highly soluble chiral PBIs 4a-c by 1- and 2-D (1)H NMR techniques, and temperature- and concentration-dependent UV/vis absorption and circular dichroism (CD) spectroscopy revealed that in π-π-stacking dimerization of these PBIs chiral self-recognition (i.e., PP and MM homodimer formation) prevails over self-discrimination (i.e., PM heterodimer formation). Our studies clearly showed that with increasing conformational flexibility of PBI cores imparted by longer bridging units, the binding strength for the dimerization process increases, however, the efficiency for chiral self-recognition decreases. These results are rationalized in terms of an induced-fit mechanism facilitating more planarized π-scaffolds of PBIs containing longer bridging units upon π-π-stacking.

Steering Asymmetric Lewis Acid Catalysis Exclusively with Octahedral Metal-Centered Chirality.

PubMed

Zhang, Lilu; Meggers, Eric

2017-02-21

Catalysts for asymmetric synthesis must be chiral. Metal-based asymmetric catalysts are typically constructed by assembling chiral ligands around a central metal. In this Account, a new class of effective chiral Lewis acid catalysts is introduced in which the octahedral metal center constitutes the exclusive source of chirality. Specifically, the here discussed class of catalysts are composed of configurationally stable, chiral-at-metal Λ-configured (left-handed propeller) or Δ-configured (right-handed propeller) iridium(III) or rhodium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (dubbed IrO and RhO) or 5-tert-butyl-2-phenylbenzothiazole (dubbed IrS and RhS) ligands in addition to two exchange-labile acetonitriles. They are synthetically accessible in an enantiomerically pure fashion through a convenient auxiliary-mediated synthesis. Such catalysts are of interest due to their intrinsic structural simplicity (only achiral ligands) and the prospect of an especially effective asymmetric induction due to the intimate contact between the chiral metal center and the metal-coordinated substrates or reagents. With respect to chiral Lewis acid catalysis, the bis-cyclometalated iridium and rhodium complexes provide excellent catalytic activities and asymmetric inductions for a variety of reactions including Michael additions, Friedel-Crafts reactions, cycloadditions, α-aminations, α-fluorinations, Mannich reactions, and a cross-dehydrogenative coupling. Mechanistically, substrates such as 2-acyl imidazoles are usually activated by two-point binding. Exceptions exist as for example for an efficient iridium-catalyzed enantioselective transfer hydrogenation of arylketones with ammonium formate, which putatively proceeds through an iridium-hydride intermediate. The bis-cyclometalated iridium complexes catalyze visible-light-induced asymmetric reactions by intertwining asymmetric catalysis and photoredox catalysis in a unique fashion. This has been applied to the visible-light-induced α-alkylation of 2-acyl imidazoles (and in some instances 2-acylpyridines) with acceptor-substituted benzyl, phenacyl, trifluoromethyl, perfluoroalkyl, and trichloromethyl groups, in addition to photoinduced oxidative α-aminoalkylations and a photoinduced stereocontrolled radical-radical coupling, each employing a single iridium complex. In all photoinduced reaction schemes, the iridium complex serves as a chiral Lewis acid catalyst and at the same time as precursor of in situ assembled photoactive species. The nature of these photoactive intermediates then determines their photochemical properties and thereby the course of the asymmetric photoredox reactions. The bis-cyclometalated rhodium complexes are also very useful for asymmetric photoredox catalysis. Less efficient photochemical properties are compensated with a more rapid ligand exchange kinetics, which permits higher turnover frequencies of the catalytic cycle. This has been applied to a visible-light-induced enantioselective radical α-amination of 2-acyl imidazoles. In this reaction, an intermediate rhodium enolate is supposed to function as a photoactivatable smart initiator to initiate and reinitiate an efficient radical chain process. If a more efficient photoactivation is required, a rhodium-based Lewis acid can be complemented with a photoredox cocatalyst, and this has been applied to efficient catalytic asymmetric alkyl radical additions to acceptor-substituted alkenes. We believe that this class of chiral-only-at-metal Lewis acid catalysts will be of significant value in the field of asymmetric synthesis, in particular in combination with visible-light-induced redox chemistry, which has already resulted in novel strategies for asymmetric synthesis of chiral molecules. Hopefully, this work will also pave the way for the development of other asymmetric catalysts featuring exclusively octahedral centrochirality.

Fast chirality reversal of the magnetic vortex by electric current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, W. L., E-mail: wlimnd@gmail.com; Liu, R. H.; Urazhdin, S., E-mail: sergei.urazhdin@emory.edu

2014-12-01

The possibility of high-density information encoding in magnetic materials by topologically stable inhomogeneous magnetization configurations such as domain walls, skyrmions, and vortices has motivated intense research into mechanisms enabling their control and detection. While the uniform magnetization states can be efficiently controlled by electric current using magnetic multilayer structures, this approach has proven much more difficult to implement for inhomogeneous states. Here, we report direct observation of fast reversal of magnetic vortex by electric current in a simple planar structure based on a bilayer of spin Hall material Pt with a single microscopic ferromagnetic disk contacted by asymmetric electrodes. Themore » reversal is enabled by a combination of the chiral Oersted field and spin current generated by the nonuniform current distribution in Pt. Our results provide a route for the efficient control of inhomogeneous magnetization configurations by electric current.« less

Enantioselective syntheses of lignin models: an efficient synthesis of B-O-4 dimers and trimers by using the Evans chiral auxiliary

Treesearch

Costyl N. Njiojob; Joseph J. Bozell; Brian K. Long; Thomas Elder; Rebecca E. Key; William T. Hartwig

2016-01-01

We describe an efficient five-step, enantioselective synthesis of (R,R)- and (S,S)-lignin dimer models possessing a B-O-4 linkage, by using the Evans chiral aldol reaction as a key step. Mitsunobu inversion of the (R,R)- or (S,S)-isomers generates the corresponding (R,S)- and (S,R)-diastereomers. We further extend this approach to the...

The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawano, Takahiro; Ji, Pengfei; McIsaac, Alexandra R.

2016-02-01

We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(I) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfullymore » recycled and reused at least seven times without loss of yield and enantioselectivity.« less

A very simple, highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands.

PubMed

Chen, Weiping; Mbafor, William; Roberts, Stanley M; Whittall, John

2006-03-29

A very simple, highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands has been developed. On the basis of this new methodology, several new families of ferrocene-based phosphine ligands have been prepared coupling chirality at phosphorus with other, more standard stereogenic features. The introduction of P-chirality into ferrocene-based phosphine ligands enhances the enantioselective discrimination produced by the corresponding Rh catalyst when a matching among the planar chirality, carbon chirality, and the chirality of phosphorus is achieved.

Enhanced Circular Dichroism via Symmetry Breaking in a Chiral Plasmonic Nanoparticle Oligomer

NASA Astrophysics Data System (ADS)

Le, Khai Q.

2018-02-01

A chiral plasmonic nanoparticle oligomer, consisting of four symmetrically arranged nanodisks of different heights and having different optical absorption responses to left and right-handed circularly polarized light illumination, has been experimentally reported in the literature. The resulting circular dichroism (CD) signal was detectable with state of the art CD spectrometers but was much weaker than those of existing chiral nanostructures, i.e., three-dimensional (3-D) chiral metamaterials. In this letter, via symmetry breaking in such an oligomer, the author demonstrates that the CD can be enhanced up to six times compared to that of a symmetric oligomer, and is in the range of a relevant 3-D chiral metamolecule. Through investigation of geometrical parameters including particle size, asymmetric and symmetric gaps, the CD evolution was reported, which provides a useful guideline for design of two-dimensional chiral oligomers adopted as efficient probes for CD spectroscopic applications.

Use of chiral derivatization for the determination of dichlorprop in tea samples by ultra performance LC with fluorescence detection.

PubMed

Inoue, Koichi; Prayoonhan, Nuntawat; Tsutsui, Haruhito; Sakamoto, Tasuku; Nishimura, Maiko; Toyo'oka, Toshimasa

2013-04-01

Dichlorprop is available for agricultural use as a chiral pesticide. In this study, the stereoselective determination of dichlorprop enantiomers in tea samples such as green, black, jasmine, and oolong was developed by ultra performance LC with fluorescence spectrometry after covalent chiral derivatization. The separation was achieved on an Acquity BEH C18 column with the mobile phase consisting of 0.1% formic acid in acetonitrile/water at a flow rate of 0.4 mL/min. In the covalent chiral derivatization using (S)-(+)-4-(N,N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole, the peak resolution between the S and R-dichlorprop enantiomers was 2.6. LODs and LOQs values were 10 and 50 ng/mL standard solution. The linearity of the calibration curves yielded the coefficients (r(2) > 0.99, ranging from 0.05 to 5 μg/mL) of determination of each of the dichlorprop enantiomers. SPE extraction was used for the sample preparation of dichlorprop in various tea samples. Recoveries were in the range of 82.4-97.6% with associated precision values (within-day: 82.4-95.8%, n = 6, and between-day: 83.7-97.6% for 3 days) for repeatability and reproducibility. Based on this result, our method has been proven to be highly efficient and suitable for the routine assay of dichlorprop enantiomers in various tea samples. We propose that the ultra performance LC assay after covalent chiral derivatization would be the renewed tools in the era of chiral stationary platform for chiral pesticide residues in foods. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantiomeric separation of six chiral pesticides that contain chiral sulfur/phosphorus atoms by supercritical fluid chromatography.

PubMed

Zhang, Lijun; Miao, Yelong; Lin, Chunmian

2018-03-01

Six chiral pesticides containing chiral sulfur/phosphorus atoms were separated by supercritical fluid chromatography with supercritical CO 2 as the main mobile phase component. The effect of the chiral stationary phase, different type and concentration of modifiers, column temperature, and backpressure on the separation efficiency was investigated to obtain the appropriate separation condition. Five chiral pesticides (isofenphos-methyl, isocarbophos, flufiprole, fipronil, and ethiprole) were baseline separated under experimental conditions, while isofenphos only obtained partial separation. The Chiralpak AD-3 column showed a better chiral separation ability than others for chiral pesticides containing chiral sulfur/phosphorus atoms. When different modifiers at the same concentration were used, the retention factor of pesticides except flufiprole decreased in the order of isopropanol, ethanol, methanol; meanwhile, the retention factor of flufiprole increased in the order of isopropanol, ethanol, methanol. For a given modifier, the retention factor and resolution decreased on the whole with the increase of its concentration. The enantiomer separation of five chiral pesticides was an "enthalpy-driven" process, and the separation factor decreased as the temperature increased. The backpressure of the mobile phase had little effect on the separation factor and resolution. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral ligand-exchange high-performance liquid chromatography with copper (II)-L-phenylalanine complexes for separation of 3,4-dimethoxy-α-methylphenylalanine racemes.

PubMed

Jia, Dong-Xu; Ai, Zheng-Gui; Xue, Ya-Ping; Zheng, Yu-Guo

2014-11-01

L-3, 4-dimethoxy-α-methylphenylalanine (L-DMMD) is an important intermediate for the synthesis of 3-hydroxy-α-methyl-L-tyrosine (L-methyldopa). This paper describes an efficient, accurate, and low-priced method of high-performance liquid chromatography (HPLC) using chiral mobile phase and conventional C18 column to separate L-DMMD from its enantiomers. The effects of ligands, copper salts, organic modifiers, pHs of mobile phase, and temperatures on the retention factors (k') and selectivity (α) were evaluated to achieve optimal separation performance. Then, thermal analysis of the optimal separation conditions was investigated as well. It was confirmed that the optimal mobile phase was composed of 20 % (v/v) methanol, 8 mM L-phenylalanine (L-Phe), and 4 mM cupric sulfate in water of pH 3.2, and the column temperature was set at 20 °C. Baseline separation of two enantiomers could be obtained through the conventional C18 column with a resolution (R) of 3.18 in less than 18 min. Thermodynamic data (∆∆H and ∆∆S) obtained by Van't Hoff plots revealed the chiral separation was an enthalpy-controlled process. To the best of our knowledge, this is the first report regarding the enantioseparation of DMMD by chiral ligand-exchange HPLC.

Enantiomeric separation of triazole fungicides with 3-μm and 5-μml particle chiral columns by reverse-phase high-performance liquid chromatography.

PubMed

Qiu, Jing; Dai, Shouhui; Zheng, Chuangmu; Yang, Shuming; Chai, Tingting; Bie, Mei

2011-07-01

This study used chiral columns packed with 3-μm and 5-μm particles to comparatively separate enantiomers of 9 triazole fungicides, and Lux Cellulose-1 columns with chiral stationary phase of cellulose-tris-(3,5-dimethylphenylcarbamate) were used on reverse-phase high-performance liquid chromatography with flow rates of 0.3 and 1.0 mL min(-1) for 3-μm and 5-μm columns, respectively. The (+)-enantiomers of hexaconazole (1), tetraconazole (4), myclobutanil (7), fenbuconazole (8) and the (-)-enantiomers of flutriafol (2), diniconazole (3), epoxiconazole (5), penconazole (6), triadimefon (9) were firstly eluted from both columns, the elution orders identified with an optical rotation detector didn't change with variety of column particles and mobile phases (acetronitrile/water and methanol/water). The plots of natural logarithms of the selectivity factors (ln α) for all fungicides except penconazole (6) versus the inverse of temperature (1/T) were linear in range of 5-40°C. The thermodynamic parameters (ΔH°, ΔS°, ΔΔH° and ΔΔS°) were calculated using Van't Hoff equations to understand the thermosynamic driving forces for enantioseparation. This work will be very helpful to obtain good enantiomeric separation and establish more efficient analytical method for triazole fungicides. Chirality, 2011. © 2011 Wiley-Liss, Inc. Copyright © 2011 Wiley-Liss, Inc.

Multi-responsible chameleon molecule with chiral naphthyl and azobenzene moieties.

PubMed

Kim, Dae-Yoon; Lee, Sang-A; Park, Minwook; Choi, Yu-Jin; Kang, Shin-Woong; Jeong, Kwang-Un

2015-04-21

A photochromic chiral molecule with azobenzene mesogens and a (R)-configuration naphthyl moiety (abbreviated as NCA2M) was specifically designed and synthesized for the demonstration of chameleon-like color changes responding to multitudinous external stimuli, such as temperature, light and electric field. The basic phase transition behaviors of NCA2M were first studied by the combination of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Based on the structure-sensitive X-ray diffraction results obtained at different temperatures, it was comprehended that the NCA2M molecule exhibited the tilted version of highly ordered smectic crystal phase with 5.45 nm layer thickness. Chiral nematic (N*) liquid crystals (LC) with helical superstructures were formed by doping the NCA2M photochromic chiral molecule in an achiral nematic (N) LC medium. By controlling the helical pitch length of N*-LC with respect to temperature, light and electric field, the wavelength of selectively reflected light from the N* photonic crystal was finely tuned. The light-induced color change of N*-LC film was the most efficient method for covering the whole visible region from blue to green and to red, which allowed us to fabricate remote-controllable photo-responsive devices.

Michael Addition Reactions between Chiral Equivalents of a Nucleophilic Glycine and (S)- or (R)-3-[(E)-Enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a General Method for Efficient Preparation of β-Substituted Pyroglutamic Acids. Case of Topographically Controlled Stereoselectivity

PubMed Central

Soloshonok*, Vadim A.; Cai, Chaozhong; Yamada, Takeshi; Ueki, Hisanori; Ohfune, Yasufumi; Hruby, Victor J.

2006-01-01

This paper describes a systematic study of addition reactions between the chiral Ni(II) complex of the Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone and (S)- or (R)-3-[(E)-enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a general and synthetically efficient approach to β-substituted pyroglutamic acids and relevant compounds. These reactions were shown to occur at room temperature in the presence of nonchelating organic bases and, most notably, with very high (>98% diastereomeric excess (de)) stereoselectivity at both newly formed stereogenic centers. The stereochemical outcome of the reactions was found to be overwhelmingly controlled by the stereochemical preferences of the Michael acceptors, and the chirality of the glycine complex influenced only the reaction rate. Thus, in the reactions of both the (S)-configured Ni(II) complex and the Michael acceptors, the reaction rates were exceptionally high, allowing preparation of the corresponding products with virtually quantitative (>98%) chemical and stereochemical yields. In contrast, reactions of the (S)-configured Ni(II) complex and (R)-configured Michael acceptors proceeded at noticeably lower rates, but the addition products were obtained in high diastereo-and enantiomeric purity. To rationalize the remarkably high and robust stereoselectivity observed in these reactions, we consider an enzyme–substrate-like mode of interaction involing a topographical match or mismatch of two geometric figures. Excellent chemical and stereochemical yields, combined with the simplicity and operational convenience of the experimental procedures, render the present method of immediate use for preparing various β-substituted pyroglutamic acids and related compounds. PMID:16248672

Michael addition reactions between chiral equivalents of a nucleophilic glycine and (S)- or (R)-3-[(E)-enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a general method for efficient preparation of beta-substituted pyroglutamic acids. Case of topographically controlled stereoselectivity.

PubMed

Soloshonok, Vadim A; Cai, Chaozhong; Yamada, Takeshi; Ueki, Hisanori; Ohfune, Yasufumi; Hruby, Victor J

2005-11-02

This paper describes a systematic study of addition reactions between the chiral Ni(II) complex of the Schiff base of glycine with (S)-o-[N-(N-benzylprolyl)amino]benzophenone and (S)- or (R)-3-[(E)-enoyl]-4-phenyl-1,3-oxazolidin-2-ones as a general and synthetically efficient approach to beta-substituted pyroglutamic acids and relevant compounds. These reactions were shown to occur at room temperature in the presence of nonchelating organic bases and, most notably, with very high (>98% diastereomeric excess (de)) stereoselectivity at both newly formed stereogenic centers. The stereochemical outcome of the reactions was found to be overwhelmingly controlled by the stereochemical preferences of the Michael acceptors, and the chirality of the glycine complex influenced only the reaction rate. Thus, in the reactions of both the (S)-configured Ni(II) complex and the Michael acceptors, the reaction rates were exceptionally high, allowing preparation of the corresponding products with virtually quantitative (>98%) chemical and stereochemical yields. In contrast, reactions of the (S)-configured Ni(II) complex and (R)-configured Michael acceptors proceeded at noticeably lower rates, but the addition products were obtained in high diastereo- and enantiomeric purity. To rationalize the remarkably high and robust stereoselectivity observed in these reactions, we consider an enzyme-substrate-like mode of interaction involving a topographical match or mismatch of two geometric figures. Excellent chemical and stereochemical yields, combined with the simplicity and operational convenience of the experimental procedures, render the present method of immediate use for preparing various beta-substituted pyroglutamic acids and related compounds.

An Investigation of Carbon-Based Nanomaterials for Efficient Energy Production And Delivery

NASA Astrophysics Data System (ADS)

Gangoli, Varun Shenoy

Carbon-based nanomaterials have been demonstrated to have different potential applications in the energy industry. However, there are challenges in the realization of these applications. Chirality of single wall carbon nanotubes (SWCNTs) defines their electronic properties, and obtaining an ensemble of SWCNTs of the same chirality has been a problem studied for over two decades with no clear solution yet. Other carbon-based nanomaterials, such as carbon black aggregates, are hydrophobic in nature and potential applications in the oil and gas industry require their dispersal in an aqueous solvent. Another application in the oil and gas industry is enhanced oil recovery (EOR), and here there is a need for an inexpensive, stable, and efficient surfactant compared to currently used industrial solutions. The challenge of producing SWCNTs of the same chirality is studied using two approaches--separation after synthesis of SWCNTs of mixed chiralities, and chemical control over chirality of as-synthesized SWCNTs. Agarose gel-based affinity chromatography was used as a means towards highly semiconductor- enriched SWCNTs using a family of nonionic surfactants. UV-vis-NIR spectroscopy, Raman spectroscopy and photoluminescence spectroscopy was used to quantify the separation efficiency of the metal- and semiconductor-enriched SWCNTs. This process is an improvement over other chromatography-based techniques at the time in that the nonionic surfactants used are less expensive, enable a higher purity of semiconductor SWCNTs (>95%) and decompose fully by simply heating in air thus leaving behind pristine SWCNTs. The second approach was based on using catalyst dopants to preferentially synthesize SWCNTs of a particular chirality at the expense of SWCNTs of other chiralities. Heterogeneous catalysis combined with the screw dislocation theory of SWCNT growth provided the background for this work, and both selenium and phosphorus were identified as chemical dopants for iron catalysts. Both selenium and phosphorus were demonstrated to have a direct effect on the average number density and length of SWCNTs, and selenium also was shown to have a direct control over the growth rate of SWCNTs. This, combined with some preliminary spectroscopy results, suggest chiral control over the carbon nanotubes. Collaborative work on phase transfer of hydrophobic carbon-based nanomaterials into aqueous solvents for applications including saturated oil residual (SOR) detection and quantification in underground reservoirs helped recognize the potential of hydrophobically modified polymers as surfactants for EOR. Polystyrene sulfonate was chosen as the polymer of study owing to ease of availability, low cost of the precursor material and aromatic sulfonates already being studied for EOR. Controlled desulfonation of PSS was achieved by rapid heating of an aqueous solution of PSS in a microwave reactor under acidic conditions, with the reactant temperature and pH having a strong effect on the degree of desulfonation of the product ranging from 4.9% (as-obtained PSS) to 40%. Dynamic light scattering of the desulfonated PSS (termed PDS) in brine showed good stability of the polymer aggregates at temperatures as high as 150 °C, and tensiometry with aromatic oils such as toluene and aliphatic oils such as Isopar L showed good surface activity with interfacial tension going as low as 10-2 mN/m. Breakthrough experiments with sand packed columns at the lab scale, and core flooding at an independent facility confirmed good propagation of PDS through materials such as Berea sandstone, with minimal plugging and adsorption losses.

Strong-field control and enhancement of chiral response in bi-elliptical high-order harmonic generation: an analytical model

NASA Astrophysics Data System (ADS)

Ayuso, David; Decleva, Piero; Patchkovskii, Serguei; Smirnova, Olga

2018-06-01

The generation of high-order harmonics in a medium of chiral molecules driven by intense bi-elliptical laser fields can lead to strong chiroptical response in a broad range of harmonic numbers and ellipticities (Ayuso et al 2018 J. Phys. B: At. Mol. Opt. Phys. 51 06LT01). Here we present a comprehensive analytical model that can describe the most relevant features arising in the high-order harmonic spectra of chiral molecules driven by strong bi-elliptical fields. Our model recovers the physical picture underlying chiral high-order harmonic generation (HHG) based on ultrafast chiral hole motion and identifies the rotationally invariant molecular pseudoscalars responsible for chiral dynamics. Using the chiral molecule propylene oxide as an example, we show that one can control and enhance the chiral response in bi-elliptical HHG by tailoring the driving field, in particular by tuning its frequency, intensity and ellipticity, exploiting a suppression mechanism of achiral background based on the linear Stark effect.

Construction of a D-amino acid oxidase reactor based on magnetic nanoparticles modified by a reactive polymer and its application in screening enzyme inhibitors.

PubMed

Mu, Xiaoyu; Qiao, Juan; Qi, Li; Liu, Ying; Ma, Huimin

2014-08-13

Developing facile and high-throughput methods for exploring pharmacological inhibitors of D-amino acid oxidase (DAAO) has triggered increasing interest. In this work, DAAO was immobilized on the magnetic nanoparticles, which were modified by a biocompatible reactive polymer, poly(glycidyl methacrylate) (PGMA) via an atom transfer radical polymerization technique. Interestingly, the enzyme immobilization process was greatly promoted with the assistance of a lithium perchlorate catalyst. Meanwhile, a new amino acid ionic liquid (AAIL) was successfully synthesized and employed as the efficient chiral ligand in a chiral ligand exchange capillary electrophoresis (CLE-CE) system for chiral separation of amino acids (AAs) and quantitation of methionine, which was selected as the substrate of DAAO. Then, the apparent Michaelis-Menten constants in the enzyme system were determined with the proposed CLE-CE method. The prepared DAAO-PGMA-Fe3O4 nanoparticles exhibited excellent reusability and good stability. Moreover, the enzyme reactor was successfully applied in screening DAAO inhibitors. These results demonstrated that the enzyme could be efficiently immobilized on the polymer-grafted magnetic nanoparticles and that the obtained enzyme reactor has great potential in screening enzyme inhibitors, further offering new insight into monitoring the relevant diseases.

Synthesis and characterization of sugar based low molecular weight gelators and the preparation of chiral sulfinamides

NASA Astrophysics Data System (ADS)

Mangunuru, Hari Prasad Reddy

Low molecular weight gelators (LMWGs) have received considerable attention in the field of chemistry from last few decades. These compounds form self-assembled fibrous networks like micelles, cylindrical, sheets, fibers, layers and so on. The fibrous network entraps the solvent and forms gel, because of the self-assembly phenomenon and their demonstrated potential uses in a variety of areas, ranging from environmental to medicinal applications. Sugars are good starting materials to synthesize the new class of LMWG's, because these are different from some expensive materials, these are natural products. We have synthesized and characterized the LMGS's based on D-glucose and D-glucosamine. D-glucosamine is the versatile starting material to make different peptoids and triazoles. Several series of compounds were synthesized using compounds 1-3 as starting material and studied the gelation behavior all the compounds. We have studied the self-assembling properties of a new class of tripeptoids, synthesized by one-pot Ugi reaction from simple starting materials. Among the focused library of tripeptoids synthesized, we found that several efficient low molecular weight organogelators were obtained for aqueous DMSO and ethanol mixtures. We have also synthesized and characterized a series of monosaccharide triazole derivatives. These compounds were synthesized from N-acetyl glucosamine and D-glucose via a Cu(I) catalyzed azide/alkyne cycloaddition reaction (CuAAc). The compounds have been screened for their gelation properties and several efficient low molecular weight organo/hydro gelators were obtained, among these compounds, five per-acetyl glucosamine derivatives and one peracetyl glucose derivative were able to form gels in water. These new molecules are expected to be useful in drug delivery and tissue engineering.*. Asymmetric synthesis of chiral amines is a challenging in synthetic organic chemistry. The development of new catalysts for asymmetric organic transformations is a very important research goal in modern synthetic organic chemistry. We have synthesized a new class of chiral oxathiozinone from chiral amino phenol. From this synthesized chiral sulfinamides, ketimines followed by reducing the ketimines synthesized the highly hindered chiral amines. *Please refer to dissertation for diagrams.

Highly enantioselective reductive amination of simple aryl ketones catalyzed by Ir-f-Binaphane in the presence of titanium(IV) isopropoxide and iodine.

PubMed

Chi, Yongxiang; Zhou, Yong-Gui; Zhang, Xumu

2003-05-16

Using an Ir-f-Binaphane complex as the catalyst, complete conversions and high enantioselectivies (up to 96% ee) were achieved in the asymmetric reductive amination of aryl ketones in the presence of Ti(O(i)()Pr)(4) and I(2). A simple and efficient method of synthesizing chiral primary amines has been realized.

Iridoids from Carbohydrates via Pauson-Khand Reaction: Synthesis of Advanced Highly Oxygenated Cyclopentane-Annulated Pyranosides from D-Glucal Derivatives.

PubMed

Marco-Contelles, José; Ruiz-Caro, Juliana

1999-10-29

The Pauson-Khand reaction on suitable 4-oxa-hept-1-en-6-ynes (1, 17) obtained from 3,4,6-tri-O-acetyl-D-glucal gives the cyclopentane-annulated pyranosides (2, 18) that can be efficiently and stereoselectivelly transformed into chiral, advanced, highly oxygenated intermediates (10, 16, 24) for the synthesis of iridoid aglycones.

Biomimetic catalytic transformation of toxic α-oxoaldehydes to high-value chiral α-hydroxythioesters using artificial glyoxalase I

NASA Astrophysics Data System (ADS)

Park, Sang Yeon; Hwang, In-Soo; Lee, Hyun-Ju; Song, Choong Eui

2017-04-01

Glyoxalase I plays a critical role in the enzymatic defence against glycation by catalysing the isomerization of hemithioacetal, formed spontaneously from cytotoxic α-oxoaldehydes and glutathione, to (S)-α-hydroxyacylglutathione derivatives. Upon the hydrolysis of the thioesters catalysed by glyoxalase II, inert (S)-α-hydroxy acids, that is, lactic acid, are then produced. Herein, we demonstrate highly enantioselective glyoxalase I mimic catalytic isomerization of in-situ-generated hemithioacetals, providing facile access to both enantiomers of α-hydroxy thioesters. Owing to the flexibility of thioesters, a family of optically pure α-hydroxyamides, which are highly important drug candidates in the pharmaceutical industry, were prepared without any coupling reagents. Similar to real enzymes, the enforced proximity of the catalyst and substrates by the chiral cage in situ formed by the incorporation of potassium salt can enhance the reactivity and efficiently transfer the stereochemical information.

Metal ion-improved complexation countercurrent chromatography for enantioseparation of dihydroflavone enantiomers.

PubMed

Han, Chao; Wang, Wenli; Xue, Guimin; Xu, Dingqiao; Zhu, Tianyu; Wang, Shanshan; Cai, Pei; Luo, Jianguang; Kong, Lingyi

2018-01-12

Cu(II) ion was selected as an additive to improve the enantioseparation efficiency of three dihydroflavone enantiomers in high-speed counter-current chromatography (HSCCC), using hydroxypropyl-β-cyclodextrin (HP-β-CyD) as the chiral selector. The influences of important parameters, including the metal ion, the concentrations of HP-β-CyD and the Cu(II) ion, and the sample size were investigated. Under optimal conditions, three dihydroflavone enantiomers, including (±)-hesperetin, (±)-naringenin, and (±)-farrerol, were successfully enantioseparated. The chiral recognition mechanism was investigated. The enantioseparation was attributed to the different thermodynamic stabilities of the binary complexes of HP-β-CyD and (±)-hesperetin, and Cu(II) ion could enhance this difference by forming ternary complexes with the binary complexes. This Cu(II) ion-improved complexation HSCCC system exhibited improved performance for chiral separation, and therefore it has great application potential in the preparative enantioseparation of other compounds with similar skeletons. Copyright © 2017 Elsevier B.V. All rights reserved.

Chiral reagents in glycosylation and modification of carbohydrates.

PubMed

Wang, Hao-Yuan; Blaszczyk, Stephanie A; Xiao, Guozhi; Tang, Weiping

2018-02-05

Carbohydrates play a significant role in numerous biological events, and the chemical synthesis of carbohydrates is vital for further studies to understand their various biological functions. Due to the structural complexity of carbohydrates, the stereoselective formation of glycosidic linkages and the site-selective modification of hydroxyl groups are very challenging and at the same time extremely important. In recent years, the rapid development of chiral reagents including both chiral auxiliaries and chiral catalysts has significantly improved the stereoselectivity for glycosylation reactions and the site-selectivity for the modification of carbohydrates. These new tools will greatly facilitate the efficient synthesis of oligosaccharides, polysaccharides, and glycoconjugates. In this tutorial review, we will summarize these advances and highlight the most recent examples.

Generalized Liquid Crystals: Giant Fluctuations and the Vestigial Chiral Order of I , O , and T Matter

NASA Astrophysics Data System (ADS)

Liu, Ke; Nissinen, Jaakko; Slager, Robert-Jan; Wu, Kai; Zaanen, Jan

2016-10-01

The physics of nematic liquid crystals has been the subject of intensive research since the late 19th century. However, the focus of this pursuit has been centered around uniaxial and biaxial nematics associated with constituents bearing a D∞ h or D2 h symmetry, respectively. In view of general symmetries, however, these are singularly special since nematic order can in principle involve any point-group symmetry. Given the progress in tailoring nanoparticles with particular shapes and interactions, this vast family of "generalized nematics" might become accessible in the laboratory. Little is known because the order parameter theories associated with the highly symmetric point groups are remarkably complicated, involving tensor order parameters of high rank. Here, we show that the generic features of the statistical physics of such systems can be studied in a highly flexible and efficient fashion using a mathematical tool borrowed from high-energy physics: discrete non-Abelian gauge theory. Explicitly, we construct a family of lattice gauge models encapsulating nematic ordering of general three-dimensional point-group symmetries. We find that the most symmetrical generalized nematics are subjected to thermal fluctuations of unprecedented severity. As a result, novel forms of fluctuation phenomena become possible. In particular, we demonstrate that a vestigial phase carrying no more than chiral order becomes ubiquitous departing from high point-group symmetry chiral building blocks, such as I , O , and T symmetric matter.

Direct organocatalytic enantioselective functionalization of SiOx surfaces.

PubMed

Parkin, John David; Chisholm, Ross; Frost, Aileen B; Bailey, Richard G; Smith, Andrew David; Hähner, Georg

2018-06-05

Traditional methods to prepare chiral surfaces involve either the adsorption of a chiral molecule onto an achiral surface, or adsorption of a species that forms a chiral template creating lattices with long range order. To date only limited alternative strategies to prepare chiral surfaces have been studied. In this manuscript a "bottom up" approach is developed that allows the preparation of chiral surfaces by direct enantioselective organocatalysis on a functionalized Si-oxide supported self-assembled monolayer (SAM). The efficient catalytic generation of enantiomerically enriched organic surfaces is achieved using a commercially available homogeneous isothiourea catalyst (HyperBTM) that promotes an enantioselective Michael-lactonization process upon a Si-oxide supported self-assembled monolayer functionalized with a reactive trifluoroenone group. Chiral atomic force microscopy (chi-AFM) is used to probe the enantiomeric enrichment of the organic films by measurement of the force distributions arising from interaction of D- or L-cysteine modified AFM tips and the organic films. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer

NASA Astrophysics Data System (ADS)

Coles, R. J.; Price, D. M.; Dixon, J. E.; Royall, B.; Clarke, E.; Kok, P.; Skolnick, M. S.; Fox, A. M.; Makhonin, M. N.

2016-03-01

Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95+/-5% and have potential to serve as the basis of spin-logic and network implementations.

Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer

PubMed Central

Coles, R. J.; Price, D. M.; Dixon, J. E.; Royall, B.; Clarke, E.; Kok, P.; Skolnick, M. S.; Fox, A. M.; Makhonin, M. N.

2016-01-01

Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations. PMID:27029961

Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer.

PubMed

Coles, R J; Price, D M; Dixon, J E; Royall, B; Clarke, E; Kok, P; Skolnick, M S; Fox, A M; Makhonin, M N

2016-03-31

Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations.

Chiral catalysts immobilized on achiral polymers: effect of the polymer support on the performance of the catalyst.

PubMed

Altava, Belén; Burguete, M Isabel; García-Verdugo, Eduardo; Luis, Santiago V

2018-04-23

Positive effects of the polymeric support on the performance of supported chiral catalysts, in terms of activity, stability and selectivity-enantioselectivity, have been reported when the support is properly selected and optimized opening the way to the design of more efficient catalytic systems.

Functional characterization of salt-tolerant microbial esterase WDEst17 and its use in the generation of optically pure ethyl (R)-3-hydroxybutyrate.

PubMed

Wang, Yilong; Xu, Yongkai; Zhang, Yun; Sun, Aijun; Hu, Yunfeng

2018-06-01

The two enantiomers of ethyl 3-hydroxybutyrate are important intermediates for the synthesis of a great variety of valuable chiral drugs. The preparation of chiral drug intermediates through kinetic resolution reactions catalyzed by esterases/lipases has been demonstrated to be an efficient and environmentally friendly method. We previously functionally characterized microbial esterase PHE21 and used PHE21 as a biocatalyst to generate optically pure ethyl (S)-3-hydroxybutyrate. Herein, we also functionally characterized one novel salt-tolerant microbial esterase WDEst17 from the genome of Dactylosporangium aurantiacum subsp. Hamdenensis NRRL 18085. Esterase WDEst17 was further developed as an efficient biocatalyst to generate (R)-3-hydroxybutyrate, an important chiral drug intermediate, with the enantiomeric excess being 99% and the conversion rate being 65.05%, respectively, after process optimization. Notably, the enantio-selectivity of esterase WDEst17 was opposite than that of esterase PHE21. The identification of esterases WDEst17 and PHE21 through genome mining of microorganisms provides useful biocatalysts for the preparation of valuable chiral drug intermediates. © 2018 Wiley Periodicals, Inc.

Polarization- and wavelength-resolved near-field imaging of complex plasmonic modes in Archimedean nanospirals

DOE PAGES

Hachtel, Jordan A.; Davidson, II, Roderick B.; Kovalik, Elena R.; ...

2018-02-15

Asymmetric nanophotonic structures enable a wide range of opportunities in optical nanotechnology because they support efficient optical nonlinearities mediated by multiple plasmon resonances over a broad spectral range. The Archimedean nanospiral is a canonical example of a chiral plasmonic structure because it supports even-order nonlinearities that are not generally accessible in locally symmetric geometries. However, the complex spiral response makes nanoscale experimental characterization of the plasmonic near-field structure highly desirable. As a result, we employ high-efficiency, high-spatial-resolution cathodoluminescence imaging in a scanning transmission electron microscope to describe the spatial, spectral, and polarization response of plasmon modes in the nanospiral geometry.

Polarization- and wavelength-resolved near-field imaging of complex plasmonic modes in Archimedean nanospirals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hachtel, Jordan A.; Davidson, II, Roderick B.; Kovalik, Elena R.

Asymmetric nanophotonic structures enable a wide range of opportunities in optical nanotechnology because they support efficient optical nonlinearities mediated by multiple plasmon resonances over a broad spectral range. The Archimedean nanospiral is a canonical example of a chiral plasmonic structure because it supports even-order nonlinearities that are not generally accessible in locally symmetric geometries. However, the complex spiral response makes nanoscale experimental characterization of the plasmonic near-field structure highly desirable. As a result, we employ high-efficiency, high-spatial-resolution cathodoluminescence imaging in a scanning transmission electron microscope to describe the spatial, spectral, and polarization response of plasmon modes in the nanospiral geometry.

Generalized Oseen transformation for and enhancement of Bragg characteristics of electro-optic structurally chiral materials

NASA Astrophysics Data System (ADS)

Lakhtakia, Akhlesh

2006-05-01

The Oseen transformation is generalized to define a non-electro-optic structurally chiral material, wherein propagation along the axis of chirality is equivalent to that in an electro-optic SCM with local 4¯2m point group symmetry. This generalization shows that the exploitation of the Pockels effect amounts to an enhancement of the effective local birefringence, which in turn can enhance the characteristics of the circular Bragg phenomenon. Electro-optic SCMs can therefore serve as efficient and electrically controllable circular- and elliptical-polarization rejection filters.

Catalytic asymmetric trifluoromethylthiolation via enantioselective [2,3]-sigmatropic rearrangement of sulfonium ylides

NASA Astrophysics Data System (ADS)

Zhang, Zhikun; Sheng, Zhe; Yu, Weizhi; Wu, Guojiao; Zhang, Rui; Chu, Wen-Dao; Zhang, Yan; Wang, Jianbo

2017-10-01

The trifluoromethylthio (SCF3) functional group has been of increasing importance in drug design and development as a consequence of its unique electronic properties and high stability coupled with its high lipophilicity. As a result, methods to introduce this highly electronegative functional group have attracted considerable attention in recent years. Although significant progress has been made in the introduction of SCF3 functionality into a variety of molecules, there remain significant challenges regarding the enantioselective synthesis of SCF3-containing compounds. Here, an asymmetric trifluoromethylthiolation that proceeds through the enantioselective [2,3]-sigmatropic rearrangement of a sulfonium ylide generated from a metal carbene and sulfide (Doyle-Kirmse reaction) has been developed using chiral Rh(II) and Cu(I) catalysts. This transformation features mild reaction conditions and excellent enantioselectivities (up to 98% yield and 98% e.e.), thus providing a unique, highly efficient and enantioselective method for the construction of C(sp3)-SCF3 bonds bearing chiral centres.

Stereoselective determination of amino acids in beta-amyloid peptides and senile plaques.

PubMed

Thorsén, G; Bergquist, J; Westlind-Danielsson, A; Josefsson, B

2001-06-01

A novel method for the determination of the enantiomeric composition of peptides is presented. In this paper, the focus has been on beta-amyloid peptides from deceased Alzheimer's disease patients. The peptides are hydrolyzed using mineral acid. The free amino acids are derivatized with the chiral reagent (+)- or (-)-1-(9-anthryl)-2-propyl chloroformate and subsequently separated using micellar electrokinetic chromatography (MEKC) and detected using laser-induced fluorescence (LIF) detection. The high separation efficiency of the MEKC-LIF system, yielding approximately 1 million theoretical plates/m for most amino acids, facilitates the simultaneous chiral determination of nine amino acids. The samples that have been analyzed were standard 1-40 beta-amyloid peptides, in vitro precipitated beta-amyloid fibrils, and human senile plaque samples.

Molecular dynamics simulation of a nanofluidic energy absorption system: effects of the chiral vector of carbon nanotubes.

PubMed

Ganjiani, Sayed Hossein; Hossein Nezhad, Alireza

2018-02-14

A Nanofluidic Energy Absorption System (NEAS) is a novel nanofluidic system with a small volume and weight. In this system, the input mechanical energy is converted to surface tension energy during liquid infiltration in the nanotube. The NEAS is made of a mixture of nanoporous material particles in a functional liquid. In this work, the effects of the chiral vector of a carbon nanotube (CNT) on the performance characteristics of the NEAS are investigated by using molecular dynamics simulation. For this purpose, six CNTs with different diameters for each type of armchair, zigzag and chiral, and several chiral CNTs with different chiral vectors (different values of indices (m,n)) are selected and studied. The results show that in the chiral CNTs, the contact angle shows the hydrophobicity of the CNT, and infiltration pressure is reduced by increasing the values of m and n (increasing the CNT diameter). Contact angle and infiltration pressure are decreased by almost 1.4% and 9% at all diameters, as the type of CNT is changed from chiral to zigzag and then to armchair. Absorbed energy density and efficiency are also decreased by increasing m and n and by changing the type of CNT from chiral to zigzag and then to armchair.

The combination of high Q factor and chirality in twin cavities and microcavity chain

PubMed Central

Song, Qinghai; Zhang, Nan; Zhai, Huilin; Liu, Shuai; Gu, Zhiyuan; Wang, Kaiyang; Sun, Shang; Chen, Zhiwei; Li, Meng; Xiao, Shumin

2014-01-01

Chirality in microcavities has recently shown its bright future in optical sensing and microsized coherent light sources. The key parameters for such applications are the high quality (Q) factor and large chirality. However, the previous reported chiral resonances are either low Q modes or require very special cavity designs. Here we demonstrate a novel, robust, and general mechanism to obtain the chirality in circular cavity. By placing a circular cavity and a spiral cavity in proximity, we show that ultra-high Q factor, large chirality, and unidirectional output can be obtained simultaneously. The highest Q factors of the non-orthogonal mode pairs are almost the same as the ones in circular cavity. And the co-propagating directions of the non-orthogonal mode pairs can be reversed by tuning the mode coupling. This new mechanism for the combination of high Q factor and large chirality is found to be very robust to cavity size, refractive index, and the shape deformation, showing very nice fabrication tolerance. And it can be further extended to microcavity chain and microcavity plane. We believe that our research will shed light on the practical applications of chirality and microcavities. PMID:25262881

Occurrence, elimination, enantiomeric distribution and intra-day variations of chiral pharmaceuticals in major wastewater treatment plants in Beijing, China.

PubMed

Duan, Lei; Zhang, Yizhe; Wang, Bin; Deng, Shubo; Huang, Jun; Wang, Yujue; Yu, Gang

2018-04-18

The occurrence, eliminations, enantiomeric distribution and intra-day variations of five chiral pharmaceuticals (three beta-blockers and two antidepressants) were investigated in eight major WWTPs in Beijing, China. The results revealed that metoprolol (MTP) and venlafaxine (VFX) were of the highest concentrations among the five determined pharmaceuticals with mean concentrations of 803 ng L -1 and 408 ng L -1 , respectively in influents, and 354 ng L -1 and 165 ng L -1 in effluents, respectively. Their removal efficiencies, intra-day concentration changes and enantiomeric profiles during wastewater treatment were further analyzed. Loads of these two chiral pharmaceuticals were also studied to reveal drug use pattern. A/A/O+MBR (anaerobic/anoxic/oxic + membrane bio-reactor) followed by joint disinfection treatment process exhibited the high removal efficiencies. No or weak enantioselectivity was observed in most WWTPs. However, obvious enantiomeric fraction (EF) changing of MTP was observed in WWTP3 employing A/A/O+MBR. Intra-day concentration fluctuations of MTP were smaller than VFX. A quick response to sudden rise influent concentration of MTP was observed in WWTP1 effluent but EF response lagged behind. Similar bihourly EF variations in influents and effluents were also observed in most WWTPs for MTP and VFX in consideration of hydraulic residence time (HRT). Copyright © 2018 Elsevier Ltd. All rights reserved.

Chiral permselectivity in surface-modified nanoporous opal films.

PubMed

Cichelli, Julie; Zharov, Ilya

2006-06-28

Nanoporous 7 mum thin opal films comprising 35 layers of 200 nm diameter SiO2 spheres were assembled on Pt electrodes and modified with chiral selector moieties on the silica surface. Diffusion of chiral redox species through the opals was studied by cyclic voltammetry. The chiral opal films demonstrate high selectivity for transport of one enantiomer over the other. This chiral permselectivity is attributed to the surface-facilitated transport utilizing noncovalent interactions between the chiral permeant molecules and surface-bound chiral selectors.

Chiral imidate-ferrocenylphosphanes: synthesis and application as P,N-ligands in iridium(I)-catalyzed hydrogenation of unfunctionalized and poorly functionalized olefins.

PubMed

Bert, Katrien; Noël, Timothy; Kimpe, Wim; Goeman, Jan L; Van der Eycken, Johan

2012-11-14

A small library of chiral imidate-ferrocenylphosphane ligands was efficiently synthesized (8 examples) and evaluated in the iridium(I)-catalyzed hydrogenation of unfunctionalized and poorly functionalized olefins. These catalysts perform very well in a range of examples (yields and ee's up to 100%).

Asymmetric catalytic cascade reactions for constructing diverse scaffolds and complex molecules.

PubMed

Wang, Yao; Lu, Hong; Xu, Peng-Fei

2015-07-21

With the increasing concerns about chemical pollution and sustainability of resources, among the significant challenges facing synthetic chemists are the development and application of elegant and efficient methods that enable the concise synthesis of natural products, drugs, and related compounds in a step-, atom- and redox-economic manner. One of the most effective ways to reach this goal is to implement reaction cascades that allow multiple bond-forming events to occur in a single vessel. This Account documents our progress on the rational design and strategic application of asymmetric catalytic cascade reactions in constructing diverse scaffolds and synthesizing complex chiral molecules. Our research is aimed at developing robust cascade reactions for the systematic synthesis of a range of interesting molecules that contain structural motifs prevalent in natural products, pharmaceuticals, and biological probes. The strategies employed to achieve this goal can be classified into three categories: bifunctional base/Brønsted acid catalysis, covalent aminocatalysis/N-heterocyclic carbene catalysis, and asymmetric organocatalytic relay cascades. By the use of rationally designed substrates with properly reactive sites, chiral oxindole, chroman, tetrahydroquinoline, tetrahydrothiophene, and cyclohexane scaffolds were successfully assembled under bifunctional base/Brønsted acid catalysis from simple and readily available substances such as imines and nitroolefins. We found that some of these reactions are highly efficient since catalyst loadings as low as 1 mol % can promote the multistep sequences affording complex architectures with high stereoselectivities and yields. Furthermore, one of the bifunctional base/Brønsted acid-catalyzed cascade reactions for the synthesis of chiral cyclohexanes has been used as a key step in the construction of the tetracyclic core of lycorine-type alkaloids and the formal synthesis of α-lycorane. Guided by the principles of covalent aminocatalysis and N-heterocyclic carbene catalysis, we synthesized chiral piperidine, indole, and cyclobutane derivatives. The synthesis of chiral cyclobutanes and pyrroloindolones showed unprecedented reactivity of substrates and catalysts. The development of the strategy of asymmetric organocatalytic relay cascades has provided a useful tool for the controlled synthesis of specific diastereomers in complex molecules. This Account gives a panoramic view and the logic of our research on the design, development, and applications of asymmetric catalytic cascade reactions that will potentially provide useful insights into exploring new reactions.

Chiral Separations

NASA Astrophysics Data System (ADS)

Stalcup, A. M.

2010-07-01

The main goal of this review is to provide a brief overview of chiral separations to researchers who are versed in the area of analytical separations but unfamiliar with chiral separations. To researchers who are not familiar with this area, there is currently a bewildering array of commercially available chiral columns, chiral derivatizing reagents, and chiral selectors for approaches that span the range of analytical separation platforms (e.g., high-performance liquid chromatography, gas chromatography, supercritical-fluid chromatography, and capillary electrophoresis). This review begins with a brief discussion of chirality before examining the general strategies and commonalities among all of the chiral separation techniques. Rather than exhaustively listing all the chiral selectors and applications, this review highlights significant issues and differences between chiral and achiral separations, providing salient examples from specific classes of chiral selectors where appropriate.

Chiral supramolecular organization from a sheet-like achiral gel: a study of chiral photoinduction.

PubMed

Royes, Jorge; Polo, Víctor; Uriel, Santiago; Oriol, Luis; Piñol, Milagros; Tejedor, Rosa M

2017-05-31

Chiral photoinduction in a photoresponsive gel based on an achiral 2D architecture with high geometric anisotropy and low roughness has been investigated. Circularly polarized light (CPL) was used as a chiral source and an azobenzene chromophore was employed as a chiral trigger. The chiral photoinduction was studied by evaluating the preferential excitation of enantiomeric conformers of the azobenzene units. Crystallographic data and density functional theory (DFT) calculations show how chirality is transferred to the achiral azomaterials as a result of the combination of chiral photochemistry and supramolecular interactions. This procedure could be applied to predict and estimate chirality transfer from a chiral physical source to a supramolecular organization using different light-responsive units.

Criteria of backscattering in chiral one-way photonic crystals

NASA Astrophysics Data System (ADS)

Cheng, Pi-Ju; Chang, Shu-Wei

2016-03-01

Optical isolators are important devices in photonic circuits. To reduce the unwanted reflection in a robust manner, several setups have been realized using nonreciprocal schemes. In this study, we show that the propagating modes in a strongly-guided chiral photonic crystal (no breaking of the reciprocity) are not backscattering-immune even though they are indeed insensitive to many types of scatters. Without the protection from the nonreciprocity, the backscattering occurs under certain circumstances. We present a perturbative method to calculate the backscattering of chiral photonic crystals in the presence of chiral/achiral scatters. The model is, essentially, a simplified analogy to the first-order Born approximation. Under reasonable assumptions based on the behaviors of chiral photonic modes, we obtained the expression of reflection coefficients which provides criteria for the prominent backscattering in such chiral structures. Numerical examinations using the finite-element method were also performed and the results agree well with the theoretical prediction. From both our theory and numerical calculations, we find that the amount of backscattering critically depends on the symmetry of scatter cross sections. Strong reflection takes place when the azimuthal Fourier components of scatter cross sections have an order l of 2. Chiral scatters without these Fourier components would not efficiently reflect the chiral photonic modes. In addition, for these chiral propagating modes, disturbances at the most significant parts of field profiles do not necessarily result in the most effective backscattering. The observation also reveals what types of scatters or defects should be avoided in one-way applications of chiral structures in order to minimize the backscattering.

Use of chiral cell shape to ensure highly directional swimming in trypanosomes

PubMed Central

2017-01-01

Swimming cells typically move along a helical path or undergo longitudinal rotation as they swim, arising from chiral asymmetry in hydrodynamic drag or propulsion bending the swimming path into a helix. Helical paths are beneficial for some forms of chemotaxis, but why asymmetric shape is so prevalent when a symmetric shape would also allow highly directional swimming is unclear. Here, I analyse the swimming of the insect life cycle stages of two human parasites; Trypanosoma brucei and Leishmania mexicana. This showed quantitatively how chirality in T. brucei cell shape confers highly directional swimming. High speed videomicrographs showed that T. brucei, L. mexicana and a T. brucei RNAi morphology mutant have a range of shape asymmetries, from wild-type T. brucei (highly chiral) to L. mexicana (near-axial symmetry). The chiral cells underwent longitudinal rotation while swimming, with more rapid longitudinal rotation correlating with swimming path directionality. Simulation indicated hydrodynamic drag on the chiral cell shape caused rotation, and the predicted geometry of the resulting swimming path matched the directionality of the observed swimming paths. This simulation of swimming path geometry showed that highly chiral cell shape is a robust mechanism through which microscale swimmers can achieve highly directional swimming at low Reynolds number. It is insensitive to random variation in shape or propulsion (biological noise). Highly symmetric cell shape can give highly directional swimming but is at risk of giving futile circular swimming paths in the presence of biological noise. This suggests the chiral T. brucei cell shape (associated with the lateral attachment of the flagellum) may be an adaptation associated with the bloodstream-inhabiting lifestyle of this parasite for robust highly directional swimming. It also provides a plausible general explanation for why swimming cells tend to have strong asymmetries in cell shape or propulsion. PMID:28141804

Chiral Responsive Liquid Quantum Dots.

PubMed

Zhang, Jin; Ma, Junkai; Shi, Fangdan; Tian, Demei; Li, Haibing

2017-08-01

How to convert the weak chiral-interaction into the macroscopic properties of materials remains a huge challenge. Here, this study develops highly fluorescent, selectively chiral-responsive liquid quantum dots (liquid QDs) based on the hydrophobic interaction between the chiral chains and the oleic acid-stabilized QDs, which have been designated as (S)-1810-QDs. The fluorescence spectrum and liquidity of thermal control demonstrate the fluorescence properties and the fluidic behavior of (S)-1810-QDs in the solvent-free state. Especially, (S)-1810-QDs exhibit a highly chiral-selective response toward (1R, 2S)-2-amino-1,2-diphenyl ethanol. It is anticipated that this study will facilitate the construction of smart chiral fluidic sensors. More importantly, (S)-1810-QDs can become an attractive material for chiral separation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral amine synthesis using ω-transaminases: an amine donor that displaces equilibria and enables high-throughput screening.

PubMed

Green, Anthony P; Turner, Nicholas J; O'Reilly, Elaine

2014-09-26

The widespread application of ω-transaminases as biocatalysts for chiral amine synthesis has been hampered by fundamental challenges, including unfavorable equilibrium positions and product inhibition. Herein, an efficient process that allows reactions to proceed in high conversion in the absence of by-product removal using only one equivalent of a diamine donor (ortho-xylylenediamine) is reported. This operationally simple method is compatible with the most widely used (R)- and (S)-selective ω-TAs and is particularly suitable for the conversion of substrates with unfavorable equilibrium positions (e.g., 1-indanone). Significantly, spontaneous polymerization of the isoindole by-product generates colored derivatives, providing a high-throughput screening platform to identify desired ω-TA activity. © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Production of natural antioxidants from vegetable oil deodorizer distillates: effect of catalytic hydrogenation.

PubMed

Pagani, María Ayelén; Baltanás, Miguel A

2010-02-01

Natural tocopherols are one of the main types of antioxidants found in living creatures, but they also have other critical biological functions. The biopotency of natural (+)-alpha-tocopherol (RRR) is 36% higher than that of the synthetic racemic mixture and 300% higher than the SRR stereoisomer. Vegetable oil deodorizer distillates (DD) are an excellent source of natural tocopherols. Catalytic hydrogenation of DD preconcentrates has been suggested as a feasible route for recovery of tocopherols in high yield. However, it is important to know whether the hydrogenation operation, as applied to these tocopherol-rich mixtures, is capable of preserving the chiral (RRR) character, which is critical to its biopotency. Fortified (i.e., (+)-alpha-tocopherol enriched) sunflower oil and methyl stearate, as well as sunflower oil DD, were fully hydrogenated using commercial Ni and Pd catalysts (120-180 degrees C; 20-60 psig). Products were analyzed by chiral HPLC. Results show that the desired chiral configuration (RRR) is fully retained. Thus, the hydrogenation route can be safely considered as a valid alternative for increasing the efficiency of tocopherol recovery processes from DDs while preserving their natural characteristics.

Enantioseparation of α-Hydroxyallylphosphonates and Phosphonoallylic Carbonate Derivatives on Chiral Stationary Phases Using Sequential UV, Polarimetric, and Refractive Index Detection.

PubMed

Hamper, Bruce C; Mannino, Michael P; Mueller, Melissa E; Harrison, Liam T; Spilling, Christopher D

2016-09-01

Chromatographic separation of the enantiomers of parent compounds dimethyl α-hydroxyallyl phosphonate and 1-(dimethoxyphosphoryl) allyl methyl carbonate was demonstrated by high-performance liquid chromatography (HPLC) using Chiralpak AS-H and ad-H chiral stationary phases (CSP), respectively, using a combination of UV, polarimetric, and refractive index detectors. A comparison was made of the separation efficiency and elution order of enantiomeric α-hydroxyallyl phosphonates and their carbonate derivatives on commercially available polysaccharide AS, ad, OD, IC-3, and Whelk-O 1 CSPs. In general, the α-hydroxyallyl phosphonates were resolved on the AS-H CSP, whereas the carbonate derivatives and were preferentially resolved on the ad-H CSP. The impact of aryl substitution on the resolution of analytes and was evaluated. Thermodynamic parameters determined for enantioselective adsorption hydroxyphosphonates and on the AS-H CSP and carbonate on the ad-H CSP demonstrated enthalpic control for separation of the enantiomers. Chirality 28:656-662, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

The kinetics of chirality assignment in catalytic single-walled carbon nanotube growth and the routes towards selective growth.

PubMed

Xu, Ziwei; Qiu, Lu; Ding, Feng

2018-03-21

Depending on its specific structure, or so-called chirality, a single-walled carbon nanotube (SWCNT) can be either a conductor or a semiconductor. This feature ensures great potential for building ∼1 nm sized electronics if chirality-selected SWCNTs could be achieved. However, due to the limited understanding of the growth mechanism of SWCNTs, reliable methods for chirality-selected SWCNTs are still pending. Here we present a theoretical model on the chirality assignment and control of SWCNTs during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of pentagons, especially the last (6 th ) one, during the nucleation stage. Our analysis showed that the chirality of a SWCNT is randomly assigned on a liquid or liquid-like catalyst surface, and two routes of synthesizing chirality-selected SWCNTs, which are verified by recent experimental achievements, are demonstrated. They are (i) by using high melting point crystalline catalysts, such as Ta, W, Re, Os, or their alloys, and (ii) by frequently changing the chirality of SWCNTs during their growth. This study paves the way for achieving chirality-selective SWCNT growth for high performance SWCNT based electronics.

Synthetic versatility of 2-substituted-6-methyl 2,3-dihydropyridinones in the synthesis of polyfunctional piperidine-based compounds and related β amino acid derivatives.

PubMed

Yang, Yang; Hardman, Clayton

2017-10-18

Chiral 2-substituted-6-methyl 2,3-dihydropyidinones 9, which can be facilely obtained from an asymmetric vinylogous Mannich reaction (VMR) with 1,3-bis-trimethysily enol ether, were used as versatile intermediates in constructing chiral polyfunctional piperidine-based compounds. The 6-methyl group of such compounds can be conveniently functionalized via alkylation and acylation reactions to provide efficient entries to the synthesis of a variety of chiral multi-substituted piperidine-based compounds. Further elaboration of the corresponding intermediates also provided access to polyfunctional indolizidine-based compounds. These methods were showcased in an asymmetric synthesis of 2,6-di-substituted piperidine compound 13, reported as the key intermediate in the synthesis of (+)-calvine and a natural alkaloid (-)-indolizidine 209D. Furthermore, selective C5 iodination of compound 9 enabled the installation of additional functional groups at this position. Finally, we demonstrated that the oxidative cleavage of 2-substituted-6-methyl-2,3-dihydropyidinones is a practical and efficient method for the enantioselective synthesis of β-amino acids, which can undergo further intra-molecular cyclization to give the corresponding chiral four-membered β-lactam derivatives.

Ultra-fast switching blue phase liquid crystals diffraction grating stabilized by chiral monomer

NASA Astrophysics Data System (ADS)

Manda, Ramesh; Pagidi, Srinivas; Sarathi Bhattacharya, Surjya; Yoo, Hyesun; T, Arun Kumar; Lim, Young Jin; Lee, Seung Hee

2018-05-01

We have demonstrated an ultra-fast switching and efficient polymer stabilized blue phase liquid crystal (PS-BPLC) diffraction grating utilizing a chiral monomer. We have obtained a 0.5 ms response time by a novel polymer stabilization method which is three times faster than conventional PS-BPLC. In addition, the diffraction efficiency was improved 2% with a much wider phase range and the driving voltage to switch the device is reduced. The polarization properties of the diffracted beam are unaffected by this novel polymer stabilization. This device can be useful for future photonic applications.

Efficient synthesis, structural characterization and anti-microbial activity of chiral aryl boronate esters of 1,2-O-isopropylidene-α-D-xylofuranose.

PubMed

Trivedi, Rajiv; Rami Reddy, E; Kiran Kumar, Ch; Sridhar, B; Pranay Kumar, K; Srinivasa Rao, M

2011-07-01

A simple and efficient synthetic approach toward a series of chiral aryl boronate esters, starting from D-xylose, as anti-microbial agents, is described herein. Minimum inhibitory concentration and zone of inhibition revealed that these derivatives exhibit potent anti-bacterial and anti-fungal properties. Herein, we report the first anti-microbial activity of this class of compounds. All products have been characterized by NMR ((1)H, (13)C and (11)B), IR, elemental and mass spectral study. Copyright © 2011 Elsevier Ltd. All rights reserved.

Enantioselective Rhodium-Catalyzed Dimerization of ω-Allenyl Carboxylic Acids: Straightforward Synthesis of C2 -Symmetric Macrodiolides.

PubMed

Steib, Philip; Breit, Bernhard

2018-04-19

Herein, we report on the first enantioselective and atom-efficient catalytic one-step dimerization method to selectively transform ω-allenyl carboxylic acids into C 2 -symmetric 14- to 28-membered bismacrolactones (macrodiolides). This convenient asymmetric access serves as an attractive route towards multiple naturally occuring homodimeric macrocyclic scaffolds and demonstrates excellent efficiency to construct the complex, symmetric core structures. By utilizing a rhodium catalyst with a modified chiral cyclopentylidene-diop ligand, the desired diolides were obtained in good to high yields, high diastereoselectivity, and excellent enantioselectivity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigating the nature of chiral near-field interactions

NASA Astrophysics Data System (ADS)

Barr, Lauren E.; Horsley, Simon A. R.; Hooper, Ian R.; Eager, Jake K.; Gallagher, Cameron P.; Hornett, Samuel M.; Hibbins, Alastair P.; Hendry, Euan

2018-04-01

In recent years, there have been reports of enhanced chiroptical interactions in the near-fields of antennas, postulated to be mediated by high spatial gradients in the electromagnetic fields. Here, using gigahertz experimentation, we investigate the nature of the chiral near-field generated by an array of staggered-rod antennas through its interaction with an array of aligned, subwavelength metallic helices. This allows us to eliminate many potential origins of enhancements, such as those associated with plasmon-exciton interactions, and search solely for enhancements due to the high spatial gradients in the chirality of the fields around chiral antennas (so-called `superchiral fields'). By comparing the strength of the chiral interaction with our helices to that of a homogeneous chiral layer with effective material parameters, we find that the strength of this chiral interaction can be predicted using a completely local effective medium approximation. This suggests no obvious enhancement in the chiral interaction in the near-field and indicates that nonlocal interactions are negligible in this system.

Enantioseparation by Capillary Electrophoresis Using Ionic Liquids as Chiral Selectors.

PubMed

Greño, Maider; Marina, María Luisa; Castro-Puyana, María

2018-11-02

Capillary electrophoresis (CE) is one of the most widely employed analytical techniques to achieve enantiomeric separations. In spite of the fact that there are many chiral selectors commercially available to perform enantioseparations by CE, one of the most relevant topics in this field is the search for new selectors capable of providing high enantiomeric resolutions. Chiral ionic liquids (CILs) have interesting characteristics conferring them a high potential in chiral separations although only some of them are commercially available. The aim of this article is to review all the works published on the use of CILs as chiral selectors in the development of enantioselective methodologies by CE, covering the period from 2006 (when the first research work on this topic was published) to 2017. The use of CILs as sole chiral selectors, as chiral selectors in dual systems or as chiral ligands will be considered. This review also provides detailed analytical information on the experimental conditions used to carry out enantioseparations in different fields as well as on the separation mechanism involved.

Experimental comparison of chiral metal-organic framework used as stationary phase in chromatography.

PubMed

Xie, Sheng-Ming; Zhang, Mei; Fei, Zhi-Xin; Yuan, Li-Ming

2014-10-10

Chiral metal-organic frameworks (MOFs) are a new class of multifunctional material, which possess diverse structures and unusual properties such as high surface area, uniform and permanent cavities, as well as good chemical and thermal stability. Their chiral functionality makes them attractive as novel enantioselective adsorbents and stationary phases in separation science. In this paper, the experimental comparison of a chiral MOF [In₃O(obb)₃(HCO₂)(H₂O)] solvent used as a stationary phase was investigated in gas chromatography (GC), high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). The potential relationship between the structure and components of chiral MOFs with their chiral recognition ability and selectivity are presented. Copyright © 2014 Elsevier B.V. All rights reserved.

[Deletion of a dynamic surface loop improves thermostability of (R)-selective amine transaminase from Aspergillus terreus].

PubMed

Xie, Dongfang; Lv, Changjiang; Fang, Hui; Yang, Weikang; Hu, Sheng; Zhao, Weirui; Huang, Jun; Mei, Lehe

2017-12-25

Chiral amines are important building blocks for the synthesis of pharmaceutical products and fine chemicals. Highly stereoselective synthesis of chiral amines compounds through asymmetric amination has attracted more and more attention. ω-transaminases (ω-TAs) are a promising class of natural biocatalysts which provide an efficient and environment-friendly access to production of chiral amines with stringent enantioselectivity and excellent catalytic efficiency. Compared with (S)-ω-TA, the research focused on (R)-ω-TA was relatively less. However, increasing demand for chiral (R)-amines as pharmaceutical intermediates has rendered industrial applications of (R)-ω-TA more attractive. Improving the thermostability of (R)-ω-TA with potential biotechnological application will facilitate the preparation of chiral amines. In this study, the dynamic surface loop with higher B-factor from Aspergillus terreus (R)-ω-TA was predicted by two computer softwares (PyMOL and YASARA). Then mutant enzymes were obtained by deleting amino acid residues of a dynamic surface loop using site-directed mutagenesis. The results showed that the best two mutants R131del and P132-E133del improved thermostability by 2.6 ℃ and 0.9 ℃ in T₅₀¹⁰ (41.1 ℃ and 39.4 ℃, respectively), and 2.2-fold and 1.5-fold in half-life (t1/2) at 40 ℃ (15.0 min and 10.0 min, respectively), compared to that of wild type. Furtherly, the thermostability mechanism of the mutant enzymes was investigated by molecular dynamics (MD) simulation and intermolecular interaction analysis. R131del in the loop region has lower root mean square fluctuation (RMSF) than the wild type at 400 K for 10 ns, and mutant enzyme P132-E133del increases four hydrogen bonds in the loop region. In this study, we obtain two stability-increased mutants of (R)-ω-TA from A. terreus by deleting its dynamic surface loop and also provide methodological guidance for the use of rational design to enhance the thermal stability of other enzymes.

Hydrolysis of ibuprofenoyl-CoA and other 2-APA-CoA esters by human acyl-CoA thioesterases-1 and -2 and their possible role in the chiral inversion of profens.

PubMed

Qu, Xiao; Allan, Amanda; Chui, Grace; Hutchings, Thomas J; Jiao, Ping; Johnson, Lawrence; Leung, Wai Y; Li, Portia K; Steel, Georgina R; Thompson, Andrew S; Threadgill, Michael D; Woodman, Timothy J; Lloyd, Matthew D

2013-12-01

Ibuprofen and related 2-arylpropanoic acid (2-APA) drugs are often given as a racemic mixture and the R-enantiomers undergo activation in vivo by metabolic chiral inversion. The chiral inversion pathway consists of conversion of the drug to the coenzyme A ester (by an acyl-CoA synthetase) followed by chiral inversion by α-methylacyl-CoA racemase (AMACR; P504S). The enzymes responsible for hydrolysis of the product S-2-APA-CoA ester to the active S-2-APA drug have not been identified. In this study, conversion of a variety of 2-APA-CoA esters by human acyl-CoA thioesterase-1 and -2 (ACOT-1 and -2) was investigated. Human recombinant ACOT-1 and -2 (ACOT-1 and -2) were both able to efficiently hydrolyse a variety of 2-APA-CoA substrates. Studies with the model substrates R- and S-2-methylmyristoyl-CoA showed that both enzymes were able to efficiently hydrolyse both of the epimeric substrates with (2R)- and (2S)- methyl groups. ACOT-1 is located in the cytosol and is able to hydrolyse 2-APA-CoA esters exported from the mitochondria and peroxisomes for inhibition of cyclo-oxygenase-1 and -2 in the endoplasmic reticulum. It is a prime candidate to be the enzyme responsible for the pharmacological action of chiral inverted drugs. ACOT-2 activity may be important in 2-APA toxicity effects and for the regulation of mitochondrial free coenzyme A levels. These results support the idea that 2-APA drugs undergo chiral inversion via a common pathway. Copyright © 2013 Elsevier Inc. All rights reserved.

A novel chiral separation material: polymerized organogel formed by chiral gelators for the separation of D- and L-phenylalanine.

PubMed

Fu, Xinjian; Yang, Yang; Wang, Ningxia; Wang, Hong; Yang, Yajiang

2007-01-01

N-Stearine-N'-stearyl-L-phenylalanine, a chiral compound, was synthesized and used as a gelator for the gelation of polymerizable solvents, such as ss-hydroxyethyl methacrylate (HEMA), styrene, etc. The scanning electron microscope (SEM) images of the gelator aggregates show fibril-like helices, typical chiral aggregates with diameters of 100-200 nm. The solvent molecules were immobilized by capillary forces in the three-dimensional network structures of the organogels. The HEMA organogels containing crosslinker polyethylene glycol dimethacrylates (PEG200DMA) were subsequently polymerized by in situ UV irradiation. A porous polymerized organogels were obtained after removal of gelator aggregates through ethanol extraction. The chiral separation of D- and L-phenylalanine was carried out by the adsorption of the polymerized organogels. The adsorption efficiency of L-phenylalanine on the polymerized organogels was found to be dependent on the concentration of the gelator and crosslinker. (c) 2007 John Wiley & Sons, Ltd.

Using heteroaryl-lithium reagents as hydroxycarbonyl anion equivalents in conjugate addition reactions with (S,S)-(+)-pseudoephedrine as chiral auxiliary; enantioselective synthesis of 3-substituted pyrrolidines.

PubMed

Alonso, Beatriz; Ocejo, Marta; Carrillo, Luisa; Vicario, Jose L; Reyes, Efraim; Uria, Uxue

2013-01-18

We have developed an efficient protocol for carrying out the stereocontrolled formal conjugate addition of hydroxycarbonyl anion equivalents to α,β-unsaturated carboxylic acid derivatives using (S,S)-(+)-pseudoephedrine as chiral auxiliary, making use of the synthetic equivalence between the heteroaryl moieties and the carboxylate group. This protocol has been applied as key step in the enantioselective synthesis of 3-substituted pyrrolidines in which, after removing the chiral auxiliary, the heteroaryl moiety is converted into a carboxylate group followed by reduction and double nucleophilic displacement. Alternatively, the access to the same type of heterocyclic scaffold but with opposite absolute configuration has also been accomplished by making use of the regio- and diastereoselective conjugate addition of organolithium reagents to α,β,γ,δ-unsaturated amides derived from the same chiral auxiliary followed by chiral auxiliary removal, ozonolysis, and reductive amination/intramolecular nucleophilic displacement sequence.

Spin-orbit beams for optical chirality measurement

NASA Astrophysics Data System (ADS)

Samlan, C. T.; Suna, Rashmi Ranjan; Naik, Dinesh N.; Viswanathan, Nirmal K.

2018-01-01

Accurate measurement of chirality is essential for the advancement of natural and pharmaceutical sciences. We report here a method to measure chirality using non-separable states of light with geometric phase-gradient in the circular polarization basis, which we refer to as spin-orbit beams. A modified polarization Sagnac interferometer is used to generate spin-orbit beams wherein the spin and orbital angular momentum of the input Gaussian beam are coupled. The out-of-phase interference between counter-propagating Gaussian beams with orthogonal spin states and lateral-shear or/and linear-phase difference between them results in spin-orbit beams with linear and azimuthal phase gradient. The spin-orbit beams interact efficiently with the chiral medium, inducing a measurable change in the center-of-mass of the beam, using the polarization rotation angle and hence the chirality of the medium are accurately calculated. Tunable dynamic range of measurement and flexibility to introduce large values of orbital angular momentum for the spin-orbit beam, to improve the measurement sensitivity, highlight the techniques' versatility.

HPLC of fluoroquinolone antibacterials using chiral stationary phase based on enantiomeric (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6.

PubMed

Choi, Hee Jung; Cho, Hwan Sun; Han, Sang Cheol; Hyun, Myung Ho

2009-02-01

A residual silanol group-protecting chiral stationary phase (CSP) based on optically active (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 was successfully applied to the resolution of fluoroquinolone compounds including gemifloxacin mesylate. The chiral recognition ability of the residual silanol group-protecting CSP was generally greater than that of the residual silanol group-containing CSP. From these results, it was concluded that the simple protection of the residual silanol groups of the latter CSP with lipophilic n-octyl groups can improve its chiral recognition ability for the resolution of racemic fluoroquinolone compounds. The chromatographic resolution behaviors were investigated as a function of the content and type of organic and acidic modifiers and the ammonium acetate concentration in aqueous mobile phase and the column temperature. Especially, the addition of ammonium acetate to the mobile phase was found to be a quite effective means of reducing the enantiomer retentions without sacrificing the chiral recognition efficiency of the CSP.

High-performance liquid chromatographic separations of stereoisomers of chiral basic agrochemicals with polysaccharide-based chiral columns and polar organic mobile phases.

PubMed

Matarashvili, Iza; Shvangiradze, Iamze; Chankvetadze, Lali; Sidamonidze, Shota; Takaishvili, Nino; Farkas, Tivadar; Chankvetadze, Bezhan

2015-12-01

The separation of the stereoisomers of 23 chiral basic agrochemicals was studied on six different polysaccharide-based chiral columns in high-performance liquid chromatography with various polar organic mobile phases. Along with the successful separation of analyte stereoisomers, emphasis was placed on the effect of the chiral selector and mobile phase composition on the elution order of stereoisomers. The interesting phenomenon of reversal of enantiomer/stereoisomer elution order function of the polysaccharide backbone (cellulose or amylose), type of derivative (carbamate or benzoate), nature, and position of the substituent(s) in the phenylcarbamate moiety (methyl or chloro) and the nature of the mobile phase was observed. For several of the analytes containing two chiral centers all four stereoisomers were resolved with at least one chiral selector/mobile phase combination. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

New stereoselective intramolecular

PubMed

Alajarin; Vidal; Tovar; Ramirez De Arellano MC; Cossio; Arrieta; Lecea

2000-11-03

Efficient 1,4-asymmetric induction has been achieved in the highly stereocontrolled intramolecular [2 + 2] cycloadditions between ketenimines and imines, leading to 1,2-dihydroazeto[2, 1-b]quinazolines. The chiral methine carbon adjacent to the iminic nitrogen controls the exclusive formation of the cycloadducts with relative trans configuration at C2 and C8. The stepwise mechanistic model, based on theoretical calculations, fully supports the stereochemical outcome of these cycloadditions.

Generalized liquid crystals: Giant fluctuations and the vestigial chiral order of I , O , and T matter

DOE PAGES

Liu, Ke; Nissinen, Jaakko; Slager, Robert -Jan; ...

2016-10-31

Here, the physics of nematic liquid crystals has been the subject of intensive research since the late 19th century. However, the focus of this pursuit has been centered around uniaxial and biaxial nematics associated with constituents bearing a D ∞h or D 2h symmetry, respectively. In view of general symmetries, however, these are singularly special since nematic order can in principle involve any point-group symmetry. Given the progress in tailoring nanoparticles with particular shapes and interactions, this vast family of “generalized nematics” might become accessible in the laboratory. Little is known because the order parameter theories associated with the highlymore » symmetric point groups are remarkably complicated, involving tensor order parameters of high rank. Here, we show that the generic features of the statistical physics of such systems can be studied in a highly flexible and efficient fashion using a mathematical tool borrowed from high-energy physics: discrete non-Abelian gauge theory. Explicitly, we construct a family of lattice gauge models encapsulating nematic ordering of general three-dimensional point-group symmetries. We find that the most symmetrical generalized nematics are subjected to thermal fluctuations of unprecedented severity. As a result, novel forms of fluctuation phenomena become possible. In particular, we demonstrate that a vestigial phase carrying no more than chiral order becomes ubiquitous departing from high point-group symmetry chiral building blocks, such as I, O, and T symmetric matter.« less

Nano-amylose-2,3-bis(3,5-dimethylphenylcarbamate)-silica hybrid sol immobilized on open tubular capillary column for capillary electrochromatography enantioseparation.

PubMed

Sun, Yaming; Wu, Qi; Shi, Xiaofeng; Gao, Jie; Dong, Shuqing; Zhao, Liang

2018-04-01

The chiral organic-inorganic hybrid materials can exhibit a high loading, and the chiral selector nanoparticles can create efficient stationary phases for open-tubular capillary electrochromatography (OT-CEC). Hence, a novel protocol for the preparation of an OT column coated with nano-amylose-2,3-bis(3,5-dimethylphenylcarbamate) (nano-ABDMPC)-silica hybrid sol through in situ layer-by-layer self-assembly method was developed for CEC enantioseparation. By controlling the assembly cycle number of nano-ABDMPC-silica hybrid sol, a homogeneous, dense and stable coating was successfully prepared, which was confirmed by SEM and elemental analysis. As the main parameter influencing the chiral separating effect, the nano-ABDMPC bearing 3-(triethoxysilyl)propyl residues concentration was investigated. The experimental results showed that 10.0 mg/mL nano-ABDMPC bearing 3-(triethoxysilyl)propyl residues coated OT capillary column possessed chiral recognition ability toward the six enantiomers (phenylalanine, tyrosine, tryptophan, phenethyl alcohol, 1-phenyl-2-propanol, and Tröger's base) at some of the different conditions tested. Additionally, the coated OT column revealed adequate repeatability concerning run-to-run, day-to-day and column-to-column. These results demonstrated the promising applicability of nano-ABDMPC-silica hybrid sol coated OT column in CEC enantioseparations. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A rapid and efficient one-pot method for the reduction of N-protected α-amino acids to chiral α-amino aldehydes using CDI/DIBAL-H.

PubMed

Ivkovic, Jakov; Lembacher-Fadum, Christian; Breinbauer, Rolf

2015-11-14

N-Protected amino acids can be easily converted into chiral α-amino aldehydes in a one-pot reaction by activation with CDI followed by reduction with DIBAL-H. This method delivers Boc-, Cbz- and Fmoc-protected amino aldehydes from proteinogenic amino acids in very good isolated yields and complete stereointegrity.

FRET ratiometric probes reveal the chiral-sensitive cysteine-dependent H2S production and regulation in living cells

NASA Astrophysics Data System (ADS)

Wei, Lv; Yi, Long; Song, Fanbo; Wei, Chao; Wang, Bai-Fan; Xi, Zhen

2014-04-01

Hydrogen sulfide (H2S) is an endogenously produced gaseous signalling molecule with multiple biological functions. In order to visualize and quantify the endogenous in situ production of H2S in living cells, here we developed two new sulphide ratiometric probes (SR400 and SR550) based on fluorescence resonance energy transfer (FRET) strategy for live capture of H2S. The FRET-based probes show excellent selectivity toward H2S in a high thiol background under physiological buffer. The probe can be used to in situ visualize cysteine-dependent H2S production in a chiral-sensitive manner in living cells. The ratiometric imaging studies indicated that D-Cys induces more H2S production than that of L-Cys in mitochondria of human embryonic kidney 293 cells (HEK293). The cysteine mimics propargylglycine (PPG) has also been found to inhibit the cysteine-dependent endogenous H2S production in a chiral-sensitive manner in living cells. D-PPG inhibited D-Cys-dependent H2S production more efficiently than L-PPG, while, L-PPG inhibited L-Cys-dependent H2S production more efficiently than D-PPG. Our bioimaging studies support Kimura's discovery of H2S production from D-cysteine in mammalian cells and further highlight the potential of D-cysteine and its derivatives as an alternative strategy for classical H2S-releasing drugs.

Emergence of Chiral Phases in Active Torque Dipole Systems

NASA Astrophysics Data System (ADS)

Fialho, Ana; Tjhung, Elsen; Cates, Michael; Marenduzzo, Davide

The common description of active particles as active force dipoles fails to take into account that active processes in biological systems often exhibit chiral asymmetries, generating active chiral processes and torque dipoles. Examples of such systems include cytoskeleton filaments which interact with motor proteins and beating cilia and flagella. In particular, the generation of active torques by the actomyosin cytoskeleton has been linked to the break of chiral symmetry at a cellular level. This phenomenon could constitute the primary determinant for the break of left-right symmetry in many living organisms, e.g. the position of the human heart within the human body. In order to account for the effects of chirality, we consider active torque dipoles which generate a chiral active stress. We characterize quasi-1D and 2D systems of torque dipoles, using a combination of linear stability analysis and numerical simulations (Lattice Boltzmann). Our results show that activity drives a spontaneous breaking of chiral symmetry, leading to the self-assembly of a chiral phase, in the absence of any thermodynamic interactions favoring cholesteric ordering. At high values of activity, we also observe labyrinthine patterns where the activity-induced chiral ordering is highly frustrated.

Broadband chirality and asymmetric transmission in ultrathin 90°-twisted Babinet-inverted metasurfaces

NASA Astrophysics Data System (ADS)

Shi, J. H.; Ma, H. F.; Guan, C. Y.; Wang, Z. P.; Cui, T. J.

2014-04-01

A broadband asymmetric transmission of linearly polarized waves with totally suppressed copolarization transmission is experimentally demonstrated in ultrathin 90°-twisted Babinet-inverted metasurfaces constructed by an array of asymmetrically split ring apertures. The only accessible direction-dependent cross-polarization transmission is allowed in this anisotropic chiral metamaterial. Through full-wave simulation and experiment results, the bilayered Babinet-inverted metasurface reveals broadband artificial chirality and asymmetric transmission, with a transmission contrast that is better than 17.7 dB within a 50% relative bandwidth for two opposite directions. In particular, we can modify polarization conversion efficiency and the bandwidth of asymmetric transmission via parametric study.

Chiral monolithic absorbent constructed by optically active helical-substituted polyacetylene and graphene oxide: preparation and chiral absorption capacity.

PubMed

Li, Weifei; Wang, Bo; Yang, Wantai; Deng, Jianping

2015-02-01

Chiral monolithic absorbent is successfully constructed for the first time by using optically active helical-substituted polyacetylene and graphene oxide (GO). The preparative strategy is facile and straightforward, in which chiral-substituted acetylene monomer (Ma), cross-linker (Mb), and alkynylated GO (Mc) undergo copolymerization to form the desired monolithic absorbent in quantitative yield. The resulting monoliths are characterized by circular dichroism, UV-vis absorption, scanning electron microscopy (SEM), FT-IR, Raman, energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), XPS, and thermogravimetric analysis (TGA) techniques. The polymer chains derived from Ma form chiral helical structures and thus provide optical activity to the monoliths, while GO sheets contribute to the formation of porous structures. The porous structure enables the monolithic absorbents to demonstrate a large swelling ratio in organic solvents, and more remarkably, the helical polymer chains provide optical activity and further enantio-differentiating absorption ability. The present study establishes an efficient and versatile methodology for preparing novel functional materials, in particular monolithic chiral materials based on substituted polyacetylene and GO. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measuring the electromagnetic chirality of 2D arrays under normal illumination.

PubMed

Garcia-Santiago, X; Burger, S; Rockstuhl, C; Fernandez-Corbaton, I

2017-10-15

We present an electromagnetic chirality measure for 2D arrays of subwavelength periodicities under normal illumination. The calculation of the measure uses only the complex reflection and transmission coefficients from the array. The measure allows the ordering of arrays according to their electromagnetic chirality, which further allows a quantitative comparison of different design strategies. The measure is upper bounded, and the extreme properties of objects with high values of electromagnetic chirality make them useful in both near- and far-field applications. We analyze the consequences that different possible symmetries of the array have on its electromagnetic chirality. We use the measure to study four different arrays. The results indicate the suitability of helices for building arrays of high electromagnetic chirality, and the low effectiveness of a substrate for breaking the transverse mirror symmetry.

Efficient palladium-catalyzed asymmetric allylic alkylation of ketones and aldehydes.

PubMed

Zhao, Xiaohu; Liu, Delong; Xie, Fang; Liu, Yangang; Zhang, Wanbin

2011-03-21

Palladium-catalyzed asymmetric allylic alkylation of ketones, via enamines generated in situ as nucleophiles, were carried out smoothly with chiral metallocene-based P,N-ligands. Under the same conditions, however, reactions of aldehydes could hardly be observed. Subsequently, this obstacle was resolved by using chiral metallocene-based P,P-ligands. Both ketones and aldehydes afforded excellent enantioselectivities with up to 98% ee and 94% ee, respectively.

Highly Enantioselective Rhodium-Catalyzed Addition of Arylboroxines to Simple Aryl Ketones: Efficient Synthesis of Escitalopram.

PubMed

Huang, Linwei; Zhu, Jinbin; Jiao, Guangjun; Wang, Zheng; Yu, Xingxin; Deng, Wei-Ping; Tang, Wenjun

2016-03-24

Highly enantioselective additions of arylboroxines to simple aryl ketones have been achieved for the first time with a Rh/(R,R,R,R)-WingPhos catalyst, thus providing a range of chiral diaryl alkyl carbinols with excellent ee values and yields. (R,R,R,R)-WingPhos has been proven to be crucial for the high reactivity and enantioselectivity. The method has enabled a new, concise, and enantioselective synthesis of the antidepressant drug escitalopram. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Asymmetric counteranion-directed Lewis acid organocatalysis for the scalable cyanosilylation of aldehydes

NASA Astrophysics Data System (ADS)

Zhang, Zhipeng; Bae, Han Yong; Guin, Joyram; Rabalakos, Constantinos; van Gemmeren, Manuel; Leutzsch, Markus; Klussmann, Martin; List, Benjamin

2016-08-01

Due to the high versatility of chiral cyanohydrins, the catalytic asymmetric cyanation reaction of carbonyl compounds has attracted widespread interest. However, efficient protocols that function at a preparative scale with low catalyst loading are still rare. Here, asymmetric counteranion-directed Lewis acid organocatalysis proves to be remarkably successful in addressing this problem and enabled a molar-scale cyanosilylation in quantitative yield and with excellent enantioselectivity. Also, the catalyst loading could be lowered to a part-per-million level (50 ppm: 0.005 mol%). A readily accessible chiral disulfonimide was used, which in combination with trimethylsilyl cyanide, turned into the active silylium Lewis acid organocatalyst. The nature of a peculiar phenomenon referred to as a ``dormant period'', which is mainly induced by water, was systematically investigated by means of in situ Fourier transform infrared analysis.

Scaleable catalytic asymmetric Strecker syntheses of unnatural α-amino acids

PubMed Central

Zuend, Stephan J.; Coughlin, Matthew P.; Lalonde, Mathieu P.; Jacobsen, Eric N.

2009-01-01

α-Amino acids are essential building blocks for protein synthesis, and are also widely useful as components of medicinally active molecules and chiral catalysts.1,2,3,4,5 Efficient chemo-enzymatic methods for the synthesis of enantioenriched α-amino acids have been devised, but the scope of these methods for the synthesis of unnatural amino acids is limited.6,7 Alkene hydrogenation is broadly useful for enantioselective catalytic synthesis of many classes of amino acids,8,9 but this approach is not applicable to the synthesis of α-amino acids bearing aryl or quaternary alkyl α-substituents. The Strecker synthesis—the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis—is an especially versatile chemical method for the synthesis of racemic α-amino acids (Fig. 1).10,11 Asymmetric Strecker syntheses using stoichiometric chiral reagents have been applied successfully on gram-to-multi-kilogram scales to the preparation of enantiomerically enriched α-amino acids.12,13,14 In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen only limited use on preparative scales (e.g., > 1 gram).15,16 The limited use of existing catalytic methodologies may be ascribed to several important practical drawbacks, including the relatively complex and precious nature of the catalysts, and the requisite use of hazardous cyanide sources. Herein we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-proteinogenic amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. Because this catalyst is robust and lacks sensitive functional groups, it is compatible with safely handled aqueous cyanide salts, and is thus adaptable to large-scale synthesis. This new methodology can be applied to the efficient syntheses of amino acids that are not readily prepared by enzymatic methods or by chemical hydrogenation. PMID:19829379

Anomalous transport from holography. Part I

NASA Astrophysics Data System (ADS)

Bu, Yanyan; Lublinsky, Michael; Sharon, Amir

2016-11-01

We revisit the transport properties induced by the chiral anomaly in a charged plasma holographically dual to anomalous U(1) V ×U(1) A Maxwell theory in Schwarzschild-AdS5. Off-shell constitutive relations for vector and axial currents are derived using various approximations generalising most of known in the literature anomaly-induced phenomena and revealing some new ones. In a weak external field approximation, the constitutive relations have all-order derivatives resummed into six momenta-dependent transport co-efficient functions: the diffusion, the electric/magnetic conductivity, and three anomaly induced functions. The latter generalise the chiral magnetic and chiral separation effects. Nonlinear transport is studied assuming presence of constant background external fields. The chiral magnetic effect, including all order nonlinearity in magnetic field, is proven to be exact when the magnetic field is the only external field that is turned on. Non-linear corrections to the constitutive relations due to electric and axial external fields are computed.

Pseudopterosin synthesis from a chiral cross-conjugated hydrocarbon through a series of cycloadditions

NASA Astrophysics Data System (ADS)

Newton, Christopher G.; Drew, Samuel L.; Lawrence, Andrew L.; Willis, Anthony C.; Paddon-Row, Michael N.; Sherburn, Michael S.

2015-01-01

The pseudopterosins are a family of diterpene marine natural products, which, by virtue of their interesting anti-inflammatory and analgesic properties, have attracted the attentions of many synthetic chemists. The most efficient syntheses reported to date are 14 and 20 steps in the longest linear sequence for chiral pool and enantioselective approaches, respectively, and all start with precursors that are easily mapped onto the natural product structure. Here, we describe an unconventional approach in which a chiral cross-conjugated hydrocarbon is used as the starting material for a series of three cycloadditions. Our approach has led to a significant reduction in the step count required to access these interesting natural products (10 steps chiral pool and 11 steps enantioselective). Furthermore it demonstrates that cross-conjugated hydrocarbons, erroneously considered by many to be too unstable and difficult to handle, are viable precursors for natural product synthesis.

Separation of piracetam derivatives on polysaccharide-based chiral stationary phases.

PubMed

Kažoka, H; Koliškina, O; Veinberg, G; Vorona, M

2013-03-15

High-performance liquid chromatography was used for the enantiomeric separation of two chiral piracetam derivatives. The suitability of six commercially available polysaccharide-based chiral stationary phases (CSPs) under normal phase mode for direct enantioseparation has been investigated. The influence of the CSPs as well the nature and content of an alcoholic modifier in the mobile phase on separation and elution order was studied. It was established that CSP Lux Amylose-2 shows high chiral recognition ability towards 4-phenylsubstituted piracetam derivatives. Copyright © 2013 Elsevier B.V. All rights reserved.

Spin-Selective Transmission and Devisable Chirality in Two-Layer Metasurfaces.

PubMed

Li, Zhancheng; Liu, Wenwei; Cheng, Hua; Chen, Shuqi; Tian, Jianguo

2017-08-15

Chirality is a nearly ubiquitous natural phenomenon. Its minute presence in most naturally occurring materials makes it incredibly difficult to detect. Recent advances in metasurfaces indicate that they exhibit devisable chirality in novel forms; this finding offers an effective opening for studying chirality and its features in such nanostructures. These metasurfaces display vast possibilities for highly sensitive chirality discrimination in biological and chemical systems. Here, we show that two-layer metasurfaces based on twisted nanorods can generate giant spin-selective transmission and support engineered chirality in the near-infrared region. Two designed metasurfaces with opposite spin-selective transmission are proposed for treatment as enantiomers and can be used widely for spin selection and enhanced chiral sensing. Specifically, we demonstrate that the chirality in these proposed metasurfaces can be adjusted effectively by simply changing the orientation angle between the twisted nanorods. Our results offer simple and straightforward rules for chirality engineering in metasurfaces and suggest intriguing possibilities for the applications of such metasurfaces in spin optics and chiral sensing.

Chiral mirror and optical resonator designs for circularly polarized light: suppression of cross-polarized reflectances and transmittances

NASA Astrophysics Data System (ADS)

Hodgkinson, Ian J.; Wu, Qi h.; Arnold, Matthew; McCall, Martin W.; Lakhtakia, Akhlesh

2002-09-01

A left-handed chiral sculptured thin film (STF) that reflects strongly at the wavelength of the circular Bragg resonance tends to partially convert the handedness of incident LCP (left-circularly-polarized) light to RCP (right-circularly-polarized). We show that the cross-polarized component of the reflected RCP beam can be eliminated by interference with an additional RCP beam that is reflected at the interface of an isotropic cover and an AR (antireflecting) layer. For best results the refractive index and thickness of the AR layer need to accommodate a phase change on reflection that occurs at the chiral film. Effective suppression of the reflectances RRR, RRL, RLR and the transmittances TRL, TLR can be achieved by sandwiching the chiral reflector between such amplitude and phase-matched AR coatings. Co-polarized chiral reflectors of this type may form efficient handed optical resonators. For LCP light the optical properties of such a handed resonator are formally the same as the properties of the isotropic passive or active Fabry-Perot resonators, but the handed resonator is transparent to RCP light.

Chromatographic peak deconvolution of constitutional isomers by multiple-reaction-monitoring mass spectrometry.

PubMed

Trapp, Oliver

2010-02-12

Highly efficient and sophisticated separation techniques are available to analyze complex compound mixtures with superior sensitivities and selectivities often enhanced by a 2nd dimension, e.g. a separation technique or spectroscopic and spectrometric techniques. For enantioselective separations numerous chiral stationary phases (CSPs) exist to cover a broad range of chiral compounds. Despite these advances enantioselective separations can become very challenging for mixtures of stereolabile constitutional isomers, because the on-column interconversion can lead to completely overlapping peak profiles. Typically, multidimensional separation techniques, e.g. multidimensional GC (MDGC), using an achiral 1st separation dimension and transferring selected analytes to a chiral 2nd separation are the method of choice to approach such problems. However, this procedure is very time consuming and only predefined sections of peaks can be transferred by column switching to the second dimension. Here we demonstrate for stereolabile 1,2-dialkylated diaziridines a technique to experimentally deconvolute overlapping gas chromatographic elution profiles of constitutional isomers based on multiple-reaction-monitoring MS (MRM-MS). The here presented technique takes advantage of different fragmentation probabilities and pathways to isolate the elution profile of configurational isomers. Copyright 2009 Elsevier B.V. All rights reserved.

QCD In Extreme Conditions

NASA Astrophysics Data System (ADS)

Wilczek, Frank

Introduction Symmetry and the Phenomena of QCD Apparent and Actual Symmetries Asymptotic Freedom Confinement Chiral Symmetry Breaking Chiral Anomalies and Instantons High Temperature QCD: Asymptotic Properties Significance of High Temperature QCD Numerical Indications for Quasi-Free Behavior Ideas About Quark-Gluon Plasma Screening Versus Confinement Models of Chiral Symmetry Breaking More Refined Numerical Experiments High-Temperature QCD: Phase Transitions Yoga of Phase Transitions and Order Parameters Application to Glue Theories Application to Chiral Transitions Close Up on Two Flavors A Genuine Critical Point! (?) High-Density QCD: Methods Hopes, Doubts, and Fruition Another Renormalization Group Pairing Theory Taming the Magnetic Singularity High-Density QCD: Color-Flavor Locking and Quark-Hadron Continuity Gauge Symmetry (Non)Breaking Symmetry Accounting Elementary Excitations A Modified Photon Quark-Hadron Continuity Remembrance of Things Past More Quarks Fewer Quarks and Reality

Helicity-Selective Phase-Matching and Quasi-Phase matching of Circularly Polarized High-Order Harmonics: Towards Chiral Attosecond Pulses

DTIC Science & Technology

2016-05-23

Invited Article Helicity-selective phase-matching and quasi -phase matching of circularly polarized high-order harmonics: towards chiral attosecond...chromatic lasers was recently predicted theoretically and demonstrated experimentally . In that work, phase matching was analyzed by assuming that the...Indeed, we present an experimentally measured chiral spectrum that can support a train of attosecond pulses with a high degree of circular polarization

Molecular dynamics simulations of adsorption and diffusion of gases in silicon-carbide nanotubes.

PubMed

Malek, Kourosh; Sahimi, Muhammad

2010-01-07

Silicon carbide nanotubes (SiCNTs) are new materials with excellent properties, such as high thermal stability and mechanical strength, which are much improved over those of their carboneous counterparts, namely, carbon nanotubes (CNTs). Gas separation processes at high temperatures and pressures may be improved by developing mixed-matrix membranes that contain SiCNTs. Such nanotubes are also of interest in other important processes, such as hydrogen production and its storage, as well as separation by supercritical adsorption. The structural parameters of the nanotubes, i.e., their diameter, curvature, and chirality, as well as the interaction strength between the gases and the nanotubes' walls, play a fundamental role in efficient use of the SiCNTs in such processes. We employ molecular dynamics simulations in order to examine the adsorption and diffusion of N(2), H(2), CO(2), CH(4), and n-C(4)H(10) in the SiCNTs, as a function of the pressure and the type of the nanotubes, namely, the zigzag, armchair, and chiral tubes. The simulations indicate the strong effect of the nanotubes' chirality and curvature on the pressure dependence of the adsorption isotherms and the self-diffusivities. Detailed comparison is made between the results and those for the CNTs. In particular, we find that the adsorption capacity of the SiCNTs for hydrogen is higher than the CNTs' under the conditions that we have studied.

Molecular dynamics simulations of adsorption and diffusion of gases in silicon-carbide nanotubes

NASA Astrophysics Data System (ADS)

Malek, Kourosh; Sahimi, Muhammad

2010-01-01

Silicon carbide nanotubes (SiCNTs) are new materials with excellent properties, such as high thermal stability and mechanical strength, which are much improved over those of their carboneous counterparts, namely, carbon nanotubes (CNTs). Gas separation processes at high temperatures and pressures may be improved by developing mixed-matrix membranes that contain SiCNTs. Such nanotubes are also of interest in other important processes, such as hydrogen production and its storage, as well as separation by supercritical adsorption. The structural parameters of the nanotubes, i.e., their diameter, curvature, and chirality, as well as the interaction strength between the gases and the nanotubes' walls, play a fundamental role in efficient use of the SiCNTs in such processes. We employ molecular dynamics simulations in order to examine the adsorption and diffusion of N2, H2, CO2, CH4, and n-C4H10 in the SiCNTs, as a function of the pressure and the type of the nanotubes, namely, the zigzag, armchair, and chiral tubes. The simulations indicate the strong effect of the nanotubes' chirality and curvature on the pressure dependence of the adsorption isotherms and the self-diffusivities. Detailed comparison is made between the results and those for the CNTs. In particular, we find that the adsorption capacity of the SiCNTs for hydrogen is higher than the CNTs' under the conditions that we have studied.

HPLC SEPARATION OF CHIRAL ORGANOPHOSPHORUS PESTICIDES ON POLYSACCHARIDE CHIRAL STATIONARY PHASES

EPA Science Inventory

High-performance liquid chromatographic separation of the individual enantiomers of 12 organophosphorus pesticides (OPs) were obtained on polysaccharide chiral HPLC columns using an alkane-alcohol mobile phase. The OP pesticides were crotoxyphos, dialifor, dyfonate, fenamiphos, ...

Study of the Mechanism of Irreversible Adsorption of Single-Walled Carbon Nanotubes to Sephacryl Hydrogel

NASA Astrophysics Data System (ADS)

Rolsma, Caleb

As a class of carbon-based nanomaterials, single-walled carbon nanotubes (SWNT) have many structural variations, called chiralities, each with different properties. Many potential applications of SWNT require the properties of a single chirality, but current synthesis methods can only produce single chiralities at prohibitive costs, or mixtures of chiralities at more affordable prices. Post-synthesis chirality separations provide a solution to this problem, and hydrogel separations are one such method. Despite much work in this field, the underlying interactions between SWNT and hydrogel are not fully understood. During separation, large quantities of SWNT are irretrievably lost due to irreversible adsorption to the hydrogel, posing a major problem to separation efficiency, while also offering an interesting scientific problem concerning the interaction of SWNT with hydrogels and surfactants. This thesis explores the problem of irreversible adsorption, offering an explanation for the process from a mechanistic viewpoint, opening new ways for improvement in separation. In brief, this work concludes adsorption follows three pathways, two of which lead to irreversible adsorption, both mediated by the presence of surfactants and limited by characteristics of the hydrogel surface. These findings stand to increase the general understanding of hydrogel SWNT separations, leading to improvements in separation, and bringing the research field closer to the many potential applications of single-chirality SWNT.

The kinetics of chirality assignment in catalytic single-walled carbon nanotube growth and the routes towards selective growth† †Electronic supplementary information (ESI) available: Details of density functional theory (DFT) calculations, definition of interfacial formation energy (IFE), cap formation energy and fitting equation, Fig. S1–S4 and Table S1. See DOI: 10.1039/c7sc04714b

PubMed Central

Xu, Ziwei; Qiu, Lu

2018-01-01

Depending on its specific structure, or so-called chirality, a single-walled carbon nanotube (SWCNT) can be either a conductor or a semiconductor. This feature ensures great potential for building ∼1 nm sized electronics if chirality-selected SWCNTs could be achieved. However, due to the limited understanding of the growth mechanism of SWCNTs, reliable methods for chirality-selected SWCNTs are still pending. Here we present a theoretical model on the chirality assignment and control of SWCNTs during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of pentagons, especially the last (6th) one, during the nucleation stage. Our analysis showed that the chirality of a SWCNT is randomly assigned on a liquid or liquid-like catalyst surface, and two routes of synthesizing chirality-selected SWCNTs, which are verified by recent experimental achievements, are demonstrated. They are (i) by using high melting point crystalline catalysts, such as Ta, W, Re, Os, or their alloys, and (ii) by frequently changing the chirality of SWCNTs during their growth. This study paves the way for achieving chirality-selective SWCNT growth for high performance SWCNT based electronics. PMID:29732090

Enantioselective simultaneous analysis of selected pharmaceuticals in environmental samples by ultrahigh performance supercritical fluid based chromatography tandem mass spectrometry.

PubMed

Camacho-Muñoz, Dolores; Kasprzyk-Hordern, Barbara; Thomas, Kevin V

2016-08-31

In order to assess the true impact of each single enantiomer of pharmacologically active compounds (PACs) in the environment, highly efficient, fast and sensitive analytical methods are needed. For the first time this paper focuses on the use of ultrahigh performance supercritical fluid based chromatography coupled to a triple quadrupole mass spectrometer to develop multi-residue enantioselective methods for chiral PACs in environmental matrices. This technique exploits the advantages of supercritical fluid chromatography, ultrahigh performance liquid chromatography and mass spectrometry. Two coated modified 2.5 μm-polysaccharide-based chiral stationary phases were investigated: an amylose tris-3,5-dimethylphenylcarbamate column and a cellulose tris-3-chloro-4-methylphenylcarbamate column. The effect of different chromatographic variables on chiral recognition is highlighted. This novel approach resulted in the baseline resolution of 13 enantiomers PACs (aminorex, carprofen, chloramphenicol, 3-N-dechloroethylifosfamide, flurbiprofen, 2-hydroxyibuprofen, ifosfamide, imazalil, naproxen, ofloxacin, omeprazole, praziquantel and tetramisole) and partial resolution of 2 enantiomers PACs (ibuprofen and indoprofen) under fast-gradient conditions (<10 min analysis time). The overall performance of the methods was satisfactory. The applicability of the methods was tested on influent and effluent wastewater samples. To the best of our knowledge, this is the first feasibility study on the simultaneous separation of chemically diverse chiral PACs in environmental matrices using ultrahigh performance supercritical fluid based chromatography coupled with tandem mass spectrometry. Copyright © 2016 Elsevier B.V. All rights reserved.

Asymmetric Michael Addition Mediated by Chiral Ionic Liquids.

PubMed

Suzuki, Yumiko

2018-06-01

Chiral ionic liquids with a focus on their applications in asymmetric Michael additions and related reactions were reviewed. The examples were classified on the basis of the mode of asymmetric induction (e.g., external induction/non-covalent interaction or internal induction/covalent bond formation), the roles in reactions (as a solvent or catalyst), and their structural features (e.g., imidazolium-based chiral cations, other chiral oniums; proline derivatives). Most of the reactions with high chiral induction are Michael addition of ketones or aldehydes to chalcones or nitrostyrenes where proline-derived chiral ionic liquids catalyze the reaction through enamine/ iminium formation. Many reports demonstrate the recyclability of ionic liquid-tagged pyrrolidines.

Chiral transcription in self-assembled tetrahedral Eu 4L 6 chiral cages displaying sizable circularly polarized luminescence

DOE PAGES

Yeung, Chi -Tung; Yim, King -Him; Wong, Ho -Yin; ...

2017-10-24

Predictable stereoselective formation of supramolecular assembly is generally believed to be an important but complicated process. Here, we show that point chirality of a ligand decisively influences its supramolecular assembly behavior. We designed three closely related chiral ligands with different point chiralities, and observe their self-assembly into europium (Eu) tetrametallic tetrahedral cages. One ligand exhibits a highly diastereoselective assembly into homochiral (either ΔΔΔΔ or ΛΛΛΛ) Eu tetrahedral cages whereas the two other ligands, with two different approaches of loosened point chirality, lead to a significant breakdown of the diastereoselectivity to generate a mixture of (ΔΔΔΔ and ΛΛΛΛ) isomers. The cagesmore » are highly emissive (luminescence quantum yields of 16(1) to 18(1)%) and exhibit impressive circularly polarized luminescence properties (|g lum |: up to 0.16). With in-depth studies, we present an example that correlates the nonlinear enhancement of the chiroptical response to the nonlinearity dependence on point chirality.« less

Lattice modes of the chirally pure and racemic phases of tyrosine crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belyanchikov, M. A.; Gorelik, V. S., E-mail: gorelik@sci.lebedev.ru; Gorshunov, B. P.

High-Q librational modes have been found to be present in the infrared absorption and Raman spectra of chirally pure L-tyrosine. Such modes can serve as terahertz radiation detectors and generators in chirally pure biostructures.

Highly convergent synthesis of chiral bicyclophosphinates by domino hydrophosphinylation/Michael/Michael reaction.

PubMed

Fourgeaud, Pierre; Daydé, Bénédicte; Volle, Jean-Noël; Vors, Jean-Pierre; Van der Lee, Arie; Pirat, Jean-Luc; Virieux, David

2011-10-07

Diastereoselective domino reactions of iminoalcohols and allenyl H-phosphinates produce chiral phosphorus bicycles in a regio- and stereoselective fashion. A predictive model for diastereoselection is used for these new chiral phosphinic esters. © 2011 American Chemical Society

Chirality in adsorption on solid surfaces.

PubMed

Zaera, Francisco

2017-12-07

In the present review we survey the main advances made in recent years on the understanding of chemical chirality at solid surfaces. Chirality is an important topic, made particularly relevant by the homochiral nature of the biochemistry of life on Earth, and many chiral chemical reactions involve solid surfaces. Here we start our discussion with a description of surface chirality and of the different ways that chirality can be bestowed on solid surfaces. We then expand on the studies carried out to date to understand the adsorption of chiral compounds at a molecular level. We summarize the work published on the adsorption of pure enantiomers, of enantiomeric mixtures, and of prochiral molecules on chiral and achiral model surfaces, especially on well-defined metal single crystals but also on other flat substrates such as highly ordered pyrolytic graphite. Several phenomena are identified, including surface reconstruction and chiral imprinting upon adsorption of chiral agents, and the enhancement or suppression of enantioselectivity seen in some cases upon adsorption of enantiomixtures of chiral compounds. The possibility of enhancing the enantiopurity of adsorbed layers upon the addition of chiral seeds and the so-called "sergeants and soldiers" phenomenon are presented. Examples are provided where the chiral behavior has been associated with either thermodynamic or kinetic driving forces. Two main approaches to the creation of enantioselective surface sites are discussed, namely, via the formation of supramolecular chiral ensembles made out of small chiral adsorbates, and by adsorption of more complex chiral molecules capable of providing suitable chiral environments for reactants by themselves, via the formation of individual adsorbate:modifier adducts on the surface. Finally, a discussion is offered on the additional effects generated by the presence of the liquid phase often required in practical applications such as enantioselective crystallization, chiral chromatography, and enantioselective catalysis.

Phenomenology of anomalous chiral transports in heavy-ion collisions

NASA Astrophysics Data System (ADS)

Huang, Xu-Guang

2018-01-01

High-energy Heavy-ion collisions can generate extremely hot quark-gluon matter and also extremely strong magnetic fields and fluid vorticity. Once coupled to chiral anomaly, the magnetic fields and fluid vorticity can induce a variety of novel transport phenomena, including the chiral magnetic effect, chiral vortical effect, etc. Some of them require the environmental violation of parity and thus provide a means to test the possible parity violation in hot strongly interacting matter. We will discuss the underlying mechanism and implications of these anomalous chiral transports in heavy-ion collisions.

Rhodium-catalyzed Asymmetric Hydrogenation of α-Dehydroamino Ketones: A General Approach to Chiral α-amino Ketones.

PubMed

Gao, Wenchao; Wang, Qingli; Xie, Yun; Lv, Hui; Zhang, Xumu

2016-01-01

Rhodium/DuanPhos-catalyzed asymmetric hydrogenation of aliphatic α-dehydroamino ketones has been achieved and afforded chiral α-amino ketones in high yields and excellent enantioselectives (up to 99 % ee), which could be reduced further to chiral β-amino alcohols by LiAlH(tBuO)3 with good yields. This protocol provides a readily accessible route for the synthesis of chiral α-amino ketones and chiral β-amino alcohols. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced chiral response from the Fabry-Perot cavity coupled meta-surfaces

NASA Astrophysics Data System (ADS)

Yang, Ze-Jian; Hu, De-Jiao; Gao, Fu-Hua; Hou, Yi-Dong

2016-08-01

The circular dichroism (CD) signal of a two-dimensional (2D) chiral meta-surface is usually weak, where the difference between the transmitted (or reflected) right and left circular polarization is barely small. We present a general method to enhance the reflective CD spectrum, by adding a layer of reflective film behind the meta-surface. The light passes through the chiral meta-surface and propagates towards the reflector, where it is reflected back and further interacts with the chiral meta-surface. The light is reflected back and forth between these two layers, forming a Fabry-Perot type resonance, which interacts with the localized surface plasmonic resonance (LSPR) mode and greatly enhances the CD signal of the light wave leaving the meta-surface. We numerically calculate the CD enhancing effect of an L-shaped chiral meta-surface on a gold film in the visible range. Compared with the single layer meta-surface, the L-shaped chiral meta-surface has a CD maximum that is dramatically increased to 1. The analysis of reflection efficiency reveals that our design can be used to realize a reflective circular polarizer. Corresponding mode analysis shows that the huge CD originates from the hybrid mode comprised of FP mode and LSPR. Our results provide a general approach to enhancing the CD signal of a chiral meta-surface and can be used in areas like biosensing, circular polarizer, integrated photonics, etc. Project supported by the National Natural Science Foundation of China (Grant No. 61377054).

[From symmetries to the laws of evolution. I. Chirality as a means of active media stratification].

PubMed

Tverdislov, V A; Sidorova, A É; Iakovenko, L V

2012-01-01

Features of the hypothetical evolution of a hierarchy of chiral objects formed by active media are discussed. On the basis of experimental facts a new synergetic generalization is made: an evolving system can repeatedly broaden the spectrum of its symmetry types within one level of organization which increases its complexity and change the sign of chirality during transition to a higher level. Switching the chirality sign of macroscopic objects provides irreversibility of stratification. The known chirality of biological structures at different levels suggests that the chiral L/D-stratification should be universal and the hierarchical paths are stable and determined. A high level enantiomorph with reciprocal chirality demonstrates a wider spectrum of functionality. A fractal description of natural hierarchical systems is pointed out to be inadequate because it implicates invariance of the chirality sign of the objects at different scales.

Chirality effect in disordered graphene ribbon junctions

NASA Astrophysics Data System (ADS)

Long, Wen

2012-05-01

We investigate the influence of edge chirality on the electronic transport in clean or disordered graphene ribbon junctions. By using the tight-binding model and the Landauer-Büttiker formalism, the junction conductance is obtained. In the clean sample, the zero-magnetic-field junction conductance is strongly chirality-dependent in both unipolar and bipolar ribbons, whereas the high-magnetic-field conductance is either chirality-independent in the unipolar or chirality-dependent in the bipolar ribbon. Furthermore, we study the disordered sample in the presence of magnetic field and find that the junction conductance is always chirality-insensitive for both unipolar and bipolar ribbons with adequate disorders. In addition, the disorder-induced conductance plateaus can exist in all chiral bipolar ribbons provided the disorder strength is moderate. These results suggest that we can neglect the effect of edge chirality in fabricating electronic devices based on the magnetotransport in a disordered graphene ribbon.

Chiral recognition and selection during the self-assembly process of protein-mimic macroanions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Panchao; Zhang, Zhi-Ming; Lv, Hongjin

The research on chiral recognition and chiral selection is not only fundamental in resolving the puzzle of homochirality, but also instructive in chiral separation and stereoselective catalysis. Here we report the chiral recognition and chiral selection during the self-assembly process of two enantiomeric wheel-shaped macroanions, [Fe28(μ3-O)8(Tart)16(HCOO)24]20- (Tart=D- or L-tartaric acid tetra-anion). The enantiomers are observed to remain self-sorted and self-assemble into their individual assemblies in their racemic mixture solution. The addition of chiral co-anions can selectively suppress the self-assembly process of the enantiomeric macroanions, which is further used to separate the two enantiomers from their mixtures on the basis ofmore » the size difference between the monomers and the assemblies. We believe that delicate long-range electrostatic interactions could be responsible for such high-level chiral recognition and selection.« less

Chiral Magnetic Effect in Condensed Matters

NASA Astrophysics Data System (ADS)

Li, Qiang

The chiral magnetic effect is the generation of electrical current induced by chirality imbalance in the presence of magnetic field. It is a macroscopic manifestation of the quantum chiral anomaly in systems possessing charged chiral fermions. In quark-gluon plasma containing nearly massless quarks, the chirality imbalance is sourced by the topological transitions. In condensed matter systems, the chiral quasiparticles emerge in the 3D Dirac and Weyl semimetals having a linear dispersion relation. Recently, the chiral magnetic effect was discovered in a 3D Dirac semimetal - zirconium pentatelluride, ZrTe5, in which a large negative magnetoresistance is observed when magnetic field is parallel with the current. It is now reported in more than a dozen Dirac and Weyl semimetals. Broadly speaking, the chiral magnetic effect can exist in a variety of condensed matters. In some cases, a material may be transformed into a Weyl semimetal by magnetic field, exhibiting the chiral magnetic effect. In other cases, the chiral magnetic current may be generated in magnetic Dirac semimetals without external magnetic field, or in asymmetric Weyl semimetals without electric field where only a magnetic field and the source of chiral quasipartiles would be necessary. In the limit of conserved quasiparticle chirality, charge transport by the chiral magnetic current is non-dissipative. The powerful notion of chirality, originally discovered in high-energy and nuclear physics, holds promise in new ways of transmitting and processing information and energy. At the same time, chiral materials have opened a fascinating possibility to study the quantum dynamics of relativistic field theory in condensed matter experiments.

Functional Characterization of a Novel Marine Microbial GDSL Lipase and Its Utilization in the Resolution of (±)-1-Phenylethanol.

PubMed

Deng, Dun; Zhang, Yun; Sun, Aijun; Liang, Jiayuan; Hu, Yunfeng

2016-04-01

A novel GDSL lipase (MT6) was cloned from the genome of Marinactinospora thermotolerans SCSIO 00652 identified from the South China Sea. MT6 showed its maximum identity of 59 % with a putative lipase from Nocardiopsis dassonville. MT6 was heterologously expressed in E. coli BL21(DE3) and further functionally characterized. MT6 could efficiently resolve racemic 1-phenylethanol and generate (R)-1-phenylethanol with high enantiomeric excess (99 %) and conversion rate (54 %) through transesterification reactions after process optimization. Our report was the first one report about the utilization of one GDSL lipase in the preparation of chiral chemicals by transesterification reactions, and the optical selectivity of MT6 was interestingly opposite to those of other common lipases. GDSL lipases represented by MT6 possess great potential for the generation of valuable chiral chemicals in industry.

Separation of profen enantiomers by capillary electrophoresis using cyclodextrins as chiral selectors.

PubMed

Blanco, M; Coello, J; Iturriaga, H; Maspoch, S; Pérez-Maseda, C

1998-01-09

A method for resolving the enantiomers of various 2-arylpropionic acids (viz. ketoprofen, ibuprofen and fenoprofen) by capillary zone electrophoresis (CZE) using a background electrolyte (BGE) containing a cyclodextrin as chiral selector is proposed. The effects of the type of cyclodextrin used and its concentration on resolution were studied and heptakis-2,3,6-tri- O-methyl-beta-cyclodextrin was found to be the sole effective choice for the quantitative enantiomeric resolution of all the compounds tested. The influence of pH, BGE concentration, capillary temperature and addition of methanol to the BGE on resolution and other separation-related parameters was also studied. The three compounds studied can be enantiomerically resolved with a high efficiency in a short time (less than 20 min) with no capillary treatment. This makes the proposed method suitable for assessing the enantiomeric purity of commercially available pharmaceuticals.

Preparation of novel beta-cyclodextrin functionalized monolith and its application in chiral separation.

PubMed

Lv, Yongqin; Mei, Danping; Pan, Xinxin; Tan, Tianwei

2010-09-15

A novel beta-cyclodextrin (beta-CD) functionalized organic polymer monolith was prepared by covalently bonding ethylenediamine-beta-CD (EDA-beta-CD) to poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (poly(GMA-co-EGDMA)) monolith via ring opening reaction of epoxy groups. SEM characterization was performed to confirm the homogeneity of the monolithic polymer. The resulting monolith was then characterized by DSC and XPS elemental analysis to study the thermal stability of the monolith, and to prove the successful immobilization of beta-CD on the polymer substrate. The beta-CD ligand density of 0.68 mmol g(-1) was obtained for the modified monolith, indicating the high reactivity and efficiency of the EDA-beta-CD modifier. The ethylenediamine-beta-CD functionalized monoliths were used for the chiral separation of ibuprofen racemic mixture and showed promising results. Copyright (c) 2010 Elsevier B.V. All rights reserved.

Chiral nanoparticles in singular light fields

PubMed Central

Vovk, Ilia A.; Baimuratov, Anvar S.; Zhu, Weiren; Shalkovskiy, Alexey G.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

2017-01-01

The studying of how twisted light interacts with chiral matter on the nanoscale is paramount for tackling the challenging task of optomechanical separation of nanoparticle enantiomers, whose solution can revolutionize the entire pharmaceutical industry. Here we calculate optical forces and torques exerted on chiral nanoparticles by Laguerre–Gaussian beams carrying a topological charge. We show that regardless of the beam polarization, the nanoparticles are exposed to both chiral and achiral forces with nonzero reactive and dissipative components. Longitudinally polarized beams are found to produce chirality densities that can be 109 times higher than those of transversely polarized beams and that are comparable to the chirality densities of beams polarized circularly. Our results and analytical expressions prove useful in designing new strategies for mechanical separation of chiral nanoobjects with the help of highly focussed beams. PMID:28378842

Chiral nanoparticles in singular light fields

NASA Astrophysics Data System (ADS)

Vovk, Ilia A.; Baimuratov, Anvar S.; Zhu, Weiren; Shalkovskiy, Alexey G.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

2017-04-01

The studying of how twisted light interacts with chiral matter on the nanoscale is paramount for tackling the challenging task of optomechanical separation of nanoparticle enantiomers, whose solution can revolutionize the entire pharmaceutical industry. Here we calculate optical forces and torques exerted on chiral nanoparticles by Laguerre-Gaussian beams carrying a topological charge. We show that regardless of the beam polarization, the nanoparticles are exposed to both chiral and achiral forces with nonzero reactive and dissipative components. Longitudinally polarized beams are found to produce chirality densities that can be 109 times higher than those of transversely polarized beams and that are comparable to the chirality densities of beams polarized circularly. Our results and analytical expressions prove useful in designing new strategies for mechanical separation of chiral nanoobjects with the help of highly focussed beams.

Photoremovable chiral auxiliary.

PubMed

Kammath, Viju Balachandran; Sebej, Peter; Slanina, Tomáš; Kříž, Zdeněk; Klán, Petr

2012-03-01

A new concept of a photoremovable chiral auxiliary (PCA), based on the chiral benzoin chromophore, is introduced. This moiety can control the asymmetric formation of a Diels-Alder adduct, and then be removed in a subsequent photochemical step in high chemical and quantum yields. Selective formation of the products at up to 96% ee was observed in the presence of a Lewis acid catalyst in the case of a 2-methoxybenzoinyl chiral auxiliary.

Asymmetric Michael Addition Mediated by Chiral Ionic Liquids

PubMed Central

Suzuki, Yumiko

2018-01-01

Chiral ionic liquids with a focus on their applications in asymmetric Michael additions and related reactions were reviewed. The examples were classified on the basis of the mode of asymmetric induction (e.g., external induction/non-covalent interaction or internal induction/covalent bond formation), the roles in reactions (as a solvent or catalyst), and their structural features (e.g., imidazolium-based chiral cations, other chiral oniums; proline derivatives). Most of the reactions with high chiral induction are Michael addition of ketones or aldehydes to chalcones or nitrostyrenes where proline-derived chiral ionic liquids catalyze the reaction through enamine/ iminium formation. Many reports demonstrate the recyclability of ionic liquid-tagged pyrrolidines. PMID:29861702

Chiral tunneling of topological states: towards the efficient generation of spin current using spin-momentum locking.

PubMed

Habib, K M Masum; Sajjad, Redwan N; Ghosh, Avik W

2015-05-01

We show that the interplay between chiral tunneling and spin-momentum locking of helical surface states leads to spin amplification and filtering in a 3D topological insulator (TI). Our calculations show that the chiral tunneling across a TI pn junction allows normally incident electrons to transmit, while the rest are reflected with their spins flipped due to spin-momentum locking. The net result is that the spin current is enhanced while the dissipative charge current is simultaneously suppressed, leading to an extremely large, gate-tunable spin-to-charge current ratio (∼20) at the reflected end. At the transmitted end, the ratio stays close to 1 and the electrons are completely spin polarized.

Characteristics of chiral plasma plumes generated in the absence of external magnetic field

NASA Astrophysics Data System (ADS)

Nie, LanLan; Liu, FengWu; Zhou, XinCai; Lu, XinPei; Xian, YuBin

2018-05-01

A chiral plasma plume has recently been generated inside a dielectric tube without the use of an external magnetic field. In this paper, we seek to further study the key properties of such a chiral plume to improve our understanding of how this interesting structure is generated and controlled. The chiral plume is generated by externally mounting a stainless steel helical coil or a ring onto the dielectric tube. By changing the pitch of the helical coil, the pitch of the plasma plume can be controlled, with the shape of the plume following the shape of the helical coil. The addition of the helical coil significantly expands the range of parameters under which the chiral plasma plume appears. When the frequency of the applied voltage increases, additional stable discharge channels appear between the adjacent helices. The addition of two helical coils results in the formation of two chiral plasma plumes, which follow the shape of the helical coils. When a metal ring is placed on the outside of the tube, there is no chiral plasma plume between the high voltage electrode and the ring; however, a chiral plasma plume appears on the right side of the ring if the distance between the ring and the high voltage electrode is small. These findings suggest that the chiral plasma can be effectively modulated and guided using an externally mounted helical coil, which acts as the floating/actual ground to reduce the impedance of the discharge and as such contributes to the emergence of the chiral plasma plume behavior.

α-Fluoro-α-nitro(phenylsulfonyl)methane as a fluoromethyl pronucleophile: Efficient stereoselective Michael addition to chalcones

PubMed Central

Prakash, G. K. Surya; Wang, Fang; Stewart, Timothy; Mathew, Thomas; Olah, George A.

2009-01-01

Highly efficient stereoselective 1,4-addition of racemic α-fluoro-α-nitro(phenylsulfonyl)methane (FNSM) as a fluoromethyl pronucleophile to α,β-unsaturated ketones using a wide range of chiral organobifunctional catalysts under moderate conditions in the absence of an additional base has been achieved. A series of catalysts was screened for the enantioselective addition of FNSM to chalcones and the catalysts CN I, CD I, QN I-IV, and QD I were found to enable this reaction, successfully providing exclusive 1,4-addition products stereoselectively in high yields (conversion, diastereomeric ratio, and enantiomeric excess). Studies involving a model reaction and systematic analysis of the absolute configuration support the suggested mechanism. PMID:19237559

Synthesis of fluorescent label, DBD-beta-proline, and the resolution efficiency for chiral amines by reversed-phase chromatography.

PubMed

Min, Jun Zhe; Toyo'oka, Toshimasa; Kato, Masaru; Fukushima, Takeshi

2005-01-01

DBD-d(and l)-beta-proline, new fluorescent chiral derivatization reagents, were synthesized from the reaction of 4-(N,N-dimethylaminosulfonyl)-7- fl uoro-2,1,3-benzoxadiazole (DBD-F) with beta-proline. The racemic mixture synthesized was separated by a chiral stationary phase (CSP) column, Chiralpak AD-H, with n-hexane-EtOH-TFA-diethylamine (70:30:0.1:0.1) as the mobile phase. The dl-forms were decided according to the results obtained from a circular dichroism (CD) detector after separation by the CSP column. The fractionated enantiomers reacted with chiral amine to produce a couple of diastereomers. The labeling proceeded in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and pyridine as the activation reagents. The reaction conditions were mild and no racemization occurred during the diastereomer formation. The resulting diastereomers fluoresced at around 570 nm (excitation at around 460 nm). Good linearity of the calibration curves was obtained in the range 1-75 pmol and the detection limits on chromatogram were less than 1 pmol. The separability of the diastereomers was compared with the diastereomers derived from DBD-d(or l)-proline. The resolution values (Rs) obtained from the diastereomers of three chiral amines with DBD-d(or l)-beta-proline were higher than those derived from DBD-d(or l)-proline, e.g. dl-phenylalanine methylester (dl-PAME), 2.23 vs 1.37; (R)(S)-1-phenylethylamine [(R)(S)-PEA], 2.09 vs 1.13; and (R)(S)-1-(1-naphthyl)ethylamines [(R)(S)-NEA], 5.19 vs 1.23. The results suggest that the position of COOH group on pyrrolidine moiety in the structures is one of the important factors for the efficient separation of a couple of the diastereomers.

Reactivity, chemoselectivity, and diastereoselectivity of the oxyfunctionalization of chiral allylic alcohols and derivatives in microemulsions: comparison of the chemical oxidation by the hydrogen peroxide/sodium molybdate system with the photooxygenation.

PubMed

Nardello, Véronique; Caron, Laurent; Aubry, Jean-Marie; Bouttemy, Sabine; Wirth, Thomas; Saha-Möller Chantu, R; Adam, Waldemar

2004-09-01

The chiral allylic alcohols 1a-d and their acetate (1e) and silyl ether (1f) derivatives have been oxidized by the H2O2/MoO4(2)- system, a convenient and efficient chemical source of singlet oxygen. This chemical peroxidation (formation of the allylic hydroperoxides 2) has been conducted in various media, which include aqueous solutions, organic solvents, and microemulsions. The reactivity, chemoselectivity, and diastereoselectivity of this chemical oxidation are compared to those of the sensitized photooxygenation, with the emphasis on preparative applications in microemulsion media. While a similar threo diastereoselectivity is observed for both modes of peroxidation, the chemoselectivity differs significantly, since in the chemical oxidation with the H2O2/MoO4(2)- system the undesirable epoxidation by the intermediary peroxomolybdate competes efficiently with the desirable peroxidation by the in situ generated singlet oxygen. A proper choice of the type of microemulsion and the reaction conditions furnishes a high chemoselectivity (up to 97%) in favor of threo-diastereoselective (up to 92%) peroxidation. Copyright 2004 American Chemical Society

Facile and efficient electrochemical enantiomer recognition of phenylalanine using β-Cyclodextrin immobilized on reduced graphene oxide.

PubMed

Zaidi, Shabi Abbas

2017-08-15

This work demonstrates the facile and efficient preparation protocol of β-Cyclodextrin-reduced graphene oxide modified glassy carbon electrode (β-CD/RGO/GCE) sensor for an impressive chiral selectivity analysis for phenylalanine enantiomers. In this work, the immobilization of β-CD over graphene sheets allows the excellent enantiomer recognition due to the large surface area and high conductivity of graphene sheets and extraordinary supramolecular (host-guest interaction) property of β-CD. The proposed sensor was well characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS) techniques. The analytical studies demonstrated that the β-CD/RGO/GCE exhibit superior chiral recognition toward L-phenylalanine as compared to D-phenylalanine. Under optimum conditions, the developed sensor displayed a good linear range from 0.4 to 40µM with the limit of detection (LOD) values of 0.10µM and 0.15µM for l- and D-phenylalanine, respectively. Furthermore, the proposed sensor exhibits good stability and regeneration capacity. Thus, the as-synthesized material can be exploited for electrochemical enantiomer recognition successfully. Copyright © 2017 Elsevier B.V. All rights reserved.

trans-2-Tritylcyclohexanol as a chiral auxiliary in permanganate-mediated oxidative cyclization of 2-methylenehept-5-enoates: application to the synthesis of trans-(+)-linalool oxide.

PubMed

Al Hazmi, Ali M; Sheikh, Nadeem S; Bataille, Carole J R; Al-Hadedi, Azzam A M; Watkin, Sam V; Luker, Tim J; Camp, Nicholas P; Brown, Richard C D

2014-10-03

The permanganate-mediated oxidative cyclization of a series of 2-methylenehept-5-eneoates bearing different chiral auxiliaries was investigated, leading to the discovery of trans-2-tritylcyclohexanol (TTC) as a highly effective chiral controller for the formation of the 2,5-substituted THF diol product with high diastereoselectivity (dr ∼97:3). Chiral resolution of (±)-TTC, prepared in one step from cyclohexene oxide, afforded (-)-(1S,2R)-TTC (er >99:1), which was applied to the synthesis of (+)-trans-(2S,5S)-linalool oxide.

Capillary electrophoresis of covalently functionalized single-chirality carbon nanotubes.

PubMed

He, Pingli; Meany, Brendan; Wang, Chunyan; Piao, Yanmei; Kwon, Hyejin; Deng, Shunliu; Wang, YuHuang

2017-07-01

We demonstrate the separation of chirality-enriched single-walled carbon nanotubes (SWCNTs) by degree of surface functionalization using high-performance CE. Controlled amounts of negatively charged and positively charged functional groups were attached to the sidewall of chirality-enriched SWCNTs through covalent functionalization using 4-carboxybenzenediazonium tetrafluoroborate or 4-diazo-N,N-diethylaniline tetrafluoroborate, respectively. Surfactant- and pH-dependent studies confirmed that under conditions that minimized ionic screening effects, separation of these functionalized SWCNTs was strongly dependent on the surface charge density introduced through covalent surface chemistry. For both heterogeneous mixtures and single-chirality-enriched samples, covalently functionalized SWCNTs showed substantially increased peak width in electropherogram spectra compared to nonfunctionalized SWCNTs, which can be attributed to a distribution of surface charges along the functionalized nanotubes. Successful separation of functionalized single-chirality SWCNTs by functional density was confirmed with UV-Vis-NIR absorption and Raman scattering spectroscopies of fraction collected samples. These results suggest a high degree of structural heterogeneity in covalently functionalized SWCNTs, even for chirality-enriched samples, and show the feasibility of applying CE for high-performance separation of nanomaterials based on differences in surface functional density. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical Chirality in Nonlinear Optics: Application to High Harmonic Generation.

PubMed

Neufeld, Ofer; Cohen, Oren

2018-03-30

Optical chirality (OC)-one of the fundamental quantities of electromagnetic fields-corresponds to the instantaneous chirality of light. It has been utilized for exploring chiral light-matter interactions in linear optics, but has not yet been applied to nonlinear processes. Motivated to explore the role of OC in the generation of helically polarized high-order harmonics and attosecond pulses, we first separate the OC of transversal and paraxial beams to polarization and orbital terms. We find that the polarization-associated OC of attosecond pulses corresponds approximately to that of the pump in the quasimonochromatic case, but not in the multichromatic pump cases. We associate this discrepancy with the fact that the polarization OC of multichromatic pumps vary rapidly in time along the optical cycle. Thus, we propose new quantities, noninstantaneous polarization-associated OC, and time-scale-weighted polarization-associated OC, and show that these quantities link the chirality of multichromatic pumps and their generated attosecond pulses. The presented extension to OC theory should be useful for exploring various nonlinear chiral light-matter interactions. For example, it stimulates us to propose a tricircular pump for generation of highly elliptical attosecond pulses with a tunable ellipticity.

Optical Chirality in Nonlinear Optics: Application to High Harmonic Generation

NASA Astrophysics Data System (ADS)

Neufeld, Ofer; Cohen, Oren

2018-03-01

Optical chirality (OC)—one of the fundamental quantities of electromagnetic fields—corresponds to the instantaneous chirality of light. It has been utilized for exploring chiral light-matter interactions in linear optics, but has not yet been applied to nonlinear processes. Motivated to explore the role of OC in the generation of helically polarized high-order harmonics and attosecond pulses, we first separate the OC of transversal and paraxial beams to polarization and orbital terms. We find that the polarization-associated OC of attosecond pulses corresponds approximately to that of the pump in the quasimonochromatic case, but not in the multichromatic pump cases. We associate this discrepancy with the fact that the polarization OC of multichromatic pumps vary rapidly in time along the optical cycle. Thus, we propose new quantities, noninstantaneous polarization-associated OC, and time-scale-weighted polarization-associated OC, and show that these quantities link the chirality of multichromatic pumps and their generated attosecond pulses. The presented extension to OC theory should be useful for exploring various nonlinear chiral light-matter interactions. For example, it stimulates us to propose a tricircular pump for generation of highly elliptical attosecond pulses with a tunable ellipticity.

Chiral separation of phenylalanine and tryptophan by capillary electrophoresis using a mixture of β-CD and chiral ionic liquid ([TBA] [L-ASP]) as selectors.

PubMed

Yujiao, Wu; Guoyan, Wang; Wenyan, Zhao; Hongfen, Zhang; Huanwang, Jing; Anjia, Chen

2014-05-01

In this paper, a simple, effective and green capillary electrophoresis separation and detection method was developed for the quantification of underivatized amino acids (dl-phenylalanine; dl-tryptophan) using β-Cyclodextrin and chiral ionic liquid ([TBA] [l-ASP]) as selectors. Separation parameters such as buffer concentrations, pH, β-CD and chiral ionic liquid concentrations and separation voltage were investigated for the enantioseparation in order to achieve the maximum possible resolution. A good separation was achieved in a background electrolyte composed of 15 mm sodium tetraborate, 5 mm β-CD and 4 mm chiral ionic liquid at pH 9.5, and an applied voltage of 10 kV. Under optimum conditions, linearity was achieved within concentration ranges from 0.08 to 10 µg/mL for the analytes with correlation coefficients from 0.9956 to 0.9998, and the analytes were separated in less than 6 min with efficiencies up to 970,000 plates/m. The proposed method was successfully applied to the determination of amino acid enantiomers in compound amino acids injections, such as 18AA-I, 18AA-II and 3AA.

Lewis-Base-Mediated Diastereoselective Silylations of Alcohols: Synthesis of Silicon-Stereogenic Dialkoxysilanes Controlled by Chiral Aryl BINMOLs.

PubMed

Bai, Xing-Feng; Zou, Jin-Feng; Chen, Mu-Yi; Xu, Zheng; Li, Li; Cui, Yu-Ming; Zheng, Zhan-Jiang; Xu, Li-Wen

2017-07-18

In the past years, stereoselective functionalizations of hydroxyl groups of alcohol substrates with chlorosilanes leading to silyl ether formation have evolved from a functional-group protection to an enantioselective synthetic strategy. This work comprises a controlled desymmetrization of dichlorosilanes by using a family of structurally specific chiral diols, chiral 1,1'-binaphthalene-2-α-arylmethanol-2'-ol (Ar-BINMOL). This process led to the facile construction of silicon-stereogenic organosilicon compounds with high yields and good diastereoselectivities. In addition, the diasteroselective silylation of chiral diols might not only be of interest for the development of highly stereoselective nucleophilic silylation, but also shed light on the construction of novel chiral phosphine ligands bearing a silicon-stereogenic center. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral separation of amino acids in biological fluids by micellar electrokinetic chromatography with laser-induced fluorescence detection.

PubMed

Thorsén, G; Bergquist, J

2000-08-18

A method is presented for the chiral analysis of amino acids in biological fluids using micellar electrokinetic chromatography (MEKC) and laser-induced fluorescence (LIF). The amino acids are derivatized with the chiral reagent (+/-)-1-(9-anthryl)-2-propyl chloroformate (APOC) and separated using a mixed micellar separation system. No tedious pre-purification of samples is required. The excellent separation efficiency and good detection capabilities of the MEKC-LIF system are exemplified in the analysis of urine and cerebrospinal fluid. This is the first time MEKC has been reported for chiral analysis of amino acids in biological fluids. The amino acids D-alanine, D-glutamine, and D-aspartic acid have been observed in cerebrospinal fluid, and D-alanine and D-glutamic acid in urine. To the best of our knowledge no measurements of either D-alanine in cerebrospinal fluid or D-glutamic acid in urine have been presented in the literature before.

Approaches for enantioselective resolution of pharmaceuticals by miniaturised separation techniques with new chiral phases based on nanoparticles and monolithis.

PubMed

Sierra, Isabel; Marina, Maria Luisa; Pérez-Quintanilla, Damián; Morante-Zarcero, Sonia; Silva, Mariana

2016-10-01

This article discusses new developments in the preparation of nanoparticles and monoliths with emphasis upon their application as the stationary and pseudo-stationary phases for miniaturised liquid phase separation techniques, which have occurred in the last 10 years (from 2006 to the actuality). References included in this review represent current trends and state of the art in the application of these materials to the analysis, by EKC, CEC and miniaturised chromatography, of chiral compounds with environmental interest such as pharmaceuticals. Due to their extraordinary properties, columns prepared with these new chiral stationary or pseudo-stationary phases, based on materials such as gold nanoparticles, metal-organic frameworks, ordered mesoporous silicas, carbonaceous materials, polymeric-based and silica-based monoliths or molecularly imprinted materials, can usually show some improvements in the separation selectivity, column efficiency and chemical stability in comparison with conventional chiral columns available commercially. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Origin of chiral interactions in cellulose supra-molecular microfibrils.

PubMed

Khandelwal, Mudrika; Windle, Alan

2014-06-15

The formation of a chiral-nematic phase from cellulose nanowhiskers has been frequently reported in the literature. The most popular theory used to explain the chiral interactions is that of twisted morphology of cellulose nanowhiskers. Two possible origins of twist have been suggested: the intrinsic chirality of cellulose chains and result of interaction of chiral surfaces. High resolution SEM and AFM have been used to locate twists in cellulose microfibrils and nanowhiskers. The origin of the twisted morphology in cellulose microfibrils has been studied with reference to the protein aggregation theory. Copyright © 2014 Elsevier Ltd. All rights reserved.

Experimental Overview of the Search for Chiral Effects at RHIC

NASA Astrophysics Data System (ADS)

Wang, Gang

2017-01-01

In high-energy heavy-ion collisions, various novel transport phenomena in local chiral domains result from the interplay of quantum anomalies with magnetic field and vorticity, and could survive the expansion of the fireball and be detected in experiments. Among these phenomena are the chiral magnetic effect, the chiral vortical effect and the chiral magnetic wave, the experimental searches for which have aroused extensive interest. This review will describe the current status of experimental studies at Relativistic Heavy Ion Collider at BNL, and outline the future work in experiment needed to eliminate the existing uncertainties in the interpretation of the data.

Induction of Chirality in Two-Dimensional Nanomaterials: Chiral 2D MoS2 Nanostructures.

PubMed

Purcell-Milton, Finn; McKenna, Robert; Brennan, Lorcan J; Cullen, Conor P; Guillemeney, Lilian; Tepliakov, Nikita V; Baimuratov, Anvar S; Rukhlenko, Ivan D; Perova, Tatiana S; Duesberg, Georg S; Baranov, Alexander V; Fedorov, Anatoly V; Gun'ko, Yurii K

2018-02-27

Two-dimensional (2D) nanomaterials have been intensively investigated due to their interesting properties and range of potential applications. Although most research has focused on graphene, atomic layered transition metal dichalcogenides (TMDs) and particularly MoS 2 have gathered much deserved attention recently. Here, we report the induction of chirality into 2D chiral nanomaterials by carrying out liquid exfoliation of MoS 2 in the presence of chiral ligands (cysteine and penicillamine) in water. This processing resulted in exfoliated chiral 2D MoS 2 nanosheets showing strong circular dichroism signals, which were far past the onset of the original chiral ligand signals. Using theoretical modeling, we demonstrated that the chiral nature of MoS 2 nanosheets is related to the presence of chiral ligands causing preferential folding of the MoS 2 sheets. There was an excellent match between the theoretically calculated and experimental spectra. We believe that, due to their high aspect ratio planar morphology, chiral 2D nanomaterials could offer great opportunities for the development of chiroptical sensors, materials, and devices for valleytronics and other potential applications. In addition, chirality plays a key role in many chemical and biological systems, with chiral molecules and materials critical for the further development of biopharmaceuticals and fine chemicals, and this research therefore should have a strong impact on relevant areas of science and technology such as nanobiotechnology, nanomedicine, and nanotoxicology.

A quantitative measure of chirality inside nucleic acid databank.

PubMed

Pietropaolo, Adriana; Parrinello, Michele

2011-08-01

We show the capability of a chirality index (Pietropaolo et al., Proteins 2008;70:667-677) to investigate nucleic acid structures because of its high sensitivity to helical conformations. By analyzing selected structures of DNA and RNA, we have found that sequences rich in cytosine and guanine have a tendency to left-handed chirality, in contrast to regions rich in adenine or thymine which show strong negative, right-handed, chirality values. We also analyze RNA structures, where specific loops and hairpin motifs are characterized by a well-defined chirality value. We find that in nucleosome the chirality is exalted, whereas in ribosome it is reduced. Our results illustrate the sensitivity of this descriptor for nucleic acid conformations. Copyright © 2011 Wiley-Liss, Inc.

Enantiopure Ferrocene-Based Planar-Chiral Iridacycles: Stereospecific Control of Iridium-Centred Chirality.

PubMed

Arthurs, Ross A; Ismail, Muhammad; Prior, Christopher C; Oganesyan, Vasily S; Horton, Peter N; Coles, Simon J; Richards, Christopher J

2016-02-24

Reaction of [IrCp*Cl2 ]2 with ferrocenylimines (Fc=NAr, Ar=Ph, p-MeOC6 H4 ) results in ferrocene C-H activation and the diastereoselective synthesis of half-sandwich iridacycles of relative configuration Sp *,RIr *. Extension to (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline gave highly diastereoselective control over the new elements of planar chirality and metal-based pseudo-tetrahedral chirality, to give both neutral and cationic half-sandwich iridacycles of absolute configuration Sc ,Sp ,RIr . Substitution reactions proceed with retention of configuration, with the planar chirality controlling the metal-centred chirality through an iron-iridium interaction in the coordinatively unsaturated cationic intermediate. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral Plasmonic Nanostructures Fabricated by Circularly Polarized Light.

PubMed

Saito, Koichiro; Tatsuma, Tetsu

2018-05-09

The chirality of materials results in a wide variety of advanced technologies including image display, data storage, light management including negative refraction, and enantioselective catalysis and sensing. Here, we introduce chirality to plasmonic nanostructures by using circularly polarized light as the sole chiral source for the first time. Gold nanocuboids as precursors on a semiconductor were irradiated with circularly polarized light to localize electric fields at specific corners of the cuboids depending on the handedness of light and deposited dielectric moieties as electron oscillation boosters by the localized electric field. Thus, plasmonic nanostructures with high chirality were developed. The present bottom-up method would allow the large-scale and cost-effective fabrication of chiral materials and further applications to functional materials and devices.

Chiral Brønsted Acid-Catalyzed Allylboration of Aldehydes

PubMed Central

Jain, Pankaj; Antilla, Jon C.

2010-01-01

The catalytic enantioselective allylation of aldehydes is a long-standing problem with considerable interest to the chemical community. We wish to disclose a new high yielding and highly enantioselective chiral Brønsted acid-catalyzed allylboration of aldehydes. The reaction is shown to be highly general, with broad substrate scope that covers aryl, heteroaryl, α,β-unsaturated, and aliphatic aldehydes. The reaction conditions were also shown to be effective for the catalytic enantioselective crotylation of aldehydes. We believe that the high reactivity of the allyl boronate is due to protonation of the boronate oxygen by the chiral phosphoric acid catalyst. PMID:20690662

One-Dimensional Chirality: Strong Optical Activity in Epsilon-Near-Zero Metamaterials.

PubMed

Rizza, Carlo; Di Falco, Andrea; Scalora, Michael; Ciattoni, Alessandro

2015-07-31

We suggest that electromagnetic chirality, generally displayed by 3D or 2D complex chiral structures, can occur in 1D patterned composites whose components are achiral. This feature is highly unexpected in a 1D system which is geometrically achiral since its mirror image can always be superposed onto it by a 180 deg rotation. We analytically evaluate from first principles the bianisotropic response of multilayered metamaterials and we show that the chiral tensor is not vanishing if the system is geometrically one-dimensional chiral; i.e., its mirror image cannot be superposed onto it by using translations without resorting to rotations. As a signature of 1D chirality, we show that 1D chiral metamaterials support optical activity and we prove that this phenomenon undergoes a dramatic nonresonant enhancement in the epsilon-near-zero regime where the magnetoelectric coupling can become dominant in the constitutive relations.

Advances in chiral separations by nonaqueous capillary electrophoresis in pharmaceutical and biomedical analysis.

PubMed

Ali, Imran; Sanagi, Mohd Marsin; Aboul-Enein, Hassan Y

2014-04-01

NACE is an alternative technique to aqueous CE in the chiral separations of partially soluble racemates. Besides, partially water-soluble or insoluble chiral selectors may be exploited in the enantiomeric resolution in NACE. The high reproducibility due to low Joule heat generation and no change in BGE concentration may make NACE a routine analytical technique. These facts attracted scientists to use NACE for the chiral resolution. The present review describes the advances in the chiral separations by NACE and its application in pharmaceutical and biomedical analysis. The emphasis has been given to discuss the selection of the chiral selectors and organic solvents, applications of NACE, comparison between NACE and aqueous CE, and chiral recognition mechanism. Besides, efforts have also been made to predict the future perspectives of NACE. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Triticonazole enantiomers: Separation by supercritical fluid chromatography and the effect of the chromatographic conditions.

PubMed

He, Jianfeng; Fan, Jun; Yan, Yilun; Chen, Xiaodong; Wang, Tai; Zhang, Yaomou; Zhang, Weiguang

2016-11-01

Enantiomeric pairs of triticonazole have been successfully separated by supercritical fluid chromatography coupled with a tris(3,5-dimethylphenylcarbamoyl) cellulose-coated chiral stationary phase in this work. The effects of co-solvent, dissolution solvent, flow rate, backpressure, and column temperature have been studied in detail with respect to retention, selectivity, and resolution of triticonazole. As indicated, the co-solvents mostly affected the retention factors and resolution, due to the different molecular structure and polarity. In addition, the dissolution solvents, namely, chloromethanes and alcohols, have been also important for enantioseparation because of the different interaction with stationary phase. Higher flow rate and backpressure led to faster elution of the triticonazole molecules, and the change of column temperature showed slight effect on the resolution of triticonazole racemate. Moreover, a comparative separation experiment between supercritical fluid chromatography and high performance liquid chromatography revealed that chiral supercritical fluid chromatography gave the 3.5 times value of R s /t R2 than high performance liquid chromatography, which demonstrated that supercritical fluid chromatography had much higher separation efficiency. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Homogeneous catalysts for stereoregular olefin polymerization

DOEpatents

Marks, Tobin J.; Eisen, Moris S.; Giardello, Michael A.

1995-01-01

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C.sub.5 R'.sub.4-x R*.sub.x) A (C.sub.5 R".sub.4-y R"'.sub.y) M Q.sub.p, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R', R", R"', and R* represent substituted and unsubstituted alkyl groups having 1-30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3.ltoreq.p.ltoreq.o. Related complexes may be prepared by alkylation of the corresponding dichorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form "cation-like" species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other .alpha.-olefin polymerization can be effected with very high efficiency and isospecificity.

Homogeneous catalysts for stereoregular olefin polymerization

DOEpatents

Marks, Tobin J.; Eisen, Moris S.; Giardello, Michael A.

1994-01-01

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C.sub.5 R'.sub.4-x R*.sub.x) A (C.sub.5 R".sub.4-y R'".sub.y) M Q.sub.p, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R', R", R'", and R* represent substituted and unsubstituted alkyl groups having 1-30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3.ltoreq.p.ltoreq.o. Related complexes may be prepared by alkylation of the corresponding dichorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form "cation-like" species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other .alpha.-olefin polymerization can be effected with very high efficiency and isospecificity.

Homogeneous catalysts for stereoregular olefin polymerization

DOEpatents

Marks, T.J.; Eisen, M.S.; Giardello, M.A.

1995-10-03

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C{sub 5}R{prime}{sub 4{minus}x}R*{sub x})A(C{sub 5}R{double_prime}{sub 4{minus}y}R{double_prime}{prime}{sub y})MQ{sub p}, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R{prime}, R{double_prime}, R{double_prime}{prime}, and R* represent substituted and unsubstituted alkyl groups having 1--30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3{>=}p{>=}0. Related complexes may be prepared by alkylation of the corresponding dichlorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form ``cation-like`` species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other {alpha}-olefin polymerization can be effected with very high efficiency and isospecificity. 1 fig.

Homogeneous catalysts for stereoregular olefin polymerization

DOEpatents

Marks, T.J.; Eisen, M.S.; Giardello, M.A.

1994-07-19

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C[sub 5]R[prime][sub 4[minus]x]R*[sub x])-A-(C[sub 5]R[double prime][sub 4[minus]y]R[prime][double prime][sub y])-M-Q[sub p], where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R[prime], R[double prime], R[prime][double prime], and R* represent substituted and unsubstituted alkyl groups having 1--30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3 [<=] p [<=] 0. Related complexes may be prepared by alkylation of the corresponding dichlorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form cation-like'' species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other [alpha]-olefin polymerization can be effected with very high efficiency and isospecificity. 1 fig.

Brilliant Sm, Eu, Tb, and Dy Chiral Lanthanide Complexes with Strong Circularly Polarized Luminescence

PubMed Central

Petoud, Stéphane; Muller, Gilles; Moore, Evan G.; Xu, Jide; Sokolnicki, Jurek; Riehl, James P.; Le, Uyen N.; Cohen, Seth M.; Raymond, Kenneth N.

2009-01-01

The synthesis, characterization, and luminescent behavior of trivalent Sm, Eu, Dy, and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, glum, recorded for the Eu(III) complex is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments. PMID:17199285

Chiral DOTA chelators as an improved platform for biomedical imaging and therapy applications.

PubMed

Dai, Lixiong; Jones, Chloe M; Chan, Wesley Ting Kwok; Pham, Tiffany A; Ling, Xiaoxi; Gale, Eric M; Rotile, Nicholas J; Tai, William Chi-Shing; Anderson, Carolyn J; Caravan, Peter; Law, Ga-Lai

2018-02-27

Despite established clinical utilisation, there is an increasing need for safer, more inert gadolinium-based contrast agents, and for chelators that react rapidly with radiometals. Here we report the syntheses of a series of chiral DOTA chelators and their corresponding metal complexes and reveal properties that transcend the parent DOTA compound. We incorporated symmetrical chiral substituents around the tetraaza ring, imparting enhanced rigidity to the DOTA cavity, enabling control over the range of stereoisomers of the lanthanide complexes. The Gd chiral DOTA complexes are shown to be orders of magnitude more inert to Gd release than [GdDOTA] - . These compounds also exhibit very-fast water exchange rates in an optimal range for high field imaging. Radiolabeling studies with (Cu-64/Lu-177) also demonstrate faster labelling properties. These chiral DOTA chelators are alternative general platforms for the development of stable, high relaxivity contrast agents, and for radiometal complexes used for imaging and/or therapy.

Asymmetric synthesis of isoindolones by chiral cyclopentadienyl-rhodium(III)-catalyzed C-H functionalizations.

PubMed

Ye, Baihua; Cramer, Nicolai

2014-07-21

Directed Cp*Rh(III)-catalyzed carbon-hydrogen (C-H) bond functionalizations have evolved as a powerful strategy for the construction of heterocycles. Despite their high value, the development of related asymmetric reactions is largely lagging behind due to a limited availability of robust and tunable chiral cyclopentadienyl ligands. Rhodium complexes comprising a chiral Cp ligand with an atropchiral biaryl backbone enables an asymmetric synthesis of isoindolones from arylhydroxamates and weakly alkyl donor/acceptor diazo derivatives as one-carbon component under mild conditions. The complex guides the substrates with a high double facial selectivity yielding the chiral isoindolones in good yields and excellent enantioselectivities. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stereocontrolled Cyanohydrin Ether Synthesis through Chiral Brønsted Acid-Mediated Vinyl Ether Hydrocyanation

PubMed Central

Lu, Chunliang; Su, Xiaoge; Floreancig, Paul E.

2013-01-01

Vinyl ethers can be protonated to generate oxocarbenium ions that react with Me3SiCN to form cyanohydrin alkyl ethers. Reactions that form racemic products proceed efficiently upon converting the vinyl ether to an α-chloro ether prior to cyanide addition in a pathway that proceeds through Brønsted acid-mediated chloride ionization. Enantiomerically enriched products can be accessed by directly protonating the vinyl ether with a chiral Brønsted acid to form a chiral ion pair. Me3SiCN acts as the nucleophile and PhOH serves as a stoichiometric proton source in a rare example of an asymmetric bimolecular nucleophilic addition reaction into an oxocarbenium ion. Computational studies provide a model for the interaction between the catalyst and the oxocarbenium ion. PMID:23968162

A chirality-based metrics for free-energy calculations in biomolecular systems.

PubMed

Pietropaolo, Adriana; Branduardi, Davide; Bonomi, Massimiliano; Parrinello, Michele

2011-09-01

In this work, we exploit the chirality index introduced in (Pietropaolo et al., Proteins 2008, 70, 667) as an effective descriptor of the secondary structure of proteins to explore their complex free-energy landscape. We use the chirality index as an alternative metrics in the path collective variables (PCVs) framework and we show in the prototypical case of the C-terminal domain of immunoglobulin binding protein GB1 that relevant configurations can be efficiently sampled in combination with well-tempered metadynamics. While the projections of the configurations found onto a variety of different descriptors are fully consistent with previously reported calculations, this approach provides a unifying perspective of the folding mechanism which was not possible using metadynamics with the previous formulation of PCVs. Copyright © 2011 Wiley Periodicals, Inc.

A Readily Accessible Class of Chiral Cp Ligands and their Application in RuII -Catalyzed Enantioselective Syntheses of Dihydrobenzoindoles.

PubMed

Wang, Shou-Guo; Park, Sung Hwan; Cramer, Nicolai

2018-05-04

Chiral cyclopentadienyl (Cp x ) ligands have a large application potential in enantioselective transition-metal catalysis. However, the development of concise and practical routes to such ligands remains in its infancy. We present a convenient and efficient two-step synthesis of a novel class of chiral Cp x ligands with tunable steric properties that can be readily used for complexation, giving Cp x Rh I , Cp x Ir I , and Cp x Ru II complexes. The potential of this ligand class is demonstrated with the latter in the enantioselective cyclization of azabenzonorbornadienes with alkynes, affording dihydrobenzoindoles in up to 98:2 e.r., significantly outperforming existing binaphthyl-derived Cp x ligands. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral dynamics with (non)strange quarks

NASA Astrophysics Data System (ADS)

Kubis, Bastian; Meißner, Ulf-G.

2017-01-01

We review the results and achievements of the project B.3. Topics addressed include pion photoproduction off the proton and off deuterium, three-flavor chiral perturbation theory studies, chiral symmetry tests in Goldstone boson decays, the development of unitarized chiral perturbation theory to next-to-leading order, the two-pole structure of the Λ(1405), the dynamical generation of the lowest S11 resonances, the theory of hadronic atoms and its application to various systems, precision studies in light-meson decays based on dispersion theory, the Roy-Steiner analysis of pion-nucleon scattering, a high-precision extraction of the elusive pion-nucleon σ-term, and aspects of chiral dynamics in few-nucleon systems.

Second Harmonic Generation Optical Rotation Solely Attributable to Chirality in Plasmonic Metasurfaces.

PubMed

Collins, Joel T; Hooper, David C; Mark, Andrew G; Kuppe, Christian; Valev, Ventsislav Kolev

2018-05-31

Chiral plasmonic nanostructures, those lacking mirror symmetry, can be designed to manipulate the polarization of incident light resulting in chiroptical (chiral optical) effects such as circular dichroism (CD) and optical rotation (OR). Due to high symmetry sensitivity, corresponding effects in second harmonic generation (SHG-CD and SHG-OR) are typically much stronger in comparison. These nonlinear effects have long been used for chiral molecular analysis and characterization, however both linear and nonlinear optical rotation can occur even in achiral structures, if the structure is birefringent due to anisotropy. Crucially, chiroptical effects resulting from anisotropy typically exhibit a strong dependence on structural orientation. Here we report large second-harmonic generation optical rotation of ±45°, due to intrinsic chirality in a highly anisotropic helical metamaterial. The SHG intensity is found to strongly relate to the structural anisotropy, however the angle of SHG-OR is invariant under sample rotation. We show that by tuning the geometry of anisotropic nanostructures, the interaction between anisotropy, chirality, and experiment geometry can allow even greater control over the chiroptical properties of plasmonic metamaterials.

Application of cyanuric chloride-based six new chiral derivatizing reagents having amino acids and amino acid amides as chiral auxiliaries for enantioresolution of proteinogenic amino acids by reversed-phase high-performance liquid chromatography.

PubMed

Bhushan, Ravi; Dixit, Shuchi

2012-04-01

Six dichloro-s-triazine (DCT) reagents having L-Leu, D-Phg, L-Val, L-Met, L-Ala and L-Met-NH(2) as chiral auxiliaries in cyanuric chloride were introduced for enantioseparation of 13 proteinogenic amino acids. Four other DCTs and six monochloro-s-triazine (MCT) reagents having amino acid amides as chiral auxiliaries were also synthesized. These 16 chiral derivatizing reagents (CDRs) were used for synthesis of diastereomers of all the 13 analytes using microwave irradiation, which were resolved by reversed-phase high-performance liquid chromatography (RP-HPLC) using C18 column and gradient eluting mixture of aqueous TFA and acetonitrile with UV detection at 230 nm. It required only 60-90 s for derivatization using microwave irradiation. Better resolution and lower retention times were observed for the diastereomers prepared with CDRs having amino acids as chiral auxiliaries as compared to counterparts prepared with reagents having amino acid amides as chiral auxiliaries. As the best resolution of all the 13 analytes was observed for their diastereomers prepared using the DCT reagent having L-Leu as chiral auxiliary, this CDR was further employed for derivatization of Lys, Tyr, His and Arg followed by RP-HPLC analysis of resulting diastereomers. The results are discussed in light of acid and amide groups of chiral auxiliaries constituting CDRs, electronegativities of the atoms of achiral moieties constituting CDRs and hydrophobicities of side chains of amino acids constituting CDRs and analytes.

Effects of molecular chirality on self-assembly and switching in liquid crystals at the cross-over between rod-like and bent shapes.

PubMed

Ocak, Hale; Poppe, Marco; Bilgin-Eran, Belkız; Karanlık, Gürkan; Prehm, Marko; Tschierske, Carsten

2016-09-21

A bent-core compound derived from a 4-cyanoresorcinol core unit with two terephthalate based rod-like wings and carrying chiral 3,7-dimethyloctyloxy side chains has been synthesized in racemic and enantiomerically pure form and characterized by polarizing microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical investigations to study the influence of molecular chirality on the superstructural chirality and polar order in lamellar liquid crystalline phases. Herein we demonstrate that the coupling of molecular chirality with superstructural layer chirality in SmCsPF domain phases (forming energetically distinct diastereomeric pairs) can fix the tilt direction and thus stabilize synpolar order, leading to bistable ferroelectric switching in the SmC* phases of the (S)-enantiomer, whereas tristable modes determine the switching of the racemate. Moreover, the mechanism of electric field induced molecular reorganization changes from a rotation around the molecular long axis in the racemate to a rotation on the tilt-cone for the (S)-enantiomer. At high temperature the enantiomer behaves like a rod-like molecule with a chirality induced ferroelectric SmC* phase and an electroclinic effect in the SmA'* phase. At reduced temperature sterically induced polarization, due to the bent molecular shape, becomes dominating, leading to much higher polarization values, thus providing access to high polarization ferroelectric materials with weakly bent compounds having only "weakly chiral" stereogenic units. Moreover, the field induced alignment of the SmCsPF(()*()) domains gives rise to a special kind of electroclinic effect appearing even in the absence of molecular chirality. Comparison with related compounds indicates that the strongest effects of chirality appear for weakly bent molecules with a relatively short coherence length of polar order, whereas for smectic phases with long range polar order the effects of the interlayer interfaces can override the chirality effects.

Spin and chirality effects in antler-topology processes at high energy $${e^+e^-}$$ colliders

DOE PAGES

Choi, S. Y.; Christensen, N. D.; Salmon, D.; ...

2015-10-01

We perform a model-independent investigation of spin and chirality correlation effects in the antler-topology processes e +e -→P +P -→(ℓ+D0)(ℓ-D¯0) at high-energy e +e - colliders with polarized beams. Generally the production process e +e -→P +P - can occur not only through the s-channel exchange of vector bosons, V0 , including the neutral Standard Model (SM) gauge bosons, γ and Z, but also through the s- and t-channel exchanges of new neutral states, S0 and T0 , and the u-channel exchange of new doubly charged states, U-- . The general set of (non-chiral) three-point couplings of the new particlesmore » and leptons allowed in a renormalizable quantum field theory is considered. The general spin and chirality analysis is based on the threshold behavior of the excitation curves for P +P - pair production in e +e - collisions with longitudinal- and transverse-polarized beams, the angular distributions in the production process and also the production-decay angular correlations. In the first step, we present the observables in the helicity formalism. Subsequently, we show how a set of observables can be designed for determining the spins and chiral structures of the new particles without any model assumptions. Finally, taking into account a typical set of approximately chiral invariant scenarios, we demonstrate how the spin and chirality effects can be probed experimentally at a high-energy e +e - collider.« less

Spin and chirality effects in antler-topology processes at high energy $$\\varvec{e^+e^-}$$ e + e - colliders

DOE PAGES

Choi, S. Y.; Christensen, N. D.; Salmon, D.; ...

2015-10-01

We perform a model-independent investigation of spin and chirality correlation effects in the antler-topology processes e+e−→P+P−→(ℓ+D0)(ℓ−D¯0) at high-energy e+e− colliders with polarized beams. Generally the production process e+e−→P+P− can occur not only through the s-channel exchange of vector bosons, V0 , including the neutral Standard Model (SM) gauge bosons, γ and Z, but also through the s- and t-channel exchanges of new neutral states, S0 and T0 , and the u-channel exchange of new doubly charged states, U−− . The general set of (non-chiral) three-point couplings of the new particles and leptons allowed in a renormalizable quantum field theory ismore » considered. The general spin and chirality analysis is based on the threshold behavior of the excitation curves for P+P− pair production in e+e− collisions with longitudinal- and transverse-polarized beams, the angular distributions in the production process and also the production-decay angular correlations. In the first step, we present the observables in the helicity formalism. Subsequently, we show how a set of observables can be designed for determining the spins and chiral structures of the new particles without any model assumptions. Finally, taking into account a typical set of approximately chiral invariant scenarios, we demonstrate how the spin and chirality effects can be probed experimentally at a high-energy e+e− collider.« less

Spin and chirality effects in antler-topology processes at high energy $${e^+e^-}$$ colliders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, S. Y.; Christensen, N. D.; Salmon, D.

We perform a model-independent investigation of spin and chirality correlation effects in the antler-topology processes e +e -→P +P -→(ℓ+D0)(ℓ-D¯0) at high-energy e +e - colliders with polarized beams. Generally the production process e +e -→P +P - can occur not only through the s-channel exchange of vector bosons, V0 , including the neutral Standard Model (SM) gauge bosons, γ and Z, but also through the s- and t-channel exchanges of new neutral states, S0 and T0 , and the u-channel exchange of new doubly charged states, U-- . The general set of (non-chiral) three-point couplings of the new particlesmore » and leptons allowed in a renormalizable quantum field theory is considered. The general spin and chirality analysis is based on the threshold behavior of the excitation curves for P +P - pair production in e +e - collisions with longitudinal- and transverse-polarized beams, the angular distributions in the production process and also the production-decay angular correlations. In the first step, we present the observables in the helicity formalism. Subsequently, we show how a set of observables can be designed for determining the spins and chiral structures of the new particles without any model assumptions. Finally, taking into account a typical set of approximately chiral invariant scenarios, we demonstrate how the spin and chirality effects can be probed experimentally at a high-energy e +e - collider.« less

Engineering an enantioselective amine oxidase for the synthesis of pharmaceutical building blocks and alkaloid natural products.

PubMed

Ghislieri, Diego; Green, Anthony P; Pontini, Marta; Willies, Simon C; Rowles, Ian; Frank, Annika; Grogan, Gideon; Turner, Nicholas J

2013-07-24

The development of cost-effective and sustainable catalytic methods for the production of enantiomerically pure chiral amines is a key challenge facing the pharmaceutical and fine chemical industries. This challenge is highlighted by the estimate that 40-45% of drug candidates contain a chiral amine, fueling a demand for broadly applicable synthetic methods that deliver target structures in high yield and enantiomeric excess. Herein we describe the development and application of a "toolbox" of monoamine oxidase variants from Aspergillus niger (MAO-N) which display remarkable substrate scope and tolerance for sterically demanding motifs, including a new variant, which exhibits high activity and enantioselectivity toward substrates containing the aminodiphenylmethane (benzhydrylamine) template. By combining rational structure-guided engineering with high-throughput screening, it has been possible to expand the substrate scope of MAO-N to accommodate amine substrates containing bulky aryl substituents. These engineered MAO-N biocatalysts have been applied in deracemization reactions for the efficient asymmetric synthesis of the generic active pharmaceutical ingredients Solifenacin and Levocetirizine as well as the natural products (R)-coniine, (R)-eleagnine, and (R)-leptaflorine. We also report a novel MAO-N mediated asymmetric oxidative Pictet-Spengler approach to the synthesis of (R)-harmicine.

Gold(III) chloride catalyzed synthesis of chiral substituted 3-formyl furans from carbohydrates: application in the synthesis of 1,5-dicarbonyl derivatives and furo[3,2-c]pyridine.

PubMed

Mal, Kanchan; Sharma, Abhinandan; Das, Indrajit

2014-09-08

This report describes a gold(III)-catalyzed efficient general route to densely substituted chiral 3-formyl furans under extremely mild conditions from suitably protected 5-(1-alkynyl)-2,3-dihydropyran-4-one using H2 O as a nucleophile. The reaction proceeds through the initial formation of an activated alkyne-gold(III) complex intermediate, followed by either a domino nucleophilic attack/anti-endo-dig cyclization, or the formation of a cyclic oxonium ion with subsequent attack by H2 O. To confirm the proposed mechanistic pathway, we employed MeOH as a nucleophile instead of H2 O to result in a substituted furo[3,2-c]pyran derivative, as anticipated. The similar furo[3,2-c]pyran skeleton with a hybrid carbohydrate-furan derivative has also been achieved through pyridinium dichromate (PDC) oxidation of a substituted chiral 3-formyl furan. The corresponding protected 5-(1-alkynyl)-2,3-dihydropyran-4-one can be synthesized from the monosaccharides (both hexoses and pentose) following oxidation, iodination, and Sonogashira coupling sequences. Furthermore, to demonstrate the potentiality of chiral 3-formyl furan derivatives, a TiBr4 -catalyzed reaction of these derivatives has been shown to offer efficient access to 1,5-dicarbonyl compounds, which on treatment with NH4 OAc in slightly acidic conditions afforded substituted furo[3,2-c]pyridine. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Free-standing mesoporous silica films with tunable chiral nematic structures.

PubMed

Shopsowitz, Kevin E; Qi, Hao; Hamad, Wadood Y; Maclachlan, Mark J

2010-11-18

Chirality at the molecular level is found in diverse biological structures, such as polysaccharides, proteins and DNA, and is responsible for many of their unique properties. Introducing chirality into porous inorganic solids may produce new types of materials that could be useful for chiral separation, stereospecific catalysis, chiral recognition (sensing) and photonic materials. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant. Efforts to impart chirality at a larger length scale using self-assembly are almost unknown. Here we describe the development of a photonic mesoporous inorganic solid that is a cast of a chiral nematic liquid crystal formed from nanocrystalline cellulose. These materials may be obtained as free-standing films with high surface area. The peak reflected wavelength of the films can be varied across the entire visible spectrum and into the near-infrared through simple changes in the synthetic conditions. To the best of our knowledge these are the first materials to combine mesoporosity with long-range chiral ordering that produces photonic properties. Our findings could lead to the development of new materials for applications in, for example, tuneable reflective filters and sensors. In addition, this type of material could be used as a hard template to generate other new materials with chiral nematic structures.

Optimization of a two-dimensional liquid chromatography-supercritical fluid chromatography-mass spectrometry (2D-LC-SFS-MS) system to assess "in-vivo" inter-conversion of chiral drug molecules.

PubMed

Goel, Meenakshi; Larson, Eli; Venkatramani, C J; Al-Sayah, Mohammad A

2018-05-01

Enantioselective analysis is an essential requirement during the pharmaceutical development of chiral drug molecules. In pre-clinical and clinical studies, the Food and Drug Administration (FDA) mandates the assessment of "in vivo" inter-conversion of chiral drugs to determine their physiological effects. In-vivo analysis of the active pharmaceutical ingredient (API) and its potential metabolites could be quite challenging due to their low abundance (ng/mL levels) and matrix interferences. Therefore, highly selective and sensitive analytical techniques are required to separate the API and its metabolites from the matrix components and one another. Additionally, for chiral APIs, further analytical separation is required to resolve the API and its potential metabolites from their corresponding enantiomers. In this work, we demonstrate the optimization of our previously designed two-dimensional liquid chromatography-supercritical fluid chromatography-mass spectrometry (2D-LC-SFC -MS) system to achieve 10 ng/mL detection limit [1]. The first LC dimension, used as a desalting step, could efficiently separate the API from its potential metabolites and matrix components. The API and its metabolites were then trapped/focused on small trapping columns and transferred onto the second SFC dimension for chiral separation. Detection can be achieved by ultra-violet (UV) or MS detection. Different system parameters such as column dimensions, transfer volumes, trapping column stationary phase, system tubing internal diameter (i.d.), and detection techniques, were optimized to enhance the sensitivity of the 2D-LC-SFC-MS system. The limit of detection was determined to be 10 ng/mL. An application is described where a mouse hepatocyte treated sample was analyzed using the optimized 2D-LC-SFC-MS system with successful assessment of the ratio of API to its metabolite (1D-LC), as well as the corresponding enantiomeric excess values (% e.e.) of each (2D-SFC). Copyright © 2018 Elsevier B.V. All rights reserved.

Four-dimensional analysis by high-speed holographic imaging reveals a chiral memory of sperm flagella.

PubMed

Muschol, Michael; Wenders, Caroline; Wennemuth, Gunther

2018-01-01

Here high-speed Digital Holographic Microscopy (DHM) records sperm flagellar waveforms and swimming paths in 4 dimensions (X, Z, and t). We find flagellar excursions into the Z-plane nearly as large as the envelope of the flagellar waveform projected onto the XY-plane. These Z-plane excursions travel as waves down the flagellum each beat cycle. DHM also tracks the heads of free-swimming sperm and the dynamics and chirality of rolling of sperm around their long axis. We find that mouse sperm roll CW at the maximum positive Z-plane excursion of the head, then roll CCW at the subsequent maximum negative Z-plane excursion. This alternating chirality of rolling indicates sperm have a chiral memory. Procrustes alignments of path trajectories for sequences of roll-counterroll cycles show that path chirality is always CW for the cells analyzed in this study. Human and bull sperm lack distinguishable left and right surfaces, but DHM still indicates coordination of Z-plane excursions and rolling events. We propose that sperm have a chiral memory that resides in a hypothetical elastic linkage within the flagellar machinery, which stores some of the torque required for a CW or CCW roll to reuse in the following counter-roll. Separate mechanisms control path chirality.

Synthesis of enantiopure trans-2,5-disubstituted trifluoromethylpyrrolidines and (2S,5R)-5-trifluoromethylproline.

PubMed

Lubin, Hodney; Pytkowicz, Julien; Chaume, Grégory; Sizun-Thomé, Gwenaëlle; Brigaud, Thierry

2015-03-06

Enantiopure trans-2,5-disubstituted trifluoromethylpyrrolidines were prepared on a several gram scale starting from a readily available chiral fluorinated oxazolidine (Fox). A pure oxazolopyrrolidine intermediate could be obtained after an efficient separation by selective diastereomer destruction. The addition of various Grignard reagents on this oxazolopyrrolidine provided disubstituted pyrrolidines with moderate to complete trans diastereoselectivity. The highly valuable compound (2S,5R)-5-trifluoromethylproline could be synthesized from the same oxazolopyrrolidine intermediate via a Strecker-type reaction.

Enantioselective Ring Opening of Epoxides with 4-Methoxyphenol Catalyzed by Gallium Heterobimetallic Complexes: An Efficient Method for the Synthesis of Optically Active 1,2-Diol Monoethers.

PubMed

Iida, Takehiko; Yamamoto, Noriyoshi; Matsunaga, Shigeki; Woo, Hee-Gweon; Shibasaki, Masakatsu

1998-09-04

Useful chiral building blocks such as 1,2-diols can be obtained by the enantioselective ring opening of achiral epoxides with oxygen nucleophiles. The ring opening is carried out effectively (up to 94 % ee) with 4-methoxyphenol and catalytic amounts of gallium complexes. The novel complex GaSO 1 displays a particularly high catalytic activity. © 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.

Conversion of alcohols to enantiopure amines through dual enzyme hydrogen-borrowing cascades

PubMed Central

Mutti, Francesco G.; Knaus, Tanja; Scrutton, Nigel S.; Breuer, Michael; Turner, Nicholas J.

2016-01-01

α-Chiral amines are key intermediates for the synthesis of a plethora of chemical compounds on industrial scale. Here we present a biocatalytic hydrogen-borrowing amination of primary and secondary alcohols that allows for the efficient and environmentally benign production of enantiopure amines. The method relies on the combination of an alcohol dehydrogenase (ADHs from Aromatoleum sp., Lactobacillus sp. and Bacillus sp.) enzyme operating in tandem with an amine dehydrogenase (AmDHs engineered from Bacillus sp.) to aminate a structurally diverse range of aromatic and aliphatic alcohols (up to 96% conversion and 99% enantiomeric excess). Furthermore, primary alcohols are aminated with high conversion (up to 99%). This redox self-sufficient network possesses high atom efficiency, sourcing nitrogen from ammonium and generating water as the sole by-product. PMID:26404833

Chiral stability of an extemporaneously prepared clopidogrel bisulfate oral suspension.

PubMed

Tynes, Clay R; Livingston, Brad; Patel, Hetesh; Arnold, John J

2014-01-01

The purpose of this study was to evaluate the chiral stability of clopidogrel bisulfate in an extemporaneously compounded oral suspension for a period of 60 days. A 5 mg/mL oral suspension of clopidogrel bisulfate was prepared from commercially available Plavix tablets. The clopidogrel suspension was then evenly divided between two light-resistant prescription bottles and stored either under refrigeration (4°C) or at room temperature (25°C). Samples were drawn from the stored suspensions immediately after preparation and on days 7, 14, 28, and 60. Samples were subsequently analyzed at each time point by high-performance liquid chromatography using a reversed-phase column, with chemical stability defined as the retention of at least 90% of the initial intact clopidogrel concentration measured. To determine the chiral stability of the suspension, samples were also analyzed by high-performance liquid chromatography using a chiral column to investigate possible enantiomeric inversion. Chiral stability was defined as the retention of at least 90% of the initial concentration of the suspension as the S-enantiomer, the active moiety of Plavix. Regardless of storage conditions, the oral suspension of clopidogrel retained at least 98% of the active S-enantiomer for 60 days after preparation. Compared with the clopidogrel suspension stored in the refrigerator, more chiral inversion was noted in the clopidogrel suspension stored at room temperature. Our investigation of chiral stability indicates that a 5 mg/mL clopidogrel oral suspension stored under refrigeration and at room temperature maintains chiral stability as the active S-enantiomer.

Strategy for large-scale isolation of enantiomers in drug discovery.

PubMed

Leek, Hanna; Thunberg, Linda; Jonson, Anna C; Öhlén, Kristina; Klarqvist, Magnus

2017-01-01

A strategy for large-scale chiral resolution is illustrated by the isolation of pure enantiomer from a 5kg batch. Results from supercritical fluid chromatography will be presented and compared with normal phase liquid chromatography. Solubility of the compound in the supercritical mobile phase was shown to be the limiting factor. To circumvent this, extraction injection was used but shown not to be efficient for this compound. Finally, a method for chiral resolution by crystallization was developed and applied to give diastereomeric salt with an enantiomeric excess of 99% at a 91% yield. Direct access to a diverse separation tool box will be shown to be essential for solving separation problems in the most cost and time efficient way. Copyright © 2016 Elsevier Ltd. All rights reserved.

Structure Study of the Chiral Lactide Molecules by Chirped-Pulse Ftmw Spectroscopy

NASA Astrophysics Data System (ADS)

Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Bialkowska-Jaworska, Ewa; Kisiel, Zbigniew

2011-06-01

Lactide is a six member cyclic diester with two chiral centers that forms from lactic acid in the presence of heat and an acid catalyst. It can form either a homo-chiral (RR) structure with both methyl groups equatorial or a hetero-chiral (RS) structure where one methyl group is equatorial and the other methyl group is axial. Structurally lactide is similar to lactic acid dimer; however, the kinked ring is covalently bonded and two waters are lost. And unlike lactic acid dimer, which has a very small dipole moment, the dipole moment of lactide is on the order of 3 Debye. Here the microwave spectra of the highly rigid homo- and hetero-chiral lactides are presented, which were first assigned in a heated lactic acid spectrum where the chemistry took place in the reservoir nozzles. Further isotopic information from a commercial sample of predominately homo-chiral lactide was obtained leading to a Kraitchman substitution structure of the homo-chiral lactide. Preliminary results of the cluster of homo-chiral lactide with one water molecule attached are also presented.

Enantioseparation of Racemic Flurbiprofen by Aqueous Two-Phase Extraction With Binary Chiral Selectors of L-dioctyl Tartrate and L-tryptophan.

PubMed

Chen, Zhi; Zhang, Wei; Wang, Liping; Fan, Huajun; Wan, Qiang; Wu, Xuehao; Tang, Xunyou; Tang, James Z

2015-09-01

A novel method for chiral separation of flurbiprofen enantiomers was developed using aqueous two-phase extraction (ATPE) coupled with biphasic recognition chiral extraction (BRCE). An aqueous two-phase system (ATPS) was used as an extracting solvent which was composed of ethanol (35.0% w/w) and ammonium sulfate (18.0% w/w). The chiral selectors in ATPS for BRCE consideration were L-dioctyl tartrate and L-tryptophan, which were screened from amino acids, β-cyclodextrin derivatives, and L-tartrate esters. Factors such as the amounts of L-dioctyl tartrate and L-tryptophan, pH, flurbiprofen concentration, and the operation temperature were investigated in terms of chiral separation of flurbiprofen enantiomers. The optimum conditions were as follows: L-dioctyl tartrate, 80 mg; L-tryptophan, 40 mg; pH, 4.0; flurbiprofen concentration, 0.10 mmol/L; and temperature, 25 °C. The maximum separation factor α for flurbiprofen enantiomers could reach 2.34. The mechanism of chiral separation of flurbiprofen enantiomers is discussed and studied. The results showed that synergistic extraction has been established by L-dioctyl tartrate and L-tryptophan, which enantioselectively recognized R- and S-enantiomers in top and bottom phases, respectively. Compared to conventional liquid-liquid extraction, ATPE coupled with BRCE possessed higher separation efficiency and enantioselectivity without the use of any other organic solvents. The proposed method is a potential and powerful alternative to conventional extraction for separation of various enantiomers. © 2015 Wiley Periodicals, Inc.

Synthesis, structures and properties of two new chiral rare earth-organic frameworks constructed by L/D-tartaric acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Gonghao; Zhang, Haitao; Miao, Hao

2015-09-15

Hydrothermal reactions of rare earth cerium with L- or D- tartaric acid afford a pair of novel chiral enantiomer coordination polymers, namely, [Ce(L-tart)(CH{sub 2}OHCH{sub 2}OH)(H{sub 2}O)]Cl (L-1) and [Ce(D-tart)(CH{sub 2}OHCH{sub 2}OH)(H{sub 2}O)]Cl (D-1). Their structures were determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, XRD, IR spectra, and TG analyses. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements proved that they are of structural chirality in the bulk samples. To the best of our knowledge, the enantiomers of L-1 and D-1 are the first 2D chiral dilayer frameworks constructed from L/D-tartrate ligands,more » ancillary ligand ethanediol and lanthanide ion Ce. - Graphical abstract: Hydrothermal reactions of rare earth cerium with L- or D- tartaric acid afford a pair of novel chiral enantiomer coordination polymers, namely, [Ce(L-tart)(CH{sub 2}OHCH{sub 2}OH)(H{sub 2}O)]Cl (L-1) and [Ce(D-tart)(CH{sub 2}OHCH{sub 2}OH)(H{sub 2}O)]Cl (D-1). Structural analysis indicates that the enantiomers of L-1 and D-1 are the first 2D chiral dilayer frameworks constructed from L/D-tartrate ligands and ancillary ligands ethanediol reacted with lanthanide ions Ce.« less

A resolution approach of racemic phenylalanine with aqueous two-phase systems of chiral tropine ionic liquids.

PubMed

Wu, Haoran; Yao, Shun; Qian, Guofei; Yao, Tian; Song, Hang

2015-10-30

Aqueous two-phase systems (ATPS) based on tropine type chiral ionic liquids and inorganic salt solution were designed and prepared for the enantiomeric separation of racemic phenylalanine. The phase behavior of IL-based ATPS was comprehensive investigated, and phase equilibrium data were correlated by Merchuk equation. Various factors were also systematically investigated for their influence on separation efficiency. Under the appropriate conditions (0.13g/g [C8Tropine]pro, 35mg/g Cu(Ac)2, 20mg/g d,l-phenylalanine, 0.51g/g H2O and 0.30g/g K2HPO4), the enantiomeric excess value of phenylalanine in solid phase (mainly containing l-enantiomer) was 65%. Finally, the interaction mechanism was studied via 1D and 2D NMR. The results indicate that d-enantiomer of phenylalanine interacts more strongly with chiral ILs and Cu(2+) based on the chiral ion-pairs space coordination mechanism, which makes it tend to remain in the top IL-rich phase. By contrast, l-enantiomer is transferred into the solid phase. Above chiral ionic liquids aqueous two-phase systems have demonstrated obvious resolution to racemic phenylalanine and could be promising alterative resolution approach for racemic amino acids in aqueous circumstance. Copyright © 2015. Published by Elsevier B.V.

Single-mode annular chirally-coupled core fibers for fiber lasers

NASA Astrophysics Data System (ADS)

Zhang, Haitao; Hao, He; He, Linlu; Gong, Mali

2018-03-01

Chirally-coupled core (CCC) fiber can transmit single fundamental mode and effectively suppresses higher-order mode (HOM) propagation, thus improve the beam quality. However, the manufacture of CCC fiber is complicated due to its small side core. To decrease the manufacture difficulty in China, a novel fiber structure is presented, defined as annular chirally-coupled core (ACCC) fiber, replacing the small side core by a larger side annulus. In this paper, we designed the fiber parameters of this new structure, and demonstrated that the new structure has a similar property of single mode with traditional CCC fiber. Helical coordinate system was introduced into the finite element method (FEM) to analyze the mode field in the fiber, and the beam propagation method (BPM) was employed to analyze the influence of the fiber parameters on the mode loss. Based on the result above, the fiber structure was optimized for efficient single-mode transmission, in which the core diameter is 35 μm with beam quality M2 value of 1.04 and an optical to optical conversion efficiency of 84%. In this fiber, fundamental mode propagates in an acceptable loss, while the HOMs decay rapidly.

Analysis of repaglinide enantiomers in pharmaceutical formulations by capillary electrophoresis using 2,6-di-o-methyl-β-cyclodextrin as a chiral selector.

PubMed

Li, Cen; Jiang, Ye

2012-09-01

This study used the general applicability of 2,6-didi-o-methyl-β-cyclodextrin (DM-β-CD) as the chiral selector in capillary electrophoresis for fast and efficient chiral separation of repaglinide enantiomers. A systematic study of the parameters affecting separation was performed with UV detection at 243 nm. The optimum conditions were determined to be 1.25% (w/v) DM-β-CD in 20 mM sodium phosphate (pH 2.5) as the running buffer and separation voltage at 20 kV. DM-β-CD had the best enantiomer resolution properties under the tested conditions, whereas other β-cyclodextrins showed inferior performances or no performance. The proposed method had a linear calibration curve in the concentration range of 12.5-400 µg/mL. The limit of detection was 100 ng/mL. The intra-day and inter-day precisions were 2.8 and 3.2%, respectively. Recoveries of 97.9-100.9% were obtained. The proposed method was fast and convenient, and was determined to be efficient for separating enantiomers and applicable for analyzing repaglinide enantiomers in quality control of pharmaceutical production.

Furo-fused BINOL based crown as a fluorescent chiral sensor for enantioselective recognition of phenylethylamine and ethyl ester of valine.

PubMed

Upadhyay, Sunil P; Pissurlenkar, Raghuvir R S; Coutinho, Evans C; Karnik, Anil V

2007-07-20

A furo-fused BINOL based chiral crown was developed as an enantioselective chiral sensor for phenylethylamine and ethyl ester of valine. Fusion of furan to BINOL has resulted in a highly stereo-discriminating backbone for the chiral crown developed. This chiral crown exhibited a fluorescence enhancement difference of 2.97 times between two enantiomers of phenylethylamine and 2.55 times between two enantiomers of ethyl ester of valine. The ratio of association constants for two diastereomeric complexes of two enantiomers of phenylethylamine was found to be 11.30, and the ratio for two enantiomers of ethyl ester of valine was 7.02.

Chiral Magnetic Effect in Heavy Ion Collisions

DOE PAGES

Liao, Jinfeng

2016-12-01

The Chiral Magnetic Effect (CME) is a remarkable phenomenon that stems from highly nontrivial interplay of QCD chiral symmetry, axial anomaly, and gluonic topology. We show it is of fundamental importance to search for the CME in experiments. The heavy ion collisions provide a unique environment where a hot chiral-symmetric quark-gluon plasma is created, gluonic topological fluctuations generate chirality imbalance, and very strong magnetic fields |Β →|~m 2 π are present during the early stage of such collisions. Significant efforts have been made to look for CME signals in heavy ion collision experiments. Lastly, in this contribution we give amore » brief overview on the status of such efforts.« less

Experimental results on chiral magnetic and vortical effects

DOE PAGES

Wang, Gang; Wen, Liwen

2017-01-12

Various novel transport phenomena in chiral systems result from the interplay of quantum anomalies with magnetic field and vorticity in high-energy heavy-ion collisions and could survive the expansion of the fireball and be detected in experiments. Among them are the chiral magnetic effect, the chiral vortical effect, and the chiral magnetic wave, the experimental searches for which have aroused extensive interest. As a result, the goal of this review is to describe the current status of experimental studies at Relativistic Heavy-Ion Collider at BNL and the Large Hadron Collider at CERN and to outline the future work in experiment neededmore » to eliminate the existing uncertainties in the interpretation of the data.« less

The Origin and Limit of Asymmetric Transmission in Chiral Resonators.

PubMed

Parappurath, Nikhil; Alpeggiani, Filippo; Kuipers, L; Verhagen, Ewold

2017-04-19

We observe that the asymmetric transmission (AT) through photonic systems with a resonant chiral response is strongly related to the far-field properties of eigenmodes of the system. This understanding can be used to predict the AT for any resonant system from its complex eigenmodes. We find that the resonant chiral phenomenon of AT is related to, and is bounded by, the nonresonant scattering properties of the system. Using the principle of reciprocity, we determine a fundamental limit to the maximum AT possible for a single mode in any chiral resonator. We propose and follow a design route for a highly chiral dielectric photonic crystal structure that reaches this fundamental limit for AT.

The Origin and Limit of Asymmetric Transmission in Chiral Resonators

PubMed Central

2017-01-01

We observe that the asymmetric transmission (AT) through photonic systems with a resonant chiral response is strongly related to the far-field properties of eigenmodes of the system. This understanding can be used to predict the AT for any resonant system from its complex eigenmodes. We find that the resonant chiral phenomenon of AT is related to, and is bounded by, the nonresonant scattering properties of the system. Using the principle of reciprocity, we determine a fundamental limit to the maximum AT possible for a single mode in any chiral resonator. We propose and follow a design route for a highly chiral dielectric photonic crystal structure that reaches this fundamental limit for AT. PMID:28470027

Enantioselective cellular uptake of chiral semiconductor nanocrystals

NASA Astrophysics Data System (ADS)

Martynenko, I. V.; Kuznetsova, V. A.; Litvinov, I. K.; Orlova, A. O.; Maslov, V. G.; Fedorov, A. V.; Dubavik, A.; Purcell-Milton, F.; Gun'ko, Yu K.; Baranov, A. V.

2016-02-01

The influence of the chirality of semiconductor nanocrystals, CdSe/ZnS quantum dots (QDs) capped with L- and D-cysteine, on the efficiency of their uptake by living Ehrlich Ascite carcinoma cells is studied by spectral- and time-resolved fluorescence microspectroscopy. We report an evident enantioselective process where cellular uptake of the L-Cys QDs is almost twice as effective as that of the D-Cys QDs. This finding paves the way for the creation of novel approaches to control the biological properties and behavior of nanomaterials in living cells.

The interplay of covalency, hydrogen bonding, and dispersion leads to a long range chiral network: The example of 2-butanol

NASA Astrophysics Data System (ADS)

Liriano, Melissa L.; Carrasco, Javier; Lewis, Emily A.; Murphy, Colin J.; Lawton, Timothy J.; Marcinkowski, Matthew D.; Therrien, Andrew J.; Michaelides, Angelos; Sykes, E. Charles H.

2016-03-01

The assembly of complex structures in nature is driven by an interplay between several intermolecular interactions, from strong covalent bonds to weaker dispersion forces. Understanding and ultimately controlling the self-assembly of materials requires extensive study of how these forces drive local nanoscale interactions and how larger structures evolve. Surface-based self-assembly is particularly amenable to modeling and measuring these interactions in well-defined systems. This study focuses on 2-butanol, the simplest aliphatic chiral alcohol. 2-butanol has recently been shown to have interesting properties as a chiral modifier of surface chemistry; however, its mode of action is not fully understood and a microscopic understanding of the role non-covalent interactions play in its adsorption and assembly on surfaces is lacking. In order to probe its surface properties, we employed high-resolution scanning tunneling microscopy and density functional theory (DFT) simulations. We found a surprisingly rich degree of enantiospecific adsorption, association, chiral cluster growth and ultimately long range, highly ordered chiral templating. Firstly, the chiral molecules acquire a second chiral center when adsorbed to the surface via dative bonding of one of the oxygen atom lone pairs. This interaction is controlled via the molecule's intrinsic chiral center leading to monomers of like chirality, at both chiral centers, adsorbed on the surface. The monomers then associate into tetramers via a cyclical network of hydrogen bonds with an opposite chirality at the oxygen atom. The evolution of these square units is surprising given that the underlying surface has a hexagonal symmetry. Our DFT calculations, however, reveal that the tetramers are stable entities that are able to associate with each other by weaker van der Waals interactions and tessellate in an extended square network. This network of homochiral square pores grows to cover the whole Au(111) surface. Our data reveal that the chirality of a simple alcohol can be transferred to its surface binding geometry, drive the directionality of hydrogen-bonded networks and ultimately extended structure. Furthermore, this study provides the first microscopic insight into the surface properties of this important chiral modifier and provides a well-defined system for studying the network's enantioselective interaction with other molecules.

The interplay of covalency, hydrogen bonding, and dispersion leads to a long range chiral network: The example of 2-butanol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liriano, Melissa L.; Lewis, Emily A.; Murphy, Colin J.

The assembly of complex structures in nature is driven by an interplay between several intermolecular interactions, from strong covalent bonds to weaker dispersion forces. Understanding and ultimately controlling the self-assembly of materials requires extensive study of how these forces drive local nanoscale interactions and how larger structures evolve. Surface-based self-assembly is particularly amenable to modeling and measuring these interactions in well-defined systems. This study focuses on 2-butanol, the simplest aliphatic chiral alcohol. 2-butanol has recently been shown to have interesting properties as a chiral modifier of surface chemistry; however, its mode of action is not fully understood and a microscopicmore » understanding of the role non-covalent interactions play in its adsorption and assembly on surfaces is lacking. In order to probe its surface properties, we employed high-resolution scanning tunneling microscopy and density functional theory (DFT) simulations. We found a surprisingly rich degree of enantiospecific adsorption, association, chiral cluster growth and ultimately long range, highly ordered chiral templating. Firstly, the chiral molecules acquire a second chiral center when adsorbed to the surface via dative bonding of one of the oxygen atom lone pairs. This interaction is controlled via the molecule’s intrinsic chiral center leading to monomers of like chirality, at both chiral centers, adsorbed on the surface. The monomers then associate into tetramers via a cyclical network of hydrogen bonds with an opposite chirality at the oxygen atom. The evolution of these square units is surprising given that the underlying surface has a hexagonal symmetry. Our DFT calculations, however, reveal that the tetramers are stable entities that are able to associate with each other by weaker van der Waals interactions and tessellate in an extended square network. This network of homochiral square pores grows to cover the whole Au(111) surface. Our data reveal that the chirality of a simple alcohol can be transferred to its surface binding geometry, drive the directionality of hydrogen-bonded networks and ultimately extended structure. Furthermore, this study provides the first microscopic insight into the surface properties of this important chiral modifier and provides a well-defined system for studying the network’s enantioselective interaction with other molecules.« less

Natural terpene derivatives as new structural task-specific ionic liquids to enhance the enantiorecognition of acidic enantiomers on teicoplanin-based stationary phase by high-performance liquid chromatography.

PubMed

Flieger, Jolanta; Feder-Kubis, Joanna; Tatarczak-Michalewska, Małgorzata; Płazińska, Anita; Madejska, Anna; Swatko-Ossor, Marta

2017-06-01

We present the specific cooperative effect of a semisynthetic glycopeptide antibiotic teicoplanin and chiral ionic liquids containing the (1R,2S,5R)-(-)-menthol moiety on the chiral recognition of enantiomers of mandelic acid, vanilmandelic acid, and phenyllactic acid. Experiments were performed chromatographically on an Astec Chirobiotic T chiral stationary phase applying the mobile phase with the addition of the chiral ionic liquids. The stereoselective binding of enantiomers to teicoplanin in presence of new chiral ionic liquids were evaluated applying thermodynamic measurements and the docking simulations. Both the experimental and theoretical methods revealed that the chiral recognition of enantiomers in the presence of new chiral ionic liquids was enthalpy driven. The changes of the teicoplanin conformation occurring upon binding of the chiral ionic liquids are responsible for the differences in the standard changes in Gibbs energy (ΔG 0 ) values obtained for complexes formed by the R and S enantiomers and teicoplanin. Docking simulations revealed the steric adjustment between the chiral ionic liquids cyclohexane ring (chair conformation) and the β-d-glucosamine ring of teicoplanin and additionally hydrophobic interactions between the decanoic aliphatic chain of teicoplanin and the alkyl group of the tested salts. The obtained terpene derivatives can be considered as "structural task-specific ionic liquids" responsible for enhancing the chiral resolution in synergistic systems with two chiral selectors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

X-ray circular dichroism signals: a unique probe of local molecular chirality

DOE PAGES

Zhang, Yu; Rouxel, Jeremy R.; Autschbach, Jochen; ...

2017-06-26

Core-resonant circular dichroism (CD) signals are induced by molecular chirality and vanish for achiral molecules and racemic mixtures. The highly localized nature of core excitations makes them ideal probes of local chirality within molecules. Simulations of the circular dichroism spectra of several molecular families illustrate how these signals vary with the electronic coupling to substitution groups, the distance between the X-ray chromophore and the chiral center, geometry, and chemical structure. As a result, clear insight into the molecular structure is obtained through analysis of the X-ray CD spectra.

X-ray circular dichroism signals: a unique probe of local molecular chirality

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yu; Rouxel, Jeremy R.; Autschbach, Jochen

Core-resonant circular dichroism (CD) signals are induced by molecular chirality and vanish for achiral molecules and racemic mixtures. The highly localized nature of core excitations makes them ideal probes of local chirality within molecules. Simulations of the circular dichroism spectra of several molecular families illustrate how these signals vary with the electronic coupling to substitution groups, the distance between the X-ray chromophore and the chiral center, geometry, and chemical structure. As a result, clear insight into the molecular structure is obtained through analysis of the X-ray CD spectra.

Magnetic nanoparticles conjugated to chiral imidazolidinone as recoverable catalyst

NASA Astrophysics Data System (ADS)

Mondini, Sara; Puglisi, Alessandra; Benaglia, Maurizio; Ramella, Daniela; Drago, Carmelo; Ferretti, Anna M.; Ponti, Alessandro

2013-11-01

The immobilization of an ad hoc designed chiral imidazolidin-4-one onto iron oxide magnetic nanoparticles (MNPs) is described, to afford MNP-supported MacMillan's catalyst. Morphological and structural analysis of the materials, during preparation, use, and recycle, has been carried out by transmission electron microscopy. The supported catalyst was tested in the Diels-Alder reaction of cyclopentadiene with cinnamic aldehyde, affording the products in good yields and enantiomeric excesses up to 93 %, comparable to those observed with the non-supported catalyst. Recovery of the chiral catalyst has been successfully performed by simply applying an external magnet to achieve a perfect separation of the MNPs from the reaction product. The recycle of the catalytic system has been also investigated. Noteworthy, this immobilized MacMillan's catalyst proved to be able to efficiently promote the reaction in pure water.

Stereoselectivity in ene reactions with 1O2: matrix effects in polymer supports, photo-oxygenation of organic salts and asymmetric synthesis.

PubMed

Griesbeck, Axel G; Bartoschek, Anna; Neudörfl, Jörg; Miara, Claus

2006-01-01

The ene reaction of chiral allylic alcohols is applied as a tool for the investigation of intrapolymer effects by means of the stereoselectivity of the singlet-oxygen addition. The diastereo selectivity strongly depends on the structure of the polymer, the substrate loading degree and also on the degree of conversion demonstrating additional supramolecular effects evolving during the reaction. The efficiency and the stability of polymer-bound sensitizers were evaluated by the ene reaction of singlet oxygen with citronellol. The ene reaction with chiral ammonium salts of tiglic acid was conducted under solution phase conditions or in polystyrene beads under chiral contact ion-pair conditions. The products thus obtained precipitate during the photoreaction as ammonium salts. Moderate asymmetric induction was observed for this procedure for the first time.

High-Throughput Genetic Analysis and Combinatorial Chiral Separations Based on Capillary Electrophoresis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Wenwan

2003-01-01

Capillary electrophoresis (CE) offers many advantages over conventional analytical methods, such as speed, simplicity, high resolution, low cost, and small sample consumption, especially for the separation of enantiomers. However, chiral method developments still can be time consuming and tedious. They designed a comprehensive enantioseparation protocol employing neutral and sulfated cyclodextrins as chiral selectors for common basic, neutral, and acidic compounds with a 96-capillary array system. By using only four judiciously chosen separation buffers, successful enantioseparations were achieved for 49 out of 54 test compounds spanning a large variety of pKs and structures. Therefore, unknown compounds can be screened in thismore » manner to identify optimal enantioselective conditions in just one rn. In addition to superior separation efficiency for small molecules, CE is also the most powerful technique for DNA separations. Using the same multiplexed capillary system with UV absorption detection, the sequence of a short DNA template can be acquired without any dye-labels. Two internal standards were utilized to adjust the migration time variations among capillaries, so that the four electropherograms for the A, T, C, G Sanger reactions can be aligned and base calling can be completed with a high level of confidence. the CE separation of DNA can be applied to study differential gene expression as well. Combined with pattern recognition techniques, small variations among electropherograms obtained by the separation of cDNA fragments produced from the total RNA samples of different human tissues can be revealed. These variations reflect the differences in total RNA expression among tissues. Thus, this Ce-based approach can serve as an alternative to the DNA array techniques in gene expression analysis.« less

Highly enantioselective organocatalytic oxidative kinetic resolution of secondary alcohols using chiral alkoxyamines as precatalysts: catalyst structure, active species, and substrate scope.

PubMed

Murakami, Keiichi; Sasano, Yusuke; Tomizawa, Masaki; Shibuya, Masatoshi; Kwon, Eunsang; Iwabuchi, Yoshiharu

2014-12-17

The development and characterization of enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols using chiral alkoxyamines as precatalysts are described. A number of chiral alkoxyamines have been synthesized, and their structure-enantioselectivity correlation study in OKR has led us to identify a promising precatalyst, namely, 7-benzyl-3-n-butyl-4-oxa-5-azahomoadamantane, which affords various chiral aliphatic secondary alcohols (ee up to >99%, k(rel) up to 296). In a mechanistic study, chlorine-containing oxoammonium species were identified as the active species generated in situ from the alkoxyamine precatalyst, and it was revealed that the chlorine atom is crucial for high reactivity and enantioselectivity. The present OKR is the first successful example applicable to various unactivated aliphatic secondary alcohols, including heterocyclic alcohols with high enantioselectivity, the synthetic application of which is demonstrated by the synthesis of a bioactive compound.

Brilliant Sm, Eu, Tb and Dy chiral lanthanide complexes withstrong circularly polarized luminescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petoud, Stephane; Muller, Gilles; Moore, Evan G.

The synthesis, characterization and luminescent behavior of trivalent Sm, Eu, Dy and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, g{sub lum}, recorded for the Eu(III) complexmore » is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments.« less

Neutron and proton electric dipole moments from N f=2+1 domain-wall fermion lattice QCD

DOE PAGES

Shintani, Eigo; Blum, Thomas; Izubuchi, Taku; ...

2016-05-05

We present a lattice calculation of the neutron and proton electric dipole moments (EDM’s) with N f = 2 + 1 flavors of domain-wall fermions. The neutron and proton EDM form factors are extracted from three-point functions at the next-to-leading order in the θ vacuum of QCD. In this computation, we use pion masses 330 and 420 MeV and 2.7 fm 3 lattices with Iwasaki gauge action and a 170 MeV pion and 4.6 fm 3 lattice with I-DSDR gauge action, all generated by the RBC and UKQCD collaborations. The all-mode-averaging technique enables an efficient, high statistics calculation; however themore » statistical errors on our results are still relatively large, so we investigate a new direction to reduce them, reweighting with the local topological charge density which appears promising. Furthermore, we discuss the chiral behavior and finite size effects of the EDM’s in the context of baryon chiral perturbation theory.« less

Torque modulates nucleosome stability and facilitates H2A/H2B dimer loss

PubMed Central

Sheinin, Maxim Y.; Li, Ming; Soltani, Mohammad; Luger, Karolin; Wang, Michelle D.

2013-01-01

The nucleosome, the fundamental packing unit of chromatin, has a distinct chirality: 147 bp of DNA are wrapped around the core histones in a left-handed, negative superhelix. It has been suggested that this chirality has functional significance, particularly in the context of the cellular processes that generate DNA supercoiling, such as transcription and replication. However, the impact of torsion on nucleosome structure and stability is largely unknown. Here we perform a detailed investigation of single nucleosome behavior on the high affinity 601 positioning sequence under tension and torque using the angular optical trapping technique. We find that torque has only a moderate effect on nucleosome unwrapping. In contrast, we observe a dramatic loss of H2A/H2B dimers upon nucleosome disruption under positive torque, while (H3/H4)2 tetramers are efficiently retained irrespective of torsion. These data indicate that torque could regulate histone exchange during transcription and replication. PMID:24113677

Characterization of an Indole-3-Acetamide Hydrolase from Alcaligenes faecalis subsp. parafaecalis and Its Application in Efficient Preparation of Both Enantiomers of Chiral Building Block 2,3-Dihydro-1,4-Benzodioxin-2-Carboxylic Acid.

PubMed

Mishra, Pradeep; Kaur, Suneet; Sharma, Amar Nath; Jolly, Ravinder S

2016-01-01

Both the enantiomers of 2,3-dihydro-1,4-benzodioxin-2-carboxylic acid are valuable chiral synthons for enantiospecific synthesis of therapeutic agents such as (S)-doxazosin mesylate, WB 4101, MKC 242, 2,3-dihydro-2-hydroxymethyl-1,4-benzodioxin, and N-[2,4-oxo-1,3-thiazolidin-3-yl]-2,3-dihydro-1,4-benzodioxin-2-carboxamide. Pharmaceutical applications require these enantiomers in optically pure form. However, currently available methods suffer from one drawback or other, such as low efficiency, uncommon and not so easily accessible chiral resolving agent and less than optimal enantiomeric purity. Our interest in finding a biocatalyst for efficient production of enantiomerically pure 2,3-dihydro-1,4-benzodioxin-2-carboxylic acid lead us to discover an amidase activity from Alcaligenes faecalis subsp. parafaecalis, which was able to kinetically resolve 2,3-dihydro-1,4-benzodioxin-2-carboxyamide with E value of >200. Thus, at about 50% conversion, (R)-2,3-dihydro-1,4-benzodioxin-2-carboxylic acid was produced in >99% e.e. The remaining amide had (S)-configuration and 99% e.e. The amide and acid were easily separated by aqueous (alkaline)-organic two phase extraction method. The same amidase was able to catalyse, albeit at much lower rate the hydrolysis of (S)-amide to (S)-acid without loss of e.e. The amidase activity was identified as indole-3-acetamide hydrolase (IaaH). IaaH is known to catalyse conversion of indole-3-acetamide (IAM) to indole-3-acetic acid (IAA), which is phytohormone of auxin class and is widespread among plants and bacteria that inhabit plant rhizosphere. IaaH exhibited high activity for 2,3-dihydro-1,4-benzodioxin-2-carboxamide, which was about 65% compared to its natural substrate, indole-3-acetamide. The natural substrate for IaaH indole-3-acetamide shared, at least in part a similar bicyclic structure with 2,3-dihydro-1,4-benzodioxin-2-carboxamide, which may account for high activity of enzyme towards this un-natural substrate. To the best of our knowledge this is the first application of IaaH in production of industrially important molecules.

Engineering of a novel carbonyl reductase with coenzyme regeneration in E. coli for efficient biosynthesis of enantiopure chiral alcohols.

PubMed

Wei, Ping; Gao, Jia-Xin; Zheng, Gao-Wei; Wu, Hong; Zong, Min-Hua; Lou, Wen-Yong

2016-07-20

The novel anti-Prelog stereospecific carbonyl reductase from Acetobacter sp. CCTCC M209061 was successfully expressed in E. coli combined with glucose dehydrogenase (GDH) to construct an efficient whole-cell biocatalyst with coenzyme NADH regeneration. The enzymatic activity of GAcCR (AcCR with a GST tag) reached 304.9U/g-dcw, even 9 folds higher than that of wild strain, and the activity of GDH for NADH regeneration recorded 46.0U/mg-protein in the recombinant E. coli. As a whole-cell biocatalyst, the recombinant E. coli BL21(DE3)pLysS (pETDuet-gaccr-gdh) possessed a broad substrate spectrum for kinds of carbonyl compounds with encouraging yield and stereoselectivity. Besides, the asymmetric reduction of ethyl 4-chloroacetoacetate (COBE) to optically pure ethyl 4-chloro-3-hydroxybutyrate (CHBE) catalyzed by the whole-cell biocatalyst was systematically investigated. Under the optimal reaction conditions, the optical purity of CHBE was over 99% e.e. for (S)-enantiomer, and the initial rate and product yield reached 8.04μmol/min and 99.4%, respectively. Moreover, the space-time yield was almost 20 folds higher than that catalyzed by the wild strain. Therefore, a new, high efficiency biocatalyst for asymmetric reductions was constructed successfully, and the enantioselective reduction of prochiral compounds using the biocatalyst was a promising approach for obtaining enantiopure chiral alcohols. Copyright © 2016 Elsevier B.V. All rights reserved.

Neuronal growth on L- and D-cysteine self-assembled monolayers reveals neuronal chiral sensitivity.

PubMed

Baranes, Koby; Moshe, Hagay; Alon, Noa; Schwartz, Shmulik; Shefi, Orit

2014-05-21

Studying the interaction between neuronal cells and chiral molecules is fundamental for the design of novel biomaterials and drugs. Chirality influences all biological processes that involve intermolecular interaction. One common method used to study cellular interactions with different enantiomeric targets is the use of chiral surfaces. Based on previous studies that demonstrated the importance of cysteine in the nervous system, we studied the effect of L- and D-cysteine on single neuronal growth. L-Cysteine, which normally functions as a neuromodulator or a neuroprotective antioxidant, causes damage at elevated levels, which may occur post trauma. In this study, we grew adult neurons in culture enriched with L- and D-cysteine as free compounds or as self-assembled monolayers of chiral surfaces and examined the effect on the neuronal morphology and adhesion. Notably, we have found that exposure to the L-cysteine enantiomer inhibited, and even prevented, neuronal attachment more severely than exposure to the D-cysteine enantiomer. Atop the L-cysteine surfaces, neuronal growth was reduced and degenerated. Since the cysteine molecules were attached to the surface via the thiol groups, the neuronal membrane was exposed to the molecular chiral site. Thus, our results have demonstrated high neuronal chiral sensitivity, revealing chiral surfaces as indirect regulators of neuronal cells and providing a reference for studying chiral drugs.

Chirality sensing with stereodynamic biphenolate zinc complexes.

PubMed

Bentley, Keith W; de Los Santos, Zeus A; Weiss, Mary J; Wolf, Christian

2015-10-01

Two bidentate ligands consisting of a fluxional polyarylacetylene framework with terminal phenol groups were synthesized. Reaction with diethylzinc gives stereodynamic complexes that undergo distinct asymmetric transformation of the first kind upon binding of chiral amines and amino alcohols. The substrate-to-ligand chirality imprinting at the zinc coordination sphere results in characteristic circular dichroism signals that can be used for direct enantiomeric excess (ee) analysis. This chemosensing approach bears potential for high-throughput ee screening with small sample amounts and reduced solvent waste compared to traditional high-performance liquid chromatography methods. © 2015 Wiley Periodicals, Inc.

Main-chain optically active riboflavin polymer for asymmetric catalysis and its vapochromic behavior.

PubMed

Iida, Hiroki; Iwahana, Soichiro; Mizoguchi, Tomohisa; Yashima, Eiji

2012-09-12

A novel optically active polymer consisting of riboflavin units as the main chain (poly-1) was prepared from naturally occurring riboflavin (vitamin B(2)) in three steps. The riboflavin residues of poly-1 were converted to 5-ethylriboflavinium cations (giving poly-2), which could be reversibly transformed into the corresponding 4a-hydroxyriboflavins (giving poly-2OH) through hydroxylation/dehydroxylation reactions. This reversible structural change was accompanied by a visible color change along with significant changes in the absorption and circular dichroism (CD) spectra. The nuclear Overhauser effect spectroscopy (NOESY) and CD spectra of poly-2 revealed a supramolecularly twisted helical structure with excess one-handedness through face-to-face stacking of the intermolecular riboflavinium units, as evidenced by the apparent NOE correlations between the interstrand riboflavin units and intense Cotton effects induced in the flavinium chromophore regions. The hydroxylation of poly-2 at the 4a-position proceeded in a diastereoselective fashion via chirality transfer from the induced supramolecular helical chirality assisted by the ribityl pendants, resulting in a 83:17 diastereomeric mixture of poly-2OH. The diastereoselectivity of poly-2 was remarkably higher than that of the corresponding monomeric model (64.5:35.5), indicating amplification of the chirality resulting from the supramolecular chirality induced in the stacked poly-2 backbones. The optically active poly-2 efficiently catalyzed the asymmetric organocatalytic oxidation of sulfides with hydrogen peroxide, yielding optically active sulfoxides with up to 60% enantiomeric excess (ee), whose enantioselectivity was higher than that catalyzed by the monomeric counterpart (30% ee). In addition, upon exposure to primary and secondary amines, poly-2 exhibited unique high-speed vapochromic behavior arising from the formation of 4a-amine adducts in the film.

Inducing Axial Chirality in a Supramolecular Catalyst.

PubMed

Wenz, Katharina Marie; Leonhardt-Lutterbeck, Günter; Breit, Bernhard

2018-03-06

A new type of ligand, which is able to form axially chiral, supramolecular complexes was designed using DFT calculations. Two chiral monomers, each featuring a covalently bound chiral auxiliary, form a bidentate phosphine ligand with a twisted, hydrogen-bonded backbone upon coordination to a transition metal center which results in two diastereomeric, tropos complexes. The ratio of the diastereomers in solution is very temperature- and solvent-dependent. Rhodium and platinum complexes were analyzed through a combination of NMR studies, ESI-MS measurements, as well as UV-VIS and circular dichroism spectroscopy. The chiral self-organized ligands were evaluated in the rhodium-catalyzed asymmetric hydrogenation of α-dehydrogenated amino acids and resulted in good conversion and high enantioselectivity. This research opens the way for new ligand designs based on stereocontrol of supramolecular assemblies through stereodirecting chiral centers. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Exotic meson decays in the environment with chiral imbalance

NASA Astrophysics Data System (ADS)

Andrianov, A. A.; Andrianov, V. A.; Espriu, D.; Iakubovich, A. V.; Putilova, A. E.

2017-10-01

An emergence of Local Parity Breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. LPB in the fireball can be produced by a difference between the number densities of right- and left-handed chiral fermions (Chiral Imbalance) which is implemented by a chiral (axial) chemical potential. The effective meson lagrangian induced by QCD is extended to the medium with Chiral Imbalance and the properties of light scalar and pseudoscalar mesons (π, α0) are analyzed. It is shown that exotic decays of scalar mesons arise as a result of mixing of π and α0 vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains an unusual parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We hope that the above pointed indications of LPB can be identified in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.

Chiral optical response of planar and symmetric nanotrimers enabled by heteromaterial selection.

PubMed

Banzer, Peter; Woźniak, Paweł; Mick, Uwe; De Leon, Israel; Boyd, Robert W

2016-10-13

Chirality is an intriguing property of certain molecules, materials or artificial nanostructures, which allows them to interact with the spin angular momentum of the impinging light field. Due to their chiral geometry, they can distinguish between left- and right-hand circular polarization states or convert them into each other. Here we introduce an approach towards optical chirality, which is observed in individual two-dimensional and geometrically mirror-symmetric nanostructures. In this scheme, the chiral optical response is induced by the chosen heterogeneous material composition of a particle assembly and the corresponding resonance behaviour of the constituents it is built from, which breaks the symmetry of the system. As a proof of principle, we investigate such a structure composed of individual silicon and gold nanoparticles both experimentally, as well as numerically. Our proposed concept constitutes an approach for designing two-dimensional chiral media tailored at the nanoscale, allowing for high tunability of their optical response.

Origin of Stereodivergence in Cooperative Asymmetric Catalysis with Simultaneous Involvement of Two Chiral Catalysts.

PubMed

Bhaskararao, Bangaru; Sunoj, Raghavan B

2015-12-23

Accomplishing high diastereo- and enantioselectivities simultaneously is a persistent challenge in asymmetric catalysis. The use of two chiral catalysts in one-pot conditions might offer new avenues to this end. Chirality transfer from a catalyst to product gets increasingly complex due to potential chiral match-mismatch issues. The origin of high enantio- and diastereoselectivities in the reaction between a racemic aldehyde and an allyl alcohol, catalyzed by using axially chiral iridium phosphoramidites PR/S-Ir and cinchona amine is established through transition-state modeling. The multipoint contact analysis of the stereocontrolling transition state revealed how the stereodivergence could be achieved by inverting the configuration of the chiral catalysts that are involved in the activation of the reacting partners. While the enantiocontrol is identified as being decided in the generation of PR/S-Ir-π-allyl intermediate from the allyl alcohol, the diastereocontrol arises due to the differential stabilizations in the C-C bond formation transition states. The analysis of the weak interactions in the transition states responsible for chiral induction revealed that the geometric disposition of the quinoline ring at the C8 chiral carbon of cinchona-enamine plays an anchoring role. The quinolone ring is noted as participating in a π-stacking interaction with the phenyl ring of the Ir-π-allyl moiety in the case of PR with the (8R,9R)-cinchona catalyst combination, whereas a series of C-H···π interactions is identified as vital to the relative stabilization of the stereocontrolling transition states when PR is used with (8S,9S)-cinchona.

Enantioselective Reduction of Ketones Catalyzed by Rare-Earth Metals Complexed with Phenoxy Modified Chiral Prolinols.

PubMed

Song, Peng; Lu, Chengrong; Fei, Zenghui; Zhao, Bei; Yao, Yingming

2018-06-01

Enantioselective reduction of ketones and α,β-unsaturated ketones by pinacolborane (HBpin) has been well-established by using chiral rare-earth metal catalysts with phenoxy modified prolinols. A number of highly optically active alcohols were obtained from reduction of simple ketones catalyzed by ytterbium complex 1 [L 4 Yb(L 4 H)] (H 2 L 4 = ( S)-2- tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol). Moreover, α,β-unsaturated ketones were selectively reduced to a wide range of chiral allylic alcohols with excellent yields, high enantioselectivity, and complete chemoselectivity, catalyzed by a single component chiral ytterbium complex 2 [L 1 Yb(L 1 H)] (H 2 L 1 = ( S)-2,4-di- tert-butyl-6-((2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)phenol).

Lanthanide tris(β-diketonates) as useful probes for chirality determination of biological amino alcohols in vibrational circular dichroism: ligand to ligand chirality transfer in lanthanide coordination sphere.

PubMed

Miyake, Hiroyuki; Terada, Keiko; Tsukube, Hiroshi

2014-06-01

A series of lanthanide tris(β-diketonates) functioned as useful chirality probes in the vibrational circular dichroism (VCD) characterization of biological amino alcohols. Various chiral amino alcohols induced intense VCD signals upon ternary complexation with racemic lanthanide tris(β-diketonates). The VCD signals observed around 1500 cm(-1) (β-diketonate IR absorption region) correlated well with the stereochemistry and enantiomeric purity of the targeted amino alcohol, while the corresponding monoalcohol, monoamine, and diol substrates induced very weak VCD signals. The high-coordination number and dynamic property of the lanthanide complex offer an effective chirality VCD probing of biological substrates. © 2014 Wiley Periodicals, Inc.

Proposal for chiral-boson search at LHC via their unique new signature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chizhov, M. V.; Bednyakov, V. A.; Budagov, J. A.

The resonance production of new chiral spin-1 bosons and their detection through the Drell-Yan process at the CERN LHC is considered. Quantitative evaluations of various differential cross sections of the chiral-boson production are made within the CalcHEP package. The new neutral chiral bosons can be observed as a Breit-Wigner resonance peak in the invariant-dilepton-mass distribution, as usual. However, unique new signatures of the chiral bosons exist. First, there is no Jacobian peak in the lepton transverse-momentum distribution. Second, the lepton angular distribution in the Collins-Soper frame for the high on-peak invariant masses of the lepton pairs has a peculiar 'swallowtail'more » shape.« less

Enantiospecific Detection of Chiral Nanosamples Using Photoinduced Force

NASA Astrophysics Data System (ADS)

Kamandi, Mohammad; Albooyeh, Mohammad; Guclu, Caner; Veysi, Mehdi; Zeng, Jinwei; Wickramasinghe, Kumar; Capolino, Filippo

2017-12-01

We propose a high-resolution microscopy technique for enantiospecific detection of chiral samples down to sub-100-nm size based on force measurement. We delve into the differential photoinduced optical force Δ F exerted on an achiral probe in the vicinity of a chiral sample when left and right circularly polarized beams separately excite the sample-probe interactive system. We analytically prove that Δ F is entangled with the enantiomer type of the sample enabling enantiospecific detection of chiral inclusions. Moreover, we demonstrate that Δ F is linearly dependent on both the chiral response of the sample and the electric response of the tip and is inversely related to the quartic power of probe-sample distance. We provide physical insight into the transfer of optical activity from the chiral sample to the achiral tip based on a rigorous analytical approach. We support our theoretical achievements by several numerical examples highlighting the potential application of the derived analytic properties. Lastly, we demonstrate the sensitivity of our method to enantiospecify nanoscale chiral samples with chirality parameter on the order of 0.01 and discuss how the sensitivity of our proposed technique can be further improved.

Chiral HPLC for a study of the optical purity of new liquid crystalline materials derived from lactic acid

NASA Astrophysics Data System (ADS)

Vojtylová, T.; Kašpar, M.; Hamplová, V.; Novotná, V.; Sýkora, D.

2014-08-01

New liquid crystalline (LC) materials were prepared by derivatization of lactic acid. First compound possesses the lactic acid unit as the only chiral center and the second group of LC materials contains two chiral centers. Mesomorphic properties of both the newly synthesized LC materials were studied and the presence of the SmA*-SmC* or exhibit the twist grain boundary (TGB) phases, namely TGBA and TGBC, in a wide range of temperatures down to the room temperature was established. The potential of high-performance liquid chromatography (HPLC) applying chiral stationary phases to separate enantiomers or diastereoisomers of the synthesized LC compounds was evaluated. Two different brands of commercial chiral sorbents, Lux Amylose-2 and Chiralpak AD-3, both based on modified silica with derivatized polysaccharide, were employed in the development of separation procedures. The optimized chiral HPLC method provided a baseline separation of the individual enantiomers for the LC material containing one chiral center. In the case of the more complex compound with two asymmetric carbon atoms, where four isomers exist, partial separation was reached only using the current chiral HPLC.

Polymeric Sulfated Amino Acid Surfactants: A New Class of Versatile Chiral Selectors for Micellar Electrokinetic Chromatography (MEKC) and MEKC-MS

PubMed Central

Ali Rizvi, Syed Asad; Zheng, Jie; Apkarian, Robert P.; Dublin, Steven N.; Shamsi, Shahab A.

2008-01-01

In this work, three amino acids derived (L-leucinol, L-isoleucinol and L-valinol) sulfated chiral surfactants are synthesized and polymerized. These chiral sulfated surfactants are thoroughly characterized to determine critical micelle concentration, aggregation number, polarity, optical rotation and partial specific volume. For the first time the morphological behavior of polymeric sulfated surfactants is revealed using cryogenic high-resolution electron microscopy (cryo-HRSEM). The polysodium N-undecenoyl-L-leucine sulfate (poly-L-SUCLS) shows distinct tubular structure, while polysodium N-undecenoyl-L-valine sulfate (poly-L-SUCVS) also shows tubular morphology but without any distinct order of the tubes. On the other hand, polysodium N-undecenoyl-L-isoleucine sulfate (poly-L-SUCILS) displays random distribution of coiled/curved filaments with heavy association of tightly and loosely bound water. All three polymeric sulfated surfactants are compared for enantio-separation of broad range of structurally diverse racemic compounds at very acidic, neutral and basic pH conditions in micellar electrokinetic chromatography (MEKC). A small combinatorial library of 10 structurally related phenylethylamines (PEAs) is investigated for chiral separation under acidic and moderately acidic to neutral pH conditions using an experimental design. In contrast to neutral pH conditions, at acidic pH, significantly enhanced chiral resolution is obtained for class I and class II PEAs due to the compact structure of polymeric sulfated surfactants. It is observed that the presence of hydroxy group on the benzene ring of PEAs resulted in deterioration of enantioseparation. A sensitive MEKC-mass spectrometry (MS) method is developed for one of the PEA (e.g., (±)-pseudoephedrine) in human urine. Very low limit of detection (LOD) is obtained at pH 2.0 (LOD 325 ng/mL), which is ca 16 times better compared to pH 8.0 (LOD 5.2 µg/mL). Other broad range of chiral analytes (β-blockers, phenoxypropionic acid, benzoin derivatives, PTH-amino acids, and benzodiazepinones) studied also provided improved chiral separation at low pH compared to high pH conditions. Among the three polymeric sulfated surfactants, poly-L-SUCILS with two chiral centers on the polymer head group provided overall higher enantioresolution for the investigated acidic, basic and neutral compounds. This work clearly demonstrates for the first time the superiority of chiral separation and sensitive MS detection at low pH over conventional high pH chiral separation and detection employing anionic chiral polymeric surfactants in MEKC and MEKC-MS. PMID:17263313

Conversion of alcohols to enantiopure amines through dual-enzyme hydrogen-borrowing cascades.

PubMed

Mutti, Francesco G; Knaus, Tanja; Scrutton, Nigel S; Breuer, Michael; Turner, Nicholas J

2015-09-25

α-Chiral amines are key intermediates for the synthesis of a plethora of chemical compounds at industrial scale. We present a biocatalytic hydrogen-borrowing amination of primary and secondary alcohols that allows for the efficient and environmentally benign production of enantiopure amines. The method relies on a combination of two enzymes: an alcohol dehydrogenase (from Aromatoleum sp., Lactobacillus sp., or Bacillus sp.) operating in tandem with an amine dehydrogenase (engineered from Bacillus sp.) to aminate a structurally diverse range of aromatic and aliphatic alcohols, yielding up to 96% conversion and 99% enantiomeric excess. Primary alcohols were aminated with high conversion (up to 99%). This redox self-sufficient cascade possesses high atom efficiency, sourcing nitrogen from ammonium and generating water as the sole by-product. Copyright © 2015, American Association for the Advancement of Science.

Two-dimensional chiral topological superconductivity in Shiba lattices

PubMed Central

Li, Jian; Neupert, Titus; Wang, Zhijun; MacDonald, A. H.; Yazdani, A.; Bernevig, B. Andrei

2016-01-01

The chiral p-wave superconductor is the archetypal example of a state of matter that supports non-Abelian anyons, a highly desired type of exotic quasiparticle. With this, it is foundational for the distant goal of building a topological quantum computer. While some candidate materials for bulk chiral superconductors exist, they are subject of an ongoing debate about their actual paring state. Here we propose an alternative route to chiral superconductivity, consisting of the surface of an ordinary superconductor decorated with a two-dimensional lattice of magnetic impurities. We furthermore identify a promising experimental platform to realize this proposal. PMID:27465127

Sheet-like chiro-optical material designs based C(Y) surfaces

NASA Astrophysics Data System (ADS)

Saba, M.; Robisch, A.-L.; Thiel, M.; Hess, O.; Schroeder-Turk, Gerd E.

2017-04-01

A spatial structure for which mirror reflection cannot be represented by rotations and translations is chiral. For photonic crystals and metamaterials, chirality implies the possibility of circular dichroism, that is, that the propagation of left-circularly polarized light may differ from that of right-circularly polarized light. Here we draw attention to chiral sheet- or surface-like geometries based on chiral triply-periodic minimal surfaces. Specifically we analyse two photonic crystal designs based on the C(Y) minimal surface, by band structure analysis and by scattering matrix calculations of the reflection coefficient, for high-dielectric contrasts.

Illuminating the chirality of Weyl fermions

NASA Astrophysics Data System (ADS)

Ma, Qiong; Xu, Su-Yang; Chan, Ching-Kit; Zhang, Cheng-Long; Chang, Guoqing; Lin, Hsin; Jia, Shuang; Lee, Patrick; Gedik, Nuh; Jarillo-Herrero, Pablo

In particle physics, Weyl fermions (WF) are elementary particles that travel at the speed of light and have a definite chirality. In condensed matter, it has been recently realized that WFs can arise as magnetic monopoles in the momentum space of a novel topological metal, the Weyl semimetal (WSM). Their chirality, given by the sign of the monopole charge, is the defining property of a WSM, since it directly serves as the topological number and gives rise to exotic properties such as Fermi arcs and the chiral anomaly. Moreover, the two chiralities, analogous to the two valleys in 2D materials, lead to a new degree of freedom in a 3D crystal, suggesting novel pathways to store and carry information. By shining circularly polarized light on the WSM TaAs, we illuminate the chirality of the WFs and achieve an electrical current that is highly controllable based on the WFs' chirality. Our results open up a wide range of new possibilities for experimentally studying and controlling the WFs and their associated quantum anomalies by optical and electrical means, which suggest the exciting prospect of ``Weyltronics''.

Chiral separation and twin-beam photonics

NASA Astrophysics Data System (ADS)

Bradshaw, David S.; Andrews, David L.

2016-03-01

It is well-known that, in a homogeneous fluid medium, most optical means that afford discrimination between molecules of opposite handedness are intrinsically weak effects. The reason is simple: the wide variety of origins for differential response commonly feature real or virtual electronic transitions that break a parity condition. Despite being electric dipole allowed, they manifest the chirality of the material in which they occur by breaking a selection rule that would otherwise preclude the simultaneous involvement of magnetic dipole or electric quadrupole forms of coupling. Although the latter are typically weaker than electric dipole effects by several orders of magnitude, it is the involvement of these weak forms of interaction that are responsible for chiral sensitivity. There have been a number of attempts to cleverly exploit novel optical configurations to enhance the relative magnitude - and hence potentially the efficiency - of chiral discrimination. The prospect of success in any such venture is enticing, because of the huge impact that such an advance might be expected to have in the health, food and medical sectors. Some of these proposals have utilized mirror reflection, and others surface plasmon coupling, or optical binding methods. Several recent works in the literature have drawn attention to a further possibility: the deployment of optical beam interference as a means to achieve chiral separations of sizeable extent. In this paper the underlying theory is fully developed to identify the true scope and limitations of such an approach.

Skyrmions in magnetic multilayers

NASA Astrophysics Data System (ADS)

Jiang, Wanjun; Chen, Gong; Liu, Kai; Zang, Jiadong; te Velthuis, Suzanne G. E.; Hoffmann, Axel

2017-08-01

Symmetry breaking together with strong spin-orbit interaction gives rise to many exciting phenomena within condensed matter physics. A recent example is the existence of chiral spin textures, which are observed in magnetic systems lacking inversion symmetry. These chiral spin textures, including domain walls and magnetic skyrmions, are both fundamentally interesting and technologically promising. For example, they can be driven very efficiently by electrical currents, and exhibit many new physical properties determined by their real-space topological characteristics. Depending on the details of the competing interactions, these spin textures exist in different parameter spaces. However, the governing mechanism underlying their physical behaviors remains essentially the same. In this review article, the fundamental topological physics underlying these chiral spin textures, the key factors for materials optimization, and current developments and future challenges will be discussed. In the end, a few promising directions that will advance the development of skyrmion based spintronics will be highlighted.

Biocatalysts for the pharmaceutical industry created by structure-guided directed evolution of stereoselective enzymes.

PubMed

Li, Guangyue; Wang, Jian-Bo; Reetz, Manfred T

2018-04-01

Enzymes have been used for a long time as catalysts in the asymmetric synthesis of chiral intermediates needed in the production of therapeutic drugs. However, this alternative to man-made catalysts has suffered traditionally from distinct limitations, namely the often observed wrong or insufficient enantio- and/or regioselectivity, low activity, narrow substrate range, and insufficient thermostability. With the advent of directed evolution, these problems can be generally solved. The challenge is to develop and apply the most efficient mutagenesis methods which lead to highest-quality mutant libraries requiring minimal screening. Structure-guided saturation mutagenesis and its iterative form have emerged as the method of choice for evolving stereo- and regioselective mutant enzymes needed in the asymmetric synthesis of chiral intermediates. The number of (industrial) applications in the preparation of chiral pharmaceuticals is rapidly increasing. This review features and analyzes typical case studies. Copyright © 2017 Elsevier Ltd. All rights reserved.

Molecular Chirality: Enantiomer Differentiation by High-Resolution Spectroscopy

NASA Astrophysics Data System (ADS)

Hirota, Eizi

2014-06-01

I have demonstrated that triple resonance performed on a three-rotational-level system of a chiral molecule of C1 symmetry exhibits signals opposite in phase for different enantiomers, thereby making enantiomer differentiation possible by microwave spectroscopy This prediction was realized by Patterson et al. on 1,2-propanediol and 1,3-butanediol. We thus now add a powerful method: microwave spectroscopy to the study of chiral molecules, for which hitherto only the measurement of optical rotation has been employed. Although microwave spectroscopy is applied to molecules in the gaseous phase, it is unprecedentedly superior to the traditional method: polarimeter in resolution, accuracy, sensitivity, and so on, and I anticipate a new fascinating research area to be opened in the field of molecular chirality. More versatile and efficient systems should be invented and developed for microwave spectroscopy, in order to cope well with new applications expected for this method For C2 and Cn (n ≥ 3)chiral molecules, the three-rotational-level systems treated above for C1 molecules are no more available within one vibronic state. It should, however, be pointed out that, if we take into account an excited vibronic state in addition to the ground state, for example, we may encounter many three-level systems. Namely, either one rotational transition in the ground state is combined with two vibronic transitions, or such a rotational transition in an excited state may be connected through two vibronic transitions to a rotational level in the ground state manifold. The racemization obviously plays a crucial role in the study of molecular chirality. However, like many other terms employed in chemistry, this important process has been "defined" only in a vague way, in other words, it includes many kinds of processes, which are not well classified on a molecular basis. I shall mention an attempt to obviate these shortcomings in the definition of racemization and also to clarify the implicit assumptions made in Hund's paradox. E. Hirota, 3rd Molecular Science Symposium, Nagoya, September 2009, E. Hirota, Proc. Jpn. Acad. Ser. B, 88, 120 (2012). D. Patterson, M. Schnell and J. M. Doyle, Nature 497, 475 (2013), D. Patterson and J. M. Doyle, Phys. Rev. Lett. 111, 023008 (2013). F. Hund, Z. Phys. 43, 805 (1927).

Chiral J-aggregates of atropo-enantiomeric perylene bisimides and their self-sorting behavior.

PubMed

Xie, Zengqi; Stepanenko, Vladimir; Radacki, Krzysztof; Würthner, Frank

2012-06-04

Herein we report on structural, morphological, and optical properties of homochiral and heterochiral J-aggregates that were created by nucleation-elongation assembly of atropo-enantiomerically pure and racemic perylene bisimides (PBIs), respectively. Our detailed studies with conformationally stable biphenoxy-bridged chiral PBIs by UV/Vis absorption, circular dichroism (CD) spectroscopy, and atomic force microscopy (AFM) revealed structurally as well as spectroscopically quite different kinds of J-aggregates for enantiomerically pure and racemic PBIs. AFM investigations showed that enantiopure PBIs form helical nanowires of unique diameter and large length-to-width ratio by self-recognition, while racemic PBIs provide irregular-sized particles by self-discrimination of the enantiomers at the stage of nucleation. Steady-state fluorescence spectroscopy studies revealed that the photoluminescence efficiency of homochiral J-aggregated nanowires (47±3%) is significantly higher than that of heterochiral J-aggregated particle-like aggregates (12±3%), which is explained in terms of highly ordered molecular stacking in one-dimensional nanowires of homochiral J-aggregates. Our present results demonstrate the high impact of homochirality on the construction of well-defined nanostructures with unique optical properties. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In ovo uptake, metabolism, and tissue-specific distribution of chiral PCBs and PBDEs in developing chicken embryos

PubMed Central

Li, Zong-Rui; Luo, Xiao-Jun; Huang, Li-Qian; Mai, Bi-Xian

2016-01-01

Fertilized chicken eggs were injected with environmental doses of 4 chiral polychlorinated biphenyls (PCBs) and 8 polybrominated biphenyl ethers (PBDEs) to investigate their uptake, metabolism in the embryo, and distribution in the neonate chicken. PCB95 uptake was the most efficient (80%) whereas BDE209 was the least (56%). Embryos metabolized approximately 52% of the PCBs absorbed. Though some degree of metabolism in the first 18 days, most of the PCBs and PBDEs was metabolized in the last three days, when BDE85, 99, 153, and 209 decrease by 11–37%. Enantioselective metabolism of the (+) enantiomers of PCB95, 149, and 132 and the (−) enantiomer of PCB91 was observed. The enantioselective reactivity was higher with the two penta-PCBs than the two tetra-PCBs. Liver, exhibited high affinity for high lipophilic chemicals, enrich all chemicals that was deflected in other tissues except for some special chemicals in a given tissues. Lipid composition, time of organ formation, and metabolism contribute to the distribution of chemicals in the neonate chicken. The result of this study will improve our understanding on the fate and potential adverse effects of PCBs and PBDEs in the neonate chicken. PMID:27819361

Development of Chiral LC-MS Methods for small Molecules and Their Applications in the Analysis of Enantiomeric Composition and Pharmacokinetic Studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desai, Meera Jay

The purpose of this research was to develop sensitive LC-MS methods for enantiomeric separation and detection, and then apply these methods for determination of enantiomeric composition and for the study of pharmacokinetic and pharmacodynamic properties of a chiral nutraceutical. Our first study, evaluated the use of reverse phase and polar organic mode for chiral LC-API/MS method development. Reverse phase methods containing high water were found to decrease ionization efficiency in electrospray, while polar organic methods offered good compatibility and low limits of detection with ESI. The use of lower flow rates dramatically increased the sensitivity by an order of magnitude.more » Additionally, for rapid chiral screening, the coupled Chirobiotic column afforded great applicability for LC-MS method development. Our second study, continued with chiral LC-MS method development in this case for the normal phase mode. Ethoxynonafluorobutane, a fluorocarbon with low flammability and no flashpoint, was used as a substitute solvent for hexane/heptane mobile phases for LC-APCI/MS. Comparable chromatographic resolutions and selectivities were found using ENFB substituted mobile phase systems, although, peak efficiencies were significantly diminished. Limits of detection were either comparable or better for ENFB-MS over heptane-PDA detection. The miscibility of ENFB with a variety of commonly used organic modifiers provided for flexibility in method development. For APCI, lower flow rates did not increase sensitivity as significantly as was previously found for ESI-MS detection. The chiral analysis of native amino acids was evaluated using both APCI and ESI sources. For free amino acids and small peptides, APCI was found to have better sensitivities over ESI at high flow rates. For larger peptides, however, sensitivity was greatly improved with the use of electrospray. Additionally, sensitivity was enhanced with the use of non-volatile additives, This optimized method was then used to simultaneously separate all 19 native amino acids enantiomerically in less than 20 minutes, making it suitable for complex biological analysis. The previously developed amino acid method was then used to enantiomerically separate theanine, a free amino acid found in tea leaves. Native theanine was found to have lower limits of detection and better sensitivity over derivatized theanine samples. The native theanine method was then used to determine the enantiomeric composition of six commercially available L-theanine products. Five out of the six samples were found to be a racemic mixture of both D- and L-theanine. Concern over the efficacy of these theanine products led to our final study evaluating the pharmacokinetics and pharmacodynamics of theanine in rats using LC-ESI/MS. Rats were administered D-, L, and QL-theanine both orally and intra-peritoneally. Oral administration data demonstrated that intestinal absorption of L-theanine was greater than that of D-theanine, while i.p. data showed equal plasma uptake of both isomers. This suggested a possible competitive binding effect with respect to gut absorption. Additionally, it was found that regardless of administration method, the presence of the other enantiomer always decreased overall theanine plasma concentration. This indicated that D- and L- theanine exhibit competitive binding with respect to urinary reabsorption as well. The large quantities of D-theanine detected in the urine suggested that D-themine was eliminated with minimal metabolism, while L-theanine was preferentially reabsorbed and metabolized to ethylamine. Clearly, the metabolic fate of racemic theanine and its individual enantiomers was quite different, placing into doubt the utility of the commercial theanine products.« less

Infrared laser induced population transfer and parity selection in 14NH3: A proof of principle experiment towards detecting parity violation in chiral molecules

NASA Astrophysics Data System (ADS)

Dietiker, P.; Miloglyadov, E.; Quack, M.; Schneider, A.; Seyfang, G.

2015-12-01

We have set up an experiment for the efficient population transfer by a sequential two photon—absorption and stimulated emission—process in a molecular beam to prepare quantum states of well defined parity and their subsequent sensitive detection. This provides a proof of principle for an experiment which would allow for parity selection and measurement of the time evolution of parity in chiral molecules, resulting in a measurement of the parity violating energy difference ΔpvE between enantiomers of chiral molecules. Here, we present first results on a simple achiral molecule demonstrating efficient population transfer (about 80% on the average for each step) and unperturbed persistence of a selected excited parity level over flight times of about 1.3 ms in the beam. In agreement with model calculations with and without including nuclear hyperfine structure, efficient population transfer can be achieved by a rather simple implementation of the rapid adiabatic passage method of Reuss and coworkers and considering also the stimulated Raman adiabatic passage technique of Bergmann and coworkers as an alternative. The preparation step uses two powerful single mode continuous wave optical parametric oscillators of high frequency stability and accuracy. The detection uses a sensitive resonantly enhanced multiphoton ionization method after free flight lengths of up to 0.8 m in the molecular beam. Using this technique, we were able to also resolve the nuclear hyperfine structure in the rovibrational levels of the ν1 and ν3 fundamentals as well as the 2ν4 overtone of 14NH3, for which no previous data with hyperfine resolution were available. We present our new results on the quadrupole coupling constants for the ν1, ν3, and 2ν4 levels in the context of previously known data for ν2 and its overtone, as well as ν4, and the ground state. Thus, now, 14N quadrupole coupling constants for all fundamentals and some overtones of 14NH3 are known and can be used for further theoretical analysis.

Infrared laser induced population transfer and parity selection in (14)NH3: A proof of principle experiment towards detecting parity violation in chiral molecules.

PubMed

Dietiker, P; Miloglyadov, E; Quack, M; Schneider, A; Seyfang, G

2015-12-28

We have set up an experiment for the efficient population transfer by a sequential two photon-absorption and stimulated emission-process in a molecular beam to prepare quantum states of well defined parity and their subsequent sensitive detection. This provides a proof of principle for an experiment which would allow for parity selection and measurement of the time evolution of parity in chiral molecules, resulting in a measurement of the parity violating energy difference ΔpvE between enantiomers of chiral molecules. Here, we present first results on a simple achiral molecule demonstrating efficient population transfer (about 80% on the average for each step) and unperturbed persistence of a selected excited parity level over flight times of about 1.3 ms in the beam. In agreement with model calculations with and without including nuclear hyperfine structure, efficient population transfer can be achieved by a rather simple implementation of the rapid adiabatic passage method of Reuss and coworkers and considering also the stimulated Raman adiabatic passage technique of Bergmann and coworkers as an alternative. The preparation step uses two powerful single mode continuous wave optical parametric oscillators of high frequency stability and accuracy. The detection uses a sensitive resonantly enhanced multiphoton ionization method after free flight lengths of up to 0.8 m in the molecular beam. Using this technique, we were able to also resolve the nuclear hyperfine structure in the rovibrational levels of the ν1 and ν3 fundamentals as well as the 2ν4 overtone of (14)NH3, for which no previous data with hyperfine resolution were available. We present our new results on the quadrupole coupling constants for the ν1, ν3, and 2ν4 levels in the context of previously known data for ν2 and its overtone, as well as ν4, and the ground state. Thus, now, (14)N quadrupole coupling constants for all fundamentals and some overtones of (14)NH3 are known and can be used for further theoretical analysis.

Highly enantioselective synthesis of γ-, δ-, and ε-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)–Cu- or Pd-catalyzed cross-coupling

PubMed Central

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

2014-01-01

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (≥99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (≥99% ee) and catalytic synthesis of various γ- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)–Cu- or Pd-catalyzed cross-coupling. ZACA–in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ω-alkene-1-ols produced both (R)- and (S)-α,ω-dioxyfunctional intermediates (3) in 80–88% ee, which were readily purified to the ≥99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These α,ω-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of γ-, δ-, and ε-chiral 1-alkanols of ≥99% ee. The MαNP ester analysis has been applied to the determination of the enantiomeric purities of δ- and ε-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Stereoselective synthesis from a process research perspective.

PubMed

Hillier, Michael C; Reider, Paul J

2002-03-01

The process chemists' primary responsibility is to develop efficient and reproducible syntheses of pharmaceutically active compounds. This task is complicated when dealing with chiral molecules that often must be made as single isomers according to regulatory guidelines. The presence of any isomeric impurity in the final product, even in small amounts, is usually not acceptable. This requirement necessitates an exquisite understanding of the methods employed in the construction of chiral drugs. However, the chemistry available for this purpose is sometimes limited and often requires a significant amount of effort and creativity to be made both functional and consistent.

Absolute Configuration of 3-METHYLCYCLOHEXANONE by Chiral Tag Rotational Spectroscopy and Vibrational Circular Dichroism

NASA Astrophysics Data System (ADS)

Evangelisti, Luca; Holdren, Martin S.; Mayer, Kevin J.; Smart, Taylor; West, Channing; Pate, Brooks

2017-06-01

The absolute configuration of 3-methylcyclohexanone was established by chiral tag rotational spectroscopy measurements using 3-butyn-2-ol as the tag partner. This molecule was chosen because it is a benchmark measurement for vibrational circular dichroism (VCD). A comparison of the analysis approaches of chiral tag rotational spectroscopy and VCD will be presented. One important issue in chiral analysis by both methods is the conformational flexibility of the molecule being analyzed. The analysis of conformational composition of samples will be illustrated. In this case, the high spectral resolution of molecular rotational spectroscopy and potential for spectral simplification by conformational cooling in the pulsed jet expansion are advantages for chiral tag spectroscopy. The computational chemistry requirements for the two methods will also be discussed. In this case, the need to perform conformer searches for weakly bound complexes and to perform reasonably high level quantum chemistry geometry optimizations on these complexes makes the computational time requirements less favorable for chiral tag rotational spectroscopy. Finally, the issue of reliability of the determination of the absolute configuration will be considered. In this case, rotational spectroscopy offers a "gold standard" analysis method through the determination of the ^{13}C-subsitution structure of the complex between 3-methylcyclohexanone and an enantiopure sample of the 3-butyn-2-ol tag.

Use and practice of achiral and chiral supercritical fluid chromatography in pharmaceutical analysis and purification.

PubMed

Lemasson, Elise; Bertin, Sophie; West, Caroline

2016-01-01

The interest of pharmaceutical companies for complementary high-performance chromatographic tools to assess a product's purity or enhance this purity is on the rise. The high-throughput capability and economic benefits of supercritical fluid chromatography, but also the "green" aspect of CO2 as the principal solvent, render supercritical fluid chromatography very attractive for a wide range of pharmaceutical applications. The recent reintroduction of new robust instruments dedicated to supercritical fluid chromatography and the progress in stationary phase technology have also greatly benefited supercritical fluid chromatography. Additionally, it was shown several times that supercritical fluid chromatography could be orthogonal to reversed-phase high-performance liquid chromatography and could efficiently compete with it. Supercritical fluid chromatography is an adequate tool for small molecules of pharmaceutical interest: synthetic intermediates, active pharmaceutical ingredients, impurities, or degradation products. In this review, we first discuss about general chromatographic conditions for supercritical fluid chromatography analysis to better suit compounds of pharmaceutical interest. We also discuss about the use of achiral and chiral supercritical fluid chromatography for analytical purposes and the recent applications in these areas. The use of preparative supercritical fluid chromatography by pharmaceutical companies is also covered. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Circularly Polarized Luminescence in Enantiopure Europium and Terbium Complexes with Modular, All-Oxygen Donor Ligands

PubMed Central

Seitz, Michael; Do, King; Ingram, Andrew J.; Moore, Evan G.; Muller, Gilles; Raymond, Kenneth N.

2009-01-01

Abstract: Circulaly polarized luminescence from terbium(III) complexed and excited by chiral antenna ligands gives strong emission The modular synthesis of three new octadentate, enantiopure ligands are reported - one with the bidentate chelating unit 2-hydroxyisophthalamide (IAM) and two with 1-hydroxy-2-pyridinone (1,2-HOPO) units. A new design principle is introduced for the chiral, non-racemic hexamines which constitute the central backbones for the presented class of ligands. The terbium(III) complex of the IAM ligand, as well as the europium(III) complexes of the 1,2-HOPO ligands are synthesized and characterized by various techniques (NMR, UV, CD, luminescence spectroscopy). All species exhibit excellent stability and moderate to high luminescence efficiency (quantum yields ΦEu = 0.05–0.08 and ΦTb = 0.30–0.57) in aqueous solution at physiological pH. Special focus is put onto the properties of the complexes in regard to circularly polarized luminescence (CPL). The maximum luminescence dissymmetry factors (glum) in aqueous solution are high with |glum|max = 0.08 – 0.40. Together with the very favorable general properties (good stability, high quantum yields, long lifetimes), the presented lanthanide complexes can be considered as good candidates for analytical probes based on CPL in biologically relevant environments. PMID:19639983

Application of Chan-Lam cross coupling for the synthesis of N-heterocyclic carbene precursors bearing strong electron donating or withdrawing groups

NASA Astrophysics Data System (ADS)

Huang, Liliang; He, Chengxiang; Sun, Zhihua

2015-07-01

Chan-Lam cross coupling allowed efficient synthesis of N,N’-disubstituted ortho-phenylene diamines bearing strong electron donating or withdrawing groups, such as nitro or methoxy groups, with moderate to high yields. These diamines can then be turned into N-heterocyclic carbene precursors after condensation with trimethyl orthoformate. The same strategy can also be utilized for the synthesis of N-monosubstituted aniline derivatives containing a functionalized ortho-aminomethyl group as intermediates for chiral 6-membered ring carbene precursors.

Asymmetric intermolecular Pauson-Khand reactions of unstrained olefins: the (o-dimethylamino)phenylsulfinyl group as an efficient chiral auxiliary.

PubMed

Rodríguez Rivero, Marta; De La Rosa, Juan Carlos; Carretero, Juan Carlos

2003-12-10

The first asymmetric version of intermolecular Pauson-Khand reactions of unstrained alkenes is described. Generally simple acyclic alkenes exhibit low reactivity and regioselectivity in intermolecular Pauson-Khand reactions; however, o-(dimethylamino)phenyl vinyl sulfoxide reacts under very mild conditions with a wide variety of terminal alkynes in a completely regioselective and highly stereoselective manner. The utility of the resulting 5-sulfinyl-2-cyclopentenones in asymmetric synthesis is illustrated by a very short enantioselective synthesis of the antibiotic (-)-pentenomycin I.

Microwave absorption properties of carbon nanocoils coated with highly controlled magnetic materials by atomic layer deposition.

PubMed

Wang, Guizhen; Gao, Zhe; Tang, Shiwei; Chen, Chaoqiu; Duan, Feifei; Zhao, Shichao; Lin, Shiwei; Feng, Yuhong; Zhou, Lei; Qin, Yong

2012-12-21

In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

Helicity-selective phase-matching and quasi-phase matching of circularly polarized high-order harmonics: towards chiral attosecond pulses

DOE PAGES

Kfir, Ofer; Grychtol, Patrik; Turgut, Emrah; ...

2016-05-23

Phase matching of circularly polarized high-order harmonics driven by counter-rotating bi-chromatic lasers was recently predicted theoretically and demonstrated experimentally. In that work, phase matching was analyzed by assuming that the total energy, spin angular momentum and linear momentum of the photons participating in the process are conserved. Here we propose a new perspective on phase matching of circularly polarized high harmonics. We derive an extended phase matching condition by requiring a new propagation matching condition between the classical vectorial bi-chromatic laser pump and harmonics fields. This allows us to include the influence of the laser pulse envelopes on phase matching.more » Here, we find that the helicity dependent phase matching facilitates generation of high harmonics beams with a high degree of chirality. Indeed, we present an experimentally measured chiral spectrum that can support a train of attosecond pulses with a high degree of circular polarization. Moreover, while the degree of circularity of the most intense pulse approaches unity, all other pulses exhibit reduced circularity. Lastly, this feature suggests the possibility of using a train of attosecond pulses as an isolated attosecond probe for chiral-sensitive experiments.« less

Copper-based metal coordination complexes with Voriconazole ligand: Syntheses, structures and antimicrobial properties

NASA Astrophysics Data System (ADS)

Zhao, Yan-Ming; Tang, Gui-Mei; Wang, Yong-Tao; Cui, Yue-Zhi; Ng, Seik Weng

2018-03-01

Three new chiral metal coordination complexes, namely, [Cu(FZ)2(CH3COO)2(H2O)]·2H2O (1), [Cu(FZ)2(NO3)2] (2), and [Cu2(FZ)2 (H2O)8](SO4)2·4H2O (3) [FZ = (2R,3S)-2-(2,4-difluorophenyl)-3-(5-fluoro-4-pyrimidiny)-1-(1H-1,2,4-triazol-1-yl)-2-butanol) (Voriconazole)] have been obtained by the reaction of Cu(II) salts and the free ligand FZ at room temperature. Complexes 1-3 were structurally characterized by X-ray single-crystal diffraction, IR, UV-vis, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Complex 1 crystallizes in the chiral space group C2, which exhibits a mono-nuclear structure. Both complexes 2 and 3 display a one-dimensional (1D) tape structure, which crystallize in chiral space group P21212 and P212121, respectively. Among these complexes, there exist a variety of hydrogen bonds and stacking interactions, through which a three-dimensional supramolecular architecture will be generated. Compared with the standard (Voriconazole), these Cu-based complexes show the more potent inhibiting efficiency against the species of Candida and Aspergillus. Moreover, among these complexes, complex 1 shows the most excellent efficiency.

The Role of Carbohydrates at the Origin of Homochirality in Biosystems

NASA Astrophysics Data System (ADS)

Toxvaerd, Søren

2013-10-01

Pasteur has demonstrated that the chiral components in a racemic mixture can separate in homochiral crystals. But with a strong chiral discrimination the chiral components in a concentrated mixture can also phase separate into homochiral fluid domains, and the isomerization kinetics can then perform a symmetry breaking into one thermodynamical stable homochiral system. Glyceraldehyde has a sufficient chiral discrimination to perform such a symmetry breaking. The requirement of a high concentration of the chiral reactant(s) in an aqueous solution in order to perform and maintain homochirality; the appearance of phosphorylation of almost all carbohydrates in the central machinery of life; the basic ideas that the biochemistry and the glycolysis and gluconeogenesis contain the trace of the biochemical evolution, all point in the direction of that homochirality was obtained just after- or at a phosphorylation of the very first products of the formose reaction, at high concentrations of the reactants in phosphate rich compartments in submarine hydrothermal vents. A racemic solution of D,L-glyceraldehyde-3-phosphate could be the template for obtaining homochiral D-glyceraldehyde-3-phosphate(aq) as well as L-amino acids.

Chiral Nickel(II) Complex Catalyzed Enantioselective Doyle-Kirmse Reaction of α-Diazo Pyrazoleamides.

PubMed

Lin, Xiaobin; Tang, Yu; Yang, Wei; Tan, Fei; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming

2018-03-07

Although high enantioselectivity of [2,3]-sigmatropic rearrangement of sulfonium ylides (Doyle-Kirmse reaction) has proven surprisingly elusive using classic chiral Rh(II) and Cu(I) catalysts, in principle it is due to the difficulty in fine discrimination of the heterotopic lone pairs of sulfur and chirality inversion at sulfur of sulfonium ylides. Here, we show that the synergistic merger of new α-diazo pyrazoleamides and a chiral N, N'-dioxide-nickel(II) complex catalyst enables a highly enantioselective Doyle-Kirmse reaction. The pyrazoleamide substituent serves as both an activating and a directing group for the ready formation of a metal-carbene- and Lewis-acid-bonded ylide intermediate in the assistance of a dual-tasking nickel(II) complex. An alternative chiral Lewis-acid-bonded ylide pathway greatly improves the product enantiopurity even for the reaction of a symmetric diallylsulfane. The majority of transformations over a series of aryl- or vinyl-substituted α-diazo pyrazoleamindes and sulfides proceed rapidly (within 5-20 min in most cases) with excellent results (up to 99% yield and 96% ee), providing a breakthrough in enantioselective Doyle-Kirmse reaction.

Biomimetic Hierarchical Assembly of Helical Supraparticles from Chiral Nanoparticles

DOE PAGES

Zhou, Yunlong; Marson, Ryan L.; van Anders, Greg; ...

2016-02-22

Chiroptical materials found in butterflies, beetles, stomatopod crustaceans, and other creatures are attributed to biocomposites with helical motifs and multiscale hierarchical organization. These structurally sophisticated materials self-assemble from primitive nanoscale building blocks, a process that is simpler and more energy efficient than many top-down methods currently used to produce similarly sized three-dimensional materials. In this paper, we report that molecular-scale chirality of a CdTe nanoparticle surface can be translated to nanoscale helical assemblies, leading to chiroptical activity in the visible electromagnetic range. Chiral CdTe nanoparticles coated with cysteine self-organize around Te cores to produce helical supraparticles. D-/L-Form of the aminomore » acid determines the dominant left/right helicity of the supraparticles. Coarse-grained molecular dynamics simulations with a helical pair-potential confirm the assembly mechanism and the origin of its enantioselectivity, providing a framework for engineering three-dimensional chiral materials by self-assembly. Finally, the helical supraparticles further self-organize into lamellar crystals with liquid crystalline order, demonstrating the possibility of hierarchical organization and with multiple structural motifs and length scales determined by molecular-scale asymmetry of nanoparticle interactions.« less

Chiral recognition ability of an (S)-naproxen- imprinted monolith by capillary electrochromatography.

PubMed

Xu, Yan-Li; Liu, Zhao-Sheng; Wang, He-Fang; Yan, Chao; Gao, Ru-Yu

2005-02-01

The racemic naproxen was selectively recognized by capillary electrochromatography (CEC) on an (S)-naproxen-imprinted monolith, which was prepared by an in situ thermal-initiated polymerization. The recognition selectivity of a selected monolith strictly relied on the CEC conditions involved. The factors that influence the imprinting selectivity as well as the electroosmotic flow (EOF), including the applied voltage, organic solvent, salt concentration and pH value of the buffer, column temperature, and surfactant modifiers were systematically studied. Once the column was prepared, the experiment results showed that the successful chiral recognition was dependent on CEC variables. For example: the recognition could be observed in acetonitrile and ethanol electrolytes, while methanol and dimethyl sulfoxide (DMSO) electrolytes had no chiral recognition ability. The buffer with pH values of 2.6 or 3.0 at a higher salt concentration had chiral recognition ability. Column temperatures of 25-35 degrees C were optimal. Three surfactants, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and polyoxyethylene sorbitan monolaurate (Tween 20), can improve the recognition. Baseline resolution was obtained under optimized conditions and the column efficiency of the later eluent (S)-naproxen was 90 000 plates/m.

Chiral phase structure of three flavor QCD at vanishing baryon number density

DOE PAGES

Bazavov, A.; Ding, H. -T.; Hegde, P.; ...

2017-04-12

In this paper, we investigate the phase structure of QCD with three degenerate quark flavors as a function of the degenerate quark masses at vanishing baryon number density. We use the highly improved staggered quarks on lattices with temporal extent N τ = 6 and perform calculations for six values of quark masses, which in the continuum limit correspond to pion masses in the range 80 MeV ≲ m π ≲ 230 MeV. By analyzing the volume and temperature dependence of the chiral condensate and chiral susceptibility, we find no direct evidence for a first-order phase transition in this rangemore » of pion mass values. Finally, relying on the universal scaling behaviors of the chiral observables near an anticipated chiral critical point, we estimate an upper bound for the critical pion mass m c π ≲ 50 MeV, below which a region of first-order chiral phase transition is favored.« less

Chiromagnetic nanoparticles and gels

NASA Astrophysics Data System (ADS)

Yeom, Jihyeon; Santos, Uallisson S.; Chekini, Mahshid; Cha, Minjeong; de Moura, André F.; Kotov, Nicholas A.

2018-01-01

Chiral inorganic nanostructures have high circular dichroism, but real-time control of their optical activity has so far been achieved only by irreversible chemical changes. Field modulation is a far more desirable path to chiroptical devices. We hypothesized that magnetic field modulation can be attained for chiral nanostructures with large contributions of the magnetic transition dipole moments to polarization rotation. We found that dispersions and gels of paramagnetic Co3O4 nanoparticles with chiral distortions of the crystal lattices exhibited chiroptical activity in the visible range that was 10 times as strong as that of nonparamagnetic nanoparticles of comparable size. Transparency of the nanoparticle gels to circularly polarized light beams in the ultraviolet range was reversibly modulated by magnetic fields. These phenomena were also observed for other nanoscale metal oxides with lattice distortions from imprinted amino acids and other chiral ligands. The large family of chiral ceramic nanostructures and gels can be pivotal for new technologies and knowledge at the nexus of chirality and magnetism.

Chiral optical response of planar and symmetric nanotrimers enabled by heteromaterial selection

PubMed Central

Banzer, Peter; Woźniak, Paweł; Mick, Uwe; De Leon, Israel; Boyd, Robert W.

2016-01-01

Chirality is an intriguing property of certain molecules, materials or artificial nanostructures, which allows them to interact with the spin angular momentum of the impinging light field. Due to their chiral geometry, they can distinguish between left- and right-hand circular polarization states or convert them into each other. Here we introduce an approach towards optical chirality, which is observed in individual two-dimensional and geometrically mirror-symmetric nanostructures. In this scheme, the chiral optical response is induced by the chosen heterogeneous material composition of a particle assembly and the corresponding resonance behaviour of the constituents it is built from, which breaks the symmetry of the system. As a proof of principle, we investigate such a structure composed of individual silicon and gold nanoparticles both experimentally, as well as numerically. Our proposed concept constitutes an approach for designing two-dimensional chiral media tailored at the nanoscale, allowing for high tunability of their optical response. PMID:27734960

Lithium Enolates in the Enantioselective Construction of Tetrasubstituted Carbon Centers with Chiral Lithium Amides as Noncovalent Stereodirecting Auxiliaries.

PubMed

Yu, Kai; Lu, Ping; Jackson, Jeffrey J; Nguyen, Thuy-Ai D; Alvarado, Joseph; Stivala, Craig E; Ma, Yun; Mack, Kyle A; Hayton, Trevor W; Collum, David B; Zakarian, Armen

2017-01-11

Lithium enolates derived from carboxylic acids are ubiquitous intermediates in organic synthesis. Asymmetric transformations with these intermediates, a central goal of organic synthesis, are typically carried out with covalently attached chiral auxiliaries. An alternative approach is to utilize chiral reagents that form discrete, well-defined aggregates with lithium enolates, providing a chiral environment conducive of asymmetric bond formation. These reagents effectively act as noncovalent, or traceless, chiral auxiliaries. Lithium amides are an obvious choice for such reagents as they are known to form mixed aggregates with lithium enolates. We demonstrate here that mixed aggregates can effect highly enantioselective transformations of lithium enolates in several classes of reactions, most notably in transformations forming tetrasubstituted and quaternary carbon centers. Easy recovery of the chiral reagent by aqueous extraction is another practical advantage of this one-step protocol. Crystallographic, spectroscopic, and computational studies of the central reactive aggregate, which provide insight into the origins of selectivity, are also reported.

Mechanisms for the inversion of chirality: global reaction route mapping of stereochemical pathways in a probable chiral extraterrestrial molecule, 2-aminopropionitrile.

PubMed

Kaur, Ramanpreet; Vikas

2015-02-21

2-Aminopropionitrile (APN), a probable candidate as a chiral astrophysical molecule, is a precursor to amino-acid alanine. Stereochemical pathways in 2-APN are explored using Global Reaction Route Mapping (GRRM) method employing high-level quantum-mechanical computations. Besides predicting the conventional mechanism for chiral inversion that proceeds through an achiral intermediate, a counterintuitive flipping mechanism is revealed for 2-APN through chiral intermediates explored using the GRRM. The feasibility of the proposed stereochemical pathways, in terms of the Gibbs free-energy change, is analyzed at the temperature conditions akin to the interstellar medium. Notably, the stereoinversion in 2-APN is observed to be more feasible than the dissociation of 2-APN and intermediates involved along the stereochemical pathways, and the flipping barrier is observed to be as low as 3.68 kJ/mol along one of the pathways. The pathways proposed for the inversion of chirality in 2-APN may provide significant insight into the extraterrestrial origin of life.

Enantioseparation of novel chiral sulfoxides on chlorinated polysaccharide stationary phases in supercritical fluid chromatography.

PubMed

West, Caroline; Konjaria, Mari-Luiza; Shashviashvili, Natia; Lemasson, Elise; Bonnet, Pascal; Kakava, Rusudan; Volonterio, Alessandro; Chankvetadze, Bezhan

2017-05-26

Asymmetric sulfoxides is a particular case of chirality that may be found in natural as well as synthetic products. Twenty-four original molecules containing a sulfur atom as a centre of chirality were analyzed in supercritical fluid chromatography on seven polysaccharide-based chiral stationary phases (CSP) with carbon dioxide - methanol mobile phases. While all the tested CSP provided enantioseparation for a large part of the racemates, chlorinated cellulosic phases proved to be both highly retentive and highly enantioselective towards these species. Favourable structural features were determined by careful comparison of the enantioseparation of the probe molecules. Molecular modelling studies indicate that U-shaped (folded) conformations were most favorable to achieve high enantioresolution on these CSP, while linear (extended) conformations were not so clearly discriminated. For a subset of these species adopting different conformations, a broad range of mobile phase compositions, ranging from 20 to 100% methanol in carbon dioxide, were investigated. While retention decreased continuously in this range, enantioseparation varied in a non-monotonous fashion. Abrupt changes in the tendency curves of retention and selectivity were observed when methanol proportion reaches about 60%, suggesting that a change in the conformation of the analytes and/or chiral selector is occurring at this point. Copyright © 2017 Elsevier B.V. All rights reserved.

Multiple exciton generation in chiral carbon nanotubes: Density functional theory based computation

NASA Astrophysics Data System (ADS)

Kryjevski, Andrei; Mihaylov, Deyan; Kilina, Svetlana; Kilin, Dmitri

2017-10-01

We use a Boltzmann transport equation (BE) to study time evolution of a photo-excited state in a nanoparticle including phonon-mediated exciton relaxation and the multiple exciton generation (MEG) processes, such as exciton-to-biexciton multiplication and biexciton-to-exciton recombination. BE collision integrals are computed using Kadanoff-Baym-Keldysh many-body perturbation theory based on density functional theory simulations, including exciton effects. We compute internal quantum efficiency (QE), which is the number of excitons generated from an absorbed photon in the course of the relaxation. We apply this approach to chiral single-wall carbon nanotubes (SWCNTs), such as (6,2) and (6,5). We predict efficient MEG in the (6,2) and (6,5) SWCNTs within the solar spectrum range starting at the 2Eg energy threshold and with QE reaching ˜1.6 at about 3Eg, where Eg is the electronic gap.

Multiple exciton generation in chiral carbon nanotubes: Density functional theory based computation.

PubMed

Kryjevski, Andrei; Mihaylov, Deyan; Kilina, Svetlana; Kilin, Dmitri

2017-10-21

We use a Boltzmann transport equation (BE) to study time evolution of a photo-excited state in a nanoparticle including phonon-mediated exciton relaxation and the multiple exciton generation (MEG) processes, such as exciton-to-biexciton multiplication and biexciton-to-exciton recombination. BE collision integrals are computed using Kadanoff-Baym-Keldysh many-body perturbation theory based on density functional theory simulations, including exciton effects. We compute internal quantum efficiency (QE), which is the number of excitons generated from an absorbed photon in the course of the relaxation. We apply this approach to chiral single-wall carbon nanotubes (SWCNTs), such as (6,2) and (6,5). We predict efficient MEG in the (6,2) and (6,5) SWCNTs within the solar spectrum range starting at the 2E g energy threshold and with QE reaching ∼1.6 at about 3E g , where E g is the electronic gap.

FAST TRACK COMMUNICATION: Ferroelectricity in low-symmetry biaxial nematic liquid crystals

NASA Astrophysics Data System (ADS)

Osipov, Mikhail A.; Gorkunov, Maxim V.

2010-09-01

Order parameters and phenomenological theory for both high- and low-symmetry biaxial nematic phases are presented and it is predicted that the chiral low-symmetry biaxial phase must be ferroelectric. This conclusion is based on general symmetry arguments and on the results of the Landau-de Gennes theory. The microscopic mechanism of the ferroelectric ordering in this chiral biaxial phase is illustrated using a simple molecular model based on dispersion interactions between biaxial molecules of low symmetry. Similar to the chiral smectic C* phase, the ferroelectricity in the chiral biaxial nematic phase is improper, i.e., polarization is not a primary order parameter and is not determined by dipolar interactions. Ferroelectric ordering in biaxial nematics may be found, in principle, in materials composed of chiral analogues of the tetrapod molecules which are known to exhibit biaxial phases.

Asymmetric Fluorination of α-Branched Cyclohexanones Enabled by a Combination of Chiral Anion Phase-Transfer Catalysis and Enamine Catalysis using Protected Amino Acids

PubMed Central

2015-01-01

We report a study involving the successful merger of two separate chiral catalytic cycles: a chiral anion phase-transfer catalysis cycle to activate Selectfluor and an enamine activation cycle, using a protected amino acid as organocatalyst. We have demonstrated the viability of this approach with the direct asymmetric fluorination of α-substituted cyclohexanones to generate quaternary fluorine-containing stereocenters. With these two chiral catalytic cycles operating together in a matched sense, high enantioselectivites can be achieved, and we envisage that this dual catalysis method has the potential to be more broadly applicable, given the breadth of enamine catalysis. It also represents a rare example of chiral enamine catalysis operating successfully on α-branched ketones, substrates commonly inert to this activation mode. PMID:24684209

Access to enantioenriched alpha-amino esters via rhodium-catalyzed 1,4-addition/enantioselective protonation.

PubMed

Navarre, Laure; Martinez, Rémi; Genet, Jean-Pierre; Darses, Sylvain

2008-05-14

Conjugate addition of potassium trifluoro(organo)borates 2 to dehydroalanine derivatives 1, mediated by a chiral rhodium catalyst and in situ enantioselective protonation, afforded straightforward access to a variety of protected alpha-amino esters 3 with high yields and enantiomeric excesses up to 95%. Among the tested chiral ligands and proton sources, Binap, in combination with guaiacol (2-methoxyphenol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions. Organostannanes have also shown to participate in this reaction. By a fine-tuning of the ester moiety, and using Difluorophos as chiral ligand, increased levels of enantioselectivity, generally close to 95%, were achieved. Deuterium labeling experiments revealed, and DFT calculation supported, an unusual mechanism involving a hydride transfer from the amido substituent to the alpha carbon explaining the high levels of enantioselectivity attained in controlling this alpha chiral center.

Strangeness at high temperatures: from hadrons to quarks.

PubMed

Bazavov, A; Ding, H-T; Hegde, P; Kaczmarek, O; Karsch, F; Laermann, E; Maezawa, Y; Mukherjee, Swagato; Ohno, H; Petreczky, P; Schmidt, C; Sharma, S; Soeldner, W; Wagner, M

2013-08-23

Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover, separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window, these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.

Breaking Symmetry in Time-Dependent Electronic Structure Theory to Describe Spectroscopic Properties of Non-Collinear and Chiral Molecules

NASA Astrophysics Data System (ADS)

Goings, Joshua James

Time-dependent electronic structure theory has the power to predict and probe the ways electron dynamics leads to useful phenomena and spectroscopic data. Here we report several advances and extensions of broken-symmetry time-dependent electronic structure theory in order to capture the flexibility required to describe non-equilibrium spin dynamics, as well as electron dynamics for chiroptical properties and vibrational effects. In the first half, we begin by discussing the generalization of self-consistent field methods to the so-called two-component structure in order to capture non-collinear spin states. This means that individual electrons are allowed to take a superposition of spin-1/2 projection states, instead of being constrained to either spin-up or spin-down. The system is no longer a spin eigenfunction, and is known a a spin-symmetry broken wave function. This flexibility to break spin symmetry may lead to variational instabilities in the approximate wave function, and we discuss how these may be overcome. With a stable non-collinear wave function in hand, we then discuss how to obtain electronic excited states from the non-collinear reference, along with associated challenges in their physical interpretation. Finally, we extend the two-component methods to relativistic Hamiltonians, which is the proper setting for describing spin-orbit driven phenomena. We describe the first implementation of the explicit time propagation of relativistic two-component methods and how this may be used to capture spin-forbidden states in electronic absorption spectra. In the second half, we describe the extension of explicitly time-propagated wave functions to the simulation of chiroptical properties, namely circular dichroism (CD) spectra of chiral molecules. Natural circular dichroism, that is, CD in the absence of magnetic fields, originates in the broken parity symmetry of chiral molecules. This proves to be an efficient method for computing circular dichroism spectra for high density-of-states chiral molecules. Next, we explore the impact of allowing nuclear motion on electronic absorption spectra within the context of mixed quantum-classical dynamics. We show that nuclear motion modulates the electronic response, and this gives rise to infrared absorption as well as Raman scattering phenomena in the computed dynamic polarizability. Finally, we explore the accuracy of several perturbative approximations to the equation-of-motion coupled-cluster methods for the efficient and accurate prediction of electronic absorption spectra.

Catalysis of partial chiral symmetry restoration by Δ matter

NASA Astrophysics Data System (ADS)

Takeda, Yusuke; Kim, Youngman; Harada, Masayasu

2018-06-01

We study the phase structure of dense hadronic matter including Δ (1232 ) as well as N (939 ) based on the parity partner structure, where the baryons have their chiral partners with a certain amount of chiral invariant masses. We show that, in symmetric matter, Δ enters into matter in the density region of about one to four times normal nuclear matter density, ρB˜1 -4 ρ0 . The onset density of Δ matter depends on the chiral invariant mass of Δ ,mΔ 0 : As mΔ 0 increases, the onset density becomes bigger. The stable Δ -nucleon matter is realized for ρB≳1.5 ρ0 , i.e., the phase transition from nuclear matter to Δ -nucleon matter is of first order for small mΔ 0, and it is of second order for large mΔ 0. We find that, associated with the phase transition, the chiral condensate changes very rapidly; i.e., the chiral symmetry restoration is accelerated by Δ matter. As a result of the accelerations, there appear N*(1535 ) and Δ (1700 ) , which are the chiral partners to N (939 ) and Δ (1232 ) , in high-density matter, signaling the partial chiral symmetry restoration. Furthermore, we find that complete chiral symmetry restoration itself is delayed by Δ matter. We also calculate the effective masses, pressure, and symmetry energy to study how the transition to Δ matter affects such physical quantities. We observe that the physical quantities change drastically at the transition density.

New thermotropic chiral nematic polymers. 3. Copolymers containing a cyanobiphenyl group and (S)-(-)-1-phenylethanol or (S)-(-)-1-phenylethylamine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mastrangelo, J.C.; Chen, S.H.

Thermotropic chiral nematics in thin films on the order of 10 [mu]m possess a unique optical property, selective wavelength reflection, that forms the basis of a number of potential applications including circular polarizers, notch filters, beamsplitters, and so on. Instead of low molar mass chiral nematics, thermotropic copolymers have been actively pursued as an alternative in view of the possibility of achieving long-term mesophase stability and optical characteristics desired for passive device applications. Cyanobiphenyl is a relatively high birefringent group which is known to contribute to the formation of low molar mass liquid crystals; it was found to exhibit amore » nematic mesophase between the glass transition and clearing temperatures in side-chain polyacrylates with spacer lengths in the 2-6 range. However, there exists only one report on the formation of a chiral nematic copolymer with cholesterol as the chiral moiety. Since several chiral building blocks other than cholesterol have been found to possess strong helical twisting powers with selected nematogenic monomers, it would be of interest to explore a cyanobiphenyl group as a building block for the synthesis of new chiral nematic copolymers.« less

A chiral sensor based on weak measurement for the determination of Proline enantiomers in diverse measuring circumstances.

PubMed

Li, Dongmei; Guan, Tian; He, Yonghong; Liu, Fang; Yang, Anping; He, Qinghua; Shen, Zhiyuan; Xin, Meiguo

2018-07-01

A new chiral sensor based on weak measurement to accurately measure the optical rotation (OR) has been developed for the estimation of a trace amount of chiral molecule. With the principle of optical weak measurement in frequency domain, the central wavelength shift of output spectra is quantitatively relative to the angle of preselected polarization. Hence, a chiral molecule (e.g., L-amino acid, or D-amino acid) can be enantioselectively determined by modifying the preselection angle with the OR, which will cause the rotation of a polarization plane. The concentration of the chiral sample, corresponding to its optical activity, is quantitatively analyzed with the central wavelength shift of output spectra, which can be collected in real time. Immune to the refractive index change, the proposed chiral sensor is valid in complicated measuring circumstance. The detections of Proline enantiomer concentration in different solvents were implemented. The results demonstrated that weak measurement acted as a reliable method to chiral recognition of Proline enantiomers in diverse circumstance with the merits of high precision and good robustness. In addition, this real-time monitoring approach plays a crucial part in asymmetric synthesis and biological systems. Copyright © 2018. Published by Elsevier B.V.

Chiral detection in high-performance liquid chromatography by vibrational circular dichroism.

PubMed

Tran, C D; Grishko, V I; Huang, G

1994-09-01

A novel chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents in the infrared region, i.e., vibrational circular dichroism (VCD). In this instrument, a solid-state spectral tunable (from 2.4 to 3.5 microns) F-center laser was used as the light source. The linearly polarized laser beam was converted into left circularly polarized light (LCPL) and right circularly polarized light (RCPL) at 42 kHz by means of a photoelastic modulator. The intensity of the LCPL and RCPL transmitted through the sample was measured by a liquid nitrogen cooled indium antimonide detector. Double modulation was employed to reduce the noise associated with the laser beam. Specifically, the linearly polarized laser beam, prior to being converted to CPL, was modulated at 85 Hz by a mechanical chopper. Demodulation and amplification were accomplished with the use of two lock-in amplifiers. In its present configuration, the instrument can be used to measure the VCD of O-H groups. Its sensitivity is so high that it was able, for the first time, to detect chirally (with limits of detection of micrograms) (R)- and (S)-2,2,2-trifluoro-1-(9- anthryl)ethanol and (R)- and (S)-benzoin when these compounds were chromatographically separated from the corresponding racemic mixtures by a Chiralcel-OD column. The main advantage of this chiral detector is, however, its universality; i.e., it can be used to virtually detect any chiral compounds which has O-H group (e.g, aliphatic alcohols such as 2-octanol).

Efficient Synthesis of Differentiated syn-1,2-Diol Derivatives by Asymmetric Transfer Hydrogenation-Dynamic Kinetic Resolution of α-Alkoxy-Substituted β-Ketoesters.

PubMed

Monnereau, Laure; Cartigny, Damien; Scalone, Michelangelo; Ayad, Tahar; Ratovelomanana-Vidal, Virginie

2015-08-10

Asymmetric transfer hydrogenation was applied to a wide range of racemic aryl α-alkoxy-β-ketoesters in the presence of well-defined, commercially available, chiral catalyst Ru(II) -(N-p-toluenesulfonyl-1,2-diphenylethylenediamine) and a 5:2 mixture of formic acid and triethylamine as the hydrogen source. Under these conditions, dynamic kinetic resolution was efficiently promoted to provide the corresponding syn α-alkoxy-β-hydroxyesters derived from substituted aromatic and heteroaromatic aldehydes with a high level of diastereoselectivity (diastereomeric ratio (d.r.)>99:1) and an almost perfect enantioselectivity (enantiomeric excess (ee)>99 %). Additionally, after extensive screening of the reaction conditions, the use of Ru(II) - and Rh(III) -tethered precatalysts extended this process to more-challenging substrates that bore alkenyl-, alkynyl-, and alkyl substituents to provide the corresponding syn α-alkoxy-β-hydroxyesters with excellent enantiocontrol (up to 99 % ee) and good to perfect diastereocontrol (d.r.>99:1). Lastly, the synthetic utility of the present protocol was demonstrated by application to the asymmetric synthesis of chiral ester ethyl (2S)-2-ethoxy-3-(4-hydroxyphenyl)-propanoate, which is an important pharmacophore in a number of peroxisome proliferator-activated receptor α/γ dual agonist advanced drug candidates used for the treatment of type-II diabetes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

SWCNT Photocatalyst for Hydrogen Production from Water upon Photoexcitation of (8, 3) SWCNT at 680-nm Light

NASA Astrophysics Data System (ADS)

Murakami, Noritake; Tango, Yuto; Miyake, Hideaki; Tajima, Tomoyuki; Nishina, Yuta; Kurashige, Wataru; Negishi, Yuichi; Takaguchi, Yutaka

2017-03-01

Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption bands depending on their chiral indices (n, m). Their application for solar energy conversion is difficult because of the large binding energy (>100 meV) of electron-hole pairs, known as excitons, produced by optical absorption. Recent development of photovoltaic devices based on SWCNTs as light-absorbing components have shown that the creation of heterojunctions by pairing chirality-controlled SWCNTs with C60 is the key for high power conversion efficiency. In contrast to thin film devices, photocatalytic reactions in a dispersion/solution system triggered by the photoexcitation of SWCNTs have never been reported due to the difficulty of the construction of a well-ordered surface on SWCNTs. Here, we show a clear-cut example of a SWCNT photocatalyst producing H2 from water. Self-organization of a fullerodendron on the SWCNT core affords water-dispersible coaxial nanowires possessing SWCNT/C60 heterojunctions, of which a dendron shell can act as support of a co-catalyst for H2 evolution. Because the band offset between the LUMO levels of (8, 3)SWCNT and C60 satisfactorily exceeds the exciton binding energy to allow efficient exciton dissociation, the (8, 3)SWCNT/fullerodendron coaxial photocatalyst shows H2-evolving activity (QY = 0.015) upon 680-nm illumination, which is E22 absorption of (8, 3) SWCNT.

Catalytic asymmetric dihydroxylation of olefins with reusable OsO(4)(2-) on ion-exchangers: the scope and reactivity using various cooxidants.

PubMed

Choudary, Boyapati M; Chowdari, Naidu S; Jyothi, Karangula; Kantam, Mannepalli L

2002-05-15

Exchanger-OsO(4) catalysts are prepared by an ion-exchange technique using layered double hydroxides and quaternary ammonium salts covalently bound to resin and silica as ion-exchangers. The ion-exchangers with different characteristics and opposite ion selectivities are specially chosen to produce the best heterogeneous catalyst that can operate using the various cooxidants in the asymmetric dihydroxylation reaction. LDH-OsO(4) catalysts composed of different compositions are evaluated for the asymmetric dihydroxylation of trans-stilbene. Resin-OsO(4) and SiO(2)-OsO(4) designed to overcome the problems associated with LDH-OsO(4) indeed show consistent activity and enantioselectivity in asymmetric dihydroxylation of olefins using K(3)Fe(CN)(6) and molecular oxygen as cooxidants. Compared to the Kobayashi heterogeneous systems, resin-OsO(4) is a very efficient catalyst for the dihydroxylation of a wide variety of aromatic, aliphatic, acyclic, cyclic, mono-, di-, and trisubstituted olefins to afford chiral vicinal diols with high yields and enantioselectivities irrespective of the cooxidant used. Resin-OsO(4) is recovered quantitatively by a simple filtration and reused for a number of cycles with consistent activity. The high binding ability of the heterogeneous osmium catalyst enables the use of an equimolar ratio of ligand to osmium to give excellent enantioselectives in asymmetric dihydroxylation in contrast to the homogeneous osmium system in which excess molar quantities of the expensive chiral ligand to osmium are invariably used. The complexation of the chiral ligand (DHQD)(2)PHAL, having very large dimension, a prerequisite to obtain higher ee, is possible only with the OsO(4)(2-) located on the surface of the supports.

Experimental demonstration of topologically protected efficient sound propagation in an acoustic waveguide network

NASA Astrophysics Data System (ADS)

Wei, Qi; Tian, Ye; Zuo, Shu-Yu; Cheng, Ying; Liu, Xiao-Jun

2017-03-01

Acoustic topological states support sound propagation along the boundary in a one-way direction with inherent robustness against defects and disorders, leading to the revolution of the manipulation on acoustic waves. A variety of acoustic topological states relying on circulating fluid, chiral coupling, or temporal modulation have been proposed theoretically. However, experimental demonstration has so far remained a significant challenge, due to the critical limitations such as structural complexity and high losses. Here, we experimentally demonstrate an acoustic anomalous Floquet topological insulator in a waveguide network. The acoustic gapless edge states can be found in the band gap when the waveguides are strongly coupled. The scheme features simple structure and high-energy throughput, leading to the experimental demonstration of efficient and robust topologically protected sound propagation along the boundary. The proposal may offer a unique, promising application for design of acoustic devices in acoustic guiding, switching, isolating, filtering, etc.

High efficiency and non-Richardson thermionics in three dimensional Dirac materials

NASA Astrophysics Data System (ADS)

Huang, Sunchao; Sanderson, Matthew; Zhang, Yan; Zhang, Chao

2017-10-01

Three dimensional (3D) topological materials have a linear energy dispersion and exhibit many electronic properties superior to conventional materials such as fast response times, high mobility, and chiral transport. In this work, we demonstrate that 3D Dirac materials also have advantages over conventional semiconductors and graphene in thermionic applications. The low emission current suffered in graphene due to the vanishing density of states is enhanced by an increased group velocity in 3D Dirac materials. Furthermore, the thermal energy carried by electrons in 3D Dirac materials is twice of that in conventional materials with a parabolic electron energy dispersion. As a result, 3D Dirac materials have the best thermal efficiency or coefficient of performance when compared to conventional semiconductors and graphene. The generalized Richardson-Dushman law in 3D Dirac materials is derived. The law exhibits the interplay of the reduced density of states and enhanced emission velocity.

Enantioselective synthesis of chiral 3-aryl-1-indanones through rhodium-catalyzed asymmetric intramolecular 1,4-addition.

PubMed

Yu, Yue-Na; Xu, Ming-Hua

2013-03-15

Enantioselective synthesis of potentially useful chiral 3-aryl-1-indanones was achieved through a rhodium-catalyzed asymmetric intramolecular 1,4-addition of pinacolborane chalcone derivatives using extraordinary simple MonoPhos as chiral ligand under relatively mild conditions. This novel protocol offers an easy access to a wide variety of enantioenriched 3-aryl-1-indanone derivatives in high yields (up to 95%) with excellent enantioselectivities (up to 95% ee).

Critical Behavior and Macroscopic Phase Diagram of the Monoaxial Chiral Helimagnet Cr 1/3NbS 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clements, Eleanor M.; Das, Raja; Li, Ling

2017-07-26

Cr 1/3NbS 2 is a unique example of a hexagonal chiral helimagnet with high crystalline anisotropy, and has generated growing interest for a possible magnetic field control of the incommensurate spin spiral. Here, we construct a comprehensive phase diagram based on detailed magnetization measurements of a high quality single crystal of Cr 1/3NbS 2 over three magnetic field regions. An analysis of the critical properties in the forced ferromagnetic region yields 3D Heisenberg exponents β = 0.3460 ± 0.040, γ = 1.344 ± 0.002, and T C = 130.78 K ± 0.044, which are consistent with the localized nature themore » of Cr 3+ moments and suggest short-range ferromagnetic interactions. We exploit the temperature and magnetic field dependence of magnetic entropy change (ΔS M) to accurately map the nonlinear crossover to the chiral soliton lattice regime from the chiral helimagnetic phase. Our observations in the low field region are consistent with the existence of chiral ordering in a temperature range above the Curie temperature, T C < T < T*, where a first-order transition has been previously predicted. An analysis of the universal behavior of ΔS M(T,H) experimentally demonstrates for the first time the first-order nature of the onset of chiral ordering.« less

Enantioselective column coupled electrophoresis employing large bore capillaries hyphenated with tandem mass spectrometry for ultra-trace determination of chiral compounds in complex real samples.

PubMed

Piešťanský, Juraj; Maráková, Katarína; Kovaľ, Marián; Havránek, Emil; Mikuš, Peter

2015-12-01

A new multidimensional analytical approach for the ultra-trace determination of target chiral compounds in unpretreated complex real samples was developed in this work. The proposed analytical system provided high orthogonality due to on-line combination of three different methods (separation mechanisms), i.e. (1) isotachophoresis (ITP), (2) chiral capillary zone electrophoresis (chiral CZE), and (3) triple quadrupole mass spectrometry (QqQ MS). The ITP step, performed in a large bore capillary (800 μm), was utilized for the effective sample pretreatment (preconcentration and matrix clean-up) in a large injection volume (1-10 μL) enabling to obtain as low as ca. 80 pg/mL limits of detection for the target enantiomers in urine matrices. In the chiral CZE step, the different chiral selectors (neutral, ionizable, and permanently charged cyclodextrins) and buffer systems were tested in terms of enantioselectivity and influence on the MS detection response. The performance parameters of the optimized ITP - chiral CZE-QqQ MS method were evaluated according to the FDA guidance for bioanalytical method validation. Successful validation and application (enantioselective monitoring of renally eliminated pheniramine and its metabolite in human urine) highlighted great potential of this chiral approach in advanced enantioselective biomedical applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

No-Drag Frame for Anomalous Chiral Fluid

DOE PAGES

Stephanov, Mikhail A.; Yee, Ho-Ung

2016-03-24

For an anomalous fluid carrying dissipationless chiral magnetic and/or vortical currents we show that there is a frame in which a stationary obstacle experiences no drag, but energy and charge currents do not vanish, resembling superfluidity. Unlike ordinary superfluid flow, the anomalous chiral currents can transport entropy in this frame. Moreover, we show that the second law of thermodynamics completely determines the amounts of these anomalous nondissipative currents in the “no-drag frame” as polynomials in temperature and chemical potential with known anomaly coefficients. These general results are illustrated and confirmed by a calculation in the chiral kinetic theory and inmore » the quark-gluon plasma at high temperature.« less

Functionalization of nanostructured gold substrates with chiral chromophores for SERS applications: The case of 5-Aza[5]helicene.

PubMed

Zanchi, Chiara; Lucotti, Andrea; Cancogni, Damiano; Fontana, Francesca; Trusso, Sebastiano; Ossi, Paolo M; Tommasini, Matteo

2018-05-31

Nanostructured gold thin films can be fabricated by controlled pulsed laser deposition to get efficient sensors, with uniform morphology and optimized plasmon resonance, to be employed as plasmonic substrates in surface enhanced Raman scattering spectroscopy. By attaching 5-aza[5]helicen-6-yl-6-hexanethiol to such gold nanostructures, used in a previous work for label-free drug sensing with biomedical purposes, we successfully prepared functionalized substrates with remarkable surface enhanced Raman scattering activity. The long-term motivation is to develop probes for drug detection at low concentrations, where sensitivity to specific chiral targets is required. © 2018 Wiley Periodicals, Inc.

Development and validation of LC-HRMS and GC-NICI-MS methods for stereoselective determination of MDMA and its phase I and II metabolites in human urine

PubMed Central

Schwaninger, Andrea E.; Meyer, Markus R.; Huestis, Marilyn A.; Maurer, Hans H.

2013-01-01

3,4-Methylenedioxymethamphetamine (MDMA) is a racemic drug of abuse and its R- and S-enantiomers are known to differ in their dose-response curve. The S-enantiomer was shown to be eliminated at a higher rate than the R-enantiomer most likely explained by stereoselective metabolism that was observed in various in vitro experiments. The aim of this work was the development and validation of methods for evaluating the stereoselective elimination of phase I and particularly phase II metabolites of MDMA in human urine. Urine samples were divided into three different methods. Method A allowed stereoselective determination of the 4-hydroxy-3-methoxymethamphetamine (HMMA) glucuronides and only achiral determination of the intact sulfate conjugates of HMMA and 3,4-dihydroxymethamphetamine (DHMA) after C18 solid-phase extraction by liquid chromatography–high-resolution mass spectrometry with electrospray ionization. Method B allowed the determination of the enantiomer ratios of DHMA and HMMA sulfate conjugates after selective enzymatic cleavage and chiral analysis of the corresponding deconjugated metabolites after chiral derivatization with S-heptafluorobutyrylprolyl chloride using gas chromatography–mass spectrometry with negativeion chemical ionization. Method C allowed the chiral determination of MDMA and its unconjugated metabolites using method B without sulfate cleavage. The validation process including specificity, recovery, matrix effects, process efficiency, accuracy and precision, stabilities and limits of quantification and detection showed that all methods were selective, sensitive, accurate and precise for all tested analytes. PMID:21656610

Degenerate and chiral states in the extended Heisenberg model on the kagome lattice

NASA Astrophysics Data System (ADS)

Gómez Albarracín, F. A.; Pujol, P.

2018-03-01

We present a study of the low-temperature phases of the antiferromagnetic extended classical Heisenberg model on the kagome lattice, up to third-nearest neighbors. First, we focus on the degenerate lines in the boundaries of the well-known staggered chiral phases. These boundaries have either semiextensive or extensive degeneracy, and we discuss the partial selection of states by thermal fluctuations. Then, we study the model under an external magnetic field on these lines and in the staggered chiral phases. We pay particular attention to the highly frustrated point, where the three exchange couplings are equal. We show that this point can be mapped to a model with spin-liquid behavior and nonzero chirality. Finally, we explore the effect of Dzyaloshinskii-Moriya (DM) interactions in two ways: a homogeneous and a staggered DM interaction. In both cases, there is a rich low-temperature phase diagram, with different spontaneously broken symmetries and nontrivial chiral phases.

Engineering chiral porous metal-organic frameworks for enantioselective adsorption and separation

NASA Astrophysics Data System (ADS)

Peng, Yongwu; Gong, Tengfei; Zhang, Kang; Lin, Xiaochao; Liu, Yan; Jiang, Jianwen; Cui, Yong

2014-07-01

The separation of racemic molecules is of substantial significance not only for basic science but also for technical applications, such as fine chemicals and drug development. Here we report two isostructural chiral metal-organic frameworks decorated with chiral dihydroxy or -methoxy auxiliares from enantiopure tetracarboxylate-bridging ligands of 1,1‧-biphenol and a manganese carboxylate chain. The framework bearing dihydroxy groups functions as a solid-state host capable of adsorbing and separating mixtures of a range of chiral aromatic and aliphatic amines, with high enantioselectivity. The host material can be readily recycled and reused without any apparent loss of performance. The utility of the present adsorption separation is demonstrated in the large-scale resolution of racemic 1-phenylethylamine. Control experiments and molecular simulations suggest that the chiral recognition and separation are attributed to the different orientations and specific binding energies of the enantiomers in the microenvironment of the framework.

Enantiospecific electrodeposition of chiral CuO films on single-crystal Cu(111).

PubMed

Bohannan, Eric W; Kothari, Hiten M; Nicic, Igor M; Switzer, Jay A

2004-01-21

Epitaxial films of monoclinic CuO have been electrodeposited on single-crystal Cu(111) from solutions containing either (S,S)- or (R,R)-tartrate. X-ray pole figure analysis reveals that the CuO film grown from (S,S)-tartrate exhibits a (1) out-of-plane orientation while the film grown from (R,R)-tartrate has a (11) orientation. Even though CuO does not crystallize within a chiral space group, the orientations obtained exhibit a surface chirality similar to that obtained from high index fcc metal surfaces. The films were shown to be enantioselective toward the catalytic oxidation of tartrate molecules by cyclic voltammetry. The technique should prove to be applicable to the electrodeposition of chiral surfaces of other low-symmetry materials on achiral substrates and should prove to be of use to those interested in the synthesis, separation, and detection of chiral molecules.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazavov, A.; Ding, H. -T.; Hegde, P.

In this paper, we investigate the phase structure of QCD with three degenerate quark flavors as a function of the degenerate quark masses at vanishing baryon number density. We use the highly improved staggered quarks on lattices with temporal extent N τ = 6 and perform calculations for six values of quark masses, which in the continuum limit correspond to pion masses in the range 80 MeV ≲ m π ≲ 230 MeV. By analyzing the volume and temperature dependence of the chiral condensate and chiral susceptibility, we find no direct evidence for a first-order phase transition in this rangemore » of pion mass values. Finally, relying on the universal scaling behaviors of the chiral observables near an anticipated chiral critical point, we estimate an upper bound for the critical pion mass m c π ≲ 50 MeV, below which a region of first-order chiral phase transition is favored.« less

Graphene chiral liquid crystals and macroscopic assembled fibres

PubMed Central

Xu, Zhen; Gao, Chao

2011-01-01

Chirality and liquid crystals are both widely expressed in nature and biology. Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals. To date, chiral liquid crystals of 2D colloids have not been explored. As a typical 2D colloid, graphene is now receiving unprecedented attention. However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method. Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations. Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance. The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles. PMID:22146390

Optical rotation based chirality detection of enantiomers via weak measurement in frequency domain

NASA Astrophysics Data System (ADS)

Li, Dongmei; Guan, Tian; Liu, Fang; Yang, Anping; He, Yonghong; He, Qinghua; Shen, Zhiyuan; Xin, Meiguo

2018-05-01

A transmission optical rotation detection scheme based on a weak measurement was proposed for the chirality detection of enantiomers. In this transmission weak measurement system in the frequency domain, the optical activity of the chiral liquid sample was estimated with the central wavelength shift, by modifying the preselected polarization state with the optical rotation (OR). The central wavelength shift of output spectra is sensitive to the OR angle but immune to the interference of the refractive index change caused by measuring circumstances. Two isomers of chiral amino acid acquired opposite responses with this system, and a resolution of 2.17 × 10-9 mol/ml for Proline detection could be obtained. Such a resolution is about 2 orders of magnitude higher than that of common methods, which shows a high sensitivity. This proposed weak measurement scenario suggested an approach to polarimetry and provided a way to accurately assess molecular chirality.

Resonant Absorption in GaAs-Based Nanowires by Means of Photo-Acoustic Spectroscopy

NASA Astrophysics Data System (ADS)

Petronijevic, E.; Leahu, G.; Belardini, A.; Centini, M.; Li Voti, R.; Hakkarainen, T.; Koivusalo, E.; Guina, M.; Sibilia, C.

2018-03-01

Semiconductor nanowires made of high refractive index materials can couple the incoming light to specific waveguide modes that offer resonant absorption enhancement under the bandgap wavelength, essential for light harvesting, lasing and detection applications. Moreover, the non-trivial ellipticity of such modes can offer near field interactions with chiral molecules, governed by near chiral field. These modes are therefore very important to detect. Here, we present the photo-acoustic spectroscopy as a low-cost, reliable, sensitive and scattering-free tool to measure the spectral position and absorption efficiency of these modes. The investigated samples are hexagonal nanowires with GaAs core; the fabrication by means of lithography-free molecular beam epitaxy provides controllable and uniform dimensions that allow for the excitation of the fundamental resonant mode around 800 nm. We show that the modulation frequency increase leads to the discrimination of the resonant mode absorption from the overall absorption of the substrate. As the experimental data are in great agreement with numerical simulations, the design can be optimized and followed by photo-acoustic characterization for a specific application.

Chiral ligand exchange high-speed countercurrent chromatography: mechanism, application and comparison with conventional liquid chromatography in enantioseparation of aromatic α-hydroxyl acids

PubMed Central

Tong, Shengqiang; Shen, Mangmang; Cheng, Dongping; Ito, Yoichiro; Yan, Jizhong

2014-01-01

This work concentrates on the separation mechanism and application of chiral ligand exchange high-speed countercurrent chromatography (HSCCC) in enantioseparations, and comparison with traditional chiral ligand exchange high performance liquid chromatography (HPLC). The enantioseparation of ten aromatic α-hydroxyl acids were performed by these two chromatographic methods. Results showed that five of the racemates were successfully enantioseparated by HSCCC while only three of the racemates could be enantioseparated by HPLC using a suitable chiral ligand mobile phase additive. For HSCCC, the two-phase solvent system was composed of butanol-water (1:1, v/v), to which N-n-dodecyl-L-proline was added in the organic phase as chiral ligand and cupric acetate was added in the aqueous phase as a transition metal ion. Various operation parameters in HSCCC were optimized by enantioselective liquid-liquid extraction. Based on the results of the present studies the separation mechanism for HSCCC was proposed. For HPLC, the optimized mobile phase composed of aqueous solution containing 6 mmol L−1 L-phenylalanine and 3 mmol L−1 cupric sulfate and methanol was used for enantioseparation. Among three ligands tested on a conventional reverse stationary phase column, only one was found to be effective. In the present studies HSCCC presented unique advantages due to its high versatility of two-phase solvent systems and it could be used as an alternative method for enantioseparations. PMID:25087742

Terbium-Aspartic Acid Nanocrystals with Chirality-Dependent Tunable Fluorescent Properties.

PubMed

Ma, Baojin; Wu, Yu; Zhang, Shan; Wang, Shicai; Qiu, Jichuan; Zhao, Lili; Guo, Daidong; Duan, Jiazhi; Sang, Yuanhua; Li, Linlin; Jiang, Huaidong; Liu, Hong

2017-02-28

Terbium-aspartic acid (Tb-Asp) nanocrystals with chirality-dependent tunable fluorescent properties can be synthesized through a facile synthesis method through the coordination between Tb and Asp. Asp with different chirality (dextrorotation/d and levogyration/l) changes the stability of the coordination center following fluorescent absorption/emission ability differences. Compared with l-Asp, d-Asp can coordinate Tb to form a more stable center, following the higher quantum yield and longer fluorescence life. Fluorescence intensity of Tb-Asp linearly increases with increase ratio of d-Asp in the mixed chirality Tb-Asp system, and the fluorescent properties of Tb-Asp nanocrystals can be tuned by adjusting the chirality ratio. Tb-Asp nanocrystals possess many advantage, such as high biocompatibility, without any color in visible light irradiation, monodispersion with very small size, and long fluorescent life. Those characteristics will give them great potential in many application fields, such as low-cost antifake markers and advertisements using inkjet printers or for molds when dispersed in polydimethylsiloxane. In addition, europium can also be used to synthesize Eu-Asp nanoparticles. Importantly, the facile, low-cost, high-yield, mass-productive "green" process provides enormous advantages for synthesis and application of fluorescent nanocrystals, which will have great impact in nanomaterial technology.

Enantioselective synthesis of allylic esters via asymmetric allylic substitution with metal carboxylates using planar-chiral cyclopentadienyl ruthenium catalysts.

PubMed

Kanbayashi, Naoya; Onitsuka, Kiyotaka

2010-02-03

An asymmetric allylic substitution with sodium carboxylate using a planar-chiral cyclopentadienyl ruthenium complex has been developed. Optically active allylic esters were prepared in good yields with high regio- and enantioselectivities.

Chiral N,N'-Dioxide-Organocatalyzed Regio-, Diastereo- and Enantioselective Michael Addition-Alkylation Reaction.

PubMed

Feng, Juhua; Yuan, Xiao; Luo, Weiwei; Lin, Lili; Liu, Xiaohua; Feng, Xiaoming

2016-10-24

A highly regio-, diastereo- and enantioselective Michael addition-alkylation reaction between α-substituted cyano ketones and (Z)-bromonitrostyrenes has been realized by using a chiral N,N'-dioxide as organocatalyst. A variety of substrates performed well in this reaction, and the corresponding multifunctionalized chiral 2,3-dihydrofurans were obtained in up to 95 % yield with 95:5 dr and 93 % ee. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantioselective Synthesis of Chiral Cyclopent-2-enones by Nickel-Catalyzed Desymmetrization of Malonate Esters.

PubMed

Karad, Somnath Narayan; Panchal, Heena; Clarke, Christopher; Lewis, William; Lam, Hon Wai

2018-05-16

The enantioselective synthesis of highly functionalized chiral cyclopent-2-enones by the reaction of alkynyl malonate esters with arylboronic acids is described. These desymmetrizing arylative cyclizations are catalyzed by a chiral phosphinooxazoline-nickel complex, and cyclization is enabled by the reversible E/Z isomerization of alkenylnickel species. The general methodology is also applicable to the synthesis of 1,6-dihydropyridin-3(2H)-ones. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pd-Catalyzed Asymmetric β-Hydride Elimination En Route to Chiral Allenes

PubMed Central

Crouch, Ian T.; Neff, Robynne K.; Frantz, Doug E.

2013-01-01

We wish to report our preliminary results on the discovery and development of a catalytic, asymmetric β-hydride elimination from vinyl Pd(II)-complexes derived from enol triflates to access chiral allenes. To achieve this, we developed a class of chiral phosphite ligands that demonstrate high enantioselectivity, allow access of either allene enantiomer, and are readily synthesized. The methodology is demonstrated on over 20 substrates and application to the formal asymmetric total synthesis of the natural product, (+)-epibatidine, is also provided. PMID:23488914

Asymmetric Iridium Catalyzed C-C Coupling of Chiral Diols via Site-Selective Redox-Triggered Carbonyl Addition

PubMed Central

Shin, Inji; Krische, Michael J.

2015-01-01

Cyclometalated π-allyliridium C,O-benzoate complexes modified by axially chiral chelating phosphine ligands display a pronounced kinetic preference for primary alcohol dehydrogenation, enabling highly site-selective redox-triggered carbonyl additions of chiral primary-secondary 1,3-diols with exceptional levels of catalyst-directed diastereoselectivity. Unlike conventional methods for carbonyl allylation, the present redox-triggered alcohol C-H functionalizations bypass the use of protecting groups, premetalated reagents, and discrete alcohol-to-aldehyde redox reactions. PMID:26187028

Formation of Coaxial Nanocables with Amplified Supramolecular Chirality through an Interaction between Carbon Nanotubes and a Chiral π-Gelator.

PubMed

Vedhanarayanan, Balaraman; Nair, Vishnu S; Nair, Vijayakumar C; Ajayaghosh, Ayyappanpillai

2016-08-22

In an attempt to gather experimental evidence for the influence of carbon allotropes on supramolecular chirality, we found that carbon nanotubes (CNTs) facilitate amplification of the molecular chirality of a π-gelator (MC-OPV) to supramolecular helicity at a concentration much lower than that required for intermolecular interaction. For example, at a concentration 1.8×10(-4)  m, MC-OPV did not exhibit a CD signal; however, the addition of 0-0.6 mg of SWNTs resulted in amplified chirality as evident from the CD spectrum. Surprisingly, AFM analysis revealed the formation of thick helical fibers with a width of more than 100 nm. High-resolution TEM analysis and solid-state UV/Vis/NIR spectroscopy revealed that the thick helical fibers were cylindrical cables composed of individually wrapped and coaxially aligned SWNTs. Such an impressive effect of CNTs on supramolecular chirality and cylindrical-cable formation has not been reported previously. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hybridation of different chiral separation techniques with ICP-MS detection for the separation and determination of selenomethionine enantiomers: chiral speciation of selenized yeast.

PubMed

Méndez, S P; González, E B; Sanz-Medel, A

2001-05-01

Enantioseparation and determination of selenomethionine enantiomers in selenized yeast was investigated using chiral separation techniques based on different principles, coupled on-line to inductively coupled plasma mass spectrometry (ICP-MS) for selenium-specific detection. High performance liquid chromatography (HPLC) on a beta-cyclodestrin (beta-CD) column, cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC), gas chromatography (GC) on a Chirasil-L-Val column, and HPLC on a Chirobiotic T column have been investigated as the chiral separation techniques. For HPLC separation on the beta-CD column, and also for CD-MEKC, selenomethionine enantiomers were derivatized with NDA/CN(-). For chiral separation by GC, selenomethionine enantiomers were converted into their N-trifluoroacetyl (TFA)-O-alkyl esters. The developed hybridation methodologies are compared with respect to enantioselectivity, sensitivity and analysis time. The usefulness of the best-suited method [HPLC (Chirobiotic T)-ICP-MS] was demonstrated by its application to the successful chiral speciation of selenium and D-and L-selenomethionine content determination in selenized yeast. Copyright 2001 John Wiley & Sons, Ltd.

Chromatographic Studies of Protein-Based Chiral Separations

PubMed Central

Bi, Cong; Zheng, Xiwei; Azaria, Shiden; Beeram, Sandya; Li, Zhao; Hage, David S.

2016-01-01

The development of separation methods for the analysis and resolution of chiral drugs and solutes has been an area of ongoing interest in pharmaceutical research. The use of proteins as chiral binding agents in high-performance liquid chromatography (HPLC) has been an approach that has received particular attention in such work. This report provides an overview of proteins that have been used as binding agents to create chiral stationary phases (CSPs) and in the use of chromatographic methods to study these materials and protein-based chiral separations. The supports and methods that have been employed to prepare protein-based CSPs will also be discussed and compared. Specific types of CSPs that are considered include those that employ serum transport proteins (e.g., human serum albumin, bovine serum albumin, and alpha1-acid glycoprotein), enzymes (e.g., penicillin G acylase, cellobiohydrolases, and α-chymotrypsin) or other types of proteins (e.g., ovomucoid, antibodies, and avidin or streptavidin). The properties and applications for each type of protein and CSP will also be discussed in terms of their use in chromatography and chiral separations. PMID:28344977

Elucidation of the Chromatographic Enantiomer Elution Order Through Computational Studies.

PubMed

Sardella, Roccaldo; Ianni, Federica; Macchiarulo, Antonio; Pucciarini, Lucia; Carotti, Andrea; Natalini, Benedetto

2018-01-01

During the last twenty years, the interest towards the development of chiral compound has exponentially been increased. Indeed, the set-up of suitable asymmetric enantioselective synthesis protocols is currently one of the focuses of many pharmaceutical research projects. In this scenario, chiral HPLC separations have gained great importance as well, both for analytical- and preparative-scale applications, the latter devoted to the quantitative isolation of enantiopure compounds. Molecular modelling and quantum chemistry methods can be fruitfully applied to solve chirality related problems especially when enantiomerically pure reference standards are missing. In this framework, with the aim to explain the molecular basis of the enantioselective retention, we performed computational studies to rationalize the enantiomer elution order with both low- and high-molecular weight chiral selectors. Semi-empirical and quantum mechanical computational procedures were successfully applied in the domains of chiral ligand-exchange and chiral ion-exchange chromatography, as well as in studies dealing with the use of polysaccharide-based enantioresolving materials. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Mechanisms for the inversion of chirality: Global reaction route mapping of stereochemical pathways in a probable chiral extraterrestrial molecule, 2-aminopropionitrile

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Ramanpreet; Vikas, E-mail: qlabspu@pu.ac.in, E-mail: qlabspu@yahoo.com

2015-02-21

2-Aminopropionitrile (APN), a probable candidate as a chiral astrophysical molecule, is a precursor to amino-acid alanine. Stereochemical pathways in 2-APN are explored using Global Reaction Route Mapping (GRRM) method employing high-level quantum-mechanical computations. Besides predicting the conventional mechanism for chiral inversion that proceeds through an achiral intermediate, a counterintuitive flipping mechanism is revealed for 2-APN through chiral intermediates explored using the GRRM. The feasibility of the proposed stereochemical pathways, in terms of the Gibbs free-energy change, is analyzed at the temperature conditions akin to the interstellar medium. Notably, the stereoinversion in 2-APN is observed to be more feasible than themore » dissociation of 2-APN and intermediates involved along the stereochemical pathways, and the flipping barrier is observed to be as low as 3.68 kJ/mol along one of the pathways. The pathways proposed for the inversion of chirality in 2-APN may provide significant insight into the extraterrestrial origin of life.« less

Influence of a change in helical twisting power of photoresponsive chiral dopants on rotational manipulation of micro-objects on the surface of chiral nematic liquid crystalline films.

PubMed

Thomas, Reji; Yoshida, Yohei; Akasaka, Takehito; Tamaoki, Nobuyuki

2012-09-24

Herein we report a group of five planar chiral molecules as photon-mode chiral switches for the reversible control of the self-assembled superstructures of doped chiral nematic liquid crystals. The chiral switches are composed of an asymmetrically substituted aromatic moiety and a photoisomerizing azobenzene unit connected in a cyclic manner through methylene spacers of varying lengths. All the molecules show conformational restriction in the rotation of the asymmetrically substituted aromatic moiety in both the E and Z states of the azobenzene units resulting in planar chirality with separable enantiomers. Our newly synthesized compounds in pure enantiomeric form show high helical twisting power (HTP) in addition to an improved change in HTP between the E and Z states. The molecule with a diphenylnaphthalene unit shows the highest ever known initial helical twisting power among chiral dopants with planar chirality. In addition to the reversible tuning of reflection colors, we employed the enantiomers of these five compounds in combination with four nematic liquid crystalline hosts to study their properties as molecular machines; the change in HTP of the chiral dopant upon photoisomerization induces rotation of the texture of the liquid crystal surfaces. Importantly, this study has revealed a linear dependence of the ratio of the difference between HTPs before and after irradiation against the absolute value of the initial HTP, not the absolute value of the change in helical twisting power between two states, on the angle of rotation of micro-objects on chiral nematic liquid crystalline films. This study has also revealed that a change in irradiation intensity does not affect the maximum angle of rotation, but it does affect the speed of rotational reorganization of the cholesteric helix. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Similarity-transformed chiral NN + 3N interactions for the ab initio description of 12C and 16O.

PubMed

Roth, Robert; Langhammer, Joachim; Calci, Angelo; Binder, Sven; Navrátil, Petr

2011-08-12

We present first ab initio no-core shell model (NCSM) calculations using similarity renormalization group (SRG) transformed chiral two-nucleon (NN) plus three-nucleon (3N) interactions for nuclei throughout the p-shell, particularly (12)C and (16)O. By introducing an adaptive importance truncation for the NCSM model space and an efficient JT-coupling scheme for the 3N matrix elements, we are able to surpass previous NCSM studies including 3N interactions. We present ground and excited states in (12)C and (16)O for model spaces up to N(max) = 12 including full 3N interactions. We analyze the contributions of induced and initial 3N interactions and probe induced 4N terms through the sensitivity of the energies on the SRG flow parameter. Unlike for light p-shell nuclei, SRG-induced 4N contributions originating from the long-range two-pion terms of the chiral 3N interaction are sizable in (12)C and (16)O.

Establishing a Mathematical Equations and Improving the Production of L-tert-Leucine by Uniform Design and Regression Analysis.

PubMed

Jiang, Wei; Xu, Chao-Zhen; Jiang, Si-Zhi; Zhang, Tang-Duo; Wang, Shi-Zhen; Fang, Bai-Shan

2017-04-01

L-tert-Leucine (L-Tle) and its derivatives are extensively used as crucial building blocks for chiral auxiliaries, pharmaceutically active ingredients, and ligands. Combining with formate dehydrogenase (FDH) for regenerating the expensive coenzyme NADH, leucine dehydrogenase (LeuDH) is continually used for synthesizing L-Tle from α-keto acid. A multilevel factorial experimental design was executed for research of this system. In this work, an efficient optimization method for improving the productivity of L-Tle was developed. And the mathematical model between different fermentation conditions and L-Tle yield was also determined in the form of the equation by using uniform design and regression analysis. The multivariate regression equation was conveniently implemented in water, with a space time yield of 505.9 g L -1  day -1 and an enantiomeric excess value of >99 %. These results demonstrated that this method might become an ideal protocol for industrial production of chiral compounds and unnatural amino acids such as chiral drug intermediates.

Enantiomeric separation by capillary electrochromatography on a sulfated poly β-cyclodextrin modified silica-based monolith.

PubMed

Yuan, Ruijuan; Wang, Yan; Ding, Guosheng

2010-01-01

A sulfated poly β-cyclodextrin (SPCD) modified silica-based monolithic column was prepared for enantiomeric separation. First, 2-hydroxy-3-allyloxy-propyl-β-cyclodextrin (allyl-β-CD) was bonded onto a bifunctional reagent 3-(methacryloxy)propyltriethoxysilane (γ-MAPS) modified silica-based monolith through radical polymerization; the column was then sulfated with chlorosulfonic acid. The SPCD chiral stationary phase resolved the boring problem associated with desalting when sulfated CDs were synthesized to act as chiral additives. The inorganic salt in the column introduced during the sulfating process could be easily removed by washing the column with water for some time. Chiral compounds investigated were successfully resolved into their enantiomers on the SPCD modified monolith in the capillary electrochromatography (CEC) mode. Due to the existence of the -SO(3)H group, electrosmotic flow (EOF) was obviously increased, and all of the separations could be carried out in 20 min with only a minor loss in the column efficiency and resolution.

A novel in situ strategy for the preparation of a β-cyclodextrin/polydopamine-coated capillary column for capillary electrochromatography enantioseparations.

PubMed

Guo, Heying; Niu, Xiaoying; Pan, Congjie; Yi, Tao; Chen, Hongli; Chen, Xingguo

2017-06-01

Inspired by the chiral recognition ability of β-cyclodextrin and the natural adhesive properties of polydopamine under alkaline conditions, in this study, a rapid and in situ modification strategy was developed to fabricate β-cyclodextrin/polydopamine composite material coated-capillary columns for open tubular capillary electrochromatography. The results of scanning electron microscopy, FTIR spectroscopy, streaming potential, and electro-osmotic flow studies indicated that β-cyclodextrin/polydopamine was successfully fixed on the inner wall of the capillary column. This coating can be achieved within 1 h affording a greatly reduced capillary preparation time. The performance of the β-cyclodextrin/polydopamine-coated capillary was validated by the analysis of seven pairs of chiral analytes, namely epinephrine, norepinephrine, isoprenaline, terbutaline, verapamil, tryptophane, carvedilol. Good enantioseparation efficiencies were achieved for all. For three consecutive runs, the relative standard deviations for the migration times of the analytes for intraday, interday, and column-to-column repeatability were in the range of 0.41-1.74, 1.03-4.18, and 1.66-8.24%, respectively. Moreover, the separation efficiency of the β-cyclodextrin/polydopamine-coated capillary column did not decrease obviously over 90 runs. The strategy should also be feasible to introduce and immobilize other chiral selectors on the inner walls surface of capillary columns. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Floquet high Chern insulators in periodically driven chirally stacked multilayer graphene

NASA Astrophysics Data System (ADS)

Li, Si; Liu, Cheng-Cheng; Yao, Yugui

2018-03-01

Chirally stacked N-layer graphene is a semimetal with ±p N band-touching at two nonequivalent corners in its Brillioun zone. We predict that an off-resonant circularly polarized light (CPL) drives chirally stacked N-layer graphene into a Floquet Chern insulators (FCIs), aka quantum anomalous Hall insulators, with tunable high Chern number C F = ±N and large gaps. A topological phase transition between such a FCI and a valley Hall (VH) insulator with high valley Chern number C v = ±N induced by a voltage gate can be engineered by the parameters of the CPL and voltage gate. We propose a topological domain wall between the FCI and VH phases, along which perfectly valley-polarized N-channel edge states propagate unidirectionally without backscattering.

Copper-catalyzed selective hydroamination reactions of alkynes

PubMed Central

Shi, Shi-Liang; Buchwald, Stephen L.

2014-01-01

The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a longstanding goal of chemical research. Despite the centrality of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective, and step-efficient synthesis of amines is still needed. In this work we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines, and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio-, and stereoselectivity. This methodology was applied to the asymmetric synthesis of rivastigmine and the formal synthesis of several other pharmaceutical agents, including duloxetine, atomoxetine, fluoxetine, and tolterodine. PMID:25515888

Color-tunable, aggregation-induced emission of a butterfly-shaped molecule comprising a pyran skeleton and two cholesteryl wings.

PubMed

Tong, Hui; Hong, Yuning; Dong, Yongqiang; Ren, Yan; Häussler, Matthias; Lam, Jacky W Y; Wong, Kam Sing; Tang, Ben Zhong

2007-03-01

A chiral pyran derivative containing two cholesteryl groups (1) is synthesized, and its optical properties are investigated. Whereas the isolated molecule of 1 is virtually nonluminescent in dilute solutions, it becomes highly emissive with a 2 orders of magnitude increase in fluorescence quantum yield upon aggregation in poor solvents or in solid state, showing a novel phenomenon of aggregation-induced emission (AIE). The color and efficiency of the AIE of 1 can be tuned by varying the morphology of its aggregates: photoluminescence of its aggregates formed in a tetrahydrofuran/water mixture progressively red-shifts (green --> yellow --> red) with increasing water content of the mixture, with the crystalline aggregates emitting bluer lights in higher efficiencies than their amorphous counterparts.

Copper-catalysed selective hydroamination reactions of alkynes

NASA Astrophysics Data System (ADS)

Shi, Shi-Liang; Buchwald, Stephen L.

2015-01-01

The development of selective reactions that utilize easily available and abundant precursors for the efficient synthesis of amines is a long-standing goal of chemical research. Despite the centrality of amines in a number of important research areas, including medicinal chemistry, total synthesis and materials science, a general, selective and step-efficient synthesis of amines is still needed. Here, we describe a set of mild catalytic conditions utilizing a single copper-based catalyst that enables the direct preparation of three distinct and important amine classes (enamines, α-chiral branched alkylamines and linear alkylamines) from readily available alkyne starting materials with high levels of chemo-, regio- and stereoselectivity. This methodology was applied to the asymmetric synthesis of rivastigmine and the formal synthesis of several other pharmaceutical agents, including duloxetine, atomoxetine, fluoxetine and tolterodine.

Light-front representation of chiral dynamics in peripheral transverse densities

DOE PAGES

Granados, Carlos G.; Weiss, Christian

2015-07-31

The nucleon's electromagnetic form factors are expressed in terms of the transverse densities of charge and magnetization at fixed light-front time. At peripheral transverse distances b = O(M_pi^{-1}) the densities are governed by chiral dynamics and can be calculated model-independently using chiral effective field theory (EFT). We represent the leading-order chiral EFT results for the peripheral transverse densities as overlap integrals of chiral light-front wave functions, describing the transition of the initial nucleon to soft pion-nucleon intermediate states and back. The new representation (a) explains the parametric order of the peripheral transverse densities; (b) establishes an inequality between the spin-independentmore » and -dependent densities; (c) exposes the role of pion orbital angular momentum in chiral dynamics; (d) reveals a large left-right asymmetry of the current in a transversely polarized nucleon and suggests a simple interpretation. The light-front representation enables a first-quantized, quantum-mechanical view of chiral dynamics that is fully relativistic and exactly equivalent to the second-quantized, field-theoretical formulation. It relates the charge and magnetization densities measured in low-energy elastic scattering to the generalized parton distributions probed in peripheral high-energy scattering processes. The method can be applied to nucleon form factors of other operators, e.g. the energy-momentum tensor.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Li; Zhang, Yun; Wei, Zhehao

We report in this work detailed measurements on the chiral and achiral sum-frequency vibrational spectra in the C-H stretching vibration region (2800-3050cm-1) of the air/liquid interfaces of R-limonene and S-limonene, using the recently developed high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS). The achiral SFG spectra of R-limonene and S-limonene, as well as the equal amount (50/50) racemic mixture show that the enantiomers are with the same interfacial orientations. The interference chiral SFG spectra of the limonene enantiomers exhibit spectral signature from chiral response of the Cα-H stretching mode, and spectral signature from prochiral response of the CH2 asymmetric stretching mode,more » respectively. The chiral spectral feature of the Cα-H stretching mode changes sign from R-limonene to S-limonene, and disappears for the 50/50 racemic mixture. While the prochiral spectral feature of the CH2 asymmetric stretching mode is the same for R-limonene and S-limonene, and also surprisingly remains the same for the 50/50 racemic mixture. These results provided detail information in understanding the structure and chirality of molecular interfaces, and demonstrated the sensitivity and potential of SFG-VS as unique spectroscopic tool for chirality characterization and chiral recognition at the molecular interface.« less

Circularly Polarized Light with Sense and Wavelengths To Regulate Azobenzene Supramolecular Chirality in Optofluidic Medium.

PubMed

Wang, Laibing; Yin, Lu; Zhang, Wei; Zhu, Xiulin; Fujiki, Michiya

2017-09-20

Circularly polarized light (CPL) as a massless physical force causes absolute asymmetric photosynthesis, photodestruction, and photoresolution. CPL handedness has long been believed to be the determining factor in the resulting product's chirality. However, product chirality as a function of the CPL handedness, irradiation wavelength, and irradiation time has not yet been studied systematically. Herein, we investigate this topic using achiral polymethacrylate carrying achiral azobenzene as micrometer-size aggregates in an optofluidic medium with a tuned refractive index. Azobenzene chirality with a high degree of dissymmetry ratio (±1.3 × 10 -2 at 313 nm) was generated, inverted, and switched in multiple cycles by irradiation with monochromatic incoherent CPL (313, 365, 405, and 436 nm) for 20 s using a weak incoherent light source (≈ 30 μW·cm -2 ). Moreover, the optical activity was retained for over 1 week in the dark. Photoinduced chirality was swapped by the irradiating wavelength, regardless of whether the CPL sense was the same. This scenario is similar to the so-called Cotton effect, which was first described in 1895. The tandem choice of both CPL sense and its wavelength was crucial for azobenzene chirality. Our experimental proof and theoretical simulation should provide new insight into the chirality of CPL-controlled molecules, supramolecules, and polymers.

Chiral analysis of UV nonabsorbing compounds by capillary electrophoresis using macrocyclic antibiotics: 1. Separation of aspartic and glutamic acid enantiomers.

PubMed

Bednar, P; Aturki, Z; Stransky, Z; Fanali, S

2001-07-01

Glycopeptide antibiotics, namely vancomycin or teicoplanin, were evaluated in capillary electrophoresis for the analysis of UV nonabsorbing compounds such as aspartic and glutamic acid enantiomers. Electrophoretic runs were performed in laboratory-made polyacrylamide-coated capillaries using the partial filling-counter current method in order to avoid the presence on the detector path of the absorbing chiral selector. The background electrolyte consisted of an aqueous or aqueous-organic buffer in the pH range of 4.5-6.5 of sorbic acid/histidine and the appropriate concentration of chiral selector. Several experimental parameters such as antibiotic concentration and type, buffer pH, organic modifier, type and concentration of absorbing co-ion (for the indirect UV detection) were studied in order to find the optimum conditions for the chiral resolution of the two underivatized amino acids in their enantiomers. Among the two investigated chiral selectors, vancomycin resulted to be the most useful chiral selector allowing relatively high chiral resolution of the studied compounds even at low concentration. The optimized method (10 mM sorbic acid/histidine, pH 5, and 10 mM of vancomycin) was used for the analysis of real samples such as teeth dentine and beer.

Normal and polar-organic-phase high-performance liquid chromatographic enantioresolution of omeprazole, rabeprazole, lansoprazole and pantoprazole using monochloro-methylated cellulose-based chiral stationary phase and determination of dexrabeprazole.

PubMed

Dixit, Shuchi; Dubey, Rituraj; Bhushan, Ravi

2014-01-01

Enantioresolution of four anti-ulcer drugs (chiral sulfoxides), namely, omeprazole, rabeprazole, lansoprazole and pantoprazole, was carried out by high-performance liquid chromatography using a polysaccharide-based chiral stationary phase consisting of monochloromethylated cellulose (Lux cellulose-2) under normal and polar-organic-phase conditions with ultraviolet detection at 285 nm. The method was validated for linearity, accuracy, precision, robustness and limit of detection. The optimized enantioresolution method was compared for both the elution modes. The optimized method was further utilized to check the enantiomeric purity of dexrabeprazole. Copyright © 2013 John Wiley & Sons, Ltd.

Rhodium/chiral diene-catalyzed asymmetric 1,4-addition of arylboronic acids to chromones: a highly enantioselective pathway for accessing chiral flavanones.

PubMed

He, Qijie; So, Chau Ming; Bian, Zhaoxiang; Hayashi, Tamio; Wang, Jun

2015-03-01

Chromone has been noted to be one of the most challenging substrates in the asymmetric 1,4-addition of α,β-unsaturated carbonyl compounds. By employing the rhodium complex associated with a chiral diene ligand, (R,R)-Ph-bod*, the 1,4-addition of a variety of arylboronic acids was realized to give high yields of the corresponding flavanones with excellent enantioselectivities (≥97% ee, 99% ee for most substrates). Ring-opening side products, which would lead to erosion of product enantioselectivity, were not observed under the stated reaction conditions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

N-Methylpyrrolidone Hydroperoxide/Cs2 CO3 as an Excellent Reagent System for the Hydroxy-Directed Diastereoselective Epoxidation of Electron-Deficient Olefins.

PubMed

Victor, Napoleon John; Gana, Janardhanan; Muraleedharan, Kannoth Manheri

2015-10-12

This report introduces N-methylpyrrolidone hydroperoxide (NMPOOH)/base as an excellent reagent system for hydroxy-directed syn selective epoxidation of electron-deficient olefins, characterized by high diastereoselectivity, short reaction times and remarkable chemoselectivity, especially in presence of oxidatively labile nitrogen or sulfur atoms. NMPOOH also proves efficient in the oxidation of electron-deficient aromatic aldehydes, in the removal of oxazolidinone chiral auxiliary, and in the functionalization of alkenes and alkynes, showing wide application potential. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-Catalyzed Asymmetric N-H Functionalization of Quinazolinones with Allenes and Allylic Carbonates: The First Enantioselective Formal Total Synthesis of (-)-Chaetominine.

PubMed

Zhou, Yirong; Breit, Bernhard

2017-12-22

An unprecedented asymmetric N-H functionalization of quinazolinones with allenes and allylic carbonates was successfully achieved by rhodium catalysis with the assistance of chiral bidentate diphosphine ligands. The high efficiency and practicality of this method was demonstrated by a low catalyst loading of 1 mol % as well as excellent chemo-, regio-, and enantioselectivities with broad functional group compatibility. Furthermore, this newly developed strategy was applied as key step in the first enantioselective formal total synthesis of (-)-chaetominine. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The development of chiral nematic mesoporous materials.

PubMed

Kelly, Joel A; Giese, Michael; Shopsowitz, Kevin E; Hamad, Wadood Y; MacLachlan, Mark J

2014-04-15

Cellulose nanocrystals (CNCs) are obtained from the sulfuric acid-catalyzed hydrolysis of bulk cellulose. The nanocrystals have diameters of ~5-15 nm and lengths of ~100-300 nm (depending on the cellulose source and hydrolysis conditions). This lightweight material has mostly been investigated to reinforce composites and polymers because it has remarkable strength that rivals carbon nanotubes. But CNCs have an additional, less explored property: they organize into a chiral nematic (historically referred to as cholesteric) liquid crystal in water. When dried into a thin solid film, the CNCs retain the helicoidal chiral nematic order and assemble into a layered structure where the CNCs have aligned orientation within each layer, and their orientation rotates through the stack with a characteristic pitch (repeating distance). The cholesteric ordering can act as a 1-D photonic structure, selectively reflecting circularly polarized light that has a wavelength nearly matching the pitch. During CNC self-assembly, it is possible to add sol-gel precursors, such as Si(OMe)4, that undergo hydrolysis and condensation as the solvent evaporates, leading to a chiral nematic silica/CNC composite material. Calcination of the material in air destroys the cellulose template, leaving a high surface area mesoporous silica film that has pore diameters of ~3-10 nm. Importantly, the silica is brilliantly iridescent because the pores in its interior replicate the chiral nematic structure. These films may be useful as optical filters, reflectors, and membranes. In this Account, we describe our recent research into mesoporous films with chiral nematic order. Taking advantage of the chiral nematic order and nanoscale of the CNC templates, new functional materials can be prepared. For example, heating the silica/CNC composites under an inert atmosphere followed by removal of the silica leaves highly ordered, mesoporous carbon films that can be used as supercapacitor electrodes. The composition of the mesoporous films can be varied by using assorted organosilica precursors. After removal of the cellulose by acid-catalyzed hydrolysis, highly porous, iridescent organosilica films are obtained. These materials are flexible and offer the ability to tune the chemical and mechanical properties through variation of the organic spacer. Chiral nematic mesoporous silica and organosilica materials, obtainable as centimeter-scale freestanding films, are interesting hosts for nanomaterials. When noble metal nanoparticles are incorporated into the pores, they show strong circular dichroism signals associated with their surface plasmon resonances that arise from dipolar coupling of the particles within the chiral nematic host. Fluorescent conjugated polymers show induced circular dichroism spectra when encapsulated in the chiral nematic host. The porosity, film structure, and optical properties of these materials could enable their use in sensors. We describe the development of chiral nematic mesoporous silica and organosilica, demonstrate different avenues of host-guest chemistry, and identify future directions that exploit the unique combination of properties present in these materials. The examples covered in this Account demonstrate that there is a rich diversity of composite materials accessible using CNC templating.

Capillary electrophoretic enantioseparation of basic drugs using a new single-isomer cyclodextrin derivative and theoretical study of the chiral recognition mechanism.

PubMed

Liu, Yongjing; Deng, Miaoduo; Yu, Jia; Jiang, Zhen; Guo, Xingjie

2016-05-01

A novel single-isomer cyclodextrin derivative, heptakis {2,6-di-O-[3-(1,3-dicarboxyl propylamino)-2-hydroxypropyl]}-β-cyclodextrin (glutamic acid-β-cyclodextrin) was synthesized and used as a chiral selector in capillary electrophoresis for the enantioseparation of 12 basic drugs, including terbutaline, clorprenaline, tulobuterol, clenbuterol, procaterol, carvedilol, econazole, miconazole, homatropine methyl bromide, brompheniramine, chlorpheniramine and pheniramine. The primary factors affecting separation efficiency, which include the background electrolyte pH, the concentration of glutamic acid-β-cyclodextrin and phosphate buffer concentration, were investigated. Satisfactory enantioseparations were obtained using an uncoated fused-silica capillary of 50 cm (effective length 40 cm) × 50 μm id with 120 mM phosphate buffer (pH 2.5-4.0) containing 0.5-4.5 mM glutamic acid-β-cyclodextrin as background electrolyte. A voltage of 20 kV was applied and the capillary temperature was kept at 20°C. The results proved that glutamic acid-β-cyclodextrin was an effective chiral selector for studied 12 basic drugs. Moreover, the possible chiral recognition mechanism of brompheniramine, chlorpheniramine and pheniramine on glutamic acid-β-cyclodextrin was investigated using the semi-empirical Parametric Method 3. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral bis(amino acid)- and bis(amino alcohol)-oxalamide gelators. Gelation properties, self-assembly motifs and chirality effects.

PubMed

Frkanec, Leo; Zinić, Mladen

2010-01-28

Bis(amino acid)- and bis(amino alcohol)oxalamide gelators represent the class of versatile gelators whose gelation ability is a consequence of strong and directional intermolecular hydrogen bonding provided by oxalamide units and lack of molecular symmetry due to the presence of two chiral centres. Bis(amino acid)oxalamides exhibit ambidextrous gelation properties, being capable to form gels with apolar and also highly polar solvent systems and tend to organise into bilayers or inverse bilayers in hydrogel or organic solvent gel assemblies, respectively. (1)H NMR and FTIR studies of gels revealed the importance of the equilibrium between the assembled network and smaller dissolved gelator assemblies. The organisation in gel assemblies deduced from spectroscopic structural studies are in certain cases closely related to organisations found in the crystal structures of selected gelators, confirming similar organisations in gel assemblies and in the solid state. The pure enantiomer/racemate gelation controversy is addressed and the evidence provided that rac-16 forms a stable toluene gel due to resolution into enantiomeric bilayers, which then interact giving gel fibres and a network of different morphology compared to its (S,S)-enantiomer gel. The TEM investigation of both gels confirmed distinctly different gel morphologies, which allowed the relationship between the stereochemical form of the gelator, the fibre and the network morphology and the network solvent immobilisation capacity to be proposed. Mixing of the constitutionally different bis(amino acid) and bis(amino alcohol)oxalamide gelators resulted in some cases in highly improved gelation efficiency denoted as synergic gelation effect (SGE), being highly dependent also on the stereochemistry of the component gelators. Examples of photo-induced gelation based on closely related bis(amino acid)-maleic acid amide and -fumaramide and stilbene derived oxalamides where gels form by irradiation of the solution of a non-gelling isomer and its photo-isomerisation into gelling isomer are provided, as well as examples of luminescent gels, gel-based fluoride sensors, LC-gels and nanoparticle-hydrogel composites.

Highly selective anti-Prelog synthesis of optically active aryl alcohols by recombinant Escherichia coli expressing stereospecific alcohol dehydrogenase.

PubMed

Li, Ming; Nie, Yao; Mu, Xiao Qing; Zhang, Rongzhen; Xu, Yan

2016-07-03

Biocatalytic asymmetric synthesis has been widely used for preparation of optically active chiral alcohols as the important intermediates and precursors of active pharmaceutical ingredients. However, the available whole-cell system involving anti-Prelog specific alcohol dehydrogenase is yet limited. A recombinant Escherichia coli system expressing anti-Prelog stereospecific alcohol dehydrogenase from Candida parapsilosis was established as a whole-cell system for catalyzing asymmetric reduction of aryl ketones to anti-Prelog configured alcohols. Using 2-hydroxyacetophenone as the substrate, reaction factors including pH, cell status, and substrate concentration had obvious impacts on the outcome of whole-cell biocatalysis, and xylose was found to be an available auxiliary substrate for intracellular cofactor regeneration, by which (S)-1-phenyl-1,2-ethanediol was achieved with an optical purity of 97%e.e. and yield of 89% under the substrate concentration of 5 g/L. Additionally, the feasibility of the recombinant cells toward different aryl ketones was investigated, and most of the corresponding chiral alcohol products were obtained with an optical purity over 95%e.e. Therefore, the whole-cell system involving recombinant stereospecific alcohol dehydrogenase was constructed as an efficient biocatalyst for highly enantioselective anti-Prelog synthesis of optically active aryl alcohols and would be promising in the pharmaceutical industry.

The phi-meson and Chiral-mass-meson production in heavy-ion collisions as potential probes of quark-gluon-plasma and Chiral symmetry transitions

NASA Technical Reports Server (NTRS)

Takahashi, Y.; Eby, P. B.

1985-01-01

Possibilities of observing abundances of phi mesons and narrow hadronic pairs, as results of QGP and Chiral transitions, are considered for nucleus-nucleus interactions. Kinematical requirements in forming close pairs are satisfied in K+K decays of S(975) and delta (980) mesons with small phi, and phi (91020) mesons with large PT, and in pi-pi decays of familiar resonance mesons only in a partially restored chiral symmetry. Gluon-gluon dominance in QGP can enhance phi meson production. High hadronization rates of primordial resonance mesons which form narrow hadronic pairs are not implausible. Past cosmic ray evidences of anomalous phi production and narrow pair abundances are considered.

Pion-nucleon scattering: from chiral perturbation theory to Roy-Steiner equations

NASA Astrophysics Data System (ADS)

Kubis, Bastian; Hoferichter, Martin; de Elvira, Jacobo Ruiz; Meißner, Ulf-G.

2016-11-01

Ever since Weinberg's seminal predictions of the pion-nucleon scattering amplitudes at threshold, this process has been of central interest for the study of chiral dynamics involving nucleons. The scattering lengths or the pion-nucleon σ-term are fundamental quantities characterizing the explicit breaking of chiral symmetry by means of the light quark masses. On the other hand, pion-nucleon dynamics also strongly affects the long-range part of nucleon-nucleon potentials, and hence has a far-reaching impact on nuclear physics. We discuss the fruitful combination of dispersion-theoretical methods, in the form of Roy-Steiner equations, with chiral dynamics to determine pion-nucleon scattering amplitudes at low energies with high precision.*

Chiral drug analysis using mass spectrometric detection relevant to research and practice in clinical and forensic toxicology.

PubMed

Schwaninger, Andrea E; Meyer, Markus R; Maurer, Hans H

2012-12-21

This paper reviews analytical approaches published in 2002-2012 for chiral drug analysis and their relevance in research and practice in the field of clinical and forensic toxicology. Separation systems such as gas chromatography, high performance liquid chromatography, capillary electromigration, and supercritical fluid chromatography, all coupled to mass spectrometry, are discussed. Typical applications are reviewed for relevant chiral analytes such as amphetamines and amphetamine-derived designer drugs, methadone, tramadol, psychotropic and other CNS acting drugs, anticoagulants, cardiovascular drugs, and some other drugs. Usefulness of chiral drug analysis in the interpretation of analytical results in clinical and forensic toxicology is discussed as well. Copyright © 2012 Elsevier B.V. All rights reserved.

Scaleable catalytic asymmetric Strecker syntheses of unnatural alpha-amino acids.

PubMed

Zuend, Stephan J; Coughlin, Matthew P; Lalonde, Mathieu P; Jacobsen, Eric N

2009-10-15

Alpha-amino acids are the building blocks of proteins and are widely used as components of medicinally active molecules and chiral catalysts. Efficient chemo-enzymatic methods for the synthesis of enantioenriched alpha-amino acids have been developed, but it is still a challenge to obtain non-natural amino acids. Alkene hydrogenation is broadly useful for the enantioselective catalytic synthesis of many classes of amino acids, but it is not possible to obtain alpha-amino acids bearing aryl or quaternary alkyl alpha-substituents using this method. The Strecker synthesis-the reaction of an imine or imine equivalent with hydrogen cyanide, followed by nitrile hydrolysis-is an especially versatile chemical method for the synthesis of racemic alpha-amino acids. Asymmetric Strecker syntheses using stoichiometric amounts of a chiral reagent have been applied successfully on gram-to-kilogram scales, yielding enantiomerically enriched alpha-amino acids. In principle, Strecker syntheses employing sub-stoichiometric quantities of a chiral reagent could provide a practical alternative to these approaches, but the reported catalytic asymmetric methods have seen limited use on preparative scales (more than a gram). The limited utility of existing catalytic methods may be due to several important factors, including the relatively complex and precious nature of the catalysts and the requisite use of hazardous cyanide sources. Here we report a new catalytic asymmetric method for the syntheses of highly enantiomerically enriched non-natural amino acids using a simple chiral amido-thiourea catalyst to control the key hydrocyanation step. This catalyst is robust, without sensitive functional groups, so it is compatible with aqueous cyanide salts, which are safer and easier to handle than other cyanide sources; this makes the method adaptable to large-scale synthesis. We have used this new method to obtain enantiopure amino acids that are not readily prepared by enzymatic methods or by chemical hydrogenation.

Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation

NASA Astrophysics Data System (ADS)

Jolliffe, John D.; Armstrong, Roly J.; Smith, Martin D.

2017-06-01

Axially chiral biaryls, as exemplified by 1,1‧-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling, de novo construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed O-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective O-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to C2-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective O-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.

Assessment of chemically separated carbon nanotubes for nanoelectronics.

PubMed

Zhang, Li; Zaric, Sasa; Tu, Xiaomin; Wang, Xinran; Zhao, Wei; Dai, Hongjie

2008-02-27

It remains an elusive goal to obtain high performance single-walled carbon-nanotube (SWNT) electronics such as field effect transistors (FETs) composed of single- or few-chirality SWNTs, due to broad distributions in as-grown materials. Much progress has been made by various separation approaches to obtain materials enriched in metal or semiconducting nanotubes or even in single chiralties. However, research in validating SWNT separations by electrical transport measurements and building functional electronic devices has been scarce. Here, we performed length, diameter, and chirality separation of DNA functionalized HiPco SWNTs by chromatography methods, and we characterized the chiralities by photoluminescence excitation spectroscopy, optical absorption spectroscopy, and electrical transport measurements. The use of these combined methods provided deeper insight to the degree of separation than either technique alone. Separation of SWNTs by chirality and diameter occurred at varying degrees that decreased with increasing tube diameter. This calls for new separation methods capable of metallicity or chirality separation of large diameter SWNTs (in the approximately 1.5 nm range) needed for high performance nanoelectronics. With most of the separated fractions enriched in semiconducting SWNTs, nanotubes placed in parallel in short-channel (approximately 200 nm) electrical devices fail to produce FETs with high on/off switching, indicating incomplete elimination of metallic species. In rare cases with a certain separated SWNT fraction, we were able to fabricate FET devices composed of small-diameter, chemically separated SWNTs in parallel, with high on-/off-current (I(on)/I(off)) ratios up to 105 owing to semiconducting SWNTs with only a few (n,m) chiralities in the fraction. This was the first time that chemically separated SWNTs were used for short channel, all-semiconducting SWNT electronics dominant by just a few (n,m)'s. Nevertheless, the results suggest that much improved chemical separation methods are needed to produce nanotube electronics at a large scale.

Neural-Network Quantum States, String-Bond States, and Chiral Topological States

NASA Astrophysics Data System (ADS)

Glasser, Ivan; Pancotti, Nicola; August, Moritz; Rodriguez, Ivan D.; Cirac, J. Ignacio

2018-01-01

Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.

Predicting CYP2C19 Catalytic Parameters for Enantioselective Oxidations Using Artificial Neural Networks and a Chirality Code

PubMed Central

Hartman, Jessica H.; Cothren, Steven D.; Park, Sun-Ha; Yun, Chul-Ho; Darsey, Jerry A.; Miller, Grover P.

2013-01-01

Cytochromes P450 (CYP for isoforms) play a central role in biological processes especially metabolism of chiral molecules; thus, development of computational methods to predict parameters for chiral reactions is important for advancing this field. In this study, we identified the most optimal artificial neural networks using conformation-independent chirality codes to predict CYP2C19 catalytic parameters for enantioselective reactions. Optimization of the neural networks required identifying the most suitable representation of structure among a diverse array of training substrates, normalizing distribution of the corresponding catalytic parameters (kcat, Km, and kcat/Km), and determining the best topology for networks to make predictions. Among different structural descriptors, the use of partial atomic charges according to the CHelpG scheme and inclusion of hydrogens yielded the most optimal artificial neural networks. Their training also required resolution of poorly distributed output catalytic parameters using a Box-Cox transformation. End point leave-one-out cross correlations of the best neural networks revealed that predictions for individual catalytic parameters (kcat and Km) were more consistent with experimental values than those for catalytic efficiency (kcat/Km). Lastly, neural networks predicted correctly enantioselectivity and comparable catalytic parameters measured in this study for previously uncharacterized CYP2C19 substrates, R- and S-propranolol. Taken together, these seminal computational studies for CYP2C19 are the first to predict all catalytic parameters for enantioselective reactions using artificial neural networks and thus provide a foundation for expanding the prediction of cytochrome P450 reactions to chiral drugs, pollutants, and other biologically active compounds. PMID:23673224

Components for monolithic fiber chirped pulse amplification laser systems

NASA Astrophysics Data System (ADS)

Swan, Michael Craig

The first portion of this work develops techniques for generating femtosecond-pulses from conventional fabry-perot laser diodes using nonlinear-spectral-broadening techniques in Yb-doped positive dispersion fiber ampliers. The approach employed an injection-locked fabry-perot laser diode followed by two stages of nonlinear-spectral-broadening to generate sub-200fs pulses. This thesis demonstrated that a 60ps gain-switched fabry-perot laser-diode can be injection-locked to generate a single-longitudinal-mode pulse and compressed by nonlinear spectral broadening to 4ps. Two problems have been identified that must be resolved before moving forward with this approach. First, gain-switched pulses from a standard diode-laser have a number of characteristics not well suited for producing clean self-phase-modulation-broadened pulses, such as an asymmetric temporal shape, which has a long pulse tail. Second, though parabolic pulse formation occurs for any arbitrary temporal input pulse profile, deviation from the optimum parabolic input results in extensively spectrally modulated self-phase-modulation-broadened pulses. In conclusion, the approach of generating self-phase-modulation-broadened pulses from pulsed laser diodes has to be modified from the initial approach explored in this thesis. The first Yb-doped chirally-coupled-core ber based systems are demonstrated and characterized in the second portion of this work. Robust single-mode performance independent of excitation or any other external mode management techniques have been demonstrated in Yb-doped chirally-coupled-core fibers. Gain and power efficiency characteristics are not compromised in any way in this novel fiber structure up to the 87W maximum power achieved. Both the small signal gain at 1064nm of 30.3dB, and the wavelength dependence of the small signal gain were comparable to currently deployed large-mode-area-fiber technology. The efficiencies of the laser and amplifier were measured to be 75% and 54% respectively. With the inherent design tradeoff between the fundamental mode loss and higher order mode suppression, loss effects on system efficiency in different configurations were investigated. From these investigations it was seen that the slope-efficiency depends only on the total loss of the active fiber, and that when loss is present, the counter-propagating configuration has substantial advantages over the co-propagating case. In this thesis chirally-coupled-core fiber as the technological basis for the next generation of monolithic high power fiber laser systems has been established.

Enantioseparation of Six Antihistamines with Immobilized Cellulose Chiral Stationary Phase by HPLC

PubMed Central

Zhou, Jie; Luo, Pei; Chen, Shanshan; Meng, Lingchang; Sun, Chong; Du, Qiuzheng; Sun, Fang

2016-01-01

A stereoselective high performance liquid chromatography method has been developed for the chiral separation of the enantiomers of six antihistamines, doxylamine, carbinoxamine, dioxopromethazine, oxomemazine, cetirizine and hydroxyzine. The effects of mobile phase additive, column temperature and flow rate on the retention time and resolution were studied. Enantiomeric separation of cetirizine, doxylamine and hydroxyzine were achieved on cellulose tris-(3,5-dichlorophenylcarbamate) immobilized on silica gel chiral stationary phase known as Chiralpak IC (RS = 3.74, RS = 1.85 and RS = 1.74, respectively). PMID:26657408

Velocity gap mode of capillary electrophoresis developed for high-resolution chiral separations.

PubMed

Li, Xue; Li, Youxin; Zhao, Lumeng; Shen, Jianguo; Zhang, Yong; Bao, James J

2014-10-01

A new CE method based on velocity gap (VG) theory has been developed for high-resolution chiral separations. In VG, two consecutive electric fields are adopted to drive analytes passing through two capillaries, which are linked together through a joint. The joint is immersed inside another buffer vial which has conductivity communication with the buffer inside the capillary. By adjusting the field strengths onto the two capillaries, it is possible to observe different velocities of an analyte when it passes through those two capillaries and there would be a net velocity change (NVC) for the same analyte. Different analytes may have different NVC which may be specifically meaningful for enantioseparations because enantiomers are usually hard to resolve. By taking advantage of this NVC, it is possible to enhance the resolution of a chiral separation if a proper voltage program is applied. The feasibility of using NVC to enhance chiral separation was demonstrated in the separations of three pairs of enantiomers: terbutaline, chlorpheniramine, and promethazine. All separations started with partial separation in a conventional CE and were significantly improved under the same experimental conditions. The results indicated that VG has the potential to be used to improve the resolving power of CE in chiral separations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cyclodextrin-modified MEKC for enantioseparation of hexaconazole, penconazole, and myclobutanil.

PubMed

Wan Ibrahim, Wan Aini; Hermawan, Dadan; Sanagi, M Marsin; Aboul-Enein, Hassan Y

2009-02-01

A CD-modified micellar EKC (CD-MEKC) method with 2-hydroxypropyl-gamma-CD (HP-gamma-CD) as chiral selector for the enantioseparation of three chiral triazole fungicides, namely hexaconazole, penconazole, and myclobutanil, is reported for the first time. Simultaneous enantioseparation of the three triazole fungicides was successfully achieved using a CD-MEKC system containing 40 mM HP-gamma-CD and 50 mM SDS in 25 mM phosphate buffer (pH 3.0) solution with resolutions (R(s)) greater than 1.60, peak efficiencies (N) greater than 200,000 for all enantiomers and an analysis time within 15 min compared to 36 min as previously reported using sulfated-beta-CD.

Aerogel materials with periodic structures imprinted with cellulose nanocrystals.

PubMed

Xu, Yi-Tao; Dai, Yiling; Nguyen, Thanh-Dinh; Hamad, Wadood Y; MacLachlan, Mark J

2018-02-22

Novel aerogel materials with periodic structures derived from chiral nematic liquid crystalline cellulose nanocrystals (CNCs) are reported. The liquid crystalline structure of phase-separated CNCs is locked by a simple solvent exchange method or silica condensation. Both cellulose and silica/cellulose aerogel materials were obtained after critical point drying, and subsequent calcination of the silica/cellulose composite afforded a silica aerogel with periodic order. Gas adsorption and electron microscopy studies revealed that these materials have high surface areas and a unique chiral nematic structure imparted from the helicoidal CNC template. This is a new, scalable approach to aerogel materials with highly anisotropic structures. The high porosity and periodic, chiral features of these new materials may make them suitable for applications that require anisotropic properties or as hard templates for the construction of other ordered aerogels.

Simultaneous chiral separation of 3,4-methylenedioxymethamphet- amine, 3-4-methylenedioxyamphetamine, 3,4-methylenedioxyethylam- phetamine, ephedrine, amphetamine and methamphetamine by capillary electrophoresis in uncoated and coated capillaries with native beta-cyclodextrin as the chiral selector: preliminary application to the analysis of urine and hair.

PubMed

Tagliaro, F; Manetto, G; Bellini, S; Scarcella, D; Smith, F P; Marigo, M

1998-01-01

The importance of the chiral analysis of amphetamine-related substances in both clandestine preparations and biological samples is widely recognized. For this purpose, capillary electrophoresis was successfully applied by several authors, but only few reports concerned ring-substituted amphetamines, which represent the main components of "ecstasy", a widely abused "recreational" substance. In the present work, the simultaneous chiral analysis of ephedrine, amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), 3-4-methylenedioxyamphetamine (MDA) and 3,4-methalenedioxyethylamphetamine (MDE) is reported, by using capillary electrophoresis with native beta-cyclodextrin (15 mM) as the chiral selector. After preliminary tests at different pH values (phosphate buffer 100 mM, pH 2.5-9.0) and with bare or coated fused-silica capillaries, the optimized conditions were: pH 2.5 phosphate, uncoated capillary (45 cm x 50 microm inner diameter), potential 10 kV. Detection was either by fixed wavelength (200 nm) or multiwavelength (190-400 nm) UV absorbance. Under these conditions, good resolution was obtained for all the analytes, with excellent chiral selectivity and efficiency. The sensitivity for the individual enantiomers was better than 0.2 microg/mL, analytical precision was characterized by relative standard deviation values < 0.8% (< or = 0.15% with internal standardization) for migration times intra-day and < 2.0% (< or = 0.54% with internal standardization) day-to-day; linearity, in the range 0.156-40 microg/mL, and accuracy were also satisfactory. After a simple liquid-liquid extraction, urine samples could be analyzed with a sensitivity well below the recommended NIDA cut-off of 500 ng/mL. For hair samples, it was necessary to increase the sensitivity by applying a field-amplified sample stacking procedure, which allowed the chiral determination of MDA, MDMA and MDE at concentrations occurring in real samples from ecstasy users, with the possibility of recording UV spectra of the peaks.

Directing the phase behavior of polyelectrolyte complexes using chiral patterned peptides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pacalin, Naomi M.; Leon, Lorraine; Tirrell, Matthew

Polyelectrolyte complexes (PECs) have a broad range of promising applications as soft materials due to their self-assembly and diversity of structure and chemical composition. Peptide polymer PECs are highly biocompatible and biodegradable, making them particularly useful for encapsulation of food additives and flavors, micellar drug delivery, medical and underwater adhesives, fetal membrane patches, and scaffolds for cell growth in tissue engineering. While parameters affecting PEC formation and stability in regards to charge effects are well researched, little is known about the effects of van der Waals interactions, hydrogen bonding, and secondary structure in these materials. Peptide chirality provides a uniquemore » opportunity to manipulate PEC phase to modulate the amount of solid-like (precipitate) or liquid-like (coacervate) character by influencing hydrogen bonding interactions among peptide chains. In previous work, we showed that chiral peptides form solid complexes, while complexes with even one racemic peptide were fluid. This raised the interesting question of how long a homochiral sequence must be to result in solid phase formation. In this work, we designed chiral patterned peptides of polyglutamic acid and polylysine ranging from 50 to 90% L-chiral residues with increasing numbers of sequential L-chiral residues before a chirality change. These polymers were mixed together to form PECs. We observed that 8 or more sequential L-chiral residues are necessary to achieve both the appearance of a precipitate phase and sustained beta-sheets in the complex, as determined by optical imaging and FTIR Spectroscopy. Less homochiral content results in formation of a coacervate phase. Thus, we show that chiral sequence can be used to control the phase transition of PECs. Understanding how to manipulate PEC phase using chiral sequence as presented here may enable tuning of the material properties to achieve the desired mechanical strength for coatings and polymer brushes, or the most effective molecular release kinetics for drug delivery applications, for example.« less

Directing the phase behavior of polyelectrolyte complexes using chiral patterned peptides

NASA Astrophysics Data System (ADS)

Pacalin, Naomi M.; Leon, Lorraine; Tirrell, Matthew

2016-10-01

Polyelectrolyte complexes (PECs) have a broad range of promising applications as soft materials due to their self-assembly and diversity of structure and chemical composition. Peptide polymer PECs are highly biocompatible and biodegradable, making them particularly useful for encapsulation of food additives and flavors, micellar drug delivery, medical and underwater adhesives, fetal membrane patches, and scaffolds for cell growth in tissue engineering. While parameters affecting PEC formation and stability in regards to charge effects are well researched, little is known about the effects of van der Waals interactions, hydrogen bonding, and secondary structure in these materials. Peptide chirality provides a unique opportunity to manipulate PEC phase to modulate the amount of solid-like (precipitate) or liquid-like (coacervate) character by influencing hydrogen bonding interactions among peptide chains. In previous work, we showed that chiral peptides form solid complexes, while complexes with even one racemic peptide were fluid. This raised the interesting question of how long a homochiral sequence must be to result in solid phase formation. In this work, we designed chiral patterned peptides of polyglutamic acid and polylysine ranging from 50 to 90% L-chiral residues with increasing numbers of sequential L-chiral residues before a chirality change. These polymers were mixed together to form PECs. We observed that 8 or more sequential L-chiral residues are necessary to achieve both the appearance of a precipitate phase and sustained β-sheets in the complex, as determined by optical imaging and FTIR Spectroscopy. Less homochiral content results in formation of a coacervate phase. Thus, we show that chiral sequence can be used to control the phase transition of PECs. Understanding how to manipulate PEC phase using chiral sequence as presented here may enable tuning of the material properties to achieve the desired mechanical strength for coatings and polymer brushes, or the most effective molecular release kinetics for drug delivery applications, for example.

Probing the importance of the hemilabile site of bis(phosphine) monoxide ligands in the copper-catalyzed addition of diethylzinc to N-phosphinoylimines: discovery of new effective chiral ligands.

PubMed

Bonnaventure, Isabelle; Charette, André B

2008-08-15

The hemilabile ligand Me-DuPHOS(O) 2 has proven to be a successful ligand for the copper-catalyzed addition of diethylzinc to N-phosphinoylimines. The corresponding alpha-chiral amines were obtained in high yields (80-98%) and enantiomeric ratios (19.0:1 to 99.0:1 er). Furthermore, this Cu* 2 catalytic system has been shown to be effective in the addition of diethylzinc to nitroalkenes and in the reduction of beta,beta-disubstituted vinyl phenyl sulfones. This paper describes a general structure/selectivity study in which the three ligand subunits (chiral phospholane-linker-labile coordinating group (Z)) are systematically modified and tested in the copper-catalyzed addition of diethylzinc to the N-phosphinoylimine 1 derived from benzaldehyde. This study led to the discovery of a new class of effective chiral ligands that combine a chiral phospholane unit and an achiral phosphine oxide.

Photochemically and Thermally Driven Full-Color Reflection in a Self-Organized Helical Superstructure Enabled by a Halogen-Bonded Chiral Molecular Switch.

PubMed

Wang, Hao; Bisoyi, Hari Krishna; Wang, Ling; Urbas, Augustine M; Bunning, Timothy J; Li, Quan

2018-02-05

Supramolecular approaches toward the fabrication of functional materials and systems have been an enabling endeavor. Recently, halogen bonding has been harnessed as a promising supramolecular tool. Herein we report the synthesis and characterization of a novel halogen-bonded light-driven axially chiral molecular switch. The photoactive halogen-bonded chiral switch is able to induce a self-organized, tunable helical superstructure, that is, cholesteric liquid crystal (CLC), when doped into an achiral liquid crystal (LC) host. The halogen-bonded switch as a chiral dopant has a high helical twisting power (HTP) and shows a large change of its HTP upon photoisomerization. This light-driven dynamic modulation enables reversible selective reflection color tuning across the entire visible spectrum. The chiral switch also displays a temperature-dependent HTP change that enables thermally driven red, green, and blue (RGB) reflection colors in the self-organized helical superstructure. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Examination of the potential for adaptive chirality of the nitrogen chiral center in aza-aspartame.

PubMed

Bouayad-Gervais, Samir H; Lubell, William D

2013-11-28

The potential for dynamic chirality of an azapeptide nitrogen was examined by substitution of nitrogen for the α-carbon of the aspartate residue in the sweetener S,S-aspartame. Considering that S,S- and R,S-aspartame possess sweet and bitter tastes, respectively, a bitter-sweet taste of aza-aspartame 9 could be indicative of a low isomerization barrier for nitrogen chirality inter-conversion. Aza-aspartame 9 was synthesized by a combination of hydrazine and peptide chemistry. Crystallization of 9 indicated a R,S-configuration in the solid state; however, the aza-residue chiral center was considerably flattened relative to its natural amino acid counterpart. On tasting, the authors considered aza-aspartame 9 to be slightly bitter or tasteless. The lack of bitter sweet taste of aza-aspartame 9 may be due to flattening from sp2 hybridization in the urea as well as a high barrier for sp3 nitrogen inter-conversion, both of which may interfere with recognition by taste receptors.

The chiral separation of triazole pesticides enantiomers by amylose-tris (3,5-dimethylphenylcarbamate) chiral stationary phase.

PubMed

Wang, Peng; Liu, Donghui; Jiang, Shuren; Xu, Yangguang; Zhou, Zhiqiang

2008-10-01

The amylose-tris(3,5-dimethylphenylcarbamate) chiral stationary phase was synthesized and used to separate the enantiomers of triazole pesticides by high-performance liquid chromatography. The mobile phase was n-hexane-isopropanol applying a flow rate of 1.0 mL/min. Six triazole pesticides were enantioselectively separated. Myclobutanil, paclobutrazol, tebuconazole, and uniconazole obtained complete separation with the resolution factors of 5.73, 2.99, 1.72, and 2.07, respectively, and imazalil and diniconazole obtained partial separation with the resolution factors of 0.79 and 0.77 under the optimized conditions. The effect of the content of isopropanol as well as column temperature on the separation was investigated. A circular dichroism detector was used to identify the enantiomers and determine the elution orders. The results showed the low temperature was good for the chiral separation except for diniconazole. The thermodynamic parameters calculated based on linear Van't Hoff plots showed the chiral separations were controlled by enthalpy.

Out-of-plane chiral domain wall spin-structures in ultrathin in-plane magnets

DOE PAGES

Chen, Gong; Kang, Sang Pyo; Ophus, Colin; ...

2017-05-19

Chiral spin textures in ultrathin films, such as skyrmions or chiral domain walls, are believed to offer large performance advantages in the development of novel spintronics technologies. While in-plane magnetized films have been studied extensively as media for current- and field-driven domain wall dynamics with applications in memory or logic devices, the stabilization of chiral spin textures in in-plane magnetized films has remained rare. Here we report a phase of spin structures in an in-plane magnetized ultrathin film system where out-of-plane spin orientations within domain walls are stable. Moreover, while domain walls in in-plane films are generally expected to bemore » non-chiral, we show that right-handed spin rotations are strongly favoured in this system, due to the presence of the interfacial Dzyaloshinskii-Moriya interaction. These results constitute a platform to explore unconventional spin dynamics and topological phenomena that may enable high-performance in-plane spin-orbitronics devices.« less

Domain wall in a quantum anomalous Hall insulator as a magnetoelectric piston

NASA Astrophysics Data System (ADS)

Upadhyaya, Pramey; Tserkovnyak, Yaroslav

2016-07-01

We theoretically study the magnetoelectric coupling in a quantum anomalous Hall insulator state induced by interfacing a dynamic magnetization texture to a topological insulator. In particular, we propose that the quantum anomalous Hall insulator with a magnetic configuration of a domain wall, when contacted by electrical reservoirs, acts as a magnetoelectric piston. A moving domain wall pumps charge current between electrical leads in a closed circuit, while applying an electrical bias induces reciprocal domain-wall motion. This pistonlike action is enabled by a finite reflection of charge carriers via chiral modes imprinted by the domain wall. Moreover, we find that, when compared with the recently discovered spin-orbit torque-induced domain-wall motion in heavy metals, the reflection coefficient plays the role of an effective spin-Hall angle governing the efficiency of the proposed electrical control of domain walls. Quantitatively, this effective spin-Hall angle is found to approach a universal value of 2, providing an efficient scheme to reconfigure the domain-wall chiral interconnects for possible memory and logic applications.

Fluorescence recognition of chiral amino alcohols by using a novel ionic liquid sensor.

PubMed

Cai, Pengfei; Wu, Datong; Zhao, Xiaoyong; Pan, Yuanjiang

2017-08-07

A novel task-specific ionic liquid derived from l-phenylalaninol was prepared as an enantioselective fluorescent sensor for the first time. Fluorescent chiral ionic liquid 1 (FCIL1) is found to exhibit highly enantioselective fluorescence enhancements toward both aromatic and non-aromatic chiral amino alcohols. When (S)-FCIL1 was treated with the enantiomers of phenylalaninol, a great fluorescence enhancement at 349 nm could be observed and the value of the enantiomeric fluorescence difference (ef) is 5.92. This demonstrated that the chiral sensor (S)-FCIL1 exhibited an excellent enantioselective response behaviour to d-phenylalaninol. Besides that, both the fluorescence intensity at 349 nm (I 349 ) and the ratio of I 349 to I 282 depend linearly on the concentration of amino alcohols. Both the concentration and the enantiomeric composition could be determined by using the chiral ionic liquid. Differently, the sensor treated with the enantiomers of 2-amino-1-butanol showed an opposite result: the fluorescence intensity of the S-enantiomer is higher than that of the R-enantiomer. Furthermore, the size of the substituents on the chiral carbon might be important for the enantioselective fluorescent response.

Effects of Composite Pions on the Chiral Condensate within the PNJL Model at Finite Temperature

NASA Astrophysics Data System (ADS)

Blaschke, D.; Dubinin, A.; Ebert, D.; Friesen, A. V.

2018-05-01

We investigate the effect of composite pions on the behaviour of the chiral condensate at finite temperature within the Polyakov-loop improved NJL model. To this end we treat quark-antiquark correlations in the pion channel (bound states and scattering continuum) within a Beth-Uhlenbeck approach that uses medium-dependent phase shifts. A striking medium effect is the Mott transition which occurs when the binding energy vanishes and the discrete pion bound state merges the continuum. This transition is triggered by the lowering of the continuum edge due to the chiral restoration transition. This in turn also entails a modification of the Polyakov-loop so that the SU(3) center symmetry gets broken at finite temperature and dynamical quarks (and gluons) appear in the system, taking over the role of the dominant degrees of freedom from the pions. At low temperatures our model reproduces the chiral perturbation theory result for the chiral condensate while at high temperatures the PNJL model result is recovered. The new aspect of the current work is a consistent treatment of the chiral restoration transition region within the Beth-Uhlenbeck approach on the basis of mesonic phase shifts for the treatment of the correlations.

Quantitation in chiral capillary electrophoresis: theoretical and practical considerations.

PubMed

D'Hulst, A; Verbeke, N

1994-06-01

Capillary electrophoresis (CE) represents a decisive step forward in stereoselective analysis. The present paper deals with the theoretical aspects of the quantitation of peak separation in chiral CE. Because peak shape is very different in CE with respect to high performance liquid chromatography (HPLC), the resolution factor Rs, commonly used to describe the extent of separation between enantiomers as well as unrelated compounds, is demonstrated to be of limited value for the assessment of chiral separations in CE. Instead, the conjunct use of a relative chiral separation factor (RCS) and the percent chiral separation (% CS) is advocated. An array of examples is given to illustrate this. The practical aspects of method development using maltodextrins--which have been proposed previously as a major innovation in chiral selectors applicable in CE--are documented with the stereoselective analysis of coumarinic anticoagulant drugs. The possibilities of quantitation using CE were explored under two extreme conditions. Using ibuprofen, it has been demonstrated that enantiomeric excess determinations are possible down to a 1% level of optical contamination and stereoselective determinations are still possible with a good precision near the detection limit, increasing sample load by very long injection times. The theoretical aspects of this possibility are addressed in the discussion.

Resonance Raman Spectroscopy of Chirality Enriched Semiconducting Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Hight Walker, A. R.; Piao, Y.; Simpson, J. R.; Lindsay, M.; Streit, J. K.; Ao, G.; Zheng, M.; Fagan, J. A.

Relative intensities of resonant Raman RBM and G modes of 11 chirality-enriched SWCNT species were established under second-order excitation. Results demonstrate an under-recognized complexity in evaluation of Raman spectra for assignment of (n,m) population distributions. Strong chiral angle and mod dependencies affect the intensity ratio of RBM/G modes and can result in misleading interpretations. We report 5 new (n,m) values for chirality-dependent G+ and G- Raman peak positions and intensity ratios, extending the available data to cover smaller diameters down to (5,4). The Raman spectral library sufficiently decouples G peaks from multiple species and enables fundamental characterization in mixed chirality samples. Our results on dispersive properties of the D modes will also be discussed. Probing defects is crucial to evaluate SWCNT quality and to understand the photophysics behind defect-induced optoelectronic features. Using high-quality, chirality-enriched semiconducting SWCNTs and tunable lasers, our results show a non-dispersive D band throughout the resonant window within the same (n,m). Our results were validated by multiple (n,m) samples and intentional covalent surface functionalization generating D peaks with increased intensity, which remain non-dispersive.

Infrared laser induced population transfer and parity selection in {sup 14}NH{sub 3}: A proof of principle experiment towards detecting parity violation in chiral molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dietiker, P.; Miloglyadov, E.; Quack, M., E-mail: Martin@Quack.ch

We have set up an experiment for the efficient population transfer by a sequential two photon—absorption and stimulated emission—process in a molecular beam to prepare quantum states of well defined parity and their subsequent sensitive detection. This provides a proof of principle for an experiment which would allow for parity selection and measurement of the time evolution of parity in chiral molecules, resulting in a measurement of the parity violating energy difference Δ{sub pv}E between enantiomers of chiral molecules. Here, we present first results on a simple achiral molecule demonstrating efficient population transfer (about 80% on the average for eachmore » step) and unperturbed persistence of a selected excited parity level over flight times of about 1.3 ms in the beam. In agreement with model calculations with and without including nuclear hyperfine structure, efficient population transfer can be achieved by a rather simple implementation of the rapid adiabatic passage method of Reuss and coworkers and considering also the stimulated Raman adiabatic passage technique of Bergmann and coworkers as an alternative. The preparation step uses two powerful single mode continuous wave optical parametric oscillators of high frequency stability and accuracy. The detection uses a sensitive resonantly enhanced multiphoton ionization method after free flight lengths of up to 0.8 m in the molecular beam. Using this technique, we were able to also resolve the nuclear hyperfine structure in the rovibrational levels of the ν{sub 1} and ν{sub 3} fundamentals as well as the 2ν{sub 4} overtone of {sup 14}NH{sub 3}, for which no previous data with hyperfine resolution were available. We present our new results on the quadrupole coupling constants for the ν{sub 1}, ν{sub 3}, and 2ν{sub 4} levels in the context of previously known data for ν{sub 2} and its overtone, as well as ν{sub 4}, and the ground state. Thus, now, {sup 14}N quadrupole coupling constants for all fundamentals and some overtones of {sup 14}NH{sub 3} are known and can be used for further theoretical analysis.« less

Asymmetric allylation of α-ketoester-derived N-benzoylhydrazones promoted by chiral sulfoxides/N-oxides Lewis bases: highly enantioselective synthesis of quaternary α-substituted α-allyl-α-amino acids.

PubMed

Reyes-Rangel, Gloria; Bandala, Yamir; García-Flores, Fred; Juaristi, Eusebio

2013-09-01

Chiral sulfoxides/N-oxides (R)-1 and (R,R)-2 are effective chiral promoters in the enantioselective allylation of α-keto ester N-benzoylhydrazone derivatives 3a-g to generate the corresponding N-benzoylhydrazine derivatives 4a-g, with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a-b were subsequently treated with SmI2, and the resulting amino esters 5a-b with LiOH to obtain quaternary α-substituted α-allyl α-amino acids 6a-b, whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data. © 2013 Wiley Periodicals, Inc.

Theory of carbon nanocones: mechanical chiral inversion of a micron-scale three-dimensional object.

PubMed

Jordan, Stephen P; Crespi, Vincent H

2004-12-17

Graphene cones have two degenerate configurations: their original shape and its inverse. When the apex is depressed by an external probe, the simulated mechanical response is highly nonlinear, with a broad constant-force mode appearing after a short initial Hooke's law regime. For chiral cones, the final state is an atomically exact chiral invert of the original system. If the local reflection symmetry of the graphene sheet is broken by the chemisorption of just five hydrogen atoms to the apex, then the maximal yield strength of the cone increases by approximately 40%. The high symmetry of the conical geometry can concentrate micron-scale mechanical work with atomic precision, providing a way to activate specific chemical bonds.

Development of achiral and chiral 2D HPLC methods for analysis of albendazole metabolites in microsomal fractions using multivariate analysis for the in vitro metabolism.

PubMed

Belaz, Kátia Roberta A; Pereira-Filho, Edenir Rodrigues; Oliveira, Regina V

2013-08-01

In this work, the development of two multidimensional liquid chromatography methods coupled to a fluorescence detector is described for direct analysis of microsomal fractions obtained from rat livers. The chiral multidimensional method was then applied for the optimization of the in vitro metabolism of albendazole by experimental design. Albendazole was selected as a model drug because of its anthelmintics properties and recent potential for cancer treatment. The development of two fully automated achiral-chiral and chiral-chiral high performance liquid chromatography (HPLC) methods for the determination of albendazole (ABZ) and its metabolites albendazole sulphoxide (ABZ-SO), albendazole sulphone (ABZ-SO2) and albendazole 2-aminosulphone (ABZ-SO2NH2) in microsomal fractions are described. These methods involve the use of a phenyl (RAM-phenyl-BSA) or octyl (RAM-C8-BSA) restricted access media bovine serum albumin column for the sample clean-up, followed by an achiral phenyl column (15.0×0.46cmI.D.) or a chiral amylose tris(3,5-dimethylphenylcarbamate) column (15.0×0.46cmI.D.). The chiral 2D HPLC method was applied to the development of a compromise condition for the in vitro metabolism of ABZ by means of experimental design involving multivariate analysis. Copyright © 2013 Elsevier B.V. All rights reserved.

Effects of the regularization on the restoration of chiral and axial symmetries

NASA Astrophysics Data System (ADS)

Costa, P.; Ruivo, M. C.; de Sousa, C. A.

2008-05-01

The effects of a type of regularization for finite temperatures on the restoration of chiral and axial symmetries are investigated within the SU(3) Nambu-Jona-Lasinio model. The regularization consists in using an infinite cutoff in the integrals that are convergent at finite temperature, a procedure that allows one to take into account the effects of high momentum quarks at high temperatures. It is found that the critical temperature for the phase transition is closer to lattice results than the one obtained with the conventional regularization, and the restoration of chiral and axial symmetries, signaled by the behavior of several observables, occurs simultaneously and at a higher temperature. The restoration of the axial symmetry appears as a natural consequence of the full recovering of the chiral symmetry that was dynamically broken. By using an additional ansatz that simulates instanton suppression effects, by means of a convenient temperature dependence of the anomaly coefficient, we found that the restoration of U(2) symmetry is shifted to lower values, but the dominant effect at high temperatures comes from the new regularization that enhances the decrease of quark condensates, especially in the strange sector.

Synthesis of Cis, syndiotactic A -alt-B Copolymers from Two Enantiomerically Pure Trans -2,3-Disubstituted-5,6-Norbornenes

DOE PAGES

Jang, Eun Sil; John, Jeremy M.; Schrock, Richard R.

2016-09-06

Cis,syndiotactic A-alt-B copolymers, where A and B are two enantiomerically pure trans-2,3-disubstituted-5,6-norbornenes with “opposite” chiralities, can be prepared with stereogenic-at-metal initiators of the type M(NR)(CHR')(OR”)(pyrrolide). Formation of a high percentage of alternating AB copolymer linkages relies on an inversion of chirality at the metal with each propagating step and a relatively fast formation of an AB sequence as a consequence of a preferred diastereomeric relationship between the chirality at the metal and the chirality of the monomer. Finally, this approach to formation of an alternating AB copolymer contrasts dramatically with the principle of forming AB copolymers from achiral monomers andmore » catalysts.« less

Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi

PubMed Central

Winter, Benjamin; Butz, Benjamin; Dieker, Christel; Schröder-Turk, Gerd E.; Mecke, Klaus; Spiecker, Erdmann

2015-01-01

The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69–88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676–11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms. PMID:26438839

Coexistence of both gyroid chiralities in individual butterfly wing scales of Callophrys rubi.

PubMed

Winter, Benjamin; Butz, Benjamin; Dieker, Christel; Schröder-Turk, Gerd E; Mecke, Klaus; Spiecker, Erdmann

2015-10-20

The wing scales of the Green Hairstreak butterfly Callophrys rubi consist of crystalline domains with sizes of a few micrometers, which exhibit a congenitally handed porous chitin microstructure identified as the chiral triply periodic single-gyroid structure. Here, the chirality and crystallographic texture of these domains are investigated by means of electron tomography. The tomograms unambiguously reveal the coexistence of the two enantiomeric forms of opposite handedness: the left- and right-handed gyroids. These two enantiomers appear with nonequal probabilities, implying that molecularly chiral constituents of the biological formation process presumably invoke a chiral symmetry break, resulting in a preferred enantiomeric form of the gyroid structure. Assuming validity of the formation model proposed by Ghiradella H (1989) J Morphol 202(1):69-88 and Saranathan V, et al. (2010) Proc Natl Acad Sci USA 107(26):11676-11681, where the two enantiomeric labyrinthine domains of the gyroid are connected to the extracellular and intra-SER spaces, our findings imply that the structural chirality of the single gyroid is, however, not caused by the molecular chirality of chitin. Furthermore, the wing scales are found to be highly textured, with a substantial fraction of domains exhibiting the <001> directions of the gyroid crystal aligned parallel to the scale surface normal. Both findings are needed to completely understand the photonic purpose of the single gyroid in gyroid-forming butterflies. More importantly, they show the level of control that morphogenesis exerts over secondary features of biological nanostructures, such as chirality or crystallographic texture, providing inspiration for biomimetic replication strategies for synthetic self-assembly mechanisms.

Competitive chiral induction in a 2D molecular assembly: Intrinsic chirality versus coadsorber-induced chirality.

PubMed

Chen, Ting; Li, Shu-Ying; Wang, Dong; Wan, Li-Jun

2017-11-01

Noncovalently introducing stereogenic information is a promising approach to embed chirality in achiral molecular systems. However, the interplay of the noncovalently introduced chirality with the intrinsic chirality of molecules or molecular aggregations has rarely been addressed. We report a competitive chiral expression of the noncovalent interaction-mediated chirality induction and the intrinsic stereogenic center-controlled chirality induction in a two-dimensional (2D) molecular assembly at the liquid/solid interface. Two enantiomorphous honeycomb networks are formed by the coassembly of an achiral 5-(benzyloxy)isophthalic acid (BIC) derivative and 1-octanol at the liquid/solid interface. The preferential formation of the globally homochiral assembly can be achieved either by using the chiral analog of 1-octanol, ( S )-6-methyl-1-octanol, as a chiral coadsorber to induce chirality to the BIC assembly via noncovalent hydrogen bonding or by covalently linking a chiral center in the side chain of BIC. Both the chiral coadsorber and the intrinsically chiral BIC derivative can act as a chiral seeds to induce a preferred handedness in the assembly of the achiral BIC derivatives. Furthermore, the noncovalent interaction-mediated chirality induction can restrain or even overrule the manifestation of the intrinsic chirality of the BIC molecule and dominate the handedness of the 2D molecular coassembly. This study provides insight into the interplay of intrinsically chiral centers and external chiral coadsorbers in the chiral induction, transfer, and amplification processes of 2D molecular assembly.

Competitive chiral induction in a 2D molecular assembly: Intrinsic chirality versus coadsorber-induced chirality

PubMed Central

Chen, Ting; Li, Shu-Ying; Wang, Dong; Wan, Li-Jun

2017-01-01

Noncovalently introducing stereogenic information is a promising approach to embed chirality in achiral molecular systems. However, the interplay of the noncovalently introduced chirality with the intrinsic chirality of molecules or molecular aggregations has rarely been addressed. We report a competitive chiral expression of the noncovalent interaction–mediated chirality induction and the intrinsic stereogenic center–controlled chirality induction in a two-dimensional (2D) molecular assembly at the liquid/solid interface. Two enantiomorphous honeycomb networks are formed by the coassembly of an achiral 5-(benzyloxy)isophthalic acid (BIC) derivative and 1-octanol at the liquid/solid interface. The preferential formation of the globally homochiral assembly can be achieved either by using the chiral analog of 1-octanol, (S)-6-methyl-1-octanol, as a chiral coadsorber to induce chirality to the BIC assembly via noncovalent hydrogen bonding or by covalently linking a chiral center in the side chain of BIC. Both the chiral coadsorber and the intrinsically chiral BIC derivative can act as a chiral seeds to induce a preferred handedness in the assembly of the achiral BIC derivatives. Furthermore, the noncovalent interaction–mediated chirality induction can restrain or even overrule the manifestation of the intrinsic chirality of the BIC molecule and dominate the handedness of the 2D molecular coassembly. This study provides insight into the interplay of intrinsically chiral centers and external chiral coadsorbers in the chiral induction, transfer, and amplification processes of 2D molecular assembly. PMID:29119137

Design of ferrocene-dipeptide bioorganometallic conjugates to induce chirality-organized structures.

PubMed

Moriuchi, Toshiyuki; Hirao, Toshikazu

2010-07-20

The highly ordered molecular assemblies in proteins can have a variety of functions, as observed in enzymes, receptors, and the like. Synthetic scientists are constructing bioinspired systems by harnessing the self-assembling properties of short peptides. Secondary structures such as alpha-helices, beta-sheets, and beta-turns are important in protein folding, which is mostly directed and stabilized by hydrogen bonding and the hydrophobic interactions of side chains. The design of secondary structure mimics that are composed of short peptides has attracted much attention, both for gaining fundamental insight into the factors affecting protein folding and for developing pharmacologically useful compounds, artificial receptors, asymmetric catalysts, and new materials. Ferrocenes are an organometallic scaffold with a central reverse-turn unit based on the inter-ring spacing of about 3.3 A, which is a suitable distance for hydrogen bonding between attached peptide strands. The conjugation of organometallic compounds with biomolecules such as amino acids, peptides, and DNA should provide novel systems that reflect properties of both the ferrocene and the biologically derived moieties. In this Account, we focus on recent advances in the design of ferrocene-peptide bioconjugates, which help illustrate the peptidomimetic basis for protein folding and the means of constructing highly ordered molecular assemblies. Ferrocene-peptide bioconjugates are constructed to form chirality-organized structures in both solid and solution states. The ferrocene serves as a reliable organometallic scaffold for the construction of protein secondary structures via intramolecular hydrogen bonding: the attached dipeptide strands are constrained within the appropriate dimensions. The introduction of the chiral dipeptide chains into the ferrocene scaffold induces the conformational enantiomerization of the ferrocenyl moiety; the chirality-organized structure results from intramolecular hydrogen bonding. The configuration and sequence of the amino acids are instrumental in the process. Regulation of the directionality and specificity of hydrogen bonding is a key component in the design of various molecular assemblies. Ferrocene-peptide bioconjugates also have a strong tendency to self-assemble through the contributions of available hydrogen-bonding donors in the solid state. Some ferrocene-peptide bioconjugates bearing only one dipeptide chain exhibit a helically ordered molecular assembly through a network of intermolecular (rather than intramolecular) hydrogen bonds. The propensity to form the chiral helicity appears to be controlled by the chirality of the dipeptide chains. Organization of host molecules is a useful strategy for forming artificial receptors. The conformationally regulated ferrocene-peptide bioconjugate provides the chirality-organized binding site for size-selective and chiral recognition of dicarboxylic acids through multipoint hydrogen bonds. Metal ions serve a variety of purposes in proteins, including structural stabilization for biological function. The complexation of ferrocene-peptide bioconjugates with palladium(II) compounds not only stabilizes the chirality conformational regulation but also induces conformational regulation of the dipeptide chain through complexation and intramolecular chirality organization. Construction of the chirality-organized ferrocene-peptide bioconjugates is also achieved by metal-directed assembly. These varied examples amply demonstrate the value of ferrocene-peptide bioconjugates in asserting architectural control over highly ordered molecular assemblies.

High-Performance Ultrathin Active Chiral Metamaterials.

PubMed

Wu, Zilong; Chen, Xiaodong; Wang, Mingsong; Dong, Jianwen; Zheng, Yuebing

2018-05-22

Ultrathin active chiral metamaterials with dynamically tunable and responsive optical chirality enable new optical sensors, modulators, and switches. Herein, we develop ultrathin active chiral metamaterials of highly tunable chiroptical responses by inducing tunable near-field coupling in the metamaterials and exploit the metamaterials as ultrasensitive sensors to detect trace amounts of solvent impurities. To demonstrate the active chiral metamaterials mediated by tunable near-field coupling, we design moiré chiral metamaterials (MCMs) as model metamaterials, which consist of two layers of identical Au nanohole arrays stacked upon one another in moiré patterns with a dielectric spacer layer between the Au layers. Our simulations, analytical fittings, and experiments reveal that spacer-dependent near-field coupling exists in the MCMs, which significantly enhances the spectral shift and line shape change of the circular dichroism (CD) spectra of the MCMs. Furthermore, we use a silk fibroin thin film as the spacer layer in the MCM. With the solvent-controllable swelling of the silk fibroin thin films, we demonstrate actively tunable near-field coupling and chiroptical responses of the silk-MCMs. Impressively, we have achieved the spectral shift over a wavelength range that is more than one full width at half-maximum and the sign inversion of the CD spectra in a single ultrathin (1/5 of wavelength in thickness) MCM. Finally, we apply the silk-MCMs as ultrasensitive sensors to detect trace amounts of solvent impurities down to 200 ppm, corresponding to an ultrahigh sensitivity of >10 5 nm/refractive index unit (RIU) and a figure of merit of 10 5 /RIU.

A Survery of the Correlation between Filament Chirality and Sigmoid Handedness

NASA Astrophysics Data System (ADS)

V, A.; Hazra, S.; Martin, S. F.; Martens, P. C.

2017-12-01

Sigmoid regions on the Sun are often the regions that cause Coronal Mass Ejections (CMEs). Large CMEs most often have filaments that erupt with them. This study focuses on the statistical relevance of the shape of the sigmoid and the chirality of the filament residing in these sigmoids. The study further extends to the relation between the directionality of filaments and the Earth-directed CMEs. Sigmoid data from Savcheva et al. (2014) between 2007 and 2012 and a compilation of data using the HEK Sigmoid Sniffer (Martens et al. 2012) along with Hinode XRT Soft X-ray images were used for analyzing data between 2013 and 2017. Hence this dataset consists of almost one solar cycle of data. A similar study done previously by Martens et al. (2013) analysed data for a solar cycle using an Advanced Automated Filament Detection & Characterization Code (Bernasconi, Rust & Hakim 2005). Considering that automated chirality detection is not foolproof, we present this study which uses manual determination of chirality for accuracy using high resolution chromospheric images. Mainly full disk images of soft X-ray obtained from Hinode XRT (X-Ray Telescope) have been used to find and ensure the S or Z shape of sigmoids. H-alpha images obtained from BBSO and Kanzelhohe Solar Observatory (KSO) are used in determining the chirality of filaments. The resolutions of BBSO and KSO data are 1k and 4k respectively. A comparison of the analysis of the chirality of filaments using both data will be presented. Although KSO gives a 4k resolution, it is still difficult to determine the chirality of small filaments. For this reason, high resolution images of H-alpha chromospheric filaments obtained from Helio Research and Solar Observing Optical Network (SOON) have been used for further analysis of chirality of those filaments that were undeterminable using the BBSO or KSO full disk images. The results of the comparison using the different resolutions are shown. The results of the correlation between sigmoid shape and filament chirality are also shown. Further, these results are used in determining the correlation with Earth directed CMEs and those that cause geo-magnetic storms. Savacheva, A. S., McKillop, S. C., McCauley, P. I., et al., 2014, 289Bernasconi, P. N., Rust, D. M., & Hakim, D., 2005, Sol. Phys., 228, 97 Martens, P., Yeates, A., & Pillai, K., 2013, IAU, 3000

Gelation induced supramolecular chirality: chirality transfer, amplification and application.

PubMed

Duan, Pengfei; Cao, Hai; Zhang, Li; Liu, Minghua

2014-08-14

Supramolecular chirality defines chirality at the supramolecular level, and is generated from the spatial arrangement of component molecules assembling through non-covalent interactions such as hydrogen bonding, van der Waals interactions, π-π stacking, hydrophobic interactions and so on. During the formation of low molecular weight gels (LMWGs), one kind of fascinating soft material, one frequently encounters the phenomenon of chirality as well as chiral nanostructures, either from chiral gelators or even achiral gelators. A view of gelation-induced supramolecular chirality will be very helpful to understand the self-assembly process of the gelator molecules as well as the chiral structures, the regulation of the chirality in the gels and the development of the "smart" chiral materials such as chiroptical devices, catalysts and chiral sensors. It necessitates fundamental understanding of chirality transfer and amplification in these supramolecular systems. In this review, recent progress in gelation-induced supramolecular chirality is discussed.

Asymmetric Synthesis of Apratoxin E.

PubMed

Mao, Zhuo-Ya; Si, Chang-Mei; Liu, Yi-Wen; Dong, Han-Qing; Wei, Bang-Guo; Lin, Guo-Qiang

2016-10-21

An efficient method for asymmetric synthesis of apratoxin E 2 is described in this report. The chiral lactone 8, recycled from the degradation of saponin glycosides, was utilized to prepare the non-peptide fragment 6. In addition to this "from nature to nature" strategy, olefin cross-metathesis (CM) was applied as an alternative approach for the formation of the double bond. Moreover, pentafluorophenyl diphenylphosphinate was found to be an efficient condensation reagent for the macrocyclization.

Electric line source illumination of a chiral cylinder placed in another chiral background medium

NASA Astrophysics Data System (ADS)

Aslam, M.; Saleem, A.; Awan, Z. A.

2018-05-01

An electric line source illumination of a chiral cylinder embedded in a chiral background medium is considered. The field expressions inside and outside of a chiral cylinder have been derived using the wave field decomposition approach. The effects of various chiral cylinders, chiral background media and source locations upon the scattering gain pattern have been investigated. It is observed that the chiral background reduces the backward scattering gain as compared to the free space background for a dielectric cylinder. It is also studied that by moving a line source away from a cylinder reduces the backward scattering gain for a chiral cylinder placed in a chiral background under some specific conditions. A unique phenomenon of reduced scattering gain has been observed at a specific observation angle for a chiral cylinder placed in a chiral background having an electric line source location of unity free space wavelength. An isotropic scattering gain pattern is observed for a chiral nihility background provided that if cylinder is chiral or chiral nihility type. It is also observed that this isotropic behaviour is independent of background and cylinder chirality.

Generating carbyne equivalents with photoredox catalysis

NASA Astrophysics Data System (ADS)

Wang, Zhaofeng; Herraiz, Ana G.; Del Hoyo, Ana M.; Suero, Marcos G.

2018-02-01

Carbon has the unique ability to bind four atoms and form stable tetravalent structures that are prevalent in nature. The lack of one or two valences leads to a set of species—carbocations, carbanions, radicals and carbenes—that is fundamental to our understanding of chemical reactivity. In contrast, the carbyne—a monovalent carbon with three non-bonded electrons—is a relatively unexplored reactive intermediate; the design of reactions involving a carbyne is limited by challenges associated with controlling its extreme reactivity and the lack of efficient sources. Given the innate ability of carbynes to form three new covalent bonds sequentially, we anticipated that a catalytic method of generating carbynes or related stabilized species would allow what we term an ‘assembly point’ disconnection approach for the construction of chiral centres. Here we describe a catalytic strategy that generates diazomethyl radicals as direct equivalents of carbyne species using visible-light photoredox catalysis. The ability of these carbyne equivalents to induce site-selective carbon-hydrogen bond cleavage in aromatic rings enables a useful diazomethylation reaction, which underpins sequencing control for the late-stage assembly-point functionalization of medically relevant agents. Our strategy provides an efficient route to libraries of potentially bioactive molecules through the installation of tailored chiral centres at carbon-hydrogen bonds, while complementing current translational late-stage functionalization processes. Furthermore, we exploit the dual radical and carbene character of the generated carbyne equivalent in the direct transformation of abundant chemical feedstocks into valuable chiral molecules.

Highly selective fluorescence detection of Cu2+ in water by chiral dimeric Zn2+ complexes through direct displacement.

PubMed

Khatua, Snehadrinarayan; Choi, Shin Hei; Lee, Junseong; Huh, Jung Oh; Do, Youngkyu; Churchill, David G

2009-03-02

Fluorescent dinuclear chiral zinc complexes were synthesized in a "one-pot" method in which the lysine-based Schiff base ligand was generated in situ. This complex acts as a highly sensitive and selective fluorescent ON-OFF probe for Cu(2+) in water at physiological pH. Other metal ions such as Hg(2+), Cd(2+), and Pb(2+) gave little fluorescence change.

Synthesis of axially chiral oxazoline-carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe(2).

PubMed

Wang, Feijun; Li, Shengke; Qu, Mingliang; Zhao, Mei-Xin; Liu, Lian-Jun; Shi, Min

2012-01-01

Axially chiral oxazoline-carbene ligands with an N-naphthyl framework were successfully prepared, and their coordination behavior with AuCl·SMe(2) was also investigated, affording the corresponding Au(I) complexes in moderate to high yields.

Theoretical Investigation of Regioselectivity and Stereoselectivity in AIBN/HSnBu3-Mediated Radical Cyclization of N-(2-Iodo-4,6-dimethylphenyl)-N,2-dimethyl-(2E)-butenamide.

PubMed

Li, Bai-Jian; Zhong, Hua; Yu, Hai-Tao

2016-12-22

In this study, we employed the density functional method to simulate AIBN/HSnBu 3 -mediated radical cyclizations with different axially chiral conformers of N-(2-iodo-4,6-dimethylphenyl)-N,2-dimethyl-(2E)-butenamide as substrates. We constructed a reaction potential energy profile using the Gibbs free energies of the located stationary points. The thermodynamic and kinetic data of the profile were further used to evaluate the regioselectivity, stereoselectivity, and product distribution of the cyclizations. Additionally, we compared the present HSnBu 3 -mediated radical cyclization with the experimentally available Heck reaction and found that such a radical cyclization can convert (M,Z) and (P,Z) o-iodoanilide substrates to centrally chiral products with high chirality transfer. The goal of this study was to estimate the practicality of theoretically predicting the memory of chirality in such radical cyclizations. The present results can provide a strategy from a theoretical viewpoint for experimentally synthesizing highly stereoselective carbocyclic and heterocyclic compounds using radical cyclization methods.

Highly Enantioselective Production of Chiral Secondary Alcohols Using Lactobacillus paracasei BD101 as a New Whole Cell Biocatalyst and Evaluation of Their Antimicrobial Effects.

PubMed

Yılmaz, Durmuşhan; Şahin, Engin; Dertli, Enes

2017-11-01

Chiral secondary alcohols are valuable intermediates for many important enantiopure pharmaceuticals and biologically active molecules. In this work, we studied asymmetric reduction of aromatic ketones to produce the corresponding chiral secondary alcohols using lactic acid bacteria (LAB) as new biocatalysts. Seven LAB strains were screened for their ability to reduce acetophenones to their corresponding alcohols. Among these strains, Lactobacillus paracasei BD101 was found to be the most successful at reducing the ketones to the corresponding alcohols. The reaction conditions were further systematically optimized for this strain and high enantioselectivity (99%) and very good yields were obtained. These secondary alcohols were further tested for their antimicrobial activities against important pathogens and significant levels of antimicrobial activities were observed although these activities were altered depending on the secondary alcohols as well as their enantiomeric properties. The current methodology demonstrates a promising and alternative green approach for the synthesis of chiral secondary alcohols of biological importance in a cheap, mild, and environmentally useful process. © 2017 Wiley-VHCA AG, Zurich, Switzerland.

d +i d chiral superconductivity in a triangular lattice from trigonal bipyramidal complexes

NASA Astrophysics Data System (ADS)

Lu, Chen; Zhang, Li-Da; Wu, Xianxin; Yang, Fan; Hu, Jiangping

2018-04-01

We model the newly predicted high-Tc superconducting candidates constructed by corner-shared trigonal bipyramidal complexes with an effective three-orbital tight-binding Hamiltonian and investigate the pairing symmetry of their superconducting states driven by electron-electron interactions. Our combined weak- and strong-coupling-based calculations consistently identify the chiral d +i d superconductivity as the leading pairing symmetry in a wide doping range with realistic interaction parameters. This pairing state has a nontrivial topological Chern number and can host gapless chiral edge modes, and the vortex cores under magnetic field can carry Majorana zero modes.

Helicity statistics in homogeneous and isotropic turbulence and turbulence models

NASA Astrophysics Data System (ADS)

Sahoo, Ganapati; De Pietro, Massimo; Biferale, Luca

2017-02-01

We study the statistical properties of helicity in direct numerical simulations of fully developed homogeneous and isotropic turbulence and in a class of turbulence shell models. We consider correlation functions based on combinations of vorticity and velocity increments that are not invariant under mirror symmetry. We also study the scaling properties of high-order structure functions based on the moments of the velocity increments projected on a subset of modes with either positive or negative helicity (chirality). We show that mirror symmetry is recovered at small scales, i.e., chiral terms are subleading and they are well captured by a dimensional argument plus anomalous corrections. These findings are also supported by a high Reynolds numbers study of helical shell models with the same chiral symmetry of Navier-Stokes equations.

Allenes in Asymmetric Catalysis. Asymmetric Ring-Opening of Meso-Epoxides Catalyzed by Allene-Containing Phosphine Oxides

PubMed Central

Pu, Xiaotao; Qi, Xiangbing; Ready, Joseph M.

2009-01-01

Unsymmetrically substituted allenes (1,2 dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically active C2 symmetric allene-containing bisphosphine oxides can catalyze the addition of SiCl4 to meso epoxides with high enantioselectivity. The epoxide-opening likely involves generation of a Lewis acidic, cationic (bisphosphine oxide)SiCl3 complex. The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development of ligands and catalysts for asymmetric synthesis. PMID:19722613

Enhancing and reducing chirality by opposite circularly-polarized light irradiation on crystalline chiral domains consisting of nonchiral photoresponsive W-shaped liquid crystal molecules.

PubMed

Choi, Suk-Won; Takezoe, Hideo

2016-09-28

We found possible chirality enhancement and reduction in chiral domains formed by photoresponsive W-shaped molecules by irradiation with circularly polarized light (CPL). The W-shaped molecules exhibit a unique smectic phase with spontaneously segregated chiral domains, although the molecules are nonchiral. The chirality control was generated in the crystalline phase, which shows chiral segregation as in the upper smectic phase, and the result appeared to be as follows: for a certain chiral domain, right-CPL stimuli enhanced the chirality, while left-CPL stimuli reduced the chirality, and vice versa for another chiral domain. Interestingly, no domain-size change could be observed after CPL irradiation, suggesting some changes in the causes of chirality. In this way, the present system can recognize the handedness of the applied chiral stimuli. In other words, the present material can be used as a sensitive chiral-stimuli-recognizing material and should find invaluable applications, including in chiroptical switches, sensors, and memories as well as in chiral recognition.

The Möbius domain wall fermion algorithm

NASA Astrophysics Data System (ADS)

Brower, Richard C.; Neff, Harmut; Orginos, Kostas

2017-11-01

We present a review of the properties of generalized domain wall Fermions, based on a (real) Möbius transformation on the Wilson overlap kernel, discussing their algorithmic efficiency, the degree of explicit chiral violations measured by the residual mass (mres) and the Ward-Takahashi identities. The Möbius class interpolates between Shamir's domain wall operator and Boriçi's domain wall implementation of Neuberger's overlap operator without increasing the number of Dirac applications per conjugate gradient iteration. A new scaling parameter (α) reduces chiral violations at finite fifth dimension (Ls) but yields exactly the same overlap action in the limit Ls → ∞. Through the use of 4d Red/Black preconditioning and optimal tuning for the scaling α(Ls) , we show that chiral symmetry violations are typically reduced by an order of magnitude at fixed Ls. We argue that the residual mass for a tuned Möbius algorithm with α = O(1 /Lsγ) for γ < 1 will eventually fall asymptotically as mres = O(1 /Ls1+γ) in the case of a 5D Hamiltonian with out a spectral gap.

Selective growth of chirality-enriched semiconducting carbon nanotubes by using bimetallic catalysts from salt precursors.

PubMed

Zhao, Xiulan; Yang, Feng; Chen, Junhan; Ding, Li; Liu, Xiyan; Yao, Fengrui; Li, Meihui; Zhang, Daqi; Zhang, Zeyao; Liu, Xu; Yang, Juan; Liu, Kaihui; Li, Yan

2018-04-19

Bimetallic catalysts play important roles in the selective growth of single-walled carbon nanotubes (SWNTs). Using the simple salts (NH4)6W7O24·6H2O and Co(CH3COO)2·4H2O as precursors, tungsten-cobalt catalysts were prepared. The catalysts were composed of W6Co7 intermetallic compounds and tungsten-dispersed cobalt. With the increase of the W/Co ratio in the precursors, the content of W6Co7 was increased. Because the W6Co7 intermetallic compound can enable the chirality specified growth of SWNTs, the selectivity of the resulting SWNTs is improved at a higher W/Co ratio. At a W/Co ratio of 6 : 4 and under optimized chemical vapor deposition conditions, we realized the direct growth of semiconducting SWNTs with the purity of ∼96%, in which ∼62% are (14, 4) tubes. Using salts as precursors to prepare tungsten-cobalt bimetallic catalysts is flexible and convenient. This offers an efficient pathway for the large-scale preparation of chirality enriched semiconducting SWNTs.

Enantiomeric determination of amino compounds with high sensitivity using the chiral reagents (+)- and (-)-1-(9-anthryl)-2-propyl chloroformate.

PubMed

Thorsén, G; Engström, A; Josefsson, B

1997-10-31

New chiral precolumn reagents, (+)- and (-)-1-(9-anthryl)-2-propyl chloroformate (APOC), are introduced for the chiral separation of amino acids and small peptides in capillary electrophoresis. Chiral separation of 17 amino acids and four small peptides as their diastereomeric 1-(9-anthryl)-2-propyl carbamate derivatives have been achieved by micellar electrokinetic chromatography. The detection limit for the derivatives is in the femtomole range with UV detection and in the attomole range with laser-induced fluorescence (LIF) detection. LIF detection was used to determine the enantiomeric excess of four APOC-derivatised peptides. The use of the new, anthracene-based reagents in conjunction with argon ion LIF makes enantiomeric determinations at ppm levels feasible. In this paper determinations below promille levels are performed without overloading the separation system.

Microsecond-range optical shutter for unpolarized light with chiral nematic liquid crystal

NASA Astrophysics Data System (ADS)

Mohammadimasoudi, Mohammad; Shin, Jungsoon; Lee, Keechang; Neyts, Kristiaan; Beeckman, Jeroen

2015-04-01

A fast electro-optic shutter is fabricated and demonstrated. The device works independently of the polarization state of the incoming light beam. Modulation between 3% transmission and 60% transmission is obtained within a wavelength range of 50 nm with a response time of 20 μs. The device consists of two partly polymerized chiral nematic liquid crystal layers separated by a half wave plate. The transmission modulation is due to a 50 nm wavelength shift of the photonic band gap of the chiral liquid crystal realized by applying an electric field over a mixture of photo-polymerized LC and non-reactive nematic LC containing a chiral dopant. The shutter features high reflectivity in the photonic band gap. We investigate the influence of the amplitude of the applied voltage on the width and the depth of the reflection band.

Exploring Cooperative Effects in Oxidative NHC Catalysis: Regioselective Acylation of Carbohydrates.

PubMed

Cramer, David L; Bera, Srikrishna; Studer, Armido

2016-05-23

The utility of oxidative NHC catalysis for both the regioselective and chemoselective functionalization of carbohydrates is explored. Chiral NHCs allow for the highly regioselective oxidative esterification of various carbohydrates using aldehydes as acylation precursors. The transformation was also shown to be amenable to both cis/trans diol isomers, free amino groups, and selective for specific sugar epimers in competition experiments. Efficiency and regioselectivity of the acylation can be improved upon using two different NHC catalysts that act cooperatively. The potential of the method is documented by the regioselective acylation of an amino-linked neodisaccharide. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation

PubMed Central

2016-01-01

In the presence of a chiral thioxanthone catalyst (10 mol %) the title compounds underwent a clean intermolecular [2 + 2] photocycloaddition with electron-deficient olefins at λ = 419 nm. The reactions not only proceeded with excellent regio- and diastereoselectivity but also delivered the respective cyclobutane products with significant enantiomeric excess (up to 95% ee). Key to the success of the reactions is a two-point hydrogen bonding between quinolone and catalyst enabling efficient energy transfer and high enantioface differentiation. Preliminary work indicated that solar irradiation can be used for this process and that the substrate scope can be further expanded to isoquinolones. PMID:27268908

Readily Accessible and Highly Efficient Ferrocene-Based Amino-Phosphine-Alcohol (f-Amphol) Ligands for Iridium-Catalyzed Asymmetric Hydrogenation of Simple Ketones.

PubMed

Yu, Jianfei; Duan, Meng; Wu, Weilong; Qi, Xiaotian; Xue, Peng; Lan, Yu; Dong, Xiu-Qin; Zhang, Xumu

2017-01-18

We have successfully developed a series of novel and modular ferrorence-based amino-phosphine-alcohol (f-Amphol) ligands, and applied them to iridium-catalyzed asymmetric hydrogenation of various simple ketones to afford the corresponding chiral alcohols with excellent enantioselectivities and conversions (98-99.9 % ee, >99 % conversion, turnover number up to 200 000). Control experiments and density functional theory (DFT) calculations have shown that the hydroxyl group of our f-Amphol ligands played a key role in this asymmetric hydrogenation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies on a new class of organogelator containing 2-anthracenecarboxylic acid: influence of gelator and solvent on stereochemistry of the photodimers.

PubMed

Dawn, Arnab; Fujita, Norifumi; Haraguchi, Shuichi; Sada, Kazuki; Tamaru, Shun-ichi; Shinkai, Seiji

2009-11-07

A new class of binary organogelator (G1, G2 and G3) based on 2-anthracenecarboxylic acid (2Ac), attached noncovalently with the gelator counterpart containing a 3,4,5-tris(n-dodecyloxy)benzoylamide backbone has been developed. Among the three gelators, two (G2 and G3) are chiral containing D-alanine or L-2-phenylglycine moieties, respectively. They can act as efficient gelators of organic solvents with varying polarity depending upon the gelator systems. Gelator G1 even gelates chiral solvents. The photoirradiation of the gel samples produces photocyclodimers having different degrees of stereoselectivity for different systems. Gels with G1 and G2 produce head-to-head (h-h) photodimers as major products, whereas the stereoselectivity is reversed for the gels with G3 producing head-to-tail (h-t) photodimers as major products. Among those, G2/cyclohexane gel shows the highest degree of stereoselectivity, producing only h-h photodimers with some significant amount of chiral induction. Other chiral systems exhibit low to moderate chiral inductions. The gelator G1 can differentiate between the racemic and enantiomerically pure varieties of a solvent by exhibiting different gel melting temperatures (T(gel)). For different gel systems, T(gel) increases in all the cases as a consequence of photoreaction, except for the G2/cyclohexane gel, where a prominent gel-to-sol phase transition can be observed during the photoreaction. Hydrogen-bonding and pi-pi stacking interactions play the principal roles in constructing the gel structure. The morphologies of the gel systems vary between one-dimensional fibrils and a fibrillar network structure. In addition, the influences of the gelator and solvent polarity on the rate of photoreactions, photoproduct distributions as well as gel structures are investigated.

Highly selective and sensitive method for Cu2 + detection based on chiroptical activity of L-Cysteine mediated Au nanorod assemblies

NASA Astrophysics Data System (ADS)

Abbasi, Shahryar; Khani, Hamzeh

2017-11-01

Herein, we demonstrated a simple and efficient method to detect Cu2 + based on amplified optical activity in the chiral nanoassemblies of gold nanorods (Au NRs). L-Cysteine can induce side-by-side or end-to-end assembly of Au NRs with an evident plasmonic circular dichroism (PCD) response due to coupling between surface plasmon resonances (SPR) of Au NRs and the chiral signal of L-Cys. Because of the obvious stronger plasmonic circular dichrosim (CD) response of the side-by-side assembly compared with the end-to-end assemblies, SS assembled Au NRs was selected as a sensitive platform and used for Cu2 + detection. In the presence of Cu2 +, Cu2 + can catalyze O2 oxidation of cysteine to cystine. With an increase in Cu2 + concentration, the L-Cysteine-mediated assembly of Au NRs decreased because of decrease in the free cysteine thiol groups, and the PCD signal decreased. Taking advantage of this method, Cu2 + could be detected in the concentration range of 20 pM-5 nM. Under optimal conditions, the calculated detection limit was found to be 7 pM.

Self-reporting inhibitors: single crystallization process to get two optically pure enantiomers.

PubMed

Wan, Xinhua; Ye, Xichong; Cui, Jiaxi; Li, Bowen; Li, Na; Zhang, Jie

2018-05-22

Collection of two optically pure enantiomers in a single crystallization process can significantly increase the chiral separation efficiency but it's hard to realize nowadays. Herein we describe, for the first time, a self-reporting strategy for visualizing the crystallization process by a kind of dyed self-assembled inhibitors made from the copolymers with tri(ethylene glycol)-grafting polymethylsiloxane as main chains and poly(N6-methacryloyl-L-lysine) as side chains. When applied with seeds together for the fractional crystallization of conglomerates, the inhibitors can label the formation of the secondary crystals and guide us to completely separate the crystallization process of two enantiomers with colorless crystals as the first product and red crystals as the secondary product. This method leads to high optical purity of D/L-Asn·H2O (99.9 ee% for D-crystals and 99.5 ee% for L-crystals) in a single crystallization process. Moreover, it requires low feeding amount of additives and shows excellent recyclability. We foresee its great potential in developing novel chiral separation methods that can be used in different scales. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Concept of improved rigidity: how to make enantioselective hydrophosphonylation of cyclic imines catalyzed by chiral heterobimetallic lanthanoid complexes almost perfect

PubMed

Schlemminger; Saida; Groger; Maison; Durot; Sasai; Shibasaki; Martens

2000-08-11

The catalytic and enantioselective hydrophosphonylation of cyclic imines using cyclic phosphites is described for the first time. In contrast to the application of acyclic phosphites, significant improvements are presented arising from the concept of improved rigidity by utilization of cyclic phosphites in the lanthanoid BINOL complex catalyzed hydrophosphonylation of 3-thiazolines. Cyclic phosphites are shown to provide certain improvements within the catalytic cycle. Influence of parameters such as concentration of the catalyst and the phosphite on the catalysis is examined as well as the effects of the substituents on the starting material. The pharmacologically interesting thiazolidinyl phosphonates are synthesized in excellent optical purities of up to 99% ee and high chemical yields of up to 99%. The required amount of catalyst is reduced to 2.5 mol %. The highest efficiency of the reaction involving cyclic phosphites is achieved using the catalytic system "2.5 mol % (S)-YbPB/2.5 equiv phosphite/50 degrees C/48 h/THF-toluene (1:7)". On the basis of the results a refinement of the proposed catalytic cycle has been provided. For comparison cyclic phosphites were used in hydrophosphonylation with a chiral titanium catalyst.

Kinetic enantioselectivity of a protonated bis(diamido)-bridged basket resorcin[4]arene towards alanine peptides.

PubMed

Fraschetti, C; Montagna, M; Crestoni, M E; Calcaterra, A; Aiello, F; Santi, L; Filippi, A

2017-02-01

Efficient enantiodiscrimination of some alanine-containing di- and tri-peptides by using chiral protonated bis(diamido)-bridged basket resorcin[4]arenes depends on several factors, including the basicity of the amino acid residues at the C- and N-termini of the peptide.

Possible formation of high temperature superconductor at an early stage of heavy-ion collisions

NASA Astrophysics Data System (ADS)

Liu, Hao; Yu, Lang; Chernodub, Maxim; Huang, Mei

2016-12-01

We investigate the effect of the inverse magnetic catalysis (IMC) on charged ρ meson condensation at finite temperature in the framework of the Nambu-Jona-Lasinio model, where mesons are calculated to the leading order of 1 /Nc expansion. The IMC for chiral condensate has been considered using three different approaches: incorporating the chiral condensate from lattice data, using the running coupling constant, and introducing the chiral chemical potential, respectively. It is observed that with no IMC effect included, the critical magnetic field e Bc for charged ρ condensation increases monotonically with the temperature. However, including IMC substantially affects the polarized charged ρ condensation around the critical temperature Tc of the chiral phase transition: first, the critical magnetic field e Bc for the charged ρ condensation decreases with the temperature, reaches its minimum value around Tc, and then increases with the temperature. It is quite surprising that the charged ρ can condense above the critical temperature of chiral phase transition with a even smaller critical magnetic field comparing its vacuum value. The Nambu-Jona-Lasinio model calculation shows that in the temperature region of 1 - 1.5 Tc , the critical magnetic field for charged ρ condensation is rather small and in the region of e Bc˜0.15 - 0.3 GeV2 , which suggests that high temperature superconductor might be created through noncentral heavy ion collisions at LHC energies.

Temperature-Triggered Switchable Helix-Helix Inversion of Poly(phenylacetylene) Bearing l-Valine Ethyl Ester Pendants and Its Chiral Recognition Ability.

PubMed

Zhou, Yanli; Zhang, Chunhong; Qiu, Yuan; Liu, Lijia; Yang, Taotao; Dong, Hongxing; Satoh, Toshifumi; Okamoto, Yoshio

2016-11-21

A phenylacetylene containing the l-valine ethyl ester pendant (PAA-Val) was synthesized and polymerized by an organorhodium catalyst (Rh(nbd)BPh₄) to produce the corresponding one-handed helical cis -poly(phenylacetylene) (PPAA-Val). PPAA-Val showed a unique temperature-triggered switchable helix-sense in chloroform, while it was not observed in highly polar solvents, such as N , N '-dimethylformamide (DMF). By heating the solution of PPAA-Val in chloroform, the sign of the CD absorption became reversed, but recovered after cooling the solution to room temperature. Even after six cycles of the heating-cooling treatment, the helix sense of the PPAA-Val's backbone was still switchable without loss of the CD intensity. The PPAA-Val was then coated on silica gel particles to produce novel chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). These novel PPAA-Val based CSPs showed a high chiral recognition ability for racemic mandelonitrile ( α = 2.18) and racemic trans - N , N '-diphenylcyclohexane-1,2-dicarboxamide ( α = 2.60). Additionally, the one-handed helical cis -polyene backbone of PPAA-Val was irreversibly destroyed to afford PPAA-Val-H by heating in dimethyl sulfoxide (DMSO) accompanied by the complete disappearance of the Cotton effect. Although PPAA-Val-H had the same l-valine ethyl ester pendants as its cis -isomer PPAA-Val, it showed no chiral recognition. It was concluded that the one-handed helical cis -polyene backbone of PPAA-Val plays an important role in the chiral recognition ability.

Enantioseparation of cetirizine by chromatographic methods and discrimination by 1H-NMR.

PubMed

Taha, Elham A; Salama, Nahla N; Wang, Shudong

2009-03-01

Cetirizine is an antihistaminic drug used to prevent and treat allergic conditions. It is currently marketed as a racemate. The H1-antagonist activity of cetirizine is primarily due to (R)-levocetirizine. This has led to the introduction of (R)-levocetirizine into clinical practice, and the chiral switching is expected to be more selective and safer. The present work represents three methods for the analysis and chiral discrimination of cetirizine. The first method was based on the enantioseparation of cetirizine on silica gel TLC plates using different chiral selectors as mobile phase additives. The mobile phase enabling successful resolution was acetonitrile-water 17: 3, (v/v) containing 1 mM of chiral selector, namely hydroxypropyl-beta-cyclodextrin, chondroitin sulphate or vancomycin hydrochloride. The second method was a validated high performance liquid chromatography (HPLC), based on stereoselective separation of cetirizine and quantitative determination of its eutomer (R)-levocetirizine on a monolithic C18 column using hydroxypropyl-beta-cyclodextrin as a chiral mobile phase additive. The resolved peaks of (R)-levocetirizine and (S)-dextrocetirizine were confirmed by further mass spectrometry. The third method used a (1)H-NMR technique to characterize cetirizine and (R)-levocetirizine. These methods are selective and accurate, and can be easily applied for chiral discrimination and determination of cetirizine in drug substance and drug product in quality control laboratory. Moreover, chiral purity testing of (R)-levocetirizine can also be monitored by the chromatographic methods. Copyright 2009 John Wiley & Sons, Ltd.

Enantiodifferentiation of whisky and cognac lactones using gas chromatography with different cyclodextrin chiral stationary phases.

PubMed

Schmarr, Hans-Georg; Mathes, Maximilian; Wall, Kristina; Metzner, Frank; Fraefel, Marius

2017-09-22

The chiral lactone 5-butyl-4-methyloxolan-2-one or 5-butyl-4-methyldihydro-2(3H)-furanone, often named whisky lactone, is found in oak wood, then contributing to the appreciated flavor of beverages stored in such wooden barrels. Its next higher homologue is named cognac lactone (5-pentyl-4-methyloxolan-2-one or 5-pentyl-4-methyldihydro-2(3H)-furanone), however is much less known, probably due to its minor concentration level. In order to study the direct enantioseparation of both lactones by gas chromatography on chiral stationary phases, individual enantiomers, particularly for cognac lactone were made available. This was achieved by baker's yeast reduction of synthesized ethyl 3-methyl-4-oxononanoate or, after hydrolysis, of the corresponding 4-ketoacid, that gave access to individual enantiomers of cognac lactone. Good enantioseparation was achieved for both whisky and cognac lactone with high values for the chiral resolution with 6-O-tert. butyl dimethylsilyl-2,3-dialkylated or 6-O-tert. butyl dimethylsilyl-2,3-diacylated cyclodextrin derivatives as chiral selectors. The influence of the nature and position of derivatization of the cyclodextrin moiety revealed a strong impact on the chiral recognition mechanism, as the investigated alkylated derivatives heptakis-(2,6-di-O-iso-pentyl-3-O-allyl)-β-cyclodextrin and octakis-(2,3-di-O-pentyl-6-O-methyl)-γ-cyclodextrin did not provide any or only minor chiral selectivity for the two lactones. Copyright © 2017 Elsevier B.V. All rights reserved.

Chiral magnetic and vortical effects in high-energy nuclear collisions—A status report

DOE PAGES

Kharzeev, D. E.; Liao, J.; Voloshin, S. A.; ...

2016-05-01

Here, the interplay of quantum anomalies with magnetic field and vorticity results in a variety of novel non-dissipative transport phenomena in systems with chiral fermions, including the quark–gluon plasma. Among them is the Chiral Magnetic Effect (CME)—the generation of electric current along an external magnetic field induced by chirality imbalance. Because the chirality imbalance is related to the global topology of gauge fields, the CME current is topologically protected and hence non-dissipative even in the presence of strong interactions. As a result, the CME and related quantum phenomena affect the hydrodynamical and transport behavior of strongly coupled quark–gluon plasma, andmore » can be studied in relativistic heavy ion collisions where strong magnetic fields are created by the colliding ions. Evidence for the CME and related phenomena has been reported by the STAR Collaboration at Relativistic Heavy Ion Collider at BNL, and by the ALICE Collaboration at the Large Hadron Collider at CERN. The goal of the present review is to provide an elementary introduction into the physics of anomalous chiral effects, to describe the current status of experimental studies in heavy ion physics, and to outline the future work, both in experiment and theory, needed to eliminate the existing uncertainties in the interpretation of the data.« less

Chiral behavior of K →π l ν decay form factors in lattice QCD with exact chiral symmetry

NASA Astrophysics Data System (ADS)

Aoki, S.; Cossu, G.; Feng, X.; Fukaya, H.; Hashimoto, S.; Kaneko, T.; Noaki, J.; Onogi, T.; Jlqcd Collaboration

2017-08-01

We calculate the form factors of the K →π l ν semileptonic decays in three-flavor lattice QCD and study their chiral behavior as a function of the momentum transfer and the Nambu-Goldstone boson masses. Chiral symmetry is exactly preserved by using the overlap quark action, which enables us to directly compare the lattice data with chiral perturbation theory (ChPT). We generate gauge ensembles at a lattice spacing of 0.11 fm with four pion masses covering 290-540 MeV and a strange quark mass ms close to its physical value. By using the all-to-all quark propagator, we calculate the vector and scalar form factors with high precision. Their dependence on ms and the momentum transfer is studied by using the reweighting technique and the twisted boundary conditions for the quark fields. We compare the results for the semileptonic form factors with ChPT at next-to-next-to-leading order in detail. While many low-energy constants appear at this order, we make use of our data of the light meson electromagnetic form factors in order to control the chiral extrapolation. We determine the normalization of the form factors as f+(0 )=0.9636 (36 )(-35+57) and observe reasonable agreement of their shape with experiment.

Optically active quantum dots

NASA Astrophysics Data System (ADS)

Gerard, Valerie; Govan, Joseph; Loudon, Alexander; Baranov, Alexander V.; Fedorov, Anatoly V.; Gun'ko, Yurii K.

2015-10-01

The main goal of our research is to develop new types of technologically important optically active quantum dot (QD) based materials, study their properties and explore their biological applications. For the first time chiral II-VI QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a weak signal. It was also demonstrated that these QDs show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. These QDs have demonstrated highly specific chiral recognition of various biological species including aminoacids. The utilisation of chiral stabilisers also allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum. Biological testing of chiral CdS nanotetrapods displayed a chiral bias for an uptake of the D- penicillamine stabilised nano-tetrapods by cancer cells. It is expected that this research will open new horizons in the chemistry of chiral nanomaterials and their application in nanobiotechnology, medicine and optical chemo- and bio-sensing.

Chiral Graphene Quantum Dots

DOE PAGES

Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; ...

2016-01-15

Chiral nanostructures from metals and semiconductors attract wide interest as components for polarization-enabled optoelectronic devices. Similarly to other fields of nanotechnology, graphene-based materials can greatly enrich physical and chemical phenomena associated with optical and electronic properties of chiral nanostructures and facilitate their applications in biology as well as other areas. Here, we report that covalent attachment of l/d-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the “crowded” edges. Circular dichroism (CD) spectra of the GQDs revealed bands at ca. 210–220 and 250–265 nm that changed their signs formore » different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210–220 nm correspond to the hybridized molecular orbitals involving the chiral center of amino acids and atoms of graphene edges. Diverse experimental and modeling data, including density functional theory calculations of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250–265 nm originates from the three-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The positive and negative low-energy CD bands correspond to the left and right helicity of GQDs, respectively. Exposure of liver HepG2 cells to l/d-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Molecular dynamics simulations demonstrated that d-GQDs have a stronger tendency to accumulate within the cellular membrane than l-GQDs. Finally, emergence of nanoscale chirality in GQDs decorated with biomolecules is expected to be a general stereochemical phenomenon for flexible sheets of nanomaterials.« less

Chiral SiO2 and Ag@SiO2 Materials Templated by Complexes Consisting of Comblike Polyethyleneimine and Tartaric Acid.

PubMed

Yao, Dong-Dong; Murata, Hiroki; Tsunega, Seiji; Jin, Ren-Hua

2015-10-26

A facile avenue to fabricate micrometer-sized chiral (L-, D-) and meso-like (dl-) SiO2 materials with unique structures by using crystalline complexes (cPEI/tart), composed of comblike polyethyleneimine (cPEI) and L-, D-, or dl-tartaric acid, respectively, as catalytic templates is reported. Interestingly, both chiral crystalline complexes appeared as regularly left- and right-twisted bundle structures about 10 μm in length and about 5 μm in diameter, whereas the dl-form occurred as circular structures with about 10 μm diameter. Subsequently, SiO2 @cPEI/tart hybrids with high silica content (>55.0 wt %) were prepared by stirring a mixture containing tetramethoxysilane (TMOS) and the aggregates of the crystalline complexes in water. The chiral SiO2 hybrids and calcined chiral SiO2 showed very strong CD signals and a nanofiber-based morphology on their surface, whereas dl-SiO2 showed no CD activity and a nanosheet-packed disklike shape. Furthermore, metallic silver nanoparticles (Ag NPs) were encapsulated in each silica hybrid to obtain chiral (D and L forms) and meso-like (dl form) Ag@SiO2 composites. Also, the reaction between L-cysteine (Lcys) and these Ag@SiO2 composites was preliminarily investigated. Only chiral L- and D-Ag@SiO2 composites promoted the reaction between Lcys and Ag NPs to produce a molecular [Ag-Lcys]n complex with remarkable exciton chirality, whereas the reaction hardly occurred in the case of meso-like (dl-) Ag@SiO2 composite. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of supercritical fluid chromatography conditions on enantioselectivity and performance of polyproline-derived chiral stationary phases.

PubMed

Novell, Arnau; Méndez, Alberto; Minguillón, Cristina

2015-07-17

The chromatographic behaviour and performance of four polyproline-derived chiral stationary phases (CSPs) were tested using supercritical fluid chromatography (SFC). A series of structurally related racemic compounds, whose enantioseparation was proved to be sensitive to the type of mobile phase used in NP-HPLC, were chosen to be tested in the SFC conditions. Good enantioselection ability was shown by the CSPs for the analytes tested in the new conditions. Resolution, efficiency and analysis time, were considerably improved with respect to NP-HPLC when CO2/alcohol mobile phases were used. Monolithic columns clearly show enhanced chromatographic parameters and improved performance respect to their bead-based counterparts. Copyright © 2015 Elsevier B.V. All rights reserved.

Chiral 2-Aminobenzimidazole as Bifunctional Catalyst in the Asymmetric Electrophilic Amination of Unprotected 3-Substituted Oxindoles.

PubMed

Benavent, Llorenç; Baeza, Alejandro; Freckleton, Megan

2018-06-06

The use of readily available chiral trans -cyclohexanediamine-benzimidazole derivatives as bifunctional organocatalysts in the asymmetric electrophilic amination of unprotected 3-substituted oxindoles is presented. Different organocatalysts were evaluated; the most successful one contained a dimethylamino moiety ( 5 ). With this catalyst under optimized conditions, different oxindoles containing a wide variety of substituents at the 3-position were aminated in good yields and with good to excellent enantioselectivities using di- tert -butylazodicarboxylate as the aminating agent. The procedure proved to be also efficient for the amination of 3-substituted benzofuranones, although with moderate results. A bifunctional role of the catalyst, acting as Brønsted base and hydrogen bond donor, is proposed according to the experimental results observed.

Preparation of imprinted cryogel cartridge for chiral separation of l-phenylalanine.

PubMed

Akgönüllü, Semra; Yavuz, Handan; Denizli, Adil

2017-06-01

l-Phe-imprinted cryogel cartridge was prepared for the chiral separation of l-Phe. N-Methacryloyl l-phenylalanine (MAPA) was used as a functional monomer for complexing with l-Phe. The selectivity of the membranes was investigated by using d-Phe, l-Trp, and d-Trp as competitor molecules. The PHEMAPA-l-Trp membranes were 6.4, 4.3, and 5.5 times more selective for l-Phe than d-Phe, l-Trp, and d-Trp, respectively. The PHEMAPA-l-Phe cryogel cartridge was incorporated into the fast protein liquid chromatography (FPLC) equipment and was able to separate D,l-Phe racemic mixture efficiently. The PHEMAPA-l-Phe membranes were shown to be reusable many times without significant loss of the adsorption capacity.

Chiral topological phases from artificial neural networks

NASA Astrophysics Data System (ADS)

Kaubruegger, Raphael; Pastori, Lorenzo; Budich, Jan Carl

2018-05-01

Motivated by recent progress in applying techniques from the field of artificial neural networks (ANNs) to quantum many-body physics, we investigate to what extent the flexibility of ANNs can be used to efficiently study systems that host chiral topological phases such as fractional quantum Hall (FQH) phases. With benchmark examples, we demonstrate that training ANNs of restricted Boltzmann machine type in the framework of variational Monte Carlo can numerically solve FQH problems to good approximation. Furthermore, we show by explicit construction how n -body correlations can be kept at an exact level with ANN wave functions exhibiting polynomial scaling with power n in system size. Using this construction, we analytically represent the paradigmatic Laughlin wave function as an ANN state.

Theoretical study of the accuracy of the elution by characteristic points method for bi-langmuir isotherms.

PubMed

Ravald, L; Fornstedt, T

2001-01-26

The bi-Langmuir equation has recently been proven essential to describe chiral chromatographic surfaces and we therefore investigated the accuracy of the elution by characteristic points method (ECP) for estimation of bi-Langmuir isotherm parameters. The ECP calculations was done on elution profiles generated by the equilibrium-dispersive model of chromatography for five different sets of bi-Langmuir parameters. The ECP method generates two different errors; (i) the error of the ECP calculated isotherm and (ii) the model error of the fitting to the ECP isotherm. Both errors decreased with increasing column efficiency. Moreover, the model error was strongly affected by the weight of the bi-Langmuir function fitted. For some bi-Langmuir compositions the error of the ECP calculated isotherm is too large even at high column efficiencies. Guidelines will be given on surface types to be avoided and on column efficiencies and loading factors required for adequate parameter estimations with ECP.

Intrinsic chirality and prochirality at Air/R-(+)- and S-(-)-limonene interfaces: spectral signatures with interference chiral sum-frequency generation vibrational spectroscopy.

PubMed

Fu, Li; Zhang, Yun; Wei, Zhe-Hao; Wang, Hong-Fei

2014-09-01

We report in this work detailed measurements of the chiral and achiral sum-frequency vibrational spectra in the C-H stretching vibration region (2800-3050 cm(-1)) of the air/liquid interfaces of R-(+)-limonene and S-(-)-limonene, using the recently developed high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS). The achiral SFG spectra of R-limonene and S-limonene, as well as the RS racemic mixture (50/50 equal amount mixture), show that the corresponding molecular groups of the R and S enantiomers are with the same interfacial orientations. The interference chiral SFG spectra of the limonene enantiomers exhibit a spectral signature from the chiral response of the Cα-H stretching mode, and a spectral signature from the prochiral response of the CH(2) asymmetric stretching mode, respectively. The chiral spectral feature of the Cα-H stretching mode changes sign from R-(+)-limonene to S-(-)-limonene surfaces, and disappears for the RS racemic mixture surface. While the prochiral spectral feature of the CH(2) asymmetric stretching mode is the same for R-(+)-limonene and S-(-)-limonene surfaces, and also surprisingly remains the same for the RS racemic mixture surface. Therefore, the structures of the R-(+)-limonene and the S-(-)-limonene at the liquid interfaces are nevertheless not mirror images to each other, even though the corresponding groups have the same tilt angle from the interfacial normal, i.e., the R-(+)-limonene and the S-(-)-limonene at the surface are diastereomeric instead of enantiomeric. These results provide detailed information in understanding the structure and chirality of molecular interfaces and demonstrate the sensitivity and potential of SFG-VS as a unique spectroscopic tool for chirality characterization and chiral recognition at the molecular interface. © 2014 Wiley Periodicals, Inc.

Evanescent-wave and ambient chiral sensing by signal-reversing cavity ringdown polarimetry.

PubMed

Sofikitis, Dimitris; Bougas, Lykourgos; Katsoprinakis, Georgios E; Spiliotis, Alexandros K; Loppinet, Benoit; Rakitzis, T Peter

2014-10-02

Detecting and quantifying chirality is important in fields ranging from analytical and biological chemistry to pharmacology and fundamental physics: it can aid drug design and synthesis, contribute to protein structure determination, and help detect parity violation of the weak force. Recent developments employ microwaves, femtosecond pulses, superchiral light or photoionization to determine chirality, yet the most widely used methods remain the traditional methods of measuring circular dichroism and optical rotation. However, these signals are typically very weak against larger time-dependent backgrounds. Cavity-enhanced optical methods can be used to amplify weak signals by passing them repeatedly through an optical cavity, and two-mirror cavities achieving up to 10(5) cavity passes have enabled absorption and birefringence measurements with record sensitivities. But chiral signals cancel when passing back and forth through a cavity, while the ubiquitous spurious linear birefringence background is enhanced. Even when intracavity optics overcome these problems, absolute chirality measurements remain difficult and sometimes impossible. Here we use a pulsed-laser bowtie cavity ringdown polarimeter with counter-propagating beams to enhance chiral signals by a factor equal to the number of cavity passes (typically >10(3)); to suppress the effects of linear birefringence by means of a large induced intracavity Faraday rotation; and to effect rapid signal reversals by reversing the Faraday rotation and subtracting signals from the counter-propagating beams. These features allow absolute chiral signal measurements in environments where background subtraction is not feasible: we determine optical rotation from α-pinene vapour in open air, and from maltodextrin and fructose solutions in the evanescent wave produced by total internal reflection at a prism surface. The limits of the present polarimeter, when using a continuous-wave laser locked to a stable, high-finesse cavity, should match the sensitivity of linear birefringence measurements (3 × 10(-13) radians), which is several orders of magnitude more sensitive than current chiral detection limits and is expected to transform chiral sensing in many fields.

Two-Dimensional Collective Hamiltonian for Chiral and Wobbling Modes

DOE PAGES

Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.; ...

2016-10-03

Here, a two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ= -30°) coupling to one h 11/2 proton particle and one h 11/2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree withmore » the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.« less

Strangeness S =-1 hyperon-nucleon interactions: Chiral effective field theory versus lattice QCD

NASA Astrophysics Data System (ADS)

Song, Jing; Li, Kai-Wen; Geng, Li-Sheng

2018-06-01

Hyperon-nucleon interactions serve as basic inputs to studies of hypernuclear physics and dense (neutron) stars. Unfortunately, a precise understanding of these important quantities has lagged far behind that of the nucleon-nucleon interaction due to lack of high-precision experimental data. Historically, hyperon-nucleon interactions are either formulated in quark models or meson exchange models. In recent years, lattice QCD simulations and chiral effective field theory approaches start to offer new insights from first principles. In the present work, we contrast the state-of-the-art lattice QCD simulations with the latest chiral hyperon-nucleon forces and show that the leading order relativistic chiral results can already describe the lattice QCD data reasonably well. Given the fact that the lattice QCD simulations are performed with pion masses ranging from the (almost) physical point to 700 MeV, such studies provide a useful check on both the chiral effective field theory approaches as well as lattice QCD simulations. Nevertheless more precise lattice QCD simulations are eagerly needed to refine our understanding of hyperon-nucleon interactions.

Two-Dimensional Collective Hamiltonian for Chiral and Wobbling Modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Q. B.; Zhang, S. Q.; Zhao, P. W.

Here, a two-dimensional collective Hamiltonian (2DCH) on both azimuth and polar motions in triaxial nuclei is proposed to investigate the chiral and wobbling modes. In the 2DCH, the collective potential and the mass parameters are determined from three-dimensional tilted axis cranking (TAC) calculations. The broken chiral and signature symmetries in the TAC solutions are restored by the 2DCH. The validity of the 2DCH is illustrated with a triaxial rotor (γ= -30°) coupling to one h 11/2 proton particle and one h 11/2 neutron hole. By diagonalizing the 2DCH, the angular momenta and energy spectra are obtained. These results agree withmore » the exact solutions of the particle rotor model (PRM) at high rotational frequencies. However, at low frequencies, the energies given by the 2DCH are larger than those by the PRM due to the underestimation of the mass parameters. In addition, with increasing angular momentum, the transitions from the chiral vibration to chiral rotation and further to longitudinal wobbling motion have been presented in the 2DCH.« less

Topology in the SU(Nf) chiral symmetry restored phase of unquenched QCD and axion cosmology

NASA Astrophysics Data System (ADS)

Azcoiti, Vicente

2018-03-01

The axion is one of the more interesting candidates to make the dark matter of the universe, and the axion potential plays a fundamental role in the determination of the dynamics of the axion field. Moreover, the way in which the U(1)A anomaly manifests itself in the chiral symmetry restored phase of QCD at high temperature could be tested when probing the QCD phase transition in relativistic heavy ion collisions. With these motivations, we investigate the physical consequences of the survival of the effects of the U(1)A anomaly in the chiral symmetric phase of QCD, and show that the free energy density is a singular function of the quark mass m, in the chiral limit, and that the σ and π susceptibilities diverge in this limit at any T ≥ Tc. We also show that the difference between the π and t;δ susceptibilities diverges in the chiral limit at any T ≥ Tc, a result that can be contrasted with the existing lattice calculations; and discuss on the generalization of these results to the Nf ≥ 3 model.

Chiral Templating of Self-Assembling Nanostructures by Circularly Polarized Light

PubMed Central

Yeom, Jihyeon; Yeom, Bongjun; Chan, Henry; Smith, Kyle W.; Dominguez-Medina, Sergio; Bahng, Joong Hwan; Zhao, Gongpu; Chang, Wei-Shun; Chang, Sung Jin; Chuvilin, Andrey; Melnikau, Dzmitry; Rogach, Andrey L.; Zhang, Peijun; Link, Stephan; Král, Petr; Kotov, Nicholas A.

2015-01-01

Chemical reactions affected by spin angular momenta of circularly polarized photons are rare and display low enantiomeric excess. High optical and chemical activity of nanoparticles (NPs) should facilitate the transfer of spin angular momenta of photons to nanoscale materials but such processes are unknown. Here we demonstrate that circularly polarized light (CPL) strongly affects self-assembly of racemic CdTe NPs. Illumination of NP dispersions with right- and left-handed CPL induces the formation of right- and left-handed twisted nanoribbons, respectively. Enantiomeric excess of such reactions exceeds 30% which is ~10 times higher than other CPL-induced reactions. Illumination with linearly polarized light and assembly in the dark led to straight nanoribbons. The mechanism of “templation” of NP assemblies by CPL is associated with selective photoactivation of chiral NPs and clusters followed by their photooxidation. Chiral anisotropy of interactions translates into chirality of the assembled ribbons. The ability of NPs to retain polarization information, or the “imprint” of incident photons opens new pathways for the synthesis of chiral photonic materials and allows for better understanding of the origins of biomolecular homochirality. PMID:25401922

Lipase-catalyzed highly enantioselective kinetic resolution of boron-containing chiral alcohols.

PubMed

Andrade, Leandro H; Barcellos, Thiago

2009-07-16

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained.

Chiral Gold Nanoclusters: Atomic Level Origins of Chirality.

PubMed

Zeng, Chenjie; Jin, Rongchao

2017-08-04

Chiral nanomaterials have received wide interest in many areas, but the exact origin of chirality at the atomic level remains elusive in many cases. With recent significant progress in atomically precise gold nanoclusters (e.g., thiolate-protected Au n (SR) m ), several origins of chirality have been unveiled based upon atomic structures determined by using single-crystal X-ray crystallography. The reported chiral Au n (SR) m structures explicitly reveal a predominant origin of chirality that arises from the Au-S chiral patterns at the metal-ligand interface, as opposed to the chiral arrangement of metal atoms in the inner core (i.e. kernel). In addition, chirality can also be introduced by a chiral ligand, manifested in the circular dichroism response from metal-based electronic transitions other than the ligand's own transition(s). Lastly, the chiral arrangement of carbon tails of the ligands has also been discovered in a very recent work on chiral Au 133 (SR) 52 and Au 246 (SR) 80 nanoclusters. Overall, the origins of chirality discovered in Au n (SR) m nanoclusters may provide models for the understanding of chirality origins in other types of nanomaterials and also constitute the basis for the development of various applications of chiral nanoparticles. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral signs of TPPS co-assemblies with chiral gelators: role of molecular and supramolecular chirality.

PubMed

Wang, Qiuling; Zhang, Li; Yang, Dong; Li, Tiesheng; Liu, Minghua

2016-10-13

A dianionic tetrakis(4-sulfonatophenyl)porphyrin (TPPS) self-assembled into J-aggregates when it co-assembled with a chiral cationic amphiphile via supramolecular gelation. The chiral signs of TPPS J aggregates followed the supramolecular chirality of amphiphilic assemblies rather than the molecular chirality of the amphiphile.

Rules for biocatalyst and reaction engineering to implement effective, NAD(P)H-dependent, whole cell bioreductions

PubMed Central

Kratzer, Regina; Woodley, John M.; Nidetzky, Bernd

2016-01-01

Access to chiral alcohols of high optical purity is today frequently provided by the enzymatic reduction of precursor ketones. However, bioreductions are complicated by the need for reducing equivalents in the form of NAD(P)H. The high price and molecular weight of NAD(P)H necessitate in situ recycling of catalytic quantities, which is mostly accomplished by enzymatic oxidation of a cheap co-substrate. The coupled oxidoreduction can be either performed by free enzymes in solution or by whole cells. Reductase selection, the decision between cell-free and whole cell reduction system, coenzyme recycling mode and reaction conditions represent design options that strongly affect bioreduction efficiency. In this paper, each option was critically scrutinized and decision rules formulated based on well-described literature examples. The development chain was visualized as a decision-tree that can be used to identify the most promising route towards the production of a specific chiral alcohol. General methods, applications and bottlenecks in the set-up are presented and key experiments required to “test” for decision-making attributes are defined. The reduction of o-chloroacetophenone to (S)-1-(2-chlorophenyl)ethanol was used as one example to demonstrate all the development steps. Detailed analysis of reported large scale bioreductions identified product isolation as a major bottleneck in process design. PMID:26343336

Series of chiral interpenetrating 3d-4f heterometallic MOFs: Luminescent sensors and magnetic properties

NASA Astrophysics Data System (ADS)

Zhang, Xiaolei; Chen, Chen; Liu, Xiaoli; Gao, Peng; Hu, Ming

2017-09-01

Series of chiral 3d-4f heterometallic MOFs based on a multidentate terpyridyl carboxylic acid ligand have been synthesized under the solvothermal conditions, namely, [LnZnL(CO3)2(H2O)]n (Ln = Eu (1), Gd (2), Dy (3), Ho (4), Er (5), Tm (6), Yb (7), Lu (8)) (HL = 4‧-(4-carboxyphenyl)-2,2‧:6‧,2″-terpyridine). Compounds 1-8 were structurally characterized by the elemental analyses, infrared spectra, and single crystal X-ray diffractions. Compounds 1-8 exhibit the chiral interpenetrating 3D frameworks. Interestingly, 1 can serve as the luminescent sensor to detect nitrobenzene molecules with high sensitivity. The investigations on CD spectra of single crystals clearly assigned the Cotton effect, indicating that there exist two chiral enantiomers of 1-8 in the course of crystallization. The magnetic properties of 2 and 7 were exploited, respectively.

Searching for Models Exhibiting High Circularly Polarized Luminescence: the Electroactive Inherently Chiral Oligothiophenes.

PubMed

Benincori, Tiziana; Appoloni, Giulio; Mussini, Patrizia Romana; Arnaboldi, Serena; Cirilli, Roberto; Quartapelle Procopio, Elsa; Panigati, Monica; Abbate, Sergio; Mazzeo, Giuseppe; Longhi, Giovanna

2018-05-02

Two new inherently chiral oligothiophenes characterized by the atropisomeric 3,3'-bithianaphtene scaffold functionalized with fused ring bithiophene derivatives, namely 4H-cyclopenta [2,1-b3:4b']dithiophene (CPDT) and dithieno[3,3-b:2',3'-d]pyrrole (DTP), were synthesized. The racemates were fully characterized and resolved into antipodes by enantioselective HPLC. The enantiomers were analyzed through different chiroptical techniques: electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) were employed to attribute the absolute configuration (AC). Comparison of experimental and calculated VCD spectra confirmed the DFT calculated conformational characteristics. The compound functionalized with two CPDT units was oxidized with FeCl3 and ECD and CPL of the resulting material were measured. Circularly Polarized Luminescence (CPL) was measured in order to verify if inherently chiral oligothiophenes could be promising systems for chiral photonics applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pion-photon reactions and chiral dynamics in Primakoff processes at COMPASS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedrich, Jan Michael

2016-01-22

With the COMPASS experiment at CERN, pion-photon reactions are investigated via the Primakoff effect, implying that high-energetic pions react with the quasi-real photon field surrounding the target nuclei. The production of a single hard photon in such a pion scattering at lowest momentum transfer to the nucleus is related to pion Compton scattering. From the measured cross-section shape, the pion polarisability is determined. The COMPASS measurement is in contradiction to the earlier dedicated measurements, and rather in agreement with the theoretical expectation from chiral perturbation theory. In the same data taking, reactions with neutral and charged pions in the finalmore » state are measured and analyzed. At low energy in the pion-photon centre-of-momentum system, these reactions are governed by chiral dynamics and contain information relevant for chiral perturbation theory. At higher energies, resonances are produced and their radiative coupling is investigated.« less

Nano-liquid chromatography applied to enantiomers separation.

PubMed

Fanali, Salvatore

2017-02-24

This paper presents the state of the art concerning the separation of chiral compounds by means of nano-liquid chromatography (nano-LC). The enantiomers' separation and determination are a subject of fundamental importance in various application fields such as pharmaceutical industry, biomedicine, food, agrochemical etc. Nano-LC is a miniaturized chromatographic technique offering some advantages over conventional ones such as low consumption of mobile phase, sample volume and amount of chiral stationary phase, reduced costs etc. This is reported in the first part of the paper illustrating the features of the nano-LC. In addition, chiral resolution methods are briefly illustrated. Some chiral selectors, used in high-performance liquid chromatography have also been applied in nano-LC including cyclodextrins, glycopeptide antibiotics, modified polysaccharides etc. This is discussed in the second part of the review. Finally some examples of the applications available in literature are reported. Copyright © 2016 Elsevier B.V. All rights reserved.