Chiral selection on inorganic crystalline surfaces

NASA Technical Reports Server (NTRS)

Hazen, Robert M.; Sholl, David S.

2003-01-01

From synthetic drugs to biodegradable plastics to the origin of life, the chiral selection of molecules presents both daunting challenges and significant opportunities in materials science. Among the most promising, yet little explored, avenues for chiral molecular discrimination is adsorption on chiral crystalline surfaces - periodic environments that can select, concentrate and possibly even organize molecules into polymers and other macromolecular structures. Here we review experimental and theoretical approaches to chiral selection on inorganic crystalline surfaces - research that is poised to open this new frontier in understanding and exploiting surface-molecule interactions.

Thiol-ene click chemistry derived cationic cyclodextrin chiral stationary phase and its enhanced separation performance in liquid chromatography.

PubMed

Yao, Xiaobin; Tan, Timothy Thatt Yang; Wang, Yong

2014-01-24

This work is the first demonstration of a simple thiol-ene click chemistry to anchor vinyl imidazolium β-CD onto thiol silica to form a novel cationic native cyclodextrin (CD) chiral stationary phase (CSP). The CSP afforded high enantioseparation ability towards dansyl (Dns) amino acids, carboxylic aryl compounds and flavonoids in chiral HPLC. The current CSP demonstrates the highest resolving ability (selectivity >1.1, resolution >1.5) towards Dns amino acids in a mobile phase buffered at pH=6.5, with the resolution of Dns-dl-leucine as high as 6.97. 2,4-dichloride propionic acid (2,4-ClPOPA) was well resolved with the selectivity and resolution of 1.37 and 4.88, respectively. Compared to a previously reported native CD-CSP based on a triazole linkage, the current cationic CD-CSP shows a stronger retention and higher resolution towards acidic chiral compounds, ascribed to the propitious strong electrostatic attraction. Stability evaluation results indicated that thiol-ene reaction can provide a facile and robust approach for the preparation of positively charged CD CSPs. Copyright © 2013 Elsevier B.V. All rights reserved.

Investigation of Chirality Selection Mechanism of Single-Walled Carbon Nanotube

DTIC Science & Technology

2015-07-17

Final 3. DATES COVERED (From - To) 01-June-2014 to 31-May-2015 4. TITLE AND SUBTITLE Investigation of Chirality Selection Mechanism of...of two significant mechanistic aspects of carbon nanotube (CNT) array growth under chemical vapor deposition conditions: chirality selectivity and...affected by the morphological evolution of catalyst particles. 15. SUBJECT TERMS Carbon Nanotubes, Chirality , Processing, Catalysis

A novel aggregation-induced emission enhancement triggered by the assembly of a chiral gelator: from non-emissive nanofibers to emissive micro-loops.

PubMed

Chen, Wenrui; Qing, Guangyan; Sun, Taolei

2016-12-22

In this study, a novel aggregation-induced emission (AIE) enhancement triggered by the self-assembly of chiral gelator is described. Tuning of molecular chirality in situ triggers different assemblies of superstructures exhibiting fluorescence. This novel AIE material can constitute an emerging library of chiral supramolecules for turn-on fluorescent sensors. It will also help in better understanding the effects of chiral factors on the photophysical process.

Immobilized-type chiral packing materials for HPLC based on polysaccharide derivatives.

PubMed

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

2008-11-01

The polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography (HPLC) have been recognized as the most powerful ones for the analyzing and preparative separating of the chiral compounds. These CPMs have been conventionally prepared by coating polysaccharide derivatives on a silica gel support. This means that the solvents, which swell or dissolve the derivatives on the silica gel and reduce the performance of the chiral columns, do not allow to be applied as components of the eluents. Therefore, the polysaccharide-based CPMs can be used with a rather limited number of eluents. In order to enhance the versatility of the eluent selection for more practical and economical chromatographic enantioseparations, the polysaccharide derivatives must be immobilized onto the silica gel. This review summarizes our latest studies on the development of the immobilized-type CPMs via the radical copolymerization and the polycondensation of the polysaccharide derivatives bearing small amounts of vinyl groups and alkoxysilyl groups, respectively.

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

Enhanced Chiral Discriminatory van der Waals Interactions Mediated by Chiral Surfaces

NASA Astrophysics Data System (ADS)

Barcellona, Pablo; Safari, Hassan; Salam, A.; Buhmann, Stefan Yoshi

2017-05-01

We predict a discriminatory interaction between a chiral molecule and an achiral molecule which is mediated by a chiral body. To achieve this, we generalize the van der Waals interaction potential between two ground-state molecules with electric, magnetic, and chiral response to nontrivial environments. The force is evaluated using second-order perturbation theory with an effective Hamiltonian. Chiral media enhance or reduce the free interaction via many-body interactions, making it possible to measure the chiral contributions to the van der Waals force with current technology. The van der Waals interaction is discriminatory with respect to enantiomers of different handedness and could be used to separate enantiomers. We also suggest a specific geometric configuration where the electric contribution to the van der Waals interaction is zero, making the chiral component the dominant effect.

In situ evidence for chirality-dependent growth rates of individual carbon nanotubes

NASA Astrophysics Data System (ADS)

Rao, Rahul; Liptak, David; Cherukuri, Tonya; Yakobson, Boris I.; Maruyama, Benji

2012-03-01

Chiral-selective growth of single-walled carbon nanotubes (SWNTs) remains a great challenge that hinders their use in applications such as electronics and medicine. Recent experimental and theoretical reports have begun to address this problem by suggesting that selectivity may be achieved during nucleation by changing the catalyst composition or structure. Nevertheless, to establish a rational basis for chiral-selective synthesis, the underlying mechanisms governing nucleation, growth, and termination of SWNTs must be better understood. To this end, we report the first measurements of growth rates of individual SWNTs through in situ Raman spectroscopy and correlate them with their chiral angles. Our results show that the growth rates are directly proportional to the chiral angles, in agreement with recent theoretical predictions. Importantly, the evidence singles out the growth stage as responsible for the chiral distribution—distinct from nucleation and termination which might also affect the final product distribution. Our results suggest a route to chiral-selective synthesis of SWNTs through rational synthetic design strategies based on kinetic control.

Insights into peptide nucleic acid (PNA) structural features: The crystal structure of a d-lysine-based chiral PNA–DNA duplex

PubMed Central

Menchise, Valeria; De Simone, Giuseppina; Tedeschi, Tullia; Corradini, Roberto; Sforza, Stefano; Marchelli, Rosangela; Capasso, Domenica; Saviano, Michele; Pedone, Carlo

2003-01-01

Peptide nucleic acids (PNAs) are oligonucleotide analogues in which the sugar-phosphate backbone has been replaced by a pseudopeptide skeleton. They bind DNA and RNA with high specificity and selectivity, leading to PNA–RNA and PNA–DNA hybrids more stable than the corresponding nucleic acid complexes. The binding affinity and selectivity of PNAs for nucleic acids can be modified by the introduction of stereogenic centers (such as d-Lys-based units) into the PNA backbone. To investigate the structural features of chiral PNAs, the structure of a PNA decamer containing three d-Lys-based monomers (namely H-GpnTpnApnGpnAdlTdlCdlApnCpnTpn-NH2, in which pn represents a pseudopeptide link and dl represents a d-Lys analogue) hybridized with its complementary antiparallel DNA has been solved at a 1.66-Å resolution by means of a single-wavelength anomalous diffraction experiment on a brominated derivative. Thed-Lys-based chiral PNA–DNA (LPD) heteroduplex adopts the so-called P-helix conformation. From the substantial similarity between the PNA conformation in LPD and the conformations observed in other PNA structures, it can be concluded that PNAs possess intrinsic conformational preferences for the P-helix, and that their flexibility is rather restricted. The conformational rigidity of PNAs is enhanced by the presence of the chiral centers, limiting the ability of PNA strands to adopt other conformations and, ultimately, increasing the selectivity in molecular recognition. PMID:14512516

Tunable chiral metal organic frameworks toward visible light–driven asymmetric catalysis

PubMed Central

Zhang, Yin; Guo, Jun; Shi, Lin; Zhu, Yanfei; Hou, Ke; Zheng, Yonglong; Tang, Zhiyong

2017-01-01

A simple and effective strategy is developed to realize visible light–driven heterogeneous asymmetric catalysis. A chiral organic molecule, which only has very weak catalytic activity in asymmetric α-alkylation of aldehydes under visible light, is utilized as the ligand to coordinate with different types of metal ions, including Zn2+, Zr4+, and Ti4+, for construction of crystalline metal organic frameworks (MOFs). Impressively, when used as heterogeneous catalysts, all of the synthesized MOFs exhibit markedly enhanced activity. Furthermore, the asymmetric catalytic performance of these MOFs could be easily altered by selecting different metal ions, owing to the tunable electron transfer property between metal ions and chiral ligands. This work will provide a new approach for fabrication of heterogeneous catalysts and trigger more enthusiasm to conduct the asymmetric catalysis driven by visible light. PMID:28835929

Switchable Chiral Selection of Aspartic Acids by Dynamic States of Brushite

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

Jiang, Wenge; Pan, Haihua; Zhang, Zhisen

Here, we show the chiral recognition and separation of aspartic acid (Asp) enantiomers by achiral brushite due to the asymmetries of their dynamical steps in its nonequilibrium states. Growing brushite has a higher adsorption affinity to d-Asp, while l-Asp is predominant on the dissolving brushite surface. Microstructural characterization reveals that chiral selection is mainly attributed to brushite [101] steps, which exhibit two different configurations during crystal growth and dissolution, respectively, with each preferring a distinct enantiomer due to this asymmetry. Because these transition step configurations have different stabilities, they subsequently result in asymmetric adsorption. Furthermore, by varying free energy barriersmore » through solution thermodynamic driving force (i.e., supersaturation), the dominant nonequilibrium intermediate states can be switched and chiral selection regulated. This finding highlights that the dynamic steps can be vital for chiral selection, which may provide a potential pathway for chirality generation through the dynamic nature.« less

Switchable Chiral Selection of Aspartic Acids by Dynamic States of Brushite

DOE PAGES

Jiang, Wenge; Pan, Haihua; Zhang, Zhisen; ...

2017-06-15

Here, we show the chiral recognition and separation of aspartic acid (Asp) enantiomers by achiral brushite due to the asymmetries of their dynamical steps in its nonequilibrium states. Growing brushite has a higher adsorption affinity to d-Asp, while l-Asp is predominant on the dissolving brushite surface. Microstructural characterization reveals that chiral selection is mainly attributed to brushite [101] steps, which exhibit two different configurations during crystal growth and dissolution, respectively, with each preferring a distinct enantiomer due to this asymmetry. Because these transition step configurations have different stabilities, they subsequently result in asymmetric adsorption. Furthermore, by varying free energy barriersmore » through solution thermodynamic driving force (i.e., supersaturation), the dominant nonequilibrium intermediate states can be switched and chiral selection regulated. This finding highlights that the dynamic steps can be vital for chiral selection, which may provide a potential pathway for chirality generation through the dynamic nature.« less

Two-stages of chiral selectivity in the molecular self-assembly of tryptophan

NASA Astrophysics Data System (ADS)

Guisinger, Nathan

Both chirality and molecular assembly are essential and key components to life. In this study we explore the molecular assembly of the amino acid tryptophan (both L- and D- chiralities) on Cu(111). Our investigation utilizes low temperature scanning tunneling microscopy to observe resulting assemblies at the molecular scale. We find that depositing a racemic mixture of both L- and D- tryptophan results in the assembly of basic 6 molecule ``Lego'' structures that are enantiopure. These enantiopure ``Legos'' further assemble into 1-dimensional chains one block at a time. These resulting chains are also enantiopure with chiral selectivity occurring at two stages of assembly. Utilizing scanning tunneling spectroscopy we are able to probe the electronic structure of the chiral Legos that give insight into the root of the observed selectivity. Two-stages of chiral selectivity in the molecular self-assembly of tryptophan.

Chiral metamirrors for broadband spin-selective absorption

NASA Astrophysics Data System (ADS)

Jing, Liqiao; Wang, Zuojia; Yang, Yihao; Zheng, Bin; Liu, Yongmin; Chen, Hongsheng

2017-06-01

Chiral metamirrors are recently proposed metadevices that have the ability of selective reflection for the designated circularly polarized waves. However, previous chiral metamirrors only work in a narrow band, which would limit their potential applications in engineering. Here, we propose an approach towards broadband spin-selective absorption. By combining the chiral resonant modes of two asymmetric split-ring resonators, we design and construct a chiral metamirror that absorbs only the left-handed circularly waves over a broad frequency range. The measured results show a bandwidth of 5.1%, almost 96% larger than that of the narrowband metamirror. Furthermore, the proposed chiral metamirror exhibits prominent performance at oblique incidence, even when high-order diffraction appears. The total thickness of the metamirror is only one-ninth of the wavelength, highly suitable for on-chip integration. Our findings may provide an efficient approach to boost the working bandwidth of the chiral metamirror and could advance its applications in optical instruments.

Review on Polarization Selective Terahertz Metamaterials: from Chiral Metamaterials to Stereometamaterials

NASA Astrophysics Data System (ADS)

Philip, Elizabath; Zeki Güngördü, M.; Pal, Sharmistha; Kung, Patrick; Kim, Seongsin Margaret

2017-09-01

In this article, recent progress and development of terahertz chiral metamaterials including stereometamaterials are thoroughly reviewed. This review mainly focuses on the fundamental principles of design and arrangement of meta-atoms in metamaterials exhibiting chirality with various asymmetry and symmetry and 2D and 3D configuration. Related optical and propagation properties in chiral metamaterials, such as optical activity, circular dichroism, and negative refraction for each different chiral metamaterials, are compared and investigated. Finally, comparison between chiral metamaterials with stereometamaterials in terms of the polarization selective operation along with the similarity and the distinction is addressed as well.

An efficient and highly stereoselective synthesis of new P-chiral 1,5-diphosphanylferrocene ligands and their use in enantioselective hydrogenation.

PubMed

Chen, Weiping; Roberts, J Stanley M; Whittall, John; Steiner, Alexander

2006-07-21

An efficient and highly stereoselective synthesis of P-chiral 1,5-diphosphanylferrocene ligands has been developed, and the introduction of P-chirality in ferrocene-based phosphine ligands enhances the enantioselective discrimination produced by the corresponding catalyst when matching of the planar chirality, the chirality at carbon and the chirality at phosphorus occurs.

Bolometric-Effect-Based Wavelength-Selective Photodetectors Using Sorted Single Chirality Carbon Nanotubes

PubMed Central

Zhang, Suoming; Cai, Le; Wang, Tongyu; Shi, Rongmei; Miao, Jinshui; Wei, Li; Chen, Yuan; Sepúlveda, Nelson; Wang, Chuan

2015-01-01

This paper exploits the chirality-dependent optical properties of single-wall carbon nanotubes for applications in wavelength-selective photodetectors. We demonstrate that thin-film transistors made with networks of carbon nanotubes work effectively as light sensors under laser illumination. Such photoresponse was attributed to photothermal effect instead of photogenerated carriers and the conclusion is further supported by temperature measurements. Additionally, by using different types of carbon nanotubes, including a single chirality (9,8) nanotube, the devices exhibit wavelength-selective response, which coincides well with the absorption spectra of the corresponding carbon nanotubes. This is one of the first reports of controllable and wavelength-selective bolometric photoresponse in macroscale assemblies of chirality-sorted carbon nanotubes. The results presented here provide a viable route for achieving bolometric-effect-based photodetectors with programmable response spanning from visible to near-infrared by using carbon nanotubes with pre-selected chiralities. PMID:26643777

FATE AND EFFECTS OF THE ENANTIOMERS OF CHIRAL ENVIRONMENTAL POLLUTANTS

EPA Science Inventory

Enantiomers, the mirror image isomers of chiral compounds, are known to be selective in their interaction with other chiral molecules, including enzymes and other biochemicals. This holds true for pesticides, about 25% of which are chiral molecules, and other chiral environmental...

Electrochemical impedance based chiral analysis of anti-ascorbutic drug: l-Ascorbic acid and d-ascorbic acid using C-dots decorated conductive polymer nano-composite electrode.

PubMed

Pandey, Indu; Kant, Rama

2016-03-15

Clinical manifestations owing to l-ascorbic acid for scurvy as comparison to d-ascorbic acid and challenges of chiral purity are overcome by using chiral selective conductive polymer nanocomposite which mimics antibodies and enzymes. A novel chiral selective imprinted polyaniline-ferrocene-sulfonic acid film has been electrochemically fabricated on C-dots modified pencil graphite electrode. The performance of the obtained l-ascorbic acid or d-ascorbic acid chiral selective sensor was investigated by electrochemical impedance spectroscopy, cyclic and differential pulse voltammetry. The surface characteristics of the C-dots, chiral sensor before and after the de-doping of chiral d- and l-ascorbic acid were characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction spectroscopy. Excellent recognition results were obtained by difference in electron transfer resistance. The proposed chiral sensor is capable of measuring d-ascorbic acid or l-ascorbic acid in aqueous as well as in real and commercial samples within the range of 0.020-0.187 nM and 0.003-0.232 nM with detection limit of 0.00073 nM and 0.00016 nM, respectively. The proposed method has also been examined for the chiral selective recognition of ascorbic acid isomers (d- and l-) quantitatively, in complicated matrices of real samples. Copyright © 2015 Elsevier B.V. All rights reserved.

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).

The engagement of optical angular momentum in nanoscale chirality

NASA Astrophysics Data System (ADS)

Andrews, David L.

2017-09-01

Wide-ranging developments in optical angular momentum have recently led to refocused attention on issues of material chirality. The connection between optical spin and circular polarization, linking to well-known and utilized probes of chirality such as circular dichroism, has prompted studies aiming to achieve enhanced means of differentiating enantiomers - molecules or particles of opposite handedness. A number of newly devised schemes for physically separating mirror-image components by optical methods have also been gaining traction, together with a developing appreciation of how the scale of physical dimensions ultimately determines any capacity to differentially select for material chirality. The scope of such enquiries has substantially widened on recognition that suitably structured, topologically charged beams of light - often known as `twisted light' or `optical vortices' can additionally convey orbital angular momentum. A case can be made that understanding the full scope and constraints upon chiroptical interactions in the nanoscale regime involves the resolution of CPT symmetry conditions governing the fundamental interactions between matter and photons. The principles provide a sound theoretical test-bed for new methodologies.

Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis

PubMed Central

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

2009-01-01

Discovery of efficient catalysts is one of the most compelling objectives of modern chemistry. Chiral catalysts are in particularly high demand, as they facilitate synthesis of enantiomerically enriched small molecules that are critical to developments in medicine, biology and materials science1. Especially noteworthy are catalysts that promote—with otherwise inaccessible efficiency and selectivity levels—reactions demonstrated to be of great utility in chemical synthesis. Here we report a class of chiral catalysts that initiate alkene metathesis1 with very high efficiency and enantioselectivity. Such attributes arise from structural fluxionality of the chiral catalysts and the central role that enhanced electronic factors have in the catalytic cycle. The new catalysts have a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are prepared stereoselectively by a ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands scarcely used in enantioselective catalysis2,3. We demonstrate the application of the new catalysts in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, through an alkene metathesis reaction that cannot be promoted by any of the previously reported chiral catalysts. PMID:19011612

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.

Chiral filtration-induced spin/valley polarization in silicene line defects

NASA Astrophysics Data System (ADS)

Ren, Chongdan; Zhou, Benhu; Sun, Minglei; Wang, Sake; Li, Yunfang; Tian, Hongyu; Lu, Weitao

2018-06-01

The spin/valley polarization in silicene with extended line defects is investigated according to the chiral filtration mechanism. It is shown that the inner-built quantum Hall pseudo-edge states with identical chirality can serve as a chiral filter with a weak magnetic field and that the transmission process is restrained/strengthened for chiral states with reversed/identical chirality. With two parallel line defects, which act as natural chiral filtration, the filter effect is greatly enhanced, and 100% spin/valley polarization can be achieved.

Analytic Optimization of Near-Field Optical Chirality Enhancement

PubMed Central

2017-01-01

We present an analytic derivation for the enhancement of local optical chirality in the near field of plasmonic nanostructures by tuning the far-field polarization of external light. We illustrate the results by means of simulations with an achiral and a chiral nanostructure assembly and demonstrate that local optical chirality is significantly enhanced with respect to circular polarization in free space. The optimal external far-field polarizations are different from both circular and linear. Symmetry properties of the nanostructure can be exploited to determine whether the optimal far-field polarization is circular. Furthermore, the optimal far-field polarization depends on the frequency, which results in complex-shaped laser pulses for broadband optimization. PMID:28239617

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.

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.

Chiral stationary phase optimized selectivity liquid chromatography: A strategy for the separation of chiral isomers.

PubMed

Hegade, Ravindra Suryakant; De Beer, Maarten; Lynen, Frederic

2017-09-15

Chiral Stationary-Phase Optimized Selectivity Liquid Chromatography (SOSLC) is proposed as a tool to optimally separate mixtures of enantiomers on a set of commercially available coupled chiral columns. This approach allows for the prediction of the separation profiles on any possible combination of the chiral stationary phases based on a limited number of preliminary analyses, followed by automated selection of the optimal column combination. Both the isocratic and gradient SOSLC approach were implemented for prediction of the retention times for a mixture of 4 chiral pairs on all possible combinations of the 5 commercial chiral columns. Predictions in isocratic and gradient mode were performed with a commercially available and with an in-house developed Microsoft visual basic algorithm, respectively. Optimal predictions in the isocratic mode required the coupling of 4 columns whereby relative deviations between the predicted and experimental retention times ranged between 2 and 7%. Gradient predictions led to the coupling of 3 chiral columns allowing baseline separation of all solutes, whereby differences between predictions and experiments ranged between 0 and 12%. The methodology is a novel tool allowing optimizing the separation of mixtures of optical isomers. Copyright © 2017 Elsevier B.V. All rights reserved.

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.

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.

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.

Chiral surface waves for enhanced circular dichroism

NASA Astrophysics Data System (ADS)

Pellegrini, Giovanni; Finazzi, Marco; Celebrano, Michele; Duò, Lamberto; Biagioni, Paolo

2017-06-01

We present a novel chiral sensing platform that combines a one-dimensional photonic crystal design with a birefringent surface defect. The platform sustains simultaneous transverse electric and transverse magnetic surface modes, which are exploited to generate chiral surface waves. The present design provides homogeneous and superchiral fields of both handednesses over arbitrarily large areas in a wide spectral range, resulting in the enhancement of the circular dichroism signal by more than two orders of magnitude, thus paving the road toward the successful combination of surface-enhanced spectroscopies and electromagnetic superchirality.

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.

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.

Chirality- and sequence-selective successive self-sorting via specific homo- and complementary-duplex formations

PubMed Central

Makiguchi, Wataru; Tanabe, Junki; Yamada, Hidekazu; Iida, Hiroki; Taura, Daisuke; Ousaka, Naoki; Yashima, Eiji

2015-01-01

Self-recognition and self-discrimination within complex mixtures are of fundamental importance in biological systems, which entirely rely on the preprogrammed monomer sequences and homochirality of biological macromolecules. Here we report artificial chirality- and sequence-selective successive self-sorting of chiral dimeric strands bearing carboxylic acid or amidine groups joined by chiral amide linkers with different sequences through homo- and complementary-duplex formations. A mixture of carboxylic acid dimers linked by racemic-1,2-cyclohexane bis-amides with different amide sequences (NHCO or CONH) self-associate to form homoduplexes in a completely sequence-selective way, the structures of which are different from each other depending on the linker amide sequences. The further addition of an enantiopure amide-linked amidine dimer to a mixture of the racemic carboxylic acid dimers resulted in the formation of a single optically pure complementary duplex with a 100% diastereoselectivity and complete sequence specificity stabilized by the amidinium–carboxylate salt bridges, leading to the perfect chirality- and sequence-selective duplex formation. PMID:26051291

Chiral Selective Chemistry Induced by Natural Selection of Spin-Polarized Electrons.

PubMed

Rosenberg, Richard A; Mishra, Debabrata; Naaman, Ron

2015-06-15

The search to understand the origin of homochirality in nature has been ongoing since the time of Pasteur. Previous work has shown that DNA can act as a spin filter for low-energy electrons and that spin-polarized secondary electrons produced by X-ray irradiation of a magnetic substrate can induce chiral selective chemistry. In the present work it is demonstrated that secondary electrons from a substrate that are transmitted through a chiral overlayer cause enantiomeric selective chemistry in an adsorbed adlayer. We determine the quantum yields (QYs) for dissociation of (R)- or (S)-epichlorohydrin adsorbed on a chiral self-assembled layer of DNA on gold and on bare gold (for control). The results show that there is a significant difference in the QYs between the two enantiomers when adsorbed on DNA, but none when they are adsorbed on bare Au. We propose that the effect results from natural spin filtering effects cause by the chiral monolayer. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adsorption differences between low coverage enantiomers of alanine on the chiral Cu{421}R surface.

PubMed

Gladys, Michael J; Han, Jeong Woo; Pedersen, Therese S; Tadich, Anton; O'Donnell, Kane M; Thomsen, Lars

2017-05-31

Chiral separation using heterogeneous methods has long been sought after. Chiral metal surfaces have the potential to make it possible to model these systems using small amino acids, the building blocks for proteins. A comparison of submonolayer concentrations of alanine enantiomers adsorbed onto Cu{421} R has revealed a large geometrical differences between the two molecules as compared to the saturated coverage. Large differences were observed in HR-XPS and NEXAFS and complemented by theoretical DFT calculations. At approximately one third of a monolayer a comparison of the C1s XPS signal showed a shift in the methyl group of more than 300 meV indicating that the two enantiomers are in different chemical environments. NEXAFS spectroscopy confirmed the XPS variations and showed large differences in the orientation of the adsorbed molecules. Our DFT results show that the l-enantiomer is energetically the most stable in the {311} microfacet configuration. In contrast to the full monolayer coverage, these lower coverages showed enhanced selectivity.

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 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.

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.

Two-Dimensional Chirality in Three-Dimensional Chemistry.

ERIC Educational Resources Information Center

Wintner, Claude E.

1983-01-01

The concept of two-dimensional chirality is used to enhance students' understanding of three-dimensional stereochemistry. This chirality is used as a key to teaching/understanding such concepts as enaniotropism, diastereotopism, pseudoasymmetry, retention/inversion of configuration, and stereochemical results of addition to double bonds. (JN)

Nanoscale chirality in metal and semiconductor nanoparticles

PubMed Central

Thomas, K. George

2016-01-01

The field of chirality has recently seen a rejuvenation due to the observation of chirality in inorganic nanomaterials. The advancements in understanding the origin of nanoscale chirality and the potential applications of chiroptical nanomaterials in the areas of optics, catalysis and biosensing, among others, have opened up new avenues toward new concepts and design of novel materials. In this article, we review the concept of nanoscale chirality in metal nanoclusters and semiconductor quantum dots, then focus on recent experimental and theoretical advances in chiral metal nanoparticles and plasmonic chirality. Selected examples of potential applications and an outlook on the research on chiral nanomaterials are additionally provided. PMID:27752651

Nanoscale chirality in metal and semiconductor nanoparticles.

PubMed

Kumar, Jatish; Thomas, K George; Liz-Marzán, Luis M

2016-10-18

The field of chirality has recently seen a rejuvenation due to the observation of chirality in inorganic nanomaterials. The advancements in understanding the origin of nanoscale chirality and the potential applications of chiroptical nanomaterials in the areas of optics, catalysis and biosensing, among others, have opened up new avenues toward new concepts and design of novel materials. In this article, we review the concept of nanoscale chirality in metal nanoclusters and semiconductor quantum dots, then focus on recent experimental and theoretical advances in chiral metal nanoparticles and plasmonic chirality. Selected examples of potential applications and an outlook on the research on chiral nanomaterials are additionally provided.

Stardust, Supernovae and the Chirality of the Amino Acids

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

Boyd, R N; Kajino, T; Onaka, T

A mechanism for creating enantiomerism in the amino acids, the building blocks of the proteins, that involves global selection of one chirality by interactions between the amino acids and neutrinos from core-collapse supernovae is described. The selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the 14N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species. The resulting amino acids could either be the source thereofmore » on Earth, or could have triggered the chirality that was ultimately achieved for Earth's amino acids.« less

Resonant absorption and amplification of circularly-polarized waves in inhomogeneous chiral media.

PubMed

Kim, Seulong; Kim, Kihong

2016-01-25

It has been found that in the media where the dielectric permittivity ε or the magnetic permeability μ is near zero and in transition metamaterials where ε or μ changes from positive to negative values, there occur a strong absorption or amplification of the electromagnetic wave energy in the presence of an infinitesimally small damping or gain and a strong enhancement of the electromagnetic fields. We attribute these phenomena to the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations and its inverse process. In this paper, we study analogous phenomena occurring in chiral media theoretically using the invariant imbedding method. In uniform isotropic chiral media, right-circularly-polarized and left-circularly-polarized waves are the eigen-modes of propagation with different effective refractive indices n(+) and n(-), whereas in the chiral media with a nonuniform impedance variation, they are no longer the eigenmodes and are coupled to each other. We find that both in uniform chiral slabs where either n(+) or n(-) is near zero and in chiral transition metamaterials where n(+) or n(-) changes from positive to negative values, a strong absorption or amplification of circularly-polarized waves occurs in the presence of an infinitesimally small damping or gain. We present detailed calculations of the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the medium, for various configurations of ε and μ with an emphasis on the influence of a nonuniform impedance. We propose possible applications of these phenomena to linear and nonlinear optical devices that react selectively to the helicity of the circular polarization.

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.

Silver Films with Hierarchical Chirality.

PubMed

Ma, Liguo; Cao, Yuanyuan; Duan, Yingying; Han, Lu; Che, Shunai

2017-07-17

Physical fabrication of chiral metallic films usually results in singular or large-sized chirality, restricting the optical asymmetric responses to long electromagnetic wavelengths. The chiral molecule-induced formation of silver films prepared chemically on a copper substrate through a redox reaction is presented. Three levels of chirality were identified: primary twisted nanoflakes with atomic crystal lattices, secondary helical stacking of these nanoflakes to form nanoplates, and tertiary micrometer-sized circinates consisting of chiral arranged nanoplates. The chiral Ag films exhibited multiple plasmonic absorption- and scattering-based optical activities at UV/Vis wavelengths based on their hierarchical chirality. The Ag films showed chiral selectivity for amino acids in catalytic electrochemical reactions, which originated from their primary atomic crystal lattices. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tunable Chiroptical Properties from the Plasmonic Band to Metal-Ligand Charge Transfer Band of the Cysteine Capped Molybdenum Oxide Nanoparticles.

PubMed

Li, Yiwen; Cheng, Jiaji; Li, Jiagen; Zhu, Xi; He, TingChao; Chen, Rui; Tang, Zikang

2018-06-25

Understanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Herein, we present chiral molybdenum oxide nanoparticles in which chirality is transferred via a bio-to-nano approach. With facile controlling on the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in plasmon region and metal-ligand charge transfer band. The obtained enhanced CD signals with tunable line-shapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics and photocatalysts. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Supernovae, neutrinos and the chirality of amino acids.

PubMed

Boyd, Richard N; Kajino, Toshitaka; Onaka, Takashi

2011-01-01

A mechanism for creating an enantioenrichment in the amino acids, the building blocks of the proteins, that involves global selection of one handedness by interactions between the amino acids and neutrinos from core-collapse supernovae is defined. The chiral selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the (14)N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. It also requires an asymmetric distribution of neutrinos emitted from the supernova. The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species. The resulting amino acids could either be the source thereof on Earth, or could have triggered the chirality that was ultimately achieved for Earth's proteinaceous amino acids.

Chirality Differentiation by Diffusion in Chiral Nematic Liquid Crystals

NASA Astrophysics Data System (ADS)

Jiang, Jinghua; Yang, Deng-Ke

2017-01-01

Chirality is of great importance in the living world. It helps differentiate biochemical reactions such as those that take place during digestion. It may also help differentiate physical processes such as diffusion. Aiming to study the latter effect, we investigate the diffusion of guest chiral molecules in chiral nematic (cholesteric) liquid-crystal hosts. We discover that the diffusion dramatically depends on the handedness of the guest and host molecules and the chiral differentiation is greatly enhanced by the proper alignment of the liquid-crystal host. The diffusion of a guest chiral molecule in a chiral host with the same handedness is much faster than in a chiral host with opposite handedness. We also observe that the differentiation of chirality depends on the diffusion direction with respect to the twisting direction (helical axis). These results might be important in understanding effects of chirality on physical processes that take place in biological organisms. In addition, this effect could be utilized for enantiomer separation.

Increments to chiral recognition facilitating enantiomer separations of chiral acids, bases, and ampholytes using Cinchona-based zwitterion exchanger chiral stationary phases.

PubMed

Wernisch, Stefanie; Pell, Reinhard; Lindner, Wolfgang

2012-07-01

The intramolecular distances of anion and cation exchanger sites of zwitterionic chiral stationary phases represent potential tuning sites for enantiomer selectivity. In this contribution, we investigate the influence of alkanesulfonic acid chain length and flexibility on enantiomer separations of chiral acids, bases, and amphoteric molecules for six Cinchona alkaloid-based chiral stationary phases in comparison with structurally related anion and cation exchangers. Employing polar-organic elution conditions, we observed an intramolecular counterion effect for acidic analytes which led to reduced retention times but did not impair enantiomer selectivities. Retention of amphoteric analytes is based on simultaneous double ion pairing of their charged functional groups with the acidic and basic sites of the zwitterionic selectors. A chiral center in the vicinity of the strong cation exchanger site is vital for chiral separations of bases. Sterically demanding side chains are beneficial for separations of free amino acids. Enantioseparations of free (un-derivatized) peptides were particularly successful in stationary phases with straight-chain alkanesulfonic acid sites, pointing to a beneficial influence of more flexible moieties. In addition, we observed pseudo-enantiomeric behavior of quinine and quinidine-derived chiral stationary phases facilitating reversal of elution orders for all analytes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis and bio-inspired optimization of drimenal: Discovery of chiral drimane fused oxazinones as promising antifungal and antibacterial candidates.

PubMed

Li, Dangdang; Zhang, Shasha; Song, Zehua; Li, Wei; Zhu, Feng; Zhang, Jiwen; Li, Shengkun

2018-01-01

The synthesis of antifungal natural product drimenal was accomplished. Bio-inspired optimization protruded chiral 8-(R)-drimane fused oxazinone D as a lead, considering favorable physicochemical profiles for novel pesticides. The improved scalable synthesis of scaffold D was implemented by Hofmann rearrangment under mild conditions. Detailed structural optimization was discussed for both antifungal and antibacterial exploration. Substituted groups (SGs) with C 3 ∼C 5 hydrocarbon chain are recommended for exploration of antifungal agents, while substituents with C 4 ∼C 6 carbon length are preferred for antibacterial ingredients. The chiral drimane fused oxazinone D8 was selected as a promising antifungal candidate against Botrytis cirerea, with an EC 50 value of 1.18 mg/L, with the enhancement of up to >25 folds and >80 folds than the mother compound D, and acyclic counterpart AB5, respectively. The in vivo bioassay confirmed much better preservative effect of D8 than that of Carbendazim. The chiral oxazinone variant D10 possessed prominent antibacterial activity, with MIC values of 8 mg/L against both Bacillus subtilis and Ralstonia solanacearum, showing advantages over the positive control streptomycin sulfate. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Chiral Process Monitoring Using Fourier Transform Microwave Spectroscopy

NASA Astrophysics Data System (ADS)

Neill, Justin L.; Muckle, Matt; Pate, Brooks

2017-06-01

We present the application of Fourier transform microwave (FTMW) spectroscopy in monitoring the chiral purity of components in a reaction mixture. This is of particular interest due to the increasing use of continuous pharmaceutical manufacturing processes, in which a number of attributes (including the chiral purity of the product) can change on short time scales. Therefore, new techniques that can accomplish this measurement rapidly are desired. The excellent specificity of FTMW spectroscopy, coupled with newly developed techniques for measuring enantiomeric excess in a mixture, have motivated this work. In collaboration with B. Frank Gupton (Virginia Commonwealth University), we are testing this application first with the synthesis of artemisinin. Artemisinin, a common drug for malaria treatment, is of high global health interest and subject to supply shortages, and therefore a strong candidate for continuous manufacturing. It also has moderately high molecular weight (282 amu) and seven chiral centers, making it a good candidate to test the capabilities of FTMW spectroscopy. Using a miniature cavity-enhanced FTMW spectrometer design, we aim to demonstrate selective component quantification in the reaction mixture. Future work that will be needed to fully realize this application will be discussed. R.D. Suenram, J.U. Grabow, A.Zuban, and I.Leonov, Rev. Sci. Instrum. 70, 2127 (1999).

Enantioselective ProPhenol-catalyzed addition of 1,3-diynes to aldehydes to generate synthetically versatile building blocks and diyne natural products.

PubMed

Trost, Barry M; Chan, Vincent S; Yamamoto, Daisuke

2010-04-14

A highly enantioselective method for the catalytic addition of terminal 1,3-diynes to aldehydes was developed using our dinuclear zinc ProPhenol (1) system. Furthermore, triphenylphosphine oxide was found to interact synergistically with the catalyst to substantially enhance the chiral recognition. The generality of this catalytic transformation was demonstrated with aryl, alpha,beta-unsaturated and saturated aldehydes, of which the latter were previously limited in alkynyl zinc additions. The chiral diynol products are also versatile building blocks that can be readily elaborated; this was illustrated through highly selective trans-hydrosilylations, which enabled the synthesis of a beta-hydroxyketone and enyne. Additionally, the development of this method allowed for the rapid total syntheses of several biologically important diynol-containing natural products.

Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)S studied by density functional theory

NASA Astrophysics Data System (ADS)

Franke, J.-H.; Kosov, D. S.

2015-01-01

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)S. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

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.

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.

Supernovae, Neutrinos and the Chirality of Amino Acids

PubMed Central

Boyd, Richard N.; Kajino, Toshitaka; Onaka, Takashi

2011-01-01

A mechanism for creating an enantioenrichment in the amino acids, the building blocks of the proteins, that involves global selection of one handedness by interactions between the amino acids and neutrinos from core-collapse supernovae is defined. The chiral selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the 14N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. It also requires an asymmetric distribution of neutrinos emitted from the supernova. The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species. The resulting amino acids could either be the source thereof on Earth, or could have triggered the chirality that was ultimately achieved for Earth’s proteinaceous amino acids. PMID:21747686

Chiral Superstructure Mesophases of Achiral Bent-Shaped Molecules - Hierarchical Chirality Amplification and Physical Properties.

PubMed

Le, Khoa V; Takezoe, Hideo; Araoka, Fumito

2017-07-01

Chiral mesophases in achiral bent-shaped molecules have attracted particular attention since their discovery in the middle 1990s, not only because of their homochirality and polarity, but also due to their unique physical/physicochemical properties. Here, the most intriguing results in the studies of such symmetry-broken states, mainly helical-nanofilament (HNF) and dark-conglomerate (DC) phases, are reviewed. Firstly, basic information on the typical appearance and optical activity in these phases is introduced. In the following section, the formation of mesoscopic chiral superstructures in the HNF and DC phases is discussed in terms of hierarchical chirality. Nanoscale phase segregation in mixture systems and gelation ability in the HNF phase are also described. In addition, some other related chiral phases of bent-shaped molecules are shown. Recent attempts to control such mesoscopic chiral structure and the alignment/confinement of HNFs are also discussed, along with several examples of their fascinating advanced physical properties, i.e. huge enhancement of circular dichroism, electro- and photo-tunable optical activities, chirality-induced nonlinear optics (second-harmonic-generation circular difference and electrogyration effect), enhanced hydrophobicity through the dual-scale surface morphological modulation, and photoconductivity in the HNF/fullerene binary system. Future prospects from basic science and application viewpoints are also indicated in the concluding section. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CAPILLARY ELECTROPHORESIS FOR ENANTIOMER SEPARATION AND MEASUREMENT OF ENANTIOSELECTIVITY OF CHIRAL POLLUTANTS IN THE ENVIRONMENT

EPA Science Inventory

Chiral pollutants exist as 2 species, -- enantiomers - that have identical physical and chemical properties except when they interact with enzymes or other chiral molecules; then they usually react selectively. This enantioselectivity results in different rates of microbial trans...

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

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.

Chirality in molecular collision dynamics

NASA Astrophysics Data System (ADS)

Lombardi, Andrea; Palazzetti, Federico

2018-02-01

Chirality is a phenomenon that permeates the natural world, with implications for atomic and molecular physics, for fundamental forces and for the mechanisms at the origin of the early evolution of life and biomolecular homochirality. The manifestations of chirality in chemistry and biochemistry are numerous, the striking ones being chiral recognition and asymmetric synthesis with important applications in molecular sciences and in industrial and pharmaceutical chemistry. Chiral discrimination phenomena, due to the existence of two enantiomeric forms, very well known in the case of interaction with light, but still nearly disregarded in molecular collision studies. Here we review some ideas and recent advances about the role of chirality in molecular collisions, designing and illustrating molecular beam experiments for the demonstration of chiral effects and suggesting a scenario for a stereo-directional origin of chiral selection.

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.

Theoretical Foundation for Electric-Dipole-Allowed Chiral-Specific Fluorescence Optical Rotary Dispersion (F-ORD) from Interfacial Assemblies.

PubMed

Deng, Fengyuan; Ulcickas, James R W; Simpson, Garth J

2016-11-03

Fluorescence optical rotary dispersion (F-ORD) is proposed as a novel chiral-specific and interface-specific spectroscopic method. F-ORD measurements of uniaxial assemblies are predicted to be fully electric-dipole-allowed, with corresponding increases in sensitivity to chirality relative to chiral-specific measurements in isotropic assemblies that are commonly interpreted through coupling between electric and magnetic dynamic dipoles. Observations of strong chiral sensitivity in prior single-molecule fluorescence measurements of chiral interfacial molecules are in excellent qualitative agreement with the predictions of the F-ORD mechanism and challenging to otherwise explain. F-ORD may provide methods to suppress background fluorescence in studies of biological interfaces, as the detected signal requires both polar local order and interfacial chirality. In addition, the molecular-level descriptions of the mechanisms underpinning F-ORD may also potentially apply to aid in interpreting chiral-specific Raman and surface-enhanced Raman spectroscopy measurements of uniaxially oriented assemblies, opening up opportunities for chiral-specific and interface-specific vibrational spectroscopy.

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

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.

The chiral magnetic effect and chiral symmetry breaking in SU(3) quenched lattice gauge theory

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

Braguta, V. V., E-mail: braguta@mail.ru; Buividovich, P. V., E-mail: buividovich@itep.ru; Kalaydzhyan, T., E-mail: tigran.kalaydzhyan@desy.de

2012-04-15

We study some properties of the non-Abelian vacuum induced by strong external magnetic field. We perform calculations in the quenched SU(3) lattice gauge theory with tadpole-improved Luescher-Weisz action and chirally invariant lattice Dirac operator. The following results are obtained: The chiral symmetry breaking is enhanced by the magnetic field. The chiral condensate depends on the strength of the applied field as a power function with exponent {nu} = 1.6 {+-} 0.2. There is a paramagnetic polarization of the vacuum. The corresponding susceptibility and other magnetic properties are calculated and compared with the theoretical estimations. There are nonzero local fluctuations ofmore » the chirality and electromagnetic current, which grow with the magnetic field strength. These fluctuations can be a manifestation of the Chiral Magnetic Effect.« less

Quasistatic limit for plasmon-enhanced optical chirality

NASA Astrophysics Data System (ADS)

Finazzi, Marco; Biagioni, Paolo; Celebrano, Michele; Duò, Lamberto

2015-05-01

We discuss the possibility of enhancing the chiroptical response from molecules uniformly distributed around nanostructures that sustain localized plasmon resonances. We demonstrate that the average optical chirality in the near field of any plasmonic nanostructure cannot be significantly higher than that in a plane wave. This conclusion stems from the quasistatic nature of the nanoparticle-enhanced electromagnetic fields and from the fact that, at optical frequencies, the magnetic response of matter is much weaker than the electric one.

The docking of chiral analytes on proline-based chiral stationary phases: A molecular dynamics study of selectivity.

PubMed

Ashtari, M; Cann, N M

2015-08-28

Molecular dynamics simulations are employed to examine the selectivity of four proline-based chiral stationary phases in two solvent environments, a relatively apolar n-hexane/2-propanol solvent and a polar water/methanol solvent. The four chiral surfaces are based on a BOC-terminated diproline, a TMA-terminated diproline, a TMA-terminated triproline and a TMA-terminated hexaproline. This range of chiral selectors allows an analysis of the impact of oligomer length and terminal group on selectivity while the two solvent environments indicate the impact of solvent hydrogen bonding and polarity. The selector-analyte interactions are examined for six closely related analytes that each have an aromatic moiety, a hydrogen, and an alcohol group directly bonded to the stereocenter. The analytes differ in the nature of the aromatic group (phenyl or anthracyl), in the attachment point (to the central ring or a side ring in the anthracyl), and in the fourth group bonded to the carbon (CH3, CF3, or C2H5). For each of the 48 solvent+selector+analyte systems, selectivity factors are calculated and, when possible, compared to experiment. The docking mode for these proline-based selectors is analyzed. Copyright © 2015 Elsevier B.V. All rights reserved.

Evaporation rate-based selection of supramolecular chirality.

PubMed

Hattori, Shingo; Vandendriessche, Stefaan; Koeckelberghs, Guy; Verbiest, Thierry; Ishii, Kazuyuki

2017-03-09

We demonstrate the evaporation rate-based selection of supramolecular chirality for the first time. P-type aggregates prepared by fast evaporation, and M-type aggregates prepared by slow evaporation are kinetic and thermodynamic products under dynamic reaction conditions, respectively. These findings provide a novel solution reaction chemistry under the dynamic reaction conditions.

Enhancement of Chiroptical Signals by Circular Differential Mie Scattering of Nanoparticles.

PubMed

Yoo, SeokJae; Park, Q-Han

2015-09-25

We enhance the weak optical signals of small chiral molecules via circular differential Mie scattering (CDMS) of nanoparticles immersed in them. CDMS is the preferential Mie scattering of left- and right-handed circularly polarized light by nanoparticles whose sizes are about the same as the wavelength of light. Solving the Mie scattering theory for chiral media, we find that the CDMS signal of the particle is linearly proportional to the chirality parameter κ of the molecules. This linear amplitude enhancement by CDMS of the particle holds, even for large particles, which have a retardation effect. We also demonstrate that the CDMS of a nanoparticle is sensitive to changes of molecular concentration, and that the nanoparticle can be utilized as a chiroptical biosensor detecting the concentration of analyte. We expect that the enhancement of molecular chiroptical signals by CDMS will pave the way for novel chiroptical spectroscopy using nanostructures.

Conformational arm-wrestling: battles for stereochemical control in benzamides bearing matched and mismatched chiral 2- and 6-substituents.

PubMed

Clayden, Jonathan; Foricher, Yann J Y; Helliwell, Madeleine; Johnson, Paul; Mitjans, David; Vinader, Victoria

2006-02-07

The orientation of a tertiary amide group adjacent to an aromatic ring may be governed by the stereochemistry of an adjacent chiral substituent. With a chiral substituent in both ortho positions, matched/mismatched pairs of isomers result. Evidence for matched stereochemistry is provided by the clean NMR spectra of single conformers, while mismatching gives poor or unexpected selectivities in the formation of chiral substituents, or mixtures of amide conformers. Attempts to use the match-mismatch effect to select for racemic pairs of enantiomeric substituents, and hence develop a "racemate-sequestering" reagent, are described, along with the use of "matching" to scavenge a single enantiomer of a diamine from material of incomplete enantiomeric purity.

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

Franke, J.-H.; Kosov, D. S.

We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with amore » functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.« less

Chirality Characterization of Dispersed Single Wall Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Namkung, Min; Williams, Phillip A.; Mayweather, Candis D.; Wincheski, Buzz; Park, Cheol; Namkung, Juock S.

2005-01-01

Raman scattering and optical absorption spectroscopy are used for the chirality characterization of HiPco single wall carbon nanotubes (SWNTs) dispersed in aqueous solution with the surfactant sodium dodecylbenzene sulfonate. Radial breathing mode (RBM) Raman peaks for semiconducting and metallic SWNTs are identified by directly comparing the Raman spectra with the Kataura plot. The SWNT diameters are calculated from these resonant peak positions. Next, a list of (n, m) pairs, yielding the SWNT diameters within a few percent of that obtained from each resonant peak position, is established. The interband transition energies for the list of SWNT (n, m) pairs are calculated based on the tight binding energy expression for each list of the (n, m) pairs, and the pairs yielding the closest values to the corresponding experimental optical absorption peaks are selected. The results reveal that (1, 11), (4, 11), and (0, 11) as the most probable chiralities of the semiconducting nanotubes. The results also reveal that (4, 16), (6, 12) and (8, 8) are the most probable chiralities for the metallic nanotubes. Directly relating the Raman scattering data to the optical absorption spectra, the present method is considered the simplest technique currently available. Another advantage of this technique is the use of the E(sup 8)(sub 11) peaks in the optical absorption spectrum in the analysis to enhance the accuracy in the results.

Site-selective benzoin-type cyclization of unsymmetrical dialdoses catalyzed by N-heterocyclic carbenes for divergent cyclitol synthesis.

PubMed

Kang, Bubwoong; Wang, Yinli; Kuwano, Satoru; Yamaoka, Yousuke; Takasu, Kiyosei; Yamada, Ken-Ichi

2017-04-18

A highly site-selective N-heterocyclic carbene (NHC)-catalyzed benzoin-type cyclization of unsymmetrical dialdoses is developed to enable a divergent cyclitol synthesis. The choice of chiral NHCs and protecting groups affects the site-selectivity. The resulting inososes are converted into epi-, muco- and myo-inositols, and their chiral protected derivatives are formed in good yields.

A complex-polarization-propagator protocol for magneto-chiral axial dichroism and birefringence dispersion.

PubMed

Cukras, Janusz; Kauczor, Joanna; Norman, Patrick; Rizzo, Antonio; Rikken, Geert L J A; Coriani, Sonia

2016-05-21

A computational protocol for magneto-chiral dichroism and magneto-chiral birefringence dispersion is presented within the framework of damped response theory, also known as complex polarization propagator theory, at the level of time-dependent Hartree-Fock and time-dependent density functional theory. Magneto-chiral dichroism and magneto-chiral birefringence spectra in the (resonant) frequency region below the first ionization threshold of R-methyloxirane and l-alanine are presented and compared with the corresponding results obtained for both the electronic circular dichroism and the magnetic circular dichroism. The additional information content yielded by the magneto-chiral phenomena, as well as their potential experimental detectability for the selected species, is discussed.

Spontaneously amplified homochiral organic-inorganic nano-helix complexes via self-proliferation.

PubMed

Zhai, Halei; Quan, Yan; Li, Li; Liu, Xiang-Yang; Xu, Xurong; Tang, Ruikang

2013-04-07

Most spiral coiled biomaterials in nature, such as gastropod shells, are homochiral, and the favoured chiral feature can be precisely inherited. This inspired us that selected material structures, including chirality, could be specifically replicated into the self-similar populations; however, a physicochemical understanding of the material-based heritage is unknown. We study the homochirality by using calcium phosphate mineralization in the presence of racemic amphiphilic molecules and biological protein. The organic-inorganic hybrid materials with spiral coiling characteristics are produced at the nanoscale. The resulted helixes are chiral with the left- and right-handed characteristics, which are agglomerated hierarchically to from clusters and networks. It is interesting that each cluster or network is homochiral so that the enantiomorphs can be separated readily. Actually, each homochiral architecture is evolved from an original chiral helix, demonstrating the heritage of the matrix chirality during the material proliferation under a racemic condition. By using the Ginzburg-Landaue expression we find that the chiral recognition in the organic-inorganic hybrid formation may be determined by a spontaneous chiral separation and immobilization of asymmetric amphiphilic molecules on the mineral surface, which transferred the structural information from the mother matrix to the descendants by an energetic control. This study shows how biomolecules guide the selective amplification of chiral materials via spontaneous self-replication. Such a strategy can be applied generally in the design and production of artificial materials with self-similar structure characteristics.

Through-space transfer of chiral information mediated by a plasmonic nanomaterial

NASA Astrophysics Data System (ADS)

Ostovar Pour, Saeideh; Rocks, Louise; Faulds, Karen; Graham, Duncan; Parchaňský, Václav; Bouř, Petr; Blanch, Ewan W.

2015-07-01

The ability to detect chirality gives stereochemically attuned nanosensors the potential to revolutionize the study of biomolecular processes. Such devices may structurally characterize the mechanisms of protein-ligand binding, the intermediates of amyloidogenic diseases and the effects of phosphorylation and glycosylation. We demonstrate that single nanoparticle plasmonic reporters, or nanotags, can enable a stereochemical response to be transmitted from a chiral analyte to an achiral benzotriazole dye molecule in the vicinity of a plasmon resonance from an achiral metallic nanostructure. The transfer of chirality was verified by the measurement of mirror image surface enhanced resonance Raman optical activity spectra for the two enantiomers of both ribose and tryptophan. Computational modelling confirms these observations and reveals the novel chirality transfer mechanism responsible. This is the first report of colloidal metal nanoparticles in the form of single plasmonic substrates displaying an intrinsic chiral sensitivity once attached to a chiral molecule.

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.

Phase behavior of thermotropic chiral liquid crystal with wide blue phase

NASA Astrophysics Data System (ADS)

Jessy, P. J.; Radha, S.; Nainesh, Patel

2018-04-01

We modified the phase transitions of a thermotropic chiral nematic liquid crystal system with various concentrations of chiral component and investigated their phase behavior and optical properties. The study shows that coupling between chirality and nematicity of liquid crystals lead to changes in phase morphology with extended temperature window of blue phase including human body temperatures and enhanced thermochromism performance. The temperature dependent refractive index analysis in the visible spectral region reveals that the optical modulation due to pitch variation of helical pattern results in the creation of new mesophases and more pronounced chirality in mixtures leading to blue phase which can be controlled by the chiral concentration. The appearance of extended blue phases with primary colors will pave way for the development of new photonic devices.

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.

Chiral quantum supercrystals with total dissymmetry of optical response

NASA Astrophysics Data System (ADS)

Baimuratov, Anvar S.; Gun'Ko, Yurii K.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

2016-03-01

Since chiral nanoparticles are much smaller than the optical wavelength, their enantiomers show little difference in the interaction with circularly polarized light. This scale mismatch makes the enhancement of enantioselectivity in optical excitation of nanoobjects a fundamental challenge in modern nanophotonics. Here we demonstrate that a strong dissymmetry of optical response from achiral nanoobjects can be achieved through their arrangement into chiral superstructures with the length scale comparable to the optical wavelength. This concept is illustrated by the example of the simple helix supercrystal made of semiconductor quantum dots. We show that this supercrystal almost fully absorbs light with one circular polarization and does not absorb the other. The giant circular dichroism of the supercrystal comes from the formation of chiral bright excitons, which are the optically active collective excitations of the entire supercrystal. Owing to the recent advances in assembly and self-organization of nanocrystals in large superparticle structures, the proposed principle of enantioselectivity enhancement has great potential of benefiting various chiral and analytical methods, which are used in biophysics, chemistry, and pharmaceutical science.

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.

Selection of Amino Acid Chirality via Neutrino Interactions with 14N in Crossed Electric and Magnetic Fields

PubMed Central

Boyd, Richard N.; Kajino, Toshitaka; Onaka, Takashi

2018-01-01

Abstract Previous work has suggested that the chirality of the amino acids could be established in the magnetic field of a nascent neutron star from a core-collapse supernova or massive collapsar. The magnetic field would orient the 14N nuclei, and the alignment of its nuclear spin with respect to those of the electron antineutrinos emitted from the collapsing star would determine the probability of destruction of the 14N nuclei by interactions with the antineutrinos. Subsequent work estimated the bulk polarization of the 14N nuclei in large rotating meteoroids in such an environment. The present work adds a crucial piece of this model by describing the details by which the selective 14N nuclear destruction would produce molecular chiral selectivity. The effects of the neutrino-induced interactions on the 14N nuclei bound in amino acids polarized in strong magnetic fields are studied. It is shown that electric fields in the reference frame of the nuclei modify the magnetic field at the nucleus, creating nuclear magnetizations that are asymmetric in chirality. The antineutrino cross sections depend on this magnetization, creating a selective destructive effect. The environmental conditions and sites in which such a selection mechanism could occur are discussed. Selective destruction of D-enantiomers results in enantiomeric excesses which may be sufficient to drive subsequent autocatalysis necessary to produce the few-percent enantiomeric excesses found in meteorites and subsequent homochirality. Molecular quantum chemical calculations were performed for alanine, and the chirality-dependent effects studied were included. A preference for left-handed molecules was found, and enantiomeric excesses as high as 0.02% were estimated for molecules in the electromagnetic conditions expected from a core-collapse supernova. Key Words: Amino acids—Supernovae—Antineutrinos—Enantiomeric excess—Chirality. Astrobiology 18, 190–206. PMID:29160728

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.

Maltodextrins as chiral selectors in CE: molecular structure effect of basic chiral compounds on the enantioseparation.

PubMed

Tabani, Hadi; Fakhari, Ali Reza; Nojavan, Saeed

2014-10-01

Prediction of chiral separation for a compound using a chiral selector is an interesting and debatable work. For this purpose, in this study 23 chiral basic drugs with different chemical structures were selected as model solutes and the influence of their chemical structures on the enantioseparation in the presence of maltodextrin (MD) as chiral selector was investigated. For chiral separation, a 100-mM phosphate buffer solution (pH 3.0) containing 10% (w/v) MD with dextrose equivalent (DE) of 4-7 as chiral selector at the temperature of 25°C and voltage of 20 kV was used. Under this condition, baseline separation was achieved for nine chiral compounds and partial separation was obtained for another six chiral compounds while no enantioseparation was obtained for the remaining eight compounds. The results showed that the existence of at least two aromatic rings or cycloalkanes and an oxygen or nitrogen atom or -CN group directly bonded to the chiral center are necessary for baseline separation. With the obtained results in this study, chiral separation of a chiral compound can be estimated with MD-modified capillary electrophoresis before analysis. This prediction will minimize the number of preliminary experiments required to resolve enantiomers and will save time and cost. © 2014 Wiley Periodicals, Inc.

Highly efficient all-dielectric optical tensor impedance metasurfaces for chiral polarization control.

PubMed

Kim, Minseok; Eleftheriades, George V

2016-10-15

We propose a highly efficient (nearly lossless and impedance-matched) all-dielectric optical tensor impedance metasurface that mimics chiral effects at optical wavelengths. By cascading an array of rotated crossed silicon nanoblocks, we realize chiral optical tensor impedance metasurfaces that operate as circular polarization selective surfaces. Their efficiencies are maximized through a nonlinear numerical optimization process in which the tensor impedance metasurfaces are modeled via multi-conductor transmission line theory. From rigorous full-wave simulations that include all material losses, we show field transmission efficiencies of 94% for right- and left-handed circular polarization selective surfaces at 800 nm.

Enantioselective determination by capillary electrophoresis with cyclodextrins as chiral selectors.

PubMed

Fanali, S

2000-04-14

This review surveys the separation of enantiomers by capillary electrophoresis using cyclodextrins as chiral selector. Cyclodextrins or their derivatives have been widely employed for the direct chiral resolution of a wide number of enantiomers, mainly of pharmaceutical interest, selected examples are reported in the tables. For method optimisation, several parameters influencing the enantioresolution, e.g., cyclodextrin type and concentration, buffer pH and composition, presence of organic solvents or complexing additives in the buffer were considered and discussed. Finally, selected applications to real samples such as pharmaceutical formulations, biological and medical samples are also discussed.

Asymmetric synthesis using chiral-encoded metal

NASA Astrophysics Data System (ADS)

Yutthalekha, Thittaya; Wattanakit, Chularat; Lapeyre, Veronique; Nokbin, Somkiat; Warakulwit, Chompunuch; Limtrakul, Jumras; Kuhn, Alexander

2016-08-01

The synthesis of chiral compounds is of crucial importance in many areas of society and science, including medicine, biology, chemistry, biotechnology and agriculture. Thus, there is a fundamental interest in developing new approaches for the selective production of enantiomers. Here we report the use of mesoporous metal structures with encoded geometric chiral information for inducing asymmetry in the electrochemical synthesis of mandelic acid as a model molecule. The chiral-encoded mesoporous metal, obtained by the electrochemical reduction of platinum salts in the presence of a liquid crystal phase and the chiral template molecule, perfectly retains the chiral information after removal of the template. Starting from a prochiral compound we demonstrate enantiomeric excess of the (R)-enantiomer when using (R)-imprinted electrodes and vice versa for the (S)-imprinted ones. Moreover, changing the amount of chiral cavities in the material allows tuning the enantioselectivity.

Chiral Alkyl Halides: Underexplored Motifs in Medicine

PubMed Central

Gál, Bálint; Bucher, Cyril; Burns, Noah Z.

2016-01-01

While alkyl halides are valuable intermediates in synthetic organic chemistry, their use as bioactive motifs in drug discovery and medicinal chemistry is rare in comparison. This is likely attributable to the common misconception that these compounds are merely non-specific alkylators in biological systems. A number of chlorinated compounds in the pharmaceutical and food industries, as well as a growing number of halogenated marine natural products showing unique bioactivity, illustrate the role that chiral alkyl halides can play in drug discovery. Through a series of case studies, we demonstrate in this review that these motifs can indeed be stable under physiological conditions, and that halogenation can enhance bioactivity through both steric and electronic effects. Our hope is that, by placing such compounds in the minds of the chemical community, they may gain more traction in drug discovery and inspire more synthetic chemists to develop methods for selective halogenation. PMID:27827902

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.

Solvent polarity effects on supramolecular chirality of a polyfluorene-thiophene copolymer.

PubMed

Hirahara, Takashi; Yoshizawa-Fujita, Masahiro; Takeoka, Yuko; Rikukawa, Masahiro

2018-06-01

This study demonstrates the supramolecular chirality control of a conjugated polymer via solvent polarity. We designed and synthesized a chiral polyfluorene-thiophene copolymer having two different chiral side chains at the 9-position of the fluorene unit. Chiral cyclic and alkyl ethers with different polarities were selected as the chiral side chains. The sign of the circular dichroism spectra in the visible wavelength region was affected by the solvent system, resulting from the change of supramolecular structure. The estimation of the solubility parameter revealed that the solubility difference of the side chains contributed to the change of the circular dichroism sign, which was also observed in spin-coated films prepared from good solvents having different polarities. © 2018 Wiley Periodicals, Inc.

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.

Optical Selection Rule of Excitons in Gapped Chiral Fermion Systems

NASA Astrophysics Data System (ADS)

Zhang, Xiaoou; Shan, Wen-Yu; Xiao, Di

2018-02-01

We show that the exciton optical selection rule in gapped chiral fermion systems is governed by their winding number w , a topological quantity of the Bloch bands. Specifically, in a CN-invariant chiral fermion system, the angular momentum of bright exciton states is given by w ±1 +n N with n being an integer. We demonstrate our theory by proposing two chiral fermion systems capable of hosting dark s -like excitons: gapped surface states of a topological crystalline insulator with C4 rotational symmetry and biased 3 R -stacked MoS2 bilayers. In the latter case, we show that gating can be used to tune the s -like excitons from bright to dark by changing the winding number. Our theory thus provides a pathway to electrical control of optical transitions in two-dimensional material.

Real-Space Mapping of the Chiral Near-Field Distributions in Spiral Antennas and Planar Metasurfaces.

PubMed

Schnell, M; Sarriugarte, P; Neuman, T; Khanikaev, A B; Shvets, G; Aizpurua, J; Hillenbrand, R

2016-01-13

Chiral antennas and metasurfaces can be designed to react differently to left- and right-handed circularly polarized light, which enables novel optical properties such as giant optical activity and negative refraction. Here, we demonstrate that the underlying chiral near-field distributions can be directly mapped with scattering-type scanning near-field optical microscopy employing circularly polarized illumination. We apply our technique to visualize, for the first time, the circular-polarization selective nanofocusing of infrared light in Archimedean spiral antennas, and explain this chiral optical effect by directional launching of traveling waves in analogy to antenna theory. Moreover, we near-field image single-layer rosette and asymmetric dipole-monopole metasurfaces and find negligible and strong chiral optical near-field contrast, respectively. Our technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future development of chiral antennas and metasurfaces and their applications.

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.

Shape selection of twist-nematic-elastomer ribbons

PubMed Central

Sawa, Yoshiki; Ye, Fangfu; Urayama, Kenji; Takigawa, Toshikazu; Gimenez-Pinto, Vianney; Selinger, Robin L. B.; Selinger, Jonathan V.

2011-01-01

How microscopic chirality is reflected in macroscopic scale to form various chiral shapes, such as straight helicoids and spiral ribbons, and how the degree of macroscopic chirality can be controlled are a focus of studies on the shape formation of many biomaterials and supramolecular systems. This article investigates both experimentally and theoretically how the chiral arrangement of liquid crystal mesogens in twist-nematic-elastomer films induces the formation of helicoids and spiral ribbons because of the coupling between the liquid crystalline order and the elasticity. It is also shown that the pitch of the formed ribbons can be tuned by temperature variation. The results of this study will facilitate the understanding of physics for the shape formation of chiral materials and the designing of new structures on basis of microscopic chirality. PMID:21464276

Controlling Chirality of Entropic Crystals

NASA Astrophysics Data System (ADS)

Damasceno, Pablo F.; Karas, Andrew S.; Schultz, Benjamin A.; Engel, Michael; Glotzer, Sharon C.

2015-10-01

Colloidal crystal structures with complexity and diversity rivaling atomic and molecular crystals have been predicted and obtained for hard particles by entropy maximization. However, thus far homochiral colloidal crystals, which are candidates for photonic metamaterials, are absent. Using Monte Carlo simulations we show that chiral polyhedra exhibiting weak directional entropic forces self-assemble either an achiral crystal or a chiral crystal with limited control over the crystal handedness. Building blocks with stronger faceting exhibit higher selectivity and assemble a chiral crystal with handedness uniquely determined by the particle chirality. Tuning the strength of directional entropic forces by means of particle rounding or the use of depletants allows for reconfiguration between achiral and homochiral crystals. We rationalize our findings by quantifying the chirality strength of each particle, both from particle geometry and potential of mean force and torque diagrams.

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.

Adsorption of lactic acid on chiral Pt surfaces—A density functional theory study

NASA Astrophysics Data System (ADS)

Franke, J.-H.; Kosov, D. S.

2013-02-01

The adsorption of the chiral molecule lactic acid on chiral Pt surfaces is studied by density functional theory calculations. First, we study the adsorption of L-lactic acid on the flat Pt(111) surface. Using the optimed PBE - van der Waals (oPBE-vdW) functional, which includes van der Waals forces on an ab initio level, it is shown that the molecule has two binding sites, a carboxyl and the hydroxyl oxygen atoms. Since real chiral surfaces are (i) known to undergo thermal roughening that alters the distribution of kinks and step edges but not the overall chirality and (ii) kink sites and edge sites are usually the energetically most favored adsorption sites, we focus on two surfaces that allow qualitative sampling of the most probable adsorption sites. We hereby consider chiral surfaces exhibiting (111) facets, in particular, Pt(321) and Pt(643). The binding sites are either both on kink sites—which is the case for Pt(321) or on one kink site—as on Pt(643). The binding energy of the molecule on the chiral surfaces is much higher than on the Pt(111) surface. We show that the carboxyl group interacts more strongly than the hydroxyl group with the kink sites. The results indicate the possible existence of very small chiral selectivities of the order of 20 meV for the Pt(321) and Pt(643) surfaces. L-lactic acid is more stable on Pt(321)S than D-lactic acid, while the chiral selectivity is inverted on Pt(643)S. The most stable adsorption configurations of L- and D-lactic acid are similar for Pt(321) but differ for Pt(643). We explore the impact of the different adsorption geometries on the work function, which is important for field ion microscopy.

Enhancement of nitric oxide release and hemocompatibility by surface chirality of D-tartaric acid grafting

NASA Astrophysics Data System (ADS)

Han, Honghong; Wang, Ke; Fan, Yonghong; Pan, Xiaxin; Huang, Nan; Weng, Yajun

2017-12-01

Nitric Oxide (NO) generation from endogenous NO-donors catalyzed by diselenide modified biomaterials has been reported. Here we reported surface chirality by L-tartaric acid and D-tartaric acid grafting on the outermost showed a significant impact on diselenide modified biomaterials, which modulated protein adsorption, NO release and anti-platelet adhesion properties. D-tartaric acid grafted surface showed more blood protein adsorption than that of L-surfaces by QCM analysis, however, ELISA analysis disclosed less fibrinogen denatured on the D surfaces. Due to the surface ratio of selenium decreasing, NO release catalyzed by L-tartaric acid grafting on the outermost significantly decreased in comparison to that of only selenocystamine immobilized surfaces. While NO release catalyzed by D-tartaric acid grafting on the outermost didn't decrease and was similar with that of selenocystamine immobilized surfaces. Surface chirality combined with NO release had synergetic effects on platelet adhesion, and it showed the lowest number of platelets adhered on the D-tartaric acid grafted surfaces. Thus surface chirality from D-tartaric acid grafting enhanced hemocompatibility of the surface in this study. Our work provides new insights into engineering novel blood contacting biomaterials by taking into account surface chirality.

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

Selective adsorption of L- and D-amino acids on calcite: Implications for biochemical homochirality

NASA Technical Reports Server (NTRS)

Hazen, R. M.; Filley, T. R.; Goodfriend, G. A.

2001-01-01

The emergence of biochemical homochirality was a key step in the origin of life, yet prebiotic mechanisms for chiral separation are not well constrained. Here we demonstrate a geochemically plausible scenario for chiral separation of amino acids by adsorption on mineral surfaces. Crystals of the common rock-forming mineral calcite (CaCO(3)), when immersed in a racemic aspartic acid solution, display significant adsorption and chiral selectivity of d- and l-enantiomers on pairs of mirror-related crystal-growth surfaces. This selective adsorption is greater on crystals with terraced surface textures, which indicates that d- and l-aspartic acid concentrate along step-like linear growth features. Thus, selective adsorption of linear arrays of d- and l-amino acids on calcite, with subsequent condensation polymerization, represents a plausible geochemical mechanism for the production of homochiral polypeptides on the prebiotic Earth.

Highly photoresponsive and wavelength-selective circularly-polarized-light detector based on metal-oxides hetero-chiral thin film.

PubMed

Lee, Seung Hee; Singh, Dhruv Pratap; Sung, Ji Ho; Jo, Moon-Ho; Kwon, Ki Chang; Kim, Soo Young; Jang, Ho Won; Kim, Jong Kyu

2016-01-22

A highly efficient circularly-polarized-light detector with excellent wavelength selectivity is demonstrated with an elegant and simple microelectronics-compatible way. The circularly-polarized-light detector based on a proper combination of the geometry-controlled TiO2-SnO2 hetero-chiral thin film as an effective chiroptical filter and the Si active layer shows excellent chiroptical response with external quantum efficiency as high as 30% and high helicity selectivity of ~15.8% in an intended wavelength range. Furthermore, we demonstrated the ability of manipulating both bandwidth and responsivity of the detector simultaneously in whole visible wavelength range by a precise control over the geometry and materials constituting hetero-chiral thin film. The high efficiency, wavelength selectivity and compatibility with conventional microelectronics processes enabled by the proposed device can result in remarkable developments in highly integrated photonic platforms utilizing chiroptical responses.

Highly photoresponsive and wavelength-selective circularly-polarized-light detector based on metal-oxides hetero-chiral thin film

PubMed Central

Lee, Seung Hee; Singh, Dhruv Pratap; Sung, Ji Ho; Jo, Moon-Ho; Kwon, Ki Chang; Kim, Soo Young; Jang, Ho Won; Kim, Jong Kyu

2016-01-01

A highly efficient circularly-polarized-light detector with excellent wavelength selectivity is demonstrated with an elegant and simple microelectronics-compatible way. The circularly-polarized-light detector based on a proper combination of the geometry-controlled TiO2-SnO2 hetero-chiral thin film as an effective chiroptical filter and the Si active layer shows excellent chiroptical response with external quantum efficiency as high as 30% and high helicity selectivity of ~15.8% in an intended wavelength range. Furthermore, we demonstrated the ability of manipulating both bandwidth and responsivity of the detector simultaneously in whole visible wavelength range by a precise control over the geometry and materials constituting hetero-chiral thin film. The high efficiency, wavelength selectivity and compatibility with conventional microelectronics processes enabled by the proposed device can result in remarkable developments in highly integrated photonic platforms utilizing chiroptical responses. PMID:26795601

Highly photoresponsive and wavelength-selective circularly-polarized-light detector based on metal-oxides hetero-chiral thin film

NASA Astrophysics Data System (ADS)

Lee, Seung Hee; Singh, Dhruv Pratap; Sung, Ji Ho; Jo, Moon-Ho; Kwon, Ki Chang; Kim, Soo Young; Jang, Ho Won; Kim, Jong Kyu

2016-01-01

A highly efficient circularly-polarized-light detector with excellent wavelength selectivity is demonstrated with an elegant and simple microelectronics-compatible way. The circularly-polarized-light detector based on a proper combination of the geometry-controlled TiO2-SnO2 hetero-chiral thin film as an effective chiroptical filter and the Si active layer shows excellent chiroptical response with external quantum efficiency as high as 30% and high helicity selectivity of ~15.8% in an intended wavelength range. Furthermore, we demonstrated the ability of manipulating both bandwidth and responsivity of the detector simultaneously in whole visible wavelength range by a precise control over the geometry and materials constituting hetero-chiral thin film. The high efficiency, wavelength selectivity and compatibility with conventional microelectronics processes enabled by the proposed device can result in remarkable developments in highly integrated photonic platforms utilizing chiroptical responses.

Chemical chiral pollution: Impact on the society and science and need of the regulations in the 21st century.

PubMed

Basheer, Al Arsh

2018-04-01

The chiral pollution is a serious issue for our health and environment due to the enantio-selective biodegradation of the chiral pollutants. It has adverse impact on our society and science. There is a big loss of our economy due to the use of racemic agrochemicals. The most notorious chiral pollutants are pesticides, polychloro biphenyls, polyaromatic hydrocarbons, brominated flame retardants, drugs, and pharmaceuticals. More than 1500 chiral pollutants are present in the environment. Unfortunately, there is no regulation and control of the chiral pollutants. Therefore, it is an urgent need of the present 21st century to develop a data bank on the chiral pollutants, guidelines for controlling the production, sale and use of the racemic agrochemicals and the other industrial products. The Governments of the different countries should come forward to initiate the regulations. US, FDA, US EPA, and WHO are the most important regulatory authorities and should think about the chiral pollutants. The present article highlights the impact of the chiral pollution on the society and science. Besides, the efforts have also been made to emphasize the need of the regulations to control the chiral pollution. © 2017 Wiley Periodicals, Inc.

Proline-based chiral stationary phases: a molecular dynamics study of the interfacial structure.

PubMed

Ashtari, M; Cann, N M

2011-09-16

Proline chains have generated considerable interest as a possible basis for new selectors in chiral chromatography. In this article, we employ molecular dynamics simulations to examine the interfacial structure of two diproline chiral selectors, one with a terminal trimethylacetyl group and one with a terminal t-butyl carbamate group. The solvents consist of a relatively apolar n-hexane/2-propanol and a polar water/methanol mixture. We begin with electronic structure calculations for the two chiral selectors to assess the energetics of conformational changes, particularly along the backbone where the amide bonds can alternate between cis and trans conformations. Force fields have been developed for the two selectors, based on these ab initio calculations. Molecular dynamics simulations of the selective interfaces are performed to examine the preferred backbone conformations, as a function of end-group and solvent. The full chiral surface includes the diproline selectors, trimethylsilyl end-caps, and silanol groups. Connection is made with selectivity measurements on these interfaces, where significant differences are observed between these two very similar selectors. Copyright © 2011 Elsevier B.V. All rights reserved.

Controlling Chirality of Entropic Crystals.

PubMed

Damasceno, Pablo F; Karas, Andrew S; Schultz, Benjamin A; Engel, Michael; Glotzer, Sharon C

2015-10-09

Colloidal crystal structures with complexity and diversity rivaling atomic and molecular crystals have been predicted and obtained for hard particles by entropy maximization. However, thus far homochiral colloidal crystals, which are candidates for photonic metamaterials, are absent. Using Monte Carlo simulations we show that chiral polyhedra exhibiting weak directional entropic forces self-assemble either an achiral crystal or a chiral crystal with limited control over the crystal handedness. Building blocks with stronger faceting exhibit higher selectivity and assemble a chiral crystal with handedness uniquely determined by the particle chirality. Tuning the strength of directional entropic forces by means of particle rounding or the use of depletants allows for reconfiguration between achiral and homochiral crystals. We rationalize our findings by quantifying the chirality strength of each particle, both from particle geometry and potential of mean force and torque diagrams.

Catalytic Enantioselective Olefin Metathesis in Natural Product Synthesis. Chiral Metal-Based Complexes that Deliver High Enantioselectivity and More

PubMed Central

Malcolmson, Steven J.; Meek, Simon J.; Zhugralin, Adil R.

2012-01-01

Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru-based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations. PMID:19967680

"Heart-cut" bidimensional achiral-chiral liquid chromatography applied to the evaluation of stereoselective metabolism, in vivo biological activity and brain response to chiral drug candidates targeting the central nervous system.

PubMed

Battisti, Umberto M; Citti, Cinzia; Larini, Martina; Ciccarella, Giuseppe; Stasiak, Natalia; Troisi, Luigino; Braghiroli, Daniela; Parenti, Carlo; Zoli, Michele; Cannazza, Giuseppe

2016-04-22

A "heart-cut" two-dimensional achiral-chiral liquid chromatography triple-quadrupole mass spectrometry method (LC-LC-MS/MS) was developed and coupled to in vivo cerebral microdialysis to evaluate the brain response to the chiral compound (±)-7-chloro-5-(3-furanyl)-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxide ((±)-1), a potent positive allosteric modulator (PAM) of AMPA receptor. The method was successfully employed to evaluate also its stereoselective metabolism and in vitro biological activity. In particular, the LC achiral method developed, employs a pentafluorinated silica based column (Discovery HS-F5) to separate dopamine, acetylcholine, serotonin, (±)-1 and its two hepatic metabolites. In the "heart-cut" two-dimension achiral-chiral configuration, (±)-1 and (±)-1-d4 eluted from the achiral column (1st dimension), were transferred to a polysaccharide-based chiral column (2nd dimension, Chiralcel OD-RH) by using an automatic six-port valve. Single enantiomers of (±)-1 were separated and detected using electrospray positive ionization mode and quantified in selected reaction monitoring mode. The method was validated and showed good performance in terms of linearity, accuracy and precision. The new method employed showed several possible applications in the evaluation of: (a) brain response to neuroactive compounds by measuring variations in the brain extracellular levels of selected neurotransmitters and other biomarkers; (b) blood brain barrier penetration of drug candidates by measuring the free concentration of the drug in selected brain areas; (c) the presence of drug metabolites in the brain extracellular fluid that could prove very useful during drug discovery; (d) a possible stereoselective metabolization or blood brain barrier stereoselective crossing of chiral drugs. Finally, compared to the methods reported in the literature, this technique avoids the necessity of euthanizing an animal at each time point to measure drug concentration in whole brain tissue and provides continuous monitoring of extracellular concentrations of single chiral drug enantiomers along with its metabolites in specific brain regions at each selected time point for a desired period by using a single animal. Copyright © 2016 Elsevier B.V. All rights reserved.

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.

Bulky melamine-based Zn-porphyrin tweezer as a CD probe of molecular chirality.

PubMed

Petrovic, Ana G; Vantomme, Ghislaine; Negrón-Abril, Yashira L; Lubian, Elisa; Saielli, Giacomo; Menegazzo, Ileana; Cordero, Roselynn; Proni, Gloria; Nakanishi, Koji; Carofiglio, Tommaso; Berova, Nina

2011-10-01

The transfer of chirality from a guest molecule to an achiral host is the subject of significant interest especially when, upon chiral induction, the chiroptical response of the host/guest complex can effectively report the absolute configuration (AC) of the guest. For more than a decade, dimeric metalloporphyrin hosts (tweezers) have been successfully applied as chirality probes for determination of the AC for a wide variety of chiral synthetic compounds and natural products. The objective of this study is to investigate the utility of a new class of melamine-bridged Zn-porphyrin tweezers as sensitive AC reporters. A combined approach based on an experimental CD analysis and a theoretical prediction of the prevailing interporphyrin helicity demonstrates that these tweezers display favorable properties for chiral recognition. Herein, we discuss the application of the melamine-bridged tweezer to the chiral recognition of a diverse set of chiral guests, such as 1,2-diamines, α-amino-esters and amides, secondary alcohols, and 1,2-amino-alcohols. The bulky periphery and the presence of a rigid porphyrin linkage lead, in some cases, to a more enhanced CD sensitivity than that reported earlier with other tweezers. Copyright © 2011 Wiley-Liss, Inc.

Chiral capillary electrophoresis and nuclear magnetic resonance investigation on the structure-enantioselectivity relationship in synthetic cyclopeptides as chiral selectors.

PubMed

De Lorenzi, E; Massolini, G; Molinari, P; Galbusera, C; Longhi, R; Marinzi, C; Consonni, R; Chiari, M

2001-04-01

In the present work, synthetic cyclohexa- and cycloheptapeptides previously singled out by a combinatorial chemistry approach have been evaluated as chiral selectors in capillary electrophoresis. By applying the countercurrent migration technique and employing a new adsorbed coating, a series of dinitrophenyl amino acids as well as some chiral compounds of pharmaceutical interest have been evaluated for enantiorecognition. The results thus obtained led to a deeper investigation of the chiral discrimination process, by carrying out nuclear magnetic resonance (NMR) studies on selected cyclopeptide-analyte complexes. These studies shed light on the chemical groups involved in the analyte-selector interaction and provided useful information for a wider application of these cyclopeptides in the separation of other drug enantiomers.

From cosmic chirality to protein structure: Lord Kelvin's legacy.

PubMed

Barron, Laurence D

2012-11-01

A selection of my work on chirality is sketched in two distinct parts of this lecture. Symmetry and Chirality explains how the discrete symmetries of parity P, time reversal T, and charge conjugation C may be used to characterize the properties of chiral systems. The concepts of true chirality (time-invariant enantiomorphism) and false chirality (time-noninvariant enantiomorphism) that emerge provide an extension of Lord Kelvin's original definition of chirality to situations where motion is an essential ingredient thereby clarifying, inter alia, the nature of physical influences able to induce absolute enantioselection. Consideration of symmetry violations reveals that strict enantiomers (exactly degenerate) are interconverted by the combined CP operation. Raman optical activity surveys work, from first observation to current applications, on a new chiroptical spectroscopy that measures vibrational optical activity via Raman scattering of circularly polarized light. Raman optical activity provides incisive information ranging from absolute configuration and complete solution structure of smaller chiral molecules and oligomers to protein and nucleic acid structure of intact viruses. Copyright © 2012 Wiley Periodicals, Inc., A Wiley Company.

Enhanced Stereoselectivity of a Cu(II) Complex Chiral Auxiliary in the Synthesis of Fmoc-L-γ-carboxyglutamic Acid | Center for Cancer Research

Cancer.gov

Bridging bioinorganic chemistry with asymmetric synthesis: a naturally occurring metalloprotein is used for the structure-based evolution of chiral auxiliaries that prove to be effective in the synthesis of Fmoc-L-γ-carboxyglutamic acid.

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.

Surface-enhanced chiroptical spectroscopy with superchiral surface waves.

PubMed

Pellegrini, Giovanni; Finazzi, Marco; Celebrano, Michele; Duò, Lamberto; Biagioni, Paolo

2018-07-01

We study the chiroptical properties of one-dimensional photonic crystals supporting superchiral surface waves by introducing a simple formalism based on the Fresnel reflection matrix. We show that the proposed framework provides useful insights on the behavior of all the relevant chiroptical quantities, allowing for a deeper understanding of surface-enhanced chiral sensing platforms based on one-dimensional photonic crystals. Finally, we analyze and discuss the limitations of such platforms as the surface concentration of the target chiral analytes is gradually increased. © 2018 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.

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

Corolla chirality does not contribute to directed pollen movement in Hypericum perforatum (Hypericaceae): mirror image pinwheel flowers function as radially symmetric flowers in pollination.

PubMed

Diller, Carolina; Fenster, Charles B

2016-07-01

Corolla chirality, the pinwheel arrangement of petals within a flower, is found throughout the core eudicots. In 15 families, different chiral type flowers (i.e., right or left rotated corolla) exist on the same plant, and this condition is referred to as unfixed/enantiomorphic corolla chirality. There are no investigations on the significance of unfixed floral chirality on directed pollen movement even though analogous mirror image floral designs, for example, enantiostyly, has evolved in response to selection to direct pollinator and pollen movement. Here, we examine the role of corolla chirality on directing pollen transfer, pollinator behavior, and its potential influence on disassortative mating. We quantified pollen transfer and pollinator behavior and movement for both right and left rotated flowers in two populations of Hypericum perforatum. In addition, we quantified the number of right and left rotated flowers at the individual level. Pollinators were indifferent to corolla chirality resulting in no difference in pollen deposition between right and left flowers. Corolla chirality had no effect on pollinator and pollen movement between and within chiral morphs. Unlike other mirror image floral designs, corolla chirality appears to play no role in promoting disassortative mating in this species.

Chiral pharmaceuticals: A review on their environmental occurrence and fate processes.

PubMed

Sanganyado, Edmond; Lu, Zhijiang; Fu, Qiuguo; Schlenk, Daniel; Gan, Jay

2017-11-01

More than 50% of pharmaceuticals in current use are chiral compounds. Enantiomers of the same pharmaceutical have identical physicochemical properties, but may exhibit differences in pharmacokinetics, pharmacodynamics and toxicity. The advancement in separation and detection methods has made it possible to analyze trace amounts of chiral compounds in environmental media. As a result, interest on chiral analysis and evaluation of stereoselectivity in environmental occurrence, phase distribution and degradation of chiral pharmaceuticals has grown substantially in recent years. Here we review recent studies on the analysis, occurrence, and fate of chiral pharmaceuticals in engineered and natural environments. Monitoring studies have shown ubiquitous presence of chiral pharmaceuticals in wastewater, surface waters, sediments, and sludge, particularly β-receptor antagonists, analgesics, antifungals, and antidepressants. Selective sorption and microbial degradation have been demonstrated to result in enrichment of one enantiomer over the other. The changes in enantiomer composition may also be caused by biologically catalyzed chiral inversion. However, accurate evaluation of chiral pharmaceuticals as trace environmental pollutants is often hampered by the lack of identification of the stereoconfiguration of enantiomers. Furthermore, a systematic approach including occurrence, fate and transport in various environmental matrices is needed to minimize uncertainties in risk assessment of chiral pharmaceuticals as emerging environmental contaminants. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mn-salen@MIL101(Al): a heterogeneous, enantioselective catalyst synthesized using a 'bottle around the ship' approach.

PubMed

Bogaerts, Thomas; Van Yperen-De Deyne, Andy; Liu, Ying-Ya; Lynen, Frederic; Van Speybroeck, Veronique; Van Der Voort, Pascal

2013-09-21

An enantioselective catalyst, consisting of a chiral Mn(III)salen complex entrapped in the MIL-101 metal organic framework, is reported. For the first time, we assemble a robust MOF-cage around a chiral complex. The heterogeneous catalyst shows the same selectivity as the homogeneous complex and is fully recyclable. Theoretical calculations provide insight into this retention of selectivity.

Novel Catalyst for the Chirality Selective Synthesis of Single Walled Carbon Nanotubes

DTIC Science & Technology

2015-05-12

hierarchical structures comprising nitrogen- doped reduced GO (rGO) and acid- oxidized SWCNTs was produced using a linear hydrothermal microreactor. Fiber...structures comprising nitrogen- doped reduced GO (rGO) and acidoxidized SWCNTs was produced using a linear hydrothermal microreactor. Fiber micro... doped into Co/SiO2 catalysts to change their chirality selectivity. Further, enrichment of (9,8) nanotubes was carried out by extraction using fluorene

An Active Metamaterial Platform for Chiral Responsive Optoelectronics.

PubMed

Kang, Lei; Lan, Shoufeng; Cui, Yonghao; Rodrigues, Sean P; Liu, Yongmin; Werner, Douglas H; Cai, Wenshan

2015-08-05

Chiral-selective non-linear optics and optoelectronic signal generation are demonstrated in an electrically active photonic metamaterial. The metamaterial reveals significant chiroptical responses in both harmonic generation and the photon drag effect, correlated to the resonance behavior in the linear regime. The multifunctional chiral metamaterial with dual electrical and optical functionality enables transduction of chiroptical responses to electrical signals for integrated photonics. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

ENANTIOMERIC COMPOSITION OF CHIRAL POLYCHLORINATED BIPHENYL ATROPISOMERS IN AQUATIC AND RIPARIAN BIOTA

EPA Science Inventory

The enantiomeric composition of polychlorinated biphenyl (PCB) atropisomers was measured in river and riparian biota (fish, bivalves, crayfish, water snakes, barn swallows) from selected sites throughout the United States by using chiral gas chromatography/mass spectrometry. Nonr...

Chirality and grain boundary effects on indentation mechanical properties of graphene coated on nickel foil

NASA Astrophysics Data System (ADS)

Yan, Yuping; Lv, Jiajiang; Liu, Sheng

2018-04-01

We investigate chirality and grain boundary (GB) effects on indentation mechanical properties of graphene coated on nickel foil using molecular dynamics simulations. The models of graphene with different chirality angles, different numbers of layers and tilt GBs were established. It was found that the chirality angle of few-layer graphene had a significant effect on the load bearing capacity of graphene/nickel systems, and this turns out to be more significant when the number of layers is greater than one. The enhancement to the contact stiffness, elastic capacity and the load bearing capacity of graphene with tilt GBs was lower than that of pristine graphene.

Superchiral Light Generation on Degenerate Achiral Surfaces

NASA Astrophysics Data System (ADS)

Vázquez-Guardado, Abraham; Chanda, Debashis

2018-03-01

A novel route of superchiral near-field generation is demonstrated based on geometrically achiral systems supporting degenerate and spatially superimposed plasmonic modes. Such systems generate a single-handed chiral near field with simultaneous zero far-field circular dichroism. The phenomenon is theoretically elucidated with a rotating dipole model, which predicts a uniform single-handed chiral near field that flips handedness solely by reversing the handedness of the source. This property allows detection of pure background free molecular chirality through near-field light-matter interaction, which is experimentally demonstrated in the precise identification of both handedness of a chiral molecule on a single substrate with about four orders of magnitude enhancement in detection sensitivity compared to its conventional volumetric counterpart.

The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

PubMed Central

Ebner, David C.; Bagdanoff, Jeffrey T.; Ferreira, Eric M.; McFadden, Ryan M.; Caspi, Daniel D.; Trend, Raissa M.

2010-01-01

The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (−)-sparteine as chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of base and hydrogen bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 °C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good to excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones. PMID:19904777

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.

Dynamic control of chirality in phosphine ligands for enantioselective catalysis

PubMed Central

Zhao, Depeng; Neubauer, Thomas M.; Feringa, Ben L.

2015-01-01

Chirality plays a fundamental role in biology and chemistry and the precise control of chirality in a catalytic conversion is a key to modern synthesis most prominently seen in the production of pharmaceuticals. In enantioselective metal-based catalysis, access to each product enantiomer is commonly achieved through ligand design with chiral bisphosphines being widely applied as privileged ligands. Switchable phosphine ligands, in which chirality is modulated through an external trigger signal, might offer attractive possibilities to change enantioselectivity in a catalytic process in a non-invasive manner avoiding renewed ligand synthesis. Here we demonstrate that a photoswitchable chiral bisphosphine based on a unidirectional light-driven molecular motor, can be used to invert the stereoselectivity of a palladium-catalysed asymmetric transformation. It is shown that light-induced changes in geometry and helicity of the switchable ligand enable excellent selectivity towards the racemic or individual enantiomers of the product in a Pd-catalysed desymmetrization reaction. PMID:25806856

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.

Organocatalytic atroposelective synthesis of axially chiral styrenes

NASA Astrophysics Data System (ADS)

Zheng, Sheng-Cai; Wu, San; Zhou, Qinghai; Chung, Lung Wa; Ye, Liu; Tan, Bin

2017-05-01

Axially chiral compounds are widespread in biologically active compounds and are useful chiral ligands or organocatalysts in asymmetric catalysis. It is well-known that styrenes are one of the most abundant and principal feedstocks and thus represent excellent prospective building blocks for chemical synthesis. Driven by the development of atroposelective synthesis of axially chiral styrene derivatives, we discovered herein the asymmetric organocatalytic approach via direct Michael addition reaction of substituted diones/ketone esters/malononitrile to alkynals. The axially chiral styrene compounds were produced with good chemical yields, enantioselectivities and almost complete E/Z-selectivities through a secondary amine-catalysed iminium activation strategy under mild conditions. Such structural motifs are important precursors for further transformations into biologically active compounds and synthetic useful intermediates and may have potential applications in asymmetric synthesis as olefin ligands or organocatalysts.

Active chiral control of GHz acoustic whispering-gallery modes

NASA Astrophysics Data System (ADS)

Mezil, Sylvain; Fujita, Kentaro; Otsuka, Paul H.; Tomoda, Motonobu; Clark, Matt; Wright, Oliver B.; Matsuda, Osamu

2017-10-01

We selectively generate chiral surface-acoustic whispering-gallery modes in the gigahertz range on a microscopic disk by means of an ultrafast time-domain technique incorporating a spatial light modulator. Active chiral control is achieved by making use of an optical pump spatial profile in the form of a semicircular arc, positioned on the sample to break the symmetry of clockwise- and counterclockwise-propagating modes. Spatiotemporal Fourier transforms of the interferometrically monitored two-dimensional acoustic fields measured to micron resolution allow individual chiral modes and their azimuthal mode order, both positive and negative, to be distinguished. In particular, for modes with 15-fold rotational symmetry, we demonstrate ultrafast chiral control of surface acoustic waves in a micro-acoustic system with picosecond temporal resolution. Applications include nondestructive testing and surface acoustic wave devices.

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.

Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals

NASA Astrophysics Data System (ADS)

Wang, Chun-Ta; Chen, Chun-Wei; Yang, Tzu-Hsuan; Nys, Inge; Li, Cheng-Chang; Lin, Tsung-Hsien; Neyts, Kristiaan; Beeckman, Jeroen

2018-01-01

Selection of the bandedge lasing mode of a photonic crystal laser has been realized in a fluorescent dye doped chiral nematic liquid crystal by exerting electrical control over the mode competition. The bandedge lasing can be reversibly switched from the short-wavelength edge mode to the long-wavelength edge mode by applying a voltage of only 20 V, without tuning the bandgap. The underlying mechanism is the field-induced change in the order parameter of the fluorescent dye in the liquid crystal. The orientation of the transition dipole moment determines the polarization state of the dye emission, thereby promoting lasing in the bandedge mode that favors the emission polarization. Moreover, the dynamic mode-selection capability is retained upon polymer-stabilizing the chiral nematic liquid crystal laser. In the polymer-stabilized system, greatly improved stability and lasing performance are observed.

π0 → γγ TO NLO IN CHPT

NASA Astrophysics Data System (ADS)

Goity, José L.

2003-04-01

The π0 → γγ width is determined to next to leading order in the combined chiral and 1/Nc expansions. It is shown that corrections driven by chiral symmetry breaking produce an enhancement of about 4.5% with respect to the width calculated in terms of the chiral-limit amplitude leading to Γπ0 → γγ = 8.10 ± 0.08 MeV. This theoretical prediction will be tested via π0 Primakoff production by the PRIMEX experiment at Jefferson Lab.

ENANTIOMERIC COMPOSITION OF CHIRAL POLYCHLORINATED BIPHENYL ATROPISOMERS IN AQUATIC BED SEDIMENT

EPA Science Inventory

Enantiomeric ratios (ERs) for eight polychlorinated biphenyl (PCB) atropisomers were measured in aquatic sediment from selected sites throughout the United States by using chiral gas chromatography/mass spectrometry. Nonracemic ERs for PCBs 91, 95, 132, 136, 149, 174, and 176 wer...

OBSERVATIONS OF ENANTIOSELECTIVITY IN THE FATE, PERSISTENCE AND EFFECTS OF MODERN PESTICIDES

EPA Science Inventory

Chiral pollutants exist as 2 (or more) species, -- enantiomers -- that are non-superimposable mirror images of each other. Enantiomers have identical physical and chemical properties except when they interact with enzymes or other chiral molecules; then they usually react select...

Enantiomer-specific analysis of multi-component mixtures by correlated electron imaging-ion mass spectrometry

NASA Astrophysics Data System (ADS)

Fanood, Mohammad M. Rafiee; Ram, N. Bhargava; Lehmann, C. Stefan; Powis, Ivan; Janssen, Maurice H. M.

2015-06-01

Simultaneous, enantiomer-specific identification of chiral molecules in multi-component mixtures is extremely challenging. Many established techniques for single-component analysis fail to provide selectivity in multi-component mixtures and lack sensitivity for dilute samples. Here we show how enantiomers may be differentiated by mass-selected photoelectron circular dichroism using an electron-ion coincidence imaging spectrometer. As proof of concept, vapours containing ~1% of two chiral monoterpene molecules, limonene and camphor, are irradiated by a circularly polarized femtosecond laser, resulting in multiphoton near-threshold ionization with little molecular fragmentation. Large chiral asymmetries (2-4%) are observed in the mass-tagged photoelectron angular distributions. These asymmetries switch sign according to the handedness (R- or S-) of the enantiomer in the mixture and scale with enantiomeric excess of a component. The results demonstrate that mass spectrometric identification of mixtures of chiral molecules and quantitative determination of enantiomeric excess can be achieved in a table-top instrument.

Enantiomer-specific analysis of multi-component mixtures by correlated electron imaging–ion mass spectrometry

PubMed Central

Fanood, Mohammad M Rafiee; Ram, N. Bhargava; Lehmann, C. Stefan; Powis, Ivan; Janssen, Maurice H. M.

2015-01-01

Simultaneous, enantiomer-specific identification of chiral molecules in multi-component mixtures is extremely challenging. Many established techniques for single-component analysis fail to provide selectivity in multi-component mixtures and lack sensitivity for dilute samples. Here we show how enantiomers may be differentiated by mass-selected photoelectron circular dichroism using an electron–ion coincidence imaging spectrometer. As proof of concept, vapours containing ∼1% of two chiral monoterpene molecules, limonene and camphor, are irradiated by a circularly polarized femtosecond laser, resulting in multiphoton near-threshold ionization with little molecular fragmentation. Large chiral asymmetries (2–4%) are observed in the mass-tagged photoelectron angular distributions. These asymmetries switch sign according to the handedness (R- or S-) of the enantiomer in the mixture and scale with enantiomeric excess of a component. The results demonstrate that mass spectrometric identification of mixtures of chiral molecules and quantitative determination of enantiomeric excess can be achieved in a table-top instrument. PMID:26104140

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.

Optical patterning and dynamics of torons and hopfions in a chiral nematic with photo-tunable equilibrium pitch

NASA Astrophysics Data System (ADS)

Sohn, Hayley; Ackerman, Paul; Smalyukh, Ivan

Three-dimensional (3D) topological solitons arise in field theories ranging from particle physics to condensed matter and cosmology. They are the 3D counterparts of 2D skyrmions (often called ``baby skyrmions''), which attract a great deal of interest in studies of chiral ferromagnets and enable the emerging field of skyrmionics. In chiral nematic liquid crystals, the stability of such solitons is enhanced by the chiral medium's tendency to twist the director field describing the 3D spatial patterns of molecular alignment. However, their experimental realization, control and detailed studies remain limited. We combine experimental realization and numerical modeling of such light-responsive solitonic structures, including elementary torons and hopfions, in confined chiral nematic liquid crystals with photo-tunable cholesteric pitch. We show that the optical tunability of the pitch allows for using low-intensity light to control the soliton stability, dimensions, spatial patterning and dynamics.

Spin-Dependent Transport through Chiral Molecules Studied by Spin-Dependent Electrochemistry

PubMed Central

2016-01-01

Conspectus Molecular spintronics (spin + electronics), which aims to exploit both the spin degree of freedom and the electron charge in molecular devices, has recently received massive attention. Our recent experiments on molecular spintronics employ chiral molecules which have the unexpected property of acting as spin filters, by way of an effect we call “chiral-induced spin selectivity” (CISS). In this Account, we discuss new types of spin-dependent electrochemistry measurements and their use to probe the spin-dependent charge transport properties of nonmagnetic chiral conductive polymers and biomolecules, such as oligopeptides, L/D cysteine, cytochrome c, bacteriorhodopsin (bR), and oligopeptide-CdSe nanoparticles (NPs) hybrid structures. Spin-dependent electrochemical measurements were carried out by employing ferromagnetic electrodes modified with chiral molecules used as the working electrode. Redox probes were used either in solution or when directly attached to the ferromagnetic electrodes. During the electrochemical measurements, the ferromagnetic electrode was magnetized either with its magnetic moment pointing “UP” or “DOWN” using a permanent magnet (H = 0.5 T), placed underneath the chemically modified ferromagnetic electrodes. The spin polarization of the current was found to be in the range of 5–30%, even in the case of small chiral molecules. Chiral films of the l- and d-cysteine tethered with a redox-active dye, toludin blue O, show spin polarizarion that depends on the chirality. Because the nickel electrodes are susceptible to corrosion, we explored the effect of coating them with a thin gold overlayer. The effect of the gold layer on the spin polarization of the electrons ejected from the electrode was investigated. In addition, the role of the structure of the protein on the spin selective transport was also studied as a function of bias voltage and the effect of protein denaturation was revealed. In addition to “dark” measurements, we also describe photoelectrochemical measurements in which light is used to affect the spin selective electron transport through the chiral molecules. We describe how the excitation of a chromophore (such as CdSe nanoparticles), which is attached to a chiral working electrode, can flip the preferred spin orientation of the photocurrent, when measured under the identical conditions. Thus, chirality-induced spin polarization, when combined with light and magnetic field effects, opens new avenues for the study of the spin transport properties of chiral molecules and biomolecules and for creating new types of spintronic devices in which light and molecular chirality provide new functions and properties. PMID:27797176

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.

Amino Acid Bound Surfactants: A New Synthetic Family of Polymeric Monoliths Open Up Possibilities for Chiral Separations in Capillary Electrochromatography

PubMed Central

He, Jun; Wang, Xiaochun; Morrill, Mike; Shamsi, Shahab A.

2012-01-01

By combining a novel chiral amino-acid surfactant containing acryloyl amide tail, carbamate linker and leucine head group of different chain lengths with a conventional cross linker and a polymerization technique, a new “one-pot”, synthesis for the generation of amino-acid based polymeric monolith is realized. The method promises to open up the discovery of amino-acid based polymeric monolith for chiral separations in capillary electrochromatography (CEC). Possibility of enhanced chemoselectivity for simultaneous separation of ephedrine and pseudoephedrine containing multiple chiral centers, and the potential use of this amino-acid surfactant bound column for CEC and CEC coupled to mass spectrometric detection is demonstrated. PMID:22607448

Chiral separation of norlaudanosoline, laudanosoline, laudanosine, chlorthalidone, and three benzoin derivatives using amino acid based molecular micelles.

PubMed

Billiot, Fereshteh H; Billiot, Eugene J; Ng, Yuen Kwun; Warner, Isiah M

2006-02-01

In this study, 18 polymeric single amino acid and dipeptide surfactants are examined, and their performances, in terms of enantioselectivity, are compared for norlaudanosoline, laudanosoline, laudanosine, chlorthalidone, benzoin, benzoin methyl, and benzoin ethyl enantiomers. Several aspects of amino acid-based polymeric surfactants including comparison of single amino acid versus dipeptide, amino acid order, steric effect, and effect of the position of the chiral center of dipeptide surfactants on the chiral selectivity of these optically active compounds are discussed.

Quantitatively analyzing the mechanism of giant circular dichroism in extrinsic plasmonic chiral nanostructures by tracking the interplay of electric and magnetic dipoles.

PubMed

Hu, Li; Tian, Xiaorui; Huang, Yingzhou; Fang, Liang; Fang, Yurui

2016-02-14

Plasmonic chirality has drawn much attention because of tunable circular dichroism (CD) and the enhancement for chiral molecule signals. Although various mechanisms have been proposed to explain the plasmonic CD, a quantitative explanation like the ab initio mechanism for chiral molecules, is still unavailable. In this study, a mechanism similar to the mechanisms associated with chiral molecules was analyzed. The giant extrinsic circular dichroism of a plasmonic splitting rectangle ring was quantitatively investigated from a theoretical standpoint. The interplay of the electric and magnetic modes of the meta-structure is proposed to explain the giant CD. We analyzed the interplay using both an analytical coupled electric-magnetic dipole model and a finite element method model. The surface charge distributions showed that the circular current yielded by the splitting rectangle ring causes the ring to behave like a magneton at some resonant modes, which then interact with the electric modes, resulting in a mixing of the two types of modes. The strong interplay of the two mode types is primarily responsible for the giant CD. The analysis of the chiral near-field of the structure shows potential applications for chiral molecule sensing.

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.

Tunable mesoporous bilayer photonic resins with chiral nematic structures and actuator properties.

PubMed

Khan, Mostofa K; Hamad, Wadood Y; Maclachlan, Mark J

2014-04-16

Chiral nematic structures with different helical pitch from layer to layer are embedded into phenol-formaldehyde bilayer resin composite films using cellulose nanocrystals (CNCs) as templates. Selective removal of CNCs results in mesoporous resins with different pore size and helical pitch between the layers. Consequently, these materials exhibit photonic properties by selectively reflecting lights of two different wavelengths and concomitant actuation properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Carbon Dioxide Bubble-Induced Vortex Triggers Co-Assembly of Nanotubes with Controlled Chirality.

PubMed

Zhang, Ling; Zhou, Laicheng; Xu, Na; Ouyang, Zhenjie

2017-07-03

It is challenging to prepare co-organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO 2 ) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co-assembled in aqueous solution. CO 2 -triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self-assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO 2 bubble-induced vortex during the co-assembly process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of the axial anomaly on the decay N (1535 )→N η

NASA Astrophysics Data System (ADS)

Olbrich, Lisa; Zétényi, Miklós; Giacosa, Francesco; Rischke, Dirk H.

2018-01-01

The decay width of N (1535 )→N η is as large as that of N (1535 )→N π . This is in evident conflict with simple expectations based on flavor symmetry and phase space. Similarly, the decay width of Λ (1670 )→Λ (1116 )η is larger than predicted by flavor symmetry. In this work, we propose that the axial U (1 )A anomaly is responsible for an enhanced coupling of (some) excited baryons to the η meson. We test this idea by including a new, chirally symmetric but U (1 )A anomalous, term in an effective hadronic model describing baryons and their chiral partners in the mirror assignment. This term enhances the decay of the chiral partners into baryons and an η meson, such as N (1535 )→N η . Moreover, a strong coupling of N (1535 ) to N η' emerges (this is important for studies of η' production processes). Our approach shows that N (1535 ) is predominantly the chiral partner of N (939 ), and Λ (1670 ) the chiral partner of Λ (1116 ). Finally, our formalism can be used to couple the pseudoscalar glueball G ˜ to baryons. We expect a large cross section for the reaction p ¯ p →G ˜ →p ¯ p (1535 ) , which can be experimentally tested in the future PANDA experiment.

Self-Assembled Chiral Photonic Crystals from a Colloidal Helix Racemate.

PubMed

Lei, Qun-Li; Ni, Ran; Ma, Yu-Qiang

2018-06-20

Chiral crystals consisting of microhelices have many optical properties, while presently available fabrication processes limit their large-scale applications in photonic devices. Here, by using a simplified simulation method, we investigate a bottom-up self-assembly route to build up helical crystals from the smectic monolayer of a colloidal helix racemate. With increasing the density, the system undergoes an entropy-driven cocrystallization by forming crystals of various symmetries with different helical shapes. In particular, we identify two crystals of helices arranged in binary honeycomb and square lattices, which are essentially composed of two sets of opposite-handed chiral crystals. Photonic calculations show that these chiral structures can have large complete photonic band gaps. In addition, in the self-assembled chiral square crystal, we also find dual polarization band gaps that selectively forbid the propagation of circularly polarized light of a specific handedness along the helical axis direction. The self-assembly process in our proposed system is robust, suggesting possibilities of using chiral colloids to assemble photonic metamaterials.

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.

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.

The Aromaticity of Pericyclic Reaction Transition States

ERIC Educational Resources Information Center

Rzepa, Henry S.

2007-01-01

An approach is presented that starts from two fundamental concepts in organic chemistry, chirality and aromaticity, and combines them into a simple rule for stating selection rules for pericyclic reactions in terms of achiral Huckel-aromatic and chiral Mobius-aromatic transition states. This is illustrated using an example that leads to apparent…

Exploiting nanospace for asymmetric catalysis: confinement of immobilized, single-site chiral catalysts enhances enantioselectivity.

PubMed

Thomas, John Meurig; Raja, Robert

2008-06-01

In the mid-1990s, it became possible to prepare high-area silicas having pore diameters controllably adjustable in the range ca. 20-200 Å. Moreover, the inner walls of these nanoporous solids could be functionalized to yield single-site, chiral, catalytically active organometallic centers, the precise structures of which could be determined using in situ X-ray absorption and FTIR and multinuclear magic angle spinning (MAS) NMR spectroscopy. This approach opened up the prospect of performing heterogeneous enantioselective conversions in a novel manner, under the spatial restrictions imposed by the nanocavities within which the reactions occur. In particular, it suggested an alternative method for preparing pharmaceutically and agrochemically useful asymmetric products by capitalizing on the notion, initially tentatively perceived, that spatial confinement of prochiral reactants (and transition states formed at the chiral active center) would provide an altogether new method of boosting the enantioselectivity of the anchored chiral catalyst. Initially, we anchored chiral single-site heterogeneous catalysts to nanopores covalently via a ligand attached to Pd(II) or Rh(I) centers. Later, we employed a more convenient and cheaper electrostatic method, relying in part on strong hydrogen bonding. This Account provides many examples of these processes, encompassing hydrogenations, oxidations, and aminations. Of particular note is the facile synthesis from methyl benzoylformate of methyl mandelate, which is a precursor in the synthesis of pemoline, a stimulant of the central nervous system; our procedure offers several viable methods for reducing ketocarboxylic acids. In addition to relying on earlier (synchrotron-based) in situ techniques for characterizing catalysts, we have constructed experimental procedures involving robotically controlled catalytic reactors that allow the kinetics of conversion and enantioselectivity to be monitored continually, and we have access to sophisticated, high-sensitivity chiral chromatographic facilities and automated high-throughput combinatorial test rigs so as to optimize the reaction conditions (e.g., H(2) pressure, temperature, time on-stream, pH, and choice of ligand and central metal ion) for high enantioselectivity. This Account reports our discoveries of selective hydrogenations and aminations of synthetic, pharmaceutical, and biological significance, and the findings of other researchers who have achieved similar success in oxidations, dehydrations, cyclopropanations, and hydroformylations. Although the practical advantages and broad general principles governing the enhancement of enantioselectivity through spatial confinement are clear, we require a deeper theoretical understanding of the details pertaining to the phenomenology involved, particularly through molecular dynamics simulations. Ample scope exists for the general exploitation of nanospace in asymmetric hydrogenations with transition metal complexes and for its deployment for the formation of C-N, C-C, C-O, C-S, and other bonds.

Development and Validation of a Reversed-Phase Chiral HPLC Method to Determine the Chiral Purity of Bulk Batches of (S)-Enantiomer in Afoxolaner.

PubMed

Padivitage, Nilusha; Kumar, Satish; Rustum, Abu

2017-01-01

Afoxolaner is a new antiparasitic molecule from the isoxazoline family that acts on insect acarine g-aminobutyric acid and glutamate receptors. Afoxolaner is a racemic mixture, which has a chiral center at the isoxazoline ring. A reversed-phase chiral HPLC method has been developed to determine the chiral purity of bulk batches of (S)-enantiomer in afoxolaner for the first time. This method can also be used to verify that afoxolaner is a racemic mixture, which was demonstrated by specific rotation. ChromSword, an artificial intelligence method development tool, was used for initial method development. The column selected for the final method was CHIRALPAK AD-RH (150 × 4.6 mm, 5 μm particle size), maintained at 45°C, and isocratic elution using water-isopropanol-acetonitrile (40 + 50 + 10, v/v/v) as the mobile phase with a detection wavelength of 312 nm. The run time for the method was 11 min. The resolution and selectivity factors of the two enantiomers were 2.3 and 1.24, respectively. LOQ and LOD of the method were 1.6 and 0.8 μg/mL, respectively. This method was appropriately validated according to International Conference on Harmonization guidelines for its intended use.

Three-dimensional Majorana fermions in chiral superconductors

DOE PAGES

Kozii, Vladyslav; Venderbos, Jorn W. F.; Fu, Liang

2016-12-07

Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary naturemore » of chiral pairing in spin-orbit–coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs 4Sb 12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions.« less

Three-dimensional Majorana fermions in chiral superconductors.

PubMed

Kozii, Vladyslav; Venderbos, Jörn W F; Fu, Liang

2016-12-01

Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit-coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs 4 Sb 12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions.

Three-dimensional Majorana fermions in chiral superconductors

PubMed Central

Kozii, Vladyslav; Venderbos, Jörn W. F.; Fu, Liang

2016-01-01

Using a systematic symmetry and topology analysis, we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-nondegenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the nonunitary nature of chiral pairing in spin-orbit–coupled superconductors. We address experimental signatures of Majorana fermions and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface, which form arcs in momentum space. We conclude by proposing the heavy fermion superconductor PrOs4Sb12 and related materials as promising candidates for nonunitary chiral superconductors hosting three-dimensional Majorana fermions. PMID:27957543

Superstructures of chiral nematic microspheres as all-optical switchable distributors of light

PubMed Central

Aβhoff, Sarah J.; Sukas, Sertan; Yamaguchi, Tadatsugu; Hommersom, Catharina A.; Le Gac, Séverine; Katsonis, Nathalie

2015-01-01

Light technology is based on generating, detecting and controlling the wavelength, polarization and direction of light. Emerging applications range from electronics and telecommunication to health, defence and security. In particular, data transmission and communication technologies are currently asking for increasingly complex and fast devices, and therefore there is a growing interest in materials that can be used to transmit light and also to control the distribution of light in space and time. Here, we design chiral nematic microspheres whose shape enables them to reflect light of different wavelengths and handedness in all directions. Assembled in organized hexagonal superstructures, these microspheres of well-defined sizes communicate optically with high selectivity for the colour and chirality of light. Importantly, when the microspheres are doped with photo-responsive molecular switches, their chiroptical communication can be tuned, both gradually in wavelength and reversibly in polarization. Since the kinetics of the “on” and “off” switching can be adjusted by molecular engineering of the dopants and because the photonic cross-communication is selective with respect to the chirality of the incoming light, these photo-responsive microspheres show potential for chiroptical all-optical distributors and switches, in which wavelength, chirality and direction of the reflected light can be controlled independently and reversibly. PMID:26400584

Advanced Applications of Vibrational Circular Dichroism: from Small Chiral Molecules to Fibrils

NASA Astrophysics Data System (ADS)

Dukor, Rina K.

2017-06-01

Vibrational Circular Dichroism (VCD), first discovered in the early 1970s, and commercialized in the late 1990's, is finally coming of age! No longer a curiosity of the few selected academic groups, it is now used by all major pharmaceutical companies, regulatory agencies, government labs and academic institutions. The main application for the technology has been determination of absolute configuration of small pharmaceutical molecules. In more recent years, this has extended to more complicated molecules such as natural products with many chiral centers and conformational flexibility. Other applications include determination of enantiomeric purity, chiral polymers, and characterization of other biological molecules such as proteins, carohydrates and nucleic acids. One of the most fascinating discoveries in the VCD field has been been unusual enhancement in intensity for proteins that form fibrils. We have demonstrated sensitivity of VCD to in situ solution-phase probe of the process of fibrillogenesis and subsequent development that currently can only be studied in detail with dried samples by such techniques as scanning electron microscopy or atomic force microscopy. We have further shown that several different proteins, that in their native state have different secondary structures, have a very similar unique signature of mature fibrils. In this presentation, we will discuss fundamentals of VCD, demonstrate a few examples of different applications and showcase the sensitivity to structure of fibrils, including new results on micro-sampling.

Chiral recognition of phenylglycinol enantiomers based on N-acetyl-L-cysteine capped CdTe quantum dots in the presence of Ag+

NASA Astrophysics Data System (ADS)

Guo, Yuan; Zeng, Xiaoqing; Yuan, Haiyan; Huang, Yunmei; Zhao, Yanmei; Wu, Huan; Yang, Jidong

2017-08-01

In this study, a novel method for chiral recognition of phenylglycinol (PG) enantiomers was proposed. Firstly, water-soluble N-acetyl-L-cysteine (NALC)-capped CdTe quantum dots (QDs) were synthesized and experiment showed that the fluorescence intensity of the reaction system slightly enhancement when added PG enantiomers to NALC-capped CdTe quantum dots (QDs), but the R-PG and S-PG could not be distinguished. Secondly, when there was Ag+ presence in the reaction system, the experiment result was extremely interesting, the PG enantiomers cloud make NALC-capped CdTe QDs produce different fluorescence signal, in which the fluorescence of S-PG + Ag+ + NALC-CdTe system was significantly enhanced, and the fluorescence of R-PG + Ag+ + NALC-CdTe system was markedly decreased. Thirdly, all the enhanced and decreased of the fluorescence intensity were directly proportional to the concentration of R-PG and S-PG in the linearly range 10- 5-10- 7 mol·L- 1, respectively. So, the new method for simultaneous determination of the PG enantiomers was built too. The experiment result of the method was satisfactory with the detection limit of PG can reached 10- 7 mol·L- 1 and the related coefficient of S-PG and R-PG are 0.995 and 0.980, respectively. The method was highly sensitive, selective and had wider detection range compared with other methods.

Applications of ultrasound to chiral crystallization, resolution and deracemization.

PubMed

Xiouras, Christos; Fytopoulos, Antonios; Jordens, Jeroen; Boudouvis, Andreas G; Van Gerven, Tom; Stefanidis, Georgios D

2018-05-01

Industrial synthesis of enantiopure compounds is nowadays heavily based on the separation of racemates through crystallization processes. Although the application of ultrasound in solution crystallization processes (sonocrystallization) has become a promising emerging technology, offering several benefits (e.g. reduction of the induction time and narrowing of the metastable zone width, control over the product size, shape and polymorphic modification), little attention has been paid so far to the effects of ultrasound on chiral crystallization processes. Several recent studies have reported on the application of acoustic energy to crystallization processes that separate enantiomers, ranging from classical (diastereomeric) resolution and preferential crystallization to new and emerging processes such as attrition-enhanced deracemization (Viedma ripening). A variety of interesting effects have been observed, which include among others, enhanced crystallization yield with higher enantiomeric purity crystals, spontaneous mirror symmetry breaking crystallization, formation of metastable conglomerate crystals and enhanced deracemization rates. The objective of this review is to provide an overview of the effects of ultrasound on chiral crystallization and outline several aspects of interest in this emerging field. Copyright © 2018 Elsevier B.V. All rights reserved.

Chiral cavity ring down polarimetry: Chirality and magnetometry measurements using signal reversals.

PubMed

Bougas, Lykourgos; Sofikitis, Dimitris; Katsoprinakis, Georgios E; Spiliotis, Alexandros K; Tzallas, Paraskevas; Loppinet, Benoit; Rakitzis, T Peter

2015-09-14

We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of α-pinene, 2-butanol, and α-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces.

Shortening anomalies in supersymmetric theories

DOE PAGES

Gomis, Jaume; Komargodski, Zohar; Ooguri, Hirosi; ...

2017-01-17

We present new anomalies in two-dimensional N = (2, 2) superconformal theories. They obstruct the shortening conditions of chiral and twisted chiral multiplets at coincident points. This implies that marginal couplings cannot be promoted to background superfields in short representations. Therefore, standard results that follow from N = (2, 2) spurion analysis are invalidated. These anomalies appear only if supersymmetry is enhanced beyond N = (2; 2). These anomalies explain why the conformal manifolds of the K 3 and T 4 sigma models are not Kähler and do not factorize into chiral and twisted chiral moduli spaces and why theremore » are no N = (2, 2) gauged linear sigma models that cover these conformal manifolds. We also present these results from the point of view of the Riemann curvature of conformal manifolds.« less

Shortening anomalies in supersymmetric theories

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

Gomis, Jaume; Komargodski, Zohar; Ooguri, Hirosi

We present new anomalies in two-dimensional N = (2, 2) superconformal theories. They obstruct the shortening conditions of chiral and twisted chiral multiplets at coincident points. This implies that marginal couplings cannot be promoted to background superfields in short representations. Therefore, standard results that follow from N = (2, 2) spurion analysis are invalidated. These anomalies appear only if supersymmetry is enhanced beyond N = (2; 2). These anomalies explain why the conformal manifolds of the K 3 and T 4 sigma models are not Kähler and do not factorize into chiral and twisted chiral moduli spaces and why theremore » are no N = (2, 2) gauged linear sigma models that cover these conformal manifolds. We also present these results from the point of view of the Riemann curvature of conformal manifolds.« less

Chiral imprinted polymers as enantiospecific coatings of stir bar sorptive extraction devices.

PubMed

Gomez-Caballero, Alberto; Guerreiro, Antonio; Karim, Kal; Piletsky, Sergey; Goicolea, M Aranzazu; Barrio, Ramon J

2011-10-15

This paper reports the design of Molecularly Imprinted Polymers (MIP) with affinity towards (S)-citalopram using computational modeling for the selection of functional monomers and monomer:template ratio. Acrylamide was selected as functional monomer and the final complex functional monomer/template resulted in a 3:1 ratio. The polymer was synthesized by radical polymerization initiated by UV onto magnetic stir-bars in order to obtain a stir bar sorptive extraction (SBSE) device capable of selective enantiomeric recognition. After successful template removal, the parameters affecting the SBSE procedure (sample volume, ionic strength, extraction time and pH) were optimized for the effective rebinding of the target analyte. The resultant chirally imprinted polymer based stir-bar was able to selectively extract (S)-citalopram from a racemic mixture in an aqueous media with high specificity (specificity factor 4) between 25 and 500 μgL(-1). The MIP coated stir-bars can have significance for enantiospecific sample pre-concentration and subsequent analysis without the need for any chiral chromatographic separation. Copyright © 2011 Elsevier B.V. All rights reserved.

Chirality detection of amino acid enantiomers by organic electrochemical transistor.

PubMed

Zhang, Lijun; Wang, Guiheng; Xiong, Can; Zheng, Lei; He, Jianbo; Ding, Yunsheng; Lu, Hongbo; Zhang, Guobing; Cho, Kilwon; Qiu, Longzhen

2018-05-15

Chiral recognition of α-amino acids is attracting increasing interest due to the importance of α-amino acids in protein metabolism as well as in food products and pharmaceuticals. Organic electrochemical transistors (OECTs) with gate electrodes modified with molecularly imprinted polymer (MIP) films were fabricated and successfully used as highly selective and sensitive chiral recognition biosensors for d/l-tryptophan (d/l-Trp) and d/l-tyrosine (d/l-Tyr). The MIP films, which can specifically recognize and has an electrocatalytic effect on the oxidation of Trp and Tyr, together with the amplification function of an OECT, provide a highly sensitive and selective OECT biosensor. The sensor showed a linear response range for l-Trp and L-Tyr from 300 nM to 10 μM with a sensitivity of 3.19 and 3.64 μA/μM, respectivity. And the detection limit for L-Trp and L-Tyr is of 2 nM and 30 nM (S/N > 3). The selectivity factors of L-Trp, D-Trp, L-Tyr and D-Tyr to their enantiomers are 11.6, 3.5, 14.5 and 2.6, respectively. This method can pave the way for widespread applications of OECT-based sensors in chiral material identification. Copyright © 2018 Elsevier B.V. All rights reserved.

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.

Chiral Symmetry Breaking and Complete Chiral Purity by Thermodynamic-Kinetic Feedback Near Equilibrium: Implications for the Origin of Biochirality

NASA Astrophysics Data System (ADS)

Viedma, Cristobal

2007-05-01

Chiral symmetry breaking occurs when a physical or chemical process spontaneously generates a large excess of one of the two enantiomers-left-handed (L) or right-handed (D)--with no preference as to which of the two enantiomers is produced. From the viewpoint of energy, these two enantiomers can exist with an equal probability, and inorganic processes that involve chiral products commonly yield a racemic mixture of both. The fact that biologically relevant molecules exist only as one of the two enantiomers is a fascinating example of complete symmetry breaking in chirality and has long intrigued the science community. The origin of this selective chirality has remained a fundamental enigma with regard to the origin of life since the time of Pasteur, some 140 years ago. Here, it is shown that two populations of chiral crystals of left and right hand cannot coexist in solution: one of the chiral populations disappears in an irreversible autocatalytic process that nurtures the other one. Final and complete chiral purity seems to be an inexorable fate in the course of the common process of growth-dissolution. This unexpected chiral symmetry breaking can be explained by the feedback between the thermodynamic control of dissolution and the kinetics of the growth process near equilibrium. This ``thermodynamic-kinetic feedback near equilibrium'' is established as a mechanism to achieve complete chiral purity in solid state from a previously solid racemic medium. The way in which this mechanism could operate in solutions of chiral biomolecules is described. Finally, based on this mechanism, experiments designed to search for chiral purity in a new way are proposed: chiral purity of amino acids or biopolymers is predicted in solid phase from a previously solid racemic medium. This process may have played a key role in the origin of biochirality.

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.

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.

Lewis base catalyzed aldol additions of chiral trichlorosilyl enolates and silyl enol ethers.

PubMed

Denmark, Scott E; Fujimori, Shinji; Pham, Son M

2005-12-23

[structures: see text] The consequences of double diastereodifferentiation in chiral Lewis base catalyzed aldol additions using chiral enoxysilanes derived from lactate, 3-hydroxyisobutyrate, and 3-hydroxybutyrate have been investigated. Trichlorosilyl enolates derived from the chiral methyl and ethyl ketones were subjected to aldolization in the presence of phosphoramides, and the intrinsic selectivity of these enolates and the external stereoinduction from chiral catalyst were studied. In the reactions with the lactate derived enolate, the strong internal stereoinduction dominated the stereochemical outcome of the aldol addition. For the 3-hydroxyisobutyrate- and 3-hydroxybutyrate derived enolates, the catalyst-controlled diastereoselectivities were observed, and the resident stereogenic centers exerted marginal influence. The corresponding trimethylsilyl enol ethers were employed in SiCl4/bisphosphoramide catalyzed aldol additions, and the effect of double diastereodifferentiation was also investigated. The overall diastereoselection of the process was again controlled by the strong external influence of the catalyst.

Stereospecific ring expansion from orthocyclophanes with central chirality to metacyclophanes with planar chirality.

PubMed

Ishida, Naoki; Sawano, Shota; Murakami, Masahiro

2014-01-01

Carbon-carbon bonds constitute the major framework of organic molecules and carbon-hydrogen bonds are abundant in their peripheries. Such nonpolar σ-bonds are thermodynamically stable and kinetically inert in general. Nonetheless, selective activation of those ubiquitous bonds may offer a straightforward method to construct and/or functionalize organic skeletons. Herein we describe ring expansion from orthocyclophanes to metacyclophanes occurring upon sequential action of light and a metal catalyst. Formally, specific non-strained carbon-hydrogen and carbon-carbon bonds are cleaved and exchanged without elimination of any leaving groups. Notably, the product is energetically uphill from the starting material, but the endergonic photocyclization step makes it possible to drive the transformation forward. The ring expansion is extended to the stereospecific synthesis of metacyclophanes possessing planar chirality, during which central chirality on a tertiary carbon is transferred to planar chirality.

Synthesis and Stereochemical Assignment of Crypto-Optically Active (2) H6 -Neopentane.

PubMed

Masarwa, Ahmad; Gerbig, Dennis; Oskar, Liron; Loewenstein, Aharon; Reisenauer, Hans Peter; Lesot, Philippe; Schreiner, Peter R; Marek, Ilan

2015-10-26

The determination of the absolute configuration of chiral molecules is at the heart of asymmetric synthesis. Here we probe the spectroscopic limits for chiral discrimination with NMR spectroscopy in chiral aligned media and with vibrational circular dichroism spectroscopy of the sixfold-deuterated chiral neopentane. The study of this compound presents formidable challenges since its stereogenicity is only due to small mass differences. For this purpose, we selectively prepared both enantiomers of (2) H6 -1 through a concise synthesis utilizing multifunctional intermediates. While NMR spectroscopy in chiral aligned media could be used to characterize the precursors to (2) H6 -1, the final assignment could only be accomplished with VCD spectroscopy, despite the fleetingly small dichroic properties of 1. Both enantiomers were assigned by matching the VCD spectra with those computed with density functional theory. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cold denaturation induces inversion of dipole and spin transfer in chiral peptide monolayers

PubMed Central

Eckshtain-Levi, Meital; Capua, Eyal; Refaely-Abramson, Sivan; Sarkar, Soumyajit; Gavrilov, Yulian; Mathew, Shinto P.; Paltiel, Yossi; Levy, Yaakov; Kronik, Leeor; Naaman, Ron

2016-01-01

Chirality-induced spin selectivity is a recently-discovered effect, which results in spin selectivity for electrons transmitted through chiral peptide monolayers. Here, we use this spin selectivity to probe the organization of self-assembled α-helix peptide monolayers and examine the relation between structural and spin transfer phenomena. We show that the α-helix structure of oligopeptides based on alanine and aminoisobutyric acid is transformed to a more linear one upon cooling. This process is similar to the known cold denaturation in peptides, but here the self-assembled monolayer plays the role of the solvent. The structural change results in a flip in the direction of the electrical dipole moment of the adsorbed molecules. The dipole flip is accompanied by a concomitant change in the spin that is preferred in electron transfer through the molecules, observed via a new solid-state hybrid organic–inorganic device that is based on the Hall effect, but operates with no external magnetic field or magnetic material. PMID:26916536

Cold denaturation induces inversion of dipole and spin transfer in chiral peptide monolayers

NASA Astrophysics Data System (ADS)

Eckshtain-Levi, Meital; Capua, Eyal; Refaely-Abramson, Sivan; Sarkar, Soumyajit; Gavrilov, Yulian; Mathew, Shinto P.; Paltiel, Yossi; Levy, Yaakov; Kronik, Leeor; Naaman, Ron

2016-02-01

Chirality-induced spin selectivity is a recently-discovered effect, which results in spin selectivity for electrons transmitted through chiral peptide monolayers. Here, we use this spin selectivity to probe the organization of self-assembled α-helix peptide monolayers and examine the relation between structural and spin transfer phenomena. We show that the α-helix structure of oligopeptides based on alanine and aminoisobutyric acid is transformed to a more linear one upon cooling. This process is similar to the known cold denaturation in peptides, but here the self-assembled monolayer plays the role of the solvent. The structural change results in a flip in the direction of the electrical dipole moment of the adsorbed molecules. The dipole flip is accompanied by a concomitant change in the spin that is preferred in electron transfer through the molecules, observed via a new solid-state hybrid organic-inorganic device that is based on the Hall effect, but operates with no external magnetic field or magnetic material.

One-step hydrothermal synthesis of chiral carbon dots and their effects on mung bean plant growth.

PubMed

Zhang, Mengling; Hu, Lulu; Wang, Huibo; Song, Yuxiang; Liu, Yang; Li, Hao; Shao, Mingwang; Huang, Hui; Kang, Zhenhui

2018-06-27

Chiral compounds/materials have important effects on the growth of plants. Chiral carbon dots (CDs), as an emerging chiral carbon nanomaterial, have great potential in bio-application and bio-nanotechnology. Herein, we report a hydrothermal method to synthesize chiral CDs from cysteine (cys) and citric acid. These chiral CDs were further demonstrated to have systemic effects on the growth of mung bean plants, in which case both l- and d-CDs can promote the growth of the root in mung bean plants, stem length of mung bean sprouts and water absorption of bean seeds. The elongation of mung bean sprouts presented an increasing trend with the treatment of chiral CDs of increasing concentration (below 500 μg mL-1). Furthermore, in the optimal concentration (100 μg mL-1), the l-CDs can improve root vigor and the activity of the Rubisco enzyme of bean sprouts by 8.4% and 20.5%, while the d-CDs increased by 28.9% and 67.5%. Due to more superior properties in improving root vigor and the activity of the Rubisco enzyme of mung bean sprouts, d-CDs are able to enhance photosynthesis better and accumulate more carbohydrate in mung bean plants.

Molecular self assembly and chiral recognition of copper octacyanophthalocyanine on Au(111): Interplay of intermolecular and molecule-substrate interactions.

NASA Astrophysics Data System (ADS)

Sk, Rejaul; Dhara, Barun; Miller, Joel; Deshpande, Aparna

Submolecular resolution scanning tunneling microscopy (STM) of copper octacyanophthalocyanine, CuPc(CN)8, at 77 K demonstrates that these achiral molecules form a two dimensional (2D) tetramer-based self-assembly upon evaporation onto an atomically flat Au(111) substrate. They assemble in two different structurally chiral configurations upon adsorption on Au(111). Scanning tunneling spectroscopy (STS),acquired at 77 K, unveils the HOMO and LUMO energy levels of this self-assembly. Voltage dependent STM images show that each molecule in both the structurally chiral configurations individually becomes chiral by breaking the mirror symmetry due to the enhanced intermolecular dipolar coupling interaction at the LUMO energy while the individual molecules remain achiral at the HOMO energy and within the HOMO-LUMO gap. At the LUMO energy, the handedness of the each chiral molecule is decided by the direction of the dipolar coupling interaction in the tetramer unit cell. This preference for LUMO energy indicates that this chirality is purely electronic in nature and it manifests on top of the organizational chirality that is present in the self-assembly independent of the orbital energy. Supported by IISER Pune and DAE-BRNS, India (Project No. 2011/20/37C/17/BRNS).

Molecular-Level Design of Heterogeneous Chiral Catalysis

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

Francisco Zaera

2012-03-21

The following is a proposal to continue our multi-institutional research on heterogeneous chiral catalysis. Our team combines the use of surface-sensitive analytical techniques for the characterization of model systems with quantum and statistical mechanical calculations to interpret experimental data and guide the design of future research. Our investigation focuses on the interrelation among the three main mechanisms by which enantioselectivity can be bestowed to heterogeneous catalysts, namely: (1) by templating chirality via the adsorption of chiral supramolecular assemblies, (2) by using chiral modifiers capable of forming chiral complexes with the reactant and force enantioselective surface reactions, and (3) by formingmore » naturally chiral surfaces using imprinting chiral agents. Individually, the members of our team are leaders in these various aspects of chiral catalysis, but the present program provides the vehicle to generate and exploit the synergies necessary to address the problem in a comprehensive manner. Our initial work has advanced the methodology needed for these studies, including an enantioselective titration procedure to identify surface chiral sites, infrared spectroscopy in situ at the interface between gases or liquids and solids to mimic realistic catalytic conditions, and DFT and Monte Carlo algorithms to simulate and understand chirality on surfaces. The next step, to be funded by the monies requested in this proposal, is to apply those methods to specific problems in chiral catalysis, including the identification of the requirements for the formation of supramolecular surface structures with enantioselective behavior, the search for better molecules to probe the chiral nature of the modified surfaces, the exploration of the transition from supramolecular to one-to-one chiral modification, the correlation of the adsorption characteristics of one-to-one chiral modifiers with their physical properties, in particular with their configuration, and the development of ways to imprint chiral centers on achiral solid surfaces. Chiral catalysis is not only a problem of great importance in its own right, but also the ultimate test of how to control selectivity in catalysis. The time is ripe for fundamental work in heterogeneous chiral catalysis to provide the U.S. with a leadership role in developing the next generation of catalytic processes for medicinal and agrochemical manufacturing. Our team provides the required expertise for a synergistic and comprehensive integration of physical and chemical experimentation with solid state and molecular reactivity theories to solve this problem.« less

The 3-amino-derivative of gamma-cyclodextrin as chiral selector of Dns-amino acids in electrokinetic chromatography.

PubMed

Giuffrida, A; Contino, A; Maccarrone, G; Messina, M; Cucinotta, V

2009-04-24

The enantioseparation of the enantiomeric pairs of 10 Dns derivatives of alpha-amino acids was successfully carried out by using for the first time the 3-amino derivative of the gamma-cyclodextrin. The effects of pH and selector concentration on the migration times and the resolutions of analytes were studied in detail. 3-Deoxy-3-amino-2(S),3(R)-gamma-cyclodextrin (GCD3AM) shows very good chiral recognition ability even at very low concentrations at all the three investigated values of pH, as shown by the very large values of selectivity and resolution towards several pairs of amino acids. The role played by the cavity, the substitution site and the protonation equilibria on the observed properties of chiral selectivity, on varying the specific amino acid involved, is discussed.

Structural and electronic properties of chiral single-wall copper nanotubes

NASA Astrophysics Data System (ADS)

Duan, YingNi; Zhang, JianMin; Xu, KeWei

2014-04-01

The structural, energetic and electronic properties of chiral ( n, m) (3⩽ n⩽6, n/2⩽ m⩽ n) single-wall copper nanotubes (CuNTs) have been investigated by using projector-augmented wave method based on density-functional theory. The (4, 3) CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions, whereas the (5, 5) and (6, 4) CuNTs should be observed in free-standing and tip-suspended conditions, respectively. The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube. Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk. Current transporting states display different periods and chirality, the combined effects of which lead to weaker chiral currents on CuNTs.

Controlling Chirality of Entropic Crystals

NASA Astrophysics Data System (ADS)

Damasceno, Pablo; Karas, Andrew; Schultz, Benjamin; Engel, Michael; Glotzer, Sharon

Colloidal crystal structures with complexity and diversity rivaling atomic and molecular crystals have been predicted and obtained for hard particles by entropy maximization. However, thus far homochiral colloidal crystals, which are candidates for photonic metamaterials, are absent. Using Monte Carlo simulations we show that chiral polyhedra exhibiting weak directional entropic forces self-assemble either an achiral crystal or a chiral crystal with limited control over the crystal handedness. Building blocks with stronger faceting exhibit higher selectivity and assemble a chiral crystal with handedness uniquely determined by the particle chirality. Tuning the strength of directional entropic forces by means of particle rounding or the use of depletants allows for reconfiguration between achiral and homochiral crystals. We rationalize our findings by quantifying the chirality strength of each particle, both from particle geometry and potential of mean force and torque diagrams. Work supported by the National Science Foundation, Division of Materials Research Award No. DMR 1120923, U.S. Army Research Office under Grant Award No. W911NF-10-1-0518, and also by the DOD/ASD (R&E) under Award No. N00244-09-1-0062.

Optically Active CdSe-Dot/CdS-Rod Nanocrystals with Induced Chirality and Circularly Polarized Luminescence.

PubMed

Cheng, Jiaji; Hao, Junjie; Liu, Haochen; Li, Jiagen; Li, Junzi; Zhu, Xi; Lin, Xiaodong; Wang, Kai; He, Tingchao

2018-05-30

Ligand-induced chirality in semiconductor nanocrystals (NCs) has attracted attention because of the tunable optical properties of the NCs. Induced circular dichroism (CD) has been observed in CdX (X = S, Se, Te) NCs and their hybrids, but circularly polarized luminescence (CPL) in these fluorescent nanomaterials has been seldom reported. Herein, we describe the successful preparation of l- and d-cysteine-capped CdSe-dot/CdS-rods (DRs) with tunable CD and CPL behaviors and a maximum anisotropic factor ( g lum ) of 4.66 × 10 -4 . The observed CD and CPL activities are sensitive to the relative absorption ratio of the CdS shell to the CdSe core, suggesting that the anisotropic g-factors in both CD and CPL increase to some extent for a smaller shell-to-core absorption ratio. In addition, the molar ratio of chiral cysteine to the DRs is investigated. Instead of enhancing the chiral interactions between the chiral molecules and DRs, an excess of cysteine molecules in aqueous solution inhibits both the CD and CPL activities. Such chiral and emissive NCs provide an ideal platform for the rational design of semiconductor nanomaterials with chiroptical properties.

Enhanced optical rotation and diminished depolarization in diffusive scattering from a chiral liquid

NASA Astrophysics Data System (ADS)

Silverman, M. P.; Strange, Wayne; Badoz, J.; Vitkin, I. A.

1996-02-01

Optical rotation and degree of polarization of linearly polarized light were observed by forward, lateral, and back scattering from solutions of D-glucose containing a dispersion of micron-size polystyrene spheres. Rotations increased linearly with glucose concentration at a rate determined by the microsphere concentration and were large even at optical thicknesses sufficiently great to extinguish transmission of the incident beam. Depolarization of light with increasing microsphere concentration occurred at a much slower rate in chiral glucose solution than in pure water. These experiments suggest new possibilities for studying turbid chiral media for which light transmission and specular reflection techniques are inappropriate.

Strategic placement of stereogenic centers in molecular materials for second harmonic generation.

PubMed

Gangopadhyay, P; Rao, D Narayana; Agranat, Israel; Radhakrishnan, T P

2002-01-01

Basic aspects of the nonlinear optical phenomenon of second harmonic generation (SHG) and the assembly of molecular materials for SHG are reviewed. Extensive use of chirality as a convenient tool to generate noncentrosymmetricity in molecular lattices, an essential requirement for the development of quadratic nonlinear optical materials, is noted. An overview of our investigations of chiral diaminodicyanoquinodimethanes is presented, which provides insight into a systematic approach to the effective deployment of chirality to achieve optimal molecular orientations for enhanced solid state SHG. Extension of these ideas to the realization of strong SHG in materials based on helical superstructures is outlined.

Micelle Enhanced Fluorimetric and Thin Layer Chromatography Densitometric Methods for the Determination of (±) Citalopram and its S – Enantiomer Escitalopram

PubMed Central

Taha, Elham A.; Salama, Nahla N.; Wang, Shudong

2009-01-01

Two sensitive and validated methods were developed for determination of a racemic mixture citalopram and its enantiomer S-(+) escitalopram. The first method was based on direct measurement of the intrinsic fluorescence of escitalopram using sodium dodecyl sulfate as micelle enhancer. This was further applied to determine escitalopram in spiked human plasma, as well as in the presence of common and co-administerated drugs. The second method was TLC densitometric based on various chiral selectors was investigated. The optimum TLC conditions were found to be sensitive and selective for identification and quantitative determination of enantiomeric purity of escitalopram in drug substance and drug products. The method can be useful to investigate adulteration of pure isomer with the cheap racemic form. PMID:19652757

Micelle enhanced fluorimetric and thin layer chromatography densitometric methods for the determination of (+/-) citalopram and its S-enantiomer escitalopram.

PubMed

Taha, Elham A; Salama, Nahla N; Wang, Shudong

2009-04-07

Two sensitive and validated methods were developed for determination of a racemic mixture citalopram and its enantiomer S-(+) escitalopram. The first method was based on direct measurement of the intrinsic fluorescence of escitalopram using sodium dodecyl sulfate as micelle enhancer. This was further applied to determine escitalopram in spiked human plasma, as well as in the presence of common and co-administrated drugs. The second method was TLC densitometric based on various chiral selectors was investigated. The optimum TLC conditions were found to be sensitive and selective for identification and quantitative determination of enantiomeric purity of escitalopram in drug substance and drug products. The method can be useful to investigate adulteration of pure isomer with the cheap racemic form.

Formation of multi-stereogenic centers using a catalytic diastereoselective Henry reaction.

PubMed

Arai, Takayoshi; Taneda, Yoshinori; Endo, Yoko

2010-11-14

A diastereoselective Henry reaction of chiral aldehydes with nitroalkanes was developed using a chiral sulfonyldiamine (L1)-CuCl complex. The reaction of (R)-2-phenylpropanal and nitromethane was smoothly catalyzed by the (S,S,S)-L1-CuCl complex to give the adduct with 99/1 syn/anti selectivity in 99% ee. In the reaction of (S)-2-phenylpropanal and nitroethane, the (R,R,R)-L1-CuCl catalyst yielded the expected three contiguous stereogenic centers in a highly syn-selective Henry reaction.

A Tunable and Enantioselective Hetero-Diels-Alder Reaction Provides Access to Distinct Piperidinoyl Spirooxindoles.

PubMed

Jayakumar, Samydurai; Louven, Kathrin; Strohmann, Carsten; Kumar, Kamal

2017-12-11

The active complexes of chiral N,N'-dioxide ligands with dysprosium and magnesium salts catalyze the hetero-Diels-Alder reaction between 2-aza-3-silyloxy-butadienes and alkylidene oxindoles to selectively form 3,3'- and 3,4'-piperidinoyl spirooxindoles, respectively, in very high yields and with excellent enantioselectivities. The exo-selective asymmetric cycloaddition successfully regaled the construction of sp 3 -rich and highly substituted natural-product-based spirooxindoles supporting many chiral centers, including contiguous all-carbon quaternary centers. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of fenoterol stereochemistry on the β2 adrenergic receptor system: ligand directed chiral recognition

PubMed Central

Jozwiak, Krzysztof; Plazinska, Anita; Toll, Lawrence; Jimenez, Lucita; Woo, Anthony Yiu-Ho; Xiao, Rui-Ping; Wainer, Irving W.

2011-01-01

The β2 adrenergic receptor (β2-AR) is a model system for studying the ligand recognition process in G-protein coupled receptors. Fenoterol (FEN) is a β2-AR selective agonist that has two centers of chirality and exists as four stereoisomers. Radioligand binding studies determined that stereochemistry greatly influences the binding affinity. Subsequent Van’t Hoff analysis shows very different thermodynamics of binding depending on the stereoconfiguration of the molecule. The binding of (S,x’)-isomers is almost entirely enthalpy controlled whereas binding of (R,x’)-isomers is purely entropy driven. Stereochemistry of FEN molecule also affects the coupling of the receptor to different G proteins. In a rat cardiomyocyte contractility model, (R,R’)-FEN was shown to selectively activate Gs protein signaling while the (S,R’)- isomer activated both Gi and Gs protein. The overall data demonstrate that the chirality at the two chiral centers of the FEN molecule influences the magnitude of binding affinity, thermodynamics of local interactions within the binding site and the global mechanism of β2-AR activation. Differences in thermodynamic parameters and non-uniform G-protein coupling suggest a mechanism of chiral recognition in which observed enantioselectivities arise from the interaction of the (R,x’)-FEN stereoisomers with a different receptor conformation than the one with which the (S,x’)-isomer interacts. PMID:21618615

Effect of fenoterol stereochemistry on the β2 adrenergic receptor system: ligand-directed chiral recognition.

PubMed

Jozwiak, Krzysztof; Plazinska, Anita; Toll, Lawrence; Jimenez, Lucita; Woo, Anthony Yiu-Ho; Xiao, Rui-Ping; Wainer, Irving W

2011-01-01

The β(2) adrenergic receptor (β(2)-AR) is a model system for studying the ligand recognition process in G protein-coupled receptors. Fenoterol (FEN) is a β(2)-AR selective agonist that has two centers of chirality and exists as four stereoisomers. Radioligand binding studies determined that stereochemistry greatly influences the binding affinity. Subsequent Van't Hoff analysis shows very different thermodynamics of binding depending on the stereoconfiguration of the molecule. The binding of (S,x')-isomers is almost entirely enthalpy controlled whereas binding of (R,x')-isomers is purely entropy driven. Stereochemistry of FEN molecule also affects the coupling of the receptor to different G proteins. In a rat cardiomyocyte contractility model, (R,R')-FEN was shown to selectively activate G(s) protein signaling while the (S,R')-isomer activated both G(i) and G(s) protein. The overall data demonstrate that the chirality at the two chiral centers of the FEN molecule influences the magnitude of binding affinity, thermodynamics of local interactions within the binding site, and the global mechanism of β(2)-AR activation. Differences in thermodynamic parameters and nonuniform G-protein coupling suggest a mechanism of chiral recognition in which observed enantioselectivities arise from the interaction of the (R,x')-FEN stereoisomers with a different receptor conformation than the one with which the (S,x')-isomer interacts. Copyright © 2011 Wiley-Liss, Inc.

Facile Isolation of Adsorbent-Free Long and Highly-Pure Chirality-Selected Semiconducting Single-Walled Carbon Nanotubes Using A Hydrogen-bonding Supramolecular Polymer.

PubMed

Toshimitsu, Fumiyuki; Nakashima, Naotoshi

2015-12-14

The ideal form of semiconducting-single-walled carbon nanotubes (sem-SWNTs) for science and technology is long, defect-free, chirality pure and chemically pure isolated narrow diameter tubes. While various techniques to solubilize and purify sem-SWNTs have been developed, many of them targeted only the chiral- or chemically-purity while sacrificing the sem-SWNT intrinsic structural identities by applying strong ultra-sonication and/or chemical modifications. Toward the ultimate purification of the sem-SWNTs, here we report a mild-conditioned extraction of the sem-SWNTs using removable supramolecular hydrogen-bonding polymers (HBPs) that are composed of dicarboxylic- or diaminopyridyl-fluorenes with ~70%-(8,6)SWNT selective extraction. Replacing conventional strong sonication techniques by a simple shaking using HPBs was found to provide long sem-SWNTs (>2.0 μm) with a very high D/G ratio, which was determined by atomic force microscopy observations. The HBPs were readily removed from the nanotube surfaces by an outer stimulus, such as a change in the solvent polarities, to provide chemically pure (8,6)-enriched sem-SWNTs. We also describe molecular mechanics calculations to propose possible structures for the HBP-wrapped sem-SWNTs, furthermore, the mechanism of the chiral selectivity for the sorted sem-SWNTs is well explained by the relationship between the molecular surface area and mass of the HBP/SWNT composites.

Frozen Chirality of Tertiary Aromatic Amides: Access to Enantioenriched Tertiary α-Amino Acid or Amino Alcohol without Chiral Reagent.

PubMed

Mai, Thi Thoa; Viswambharan, Baby; Gori, Didier; Guillot, Régis; Naubron, Jean-Valère; Kouklovsky, Cyrille; Alezra, Valérie

2017-04-27

One of the fundamental and intriguing aspects of life is the homochirality of the essential molecules. In this field, the absolute asymmetric synthesis of α-amino acids is a major challenge. Herein, we report access, by chemical means, to tertiary α-amino acid derivatives in up to 96 % ee without using any chiral reagent. In our strategy, the dynamic axial chirality of tertiary aromatic amides is frozen in a crystal and is responsible for the stereoselectivity of the subsequent steps. Furthermore, we could control the configuration of the final product by manually sorting and selecting the initial crystals. Based on vibrational circular dichroism studies, we could rationalize the observed stereoselectivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-shot preparation of an inherently chiral trifunctional calix[4]arene from an easily available cone-triformylcalix[4]arene.

PubMed

Ciaccia, Maria; Tosi, Irene; Cacciapaglia, Roberta; Casnati, Alessandro; Baldini, Laura; Di Stefano, Stefano

2013-06-14

Via selective 1,3-distal intramolecular Cannizzaro disproportionation of an easily available cone-triformylcalix[4]arene, an inherently chiral trifunctional cone-calix[4]arene derivative has been prepared. The presence of three different functional groups (-CH2OH, -CHO and -COOH) at the upper rim of the calixarene scaffold makes this compound a versatile intermediate for the development of multifunctional devices. Interesting chiral discrimination of serine derivatives has been observed, presumably thanks to a multipoint-interaction involving the reversible imine bond formation and the hydrogen bonding of the hydroxyl group of the amino acid side-chain with the upper rim functional groups. Consistently, chiral discrimination was not observed with alanine and valine derivatives, lacking hydrogen bonding groups on the side-chain.

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).

A Helicene Nanoribbon with Greatly Amplified Chirality.

PubMed

Schuster, Nathaniel J; Hernández Sánchez, Raúl; Bukharina, Daria; Kotov, Nicholas A; Berova, Nina; Ng, Fay; Steigerwald, Michael L; Nuckolls, Colin

2018-05-14

We report the synthesis and characterization of a chiral, shape-persistent, perylene-diimide-based nanoribbon. Specifically, the fusion of three perylene-diimide monomers with intervening naphthalene subunits resulted in a helical superstructure with two [6]helicene subcomponents. This π-helix-of-helicenes exhibits very intense electronic circular dichroism, including one of the largest Cotton effects ever observed in the visible range. It also displays more than an order of magnitude increase in circular dichroism for select wavelengths relative to its smaller homologue. These impressive chiroptical properties underscore the potential of this new nanoribbon architecture in the context of chiral electronic materials.

Spatial control of chemical processes on nanostructures through nano-localized water heating.

PubMed

Jack, Calum; Karimullah, Affar S; Tullius, Ryan; Khorashad, Larousse Khosravi; Rodier, Marion; Fitzpatrick, Brian; Barron, Laurence D; Gadegaard, Nikolaj; Lapthorn, Adrian J; Rotello, Vincent M; Cooke, Graeme; Govorov, Alexander O; Kadodwala, Malcolm

2016-03-10

Optimal performance of nanophotonic devices, including sensors and solar cells, requires maximizing the interaction between light and matter. This efficiency is optimized when active moieties are localized in areas where electromagnetic (EM) fields are confined. Confinement of matter in these 'hotspots' has previously been accomplished through inefficient 'top-down' methods. Here we report a rapid 'bottom-up' approach to functionalize selective regions of plasmonic nanostructures that uses nano-localized heating of the surrounding water induced by pulsed laser irradiation. This localized heating is exploited in a chemical protection/deprotection strategy to allow selective regions of a nanostructure to be chemically modified. As an exemplar, we use the strategy to enhance the biosensing capabilities of a chiral plasmonic substrate. This novel spatially selective functionalization strategy provides new opportunities for efficient high-throughput control of chemistry on the nanoscale over macroscopic areas for device fabrication.

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.

Enantioselective Fluorescent Recognition of Chiral Acids by Cyclohexane-1,2-diamine-Based Bisbinaphthyl Molecules

PubMed Central

Li, Zi-Bo; Lin, Jing; Sabat, Michal; Hyacinth, Marilise; Pu, Lin

2008-01-01

The cyclohexane-1,2-diamine-based bisbinaphthyl macrocycles (S)-/(R)-5 and their cyclic and acyclic analogs are synthesized. The interactions of these compounds with various chiral acids are studied. Compounds (S)-/(R)-5 exhibit highly enantioselective fluorescent responses and high fluorescent sensitivity toward α-hydroxycarboxylic acids and N-protected amino acids. Among these interactions, (S)-mandelic acid (10−3 M) led to over 20 fold fluorescence enhancement of (S)-5 (1.0 × 10−5 M in benzene/0.05% DME) at the monomer emission and (S)-hexahydromandelic acid (10−3 M) led to over 80 fold fluorescence enhancement. These results demonstrate that (S)-5 is useful as an enantioselective fluorescent sensor for the recognition of the chiral acids. On the basis of the study of the structures of (S)-5 and the previously reported 1,2-diphenylethylenediamine-based bisbinaphthyl macrocycle (S)-4, the large fluorescence enhancement of (S)-5 with achirality-matched α-hydroxycarboxylic acid is attributed to the formation of a structurally rigidified host-guest complex and the further interaction of this complex with the acid to suppress the photo-induced electron transfer fluorescent quenching caused by the nitrogens in (S)-5. PMID:17530897

Amino acid ionic liquids as chiral ligands in ligand-exchange chiral separations.

PubMed

Liu, Qian; Wu, Kangkang; Tang, Fei; Yao, Lihua; Yang, Fei; Nie, Zhou; Yao, Shouzhuo

2009-09-28

Recently, amino acid ionic liquids (AAILs) have attracted much research interest. In this paper, we present the first application of AAILs in chiral separation based on the chiral ligand exchange principle. By using 1-alkyl-3-methylimidazolium L-proline (L-Pro) as a chiral ligand coordinated with copper(II), four pairs of underivatized amino acid enantiomers-dl-phenylalanine (dl-Phe), dl-histidine (dl-His), dl-tryptophane (dl-Trp), and dl-tyrosine (dl-Tyr)-were successfully separated in two major chiral separation techniques, HPLC and capillary electrophoresis (CE), with higher enantioselectivity than conventionally used amino acid ligands (resolution (R(s))=3.26-10.81 for HPLC; R(s)=1.34-4.27 for CE). Interestingly, increasing the alkyl chain length of the AAIL cation remarkably enhanced the enantioselectivity. It was inferred that the alkylmethylimidazolium cations and L-Pro form ion pairs on the surface of the stationary phase or on the inner surface of the capillary. The ternary copper complexes with L-Pro are consequently attached to the support surface, thus inducing an ion-exchange type of retention for the dl-enantiomers. Therefore, the AAIL cation plays an essential role in the separation. This work demonstrates that AAILs are good alternatives to conventional amino acid ligands for ligand-exchange-based chiral separation. It also reveals the tremendous application potential of this new type of task-specific ILs.

Theory of interaction-induced renormalization of Drude weight and plasmon frequency in chiral multilayer graphene

NASA Astrophysics Data System (ADS)

Li, Xiao; Tse, Wang-Kong

2017-02-01

We develop a theory for the optical conductivity of doped ABC-stacked multilayer graphene including the effects of electron-electron interactions. Applying the quantum kinetic formalism, we formulate a set of pseudospin Bloch equations that govern the dynamics of the nonequilibrium density matrix driven by an external ac electric field under the influence of Coulomb interactions. These equations reveal a dynamical mechanism that couples the Drude and interband responses arising from the chirality of pseudospin textures in multilayer graphene systems. We demonstrate that this results in an interaction-induced enhancement of the Drude weight and plasmon frequency strongly dependent on the pseudospin winding number. Using bilayer graphene as an example, we also study the influence of higher-energy bands and find that they contribute considerable renormalization effects not captured by a low-energy two-band description. We argue that this enhancement of Drude weight and plasmon frequency occurs generally in materials characterized by electronic chirality.

Ultrafast Imaging of Chiral Surface Plasmon by Photoemission Electron Microscopy

NASA Astrophysics Data System (ADS)

Dai, Yanan; Dabrowski, Maciej; Petek, Hrvoje

We employ Time-Resolved Photoemission Electron Microscopy (TR-PEEM) to study surface plasmon polariton (SPP) wave packet dynamics launched by tunable (VIS-UV) femtosecond pulses of various linear and circular polarizations. The plasmonic structures are micron size single-crystalline Ag islands grown in situ on Si surfaces and characterized by Low Energy Electron Microscopy (LEEM). The local fields of plasmonic modes enhance two and three photon photoemission (2PP and 3PP) at the regions of strong field enhancement. Imaging of the photoemission signal with PEEM electron optics thus images the plasmonic fields excited in the samples. The observed PEEM images with left and right circularly polarized light show chiral images, which is a consequence of the transverse spin momentum of surface plasmon. By changing incident light polarization, the plasmon interference pattern shifts with light ellipticity indicating a polarization dependent excitation phase of SPP. In addition, interferometric-time resolved measurements record the asymmetric SPP wave packet motion in order to characterize the dynamical properties of chiral SPP wave packets.

Enantioseparation of thalidomide and its hydroxylated metabolites using capillary electrophoresis with various cyclodextrins and their combinations as chiral buffer additives.

PubMed

Meyring, M; Chankvetadze, B; Blaschke, G

1999-09-01

The separation of thalidomide (TD) and its hydroxylated metabolites including their simultaneous enantioseparation was studied in capillary electrophoresis (CE) using four different randomly substituted charged cyclodextrin (CD) derivatives, the combinations of some of them with each other, and beta-CD. TD, as well as two metabolites recently found in incubations of human liver microsomes and human blood, 5-hydroxythalidomide (5-OH-TD) and one of the diastereomeric 5'-hydroxythalidomides (5'-OH-TD), are neutral compounds. Therefore, they were resolved using charged chiral selectors in CE. Two different separation modes (normal polarity and carrier mode) and two different capillaries (fused-silica and polyacrylamide-coated) were tested. Based on the behavior of the individual CDs, their designed combinations were selected in order to improve the separation selectivity and enantioselectivity. Under optimized conditions all three chiral compounds and their enantiomers were resolved simultaneously.

How to prepare a chiral Grignard reagent: a theoretical proposal.

PubMed

Chen, Zhe-Ning; Fu, Gang; Xu, Xin

2011-04-15

It is shown that two competitive pathways (T2 vs T4) exist for Grignard reagent formation. While the nonradical pathway T2 leads to retention of the configuration, the radical pathway T4 gives racemization. Our calculations suggest the way that T2 can be enhanced, which should be of significance to prompt new synthesis approaches for the preparation of chiral Grignard reagents. © 2011 American Chemical Society

Chiral light intrinsically couples to extrinsic/pseudo-chiral metasurfaces made of tilted gold nanowires

PubMed Central

Belardini, Alessandro; Centini, Marco; Leahu, Grigore; Hooper, David C.; Li Voti, Roberto; Fazio, Eugenio; Haus, Joseph W.; Sarangan, Andrew; Valev, Ventsislav K.; Sibilia, Concita

2016-01-01

Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second harmonic generation circular dichroism in such extrinsic/pseudo-chiral materials can be understood in terms of effective nonlinear susceptibility tensor elements that switch sign depending on the orientation of the metasurface. By providing fundamental understanding of the chiroptical interactions in achiral metasurfaces, our work opens up new perspectives for the optimisation of their properties. PMID:27553888

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.

Molecular mechanism of polyacrylate helix sense switching across its free energy landscape.

PubMed

Pietropaolo, Adriana; Nakano, Tamaki

2013-04-17

Helical polymers with switchable screw sense are versatile frameworks for chiral functional materials. In this work, we reconstructed the free energy landscape of helical poly(2,7-bis(4-tert-butylphenyl)fluoren-9-yl acrylate) [poly(BBPFA)], as its racemization is selectively driven by light without any rearrangement of chemical bonds. The chirality inversion was enforced by atomistic free energy simulations using chirality indices as reaction coordinates. The free energy landscape reproduced the experimental electronic circular dichroism spectra. We propose that the chirality inversion of poly(BBPFA) proceeds from a left-handed 31 helix via multistate free energy pathways to reach the right-handed 31 helix. The inversion is triggered by the rotation of biphenyl units with an activation barrier of 38 kcal/mol. To the best of our knowledge, this is the first report on the chiral inversion mechanism of a helical polymer determined in a quantitative way in the framework of atomistic free energy simulations.

Objects of Maximum Electromagnetic Chirality

NASA Astrophysics Data System (ADS)

Fernandez-Corbaton, Ivan; Fruhnert, Martin; Rockstuhl, Carsten

2016-07-01

We introduce a definition of the electromagnetic chirality of an object and show that it has an upper bound. Reciprocal objects attain the upper bound if and only if they are transparent for all the fields of one polarization handedness (helicity). Additionally, electromagnetic duality symmetry, i.e., helicity preservation upon interaction, turns out to be a necessary condition for reciprocal objects to attain the upper bound. We use these results to provide requirements for the design of such extremal objects. The requirements can be formulated as constraints on the polarizability tensors for dipolar objects or on the material constitutive relations for continuous media. We also outline two applications for objects of maximum electromagnetic chirality: a twofold resonantly enhanced and background-free circular dichroism measurement setup, and angle-independent helicity filtering glasses. Finally, we use the theoretically obtained requirements to guide the design of a specific structure, which we then analyze numerically and discuss its performance with respect to maximal electromagnetic chirality.

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.

Stereoselective Degradation and Molecular Ecological Mechanism of Chiral Pesticides Beta-Cypermethrin in Soils with Different pH Values.

PubMed

Yang, Zhong-Hua; Ji, Guo-Dong

2015-12-15

For decades, pesticides have been widely used for agricultural activities around the world, and the environmental problems caused by these compounds have raised widespread concern. However, the different enantioselective behaviors of chiral pesticide enantiomers are often ignored. Here, the selective degradation patterns and mechanisms of chiral pesticide enantiomers were successfully investigated for the first time in the soils of three cultivation areas with different pH values. Beta-cypermethrin was chosen as the target analyte. We found that the degradation rates of the four isomers of beta-cypermethrin were different. We used stepwise regression equations between degradation rates and functional genes to quantitatively study their relationships. Quantitative response analysis revealed that different isomers have different equations even under identical conditions. The results of path analysis showed that a single functional gene can make different direct and indirect contributions to the degradation of different isomers. Finally, the high-throughput technology was used to analysis the genome of the three tested soils and then compared the main microbial communities in them. We have successfully devised a method to investigate the molecular biological mechanisms of the selective degradation behavior of chiral compounds, thus enabling us to better understand these mechanisms.

Enantioselective induction of cytotoxicity by o,p'-DDD in PC12 cells: implications of chirality in risk assessment of POPs metabolites.

PubMed

Wang, Cui; Li, Zhuoyu; Zhang, Quan; Zhao, Meirong; Liu, Weiping

2013-04-16

The increased release of chiral persistent organic pollutants (POPs) into the environment has resulted in more attention to the role of enantioselectivity in the fate and ecotoxicological effects of these compounds. Although the enantioselectivity of chiral POPs has been considered in previous studies, little effort has been expended to discern the enantiospecific effects of chiral POPs metabolites, which may impede comprehensive risk assessments of these chemicals. In the present study, o,p'-DDD, the chiral metabolite of o,p'-DDT, was used as a model chiral metabolite. First, a preferential chiral separation at 100% ethanol was employed to obtain a pure enantiomer. The enantioselective cytotoxicity of o,p'-DDD in rat cells (PC12) was evaluated by detecting activation of the cellular apoptosis and oxidative stress systems and microarray analysis. We have documented for the first time that R-(+)-o,p'-DDD increases apoptosis by selectively disturbing the oxidative system (enzymes and molecules) and regulating the transcription of Aven, Bid, Cideb and Tp53. By comparing the data from the present study to data derived from the parent compound, we concluded that the R-enantiomer is the more detrimental stereostructure for both o,p'-DDT and o,p'-DDD. This observed stereostructural effect is in line with the structure-activity relationship formulated at other structural levels. Biological activities of the chiral metabolites are likely to occur in the same absolute configuration between chiral POPs and their metabolites provided that they have the similar stereostructures.

Eu2P7X and Ba2As7X (X = Br, I): Chiral double-Zintl salts containing heptapnictotricyclane clusters

NASA Astrophysics Data System (ADS)

Dolyniuk, Juli-Anna; Lee, Shannon; Tran, Nhon; Wang, Jian; Wang, Lin-Lin; Kovnir, Kirill

2018-07-01

Chiral double Zintl salts present tunable crystal structures with enhanced structural flexibilities and potential for applications requiring chiral control and enantioselectivity. To accompany the chiral Sr2P7I and Sr2P7Br double Zintl salts reported by us previously, six new chiral Zintl salts of the form Ba2-ySryAs7I (y = 0, 0.23, 2), Eu2P7I, Eu2P7Br, and Eu1.3Ba0.7P7Br have been synthesized and characterized by single crystal X-ray diffraction and SEM-EDS analyses. All new compounds crystallize in the Sohncke space group P213 (No. 198) with variations of P73- (heptaphosphanortricyclane) or As73- (heptaarsanortricyclane) clusters surrounded by alkaline-earth or Eu cations and halogen anions. Band structure calculations predict semiconducting properties for all synthesized compounds. Diffuse reflectance UV-vis spectroscopy indicates that Eu2P7I is a direct bandgap semiconductor with Eg of 1.7 eV.

Cholesteric liquid crystals doped with gold nanoparticles

NASA Astrophysics Data System (ADS)

Bitar, Rajaa; Agez, Gonzague; Mitov, Michel

2012-10-01

The reflection color of a cholesteric liquid crystal depends on material parameters such as the molecular chirality or the concentration of chiral dopant, the helical pitch of the twisted structure and the optical indices. We show that the color may be selected simply by varying the annealing time of an open cholesteric oligomer film with hybrid anchoring. The 3D representation of the structure is provided by combining complementary imaging techniques. The color selectivity is due to controlled changes of the orientation of the helix axis with respect to the air-material interface. Potential applications are chiral microreflectors and microlenses. Then, we demonstrate the symbiotic association of gold nanoparticles within such cholesteric textures and their long-range self-organized arrangements. We show that the nanoparticles can be patterned on demand only by playing with the film thickness and the interfacial properties of the CLC film. We investigate how the selective reflection is affected by the in situ organization of gold nanoparticles and what is the plasmon response of nanoparticle chains. Potential applications are envisioned in the field of soft nanotechnology and optical materials.

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.

Strong cation exchange-type chiral stationary phase for enantioseparation of chiral amines in subcritical fluid chromatography.

PubMed

Wolrab, Denise; Kohout, Michal; Boras, Mario; Lindner, Wolfgang

2013-05-10

A new strong cation exchange type chiral stationary phase (SCX CSP) based on a syringic acid amide derivative of trans-(R, R)-2-aminocyclohexanesulfonic acid was applied to subcritical fluid chromatography (SFC) for separation of various chiral basic drugs and their analogues. Mobile phase systems consisting of aliphatic alcohols as polar modifiers and a broad range of amines with different substitution patterns and lipophilicity were employed to evaluate the impact on the SFC retention and selectivity characteristics. The observed results point to the existence of carbonic and carbamic acid salts formed as a consequence of reactions occurring between carbon dioxide, the alcoholic modifiers and the amine species present in the sub/supercritical fluid medium, respectively. Evidence is provided that these species are essential for affecting ion exchange between the strongly acidic chiral selector units and the basic analytes, following the well-established stoichiometric displacement mechanisms. Specific trends were observed when different types of amines were used as basic additives. While ammonia gave rise to the formation of the most strongly eluting carbonic and carbamic salt species, simple tertiary amines consistently provided superior levels of enantioselectivity. Furthermore, trends in the chiral SFC separation characteristics were investigated by the systematic variation of the modifier content and temperature. Different effects of additives are interpreted in terms of changes in the relative concentration of the transient ionic species contributing to analyte elution, with ammonia-derived carbamic salts being depleted at elevated temperatures by decomposition. Additionally, in an effort to optimize SFC enantiomer separation conditions for selected analytes, the impact of the type of the organic modifier, temperature, flow rate and active back pressure were also investigated. Copyright © 2013 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.

A planar chiral meta-surface for optical vortex generation and focusing

PubMed Central

Ma, Xiaoliang; Pu, Mingbo; Li, Xiong; Huang, Cheng; Wang, Yanqin; Pan, Wenbo; Zhao, Bo; Cui, Jianhua; Wang, Changtao; Zhao, ZeYu; Luo, Xiangang

2015-01-01

Data capacity is rapidly reaching its limit in modern optical communications. Optical vortex has been explored to enhance the data capacity for its extra degree of freedom of angular momentum. In traditional means, optical vortices are generated using space light modulators or spiral phase plates, which would sharply decrease the integration of optical communication systems. Here we experimentally demonstrate a planar chiral antenna array to produce optical vortex from a circularly polarized light. Furthermore, the antenna array has the ability to focus the incident light into point, which greatly increases the power intensity of the generated optical vortex. This chiral antenna array may have potential application in highly integrated optical communication systems. PMID:25988213

A loop-gap resonator for chirality-sensitive nuclear magneto-electric resonance (NMER)

NASA Astrophysics Data System (ADS)

Garbacz, Piotr; Fischer, Peer; Krämer, Steffen

2016-09-01

Direct detection of molecular chirality is practically impossible by methods of standard nuclear magnetic resonance (NMR) that is based on interactions involving magnetic-dipole and magnetic-field operators. However, theoretical studies provide a possible direct probe of chirality by exploiting an enantiomer selective additional coupling involving magnetic-dipole, magnetic-field, and electric field operators. This offers a way for direct experimental detection of chirality by nuclear magneto-electric resonance (NMER). This method uses both resonant magnetic and electric radiofrequency (RF) fields. The weakness of the chiral interaction though requires a large electric RF field and a small transverse RF magnetic field over the sample volume, which is a non-trivial constraint. In this study, we present a detailed study of the NMER concept and a possible experimental realization based on a loop-gap resonator. For this original device, the basic principle and numerical studies as well as fabrication and measurements of the frequency dependence of the scattering parameter are reported. By simulating the NMER spin dynamics for our device and taking the 19F NMER signal of enantiomer-pure 1,1,1-trifluoropropan-2-ol, we predict a chirality induced NMER signal that accounts for 1%-5% of the standard achiral NMR signal.

On the effect of basic and acidic additives on the separation of the enantiomers of some basic drugs with polysaccharide-based chiral selectors and polar organic mobile phases.

PubMed

Mosiashvili, L; Chankvetadze, L; Farkas, T; Chankvetadze, B

2013-11-22

This article reports the systematic study of the effect of basic and acidic additives on HPLC separation of enantiomers of some basic chiral drugs on polysaccharide-based chiral columns under polar organic mobile-phase conditions. In contrary to generally accepted opinion that the basic additives improve the separation of enantiomers of basic compounds, the multiple scenarios were observed including the increase, decrease, disappearance and appearance of separation, as well as the reversal of the enantiomer elution order of studied basic compounds induced by the acidic additives. These effects were observed on most of the studied 6 chiral columns in 2-propanol and acetonitrile as mobile phases and diethylamine as a basic additive. As acidic additives formic acid was used systematically and acetic acid and trifluoroacetic acid were applied for comparative purposes. This study illustrates that the minor acidic additives to the mobile phase can be used as for the adjustment of separation selectivity and the enantiomer elution order of basic compounds, as well as for study of chiral recognition mechanisms with polysaccharide-based chiral stationary phases. Copyright © 2013 Elsevier B.V. All rights reserved.

Enantioselective catalysis of photochemical reactions.

PubMed

Brimioulle, Richard; Lenhart, Dominik; Maturi, Mark M; Bach, Thorsten

2015-03-23

The nature of the excited state renders the development of chiral catalysts for enantioselective photochemical reactions a considerable challenge. The absorption of a 400 nm photon corresponds to an energy uptake of approximately 300 kJ mol(-1) . Given the large distance to the ground state, innovative concepts are required to open reaction pathways that selectively lead to a single enantiomer of the desired product. This Review outlines the two major concepts of homogenously catalyzed enantioselective processes. The first part deals with chiral photocatalysts, which intervene in the photochemical key step and induce an asymmetric induction in this step. In the second part, reactions are presented in which the photochemical excitation is mediated by an achiral photocatalyst and the transfer of chirality is ensured by a second chiral catalyst (dual catalysis). © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laser R2PI spectroscopic and mass spectrometric studies of chiral neurotransmitters

NASA Astrophysics Data System (ADS)

Giardini, A.; Marotta, V.; Paladini, A.; Piccirillo, S.; Rondino, F.; Satta, M.; Speranza, M.

2007-07-01

One color, mass selected resonant two-photon ionization (1cR2PI) spectra of supersonically expanded bare neurotransmitter, (1 S,2 S)-(+)- N-methyl pseudoephedrine (MPE), and its complexes with chiral and achiral molecules have been investigated. The excitation spectrum of bare MPE has been analyzed and discussed on the basis of theoretical predictions at the B3LYP/6-31G** level of theory. The results allowed to get information on the possible conformers of MPE molecule and on the intermolecular forces on its cluster formed with a variety of solvent molecules, including chiral alcohols, lactates and water. Further information on intermolecular interactions have been obtained with ESI-CID-MS 2 technique, applied to chiral biomolecules linked through a metal ion to the neurotransmitter. The experimental results are compared with theoretical predictions.

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.

Novel smart chiral magnetic microspheres for enantioselective adsorption of tryptophan enantiomers

NASA Astrophysics Data System (ADS)

Guo, Lian-Di; Song, Ya-Ya; Yu, Hai-Rong; Pan, Li-Ting; Cheng, Chang-Jing

2017-06-01

Multifunctional microspheres simultaneously possessing chirality, magnetism and thermosensitivity show great potentials in direct enantiomeric separation. Herein we report a novel type of smart chiral magnetic microspheres with core/shell/shell structures (Fe3O4@SiO2@PNCD) and its application in enantioselective adsorption of tryptophan (Trp) enantiomers. The prepared Fe3O4@SiO2@PNCD are composed of a Fe3O4 nanoparticle core, an acidic-resistant SiO2 middle shell and a thermosensitive microgel functional shell (PNCD). The PNCD plays an important role in the enantioselective adsorption of Trp enantiomers. The β-cyclodextrin (β-CD) molecules on the PNCD act as smart receptors or chiral selectors, and can selectively recognize and bind L-Trp enantiomers into their cavities by forming host-guest inclusion complexes. The poly(N-isopropylacrylamide) (PNIPAM) chains on the PNCD serve as microenvironmental adjustors for the association constants of β-CD/L-Trp complexes. The fabricated Fe3O4@SiO2@PNCD demonstrate fascinating temperature-responsive chiral recognition and adsorption selectivity toward Trp enantiomers. Most importantly, the desorption of Trp enantiomers and the regeneration of the Fe3O4@SiO2@PNCD can be easily achieved via simply changing the operation temperature. Moreover, the regenerated Fe3O4@SiO2@PNCD can be readily recovered from the amino acids enantiomeric solution under an external magnetic field for reuse. The present study provides a novel strategy for the direct enantioselective adsorption and separation of various enantiomeric compounds.

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.

Impact of pyrrolidine-bispyrrole DNA minor groove binding agents and chirality on global proteomic profile in Escherichia Coli.

PubMed

Yang, Ya-Ting; Lin, Chun-Yu; Jeng, Jingyueh; Ong, Chi-Wi

2013-05-23

There is great interest in the design of small molecules that selectively target minor grooves of duplex DNA for controlling specific gene expression implicated in a disease. The design of chiral small molecules for rational drug design has attracted increasing attention due to the chirality of DNA. Yet, there is limited research on the chirality effect of minor groove binders on DNA interaction, especially at the protein expression level. This paper is an attempt to illustrate that DNA binding affinity might not provide a full picture on the biological activities. Drug interacting at the genomic level can be translated to the proteomic level. Here we have illustrated that although the chiral bispyrrole-pyrrolidine-oligoamides, PySSPy and PyRSPy, showed low binding affinity to DNA, their influence at the proteomic level is significant. More importantly, the chirality also plays a role. Two-dimensional proteomic profile to identify the differentially expressed protein in Escherichia coli DH5α (E coli DH5α) were investigated. E coli DH5α incubated with the chiral PySSPy and PyRSPy, diastereomeric at the pyrrolidine ring, showed differential expression of eighteen proteins as observed through two dimensional proteomic profiling. These eighteen proteins identified by MALDI_TOF/TOF MS include antioxidant defense, DNA protection, protein synthesis, chaperone, and stress response proteins. No statistically significant toxicity was observed at the tested drug concentrations as measured via MTT assay. The current results showed that the chiral PySSPy and PyRSPy impact on the proteomic profiling of E coli DH5α, implicating the importance of drug chirality on biological activities at the molecular level.

An aptamer-based fluorescence bio-sensor for chiral recognition of arginine enantiomers

NASA Astrophysics Data System (ADS)

Yuan, Haiyan; Huang, Yunmei; Yang, Jidong; Guo, Yuan; Zeng, Xiaoqing; Zhou, Shang; Cheng, Jiawei; Zhang, Yuhui

2018-07-01

In this study, a novel aptamer - based fluorescence bio-sensor (aptamer-AuNps) was developed for chiral recognition of arginine (Arg) enantiomers based on aptamer and gold nanoparticles (AuNps). Carboxyfluorescein (FAM) labeled aptamers (Apt) were absorbed on AuNps and their fluorescence intensity could be significantly quenched by AuNps based on fluorescence resonance energy transfer (FRET). Once D-Arg or L-Arg were added into the above solution, the aptamer specifically bind to Arg enantiomers and released from AuNps, so the fluorescence intensity of D-Arg system and L-Arg system were all enhanced. The affinity of Apt to L-Arg is tighter to D-Arg, so the enhanced fluorescence signals of L-Arg system was stronger than D-Arg system. What's more, the enhanced fluorescence were directly proportional to the concentration of D-Arg and L-Arg ranging from 0-300 nM and 0-400 nM with related coefficients of 0.9939 and 0.9952, respectively. Furthermore, the method was successfully applied to detection L-Arg in human urine samples with satisfactory results. Eventually, a simple "OR" logic gate with D-Arg &L-Arg as inputs and AuNps aggregation state as outputs was fabricated, which can help us understand the chiral recognition process deeply.

An in-plane magnetic chiral dichroism approach for measurement of intrinsic magnetic signals using transmitted electrons

PubMed Central

Song, Dongsheng; Tavabi, Amir H.; Li, Zi-An; Kovács, András; Rusz, Ján; Huang, Wenting; Richter, Gunther; Dunin-Borkowski, Rafal E.; Zhu, Jing

2017-01-01

Electron energy-loss magnetic chiral dichroism is a powerful technique that allows the local magnetic properties of materials to be measured quantitatively with close-to-atomic spatial resolution and element specificity in the transmission electron microscope. Until now, the technique has been restricted to measurements of the magnetic circular dichroism signal in the electron beam direction. However, the intrinsic magnetization directions of thin samples are often oriented in the specimen plane, especially when they are examined in magnetic-field-free conditions in the transmission electron microscope. Here, we introduce an approach that allows in-plane magnetic signals to be measured using electron magnetic chiral dichroism by selecting a specific diffraction geometry. We compare experimental results recorded from a cobalt nanoplate with simulations to demonstrate that an electron magnetic chiral dichroism signal originating from in-plane magnetization can be detected successfully. PMID:28504267

Chirality-selected phase behaviour in ionic polypeptide complexes

DOE PAGES

Perry, Sarah L.; Leon, Lorraine; Hoffmann, Kyle Q.; ...

2015-01-14

In this study, polyelectrolyte complexes present new opportunities for self-assembled soft matter. Factors determining whether the phase of the complex is solid or liquid remain unclear. Ionic polypeptides enable examination of the effects of stereochemistry on complex formation. Here we demonstrate that chirality determines the state of polyelectrolyte complexes, formed from mixing dilute solutions of oppositely charged polypeptides, via a combination of electrostatic and hydrogen-bonding interactions. Fluid complexes occur when at least one of the polypeptides in the mixture is racemic, which disrupts backbone hydrogen-bonding networks. Pairs of purely chiral polypeptides, of any sense, form compact, fibrillar solids with amore » β-sheet structure. Analogous behaviour occurs in micelles formed from polypeptide block copolymers with polyethylene oxide, where assembly into aggregates with either solid or fluid cores, and eventually into ordered phases at high concentrations, is possible. Chirality is an exploitable tool for manipulating material properties in polyelectrolyte complexation.« less

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.

Optical activity in chiral stacks of 2D semiconductors

NASA Astrophysics Data System (ADS)

Poshakinskiy, Alexander V.; Kazanov, Dmitrii R.; Shubina, Tatiana V.; Tarasenko, Sergey A.

2018-03-01

We show that the stacks of two-dimensional semiconductor crystals with the chiral packing exhibit optical activity and circular dichroism. We develop a microscopic theory of these phenomena in the spectral range of exciton transitions that takes into account the spin-dependent hopping of excitons between the layers in the stack and the interlayer coupling of excitons via electromagnetic field. For the stacks of realistic two-dimensional semiconductors such as transition metal dichalcogenides, we calculate the rotation and ellipticity angles of radiation transmitted through such structures. The angles are resonantly enhanced at the frequencies of both bright and dark exciton modes in the stack. We also study the photoluminescence of chiral stacks and show that it is circularly polarized.

Anion-π Catalysts with Axial Chirality.

PubMed

Wang, Chao; Matile, Stefan

2017-09-04

The idea of anion-π catalysis is to stabilize anionic transition states by anion-π interactions on aromatic surfaces. For asymmetric anion-π catalysis, π-acidic surfaces have been surrounded with stereogenic centers. This manuscript introduces the first anion-π catalysts that operate with axial chirality. Bifunctional catalysts with tertiary amine bases next to π-acidic naphthalenediimide planes are equipped with a bulky aromatic substituent in the imide position to produce separable atropisomers. The addition of malonic acid half thioesters to enolate acceptors is used for evaluation. In the presence of a chiral axis, the selective acceleration of the disfavored but relevant enolate addition was much better than with point chirality, and enantioselectivity could be observed for the first time for this reaction with small-molecule anion-π catalysts. Enantioselectivity increased with the π acidity of the π surface, whereas the addition of stereogenic centers around the aromatic plane did not cause further improvements. These results identify axial chirality of the active aromatic plane generated by atropisomerism as an attractive strategy for asymmetric anion-π catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembly of chiral (1R,2S)-ephedrine and (1S,2S)-pseudoephedrine into low-dimensional aluminophosphate materials driven by their amphiphilic nature.

PubMed

Bernardo-Maestro, Beatriz; Garrido-Martín, Elisa; López-Arbeloa, Fernando; Pérez-Pariente, Joaquín; Gómez-Hortigüela, Luis

2018-03-28

In an attempt to promote the crystallization of chiral inorganic frameworks, we explore the ability of chiral (1R,2S)-ephedrine and its diastereoisomer (1S,2S)-pseudoephedrine to act as organic building blocks for the crystallization of hybrid organo-inorganic aluminophosphate frameworks in the presence of fluoride. These molecules were selected because of their particular molecular asymmetric structure, which enables a rich supramolecular chemistry and a potential chiral recognition phenomenon during crystallization. Up to four new low-dimensional materials have been produced, wherein the organic molecules form an organic bilayer in-between the inorganic networks. We analyze by molecular simulations the trend of these chiral molecules to form these types of framework, which is directly related to their amphiphilic nature that triggers a strong self-assembly through hydrophobic interactions between aromatic rings and hydrophilic interactions with the fluoro-aluminophosphate inorganic units. Such a self-assembly process is strongly dependent on the concentration of the organic molecules.

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

Three-Dimensional Majorana Fermions in Chiral Superconductors

NASA Astrophysics Data System (ADS)

Kozii, Vladyslav; Venderbos, Jorn; Fu, Liang

Through a systematic symmetry and topology analysis we establish that three-dimensional chiral superconductors with strong spin-orbit coupling and odd-parity pairing generically host low-energy nodal quasiparticles that are spin-non-degenerate and realize Majorana fermions in three dimensions. By examining all types of chiral Cooper pairs with total angular momentum J formed by Bloch electrons with angular momentum j in crystals, we obtain a comprehensive classification of gapless Majorana quasiparticles in terms of energy-momentum relation and location on the Fermi surface. We show that the existence of bulk Majorana fermions in the vicinity of spin-selective point nodes is rooted in the non-unitary nature of chiral pairing in spin-orbit-coupled superconductors. We address experimental signatures of Majorana fermions, and find that the nuclear magnetic resonance spin relaxation rate is significantly suppressed for nuclear spins polarized along the nodal direction as a consequence of the spin-selective Majorana nature of nodal quasiparticles. Furthermore, Majorana nodes in the bulk have nontrivial topology and imply the presence of Majorana bound states on the surface that form arcs in momentum space. This work is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award de-sc0010526 (LF and VK), and the Netherlands Organization for Scientific Research (NWO) through a Rubicon Grant (JV).

Exerting control over the helical chirality in the main chain of sergeants-and-soldiers-type poly(quinoxaline-2,3-diyl)s by changing from random to block copolymerization protocols.

PubMed

Nagata, Yuuya; Nishikawa, Tsuyoshi; Suginome, Michinori

2015-04-01

Chiral random poly(quinoxaline-2,3-diyl) polymers of the sergeants-and-soldiers-type (sergeant units bearing (S)-3-octyloxymethyl groups) adopt an M- or P-helical conformation in the presence of achiral units bearing propoxymethyl or butoxy groups (soldier units), respectively. Unusual bidirectional induction of the helical sense can be observed for a copolymer with butoxy soldier units upon changing the mole fraction of the sergeant units. In the presence of 16-20% of sergeant units, the selective induction of a P-helix was observed, while the selective induction of an M-helix was observed for a mole fraction of sergeant units of more than 60%. This phenomenon could be successfully employed to control the helical chirality of copolymers by applying either random or block copolymerization protocols. Random or block copolymerization of sergeant and soldier monomers in a 18:82 ratio resulted in the formation of 250mers with almost absolute P- or M-helical conformation, respectively (>99% ee). Incorporation of a small amount of coordination sites into the random and block copolymers resulted in chiral macromolecular ligands, which allowed the enantioselective synthesis of both enantiomers in the Pd-catalyzed asymmetric hydrosilylation of β-methylstyrene.

Two multidimensional chromatographic methods for enantiomeric analysis of o,p'-DDT and o,p'-DDD in contaminated soil and air in a malaria area of South Africa.

PubMed

Naudé, Yvette; Rohwer, Egmont R

2012-06-12

In rural parts of South Africa the organochlorine insecticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) is still used for malaria vector control where traditional dwellings are sprayed on the inside with small quantities of technical DDT. Since o,p'-DDT may show enantioselective oestrogenicity and biodegradability, it is important to analyse enantiomers of o,p'-DDT and its chiral degradation product, o,p'-DDD, for both health and environmental-forensic considerations. Generally, chiral analysis is performed using heart-cut multidimensional gas chromatography (MDGC) and, more recently, comprehensive two-dimensional gas chromatography (GC×GC). We developed an off-line gas chromatographic fraction collection (heart-cut) procedure for the selective capturing of the appropriate isomers from a first apolar column, followed by reinjection and separation on a second chiral column. Only the o,p'-isomers of DDT and DDD fractions from the first dimension complex chromatogram (achiral apolar GC column separation) were selectively collected onto a polydimethylsiloxane (PDMS) multichannel open tubular silicone rubber trap by simply placing the latter device on the flame tip of an inactivated flame ionisation detector (FID). The multichannel trap containing the o,p'-heart-cuts was then thermally desorbed into a GC with time-of-flight mass spectrometry detection (GC-TOFMS) for second dimension enantioselective separation on a chiral column (β-cyclodextrin-based). By selectively capturing only the o,p'-isomers from the complex sample chromatogram, (1)D separation of ultra-trace level enantiomers could be achieved on the second chiral column without matrix interference. Here, we present solventless concentration techniques for extraction of DDT from contaminated soil and air, and report enantiomeric fraction (EF) values of o,p'-DDT and o,p'-DDD obtained by a new multidimensional approach for heart-cut gas chromatographic fraction collection for off-line second dimension enantiomeric separation by (1)D GC-TOFMS of selected isomers. This multidimensional method is compared to the complementary technique of comprehensive GC×GC-TOFMS using the same enantioselective column, this time as the first dimension of separation. Copyright © 2012 Elsevier B.V. All rights reserved.

Multiple scattering in chiral media: border effects, reduced depolarization, and sensitivity limit

NASA Astrophysics Data System (ADS)

Delplancke, Francoise; Badoz, Jacques P.; Boccara, A. Claude

1997-10-01

Suspensions of polystyrene latex beads in chiral solutions were investigated. The rotatory power, induced by solubilized sucrose, in near-forward scattering was measured via a method using polarization modulation by photo-elastic modulator. The sensitivity of the measurement was enhanced and optimized in order to measure sucrose concentrations as low as 5 mg/ml in a cell 5 mm thick only. Different concentrations and diameters of latex particles were used in combination with different sucrose concentrations going from 1 mg/ml up to saturation. The experiments showed that the apparent rotatory power is enhanced by multiple scattering, that depolarization effects are less important with highly concentrated sucrose solutions and that attention has to be paid to cell border effects in order to avoid important artifacts, in case of highly scattering suspensions. Qualitative and theoretical explanations of those observations are presented. One possible application of this method is to measure the sugar content in human blood, in vivo, non-invasively, through the skin. The concentration to be evaluated is at the sensitivity limit. So any artifact has to be removed carefully, e.g. skin cell birefringence or chirality.

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

Simultaneous analysis of D-alanine, D-aspartic acid, and D-serine using chiral high-performance liquid chromatography-tandem mass spectrometry and its application to the rat plasma and tissues.

PubMed

Karakawa, Sachise; Shimbo, Kazutaka; Yamada, Naoyuki; Mizukoshi, Toshimi; Miyano, Hiroshi; Mita, Masashi; Lindner, Wolfgang; Hamase, Kenji

2015-11-10

A highly sensitive and selective chiral LC-MS/MS method for D-alanine, D-aspartic acid and D-serine has been developed using the precolumn derivatization reagents, 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AccQ-Tag) or p-N,N,N-trimethylammonioanilyl N'-hydroxysuccinimidyl carbamate iodide (TAHS). The thus N-tagged enantiomers of the derivatized amino acids were nicely separated within 20min using the cinchona alkaloid-based zwittterionic ion-exchange type enantioselective column, Chiralpak ZWIX(+). The selected reaction monitoring was applied for detecting the target d-amino acids in biological matrices. By using the present chiral LC-MS/MS method, the three d-amino acids and their l-forms could be simultaneously determined in the range of 0.1-500nmol/mL. Finally, the technique was successfully applied to rat plasma and tissue samples. Copyright © 2015 Elsevier B.V. All rights reserved.

Tuning the Carbon Nanotube Selectivity: Optimizing Reduction Potentials and Distortion Angles in Perylenediimides.

PubMed

Münich, Peter W; Schierl, Christoph; Dirian, Konstantin; Volland, Michel; Bauroth, Stefan; Wibmer, Leonie; Syrgiannis, Zois; Clark, Timothy; Prato, Maurizio; Guldi, Dirk M

2018-04-25

Different water-soluble perylenediimides (PDIs) have been used to individualize and stabilize single-walled carbon nanotubes (SWCNTs) in aqueous media. A key feature of the PDIs is that they can be substituted at the bay positions via the addition of two and/or four bromines. This enables control over structural and electronic PDI characteristics, which prompted us to conduct comparative assays with focus on SWCNTs' chirality and charge transfer. Electrochemical, microscopic, and spectroscopic experiments were used to investigate the SWCNT chiral selectivity of PDIs, on the one hand, and charge-transfer reactions between SWCNTs and PDIs, on the other hand.

The evolution of nucleotides

NASA Technical Reports Server (NTRS)

Usher, D. A.; Needels, M. C.

1986-01-01

Examples of chiral selection in nonenzymatic aminoacylation of internal 2-prime hydroxyl groups of oligo- and polynucleotides are discussed as an evidence for the early evolution of bionucleotides. Some factors that could influence the degree of this chiral selection and its direction are discussed. These include the structure of the aminoacyl component, the structure of the nucleoside component, and the reaction conditions. Investigation of the mechanism of this reaction was aided by the use of 3-prime inosine methyl phosphate (as a simplified model for a dinucleoside monophosphate) and proton NMR spectroscopy of t-butoxycarbonyl-alanyl esters of nucleosides as models for the transition state of the aminoacylation reaction itself.

Band selective small flip angle COSY: a simple experiment for the analyses of 1H NMR spectra of small chiral molecules.

PubMed

Prabhu, Uday Ramesh; Suryaprakash, N

2008-12-01

The NMR spectroscopic discrimination of enantiomers in the chiral liquid crystalline solvent is more often carried out using (2)H detection in its natural abundance. The employment of (1)H detection for such a purpose is severely hampered due to significant loss of resolution in addition to indistinguishable overlap of the spectra from the two enantiomers. This study demonstrates that the band selected small flip angle homonuclear correlation experiment is a simple and robust technique that provides unambiguous discrimination, very high spectral resolution, reduced multiplicity of transitions, relative signs of the couplings and enormous saving of instrument time.

Comparing the selectivity and chiral separation of d- and l- fluorenylmethyloxycarbonyl chloride protected amino acids in analytical high performance liquid chromatography and supercritical fluid chromatography; evaluating throughput, economic and environmental impact.

PubMed

Vera, C M; Shock, D; Dennis, G R; Farrell, W; Shalliker, R A

2017-04-14

The chiral separation of d- and l- FMOC amino acids was undertaken using the Lux Cellulose-1 polysaccharide based chiral column in HPLC (normal phase and reverse phase) and SFC conditions. This was done to compare the relative selectivity and separation between the three separation modes and to evaluate the potential benefits of SFC separations with regards to resolution, throughput, economic and environmental impact. It was established that the separation of d- and l- FMOC amino acids in SFC displayed behaviours that were similar to both normal phase and reversed phase, rather than distinctly one or the other. Additionally, although reversed phase conditions yielded significantly higher resolution values between enantiomers across the range of amino acids studied, improvements in selectivity in SFC via the introduction of higher concentrations of formic acid in the mobile phase allowed for better resolution per unit of time. Moreover since the SFC mobile phase is composed mostly of recyclable CO 2 , there is a reduction in organic solvent consumption, which minimises the economic and environmental costs. Copyright © 2017. Published by Elsevier B.V.

Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

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

Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.

Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of amore » blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.« less

Regio- and enantiofacial selectivity of epoxyeicosatrienoic acid hydration by cytosolic epoxide hydrolase.

PubMed

Zeldin, D C; Kobayashi, J; Falck, J R; Winder, B S; Hammock, B D; Snapper, J R; Capdevila, J H

1993-03-25

The hydration of cis-epoxyeicosatrienoic acids to the corresponding vic-dihydroxyeicosatrienoic acids by cytosolic epoxide hydrolase demonstrates moderate regioselectivity with rates of hydration highest for the 14,15-epoxide and lower for the 11,12- and 8,9-epoxide (4.5, 1.6, and 1.5 mumol of product/mg of protein/min, respectively). Incubations of the 8,9- and 14,15-epoxides with cytosolic epoxide hydrolase show stereoselective formation of diols (7:3 and 4:1 ratio of antipodes, respectively) and concomitant chiral enrichment of the remaining unmetabolized substrate. In contrast, hydration of the 11,12-epoxide is nonenantioselective. The Km value of the enzyme for the 14(R),15(S)-epoxide is 3 microM. Incubations of the enantiomerically pure 8,9- and 14,15-epoxides with lung or liver cytosol, followed by chiral analysis of the resulting diols demonstrate selective cleavage of the oxirane ring at C9 and C15, respectively. On the other hand, cleavage of the 11,12- oxirane ring was less selective. The stereochemical preference of the cytosolic epoxide hydrolase, together with the known chiral composition of the endogenous arachidonate epoxide pools, suggests a functional role for this enzyme in the metabolism of these important compounds.

Chiral determination of cinchonine using an electrochemiluminescent sensor with molecularly imprinted membrane on the surfaces of magnetic particles.

PubMed

Yuan, Xingyi; Tan, Yanji; Wei, Xiaoping; Li, Jianping

2017-11-01

A novel molecular imprinting electrochemiluminescence sensor for detecting chiral cinchonine molecules was developed with a molecularly imprinted polymer membrane on the surfaces of magnetic microspheres. Fe 3 O 4 @Au nanoparticles modified with 6-mercapto-beta-cyclodextrin were used as a carrier, cinchonine as a template molecule, methacrylic acid as a functional monomer and N,N'-methylenebisacrylamide as a cross-linking agent. Cinchonine was specifically recognized by the 6-mercapto-beta-cyclodextrin functional molecularly imprinted polymer and detected based on enhancement of the electrochemiluminescence intensity caused by the reaction of tertiary amino structures of cinchonine molecules with Ru(bpy) 3 2+ . Cinchonine concentrations of 1 × 10 -10 to 4 × 10 -7  mol/L showed a good linear relationship with changes of the electrochemiluminescence intensity, and the detection limit of the sensor was 3.13 × 10 -11  mol/L. The sensor has high sensitivity and selectivity, and is easy to renew. It was designed for detecting serum samples, with recovery rates of 98.2% to 107.6%. Copyright © 2017 John Wiley & Sons, Ltd.

Molecular spinning by a chiral train of short laser pulses

NASA Astrophysics Data System (ADS)

Floß, Johannes; Averbukh, Ilya Sh.

2012-12-01

We provide a detailed theoretical analysis of molecular rotational excitation by a chiral pulse train, a sequence of linearly polarized pulses with the polarization direction rotating from pulse to pulse by a controllable angle. Molecular rotation with a preferential rotational sense (clockwise or counterclockwise) can be excited by this scheme. We show that the directionality of the rotation is caused by quantum interference of different excitation pathways. The chiral pulse train is capable of selective excitation of molecular isotopologs and nuclear spin isomers in a mixture. We demonstrate this using 14N2 and 15N2 as examples for isotopologs and para- and ortho-nitrogen as examples for nuclear-spin isomers.

The even-handed approach: strategies for the deployment of racemic chiral catalysts.

PubMed

Evans, Louise A; Hodnett, Neil S; Lloyd-Jones, Guy C

2012-02-13

Asymmetric catalysis is predominantly associated with the use of enantiomerically pure chiral ligands and catalysts. Although racemic chiral catalysts have been employed quite extensively in polymerization, their utility in mainstream organic synthesis and catalyst development has arguably been rather overlooked. This Minireview collates various themes for the strategic application of racemic ligands and catalysts, ranging from the estimation of selectivity and determination of enantiomeric excess, through to control of regio- and stereochemical outcomes, and mechanistic studies. What emerges is a clear picture that, in isolation or in concert with enantiopure catalysts, the "even-handed" approach has much to offer. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

New Materials Directions for the Realization of Ultra-High Performance 3rd Order Non-Linear Optical Organics

DTIC Science & Technology

2015-03-13

Nowacki, H.S. Oh, C. Zanlorenzi, H.S. Jee, A. Baev, P.N. Prasad, and L. Akcelrud, "Design and synthesis of polymers for chiral photonics ...rationally design and create organic materials with high nonlinear refractive index and low single· and two- photon absorption at wavelengths relevant to...can also enhance 3rd-order NLO response through microscopic cascading of 2nd-order nonlinearity. Chiral control of nonlinearity bas also been

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.

Controlling electric, magnetic, and chiral dipolar emission with PT-symmetric potentials

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

Alaeian, Hadiseh; Dionne, Jennifer A.

We investigate the effect of parity-time (PT) symmetric optical potentials on the radiation of achiral and chiral dipole sources. Two properties unique to PT-symmetric potentials are observed. First, the dipole can be tuned to behave as a strong optical emitter or absorber based on the non-Hermiticity parameter and the dipole location. Second, exceptional points give rise to new system resonances that lead to orders-of-magnitude enhancements in the dipolar emitted or absorbed power. Utilizing these properties, we show that enantiomers of chiral molecules near PT-symmetric metamaterials exhibit a 4.5-fold difference in their emitted power and decay rate. The results of thismore » work could enable new atom-cavity interactions for quantum optics, as well as all-optical enantioselective separation.« less

An aptamer-based fluorescence bio-sensor for chiral recognition of arginine enantiomers.

PubMed

Yuan, Haiyan; Huang, Yunmei; Yang, Jidong; Guo, Yuan; Zeng, Xiaoqing; Zhou, Shang; Cheng, Jiawei; Zhang, Yuhui

2018-07-05

In this study, a novel aptamer - based fluorescence bio-sensor (aptamer-AuNps) was developed for chiral recognition of arginine (Arg) enantiomers based on aptamer and gold nanoparticles (AuNps). Carboxyfluorescein (FAM) labeled aptamers (Apt) were absorbed on AuNps and their fluorescence intensity could be significantly quenched by AuNps based on fluorescence resonance energy transfer (FRET). Once d-Arg or l-Arg were added into the above solution, the aptamer specifically bind to Arg enantiomers and released from AuNps, so the fluorescence intensity of d-Arg system and l-Arg system were all enhanced. The affinity of Apt to l-Arg is tighter to d-Arg, so the enhanced fluorescence signals of l-Arg system was stronger than d-Arg system. What's more, the enhanced fluorescence were directly proportional to the concentration of d-Arg and l-Arg ranging from 0-300 nM and 0-400 nM with related coefficients of 0.9939 and 0.9952, respectively. Furthermore, the method was successfully applied to detection l-Arg in human urine samples with satisfactory results. Eventually, a simple "OR" logic gate with d-Arg &l-Arg as inputs and AuNps aggregation state as outputs was fabricated, which can help us understand the chiral recognition process deeply. Copyright © 2018 Elsevier B.V. All rights reserved.

Chiral templating of self-assembling nanostructures by circularly polarized light

DOE PAGES

Yeom, Jihyeon; Yeom, Bongjun; Chan, Henry; ...

2014-11-17

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 andmore » 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. Lastly, 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.« less

Quality profile determination of Chios mastic gum essential oil and detection of adulteration in mastic oil products with the application of chiral and non-chiral GC-MS analysis.

PubMed

Paraschos, Sotirios; Magiatis, Prokopios; Gikas, Evagelos; Smyrnioudis, Ilias; Skaltsounis, Alexios-Leandros

2016-10-01

The determination of mastic oil profile, with emphasis on its chiral characteristics, could serve as a method for detecting adulteration in products found in the market with a claim of mastic oil content aiming towards protecting it from counterfeiting. Furthermore the evaluation of the raw material is crucial, as the profile is potentially affected by factors as mastic origin and storage time. Thus 45 authentic mastic oil samples were analyzed by GC-MS employing a chiral column and content limits for all major constituents were determined. The chiral GC-MS analysis proved that selected concentration ratios between these constituents, namely those of (-)/(+)-α-pinene (≤1:100) and (-)-α-pinene/myrcene (1.9:100-11:100) could serve as markers for the determination of mastic oil authenticity. Employing this methodology, the analysis of 25 mastic oils contained in cosmetic and dietary products, as well as an artificial mastic oil sample, exhibited several differentiations that could indicate adulteration either with artificial essential oils or volatile compounds, or the use of aged mastic oil. Copyright © 2016 Elsevier B.V. All rights reserved.

Geometrical protection of topological magnetic solitons in microprocessed chiral magnets

NASA Astrophysics Data System (ADS)

Mito, Masaki; Ohsumi, Hiroyuki; Tsuruta, Kazuki; Kotani, Yoshinori; Nakamura, Tetsuya; Togawa, Yoshihiko; Shinozaki, Misako; Kato, Yusuke; Kishine, Jun-ichiro; Ohe, Jun-ichiro; Kousaka, Yusuke; Akimitsu, Jun; Inoue, Katsuya

2018-01-01

A chiral soliton lattice stabilized in a monoaxial chiral magnet CrNb3S6 is a magnetic superlattice consisting of magnetic kinks with a ferromagnetic background. The magnetic kinks are considered to be topological magnetic solitons (TMSs). Changes in the TMS number yield discretized responses in magnetization and electrical conductivity, and this effect is more prominent in smaller crystals. We demonstrate that, in microprocessed CrNb3S6 crystals, TMSs are geometrically protected through element-selected micromagnetometry using soft x-ray magnetic circular dichroism (MCD). A series of x-ray MCD data is supported by mean-field and micromagnetic analyses. By designing the microcrystal geometry, TMS numbers can be successfully changed and fixed over a wide range of magnetic fields.

Low-Energy Collisions of Protonated Enantiopure Amino Acids with Chiral Target Gases

NASA Astrophysics Data System (ADS)

Kulyk, K.; Rebrov, O.; Ryding, M.; Thomas, R. D.; Uggerud, E.; Larsson, M.

2017-12-01

Here we report on the gas-phase interactions between protonated enantiopure amino acids ( l- and d-enantiomers of Met, Phe, and Trp) and chiral target gases [( R)- and ( S)-2-butanol, and ( S)-1-phenylethanol] in 0.1-10.0 eV low-energy collisions. Two major processes are seen to occur over this collision energy regime, collision-induced dissociation and ion-molecule complex formation. Both processes were found to be independent of the stereo-chemical composition of the interacting ions and targets. These data shed light on the currently debated mechanisms of gas-phase chiral selectivity by demonstrating the inapplicability of the three-point model to these interactions, at least under single collision conditions. [Figure not available: see fulltext.

Experimental design methodologies in the optimization of chiral CE or CEC separations: an overview.

PubMed

Dejaegher, Bieke; Mangelings, Debby; Vander Heyden, Yvan

2013-01-01

In this chapter, an overview of experimental designs to develop chiral capillary electrophoresis (CE) and capillary electrochromatographic (CEC) methods is presented. Method development is generally divided into technique selection, method optimization, and method validation. In the method optimization part, often two phases can be distinguished, i.e., a screening and an optimization phase. In method validation, the method is evaluated on its fit for purpose. A validation item, also applying experimental designs, is robustness testing. In the screening phase and in robustness testing, screening designs are applied. During the optimization phase, response surface designs are used. The different design types and their application steps are discussed in this chapter and illustrated by examples of chiral CE and CEC methods.

On chirality transfer in electron donor-acceptor complexes. A prediction for the sulfinimine···BF3 system.

PubMed

Rode, Joanna E; Dobrowolski, Jan Cz

2012-01-01

Stabilization energies of the electron donor-acceptor sulfinimine···BF(3) complexes calculated at either the B3LYP/aug-cc-pVTZ or the MP2/aug-cc-pVTZ level do not allow to judge, whether the N- or O-atom in sulfinimine is stronger electron-donor to BF(3) . The problem seems to be solvable because chirality transfer phenomenon between chiral sulfinimine and achiral BF(3) is expected to be vibrational circular dichroism (VCD) active. Moreover, the bands associated with the achiral BF(3) molecule are predicted to be the most intense in the entire spectrum. However, the VCD band robustness analyses show that most of the chirality transfer modes of BF(3) are unreliable. Conversely, variation of VCD intensity with change of intermolecular distance, angle, and selected dihedrals between the complex partners shows that to establish the robustness of chirality transfer mode. It is also necessary to determine the influence of the potential energy surface (PES) shape on the VCD intensity. At the moment, there is still no universal criterion for the chirality transfer mode robustness and the conclusions formulated based on one system cannot be directly transferred even to a quite similar one. However, it is certain that more attention should be focused on relation of PES shape and the VCD mode robustness problem. Copyright © 2011 Wiley Periodicals, Inc.

Radioracemization and radiation-induced chiral amplification of chiral terpenes measured by optical rotatory dispersion (ORD) spectroscopy

NASA Astrophysics Data System (ADS)

Cataldo, Franco; Ursini, Ornella; Angelini, Giancarlo

2008-08-01

For the first time the radioracemization of α(+)pinene and α(-)pinene, of turpentine and of R(-)- α-phellandrene has been studied by optical rotatory dispersion (ORD) spectroscopy. For all these compounds, the radioracemization implies a shift of the ORD curves toward lower levels of specific optical rotation. The radioracemization degree ( RR) has been defined and calculated for all the compounds studied. It has been found that for radiation dose of 1 MGy the radioracemization degree is about 4.5% for the compound with the highest optical purity and reaches 7-8% for the less optically pure compounds, demonstrating that impurities can affect greatly the radioracemization. In contrast with the general radioracemization effect exerted by high-energy radiation on chiral molecules, β(-)pinene, β(+)pinene when irradiated show an increment of their specific optical rotation. This fact has been measured for the first time by ORD spectroscopy and the amplification degree of chirality can reach 1000% in the near UV. This phenomenon is due to the formation of a chiral polymer, poly- β-pinene, which forms a solution with the monomer enhancing its optical activity. The implications for the theories of the origin of life of such unexpected phenomenon are discussed briefly.

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.

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.

Enantiomer fractions of polychlorinated biphenyls in three selected Standard Reference Materials.

PubMed

Morrissey, Joshua A; Bleackley, Derek S; Warner, Nicholas A; Wong, Charles S

2007-01-01

The enantiomer composition of six chiral polychlorinated biphenyls (PCBs) were measured in three different certified Standard Reference Materials (SRMs) from the US National Institute of Standards and Technology (NIST): SRM 1946 (Lake Superior fish tissue), SRM 1939a (PCB Congeners in Hudson River Sediment), and SRM 2978 (organic contaminants in mussel tissue--Raritan Bay, New Jersey) to aid in quality assurance/quality control methodologies in the study of chiral pollutants in sediments and biota. Enantiomer fractions (EFs) of PCBs 91, 95, 136, 149, 174, and 183 were measured using a suite of chiral columns by gas chromatography/mass spectrometry. Concentrations of target analytes were in agreement with certified values. Target analyte EFs in reference materials were measured precisely (<2% relative standard deviation), indicating the utility of SRM in quality assurance/control methodologies for analyses of chiral compounds in environmental samples. Measured EFs were also in agreement with previously published analyses of similar samples, indicating that similar enantioselective processes were taking place in these environmental matrices.

Is Supramolecular Filament Chirality the Underlying Cause of Major Morphology Differences in Amyloid Fibrils?

PubMed Central

2015-01-01

The unique enhanced sensitivity of vibrational circular dichroism (VCD) to the formation and development of amyloid fibrils in solution is extended to four additional fibril-forming proteins or peptides where it is shown that the sign of the fibril VCD pattern correlates with the sense of supramolecular filament chirality and, without exception, to the dominant fibril morphology as observed in AFM or SEM images. Previously for insulin, it has been demonstrated that the sign of the VCD band pattern from filament chirality can be controlled by adjusting the pH of the incubating solution, above pH 2 for “normal” left-hand-helical filaments and below pH 2 for “reversed” right-hand-helical filaments. From AFM or SEM images, left-helical filaments form multifilament braids of left-twisted fibrils while the right-helical filaments form parallel filament rows of fibrils with a flat tape-like morphology, the two major classes of fibril morphology that from deep UV resonance Raman scattering exhibit the same cross-β-core secondary structure. Here we investigate whether fibril supramolecular chirality is the underlying cause of the major morphology differences in all amyloid fibrils by showing that the morphology (twisted versus flat) of fibrils of lysozyme, apo-α-lactalbumin, HET-s (218–289) prion, and a short polypeptide fragment of transthyretin, TTR (105–115), directly correlates to their supramolecular chirality as revealed by VCD. The result is strong evidence that the chiral supramolecular organization of filaments is the principal underlying cause of the morphological heterogeneity of amyloid fibrils. Because fibril morphology is linked to cell toxicity, the chirality of amyloid aggregates should be explored in the widely used in vitro models of amyloid-associated diseases. PMID:24484302

Is supramolecular filament chirality the underlying cause of major morphology differences in amyloid fibrils?

PubMed

Kurouski, Dmitry; Lu, Xuefang; Popova, Ludmila; Wan, William; Shanmugasundaram, Maruda; Stubbs, Gerald; Dukor, Rina K; Lednev, Igor K; Nafie, Laurence A

2014-02-12

The unique enhanced sensitivity of vibrational circular dichroism (VCD) to the formation and development of amyloid fibrils in solution is extended to four additional fibril-forming proteins or peptides where it is shown that the sign of the fibril VCD pattern correlates with the sense of supramolecular filament chirality and, without exception, to the dominant fibril morphology as observed in AFM or SEM images. Previously for insulin, it has been demonstrated that the sign of the VCD band pattern from filament chirality can be controlled by adjusting the pH of the incubating solution, above pH 2 for "normal" left-hand-helical filaments and below pH 2 for "reversed" right-hand-helical filaments. From AFM or SEM images, left-helical filaments form multifilament braids of left-twisted fibrils while the right-helical filaments form parallel filament rows of fibrils with a flat tape-like morphology, the two major classes of fibril morphology that from deep UV resonance Raman scattering exhibit the same cross-β-core secondary structure. Here we investigate whether fibril supramolecular chirality is the underlying cause of the major morphology differences in all amyloid fibrils by showing that the morphology (twisted versus flat) of fibrils of lysozyme, apo-α-lactalbumin, HET-s (218-289) prion, and a short polypeptide fragment of transthyretin, TTR (105-115), directly correlates to their supramolecular chirality as revealed by VCD. The result is strong evidence that the chiral supramolecular organization of filaments is the principal underlying cause of the morphological heterogeneity of amyloid fibrils. Because fibril morphology is linked to cell toxicity, the chirality of amyloid aggregates should be explored in the widely used in vitro models of amyloid-associated diseases.

Synthesis and studies of axial chiral bisbenzocoumarins: Aggregation-induced emission enhancement properties and aggregation-annihilation circular dichroism effects

NASA Astrophysics Data System (ADS)

Chen, Shaojin; Liu, Wei; Ge, Zhaohai; Zhang, Wenxuan; Wang, Kunpeng; Hu, Zhiqiang

2018-03-01

Axial chiral bisbenzocoumarins were synthesized for the first time by converting naphthanol units in 1,1‧-binaphthol (BINOL) molecule to the benzocoumarin rings. The substitute groups on 3,3‧-positions of bisbenzocoumarins showed significant influence on their aggregation-induced emission enhancement (AEE) properties. It was also found that BBzC1 with ester groups on 3,3‧-positions exhibit an abnormal aggregation-annihilation circular dichroism (AACD) phenomenon, which could be caused by the decrease of the dihedral angle between adjacent benzocoumarin rings in the aggregation state. The single crystal structure of BBzC1 showed that the large dihedral angle in molecule prohibited the strong π-π stacking interactions, which could be main factors for its AEE properties.

Synthesis of Phosphatidylserine and Its Stereoisomers: Their Role in Activation of Blood Coagulation.

PubMed

Mallik, Suman; Prasad, Ramesh; Bhattacharya, Anindita; Sen, Prosenjit

2018-05-10

Natural phosphatidylserine (PS), which contains two chiral centers, enhances blood coagulation. However, the process by which PS enhanced blood coagulation is not completely understood. An efficient and flexible synthetic route has been developed to synthesize all of the possible stereoisomers of PS. In this study, we examined the role of PS chiral centers in modulating the activity of the tissue factor (TF)-factor VIIa coagulation initiation complex. Full length TF was relipidated with phosphatidylcholine, and the synthesized PS isomers were individually used to estimate the procoagulant activity of the TF-FVIIa complex via a FXa generation assay. The results revealed that the initiation complex activity was stereoselective and had increased sensitivity to the configuration of the PS glycerol backbone due to optimal protein-lipid interactions.

Amino Acid Chiral Selection Via Weak Interactions in Stellar Environments: Implications for the Origin of Life.

PubMed

Famiano, Michael A; Boyd, Richard N; Kajino, Toshitaka; Onaka, Takashi; Mo, Yirong

2018-06-11

Magnetochiral phenomena may be responsible for the selection of chiral states of biomolecules in meteoric environments. For example, the Supernova Amino Acid Processing (SNAAP) Model was proposed previously as a possible mode of magnetochiral selection of amino acids by way of the weak interaction in strong magnetic fields. In earlier work, this model was shown to produce an enantiomeric excess (ee) as high as 0.014% for alanine. In this paper we present the results of molecular quantum chemistry calculations from which ees are determined for the α-amino acids plus isovaline and norvaline, which were found to have positive ees in meteorites. Calculations are performed for both isolated and aqueous states. In some cases, the aqueous state was found to produce larger ees reaching values as high as a few percent under plausible conditions.

Catalytic allylic oxidation of internal alkenes to a multifunctional chiral building block

NASA Astrophysics Data System (ADS)

Bayeh, Liela; Le, Phong Q.; Tambar, Uttam K.

2017-07-01

The stereoselective oxidation of hydrocarbons is one of the most notable advances in synthetic chemistry over the past fifty years. Inspired by nature, enantioselective dihydroxylations, epoxidations and other oxidations of unsaturated hydrocarbons have been developed. More recently, the catalytic enantioselective allylic carbon-hydrogen oxidation of alkenes has streamlined the production of pharmaceuticals, natural products, fine chemicals and other functional materials. Allylic functionalization provides a direct path to chiral building blocks with a newly formed stereocentre from petrochemical feedstocks while preserving the olefin functionality as a handle for further chemical elaboration. Various metal-based catalysts have been discovered for the enantioselective allylic carbon-hydrogen oxidation of simple alkenes with cyclic or terminal double bonds. However, a general and selective allylic oxidation using the more common internal alkenes remains elusive. Here we report the enantioselective, regioselective and E/Z-selective allylic oxidation of unactivated internal alkenes via a catalytic hetero-ene reaction with a chalcogen-based oxidant. Our method enables non-symmetric internal alkenes to be selectively converted into allylic functionalized products with high stereoselectivity and regioselectivity. Stereospecific transformations of the resulting multifunctional chiral building blocks highlight the potential for rapidly converting internal alkenes into a broad range of enantioenriched structures that can be used in the synthesis of complex target molecules.

A circular dichroism sensor for selective detection of Cd2 + and S2 - based on the in-situ generation of chiral CdS quantum dots

NASA Astrophysics Data System (ADS)

Sianglam, Pradthana; Kulchat, Sirinan; Tuntulani, Thawatchai; Ngeontae, Wittaya

2017-08-01

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2 + and S2 - based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2 +, S2 -, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2 + or S2 - concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2 + and S2 -, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200 μM and 7-125 μM with detection limits of 59.7 and 1.6 μM for Cd2 + and S2 -, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2 +) and HPLC (for S2 -).

Giant optical activity of sugar in thin soap films.

PubMed

Emile, Janine; Emile, Olivier; Ghoufi, Aziz; Moréac, Alain; Casanova, Federico; Ding, Minxia; Houizot, Patrick

2013-10-15

We report on enhanced experimental optical activity measurements of thin soap films in the presence of sugar. This unusual optical activity is linked to the intramolecular chiral conformation of the glucose molecules at the air/liquid interface. Choosing sodium dodecylsulfate (SDS) as a model surfactant and glucose as model sugar, favorable interactions between the anionic group -OSO3(-)- and the glucose molecules are highlighted. This induces an interfacial anchoring of glucose molecules leading to a perturbing influence of the asymmetric chiral environment. Copyright © 2013 Elsevier Inc. All rights reserved.

Chiral primordial blue tensor spectra from the axion-gauge couplings

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

Obata, Ippei, E-mail: obata@tap.scphys.kyoto-u.ac.jp

We suggest the new feature of primordial gravitational waves sourced by the axion-gauge couplings, whose forms are motivated by the dimensional reduction of the form field in the string theory. In our inflationary model, as an inflaton we adopt two types of axion, dubbed the model-independent axion and the model-dependent axion, which couple with two gauge groups with different sign combination each other. Due to these forms both polarization modes of gauge fields are amplified and enhance both helicies of tensor modes during inflation. We point out the possibility that a primordial blue-tilted tensor power spectra with small chirality aremore » provided by the combination of these axion-gauge couplings, intriguingly both amplitudes and chirality are potentially testable by future space-based gravitational wave interferometers such as DECIGO and BBO project.« less

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

Boehringer Ingleheim's selective glucocorticoid receptor agonist development candidate: evaluation of WO2010141331, WO2010141332 and WO2010141333.

PubMed

Norman, Peter

2011-07-01

Three applications from Boehringer Ingelheim all relate to the preparation of non-steroidal glucocorticoid receptor agonists useful in the treatment of inflammatory respiratory diseases. The first two applications claim chiral processes for the preparation of these compounds or intermediates useful therein. These provide two alternative routes, respectively, using achiral and chiral reagents. The third application relates to the preparation of a crystalline salt of the preferred compound on a multi-kilogram scale in micronised form.

Chiral phosphoric acid catalysis: from numbers to insights.

PubMed

Maji, Rajat; Mallojjala, Sharath Chandra; Wheeler, Steven E

2018-02-19

Chiral phosphoric acids (CPAs) have emerged as powerful organocatalysts for asymmetric reactions, and applications of computational quantum chemistry have revealed important insights into the activity and selectivity of these catalysts. In this tutorial review, we provide an overview of computational tools at the disposal of computational organic chemists and demonstrate their application to a wide array of CPA catalysed reactions. Predictive models of the stereochemical outcome of these reactions are discussed along with specific examples of representative reactions and an outlook on remaining challenges in this area.

Preliminary Understanding of Surface Plasmon-Enhanced Circular Dichroism Spectroscopy by Single Particle Imaging

NASA Astrophysics Data System (ADS)

Zhan, Kangshu

Monitoring chiral optical signals of biomolecules as their conformation changes is an important means to study their structures, properties, and functions. Most measurements, however, are ensemble measurements because chiral optical signals from a single biomolecule is often too weak to be detected. In this dissertation, I present my early attempts to study conformational changes of adsorbed proteins by taking advantage of the enhanced electromagnetic (EM) field around a well-designed plasmonic nanofeature. In particular, I discuss the detection of protein adsorption and denaturation on metallic nanoparticles using single particle scattering and CD spectroscopic imaging. Particles of two distinctively different sizes were compared and two different sample protein molecules were studied. A combination of experimental and computational tools was used to simulate and interpret the collected scattering and CD results. The first chapter provides a brief overview of the state-of-art research in CD spectroscopic studies at the single particle level. Three different means to make particles capable of chiral detection are discussed. Various applications beyond single particle imaging are presented to showcase the potential of the described research project, beyond our immediate goals. The second chapter describes my initial characterization of large, metallic, anisotropic nanorods and the establishment of experimental procedures used later for spectrum reconstruction, data visualization and analysis. The physical shape and structure of the particles were imaged by scanning electron microscopy (SEM), the chemical composition by energy dispersive X-ray Spectroscopy (EDS), and the optical properties by darkfield microscopy. An experimental protocol was developed to connect information collected from separate techniques for the same particle, with the aims of discovering any possible structural-property correlation. The reproducibility of the single particle imaging method was evaluated. Full spectrum reconstruction using a set of selected optical filters was carried out and data visualization using a Matlab based 3D mapping method was demonstrated. The third chapter describes the introduction of biomolecules in chiral particle studies. By measuring the circular dichroism spectrum and image of nanorods during lysozyme adsorption and denaturation, I was able to monitor the conformation change of proteins on large gapped nanorods. Experiment results suggested that the conformational change of absorbed protein could lead to the change of chiral signal of nanoparticles, suggesting the potentials of detecting biomolecular structural changes at the single nanoparticle level, though much uncertainty still present. The inherent high background of large, gapped nanoparticles when they interact with biomolecules led to the research described in the 4th chapter where I studied small palladium-silver coreshell nanoparticle properties and its interaction with proteins. SEM was used to characterize particles structures; UV-Vis and darkfield microscopy was used to capture particles' optical responses; and the finite-difference time-domain (FDTD) method was used to simulate resulting spectra and to compare with experimental outcomes. Lysozyme and bovine serum albumin (BSA) were used as the model molecules to study their conformational changes after being adsorbed onto particles. Last but the least, the 5th chapter is dedicated to FDTD simulation of a pair of perfectly shaped triangle nanoprisms to illustrate possible CD responses to be expected from extreme particles with sharp corners and much concentrated local EM field. Different coupling modes of triangle nanoprism were analyzed. It is found that many factors, such as particle orientation, spacing, and their relative position, could lead to significantly different coupling efficient, for both homodimers and heterodimers. The modeling data suggested interesting potentials of nanoparticles of extreme geometric features for high sensitivity surface plasmon-enhanced CD imaging at the signal particle level.

Observation of acoustic valley vortex states and valley-chirality locked beam splitting

NASA Astrophysics Data System (ADS)

Ye, Liping; Qiu, Chunyin; Lu, Jiuyang; Wen, Xinhua; Shen, Yuanyuan; Ke, Manzhu; Zhang, Fan; Liu, Zhengyou

2017-05-01

We report an experimental observation of the classical version of valley polarized states in a two-dimensional hexagonal sonic crystal. The acoustic valley states, which carry specific linear momenta and orbital angular momenta, were selectively excited by external Gaussian beams and conveniently confirmed by the pressure distribution outside the crystal, according to the criterion of momentum conservation. The vortex nature of such intriguing bulk crystal states was directly characterized by scanning the phase profile inside the crystal. In addition, we observed a peculiar beam-splitting phenomenon, in which the separated beams are constructed by different valleys and locked to the opposite vortex chirality. The exceptional sound transport, encoded with valley-chirality locked information, may serve as the basis of designing conceptually interesting acoustic devices with unconventional functions.

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.

Multicomponent order parameter superconductivity of Sr2RuO4 revealed by topological junctions

NASA Astrophysics Data System (ADS)

Anwar, M. S.; Ishiguro, R.; Nakamura, T.; Yakabe, M.; Yonezawa, S.; Takayanagi, H.; Maeno, Y.

2017-06-01

Single crystals of the Sr2RuO4 -Ru eutectic system are known to exhibit enhanced superconductivity at 3 K in addition to the bulk superconductivity of Sr2RuO4 at 1.5 K. The 1.5 K phase is believed to be a spin-triplet, chiral p -wave state with a multicomponent order parameter, giving rise to chiral domain structure. In contrast, the 3 K phase is attributable to enhanced superconductivity of Sr2RuO4 in the strained interface region between Ru inclusion of a few to tens of micrometers in size and the surrounding Sr2RuO4 . We investigate the dynamic behavior of a topological junction, where a superconductor is surrounded by another superconductor. Specifically, we fabricated Nb/Ru/Sr2RuO4 topological superconducting junctions, in which the difference in phase winding between the s -wave superconductivity in Ru microislands induced from Nb and the superconductivity of Sr2RuO4 mainly governs the junction behavior. Comparative results of the asymmetry, hysteresis, and noise in junctions with different sizes, shapes, and configurations of Ru inclusions are explained by the chiral domain-wall motion in these topological junctions. Furthermore, a striking difference between the 1.5 and 3 K phases is clearly revealed: the large noise in the 1.5 K phase sharply disappears in the 3 K phase. These results confirm the multicomponent order-parameter superconductivity of the bulk Sr2RuO4 , consistent with the chiral p -wave state, and the proposed nonchiral single-component superconductivity of the 3 K phase.

Chemical synthesis of chiral conducting polymers

DOEpatents

Wang, Hsing-Lin [Los Alamos, NM; Li, Wenguang [Los Alamos, NM

2009-01-13

An process of forming a chiral conducting polymer, e.g., polyaniline, is provided including reacting a monomer, e.g., an aniline monomer, in the presence of a chiral dopant acid to produce a first reaction mixture by addition of a solution including a first portion of an oxidizing agent, the first portion of oxidizing agent characterized as insufficient to allow complete reaction of the monomer, and further reacting the first reaction mixture in the presence of the chiral dopant acid by addition of a solution including a second portion of the oxidizing agent, the second portion of oxidizing agent characterized as insufficient to allow complete reaction of the monomer, and repeating the reaction by addition of further portions of the oxidizing agent until the monomer reaction is complete to produce a chiral conducting polymer, e.g., polyaniline. A preferred process includes addition of a catalyst during the reaction, the catalyst selected from among the group consisting of phenylene diamine, aniline oligomers and amino-capped aniline oligomers and metal salts.The processes of the present invention further provide a resultant polyaniline product having a chirality level defined by a molar ellipticity of from about 40.times.10.sup.3 degree-cm.sup.2/decimole to about 700.times.10.sup.3 degree-cm.sup.2/decimole. The processes of the present invention further provide a resultant polyaniline product having a nanofiber structure with a diameter of from about 30 nanometers to about 120 nanometers and from about 1 micron to about 5 microns in length.

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

Optical resolution of rotenoids

USGS Publications Warehouse

Abidi, S.L.

1987-01-01

Optical resolution of selected rotenoids containing 1-3 asymmetric centers in dihydrobenzopyranofuroben-zopyranone and dihydrobisbenzopyranopyranone series has been achieved on two chiral high-performance liquid chromatographic (hplc) stationary phases. In most cases, the absolute stereochemistry at the cis-B/C ring junction of the rotenoidal antipodes can be related to their elution order. Generally, the 6aα,12aα-enantiomers were more strongly retained by the chiral substrate than their corresponding optical antipodes. The elution-configuration relationship provides potential utility for predicting the absolute configuration of related rotenoidal compounds. Chiral phase hplc on amino-acid-bonded-silica yielded results explicable in terms of Pirkle's bonding schemes for chiral recognition. Resolution data for 12a-hydroxy-, 12a-methoxy-, and 12-hydroxyiminorotenoids further corroborate the mechanistic rationale, and demonstrate that nonpolar π-π interactions appeared to be important for enantiomeric separation on helic poly-triphenylmethylacryl-ate-silica (CPOT). In the latter system, steric effects and conformational factors in association with the modification of E-ring structures might play significant roles in the chiral separation process in view of the reversal to the elution order observed for all methoxylated rotenoids and elliptone derivatives including the parent deguelin. The unique separability (α = 1.44) of 12a-hydroxyelliptone on CPOT was suggestive of structural effects of the 5-side chain on the resolution of the rotenoids having a five-membered-E-ring. The results obtained with two different types of chiral phases are complementary and useful for optical resolution of a wide variety of natural and synthetic rotenoidal compounds.

Current status of chirality in agrochemicals.

PubMed

Jeschke, Peter

2018-04-27

The agrochemical industry is continuously searching for new pesticides to develop products with optimal efficacy, lower application rates in the field, increased selectivity, favorable toxicological and environmental safety, enhanced user friendliness and better economic viability. One strategy to achieve these ambitious goals makes use of the unique properties of molecules containing asymmetric centers. In the past, many natural products and their congeners have been a source of inspiration for designing new active ingredients, and the molecular structure of the resulting molecules have become increasingly complex. 30% contain fragments with asymmetric centers. However, despite the enormous progress that has been made in catalytic asymmetric processes over the last decade, only few agrochemicals are produced in enantiomerically pure or enriched form on an industrial scale. Since 2007, around 43% of the 44 launched products (insecticides, acaricides, fungicides, nematicides, and herbicides) contain one or more asymmetric centers in the molecule (≈ 47 %) and most of them were launched as racemic mixtures of enantiomers or diastereomers. This review gives an overview of the current status of chiral agrochemicals launched over the past 10 years and describes the inherently connected challenges of modern agricultural chemistry by managing important aspects resulting from stereochemistry of these innovative products. This article is protected by copyright. All rights reserved.

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

Application of chiral critical clusters to assymetric synthesis

DOEpatents

Ferrieri, Richard A.

2002-01-01

Disclosed is a composition, a method of making and a method of using critical clusters for asymmetric synthesis using substantially optically-pure chiral solvent molecules in a supercritical fluid. The solvent molecules are capable of forming a multipoint hydrogen bonded solvate as they encage at least one solute molecule. The encaged solute molecule is capable of reacting to form an optically active chiral center. In another aspect, there is disclosed a method of directing the position of bonding between a solute molecule and a ligand involving encaging the solute molecule and the ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution in the solute molecule. In yet another aspect, disclosed is a method of making pharmaceutical compounds involving encaging a solute molecule, which is capable of forming a chiral center, and a ligand with polar solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to change electric charge distribution of the solute molecule. The solute molecule and ligand are then reacted whereby the ligand bonds to the solute molecule forming a chiral center. Also disclosed is a method for racemic resolution using critical clusters involving encaging racemic mixtures of solute molecules with substantially optically-pure chiral solvent molecules in a supercritical fluid under conditions of temperature and pressure sufficient to form critical clusters. The solvent molecules are capable of multipoint hydrogen bonding with the solute molecules. The encaged solute molecules are then nonenzymatically reacted to enhance the optical purity of the solute molecules.

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.

Chirality and angular momentum in optical radiation

NASA Astrophysics Data System (ADS)

Coles, Matt M.; Andrews, David L.

2012-06-01

This paper develops, in precise quantum electrodynamic terms, photonic attributes of the “optical chirality density,” one of several measures long known to be conserved quantities for a vacuum electromagnetic field. The analysis lends insights into some recent interpretations of chiroptical experiments, in which this measure, and an associated chirality flux, have been treated as representing physically distinctive “superchiral” phenomena. In the fully quantized formalism the chirality density is promoted to operator status, whose exploration with reference to an arbitrary polarization basis reveals relationships to optical angular momentum and helicity operators. Analyzing multimode beams with complex wave-front structures, notably Laguerre-Gaussian modes, affords a deeper understanding of the interplay between optical chirality and optical angular momentum. By developing theory with due cognizance of the photonic character of light, it emerges that only the spin-angular momentum of light is engaged in such observations. Furthermore, it is shown that these prominent measures of the helicity of chiral electromagnetic radiation have a common basis in differences between the populations of optical modes associated with angular momenta of opposite sign. Using a calculation of the rate of circular dichroism as an example, with coherent states to model the electromagnetic field, it is discovered that two terms contribute to the differential effect. The primary contribution relates to the difference in left- and right-handed photon populations; the only other contribution, which displays a sinusoidal distance dependence corresponding to the claim of nodal enhancements, is connected with the quantum photon number-phase uncertainty relation. From the full analysis, it appears that the term “superchiral” can be considered redundant.

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.

Chiral fiber sensors

NASA Astrophysics Data System (ADS)

Kopp, Victor I.; Churikov, Victor M.; Singer, Jonathan; Neugroschl, Daniel; Genack, Azriel Z.

2010-04-01

We have fabricated a variety of chiral fiber sensors by twisting one or more standard or custom optical fibers with noncircular or nonconcentric core as they pass though a miniature oven. The resulting structures are as stable as the glass material and can be produced with helical pitch ranging from microns to hundreds of microns. The polarization selectivity of the chiral gratings is determined by the geometry of the fiber cross section. Single helix structures are polarization insensitive, while double helix gratings interact only with a single optical polarization component. Both single and double helix gratings may function as a fiber long period grating, coupling core and cladding modes or as a diffraction grating scattering light from the fiber core out of the fiber. The resulting dips in the transmission spectrum are sensitive to fiber elongation, twist and temperature, and (in the case of the long period gratings) to the refractive index of the surrounding medium. The suitability of chiral gratings for sensing temperature, elongation, twist and liquid levels will be discussed. Gratings made of radiation sensitive glass can be used to measure the cumulative radiation dose, while gratings made of radiation-hardened glass are suitable for stable sensing of the environment in nuclear power plants. Excellent temperature stability up to 900°C is found in pure silica chiral diffraction grating sensors.

Fragment screening of cyclin G-associated kinase by weak affinity chromatography.

PubMed

Meiby, Elinor; Knapp, Stefan; Elkins, Jonathan M; Ohlson, Sten

2012-11-01

Fragment-based drug discovery (FBDD) has become a new strategy for drug discovery where lead compounds are evolved from small molecules. These fragments form low affinity interactions (dissociation constant (K(D)) = mM - μM) with protein targets, which require fragment screening methods of sufficient sensitivity. Weak affinity chromatography (WAC) is a promising new technology for fragment screening based on selective retention of fragments by a drug target. Kinases are a major pharmaceutical target, and FBDD has been successfully applied to several of these targets. In this work, we have demonstrated the potential to use WAC in combination with mass spectrometry (MS) detection for fragment screening of a kinase target-cyclin G-associated kinase (GAK). One hundred seventy fragments were selected for WAC screening by virtual screening of a commercial fragment library against the ATP-binding site of five different proteins. GAK protein was immobilized on a capillary HPLC column, and compound binding was characterized by frontal affinity chromatography. Compounds were screened in sets of 13 or 14, in combination with MS detection for enhanced throughput. Seventy-eight fragments (46 %) with K(D) < 200 μM were detected, including a few highly efficient GAK binders (K(D) of 2 μM; ligand efficiency = 0.51). Of special interest is that chiral screening by WAC may be possible, as two stereoisomeric fragments, which both contained one chiral center, demonstrated twin peaks. This ability, in combination with the robustness, sensitivity, and simplicity of WAC makes it a new method for fragment screening of considerable potential.

Chiral mirrors

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

Plum, Eric, E-mail: erp@orc.soton.ac.uk; Zheludev, Nikolay I., E-mail: niz@orc.soton.ac.uk; The Photonics Institute and Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore 637378

2015-06-01

Mirrors are used in telescopes, microscopes, photo cameras, lasers, satellite dishes, and everywhere else, where redirection of electromagnetic radiation is required making them arguably the most important optical component. While conventional isotropic mirrors will reflect linear polarizations without change, the handedness of circularly polarized waves is reversed upon reflection. Here, we demonstrate a type of mirror reflecting one circular polarization without changing its handedness, while absorbing the other. The polarization-preserving mirror consists of a planar metasurface with a subwavelength pattern that cannot be superimposed with its mirror image without being lifted out of its plane, and a conventional mirror spacedmore » by a fraction of the wavelength from the metasurface. Such mirrors enable circularly polarized lasers and Fabry-Pérot cavities with enhanced tunability, gyroscopic applications, polarization-sensitive detectors of electromagnetic waves, and can be used to enhance spectroscopies of chiral media.« less

Arrays of horizontal carbon nanotubes of controlled chirality grown using designed catalysts

NASA Astrophysics Data System (ADS)

Zhang, Shuchen; Kang, Lixing; Wang, Xiao; Tong, Lianming; Yang, Liangwei; Wang, Zequn; Qi, Kuo; Deng, Shibin; Li, Qingwen; Bai, Xuedong; Ding, Feng; Zhang, Jin

2017-02-01

The semiconductor industry is increasingly of the view that Moore’s law—which predicts the biennial doubling of the number of transistors per microprocessor chip—is nearing its end. Consequently, the pursuit of alternative semiconducting materials for nanoelectronic devices, including single-walled carbon nanotubes (SWNTs), continues. Arrays of horizontal nanotubes are particularly appealing for technological applications because they optimize current output. However, the direct growth of horizontal SWNT arrays with controlled chirality, that would enable the arrays to be adapted for a wider range of applications and ensure the uniformity of the fabricated devices, has not yet been achieved. Here we show that horizontal SWNT arrays with predicted chirality can be grown from the surfaces of solid carbide catalysts by controlling the symmetries of the active catalyst surface. We obtained horizontally aligned metallic SWNT arrays with an average density of more than 20 tubes per micrometre in which 90 per cent of the tubes had chiral indices of (12, 6), and semiconducting SWNT arrays with an average density of more than 10 tubes per micrometre in which 80 per cent of the nanotubes had chiral indices of (8, 4). The nanotubes were grown using uniform size Mo2C and WC solid catalysts. Thermodynamically, the SWNT was selectively nucleated by matching its structural symmetry and diameter with those of the catalyst. We grew nanotubes with chiral indices of (2m, m) (where m is a positive integer), the yield of which could be increased by raising the concentration of carbon to maximize the kinetic growth rate in the chemical vapour deposition process. Compared to previously reported methods, such as cloning, seeding and specific-structure-matching growth, our strategy of controlling the thermodynamics and kinetics offers more degrees of freedom, enabling the chirality of as-grown SWNTs in an array to be tuned, and can also be used to predict the growth conditions required to achieve the desired chiralities.

Influence of chirality on catalytic generation of nitric oxide and platelet behavior on selenocystine immobilized TiO2 films.

PubMed

Fan, Yonghong; Pan, Xiaxin; Wang, Ke; Wu, Sisi; Han, Honghong; Yang, Ping; Luo, Rifang; Wang, Hong; Huang, Nan; Tan, Wei; Weng, Yajun

2016-09-01

As nitric oxide (NO) plays vital roles in the cardiovascular system, incorporating this molecule into cardiovascular stents is considered as an effective method. In the present study, selenocystine with different chirality (i.e., l- and d-selenocystine) was used as the catalytic molecule immobilized on TiO2 films for decomposing endogenous NO donor. The influences of surface chirality on NO release and platelet behavior were evaluated. Results show that although the amount of immobilized l-selenocystine on the surface was nearly the same as that of immobilized d-selenocystine, in vitro catalytic NO release tests showed that l-selenocystine immobilized surfaces were more capable of catalyzing the decomposition of S-nitrosoglutathione and thus generating more NO. Accordingly, l-selenocystine immobilized surfaces demonstrated significantly increased inhibiting effects on the platelet adhesion and activation, when compared to d-selenocystine immobilized ones. Measurement of the cGMP concentration of platelets further confirmed that surface chirality played an important role in regulating NO generation and platelet behaviors. Additionally, using bovine serum albumin and fibrinogen as model proteins, the protein adsorption determined with quartz crystal microbalance showed that the l-selenocystine immobilized surface enhanced protein adsorption. In conclusion, surface chirality significantly influences protein adsorption and NO release, which may have significant implications in the design of NO-generating cardiovascular stents. Copyright © 2016 Elsevier B.V. All rights reserved.

Transverse shifts of a light beam reflected from a uniaxially anisotropic chiral slab

NASA Astrophysics Data System (ADS)

Xu, Guoding; Li, Jun; Xiao, Yuting; Mao, Hongmin; Sun, Jian; Pan, Tao

2015-01-01

We study for the first time the transverse shifts of a Gaussian beam reflected from a uniaxially anisotropic chiral (UAC) slab, where the chirality appears only in one direction and the host medium is a uniaxial crystal or an electric plasma. The results indicate that the transverse shifts are closely related to the propagation behaviors of the eigenwaves in the slab. Specifically, when one or both of the eigenwaves are totally reflected at the second interface of the slab, the spatial transverse shift becomes resonances but is not enhanced; when one eigenwave is totally reflected at the first interface and the other is transmitted at the second interface, the larger and negative transverse shifts can be obtained. The propagation behaviors of the eigenwaves in the UAC slab provide more abundant information about the transverse shifts than in a single interface structure.

Enhancing biocompatibility of D-oligopeptide hydrogels by negative charges.

PubMed

Hyland, Laura L; Twomey, Julianne D; Vogel, Savannah; Hsieh, Adam H; Yu, Y Bruce

2013-02-11

Oligopeptide hydrogels are emerging as useful matrices for cell culture with commercial products on the market, but L-oligopeptides are labile to proteases. An obvious solution is to create D-oligopeptide hydrogels, which lack enzymatic recognition. However, D-oligopeptide matrices do not support cell growth as well as L-oligopeptide matrices. In addition to chiral interactions, many cellular activities are strongly governed by charge-charge interactions. In this work, the effects of chirality and charge on human mesenchymal stem cell (hMSC) behavior were studied using hydrogels assembled from oppositely charged oligopeptides. It was found that negative charges significantly improved hMSC viability and proliferation in D-oligopeptide gels but had little effect on their interactions with L-oligopeptide gels. This result points to the possibility of using charge and other factors to engineer biomaterials whose chirality is distinct from that of natural biomaterials, but whose performance is close to that of natural biomaterials.

Active Terahertz Chiral Metamaterials Based on Phase Transition of Vanadium Dioxide (VO2).

PubMed

Wang, Shengxiang; Kang, Lei; Werner, Douglas H

2018-01-09

Compared with natural materials, chiral metamaterials have been demonstrated with orders of magnitude stronger chiroptical response, which provides the basis for applications such as ultracompact polarization components and plasmonic-enhanced biosensing. Terahertz chiral metamaterials that allow dynamic polarization control of terahertz waves are of great practical interest, but remain extremely rare. Here, we show that hybrid metamaterials integrated with vanadium dioxide (VO 2 ) exhibiting phase transition can enable dynamically tunable chiroptical responses at terahertz frequencies. In particular, a circular dichroism of ~40° and a maximum polarization rotation of ~200°/λ are observed around 0.7 THz. Furthermore, our study also reveals that the chiroptical response from the proposed metamaterials is strongly dependent on the phase transition of VO 2 , leading to actively controllable polarization states of the transmitted terahertz waves. This work paves the way for the development of terahertz metadevices capable of enabling active polarization manipulation.

Micro-flock patterns and macro-clusters in chiral active Brownian disks

NASA Astrophysics Data System (ADS)

Levis, Demian; Liebchen, Benno

2018-02-01

Chiral active particles (or self-propelled circle swimmers) feature a rich collective behavior, comprising rotating macro-clusters and micro-flock patterns which consist of phase-synchronized rotating clusters with a characteristic self-limited size. These patterns emerge from the competition of alignment interactions and rotations suggesting that they might occur generically in many chiral active matter systems. However, although excluded volume interactions occur naturally among typical circle swimmers, it is not yet clear if macro-clusters and micro-flock patterns survive their presence. The present work shows that both types of pattern do survive but feature strongly enhance fluctuations regarding the size and shape of the individual clusters. Despite these fluctuations, we find that the average micro-flock size still follows the same characteristic scaling law as in the absence of excluded volume interactions, i.e. micro-flock sizes scale linearly with the single-swimmer radius.

dxz/yz subband structure and Chiral Orbital Angular Momentum of Nb doped SrTiO3 surface states

NASA Astrophysics Data System (ADS)

Soltani, Shoresh; Cho, Soohyun; Ryu, Hanyoung; Han, Garam; Kim, Timur; Hoesch, Moritz; Kim, Changyoung

Using angle resolved photoemission spectroscopy (ARPES), we investigate subband structure and chiral orbital angular momentum (OAM) texture on the surface of lightly electron doped SrTiO3 single crystals. Our linearly polarized light ARPES data taken with 51 eV photons, reveal additional subbands for out-of-plane dxz/yzorbitals in addition to the previously reported ones. Our CD-ARPES data reveal a chiral OAM structure which we use as a clue to explain the origin of linear Rashba-like surface band splitting of Ti 3d t2g orbitals. The observed CD signal is enhanced near crossing points, where different orbitals hybridize, compatible with a linear Rashba-like surface band splitting. The work was supported by IBS-R009-G2. S.S., S.C., H.Y. and G. H. acknowledge were supported by Yonsei university, BK21 program.

Theoretical study of high-Q Fano resonance and extrinsic chirality in an ultrathin Babinet-inverted metasurface

NASA Astrophysics Data System (ADS)

Wang, Feng; Wang, Zhengping; Shi, Jinhui

2014-10-01

A high-Q Fano resonance and giant extrinsic chirality have been demonstrated in an ultrathin Babinet-inverted metasurface composed of asymmetrical split ring apertures (ASRAs) perforated through a metal plate based on the full-wave simulations. The performance of the Fano resonance at normal incidence strongly depends on the asymmetry of the ASRA. The quality factor is larger than 1000 and the local field enhancement is an order of 104. For oblique incidence, giant extrinsic chirality can be achieved in the Babinet-inverted metasurface. It reveals a cross-polarization transmission band with a ripple-free peak and also a spectrum split for large angles of incidence. The electromagnetic response of the metasurface can be easily tuned via angles of incidence and asymmetry. The proposed ASRA metasurface is of importance to develop many metamaterial-based devices, such as filters and circular polarizers.

Analyzing the Fierz rearrangement freedom for local chiral two-nucleon potentials

NASA Astrophysics Data System (ADS)

Huth, L.; Tews, I.; Lynn, J. E.; Schwenk, A.

2017-11-01

Chiral effective field theory is a framework to derive systematic nuclear interactions. It is based on the symmetries of quantum chromodynamics and includes long-range pion physics explicitly, while shorter-range physics is expanded in a general operator basis. The number of low-energy couplings at a particular order in the expansion can be reduced by exploiting the fact that nucleons are fermions and therefore obey the Pauli exclusion principle. The antisymmetry permits the selection of a subset of the allowed contact operators at a given order. When local regulators are used for these short-range interactions, however, this "Fierz rearrangement freedom" is violated. In this paper, we investigate the impact of this violation at leading order (LO) in the chiral expansion. We construct LO and next-to-leading order (NLO) potentials for all possible LO-operator pairs and study their reproduction of phase shifts, the 4He ground-state energy, and the neutron-matter energy at different densities. We demonstrate that the Fierz rearrangement freedom is partially restored at NLO where subleading contact interactions enter. We also discuss implications for local chiral three-nucleon interactions.

Surface chirality of CuO thin films.

PubMed

Widmer, Roland; Haug, Franz-Josef; Ruffieux, Pascal; Gröning, Oliver; Bielmann, Michael; Gröning, Pierangelo; Fasel, Roman

2006-11-01

We present X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD) investigations of CuO thin films electrochemically deposited on an Au(001) single-crystal surface from a solution containing chiral tartaric acid (TA). The presence of enantiopure TA in the deposition process results in a homochiral CuO surface, as revealed by XPD. On the other hand, XPD patterns of films deposited with racemic tartaric acid or the "achiral" meso-tartaric acid are completely symmetric. A detailed analysis of the experimental data using single scattering cluster calculations reveals that the films grown with l(+)-TA exhibit a CuO(1) orientation, whereas growth in the presence of d(-)-TA results in a CuO(11) surface orientation. A simple bulk-truncated model structure with two terminating oxygen layers reproduces the experimental XPD data. Deposition with alternating enantiomers of tartaric acid leads to CuO films of alternating chirality. Enantiospecifity of the chiral CuO surfaces is demonstrated by further deposition of CuO from a solution containing racemic tartaric acid. The pre-deposited homochiral films exhibit selectivity toward the same enantiomeric deposition pathway.

Chirally directed formation of nanometer-scale proline clusters.

PubMed

Myung, Sunnie; Fioroni, Marco; Julian, Ryan R; Koeniger, Stormy L; Baik, Mu-Hyun; Clemmer, David E

2006-08-23

Ion mobility measurements, combined with molecular mechanics simulations, are used to study enantiopure and racemic proline clusters formed by electrospray ionization. Broad distributions of cluster sizes and charge states are observed, ranging from clusters containing only a few proline units to clusters that contain more than 100 proline units (i.e., protonated clusters of the form [xPro + nH](n+) with x = 1 to >100 and n = 1-7). As the sizes of clusters increase, there is direct evidence for nanometer scale, chirally induced organization into specific structures. For n = 4 and 5, enantiopure clusters of approximately 50 to 100 prolines assemble into structures that are more elongated than the most compact structure that is observed from the racemic proline clusters. A molecular analogue, cis-4-hydroxy-proline, displays significantly different behavior, indicating that in addition to the rigidity of the side chain ring, intermolecular interactions are important in the formation of chirally directed clusters. This is the first case in which assemblies of chirally selective elongated structures are observed in this size range of amino acid clusters. Relationships between enantiopurity, cluster shape, and overall energetics are discussed.

Chirality-induced spin polarization places symmetry constraints on biomolecular interactions.

PubMed

Kumar, Anup; Capua, Eyal; Kesharwani, Manoj K; Martin, Jan M L; Sitbon, Einat; Waldeck, David H; Naaman, Ron

2017-03-07

Noncovalent interactions between molecules are key for many biological processes. Necessarily, when molecules interact, the electronic charge in each of them is redistributed. Here, we show experimentally that, in chiral molecules, charge redistribution is accompanied by spin polarization. We describe how this spin polarization adds an enantioselective term to the forces, so that homochiral interaction energies differ from heterochiral ones. The spin polarization was measured by using a modified Hall effect device. An electric field that is applied along the molecules causes charge redistribution, and for chiral molecules, a Hall voltage is measured that indicates the spin polarization. Based on this observation, we conjecture that the spin polarization enforces symmetry constraints on the biorecognition process between two chiral molecules, and we describe how these constraints can lead to selectivity in the interaction between enantiomers based on their handedness. Model quantum chemistry calculations that rigorously enforce these constraints show that the interaction energy for methyl groups on homochiral molecules differs significantly from that found for heterochiral molecules at van der Waals contact and shorter (i.e., ∼0.5 kcal/mol at 0.26 nm).

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.

Self-Assemblies of Single-Walled Carbon Nanotubes through Tunable Tethering of Pyrenes by Dextrin for Rapidly Chiral Sensing

PubMed Central

Wei, Wei-Li; Chen, Qiushui; Li, Haifang; Lin, Jin-Ming

2011-01-01

Pyrene-modified dextrin (Py-Dex) was synthesized via the Schiff base reaction between reducing end of dextrins and 1-aminopyrene, and then self-assemblies of single-walled carbon nanotubes (SWNTs) were fabricated through the tunable tethering of pyrene to SWNTs by dextrin chains. The Py-Dex-SWNTs assemblies were found to be significantly water-soluble because of the synergistic effect of dextrin chains and pyrene moieties. Py-Dex and Py-Dex-SWNTs were adequately characterized by NMR, UV-vis, fluorescence spectroscopy, Raman spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectroscopy, and transmission electron microscopy. The tethering effect of dextrin toward pyrene moieties was clearly revealed and was found to be tunable by adjusting the length of dextrin chains. The fluorescence of pyrene moieties was sufficiently quenched by SWNTs with the support of dextrin chains. Furthermore, the Py-Dex-SWNTs assemblies were used for chiral selective sensing by introducing cyclodextrins as chiral binding sites. The rapid chiral sensing was successfully tested for different enantiomers. PMID:21811502

Characterization of a single-isomer carboxymethyl-beta-cyclodextrin in chiral capillary electrophoresis.

PubMed

Fejős, Ida; Varga, Erzsébet; Benkovics, Gábor; Malanga, Milo; Sohajda, Tamás; Szemán, Julianna; Béni, Szabolcs

2017-08-01

In this work, the synthesis, characterization, and chiral capillary electrophoretic study of heptakis-(2,3-di-O-methyl-6-O-carboxymethyl)-β-CD (HDMCM), a single-isomer carboxymethylated CD, are presented. The pH-dependent and selector concentration-dependent enantiorecognition properties of HDMCM were investigated and discussed herein. The enantioseparation was assessed applying a structurally diverse set of noncharged, basic, and zwitterionic racemates. The increase in the selector concentration and gross negative charge of HDMCM improved the enantioseparation that could be observed in the majority of the cases. HDMCM was also successfully applied as BGE additive in NACE using a methanol-based system in order to prove the separation selectivity features and to highlight the broad applicability of HDMCM. Over 25 racemates showed partial or baseline separation with HDMCM under the conditions investigated, among which optimal enantiomer migration order was found for the four stereoisomers of tadalafil, tapentadol, and dapoxetine, offering the possibility of a chiral CE method development for chiral purity profiling of these drugs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laser mass spectrometry with circularly polarized light: circular dichroism of cold molecules in a supersonic gas beam.

PubMed

Titze, Katharina; Zollitsch, Tilo; Heiz, Ulrich; Boesl, Ulrich

2014-09-15

An experiment on chiral molecules that combines circular dichroism (CD) spectroscopy, mass-selective detection by laser mass spectrometry (MS), and cooling of molecules by using a supersonic beam is presented. The combination of the former two techniques (CD-laser-MS) is a new method to investigate chiral molecules and is now used by several research groups. Cooling in a supersonic beam supplies a substantial increase in spectroscopic resolution, a feature that has not yet been used in CD spectroscopy. In the experiments reported herein, a large variation in the electronic CD of carbonyl 3-methylcyclopentanone was observed depending on the excited vibrational modes in the n → π* transition. This finding should be of interest for the detection of chiral molecules and for the theoretical understanding of the CD of vibronic bands. It is expected that this effect will show up in other chiral carbonyls because the n → π* transition is typical for the carbonyl group. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Observation of extraordinary optical activity in planar chiral photonic crystals.

PubMed

Konishi, Kuniaki; Bai, Benfeng; Meng, Xiangfeng; Karvinen, Petri; Turunen, Jari; Svirko, Yuri P; Kuwata-Gonokami, Makoto

2008-05-12

Control of light polarization is a key technology in modern photonics including application to optical manipulation of quantum information. The requisite is to obtain large rotation in isotropic media with small loss. We report on extraordinary optical activity in a planar dielectric on-waveguide photonic crystal structure, which has no in-plane birefringence and shows polarization rotation of more than 25 degrees for transmitted light. We demonstrate that in the planar chiral photonic crystal, the coupling of the normally incident light wave with low-loss waveguide and Fabry-Pérot resonance modes results in a dramatic enhancement of the optical activity.

Tuning the photonic band gap in cholesteric liquid crystals by temperature-dependent dopant solubility.

PubMed

Huang, Yuhua; Zhou, Ying; Doyle, Charlie; Wu, Shin-Tson

2006-02-06

We have investigated the physical and optical properties of the left-handed chiral dopant ZLI-811 mixed in a nematic liquid crystal (LC) host BL006. The solubility of ZLI-811 in BL006 at room temperature is ~24 wt%, but can be enhanced by increasing the temperature. Consequently, the photonic band gap of the cholesteric liquid crystal (CLC) mixed with more than 24 wt% chiral dopant ZLI-811 is blue shifted as the temperature increases. Based on this property, we demonstrate two applications in thermally tunable band-pass filters and dye-doped CLC lasers.

Expedited Selection of NMR Chiral Solvating Agents for Determination of Enantiopurity

PubMed Central

2016-01-01

The use of NMR chiral solvating agents (CSAs) for the analysis of enantiopurity has been known for decades, but has been supplanted in recent years by chromatographic enantioseparation technology. While chromatographic methods for the analysis of enantiopurity are now commonplace and easy to implement, there are still individual compounds and entire classes of analytes where enantioseparation can prove extremely difficult, notably, compounds that are chiral by virtue of very subtle differences such as isotopic substitution or small differences in alkyl chain length. NMR analysis using CSAs can often be useful for such problems, but the traditional approach to selection of an appropriate CSA and the development of an NMR-based analysis method often involves a trial-and-error approach that can be relatively slow and tedious. In this study we describe a high-throughput experimentation approach to the selection of NMR CSAs that employs automation-enabled screening of prepared libraries of CSAs in a systematic fashion. This approach affords excellent results for a standard set of enantioenriched compounds, providing a valuable comparative data set for the effectiveness of CSAs for different classes of compounds. In addition, the technique has been successfully applied to challenging pharmaceutical development problems that are not amenable to chromatographic solutions. Overall, this methodology provides a rapid and powerful approach for investigating enantiopurity that compliments and augments conventional chromatographic approaches. PMID:27280168

Enantioselective separation of chiral aromatic amino acids with surface functionalized magnetic nanoparticles.

PubMed

Ghosh, Sudipa; Fang, Tan Hui; Uddin, M S; Hidajat, K

2013-05-01

Chiral resolution aromatic amino acids, DL-tryptophan (DL-Trp), DL-phenylalanine (DL-Phe), DL-tyrosine (DL-Tyr) from phosphate buffer solution was achieved in present study employing the concept of selective adsorption by surface functionalized magnetic nanoparticles (MNPs). Surfaces of magnetic nanoparticles were functionalized with silica and carboxymethyl-β-cyclodextrin (CMCD) to investigate their adsorption resolution characteristics. Resolution of enantiomers from racemic mixture was quantified in terms of enantiomeric excess using chromatographic method. The MNPs selectively adsorbed L-enantiomers of DL-Trp, DL-Phe, and DL-Tyr from racemic mixture and enantiomeric excesses (e.e.) were determined as 94%, 73% and 58%, respectively. FTIR studies demonstrated that hydrophobic portion of enantiomer penetrated into hydrophobic cavity of cyclodextrin molecules to form inclusion complex. Furthermore, adsorption site was explored using XPS and it was revealed that amino group at chiral center of the amino acid molecule formed hydrogen bond with secondary hydroxyl group of CMCD molecule and favorability of hydrogen bond formation resulted in selective adsorption of L-enantiomer. Finally, stability constant (K) and Gibbs free energy change (-ΔG°) for inclusion complexation of CMCD with L-/D-enantiomers of amino acids were determined using spectroflurometry in aqueous buffer solution. Higher binding constants were obtained for inclusion complexation of CMCD with L-enantiomers compared to D-enantiomers which stimulated enantioselective properties of CMCD functionalized magnetite silica nanoparticles. Copyright © 2013 Elsevier B.V. All rights reserved.

The Clusters-in-a-Liquid Approach for Solvation: New Insights from the Conformer Specific Gas Phase Spectroscopy and Vibrational Optical Activity Spectroscopy

PubMed Central

Perera, Angelo S.; Thomas, Javix; Poopari, Mohammad R.; Xu, Yunjie

2016-01-01

Vibrational optical activity spectroscopies, namely vibrational circular dichroism (VCD) and Raman optical activity (ROA), have been emerged in the past decade as powerful spectroscopic tools for stereochemical information of a wide range of chiral compounds in solution directly. More recently, their applications in unveiling solvent effects, especially those associated with water solvent, have been explored. In this review article, we first select a few examples to demonstrate the unique sensitivity of VCD spectral signatures to both bulk solvent effects and explicit hydrogen-bonding interactions in solution. Second, we discuss the induced solvent chirality, or chiral transfer, VCD spectral features observed in the water bending band region in detail. From these chirality transfer spectral data, the related conformer specific gas phase spectroscopic studies of small chiral hydration clusters, and the associated matrix isolation VCD experiments of hydrogen-bonded complexes in cold rare gas matrices, a general picture of solvation in aqueous solution emerges. In such an aqueous solution, some small chiral hydration clusters, rather than the chiral solutes themselves, are the dominant species and are the ones that contribute mainly to the experimentally observed VCD features. We then review a series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs to emphasize the importance of the inclusion of the bulk solvent effects. These experimental data and the associated theoretical analyses are the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively. We present several approaches to identify and build such representative chiral hydration clusters. Recent studies which applied molecular dynamics simulations and the subsequent snapshot averaging approach to generate the ROA, VCD, electronic CD, and optical rotatory dispersion spectra are also reviewed. Challenges associated with the molecular dynamics snapshot approach are discussed and the successes of the seemingly random “ad hoc explicit solvation” reported before are also explained. To further test and improve the “clusters-in-a-liquid” model in practice, future work in terms of conformer specific gas phase spectroscopy of sequential solvation of a chiral solute, matrix isolation VCD measurements of small chiral hydration clusters, and more sophisticated models for the bulk solvent effects would be highly valuable. PMID:26942177

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.

Dynamics of chiral domain wall under the spin-orbit torques in heavy metal/ferromagnet bilayers with in-plane anisotropy

NASA Astrophysics Data System (ADS)

Yan, Han; He, Peng-Bin; Cai, Meng-Qiu; Li, Zai-Dong

2017-11-01

The dynamics of domain wall driven by the spin-orbit torques is theoretically studied in the heavy metal/ferromagnet bilayer with Dzyaloshinskii-Moriya interaction (DMI) and in-plane magnetic anisotropy. Based on the Walker profile, we infer that DMI has a selectivity for the chirality of head-to-head (tail-to-tail) static wall. By analyzing the dynamic equations obtained from the collective coordinates methods, we find that there exists a switching or a hysteresis of the polarity of wall in the low-current regime. In the presence of DMI, the wall can keep sustained propagation which velocity saturates for high current and is proportional to the strength of DMI. Furthermore, the DMI makes the adjacent walls possess the same chirality and move in the same direction.

Computational Optimization and Characterization of Molecularly Imprinted Polymers

NASA Astrophysics Data System (ADS)

Terracina, Jacob J.

Molecularly imprinted polymers (MIPs) are a class of materials containing sites capable of selectively binding to the imprinted target molecule. Computational chemistry techniques were used to study the effect of different fabrication parameters (the monomer-to-target ratios, pre-polymerization solvent, temperature, and pH) on the formation of the MIP binding sites. Imprinted binding sites were built in silico for the purposes of better characterizing the receptor - ligand interactions. Chiefly, the sites were characterized with respect to their selectivities and the heterogeneity between sites. First, a series of two-step molecular mechanics (MM) and quantum mechanics (QM) computational optimizations of monomer -- target systems was used to determine optimal monomer-to-target ratios for the MIPs. Imidazole- and xanthine-derived target molecules were studied. The investigation included both small-scale models (one-target) and larger scale models (five-targets). The optimal ratios differed between the small and larger scales. For the larger models containing multiple targets, binding-site surface area analysis was used to evaluate the heterogeneity of the sites. The more fully surrounded sites had greater binding energies. Molecular docking was then used to measure the selectivities of the QM-optimized binding sites by comparing the binding energies of the imprinted target to that of a structural analogue. Selectivity was also shown to improve as binding sites become more fully encased by the monomers. For internal sites, docking consistently showed selectivity favoring the molecules that had been imprinted via QM geometry optimizations. The computationally imprinted sites were shown to exhibit size-, shape-, and polarity-based selectivity. This represented a novel approach to investigate the selectivity and heterogeneity of imprinted polymer binding sites, by applying the rapid orientation screening of MM docking to the highly accurate QM-optimized geometries. Next, we sought to computationally construct and investigate binding sites for their enantioselectivity. Again, a two-step MM [special characters removed] QM optimization scheme was used to "computationally imprint" chiral molecules. Using docking techniques, the imprinted binding sites were shown to exhibit an enantioselective preference for the imprinted molecule over its enantiomer. Docking of structurally similar chiral molecules showed that the sites computationally imprinted with R- or S-tBOC-tyrosine were able to differentiate between R- and S-forms of other tyrosine derivatives. The cross-enantioselectivity did not hold for chiral molecules that did not share the tyrosine H-bonding functional group orientations. Further analysis of the individual monomer - target interactions within the binding site led us to conclude that H-bonding functional groups that are located immediately next to the target's chiral center, and therefore spatially fixed relative to the chiral center, will have a stronger contribution to the enantioselectivity of the site than those groups separated from the chiral center by two or more rotatable bonds. These models were the first computationally imprinted binding sites to exhibit this enantioselective preference for the imprinted target molecules. Finally, molecular dynamics (MD) was used to quantify H-bonding interactions between target molecules, monomers, and solvents representative of the pre-polymerization matrix. It was found that both target dimerization and solvent interference decrease the number of monomer - target H-bonds present. Systems were optimized via simulated annealing to create binding sites that were then subjected to molecular docking analysis. Docking showed that the presence of solvent had a detrimental effect on the sensitivity and selectivity of the sites, and that solvents with more H-bonding capabilities were more disruptive to the binding properties of the site. Dynamic simulations also showed that increasing the temperature of the solution can significantly decrease the number of H-bonds formed between the targets and monomers. It is believed that the monomer - target complexes formed within the pre-polymerization matrix are translated into the selective binding cavities formed during polymerization. Elucidating the nature of these interactions in silico improves our understanding of MIPs, ultimately allowing for more optimized sensing materials.

Effect of channel-width and chirality on graphene field-effect transistor based real-time biomolecule sensing

NASA Astrophysics Data System (ADS)

Lyu, Letian; Jaswal, Perveshwer; Xu, Guangyu

2018-03-01

Graphene field-effect transistors (GFET) hold promise in biomolecule sensing due to the outstanding properties of graphene materials. Charges in biomolecules are transduced into a change in the GFET current, which allows real-time monitoring of the biomolecule concentrations. Here we theoretically evaluate the performance of GFET based real-time biomolecule sensing, aiming to better understand the width-scaling limit in GFET based biosensors. In particular, we study the effect of the channel-width and the chirality on FET sensitivity by taking the percentage change of the FET current per unit charge density as the sensing signal. Firstly, GFETs made of graphene nanoribbons (GNR) and graphene sheets (GS) show comparable sensing signals to each other when gated at 1011 - 1012 cm-2 carrier densities. Sensing signals in GNRs are enhanced when gated near the sub-band thresholds, and increase their values in wider GNRs due to the change in device conductance and quantum capacitance. Secondly, the GNR chirality is found to fine tune the sensing signals. Armchair GNRs with smaller energy bandgaps appear to have an enhanced sensing signal close to 1011 cm-2 carrier densities. These results may help understand the scaling limit in GFET based biosensors along the width direction, and shed light on forming all-electrical bio-arrays.

Examination of new chiral smectics with four aromatic rings

NASA Astrophysics Data System (ADS)

Żurowska, Magdalena; Czerwiński, Michał; Dziaduszek, Jerzy; Filipowicz, Marek

2018-05-01

This paper presents the results of the study of four chiral mesogens with the acronym (4X1X2). The investigated compounds might be of interest for use as components of multicomponent mixtures useful in technical devices. The compounds have high chemical stability. Their mesomorphic properties were tested by means of polarizing optical microscopy and differential scanning calorimetry. The helical pitch of the prepared compounds and mixtures was estimated using the selective reflection method. Their phase smectic layer structure and usefulness for formulation of multicomponent antiferroelectric mixtures were then reported.

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.

Asymmetry at the molecular level in biology

NASA Astrophysics Data System (ADS)

Johnson, Louise N.

2005-10-01

Naturally occurring biological molecules are made of homochiral building blocks. Proteins are composed of L-amino acids (and not D-amino acids); nucleic acids such as DNA have D-ribose sugars (and not L-ribose sugars). It is not clear why nature selected a particular chirality. Selection could have occurred by chance or as a consequence of basic physical chemistry. Possible proposals, including the contribution of the parity violating the weak nuclear force, are discussed together with the mechanisms by which this very small contribution might be amplified. Homochirality of the amino acids has consequences for protein structure. Helices are right handed and beta sheets have a left-hand twist. When incorporated into the tertiary structure of a protein these chiralities limit the topologies of connections between helices and sheets. Polypeptides comprised of D-amino acids can be synthesized chemically and have been shown to adopt stable structures that are the mirror image of the naturally occurring L-amino acid polypeptides. Chirality is important in drug design. Three examples are discussed: penicillin; the CD4 antagonistic peptides; and thalidomide. The absolute hand of a biological structure can only be established by X-ray crystallographic methods using the technique of anomalous scattering.

On the nature and correction of the spurious S-wise spiral galaxy winding bias in Galaxy Zoo 1

NASA Astrophysics Data System (ADS)

Hayes, Wayne B.; Davis, Darren; Silva, Pedro

2017-04-01

The Galaxy Zoo 1 catalogue displays a bias towards the S-wise winding direction in spiral galaxies, which has yet to be explained. The lack of an explanation confounds our attempts to verify the Cosmological Principle, and has spurred some debate as to whether a bias exists in the real Universe. The bias manifests not only in the obvious case of trying to decide if the universe as a whole has a winding bias, but also in the more insidious case of selecting which Galaxies to include in a winding direction survey. While the former bias has been accounted for in a previous image-mirroring study, the latter has not. Furthermore, the bias has never been corrected in the GZ1 catalogue, as only a small sample of the GZ1 catalogue was reexamined during the mirror study. We show that the existing bias is a human selection effect rather than a human chirality bias. In effect, the excess S-wise votes are spuriously 'stolen' from the elliptical and edge-on-disc categories, not the Z-wise category. Thus, when selecting a set of spiral galaxies by imposing a threshold T so that max (PS, PZ) > T or PS + PZ > T, we spuriously select more S-wise than Z-wise galaxies. We show that when a provably unbiased machine selects which galaxies are spirals independent of their chirality, the S-wise surplus vanishes, even if humans still determine the chirality. Thus, when viewed across the entire GZ1 sample (and by implication, the Sloan catalogue), the winding direction of arms in spiral galaxies as viewed from Earth is consistent with the flip of a fair coin.

Enantioresolution in electrokinetic chromatography-complete filling technique using sulfated gamma-cyclodextrin. Software-free topological anticipation.

PubMed

Escuder-Gilabert, Laura; Martín-Biosca, Yolanda; Medina-Hernández, María José; Sagrado, Salvador

2016-10-07

Few papers have tried to predict the resolution ability of chiral selectors in capillary electrophoresis for the separation of the enantiomers of chiral compounds. In a previous work, we have used molecular information available on-line to establish enantioresolution levels of basic compounds using highly sulfated β-CD (HS-β-CD) as chiral selector in electrokinetic chromatography-complete filling technique (EKC-CFT). The present study is a continuation of this previous work, introducing some novelties. In this work, the ability of sulfated γ-cyclodextrin (S-γ-CD) as chiral selector in EKC-CFT is modelled for the first time. Thirty-three structurally unrelated cationic and neutral compounds (drugs and pesticides) are studied. Categorical enantioresolution levels (RsC, 0 or 1) are assigned from experimental enantioresolution values obtained at different S-γ-CD concentrations. Novel topological parameters connected to the chiral carbon (C * -parameters) are introduced. Four C * -parameters and a topological parameter of the whole molecule (aromatic atom count) are the most important variables according to a discriminant partial least squares-variable selection process. It suggests the preponderance of the topology adjacent to the chiral carbon to anticipate the RsC levels. A software-free anticipation protocol for new molecules is proposed. Over the current set of molecules evaluated, 100% of correct anticipations (resolved and non-resolved compounds) are obtained, while anticipation of some compounds remains undetermined. A criterion is introduced to alert on compounds which should not be anticipated. Copyright © 2016 Elsevier B.V. All rights reserved.

Chemical synthesis of chiral conducting polymers

DOEpatents

Wang, Hsing-Lin; Li, Wenguang

2006-07-11

An process of forming a chiral conducting polymer, e.g., polyaniline, is provided including reacting a monomer, e.g., an aniline monomer, in the presence of a chiral dopant acid to produce a first reaction mixture by addition of a solution including a first portion of an oxidizing agent, the first portion of oxidizing agent characterized as insufficient to allow complete reaction of the monomer, and further reacting the first reaction mixture in the presence of the chiral dopant acid by addition of a solution including a second portion of the oxidizing agent, the second portion of oxidizing agent characterized as insufficient to allow complete reaction of the monomer, and repeating the reaction by addition of further portions of the oxidizing agent until the monomer reaction is complete to produce a chiral conducting polymer, e.g., polyaniline. A preferred process includes addition of a catalyst during the reaction, the catalyst selected from among the group consisting of phenylene diamine, aniline oligomers and amino-capped aniline oligomers and metal salts. The processes of the present invention further provide a resultant polyaniline product having a chirality level defined by a molar ellipticity of from about 40.times.10³ degree-cm²/decimole to about 700.times.10³ degree-cm²/decimole. The processes of the present invention further provide a resultant polyaniline product having a nanofiber structure with a diameter of from about 30 nanometers to about 120 nanometers and from about 1 micron to about 5 microns in length.

Applicability of bioanalysis of multiple analytes in drug discovery and development: review of select case studies including assay development considerations.

PubMed

Srinivas, Nuggehally R

2006-05-01

The development of sound bioanalytical method(s) is of paramount importance during the process of drug discovery and development culminating in a marketing approval. Although the bioanalytical procedure(s) originally developed during the discovery stage may not necessarily be fit to support the drug development scenario, they may be suitably modified and validated, as deemed necessary. Several reviews have appeared over the years describing analytical approaches including various techniques, detection systems, automation tools that are available for an effective separation, enhanced selectivity and sensitivity for quantitation of many analytes. The intention of this review is to cover various key areas where analytical method development becomes necessary during different stages of drug discovery research and development process. The key areas covered in this article with relevant case studies include: (a) simultaneous assay for parent compound and metabolites that are purported to display pharmacological activity; (b) bioanalytical procedures for determination of multiple drugs in combating a disease; (c) analytical measurement of chirality aspects in the pharmacokinetics, metabolism and biotransformation investigations; (d) drug monitoring for therapeutic benefits and/or occupational hazard; (e) analysis of drugs from complex and/or less frequently used matrices; (f) analytical determination during in vitro experiments (metabolism and permeability related) and in situ intestinal perfusion experiments; (g) determination of a major metabolite as a surrogate for the parent molecule; (h) analytical approaches for universal determination of CYP450 probe substrates and metabolites; (i) analytical applicability to prodrug evaluations-simultaneous determination of prodrug, parent and metabolites; (j) quantitative determination of parent compound and/or phase II metabolite(s) via direct or indirect approaches; (k) applicability in analysis of multiple compounds in select disease areas and/or in clinically important drug-drug interaction studies. A tabular representation of select examples of analysis is provided covering areas of separation conditions, validation aspects and applicable conclusion. A limited discussion is provided on relevant aspects of the need for developing bioanalytical procedures for speedy drug discovery and development. Additionally, some key elements such as internal standard selection, likely issues of mass detection, matrix effect, chiral aspects etc. are provided for consideration during method development.

A Review of the Updated Pharmacophore for the Alpha 5 GABA(A) Benzodiazepine Receptor Model

PubMed Central

Clayton, Terry; Poe, Michael M.; Rallapalli, Sundari; Biawat, Poonam; Savić, Miroslav M.; Rowlett, James K.; Gallos, George; Emala, Charles W.; Kaczorowski, Catherine C.; Stafford, Douglas C.; Arnold, Leggy A.; Cook, James M.

2015-01-01

An updated model of the GABA(A) benzodiazepine receptor pharmacophore of the α5-BzR/GABA(A) subtype has been constructed prompted by the synthesis of subtype selective ligands in light of the recent developments in both ligand synthesis, behavioral studies, and molecular modeling studies of the binding site itself. A number of BzR/GABA(A) α5 subtype selective compounds were synthesized, notably α5-subtype selective inverse agonist PWZ-029 (1) which is active in enhancing cognition in both rodents and primates. In addition, a chiral positive allosteric modulator (PAM), SH-053-2′F-R-CH3 (2), has been shown to reverse the deleterious effects in the MAM-model of schizophrenia as well as alleviate constriction in airway smooth muscle. Presented here is an updated model of the pharmacophore for α5β2γ2 Bz/GABA(A) receptors, including a rendering of PWZ-029 docked within the α5-binding pocket showing specific interactions of the molecule with the receptor. Differences in the included volume as compared to α1β2γ2, α2β2γ2, and α3β2γ2 will be illustrated for clarity. These new models enhance the ability to understand structural characteristics of ligands which act as agonists, antagonists, or inverse agonists at the Bz BS of GABA(A) receptors. PMID:26682068

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.

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

Chemo-Enzymatic Synthesis of Each Enantiomer of Orthogonally-Protected 4,4-Difluoroglutamic Acid – A Candidate Monomer for Chiral Brønsted-Acid Peptide-Based Catalysts

PubMed Central

Li, Yang

2011-01-01

We have accomplished an asymmetric synthesis of each enantiomer of 4,4-difluoroglutamic acid. This α-amino acid has been of interest in medicinal chemistry circles. Key features of the synthesis include highly scalable procedures, a Reformatsky-based coupling reaction, and straightforward functional group manipulations to make the parent amino acid. Enantioenrichment derives from an enzymatic resolution of the synthetic material. Conversion of the optically enriched compounds to orthogonally protected forms allows selective formation of peptide bonds. 4,4- Difluoroglutamic acid, in a suitably protected form, is also shown to exhibit enhanced catalytic activity in both an oxidation reaction and a reduction reaction, in comparison to the analogous glutamic acid derivative. PMID:22039908

[Preparation and performance characterization of gold nanoparticles modified chiral capillary electrochromatography stationary phase].

PubMed

Xiong, Lele; Li, Ruijun; Ji, Yibing

2017-07-08

Gold nanoparticles (GNPs, 15 nm) were prepared and introduced to amino groups derived silica monolithic column. Bovine serum albumin (BSA) was immobilized via covalent modification method onto the carboxylic functionalized GNPs to afford chiral stationary phase (CSP) for enantioseparation. GNPs were well dispersed and successfully incorporated onto the columns with the contents as high as 17.18% by characterization method such as transmission electron microscopy (TEM), ultraviolet (UV)-visible absorption spectra and scanning electron microscopy (SEM). The preparation conditions of the BSA modified CSP were optimized and 10% (v/v) 3-aminopropyltriethoxysilane (APTES) and 15 g/L BSA were selected as appropriate reaction conditions. The enantioseparation performance of the BSA modified CSP has been investigated by capillary electrochromatography (CEC). Enantiomers of tryptophan, ephedrine and atenolol were resolved, and the baseline separation of tryptophan was achieved. Meanwhile, the influences of pH value, buffer concentrations and applied voltages used on the chiral separation were studied, and the optimal separation conditions were 10 mmol/L phosphate buffer at pH 7.4 and 15 kV applied voltages. In comparison with the BSA modified CSP prepared by physical adsorption, the CSP prepared by covalent modification method had better separation results, and the analytes could be separated directly without pre-column derivatization. In addition, the prepared BSA modified CSP exhibited good run to run repeatability with relative standard deviations (RSDs) of the migration times and selectivity factors not more than 2.3% and 0.96%, respectively. This work offers a good thinking for modification with other proteins or other types of chiral selectors.

Quantitation of the enantiomers of tramadol and its three main metabolites in human whole blood using LC-MS/MS.

PubMed

Haage, Pernilla; Kronstrand, Robert; Carlsson, Björn; Kugelberg, Fredrik C; Josefsson, Martin

2016-02-05

The analgesic drug tramadol and its metabolites are chiral compounds, with the (+)- and (-)-enantiomers showing different pharmacological and toxicological effects. This novel enantioselective method, based on LC-MS/MS in reversed phase mode, enabled measurement of the parent compound and its three main metabolites O-desmethyltramadol, N-desmethyltramadol and N,O-didesmethyltramadol simultaneously. Whole blood samples of 0.5g were fortified with internal standards (tramadol-(13)C-D3 and O-desmethyl-cis-tramadol-D6) and extracted under basic conditions (pH 11) by liquid-liquid extraction. Chromatography was performed on a chiral alpha-1-acid glycoprotein (AGP) column preceded by an AGP guard column. The mobile phase consisted of 0.8% acetonitrile and 99.2% ammonium acetate (20mM, pH 7.2). A post-column infusion with 0.05% formic acid in acetonitrile was used to enhance sensitivity. Quantitation as well as enantiomeric ratio measurements were covered by quality controls. Validation parameters for all eight enantiomers included selectivity (high), matrix effects (no ion suppression/enhancement), calibration model (linear, weight 1/X(2), in the range of 0.25-250ng/g), limit of quantitation (0.125-0.50ng/g), repeatability (2-6%) and intermediate precision (2-7%), accuracy (83-114%), dilution integrity (98-115%), carry over (not exceeding 0.07%) and stability (stable in blood and extract). The method was applied to blood samples from a healthy volunteer administrated a single 100mg dose and to a case sample concerning an impaired driver, which confirmed its applicability in human pharmacokinetic studies as well as in toxicological and forensic investigations. Copyright © 2015 Elsevier B.V. All rights reserved.

Hydrotalcite catalysis for the synthesis of new chiral building blocks.

PubMed

Rodilla, Jesus M; Neves, Patricia P; Pombal, Sofia; Rives, Vicente; Trujillano, Raquel; Díez, David

2016-01-01

The use of hydrotalcites for the synthesis of two chiral building blocks in a simple way is described as a new and green methodology. The synthesis of these compounds implies a regioselective Baeyer-Villiger reaction in a very selective way with ulterior opening and lactonisation. This methodology should be considered green for the use of hydrogen peroxide as the only oxidant and hydrotalcites as the catalyst, and because no residues are produced apart from water. The procedure is very adequate for using in gram scale, in order to increase the value of the obtained compounds. The conditions are excellent and can be applied for nonstable compounds, as they are very mild. The synthesised compounds are magnific starting materials for the synthesis of biologically active or natural compounds. The use of a cheap, commercial and chiral compound as carvone disposable in both enantiomeric forms adds an extra value to this methodology.

First measurement of chiral dynamics in π- γ → π- π- π+.

PubMed

Adolph, C; Alekseev, M G; Alexakhin, V Yu; Alexandrov, Yu; Alexeev, G D; Amoroso, A; Antonov, A A; Austregesilo, A; Badełek, B; Balestra, F; Barth, J; Baum, G; Bedfer, Y; Bernhard, J; Bertini, R; Bettinelli, M; Bicker, K A; Birsa, R; Bisplinghoff, J; Bordalo, P; Bradamante, F; Braun, C; Bravar, A; Bressan, A; Burtin, E; Chaberny, D; Chiosso, M; Chung, S U; Cicuttin, A; Crespo, M L; Dalla Torre, S; Das, S; Dasgupta, S S; Denisov, O Yu; Dhara, L; Donskov, S V; Doshita, N; Duic, V; Dünnweber, W; Dziewiecki, M; Efremov, A; Elia, C; Eversheim, P D; Eyrich, W; Faessler, M; Ferrero, A; Filin, A; Finger, M; Finger, M; Fischer, H; Franco, C; du Fresne von Hohenesche, N; Friedrich, J M; Garfagnini, R; Gautheron, F; Gavrichtchouk, O P; Gazda, R; Gerassimov, S; Geyer, R; Giorgi, M; Gnesi, I; Gobbo, B; Goertz, S; Grabmüller, S; Grasso, A; Grube, B; Gushterski, R; Guskov, A; Haas, F; von Harrach, D; Hasegawa, T; Heinsius, F H; Herrmann, F; Hess, C; Hinterberger, F; Horikawa, N; Höppner, Ch; d'Hose, N; Huber, S; Ishimoto, S; Ivanov, O; Ivanshin, Yu; Iwata, T; Jahn, R; Jasinski, P; Jegou, G; Joosten, R; Kabuss, E; Kang, D; Ketzer, B; Khaustov, G V; Khokhlov, Yu A; Kisselev, Yu; Klein, F; Klimaszewski, K; Koblitz, S; Koivuniemi, J H; Kolosov, V N; Kondo, K; Königsmann, K; Konorov, I; Konstantinov, V F; Korzenev, A; Kotzinian, A M; Kouznetsov, O; Krämer, M; Kroumchtein, Z V; Kunne, F; Kurek, K; Lauser, L; Lednev, A A; Lehmann, A; Levorato, S; Lichtenstadt, J; Maggiora, A; Magnon, A; Makke, N; Mallot, G K; Mann, A; Marchand, C; Martin, A; Marzec, J; Massmann, F; Matsuda, T; Meyer, W; Michigami, T; Mikhailov, Yu V; Moinester, M A; Morreale, A; Mutter, A; Nagaytsev, A; Nagel, T; Nerling, F; Neubert, S; Neyret, D; Nikolaenko, V I; Nowak, W-D; Nunes, A S; Olshevsky, A G; Ostrick, M; Padee, A; Panknin, R; Panzieri, D; Parsamyan, B; Paul, S; Perevalova, E; Pesaro, G; Peshekhonov, D V; Piragino, G; Platchkov, S; Pochodzalla, J; Polak, J; Polyakov, V A; Pontecorvo, G; Pretz, J; Quintans, C; Rajotte, J-F; Ramos, S; Rapatsky, V; Reicherz, G; Richter, A; Rocco, E; Rondio, E; Rossiyskaya, N S; Ryabchikov, D I; Samoylenko, V D; Sandacz, A; Sapozhnikov, M G; Sarkar, S; Savin, I A; Sbrizzai, G; Schiavon, P; Schill, C; Schlüter, T; Schmitt, L; Schönning, K; Schopferer, S; Schröder, W; Shevchenko, O Yu; Siebert, H-W; Silva, L; Sinha, L; Sissakian, A N; Slunecka, M; Smirnov, G I; Sosio, S; Sozzi, F; Srnka, A; Stolarski, M; Sulc, M; Sulej, R; Sznajder, P; Takekawa, S; Ter Wolbeek, J; Tessaro, S; Tessarotto, F; Teufel, A; Tkatchev, L G; Uhl, S; Uman, I; Vandenbroucke, M; Virius, M; Vlassov, N V; Windmolders, R; Wiślicki, W; Wollny, H; Zaremba, K; Zavertyaev, M; Zemlyanichkina, E; Ziembicki, M; Zhuravlev, N; Zvyagin, A

2012-05-11

The COMPASS Collaboration at CERN has investigated the π- γ → π- π- π+ reaction at center-of-momentum energy below five pion masses, sqrt[s]<5m(π), embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasireal photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, t'<0.001  GeV2/c2. Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the 3π-invariant mass m(3π)=sqrt[s] were extracted. The absolute cross section was determined in seven bins of sqrt[s] with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.

Thermally controllable reflective characteristics from rupture and self-assembly of hydrogen bonds in cholesteric liquid crystals.

PubMed

Hu, Wang; Cao, Hui; Song, Li; Zhao, Haiyan; Li, Sijin; Yang, Zhou; Yang, Huai

2009-10-22

A cholesteric liquid crystal (Ch-LC) composite, made of a series of cholesteryl esters, a nematic LC, and a hydrogen bond (H-bond) chiral dopant (HCD), was prepared and filled into a planar treated cell. When the cell was heated, the selective reflection of the cell exhibited an unusual blue shift. One of the reasonable mechanisms was that the helical twisting power (HTP) value of cholesteryl esters increased with an increasing temperature. The other one was that the H-bonds of HCD were ruptured when the temperature was above 60.0 degrees C and HCD was split into two kinds of new chiral dopants, which made the HTP value of the chiral dopants change a lot, thus changing the pitch length of the composite greatly. On the basis of this mechanism, a novel thermally controllable reflective color paper could be achieved.

Enantiomeric switching of chiral metamaterial for terahertz polarization modulation employing vertically deformable MEMS spirals

NASA Astrophysics Data System (ADS)

Kan, Tetsuo; Isozaki, Akihiro; Kanda, Natsuki; Nemoto, Natsuki; Konishi, Kuniaki; Takahashi, Hidetoshi; Kuwata-Gonokami, Makoto; Matsumoto, Kiyoshi; Shimoyama, Isao

2015-10-01

Active modulation of the polarization states of terahertz light is indispensable for polarization-sensitive spectroscopy, having important applications such as non-contact Hall measurements, vibrational circular dichroism measurements and anisotropy imaging. In the terahertz region, the lack of a polarization modulator similar to a photoelastic modulator in the visible range hampers expansion of such spectroscopy. A terahertz chiral metamaterial has a huge optical activity unavailable in nature; nevertheless, its modulation is still challenging. Here we demonstrate a handedness-switchable chiral metamaterial for polarization modulation employing vertically deformable Micro Electro Mechanical Systems. Vertical deformation of a planar spiral by a pneumatic force creates a three-dimensional spiral. Enantiomeric switching is realized by selecting the deformation direction, where the polarity of the optical activity is altered while maintaining the spectral shape. A polarization rotation as high as 28° is experimentally observed, thus providing a practical and compact polarization modulator for the terahertz range.

Enantiomeric switching of chiral metamaterial for terahertz polarization modulation employing vertically deformable MEMS spirals.

PubMed

Kan, Tetsuo; Isozaki, Akihiro; Kanda, Natsuki; Nemoto, Natsuki; Konishi, Kuniaki; Takahashi, Hidetoshi; Kuwata-Gonokami, Makoto; Matsumoto, Kiyoshi; Shimoyama, Isao

2015-10-01

Active modulation of the polarization states of terahertz light is indispensable for polarization-sensitive spectroscopy, having important applications such as non-contact Hall measurements, vibrational circular dichroism measurements and anisotropy imaging. In the terahertz region, the lack of a polarization modulator similar to a photoelastic modulator in the visible range hampers expansion of such spectroscopy. A terahertz chiral metamaterial has a huge optical activity unavailable in nature; nevertheless, its modulation is still challenging. Here we demonstrate a handedness-switchable chiral metamaterial for polarization modulation employing vertically deformable Micro Electro Mechanical Systems. Vertical deformation of a planar spiral by a pneumatic force creates a three-dimensional spiral. Enantiomeric switching is realized by selecting the deformation direction, where the polarity of the optical activity is altered while maintaining the spectral shape. A polarization rotation as high as 28° is experimentally observed, thus providing a practical and compact polarization modulator for the terahertz range.

Efficient optical resolution of amino acid by alanine racemaze chiral analogue supported on mesoporous carbon

NASA Astrophysics Data System (ADS)

Jang, D.; Kim, K.; Park, D.; Kim, G.

2012-09-01

Optically pure D-amino acids are industrially important chiral building blocks for the synthesis of pharmaceuticals, food ingredients, and drug intermediates. Chemoenzymatic dynamic kinetic-resolution processes have recently been developed for deracemization of amino acids. S-ARCA would be a good candidate for the selective adsorption of D amino acid through the imine formation reaction. The organic phase containing S-ARCA adsorbent, TPPC or Ionic Liquid (as a phase transfer catalyst) in MC were coated on the surfaces of mesoporous carbon C-SBA-15(CMK). The aqueous solution of racemic D/L-amino acid and NaOH were added to the carbon support coated with ARCA. The D/L ratios on ARCA and in solution were determined with increasing reaction time. S-ARCA has a unique property for the selective adsorption of D- amino acid (up to 90% selcetivity) in the racemic mixture. The fixed bed reactor containing ARCA/carbon support was also adopted successfully for the selective separation of amino acid.

Valley Vortex States in Sonic Crystals

NASA Astrophysics Data System (ADS)

Lu, Jiuyang; Qiu, Chunyin; Ke, Manzhu; Liu, Zhengyou

2016-03-01

Valleytronics is quickly emerging as an exciting field in fundamental and applied research. In this Letter, we study the acoustic version of valley states in sonic crystals and reveal a vortex nature of such states. In addition to the selection rules established for exciting valley polarized states, a mimicked valley Hall effect of sound is proposed further. The extraordinary chirality of valley vortex states, detectable in experiments, may open a new possibility in sound manipulations. This is appealing to scalar acoustics that lacks a spin degree of freedom inherently. In addition, the valley selection enables a handy way to create vortex matter in acoustics, in which the vortex chirality can be controlled flexibly. Potential applications can be anticipated with the exotic interaction of acoustic vortices with matter, such as to trigger the rotation of the trapped microparticles without contact.

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.

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.

Open tubular capillary columns with basic templates made by the generalized preparation protocol in capillary electrochromatography chiral separation and template structural effects on chiral separation capability.

PubMed

Zaidi, Shabi Abbas; Lee, Seung Mi; Cheong, Won Jo

2011-03-04

Some open tubular (OT) molecule imprinted polymer (MIP) silica capillary columns have been prepared using atenolol, sulpiride, methyl benzylamine (MBA) and (1-naphthyl)-ethylamine (NEA) as templates by the pre-established generalized preparation protocol. The four MIP thin layers of different templates showed quite different morphologies. The racemic selectivity of each MIP column for the template enantiomers was optimized by changing eluent composition and pH. The template structural effects on chiral separation performance have been examined. This work verifies the versatility of the generalized preparation protocol for OT-MIP silica capillary columns by extending its boundary toward templates with basic functional group moieties. This study is the very first report to demonstrate a generalized MIP preparation protocol that is valid for both acidic and basic templates. The chiral separation performances of atenolol and sulpiride by the MIPs of this study were found better than or comparable to those of atenolol and sulpiride obtained by non-MIP separation techniques and those of some basic template enantiomers obtained by MIP based techniques. Copyright © 2011 Elsevier B.V. All rights reserved.

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

[Resolution of chiral molecules of pharmaceutical interest by means of preferential crystallization].

PubMed

Coquerel, G

2009-07-01

Various aspects of the chiral discrimination in the solid state are examined. The interests of the conglomerate are illustrated by two applications: the preparative enantiomeric purification and the preferential crystallization. The latter process is described by a careful examination of the heterogeneous equilibria that govern the crystallization and its selectivity. Two variants of the preferential crystallization are detailed. A "good" example illustrates the productivity at the laboratory scale. The ratio between homochiral interaction energies and heterochiral interaction energies at different (hkl) interfaces are involved in the "difficult" cases where the entrainment effect is limited.

Rapid chiral separation of atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid using supercritical fluid chromatography-tandem mass spectrometry - Application to wetland microcosms.

PubMed

Svan, Alfred; Hedeland, Mikael; Arvidsson, Torbjörn; Jasper, Justin T; Sedlak, David L; Pettersson, Curt E

2015-08-28

A method for enantiomeric separation of the three β-blocking agents atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid, a major metabolite of both metoprolol and in environmental matrices also atenolol, has been developed. By use of supercritical fluid chromatography and the polysaccharide-based Chiralpak(®) IB-3, all four compounds were simultaneously enantiomerically separated (Rs>1.5) within 8min. Detection was performed using tandem mass spectrometry, and to avoid isobaric interference between the co-eluting metoprolol and metoprolol acid, the achiral column Acquity(®) UPC(2) BEH 2-EP was attached ahead of to the chiral column. Carbon dioxide with 18% methanol containing 0.5% (v/v) of the additives trifluoroacetic acid and ammonia in a 2:1 molar ratio were used as mobile phase. A post column make-up flow (0.3mL/min) of methanol containing 0.1% (v/v) formic acid was used to enhance the positive electrospray ionization. Detection was carried out using a triple quadrupole mass spectrometer operating in the selected reaction monitoring mode, using one transition per analyte and internal standard. The method was successfully applied for monitoring the enantiomeric fraction change over time in a laboratory scale wetland degradation study. It showed good precision, recovery, sensitivity and low effect of the sample matrix. Copyright © 2015. Published by Elsevier B.V.

Optical activity of chirally distorted nanocrystals

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

Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.

2016-05-21

We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ bymore » a factor of 10{sup 5}. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.« less

Vibrationally induced inversion of photoelectron forward-backward asymmetry in chiral molecule photoionization by circularly polarized light

PubMed Central

Garcia, Gustavo A.; Nahon, Laurent; Daly, Steven; Powis, Ivan

2013-01-01

Electron–nuclei coupling accompanying excitation and relaxation processes is a fascinating phenomenon in molecular dynamics. A striking and unexpected example of such coupling is presented here in the context of photoelectron circular dichroism measurements on randomly oriented, chiral methyloxirane molecules, unaffected by any continuum resonance. Here, we report that the forward-backward asymmetry in the electron angular distribution, with respect to the photon axis, which is associated with photoelectron circular dichroism can surprisingly reverse direction according to the ion vibrational mode excited. This vibrational dependence represents a clear breakdown of the usual Franck–Condon assumption, ascribed to the enhanced sensitivity of photoelectron circular dichroism (compared with other observables like cross-sections or the conventional anisotropy parameter-β) to the scattering phase off the chiral molecular potential, inducing a dependence on the nuclear geometry sampled in the photoionization process. Important consequences for the interpretation of such dichroism measurements within analytical contexts are discussed. PMID:23828557

Quantum optical rotatory dispersion

PubMed Central

Tischler, Nora; Krenn, Mario; Fickler, Robert; Vidal, Xavier; Zeilinger, Anton; Molina-Terriza, Gabriel

2016-01-01

The phenomenon of molecular optical activity manifests itself as the rotation of the plane of linear polarization when light passes through chiral media. Measurements of optical activity and its wavelength dependence, that is, optical rotatory dispersion, can reveal information about intricate properties of molecules, such as the three-dimensional arrangement of atoms comprising a molecule. Given a limited probe power, quantum metrology offers the possibility of outperforming classical measurements. This has particular appeal when samples may be damaged by high power, which is a potential concern for chiroptical studies. We present the first experiment in which multiwavelength polarization-entangled photon pairs are used to measure the optical activity and optical rotatory dispersion exhibited by a solution of chiral molecules. Our work paves the way for quantum-enhanced measurements of chirality, with potential applications in chemistry, biology, materials science, and the pharmaceutical industry. The scheme that we use for probing wavelength dependence not only allows one to surpass the information extracted per photon in a classical measurement but also can be used for more general differential measurements. PMID:27713928

Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials

PubMed Central

Khanikaev, A. B.; Arju, N.; Fan, Z.; Purtseladze, D.; Lu, F.; Lee, J.; Sarriugarte, P.; Schnell, M.; Hillenbrand, R.; Belkin, M. A.; Shvets, G.

2016-01-01

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating. PMID:27329108

Optical properties of two-dimensional charge density wave materials

NASA Astrophysics Data System (ADS)

Sayers, Charles; Karbassi, Sara; Friedemann, Sven; da Como, Enrico

Titanium diselenide (TiSe2) is a member of the layered transition metal dichalcogenide (TMD) materials. It exhibits unusual chiral charge ordering below 190 K after undergoing an initial phase transition to a commensurate (2 x 2 x 2) charge density wave (CDW) at 200 K which is enhanced further in the monolayer. Recently, the first evidence of chirality in a CDW system was discovered in this material by scanning tunneling microscopy and time-resolved reflectivity experiments, where separate left and right handed charge-ordered domains were found to exist within a single sample. We have prepared single crystals of 1T-TiSe2 using iodine vapour transport, and confirmed their quality by x-ray analysis and charge transport measurements. Using a combination of polarised optical spectroscopy techniques in the mid to far infrared (4 to 700 meV photon energy), we have measured an anisotropy relating to the CDW gap. We discuss the results on the basis of chiral domains with different handedness and the nature of the CDW transition.

Enhanced biosynthesis of chiral phenyllactic acid from L-phenylalanine through a new whole-cell biocatalyst.

PubMed

Zheng, Zhaojuan; Xia, Meijuan; Fang, Xuchao; Jiang, Ting; Ouyang, Jia

2018-06-22

Phenyllactic acid (PLA) is a high-value compound, which was usually produced by lactic acid bacteria (LAB) as biocatalysts and glucose or phenylpyruvic acid (PPA) as starting materials for PLA synthesis in previous studies. However, the PLA produced using LAB is a racemic mixture. Besides, both glucose and PPA were unsatisfactory substrates, as the former could not produce high concentrations of PLA while the latter is not a renewable and green substrate. To overcome these drawbacks, in this study, a new biotransformation process was developed for chiral PLA production from L-phenylalanine via the intermediate PPA using recombinant Escherichia coli co-expressing L-amino acid deaminase, NAD-dependent L-lactate dehydrogenase or NAD-dependent D-lactate dehydrogenase, and formate dehydrogenase. After optimization, the recombinant E. coli produced L- and D-PLA at concentrations of 59.9 and 60.3 mM in 6 h, respectively. Hence, this process provides an effective and promising alternative method for chiral PLA production.

Colossal thermomagnetic response in chiral d-wave superconductor URu2Si2

NASA Astrophysics Data System (ADS)

Matsuda, Yuji

The heavy-fermion compound URu2Si2 exhibits unconventional superconductivity at Tc = 1.45 K deep inside the so-called hidden order phase. An intriguing aspect is that this system has been suggested to be a candidate of a chiral d-wave superconductor, and possible Weyl-type topological superconducting states have been discussed recently. Here we report on the observation of a highly unusual Nernst signal due to the superconducting fluctuations above Tc. The Nernst coefficient is anomalously enhanced (by a factor of ~106) as compared with the theoretically expected value of the Gaussian fluctuations. This colossal Nernst effect intimately reflects the highly unusual superconducting state of URu2Si2. The results invoke possible chiral or Berry-phase fluctuations associated with the broken time-reversal symmetry of the superconducting order parameter. In collaboration with T. Yamashita, Y. Shimoyama, H. Sumiyoshi (Kyoto), S. Fujimoto (Osaka), T. Shibauchi (Tokyo), Y. Haga (JAEA), T. D. Matsuda (TMU) , Y. Onuki (Ryukyus), A. Levchenko (Wisconsin-Madison).

Optical activity of chirally distorted nanocrystals

NASA Astrophysics Data System (ADS)

Tepliakov, Nikita V.; Baimuratov, Anvar S.; Baranov, Alexander V.; Fedorov, Anatoly V.; Rukhlenko, Ivan D.

2016-05-01

We develop a general theory of optical activity of semiconductor nanocrystals whose chirality is induced by a small perturbation of their otherwise achiral electronic subsystems. The optical activity is described using the quantum-mechanical expressions for the rotatory strengths and dissymmetry factors introduced by Rosenfeld. We show that the rotatory strengths of optically active transitions are decomposed on electric dipole and magnetic dipole contributions, which correspond to the electric dipole and magnetic dipole transitions between the unperturbed quantum states. Remarkably, while the two kinds of rotatory strengths are of the same order of magnitude, the corresponding dissymmetry factors can differ by a factor of 105. By maximizing the dissymmetry of magnetic dipole absorption one can significantly enhance the enantioselectivity in the interaction of semiconductor nanocrystals with circularly polarized light. This feature may advance chiral and analytical methods, which will benefit biophysics, chemistry, and pharmaceutical science. The developed theory is illustrated by an example of intraband transitions inside a semiconductor nanocuboid, whose rotatory strengths and dissymmetry factors are calculated analytically.

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

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

Singh, Ram Sevak, E-mail: singh915@gmail.com

2015-11-15

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to havemore » metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.« less

Thermodynamic models to elucidate the enantioseparation of drugs with two stereogenic centers by micellar electrokinetic chromatography.

PubMed

Guo, Xuming; Liu, Qiuxia; Hu, Shaoqiang; Guo, Wenbo; Yang, Zhuo; Zhang, Yonghua

2017-08-25

An equilibrium model depicting the simultaneous protonation of chiral drugs and partitioning of protonated ions and neutral molecules into chiral micelles in micellar electrokinetic chromatography (MEKC) has been introduced. It was used for the prediction and elucidation of complex changes in migration order patterns with experimental conditions in the enantioseparation of drugs with two stereogenic centers. Palonosetron hydrochloride (PALO), a weakly basic drug with two stereogenic centers, was selected as a model drug. Its four stereoisomers were separated by MEKC using sodium cholate (SC) as chiral selector and surfactant. Based on the equilibrium model, equations were derived for a calculation of the effective mobility and migration time of each stereoisomer at a certain pH. The migration times of four stereoisomers at different pHs were calculated and then the migration order patterns were constructed with derived equations. The results were in accord with the experiment. And the contribution of each mechanism to the separation and its influence on the migration order pattern was analyzed separately by introducing virtual isomers, i.e., hypothetical stereoisomers with only one parameter changed relative to a real PALO stereoisomer. A thermodynamic model for a judgment of the correlation of interactions between two stereogenic centers of stereoisomers and chiral selector was also proposed. According to this model, the interactions of two stereogenic centers of PALO stereoisomers in both neutral molecules and protonated ions with chiral selector are not independent, so the chiral recognition in each pair of enantiomers as well as the recognition for diastereomers is not simply the algebraic sum of the contributions of two stereogenic centers due to their correlation. Copyright © 2017 Elsevier B.V. All rights reserved.

Comparative evaluation of the chiral recognition potential of single-isomer sulfated beta-cyclodextrin synthesis intermediates in non-aqueous capillary electrophoresis.

PubMed

Fejős, Ida; Varga, Erzsébet; Benkovics, Gábor; Darcsi, András; Malanga, Milo; Fenyvesi, Éva; Sohajda, Tamás; Szente, Lajos; Béni, Szabolcs

2016-10-07

The enantioselectivity of neutral single-isomer synthetic precursors of sulfated-β-cyclodextrins was studied. Four neutral single-isomer cyclodextrins substituted on the secondary side with acetyl and/or methyl functional groups, heptakis(2-O-methyl-3,6-dihydroxy)-β-cyclodextrin (HM-β-CD), heptakis(2,3-di-O-acetyl-6-hydroxy)-β-cyclodextrin (HDA-β-CD), heptakis(2,3-di-O-methyl-6-hydroxy)-β-cyclodextrin (HDM-β-CD), heptakis(2-O-methyl-3-O-acetyl-6-hydroxy)-β-cyclodextrin (HMA-β-CD), and their sulfated analogs the negatively charged heptakis(2,3-di-O-methyl-6-sulfato)-β-cyclodextrin (HDMS-β-CD) and heptakis(2,3-di-O-acetyl-6-sulfato)-β-cyclodextrin (HDAS-β-CD) were investigated by non-aqueous capillary electrophoresis in the view of enantiodiscrimination for various drugs and related pharmaceutical compounds. The focus of the present work was on the chiral selectivity studies of the neutral derivatives, which are the synthesis intermediates of the sulfated products. The chiral recognition experiments proved that among the neutral compounds the HMA-β-CD shows remarkable enantioselectivity towards chiral guests in non-aqueous capillary electrophoresis, while HM-β-CD, HDA-β-CD and HDM-β-CD failed to resolve any of the 25 studied racemates under the applied experimental conditions. In order to get deeper insight into the molecular interactions between the studied single-isomer cyclodextrin and chiral fluoroquinolones (ofloxacin, gatifloxacin and lomefloxacin) and β-blockers (propranolol), 1 H and ROESY NMR experiments were performed. The 2-O-methylation in combination with the 3-O-acetylation of the host was evidenced to exclusively carry the essential spatial arrangement for chiral recognition. Copyright © 2016 Elsevier B.V. All rights reserved.

POLLUTION PREVENTION AND ENHANCEMENT OF BIODEGRADABILITY VIA ISOMER ELIMINATION IN CONSUMER PRODUCTS

EPA Science Inventory

The purpose of this project is to develop novel methodologies for the analysis and detection of chiral environmental contaminants. Conventional analytical techniques do not discriminate between enantiomers. By using newly developed enantioselective methods, the environmental pers...

Construction of chiral ligand exchange capillary electrochromatography for d,l-amino acids enantioseparation and its application in glutaminase kinetics study.

PubMed

Zhao, Liping; Qiao, Juan; Zhang, Ke; Li, Dan; Zhang, Hongyi; Qi, Li

2018-05-04

A chiral ligand exchange capillary electrochromatography (CLE-CEC) protocol was designed and implemented for d,l-amino acids enantioseparation with poly(maleic anhydride-styrene-methacryloyl-l-arginine methyl ester) as the coating. The block copolymer was synthesized through the reversible addition fragmentation chain transfer reaction. In the constructed CLE-CEC system, poly (methacryloyl-l-arginine methyl ester) moiety of the block copolymer played the role as the immobilized chiral ligand and Zn (II) was used as the central ion. Key factors, including pH of buffer solution, ratio of Zn (II) to ligands, the mass ratio of monomers in the block copolymer, which affect the enantioresolution were investigated. Comparing with the bare capillary, the CLE-CEC enantioresolution was enhanced greatly with the coating one. 5 Pairs of d,l-amino acids enantiomers obtained baseline separation with 5 pairs partly separated. The mechanism of enhancement enantioresolution of the developed CLE-CEC system was explored briefly. Further, good linearities were achieved in the range of 25.0 μM-5.0 mM for quantitative analysis of d-glutamine (r 2  = 0.997) and l-glutamine (r 2  = 0.991). Moreover, the proposed CLE-CEC assay was successfully applied in the kinetics study of glutaminase by using l-glutamine as the substrate. Copyright © 2018 Elsevier B.V. All rights reserved.

Copper-Catalyzed SN2'-Selective Allylic Substitution Reaction of gem-Diborylalkanes.

PubMed

Zhang, Zhen-Qi; Zhang, Ben; Lu, Xi; Liu, Jing-Hui; Lu, Xiao-Yu; Xiao, Bin; Fu, Yao

2016-03-04

A Cu/(NHC)-catalyzed SN2'-selective substitution reaction of allylic electrophiles with gem-diborylalkanes is reported. Different substituted gem-diborylalkanes and allylic electrophiles can be employed in this reaction, and various synthetic valuable functional groups can be tolerated. The asymmetric version of this reaction was initially researched with chiral N-heterocyclic carbene (NHC) ligands.

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.

Synthesis and evaluation of the inhibitory activity of the four stereoisomers of the potent and selective human γ-glutamyl transpeptidase inhibitor GGsTop.

PubMed

Watanabe, Bunta; Tabuchi, Yukiko; Wada, Kei; Hiratake, Jun

2017-11-01

2-Amino-4-{[3-(carboxymethyl)phenoxy](methoxy)phosphoryl}butanoic acid (GGsTop) is a potent, highly selective, nontoxic, and irreversible inhibitor of γ-glutamyl transpeptidase (GGT). GGsTop has been widely used in academic and medicinal research, and also as an active ingredient (Nahlsgen) in commercial anti-aging cosmetics. GGsTop consists of four stereoisomers due to the presence of two stereogenic centers, i.e., the α-carbon atom of the glutamate mimic (l/d) and the phosphorus atom (R P /S P ). In this study, each stereoisomer of GGsTop was synthesized stereoselectively and their inhibitory activity against human GGT was evaluated. The l- and d-configurations of each stereoisomer were determined by a combination of a chiral pool synthesis and chiral HPLC analysis. The synthesis of the four stereoisomers of GGsTop used chiral synthetic precursors that were separated by chiral HPLC on a preparative scale. With respect to the configuration of the α-carbon atom of the glutamate mimic, the l-isomer (k on =174M -1 s -1 ) was ca. 8-fold more potent than the d-isomer (k on =21.5M -1 s -1 ). In contrast, the configuration of the phosphorus atom is critical for GGT inhibitory activity. Based on a molecular modeling approach, the absolute configuration of the phosphorus atom of the active GGsTop isomers was postulated to be S P . The S P -isomers inhibited human GGT (k on =21.5-174M -1 s -1 ), while the R P -isomers were inactive even at concentrations of 0.1mM. Copyright © 2017 Elsevier Ltd. All rights reserved.

Molecular Recognition of Fluorine Impacts Substrate Selectivity in the Fluoroacetyl-CoA Thioesterase FlK

PubMed Central

2015-01-01

The fluoroacetate-producing bacterium Streptomyces cattleya has evolved a fluoroacetyl-CoA thioesterase (FlK) that exhibits a remarkably high level of discrimination for its cognate substrate compared to the cellularly abundant analogue acetyl-CoA, which differs only by the absence of the fluorine substitution. A major determinant of FlK specificity derives from its ability to take advantage of the unique properties of fluorine to enhance the reaction rate, allowing fluorine discrimination under physiological conditions where both substrates are likely to be present at saturating concentrations. Using a combination of pH–rate profiles, pre-steady-state kinetic experiments, and Taft analysis of wild-type and mutant FlKs with a set of substrate analogues, we explore the role of fluorine in controlling the enzyme acylation and deacylation steps. Further analysis of chiral (R)- and (S)-[2H1]fluoroacetyl-CoA substrates demonstrates that a kinetic isotope effect (1.7 ± 0.2) is observed for only the (R)-2H1 isomer, indicating that deacylation requires recognition of the prochiral fluoromethyl group to position the α-carbon for proton abstraction. Taken together, the selectivity for the fluoroacetyl-CoA substrate appears to rely not only on the enhanced polarization provided by the electronegative fluorine substitution but also on molecular recognition of fluorine in both formation and breakdown of the acyl-enzyme intermediate to control active site reactivity. These studies provide insights into the basis of fluorine selectivity in a naturally occurring enzyme–substrate pair, with implications for drug design and the development of fluorine-selective biocatalysts. PMID:24635371

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

Optical activity of helical quantum-dot supercrystals

NASA Astrophysics Data System (ADS)

Baimuratov, A. S.; Tepliakov, N. V.; Gun'ko, Yu. K.; Baranov, A. V.; Federov, A. V.; Rukhlenko, I. D.

2017-01-01

The size of chiral nanoparticles is much smaller than the optical wavelength. As a result, the difference in interaction of enantiomers with circularly polarized light of different handedness is practically unobservable. Due to the large mismatch in scale, the problem of enhancement of enantioselectivity of optical properties of nanoparticles is particularly important for modern photonics. In this work, we show that ordering of achiral nanoparticles into a chiral supercrystal with dimensions comparable to the wavelength of light allows achieving nearly total dissymmetry of optical absorption and demonstrate this using a helical super-crystal made of semiconductor quantum dots as an example. The proposed approach may find numerous applications in various optical and analytical methods used in biomedicine, chemistry, and pharmacology.

On the stereoselective aminoacylation of RNA

NASA Technical Reports Server (NTRS)

Usher, D. A.; Needels, M. C.

1984-01-01

Gabbay and Kleinman (1970) have found that stereospecific complex formation (noncovalent) occurs between nucleic acids and a number of derivatives of amino acids. However, until recently, chiral selection in any nonenzymatic RNA-aminoacylation reaction was unknown. Profy and Usher (1984) reported that aminoacylation of the 'internal' 2-prime-ester occurred with a significant amount of stereoselection. Profy and Usher (1984) have also observed that aminoacylation of the 'internal' 2-prime-hydroxyl groups of polyribonucleotides by the imidazolide of N-3,5-dinitrobenzoylalanine occurs with chiral selection. In order to obtain further information regarding the considered phenomena, a systematic investigation was initiated of the factors which contribute to the observed stereoselectivity of the aminoacylation reaction. In the present paper, the effect of a change in the amino acid from alanine to leucine is considered along with an investigation of the D- and L-alanyl internal' 2-prime esters of the dinucleoside monophosphate of 3-prime,5-prime-ApA.

Review of the Functions of Archimedes’ Spiral Metallic Nanostructures

PubMed Central

Li, Zixiang; Zhang, Jingran; Guo, Kai; Shen, Fei; Zhou, Qingfeng; Zhou, Hongping

2017-01-01

Here, we have reviewed some typical plasmonic structures based on Archimedes’ spiral (AS) architectures, which can produce polarization-sensitive focusing phenomenon and generate plasmonic vortices (PVs) carrying controllable orbital angular momentum (OAM) because of the relation between the incident polarized states and the chiralities of the spiral structures. These features can be used to analyze different circular polarization states, which has been one of the rapidly developing researching topics in nanophotonics in recent years. Many investigations demonstrate that the multifunctional spiral-based plasmonic structures are excellent choices for chiral selection and generating the transmitted field with well-defined OAM. The circular polarization extinction ratio, as an evaluation criterion for the polarization selectivity of a designed structure, could be effectively improved by properly modulating the parameters of spiral structures. Such functional spiral plasmonic nanostructures are promising for applications in analyzing circular polarization light, full Stokes vector polarimetric sensors, near-field imaging, and so on. PMID:29165382

Green chiral HPLC study of the stability of Chiralcel OD under high temperature liquid chromatography and subcritical water conditions.

PubMed

Droux, S; Roy, M; Félix, G

2014-10-01

We report here the study of the stability under subcritical water conditions of one of the most popular polysaccharide chiral stationary phase (CSP): Chiralcel OD. This CSP was used under high temperature and reversed phase conditions with acetonitrile and 2-propanol as modifier, respectively. The evolution of selectivity and resolution was investigated both in normal and reversed mode conditions with five racemates after packing, heating at 150 °C and separations of some racemic compounds under different high temperatures and mobile phase conditions. The results show that after using at high temperature and subcritical water conditions the selectivity was only moderately affected while the resolution fell dramatically especially in reversed mode due to the creation of a void at the head of the columns which reflects the dissolution of the silica matrix. Copyright © 2014 Elsevier B.V. All rights reserved.

Coherent Population Transfer in Chiral Molecules Using Tailored Microwave Pulses

NASA Astrophysics Data System (ADS)

Perez, Cristobal; Steber, Amanda; Domingos, Sergio R.; Krin, Anna; Schmitz, David; Schnell, Melanie

2017-06-01

Over the last years, microwave three-wave mixing (M3WM) experiments have been shown to provide a sensitive way to generate and measure enantiomer-specific molecular responses. These experiments opened the door for enantiomeric excess determination in complex samples without previous separation or purification. We present here a new type of experiment, based on M3WM, to achieve enantiomeric enrichment of a chiral sample by using microwave pulses. We will show that control over the relative phases and polarizations of pulses provides a way to selectively populate a specific quantum rotational state with an enantiomer of choice. The experimental implementation as well as the characterization of the observed enantiomer-selective responses will be presented and discussed. As a proof of concept and to showcase the applicability of our approach we will present the enantiomer enrichment of several terpenes. Sandra Eibenberger, John Doyle, and David Patterson, arXiv:1608.04691 (2016)

Unique Chiral Interpenetrating d-f Heterometallic MOFs as Luminescent Sensors.

PubMed

Wu, Zhi-Lei; Dong, Jie; Ni, Wei-Yan; Zhang, Bo-Wen; Cui, Jian-Zhong; Zhao, Bin

2015-06-01

One novel three-dimensional (3D) 3d-4f metal-organic framework (MOF), [TbZn(L)(CO3)2(H2O)]n (1) [HL = 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine], has been successfully synthesized and structurally characterized. Structural analysis shows that compound 1 features a unique chiral interpenetrating 3D framework for the first time. The resulting crystals of 1 are composed of enantiomers 1a (P41) and 1b (P43), as was clearly confirmed by the crystal structure and the corresponding circular dichroism (CD) analyses of eight randomly selected crystals. The investigations on CD spectra based on every single crystal clearly assigned the Cotton effect signals. The powder X-ray diffraction measurement of 1 after being immersed in common solvents reveals that 1 possess excellent solvent stability. Furthermore, luminescent studies imply that 1 displays highly selective luminescent sensing of aldehydes, such as formol, acetaldehyde, and propanal.

Electromagnetic transitions in multiple chiral doublet bands

NASA Astrophysics Data System (ADS)

Jia, Hui; Qi, Bin; Wang, Shou-Yu; Wang, Shuo; Liu, Chen

2016-12-01

Multiple chiral doublet bands (MχD) in the 80, 130 and 190 mass regions are studied by the model of γ = 90° triaxial rotor coupled with identical symmetric proton-neutron configurations. By selecting a suitable basis, the calculated wave functions are explicitly exhibited to be symmetric under the operator Â, which is defined as rotation by 90° about the 3-axis with the exchange of valance proton and neutron. We found that both M1 and E2 transitions are allowed between levels with different values of A, while they are forbidden between levels with same values of A. Such a selection rule holds true for MχD in different mass regions. Supported by National Natural Science Foundation of China (11675094, 11622540, 11545011, 11405096, 11461141001, U1432119), Shandong Natural Science Foundation (ZR2014AQ012), and Young Scholars Program of Shandong University, Weihai (2015WHWLJH01)

Hydrodynamic Effects in Soft-matter Self-assembly: The Case of J-Aggregates of Amphiphilic Porphyrins.

PubMed

Ribo, Josep M; El-Hachemi, Zoubir; Arteaga, Oriol; Canillas, Adolf; Crusats, Joaquim

2017-07-01

Chiral J-aggregates of achiral amphiphilic porphyrins (4-sulfonatophenyl and aryl meso-substituted porphyrins) show several effects under the hydrodynamic forces of common stirring. These effects can be classified as pure mechanic (e. g. elasticity, plasticity and breaking of the self-assembly non-covalent bonding) and chemically selective as detected in the formation/growth of the nanoparticles. Diastereoselective, enantioselective and, depending on the sign of chiral shear forces, even enantiospecific selections have been described. Some types of these effects have been reported in other type of J-aggregates. Reversible and irreversible structural effects have been studied by atomic force imaging. The determination of the optical polarization properties (linear and circular) of their solutions is best done using Mueller matrix polarimetry methods. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantioselective supercritical fluid chromatography-tandem mass spectrometry method for simultaneous estimation of risperidone and its 9-hydroxyl metabolites in rat plasma.

PubMed

Prasad, Thatipamula R; Joseph, Siji; Kole, Prashant; Kumar, Anoop; Subramanian, Murali; Rajagopalan, Sudha; Kr, Prabhakar

2017-11-01

Objective of the current work was to develop a 'green chemistry' compliant selective and sensitive supercritical fluid chromatography-tandem mass spectrometry method for simultaneous estimation of risperidone (RIS) and its chiral metabolites in rat plasma. Methodology & results: Agilent 1260 Infinity analytical supercritical fluid chromatography system resolved RIS and its chiral metabolites within runtime of 6 min using a gradient chromatography method. Using a simple protein precipitation sample preparation followed by mass spectrometric detection achieved a sensitivity of 0.92 nM (lower limit of quantification). With linearity over four log units (0.91-7500 nM), the method was found to be selective, accurate, precise and robust. The method was validated and was successfully applied for simultaneous estimation of RIS and 9-hydroxyrisperidone metabolites (R & S individually) after intravenous and per oral administration to rats.

Development of a composite chiral stationary phase from BSA and β-cyclodextrin-bonded silica.

PubMed

Yao, Bixia; Yang, Xinmei; Guo, Lizhen; Kang, Shanshan; Weng, Wen

2014-01-01

A composite chiral stationary phase (CSP) derived from bovine serum albumin (BSA) and β-cyclodextrin (CD)-bonded silica was prepared. 2,4,6-Trichloro-1,3,5-triazine was used as a cross-linker. The obtained CSP was applied to the enantioseparation of tryptophan, hydrobenzoin, phenylalanine and mandelic acid. The influences of eluent pH value, organic modifier and column temperature on the retention and enantioseparation were discussed. Tryptophan and hydrobenzoin achieved excellent resolution on the composite CSP. For tryptophan, the highest selectivity, 2.79, was achieved with 1% of methanol at pH 8.0. For hydrobenzoin, the selectivity could reach 1.42. The chromatographic results were compared with that on β-CD-bonded or BSA-immobilized CSP. © The Author [2014]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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.

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.

Effect of additives on eremomycin sorbent selectivity in separation of salbutamol enantiomers using supercritical fluid chromatography

NASA Astrophysics Data System (ADS)

Pokrovskiy, O. I.; Kayda, A. S.; Usovich, O. I.; Parenago, O. O.; Lunin, V. V.

2017-11-01

A regime is found in which chiral stationary phase based on macrocyclic glycopeptide eremomycin allows separation of salbutamol sulfate enantiomers in supercritical fluid chromatography. Enantioseparation occurs only when two dynamic modifiers are used simultaneously: isopropylamin + trifluoroacetic acid or isopropylamin + ammonium acetate. Amine molar concentration in mobile phase has to be higher than acid molar concentration, otherwise enantiomers coelute. We suppose that with amine excess a mechanism of enantiorecognition is realized which involves ionic sorbent-sorbate interactions. Such mechanism is well-known for glycopeptide chiral selectors in liquid chromatography, but for supercritical fluid chromatography it is reported for the first time.

Ring-Opening Polymerization of rac-Lactide with Aluminum Chiral Anilido-Oxazolinate Complexes

PubMed Central

2015-01-01

A series of dimethylaluminum complexes (L1a–i)AlMe2 (2a–i, where HL1a–i = 2-(2′-ArNH)phenyl-4-R1-oxazoline) bearing chiral, bidentate anilido-oxazolinate ligands have been prepared and characterized. Six of the complexes, in the presence of an alcohol cocatalyst, are shown to be active initiators for the stereoselective ring-opening polymerization of rac-lactide in toluene solution and under bulk conditions, yielding polylactides with a range of tacticity from slightly isotactic to moderately heterotactic. The reactivity and selectivity of these catalysts are discussed on the basis of the effect of their substituents. PMID:24891754

Enantioselective Synthesis of SNAP-7941

PubMed Central

Goss, Jennifer M.; Schaus, Scott E.

2009-01-01

An enantioselective synthesis of SNAP-7941, a potent melanin concentrating hormone receptor antagonist, was achieved using two organocatalytic methods. The first method utilized to synthesize the enantioenriched dihydropyrimidone core was the Cinchona alkaloid-catalyzed Mannich reaction of β-keto esters to acyl imines and the second was chiral phosphoric acid-catalyzed Biginelli reaction. Completion of the synthesis was accomplished via selective urea formation at the N3 position of the dihydropyrimidone with the 3-(4-phenylpiperidin-1-yl)propyl amine side chain fragment. The synthesis of SNAP-7921 highlights the utility of asymmetric organocatalytic methods in the construction of an important class of chiral heterocycles. PMID:18767801

Asymmetric synthesis of 5-arylcyclohexenones by rhodium(I)-catalyzed conjugate arylation of racemic 5-(trimethylsilyl)cyclohexenone with arylboronic acids.

PubMed

Chen, Qian; Kuriyama, Masami; Soeta, Takahiro; Hao, Xinyu; Yamada, Ken-ichi; Tomioka, Kiyoshi

2005-09-29

[reaction: see text] A catalytic asymmetric conjugate arylation of racemic 5-(trimethylsilyl)cyclohex-2-enone with arylboronic acids was catalyzed by 3 mol % chiral amidophosphane- or BINAP-Rh(I) in dioxane-water (10:1) to afford trans- and cis-3-aryl-5-(trimethylsilyl)cyclohexanones in high enantioselectivity. Dehydrosilylation of the product mixture with cupric chloride in DMF gave 5-arylcyclohex-2-enones with up to 93% ee in good yield. Enantiofacial selectivity with chiral phosphane-Rh(I) exceeds the trans-diastereoselectivity that is maintained in the achiral or racemic phosphane-Rh(I)-catalyzed conjugate arylation of 5-(trimethylsilyl)cyclohexenone.

Diastereoselective auxiliary- and catalyst-controlled intramolecular aza-Michael reaction for the elaboration of enantioenriched 3-substituted isoindolinones. Application to the synthesis of a new pazinaclone analogue

PubMed Central

Sallio, Romain; Lebrun, Stéphane; Capet, Frédéric; Agbossou-Niedercorn, Francine

2018-01-01

A new asymmetric organocatalyzed intramolecular aza-Michael reaction by means of both a chiral auxiliary and a catalyst for stereocontrol is reported for the synthesis of optically active isoindolinones. A selected cinchoninium salt was used as phase-transfer catalyst in combination with a chiral nucleophile, a Michael acceptor and a base to provide 3-substituted isoindolinones in good yields and diastereomeric excesses. This methodology was applied to the asymmetric synthesis of a new pazinaclone analogue which is of interest in the field of benzodiazepine-receptor agonists. PMID:29623121

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.

Iron(II)-catalyzed intramolecular aminohydroxylation of olefins with functionalized hydroxylamines.

PubMed

Liu, Guan-Sai; Zhang, Yong-Qiang; Yuan, Yong-An; Xu, Hao

2013-03-06

A diastereoselective aminohydroxylation of olefins with a functionalized hydroxylamine is catalyzed by new iron(II) complexes. This efficient intramolecular process readily affords synthetically useful amino alcohols with excellent selectivity (dr up to > 20:1). Asymmetric catalysis with chiral iron(II) complexes and preliminary mechanistic studies reveal an iron nitrenoid is a possible intermediate that can undergo either aminohydroxylation or aziridination, and the selectivity can be controlled by careful selection of counteranion/ligand combinations.

Recycling Frank: Spontaneous emergence of homochirality in noncatalytic systems

PubMed Central

Plasson, Raphaël; Bersini, Hugues; Commeyras, Auguste

2004-01-01

In this work, we introduce a prebiotically relevant protometabolic pattern corresponding to an engine of deracemization by using an external energy source. The spontaneous formation of a nonracemic mixture of chiral compounds can be observed in out-of-equilibrium systems via a symmetry-breaking phenomenon. This observation is possible thanks to chirally selective autocatalytic reactions (Frank's model) [Frank, F. C. (1953) Biochim. Biophys. Acta 11, 459–463]. We show that the use of a Frank-like model in a recycled system composed of reversible chemical reactions, rather than the classical irreversible system, allows for the emergence of a synergetic autoinduction from simple reactions, without any autocatalytic or even catalytic reaction. This model is described as a theoretical framework, based on the stereoselective reactivity of preexisting chiral monomeric building blocks (polymerization, epimerization, and depolymerization) maintained out of equilibrium by a continuous energy income, via an activation reaction. It permits the self-conversion of all monomeric subunits into a single chiral configuration. Real prebiotic systems of amino acid derivatives can be described on this basis. They are shown to be able to spontaneously reach a stable nonracemic state in a few centuries. In such systems, the presence of epimerization reactions is no more destructive, but in contrast is the central driving force of the unstabilization of the racemic state. PMID:15548617

The thermodynamic parameters of sorption and enantioselectivity of the chiral smectic liquid crystal 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid

NASA Astrophysics Data System (ADS)

Onuchak, L. A.; Stepanova, R. F.; Akopova, O. B.; Glebova, O. V.; Chernova, O. M.

2008-06-01

The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and optical isomers of camphene and butanediol-2,3 by a chiral smectic liquid crystal, 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid, from the gas phase were studied over the temperature range including the S*C and S*A mesophases and isotropic phase. The standard and excess thermodynamic functions of sorption were determined for 26 sorbates of the classes of substances specified. The S*C and S*A mesophases exhibited selectivity with respect to the separation of para and meta xylenes (α p/m = 1.06 1.07, 90 108°C) and pronounced enantioselectivity (αR/S = 1.05 1.09, 87 108°C). The helically twisted structure of the smectic liquid crystal was shown to play an important role in the mechanism of the chiral recognition of optical isomers of polar and low-polarity compounds under gas-liquid chromatography conditions.

Defect topologies in chiral liquid crystals confined to mesoscopic channels

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

Schlotthauer, Sergej, E-mail: s.schlotthauer@mailbox.tu-berlin.de; Skutnik, Robert A.; Stieger, Tillmann

2015-05-21

We present Monte Carlo simulations in the grand canonical and canonical ensembles of a chiral liquid crystal confined to mesochannels of variable sizes and geometries. The mesochannels are taken to be quasi-infinite in one dimension but finite in the two other directions. Under thermodynamic conditions chosen and for a selected value of the chirality coupling constant, the bulk liquid crystal exhibits structural characteristics of a blue phase II. This is established through the tetrahedral symmetry of disclination lines and the characteristic simple-cubic arrangement of double-twist helices formed by the liquid-crystal molecules along all three axes of a Cartesian coordinate system.more » If the blue phase II is then exposed to confinement, the interplay between its helical structure, various anchoring conditions at the walls of the mesochannels, and the shape of the mesochannels gives rise to a broad variety of novel, qualitative disclination-line structures that are reported here for the first time.« less

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.

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.

A diversity oriented synthesis of natural product inspired molecular libraries.

PubMed

Chauhan, Jyoti; Luthra, Tania; Gundla, Rambabu; Ferraro, Antonio; Holzgrabe, Ulrike; Sen, Subhabrata

2017-11-07

Natural products are the source of innumerable pharmaceutical drug candidates and also form an important aspect of herbal remedies. They are also a source of various bioactive compounds. Herein we have leveraged the structural attributes of several natural products in building a library of architecturally diverse chiral molecules by harnessing R-tryptophan as the chiral auxiliary. It is converted to its corresponding methyl ester 1 which in turn provided a bevy of 1-aryl-tetrahydro-β-carbolines 2a-d, which were then converted to chiral compounds via a diversity oriented synthetic strategy (DOS). In general, intermolecular and intramolecular ring rearrangements facilitated the formation of the final compounds. Four different classes of molecules with distinct architectures were generated, adding up to nearly twenty-two individual molecules. Phenotypic screening of a representative section of the library revealed two molecules that selectively inhibit MCF7 breast cancer cells with IC 50 of ∼5 μg mL -1 potency.

Chiral Selectivity as a Bridge to Homochirality

NASA Technical Reports Server (NTRS)

Burton, A. S.; Berger, E. L.

2017-01-01

In abiotic reactions, equal mixtures of L- and D- amino acid enantiomers are produced unless conditions that favor one enantiomer over the other are present. Understanding how the transition from racemic, abiotic chemistry to homochiral polymers used in proteins occurred is fundamental to our understanding of the origins of life on Earth and the search for signs of life elsewhere, but this transition is still poorly understood. We have begun investigations into whether enantiopure amino acid pools are a necessary condition, or if the polymerization process itself can impart some added degree of stereoselectivity. More specifically, we are exploring the polymerization behavior of chiral amino acids to determine if they show a preference for homochiral or heterochiral polymerization. We are also determining the effects of different amino acid chiral ratios (L greater than D) to determine at what level of enantiomeric enrichment homochiral peptides become predominant. These data will allow us to evaluate the plausibility of homochiral polymers arising by known abiotic mechanisms.

Tunable Optical Polymer Systems (TOPS)

DTIC Science & Technology

2001-05-01

pixelation o1 displays is done. One team member has combined this work with self-assembling layers so that it is possible to make three-dimensional...I THERMOCHROMISM I ELECTROCHEMILUMINESCENCE (ECL) I MAGNETOCHROMISM I TUNABLE ELECTROLUMINESCENCE (EL) PROTONIC BAND GAP (PBG) SELECTIVE...via Selective Reflection • Chiral-nematic liquid crystalline film as a helical stack of quasinematic layers , illustrated below with a LH structure

Static weak dipole moments of the τ lepton via renormalizable scalar leptoquark interactions

NASA Astrophysics Data System (ADS)

Bolaños, A.; Moyotl, A.; Tavares-Velasco, G.

2014-03-01

The weak dipole moments of elementary fermions are calculated at the one-loop level in the framework of a renormalizable scalar leptoquark model that forbids baryon number violating processes and so is free from the strong constraints arising from experimental data. In this model there are two scalar leptoquarks accommodated in a SUL(2)×UY(1) doublet: One of these leptoquarks is nonchiral and has electric charge of 5/3e, whereas the other one is chiral and has electric charge 2/3e. In particular, a nonchiral leptoquark contributes to the weak properties of an up fermion via a chirality-flipping term proportional to the mass of the virtual fermion, and can also induce a nonzero weak electric dipole moment provided that the leptoquark couplings are complex. The numerical analysis is focused on the weak properties of the τ lepton since they offer good prospects for experimental study. The constraints on leptoquark couplings are briefly discussed for a nonchiral leptoquark with nondiagonal couplings to the second and third fermion generations, a third-generation nonchiral leptoquark, and a third-generation chiral leptoquark. It is found that although the chirality-flipping term can enhance the weak properties of the τ lepton via the top quark contribution, such an enhancement would be offset by the strong constraints on the leptoquark couplings. So, the contribution of scalar leptoquarks to the weak magnetic dipole moment of the τ lepton are smaller than the standard model (SM) contributions but can be of similar size to those arising in some SM extensions. A nonchiral leptoquark can also give contributions to the weak electric dipole moment larger than the SM one but well below the experimental limit. We also discuss the case of the off-shell weak dipole moments and, for completeness, analyze the behavior of the τ electromagnetic properties.

Dissecting the Dynamic Pathways of Stereoselective DNA Threading Intercalation

PubMed Central

Almaqwashi, Ali A.; Andersson, Johanna; Lincoln, Per; Rouzina, Ioulia; Westerlund, Fredrik; Williams, Mark C.

2016-01-01

DNA intercalators that have high affinity and slow kinetics are developed for potential DNA-targeted therapeutics. Although many natural intercalators contain multiple chiral subunits, only intercalators with a single chiral unit have been quantitatively probed. Dumbbell-shaped DNA threading intercalators represent the next order of structural complexity relative to simple intercalators, and can provide significant insights into the stereoselectivity of DNA-ligand intercalation. We investigated DNA threading intercalation by binuclear ruthenium complex [μ-dppzip(phen)4Ru2]4+ (Piz). Four Piz stereoisomers are defined by the chirality of the intercalating subunit (Ru(phen)2dppz) and the distal subunit (Ru(phen)2ip), respectively, each of which can be either right-handed (Δ) or left-handed (Λ). We used optical tweezers to measure single DNA molecule elongation due to threading intercalation, revealing force-dependent DNA intercalation rates and equilibrium dissociation constants. The force spectroscopy analysis provided the zero-force DNA binding affinity, the equilibrium DNA-ligand elongation Δxeq, and the dynamic DNA structural deformations during ligand association xon and dissociation xoff. We found that Piz stereoisomers exhibit over 20-fold differences in DNA binding affinity, from a Kd of 27 ± 3 nM for (Δ,Λ)-Piz to a Kd of 622 ± 55 nM for (Λ,Δ)-Piz. The striking affinity decrease is correlated with increasing Δxeq from 0.30 ± 0.02 to 0.48 ± 0.02 nm and xon from 0.25 ± 0.01 to 0.46 ± 0.02 nm, but limited xoff changes. Notably, the affinity and threading kinetics is 10-fold enhanced for right-handed intercalating subunits, and 2- to 5-fold enhanced for left-handed distal subunits. These findings demonstrate sterically dispersed transition pathways and robust DNA structural recognition of chiral intercalators, which are critical for optimizing DNA binding affinity and kinetics. PMID:27028636

Interplay of Metalloligand and Organic Ligand to Tune Micropores within Isostructural Mixed-Metal Organic Frameworks (M MOFs) for Their Highly Selective Separation of Chiral and Achiral Small Molecules

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

Madhab, Das; He, Yabing; Kim, Jaheon

2012-01-01

Four porous isostructural mixed-metal-organic frameworks (M'MOFs) have been synthesized and structurally characterized. The pores within these M'MOFs are systematically tuned by the interplay of both the metalloligands and organic ligands which have enabled us not only to direct their highly selective separation of chiral alcohols 1-phenylethanol (PEA), 2-butanol (BUT), and 2-pentanol (2-PEN) with the highest ee up to 82.4% but also to lead highly selective separation of achiral C{sub 2}H{sub 2}/C{sub 2}H{sub 4} separation. The potential application of these M'MOFs for the fixed bed pressure swing adsorption (PSA) separation of C{sub 2}H{sub 2}/C{sub 2}H{sub 4} has been further examined andmore » compared by the transient breakthrough simulations in which the purity requirement of 40 ppm in the outlet gas can be readily fulfilled by the fixed bed M'MOF-4a adsorber at ambient conditions.« less

Enantioselective Determination of Polycyclic Musks in River and Wastewater by GC/MS/MS

PubMed Central

Lee, Injung; Gopalan, Anantha-Iyengar; Lee, Kwang-Pill

2016-01-01

The separation of chiral compounds is an interesting and challenging topic in analytical chemistry, especially in environmental fields. Enantioselective degradation or bioaccumulation has been observed for several chiral pollutants. Polycyclic musks are chiral and are widely used as fragrances in a variety of personal care products such as soaps, shampoos, cosmetics and perfumes. In this study, the gas chromatographic separation of chiral polycyclic musks, 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclo-penta-γ-2-benzopyrane (HHCB), 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetra-hydronaphthalene (AHTN), 6-acetyl-1,1,2,3,3,5-hexamethylindane (AHDI), 5-acetyl-1,1,2,6-tetramethyl-3-iso-propylindane (ATII), and 6,7-dihydro-1,1,2,3,3-pentamethyl-4(5H)-indanone (DPMI) was achieved on modified cyclodextrin stationary phase (heptakis (2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl-β-CD in DV-1701)). Separation techniques are coupled to tandem mass spectrometry (MS-MS), as it provides the sensitivity and selectivity needed. River and wastewaters (influents and effluents of wastewater treatment plants (WWTPs)) in the Nakdong River were investigated with regard to the concentrations and the enantiomeric ratios of polycyclic musks. HHCB was most frequently detected in river and wastewaters, and an enantiomeric enrichment was observed in the effluents of one of the investigated wastewater treatment plants (WWTPs). We reported the contamination of river and wastewaters in Korea by chiral polycyclic musks. The results of this investigation suggest that enantioselective transformation may occur during wastewater treatment. PMID:27011195

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.

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.

Mid-infrared Plasmonic Circular Dichroism Generated by Graphene Nanodisk Assemblies.

PubMed

Kong, Xiang-Tian; Zhao, Runbo; Wang, Zhiming; Govorov, Alexander O

2017-08-09

It is very interesting to bring plasmonic circular dichroism spectroscopy to the mid-infrared spectral interval, and there are two reasons for this. This spectral interval is very important for thermal bioimaging, and simultaneously, this spectral range includes vibrational lines of many chiral biomolecules. Here we demonstrate that graphene plasmons indeed offer such opportunity. In particular, we show that chiral graphene assemblies consisting of a few graphene nanodisks can generate strong circular dichroism (CD) in the mid-infrared interval. The CD signal is generated due to the plasmon-plasmon coupling between adjacent nanodisks in the specially designed chiral graphene assemblies. Because of the large dimension mismatch between the thickness of a graphene layer and the incoming light's wavelength, three-dimensional configurations with a total height of a few hundred nanometers are necessary to obtain a strong CD signal in the mid-infrared range. The mid-infrared CD strength is mainly governed by the total dimensions (total height and helix scaffold radius) of the graphene nanodisk assembly and by the plasmon-plasmon interaction strength between its constitutive nanodisks. Both positive and negative CD bands can be observed in the graphene assembly array. The frequency interval of the plasmonic CD spectra overlaps with the vibrational modes of some important biomolecules, such as DNA and many different peptides, giving rise to the possibility of enhancing the vibrational optical activity of these molecular species by attaching them to the graphene assemblies. Simultaneously the spectral range of chiral mid-infrared plasmons in our structures appears near the typical wavelength of the human-body thermal radiation, and therefore, our chiral metastructures can be potentially utilized as optical components in thermal imaging devices.

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.

Constraints on the s - s bar asymmetry of the proton in chiral effective theory

NASA Astrophysics Data System (ADS)

Wang, X. G.; Ji, Chueng-Ryong; Melnitchouk, W.; Salamu, Y.; Thomas, A. W.; Wang, P.

2016-11-01

We compute the s - s bar asymmetry in the proton in chiral effective theory, using phenomenological constraints based upon existing data. Unlike previous meson cloud model calculations, which accounted for kaon loop contributions with on-shell intermediate states alone, this work includes off-shell terms and contact interactions, which impact the shape of the s - s bar difference. We identify a valence-like component of s (x) which is balanced by a δ-function contribution to s bar (x) at x = 0, so that the integrals of s and s bar over the experimentally accessible region x > 0 are not equal. Using a regularization procedure that preserves chiral symmetry and Lorentz invariance, we find that existing data limit the integrated value of the second moment of the asymmetry to the range - 0.07 ×10-3 ≤ < x (s - s bar) > ≤ 1.12 ×10-3 at a scale of Q2 = 1 GeV2. This is too small to account for the NuTeV anomaly and of the wrong sign to enhance it.

DISTRIBUTION OF CHIRAL PCBS IN SELECTED TISSUES IN THE LABORATORY RAT

EPA Science Inventory

Polychlorinated biphenyls (PCBs) were manufactured for a large number of technical applications including for use in transformers and capacitors. The widespread commercial utilization of PCBs and their persistence in the environment have resulted in their worldwide distribution. ...

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.

Development of Bottom-Up Chemical Approaches to 3-D Negative Index Meta-Materials: Two Photon Lithographic Approach-Chiral Chemical Synthesis Approach

DTIC Science & Technology

2014-06-30

2014). 15. F. Alali, Y.H. Kim, A. Baev, E.P Furlani, "Plasmon-enhanced Metasurfaces for Controlling Optical Polarization," ACS Photonics 1(6), 507-515 (2014). DISTRIBUTION A: Distribution approved for public release.

Turning Cucurbit[8]uril into a Supramolecular Nanoreactor for Asymmetric Catalysis

PubMed Central

Zheng, Lifei; Sonzini, Silvia; Ambarwati, Masyitha; Rosta, Edina

2015-01-01

Abstract Chiral macromolecules have been widely used as synthetic pockets to mimic natural enzymes and promote asymmetric reactions. An achiral host, cucurbit[8]uril (CB[8]), was used for an asymmetric Lewis acid catalyzed Diels–Alder reaction. We achieved a remarkable increase in enantioselectivity and a large rate acceleration in the presence of the nanoreactor by using an amino acid as the chiral source. Mechanistic and computational studies revealed that both the amino acid–Cu2+ complex and the dienophile substrate are included inside the macrocyclic host cavity, suggesting that contiguity and conformational constraints are fundamental to the catalytic process and rate enhancement. These results pave the way towards new studies on asymmetric reactions catalyzed in confined achiral cavities. PMID:27478269

Turning Cucurbit[8]uril into a Supramolecular Nanoreactor for Asymmetric Catalysis

PubMed Central

Zheng, Lifei; Sonzini, Silvia; Ambarwati, Masyitha; Rosta, Edina; Scherman, Oren A; Herrmann, Andreas

2015-01-01

Chiral macromolecules have been widely used as synthetic pockets to mimic natural enzymes and promote asymmetric reactions. An achiral host, cucurbit[8]uril (CB[8]), was used for an asymmetric Lewis acid catalyzed Diels–Alder reaction. We achieved a remarkable increase in enantioselectivity and a large rate acceleration in the presence of the nanoreactor by using an amino acid as the chiral source. Mechanistic and computational studies revealed that both the amino acid–Cu2+ complex and the dienophile substrate are included inside the macrocyclic host cavity, suggesting that contiguity and conformational constraints are fundamental to the catalytic process and rate enhancement. These results pave the way towards new studies on asymmetric reactions catalyzed in confined achiral cavities. PMID:26383272

High-Throughput Nanofabrication of Infra-red and Chiral Metamaterials using Nanospherical-Lens Lithography

PubMed Central

Chang, Yun-Chorng; Lu, Sih-Chen; Chung, Hsin-Chan; Wang, Shih-Ming; Tsai, Tzung-Da; Guo, Tzung-Fang

2013-01-01

Various infra-red and planar chiral metamaterials were fabricated using the modified Nanospherical-Lens Lithography. By replacing the light source with a hand-held ultraviolet lamp, its asymmetric light emission pattern produces the elliptical-shaped photoresist holes after passing through the spheres. The long axis of the ellipse is parallel to the lamp direction. The fabricated ellipse arrays exhibit localized surface plasmon resonance in mid-infra-red and are ideal platforms for surface enhanced infra-red absorption (SEIRA). We also demonstrate a way to design and fabricate complicated patterns by tuning parameters in each exposure step. This method is both high-throughput and low-cost, which is a powerful tool for future infra-red metamaterials applications. PMID:24284941

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.

Stereodivergent catalytic doubly diastereoselective nitroaldol reactions using heterobimetallic complexes.

PubMed

Sohtome, Yoshihiro; Kato, Yuko; Handa, Shinya; Aoyama, Naohiro; Nagawa, Keita; Matsunaga, Shigeki; Shibasaki, Masakatsu

2008-06-05

Stereodivergent construction of three contiguous stereocenters in catalytic doubly diastereoselective nitroaldol reactions of alpha-chiral aldehydes with nitroacetaldehyde dimethyl acetal using two types of heterobimetallic catalysts is described. A La-Li-BINOL (LLB) catalyst afforded anti,syn-nitroaldol products in >20:1-14:1 selectivity, and a Pd/La/Schiff base catalyst afforded complimentary syn,syn-nitroaldol products in 10:1-5:1 selectivity.

Chirality-Controlled Synthesis and Applications of Single-Wall Carbon Nanotubes.

PubMed

Liu, Bilu; Wu, Fanqi; Gui, Hui; Zheng, Ming; Zhou, Chongwu

2017-01-24

Preparation of chirality-defined single-wall carbon nanotubes (SWCNTs) is the top challenge in the nanotube field. In recent years, great progress has been made toward preparing single-chirality SWCNTs through both direct controlled synthesis and postsynthesis separation approaches. Accordingly, the uses of single-chirality-dominated SWCNTs for various applications have emerged as a new front in nanotube research. In this Review, we review recent progress made in the chirality-controlled synthesis of SWCNTs, including metal-catalyst-free SWCNT cloning by vapor-phase epitaxy elongation of purified single-chirality nanotube seeds, chirality-specific growth of SWCNTs on bimetallic solid alloy catalysts, chirality-controlled synthesis of SWCNTs using bottom-up synthetic strategy from carbonaceous molecular end-cap precursors, etc. Recent major progresses in postsynthesis separation of single-chirality SWCNT species, as well as methods for chirality characterization of SWCNTs, are also highlighted. Moreover, we discuss some examples where single-chirality SWCNTs have shown clear advantages over SWCNTs with broad chirality distributions. We hope this review could inspire more research on the chirality-controlled preparation of SWCNTs and equally important inspire the use of single-chirality SWCNT samples for more fundamental studies and practical applications.

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.

Circular polarization analyzer with polarization tunable focusing of surface plasmon polaritons

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

Wang, Sen; Zhang, Yan, E-mail: yzhang@mail.cnu.edu.cn; Beijing Key Laboratory for Metamaterials and Devices, and Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048

2015-12-14

A practical circular polarization analyzer (CPA) that can selectively focus surface plasmon polaritons (SPPs) at two separate locations, according to the helicity of the circularly polarized light, is designed and experimentally verified in the terahertz frequency range. The CPA consists of fishbone-slit units and is designed using the simulated annealing algorithm. By differentially detecting the intensities of the two SPPs focuses, the helicity of the incident circularly polarized light can be obtained and the CPA is less vulnerable to the noise of incident light. The proposed device may also have wide potential applications in chiral SPPs photonics and the analysismore » of chiral molecules in biology.« less

Asymmetric cooperative catalysis of strong Brønsted acid-promoted reactions using chiral ureas.

PubMed

Xu, Hao; Zuend, Stephan J; Woll, Matthew G; Tao, Ye; Jacobsen, Eric N

2010-02-19

Cationic organic intermediates participate in a wide variety of useful synthetic transformations, but their high reactivity can render selectivity in competing pathways difficult to control. Here, we describe a strategy for inducing enantioselectivity in reactions of protio-iminium ions, wherein a chiral catalyst interacts with the highly reactive intermediate through a network of noncovalent interactions. This interaction leads to an attenuation of the reactivity of the iminium ion and allows high enantioselectivity in cycloadditions with electron-rich alkenes (the Povarov reaction). A detailed experimental and computational analysis of this catalyst system has revealed the precise nature of the catalyst-substrate interactions and the likely basis for enantioinduction.

Asymmetric Cooperative Catalysis of Strong Brønsted Acid-Promoted Reactions Using Chiral Ureas

PubMed Central

Xu, Hao; Zuend, Stephan J.; Woll, Matthew G.; Tao, Ye; Jacobsen, Eric N.

2010-01-01

Cationic organic intermediates participate in a wide variety of useful synthetic transformations, but their high reactivity can render selectivity in competing pathways difficult to control. We describe a strategy for inducing enantioselectivity in reactions of protio-iminium ions, wherein a chiral catalyst interacts with the highly reactive intermediate through a network of non-covalent interactions. This leads to an attenuation of the reactivity of the iminium ion, and allows high enantioselectivity in cycloadditions with electron-rich alkenes (the Povarov reaction). A detailed experimental and computational analysis of this catalyst system has revealed the precise nature of the catalyst-substrate interactions and the likely basis for enantioinduction. PMID:20167783

Light scattering by magnons in whispering gallery mode cavities

NASA Astrophysics Data System (ADS)

Sharma, Sanchar; Blanter, Yaroslav M.; Bauer, Gerrit E. W.

2017-09-01

Brillouin light scattering is an established technique to study magnons, the elementary excitations of a magnet. Its efficiency can be enhanced by cavities that concentrate the light intensity. Here, we theoretically study inelastic scattering of photons by a magnetic sphere that supports optical whispering gallery modes in a plane normal to the magnetization. Magnons with low angular momenta scatter the light in the forward direction with a pronounced asymmetry in the Stokes and the anti-Stokes scattering strength, consistent with earlier studies. Magnons with large angular momenta constitute Damon-Eschbach modes which are shown to inelastically reflect light. The reflection spectrum contains either a Stokes or anti-Stokes peak, depending on the direction of the magnetization, a selection rule that can be explained by the chirality of the Damon-Eshbach magnons. The controllable energy transfer can be used to manage the thermodynamics of the magnet by light.

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.

Hierarchical chirality transfer in the growth of Towel Gourd tendrils

PubMed Central

Wang, Jian-Shan; Wang, Gang; Feng, Xi-Qiao; Kitamura, Takayuki; Kang, Yi-Lan; Yu, Shou-Wen; Qin, Qing-Hua

2013-01-01

Chirality plays a significant role in the physical properties and biological functions of many biological materials, e.g., climbing tendrils and twisted leaves, which exhibit chiral growth. However, the mechanisms underlying the chiral growth of biological materials remain unclear. In this paper, we investigate how the Towel Gourd tendrils achieve their chiral growth. Our experiments reveal that the tendrils have a hierarchy of chirality, which transfers from the lower levels to the higher. The change in the helical angle of cellulose fibrils at the subcellular level induces an intrinsic torsion of tendrils, leading to the formation of the helical morphology of tendril filaments. A chirality transfer model is presented to elucidate the chiral growth of tendrils. This present study may help understand various chiral phenomena observed in biological materials. It also suggests that chirality transfer can be utilized in the development of hierarchically chiral materials having unique properties. PMID:24173107

Direct Detection of Hardly Detectable Hidden Chirality of Hydrocarbons and Deuterated Isotopomers by a Helical Polyacetylene through Chiral Amplification and Memory.

PubMed

Maeda, Katsuhiro; Hirose, Daisuke; Okoshi, Natsuki; Shimomura, Kouhei; Wada, Yuya; Ikai, Tomoyuki; Kanoh, Shigeyoshi; Yashima, Eiji

2018-03-07

We report the first direct chirality sensing of a series of chiral hydrocarbons and isotopically chiral compounds (deuterated isotopomers), which are almost impossible to detect by conventional optical spectroscopic methods, by a stereoregular polyacetylene bearing 2,2'-biphenol-derived pendants. The polyacetylene showed a circular dichroism due to a preferred-handed helix formation in response to the hardly detectable hidden chirality of saturated tertiary or chiroptical quaternary hydrocarbons, and deuterated isotopomers. In sharp contrast to the previously reported sensory systems, the chirality detection by the polyacetylene relies on an excess one-handed helix formation induced by the chiral hydrocarbons and deuterated isotopomers via significant amplification of the chirality followed by its static memory, through which chiral information on the minute and hidden chirality can be stored as an excess of a single-handed helix memory for a long time.

Chiral Recognition and Separation by Chirality-Enriched Metal-Organic Frameworks.

PubMed

Das, Saikat; Xu, Shixian; Ben, Teng; Qiu, Shilun

2018-05-16

Endowed with chiral channels and pores, chiral metal-organic frameworks (MOFs) are highly useful; however, their synthesis remains a challenge given that most chiral building blocks are expensive. Although MOFs with induced chirality have been reported to avoid this shortcoming, no study providing evidence for the ee value of such MOFs has yet been reported. We herein describe the first study on the efficiency of chiral induction in MOFs using inexpensive achiral building blocks and fully recoverable chiral dopants to control the handedness of racemic MOFs. This method yielded chirality-enriched MOFs with accessible pores. The ability of the materials to form host-guest complexes was probed with enantiomers of varying size and coordination and in solvents with varying polarity. Furthermore, mixed-matrix membranes (MMMs) composed of chirality-enriched MOF particles dispersed in a polymer matrix demonstrated a new route for chiral separation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Combined use of chiral ionic liquid surfactants and neutral cyclodextrins: evaluation of ionic liquid head groups for enantioseparation of neutral compounds in capillary electrophoresis.

PubMed

Liu, Yijin; Shamsi, Shahab A

2014-09-19

Cyclodextrins (CDs) are most commonly used chiral selectors in capillary electrophoresis (CE). Although the use of neutral CDs and its derivatives have shown to resolve plethora of charged enantiomers, they cannot resolve neutral enantiomers. The use of ionic liquids (ILs) surfactants forming successful complex with CDs present itself an opportunity to resolve neutral enantiomers. In this work, the effect of IL head groups and their complexation ability with heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin (TM-β-CD) was studied for the separation of neutral enantiomers by CE. First, cationic IL type surfactants with different chiral head groups were synthesized. Physicochemical properties such as critical micelle concentration were determined by surface tension, whereas aggregation and polarity were determined by fluorescence spectroscopy. The complexation ability of ILs with TM-β-CD was characterized in the gas phase by CE-mass spectrometry. The influence of the type of ILs head group and its concentration on chiral resolution, resolution per unit time and selectivity were investigated for four structurally diverse neutral compounds. The binding constants of the neutral analytes to the IL-CD complex were estimated by y-reciprocal method. The hydrophobicity of the side chain of the IL head group displayed significant effect on the binding constants and enantioseparations. Copyright © 2014 Elsevier B.V. All rights reserved.

Analytical and semipreparative chiral separation of cis-itraconazole on cellulose stationary phases by high-performance liquid chromatography.

PubMed

Kurka, Ondřej; Kučera, Lukáš; Bednář, Petr

2016-07-01

cis-Itraconazole is a chiral antifungal drug administered as a racemate. The knowledge of properties of individual cis-itraconazole stereoisomers is vital information for medicine and biosciences as different stereoisomers of cis-itraconazole may possess different affinity to certain biological pathways in the human body. For this purpose, either chiral synthesis of enantiomers or chiral separation of racemate can be used. This paper presents a two-step high-performance liquid chromatography approach for the semipreparative isolation of four stereoisomers (two enantiomeric pairs) of itraconazole using polysaccharide stationary phases and volatile organic mobile phases without additives in isocratic mode. The approach used involves the separation of the racemate into three fractions (i.e. two pure stereoisomers and one mixed fraction containing the remaining two stereoisomers) in the first run and consequent separation of the collected mixed fraction in the second one. For this purpose, combination of cellulose tris-(4-methylbenzoate) and cellulose tris-(3,5-dimehylphenylcarbamate) columns with complementary selectivity for cis-itraconazole provided full separation of all four stereoisomers (with purity of each isomer > 97%). The stereoisomers were collected, their optical rotation determined and their identity confirmed based on the results of a previously published study. Pure separated stereoisomers are subjected to further biological studies. © 2016 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.

Enantioselective Phytotoxicity and the Relative Mechanism of Current Chiral Herbicides.

PubMed

Wang, Cui; Lu, Dezhao; Yang, Jinhuan; Xu, Yingling; Gong, Chenxue; Li, Zhuoyu

2017-01-01

Regardless of the achievable of chiral switch, most of the chiral nature agrochemical is still sold as racemate or enantiomer-enriched pesticides. Herbicides, accounted for a large proportion in pesticide market, are of great concern due to the frequent occurrence in environment and the structure selective phyto-biochemical impact on plants. We give a systematic search on the literature database and included approximately 50 papers which were related to the review. We do careful categories for the chiral herbicides according to their structure and listed out the acute phytotoxicity endpoints. The potential mechanism for the enantioselective toxicity was concluded into 5 main points. The enantiomer-specific toxicity on plant growth and flowers are limited on phenoxyalkanoic acid herbicide, aryloxyphenoxypropanoic acid, imidazolinone herbicide, and acetamide pesticide. Data available on the potential mechanism explanation of enantioselective phytotoxicity has been concerned on the genetic transcription, oxidative stress, and photosynthesis disruption, etc. A comparison between the two enantiomers' enantioselective effects identified an organ-specific and species-specific phenomenon for several herbicides. Moreover, a more herbicidal activity enantiomer is also displayed the more toxicity than its antipode. The review elucidated a paucity of information on the enantioselective effect research on various types of plants at the different life stages. It appealed us to conduct a more holistic approach to balance the benefit between herbicidal activity and phytotoxicity when try to develop an enantio-pure herbicide.

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

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.

Can a Non-Chiral Object Be Made of Two Identical Chiral Moieties?

ERIC Educational Resources Information Center

LeMarechal, Jean Francois

2008-01-01

Several pedagogical objects can be used to discuss chirality. Here, we use the cut of an apple to show that the association of identical chiral moieties can form a non-chiral object. Octahedral chirality is used to find situations equivalent to the cut of the apple. (Contains 5 figures.)

Chiral discrimination of sibutramine enantiomers by capillary electrophoresis and proton nuclear magnetic resonance spectroscopy.

PubMed

Lee, Yong-Jae; Choi, Seungho; Lee, Jinhoo; Nguyen, NgocVan Thi; Lee, Kyungran; Kang, Jong Seong; Mar, Woongchon; Kim, Kyeong Ho

2012-03-01

Capillary electrophoresis (CE) and proton nuclear magnetic resonance spectroscopy ((1)H-NMR) have been used to discriminate the enantiomers of sibutramine using cyclodextrin derivatives. Possible correlation between CE and (1)H-NMR was examined. Good correlation between the (1)H-NMR shift non-equivalence data for sibutramine and the degree of enantioseparation in CE was observed. In CE study, a method of enantiomeric separation and quantitation of sibutramine was developed using enantiomeric standards. The method was based on the use of 50 mM of phosphate buffer of pH 3.0 with 10 mM of methyl-beta-cyclodextrin (M-β-CD). 0.05% of LOD, 0.2% of LOQ for S-sibutramine enantiomer was achieved, and the method was validated and applied to the quantitative determination of sibutramine enantiomers in commercial drugs. On a 600 MHz (1)H-NMR analysis, enantiomer signal separation of sibutramine was obtained by fast diastereomeric interaction with a chiral selector M-β-CD. For chiral separation and quantification, N-methyl proton peaks (at 2.18 ppm) were selected because of its being singlet and simple for understanding of diastereomeric interaction. Effects of temperature and concentration of chiral selector on enantiomer signal separation were investigated. The optimum condition was 0.5 mg/mL of sibutramine and 10 mg/mL of M-β-CD at 10°C. Distinguishment of 0.5% of S-sibutramine in R-sibutramine was found to be possible by (1)H-NMR with M-β-CD as chiral selector. Host-guest interaction between sibutramine and M-β-CD was confirmed by (1)H-NMR studies and CE studies. A Structure of the inclusion complex was proposed considering (1)H-NMR and 2D ROESY studies.

Enhanced Circular Dichroism of Gold Bilayered Slit Arrays Embedded with Rectangular Holes.

PubMed

Zhang, Hao; Wang, Yongkai; Luo, Lina; Wang, Haiqing; Zhang, Zhongyue

2017-01-01

Gold bilayered slit arrays with rectangular holes embedded into the metal surface are designed to enhance the circular dichroism (CD) effect of gold bilayered slit arrays. The rectangular holes in these arrays block electric currents and generate localized surface plasmons around these holes, thereby strengthening the CD effect. The CD enhancement factor depends strongly on the rotational angle and the structural parameters of the rectangular holes; this factor can be enhanced further by drilling two additional rectangular holes into the metal surfaces of the arrays. These results help facilitate the design of chiral structures to produce a strong CD effect and large electric fields.

APPLICATION OF CYCLODEXTRIN-MODIFIED MICELLAR ELECTRONKINETIC CHROMATOGRAPHY TO THE SEPARATIONS OF SELECTED NEUTRAL PESTICIDES AND THEIR ENANTIOMERS

EPA Science Inventory

The environmental chemistry of chiral pesticides is receiving increased attention - enantiomeric ratios are being measured and enantioselective degradation processes are being reported. The requisite analysis involves separation of the various enantiomers. Mixtures of three class...

Meta-Chirality: Fundamentals, Construction and Applications

PubMed Central

Ma, Xiaoliang; Pu, Mingbo; Li, Xiong; Guo, Yinghui; Gao, Ping; Luo, Xiangang

2017-01-01

Chiral metamaterials represent a special type of artificial structures that cannot be superposed to their mirror images. Due to the lack of mirror symmetry, cross-coupling between electric and magnetic fields exist in chiral mediums and present unique electromagnetic characters of circular dichroism and optical activity, which provide a new opportunity to tune polarization and realize negative refractive index. Chiral metamaterials have attracted great attentions in recent years and have given rise to a series of applications in polarization manipulation, imaging, chemical and biological detection, and nonlinear optics. Here we review the fundamental theory of chiral media and analyze the construction principles of some typical chiral metamaterials. Then, the progress in extrinsic chiral metamaterials, absorbing chiral metamaterials, and reconfigurable chiral metamaterials are summarized. In the last section, future trends in chiral metamaterials and application in nonlinear optics are introduced. PMID:28513560

Internally resonating lattices for bandgap generation and low-frequency vibration control

NASA Astrophysics Data System (ADS)

Baravelli, Emanuele; Ruzzene, Massimo

2013-12-01

The paper reports on a structural concept for high stiffness and high damping performance. A stiff external frame and an internal resonating lattice are combined in a beam-like assembly which is characterized by high frequency bandgaps and tuned vibration attenuation at low frequencies. The resonating lattice consists of an elastomeric material arranged according to a chiral topology which is designed to resonate at selected frequencies. The concept achieves high damping performance by combining the frequency-selective properties of internally resonating structures, with the energy dissipation characteristics of their constituent material. The flexible ligaments, the circular nodes and the non-central interactions of the chiral topology lead to dynamic deformation patterns which are beneficial to energy dissipation. Furthermore, tuning and grading of the elements of the lattice allows for tailoring of the resonating properties so that vibration attenuation is obtained over desired frequency ranges. Numerical and experimental results demonstrate the tuning flexibility of this concept and suggest its potential application for load-carrying structural members parts of vibration and shock prone systems.

Effect of the ionic strength of a mobile phase on the chromatographic retention and thermodynamic characteristics of the adsorption of enantiomers of α-phenylcarboxylic acids on a chiral adsorbent with grafted antibiotic eremomycin

NASA Astrophysics Data System (ADS)

Reshetova, E. N.

2017-01-01

The effect the ionic strength of an aqueous ethanol mobile phase containing buffer salt has the on retention and thermodynamics of adsorption of optical isomers of some α-phenylcarboxylic acids on chiral adsorbent Nautilus-E with grafted antibiotic eremomycin is investigated. It is shown that ion exchange processes participate in the adsorption of enantiomers of α-phenylcarboxylic acids. It is established that electrostatic interactions contribute to the retention of enantiomers of α-phenylcarboxylic acids and affect selectivity only slightly. The dependences of retention characteristics, selectivity, and thermodynamic parameters on the concentration of the buffer salt in the eluent are determined. A statistical analysis of enthalpy-entropy compensation is performed, and the compensation effect is shown to be true. It is found that the points corresponding to the investigated adsorbates are distributed over the compensation dependence according to the spatial structural characteristics of molecules.

Influence of Soil Factors on the Stereoselective Fate of a Novel Chiral Insecticide, Paichongding, in Flooded Paddy Soils.

PubMed

Li, Juying; Huang, Tuo; Li, Lizong; Ding, Tengda; Zhu, Hong; Yang, Bo; Ye, Qingfu; Gan, Jay

2016-11-02

In this study, the fate of paichongding was investigated in three soils with contrasting soil properties. In general, low soil pH has the potential to retard the mineralization and promote the dissipation of paichongding and the formation of its primary transformation product and to accelerate the formation of bound residue. The dissipation of paichongding stereoisomers was very fast and diastereoselective. This selectivity was found only between diastereomers and not between enantiomers and was observed to be soil dependent. In the acidic soil, the enantiomers (5R,7R)- and (5S,7S)-paichongding were degraded more quickly than (5R,7S)- and (5S,7R)-paichongding, whereas a contrary trend was observed in the neutral soil, and such selectivity did not occur in the alkaline soil. The OM and clay contents also played important roles in the fate of paichongding. This effect of soil properties should be considered in risk assessment of chiral pesticides and their application in the field.

Displacement chromatography on cyclodextrin silicas. IV. Separation of the enantiomers of ibuprofen.

PubMed

Farkas, G; Irgens, L H; Quintero, G; Beeson, M D; al-Saeed, A; Vigh, G

1993-08-13

A displacement chromatographic method has been developed for the preparative separation of the enantiomers of ibuprofen using a beta-cyclodextrin silica stationary phase. The retention behavior of ibuprofen was studied in detail: the log k' vs. polar organic modifier concentration, the log k' vs. pH, the log k' vs. buffer concentration and the log k' vs. 1/T relationships; also, the alpha vs. polar organic modifier concentration, the alpha vs. pH, the alpha vs. buffer concentration and the log alpha vs. 1/T relationships have been determined in order to find the carrier solution composition which results in maximum chiral selectivity and sufficient, but not excessive solute retention (1 < k' < 30). 4-tert.-Butylcyclohexanol, a structurally similar but more retained compound than ibuprofen, was selected as displacer for the separation. Even with an alpha value as small as 1.08, good preparative chiral separations were observed both in the displacement mode and in the overloaded elution mode, up to a sample load of 0.5 mg.

Enantioselective extraction of (+)-(S)-citalopram and its main metabolites using a tailor-made stir bar chiral imprinted polymer for their LC-ESI-MS/MS quantitation in urine samples.

PubMed

Unceta, Nora; Gómez-Caballero, Alberto; García, Deiene; Díaz, Goretti; Guerreiro, Antonio; Piletsky, Sergey; Goicolea, M Aránzazu; Barrio, Ramón J

2013-11-15

This paper reports the application of a chiral imprinted polymer (CIP)-coated stir bar for the selective extraction of (+)-(S)-citalopram (SCIT) and its main metabolites, (+)-(S)-desmethylcitalopram (SDCIT) and (+)-(S)-didesmethylcitalopram (SDDCIT), from urine samples. The developed device has been demonstrated to be capable of selectively extracting the three target analytes from urine samples without saturating the imprinted sites. A CIP-coated stir bar sorptive extraction procedure (CIP-SBSE) is proposed for the isolation of SCIT, SDCIT and SDDCIT followed by their subsequent analysis using liquid chromatography ion trap mass spectrometry (LC-ITMS). Deuterated SCIT-d6 was used as an internal standard. The method was validated using a standard procedure, which revealed that a quantification of 5 ng mL(-1) was obtained in urine samples and that the accuracy and precision were within the established values while no matrix effect was observed. Copyright © 2013 Elsevier B.V. All rights reserved.

Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions.

PubMed

Denmark, Scott E; Heemstra, John R

2007-07-20

The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.

Natural selection in the colloid world: active chiral spirals.

PubMed

Zhang, Jie; Granick, Steve

2016-10-06

We present a model system in which to study natural selection in the colloid world. In the assembly of active Janus particles into rotating pinwheels when mixed with trace amounts of homogeneous colloids in the presence of an AC electric field, broken symmetry in the rotation direction produces spiral, chiral shapes. Locked into a central rotation point by the centre particle, the spiral arms are found to trail rotation of the overall cluster. To achieve a steady state, the spiral arms undergo an evolutionary process to coordinate their motion. Because all the particles as segments of the pinwheel arms are self-propelled, asymmetric arm lengths are tolerated. Reconfiguration of these structures can happen in various ways and various mechanisms of this directed structural change are analyzed in detail. We introduce the concept of VIP (very important particles) to express that sustainability of active structures is most sensitive to only a few particles at strategic locations in the moving self-assembled structures.

Critical evaluation of monitoring strategy for the multi-residue determination of 90 chiral and achiral micropollutants in effluent wastewater.

PubMed

Petrie, Bruce; Proctor, Kathryn; Youdan, Jane; Barden, Ruth; Kasprzyk-Hordern, Barbara

2017-02-01

It is essential to monitor the release of organic micropollutants from wastewater treatment plants (WWTPs) for developing environmental risk assessment and assessing compliance with legislative regulation. In this study the impact of sampling strategy on the quantitative determination of micropollutants in effluent wastewater was investigated. An extended list of 90 chiral and achiral micropollutants representing a broad range of biological and physico-chemical properties were studied simultaneously for the first time. During composite sample collection micropollutants can degrade resulting in the under-estimation of concentration. Cooling collected sub-samples to 4°C stabilised ≥81 of 90 micropollutants to acceptable levels (±20% of the initial concentration) in the studied effluents. However, achieving stability for all micropollutants will require an integrated approach to sample collection (i.e., multi-bottle sampling with more than one stabilisation method applied). Full-scale monitoring of effluent revealed time-paced composites attained similar information to volume-paced composites (influent wastewater requires a sampling mode responsive to flow variation). The option of monitoring effluent using time-paced composite samplers is advantageous as not all WWTPs have flow controlled samplers or suitable sites for deploying portable flow meters. There has been little research to date on the impact of monitoring strategy on the determination of chiral micropollutants at the enantiomeric level. Variability in wastewater flow results in a dynamic hydraulic retention time within the WWTP (and upstream sewerage system). Despite chiral micropollutants being susceptible to stereo-selective degradation, no diurnal variability in their enantiomeric distribution was observed. However, unused medication can be directly disposed into the sewer network creating short-term (e.g., daily) changes to their enantiomeric distribution. As enantio-specific toxicity is observed in the environment, similar resolution of enantio-selective analysis to more routinely applied achiral methods is needed throughout the monitoring period for accurate risk assessment. Copyright © 2016 British Geological Survey, NERC. Published by Elsevier B.V. All rights reserved.

Nona-coordinated chiral Eu(III) complexes with stereoselective ligand-ligand noncovalent interactions for enhanced circularly polarized luminescence.

PubMed

Harada, Takashi; Tsumatori, Hiroyuki; Nishiyama, Katsura; Yuasa, Junpei; Hasegawa, Yasuchika; Kawai, Tsuyoshi

2012-06-18

Circularly polarized luminescence (CPL) of chiral Eu(III) complexes with nona- and octa-coordinated structures, [Eu(R/S-iPr-Pybox)(D-facam)(3)] (1-R/1-S; R/S-iPr-Pybox, 2,6-bis(4R/4S-isopropyl-2-oxazolin-2-yl)pyridine; D-facam, 3-trifluoroacetyl-d-camphor), [Eu(S,S-Me-Ph-Pybox)(D-facam)(3)] (2-SS; S,S-Me-Ph-Pybox, 2,6-bis(4S-methyl-5S-phenyl-2-oxazolin-2-yl)pyridine), and [Eu(Phen)(D-facam)(3)] (3; Phen, 1,10-phenanthroline) are reported, and their structural features are discussed on the basis of X-ray crystallographic analyses. These chiral Eu(III) complexes showed relatively intense photoluminescence due to their (5)D(0) → (7)F(1) (magnetic-dipole) and (5)D(0) → (7)F(2) (electric-dipole) transition. The dissymmetry factors of CPL (g(CPL)) at the former band of 1-R and 1-S were as large as -1.0 and -0.8, respectively, while the g(CPL) of 3 at the (5)D(0) → (7)F(1) transition was relatively small (g(CPL) = -0.46). X-ray crystallographic data indicated specific ligand-ligand hydrogen bonding in these compounds which was expected to stabilize their chiral structures even in solution phase. CPL properties of 1-R and 1-S were discussed in terms of transition nature of lanthanide luminescence.

Chiral acidic amino acids induce chiral hierarchical structure in calcium carbonate

PubMed Central

Jiang, Wenge; Pacella, Michael S.; Athanasiadou, Dimitra; Nelea, Valentin; Vali, Hojatollah; Hazen, Robert M.; Gray, Jeffrey J.; McKee, Marc D.

2017-01-01

Chirality is ubiquitous in biology, including in biomineralization, where it is found in many hardened structures of invertebrate marine and terrestrial organisms (for example, spiralling gastropod shells). Here we show that chiral, hierarchically organized architectures for calcium carbonate (vaterite) can be controlled simply by adding chiral acidic amino acids (Asp and Glu). Chiral, vaterite toroidal suprastructure having a ‘right-handed' (counterclockwise) spiralling morphology is induced by L-enantiomers of Asp and Glu, whereas ‘left-handed' (clockwise) morphology is induced by D-enantiomers, and sequentially switching between amino-acid enantiomers causes a switch in chirality. Nanoparticle tilting after binding of chiral amino acids is proposed as a chiral growth mechanism, where a ‘mother' subunit nanoparticle spawns a slightly tilted, consequential ‘daughter' nanoparticle, which by amplification over various length scales creates oriented mineral platelets and chiral vaterite suprastructures. These findings suggest a molecular mechanism for how biomineralization-related enantiomers might exert hierarchical control to form extended chiral suprastructures. PMID:28406143

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.

Cell Chirality Drives Left-Right Asymmetric Morphogenesis.

PubMed

Inaki, Mikiko; Sasamura, Takeshi; Matsuno, Kenji

2018-01-01

Most macromolecules found in cells are chiral, meaning that they cannot be superimposed onto their mirror image. However, cells themselves can also be chiral, a subject that has received little attention until very recently. In our studies on the mechanisms of left-right (LR) asymmetric development in Drosophila , we discovered that cells can have an intrinsic chirality to their structure, and that this "cell chirality" is generally responsible for the LR asymmetric development of certain organs in this species. The actin cytoskeleton plays important roles in the formation of cell chirality. In addition, Myosin31DF ( Myo31DF ), which encodes Drosophila Myosin ID, was identified as a molecular switch for cell chirality. In other invertebrate species, including snails and Caenorhabditis elegans , chirality of the blastomeres, another type of cell chirality, determines the LR asymmetry of structures in the body. Thus, chirality at the cellular level may broadly contribute to LR asymmetric development in various invertebrate species. Recently, cell chirality was also reported for various vertebrate cultured cells, and studies suggested that cell chirality is evolutionarily conserved, including the essential role of the actin cytoskeleton. Although the biological roles of cell chirality in vertebrates remain unknown, it may control LR asymmetric development or other morphogenetic events. The investigation of cell chirality has just begun, and this new field should provide valuable new insights in biology and medicine.

Cell chirality: its origin and roles in left–right asymmetric development

PubMed Central

Inaki, Mikiko; Liu, Jingyang

2016-01-01

An item is chiral if it cannot be superimposed on its mirror image. Most biological molecules are chiral. The homochirality of amino acids ensures that proteins are chiral, which is essential for their functions. Chirality also occurs at the whole-cell level, which was first studied mostly in ciliates, single-celled protozoans. Ciliates show chirality in their cortical structures, which is not determined by genetics, but by ‘cortical inheritance’. These studies suggested that molecular chirality directs whole-cell chirality. Intriguingly, chirality in cellular structures and functions is also found in metazoans. In Drosophila, intrinsic cell chirality is observed in various left–right (LR) asymmetric tissues, and appears to be responsible for their LR asymmetric morphogenesis. In other invertebrates, such as snails and Caenorhabditis elegans, blastomere chirality is responsible for subsequent LR asymmetric development. Various cultured cells of vertebrates also show intrinsic chirality in their cellular behaviours and intracellular structural dynamics. Thus, cell chirality may be a general property of eukaryotic cells. In Drosophila, cell chirality drives the LR asymmetric development of individual organs, without establishing the LR axis of the whole embryo. Considering that organ-intrinsic LR asymmetry is also reported in vertebrates, this mechanism may contribute to LR asymmetric development across phyla. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’. PMID:27821533

Cell chirality: its origin and roles in left-right asymmetric development.

PubMed

Inaki, Mikiko; Liu, Jingyang; Matsuno, Kenji

2016-12-19

An item is chiral if it cannot be superimposed on its mirror image. Most biological molecules are chiral. The homochirality of amino acids ensures that proteins are chiral, which is essential for their functions. Chirality also occurs at the whole-cell level, which was first studied mostly in ciliates, single-celled protozoans. Ciliates show chirality in their cortical structures, which is not determined by genetics, but by 'cortical inheritance'. These studies suggested that molecular chirality directs whole-cell chirality. Intriguingly, chirality in cellular structures and functions is also found in metazoans. In Drosophila, intrinsic cell chirality is observed in various left-right (LR) asymmetric tissues, and appears to be responsible for their LR asymmetric morphogenesis. In other invertebrates, such as snails and Caenorhabditis elegans, blastomere chirality is responsible for subsequent LR asymmetric development. Various cultured cells of vertebrates also show intrinsic chirality in their cellular behaviours and intracellular structural dynamics. Thus, cell chirality may be a general property of eukaryotic cells. In Drosophila, cell chirality drives the LR asymmetric development of individual organs, without establishing the LR axis of the whole embryo. Considering that organ-intrinsic LR asymmetry is also reported in vertebrates, this mechanism may contribute to LR asymmetric development across phyla.This article is part of the themed issue 'Provocative questions in left-right asymmetry'. © 2016 The Authors.

Circular Dichroism Control of Tungsten Diselenide (WSe2) Atomic Layers with Plasmonic Metamolecules.

PubMed

Lin, Hsiang-Ting; Chang, Chiao-Yun; Cheng, Pi-Ju; Li, Ming-Yang; Cheng, Chia-Chin; Chang, Shu-Wei; Li, Lance L J; Chu, Chih-Wei; Wei, Pei-Kuen; Shih, Min-Hsiung

2018-05-09

Controlling circularly polarized (CP) states of light is critical to the development of functional devices for key and emerging applications such as display technology and quantum communication, and the compact circular polarization-tunable photon source is one critical element to realize the applications in the chip-scale integrated system. The atomic layers of transition metal dichalcogenides (TMDCs) exhibit intrinsic CP emissions and are potential chiroptical materials for ultrathin CP photon sources. In this work, we demonstrated CP photon sources of TMDCs with device thicknesses approximately 50 nm. CP photoluminescence from the atomic layers of tungsten diselenide (WSe 2 ) was precisely controlled with chiral metamolecules (MMs), and the optical chirality of WSe 2 was enhanced more than 4 times by integrating with the MMs. Both the enhanced and reversed circular dichroisms had been achieved. Through integrations of the novel gain material and plasmonic structure which are both low-dimensional, a compact device capable of efficiently manipulating emissions of CP photon was realized. These ultrathin devices are suitable for important applications such as the optical information technology and chip-scale biosensing.

Enhanced hydrogenation activity and diastereomeric interactions of methyl pyruvate co-adsorbed with R-1-(1-naphthyl)ethylamine on Pd(111)

DOE PAGES

Mahapatra, Mausumi; Burkholder, Luke; Garvey, Michael; ...

2016-08-04

Unmodified racemic sites on heterogeneous chiral catalysts reduce their overall enantioselectivity, but this effect is mitigated in the Orito reaction (methyl pyruvate (MP) hydrogenation to methyl lactate) by an increased hydrogenation reactivity. Here, this effect is explored on a R-1-(1-naphthyl)ethylamine (NEA)-modified Pd(111) model catalyst where temperature-programmed desorption experiments reveal that NEA accelerates the rates of both MP hydrogenation and H/D exchange. NEAþMP docking complexes are imaged using scanning tunneling microscopy supplemented by density functional theory calculations to allow the most stable docking complexes to be identified. The results show that diastereomeric interactions between NEA and MP occur predominantly by bindingmore » of the C=C of the enol tautomer of MP to the surface, while simultaneously optimizing C=O...H 2N hydrogen-bonding interactions. In conclusion, the combination of chiral-NEA driven diastereomeric docking with a tautomeric preference enhances the hydrogenation activity since C=C bonds hydrogenate more easily than C=O bonds thus providing a rationale for the catalytic observations.« less

Chiral anomaly enhancement and photoirradiation effects in multiband touching fermion systems

NASA Astrophysics Data System (ADS)

Ezawa, Motohiko

2017-05-01

Multiband touchings together with the emergence of fermions exhibiting linear dispersions have recently been predicted and realized in various materials. We first investigate the Adler-Bell-Jackiw chiral anomaly in these multiband touching semimetals when they are described by the pseudospin operator in high-dimensional representation. By evaluating the Chern number, we show that the anomalous Hall effect is enhanced depending on the magnitude of the pseudospin. It is also confirmed by the analysis of the Landau levels when magnetic field is applied. Namely, charge pumping occurs from one multiband touching point to another through multichannel Landau levels in the presence of parallel electric and magnetic fields. We also show a pair annihilation of two multiband touching points by photoirradiation. Furthermore, we propose generalizations of Dirac semimetals, multiple Weyl semimetals, and loop-nodal semimetals to those composed of fermions carrying pseudospins in high-dimensional representation. Finally we investigate the three-band touching protected by the C3 symmetry. We show that the three-band touching point is broken into two Weyl points by photoirradiation.

Direct high-performance liquid chromatographic determination of the enantiomeric purity of levodopa and methyldopa: comparison with pharmacopoeial polarimetric methods.

PubMed

Dolezalová, M; Tkaczyková, M

1999-03-01

Chiral high-performance liquid chromatography was employed for determination of the enantiomeric purity of levodopa and methyldopa. The determination of D-DOPA in levodopa was accomplished using a chiral ligand-exchange chromatograpy with an ordinary C18 column and a chiral mobile phase containing N,N-dimethyl-L-phenylalanine and Cu(II) acetate or by means of LC on a teicoplanin column in conjunction with ethanol-water (65:35, v/v). Both methods gave good performance, however, the latter was faster and more convenient and suitable for routine analyses. For the determination of D-methyldopa a LC method based on the use of a teicoplanin column in polar organic mode with methanol-acetic acid-triethylamine (1,000:0.05:0.05, v/v/v) mobile phase was developed. The precision, accuracy, linearity and selectivity were satisfactory. In comparison with pharmacopoeial polarimetric methods (according to the European Pharmacopoeia and the Pharmacopoea Bohemoslovaca), the LC methods proved to be much more sensitive giving detection limits 0.04% of D-DOPA and 0.3% of D-methyldopa.

An enantiomer-based virtual screening approach: Discovery of chiral organophosphates as acetyl cholinesterase inhibitors.

PubMed

Zhang, Aiqian; Mu, Yunsong; Wu, Fengchang

2017-04-01

Chiral organophosphates (OPs) have been used widely around the world, very little is known about binding mechanisms with biological macromolecules. An in-depth understanding of the stereo selectivity of human AChE and discovering bioactive enantiomers of OPs can decrease health risks of these chiral chemicals. In the present study, a flexible molecular docking approach was conducted to investigate different binding modes of twelve phosphorus enantiomers. A pharmacophore model was then developed on basis of the bioactive conformations of these compounds. After virtual screening, twenty-four potential bioactive compounds were found, of which three compounds (Ethyl p-nitrophenyl phenylphosphonate (EPN), 1-naphthaleneacetic anhydride and N,4-dimethyl-N-phenyl-benzenesulfonamide) were tested by use of different in vitro assays. S-isomer of EPN was also found to exhibit greater inhibitory activity towards human AChE than the corresponding R-isomer. These findings affirm that stereochemistry plays a crucial role in virtual screening, and provide a new insight into designing safer organ phosphorus pesticides on human health. Copyright © 2017 Elsevier Inc. All rights reserved.

Trajectory and chirality of vortex domain walls in ferromagnetic nanowires with an asymmetric Y-branch

NASA Astrophysics Data System (ADS)

Brandão, J.; Mello, A.; Garcia, F.; Sampaio, L. C.

2017-03-01

The motion and trajectory of vortex domain walls (VDWs) driven by magnetic field were investigated in Fe80Ni20 nanowires with an asymmetric Y-shape branch. By using the focused magneto-optical Kerr effect, we have probed the injection, pinning, and propagation of VDWs in the branch and in the wire beyond the branch entrance. Hysteresis cycles measured at these points show 3 and 4 jumps in the magnetization reversal, respectively. Micromagnetic simulations were carried out to obtain the number of jumps in the hysteresis cycles, and the magnetization process involved in each jump. Based on simulations and from the size of the jumps in the measured hysteresis cycles, one obtains the histogram of the domain wall type probability. While in the branch domain walls of different types are equiprobable, in the nanowire vortex domain walls with counter clockwise and clockwise chiralities and transverse-down domain walls are measured with probabilities of 65%, 25%, and 10%, respectively. These results provide an additional route to select the trajectory and chirality of VDWs in magnetic nanostructures.

Self-Assembly of Topological Solitons and Functional Nanoparticles in Liquid Crystals

NASA Astrophysics Data System (ADS)

Ackerman, Paul Jeffrey

As a result of their intrinsic orientational order, soft elasticity, and facile response to external stimuli, liquid crystals (LCs) provide a rich environment for both fundamental science and viable technological applications. In this thesis I explore the emergent properties of confinement-frustrated chiral nematic LCs and nanoparticle-LC composites. Due to a complex free energy landscape, con- fined LCs exhibit a large number of local and global energy minima and can facilitate self-assembly of many types of topological solitons. These localized configurations of molecular orientation field are useful for technological applications, have properties that are enhanced by colloidal inclusions and enable the fundamental studies of nanoparticle interactions. Experimental and numerical ex- ploration of these topologically nontrivial solitons may influence the experimental realization of their analogs in physical systems ranging from elementary particles to cosmology. The delicate interplay of topology, chirality and confinement of LCs can enable spontaneous or optical vortex initiated self-assembly of solitons. In turn, the optical generation and patterning of reconfigurable LC solitons can enable the production of optical vortices in laser beams, demon- strating hierarchical control of defects in matter and light with potential technological applications. The elasticity and facile response of LCs to applied fields facilitates the self-assembly of crystals and chains of solitons, giant electrostriction, as well as electrically driven nonequilibrium dynamics in the form of reversible directional motion of stable defect pairs. Concepts of chirality and topo- logical invariants, such as Hopf index and Skyrmion number, are invoked to examine and classify a variety of spatial solitons, including Skyrmions, Hopfions, and torons, as well as to analyze the role of chirality and the unexpected observation of twist handedness reversal that enables soliton stability. By introducing colloidal particles to the confined chiral LCs, we probe how new composite material properties can emerge spontaneously or be pre-designed and then probed by combining the facile response of the LC host and the unique properties of nanoparticles. This allows us to achieve polar ferromagnetic response in chiral ferromagnetic LC colloids as well as to probe plasmon- exciton interactions through controlling metal and semiconductor quantum dot nanoparticles within topological defects.

de Vries liquid crystals based on a chiral 5-phenylpyrimidine benzoate core with a tri- and tetra-carbosilane backbone

NASA Astrophysics Data System (ADS)

Sreenilayam, S. P.; Rodriguez-Lojo, D.; Agra-Kooijman, D. M.; Vij, J. K.; Panov, V. P.; Panov, A.; Fisch, M. R.; Kumar, Satyendra; Stevenson, P. J.

2018-02-01

New chiral de Vries smectic liquid-crystalline compounds are designed, synthesized, and investigated for perspective applications in defect-free bistable surface-stabilized ferroelectric liquid-crystal displays. In these compounds, a 5-phenyl-pyrimidine benzoate core is terminated on one side by a tri- or tetra-carbosilane group linked through an alkoxy group and an alkyl spacer and on the opposite side terminated by a chiral 2-octanol group. The stereogenic center contains either a methyl or perfluoromethyl functional group. These compounds exhibit Iso-Sm A*-Sm C*-Sm X -Cr phases under cooling from the isotropic state. Measurements of the temperature-dependent smectic layer spacing by x-ray diffraction experiments combined with the measured apparent optical tilt angle and the birefringence reveal that Sm A* phase in these compounds is of the de Vries type. In addition, the chiral compound with a tetra-carbosilane backbone, DR277, exhibits good de Vries properties with the Sm C* phase exhibited over a wide temperature range. By varying the carbosilane end group, the de Vries properties are enhanced, that is, the layer shrinkage of ˜1.9 % for the tri-carbosilane DR276 is reduced to ˜0.9 % for tetra-carbosilane DR277 at 10°C below Sm A* to Sm C* transition temperature, TAC. For DR277, the reduction factor R ≈0.22 for T =(TAC-10 )°C is reasonably low and the apparent optical tilt angle θapp=35.1°, hence this compound is a "good de Vries smectic" LC. Therefore, synthesis of the chiral mesogen with an even higher number of carbosilane groups may lead to a further reduction or even zero-layer shrinkage exhibited at TAC with Sm C* phase extending over a wide temperature range close to the room temperature for perspective suitability in device applications. Our results for 5-phenyl-pyrimidine benzoate core-based compounds support a recently drawn conclusion by Schubert et al. [J. Mater. Chem. C 4, 8483 (2016), 10.1039/C6TC03120J] from a different compound, namely that a carbosilane backbone in chiral mesogens strongly influences the de Vries properties.

Switching chiral solitons for algebraic operation of topological quaternary digits

NASA Astrophysics Data System (ADS)

Kim, Tae-Hwan; Cheon, Sangmo; Yeom, Han Woong

2017-02-01

Chiral objects can be found throughout nature; in condensed matter chiral objects are often excited states protected by a system's topology. The use of chiral topological excitations to carry information has been demonstrated, where the information is robust against external perturbations. For instance, reading, writing, and transfer of binary information have been demonstrated with chiral topological excitations in magnetic systems, skyrmions, for spintronic devices. The next step is logic or algebraic operations of such topological bits. Here, we show experimentally the switching between chiral topological excitations or chiral solitons of different chirality in a one-dimensional electronic system with Z4 topological symmetry. We found that a fast-moving achiral soliton merges with chiral solitons to switch their handedness. This can lead to the realization of algebraic operation of Z4 topological charges. Chiral solitons could be a platform for storage and operation of robust topological multi-digit information.

Chirality-controlled crystallization via screw dislocations.

PubMed

Sung, Baeckkyoung; de la Cotte, Alexis; Grelet, Eric

2018-04-11

Chirality plays an important role in science from enantiomeric separation in chemistry to chiral plasmonics in nanotechnology. However, the understanding of chirality amplification from chiral building blocks to ordered helical superstructures remains a challenge. Here, we demonstrate that topological defects, such as screw dislocations, can drive the chirality transfer from particle to supramolecular structure level during the crystallization process. By using a model system of chiral particles, which enables direct imaging of single particle incorporation into growing crystals, we show that the crystallization kinetic pathway is the key parameter for monitoring, via the defects, the chirality amplification of the crystalline structures from racemic to predominantly homohelical. We provide an explanation based on the interplay between geometrical frustration, racemization induced by thermal fluctuations, and particle chirality. Our results demonstrate that screw dislocations not only promote the growth, but also control the chiral morphology and therefore the functionality of crystalline states.

Influence of Chirality in Ordered Block Copolymer Phases

NASA Astrophysics Data System (ADS)

Prasad, Ishan; Grason, Gregory

2015-03-01

Block copolymers are known to assemble into rich spectrum of ordered phases, with many complex phases driven by asymmetry in copolymer architecture. Despite decades of study, the influence of intrinsic chirality on equilibrium mesophase assembly of block copolymers is not well understood and largely unexplored. Self-consistent field theory has played a major role in prediction of physical properties of polymeric systems. Only recently, a polar orientational self-consistent field (oSCF) approach was adopted to model chiral BCP having a thermodynamic preference for cholesteric ordering in chiral segments. We implement oSCF theory for chiral nematic copolymers, where segment orientations are characterized by quadrupolar chiral interactions, and focus our study on the thermodynamic stability of bi-continuous network morphologies, and the transfer of molecular chirality to mesoscale chirality of networks. Unique photonic properties observed in butterfly wings have been attributed to presence of chiral single-gyroid networks, this has made it an attractive target for chiral metamaterial design.

Enhanced Electroweak Penguin Amplitude in B{yields}VV Decays

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

Beneke, M.; Rohrer, J.; Yang, D.

2006-04-14

We discuss a novel electromagnetic penguin contribution to the transverse helicity amplitudes in B decays to two vector mesons, which is enhanced by two powers of m{sub B}/{lambda} relative to the standard penguin amplitudes. This leads to unique polarization signatures in penguin-dominated decay modes such as B{yields}{rho}K* similar to polarization effects in the radiative decay B{yields}K*{gamma} and offers new opportunities to probe the magnitude and chirality of flavor-changing neutral current couplings to photons.

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

Chiral magnetic effect without chirality source in asymmetric Weyl semimetals

NASA Astrophysics Data System (ADS)

Kharzeev, Dmitri E.; Kikuchi, Yuta; Meyer, René

2018-05-01

We describe a new type of the chiral magnetic effect (CME) that should occur in Weyl semimetals (WSMs) with an asymmetry in the dispersion relations of the left- and right-handed (LH and RH) chiral Weyl fermions. In such materials, time-dependent pumping of electrons from a non-chiral external source can generate a non-vanishing chiral chemical potential. This is due to the different capacities of the LH and RH chiral Weyl cones arising from the difference in the density of states in the LH and RH cones. The chiral chemical potential then generates, via the chiral anomaly, a current along the direction of an applied magnetic field even in the absence of an external electric field. The source of chirality imbalance in this new setup is thus due to the band structure of the system and the presence of (non-chiral) electron source, and not due to the parallel electric and magnetic fields. We illustrate the effect by an argument based on the effective field theory, and by the chiral kinetic theory calculation for a rotationally invariant WSM with different Fermi velocities in the left and right chiral Weyl cones; we also consider the case of a WSM with Weyl nodes at different energies. We argue that this effect is generically present in WSMs with different dispersion relations for LH and RH chiral Weyl cones, such as SrSi2 recently predicted as a WSM with broken inversion and mirror symmetries, as long as the chiral relaxation time is much longer than the transport scattering time.

Strong circularly polarized luminescence from the supramolecular gels of an achiral gelator: tunable intensity and handedness.

PubMed

Shen, Zhaocun; Wang, Tianyu; Shi, Lin; Tang, Zhiyong; Liu, Minghua

2015-07-01

Although the importance of circularly polarized luminescence (CPL) materials has been widely recognized, the CPL responses of supramolecular gels are still rarely studied. Moreover, developing CPL materials based on supramolecular gels is of great significance, due to their special advantages and important applications. Herein, we report the first circularly polarized supramolecular gels self-assembled exclusively from a simple achiral C 3 -symmetric molecule. Most importantly, the excellent tunability of these novel CPL materials, which benefits from achiral molecular building blocks as well as the nature of supramolecular gels, has been investigated. Thus, the CPL intensity of these supramolecular gels is easily enhanced by mechanical stirring or doping chiral amines. The handedness of CPL signals is controlled by the chirality of organic amines.

Extended skyrmion lattice scattering and long-time memory in the chiral magnet Fe1 -xCoxSi

NASA Astrophysics Data System (ADS)

Bannenberg, L. J.; Kakurai, K.; Qian, F.; Lelièvre-Berna, E.; Dewhurst, C. D.; Onose, Y.; Endoh, Y.; Tokura, Y.; Pappas, C.

2016-09-01

Small angle neutron scattering measurements on a bulk single crystal of the doped chiral magnet Fe1 -xCoxSi with x =0.3 reveal a pronounced effect of the magnetic history and cooling rates on the magnetic phase diagram. The extracted phase diagrams are qualitatively different for zero and field cooling and reveal a metastable skyrmion lattice phase outside the A phase for the latter case. These thermodynamically metastable skyrmion lattice correlations coexist with the conical phase and can be enhanced by increasing the cooling rate. They appear in a wide region of the phase diagram at temperatures below the A phase but also at fields considerably smaller or higher than the fields required to stabilize the A phase.

Resonance in quantum dot fluorescence in a photonic bandgap liquid crystal host.

PubMed

Lukishova, Svetlana G; Bissell, Luke J; Winkler, Justin; Stroud, C R

2012-04-01

Microcavity resonance is demonstrated in nanocrystal quantum dot fluorescence in a one-dimensional (1D) chiral photonic bandgap cholesteric-liquid crystal host under cw excitation. The resonance demonstrates coupling between quantum dot fluorescence and the cholesteric microcavity. Observed at a band edge of a photonic stop band, this resonance has circular polarization due to microcavity chirality with 4.9 times intensity enhancement in comparison with polarization of the opposite handedness. The circular-polarization dissymmetry factor g(e) of this resonance is ~1.3. We also demonstrate photon antibunching of a single quantum dot in a similar glassy cholesteric microcavity. These results are important in cholesteric-laser research, in which so far only dyes were used, as well as for room-temperature single-photon source applications.

A chiroptical switch based on supramolecular chirality transfer through alkyl chain entanglement and dynamic covalent bonding.

PubMed

Lv, Kai; Qin, Long; Wang, Xiufeng; Zhang, Li; Liu, Minghua

2013-12-14

Chirality transfer is an interesting phenomenon in Nature, which represents an important step to understand the evolution of chiral bias and the amplification of the chirality. In this paper, we report the chirality transfer via the entanglement of the alkyl chains between chiral gelator molecules and achiral amphiphilic Schiff base. We have found that although an achiral Schiff base amphiphile could not form organogels in any kind of organic solvents, it formed co-organogels when mixed with a chiral gelator molecule. Interestingly, the chirality of the gelator molecules was transferred to the Schiff base chromophore in the mixed co-gels and there was a maximum mixing ratio for the chirality transfer. Furthermore, the supramolecular chirality was also produced based on a dynamic covalent chemistry of an imine formed by the reaction between an aldehyde and an amine. Such a covalent bond of imine was formed reversibly depending on the pH variation. When the covalent bond was formed the chirality transfer occurred, when it was destroyed, the transfer stopped. Thus, a supramolecular chiroptical switch is obtained based on supramolecular chirality transfer and dynamic covalent chemistry.

The stereochemistry of chlorophyll-c₃ from the haptophyte Emiliania huxleyi: the (13²R)-enantiomers of chlorophylls-c are exclusively selected as the photosynthetically active pigments in chromophyte algae.

PubMed

Mizoguchi, Tadashi; Kimura, Yuki; Yoshitomi, Taichi; Tamiaki, Hitoshi

2011-11-01

Chlorophyll(Chl)-c pigments in algae, diatoms and some prokaryotes are characterized by the fully conjugated porphyrin π-system as well as the acrylate residue at the 17-position. The precise structural characterization of Chl-c(3) from the haptophyte Emiliania huxleyi was performed. The conformations of the π-conjugated peripheral substituents, the 3-/8-vinyl, 7-methoxycarbonyl and 17-acrylate moieties were evaluated, in a solution, using nuclear Overhauser enhancement correlations and molecular modeling calculations. The rotation of the 17-acrylate residue was considerably restricted, whereas the other three substituents readily rotated at ambient temperature. Moreover, the stereochemistry at the 13²-position was determined by combination of chiral high-performance liquid chromatography (HPLC) with circular dichroism (CD) spectroscopy. Compared with the CD spectra of the structurally related, synthetic (13²R)- and (13²S)-protochlorophyllide(PChlide)-a, naturally occurring Chl-c₃ had exclusively the (13²R)-configuration. To elucidate this natural selection of a single enantiomer, we analyzed the three major Chl-c pigments (Chl-c₁, c₂ and c₃) in four phylogenetically distinct classes of Chl-c containing algae, i.e., heterokontophyta, dinophyta, cryptophyta and haptophyta using chiral HPLC. All the photosynthetic organisms contained only the (13²R)-enantiomerically pure Chls-c, and lacked the corresponding enantiomeric (13²S)-forms. Additionally, Chl-c₂ was found in all the organisms as the common Chl-c. These results throw a light on the biosynthesis as well as photosynthetic function of Chl-c pigments: Chl-c₂ is derived from 8-vinyl-PChlide-a by dehydrogenation of the 17-propionate to acrylate residues as generally proposed, and the (13²R)-enantiomers of Chls-c function as photosynthetically active, light-harvesting pigments together with the principal Chl-a and carotenoids. 2011 Elsevier B.V. All rights reserved.

Chemical synthesis of water-soluble, chiral conducting-polymer complexes

DOEpatents

Wang, Hsing-Lin; McCarthy, Patrick A.; Yang, Sze Cheng

2003-01-01

The template-guided synthesis of water-soluble, chiral conducting polymer complexes is described. Synthesis of water-soluble polyaniline complexes is achieved by carefully controlling the experimental parameters such as; acid concentration, ionic strength, monomer/template ratio, total reagent concentration, and order of reagent addition. Chiral (helical) polyaniline complexes can be synthesized by addition of a chiral inducing agent (chiral acid) prior to polymerization, and the polyaniline helix can be controlled by the addition of the (+) or (-) form of the chiral acid. Moreover the quantity of chiral acid and the salt content has a significant impact on the degree of chirality in the final polymer complexes. The polyaniline and the template have been found to be mixed at the molecular level which results in chiral complexes that are robust through repeated doping and dedoping cycles.

Homochiral Evolution in Self-Assembled Chiral Polymers and Block Copolymers.

PubMed

Wen, Tao; Wang, Hsiao-Fang; Li, Ming-Chia; Ho, Rong-Ming

2017-04-18

The significance of chirality transfer is not only involved in biological systems, such as the origin of homochiral structures in life but also in man-made chemicals and materials. How the chiral bias transfers from molecular level (molecular chirality) to helical chain (conformational chirality) and then to helical superstructure or phase (hierarchical chirality) from self-assembly is vital for the chemical and biological processes in nature, such as communication, replication, and enzyme catalysis. In this Account, we summarize the methodologies for the examination of homochiral evolution at different length scales based on our recent studies with respect to the self-assembly of chiral polymers and chiral block copolymers (BCPs*). A helical (H*) phase to distinguish its P622 symmetry from that of normal hexagonally packed cylinder phase was discovered in the self-assembly of BCPs* due to the chirality effect on BCP self-assembly. Enantiomeric polylactide-containing BCPs*, polystyrene-b-poly(l-lactide) (PS-PLLA) and polystyrene-b-poly(d-lactide) (PS-PDLA), were synthesized for the examination of homochiral evolution. The optical activity (molecular chirality) of constituted chiral repeating unit in the chiral polylactide is detected by electronic circular dichroism (ECD) whereas the conformational chirality of helical polylactide chain can be explicitly determined by vibrational circular dichroism (VCD). The H* phases of the self-assembled polylactide-containing BCPs* can be directly visualized by 3D transmission electron microscopy (3D TEM) technique at which the handedness (hierarchical chirality) of the helical nanostructure is thus determined. The results from the ECD, VCD, and 3D TEM for the investigated chirality at different length scales suggest the homochiral evolution in the self-assembly of the BCPs*. For chiral polylactides, twisted lamellae in crystalline banded spherulite can be formed by dense packing scheme and effective interactions upon helical chains from self-assembly. The handedness of the twisted lamella can be determined by using rotation experiment of polarized light microscopy (PLM). Similar to the self-assembly of BCPs*, the examined results suggest the homochiral evolution in the crystallized chiral polylactides. The results presented in this Account demonstrate the notable progress in the spectral and morphological determination for the examination of molecular, conformational, and hierarchical chirality in self-assembled twisted superstructures of chiral polymers and helical phases of block copolymers and suggest the attainability of homochiral evolution in the self-assembly of chiral homopolymers and BCPs*. The suggested methodologies for the understanding of the mechanisms of the chirality transfer at different length scales provide the approaches to give Supporting Information for disclosing the mysteries of the homochiral evolution from molecular level.

Analysis of Species-Selectivity of Human, Mouse and Rat Cytochrome P450 1A and 2B Subfamily Enzymes using Molecular Modeling, Docking and Dynamics Simulations.

PubMed

Karthikeyan, Bagavathy Shanmugam; Suvaithenamudhan, Suvaiyarasan; Akbarsha, Mohammad Abdulkader; Parthasarathy, Subbiah

2018-06-01

Cytochrome P450 (CYP) 1A and 2B subfamily enzymes are important drug metabolizing enzymes, and are highly conserved across species in terms of sequence homology. However, there are major to minor structural and macromolecular differences which provide for species-selectivity and substrate-selectivity. Therefore, species-selectivity of CYP1A and CYP2B subfamily proteins across human, mouse and rat was analyzed using molecular modeling, docking and dynamics simulations when the chiral molecules quinine and quinidine were used as ligands. The three-dimensional structures of 17 proteins belonging to CYP1A and CYP2B subfamilies of mouse and rat were predicted by adopting homology modeling using the available structures of human CYP1A and CYP2B proteins as templates. Molecular docking and dynamics simulations of quinine and quinidine with CYP1A subfamily proteins revealed the existence of species-selectivity across the three species. On the other hand, in the case of CYP2B subfamily proteins, no role for chirality of quinine and quinidine in forming complexes with CYP2B subfamily proteins of the three species was indicated. Our findings reveal the roles of active site amino acid residues of CYP1A and CYP2B subfamily proteins and provide insights into species-selectivity of these enzymes across human, mouse, and rat.

Spin Chirality of Cu3 and V3 Nanomagnets. 1. Rotation Behavior of Vector Chirality, Scalar Chirality, and Magnetization in the Rotating Magnetic Field, Magnetochiral Correlations.

PubMed

Belinsky, Moisey I

2016-05-02

The rotation behavior of the vector chirality κ, scalar chirality χ, and magnetization M in the rotating magnetic field H1 is considered for the V3 and Cu3 nanomagnets, in which the Dzialoshinsky-Moriya coupling is active. The polar rotation of the field H1 of the given strength H1 results in the energy spectrum characterized by different vector and scalar chiralities in the ground and excited states. The magnetochiral correlations between the vector and scalar chiralities, energy, and magnetization in the rotating field were considered. Under the uniform polar rotation of the field H1, the ground-state chirality vector κI performs sawtooth oscillations and the magnetization vector MI performs the sawtooth oscillating rotation that is accompanied by the correlated transformation of the scalar chirality χI. This demonstrates the magnetochiral effect of the joint rotation behavior and simultaneous frustrations of the spin chiralities and magnetization in the rotating field, which are governed by the correlation between the chiralities and magnetization.

Timoshenko beam model for chiral materials

NASA Astrophysics Data System (ADS)

Ma, T. Y.; Wang, Y. N.; Yuan, L.; Wang, J. S.; Qin, Q. H.

2017-12-01

Natural and artificial chiral materials such as deoxyribonucleic acid (DNA), chromatin fibers, flagellar filaments, chiral nanotubes, and chiral lattice materials widely exist. Due to the chirality of intricately helical or twisted microstructures, such materials hold great promise for use in diverse applications in smart sensors and actuators, force probes in biomedical engineering, structural elements for absorption of microwaves and elastic waves, etc. In this paper, a Timoshenko beam model for chiral materials is developed based on noncentrosymmetric micropolar elasticity theory. The governing equations and boundary conditions for a chiral beam problem are derived using the variational method and Hamilton's principle. The static bending and free vibration problem of a chiral beam are investigated using the proposed model. It is found that chirality can significantly affect the mechanical behavior of beams, making materials more flexible compared with nonchiral counterparts, inducing coupled twisting deformation, relatively larger deflection, and lower natural frequency. This study is helpful not only for understanding the mechanical behavior of chiral materials such as DNA and chromatin fibers and characterizing their mechanical properties, but also for the design of hierarchically structured chiral materials.

Timoshenko beam model for chiral materials

NASA Astrophysics Data System (ADS)

Ma, T. Y.; Wang, Y. N.; Yuan, L.; Wang, J. S.; Qin, Q. H.

2018-06-01

Natural and artificial chiral materials such as deoxyribonucleic acid (DNA), chromatin fibers, flagellar filaments, chiral nanotubes, and chiral lattice materials widely exist. Due to the chirality of intricately helical or twisted microstructures, such materials hold great promise for use in diverse applications in smart sensors and actuators, force probes in biomedical engineering, structural elements for absorption of microwaves and elastic waves, etc. In this paper, a Timoshenko beam model for chiral materials is developed based on noncentrosymmetric micropolar elasticity theory. The governing equations and boundary conditions for a chiral beam problem are derived using the variational method and Hamilton's principle. The static bending and free vibration problem of a chiral beam are investigated using the proposed model. It is found that chirality can significantly affect the mechanical behavior of beams, making materials more flexible compared with nonchiral counterparts, inducing coupled twisting deformation, relatively larger deflection, and lower natural frequency. This study is helpful not only for understanding the mechanical behavior of chiral materials such as DNA and chromatin fibers and characterizing their mechanical properties, but also for the design of hierarchically structured chiral materials.

Some recent experimental results related to nuclear chirality

NASA Astrophysics Data System (ADS)

Timár, J.; Kuti, I.; Sohler, D.; Starosta, K.; Koike, T.; Paul, E. S.

2014-09-01

Detailed band structures of three chiral-candidate nuclei, 134Pr, 132La and 103Rh have been studied. The aim of the study was twofold. First, to try to explore the reasons behind the contradiction between the theoretically predicted chirality in these nuclei and the recently observed fingerprints that suggest non-chiral interpretation for the previous chiral candidate band doublets. Second, to search for multiple chiral bands of different types in these nuclei. In 134Pr a new πh11/2vh11/2 band has been observed besides the previously known chiral-candidate πh11/2vh11/2 doublet. This new band and the yrare πh11/2vh11/2 band show the expected features of a chiral doublet structure. This fact combined with the observed similarity between the band structures of 134Pr and 132La suggests that chirality might exist in these nuclei. The detailed study of the 103Rh band structure resulted in the observation of two new chiral-doublet looking structures besides the previously known one. This is indicative of possible existence of multiple chiral doublet structure in this nucleus.

Rashba spin-orbit coupling and orbital chirality in magnetic bilayers

NASA Astrophysics Data System (ADS)

Lee, Hyun-Woo

2013-03-01

The phenomenon of the Rashba spin-orbit coupling is examined theoretically for an ultrathin magnetic layer in contact with a non-magnetic heavy metal layer. From first-principles calculation, large Rashba parameter of order 1 eV .Å is obtained, which is strong enough to generate large spin transfer torque of spin-orbit coupling origin. Large Rashba parameter is attributed to the orbital mixing of 3 d magnetic atoms and non-magnetic heavy elements with significant atomic spin-orbit coupling. Interestingly the magnitude and sign of the parameter vary from energy bands to bands, which we attribute to band-specific chiral ordering of orbital angular momentum. Through a simple tight-binding model analysis, we demonstrate that d-orbital hybridization allowed by the breaking of structural inversion symmetry generates band-specific chiral ordering of orbital angular momentum, which combines with atomic spin-orbit coupling to give rise to band-specific Rashba parameter. The band-dependence of the Rashba parameter is discussed in connection with recent experiments and we argue that the dependence may be utilized to enhance device application potentials. This work is supported by NRF grant (2010-0008529, 2011-0015631, 2010-0014109, 2011-0030789).

Vectorial control of nonlinear emission via chiral butterfly nanoantennas: generation of pure high order nonlinear vortex beams.

PubMed

Lesina, Antonino Cala'; Berini, Pierre; Ramunno, Lora

2017-02-06

We report on a chiral gap-nanostructure, which we term a "butterfly nanoantenna," that offers full vectorial control over nonlinear emission. The field enhancement in its gap occurs for only one circular polarization but for every incident linear polarization. As the polarization, phase and amplitude of the linear field in the gap are highly controlled, the linear field can drive nonlinear emitters within the gap, which behave as an idealized Huygens source. A general framework is thereby proposed wherein the butterfly nanoantennas can be arranged in a metasurface, and the nonlinear Huygens sources exploited to produce a highly structured far-field optical beam. Nonlinearity allows us to shape the light at shorter wavelengths, not accessible by linear plasmonics, and resulting in high purity beams. The chirality of the butterfly allows us to create orbital angular momentum states using a linearly polarized excitation. A third harmonic Laguerre-Gauss beam carrying an optical orbital angular momentum of 41 is demonstrated as an example, through large-scale simulations on a high-performance computing platform of the full plasmonic metasurface with an area large enough to contain up to 3600 nanoantennas.