Artykuły w czasopismach: „Chiral Geometries”

1

De Santo, Maria Penelope, Lorenza Spina i Federica Ciuchi. "Chiral Chromonics Confined in Spherical Geometries". Applied Sciences 13, nr 7 (2.04.2023): 4507. http://dx.doi.org/10.3390/app13074507.

Pełny tekst źródła

Streszczenie:

Chromonic liquid crystals have recently received a lot of attention due to their spontaneous self-assembly in supramolecular columnar structures that, depending on their concentration in water, align to form a nematic liquid crystalline phase. The chirality may be induced in chromonics by adding chiral moieties to the nematic phase or enhanced by confining them in curved geometrical constraints. This review summarizes the recent research developments on chiral chromonic liquid crystals confined in spherical geometry, relating the results to what was observed for thermotropic liquid crystals in the same conditions. The review focuses on the studies carried out on commercially available nematic chromonics, investigating the effects on their topologies in different anchoring conditions and different chiral dopants and suggesting an application in the sensor field.

Style APA, Harvard, Vancouver, ISO itp.

2

Leemans, Dimitri, i Philippe Tranchida. "On residual connectedness in chiral geometries". Algebraic Combinatorics 4, nr 3 (22.06.2021): 491–99. http://dx.doi.org/10.5802/alco.162.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

3

Lowe, David A., i Shubho Roy. "Chiral geometries of (2+1)-d AdS gravity". Physics Letters B 668, nr 2 (październik 2008): 159–62. http://dx.doi.org/10.1016/j.physletb.2008.08.026.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

4

Öeren, Mario, Elena Shmatova, Toomas Tamm i Riina Aav. "Computational and ion mobility MS study of (all-S)-cyclohexylhemicucurbit[6]uril structure and complexes". Phys. Chem. Chem. Phys. 16, nr 36 (2014): 19198–205. http://dx.doi.org/10.1039/c4cp02202e.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

5

Ma, Wei, Changlong Hao, Maozhong Sun, Liguang Xu, Chuanlai Xu i Hua Kuang. "Tuning of chiral construction, structural diversity, scale transformation and chiroptical applications". Materials Horizons 5, nr 2 (2018): 141–61. http://dx.doi.org/10.1039/c7mh00966f.

Pełny tekst źródła

Streszczenie:

Dissymmetry is crucial for chiral geometries that utilize either intrinsic anisotropy forces around nanoparticles (NPs) or external organization associated with templates or applied fields and alignment.

Style APA, Harvard, Vancouver, ISO itp.

6

Chen, Sicong, Qiwen Teng i Shi Wu. "Theoretical studies on the binding affinities of β-cyclodextrin to small molecules and monosaccharides". Open Chemistry 4, nr 2 (1.06.2006): 223–33. http://dx.doi.org/10.2478/s11532-006-0013-5.

Pełny tekst źródła

Streszczenie:

AbstractEquilibrium geometries and electronic structures of complexes between β-cyclodextrin (β-CD) and some small molecules as well as monosaccharides were investigated by Austin Model 1 (AM1) to obtain binding energy of the complexes. It was indicated that β-CD could bind the structurally similar solvent molecules and monosaccharides because of the negative binding energy of the complexes, and especially could show the chiral binding ability to monosaccharides with more hydroxyl groups, due to its chiral characteristics. The complexes were stabilized by the hydrogen bonding between β-CD and guests. Based on the AM1 optimized geometries, the IR spectra were calculated by AM1 method. Vibration frequencies of O-H bonds in the guests were red-shifted owing to the weakening of the O-H bonds with the formation of the complexes.

Style APA, Harvard, Vancouver, ISO itp.

7

Skolnick, Jeffrey, Hongyi Zhou i Mu Gao. "On the possible origin of protein homochirality, structure, and biochemical function". Proceedings of the National Academy of Sciences 116, nr 52 (10.12.2019): 26571–79. http://dx.doi.org/10.1073/pnas.1908241116.

Pełny tekst źródła

Streszczenie:

Living systems have chiral molecules, e.g., native proteins that almost entirely contain L-amino acids. How protein homochirality emerged from a background of equal numbers of L and D amino acids is among many questions about life’s origin. The origin of homochirality and its implications are explored in computer simulations examining the stability and structural and functional properties of an artificial library of compact proteins containing 1:1 (termed demi-chiral), 3:1, and 1:3 ratios of D:L and purely L or D amino acids generated without functional selection. Demi-chiral proteins have shorter secondary structures and fewer internal hydrogen bonds and are less stable than homochiral proteins. Selection for hydrogen bonding yields a preponderance of L or D amino acids. Demi-chiral proteins have native global folds, including similarity to early ribosomal proteins, similar small molecule ligand binding pocket geometries, and many constellations of L-chiral amino acids with a 1.0-Å RMSD to native enzyme active sites. For a representative subset containing 550 active site geometries matching 457 (2) 4-digit (3-digit) enzyme classification (E.C.) numbers, native active site amino acids were generated at random for 472 of 550 cases. This increases to 548 of 550 cases when similar residues are allowed. The most frequently generated sequences correspond to ancient enzymatic functions, e.g., glycolysis, replication, and nucleotide biosynthesis. Surprisingly, even without selection, demi-chiral proteins possess the requisite marginal biochemical function and structure of modern proteins, but were thermodynamically less stable. If demi-chiral proteins were present, they could engage in early metabolism, which created the feedback loop for transcription and cell formation.

Style APA, Harvard, Vancouver, ISO itp.

8

Cirilo-Lombardo, Diego Julio. "Born-Infeld generalization: Axion and Kalb-Ramond from dynamical torsion fields". Europhysics Letters 135, nr 6 (1.09.2021): 61001. http://dx.doi.org/10.1209/0295-5075/ac2cfa.

Pełny tekst źródła

Streszczenie:

Abstract We show that in theories of gravitation based on affine geometries the torsion field, that takes a dynamical character, not only the chiral magnetic effect (CME) intervenes in the wash up of the chiral anomaly but also the chiral vortical effect (CVE) and the coupled chiral effect (CCE) coming from the hypermagnetic field interaction with the primordial plasma are crucial in a realistic physical scenario, as in the case of the early universe. We also show that the equation governing the wash up takes the form given in this paper, supplemented with the dynamical equation for the torsion vector containing the helicities and other axial couplings. The role played by the neutrinos in the interaction with the axion field in this theoretical framework is briefly discussed.

Style APA, Harvard, Vancouver, ISO itp.

9

BRACKEN, PAUL. "LINKS BETWEEN THE QUANTUM HALL EFFECT, CHIRAL BOSON THEORIES AND STRING THEORY". International Journal of Modern Physics E 13, nr 05 (październik 2004): 961–71. http://dx.doi.org/10.1142/s021830130400251x.

Pełny tekst źródła

Streszczenie:

Chiral boson theory is introduced and its relevance to the quantum Hall effect is explained. It is shown that the chiral boson theory admits mode expansions which are essentially those which appear and are made use of in bosonic string theories. This immediately leads to a way of quantizing the theory. Restrictions on various parameters appearing in the model can be imposed in a natural way. Finally, it is suggested that some of these ideas have important applications to other geometries which could give rise to new types of physical behavior.

Style APA, Harvard, Vancouver, ISO itp.

10

Sevrin, Alexander, Wieland Staessens i Alexander Wijns. "AnN= 2 worldsheet approach to D-branes in bihermitian geometries: I. Chiral and twisted chiral fields". Journal of High Energy Physics 2008, nr 10 (29.10.2008): 108. http://dx.doi.org/10.1088/1126-6708/2008/10/108.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

11

Rozanski, S. A., L. Naji, F. Kremer i R. Stannarius. "Influence of Confining Geometries on Collective Dynamic Modes in Chiral Smectogens". Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 329, nr 1 (sierpień 1999): 483–90. http://dx.doi.org/10.1080/10587259908025972.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

12

Buß, Volker, Verena Haas i Ute Wingen. "Strukturuntersuchungen an chiralen Schiff-Basen des 11-cis-Retinals/Structure Investigation of Chiral Schiff Bases of 11-cis-Retinal". Zeitschrift für Naturforschung B 44, nr 3 (1.03.1989): 333–44. http://dx.doi.org/10.1515/znb-1989-0315.

Pełny tekst źródła

Streszczenie:

CD and UV spectra of four chiral 11-cis-retinal Schiff bases obtained by condensing the aldehyde with asymmetric amines are used to gain structural information about the polyene conformation. The spectra are temperature-dependent indicating the same 12-s-cis/trans equilibrium as in 11-cis-retinal. In addition, CD absorptions arise at lower temperatures whose only origin is the inherent dissymmetric nature of the retinylidene Chromophore. CNDO /S-calculations performed on the basis of force-field optimized geometries give results which can partially be rationalized on the basis of experimental data. Quantitative agreement is obtained in the case of chiral hydrogen-bonded dimers.

Style APA, Harvard, Vancouver, ISO itp.

13

Jang, Dongmin, Yoonbai Kim, O.-Kab Kwon i D. D. Tolla. "Exact Holography of Massive M2-brane Theories and Entanglement Entropy". EPJ Web of Conferences 168 (2018): 07002. http://dx.doi.org/10.1051/epjconf/201816807002.

Pełny tekst źródła

Streszczenie:

We test the gauge/gravity duality between the N = 6 mass-deformed ABJM theory with Uk(N) × U-k(N) gauge symmetry and the 11-dimensional supergravity on LLM geometries with SO(4)=ℤk × SO(4)=ℤk isometry. Our analysis is based on the evaluation of vacuum expectation values of chiral primary operators from the supersymmetric vacua of mass-deformed ABJM theory and from the implementation of Kaluza-Klein (KK) holography to the LLM geometries. We focus on the chiral primary operator (CPO) with conformal dimension Δ = 1. The non-vanishing vacuum expectation value (vev) implies the breaking of conformal symmetry. In that case, we show that the variation of the holographic entanglement entropy (HEE) from it’s value in the CFT, is related to the non-vanishing one-point function due to the relevant deformation as well as the source field. Applying Ryu Takayanagi’s HEE conjecture to the 4-dimensional gravity solutions, which are obtained from the KK reduction of the 11-dimensional LLM solutions, we calculate the variation of the HEE. We show how the vev and the value of the source field determine the HEE.

Style APA, Harvard, Vancouver, ISO itp.

14

Sereda, Olha, i Helen Stoeckli-Evans. "Crystal structures of {[Cu(Lpn)2][Fe(CN)5(NO)]·H2O}nand {[Cu(Lpn)2]3[Cr(CN)6]2·5H2O}n[where Lpn = (R)-propane-1,2-diamine]: two heterometallic chiral cyanide-bridged coordination polymers". Acta Crystallographica Section E Crystallographic Communications 71, nr 4 (21.03.2015): 392–97. http://dx.doi.org/10.1107/s2056989015005253.

Pełny tekst źródła

Streszczenie:

The title compounds,catena-poly[[[bis[(R)-propane-1,2-diamine-κ2N,N′]copper(II)]-μ-cyanido-κ2N:C-[tris(cyanido-κC)(nitroso-κN)iron(III)]-μ-cyanido-κ2C:N] monohydrate], {[Cu(Lpn)2][Fe(CN)5(NO)]·H2O}n, (I), and poly[[hexa-μ-cyanido-κ12C:N-hexacyanido-κ6C-hexakis[(R)-propane-1,2-diamine-κ2N,N′]dichromium(III)tricopper(II)] pentahydrate], {[Cu(Lpn)2]3[Cr(CN)6]2·5H2O}n, (II) [where Lpn = (R)-propane-1,2-diamine, C3H10N2], are new chiral cyanide-bridged bimetallic coordination polymers. The asymmetric unit of compound (I) is composed of two independent cation–anion units of {[Cu(Lpn)2][Fe(CN)5)(NO)]} and two water molecules. The FeIIIatoms have distorted octahedral geometries, while the CuIIatoms can be considered to be pentacoordinate. In the crystal, however, the units align to form zigzag cyanide-bridged chains propagating along [101]. Hence, the CuIIatoms have distorted octahedral coordination spheres with extremely long semicoordination Cu—N(cyanido) bridging bonds. The chains are linked by O—H...N and N—H...N hydrogen bonds, forming two-dimensional networks parallel to (010), and the networks are linkedviaN—H...O and N—H...N hydrogen bonds, forming a three-dimensional framework. Compound (II) is a two-dimensional cyanide-bridged coordination polymer. The asymmetric unit is composed of two chiral {[Cu(Lpn)2][Cr(CN)6]}−anions bridged by a chiral [Cu(Lpn)2]2+cation and five water molecules of crystallization. Both the CrIIIatoms and the central CuIIatom have distorted octahedral geometries. The coordination spheres of the outer CuIIatoms of the asymmetric unit can be considered to be pentacoordinate. In the crystal, these units are bridged by long semicoordination Cu—N(cyanide) bridging bonds forming a two-dimensional network, hence these CuIIatoms now have distorted octahedral geometries. The networks, which lie parallel to (10-1), are linkedviaO—H...O, O—H...N, N—H...O and N—H...N hydrogen bonds involving all five non-coordinating water molecules, the cyanide N atoms and the NH2groups of the Lpn ligands, forming a three-dimensional framework.

Style APA, Harvard, Vancouver, ISO itp.

15

Pang, Xiaojuan, Chenwei Jiang, Yongnan Qi, Ling Yuan, Deping Hu, Xiuxing Zhang, Di Zhao, Dongdong Wang, Zhenggang Lan i Fuli Li. "Ultrafast unidirectional chiral rotation in the Z–E photoisomerization of two azoheteroarene photoswitches". Physical Chemistry Chemical Physics 20, nr 40 (2018): 25910–17. http://dx.doi.org/10.1039/c8cp04762f.

Pełny tekst źródła

Streszczenie:

Based on a large number of trajectories starting from the Z-isomer, for both azoheteroarenes, more than 99% of the trajectories decay through conical intersections with the same helicities as their initial geometries.

Style APA, Harvard, Vancouver, ISO itp.

16

Bracho, Javier, Isabel Hubard i Daniel Pellicer. "Chiral Polyhedra in 3-Dimensional Geometries and from a Petrie–Coxeter Construction". Discrete & Computational Geometry 66, nr 3 (30.08.2021): 1025–52. http://dx.doi.org/10.1007/s00454-021-00317-0.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

17

Zeng, Yang, Federico Masini, Anton M. H. Rasmussen, Michael N. Groves, Vincent Albert, John Boukouvalas i Peter H. McBreen. "The most stable adsorption geometries of two chiral modifiers on Pt(111)". Surface Science 676 (październik 2018): 17–22. http://dx.doi.org/10.1016/j.susc.2018.02.008.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

18

Benito-Garagorri, David, Kurt Mereiter i Karl Kirchner. "Synthesis and Characterization of Ni(II) and Pd(II) Complexes Bearing Achiral and Chiral Bidentate Aminophosphine Ligands". Collection of Czechoslovak Chemical Communications 72, nr 4 (2007): 527–40. http://dx.doi.org/10.1135/cccc20070527.

Pełny tekst źródła

Streszczenie:

The synthesis of a range of achiral and chiral bidentate aminophosphine ligands and their complexes with nickel(II) and palladium(II) has been investigated. The ligands and the complexes have been characterized by NMR spectroscopy, and X-ray structures of representative compounds have been determined. In addition, DFT calculations have been performed to investigate different geometries of the nickel(II) complexes in the solid state and in solution.

Style APA, Harvard, Vancouver, ISO itp.

19

Lorenzo, Salvatore, Benedetto Militello, Anna Napoli, Roberta Zambrini i G. Massimo Palma. "Quantum synchronisation and clustering in chiral networks". New Journal of Physics 24, nr 2 (1.02.2022): 023030. http://dx.doi.org/10.1088/1367-2630/ac51a9.

Pełny tekst źródła

Streszczenie:

Abstract We study the emergence of synchronisation in a chiral network of harmonic oscillators. The network consists of a set of locally incoherently pumped harmonic oscillators coupled pairwise in cascade with travelling field modes. Such cascaded coupling leads to feedback-less dissipative interaction between the harmonic oscillators of the pair which can be described in terms of an effective pairwise Hamiltonian a collective pairwise decay. The network is described mathematically in terms of a directed graph. By analysing geometries of increasing complexity we show how the onset of synchronisation depends strongly on the network topology, with the emergence of synchronised communities in the case of complex networks. The quantum nature of the non local correlation between network nodes is assessed.

Style APA, Harvard, Vancouver, ISO itp.

20

Dincer, Furkan, Oguzhan Akgol, Muharrrem Karaaslan, Emin Unal, Ekrem Demirel i Cumali Sabah. "New generation chiral metamaterials based on omega resonators with small and smooth chirality over a certain frequency band". Modern Physics Letters B 30, nr 05 (20.02.2016): 1650040. http://dx.doi.org/10.1142/s0217984916500408.

Pełny tekst źródła

Streszczenie:

In this paper, we have designed, simulated and analyzed a new generation chiral metamaterials (MTMs) with two geometries. There are various types of chiral MTM structures in the literature and almost all of them are indented to be designed for high level of chirality. In fact, small chirality and its application areas were mostly ignored by researchers. In this sense, our study is one of the pioneer works for this type of research. Each structure based on omega resonators (ORs) with small chirality value is investigated both numerically and experimentally. The results are in very good agreement which will lead us to conclude that our structures can be easily used as devices for controlling polarization, EM wave transmission filtering, antireflection and so on for a wide range of the EM spectrum.

Style APA, Harvard, Vancouver, ISO itp.

21

Rubino, S., P. Schattschneider, M. Stöger-Pollach, C. Hébert, J. Rusz, L. Calmels, B. Warot-Fonrose, F. Houdellier, V. Serin i P. Novak. "Energy-loss magnetic chiral dichroism (EMCD): Magnetic chiral dichroism in the electron microscope". Journal of Materials Research 23, nr 10 (październik 2008): 2582–90. http://dx.doi.org/10.1557/jmr.2008.0348.

Pełny tekst źródła

Streszczenie:

A new technique called energy-loss magnetic chiral dichroism (EMCD) has recently been developed [P. Schattschneider, et al. Nature441, 486 (2006)] to measure magnetic circular dichroism in the transmission electron microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of x-ray magnetic circular dichroism, which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods that can be used to measure the EMCD signal [P. Schattschneider, et al. Nature441, 486 (2006); C. Hébert, et al. Ultramicroscopy108(3), 277 (2008); B. Warot-Fonrose, et al. Ultramicroscopy108(5), 393 (2008); L. Calmels, et al. Phys. Rev. B76, 060409 (2007); P. van Aken, et al. Microsc. Microanal.13(3), 426 (2007)] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals iron, cobalt, and nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique consist of measuring atomic specific magnetic moments, using suitable spin and orbital sum rules, [L. Calmels, et al. Phys. Rev. B76, 060409 (2007); J. Rusz, et al. Phys. Rev. B76, 060408 (2007)] with a resolution down to 2 to 3 nm.

Style APA, Harvard, Vancouver, ISO itp.

22

GUNARA, BOBBY E., FREDDY P. ZEN, FIKI T. AKBAR, AGUS SUROSO i ARIANTO. "SOME ASPECTS OF SPHERICAL SYMMETRIC EXTREMAL DYONIC BLACK HOLES IN 4D N = 1 SUPERGRAVITY". International Journal of Modern Physics A 28, nr 18 (20.07.2013): 1350084. http://dx.doi.org/10.1142/s0217751x1350084x.

Pełny tekst źródła

Streszczenie:

In this paper, we study several aspects of extremal spherical symmetric black hole solutions of four-dimensional N = 1 supergravity coupled to vector and chiral multiplets with the scalar potential turned on. In the asymptotic region, the complex scalars are fixed and regular which can be viewed as the critical points of the black hole and the scalar potentials with vanishing scalar charges. It follows that the asymptotic geometries are of a constant and nonzero scalar curvature which are generally not Einstein. These spaces could also correspond to the near horizon geometries which are the product spaces of a two anti-de Sitter surface and the two sphere if the value of the scalars in both regions coincide. In addition, we prove the local existence of nontrivial radius dependent complex scalar fields which interpolate between the horizon and the asymptotic region. We finally give some simple ℂn-models with both linear superpotential and gauge couplings.

Style APA, Harvard, Vancouver, ISO itp.

23

Korytár, Richard, i Ferdinand Evers. "Current-induced mechanical torque in chiral molecular rotors". Beilstein Journal of Nanotechnology 14 (12.06.2023): 711–21. http://dx.doi.org/10.3762/bjnano.14.57.

Pełny tekst źródła

Streszczenie:

There has been great endeavor to engineer molecular rotors operated by an electrical current. A frequently met operation principle is the transfer of angular momentum taken from the incident flux. In this paper, we present an alternative driving agent that works also in situations where angular momentum of the incoming flux is conserved. This situation arises typically with molecular rotors that exhibit an easy axis of rotation. For quantitative analysis we investigate here a classical model where molecule and wires are represented by a rigid curved path. We demonstrate that in the presence of chirality, the rotor generically undergoes a directed motion, provided that the incident current exceeds a threshold value. Above this threshold, the corresponding rotation frequency (per incoming particle current) for helical geometries turns out to be 2πm/M1, where m/M1 is the ratio of the mass of an incident charge carrier and the mass of the helix per winding number.

Style APA, Harvard, Vancouver, ISO itp.

24

Ferreira-Gomes, Bruno, Osvaldo N. Oliveira i Jorge Ricardo Mejía-Salazar. "Chiral Dielectric Metasurfaces for Highly Integrated, Broadband Circularly Polarized Antenna". Sensors 21, nr 6 (16.03.2021): 2071. http://dx.doi.org/10.3390/s21062071.

Pełny tekst źródła

Streszczenie:

We report on the design of a low-profile integrated millimeter-wave antenna for efficient and broadband circularly polarized electromagnetic radiation. The designed antenna comprises a chiral dielectric metasurface built with a 2×2 arrangement of dielectric cylinders with slanted-slots at the center. A broadbeam high-gain with wide axial ratio (AR)<3 dB bandwidth was reached by pairing the electric and magnetic resonances of the dielectric cylinders and the slanted slots when excited by an elliptically polarized driven-patch antenna. This electric-magnetic pairing can be tuned by varying the cylinders diameter and the tilting and rotation angles of the slanted slots. The simulation results indicate impedance-matching bandwidths up to 22.6% (25.3–31.6 GHz) with 3-dB AR bandwidths of 11.6% (26.9–30.2 GHz), which in terms of compactness (0.95λ0×0.95λ0) and performance are superior to previous antenna designs. Since the simulations were performed by assuming materials and geometries easily implementable experimentally, it is hoped that circularly polarized antennas based on chiral metasurfaces can be integrated into 5G and satellite communications.

Style APA, Harvard, Vancouver, ISO itp.

25

Terasaki, Osamu, Zheng Liu, Tetsu Ohsuna, Hyun June Shin i Ryong Ryoo. "Electron Microscopy Study of Novel Pt Nanowires Synthesized in the Spaces of Silica Mesoporous Materials". Microscopy and Microanalysis 8, nr 1 (luty 2002): 35–39. http://dx.doi.org/10.1017/s1431927602010073.

Pełny tekst źródła

Streszczenie:

Structures of Pt-nanowires, synthesized in channels of silica mesoporous materials MCM-41, SBA-15 and MCM-48, were investigated by transmission electron microscopy. One dimensional (1D) Pt-nanowires were formed inside the channels of the MCM-41, and were single crystals with a length of several tens to several hundreds nanometers and a diameter of ca. 3 nm Pt-nanowires synthesized in SBA-15 formed a new 3D-network following 3D-pore geometry of SBA-15; that is, the main 1D-channels are interconnected to each other through randomly distributed tunnels. These Pt-nanowires showed a well single crystalline. MCM-48 has two non-intersecting chiral channels, and Pt-networks were mostly formed in one of the two channels. Therefore the networks were also chiral; however, the chirality of Pt-networks remained to be determined. It was shown that all Pt-nanowires were formed following the channel geometries of silica mesoporous materials used.

Style APA, Harvard, Vancouver, ISO itp.

26

Știufiuc, Gabriela Fabiola, Valentin Toma, Anca Onaciu, Vasile Chiș, Constantin Mihai Lucaciu i Rareș Ionuț Știufiuc. "Proving Nanoscale Chiral Interactions of Cyclodextrins and Propranolol Enantiomers by Means of SERS Measurements Performed on a Solid Plasmonic Substrate". Pharmaceutics 13, nr 10 (1.10.2021): 1594. http://dx.doi.org/10.3390/pharmaceutics13101594.

Pełny tekst źródła

Streszczenie:

Chiral separation is an important issue for the pharmaceutical industry. Over the years, several separation methods have been developed, mainly based on chromatography. Their working principle is based on the formation of transient diastereoisomers, but the very subtle nanoscale interactions responsible for separation are not always understood. Recently, Raman and surface-enhanced Raman (SERS) spectroscopy have provided promising results in this field. Here we present Raman/SERS experimental data that provide useful information concerning the nanoscale interactions between propranolol enantiomers and α, β, and γ cyclodextrins. Raman spectroscopy was used to prove the formation of host–guest intermolecular complexes having different geometries of interaction. The occurrence of new vibrational bands and a change in the intensities of others are direct proofs of complexes’ formation. These observations were confirmed by DFT calculations. By performing SERS measurements on a new type of plasmonic substrate, we were able to prove the intermolecular interactions responsible for PRNL discrimination. It turned out that the interaction strength between the substrate and the intermolecular complexes is of paramount importance for SERS-based chiral discrimination. This approach could represent a very good starting point for the evaluation of molecular interactions manifesting between other pharmaceutical compounds and different classes of chiral selectors.

Style APA, Harvard, Vancouver, ISO itp.

27

Golze, Spencer D., Stefania Porcu, Chen Zhu, Eli Sutter, Pier Carlo Ricci, Edward C. Kinzel, Robert A. Hughes i Svetlana Neretina. "Sequential Symmetry-Breaking Events as a Synthetic Pathway for Chiral Gold Nanostructures with Spiral Geometries". Nano Letters 21, nr 7 (25.03.2021): 2919–25. http://dx.doi.org/10.1021/acs.nanolett.0c05105.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

28

Ito, Jun-ichi, Takahiro Ishihara, Takaki Fukuoka, Siti Rokiah Binti Mat Napi, Hajime Kameo i Hisao Nishiyama. "Modulation of the coordination geometries of NCN and NCNC Rh complexes for ambidextrous chiral catalysts". Chemical Communications 55, nr 85 (2019): 12765–68. http://dx.doi.org/10.1039/c9cc06520b.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

29

Pointner, Andreas, i Rudolf Herrmann. "Transition State Geometry and Solvent Effects in the Enantioselective Oxidation of Sulfides to Chiral Sulfoxides by Oxaziridines". Zeitschrift für Naturforschung B 50, nr 9 (1.09.1995): 1396–403. http://dx.doi.org/10.1515/znb-1995-0917.

Pełny tekst źródła

Streszczenie:

AbstractFor the enantioselective oxidation of methyl phenyl sulfide and tert-butyl methyl sulfide to the corresponding chiral sulfoxides by 3,3-dibromo-(camphorsulfonyl)oxaziridine, semiempirical calculations (MNDO, AMI, PM3) concerning transition state geometries were performed. The results show that only PM3 is able to localize a transition state. For methyl phenyl sulfide, a spiro arrangement of the oxaziridine ring and the sulfur atom explains the observed direction of the selectivity better than a planar transition state. The solvent dependence of the observed enantioselectivity is related to the calculated dipole moment of the transition state by the Kirkwood-Onsager model. In THF as solvent, its direct participation in the transition state has to be considered

Style APA, Harvard, Vancouver, ISO itp.

30

Øwre, Anders, Morten Vinum, Michal Kern, Joris van Slageren, Jesper Bendix i Mauro Perfetti. "Chiral, Heterometallic Lanthanide–Transition Metal Complexes by Design". Inorganics 6, nr 3 (19.07.2018): 72. http://dx.doi.org/10.3390/inorganics6030072.

Pełny tekst źródła

Streszczenie:

Achieving control over coordination geometries in lanthanide complexes remains a challenge to the coordination chemist. This is particularly the case in the field of molecule-based magnetism, where barriers for magnetic relaxation processes as well as tunneling pathways are strongly influenced by the lanthanide coordination geometry. Addressing the challenge of design of 4f-element coordination environments, the ubiquitous Ln(hfac)3 moieties have been shown to be applicable as Lewis acids coordinating transition metal acetylacetonates facially leading to simple, chiral lanthanide–transition metal heterodinuclear complexes. The broad scope of this approach is illustrated by the synthesis of a range of such complexes LnM: LnM(hfac)3(μ2-acac-O,O,O′)3 (Ln = La, Pr, Gd; M = Cr, Fe, Ga), with approximate three-fold symmetry. The complexes have been crystallographically characterized and exhibit polymorphism for some combinations of 4f and 3d metal centers. However, an isostructural set of systems spanning several lanthanides which exhibit spontaneous resolution in the orthorhombic Sohncke space group P212121 is presented here. The electronic structure and ensuing magnetic properties have been studied by EPR spectroscopy and magnetometry. The GdFe, PrFe, and PrCr complexes exhibit ferromagnetic coupling, while GdCr exhibits antiferromagnetic coupling. GdGa exhibits slow relaxation of the magnetization in applied static fields.

Style APA, Harvard, Vancouver, ISO itp.

31

Vassakis, Emmanouil, Ioannis Orfanos, Ioannis Liontos i Emmanouil Skantzakis. "Generation of Energetic Highly Elliptical Extreme Ultraviolet Radiation". Photonics 8, nr 9 (9.09.2021): 378. http://dx.doi.org/10.3390/photonics8090378.

Pełny tekst źródła

Streszczenie:

In this study, the generation of energetic coherent extreme ultraviolet (XUV) radiation with the potential for controlled polarization is reported. The XUV radiation results from the process of high harmonic generation (HHG) in a gas phase atomic medium, driven by an intense two-color circularly polarized counter-rotating laser field, under loose focusing geometry conditions. The energy of the XUV radiation emitted per laser pulse is found to be of the order of ~100 nJ with the spectrum spanning from 17 to 26 eV. The demonstrated energy values (along with tight XUV focusing geometries) are sufficient to induce nonlinear processes. Our results challenge current perspectives regarding ultrafast investigations of chiral phenomena in the XUV spectral region.

Style APA, Harvard, Vancouver, ISO itp.

32

Saberi, Ingmar, i Brian R. Williams. "Twisted characters and holomorphic symmetries". Letters in Mathematical Physics 110, nr 10 (3.08.2020): 2779–853. http://dx.doi.org/10.1007/s11005-020-01319-4.

Pełny tekst źródła

Streszczenie:

Abstract We consider holomorphic twists of arbitrary supersymmetric theories in four dimensions. Working in the BV formalism, we rederive classical results characterizing the holomorphic twist of chiral and vector supermultiplets, computing the twist explicitly as a family over the space of nilpotent supercharges in minimal supersymmetry. The BV formalism allows one to work with or without auxiliary fields, according to preference; for chiral superfields, we show that the result of the twist is an identical BV theory, the holomorphic $$\beta \gamma $$ β γ system with superpotential, independent of whether or not auxiliary fields are included. We compute the character of local operators in this holomorphic theory, demonstrating agreement of the free local operators with the usual index of free fields. The local operators with superpotential are computed via a spectral sequence and are shown to agree with functions on a formal mapping space into the derived critical locus of the superpotential. We consider the holomorphic theory on various geometries, including Hopf manifolds and products of arbitrary pairs of Riemann surfaces, and offer some general remarks on dimensional reductions of holomorphic theories along the $$(n-1)$$ ( n - 1 ) -sphere to topological quantum mechanics. We also study an infinite-dimensional enhancement of the flavor symmetry in this example, to a recently studied central extension of the derived holomorphic functions with values in the original Lie algebra, that generalizes the familiar Kac–Moody enhancement in two-dimensional chiral theories.

Style APA, Harvard, Vancouver, ISO itp.

33

Nair, Greshma, Haobijam Johnson Singh, Debadrita Paria, Murugesan Venkatapathi i Ambarish Ghosh. "Plasmonic Interactions at Close Proximity in Chiral Geometries: Route toward Broadband Chiroptical Response and Giant Enantiomeric Sensitivity". Journal of Physical Chemistry C 118, nr 9 (24.02.2014): 4991–97. http://dx.doi.org/10.1021/jp4117535.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

34

Zhang, Xin Wei, Cun Li i Jun Qi Xu. "Study on the Second-Order Nonlinear Optical Properties of [6]Helicenes with Chromophores". Applied Mechanics and Materials 303-306 (luty 2013): 2563–66. http://dx.doi.org/10.4028/www.scientific.net/amm.303-306.2563.

Pełny tekst źródła

Streszczenie:

A series of chiral [6]helicenes have been designed using the molecular engineering of organic nonlinear optical materials. The geometries of [6]helicenes 1, 2, 3, 4,5 are optimized using density functional theory (DFT-B3LYP) method at the 6-31g (d, p) basis set level. Based on the obtained stable molecular configuration, we adopt the TDHT/PM3 method and time-dependent density-functional theory (TD-DFT) to calculate the nonlinear optical (NLO) properties and electronic spectra of these molecules. Results show that the static hyperpolarizability βµ alternates between positive value and negative value, whereas it remains positive for the molecues 2 and 3 which have medium magnitudes βµ, 3.4×10-30esu and 9.6×10-30esu respectively. In molecule 5, there exists two competitive charge transfers that reduce the hyperpolarizability β.

Style APA, Harvard, Vancouver, ISO itp.

35

Starodubtsev, Evgenii. "Reflection and transmission of nanoresonators including bi-isotropic and metamaterial layers: opportunities to control and amplify chiral and nonreciprocal effects for nanophotonics applications". EPJ Applied Metamaterials 10 (2023): 5. http://dx.doi.org/10.1051/epjam/2023002.

Pełny tekst źródła

Streszczenie:

Electromagnetic waves reflected from and transmitted through the multilayer nanoresonators including the main layer made of a bi-isotropic material or metamaterial sandwiched between dielectric, epsilon-near-zero or metallic spacer layers have been analytically modeled. The numerical and graphical analysis, based on the exact solution of the electromagnetic boundary problem, confirms opportunities to use such nanoresonators as utracompact polarization converters. The proposed systems are characterized by wide ranges of parameters and significantly reduced (subwavelength) thicknesses. The spacer layers can provide modification, control, and amplification of chiral and nonreciprocal effects for the reflected and transmitted radiation. The concept can be realized for various geometries of dielectric, epsilon-near-zero, metallic, bi-isotropic, metamaterial layers and used to develop new ultrathin, large area, and relatively easy-to-manufacture polarization and other devices for nanophotonics.

Style APA, Harvard, Vancouver, ISO itp.

36

Wang, Yuekui, i Chunxia Zhang. "Theoretical Analysis of the Unusual Vicinal Effects on Electronic Circular Dichroism Spectra of Cobalt(III) Complexes with ED3A-Type and Related Ligands". Zeitschrift für Naturforschung A 69, nr 7 (1.07.2014): 371–84. http://dx.doi.org/10.5560/zna.2014-0032.

Pełny tekst źródła

Streszczenie:

To investigate the origin of unusual N-vicinal effects, the geometries of the two series of cobalt(III) complexes, [Co(ED3A-type)(X)]-(X = CN-, NO2-) and [Co(EDDS-type)]-, with the pentadentate ethylenediamine-N;N;N0-triacetate (ED3A), hexadentate (S,S)-ethylenediamine-N;N0-dissuccinate (EDDS), and their N-alkyl-substituted ligands in aqueous solution have been optimized at the DFT/B3P86/6-311++G(2d,p) level of theory. Based on the optimized geometries, the excitation energies and rotational strengths have been calculated using the time dependent density functional theory (TDDFT) method with the same functional and basis set. The optimized geometries and calculated electronic circular dichroism (ECD) curves are in good agreement with the observed ones. Based on this agreement, the characteristics of usual and unusual N-vicinal effects as well as the related chiral stereochemistry phenomena have been discussed. To reveal the origin of the unusual N-vicinal effects, a novel calculation scheme has been proposed, which permits efficiently assessing the contribution of the octahedral core to the optical activities of the chelates. The results show that the substituent effects and conformational relaxation effects make opposite contributions to the overall N-vicinal effects with the former being dominant. The unusual N-vicinal effects originate from the negligible chirality of the octahedral core in the unsubstituted [Co(ED3A)(X)]-chelates. For this reason, their optical activity is dominated by the asymmetric nitrogens and behaves different from the normal cases. The unusual vicinal effects observed in the N-alkyl-substituted ED3A-type chelates reflect an increase in the contribution of the octahedral core to their optical activity, which recovers the ECD spectra from the special cases to the normal ones. These findings provide some insight into the unusual N-vicinal effects as well as the chiroptical properties of the chelates.

Style APA, Harvard, Vancouver, ISO itp.

37

Bocian, Wojciech, Elżbieta Bednarek i Katarzyna Michalska. "Explanation of the Formation of Complexes between Representatives of Oxazolidinones and HDAS-β-CD Using Molecular Modeling as a Complementary Technique to cEKC and NMR". International Journal of Molecular Sciences 22, nr 13 (1.07.2021): 7139. http://dx.doi.org/10.3390/ijms22137139.

Pełny tekst źródła

Streszczenie:

Molecular modeling (MM) results for tedizolid and radezolid with heptakis-(2,3-diacetyl-6-sulfo)-β-cyclodextrin (HDAS-β-CD) are presented and compared with the results previously obtained for linezolid and sutezolid. The mechanism of interaction of chiral oxazolidinone ligands belonging to a new class of antibacterial agents, such as linezolid, tedizolid, radezolid, and sutezolid, with HDAS-β-CD based on capillary electrokinetic chromatography (cEKC), nuclear magnetic resonance (NMR) spectroscopy, and MM methods was described. Principles of chiral separation of oxazolidinone analogues using charged single isomer derivatives of cyclodextrin by the cEKC method were presented, including the selection of the optimal chiral selector and separation conditions, complex stoichiometry, and binding constants, which provided a comprehensive basis for MM studies. In turn, NMR provided, where possible, direct information on the geometry of the inclusion complexes and also provided the necessary structural information to validate the MM calculations. Consequently, MM contributed to the understanding of the structure of diastereomeric complexes, the thermodynamics of complexation, and the visualization of their structures. The most probable mean geometries of the studied supramolecular complexes and their dynamics (geometry changes over time) were determined by molecular dynamics methods. Oxazolidinone ligands have been shown to complex mainly the inner part of cyclodextrin, while the external binding is less privileged, which is consistent with the conclusions of the NMR studies. Enthalpy values of binding of complexes were calculated using long-term molecular dynamics in explicit water as well as using molecular mechanics, the Poisson–Boltzmann or generalized Born, and surface area continuum solvation (MM/PBSA and MM/GBSA) methods. Computational methods predicted the effect of changes in pH and composition of the solution on the strength and complexation process, and it adapted the conditions selected as optimal during the cEKC study. By changing the dielectric constant in the MM/PBSA and MM/GBSA calculations, the effect of changing the solution to methanol/acetonitrile was investigated. A fairly successful attempt was made to predict the chiral separation of the oxazolidinones using the modified cyclodextrin by computational methods.

Style APA, Harvard, Vancouver, ISO itp.

38

Govorov, Alexander O. "Plasmon-Induced Circular Dichroism of a Chiral Molecule in the Vicinity of Metal Nanocrystals. Application to Various Geometries". Journal of Physical Chemistry C 115, nr 16 (kwiecień 2011): 7914–23. http://dx.doi.org/10.1021/jp1121432.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

39

Zhuo, Wang, Shulin Sun, Qiong He i Lei Zhou. "A review of high-efficiency Pancharatnam–Berry metasurfaces". Terahertz Science and Technology 13, nr 3 (wrzesień 2020): 73–89. http://dx.doi.org/10.1051/tst/2020133073.

Pełny tekst źródła

Streszczenie:

Manipulating circularly polarized (CP) electromagnetic waves as desired is important for a wide range of applications ranging from chiral-molecule manipulations to optical communication, but conventional natural-materials-based devices suffer from bulky configuration and low efficiencies. Recently, Pancharatnam–Berry (PB) metasurfaces have demonstrated strong capabilities to control CP waves in different frequency domains. In this article, we present a concise review on PB metasurfaces for CP light manipulations, focusing mainly on the research works done by our own group. After briefly introducing the working principles of PB metasurfaces, we separately discuss how to construct high-efficiency PB metasurfaces in reflection and transmission geometries, and how to utilize them to control CP waves in different frequency domains, including meta-lensing, meta-hologram, and surface couplers. Finally, we conclude this review with our perspectives on future developments of PB metasurfaces.

Style APA, Harvard, Vancouver, ISO itp.

40

Liu, Ya-Ling, Pei Zou, Hao Wu, Min-Hao Xie i Shi-Neng Luo. "3,4,6-Tri-O-acetyl-1,2-O-[1-(exo-ethoxy)ethylidene]-β-D-mannopyranose 0.11-hydrate". Acta Crystallographica Section C Crystal Structure Communications 68, nr 9 (1.08.2012): o338—o340. http://dx.doi.org/10.1107/s0108270112032076.

Pełny tekst źródła

Streszczenie:

The title compound, C16H24O10·0.11H2O, is a key intermediate in the synthesis of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG), which is the most widely used molecular-imaging probe for positron emission tomography (PET). The crystal structure has two independent molecules (AandB) in the asymmetric unit, with closely comparable geometries. The pyranose ring adopts a4C1conformation [Cremer–Pople puckering parameters:Q= 0.553 (2) Å, θ = 16.2 (2)° and ϕ = 290.4 (8)° for moleculeA, andQ= 0.529 (2) Å, θ =15.3 (3)° and ϕ = 268.2 (9)° for moleculeB], and the dioxolane ring adopts an envelope conformation. The chiral centre in the dioxolane ring, introduced during the synthesis of the compound, has anRconfiguration, with the ethoxy groupexoto the mannopyranose ring. The asymmetric unit also contains one water molecule with a refined site-occupancy factor of 0.222 (8), which bridges between moleculesAandB viaO—H...O hydrogen bonds.

Style APA, Harvard, Vancouver, ISO itp.

41

Shastry, B. Sriram, i Boris I. Shraiman. "Raman Scattering in Mott-Hubbard Systems". International Journal of Modern Physics B 05, nr 01n02 (styczeń 1991): 365–88. http://dx.doi.org/10.1142/s0217979291000237.

Pełny tekst źródła

Streszczenie:

We present a theory of Raman Scattering in the Hubbard model. The scattering of light has resonant and non-resonant contributions. The resonant term gives rise to scattering by spin degrees of freedom in the insulating case, for which we derive a general form of the effective scattering Hamiltonian. The later involves four terms with distinct symmetry properties, one of them being the “chiral” spin operator ∑ Si · (Sj×Sk). The corresponding four distinct correlation function can be measured directly in the experiments with different scattering geometries. The nonresonant term contributes to the scattering in the doped case and is shown to probe the fluctuations of the “stress tensor”. This quantity is not conserved and hence its fluctuations at small q inherent in optical experiments, need not be small, in striking contrast with the density fluctuation in usual metals.

Style APA, Harvard, Vancouver, ISO itp.

42

Miranda, Alexandre S., Paula M. Marcos, José R. Ascenso, Mário N. Berberan-Santos, Rachel Schurhammer, Neal Hickey i Silvano Geremia. "Dihomooxacalix[4]arene-Based Fluorescent Receptors for Anion and Organic Ion Pair Recognition". Molecules 25, nr 20 (14.10.2020): 4708. http://dx.doi.org/10.3390/molecules25204708.

Pełny tekst źródła

Streszczenie:

Fluorescent dihomooxacalix[4]arene-based receptors 5a–5c, bearing two naphthyl(thio)ureido groups at the lower rim via a butyl spacer, were synthesised and obtained in the cone conformation in solution. The X-ray crystal structures of 1,3- (5a) and 3,4-dinaphthylurea (5b) derivatives are reported. Their binding properties towards several anions of different geometries were assessed by 1H-NMR, UV-Vis absorption and fluorescence titrations. Structural and energetic insights of the naphthylurea 5a and 5b complexes were also obtained using quantum mechanical calculations. The data showed that all receptors follow the same trend, the association constants increase with the anion basicity, and the strongest complexes were obtained with F−, followed by the oxoanions AcO− and BzO−. Proximal urea 5b is a better anion receptor compared to distal urea 5a, and both are more efficient than thiourea 5c. Compounds 5a and 5b were also investigated as heteroditopic receptors for biologically relevant alkylammonium salts, such as the neurotransmitter γ-aminobutyric acid (GABA·HCl) and the betaine deoxycarnitine·HCl. Chiral recognition towards the guest sec-butylamine·HCl was also tested, and a 5:2 selectivity for (R)-sec-BuNH3+·Cl− towards (P) or (M) enantiomers of the inherently chiral receptor 5a was shown. Based on DFT calculations, the complex [(S)-sec-BuNH3+·Cl−/(M)-5a] was indicated as the more stable.

Style APA, Harvard, Vancouver, ISO itp.

43

Novotná, Vladimíra, Lubor Lejček, Věra Hamplová i Jana Vejpravová. "Defect Structures of Magnetic Nanoparticles in Smectic A Liquid Crystals". Molecules 26, nr 18 (21.09.2021): 5717. http://dx.doi.org/10.3390/molecules26185717.

Pełny tekst źródła

Streszczenie:

Topological defects in anisotropic fluids like liquid crystals serve as a playground for the research of various effects. In this study, we concentrated on a hybrid system of chiral rod-like molecules doped by magnetic nanoparticles. In textures of the smectic A phase, we observed linear defects and found that clusters of nanoparticles promote nucleation of smectic layer defects just at the phase transition from the isotropic to the smectic A (SmA) phase. In different geometries, we studied and analysed creation of defects which can be explained by attractive elastic forces between nanoparticles in the SmA phase. On cooling the studied hybrid system, clusters grow up to the critical dimension, and the smectic texture is stabilised. The presented effects are theoretically described and explained if we consider the elastic interaction of two point defects and stabilisation of prismatic dislocation loops due to the presence of nanoparticles.

Style APA, Harvard, Vancouver, ISO itp.

44

Sortino, S., G. De Guidi, S. Fazio, S. Giuffrida, M. G. Salemi i S. Monti. "On the absorption and emission properties of three new non-steroidal anti-inflammatory drugs-β-cyclodextrin host-guest inclusion complexes: differentiated sensitivity to the microenvironment upon light excitation". International Journal of Photoenergy 1, nr 1 (1999): 19–23. http://dx.doi.org/10.1155/s1110662x99000045.

Pełny tekst źródła

Streszczenie:

The effects ofβ-cyclodextrin (β-CD) complexation on the absorption and emission properties of the non-steroidal anti-inflammatory drugs tolmetin (TM), diflunisal (DF), and fenbufen (FB) have been investigated. The absorption spectra of all these compounds are only slightly affected by the addition ofβ-CD. In contrast, the emission properties were markedly influenced by CD complexation and in a different manner for the three compounds due to a differentiated sensitivity of the excited drugs to the microenvironment. The complexes are all characterised by a 1: 1 stoichiometry and two different inclusion geometries for TM-β-CD complexes have been observed. Induced circular dichroism (icd) is observed due to the interaction of the compounds with the CD chiral cavity. The icd spectra are characterized by maxima well corresponding to those of the absorption spectra. A nonlinear analysis of the dependence of the icd signal magnitude on the CD concentration provided association constants valuesKass=1400±100M−1, and2600±150M−1for TM, DF, and FB respectively.

Style APA, Harvard, Vancouver, ISO itp.

45

Komen, Irina, Sabrya E. van Heijst, Martin Caldarola, Sonia Conesa-Boj i L. Kuipers. "Revealing the nanogeometry of WS₂ nanoflowers by polarization-resolved Raman spectroscopy". Journal of Applied Physics 132, nr 17 (7.11.2022): 173103. http://dx.doi.org/10.1063/5.0102381.

Pełny tekst źródła

Streszczenie:

Recent studies of transition metal dichalcogenides (TMDs) have revealed exciting optical properties, such as stable excitons and chiral light–matter interactions. Chemical vapor deposition techniques provide a platform for the fabrication of nanostructures with diverse geometries, ranging from horizontal flakes to flower-like structures. Raman spectroscopy is commonly used to characterize TMDs and their properties. Here, we use polarization-resolved Raman spectroscopy to probe the nanogeometry and orientation of [Formula: see text] nanoflower petals. Exciting the nanoflowers with linearly polarized light, we observe an enhanced Raman response from flower petals oriented along the excitation polarization direction. Furthermore, the helicity-resolved Raman response of vertically oriented wall-like flower petals exhibits clear differences with horizontally oriented flakes. Although the photoluminescence from the nanoflowers is strongly reduced, the Raman response upon excitation in resonance with the [Formula: see text] excitonic transition does reveal the presence of the exciton, which results in a distinct temperature dependence of the Raman response.

Style APA, Harvard, Vancouver, ISO itp.

46

Planas, Ferran, Michael J. McLeish i Fahmi Himo. "Computational characterization of enzyme-bound thiamin diphosphate reveals a surprisingly stable tricyclic state: implications for catalysis". Beilstein Journal of Organic Chemistry 15 (16.01.2019): 145–59. http://dx.doi.org/10.3762/bjoc.15.15.

Pełny tekst źródła

Streszczenie:

Thiamin diphosphate (ThDP)-dependent enzymes constitute a large class of enzymes that catalyze a diverse range of reactions. Many are involved in stereospecific carbon–carbon bond formation and, consequently, have found increasing interest and utility as chiral catalysts in various biocatalytic applications. All ThDP-catalyzed reactions require the reaction of the ThDP ylide (the activated state of the cofactor) with the substrate. Given that the cofactor can adopt up to seven states on an enzyme, identifying the factors affecting the stability of the pre-reactant states is important for the overall understanding of the kinetics and mechanism of the individual reactions. In this paper we use density functional theory calculations to systematically study the different cofactor states in terms of energies and geometries. Benzoylformate decarboxylase (BFDC), which is a well characterized chiral catalyst, serves as the prototypical ThDP-dependent enzyme. A model of the active site was constructed on the basis of available crystal structures, and the cofactor states were characterized in the presence of three different ligands (crystallographic water, benzoylformate as substrate, and (R)-mandelate as inhibitor). Overall, the calculations reveal that the relative stabilities of the cofactor states are greatly affected by the presence and identity of the bound ligands. A surprising finding is that benzoylformate binding, while favoring ylide formation, provided even greater stabilization to a catalytically inactive tricyclic state. Conversely, the inhibitor binding greatly destabilized the ylide formation. Together, these observations have significant implications for the reaction kinetics of the ThDP-dependent enzymes, and, potentially, for the use of unnatural substrates in such reactions.

Style APA, Harvard, Vancouver, ISO itp.

47

Donnelly, Claire, Aurelio Hierro-Rodríguez, Claas Abert, Katharina Witte, Luka Skoric, Dédalo Sanz-Hernández, Simone Finizio i in. "Complex free-space magnetic field textures induced by three-dimensional magnetic nanostructures". Nature Nanotechnology 17, nr 2 (20.12.2021): 136–42. http://dx.doi.org/10.1038/s41565-021-01027-7.

Pełny tekst źródła

Streszczenie:

AbstractThe design of complex, competing effects in magnetic systems—be it via the introduction of nonlinear interactions1–4, or the patterning of three-dimensional geometries5,6—is an emerging route to achieve new functionalities. In particular, through the design of three-dimensional geometries and curvature, intrastructure properties such as anisotropy and chirality, both geometry-induced and intrinsic, can be directly controlled, leading to a host of new physics and functionalities, such as three-dimensional chiral spin states7, ultrafast chiral domain wall dynamics8–10 and spin textures with new spin topologies7,11. Here, we advance beyond the control of intrastructure properties in three dimensions and tailor the magnetostatic coupling of neighbouring magnetic structures, an interstructure property that allows us to generate complex textures in the magnetic stray field. For this, we harness direct write nanofabrication techniques, creating intertwined nanomagnetic cobalt double helices, where curvature, torsion, chirality and magnetic coupling are jointly exploited. By reconstructing the three-dimensional vectorial magnetic state of the double helices with soft-X-ray magnetic laminography12,13, we identify the presence of a regular array of highly coupled locked domain wall pairs in neighbouring helices. Micromagnetic simulations reveal that the magnetization configuration leads to the formation of an array of complex textures in the magnetic induction, consisting of vortices in the magnetization and antivortices in free space, which together form an effective B field cross-tie wall14. The design and creation of complex three-dimensional magnetic field nanotextures opens new possibilities for smart materials15, unconventional computing2,16, particle trapping17,18 and magnetic imaging19.

Style APA, Harvard, Vancouver, ISO itp.

48

Jaycox, Gary D. "Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior". Polymer Journal 34, nr 4 (kwiecień 2002): 280–90. http://dx.doi.org/10.1295/polymj.34.280.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

49

Fantuzzi, Nicholas, Patrizia Trovalusci i Raimondo Luciano. "Material Symmetries in Homogenized Hexagonal-Shaped Composites as Cosserat Continua". Symmetry 12, nr 3 (10.03.2020): 441. http://dx.doi.org/10.3390/sym12030441.

Pełny tekst źródła

Streszczenie:

In this work, material symmetries in homogenized composites are analyzed. Composite materials are described as materials made of rigid particles and elastic interfaces. Rigid particles of arbitrary hexagonal shape are considered and their geometry described by a limited set of parameters. The purpose of this study is to analyze different geometrical configurations of the assemblies corresponding to various material symmetries such as orthotetragonal, auxetic and chiral. The problem is investigated through a homogenization technique which is able to carry out constitutive parameters using a principle of energetic equivalence. The constitutive law of the homogenized continuum has been derived within the framework of Cosserat elasticity, wherein the continuum has additional degrees of freedom with respect to classical elasticity. A panel composed of material with various symmetries, corresponding to some particular hexagonal geometries defined, is analyzed under the effect of localized loads. The results obtained show the difference of the micropolar response for the considered material symmetries, which depends on the non-symmetries of the strain and stress tensor as well as on the additional kinematical and work-conjugated statical descriptors. This work underlines the importance of resorting to the Cosserat theory when analyzing anisotropic materials.

Style APA, Harvard, Vancouver, ISO itp.

50

Xu, Yao-Chang, Andrew L. Roughton, Raymond Plante, Solo Goldstein i Pierre Deslongchamps. "Stereocontrolled construction of 1,7-dimethyl A.B.C.[6.6.6] tricycles. Part I. Transannular Diels–Alder reactions of 14-membered macrocycles containing trans-dienophiles". Canadian Journal of Chemistry 71, nr 8 (1.08.1993): 1152–68. http://dx.doi.org/10.1139/v93-152.

Pełny tekst źródła

Streszczenie:

Transannular Diels–Alder reactions of 14-membered macrocyclic trienes possessing a methyl substituent on both the diene and dienophile moiety have been investigated. Macrocyclic structures 1a, 1b, and 1c having cis-trans-trans (CTT), trans-cis-trans (TCT), and trans-trans-trans (TTT) geometries could be stereoselectively constructed by coupling appropriately functionalized dienes 5 and dienophile 4 following an intramolecular displacement of an allylic halide by the anion of an appropriately located dimethyl malonate unit. The transannular Diels–Alder reaction performed on 1a led to a mixture of four major tricyclic products, including 34 possessing the unexpected trans-anti-cis (TAC) stereochemistry. When heated at 300 °C, macrocycle 1b underwent an unique conversion via an ene–retroene, Diels–Alder process, producing the unexpected tricycle 41 (racemic form) containing five contiguous chiral centers. A rationale for the above experimental facts is presented. In contrast to the previous results, the transannular Diels–Alder reaction of macrocycle 1c was straightforward, producing a 95% isolated yield of trans-anti-cis (TAC) tricycle 34. This investigation demonstrates a general methodology for the stereocontrolled synthesis of 1,2-dimethyl A.B.C[6.6.6] tricyclic compounds, which are potential precursors to polycyclic natural products such as steroids and terpenes.

Style APA, Harvard, Vancouver, ISO itp.

Artykuły w czasopismach na temat „Chiral Geometries”

Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych