Search results for "Chiral"
showing 10 items of 752 documents
Aminosäureester als chirale Hilfsgruppen in Lewis-Säure-katalysierten Umsetzungen elektronenreicher Siloxydiene mit Iminen
1990
Generation of Stereocenters Around a C3-Symmetric Cyclotriveratrylene Crown
2012
The oxidation of racemic methylthio-substituted C3-symmetric cyclotriveratrylene (CTV) 2 produces the corresponding trisulfoxides 3 as follows. Oxidation with m-chloroperoxybenzoic acid (m-CPBA) in dichloromethane leads to the formation of a distribution of the four possible diastereomers that is relatively close to the statistical outcome, in which the C3-symmetric stereoisomers are the minor species. In contrast, the optically active Davis reagent [oxaziridine (+)-4] in carbon tetrachloride at room temperature leads to a biased (73 %) distribution in favor of the C3-symmetric MRRR/PSSS diastereomer of 3 with 56 % ee (PSSS enantiomer according to the model of Davis). Interestingly, when th…
Applications and stereoselective syntheses of P-chirogenic phosphorus compounds.
2016
International audience; Phosphorus compounds bearing chirality on the P-center are usually qualified as P-chirogenic or P-stereogenic. This chemical class concerns natural products, agrochemistry, molecular materials, biology and pharmacy, although it is certainly in coordination chemistry and in asymmetric catalysis using chiral transition metal complexes that P-chirogenic phosphorus compounds are the most used. The chiral phosphine ligands and their uses in asymmetric metal-catalyzed reactions have been widely reviewed in literature. However, an overview covering the applications as well as the stereoselective syntheses of all classes of phosphorus compounds has not yet been provided. Thi…
Chiral Inversion of Thiolate-Protected Gold Nanoclusters via Core Reconstruction without Breaking an Au-S Bond
2019
Based on density functional theory computations of the well-known chiral Au38(SR)24 nanocluster and its Pd- and Ag-doped derivatives, we propose here a mechanism for chiral inversion that does not require breaking of a metal-sulfur bond at the metal-ligand interface, but features a collective rotation of the gold core. The calculated energy barriers for this mechanism for Au38 and Pddoped Au38 are in the range of 1 – 1.5 eV, significantly lower than barriers involving breakage of Au-S bonds (2.5 eV). For Ag-doped Au38, barriers for both mechanisms are similar (1.3 – 1.5 eV). Inversion barriers for a larger chiral Au144(SR)60 are much higher (2.8 eV). Our computed barriers are in a good agre…
Charge-dependent flow and the search for the chiral magnetic wave in Pb-Pb collisions at √sNN = 2.76 TeV
2016
We report on measurements of a charge-dependent flow using a novel three-particle correlator with ALICE in Pb-Pb collisions at the CERN Large Hadron Collider (LHC), and discuss the implications for observation of local parity violation and the chiral magnetic wave (CMW) in heavy-ion collisions. Charge-dependent flow is reported for different collision centralities as a function of the event charge asymmetry. While our results are in qualitative agreement with expectations based on the CMW, the nonzero signal observed in higher harmonics correlations indicates a possible significant background contribution. We also present results on a differential correlator, where the flow of positive and …
Orientation-Dependent Handedness of Chiral Plasmons on Nanosphere Dimers: How to Turn a Right Hand into a Left Hand
2016
Optical activity, which is used as a discriminator of chiral enantiomers, is demonstrated to be orientation dependent on individual, and nominally achiral, plasmonic nanosphere dimers. Through measurements of their giant Raman optical activity, we demonstrate that L/R-handed enantiomers can be continuously turned into their R/L-handed mirror images without passing through an achiral state. The primitive uniaxial multipolar response, with demonstrable broken parity and time reversal symmetry, reproduces the observations as resonant Raman scattering on plasmons that carry angular momentum. The analysis underscores that chirality does not have a quantitative continuous measure and recognizes t…
Synthesis, crystal structure and Hirshfeld analysis of a crystalline compound comprising a 1/1 mixture of 1-[(1R,4S)- and 1-[(1S,4R)-1,7,7-trimethyl-…
2020
A racemic mixture of (R)- and (S)-camphor thiosemicarbazone, which crystallizes in the centrosymmetric space group C2/c, is reported.
Spontaneous Resolution of an Electron‐Deficient Tetrahedral Fe4L4cage
2015
A highly electron-deficient C3-symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)2, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M4L4 cages. This homochiral T-symmetric cage containing a relatively large cavity of 330 A(3) is capable of encapsulating an anionic guest, as was determined by mass spectrometry, (19)F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH3CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH3 OH resulted in crystals containing only the right-handed (ΔΔΔΔ) cage. The difference in the…