Search results for "chirality"
showing 10 items of 188 documents
Cooperative supramolecular polymerization and amplification of chirality in C3-symmetrical OPE-based trisamides.
2011
Sergeants-and-soldiers experiments demonstrate the amplification of chirality that transforms the racemic mixture of helical columns formed from OPE-based trisamides into enantiomerically enriched helical structures (see scheme).The cooperative supramolecular polymerization of the trisamides is investigated by theoretical calculations and temperature-dependent UV/Vis and CD experiments. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Design and Optimization of Chromophores for Liquid Crystal and Photorefractive Applications
1999
ABSTRACTOrganic chromophores have been exploited for a wide range of discrete optical and electronic functions as well as a growing number of combined opto-electronic functions. We are pursuing development of organic and polymer materials for a range of applications that require properties including liquid crystallinity, second order optical nonlinearity, photorefractivity and, more recently, special nonlinear optical behavior involving molecular chirality.
Parity violation energy of biomolecules - III: RNA
2006
The energy of parity-violation associated with a typical DNA double helix is estimated with ab initio techniques. It is shown that weak-nuclear interactions do not favor the formation of the double helices found in nature. Possible implications regarding the potential effect of parity-violation interactions on the evolution of biological homochirality are discussed.
LC-Polymers with Axial Chirality
1991
Abstract Liquid crystalline polymers with axial chirality are prepared. These polymers are chiral, not due to a single asymmetric carbon atom, but due to a larger molecular fragment, which is chiral as a whole. They exhibit cholesteric and chiral smectic C* phases. Dielectric spectroscopy proves strong ferroelectric properties in the chiral smectic C* phases of these polymers.
Ferrochirality: A simple theoretical model of interacting dynamically invertible helical polymers, 1. The basic effects
1994
The effect of interaction between reversible helical polymers of the poly(hexyl isocyanate) type is investigated by using a molecular field model. It is shown that for interacting helices a critical temperature exists below which they must adopt a common helix-sense spontaneously, even in the absence of any external or intrinsic chiral force
Mannich Reactions with Amino Alcohols
2000
The condensation of resorcarenes 1 with various amino alcohols and an excess of formaldehyde was studied. The tetrabenzoxazines 2a−e were found as the only products in the reaction with 6-aminohexan-1-ol, 4-aminobutan-1-ol, and 2-aminoethanol, while 3-aminopropan-1-ol forms the tetraoxazine 3 as the main product. In the case of aminoethanols substituted at the 2-position with alkyl groups, the tetraoxazolidines 4 are the preferred reaction products, while 1-methyl aminoethanol (1-amino-propan-2-ol) yields predominantly the tetrabenzoxazine 2f. The structures of all these compounds have been confirmed by NMR spectroscopy and additionally by single-crystal X-ray analysis in the case of 2a and…
Vergleichende dimerisierung der enantiomere von Oct-1-in-3-ol mit chiralen rhodium-phosphan-komplexen
1996
Abstract Three optically active phosphanes ([(S)-2-methylbutyl]3−nP[phenyl]n(n = 0, 1, 2), were tested as ligands in rhodium(I) complexes to form catalysts for the enantioselective dimerisation of (R)- and (S)-oct-1-yn-3-ol. The catalytic reaction provides enantioselectivity for this type of CC bond formation. For reactions at 45–75°C and depending on the P-ligand used the rates vary for both enantiomers from 6:1 to 50:1 in favour of the (S)-octynol.
Impact of Molecular Size and Shape on the Supramolecular Co‐Assembly of Chiral Tricarboxamides: A Comparative Study
2020
We report herein a comparative investigation of the chiral amplification features of a series of three families of C 3 -symmetric tricarboxamides: 1,3,5-triphenylbenzenetricarboxamides (TPBAs), benzenetricarboxamides (BTAs) and oligo(phenylene ethynylene) tricarboxamides (OPE-TAs). As previously observed for BTAs and OPE-TAs, a similar dichroic response is obtained for TPBAs decorated with three, two or only one chiral side chain bearing stereogenic centers, thus confirming the efficient transfer of point chirality to the supramolecular helical aggregates. Unlike BTAs and OPE-TAs, the chiral amplification ability of TPBAs in majority rules experiments shows a negligible dependence on the nu…
Decoding the Consequences of Increasing the Size of Self-Assembling Tricarboxamides on Chiral Amplification
2019
A complete series of experimental and theoretical investigations on the supramolecular polymerization of chiral (1 and 2) and achiral (3) oligo(phenylene ethynylene) tricarboxamides (OPE-TAs) is reported. The performance of seargents-and-soldiers (SaS) and majority rules (MR) experiments has allowed deriving a full set of thermodynamic parameters, including the helix reversal penalty (HRP) and the mismatch penalty (MMP). The results described illustrate the influence exerted by the number of stereogenic centers per monomeric unit and the temperature on the chiral amplification phenomenon. While the HRP decreases upon decreasing the number of chiral side chains, the MMP follows an opposite t…
ChemInform Abstract: Carbohydrates as Chiral Templates: Diastereoselective Synthesis of N- Glycosyl-N-homoallylamines and β-Amino Acids from Imines.
2010
Complexing properties and chirality of carbohydrates were utilized in diastereoselective reactions of 0-pivaloylated N-galactosylimines with allylsilanes and -stannaries. With dyltrimethylsilane in the presence of SnCl4, imines 2 of aromatic and heteroaromatic aldehydes were converted to homdylamines 3, giving ratios of diastereomers higher than 7:1. No addition products derived from α-anomeric aromatic imines were formed. Aliphatic homdylamines 3 were synthesized by using allyltributylstannane in the presence of SnCl4. Both α- and β-anomeric aliphatic imines reacted with the allylstannane. They gave the same ratio of diastereomers and showed the same sense of asymmetric induction.