Chiral Terminal Groups Research Articles

Metadynamics simulations on the key factors of handedness induction of quinoline oligoamide foldamers with a terminal chiral group

AbstractMetadynamics simulation has been used to determine the conformational energy landscapes of several helical quinoline oligoamides bearing β‐pinene‐derived pyridine at either the C or N‐terminus. Based on the experimental results, the helix‐sense preference for four types of foldamers with the chiral terminal group has been verified. To compare to the key factors inducing handedness to helix‐sense preference, a terminal group with three hydrogen bond sites is designed and corresponding foldamers are built. The calculated results show that the delocalization effect and steric hindrance are mainly responsible for a particular helix‐sense preference for the investigated foldamers. The more hydrogen bonds between the terminal group and oligoamide units are formed, the more stable foldamers are.

Non-symmetrical bent-shaped compounds containing a chiral moiety

The synthesis and mesomorphic properties of new non-symmetrical bent-shaped compounds containing a chiral moiety are reported. These materials were built up from 3-hydroxybenzoic acid as a central unit with a chiral terminal group derived from lactic acid. A columnar phase of the B1REV type with tilted molecules was observed in a wide temperature range down to room temperature. The ferroelectric-like character of switching with one peak in a half-period of the triangular electric field was observed and supported by texture observations and electro-optical changes. A longer terminal group ending with a double bond makes the compounds ready for polymerisation.

Improvement of peptoid chiral stationary phases by modifying the terminal group of selector

The role of a terminal group of a peptoid selector in a chiral separation was investigated. Six chiral stationary phases (CSPs) with the terminal groups replaced by achiral alkyl groups (n-butyl, t-butyl and diisopropyl) and chiral groups ((1R, 2R)-2-aminocyclohexyl phenylcarbamate, N’-phenyl-L-proline amide and N’-phenyl-L-leucine amide) were synthesized. Achiral terminal groups with different steric hindrances did not broaden the enantioselectivity, but improved the separation factors for some analytes, probably due to the improvement of interactions between the analytes and peptoid chain. Introducing new chiral terminal groups proved an effective way to broaden the applicable spectrum of peptoid CSPs.

Synthesis of Poly(amidoamine) Dendrimer with a Diphenyl Diselenide Core

We succeeded in the synthesis of a novel poly(amidoamine) dendrimer having diphenyl diselenide at the core. Modification of the dendrimer diselenide by the reaction with glucono-δ-lactone in methanol gave a water-soluble dendrimer diselenide having chiral terminal groups. The structures of dendrimers were satisfactorily confirmed by MAIDI-TOF MS spectrometry, elemental analysis, and NMR spectroscopy. Interestingly, induced circular dichroism (ICD) of the interaction between the diphenyl diselenide core and D-gluconamide periphery of the dendrimer was observed at 300 nm. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

Synthesis and structure of an optically active π‐stacked poly(dibenzofulvene) bearing chiral terminal group

AbstractDibenzofulvene (DBF) affords a polymer having π‐stacked conformation by anionic, cationic, and free‐radical polymerization. In this study, DBF was polymerized anionically using potassium menthoxide as initiator to obtain optically active poly(DBF) having a chiral menthoxy group as a terminal group. The obtained polymer indicated circular dichroism (CD) absorption bands in the absorption wavelength range of fluorenyl group, indicating that chiral conformation was induced to the stacked main chain by the influence of the terminal group. The CD intensity was reversibly affected by temperature of measurement; hence, the chiral conformation may be rather dynamic. The effect of the terminal group was found to decrease as the chain length increased. Theoretical CD calculation indicated that the obtained polymer has a left‐handed helical conformation and that the dihedral angle between neighboring monomeric units might be about 10–20°. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 239–246, 2009

Synthesis and properties of a new series of mesogenic compounds with pyridine, oxidopyridinium, thienyl and furyl moieties

This paper presents the synthesis and mesophase properties of several homologous series of structurally related compounds in which the aromatic ring attached to 4′-alkyloxybiphenyl-4-ol was systematically changed. The homologues with achiral and chiral terminal groups were studied. New compounds forming both antiferroelectric and ferroelectric phases were obtained for pyridyl and phenyl derivatives.

New ferroelectric liquid crystals with cyclic and non-cyclic chiral groups

New liquid crystalline materials with cyclic proline alkyl ester, fenchyl, bornyl, verbenyl and 2-decalinyl and non-cyclic 1-methyl-alkyl and ethyl-lactate chiral terminal groups were studied. Ferroelectric and antiferroelectric smectic phases were found for compounds with the semi-flexible chiral group while derivatives with the ring chiral moieties form exclusively ferroelectric smectics. The Ps values as high as 270 nC/cm2 in the hexatic SmI* phase were detected for the 1-methyl-alkyl derivatives. Generally, a lower spontaneous polarisation was detected for the materials with cyclic groups. This is either due to large size of the bulky groups causing less hindered rotation of molecules or due to admixture of conformers with opposite Ps sign.

Dynamics of electric-field-induced molecular reorientation and segmental mobility in the smectic-C^{*} phase of a ferroelectric liquid crystal: Faster reorientation of cores than the alkyl chains revealed by time-resolved infrared spectroscopy

We report a study of the dynamics of molecular reorientation and segmental mobility of a ferroelectric liquid crystal in the smectic-${C}^{*}$ (Sm-${C}^{*}$) phase having 2-hydroxy-benzilidenianiline as the mesogen core and $(S)\ensuremath{-}$ 2-chloro-3-methylbutanoyl as the chiral terminal group, at different temperatures during electric-field-induced switching between the two surface-stabilized states by use of a time-resolved Fourier-transform infrared technique. From polarized infrared spectra under static dc electric fields, details of mutual arrangement of different molecular segments in the Sm-${C}^{*}$ phase have been obtained. Contrary to the usual expectations, the average alkyl chain axis does not coincide with the mesogen axis and is less tilted with respect to the layer normal than the mesogen. On the other hand, motion of the carbonyl groups is found to be strongly hindered and the distribution function for the $\mathrm{C}\mathrm{=}\mathrm{=}\mathrm{O}$ bonds is not cylindrically symmetric with respect to the long molecular axis. Time-resolved infrared measurements at different temperatures and voltages have revealed that, on switching the polarity of the electric field, the hydrogen-bonded $\mathrm{C}\mathrm{=}\mathrm{=}\mathrm{O}$ group moves with the mesogen which reaches equilibrium orientations at a faster rate compared to the alkyl chain at the temperatures and voltages employed in this study.

Properties of chiral liquid crystals with inner hydrogen bonds

D. Pociecha, A. Krówczyński, J. Szydłowska, E. Górecka, M. Glogarova and J. Przedmojski, J. Mater. Chem., 1997, 7, 1709 DOI: 10.1039/A701129F

New side chain LC polysiloxanes with carbonyl-bound chiral terminal group

Abstract A synthetic route has been developed to a new series of homo- and co-polysiloxanes with a terminal chiral 2-(S)-butyl fragment attached to the mesogenic biphenyl core via the ketone binding group, >C˭O. The synthesis, structure and ferroelectric properties of the polymers are reported. All the polymers show in their SA phases an unusual decrease in the interlayer distance with increasing temperature.

Highly Branched Liquid Crystalline Polymers with Chiral Terminal Groups

Highly Branched Liquid Crystalline Polymers with Chiral Terminal Groups

Liquid crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain, 2. Influence of the nature of the chiral group

AbstractAcrylate monomers with a chiral group have been synthesized bearing a propyl, isopropyl or benzyl substituent on the asymmetric carbon. All of the monomers are crystalline. Above their melting point, they give a clear, isotropic melt. The corresponding polymers have been prepared by free radical polymerization. They were examined by differential scanning calorimetry, optical microscopy and X‐ray diffraction. They were found to show a reproducible liquid‐crystal behavior. On cooling from the isotropic state, SA, S (or S) and crystal‐like (probably SH or SH′) phases become evident. Our results do not preclude the existence of a S phase between the SA and S phases. It is noteworthy that polyacrylates of the same series but with side chains terminated by a chiral group bearing a methyl substituent exhibit SA, SB and crystal‐like (probably SE) phases.

Liquid‐crystalline polyacrylates containing biphenyl and chiral terminal groups in the side chain, 1. Influence of the spacer length on the liquid‐crystal behavior

AbstractThree acrylate monomers having mesogenic moieties based on 4‐(n)‐alkyloxy‐4′‐(2‐chloro‐propanoyloxy)biphenyl (n = 6, 8 or 10) have been synthesized. There is no evidence for liquid‐crystal properties in any of the three new monomers. The corresponding polymers have been prepared by free‐radical polymerization. Their liquid‐crystal behavior has been investigated by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. On cooling from the isotropic liquid, smectic A (SA), smectic B (SB) and crystalline phases (probably crystal‐like SE phases) have been evidenced. It should be noted that the chlorine atoms in the chiral groups do impose a local ordering of the mesogenic side groups.

Order-parameter fluctuations in a ferroelectric liquid crystal by broadband dielectric spectroscopy.

Broadband dielectric spectroscopy (${10}^{\mathrm{\ensuremath{-}}1}$--${10}^{9}$ Hz, 100--450 K) was employed to study a pure ferroelectric liquid crystal containing only a single dipole moment in the chiral terminal group. In addition to the Goldstone and soft mode the high-frequency order-parameter fluctuations in the smectic-A phase and chiral-smectic-C phase could be found as predicted theoretically by Blinc and \ifmmode \check{Z}\else \v{Z}\fi{}ek\ifmmode \check{s}\else \v{s}\fi{} [Phys. Rev. A 18, 740 (1978)].