Series Of Chiral Compounds Research Articles

Concentration-dependence of specific rotation of optically active glycerol analogues and structurally related compounds: The significance of intermolecular hydrogen bonding

Specific rotation of optically active glycerol analogues, (S)-3-(benzyloxy)propane-1,2-diol [(S)-1], (S)-3-methoxypropane-1,2-diol [(S)-6] and (S)-3-phenoxypropane-1,2-diol [(S)-13], changed its sign from (+) to (–) with increasing concentration in CHCl3, whereas no significant concentration-dependent change was observed in MeOH. The 1H NMR spectrum of (S)-1 showed concentration-dependent changes of the chemical shift in CDCl3. Intermolecular interaction by OH⋯OH hydrogen bonds was suggested by single crystal X-ray crystallography of (S)-13. The concentration-dependent changes of specific rotation of (S)-1, (S)-6, and (S)-13 in CHCl3 can therefore be presumed to be due to self-assembly of these compounds via intermolecular hydrogen bonding at high concentration. The remarkable concentration-dependent changes in specific rotation were also observed to occur in the compounds with related chemical structures, such as (S)-3-hydroxy-4-methoxy-4-oxobutanoic acid [(S)-10], (S)-1-[(2-methylpropan-2-yl)oxycarbonyl]pyrrolidine-2-carboxylic acid [Boc-L-Pro-OH, (S)-14], (R)-3-hydroxy-4,4-dimethylhydrofran-2(3H)-one [(R)-15], (R)-tetrahydrofuran-2-carboxylic acid [(R)-16], (S)-3-methyl-2-[(2-methylpropan-2-yl)oxycarbonylamino]butanoic acid [Boc-L-Val-OH, (S)-17], (R)-oxiran-2-ylmethanol [(R)-18], and (4S)-4-isopropyloxazolidin-2-one [(S)-19]. The existence of intermolecular interaction by C=O⋯HO hydrogen bonds was suggested by single crystal X-ray crystallography of (S)-10, (S)-13, and (S)-14. Thus, this series of chiral compounds have multiple functional groups in appropriate positions that serve as hydrogen-bond donors and/or acceptors, resulting in significant concentration-dependent changes of specific rotation.

Terminal Effect of the Semi-fluorocarbon Chain on the Liquid Crystalline Behaviors of Some Compounds

Two series of chiral compounds with semi-perfluorocarbon chains and alkoxy ones, nBP4F and nBP6F, are synthesized. Enantiotropic SmA phase is identified in all of these compounds. When the alkoxy chain length is short, enantiotropic SmB is also identified. When the alkoxy chain length is longer than 6 carbons, enantiotropic SmC* phase is formed. Their clearing points increase with increasing the perfluorocarbon chain length. Comparison of compounds with -CF3, -CHF2 and -CF2Cl groups at the terminals of the fluorocarbon chains, the clearing point sequence is -CHF2 < -CF2Cl < -CF3; and the melting point sequence is -CF3 < -CHF2 < -CF2Cl. Therefore, the compounds with semi-perfluorocarbon chains show the widest liquid crystalline temperature range. Moreover, the SmC* phase of the compounds with -CF3 at the terminals shows the highest thermostability.

New chiral liquid crystal materials based on menthol: Synthesis and phase behavior

ABSTRACTTo study structure-mesomorphism relationships of chiral materials based on menthol, a series of chiral compounds containing menthyl group were synthesized. Their chemical structures, formula, and the purity were characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and elemental analyses. The corresponding phase behavior was investigated with differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The effect of the mesogenic core, flexible spacer, and terminal groups on the mesophase formation and type was discussed. The compound 4-menthyloxyacetoxybenzoyloxy-4′- (6-bromohexyloxy)biphenyl showed the smectic A (SA) and cholesteric phases on heating cycle, and a cubic Blue Phase, chiral smectic C (SC*), SA and cholesteric phases on cooling cycle. However, the compound 4-menthyloxyacetoxybenzoyloxy-4′-(4-bromobutoxy)biphenyl showed enantiotropic SC*, SA and cholesteric phases, moreover, the platelet texture of a cubic Blue Phase was also observed on cooling cycle. The methacrylate monomer with six flexible methylene units and three phenyl rings as mesogenic core only showed cholesteric phase, while the methacrylate monomer with four methylene unit and three phenyl rings showed the SC* and cholesteric phases. However, when the terminal methacryloyloxy groups in the monomers were substituted by thiophenylacryloyloxy groups, the corresponding monomers all show no mesophase. With increasing the rigidity of mesogenic core or decreasing the flexible methylene spacer length, the corresponding melting temperature (Tm) or isotropic temperature (Ti) increased.

Mesomorphism Behavior of Two Series of Chiral Compounds with Semiperfluorocarbon Chains

Thermotropic liquid crystals with fluorocarbon chains have attracted much attention, because they are feasible to form smectic phases. Herein, two series of chiral compounds with semiperfluorocarbon chains were designed and synthesized. These compounds were characterized by IR, 1H NMR, 19F NMR, mass spectroscopy, and elemental analysis. Phase transition behavior was investigated by differential scanning calorimetry and polarized optical microscopy. Members of the two-ring series do not exhibit liquid crystalline phases. However, the three-ring analogues exhibit an enantiotropic SmA phase. When the length of alkyl chains is sufficient, an enantiotropic SmB phase is also identified.

Mesomorphic Properties of Some Liquid Crystals with Semifluorocarbon Chains

Three series of chiral compounds with semifluorocarbon chains have been synthesized. These compounds were characterized by infra-red spectra (IR), 1H nuclear magnetic resonance (1H NMR), 19F nuclear magnetic resonance (19F NMR), mass spectra (MS), and elemental analysis. Their phase-transition behavior was investigated by differential scanning calorimeter (DSC) and polarizing optical microscopy. To a certain compound, when the terminal hydrogen atom in the semifluoroalkyl chain was substituted by a chlorine atom, both the clearing point and the melting point were increased and the thermal stability of the SmC phase was enhanced. Moreover, with the introduction of a triple bond in the core, both the melting point and the clearing point were increased.

The effect of a single atom in the terminal position of a fluorocarbon chain on liquid crystalline properties

Eight series of chiral compounds with semi‐fluorocarbon chains have been synthesized. The compounds were characterized by IR, 1H NMR, 19F NMR and mass spectroscopies and elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry and polarizing optical microscopy. Their clearing points increase with an increase of the length of fluorocarbon chain. For a certain compound, when the terminal hydrogen atom in the semi‐fluoroalkyl chain was substituted by a chlorine atom, both the clearing point and melting point were increased, and the thermal stability of the chiral smectic C (SmC*) phase was enhanced. However, the clearing point decreased and the melting point increased with the introduction of a triple bond into the core.

Synthesis and Mesomorphic Properties of Some Chiral Liquid Crystals with Semifluorinated Chains

Three series of chiral compounds with semifluorinated chains have been synthesized. These compounds were characterized by IR, 1H NMR, 19F NMR, MS-mass spectrum, and elemental analysis. Their phase-transition behavior was investigated by DSC-differential scanning calorimetry and polarizing optical microscopy. Both the introduction of a triple bond and lateral difluorosubstitution in the core decrease the clearing points and suppress the formation of the SmC* phase.

Elucidation of chiral recognition processes of macrocyclic antibiotic vancomycin

A theoretical investigation was carried out on the retention and separation of enantiomeric molecules including nonsteroidal anti-inflammatory drugs, anti-neoplastic compounds and N-derivatized amino acids by capillary electrophoresis using macrocyclic antibiotics, a new class of chiral selectors, as stationary phase. Firstly docking methods were used to study the enantiorecognition in chiral electrophoresis. The molecular dynamics simulations of the two diastereoisomer complexes were then performed in order to understand how these antibiotics recognize the enantiomers. Another approach was applied in this study to establish a quantitative structure-enantioselectivity relationship (QSER) model, able to describe the resolution of a series of chiral compounds in capillary electrophoresis using vancomycin as the resolving agent.

Ferroelectric liquid crystals containing a 2(S)-[2(S)-methylbutoxy]propionyloxy unit

Abstract A new chiral organic acid, 2(S)-[2(S)-methylbutoxy]propionic acid (2), was synthesized from ethyl lactate and (S)-1-iodo-2-methylbutane. The acid 2 containing two centres of chirality was used as a building block for preparing ferroelectric liquid crystals. Three series of chiral compounds were synthesized to study the influence of the molecular structures on the formation of liquid crystal phases. They are 4-{2(S)-[2(S)-methylbutoxy]propionyloxy}phenyl 4-(4-n-alkoxyphenyl) (series B), and 4-{2(S)-[2(S)-methylbutoxy]propionyloxy}phenyl 4-(4-n-alkoxyphenyl) benzoate (series B), and 4-{2(S)-[2(S)-methylbutoxy] propionyloxy}-4′-biphenyl 4-n-alkoxy benzoate (series C). Only one member of series A, 4-{2(S)-[2(S)-methylbutoxy]propionyloxy}phenyl 4-n-octyloxybenzoate (5c), exhibits a monotropic SA phase. The n-alkoxy chain length at the biphenyl ring of series B has a remarkable efect on the S*C phase formation. An enantiotropic S*C phase can only be observed when the n-alkoxy chain is longer than the n-octyloxy group. The n-heptyloxy and n-octyloxy homologues exhibit a monotropic S*C phase. However, all members of series C possess an enantiotropic S*C phase. The occurrence of the phase sequence C-S*C-SA-I or C-S*C-N*-I depends on the position of the biphenyl ring. The S* phase temperature range in series B and C is up to 70°C.