Influence of fluorination extent on liquid crystalline properties of semi-perfluorinated phenylpyrimidine ferroelectric liquid crystals

A series of semi-perfluorinated ferroelectric liquid crystals, 2-[4-(2-fluoro-octyloxy)phenyl]- 5-(omega-n-perfluoroalkylalkyloxy)pyrimidines were prepared and their physical properties evaluated. All of the fluorinated phenylpyrimidines exhibited a chiral smectic C phase enantiotropically. The results showed that high fluorination extent favours the tilted chiral smectic C phase. Also, highly fluorinated compounds exhibited a large cone tilt angle and large spontaneous polarization. However, the response became slow as the fluorination extent increased. Although the compounds showed a large spontaneous polarization in the pure state, their spontaneous polarization power as chiral dopants was so small that very little spontaneous polarization could be measured.     

Amino acids as chiral selectors in enantioresolution by liquid chromatography

Amino acids are unique in terms of their structural features and multidimensional uses. With their simple structures and the ready availability of both enantiomers, amino acids not only serve as a chiral pool for synthesis but also provide an inexpensive pool for resolution studies. There has been no attempt to review the application of amino acids as chiral selectors for chromatographic enantioresolution of pharmaceuticals and other compounds. The present paper deals with application of l-amino acids and complexes of l-amino acids with a metal ion, particularly Cu(II), as an impregnating reagent in thin-layer chromatography or as a chiral ligand exchange reagent or a chiral mobile phase additive in both thin-layer chromatography and high-performance liquid chromatography. Enantiomeric resolution of β-blockers, nonsteroidal anti-inflammatories, amino acids (and their derivatives) and certain other compounds is discussed.     

Enantioseparation using alkoxyphenylcarbamates of cellulose and amylose as chiral stationary phase for high-performance liquid chromatography

Cellulose and amylose phenylcarbamates having one or two alkoxy groups on a phenyl ring were synthesized, and their chiral recognition abilities as chiral stationary phases for HPLC were evaluated. Compared to the 4-methoxyphenylcarbamates of cellulose and amylose, which are known to show a poor chiral recognition, the 3-methoxyphenylcarbamates exhibited much higher chiral recognitions. For cellulose derivatives, as the bulkiness of the 3-alkoxy group increased, the chiral recognition ability increased. On the other hand, for the amylose derivatives, a clear relation between the chiral recognition and the bulkiness of the alkoxy group was not observed, and the 3-methoxy, ethoxy, and isopropoxyphenylcarbamates showed relatively high chiral recognitions. The introduction of two methoxy groups to the meta-positions decreased the chiral recognition ability. In order to discuss the relationship between the structure and chiral recognition ability of the alkoxyphenylcarbamates, their molecular models were constructed.     

Chiral separation of quinolones by liquid chromatography and capillary electrophoresis

The quinolones are derivatives of oxoquinolines and mostly known for their antibacterial and antiviral activities. Many quinolones are chiral compounds having asymmetric centers and important due to their enantioselective biological activities. In order to study the biological activities of quinolone enantiomers, to control the manufacturing of homochiral drugs and to prepare necessary quantities of pure enantiomers for preclinical or clinical trials, respective chiral separation methods are urgently needed. In this context, the present review discusses chromatographic and electrophoretic methods for the enantioseparation of chiral quinolones and provides some useful information on their physical and pharmaceutical properties. The drawbacks of currently used techniques are revealed and ways to overcome them are outlined. Moreover, recommendations for an optimal choice of a separation protocol are given.     

Synthesis and characterization of non-symmetrical liquid crystals containing a cholesteryl ester moiety

In this paper,a series of chiral non-symmetrical liquid crystals(nBA-chol)consisting of a cholesteryl ester moiety as chiral entity and a biphenyl aromatic core with different terminal alkyl chain has been synthesized and investigated for their liquid crystalline properties.Effects of numbers of methylene units in the terminal alkyl chain on the phase transition temperatures and on the temperature-dependent pitch lengths of the chiral liquid crystals have been studied.The long terminal alkyl chain tends ...     

Synthesis and characterization of chiral compounds containing cationic groups as chiral dopants in liquid crystals

Novel chiral molecules containing cationic groups, (N-[4-triethylammoniomethyl]-benzoyl ester)-ethyl lactate chloride and bi-(N-[4-triethylammoniomethyl]-benzoyl ester)-isosorbide chloride, were designed and synthesized. Chemical structures of the molecules were characterized by elemental analysis, FT-IR, and (1)H NMR. The photochemical properties of the chiral compounds and their textures in nematic liquid crystals (LCs) were investigated by optical rotation, circular dichroism (CD), and polarizing optical microscopy (POM). The novel chiral molecules exhibited good optical activity. The chiral compound based on a L-ethyl lactate chiral center had a left-handed configuration. The chiral compound based on an isosorbide chiral center had a right-handed configuration. The cationic polar groups did not affect the direction of optical rotation, but could effluence the molar rotation of chiral compounds. The mixtures with dopants showed oily streak textures. Doping of a nematic phase liquid crystal with the chiral molecules converted it to the cholesteric phase.     

Current topics in smectic liquid crystal research.

Interest in the smectic liquid-crystalline state of matter received a substantial boost with the discovery by Meyer in the mid-1970s that a chiral smectic C (SmC*) phase exhibits a spontaneous electric polarization, and with the subsequent demonstration by Clark and Lagerwall of the surface-stabilized SmC* ferroelectric liquid crystal at the beginning of the 1980s. Since then, chiral smectic phases and their plethora of polar effects have dominated the research in this field, which today has reached a mature state where the first commercial microdisplay applications are now shipping in millions-per-year quantities. In this Review we discuss some of the topics of highest interest in current smectic liquid crystal research, and address application-relevant research (de Vries-type tilting transitions without defect generation and high-tilt antiferroelectric liquid crystals with perfect dark state) as well as more curiosity-driven research (the nature and origin of the chiral smectic C subphases and their intermediate frustrated states between ferro- and antiferroelectricity).     

New ferroelectric liquid crystals with a trifluoromethyl group

New chiral dopants, possessing a trifluoromethyl group, have been synthesized. These dopants have different polar groups, located between the chiral centre and the diphenylacetylene core. The polar part is chosen from ester, methylene ether and ether linkages. Each new chiral dopant was mixed with a non-chiral liquid crystal mixture or a ferroelectric liquid crystal mixture, and their transition temperatures and electrooptic properties measured. The largest spontaneous polarization, 4·1 nC cm^-2, was obtained at 25°C for the ferroelectric liquid crystal mixture in which the dopant, with a methylene ether linkage, was incorporated. Molecular orbital calculations (MNDO method) for the dopants show that the calculated dipole moments are correlated with the measured spontaneous polarization, and the calculated results explain the experimental results quite well. In addition, it has been found that the conformation of the chiral part is an important factor which affects the magnitude of spontaneous polarization.     

New ferroelectric liquid crystals with a trifluoromethyl group

Abstract

New chiral dopants, possessing a trifluoromethyl group, have been synthesized. These dopants have different polar groups, located between the chiral centre and the diphenylacetylene core. The polar part is chosen from ester, methylene ether and ether linkages. Each new chiral dopant was mixed with a non-chiral liquid crystal mixture or a ferroelectric liquid crystal mixture, and their transition temperatures and electrooptic properties measured. The largest spontaneous polarization, 4·1 nC cm^?2, was obtained at 25°C for the ferroelectric liquid crystal mixture in which the dopant, with a methylene ether linkage, was incorporated. Molecular orbital calculations (MNDO method) for the dopants show that the calculated dipole moments are correlated with the measured spontaneous polarization, and the calculated results explain the experimental results quite well. In addition, it has been found that the conformation of the chiral part is an important factor which affects the magnitude of spontaneous polarization.     

Covalently bonded polysaccharide derivatives as chiral stationary phases in high-performance liquid chromatography

Polysaccharide derivatives have been extensively used as chromatographic chiral selectors in chiral stationary phases (CSPs) for the separation of enantiomers by HPLC. When coated onto a silica matrix, they represent nowadays one of the most popular type of CSPs. However, they are only compatible with a limited choice of solvents. The main drawback of these CSPs is related to the solubility of the chiral selector in a number of solvents, which limits their applicability. The different attempts which have been described up to now to overcome this problem by covalently fixing the chiral selector to a matrix are reviewed in this paper.     

Influence of chirality on phase transitions in ferroelectric liquid crystals

The transition temperatures between various smectic liquid crystal phases are determined as a function of the enantiomeric excess for three different chiralracemic systems (i.e. binary mixtures consisting of a chiral enantiomer and its racemate). It is shown that transitions involving a ferroelectric phase occur in the chiral compounds at higher temperatures compared to their racemates, the temperature shift being proportional to the square of the enantiometric excess. In contrast, for transitions between two non-ferroelectric phases no difference between the chiral and the racemic compounds is found. Various reasons for the experimental behaviour are discussed. A chirality dependence of the transition temperature is also observed for the smectic A-isotropic transition.     

Chiral recognition based on the kinetics of ion transfers across liquid/liquid interface

Three-phase electrodes in combination with square-wave voltammetry are applied to study the transfer kinetics of chiral anions from water to the chiral 2-octanol. The experimental system used consists of a pyrolytic graphite electrode partly modified with a thin film of one of the enantiomers of 2-octanol, which was immersed into an aqueous solution containing anions of chiral 2-chloropropionic acid, 2-bromopropionic acid, or lactic acid. It is demonstrated that the kinetics of the ion transfer is a stereoselective. The rate of the ion transfer is higher when uncomplimentary transferring ion–solvent chiral isomers are used, i.e., (R)-ion and (S)-solvent, or (S)-ion and (R)-solvent. To the best of our knowledge this is the first evidence for the difference in the ion transfer kinetics of chiral isomers across water/chiral organic solvent interface.     

New dimeric liquid crystals with chiral flexible spacers

In order to obtain chiral compounds of low molecular weight expected to exhibit mesogenic and ferroelectric properties, the asymmetric carbon was introduced into the central part of the molecule. The series consists of nine chiral dimers in which the chiral flexible spacer derives from S-2-chlorosuccinic acid. The mesomorphic properties of the compounds were studied and all of them were found to be mesogenic. From n = 6 onwards the mesophases were chiral smectic C. Some analogous compounds derived from S-2-chloroglutaric acid were also prepared; these were not found to be mesogenic. The thermal instability of the 2-chlorosuccinic acid derivatives prevented the study of their ferroelectric properties. We attempted to perform this study for several mixtures involving 3-methyladipic acid derivatives and both 2-chlorosuccinic and 2-chloroglutaric acids derivatives. All the mixtures studied show chiral smectic C phases. The mixtures containing 2-chlorosuccinoyl derivatives show thermal instability; however those containing 2-chloroglutaroyl derivatives are stable, but do not show significant values of spontaneous polarization.     

New dimeric liquid crystals with chiral flexible spacers

In order to obtain chiral compounds of low molecular weight expected to exhibit mesogenic and ferroelectric properties, the asymmetric carbon was introduced into the central part of the molecule. The series consists of nine chiral dimers in which the chiral flexible spacer derives from S-2-chlorosuccinic acid. The mesomorphic properties of the compounds were studied and all of them were found to be mesogenic. From n = 6 onwards the mesophases were chiral smectic C. Some analogous compounds derived from S-2-chloroglutaric acid were also prepared; these were not found to be mesogenic. The thermal instability of the 2-chlorosuccinic acid derivatives prevented the study of their ferroelectric properties. We attempted to perform this study for several mixtures involving 3-methyladipic acid derivatives and both 2-chlorosuccinic and 2-chloroglutaric acids derivatives. All the mixtures studied show chiral smectic C phases. The mixtures containing 2-chlorosuccinoyl derivatives show thermal instability; however those containing 2-chloroglutaroyl derivatives are stable, but do not show significant values of spontaneous polarization.     

Chiral liquid crystalline polymers: Recent issues and perspectives

The syntheses and structures of chiral liquid crystalline polymers (LCPs) are briefly reviewed with emphasis on the established structure-property correlations. The most recent advances and future trends in their potential applications in optics and electrooptics are also outlined, with particular reference to the ferroelectric, electroclinic, piezoelectric, and nonlinear optical properties of chiral LCPs.     

新型糖基聚合物的合成及其作为高效液相色谱手性固定相的应用(英文)

Two novel polymers containing glucose units as the main-chain that only differ in terms of their regioregularity were synthesized to evaluate their chiral recognition abilities as chiral stationary phases(CSPs)for high performance liquid chromatography(HPLC).The regioregular polymer(poly-5)shows clear resolution ability for the racemate of cobalt(Ⅲ)acetylacetonate(Co(acac)3),whereas the corresponding regioirregular polymer(poly-3)does not show any chiral recognition for Co(acac)3.The regioregular polymer main-chain seems to play an important role not only in providing an efficient interaction with the racemate but also in expressing the chiral recognition ability as a CSP for HPLC.     

Structure-property relationships in dopant-induced ferroelectric liquid crystals

Measurements are reported of the ferroelectric polarization P_s induced in a non-chiral smectic C phase by a variety of chiral dopants having different molecular structural features. Using molecular calculations of contributing dipole moments, ferroelectric order parameters are determined from the experimental results. The relationships between the P_s and various other molecular properties are discussed, and it is shown that restricted rotation of the molecule due to its shape and internal energy barriers to rotation can result in relatively high values of P_s. In contrast dipolar groups flexibly attached to a chiral centre may have their contribution to P_s greatly reduced through internal rotation.     

Ferroelectric liquid crystal siloxane homo and copolymers

Several new chiral liquid crystal siloxane homopolymers and copolymers have been synthesized and studied as to their mesomorphic and ferroelectric behaviour. Almost all of them exhibit chiral smectic C phases over wide temperature ranges. DSC and X-ray measurements are presented; spontaneous polarizations, response times and tilt angles are also given. Some of the spontaneous polarizations are very high, more than 100 nC/cm², and the response times are found to be among the fastest for liquid-crystalline polymers, less than 1 ms.     

Chiral high-performance liquid chromatography of N-octyl bicycloheptene dicarboximide and confirmatory studies using liquid chromatography-tandem mass spectrometry and two-dimensional nuclear magnetic resonance spectroscopy

N-Octyl bicycloheptene dicarboximide (MGK 264) has exo and endo diastereomers. Each structure has a chiral center at the nitrogen side chain. Enantioselective separation of MGK 264 was achieved by normal-phase high-performance liquid chromatography (HPLC) using cellulose-based Chiralcel OD column with diode-array and optical rotation detectors. Peaks were isolated with the purpose of identifying their stereochemical structures. Molecular mass of the HPLC peaks and their structural information was determined by liquid chromatography-electrospray tandem mass spectrometry (LC-ES-MS-MS). A two-dimensional nuclear magnetic resonance (NMR) spectroscopic technique was used to establish the structural features. Correlation of the data obtained from chiral separation and NMR facilitated in unambiguous assignment of the HPLC peaks.