Chiral Mixtures Research Articles

U-shaped oligomers with a molecular biaxiality stabilizing blue phases

After preparing catechol or biphenyl derivatives possessing two 2,3-difluoro-1,4-diphenylbenzene units, we investigated the phase transition behaviour of their mixture with a chiral additive with a high twisting power. Their transition behaviour was dependent on the methylene number in the spacer. Both derivatives possessing a hexamethylene unit in the spacer were found to exhibit wide-temperature blue phases in the chiral mixture. The appearance of the blue phases was discussed in terms of helical twisting power, elasticity, and molecular biaxiality. It was independent of the helical twisting power. A large molecular biaxiality or small bend elastic constant might stabilize the blue phases. The results provide important information related to molecular design for optically isotropic blue phases with frustrated molecular organization.

Separation of chiral colloidal particles in a helical flow field

Stereoisomeric molecules with opposite chirality, so-called enantiomers, often vary regarding their sensory, pharmacological and toxicological properties. Such enantiomer specific effects play a central role in the development, testing and evaluation of drugs, pesticides and food related products. Accordingly, efficient techniques for separation of chiral mixtures into enantiopure compounds are of enormous practical relevance. Most current enantiomer separation methods are based on enantioselective interactions with an auxiliary substance which has to be developed and optimized for different chiral molecules in an elaborate and costly process. Here, we experimentally demonstrate the separation of micron-sized chiral particles in a helical fluid flow which is created inside a microfluidic device patterned with slanted grooves. We observe that the retention time of particles in a helical flow field strongly depends on their chirality which leads to an effective chiral separation within the channel. Our experimental results are confirmed by numerical calculations which demonstrate how the coupling of rotational and translational degrees of freedom leads to differences in the trajectories of particles with opposite chirality. Since our separation mechanism does not rely on material specific interactions, this offers considerable advantages over existing methods. We expect that our approach can be also applied at nanometre length scales by using channels with smaller diameters and with an optimized geometry.

Ion mobility spectrometry‐mass spectrometry (IMS‐MS) of small molecules: Separating and assigning structures to ions

The phenomenon of ion mobility (IM), the movement/transport of charged particles under the influence of an electric field, was first observed in the early 20th Century and harnessed later in ion mobility spectrometry (IMS). There have been rapid advances in instrumental design, experimental methods, and theory together with contributions from computational chemistry and gas-phase ion chemistry, which have diversified the range of potential applications of contemporary IMS techniques. Whilst IMS-mass spectrometry (IMS-MS) has recently been recognized for having significant research/applied industrial potential and encompasses multi-/cross-disciplinary areas of science, the applications and impact from decades of research are only now beginning to be utilized for "small molecule" species. This review focuses on the application of IMS-MS to "small molecule" species typically used in drug discovery (100-500 Da) including an assessment of the limitations and possibilities of the technique. Potential future developments in instrumental design, experimental methods, and applications are addressed. The typical application of IMS-MS in relation to small molecules has been to separate species in fairly uniform molecular classes such as mixture analysis, including metabolites. Separation of similar species has historically been challenging using IMS as the resolving power, R, has been low (3-100) and the differences in collision cross-sections that could be measured have been relatively small, so instrument and method development has often focused on increasing resolving power. However, IMS-MS has a range of other potential applications that are examined in this review where it displays unique advantages, including: determination of small molecule structure from drift time, "small molecule" separation in achiral and chiral mixtures, improvement in selectivity, identification of carbohydrate isomers, metabonomics, and for understanding the size and shape of small molecules. This review provides a broad but selective overview of current literature, concentrating on IMS-MS, not solely IMS, and small molecule applications.

40.1: Invited Paper: Ultrafast High Optical Contrast Flexoelectric Displays for Video Frame Rates

AbstractWe describe wide temperature range bimesogenic chiral nematic liquid crystals mixtures with high flexoelectro‐optic coefficients (e/K), of the order of 2.0–4.0 CN−1 m−1, with 50–100μs response times. Gray scale devices in both the ULH texture, with an optimum optical in plane switch of 45° at fields of <2Vμm−1, and the USH mode, with a unique optically isotropic “field off” black state (∼0.7 nits) and contrast ratios of ∼5000:1, using “in plane” electric fields driving will be described. The new materials and devices give μs level to level switching and may be used in FSC video rate displays.

Cyanoalkyl difluoro-terphenyl-carboxylate chiral dopants

A liquid crystal like difluoroterphenyl chiral dopant was synthesized to match the dimensions of a host chiral dopant mixture. The melting point of the chiral dopants was decreased by increasing the length of the alkyl chain. The melting point of the chiral dopants also decreased when fluorine was on the same ring as the ester i.e. at 2″, 3″ position. These dopants were formulated with terphenyl host mixture and liquid crystal properties were assessed. New dopants, when added to the host mixture, maintain SmA11Smectic A. but the SmC22Smectic C. phase was reduced markedly. There was a decrease in spontaneous polarisation when fluorine was on the same ring as the ester i.e. at 2″, 3″ position. As the molecular weight of the chiral dopant increased (pentyl→heptyl→nonyl), spontaneous polarisation decreased.

Improvement of electro-optical properties on polymer-stabilised optically isotropic liquid crystals

A relation between preparation conditions of polymer-stabilised optically isotropic liquid crystals and their electro-optical properties was investigated based on a cyclic voltammetric (CV) method. The polymer-stabilised optically isotropic liquid crystals were prepared by an in-situ photo-polymerisation of a precursor consisting of a chiral liquid crystalline mixture with monomers in an isotropic phase with a metal halide lamp. The CV response of the cell filled with the sample showed an asymmetric profile and a symmetric profile between the positive and negative applied voltages when the cell was irradiated with the metal halide lamp without filter and with a cut-off wavelength filter (> 390 nm), respectively. The CV response profile depends on a distributed state of the polymer generated in the cell. The residual birefringence of the polymer-stabilised optically isotropic phase was suppressed when the CV profile showed a symmetric profile.

Sub-hertz relaxation process in chiral smectic mixtures doped with silver nanoparticles

A thermal activated sub-hertz frequency dielectric absorption process in both SmC* and SmA* phases along with characteristic Goldstone mode have been observed in both pure and silver nano particle doped liquid crystal mixtures. This process is well resolved, in particular, in the composites probably due to capturing of ions/charges inside the thiol group layer around the silver particles surface, thereby increasing the resistivity of the composites. The process is interpreted as space charge accumulation of ions/charges at the interface between liquid crystals and the cell polymer layer close to the electrodes. Improved switching characteristics and reduced spontaneous polarization have been detected.

A versatile resolving agent for diffusion edited separation of enantiomers, complex mixtures and constitutional isomers

The study is the first report of the utilization of a crown ether as a new and versatile resolving agent for the diffusion edited separation of enantiomers, complex mixtures and constitutional isomers. As a consequence of different binding affinities of enantiomers of a chiral molecule and individual components of the complex mixtures with the crown ether, the molecules diffuse at different rates. The enhanced separation achieved due to matrix assisted diffusion permitted their separation in the diffusion dimension. The generality and wide utility of the new resolving agent and the methodology are demonstrated on diverse examples, such as an organic chiral molecule, constitutional isomers and complex mixture of molecules possessing different functional groups that possess nearly identical molecular weights.

Self-assembly of osmium complexes on reduced graphene oxide: A case study toward electrochemical chiral sensing

An electrochemical sensor was constructed via self-assembly of chiral metal complexes Λ-[Os(phen)3(ClO4)2] on reduced graphene oxide (rGO) sheet. Cyclic voltammetry and differential pulse voltammetry illustrate that the sensor could detect 1,1′-2-binaphthol lower than 10μM. The response current of S-1,1′-2-binaphthol is 1.4 times higher than that of R-1,1′-2-binaphthol. A linear concentration range was attained for the response peak current. In comparison to clay/indium tin oxide substrate based chiral sensor, rGO has clearly enhanced the sensitivity of chiral sensing. Preliminary measurement indicates that the rGO/Λ-[Os(phen)3]2+ sensor can also be applied to determine compositions of a chiral mixture.

Asymmetric ring opening of terminal epoxides via kinetic resolution catalyzed by chiral (salen)Co mixture

The highly enantioselective hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by bimetallic chiral (salen)Co and (salen)Co(III)-OAc mixture provides a simple and effective method for the synthesis of enantiomerically enriched terminal epoxides (ee > 99%) and diols. At the equimolar amounts of bimetallic chiral (salen)Co and (salen)Co(II)-OAc, the catalytic activity increases more than two times in comparison with (salen)Co(III)-OAc used alone. The mixed catalytic system can be recycled and reused. No significant loss of catalytic activity was observed after three runs.

Application of Cholesteryl Alkanoate Liquid Crystals for Light Polarization Control

Chiral LC mixtures based on cholesterol esters with strong temperature dependence of the helical pitch were used for realization of the light-controlled adjustment of the selective reflection (SR) spectral position. Subtle variations of composition allowed obtaining mixtures with helical pitch rapidly decreasing with temperature and providing the fine tuning of the SR band with respect to the laser emission wavelength. Control of light polarization plane in the spectral region of the SR band was investigated; potential applications in different aspects of optical signal processing, all-optical switching and photonics are discussed.

Printed black internal conducting electrodes for flexible bistable cholesteric displays

We report flexible, bistable cholesteric displays utilizing polyester (PET) substrates with printed internal black electrodes. The black electrodes consist of carbon ink dispersed in butyl carbitol using a patented roll-to-roll gravure-offset printing. A transparent conducting polymer printed on PET serves as the counter electrode. The electro-optic material is a chiral nematic mixture dispersed in a low-concentration polymer binder. The device can be switched between scattering (black) and reflective (vibrant green) states upon application of an electric pulse. The internal black electrode enhances the contrast of the display and simplifies the roll-to-roll manufacture of flexible displays.

Simplified preparation of polymer-encapsulated LC layers by thermally induced phase separation

Stabilisation of functional layers in flexible liquid crystal displays (LCDs) is essential if they are to find use in advanced applications. Among the various methods for encapsulation of liquid crystals (LCs) by spatially controlled polymer wall formation within LCD cells, we have devoted particular attention to thermally induced phase separation (TIPS) in LC/polymer systems. A drawback of the standard TIPS procedure is the requirement to fill cells with the isotropic LC/polymer mixture at elevated temperatures. We have demonstrated that compartmentalisation can be simplified by precoating the substrate with an appropriate thermoplastic matrix polymer, for example poly(1-tetralyl methacrylate) (PTMA), before assembling and filling the cell with polymer-free LC at ambient temperature. The insular morphology originating from subsequent TIPS in different types of display cells prepared with nematic or chiral nematic mixtures has been examined by polarising microscopy and scanning electron microscopy. The electro-optical characteristics of test devices based on polymer-free LC films or on LC/polymer composites, prepared by both standard TIPS and our novel technique, are compared.

Chiral effects of blue phase stabilisation of a binaphthyl derivative

We have recently reported a binaphthyl liquid crystal exhibiting on cooling a cubic blue phase over a wide temperature range. On heating, however, a chiral nematic phase appeared in place of the blue phase. To elucidate the origin of blue phase stabilisation we have prepared a homologous series of binaphthyl derivatives possessing two 2,3-difluoro-1,4-diphenylbenzene units and have investigated the phase transition behaviour and helical twisting power. A binaphthyl derivative exhibiting the blue phase was found to induce helical twist inversion in a chiral nematic mixture with a host liquid crystal, whereas other compounds without the blue phase induced short helical pitches independently of temperature. The blue phase material is thought to have two possible origins for its twisting power, which are able to stabilise the double-twist structure of the phase.

Amphiphilic liquid crystal possessing a SmA-promoting tail and a SmC-promoting core

A novel amphiphilic compound (1) comprising a semi-perfluorinated alkyl chain and a 2,3-difluoro-1,4-diphenylbenzene core has been prepared and its physical properties investigated using optical microscopy, differential scanning calorimetry and X-ray diffraction. The compound exhibited SmA and SmC phases. The maximum layer contraction in the SmC phase was found to be 2.0% at T – T AC = –40 K, and the optical tilt angle was 21.8°. The electro-optical properties of a mixture of the compound with a ferroelectric liquid crystal were investigated, and it was found that the chiral mixture exhibited fast electro-optical switching, with a response time of 10 μs in the chiral SmA phase, in spite of the absence of the SmC* phase.

Bandwidth-controllable reflective polarisers based on the temperature-dependent chiral conflict in binary chiral mixtures

In this study, we demonstrate a new method for obtaining a binary chiral mixture (BCM) which exhibits an unprecedented temperature-dependent helical twisting power (HTP) by utilising the chiral conflict between two chiral dopants with opposite handedness and HTP temperature dependence. Different from the common chiral dopant reported before, the addition of such a BCM could increase the clearing temperature of the host liquid crystal (LC). Due to the sufficiently large HTP value of the BCM, the three primary colours (blue, green and red) can be easily reflected by the nematic liquid crystal (N-LC)/BCM mixture at different temperatures. Moreover, the large HTP temperature dependence could be maintained and even enhanced in the longer wavelength region by adjusting the content of the BCM. Finally, based on the large HTP temperature dependence and the positive affect on the host LC of the BCM, a thermally bandwidth-controllable reflective polariser that could work in the visible region (400–750 nm) was prepared from the N-LC/BCM/polymer network composite.

Preferential selection of isomer binding from chiral mixtures: alternate binding modes observed for the E and Z isomers of a series of 5-substituted 2,4-diaminofuro[2,3-d]pyrimidines as ternary complexes with NADPH and human dihydrofolate reductase.

The crystal structures of six human dihydrofolate reductase (hDHFR) ternary complexes with NADPH and a series of mixed E/Z isomers of 5-substituted 5-[2-(2-methoxyphenyl)-prop-1-en-1-yl]furo[2,3-d]pyrimidine-2,4-diamines substituted at the C9 position with propyl, isopropyl, cyclopropyl, butyl, isobutyl and sec-butyl (E2-E7, Z3) were determined and the results were compared with the resolved E and Z isomers of the C9-methyl parent compound. The configuration of all of the inhibitors, save one, was observed as the E isomer, in which the binding of the furopyrimidine ring is flipped such that the 4-amino group binds in the 4-oxo site of folate. The Z3isomer of the C9-isopropyl analog has the normal 2,4-diaminopyrimidine ring binding geometry, with the furo oxygen near Glu30 and the 4-amino group interacting near the cofactor nicotinamide ring. Electron-density maps for these structures revealed the binding of only one isomer to hDHFR, despite the fact that chiral mixtures (E:Z ratios of 2:1, 3:1 and 3:2) of the inhibitors were incubated with hDHFR prior to crystallization. Superposition of the hDHFR complexes with E2 and Z3 shows that the 2'-methoxyphenyl ring of E2 is perpendicular to that of Z3. The most potent inhibitor in this series is the isopropyl analog Z3 and the least potent is the isobutyl analog E6, consistent with data that show that the Z isomer makes the most favorable interactions with the active-site residues. The isobutyl moiety of E6 is observed in two orientations and the resultant steric crowding of the E6 analog is consistent with its weaker activity. The alternative binding modes observed for the furopyrimidine ring in these E/Z isomers suggest that new templates can be designed to probe these binding regions of the DHFR active site.

Blue Phase Temperature Range at n-Cyanobiphenyl Homologue Chiral Nematic Liquid-Crystal Mixtures

Blue phase (BP) stability is dependent upon chemical structure as well as the physical properties of the chiral nematic liquid-crystal (LC) mixture. In this study, the dependence of blue phase temperature range on alkyl chain length was investigated in order to evaluate the relationship between blue phase stability and the molecular structures of four kinds of n-cyanobiphenyl (CB) homologue chiral nematic liquid-crystal mixtures composed of rod-like nematic LC. It was confirmed that blue phase temperature range was strongly dependent upon the length of the alkyl chain and the elastic constant in n-CB homologues chiral nematic LC mixtures.

On the application of chiral amplification via adsorption

Chiral amplification is a known phenomenon in crystallization. Recent atomistic simulations have shown that amplification can also occur in equilibrium processes when a mixtures of chiral molecules adsorb in metal-substituted zeolites that are not chiral by themselves. In this article we investigate how this process could be exploited for enantiopurification and separation in a pressure-swing adsorption process. For this purpose, we develop a mathematical model that reproduces the main features of the full-atom simulations and allows us to study the impact of several parameters on the enantioselectivity on a macroscopic scale. Besides numerical solutions of this model, we provide some analytic results which suggests that the enantioselective materials prohibit a phase transition as a function of temperature. Below a certain critical temperature, the enantiomeric content of the adsorbed phase becomes a discontinuous function of the enantiomeric gas content. This has the following consequences: (i) the adsorbed phase in racemic conditions becomes unstable, (ii) a sudden increase in efficiency of the purification process, and (iii) the possibility to not only purify but also fully separate chiral mixtures using a parallel batch process in which both lines use an input that is enriched with opposite enantiomer.

Anesthesia Literature Review

Anesthesia Literature Review