Tolane liquid crystals bearing fluorinated terminal group and their mid-wave infrared properties

This paper describes the synthesis and characterisation of several liquid crystal (LC) compounds having a tolane core structure and a trifluoromethoxy terminal group. The mesomorphic properties, mid-wave infrared (IR) absorption and birefringence were investigated. These materials exhibit low absorption in mid-wave IR regions (MWIR) and high birefringence (Δn ~ 0.26–0.29). The impact of fluorine substitution was investigated. Compounds with monofluorine exhibit wide mesophase temperature (88.5°C), and the mesomorphic behaviour weakened with increasing fluorine atom. The results show that they are promising LC materials for applications in the MWIR.     

A direct assessment of refractive indices of nematic liquid crystals at broad VIS - MWIR range

We developed an interference method for determination refractive indices of nematic liquid crystals in a broad electromagnetic spectrum. Values of ordinary and extraordinary refractive indices were measured in VIS (from 0.4 to 0.8 μm), NIR (from 0.8 to 1.4 μm), SWIR (from 1.4 to 3.0 μm) and at an edge of MWIR (from 3.0 to 4.2 μm) regions. The main task of this work was to develop the efficient and accurate interference method. The absolute error of these measurements is not higher than 0.02. The method was tested on two newly designed mixtures. The first one was a high birefringence liquid crystal mixture for the laser rangefinder, while the second one is intentionally prepared for breathalyser application. The mixture does not possess high absorption bands at 3.4 μm. To measure a dispersion of the refractive indices cells with various thicknesses and dielectric mirrors were prepared. The paper presents a theoretical discussion and experimental results.     

Isolation and structural elucidation of novel antimicrobial compounds from maggots of Chrysomyis megacephala Fabricius

The excretions/secretions from the maggot of Chrysomyis megacephala Fabricius are traditionally used to treat serious infections in China. In this study, bioassay-guided fractionation led to the isolation of three novel antibacterial compounds (1–3), including important fluorinated compounds (3 and 5), together with other nine known compounds from 70% methanol extract of C. megacephala. The structures of the new compounds were elucidated by NMR spectroscopic analysis and high-resolution mass spectroscopy. The antibacterial activities of the isolated compounds were evaluated using agar disc diffusion method. New compounds 1 and 2 exhibited moderate activity against Bacillus subtilis with a minimum inhibitory concentration (MIC) of 250 μg mL^? 1. The most active compounds 3 and 5 displayed a broad spectrum of antimicrobial activity with an MIC of 125 μg mL^? 1 against G⁺ and G^?  bacteria. The structure of the above-mentioned novel compounds and their antimicrobial activities are herein reported for the first time from the natural product of insects.     

A novel sorbent for chromatographic separations: A silica matrix modified with non‐covalently bonded tetrakis(β‐cyclodextrin)–porphyrin conjugates

We prepared new phases for LC that consisted of silica modified with non‐covalently bonded tetrakis(β‐cyclodextrin)–porphyrin (where cyclodextrin is CD) conjugates. The effects of the porphyrin core, type of spacer and β‐CD moieties on the behaviours of the modified phases for the separation of aromatic compounds (benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, o‐terphenyl, triphenylene, phenol and caffeine) and fluorinated aromatic compounds (pentafluorobenzonitrile, pentafluoronitrobenzene and hexafluorobenzene) were studied using the Tanaka test. The results indicate that the non‐covalent substitution of silica with CD‐based macromolecules that have a porphyrin core can be a very effective method for preparing novel sorbents with specific chromatographic properties for applications in LC.     

Ionic self-assembled fluorescent microfibres with electrochemical properties

The fluorescent microfibres with redox-responsive properties were prepared via the ionic self-assembly route from complexes of redox-responsive N,N-dimethylferrocenylmethylhexadecylammonium bromide and methyl orange dye molecule. The length of microfibres is from tens of micrometres to almost a millimetre and the width is about 500 mm to 2 μm. Steady state fluorescence spectroscopy shows strong fluorescent properties of the supramolecular self-assembled microfibres, which may have potential applications in electro-photo molecular switching device.     

Experimental and computational approaches to reveal the potential of Ficus deltoidea leaves extract as α-amylase inhibitor

Ficus deltoidea leaves extract are known to have good therapeutic properties such as antioxidant, anti-inflammatory and anti-diabetic. We showed that 50% ethanol-water extract of F. deltoidea leaves and its pungent compounds vitexin and isovitexin exhibited significant (p < 0.05) α-amylase inhibition with IC₅₀ (vitexin: 4.6 μM [0.02 μg/mL]; isovitexin: 0.06 μg/mL [13.8 μM] and DPPH scavenging with IC₅₀ (vitexin: 92.5 μM [0.4 μg/mL]; isovitexin: 0.5 μg/mL [115.4 μM]). Additionally, molecular docking analysis confirmed that vitexin has a higher binding affinity (-7.54 kcal/mol) towards α-amylase compared to isovitexin (?5.61 kcal/mol). On the other hand, the molecular dynamics findings showed that vitexin-α-amylase complex is more stable during the simulation of 20 ns when compared to the isovitexin-α-amylase complex. Our results suggest that vitexin is more potent and stable against α-amylase enzyme, thus it could develop as a therapeutic drug for the treatment of diabetes.     

Synthesis and characterization of soluble polyimides derived from [1,1′;4′,1″]terphenyl‐2′,5′‐diol and biphenyl‐2,5‐diol

Two series of polyimides based on laterally attached p‐terphenyl and biphenyl groups were synthesized. The solubility and thermal properties were studied using DSC, thermogravimetric analysis, and the solubility test. These polymers exhibited good thermal stability and excellent solubility. The high solubility for both polymer series was attributed to the non‐coplanarity of diamine monomers and the use of fluorinated dianhydride, whereas the slightly better solubility for polymers based on p‐terphenyl was attributed to further weakening of interchain interaction of the polymers. Both polymer series exhibited glass‐transition temperatures (T_g's) in the range of 244–272 °C. The T_g's of polymers containing laterally attached p‐terphenyls were higher than those of their counterparts containing biphenyls by 5–17 °C. This was attributed to the formation of an interdigitated structure that hinders the segmental movement of polymer chains. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2998–3007, 2001     

Hydrolates from lavender (Lavandula angustifolia) – their chemical composition as well as aromatic,antimicrobial and antioxidant properties

It was shown that the method for obtaining hydrolates from lavender (Lavandula angustifolia) influences the content of active compounds and the aromatic, antimicrobial and antioxidant properties of the hydrolates. The content of volatile organic compounds ranged from 9.12 to 97.23 mg/100 mL of hydrolate. Lavender hydrolate variants showed low antimicrobial activity (from 0% to 0.05%). The radical scavenging activity of DPPH was from 3.6 ± 0.5% to 3.8 ± 0.6% and oxygen radical absorbance capacity (ORAC_FL) results were from 0 to 266 μM Trolox equivalent, depending on the hydrolate variant.     

Estimation of the contribution of absorption bands for overtones and composite frequencies in IR spectra of olefins and heteroatomic organic compounds

Intensities of fundamental, overtone, and composite absorption bands for 11 olefins, 17 nitrogen- and oxygen-containing organic compounds, and 12 sulfur-containing organic compounds are calculated in the anharmonic approximation. The first and second derivatives of the electric dipole moment of a molecule were calculated by the quantum-chemical ab initio MP2/6-31G(1d) approach. It is shown that, for the studied compounds, the average contribution of overtones and composite frequencies to absorption in the region from 100 to 4000 cm⁻¹ is of about 10%. The major contribution (on the average 80%) of overtones and composite frequencies falls in the regions (mainly from 1600 to 2800 cm⁻¹) where fundamental transitions are rarely observed. The calculations well describe the centers and intensities of the fundamental, overtone, and composite absorption bands and can be used for the standard-free spectrochemical determination of the compounds of interest by their overtone spectra.     

Fluorinated poly(ether sulfone)s

New fluorinated poly(ether sulfone)s were prepared from bisphenols and α,ωbis(4-fluorophenylsulfonyl)perfluoroalkanes. The fluorinated sulfone monomers were synthesized by reaction of 4-fluorobenzenethiol salts with perfluoroalkylene diiodides, followed by oxidation. Sodium carbonate mediated polymerization gave high molecular weight polymers in excellent yield. The polymers are generally soluble in chlorinated hydrocarbons and some dipolar solvents, are amorphous with T_g's in the range of 120–160°C and are stable to 400°C. They form clear, colorless films by solution casting. Cast films have dielectric constants and dissipation factors somewhat below those of typical poly(ether sulfone)s, and show good permeability and selectivity for O₂/N₂ gas separations.     

Estimation of the contributions of absorption bands for overtones and composite frequencies in infrared spectra of brominated and oxygen-containing organic compounds

Intensities of fundamental, overtone, and composite absorption bands for 27 brominated hydrocarbons and 20 oxygen-containing organic compounds are calculated in an anharmonic approach. The first and second derivatives of the electric dipole moment of the molecule with respect to normal coordinates are determined using ab initio quantum-chemical MP2/6-31G(1d) calculations. For the studied compounds, the average contributions of overtones and composite frequencies to absorption in the region 100–4000 cm⁻¹ is 4.8% for brominated hydrocarbons and 3.2% for oxygen-containing compounds. The major part of the contribution of overtones and composite frequencies falls into the regions (mainly from 1600 to 2800 cm⁻¹) where fundamental transitions are observed rarely. The calculation performed well describe the positions of maxima and the intensities of fundamental, overtone, and composite absorption bands and can be used for the standardless spectrochemical analysis of compounds by their overtone spectra.     

Model Compounds for Asphaltenes and C80 Isoprenoid Tetraacids. Part I: Synthesis and Interfacial Activities

Three model compounds for asphaltenes and two model compounds for the C₈₀ isoprenoid tetraacids (ARN) have been synthesized and their interfacial and solubility properties were investigated. All compounds exhibit high interfacial activities. The asphaltene models lowered the interfacial tension between toluene and pH 9 to around 5 mN/m at 12.5–35 μM and the tetraacid models gave a drop in the interfacial tension between chloroform and pH 9 to 13 mN/m at only 5 μM, which is consistent with previous findings for the natural occurring C₈₀ tetraacids. A sudden drop in the IFT over a very narrow concentration range was observed for two of three asphaltene models. NIR spectroscopy studies indicated an aggregation most likely a result of polar and hydrogen bond interactions. The IFT results also showed different behavior with only small changes in chemical structure. The tetraacid models have similar interfacial behavior as the C₈₀ tetraacids and will thus be suitable model compounds with their highly UV active and fluorescent properties.     

Synthesis and structure of lateral halogenated V-shaped liquid crystal molecules based on a 1,7-naphthalene central core and alkylthio tails

A series of small angle bent-core (V-shaped) mesogens carrying 1,7-naphthalene as a central core linked with lateral halogenated (chlorinated or fluorinated) Schiff-base side wings and alkylthio terminal tails of variable carbon number (n = 12, 16) was synthesised in order to reduce the transition temperature and improve the phase stability of bent-core liquid crystal molecules. Differential scanning calorimetry (DSC), polarising optical microscopy (POM), small-angle X-ray scattering system (SAXS) and two-dimensional X-ray diffractometer were applied to ascertain the mesomorphic structure and phase transition temperatures of the compounds. The results confirm that all the molecules show thermotropic liquid crystalline behaviour and exhibit hexagonal columnar phase (Col_h) in a certain temperature range. Compared with the homologous compounds without lateral halogen, the cleaning point temperature of lateral halogenated V-shaped compounds generally decrease and the Col_h phase ranges are more extensive. The influence of lateral chlorine on the cleaning point temperature is more obvious, as well as the effect of lateral fluorine on the range of Col_h phase.     

Synthesis and properties of soluble trifluoromethyl‐substituted polyimides containing laterally attached p‐Terphenyls

A new fluorinated diamine monomer, 2′,5′‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐p‐terphenyl, was synthesized from the chloro‐displacement of 2‐chloro‐5‐nitrobenzotrifluoride with the potassium phenolate of 2,5‐diphenylhydroquinone, followed by hydrazine palladium‐catalyzed reduction. A series of trifluoromethyl‐substituted polyimides containing flexible ether linkages and laterally attached side rods were synthesized from the diamine with various aromatic dianhydrides via a conventional two‐step process. The inherent viscosities of the poly(amic acid) precursors were 0.84–1.26 dL/g. All the polyimides afforded flexible and tough films. The use of 4,4′‐oxydiphthalic anhydride and 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride produced essentially colorless polyimide films. Most of the polyimides revealed an excellent solubility in many organic solvents. The glass‐transition temperatures of these polyimides were recorded between 254 and 299 °C by differential scanning calorimetry, and the softening temperatures of the polymer films stayed in the range of 253–300 °C according to thermomechanical analysis. The polyimides did not show significant decomposition before 500 °C in air or under nitrogen. These polyimides also showed low dielectric constants (2.83–3.34 at 1 MHz) and low moisture absorption (0.4–2.2%). For a comparative study, a series of analogous polyimides based on the nonfluorinated diamine 2′,5′‐bis(4‐aminophenoxy)‐p‐terphenyl were also prepared and characterized. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1255–1271, 2004     

GC×GC/qMS analyses of Campomanesia guazumifolia (Cambess.) O. Berg essential oils and their antioxidant and antimicrobial activity

The present study investigated the essential oil obtained from Campomanesia guazumifolia (Cambess.) O. Berg, an aromatic plant used in Brazilian folk medicine. The chemical composition was performed by GC×GC/qMS. The antioxidant and antimicrobial activities were evaluated by DPPH and BCB and, MIC assays, respectively. Sixty-eight compounds were identified in the oil, where the major compounds were bicyclogermacrene (15%), globulol (5%) and spathulenol (5%). Sesquiterpene hydrocarbons (29 compounds) and oxygenated sesquiterpenes (20 compounds) were the most representative classes of terpenes. DPPH (IC₅₀ value 26.1 ± 0.5 μg/mL) and BCB (68.3 ± 1.5%) values indicated a significant antioxidant activity. The essential oil strongly inhibited Staphylococcus aureus (MIC 15 ± 0.1 μg/mL), Escherichia coli (MIC 25 ± 0.2 μg/mL) and Candida albicans (MIC 5 ± 0.1 μg/mL). The results give a deeper understanding of the chemical composition and report for the first time the antioxidant and antimicrobial potential of the C. guazumifolia essential oil.     

Synthesis,mesogenic and dielectric properties of fluorosubstituted isothiocyanatoterphenyls

The synthesis, mesomorphic and physical properties of 14 homologous series of laterally fluorinated 4?-alkyl-4-isothiocyanatoterphenyls were described. Influence of the number of fluorine atoms and their position in the terphenyl core on the phase transition temperatures, nematic range, dielectric and optic anisotropy as well as bulk viscosity were discussed. The compounds with the most optimal properties for formulation of nematic mixtures were selected, and mixture examples with low viscosity and medium or high birefringence were presented.     

Improved thermal stability of an organic zeolite by fluorination

The thermal stability of an organic zeolite material, namely 2,4,6-tris(4-bromo-3,5-difluorphenoxy)-1,3,5-triazin (Br-3,5-DFPOT), was improved by fluorination of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazin (BrPOT). The open pore structure (van der Waals diameter of 10.5 Å) of the modified zeolite was observed up to 110 °C in comparison to 70 °C for BrPOT. Nitrogen sorption at low temperature showed a type I isotherm and derived pore volumes thereof are in agreement with structural data. It was observed here that Br-3,5-DFPOT crystals preserving the open pore structure could only be obtained below a typical size of about 50 μm. The improved thermal stability of the fluorinated system is attributed to an enhancement of the strength of the Br₃-synthon.     

Anti-leptospiral activities of an endemic plant Glyptopetalum calocarpum (Kurz.) Prain used as a medicinal plant by Nicobarese of Andaman and Nicobar Islands

Leaves of an endemic plant Glyptopetalum calocarpum are used by Nicobarese tribes of Andaman and Nicobar Islands, India, to prepare traditional medicine for treating fever. In the present investigation, pharmacologically active compounds were isolated from this plant and their antimicrobial efficacy was evaluated against the leptospiral strains. The anti-leptospiral activity of six plant-derived compounds was determined by both microdilution and macrodilution methods. Two out of six compounds, namely lupenone and stigmasterol, showed anti-leptospiral activity. The minimum inhibitory concentrations of the two compounds tested against pathogenic leptospiral strains belonging to 10 serovars were in the range of 100–200 μg/mL. The range of minimum bactericidal concentrations was 400–800 μg/mL. Compounds lupenone, stigmasterol, lupeol, β-amyrin and β-amyrin acetate had negligible or no haemolytic activity, exhibiting IC₅₀ values of greater than 5 mg/mL. Further in vivo studies are needed to investigate the pharmacological and toxicological properties of G. calocarpum before it can be considered as a new anti-leptospiral agent.     

Progress in the syndiotactic polymerization of styrene with metallocene/mao catalysts

Metallocene/MAO catalysts are useful for the production of syndiotactic polystyrene - a new class of high performance polymers. The melting point of the obtained syndiotactic polystyrene depends on the metallocene used and can reach up to 275 °C. In the past, the most active catalysts in polymerization have been half-sandwich titanocenes such as CpTiCl₃ and Cp*TiCl₃. If the chlorinated compounds are changed into the fluorinated compounds as CpTiF₃ and Cp*TiF₃, the activity increases by a factor of 5 to 100. The fluorinated titanocenes are more stable at higher temperatures and need a lower MAO excess in order to obtain optimal activities. Polymers obtained with the unsubstituted CpTiF₃ show melting points which are 17 °C lower than those synthesized by pentamethylcyclopentadienyltitaniumtrifluoride. Especially Cp*TiF₃ shows a much higher activity and, compared with the chlorinated compound, gives polymers with a higher molecular weight. Substituted cyclopentadienyltitanocenes have even higher activities. Ethene/styrene copolymers can be obtained by catalysis with zirconocene compounds.     

Chemical composition,N-nitrosamine inhibition and antioxidant and antimicrobial properties of essential oil from Coreopsis tinctoria flowering tops

Coreopsis tinctoria flowering (CTF) tops from the Kunlun Mountains in Xinjing (north-western China) have been used for tea production for about a century. This study was to assess antioxidant, nitrite-scavenging and N-nitrosamine inhibitory and antimicrobial activities of the essential oil extracted from CTF tops. The essential oil was extracted through hydrodistillation and its chemical compositions were analysed by GC–MS. Seventy compounds of the oil were identified, representing 81.87% of total oil. The antioxidant capacities of the oil with IC₅₀ values for scavenging DPPH and ABTS were 287.66 ± 12.60 and 1.251 ± 0.127 μg mL^? 1, respectively. The nitrite-scavenging and N-nitrosamine inhibitory activities (IC₅₀) were 0.3912 ± 0.0127 and 0.6564 ± 0.036 μg mL^? 1, respectively. The oil has a certain antimicrobial capacity, but its capacity was weaker than that of penicillinG (24 μg mL^? 1). The oil showed antioxidant and antimicrobial capacities and had a stronger nitrite-scavenging and N-nitrosamine inhibitory properties.