New 1,3-dioxan-type ionic liquid crystal compounds having a large dielectric constant

New pyridinium-type thermotropic ionic liquid crystal materials having a 1,3-dioxan ring in its central core: N-substituted-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6) were synthesized. The mesomorphic behaviour of these compounds and dielectric constant perpendicular to the molecular axis were measured. The principal features of these compounds are that they exhibit a smectic A phase over a wide temperature range including room temperature - for example 6f: g -9 SmA 181 I (°C)-and they have a large dielectric constant perpendicular to the molecular axis.     

Liquid crystal properties of new ionic liquid crystal compounds having a 1,3-dioxane ring

New pyridinium type chiral ionic liquid crystal materials having a 1,3-dioxane ring in the central core, (+)- N -2-methylbutyl-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6), were synthesized. Mixture A was made by adding 5.9 wt % of compound 6?3 to the ferroelectric liquid crystal mixture Merck 4655-100; its phase transitions and some liquid crystal properties were measured. In spite of a large decrease of P_s for mixture A, its response time A was the same as that of Merck 4655-100. The dielectric constants perpendicular to the molecular axis for the smectic C* and smectic A phases were measured for the mixture and Merck 4655?100: in the smectic C phase, these dielectric constants were almost the same (4.5～5.5), but in the smectic A phase, the perpendicular dielectric constant of the mixture was 47.0 and that of Merck 4655?100 was 4.5.     

Liquid crystal properties of new ionic liquid crystal compounds having a 1,3-dioxane ring

New pyridinium type chiral ionic liquid crystal materials having a 1,3-dioxane ring in the central core, (+)- N -2-methylbutyl-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides ( 6 ), were synthesized. Mixture A was made by adding 5.9 wt % of compound 6-3 to the ferroelectric liquid crystal mixture Merck 4655-100; its phase transitions and some liquid crystal properties were measured. In spite of a large decrease of P s for mixture A, its response time A was the same as that of Merck 4655-100. The dielectric constants perpendicular to the molecular axis for the smectic C* and smectic A phases were measured for the mixture and Merck 4655-100: in the smectic C phase, these dielectric constants were almost the same (4.5~5.5), but in the smectic A phase, the perpendicular dielectric constant of the mixture was 47.0 and that of Merck 4655-100 was 4.5.     

Polar 2‐alkoxyethoxy‐substituted nematic liquid crystals

The synthesis is reported of a series of polar nematic liquid crystals incorporating an alkoxyalkoxy chain attached in a terminal position to a molecular core consisting of two aromatic rings. The dependence of the mesomorphism and phase transition temperatures on the nature of this terminal chain was studied. The shape anisotropy of the core is increased by the presence of an additional 1,4‐disubstituted phenyl unit in a number of p‐terphenyls. A number of highly polar esters with a terminal methoxyethoxy chain have been prepared as dopants to lower the threshold voltage of LCDs. The presence of the methoxyethoxy chain leads to an increase in the molecular dipole moment, the dielectric anisotropy and the dielectric constant perpendicular to the molecular long axis. Several compounds with a four‐unit diether central linkage were also prepared.     

Dielectric studies of liquid crystals under high pressure III. Low frequency relaxation process in 4-(trans-4′-n-hexylcyclohexyl)isothiocyanato benzene

Abstract

Dielectric studies of 4-(trans-4′-n-hexylcyclohexyl) isothiocyanatobenzene (6CHBT) were performed in the pressure range 0·1–150 MPa, the frequency range 1 kHz–13 MHz and the temperature range 295–325 K. The temperature and pressure dependencies of the static permittivity ?_0∥ and of the relaxation time τ_∥ are analysed and compared with the analogous data obtained recently for 4-n-pentyl-4′-cyanobiphenyl (5CB) (Parts I and II of this series). Marked differences in the dielectric properties of the nematic phases of the two substances are observed. They are interpreted as a result of varying degrees of molecular association in particular compounds. It is concluded that in the nematic phase of 6CHBT dipole–dipole correlations do not exist or are very weak, whereas for 5CB they are easily broken by a relatively low pressure.     

Synthesis,characterization, and investigations of antimicrobial activity of benzopyrans,benzofurans and spiro[4.5]decanes

In this study, the radical cyclization reactions of cyclic 1,3-dicarbonyl compounds (1a–c) and α,β-unsaturated alcohols (2a–d) through Mn(OAc)₃ were performed. A series of biologically interesting dihydropyrans (3–5) and dihydrofurans (6–18) were synthesized as a result of these reactions. Spiro compounds (19–20) were obtained from the reactions of 1,3-dicarbonyl compounds and (E)-2,4-diphenyl-but-3-en-2-ol (2e). The unique structure of compound 19 was also confirmed by X-ray crystallography. In addition, the antibacterial activities of synthesized compounds were screened against some bacteria. Their zone diameters showed better results than some known antibiotics.     

New terphenyl liquid crystals terminated by 2-chloro-3,3,3-trifluoropropenyl group

New liquid crystal (LC) compounds composed of terphenyl as a core and 2-chloro-3,3,3-trifluoropropenyl terminal group were synthesised. Their structures were confirmed by nuclear magnetic resonance, mass spectra and infrared spectrometry. The mesomorphic and physical properties were evaluated. The results show that these compounds have a smectic phase, large dielectric anisotropy, high birefringence and suitable rotational viscosity. The lateral fluorine substitutions lead to a large perpendicular component of the dielectric constant, and a small value of Δε/ε_⊥. These characteristics are significant for the fringe-field switching LC display mode.     

Dielectric properties of some semiconducting polyazophenylenes

The dielectric properties of a series of semiconducting polyazophenylenes were studied as a function of temperature and molecular weight in the temperature range 293–600°K and for molecular weights between 5,100 and 62,800 at a constant frequency of 1 kHz. The compounds studied included poly-2,4-diaminotoluene, poly-2,4-diaminoanisole, and poly-2,5-diaminotoluene. The dielectric properties are presented in the usual way in terms of a complex dielectric constant ε^* = ε′—jε″. Activation energies of relaxation processes were evaluated from the areas and widths of the dielectric loss factor, ε″, against reciprocal temperature at constant frequency. The dielectric activation energies were found to be roughly equal to the activation energies from the DC conductivity. This indicates that the conduction mechanism is based on rotational movements of molecules or parts of molecules.     

Characterization of bioactive thiophenes from the dichloromethane extract of Echinops grijisii as Michael addition acceptors

Michael addition acceptors are considered as biologically active molecules, which regulate many signal pathways in cells. In the present study, it was demonstrated that the dichloromethane extract of Echinops grijisii had phase II detoxifying enzyme-inducing and nuclear factor-κB (NF-κB)-inhibiting activities, which might be attributed to the modification of key cysteine residues in Keap1 and NF-κB by Michael addition acceptors in it. To screen these Michael addition acceptors, glutathione (GSH) was employed, and a simple liquid chromatography–tandem mass spectrometry screening method was established to investigate the formation of GSH conjugates. Three thiophenes, 5-(penta-1,3-diynyl)-2-(3,4-diacetoxybut-1-ynyl)-thiophene (6), 2-(penta-1,3-diynyl)-5-(4-hydroxybut-1-ynyl)-thiophene (7), and 2-(penta-1,3-diynyl)-5-(3,4-dihydroxybut-1-ynyl)-thiophene (8) were demonstrated to react with GSH. Then NAD(P)H/quinone oxidoreductase1(NQO1) induction assay and an ultrafiltration mass spectrometric screening method were performed to investigate whether the above three compounds had NQO1-inducing and NF-κB (p65) alkylating activities. The result indicated that compounds 6–8, which had a common structural moiety, a penta-1,3-diynyl group, had strong NQO1-inducing activities, and compounds 7 and 8 could effectively alkylate the cysteine residues in NF-κB (p65).     

Synthesis and mesomorphic properties of four-ring liquid crystals containing 2,3-difluorophenyl and 1,3-dioxane units

Two series of novel liquid crystalline materials were synthesized: 2-(2,3-difluoro-4-alkoxyphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (A _m-n and 2-(2,3-difluoro-4-alkylphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (B _m-n ). Their mesmorphic properties were characterized by polarizing optical microscopy and differential scanning calorimetry. All these compounds exhibit broad mesomorphic phases, and most of them show wide smectic C phases and the phase sequence Cr-SmC-SmA-N-I. The relationship between properties and chemical structures is discussed in detail.     

NMR experiments on acetals—XXV: Conformational energy for the chair-twist interconversion of the 1,3-dioxane system

Trans-4-t-Bu-6-R-1,3-dioxanes (R = Me, Prⁱ and cyclohexyl) show temperature-dependent values for ²J(H—2) and ³J(H—4(6), H—5) in their PMR spectra. This is the result of the presence of twist-boat conformations. With the aid of typical limit-values of ²J(H—2) for the chair and twist forms, the amount of flexible conformations were determined as a function of temperature (Table 2), allowing the determination of the enthalpy change for chair-twist interconversion in 1,3-dioxane itself (6·2 ± 0·3 kcal/mole). Typical values for ²J(H—2) were obtained from a study of low temperature spectra and from appropriate model compounds of which 4-(1′-adamantyl)-6-t-Bu-1,3-dioxane served as the model for a genuine twist form with a twofold axis through C-2/C-5.     

Cleavage of 2-(1,2,3,4-tetrahydroisoquinolin-1-yl)-2-phenyl-1,3-dithianes with HgO/BF3

Summary The title compounds (5) were prepared by addition of 2-phenyl-1,3-dithiane anion (2-lithiated10) to adequately substituted N-alkyl-3,4-dihydroisoquinolinium salts (7a–7g). Cleavage of compounds5 with HgO/BF₃ affords S-benzoyl-1,3-propanedithiol (4a) and the corresponding disulfide4c, benzaldehyde, and Hg(I) ions. In contrast to the title compounds, 2-(-dialkylaminobenzyl)-2-phenyl-1,3-dithianes (6) yield benzil under these conditions.In commemoration of the late Prof. Dr. Dr. h.c. mult.Horst Böhme, Marburg/Germany, an outstanding representative of Pharmaceutical Chemistry     

Effect of the variation of swallow-tailed groups on the mesomorphic and electro-optical properties of chiral compounds derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid

Three homologous series of chiral swallow-tailed compounds, alkyl (S)-2-{6-[4-(4′-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionates, (S)HNP(p,n,q) derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid in conjugation with a variety of swallow-tailed groups, attached to the external side of the chiral centre, have been synthesized and their mesomorphic and electro-optical properties studied. Both (S)HNP(p,1,2) and (S)HNP(p,1,3) exhibited an enantiotropic antiferroelectric SmC*_A phase. This implys that the swallow-tailed groups in the molecules favour zigzag pairing of the molecules in the smectic phase. The maximum P _S values of compounds (S)HNP(p,1,2) in the antiferroelectric phase were measured in the range 21–30 nC cm^-2; those of compounds (S)HNP(p,1,3) were in the range 15–23 nC cm^-2, indicating that these chiral compounds possess low polarity. The electro-optical response of the compounds in the antiferroelectric SmC*_A phase displayed thresholdless V-shaped switching.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Zur Umsetzung des 3,4,5,6-Tetrahydro-6-hydroxy-4,4,6-trimethyl-1,3-thiazin-2-thions mit primären Aminen

Tetrahydro-6-hydroxy-4,4,6-trimethyl-1,3-thiazine-2-thione (1 a) reacts with methyl-, ethyl- and n-butylamine to the corresponding 1-alkyl-6-alkylaminotetrahydro-2(1H)-pyrimidinethione12 but withi-propylamine to tetrahydro-6-isopropylamino-1,3-thiazine-2-thione (6 d). On treatment withDCC,6 d is rearranged to dihydro-4-isopropylamino-2(1H)-pyridinethione (8 d), and 6-amino-tetrahydro-1,3-thiazinethione (6 a) to dihydro-4,4,6-trimethyl-2(1H)-pyrimidinethione (10 a). The reaction of 6-aminothiazinethiones6 a, d and 6-(4-morpholinyl)-thiazinethione13 resp., with methylamine leads to 1-methyl-6-methylamino-pyridinethione12 b. 1-Alkyl-6-alkylamino-tetrahydro-2(1H)-pyrimidinethiones (12) react at reflux temperature to dihydro-1-alkylpyrimidinethiones10. With methylamine only 6-methylamino-3,4,4,6-tetramethyl-1,3-thiazine-2-thione (6 f) is formed from tetrahydro-6-hydroxy-tetramethyl-1,3-thiazine-2-thione (1 b).     

Synthesis,DFT study,molecular docking and insecticidal evaluation of some pyrazole-based tetrahydropyrimidine derivatives

Abstract

The building block synthon, 1-(4-(1,3-diphenyl-1H-pyrazol-4-yl)-6-methyl-2-thioxo-1,2,3,4-tetrahydropyrimidin-5-yl)ethan-1-one was efficiently synthesized by Biginelli reaction of 1,3-diphenyl-1H-pyrazole-4-carbaldehdye, acetylacetone, and thiourea and submitted to react with ethyl chloroacetate and chloroacetyl chloride under different conditions to afford some N-heterocycles integrated with pyrazole scaffold. Hydrazinolysis of the pyrimidinethione was studied under different conditions. The insecticidal activity for these compounds, DFT calculations, and docking were run and discussed. Some of them exhibited 100% mortality against Nilaparvata lugens and Mythimna separata.     

Dielectric behavior of some aromatic polyimide films

Aromatic polyimides were prepared by polycondensation reaction of two aromatic diamines, such as 4,4′-diaminodiphenylmethane (DDM) and 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDDM), with aromatic dianhydrides, such as 4,4′-isopropylidene-diphenoxy-bis(phthalic anhydride) (6HDA), benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene-bis (phthalic anhydride) (6FDA). These polymers are soluble in polar aprotic solvents and can be cast into thin films from such solutions. The polyimides show high thermal stability, with decomposition temperature being above 430 °C in air, and high glass transition temperature being in the range of 200–287 °C. The free standing films, having the thickness of tens of micrometers, exhibited good mechanical and electrical insulating properties. The dielectric constant, molecular mobility and AC conductivity of thin films prepared from these polymers were investigated in detailed. The study of their dielectric behavior evidenced low dielectric constant values, in the range of 2.88–3.48 at 1 Hz at room temperature, and three relaxation processes (γ,β₁ and β₂) were observed at sub-glass temperatures for polyimides based on 6HDA and 6FDA and only two (γ and β) relaxations were detected for polyimides based on BTDA. The cooperativity of the molecular motions associated with the relaxation processes was discussed.     

Three new 2,5-diketopiperazines from the fish intestinal Streptomyces sp. MNU FJ-36

The gut actinobacteria of marine-inhabited fish is one of the most important reservoirs of novel natural products. Currently, the Streptomyces sp. MNU FJ-36 was isolated from the intestinal fabric of Katsuwonus sp. and determined by 16S rRNA analysis. From the cultures of the S. sp. MNU FJ-36, three new 2,5-diketopiperazines (2,5-DKPs) were discovered and identified as 3-(3-hydroxy-4-methoxybenzyl)-6-isobutyl-2,5-diketopiperazine (1), 3-(1,3-benzodioxol-5-ylmethyl)-6-isobutyl-2,5-diketopiperazine (2) and 3-(1,3-benzodioxol-5-ylmethyl)-6-isopropyl-2,5-diketopiperazine (3). Their structures were elucidated on the basis of spectroscopic data analysis. All the compounds were also evaluated for their inhibitory activity against P388, A-549 and HCT-116 cell lines with the MTT assay.     

Creation of a nematic phase in mixtures of smectic A1 phases

Abstract

Phase diagrams were determined for binary mixtures consisting of two 5-n-alkyl-2-(4'-isothiocyanatophenyl)-1,3-dioxane compounds (n-DBT) or 4'-isothio-cyanatophenyl 4-(trans-4'-n-decylcyclohexyl)benzoate and n-DBT. All compounds investigated have monolayer smectic A phases. A nematic phase in the upper temperature range and a nematic gap between two smectic regions also were observed, with the smectic layer spacing ratio, d/d', of 1.23 and 1.87 respectively. The variation of the enthalpy of transition with mixture composition in relation to changes of layer spacing ratio are also discussed for these systems.     

Influence of internal flexibility on the double glass transition in a series of odd non-symmetric liquid crystal dimers characterised by dielectric measurements

Dielectric measurements (thermally stimulated depolarisation currents and broadband dielectric spectroscopy) have been performed near the glass transition to study the glass transition on the odd non-symmetric liquid crystal (LC) dimers of the series α-(4-cyanobiphenyl-4'-oxy)-ω-(1-pyreniminebenzylidene-4'-oxy) alkanes (CBOnO.Py) with n ranging from 3 to 9. A previous study [S. Diez-Berart et al., Materials 8 (2015) 3334] carried out in CBO11O.Py showed the presence of two glass transition temperatures, attributed to different molecular motions of the terminal groups. The study performed allows us to analyse the molecular dynamics in the rest of the series and determine the role played by the flexible spacer. Parallel and perpendicular orientations of the molecular director with regards to the probe electric field have been investigated. The low and intermediate observed relaxations are explained in the framework of Stocchero’s theoretical model [M. Stocchero, J. Chem. Phys. 121 (2004) 8079] for the dielectric behaviour of non-symmetric LCs dimers, as independent end-over-end rotations of each terminal semi-rigid unit. As the length of the spacer chain in the series of compounds decreases, the different relaxations become progressively more coupled at the glass transition. Numerical simulations of the calorimetric response from the obtained kinetic parameters show good agreement with experimental behaviour.