Thermal studies on polythiophene containing mesogenic side chains

Series of thiophenes containing mesogenic side chains at the 3^rd position are synthesized. The thermal transitions and thermal stability of the synthesized monomers and polymers are studied. The polarizing microscopic studies of synthesized monomers showed nematic liquid crystalline phase and these mesophases further confirmed by differential scanning calorimetric study. The obtained melting and the isotropic temperatures decrease linearly with the increase of aliphatic chain length. The transition temperatures determined from DSC analysis, overlap well with the temperatures obtained from optical microscopy studies. Thermal stability of the compounds is analysed using thermogravimetric studies. Thermal stability of monomers and polymers has been determined by calculating IPDT values. Structural influence on thermal degradation patterns of monomers and polymers are also discussed.     

Dynamic mechanical and thermal behavior of liquid-crystalline polybutadiene-diols with mesogenic groups in side chains

Liquid-crystalline polybutadiene-diols (LCPBDs) with the comb-like architecture were synthesized by reaction of a LC thiol with the double bonds of telechelic HO-terminated polybutadiene (PBD). LCPBDs with various initial molar ratios of thiol to double bonds of PBD, R₀, in the range from 0.15 to 1, were prepared by the radical reaction at temperature 60 °C for 48 h. The experimentally obtained degree of modification, R_e, after the reaction and purification, was determined from elemental analysis - from the amount of sulphur bounded in LCPBDs, GPC and from ¹H NMR spectra. The physical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. With increasing R_e ratio the glass transition temperature of LCPBDs, T_g, increases from ∼ − 45 °C (neat PBD) to ∼20 °C (R_e ∼ 0.5). LC transition starts at R_e ∼ 0.27 (the transition temperature T_m ∼ 27 °C). With increasing R_e temperature T_m increases and for R_e ∼ 0.5 reaches the value T_m ∼ 74 °C; at the same time also the change in enthalpy at LC transition increases. The LC transition could be detected also by the dynamic mechanical spectroscopy; especially shape and position of mechanical functions on frequency and free volume parameters strongly depend on degree of modification.     

Antimicrobial prospect of newly synthesized 1,3-thiazole derivatives

A new series of 1,3-thiazole and benzo[d]thiazole derivatives 10-15 has been developed, characterized, and evaluated for in vitro antimicrobial activity at concentrations of 25-200 μg/mL against Gram+ve organisms such as methicillin-resistant Staphylococcus aureus (MRSA), Gram-ve organisms such as Escherichia coli (E. coli), and the fungal strain Aspergillus niger (A. niger) by the cup plate method. Ofloxacin and ketoconazole (10 μg/mL) were used as reference standards for antibacterial and antifungal activity, respectively. Compounds 11 and 12 showed notable antibacterial and antifungal activities at higher concentrations (125-200 μg/mL), whereas benzo[d]thiazole derivatives 13 and 14 were found to display significant antibacterial or antifungal activity (50-75 μg/mL) against the Gram+ve, Gram-ve bacteria, or fungal cells used in the present study. In addition, a correlation between calculated and determined partition coefficient (log P) was established which allows future development of compounds within this series to be carried out based on calculated log P values. Moreover, compounds 13 and 14 show that the optimum logarithm of partition coefficient (log P) should be around 4.     

Oxidation of the side chains of ergosterol derivatives

Summary The acetate of bisnorlithocholic acid has been obtained with a yield of 65% from the acetate of 5-ergost-22-en-3-ol by permanganate-periodate oxidation.S. Ordzhonikidze All-Union Scientific-Research Institute of Pharmaceutical Chemistry, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 88–91, January–February, 1978.     

Structure–property studies and orientation effects of polythiophenes containing mesogenic side chains

Liquid crystalline materials display unique properties, which can be exploited in organic light emitting diodes. Polythiophene model compounds containing phenyl groups linked with azomethine, ester, and alkoxy groups [thiophene‐3‐alkyloxy benzoyloxy aniline series (N series) and thiophene‐3‐alkoxy phenoxy amino benzoate series (R Series)] were synthesized. Molecular orbital calculations were performed and the predicted band gaps compared to understand the effects of spacer length and linkage. The experimental photoabsorption characteristics are compared with the theoretically predicted band gap. Photoabsorption and emission studies on N series and R series polymers as the function of polarizer angle suggest that polymers of both series emit polarized light in all base color ranges. The electroemission characteristics of the above‐synthesized polymers were also recorded as the function of polarizer angle. The results show that the compounds also emit polarized electroemission, and the EL polarization ratio decreases with the increase of alkoxy chain length for N and R polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1463–1477, 2008     

New hydrogen-bonded comblike polyimides with mesogenic side chains for stable orientation and fast switching of liquid crystals

ABSTRACT

New supramolecular comblike polyimides with mesogenic side chains for stable homeotropic orientation and fast electro-optical switching of liquid crystals (LCs) have been prepared through selective intermolecular hydrogen bonding between 4-(4-heptylphenyl)benzoic acid (4HPB) and host polyimide. A low concentration of 4HPB as the mesogenic guest molecule was hydrogen-bonded to polyimide backbone leading to the self-assembled comblike polyimide with enhanced homeotropic orientation properties. The electro-optical characteristics of the LC device containing hydrogen-bonded comblike polyimide exhibited better performance than those of LC cell with conventional polyimide. Because the conventional covalent approach for preparation of polyimides requires considerable synthetic efforts to achieve new functionality in polyimide materials, the proposed noncovalent method is a simple one and highly cost effective. Our controlled methodology should find wide application for the fabrication of functional alignment materials requiring high orientation ability.     

Physicomechanical studies on the langmuir‐blodgett films of polythiophene containing mesogenic side chains

Liquid crystalline materials display unique properties, which can be exploited in various optoelectronic device applications. The Langmuir‐Blodgett (LB) film characteristics of polythiophene model compounds containing phenyl rings linked with azomethine, ester, and alkoxy functional groups poly‐4‐{[(E)‐thiophen‐3‐ylmethylidene]amino}phenyl 4‐alkyloxybenzoate (PTAPAB series) and poly‐4‐alkyloxy phenyl 4‐{[(E)‐thiophen‐3‐ylmethylidene]amino}benzoate (PAPTAB Series) were explored in this study. The AM1 optimized geometries of the aforementioned compounds showed that the films have different type of orientation in space because of the change in the linking functional group. The LB film characteristics were studied by applying the concepts of the failure mechanism in tensile failure. The compression‐expansion hysteresis cycle of the LB films at predetermined area per repeat unit was used to study the viscous, elastic, and plastic nature of the films. The results showed that in PAPTAB series compounds, the LB films were more flexible and took less surface energy than its PTAPAB series homologues, which formed into LB films of rigid nature. The LB films of PAPTAB series compounds were of more viscoplastic in nature. The studies suggested that PAPTAB series structures exhibited good thin film forming nature than its PTAPAB series homologues. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 173–182, 2009     

In vitro antischistosomal evaluation of some newly synthesized praziquantel derivatives

Praziquantel, 2-(cyclohexylcarbonyl)-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one, was used as the parent starting material to synthesize a new series of praziquantel-3-arylidene derivatives 1a–c and praziquantel–Mannich bases 2a–d, hoping to obtain new antischistosomal compounds of more activity and lower adverse effects. The antischistosomal activity of the newly synthesized compounds was evaluated using in vitro Schistosoma mansoni worm killing tests. Both compounds 2c and 2d exhibited significant in vitro antischistosomal activity and may offer promising use as an antischistosomal drug either alone or in combination with praziquantel.     

Liquid crystalline dimers with bent-core mesogenic units

Two series of dimers, in which two identical aromatic bent core mesogenic units are connected via an organosiloxane or an alkylene spacer, have been investigated. The dimers with a spacer consisting of a trisiloxane central group and relatively long alkylene groups show an intercalated tilted smectic structure. The layer spacings appear to be very weakly dependent on the terminal chain lengths. In these dimers the smectic phase is stabilized for the compounds with a short terminal chain. Dimers with an aliphatic alkylene spacer are liquid crystalline only when the spacer is relatively short and the terminal chains are long. For these dimers a monolayer tilted smectic phase is observed.     

Elastic deformations in a magnetic field of a liquid-crystalline polymer with mesogenic groups in the main and side chains

Orientational elastic deformations in a magnetic field and phase transition temperatures of a thermotropically mesogenic “combined” aromatic polyester with mesogenic groups, both in the main and in the side chains, have been investigated in the range of 900 to 10,200 mol. wt. It was shown that in this molecular weight range the birefringence of a completely oriented nematic and correspondingly, the degree of its orientational order S are independent on molecular weight. When the relative temperature ΔT changes from −2 to −30°C the orientational order parameter increases from 0.35 to 0.55. The bend elasticity constants K₃ coincide in the order of magnitude with those for high and low molecular weight nematics investigated previously and their dependence on molecular weight has not been detected.     

Synthesis and gastrointestinal prokinetic activity of novel benzamide derivatives with amphoteric side chains

Novel benzamide derivatives (19-24, 32a-c, 43d-f), each possessing a cycloaminoalkanecarboxylic acid side chain, were synthesized and their gastrointestinal prokinetic and dopamine D2 receptor antagonist activities were evaluated. 4-[(4-Amino-5-chloro-2-methoxybenzoyl)amino]-1-piperidineacetic acid (19) exhibited the most potent gastro- and colon-prokinetic activities, through intravenous administration to conscious dogs, and also showed the reduced dopamine D2 receptor antagonistic activity. However, 19 showed only weak gastrointestinal prokinetic activity after oral administration. Several ester prodrugs (44-62) of 19 were tested for pharmacological activities as well as physicochemical and metabolic stability; the butyl ester (46) was consequently selected as a promising gastrointestinal prokinetic agent with reduced side effects.     

Novel uracil derivatives: newly synthesized centrally acting agents.

A series of 1-amino-5-substituted uracils and their 4-thio or 2,4-dithio substituted analogues were synthesized and assayed for anti-conflict activity in rats and anesthetic activity in mice. 1-Amino-5-halogenouracils 3b-e, 1-amino-4-thiouracil (9a), and 1-amino-5-halogeno-4-thiouracils 9c, d showed both anti-conflict and anesthetic activities. The most active compound was 1-amino-5-chloro-4-thiouracil (9d) which showed anxiolytic activity at 2 mg/kg of oral administration (p.o.) on a modified Geller-Seifter conflict schedule. Its minimum effective dose (MED) was lower than that of diazepam. The 50 percent effective dose (ED50) for anesthetic activity in mice of the compound (9d) was 32.9 mg/kg, p.o.     

Liquid crystal comb polymer with polar mesogenic and aliphatic side groups I. Preparation and structural properties

A liquid crystal comb polymer of potential interest for electro-optical applications has been synthesized and characterized. The polymer has a polyacrylamide main chain and two different types of side group, built up of 4'-undecanoyloxy-4-cyanobiphenyl groups (68 mol %) and of shorter aliphatic groups (32 mol %). The two types of side group occur randomly along the polymer's main chain. The preparation steps and the liquid crystalline structure of the resulting copolymer are compared with those of a homopolymer whose side groups (built up of 4'-undecanoyloxy-4-cyanobiphenyl groups) are all identical. X-ray diffraction shows that the polymers display different mesophases over different temperature ranges. However, the homopolymer exhibits two smectic phases (SmC2 and SmA2), while the new copolymer exhibits a SmC2 phase and a nematic mesophase at higher temperature. The mesophase thermal stability of the copolymer is significantly lower than that of the homopolymer.     

Well-defined polymers with acetal side chains as reactive scaffolds synthesized by atom transfer radical polymerization

The synthesis of a polymer with acetal functionalized side chains, deprotection to aldehydes, and conjugation of aminooxy-modified molecules is reported. Poly(3,3′-diethoxypropyl methacrylate) (PDEPMA) was prepared by atom transfer radical polymerization (ATRP). Kinetic investigation of the ATRP of DEPMA from ethyl 2-bromoisobutyrate in methanol with copper (I) bromide and 2,2′-bipyridine (BIPY) at ambient temperature revealed a controlled polymerization. Altering the initial monomer to initiator ratios resulted in 75–93% conversion to polymers with different molecular weights and narrow molecular weight distributions (PDIs < 1.3). Reactive aldehyde groups were produced by hydrolysis of the acetals in dilute acid. Aminooxy-functionalized oligo(ethylene glycol) and O-(carboxymethyl)hydroxylamine were conjugated to the side chains via oxime linkages. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5004–5013, 2006     

A study of the fluorescence of some newly synthesized europium complexes with pyrazolone derivatives

Some europium complexes with pyrazolone derivatives and 1,10-phenanthroline were synthesized and characterized. The europium ion was found to coordinate to O atoms of the pyrazolone derivatives and to N atoms of 1,10-phenanthroline. A strongly ligand-localized UV absorption leads to the europium-centered emissions between 580 and 750 nm which were assigned as the 5D0-->7F0,1,2,3,4 and 5D1-->7F3,4 transitions. A low site symmetry for the Eu3+ ion was confirmed from the observation of 5D0-->7F0 emission and from the splitting of the other bands. In contrast to many Eu complexes that have been investigated a rather weak emission was measured by introduction of a Schiff base to form a ternary complex with the pyrazolone derivative. The long fluorescence lifetimes of these complexes suggest an energy transfer process from ligands to Eu3+ ion through the triplet state of the ligands.     

Liquid crystal comb polymer with polar mesogenic and aliphatic side groups I. Preparation and structural properties

A liquid crystal comb polymer of potential interest for electro-optical applications has been synthesized and characterized. The polymer has a polyacrylamide main chain and two different types of side group, built up of 4'-undecanoyloxy-4-cyanobiphenyl groups (68 mol %) and of shorter aliphatic groups (32 mol %). The two types of side group occur randomly along the polymer's main chain. The preparation steps and the liquid crystalline structure of the resulting copolymer are compared with those of a homopolymer whose side groups (built up of 4'-undecanoyloxy-4-cyanobiphenyl groups) are all identical. X-ray diffraction shows that the polymers display different mesophases over different temperature ranges. However, the homopolymer exhibits two smectic phases (SmC₂ and SmA₂), while the new copolymer exhibits a SmC₂ phase and a nematic mesophase at higher temperature. The mesophase thermal stability of the copolymer is significantly lower than that of the homopolymer.     

Liquid crystal comb polymer with polar mesogenic and aliphatic side groups II. Noise of the scattered light

Measurements of static light scattering and of the stationary noise of the scattered light have been performed as functions of temperature on the comb polymer whose synthesis and static structural properties are discussed in the preceding paper, Part I. The intrinsic optical noise strongly increases when the nematic phase is entered. An additional maximum in the noise, observed at lower temperatures, is attributed to a rearrangement of optical domains, introducing boundary regions where the fluctuations of loosely packed side groups are enhanced. The spectral density of the observed noise is definitely non-Lorentzian and can be fitted by the superposition of two pure Lorentzian components with different cut-off frequencies, attributed to the statistically independent random motion of mesogenic and aliphatic side chains. The noise level is reduced at all temperatures by an applied electrical field; in particular, the field is effective in selectively damping the fluctuations of polar side groups.     

Liquid crystal comb polymer with polar mesogenic and aliphatic side groups II. Noise of the scattered light

Measurements of static light scattering and of the stationary noise of the scattered light have been performed as functions of temperature on the comb polymer whose synthesis and static structural properties are discussed in the preceding paper, Part I. The intrinsic optical noise strongly increases when the nematic phase is entered. An additional maximum in the noise, observed at lower temperatures, is attributed to a rearrangement of optical domains, introducing boundary regions where the fluctuations of loosely packed side groups are enhanced. The spectral density of the observed noise is definitely non-Lorentzian and can be fitted by the superposition of two pure Lorentzian components with different cut-off frequencies, attributed to the statistically independent random motion of mesogenic and aliphatic side chains. The noise level is reduced at all temperatures by an applied electrical field; in particular, the field is effective in selectively damping the fluctuations of polar side groups.     

Liquid crystals with partially fluorinated side chains: Highly polar materials with very low birefringence

Highly polar liquid crystals with very low birefringence were synthesized by a reaction sequence starting with the radical addition of a secondary alcohol to pentafluoropropene and perfluoropropene, respectively. The mesophases and electrooptical properties of the new materials were interpreted using a detailed computational analysis of the conformational equilibrium.