Impact of Charge Transfer Complex on the Dielectric Relaxation Processes in Poly(methyl methacrylate) Polymer.

The impact of the charge transfer complex on the dielectric relaxation processes in free poly(methyl methacrylate) (PMMA) polymer sheets was investigated. The frequency dependence of dielectric properties was obtained over the frequency range 0.1 Hz-1 MHz at temperatures ranging between 303 K and 373 K for perylene dye and acceptors (picric acid (PA) and chloranilic acid (CLA)) in an in situ PMMA polymer. The TG/dTG technique was used to investigate the thermal degradation of the synthesized polymeric sheets. Additionally, the kinetic parameters have been assessed using the Coats-Redfern relation. The dielectric relaxation spectroscopy of the synthesized polymeric sheets was analyzed in terms of complex dielectric constant, dielectric loss, electrical modulus, electrical conductivity, and Cole-Cole impedance spectroscopy. α- and ß-relaxation processes were detected and discussed. The σ(ω) dispersion curves of the synthesized polymeric sheets show two distinct regions with increasing frequency. The impedance data of the synthesized polymeric sheets can be represented by the equivalent circuit (parallel RC).

Synthesis and Cytotoxic Activity of New Thiazolopyrimidine Sugar Hydrazones and Their Derived Acyclic Nucleoside Analogues.

New thienyl- or chlorophenyl-substituted thiazolopyrimidine derivatives and their derived sugar hydrazones incorporating acyclic d-galactosyl or d-xylosyl sugar moieties in addition to their per-O-acetylated derivatives were synthesized. Heterocyclization of the formed sugar hydrazones afforded the derived acyclic nucleoside analogues possessing the 1,3,4-oxadiazoline as modified nucleobase via acetylation followed by the cyclization process. The cytotoxic activity of the synthesized compounds was studied against human breast cancer MCF7 and MDA-MB-231 cell lines as well as human colorectal cancer HCT 116 and Caco-2 cell lines. High activities were revealed by compounds 1, 8, 10, 11, and 13 against Caco-2 and MCF7 cells in addition to moderate activities exhibited by other compounds against HCT116 or MDA-MB-231 cells.

The preparation of carbon nanofillers and their role on the performance of variable polymer nanocomposites.

New synergic behavior is always inspiring scientists toward the formation of nanocomposites aiming at getting advanced materials with superior performance and/or novel properties. Carbon nanotubes (CNT), graphene, fullerene, and graphite as carbon-based are great fillers for polymeric materials. The presence of these materials in the polymeric matrix would render it several characteristics, such as electrical and thermal conductivity, magnetic, mechanical, and as sensor materials for pressure and other environmental changes. This review presents the most recent works in the use of CNT, graphene, fullerene, and graphite as filler in different polymeric matrixes. The primary emphasis of this review is on CNT preparation and its composites formation, while others carbon-based nano-fillers are also introduced. The methods of making polymer nanocomposites using these fillers and their impact on the properties obtained are also presented and discussed.

Nanocomposites containing polyvinyl alcohol and reinforced carbon-based nanofiller: A super effective biologically active material.

A new class of biologically active polymer nanocomposites based on polyvinyl alcohol and reinforced mixed graphene/carbon nanotube as carbon-based nanofillers with a general abbreviation (polyvinyl alcohol/mixed graphene-carbon nanotubes) has been successfully synthesized by an efficient solution mixing method with the help of ultrasonic radiation. Mixed graphene and carbon nanotubes ratio has been prepared (50%:50%) wt by wt. Different loading of mixed graphene-carbon nanotubes (2, 5, 10, 15, and 20 wt%) were added to the host polyvinyl alcohol polymer. In this study, polyvinyl alcohol/mixed graphene-carbon nanotubesa-e nanocomposites were characterized and analyzed by X-ray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and the thermal stability was measured by thermogravimetric analysis and derivative thermal gravimetric. Fourier transform infrared and X-ray diffraction spectra proved the addition of mixed graphene-carbon nanotubes into polyvinyl alcohol matrix. X-ray diffraction patterns for these nanocomposites showed 2θ = 19.35° and 40° due to the crystal nature of polyvinyl alcohol in addition to 2θ = 26.5° which attributed to the graphite plane of carbon-based nanofillers. Thermal stability of polyvinyl alcohol/mixed graphene-carbon nanotubes nanocomposites was enhanced comparing with pure polyvinyl alcohol. The main degradation step ranged between 360° and 450°C. Moreover, maximum composite degradation temperature has appeared at range from 285°C to 267°C and final composite degradation temperature (FCDT) displayed at a temperature range of 469-491°C. Antibacterial property of polyvinyl alcohol/mixed graphene-carbon nanotubesa-e nanocomposites were tested against Escherichia coli bacteria using the colony forming units technique. Results showed an improvement of antibacterial property. The rate percentages of polyvinyl alcohol/mixed graphene-carbon nanotubesb, polyvinyl alcohol/mixed graphene-carbon nanotubesc, and polyvinyl alcohol/mixed graphene-carbon nanotubesd nanocomposites after 24 h are 6%, 5%, and 7% respectively. However, polyvinyl alcohol/mixed graphene-carbon nanotubese nanocomposite showed hyperactivity, where its reduction percentage remarkably raised up to 100% which is the highest inhibition rate percentage. In addition, polyvinyl alcohol and polyvinyl alcohol/graphene-carbon nanotubesa-d showed colony forming units values/ml 70 × 106 and 65 ± 2 × 106 after 12 h. After 24 h, the colony forming units values/ml were in the range of 86 × 106-95 × 106.

Experimental and theoretical study of donor-π-acceptor compounds based on malononitrile.

A set of different donor-π-acceptor compounds having dicyanovinyl as the acceptor and aryl moieties as donors were synthesized by Knoevenagel condensation. The UV-visible absorption and fluorescence spectra were investigated in different solvents. The optical band gab energy (Eg) was linearly correlated with the Hammett resonance effect of the donor to reveal that the higher the value of Hammett resonance effect of a donor, the lower the Eg of the molecule. The photophysical data revealed that compounds M4-M6 are typical molecular rotors with fluorescence due to twisted intramolecular charge transfer. Compound M5 revealed the largest Stokes shift (11,089 cm-1) making it a useful fluorescent sensor for the changes of the microenvironment. The effect of substituents on the optical properties of donor-π-acceptor compounds having dicyanovinyl as the acceptor are studied using density functional theory and time-dependent density functional theory (DFT/TD-DFT). The optical transitions are thoroughly examined to reveal the impact of subtituents on both absorption and fluorescence, mainly through the modification of the structure in the excited state. The theoretical results have shown that TD-DFT calculations, with a hybrid exchange-correlation and the long-range corrected density functional PBEPBE with a 6-311++G** basis set, was reasonably capable of predicting the excitation energies, the absorption and the emission spectra of these molecules.

Experimental and theoretical study of o-substituent effect on the fluorescence of 8-hydroxyquinoline.

The synthesis and characterization of different ether and ester derivatives of 8-hydroxyquinoline have been made. UV-visible and fluorescence spectra of these compounds have revealed spectral dependence on both solvent and O-substituent. The fluorescence intensity of ether derivatives revealed higher intensity for 8-octyloxyquinoline compared with 8-methoxyquinoline, whereas those of ester derivatives had less fluorescence than 8-hydroxyquinoline. Theoretical calculations based on Time-dependent density functional theory (TD-DFT) were carried out for the quinolin-8-yl benzoate (8-OateQ) compound to understand the effect of O-substituent on the electronic absorption of 8-hydroxyquinaline (8-HQ). The calculations revealed comparable results with those obtained from the experimental data. Optimized geometrical structure was calculated with DFT at B3LYP/6-311++G** level of theory. The results indicated that 8-OateQ is not a coplanar structure. The absorption spectra of the compound were computed in gas-phase and solvent using B3LYP and CAM-B3LYP methods with 6-311++G ** basis set. The agreement between calculated and experimental wavelengths was very good at CAM-B3LYP/6-311++G** level of theory.