Photogenerated cumulenic structure of adamantyl endcapped linear carbon chains: an experimental and computational investigation based on infrared spectroscopy

The infrared (IR) spectrum of an adamantyl endcapped α, ω-polyyne (the hexayne, Ad-C(12)-Ad) is investigated both experimentally and computationally. A new IR band is observed upon UV photoexcitation of the compound (embedded in a poly methyl methacrylate matrix at 78 K), thus, revealing the existence of new photogenerated molecular structure trapped at low temperature. Complete reversibility is found, thus, demonstrating that the photoexcitation is responsible for the generation of metastable excited states of the molecule. Density functional theory and time dependent density functional theory calculations indicate that these metastable states result from the forbidden singlet (S(1)) or triplet (T(1)) excited states, and geometry optimizations of the polyyne trapped in either S(1) and/or T(1) states demonstrate that the carbon chain takes on a cumulenic structure. Comparison of the experimental and the computed IR spectra for the molecule trapped in the forbidden states confirms that the new IR features are clear markers of cumulenic species. The temperature and time dependent behavior of the new IR band is analyzed, while the experimentally determined value of the activation energy highlights the low stability of these molecular structures.     

Identification of Phenolic Compounds by LC-MS/MS and Evaluation of Bioactive Properties of Two Edible Halophytes: Limonium effusum and L. sinuatum

This work aimed to evaluate the phenolic content and in vitro antioxidant, antimicrobial and enzyme inhibitory activities of the methanol extracts and their fractions of two edible halophytic Limonium species, L. effusum (LE) and L. sinuatum (LS). The total phenolic content resulted about two-fold higher in the ethyl acetate fraction of LE (522.82 ± 5.67 mg GAE/g extract) than in that of LS (274.87 ± 1.87 mg GAE/g extract). LC-MS/MS analysis indicated that tannic acid was the most abundant phenolic acid in both species (71,439.56 ± 3643.3 µg/g extract in LE and 105,453.5 ± 5328.1 µg/g extract in LS), whereas hyperoside was the most abundant flavonoid (14,006.90 ± 686.1 µg/g extract in LE and 1708.51 ± 83.6 µg/g extract in LS). The antioxidant capacity was evaluated by DPPH and TAC assays, and the stronger antioxidant activity in ethyl acetate fractions was highlighted. Both species were more active against Gram-positive bacteria than Gram negatives and showed considerable growth inhibitions against tested fungi. Interestingly, selective acetylcholinesterase (AChE) activity was observed with LE and LS. Particularly, the water fraction of LS strongly inhibited AChE (IC₅₀ = 0.199 ± 0.009 µg/mL). The ethyl acetate fractions of LE and LS, as well as the n-hexane fraction of LE, exhibited significant antityrosinase activity (IC₅₀ = 245.56 ± 3.6, 295.18 ± 10.57 and 148.27 ± 3.33 µg/mL, respectively). The ethyl acetate fraction and methanol extract of LS also significantly inhibited pancreatic lipase (IC₅₀ = 83.76 ± 4.19 and 162.2 ± 7.29 µg/mL, respectively). Taken together, these findings warrant further investigations to assess the potential of LE and LS as a bioactive source that can be exploited in pharmaceutical, cosmetics and food industries.     

A brief survey on the copper‐catalyzed allylation of alkylzinc and Grignard reagents under Barbier conditions

The same regioselectivity can be obtained in the CuI catalyzed allylic coupling of n‐butylzinc reagents prepared by either pre‐transmetallation or in situ transmetallation of Grignard reagents in the presence of allylic partner and catalyst. n‐Butylzinc bromide and di‐n‐butylzinc undergo γ‐selective allylation whereas tri‐n‐butylzincate gives preferential α‐selectivity. The regioselectivity obtained in the reaction of n‐butyl bromide and E‐crotyl chloride in the presence of Mg and CuCN is parallel to the coupling of preformed n‐butylmagnesium bromide. It is remarkable that the regiochemical outcome of copper catalyzed alkyl‐allyl coupling can be controlled by using Grignard reagents prepared under Barbier conditions and alkylzincs prepared by in situ transmetallation. Copyright © 2006 John Wiley & Sons, Ltd.     

Swelling behavior of poly{N‐[3‐(dimethylaminopropyl)] methacrylamide‐co‐acrylamide} hydrogels in aqueous solutions of surfactants

Temperature sensitive poly{N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐acrylamide} [P(DMAPMA‐co‐AAm)] hydrogels were prepared by the free‐radical crosslinking copolymerization of corresponding monomers in water with N,N‐methylenebisacrylamide as the crosslinker, ammonium persulfate as the initiator, and N,N,N′,N′‐tetramethylethylenediamine as the activator. The swelling equilibrium of the P(DMAPMA‐co‐AAm) hydrogels was investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate and the cationic surfactant dodecyltrimethylammonium bromide. In pure water, regardless of the amount of N,N‐methylenebisacrylamide, the P(DMAPMA‐co‐AAm) hydrogels showed a discontinuous phase transition between 30 and 36 °C. However, the transition temperature changed from discontinuous to continuous with the addition of surfactants; this was ascribed to the conversion of nonionic P(DMAPMA‐co‐AAm) hydrogels into polyelectrolyte hydrogels due to the binding of surfactants through hydrophobic interactions. Additionally, the concentrations of free sodium dodecyl sulfate and dodecyltrimethylammonium bromide ions were measured at different temperatures by conductometry, and it was found that the electric conductivity of the P(DMAPMA‐co‐AAm)–surfactant systems depended strongly on the swelling ratio; most notably, it changed drastically near the phase‐transition temperature of the P(DMAPMA‐co‐AAm) hydrogel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1645–1652, 2006     

On the exact solutions and conservation laws to the Benjamin-Ono equation

In the present work, we dealt with exact solutions and conservation laws of the Benjamin-Ono equation. We obtained exact solutions of given equation via the exp$(-\Phi (\xi ))$ method. The obtained solutions are included the hyperbolic functions, trigonometric functions and rational functions. By using the multiplier approach, the conservation laws of the mentioned equation was founded.     

Copper catalyzed magnesium-Barbier reaction for γ-selective alkyl-allyl coupling

CuCN catalyzed alkyl-allyl coupling under magnesium-Barbier conditions occurs regioselectively and affords predominantly the γ-products in good to high yields. This one-pot CuCN catalyzed reaction utilising Mg, an alkyl halide and an allylic substrate in THF at room temperature provides an easy alternative to the classical CuCN catalyzed γ-allylation of alkyl Grignard reagents.     

Design of a palladium nanocatalyst produced from Schiff base modified dialdehyde cellulose and its application in aryl halide cyanation and reduction of nitroarenes

In this paper, a versatile heterogeneous catalyst system (Pd-DAC-Sch) based on stabilization of palladium nanoparticles on dialdehyde cellulose Schiff base (DAC-Sch) was developed and characterized thoroughly by a variety of spectroscopic (FT-IR, XRD, ¹³C CPMAS, and TG) and microscopic (SEM/EDS and TEM) methods. Then the prepared Pd-DAC-Sch system was evaluated as a heterogeneous nanocatalyst for aryl halide cyanation in the presence of K₄[Fe(CN)₆] and for reduction of nitroarenes to amines using NaBH₄ in water at room temperature. Pd-DAC-Sch nanocatalyst efficiently cyanated various aryl halides by providing satisfactory reaction yields of 87–98%. Moreover, Pd-DAC-Sch catalyzed 4-nitrophenole (4-NA), 2-nitroaniline (2-NA), and 4-nitroaniline (4-NA) reductions in short reaction time. More importantly, Pd-DAC-Sch nanocatalyst was reapplied up to six successive runs by giving a yield of 86% without any important changes in its morphology and structure. This paper shows that Pd-DAC-Sch is a highly effective, reusable, chemically stable, and therefore a useful nanocatalyst.

     

Applications of two reliable methods for solving a nonlinear conformable time-fractional equation

The current work presents analytical solutions of a nonlinear conformable time-fractional equation by using two different techniques. These are the modified simple equation method and the exponential rational function method. Based on the conformable fractional derivative and traveling wave transformation, the fractional partial differential equation is turned into the nonlinear non-fractional ordinary differential equation. Therefore, we implement the algorithms to this nonlinear non-fractional ordinary differential equation. To the best of our knowledge, the exact solutions obtained in this paper might be very useful in various areas of applied mathematics in interpreting some physical phenomena.     

Electrochemical copolymerization of thiophene and aniline

In this study homopolymer, copolymer, and composites of aniline and thiophene were synthesized in nitrogen atmosphere by using TEATFB (Tetraethyl ammonium tetrafluoroborate) and Lithium perchlorate as supporting electrolytes. In order to analyze their structure and characteristics, IR spectrums of the samples were taken and thermogravimetric analysis (TGA) was applied. Also, the samples were photographed under scanning electron microscope (SEM) for microstructure analysis and their electrochemical properties were observed and conductivities were obtained by four probe method. Homopolymerization and copolymerization reactions were carried out in two different solvents viz. acetonitrile and benzonitrile in order to see the solvent effect on polymerization. However, changing the solvent was found to have no significant effect on the resulting properties. It was concluded that changing the supporting electrolyte caused a structural difference in the resulting homopolymer. It also affects the properties considerably. During the bilayer preparation changing the coating turn led to variations in the properties of the samples. When polythiophene (PT) was coated with polyaniline (PA), the resulting system was a composite. However, in coating PA with PT the system was identified to be a copolymer. © 1996 John Wiley & Sons, Inc.