Photolysis of xylylbischromones

Photoreorganisation of xylylbischromones occurring through 1,4-biradical is described. In these bischromones, the two chromophores have been found to behave independently.     

Attempted polymerization of substituted pipecolic acid NCA's: Dimerization and mechanism

Racemic and optically active N-carboxyanhydrides (NCA)s of 2-methyl- and cis-6-methylpipecolic acid, when subjected to polymerization conditions in solution or in bulk whether with “weak” or “strong” base initiators, resisted polymerization under all conditions tried. Instead, the NCA of 2-methylpipecolic acid gave the corresponding cyclic dipeptide and the NCA of cis-6-methylpipecolic acid formed the cyclic dipeptide derived from trans-6-methylpipecolic acid. The mechanism of dimerization of these NCA's was investigated. Evidence was provided for the proposed mechanism in which the active moiety is not a carbamate ion but an amino group. Methyl 2-methylpipecolate underwent an intermolecular S_N2-type reaction upon heating, yielding equimolar quantities of methyl N-methyl-2-methylpipecolate and 2-methylpipecolic acid.     

Metrization and Semimetrization Theorems with Applications to Manifolds

This paper is a study of conditions under which a space with S₂ is metrizable, o-semimetrizable or semimetrizable. It is shown that: a wMN, w-space is metrizable if and only if it has S₂, a quasi--space is metrizable if and only if it is a pseudo wN-space with S₂, a separable manifold is metrizable if and only if it has S₂ with property (*), a perfectly normal manifold with q quasi-G ^* diagonal is metrizable and a separable manifold is a hereditarily separable metrizable if and only if it has -S₂.     

The Role of Multiwall Carbon Nanotubes in Cu‐BTC Metal‐Organic Frameworks for CO2 Adsorption

The discovery of natural gas fields with a high content of CO₂ in world gas reservoirs poses new challenges for CO₂ capture. This work investigates the use of the metal‐organic framework (MOF) Cu‐BTC and hybrid MWCNTs@Cu‐BTC for CO₂ adsorption. Cu‐BTC and hybrid MWCNTs@Cu‐BTC were synthesized by the solvothermal method. The results of imaging of intact MOF pores in Cu‐BTC and hybrid MWCNTs@Cu‐BTC nanocrystals by high‐resolution transmission electron microscopy (HRTEM) under liquid nitrogen conditions are presented. Physical characterizations of the solid adsorbents were made by using a selection of different techniques, including field‐emission scanning electron microscopy (FESEM), X‐ray powder diffraction (XRD), Fourier transform infrared (FT‐IR) spectroscopy, thermogravimetric analysis (TGA), Brunauer–Emmet–Teller (BET) surface area, and CO₂ adsorption and physisorption measurements. HRTEM and FESEM confirmed that Cu‐BTC has an octahedral shape and that the surface morphology of Cu‐BTC changes by the intercalation of MWCTNs. The results show that the modified Cu‐BTC improved the CO₂ adsorption compared to pure Cu‐BTC. The increase in the CO₂ uptake capabilities of hybrid MWCNTs@Cu‐BTC was ascribed to the intercalation of MWCNTs with Cu‐BTC crystals. The CO₂ sorption capacities of Cu‐BTC and hybrid MWCNTs@Cu‐BTC were found to increase from 1.91701 to 3.25642 mmol/g at ambient conditions.     

Investigation of structural and textural properties of Ge<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript>MoO<Subscript>3</Subscript> system,promising catalyst for photocatalytic applications

The main objective of this work is to control the structural, textural and electrical properties of the system prepared by mixing molybdenum oxide with different amounts of germanium. The system is expected to be suitable as a catalyst for the photodegradation of methyl red (one of the dyes group) and the results of this study can throw some light on the relationship between the properties of this system and the extent of the dye degradation as indicated by the measurements of the photocatalytic activity. The composite materials (Ge_xMoO₃) were prepared by solid-state reaction between germanium and molybdenum oxide. The mixtures were made in Ge/MoO₃ molar ratios of 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0. The reaction was conducted in air at 700°C. The prepared samples were characterized by X-ray powder diffraction, micro-Raman spectroscopy, nitrogen adsorption measurements, diffuse reflectance spectrometry and UV-Vis absorption spectrophotometry. The addition of germanium has affected the photocatalytic activity of MoO₃ as evidenced by an increase in the degradation extent of methyl red from about 14% (for pure oxide) to about 97% for Ge_xMoO₃ (x = 1). An enhancement in the photocatalytic activity was attributed to the change in the band gap and modification of the textural properties associated with the formation of Ge_xMoO₃ composites.     

The effect of terminal substituents on crystal structure,mesophase behaviour and optical property of azo-ester linked materials

A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH₃, –OC₂H₅ and –OC₃H₇) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R¹₂(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R²₂(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH₃, –OC₂H₅ and –OC₃H₇) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λ_max) of nearly 370 nm.     

Chromatographic and Spectroscopic Studies on β-Cyclodextrin Functionalized Ionic Liquid as Chiral Stationary Phase: Enantioseparation of Flavonoids

In this study, β-cyclodextrin functionalized ionic liquid was prepared by adding 1-benzylimidazole onto 6-monotosyl-6-deoxy-β-cyclodextrin (β-CDOTs) to obtain β-CD-BIMOTs. β-CD-BIMOTs were then bonded onto the modified silica to produce chiral stationary phases (β-CD-BIMOTs-CSP). The performance of β-CD-BIMOTs-CSP was evaluated by observing the enantioseparation of flavonoids. The performance of β-CD-BIMOTs stationary phase was also compared with native β-CD stationary phase. For the selected flavonoids, flavanone and hesperetin obtained a high resolution factor in reverse phase mode. Meanwhile, naringenin and eriodictyol attained partial enantioseparation in polar organic mode. In order to understand the mechanism of separation, the interaction of selected flavonoids and β-CD-BIMOTs was studied using spectroscopic methods (¹H NMR, NOESY and UV–Vis spectrophotometry). The enantioseparated flavanone and hesperetin were found to form an inclusion complex with β-CD-BIMOTs. However, naringenin and eriodictyol were not enantioseparated due to the formation of hydrogen bonding at exterior torus of β-CD-BIMOTs.

     

Existence of Conservation Laws and characterization of recursion operators for completely integrable systems

Using the Spencer-Goldschmidt version of the Cartan-Kähler theorem, we give conditions for (local) existence of conservation laws for analytical quasi-linear systems of two independent variables. This result is applied to characterize the recursion operator (in the sense of Magri) of completely integrable systems.

     

Photoinduced deposition of gold nanoparticles on TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanotube films as efficient photoanodes for solar water splitting

Gold-modified TiO₂–WO₃ nanotubes with different amounts of gold were obtained by two methods; photoassisted deposition and one-step electrochemical anodizing method. The morphology, crystallinity and elemental composition were studied by FE-SEM, XRD and EDX. The photoelectrochemical performance was examined under Xe light illumination in 1 M NaOH electrolyte. Characterization of the as-prepared TiO₂–WO₃ samples indicated that sodium tungstate concentration in anodizing solution significantly influenced the morphology and photoelectrochemical activity of fabricated films. Also, photoelectrochemical characterizations show that the photocatalytic activity of Au/TiO₂–WO₃ nanotubes was improved as compared with that of bare TiO₂–WO₃ nanotubes. The experimental results showed that the photocatalytic activities of Au/TiO₂–WO₃ were significantly affected by the amount of Au nanoparticles. The amount of gold nanoparticles was effectively controlled by time of photoreduction of the chloroauric acid solution. These new photoanodes showed enhanced high photocurrent density with good stability and are a highly promising photoanodes for photocatalytic hydrogen production.     

Polypyrrole-coated cotton textile as adsorbent of methylene blue dye

Pollution caused by organic dyes is of serious environmental and health concern to the population. Dyes are widely used in textile coloring applications. In the present work, cotton textile was coated with a conducting polymer, polypyrrole (PPy), in situ during the oxidative polymerization of pyrrole. The resulting materials were utilized as easily separated and recyclable adsorbent for the removal of methylene blue (MB) as a model of cationic dyes in alkaline solutions. It showed also some affinity to remove Acid Green 25 as an anionic dye in acidic medium. The adsorption was assessed by monitoring the decrease in dye concentration by UV–Visible absorption spectroscopy. The influence of various parameters such as initial dye concentration, contact time, pH, temperature, and adsorbent dose on the adsorption process was studied. The pseudo-second-order kinetic model and Freundlich isotherm model were found to describe the adsorption process. The thermodynamic study revealed that the adsorption of MB by PPy was feasible, spontaneous, and exothermic process. Investigation of the substrate regeneration revealed that PPy deposited on cotton textile can be reused for dye adsorption several times with good efficiency and it allows for the recovery of MB for recycling purposes.