Adsorption properties and synthesis of silica aerogel-hollow silica microsphere hybrid (sandwich) structure

Journal of Sol-Gel Science and Technology - Silica aerogels have the potential use in many applications due to their large specific surface area and high porosity. One of these applications can be...     

Mound morphology and growth dynamic of the wedding-cake interfaces

We aimed in this work to study numerically the scaling behavior and the mound morphological properties of the interfaces generated by the multilayer deposition process. We have found that when the diffusion process dominates strongly the deposition one, the obtained interfaces consist of wedding-cake like structures. The width of the surface is a self-affine fractal exhibiting non-trivial scaling with the surface height and the system size, and the obtained interfaces follow the Family–Vicsek law with exponent values more consisting with the Edwards–Wilkinson model.     

Dynamics of Cu monomer,dimer and trimer on Ag (110) (1 × 2) missing‐row reconstructed surface

The authors aimed to investigate the diffusion of Cu monomer, dimer and trimer on Ag (110) (1×2) missing‐row surface. This problem is addressed through molecular dynamic simulation based on semi‐empirical many‐body potential, derived from the embedded atom method. Within this approach, we have identified and calculated the activation energy of each microscopic mechanism. Thus, for Cu monomer, the diffusion process occurs essentially by simple hopping between nearest‐neighbor sites. While for the Cu dimer, three processes have been identified such as dissociation–reassociation (DR), concerted jump (CJ) and leapfrog mechanisms (LF) with a slight predominance of DR process and a dual competition between CJ and LF processes. But, in the case of small one‐dimensional cluster such as trimer on (110)(1×2) missing‐row reconstructed surface, the main diffusion mechanism is the LF process. These results shed light on the diffusion processes on missing‐row reconstructed surfaces, especially for heterogeneous systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Erratum to: Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

Mesoporous WO₃–TiO₂ composite films were prepared by a sol gel based two stage dip coating method and subsequent annealing at 450, 500 and 600 °C. An organically modified silicate based templating strategy was adopted in order to obtain a mesoporous structure. The composite films were prepared on ITO coated glass substrates. The porosity, morphology, and microstructures of the resultant products were characterized by scanning electron microscopy, N₂ adsorption–desorption measurements, μ-Raman spectroscopy and X-ray diffraction. Calcination of the films at 450, and 500 °C resulted in mixed hexagonal (h) plus monoclinic phases, and pure monoclinic (m) phase of WO₃, respectively. The degree of crystallization of TiO₂ present in these composite films was not evident. The composite films annealed at 600 °C, however, consist of orthorhombic (o) WO₃ and anatase TiO₂. It was found that the o-WO₃ phase was stabilized by nanocrystalline anatase TiO₂. The thus obtained mesoporous WO₃–TiO₂ composite films were dye sensitized and applied for the construction of photochromic devices. The device constructed using dye sensitized WO₃–TiO₂ composite layer heat treated at 600 °C showed an optical modulation of 51 % in the NIR region, whereas the devices based on the composite layers heat treated at 450, and 500 °C showed only a moderate optical modulation of 24.9, and 38 %, respectively. This remarkable difference in the transmittance response is attributed to nanocrystalline anatase TiO₂ embedded in the orthorhombic WO₃ matrix of the WO₃–TiO₂ composite layer annealed at 600 °C.     

Multiclass analysis on repaglinide,flubendazole, robenidine hydrochloride and danofloxacin drugs

The drugs under study; repaglinide (Repag), flubendazole (Flu), robenidine hydrochloride (Roben) and danofloxacin (Dano) are antidiabetic, anthelmintic, anticoccidial, and antibiotic drugs. In the present study, they are investigated using electron impact mass spectral (EI-MS) fragmentation at 70 eV, in comparison with thermal analyses measurements (TGA/DrTGA and DTA) and molecular orbital calculation (MO). Semi-empirical MO calculation, AM1 procedure, has been carried out on Repag, Flu, Roben and Dano both as neutral molecules (in TA) and the corresponding positively charged species (in MS). The calculated MO parameters include bond length, bond order, charge distribution on different atoms and heat of formation. The fragmentation pathways of Repag, Flu, Roben and Dano in EI-MS led to the formation of important primary and secondary fragment ions. The mechanism of formation of some important daughter ions can be illuminated from comparing with that obtained using mass spectrometer through the accurate mass measurement determination. The MO provides a base for fine distinction among sites of initial bond cleavage and subsequent fragmentation of drug molecules in both thermal analysis and MS techniques. The activation thermodynamic parameters, such as, (activation energy E¹), (enthalpy ΔH¹), (entropy ΔS¹) and (Gibbs free energy ΔG¹) are calculated from the DrTGA curves using Coats–Redfern and Horowitz–Mitzger methods.     

Facile and Convenient Synthesis of Pyrazole,Pyridine, Pyridazine,Pyrazolo[3,4-b]pyridine,and Pyrazolo[5,1-c][1,2,4]triazine Derivatives

Abstract

A convenient synthesis of a series of pyrazole, pyridine, pyridinethione, pyridazine, pyrazolo[3,4-b]pyridine, imidazo[1,2-a]pyrimidine, and pyrazolo[5,1-c][1 Kumar , R. 5-(1-Substituted)alkyl pyrimidine nucleosides as antiviral (herpes) agents . Curr. Med. Chem. 2004 , 11 , 2749 – 2766 . [Google Scholar] 2 Holy , A. ; Günter , J. ; Dvoráková , H. ; Masojídková , M. ; Andrei , G. ; Snoeck , R. ; Balzarini , J. ; De Clercq , E. Structure–antiviral activity relationship in the series of pyrimidine and purine N-[2-(2-phosphonomethoxy)ethyl] nucleotide analogues, 1: Derivatives substituted at the carbon atoms of the base . J. Med. Chem. 1999 , 42 , 2064 – 2086 . [Google Scholar] 4 Brandes , W. ; Daum , W. ; Krauss , P. Fungicidal oxime ethers. Ger. Patent 2,623,847, 1977; Chem. Abstr . 1978 , 88 , 120822h . [Google Scholar]]triazine derivatives incorporating a pyrimidine moiety, via the reactions of the versatile, readily accessible 3-oxo-N-(pyrimid-2-yl)butanamide with the appropriate reagents, is described.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Raman study of oriented ZnO thin films deposited by sol-gel method

ZnO films with preferred orientation along the (0 0 2) plane were successfully deposited by the sol-gel method using Zn(CH3COO)2.2H2O as starting material and inorganic precursor. A homogeneous and stable solution was prepared by dissolving the zinc acetate in a solution of ethanol and monoethanolamine. Thin films are obtained by spin-coating on glass substrates. ZnO films were obtained by preheating the spin-coated films at 300 degrees C for 10 min after each coating and postheating upto 550 degrees C for 2h. The as-deposited films are transformed into mono-oriented ZnO upon thermal treatment. The films consist of spongy particles aggregates with an uniform size and homogenous surface. The films aim to be used in optoelectronic devices. Raman spectroscopy from ZnO films and deposit solutions has been investigated. New Raman results of the deposit solution suggest that Zn-O bond forms first in solution and that these entities play the role of germs initiating the crystallization mechanisms during films annealing. Raman spectra of the annealed films show the presence of a compressive stress within the film structure.     

Can undoped calcium tetraborides exist? An answer from the comparison of its density functional theory electronic structure with that of rare-earth metal tetraboride

Periodic density functional theory calculations are used to discuss the existence of metal tetraborides MB4 with divalent metals. Tetraborides which contain metal atoms inserted in a three-dimensional boron network made of B6 octahedra and B2 dumbbells exhibit a pseudo energy gap for a count of 60 valence electrons per M4(B6)2(B2)2 formula unit. Such a count satisfies the stability electron requirement for B6(2-) (20 electrons) octahedra and B2(2-) (8 electrons) units and allows the filling of two supplementary low-lying bands deriving from the valence metallic d atomic orbitals. This favored electron count is not reached for CaB4 which is then formally deficient by one electron per metal atom. This indicates that CaB4 is unlikely to exist without n-doping.     

Synthesis and chemical characterisation of some new diheteroaryl thienothiophene derivatives

Treatment of 1-(5-acetyl-3,4-dimethythieno[2,3-b]thiophene-2yl)ethanone (1) with dimethylformamide dimethyl acetal afforded enaminone derivative 2, which reacted with amino derivatives to give the corresponding bis-pyrimidine, bis-pyrazole, bis-triazolo-pyrimidine and bis-benzoimidazopyrimidine derivatives.