Synthesis, structural studies and catalytic activity of dioxidomolybdenum(VI) complexes with aroylhydrazones of naphthol-derivative

Reaction of the salicylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L1), anthranylhydrazone of 2hydroxy-l-naphthaldehyde (H2L2), benzoylhydrazone of 2-hydroxy-1-acetonaphthone (H2L3) and anthranylhydrazone of 2-hydroxy-1-acetonaphthone (H2L4; general abbreviation H2L) with MoO2(acac)21 afforded a series of 5- and 6- coordinate Mo(VI) complexes of the type MoO2L1-2(ROH)] where R = C2H5 (1) and CH3 (2)], and MoO2L3-4] (3 and 4). The substrate binding capacity of 1 has been demonstrated by the formation of one mononuclear mixed-ligand dioxidomolybdenum complex MoO2L1(Q)] (where Q= gamma-picoline (la)). Molecular structure of all the complexes (I, la, 2,3 and 4) is determined by X-ray crystallography, demonstrating the dibasic tridentate behavior of ligands. All the complexes show two irreversible reductive responses within the potential window -0.73 to -1.08 V, due to Movl/Mov and Mov/Mow processes. Catalytic potential of these complexes was tested for the oxidation of benzoin using 30% aqueous H2O2 as an oxidant in methanol. At least four reaction products, benzoic acid, benzaldehydedimethylacetal, methyl benzoate and benzil were obtained with the 95-99% conversion under optimized reaction conditions. Oxidative bromination of salicylaldehyde, a functional mimic of haloperoxidases, in aqueous 1-1202/KEr in the presence of HC1O4 at room temperature has also been carried out successfully. (C) 2013 Elsevier Ltd. All rights reserved.

Size dependent structural relaxations and dielectric properties induced by surface functionalized MWNTs in poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Structural dynamics, dielectric permittivity and ferroelectric properties in poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) (PVDF/PMMA) blends with respect to crystalline morphology was systematically investigated in presence of amine functionalized MWNTs (NH2-MWNTs) using dielectric spectroscopy. The crystalline morphology and the crystallization driven demixing in the blends was assessed by light microscopy (LM), wide angle X-ray diffraction (WXRD) and, in situ, by shear rheology. The crystal nucleation activity of PVDF was greatly induced by NH2-MWNTs, which also showed two distinct structural relaxations in dielectric loss owing to mobility confinement of PVDF chains and smaller cooperative lengths. The presence of crystal-amorphous interphase was supported by the presence of interfacial polarization at lower frequencies in the dielectric loss spectra. On contrary, the control blends showed a single broad relaxation at higher frequency due to defective crystal nuclei. This was further supported by monitoring the dielectric relaxations during isothermal crystallization of PVDF in the blends. These observations were addressed with respect to the spherulite sizes which were observed to be larger in case of blends with NH2-MWNTs. Higher dielectric permittivity with minimal losses was also observed in blends with NH2-MWNTs as compared to neat PVDF. Polarization obtained using P-E (polarization-electric field) hysteresis loops was higher in case of blends with NH2-MWNTs in contrast to control blends and PVDF. These observations were corroborated with the charge trapped at the crystal-amorphous interphase and larger crystal sizes in the blends with NH2-MWNTs. The microstructure and localization of MWNTs were assessed using SEM.

DNA STRUCTURAL FEATURES AND ARCHITECTURE OF PROMOTER REGIONS PLAY A ROLE IN GENE RESPONSIVENESS OF S. CEREVISIAE

Gene expression is the most fundamental biological process, which is essential for phenotypic variation. It is regulated by various external (environment and evolution) and internal (genetic) factors. The level of gene expression depends on promoter architecture, along with other external factors. Presence of sequence motifs, such as transcription factor binding sites (TFBSs) and TATA-box, or DNA methylation in vertebrates has been implicated in the regulation of expression of some genes in eukaryotes, but a large number of genes lack these sequences. On the other hand, several experimental and computational studies have shown that promoter sequences possess some special structural properties, such as low stability, less bendability, low nucleosome occupancy, and more curvature, which are prevalent across all organisms. These structural features may play role in transcription initiation and regulation of gene expression. We have studied the relationship between the structural features of promoter DNA, promoter directionality and gene expression variability in S. cerevisiae. This relationship has been analyzed for seven different measures of gene expression variability, along with two different regulatory effect measures. We find that a few of the variability measures of gene expression are linked to DNA structural properties, nucleosome occupancy, TATA-box presence, and bidirectionality of promoter regions. Interestingly, gene responsiveness is most intimately correlated with DNA structural features and promoter architecture.

Nanostructured CexZn1-xO thin films: Influence of Ce doping on the structural, optical and electrical properties

Thin films of CexZn1-xO thin films were deposited on glass substrates at 400 degrees C by nebulizer spray pyrolysis technique. Ce doping concentration (x) was varied from 0 to 10%, in steps of 2.5%. X-ray diffraction reveals that all the films have polycrystalline nature with hexagonal crystal structure and high preferential orientation along (002) plane. Optical parameters such as; transmittance, band gap energy, refractive index (n), extinction coefficient (k), complex dielectric constants (epsilon(r), epsilon(i)) and optical conductivity (sigma(r), sigma(i)) have been determined and discussed with respect to Ce concentration. All the films exhibit transmittance above 80% in the wavelength range from 330 to 2500 nm. Optical transmission measurements indicate the decrease of direct band gap energy from 3.26 to 3.12 eV with the increase of Ce concentration. Photoluminescence spectra show strong near band edge emission centered similar to 398 nm and green emission centered similar to 528 nm with excitation wavelength similar to 350 nm. High resolution scanning electron micrographs indicate the formation of vertical nano-rod like structures on the film surface with average diameter similar to 41 nm. Electrical properties of the Ce doped ZnO film have been studied using ac impedance spectroscopy in the frequency range from 100 Hz-1 MHz at different temperatures. (C) 2013 Elsevier B.V. All rights reserved.

Structural, thermal and electrical properties of poly(methyl methacrylate)/CaCu3Ti4O12 composite sheets fabricated via melt mixing

Poly(methyl methacrylate) (PMMA) and CaCu3Ti4O12 (CCTO) composites were fabricated via melt mixing followed by hot pressing technique. These were characterized using X-ray diffraction, thermo gravimetric, thermo mechanical, differential scanning calorimetry, fourier transform infrared (FTIR) and Impedance analyser for their structural, thermal and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. However, there was no significant difference in the glass transition (T (g) ) temperature between the polymer and the composite. The appearance of additional vibrational frequencies in the range 400-600 cm(-1) in FTIR spectra indicated a possible interaction between PMMA and CCTO. The composite, with 38 vol% of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low-frequency relaxation is attributed to the interfacial polarization/MWS effect. The origin of AC conductivity particularly in the high-frequency region was attributed to the electronic polarization.

Optical, Electrochemical, and Structural Properties of Spray Coated Dihexyl Substituted Poly (3,4 propylene dioxythiophene) Film for Optoelectronics Devices

The dihexyl substituted poly (3,4-propylenedioxythiophene) (PProDOT-Hx(2)) thin films uniformly deposited by cost effective spray coating technique on transparent conducting oxide coated substrates. The electro-optical properties of PProDOT-Hx(2) films were studied by UV-Vis spectroscopy that shows the color contrast about 45% with coloration efficiency of approximate to 185cm(2)/C. The electrochemical properties of PProDOT-Hx(2) films were studied by cyclic voltammetry and AC impedance techniques. The cyclic voltammogram shows that redox reaction of films are diffusion controlled and ions transportation will be faster on the polymer film at higher scan rate. Impedance spectra indicate that polymer films are showing interface charge transfer process as well as capacitive behavior between the electrode and electrolyte. The XRD of the PProDOT-Hx(2) thin films revealed that the films are in amorphous nature, which accelerates the transportation of ions during redox process.

Common recognition principles across diverse sequence and structural families of sialic acid binding proteins

Sialic acids form a large family of 9-carbon monosaccharides and are integral components of glycoconjugates. They are known to bind to a wide range of receptors belonging to diverse sequence families and fold classes and are key mediators in a plethora of cellular processes. Thus, it is of great interest to understand the features that give rise to such a recognition capability. Structural analyses using a non-redundant data set of known sialic acid binding proteins was carried out, which included exhaustive binding site comparisons and site alignments using in-house algorithms, followed by clustering and tree computation, which has led to derivation of sialic acid recognition principles. Although the proteins in the data set belong to several sequence and structure families, their binding sites could be grouped into only six types. Structural comparison of the binding sites indicates that all sites contain one or more different combinations of key structural features over a common scaffold. The six binding site types thus serve as structural motifs for recognizing sialic acid. Scanning the motifs against a non-redundant set of binding sites from PDB indicated the motifs to be specific for sialic acid recognition. Knowledge of determinants obtained from this study will be useful for detecting function in unknown proteins. As an example analysis, a genome-wide scan for the motifs in structures of Mycobacterium tuberculosis proteome identified 17 hits that contain combinations of the features, suggesting a possible function of sialic acid binding by these proteins.

Synthesis, structural and thermoluminescence properties of YAlO3:Dy3+ nanophosphors

Thermoluminescence properties of YAlO3:Dy3+ nanophosphor prepared by a low temperature solution combustion (SC) method using oxalyl dihydrazide as a fuel were studied and the results were compared to bulk phosphor prepared by solid state (SS) synthesis. Powder X-ray diffraction patterns confirm the orthorhombic phase of SC and SS methods. Rietveld refinement was used to estimate the cell parameters of undoped and Dy3+ doped YAlO3. Scanning electron micrographs reveal dumbbell shape particles. Electron paramagnetic resonance spectra of YAlO3:Dy3+ nanophosphors were studied at 293 K, 77 K and 10 K. Thermoluminescence responses of SC and SS prepared phosphor were studied using gamma irradiation in the dose range 0.1-6 kGy at a warming rate of 1 degrees C s (1) at room temperature (RT). The optimized concentrations of Dy3+ ions in YAlO3 was found to be 3 mol%. The trapping parameters (i. e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen's method. The low fading and linear response in the wide range (0.1-1 kGy) suggests the possibility of usage of SC prepared phosphor in dosimeter applications. (C) 2013 Elsevier B. V. All rights reserved.

Structural Evolution and Phase Stability of Hume-Rothery Phase in a Mechanically Driven Nanostructured Ag-15 at. pct Sn Alloy

The paper reports phase evolution in mechanically driven Ag-15 at. pct Sn alloy powder starting with elemental powders in order to establish the feasibility of designing nanocomposites of a Ag-Sn solid solution. This alloy lies in the phase field of the hexagonal zeta-phase which is a well-known Hume-Rothery electron compound with an electron-to-atom ratio of about 1.45 and hexagonal crystal structure (a = 0.2966 nm, c = 0.4782 nm). Through a systematic use of X-ray diffraction and transmission electron microscopy, the results establish the formation of the zeta-phase which co-exists with the Ag solid solution during the initial phase of milling. Mechanical milling for long duration (55 hours) destabilizes the zeta-phase. A complete solid solution of Ag with a grain size of similar to 8 nm could be achieved after 60 hours of milling. Additional milling can induce decomposition of the solid solution that results in a reappearance of zeta-phase. We present a detailed thermodynamic calculation which indicates that complete Ag solid solution of the present alloy composition would be possible if the crystallites size can be reduced below a certain critical size. In particular, we show that both Ag and zeta-phase grain sizes need to be taken into account for determining the metastable equilibrium and the phase change that has been experimentally observed. Finally, we argue that recrystallization processes set a limit to the achievable size of the nanoparticles with metastable Ag solid solution.

Structural Insights into Proton Conduction in Gallic Acid-Isoniazid Cocrystals

Hydrated cocrystal of gallic acid-isoniazid displays a single crystal-to-single crystal transformation upon dehydration, resulting in a difference of three orders of magnitude in proton conduction. The conduction pathway is shown to follow the Grotthus mechanism, supported by theoretical (DFT) calculations.

A structural and spectroscopic investigation of reduced graphene oxide under high pressure

The effect of high pressure on reduced graphene oxide (RGO) has been investigated using X-ray diffraction (XRD) and infrared (IR) absorption spectroscopy. Our XRD measurements show two-step reversible compression in the inter-layer spacing of RGO whereas intra-layer ordering exhibits a high pressure behavior similar to that of graphite up to 20 GPa. The line shape analysis of (100) peak, representing the intra-layer ordering, suggests presence of local out of plane distortions in RGO in the form of puckered regions which progressively straighten out as a function of pressure. IR measurements show reversible changes in spectroscopic features attributed to remnant functional groups in the inter-layer region. These measurements suggest high stability and recovering ability of RGO under pressure cycling. (C) 2014 Elsevier Ltd. All rights reserved.

Low temperature synthesis of pure cubic ZrO2 nanopowder: Structural and luminescence studies

Pure cubic zirconia (ZrO2) nanopowder is prepared for the first time by simple low temperature solution combustion method without calcination. The product is characterized by Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infra Red spectroscopy (FTIR) and Ultraviolet-Visible spectroscopy (UV-Vis). The PXRD showed the formation of pure stable cubic ZrO2 nanopowders with average crystallite size ranging from 6 to 12 nm. The lattice parameters were calculated from Rietveld refinement method. SEM micrograph shows fluffy, mesoporous, agglomerated particles with large number of voids. TEM micrograph shows honey comb like arrangement of particles with particle size similar to 10 nm. The PL emission spectrum excited at 210 nm and 240 nm consists of intense bands centered at similar to 365 and similar to 390 nm. Both the samples show shoulder peak at 420 nm, along with four weak emission bands at similar to 484, similar to 528, similar to 614 and similar to 726 nm. TL studies were carried out pre-irradiating samples with gamma-rays ranging from 1 to 5 KGy at room temperature. A well resolved glow peak at 377 degrees C is recorded which can be ascribed to deep traps. With increase in gamma radiation there is linear increase in TL intensity which shows the possible use of ZrO2 as dosimetric material. (C) 2013 Elsevier B.V. All rights reserved.

Scalable sequential alternating proximal methods for sparse structural SVMs and CRFs

Structural Support Vector Machines (SSVMs) and Conditional Random Fields (CRFs) are popular discriminative methods used for classifying structured and complex objects like parse trees, image segments and part-of-speech tags. The datasets involved are very large dimensional, and the models designed using typical training algorithms for SSVMs and CRFs are non-sparse. This non-sparse nature of models results in slow inference. Thus, there is a need to devise new algorithms for sparse SSVM and CRF classifier design. Use of elastic net and L1-regularizer has already been explored for solving primal CRF and SSVM problems, respectively, to design sparse classifiers. In this work, we focus on dual elastic net regularized SSVM and CRF. By exploiting the weakly coupled structure of these convex programming problems, we propose a new sequential alternating proximal (SAP) algorithm to solve these dual problems. This algorithm works by sequentially visiting each training set example and solving a simple subproblem restricted to a small subset of variables associated with that example. Numerical experiments on various benchmark sequence labeling datasets demonstrate that the proposed algorithm scales well. Further, the classifiers designed are sparser than those designed by solving the respective primal problems and demonstrate comparable generalization performance. Thus, the proposed SAP algorithm is a useful alternative for sparse SSVM and CRF classifier design.

Cooperativity and Structural Relaxations in PVDF/PMMA Blends in the Presence of MWNTs: An Assessment through SAXS and Dielectric Spectroscopy

Intermolecular cooperativity and structural relaxations in PVDF/PMMA blends were studied in this work with respect to different surface modified (amine, similar to NH2; carboxyl acid, similar to COOH and pristine) multiwalled nanotubes (MWNTs) at 1 wt % near blend's T-g and in the vicinity of demixing using dielectric spectroscopy, SAXS, DSC, and WAXD. Intermolecular cooperativity at T-g and configurational entropy was addressed in the framework of cooperative rearranging region (CRR) at T-g. Because of specific interactions between PVDF and NH2-MWNTs, the local composition fluctuates at its average value resulting in a broad T-g. The scale of cooperativity (xi(CRR)) and the number of segments in the cooperative volume (N-CRR) is comparatively smaller in the blends with NH2-MWNTs. This clearly suggests that the number of segments cooperatively relaxing is reduced in the blends due to specific interactions leading to more heterogeneity. The configurational entropy at T-g, as derived from Vogel-Fulcher and Adam-Gibbs analysis, was reduced in the blends in presence of MWNTs manifesting in entropic penalty of the chains. The crystallite size and the amorphous miscibility was evaluated using SAXS and was observed to be strongly contingent on the surface functional groups on MWNTs. Three distinct relaxations-alpha(c) due to relaxations in the crystalline phase of PVDF, alpha(m) indicating the amorphous miscibility in PVDF/PMMA blends, and alpha beta concerning the segmental dynamics of PMMA-were observed in the blends in the temperature range T-g < T < T-c. The dynamics as well as the nature of relaxations were observed to be dependent the surface functionality on the MWNTs. The dielectric permittivity was also enhanced in presence of MWNTs, especially with NH2-MWNTs, with minimal losses. The influence of the MWNTs on the spherulite size and crystalline morphology of the blends was also confirmed by POM and SEM.

Effect of pH on structural and magnetic properties of nanocrystalline Y3Fe5O12 by aqueous co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesised at different pH using co-precipitation method. The effect of pH on the phase formation of YIG is characterised using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 13, 19 and 28 nm for pH=10, 11 and 12 respectively. It is found that as the pH of the solution increase the particle size is also increases. It is also clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 600, 700, 800 and 900 degrees C for 5 h using conventional sintering method. The phase formation is completed at 800 degrees C/5 h which is correlated with TG/DTA. The average grain size of the samples is found to be similar to 161 nm. The high values of M-s=23 emu g(-1) and H-c=22 Oe were recorded for the sample sintered at 900 degrees C.