Mononitration of phenol derivatives by guanidinium nitrate and silica sulfuric acid under mild conditions

A mixture of guanidinium nitrate and silica sulfuric acid acts as mild and heterogeneous media for the efficient mono nitration of phenolic compounds in dichloromethane at room temperature.     

Hydrogen bonding interactions between α-, β-glucose,and methacrylic acid

Intermolecular interactions between α-, β-glucose, and methacrylic acid (MAA) have been investigated. Twenty-two possible conformations have been optimized at the DFT(B3LYP) level of theory with the 6-31G(d) basis set. The geometrical parameters for the most stable configurations of hydrogen bonding sites in the optimized systems have been determined. The binding energies ΔE _bind have been calculated at the MP2/6-311++G(d,p) level of approximation taking into account the basis set superposition error (BSSE) and the zero-point vibrational energies corrections. Results indicate that the most stabilized complexes form hydrogen bonds either through carboxylic and hemiacetal oxygen atoms acting as proton acceptors. Both, α- and β-anomers are studied in the pyranose six-membered ring. In all complexes, the nuclear quadrupole coupling constants (χ) for ¹⁷O nuclei were obtained about 10.0 MHz, while for the ²H atoms they vary from ≈200.0 to ≈350.0 kHz.     

Cadmium(II) N-acetylcysteine complex formation in aqueous solution

The complex formation between Cd(II) ions and N-acetylcysteine (H(2)NAC) in aqueous solution was investigated using Cd K- and L(3)-edge X-ray absorption and (113)Cd NMR spectroscopic techniques. Two series of 0.1 M Cd(II) solutions with the total N-acetylcysteine concentration c(H2NAC) varied between 0.2-2 M were studied at pH 7.5 and 11.0, respectively. At pH = 11 a novel mononuclear [Cd(NAC)(4)](6-) complex with the average Cd-S distance 2.53(2) ? and the chemical shift δ((113)Cd) = 677 ppm was found to dominate at a concentration of the free deprotonated ligand [NAC(2-)] > 0.1 M, consistent with our previous reports on cadmium tetrathiolate complex formation with cysteine and glutathione. At pH 7.5 much higher ligand excess ([HNAC(-)] > 0.6 M) is required to make this tetrathiolate complex the major species. The (113)Cd NMR spectrum of a solution containing c(Cd(II)) = 0.5 M and c(H2NAC) = 1.0 M measured at 288 K showed three broad signals at 421, 583 and 642 ppm, which can be attributed to CdS(3)O(3), CdS(3)O and CdS(4) coordination sites, respectively, in oligomeric Cd(II)-NAC species with single thiolate bridges between the cadmium ions.     

Synthesis and application of a novel solid-phase microextraction adsorbent: Hollow fiber supported carbon nanotube reinforced sol–gel for determination of phenobarbital

A novel solid-phase microextraction technique using a hollow fiber-supported sol–gel combined with multi-walled carbon nanotubes was employed in the determination of phenobarbital in wastewater. In this new technique, a silica-based, organic–inorganic polymer containing functionalized multi-walled carbon nanotubes (MWCNTs) was prepared with sol–gel technology via the reaction of tetraethylorthosilicate (TEOS) with an acidic catalyst (HCl). This sol was injected into a polypropylene hollow fiber segment for in situ gelation. This device operated in direct immersion sampling mode. The experimental setup is simple and affordable, and the device is disposable, so there is no risk of cross-contamination or carry-over. Parameters affecting extraction such as pH of the aqueous solution, ageing and extraction times, aqueous sample volume, agitation speed and carbon nanotube amount were optimized. Linearity was observed over a range of 0.50–5000 ng mL⁻¹, with an estimation coefficient (r²) higher than 0.982. The limit of detection (LOD) was 0.32 ng mL⁻¹ (n = 5), and repeatability (RSD% = 2.9) was from the average of three levels of analyte concentrations (1, 1000 and 4500 ng mL⁻¹) with three replicates for each within a single day. Finally, a pre-concentration factor of 2100 was obtained for phenobarbital.     

Comparison of luminescence ADP production assay and radiometric scintillation proximity assay for Cdc7 kinase

Several assay technologies have been successfully adapted and used in HTS to screen for protein kinase inhibitors; however, emerging comparative analysis studies report very low hit overlap between the different technologies, which challenges the working assumption that hit identification is not dependent on the assay method of choice. To help address this issue, we performed two screens on the cancer target, Cdc7-Dbf4 heterodimeric protein kinase, using a direct assay detection method measuring [(33)P]-phosphate incorporation into the substrate and an indirect method measuring residual ADP production using luminescence. We conducted the two screens under similar conditions, where in one, we measured [(33)P]-phosphate incorporation using scintillation proximity assay (SPA), and in the other, we detected luminescence signal of the ATP-dependent luciferase after regenerating ATP from residual ADP (LUM). Surprisingly, little or no correlation were observed between the positives identified by the two methods; at a threshold of 30% inhibition, 25 positives were identified in the LUM screen whereas the SPA screen only identified two positives, Tannic acid and Gentian violet, with Tannic acid being common to both. We tested 20 out of the 25 positive compounds in secondary confirmatory study and confirmed 12 compounds including Tannic acid as Cdc7-Dbf4 kinase inhibitors. Gentian violet, which was only positive in the SPA screen, inhibited luminescence detection and categorized as a false positive. This report demonstrates the strong impact in detection format on the success of a screening campaign and the importance of carefully designed confirmatory assays to eliminate those compounds that target the detection part of the assay.     

Cyclicity of the adjoint of weighted composition operators on the hilbert space of analytic functions

In this paper, we discuss the hypercyclicity, supercyclicity and cyclicity of the adjoint of a weighted composition operator on a Hilbert space of analytic functions.     

Variation of the electronic properties of zigzag boron nitride nanotubes by Al-doping: a DFT study

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes.     

A recursive color image edge detection method using Green's function approach

In this paper, an extended version of image edge detector using Green's function approach is proposed for detection of edges in the color vector space field. In the proposed method, the relationship between the Red, Green and Blue components is considered to design a differential operator for detection of edges in color images. By using the proposed operator, partial derivatives of all components of color image can simultaneously affect on the edge detection process. Therefore the proposed method can preserve the vector nature of color images during the edge processing stages. Also, the proposed method is compared both quantitatively and qualitatively with other color edge detectors. Experimental results show that the proposed method can efficiently preserve the edges even when the color images corrupted with different levels of noise.     

The lithiation studies of nanostructured tungsten oxide film prepared via electrochemical precipitation

In this work, nanostructured tungsten oxide was electrodeposited by cyclic voltammetric technique onto a stainless steel surface. The structure and surface morphology of the resulting oxide film were characterized by means of X-ray diffraction, scanning probe microscopy, and scanning electron microscopy. The electrochemical intercalation of lithium into the nanostructured tungsten oxide was studied using cyclic voltammetry, galvanostatic charge–discharge curves, and electrochemical impedance spectroscopy in a liquid electrolyte consisting of 1 M LiClO₄ in propylene carbonate. The as-deposited tungsten oxide indicated the capacity for electrochemical lithium insertion. The specific capacitance of 108.05 F?g^?1 was obtained at the constant discharge density of 0.07 mA?cm^?2.