Synthesis of spongy gold nanocrystals with pronounced catalytic activities

A simple and easier chemical method for preparing spongy gold nanocrystals has been developed on the basis of a modified-citrate reduction technique of the corresponding gold salt at 25 degrees C in the absence of template. These nanocrystals possessed autocatalytic behavior and exhibited pronounced catalytic activity in the borohydride reduction of 4-nitrophenol due to their unique spongy morphology.     

Transparent,Versatile Chemical Vapor Sensor Using Supramolecular Assembly of Block Copolymer and Carbon Nanotubes

Here, a simple and novel approach is reported for developing a new class of transparent chemical vapor sensors with a low power consumption, high sensitivity, good selectivity, and excellent environmental stability by depositing multiwalled carbon nanotubes on prepatterned polymer substrates using supramolecular assembly. The patterned polymer substrates were fabricated from block copolymers, whereas the supramolecular assembly between the carbon nanotubes and block copolymer is utilized for the selective localization of carbon nanotubes at the block copolymer–air interface. The thin film devices made from the block copolymer and carbon nanotubes are highly transparent (transmittance > 90%) and respond to a wide range of solvents of different polarity, both hydrophilic and hydrophobic, with good selectivity and fast response time.

     

UV-vis-NIR and EPR characterisation of the redox series [MQ(3)](2+,+,0,-,2-), M = Ru or Os, and Q = o-quinone derivative

The neutral title compounds with Q = 3,5-di-tert-butyl-o-quinone or 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone (Q(x)) were studied by UV-vis-NIR spectroelectrochemistry and by EPR spectroscopy in the case of the odd-electron monocation and monoanion intermediates. Supported by DFT and TD-DFT calculations, the results indicate stepwise electron removal from predominantly ligand-based delocalised MOs on oxidation whereas the stepwise electron uptake on reduction involves unoccupied MOs with considerably metal-ligand mixed character. In both cases, the strong near-infrared absorption of the neutral precursors diminishes. In comparison to the ruthenium series, the osmium analogues exhibit larger transition energies from enhanced MO splitting and a different EPR response due to the higher spin-orbit coupling. The main difference between the quinone (1(n), 2(n)) and corresponding monoiminoquinone systems (3(n), 4(n)) is the shift of about 0.6 V to lower potentials for the monoimino analogues. While the absorption features do not differ markedly, the EPR data reflect a higher degree of covalent bonding for the complexes with monoimino ligands.     

Determination of the Association Constants of Charge-Transfer Complexes Between N,N-Diethylaniline and Nitro Explosives Using High Performance Thin Layer Chromatography with Scanning Video Densitometry and Spectrophotometry

Charge-transfer (CT) or electron donor-acceptor (EDA) complex formation between organic donors and acceptors has been extensively studied by spectrophotometry and other methods. High performance thin layer chromatography (HPTLC), although extensively used for the identification and quantification of drugs and explosives, has not been used until now to determine the extent of association and the association constants K _DA of charge transfer or EDA complexes between donor (D) and acceptor (A). This paper describes the use of the HPTLC technique with scanning densitometry to identify and determine the association constants K _DA of charge-transfer complexes of N,N-diethylaniline (DEA) with different nitro explosives, namely 1,4-dinitrobenzene (DNB), 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), in chloroform. Advantages of the HPTLC method are highlighted. The association constants K _DA of the complexes determined using the HPTLC method have been verified and validated spectrophotometrically when the concentrations of D and A are in their stoichiometric ratio. The thermodynamics of the complex formation reaction were obtained spectrophotometrically from measurements of the association constants K _DA at five different temperatures ranging from 293 to 313 K, when D and A are in their stoichiometric ratio and also when A≫D.     

Lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene: synthesis, characterization, and selective recognition of Hg2+ and its sensitivity toward pyrimidine bases

The structurally characterized lower rim 1,3-di{4-antipyrine}amide conjugate of calix[4]arene (L) exhibits high selectivity toward Hg(2+) among other biologically important metal ions, viz., Na(+), K(+), Ca(2+), Mg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), and Ag(+) as studied by fluorescence, absorption, and ESI MS. L acts as a sensor for Hg(2+) by switch-off fluorescence and exhibits a lowest detectable concentration of 1.87 ± 0.1 ppm. The complex formed between L and Hg(2+) is found to be 1:1 on the basis of absorption and fluorescence titrations and was confirmed by ESI MS. The coordination features of the mercury complex of L were derived on the basis of DFT computations and found that the Hg(2+) is bound through an N(2)O(2) extending from both the arms to result in a distorted octahedral geometry with two vacant sites. The nanostructural features such as shape and size obtained using AFM and TEM distinguishes L from its Hg(2+) complex and were different from those of the simple mercuric perchlorate. L is also suited to sense pyrimidine bases by fluorescence quenching with a minimum detection limit of 1.15 ± 0.1 ppm in the case of cytosine. The nature of interaction of pyrimidine bases with L has been further studied by DFT computational calculations and found to have interactions through a hydrogen bonding and NH-π interaction between the host and the guest.     

Imaging of a convective field in a rectangular cavity using interferometry, schlieren and shadowgraph

The present study is concerned with the quantitative imaging of buoyancy-driven convection in a fluid medium that is confined in a horizontal differentially heated rectangular cavity. The horizontal surfaces of the cavity provide a temperature difference, for initiating convection in the fluid. The vertical side walls are thermally insulated. Three imaging techniques, namely laser interferometry, schlieren, and shadowgraph have been utilized. Experiments have been conducted in a cavity of length 447 mm and 32 mm vertical height. The cavity is square in cross-section, and the imaging direction is parallel to its longer side. Convection in air and water have been investigated. Temperature differences in the range of 5–50 K for air and 3–10 K for water have been employed in the experiments. Quantities of interest are the temperature profiles in unsteadiness in the thermal field. At lower temperature differences across the fluid region, temperatures as recorded by interferometry and schlieren are in good agreement with each other. Further, they match the numerical predictions, as well as correlations available in the literature. Imaging based on shadowgraph is not as satisfactory at lower temperature differences. At larger cavity temperature differences, the shadowgraph images become clear enough for quantitative analysis, but the flow becomes time-dependent. The three techniques reveal similar trends in terms of the spatial distribution of temperature gradients and the time scales of unsteadiness. The schlieren and shadowgraph are more suitable for high gradients and interferometry is suitable for low gradients and all these three techniques are not flow visualization tools alone but are appropriate for quantitative imaging of thermal field.     

One pot low temperature synthesis of graphene coupled Gd-doped ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite for effective removal of antibiotic levofloxacin drug

Nanocomposites of reduced graphene oxide (rGO) coupled gadolinium doped ZnFe₂O₄ (GZFG) have been successfully one pot in-situ synthesized adopting low temperature solution process from zinc nitrate, iron nitrate, gadolinium acetate and graphene oxide with varying concentrations of gadolinium (upto 10% Gd with respect to Zn) in the precursor medium. X-ray diffraction and transmission electron microscopy studies confirm the presence of single phase cubic spinel structure of ZnFe₂O₄ that uniformly distributed over the rGO layers. With increasing Gd doping concentration in precursor medium, the average crystallite size of ZnFe₂O₄ diminishes gradually from ~11 to ~5.5?nm. Raman and X-ray photoelectron spectral analyses confirm an existence of interaction between rGO and ZnFe₂O₄ in GZFG samples. Using antibiotic levofloxacin in water, the drug removal capacity (DRC) of GZFG has been performed by optimization of parameters such as gadolinium doping concentration in precursor medium, solution pH, etc. However, the gadolinium doping leads to an improvement in DRC of the nanocomposite and the 5% Gd doped sample shows about 86% DRC at the optimized condition. This simple strategy can be utilized in the synthesis of rGO coupled Gd doped other metal oxide nanocomposites for DRC application.

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Rhodium-catalysed chemo- and regio-selective [3 + 2+2] cycloadditions of bis(methylenecyclopropanes) and alkynes: Synthesis of spirocyclic 5–7 condensed cycloheptenes

Abstract

Rhodium-catalyzed intermolecular [3?+?2+2] cycloaddition reactions of bis(methylenecyclopropanes) with different alkynes are described. The rhodium-catalyzed [3?+?2+2] cycloadditions resulted in the formation of functionalized 5–7–3 spirocyclic carbocycles in moderate yields with excellent regio- and chemo-selectivity.