Thermoanalytical studies of oxovanadium(IV)hydroxamate complexes

The thermal decomposition behavior of oxovanadium(IV)hydroxamate complexes of composition [VO(acac)(C₆H₅C(O)NHO)] (I), [VO(C₆H₅C(O)NHO)₂] (II), [VO(acac)(4-ClC₆H₄C(O)NHO)] (III), [VO(4-ClC₆H₄C(O)NHO)₂] (IV) (where acac = (CH₃COCHCOCH₃ ^–) synthesized from the reactions of VO(acac)₂ with equi- and bimolar amounts of potassium benzohydroxamate and potassium 4-chlorobenzohydroxamate in THF + MeOH solvent medium has been studied by TG and DTA techniques. TG curves indicated that complexes I, II, and IV undergo decomposition in single step to yield VO₂ as the final residue, while complex III decomposes in two steps to yield VO(acac) as the likely intermediate and VO₂ as the ultimate product of decomposition. The formation of VO₂ has been authenticated by IR and XRD studies. From the initial decomposition temperatures, the order of thermal stability for the complexes has been inferred as IV > I > III > II.     

Redox Behavior of Neptunium(V) in Tributyl Phosphate and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dihexyl Octanamide Extractants Dissolved in <Emphasis Type="Italic">n</Emphasis>-Dodecane

Spectrophotometric investigations have been carried out on the disproportionation of Np(V) to form Np(IV) and Np(VI) in 1.1 mol⋅L⁻¹ solutions of tributyl phosphate (TBP) and in N,N-dihexyl octanamide (DHOA) in n-dodecane medium. The Np(V) was found to coordinate with Np(IV) in 1.1 mol⋅L⁻¹ TBP solution in n-dodecane to form a mixed valence “cation–cation” complex by bonding through an axial oxo group on Np(V). By contrast, this interaction was less prominent in the case of 1.1 mol⋅L⁻¹ DHOA solutions. The effect of 1-octanol, added as phase modifier, on the disproportionation behavior of Np(V) was also investigated. An attempt was made to calculate the disproportionation/reduction rate constants for Np(V) under the conditions of these studies. Absorbance measurements on the Np stripped from organic phases revealed the occurrence of Np(V) in the aqueous phase.     

Transient MHD stagnation flow of a non-Newtonian fluid due to impulsive motion from rest

The transient boundary layer flow and heat transfer of a viscous incompressible electrically conducting non-Newtonian power-law fluid in a stagnation region of a two-dimensional body in the presence of an applied magnetic field have been studied when the motion is induced impulsively from rest. The non-linear partial differential equations governing the flow and heat transfer have been solved by the homotopy analysis method and by an implicit finite-difference scheme. For some cases, analytical or approximate solutions have also been obtained. The special interest are the effects of the power-law index, magnetic parameter and the generalized Prandtl number on the surface shear stress and heat transfer rate. In all cases, there is a smooth transition from the transient state to steady state. The shear stress and heat transfer rate at the surface are found to be significantly influenced by the power-law index N except for large time and they show opposite behaviour for steady and unsteady flows. The magnetic field strongly affects the surface shear stress, but its effect on the surface heat transfer rate is comparatively weak except for large time. On the other hand, the generalized Prandtl number exerts strong influence on the surface heat transfer. The skin friction coefficient and the Nusselt number decrease rapidly in a small interval 0<t^*<1 and reach the steady-state values for t^*≥4.     

Natural Convection on a Horizontal Cone in a Porous Medium with Non-Uniform Wall Temperature/Concentration or Heat/Mass Flux and Suction/Injection

The steady natural convection flow on a horizontal cone embedded in a saturated porous medium with non-uniform wall temperature/concentration or heat/mass flux and suction/injection has been investigated. Non-similar solutions have been obtained. The nonlinear coupled differential equations under boundary layer approximations governing the flow have been numerically solved. The Nusselt and Sherwood numbers are found to depend on the buoyancy forces, suction/injection rates, variation of wall temperature/concentration or heat/mass flux, Lewis number and the non-Darcy parameter.     

Chromophore and spectrum of the glycogen–iodine complex

The experimental UV-vis spectrum of the glycogen-iodine (GI) complex shows certain features remarkably similar to that of the amylopectin-iodine (API) complex [J. Polymer. Chem. 32, 2257 (1994)], suggesting a strong similarity between the API and the GI structures. As in the API complex, a nearly linear polyiodine unit, I₄, at an interiodine distance of around 3 Å is expected to exist within the helix of 11 anhydroglucose units (AGUs). There are several other spectral features that suggest the presence of another similar but more loosely bound iodine species with a longer interiodine distance of 3.1 Å. These findings suggest the involvement of two different types of glycogen chains in binding iodine molecules. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of terbium doped TiO2 nanoparticles and their use as recyclable and reusable heterogeneous catalyst for efficient and environmentally sustainable synthesis of spiroannulated indolo[3,2-c]quinolines- mimetic scaffolds of isocryptolepine

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated indolo[3,2-c]quinolines involving three component sequential reaction of phenylhydrazine, o-aminoacetophenone and cyclic ketones using nanostructured terbium doped TiO₂ as recyclable and reusable heterogeneous catalyst. The nanostructured catalyst was synthesized successfully and characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), EDX and Fourier transform infra-red spectroscopy (FTIR). The substitution of Ti⁺⁴ with Tb⁺³ and the formation of Ti-O-Tb bonds as a result of doping of Terbium with TiO₂ NPs increases the catalytic efficiency and facilitates the reaction to provide the products in excellent yields. The present protocol with special features; operational simplicity, atom-economy, mild reaction conditions, environmental sustainability and high synthetic efficiency with recyclability and reusability of catalyst has been reported for the first time to synthesize spiroannulated indoloquinolines and expecting to provide the library of promising new leads in drug discovery research.     

Molecular dynamics in chloronitrobenzenes using NQR data

The torsional frequencies have been rigorously evalulated in the compounds 1,2,4,5-tetrachloro-3,6-dinitrobenzene and 1,3,5-trichloro-2,4-dinitrobenzene over an extended temperature range (77K–392K) using the experimental results of NQR and crystal structure data. The values have been compared with those obtained by using the X-ray thermal parameters.     

Electrical characterization of tin disulphide crystals

Tin disulphide crystals have been grown by the physical vapour transport method and the electrical conduction mechanism in these crystals using MIM structures is reported. The conduction is found to be space charge limited. Trap concentration, trap depth, free carrier mobility and Fermi level etc. have been determined. Dependence of the current on temperature in the ohmic region gives an activation energy of 0.40 ± 0.05 eV.     

C-V studies on metal-ferroelectric bismuth vanadate (Bi2VO5.5)-semiconductor structure

Ferroelectric bismuth vanadate Bi₂VO_5.5 (BVO) thin films have been successfully grown on p-type Si(100) substrate by using chemical solution decomposition (CSD) technique followed by rapid thermal annealing (RTA). The crystalline nature of the films has been studied by X-ray diffraction (XRD). Atomic force microscopy (AFM) was used to study the microstructure of the films. The dielectric properties of the films were studied. The capacitance-voltage characteristics have been studied in metal-ferroelectric-insulator-semiconductor (MFIS) configuration. The dielectric constant of BVO thin films formed on Si(100) is about 146 measured at a frequency of 100 kHz at room temperature. The capacitance-voltage plot of a Bi₂VO_5.5 MFIS capacitor subjected to a dc polarizing voltages shows a memory window of 1.42 V during a sweep of ±5 V gate bias. The flatband voltage (V_f) shifts towards the positive direction rather than negative direction. This leads to the asymmetric behavior of the C-V curve and decrease in memory window. The oxide trap density at a ramp rate of 0.2 V/s was estimated to be as high as 1.45×10¹² cm⁻².