Stability Analysis of a Vertical Curved Channel Flow with a Radial Temperature Gradient

The linear stability analysis of a Newtonian incompressible fluid in a vertical curved channel formed by two coaxial cylindrical surfaces with a radial temperature gradient and an azimuthal pressure gradient shows that critical modes are oscillatory and non-axisymmetric. We have derived a generalized Rayleigh discriminant which includes both the curvature and buoyancy effects. Centrifugal buoyancy induces weak asymmetry of the dependence of the control parameter critical values on the sign of the temperature gradient. The critical parameters depend on the temperature gradient, the radius ratio and the nature of the fluid. For a wide curvature channel flow, there are two critical modes: oscillatory Dean modes for small temperature gradients and oscillatory centrifugal-thermal modes for relatively large temperature gradients. Received 14 November 2001 and accepted 29 March 2002 Published online: 2 October 2002 Communicated by H.J.S. Fernando     

Isolation,structure elucidation and enzyme inhibition studies of a new hydroxy ester and other compounds from Berberis jaeschkeana Schneid stem

Bioassay-guided isolation and fractionation of Berberis jaeschkeana Schneid var. jaeschkeana stem resulted in the isolation and characterisation of a new long chain hydroxy ester named as berberinol (1) along with six known compounds (2–7). All the structures were established from 1D and 2D spectroscopic data. Crude extract, sub-fractions and all the isolated compounds were evaluated for their anti-fungal and urease enzyme inhibition properties. All of the sub-fractions and compounds showed good anti-fungal and urease enzyme inhibition properties. Minimum inhibitory concentrations (MICs) were calculated for all active samples in case of urease enzyme inhibition. MICs values were found to be in the range of 39.03–49.78 μg/mL for urease enzyme inhibition.     

In vitro anti-oxidant potential of new metabolites from Hypericum oblongifolium (Guttiferae)

Phytochemical investigations on Hypericum oblongifolium led to the isolation of a flavone named folicitin (1) and a bicyclic conjugated lactone, folenolide (2) from the ethyl acetate fraction of methanolic extract. Both metabolites were characterised as new compounds based on detailed spectroscopic analyses. In vitro anti-oxidant potential of both the compounds was evaluated by the DPPH radical scavenging assay. Compound 1 exhibited significant antioxidant activity while compound 2 was found inactive.     

Inhibition of thermal induced protein denaturation of extract/fractions of Withania somnifera and isolated withanolides

This study describes the in vitro inhibition of protein denaturation of extract/fractions of Withania somnifera and isolated withanolides including 20β hydroxy-1-oxo(22R)-witha-2,5,24 trienolide (1), (20R,22R-14α,20α)-dihydroxy-1-oxowitha-2,5,16,24 tetraenolide (2). The results showed that the extract/fractions of the plant evoked profound inhibitory effect on thermal-induced protein denaturation. The chloroform fraction caused the most dominant attenuation of 68% at 500 μg/mL. The bioactivity-guided isolation from chloroform fraction led to the isolation of compounds 1 and 2 that showed profound protein inhibition with 78.05% and 80.43% effect at 500 μg/mL and thus strongly complimented the activity of extract/fractions. In conclusion, extract/fractions of W. somnifera possessed strong inhibition of protein denaturation that can be attributed to these isolated withanolides.     

Stepwise isolation of low-valent,low-coordinate Sn and Pb mono- and dications in the coordination sphere of platinum

Synthetic access to low-coordinate Pb mono- and dications is in general impeded due to their poor solubility and highly electrophilic nature. However, the electrophilicity of these cations can be tamed by attaching them to electron-rich transition metals. Following this principle we have isolated low-valent Pb mono- ([(Cy₃P)₂Pt–PbCl]₂[AlCl₄]₂, 8a) and dications ([(Cy₃P)₂Pt(Pb)][AlCl₄]₂, 11) in the coordination sphere of platinum. The same approach then has been implemented for the isolation of analogous low-valent Sn mono- (7a) and dications (10). An energy decomposition analysis (EDA-NOCV) was performed to investigate the nature of Pt–Pb and Pb–Cl bonding in [(Cy₃P)₂Pt(PbCl₂)] (2), 8a and 11. The results show that the Pt–Pb bonds in 8a and 11 are electron-sharing in nature, whereas that of the precursor 2 is a dative bond. The breakdown of attractive interactions in 2, 8a and 11 reveals that the ionic interactions in the analyzed Pt–Pb and Pb–Cl bonds are always stronger than the covalent interactions, except for the Pb–Cl bond in 8a. The calculated D3 dispersion energies show that dispersion interactions play a key role in the thermodynamic stability of 2, 8a and 11.     

Extreme red shifted SERS nanotags

Surfaced enhanced Raman scattering (SERS) nanotags operating with 1280 nm excitation were constructed from reporter molecules selected from a library of 14 chalcogenopyrylium dyes containing phenyl, 2-thienyl, and 2-selenophenyl substituents and a surface of hollow gold nanoshells (HGNs). These 1280 SERS nanotags are unique as they have multiple chalcogen atoms available which allow them to adsorb strongly onto the gold surface of the HGN thus producing exceptional SERS signals at this long excitation wavelength. Picomolar limits of detection (LOD) were observed and individual reporters of the library were identified by principal component analysis and classified according to their unique structure and SERS spectra.     

Modified carbon nanotubes as a sorbent for solid-phase extraction of gold,and its determination by graphite furnace atomic absorption spectrometry

A simple, sensitive and accurate method was developed for solid-phase extraction and preconcentration of trace levels of gold in various samples. It is based on the adsorption of gold on modified oxidized multi-walled carbon nanotubes prior to its determination by graphite furnace atomic absorption spectrometry. The type and volume of eluent solution, sample pH value, flow rates of sample and eluent, sorption capacity and breakthrough volume were optimized. Under these conditions, the method showed linearity in the range of 0.2–6.0 ng L⁻¹ with coefficients of determination of >0.99 in the sample. The relative standard deviation for seven replicate determinations of gold (at a level of 0.6 ng L⁻¹) is ±3.8 %, the detection limit is 31 pg L⁻¹ (in the initial solution and at an S/N ratio of 3; for n = 8), and the enrichment factor is 200. The sorption capacity of the modified MWCNTs for gold(III) is 4.15 mg g⁻¹. The procedure was successfully applied to the determination of gold in (spiked) water samples, human hair, human urine and standard reference material with recoveries ranging from 97.0 to 104.2 %.

A sorbent based on modified carbon nanotubes was prepared and used to extract gold ion from various samples prior to its determination by graphite furnace atomic absorption spectrometry

     

Solid phase extraction of antidepressant drugs amitriptyline and nortriptyline from plasma samples using core-shell nanoparticles of the type Fe3O4@ZrO2@N- cetylpyridinium,and their subsequent determination by HPLC with UV detection

The solid phase extraction (SPE) is described for preconcentration of the antidepressant drugs amitriptyline and nortriptyline prior to their determination by HPLC with UV detection. It is based on the use of water-dispersible core-shell nanoparticles (NPs) of the Fe₃O₄@ZrO₂@N-cetylpyridinium type. The positively charged surfactant N-cetylpyridinium forms mixed aggregates with the drugs on the surface of the core-shell and thereby improves the adsorption of amitriptyline and nortriptyline through hydrophobic and/or ionic interactions. Their extraction depends on the type and amount of surfactant, sample pH, extraction time, desorption conditions, sample volume and amount of NPs that were optimized by application of experimental design. The enrichment factors are 220 and 250, respectively, for amitriptyline and nortriptyline, and the detection limits are 0.04 and 0.08 ng·mL‾¹. This protocol enables accurate and precise quantification of the two drugs in complex and low content samples. It was applied to the determination of the two drugs in plasma samples with relative recoveries in the range from 89 to 105 % and RSDs less than 4 %.

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