Sensitive and simple cloud-point preconcentration atomic absorption spectrometry: application to the determination of cobalt in urine samples.

A new approach for developing a cloud-point extraction-flame atomic absorption spectrometric method has been described and used for the determination of cobalt. In this approach, water was removed from the final diluted surfactant rich phase obtained in cloud-point extraction procedure. The results indicated that removing water from this phase increased the enhancement factor by 4-fold. 1-(2-Pyridylazo)-2-naphthol (PAN) and octylphenoxypolyethoxyethanol (Triton X-114) were used as a hydrophobic ligand and a nonionic surfactant, respectively. The chemical variables affecting the preconcentration step were optimized. The effect of the water concentration in the final diluted methanolic surfactant solution on the analytical signal was investigated. The results showed that the analytical signal decreased by 30% and 52% in 15% and 25% water concentrations in methanol, respectively. An enhancement factor of 115 was obtained for cobalt extracted from only 10 ml of a sample. The detection limit obtained under the optimal condition was 0.38 microg l(-1). The proposed procedure was applied to the determination of cobalt in urine samples.     

Spectrofluorimetric study of host-guest complexation of ibuprofen with beta-cyclodextrin and its analytical application

The characteristics of host-guest complexation between beta-cyclodextrin (beta-CD) and two forms of ibuprofen (protonated and deprotonated) were investigated by fluorescence spectrometry. 1:1 stoichiometries for both complexes were established and their association constants at different temperatures were calculated by applying a non-linear regression method to the change in the fluorescence of ibuprofen that brought about by the presence of beta-CD. The thermodynamic parameters (deltaH, deltaS and deltaG) associated with the inclusion process were also determined. Based on the obtained results, a sensitive spectrofluorimetric method for the determination of ibuprofen was developed with a linear range of 0.1-2 microg ml(-1) and a detection limit of 0.03 microg ml(-1). The method was applied satisfactorily to the determination of ibuprofen in pharmaceutical preparations.     

Photometric determination of tetracycline based on surface plasmon resonance of silver nanoparticles

We report on a simple and sensitive method for the determination of tetracycline based on its reducing action on AgNO₃ in alkaline medium containing ammonia and sodium hydroxide at 65°C. As a result of this reaction, silver nanoparticles (AgNPs) are formed. The AgNPs are stabilized in solution by adding poly(vinyl pyrrolidone) as a capping agent. The formed AgNPs were identified by surface plasmon resonance absorption spectrum and transmission electron microscopy image. The plasmon absorption peak at 411 nm is proportional to the concentration of tetracycline. The calibration graph is linear in the concentration range of 0.05–5.0 mg/L with a detection limit of 0.013 mg/L. This method was applied to the determination of tetracycline in pharmaceutical products.     

Synthesis of the Three Mixed-ligand Metal Complexes and One Organic Salt of 3,5-Dinitrobenzoic Acid for Biopharmaceutical Optimization Through Monoethanolamine: Structures and DFT Studies of Complexes

Journal of Chemical Crystallography - The simplest derivatives of benzoic acid show a wide spectrum of the biological action mostly being poor water soluble. In order to demonstrate on example of...     

Synthesis,characterization and heterogeneous catalytic application of a nickel(II) Schiff base complex immobilized on MWCNTs for the Hantzsch four-component condensation

A nickel(II) Schiff base complex immobilized on multi-wall carbon nanotubes (MWCNTs) surface as a highly efficient heterogeneous catalyst was synthesized and characterized by IR, X-ray diffraction patterns, scanning electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma, elemental analysis, and thermal gravimetric analysis. Then a facile and environmentally benign procedure was developed for synthesis of polyhydroquinoline derivatives via Hantzsch one-pot condensation reaction of aromatic aldehydes, 1,3-diones, ethyl acetoacetate, and ammonium acetate in the presence of above synthesized catalyst under solvent-free conditions. This protocol has the advantages of stability, easy availability, recyclability and eco-friendly nature of catalyst, simple experimental and work-up procedure, and also high to excellent yields. Considering the solvent-free condition and also temperature, time, and yield of the model reaction, the nanocatalyst reported here is among the best catalysts reported so far for synthesis of polyhydroquinolines.     

Fischer-Tropsch synthesis by nano-structured iron catalyst

Effects of nanoscale iron oxide particles on textural structure, reduction, carburization and catalytic behavior of precipitated iron catalyst in Fischer-Tropsch synthesis (FTS) are investigated. Nanostructured iron catalysts were prepared by microemulsion method in two series. Firstly, Fe2O3, CuO and La2O3 nanoparticles were prepared separately and were mixed to attain Fe/Cu/La nanostructured catalyst (sep-nano catalyst); Secondly nanostructured catalyst was prepared by co-precipitation in a water-in-oil microemulsion method (mix-nano catalyst). Also, conventional iron catalyst was prepared with common co-precipitation method. Structural characterizations of the catalysts were performed by TEM, XRD, H2 and CO-TPR tests. Particle size of iron oxides for sep-nano and mix-nano catalysts, which were determined by XRD pattern (Scherrer equation) and TEM images was about 20 and 21.6 nm, respectively. Catalyst evaluation was conducted in a fixed-bed stainless steel reactor and compared with conventional iron catalyst. The results revealed that FTS reaction increased while WGS reaction and olefin/paraffin ratio decreased in nanostructured iron catalysts.     

Deactivation studies of nano-structured iron catalyst in Fischer-Tropsch synthesis

A nano-structured iron catalyst for syngas conversion to hydrocarbons in Fischer-Tropsch synthesis (FTS) was prepared by micro-emulsion method. Compositions of bulk iron phase and phase transformations of carbonaceous species during catalyst deactivation in FTS reaction were characterized by temperature-programmed surface reaction with hydrogen (TPSR-H2), and XRD techniques. Many carbonaceous species on surface and bulk of the nano-structured iron catalysts were completely identified by combined TPSR-H2 and XRD spectra and which were compared with those recorded on conventional co-precipitated iron catalyst. The results reveal that the catalyst deactivation results from the formation of inactive carbide phases and surface carbonaceous species like graphite, and it will be increased when the particle size of iron oxides was reduced in FTS iron catalyst.     

A comparison of the inclusion behavior of human serum albumin and holo transferrin with fluoxymesterone in the presence of three different cyclodextrins

This article describes the interaction of fluoxymesterone (Flu) with HSA and HTF in the absence and presence of cyclodextrins (CDs) (α, β and γ). According to fluorescence data, the binding of Flu to the proteins caused strong static quenching in the binary and ternary systems. The fluorescence quenching results demonstrated that HSA and HTF had two and one class of apparent binding sites with a distinct binding constant in the presence of the CDs, respectively. The effects of Flu on the structure of HSA and HTF were analyzed using synchronous fluorescence spectroscopy, which showed that the interaction of Flu with both proteins in the binary and ternary systems altered the microenvironment around the Trp and Tyr residues. The distance, r, between Flu and the proteins was obtained according to FRET which pointed at a successful formation of a drug-protein complex. Far-UV CD spectra indicated that the binding of the drug to both proteins induced changes in the secondary structure of HSA and HTF in the binary and ternary systems. Finally, molecular modeling provided possible binding sites of Flu within the proteins for the binary and ternary systems and also confirmed the experimental results. The obtained data can be useful for determining usage drug doses in drug delivery.