Second-derivative synchronous fluorescence spectroscopy for the simultaneous determination of cinnarizine and nicergoline in pharmaceutical preparations

A rapid, simple, and highly sensitive second-derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixtures of cinnarizine (CN) and nicergoline (NIC). The method is based upon measurement of the native fluorescence of these drugs at constant wavelength difference (Deltalambda) = 80 nm in aqueous methanol (50%, v/v). The different experimental parameters affecting the native fluorescence of the studied drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.025-1.5 and 0.25-5.5 microg/mL for CN and NIC, respectively, with lower detection limits of 0.58 and 0.82 ng/mL and quantitation limits of 1.93 and 2.73 ng/mL for CN and NIC, respectively. The proposed method was successfully applied for the determination of the studied compounds in synthetic mixtures and in commercial tablets. The results obtained were in good agreement with those obtained with reference methods. The high sensitivity attained by the proposed method allowed the determination of CN in real and spiked human plasma. The mean recovery in the case of spiked human plasma [number of trials (n) = 3] was 102.82 +/- 2.17%, while that in real human plasma (n = 3) was 105.25 +/- 2.05.     

Stability-Indicating LC Method for the Determination of Lacidipine in Tablets. Application to Degradation Kinetics and Content Uniformity Testing

A simple, stability-indicating, reversed-phase liquid chromatographic method was developed for the determination of lacidipine in the presence of its degradation products. The analysis was carried out using a 150 mm × 4.6 mm i.d., 5 μm particle size Nucleodur MN-C18 column. Mobile phase containing a mixture of acetonitrile and 0.02 M phosphate buffer (70:30) at pH = 5.0 was pumped at a flow rate of 1 mL min⁻¹ with UV-detection at 254 nm. The method showed good linearity in the range of 0.06–15 μg mL⁻¹ with a limit of detection (S/N = 3) of 0.016 μg mL⁻¹ (3.5 × 10⁻⁸ M). The suggested method was successfully applied for the analysis of lacidipine in bulk and in commercial tablets with average recoveries of 100.19 ± 0.81% and 100.05 ± 0.69%, respectively. The results were favorably compared to those obtained by a reference method. The suggested method was utilized to investigate the kinetics of alkaline, acidic, peroxide and photo-induced degradation of the drug. The apparent first-order rate constant, half-life times and activation energies of the degradation process were calculated. The pH profile curve was derived. The proposed method was successfully applied to the content uniformity testing of tablets.

     

Rapid Estimation of Thermodynamic Parameters and Vapor Pressures of Volatile Materials at Nanoscale

Non‐isothermal measurements of thermodynamic parameters and vapor pressures of low‐volatile materials are favored when time is a crucial factor to be considered, such as in the case of detection of hazardous materials. In this article, we demonstrate that optical absorbance spectroscopy can be used non‐isothermally to estimate the thermodynamic properties and vapor pressures of volatile materials with good accuracy. This is the first method to determine such parameters in nanoscale in just minutes. Trinitrotoluene (TNT) is chosen because of its low melting temperature, which makes it impossible to determine its thermodynamic parameter by other rising‐temperature techniques, such as thermogravimetric analysis (TGA). The well‐characterized vapor pressure of benzoic acid is used to calibrate the spectrometer in order to determine the vapor pressure of low‐volatile TNT. The estimated thermodynamic properties of both benzoic acid and TNT are in excellent agreement with the literature. The estimated vapor pressure of TNT is one order of magnitude larger than that determined isothermally using the same method. However, the values are still within the range reported in the literature. The data indicate the high potential for use of rising‐temperature absorbance spectroscopy in determining vapor pressures of materials at nanometer scale in minutes instead of hours or days.     

Direct palladium/copper oxidative cross-coupling of α-methylstyrene with acrylates

Fully palladium/copper catalytic oxidative cross-coupling of acrylates with α-methylstyrene was performed in a DMSO/AcOH (1:1) mixture at 60 °C in the air. This improves previous procedures which employed stoichiometric amounts of copper and oxygen. Thus various acrylates were effectively coupled to α-methylstyrene giving the expected compounds in moderate to good yields (44%–65%) as a mixture of E and Z isomers.     

Identification of minerals and organic materials in Middle Eocene ironstones from the Bahariya Depression in the Western Desert of Egypt by means of micro‐Raman spectroscopy

The Middle Eocene ironstones of the Bahariya Depression consist of four iron ore types: manganiferous mud‐ironstone, fossiliferous ironstone, stromatolitic ironstone and nummulitic–ooidal–oncoidal ironstone. The upper surfaces of these sequences were subjected to subaerial weathering and a lateritic iron ore type was formed. The chemical composition of these ironstone types was investigated by means of micro‐Raman spectroscopy. Various closely related iron‐containing and manganese‐containing minerals were detected by means of the above‐mentioned approach. The high spatial resolution and sensitivity of this method allowed us to identify minerals that could not be detected by other techniques. Well‐preserved organic materials were observed in one type of ironstones. Therefore, using Raman spectroscopy, we were able to provide evidence that the formation of some of the investigated rocks was biologically mediated. The application of Raman spectroscopy is considered a powerful technique for the identification of both organic and inorganic substances in the studied iron ore deposits. Copyright © 2011 John Wiley & Sons, Ltd.     

Lipid rafts mediate ultraviolet light-induced Fas aggregation in M624 melanoma cells

Ultraviolet light (UV) induces aggregation of Fas-receptor through a Fas-ligand-independent pathway. However, the mechanism of ultraviolet light-induced Fas-receptor aggregation is not known. In this report, we show that lipid rafts mediate ultraviolet light-induced aggregation of Fas. Our data show that UV induces a redistribution of Fas-receptor in a 25-5% Optiprep continuous gradient. The amount of Fas-receptorS is significantly increased in a gradient fraction that contain lipid rafts and is associated with an increase of FADD and caspase-8. Our data also show that the active dimeric form of caspase-8 (p44/p41) is increased in the lipid raft fraction. In addition, our data show that cholesterol, a major component of lipid rafts, is significantly reduced in only the lipid raft fractions after UV-irradiation. However, ceramide, another major lipid raft component, is increased evenly in all gradient fractions after UV-irradiation. These results suggest that UV alters the composition of major lipid raft components, which leads to the recruitment of Fas-receptor and FADD, with subsequent activation of caspase-8. Based on our results, we propose a novel mechanism by which UV induces apoptosis through a membrane lipid raft-mediated signaling pathway.     

Solvent effect on the alkaline hydrolysis of 2‐thiophenyl‐ 3,5‐dinitropyridine

The kinetics of the alkaline hydrolysis of 2‐thiophenyl‐3,5‐dinitropyridine were studied spectrophotometrically in different aquo‐organic solvents such as methanol, ethanol, n‐propyl alcohol, iso‐propyl alcohol, t‐butyl alcohol, acetonitrile, dimethyl sulfoxide, dioxane, and acetone at 30°C with various solvent compositions up to 80% (v/v) of organic components. An increase in the organic solvent percentage (v/v) has different effects on the reaction rate constants presumably due to hydrogen bond donor HBD and acceptor HBA of the medium and other solvatochromic parameters. Linear and nonlinear plots of log k against the reciprocal of the dielectric constant of the solvent were obtained. The effects are too complex to be analyzed in terms of a single parameter, but an approach using the Kamlet–Taft solvatochromic parameters is applied successfully to six mixed aquo‐organic solvent systems. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 159–165, 2006     

Morphology,tensile properties,and fracture toughness of epoxy/Al2O3 nanocomposites

Epoxy/Al₂O₃ nanocomposites were prepared using an epoxy resin, diglycidyl ether of bisphenol A, and cured with a polyoxypropylene diamine (Jeffamine D‐400). Transmission electron microscopy and wide angle X‐ray diffraction were employed to reveal the morphology of epoxy/Al₂O₃ nanocomposites. Dynamic mechanical analysis results showed that the storage modulus and the glass transition temperature (T_g) of epoxy were improved. Tensile strength and Young's modulus also increased with increasing Al₂O₃ loading. Fracture toughness, as indicated by the stress intensity factor, K_Q, was determined using single edge notch bending method, and 40% increase in K_Q was observed with only 2 vol % Al₂O₃. Scanning electron microscopy study of fracture surface showed a rather smooth and flat morphology for neat epoxy. However, massive plastic deformation was observed for epoxy/Al₂O₃ nanocomposites, leading to the significant increase in fracture toughness. The influence of spherical Al₂O₃ nanoparticles on thermophysical properties of epoxy was discussed and compared with that of sheet‐like nanoclays. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1466–1473, 2006