Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography

A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r² = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples.     

Effect of metal type on the metallocene-catalyzed oligomerization of 1-hexene and 1-octene to produce polyα-olefin-based synthetic lubricants

1-Hexene and 1-octene oligomerization reactions were performed with Cp₂ZrCl₂ and Cp₂HfCl₂ in the presence of methylaluminoxane as cocatalyst at 25 and 80 °C to produce polyα-olefin-type oils. By examining the molecular weight results, obtained from gel permeation chromatography, the oligomeric structure of the products was confirmed. Hafnocene produced oligomers with higher molecular weights in comparison with zirconocene under the same reaction condition. In addition, with increasing temperature, the molecular weight decreased. Differential scanning calorimetry analysis of the poly1-hexene- and poly1-octene-type oligomers confirmed their amorphous nature. ¹H-nuclear magnetic resonance (NMR) analysis was performed to study the mechanism of termination reactions. The results obtained from the ¹H-NMR analysis confirmed the vinylidine form (vd) as the only unsaturated structure in all synthesized oligomers. Therefore, in the 1-hexene and 1-octene oligomerization reactions with these two catalytic systems, the chain termination is totally accomplished by β-hydride elimination at both reaction temperatures.     

A novel CuFe2O4@Ag nanocomposite biosynthesized by Spirulina platensis exhibits an anticancer effect on human gastric adenocarcinoma and Michigan Cancer Foundation-7 breast cancer cell lines

In recent years, the increasing cancer incidence and mortality rate has posed a significant challenge to scientists to develop novel therapeutic drugs against cancerous cells. One of the investigated techniques for cancer therapeutics is the green synthesis of nanoparticles (NPs). In this study, we reported the green synthesis and characterization of the CuFe₂O₄@Ag nanocomposite using Spirulina platensis and its cytotoxic activity on two cancer cell lines: human gastric adenocarcinoma (AGS) and Michigan Cancer Foundation-7 (MCF-7) breast cancer. The physical and chemical properties of the biosynthesized nanocomposite were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, energy-dispersive X-ray analysis, dynamic light scattering, ultraviolet–visible spectroscopy, scanning electron microscopy, transmission electron microscopy, and zeta potential analyses. The anticancer properties of the CuFe₂O₄@Ag nanocomposite and imatinib drug on both cancer cell lines were evaluated using 3-(4,5-dimethylthiazoyl-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay. Also, apoptosis induced by the nanocomposite was assessed using annexin V/propidium iodide staining followed by flow cytometry analysis, Hoechst 33432 staining, and caspase-3 activity assay. Finally, the effect of the CuFe₂O₄@Ag nanocomposite on the expression of BAX and BCL2 genes was assessed by real-time polymerase chain reaction. The result of the MTT test showed an increase in the cellular uptake of CuFe₂O₄@Ag nanocomposite and cell viability loss in a concentration-dependent manner with the 50% minimum inhibitory concentration (IC₅₀) of 180 and 220 μg/ml for MCF-7 and AGS cell lines, respectively. The mean expression of BAX was significantly higher than that of BCL2 in cells treated with the nanocomposite. The results of flow cytometry, Hoechst 33432 staining, and caspase-3 activity assay indicated the stimulation of apoptosis through an increase in caspase-3 and nucleus fragmentation. In general, our results demonstrated the cytotoxic activity of the CuFe₂O₄@Ag nanocomposite. However, further in vivo studies are required to evaluate the accumulation of this nanocomposite in organs such as liver, kidneys, brain, and testes and its potential toxic effects.     

Nonlinear Oscillations of Viscoelastic Rectangular Plates

Nonlinear oscillations of viscoelastic simply supported rectangular plates are studied by assuming the Voigt–Kelvin constitutive model. Using Hamilton's principle in conjunction with the kinematics associated with Kirchhoff's plate model, the governing equations of motion including the effect of damping are represented in terms of the transversal deflection and a stress function. Utilizing the Bubnov–Galerkin method, the nonlinear partial differential equations are reduced to an ordinary differential equation which is studied geometrically by approximate construction of the Poincaré maps. Explicit expressions are given for periodic solutions.     

Integrating cognitive mapping and MCDA for bankruptcy prediction in small- and medium-sized enterprises

The 2008 global financial crisis and its aftermath have shown the ability to predict bankruptcy to be a vital management skill and that the methodologies used for that purpose should be as close to reality as possible. This study aims to develop a multiple criteria system to predict bankruptcy in small- and medium-sized enterprises (SMEs). It combines cognitive mapping with the measuring attractiveness by a categorical based evaluation technique (MACBETH), resulting in a more complete and transparent process for evaluating SMEs and their risk of bankruptcy. What differentiates this framework is the fact that it is based on information obtained directly from managers and bank analysts who deal with this type of adversity on a daily basis. The results highlight the importance of financial and strategic aspects, among others, and demonstrate how cognitive mapping can improve the understanding of the decision situation at hand, while MACBETH facilitates the calculation of trade-offs among evaluation criteria.     

Periodicity and chaos in a flexible crank-rocker mechanism

In this paper we introduce a crank-rocker mechanism at which the rocker is flexible. Using Hamilton’s principle we obtain the governing equations of motion for the elastic mode of the rocker. By applying the Bubnov–Galerkin global averaging method, we reduce the governing equations of motion to an ordinary differential equation which is Duffing’s oscillator with time varying coefficients. Through the application of Banach’s fixed-point theorem we predict the periodic solutions. Then we study the geometrical features of the motion near the 1 : 1, 1 : 2 and 2 : 1 commensurabilities. It is also shown that homoclinic and heteroclinic orbits can exist for the system.     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.