Selective Densitometric Analysis of Cephalosporins Using Dragendorff’s Reagent

A simple, selective, precise, and stability-indicating thin-layer chromatographic method has been developed and validated for analysis of the cephalosporins cefpodoxime proxetil, ceftriaxone sodium, ceftazidime pentahydrate, cefotaxime sodium, cefoperazone sodium, cefazolin sodium, and cefixime in the bulk drug and in pharmaceutical formulations. TLC was performed on aluminium sheets precoated with silica gel G 60F₂₅₄ as stationary phase. The mobile phases chosen for development gave compact spots for all the drugs (R _F values 0.43–0.60). The separated compounds were visualized as orange spots by spraying with Dragendorff’s reagent. Linear regression analysis data for the calibration plots revealed good linear relationships between response and amounts of the drugs with correlation coefficients ranging from 0.9977 to 0.9998 and determination coefficients ranging from 0.9954 to 0.9996 over the concentration ranges 5–25 μg per spot for cefpodoxime proxetil, ceftriaxone sodium, and ceftazidime pentahydrate and 10–50 μg per spot for cefotaxime sodium, cefoperazone sodium, cefazolin sodium, and cefixime. The method was validated for precision, recovery, and robustness. Limits of detection and quantitation for the drugs ranged from 0.35 to 2.48 and from 1.07 to 7.50 μg per spot, respectively. The method was successfully applied to analysis of the drugs in their pharmaceutical dosage forms with good precision and accuracy. The method can also be used as a stability-indicating assay.     

Structural and selectivity of 18-crown-6 ligand in lanthanide-picrate complexes

The selectivity factor in the separation of lanthanide could be associated with the coordination behaviour. Thus, we observed the study in the solid phase to understand the coordination pattern of Ln(III) with the 18-crown-6 (18C6) ligand. Good selectivity of the rigid 18C6 ligand toward Ln(III) depends on gradually smaller their ionic radii of Ln(III) in the complexes formation in the presence of picrate anion (Pic⁻), i.e. lanthanide contraction and steric effects as clearly shown in the series of [Ln(Pic)₂(18C6)]⁺(Pic)⁻ {Ln = La, Ce, Pr, Nd, Sm, Gd} and [Ln(Pic)₃(OH₂)₃] · 2(18C6) · 4H₂O {Ln = Tb, Ho} complexes. The La-Gd complexes crystallized in an orthorhombic with space group Pbca, while the Ho complex crystallized in triclinic with space group . The lighter lanthanides complexes [La-Sm] had a 10-coordination number from the 18C6 ligand and the two picrates, forming a bicapped square-antiprismatic geometry. Meanwhile, the middle lanthanide complex [Gd] had a nine-coordination number from the 18C6 ligand and the two picrates, forming a tricapped trigonal prismatic geometry. The heavier lanthanide [Ho] is rather unique, since Ho(III) coordinated with nine oxygen atoms from three picrates and three water molecules in the opposite direction whereas three 18C6 molecules surrounded in the inner coordination sphere, forming a trigonal tricapped prismatic geometry. The 18C6 ligand is effective in controlling the molecular geometry and coordination bonding of Ln-O and can use a crystal engineering approach. No dissociation of Ln-O bonds in solution was observed in NMR studies conducted at different temperatures. The photoluminescence spectrum of the Pr complex has typical 4f-4f emission transitions, i.e. ³P₀ → ³F₂ (650 nm), ¹D₂ → ³F₂ (830 nm) and ¹D₂ → ³F₄ (950 nm).     

Design of LMI‐based sliding mode controller with an exponential policy for a class of underactuated systems

In this article, a novel sliding mode control (SMC) approach is proposed for the control of a class of underactuated systems which are featured as in cascaded form with external disturbances. The asymptotic stability conditions on the error dynamical system are expressed in the form of linear matrix inequalities. The control objective is to construct a controller such that would force the state trajectories to approach the sliding surface with an exponential policy. The proposed SMC has a simple structure because it is derived from the associated first‐order differential equation and is capable of handling system disturbances and nonlinearities. The effectiveness of the proposed control method is validated using intensive simulations. © 2014 Wiley Periodicals, Inc. Complexity 21: 117–124, 2016     

Immobilization of Horseradish Peroxidase on Nonwoven Polyester Fabric Coated with Chitosan

The immobilization of horseradish peroxidase (HRP) on composite membrane has been investigated. This membrane was prepared by coating nonwoven polyester fabric with chitosan glutamate in the presence of glutraldehyde as a crosslinking agent. The physico-chemical properties of soluble and immobilized HRP were evaluated. The soluble HRP lost 90% of its activity after 4 weeks of storage at 4°C, whereas the immobilized enzyme retained 85% of its original activity at the same time. A reusability study of immobilized HRP showed that the enzyme retained 54% of its activity after 10 cycles of reuse. Soluble and immobilized HRP showed the same pH optima at pH 5.5. The immobilized enzyme had significant stability at different pH values, where it had maximum stability at pH 3.0 and 6.0. The kinetic properties indicated that the immobilized enzyme had more affinity toward substrates than soluble enzyme. The soluble and immobilized enzymes had temperature optima at 30 and 40°C and were stable up to 40 and 50°C, respectively. The stability of HRP against metal ion inactivation was improved after immobilization. Immobilized HRP exhibited high resistance to proteolysis by trypsin. The immobilized HRP was more resistant to inactivation induced by urea, Triton X-100, and organic solvents compared to its soluble counterpart. The immobilized HRP showed very high yield of immobilization and markedly high stabilization against several forms of denaturants that offer potential for several applications.     

Thermal properties of biostimulant-infused potato fibers

Crushing or otherwise processing potato and subsequent mild washing of the pulp produces mostly granular and fibrous starch. These fibers are experimental carrier material for microbes in bioremediation of polluted waters. This method offers the benefit of increasing the exposure of the microbes to the pollutant by increasing their residency within the site. Because of the physical nature of the material, it also offers the possibility of carrying, in addition to the microbes, essential macronutrients such as nitrogen and phosphorous that would be limited in availability in contaminated waters. We have previously reported on the physical nature of these fibers through thermal analysis and on their ability to bind/aggregate bacteria. We have extended that study in this report by infusing the fibers with a source of nitrogen and phosphorous, namely ammonium phosphate. The TG curves for ammonium phosphate-infused white and sweet potato fibers exhibited three main mass loss steps corresponding to the three exothermic DTG peaks. Infusion with the ammonium phosphate salt also affected the bacterial binding/aggregation capacities. The range of their binding capacities decreased to a range of 26.9–43.3% compared to untreated fibers.     

Exact solutions for nonlinear partial fractional differential equations

In this article,we use the fractional complex transformation to convert nonlinear partial fractional differential equations to nonlinear ordinary differential equations.We use the improved(G’/G)-expansion function method to calculate the exact solutions to the time-and space-fractional derivative foam drainage equation and the time-and space-fractional derivative nonlinear KdV equation.This method is efficient and powerful for solving wide classes of nonlinear evolution fractional order equations.     

Probe functionalization with a Rhop-3 antibody: toward a Rhop-3 antigen immunosensor for detection of malaria

The antibody specific for the malaria protein, Rhop-3, and FL-Rhop-3, were immobilized on the surface of a gold electrode modified with cysteamine. Colloidal gold was used to enhance the detection signal for Rhop-3 antigens. The Rhop-3 antibody was also immobilized on gold electrodes preactivated with dithiobis(succinimidyl proprionate) (DSP). Immobilization was performed at room temperature and at 37 °C. Cyclic voltammetry (CV) was used to monitor the interaction between the immobilized antibody and its cognate antigen in solution, using ferricyanide, K₃Fe(CN)₆, as reporting electroactive probe. Tests indicate recognition of Rhop-3 protein by the immobilized antibody. Antigen recognition was enhanced by incubation at 37 °C compared with room-temperature incubation. Our results suggest that an immunosensor can be developed and optimized to aid detection of Rhop-3 antigens in samples from malaria patients. As far as we are aware, this is the first amperometric immunosensor targeting Rhop-3 antigen as a malaria biomarker.     

Synthesis and anti‐HIV activity of new 2‐thiolumazine and 2‐thiouracil metal complexes

A series of new Cu(II), Pt(II), VO(II), Fe(II), and Co(II) complexes ( 1‐‐5 ) with 3‐methyl‐6,7‐diphenyllumazine are described. Similarly, complexes from 2‐thiouracil with Cu(II) ( 6,7 ) and Pt(II) ( 8 ) have been prepared and characterized by spectroscopic methods. All the complexes were assayed for their anti‐HIV‐1 and HIV‐2 activity by examination of their inhibition of HIV‐induced cytopathogenicity in MT‐4 cells. Compound 3 was found to be the most active inhibitor against HIV‐2 in cell culture (EC₅₀ = >18.9 μ g/mL, selectivity index (SI) = 3), which provided a good lead for further optimization. Compounds 6 and 7 exhibited some activity (EC₅₀ = >7.12 μ g/mL and >2.23 μ g/mL) against HIV‐1 and HIV‐2, but no selectivity was observed (SI <1). © 2010 Wiley Periodicals, Inc. Heteroatom Chem 22:44–50, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20654     

Computational study on the reaction mechanism of the gas-phase atom-negative ion of S?+?NO2 ?: comparative study of mechanism with S?+?O3 reaction as isoelectronic and isostructure systems

The reaction mechanism of sulfur vapor (S) with nitrite ion (NO₂ ⁻) has been investigated theoretically on the triplet and singlet potential energy surfaces (PESs). All stationary points for the title reaction have been optimized at the B3LYP/6-311+G(3df) level. The energetic data have been obtained at the CCSD(T)//B3LYP level employing the 6-311+G(3df) basis set. Five stable collision complexes, ³IN1 (S–ONO⁻), ³IN2 (cyclic SONO⁻), ¹IN1 (cis S–ONO⁻), ¹IN2 (S–NO₂ ⁻), and ¹IN3 (trans S–ONO⁻), have been considered on the triplet and singlet PESs through barrier-less and exothermic processes. By starting from these complexes, a simple mechanism has been obtained on the triplet PES while a complex mechanism has been considered on the singlet PES. The calculated results show that there are no favorable paths for the reaction of S with NO₂ ⁻ on the singlet PES. Therefore, the S + NO₂ ⁻ reaction proceeds only on the triplet PES to produce ³SO + ³NO⁻ as main products. The results from the comparative study of S + NO₂ ⁻ reaction mechanism with S + O₃ (as isoelectronic and isostructure reactions) on the singlet PES show similarities in the overall trend of reaction mechanism and atom connectivity and differences in the stability of intermediates and the energy barriers of transition states.