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.     

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.     

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     

Expedient one-pot synthesis of N-aryliminoethers via mild electrophilic activation of secondary amides

Abstract  

The direct transformation of various secondary amides into N-aryliminoethers via mild electrophilic activation with trifluoromethanesulfonic anhydride in the presence of 2-chloropyridine is described. Low temperature amide activation followed by warming to 0 °C and subsequent treatment with phenols provides the desired products with short overall reaction times and moderate to high reaction yields.     

Fluorescence Enhancement of Carbendazim Fungicide in Cucurbit[6]uril

The potential increase in fluorescence of a benzimidazole-type fungicide (carbendazim) due to complexation with cucurbit[6]uril is reported. The fluorescence of the probe carbendazim in aqueous Na₂SO₄ solution (pH=7.61) at room temperature is found to increase by a maximum factor of ∼10.0 and blue-shifted up to ∼11±1 nm with the increase in cucurbit[6]uril concentration up to ∼5 mM. This fluorescence enhancement is the result of formation of a 1:1 guest-host inclusion complex, in which the guest carbendazim is incorporated inside the hydrophobic cavity of the host curbit[6]uril through the amido-ester part. Such mode of inclusion is supported by NMR spectral measurements, in which upon encapsulation, the resonance of the methyl-protons of the amido-ester moiety is shifted significantly to upfield in the ¹H NMR spectrum. Also, to assess the formation of inclusion complex, solid samples prepared by co-evaporation have been studied, using differential scanning calorimetry (DSC). Measurement of the enhancement as a function of cucurbit[6]uril concentrations yielded a value of the equilibrium constant (K _a ) of 271±10 M⁻¹ at 25°C. From the temperature dependence of the equilibrium constants, ΔH and ΔS values have been negative in sign, indicating the dipole-dipole interactions and the steric factors associated with the formation of this inclusion complex. It might be proposed that the spectral changes due to the inclusion of carbendazim are the result of decrease in the polarity of the surrounded media rather than the loss of carbendazim rotational mobility.     

Photochromism of dihydroindolizines. Part 16: Tuning of the photophysical behavior of photochromic dihydroindolizines in solution and in polymeric thin film

In this work, photochromic materials based on the dihydroindolizine (DHI) system were synthesized in multistep reactions using chemical and photochemical methods. Some of the synthesized photochromic dihydroindolizine derivatives were substituted on the fluorene (region A) and pyridazine (region C) moieties in order to provide the appropriate functionality for optimal tuning of the photochromic properties of the system. Irradiation of the photochromic DHIs with polychromatic light led to ring opened colored betaines, which underwent thermal 1,5-electrocyclization. The red to green colored betaines produced after UV irradiation returned back through 1,5-electrocyclization to the corresponding DHIs with different rate constants depending on the substituents in both fluorene and pyridazine regions. The kinetic measurements of the thermal 1,5-electrocyclization under different temperatures that ranged from −10 to 25 °C showed that the half-lives of the colored betaines fall in the second to hours domain. Interestingly, these materials showed a very good photochromic behavior not only in solution but also in the PMMA matrix. Irradiation of a slide prepared by the deep-coating method led to the formation of the colored betaine and the kinetics of the thermally reversible 1,5-electrocyclization and the AFM image of the film has been recorded. Indeed, the chemical and thermal stability of the investigated betaines in polymer (PMMA) will render such species useful for a plethora of new of applications.     

Simultaneous determination of preservatives (benzoic acid, sorbic acid, methylparaben and propylparaben) in foodstuffs using high-performance liquid chromatography

A reversed-phased HPLC method that allows the separation and simultaneous determination of the preservatives benzoic (BA) and sorbic acids (SA), methyl- (MP) and propylparabens (PP) is described. The separations were effected by using an initial mobile phase of methanol-acetate buffer (pH 4.4) (35:65) to elute BA, SA and MP and changing the mobile phase composition to methanol-acetate buffer (pH 4.4) (50:50) thereafter. The detector wavelength was set at 254 nm. Under these conditions, separation of the four components was achieved in less than 23 min. Analytical characteristics of the separation such as limit of detection, limit of quantification, linear range and reproducibility were evaluated. The developed method was applied to the determination of 67 foodstuffs (mainly imported), comprising soft drinks, jams, sauces, canned fruits/vegetables, dried vegetables/fruits and others. The range of preservatives found were from not detected (nd)--1260, nd--1390, nd--44.8 and nd--221 mg kg(-1) for BA, SA, MP and PP, respectively.     

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.     

Novel mercury (II) ion-selective polymeric membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate

Mercury (II) ion-selective PVC membrane sensor based on ethyl-2-benzoyl-2-phenylcarbamoyl acetate (EBPCA) as a novel nitrogen containing sensing material is successfully developed. The sensor exhibits good linear response of 30 mV per decade within the concentration range 10(-6)-10(-3) mol l(-1) Hg(II). The sensor shows good selectivity for mercury (II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The EBPCA-based sensor is suitable for use with aqueous solutions of pH 2.0-4.5 and exhibits minimal interference by Ag(I) and Fe(III), which are known to interfere with other previously suggested sensors. The nature and composition of the sensing material and its mercury complex are examined using Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques. The proposed sensor is applied as a sensor for the determination of Hg(II) content in some amalgam alloys. The results show good correlation with data obtained by atomic absorption spectrometric method.