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.     

Ni(II)-Schiff base/SBA-15: a nanostructure and reusable catalyst for one-pot three-component green synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives

Research on Chemical Intermediates - An efficient, rapid, and environmentally benign Ni(II)-Schiff base/SBA-15-catalyzed one-pot three-component cyclocondensation process was described via the...     

Antiinfective properties of ursolic acid-loaded chitosan nanoparticles against Staphylococcus aureus

The present study aimed to synthesize ursolic acid-loaded chitosan nanoparticles (UA-Ch-NPs) as an antiinfective agent against 21 Staphylococcus aureus isolates. The UA-Ch-NPs were synthesized by a simple method and then characterized by TEM, FTIR, DLS-zeta potential, and XRD analyses. According to the characterization results, highly dispersed spherical nanoparticles with a mean diameter of 258 nm and a zeta potential of + 40.1 mV were developed. The antibacterial properties of UA-Ch-NPs were investigated and their inhibitory effect on biofilm formation was demonstrated by AFM. Finally, the expression levels of icaA and icaD were measured using real-time PCR. Results indicated that the minimum inhibitory concentration (MIC) of UA and UA-Ch-NPs against S. aureus was 64 and 32 µg/mL, respectively. The treatment of bacterial cells with UA-Ch-NPs significantly decreased the expression of icaA and icaD genes which are engaged in biofilm formation. Our results indicated that UA-Ch-NPs could be a promising material for antibacterial and antibiofilm applications.     

A novel microwave assisted reverse micelle fabrication route for Th (IV)‐MOFs as highly efficient adsorbent nanostructures with controllable structural properties to CO and CH4 adsorption: Design,and a systematic study

Reducing gas contaminants by affordable and effective adsorbents is a major challenge in the 21^st century. In the present study, thorium metal organic framework (Th‐MOF) nanostructures are introduced as highly efficient adsorbents. These compounds were manufactured via a novel route resulting from the development of microwave assisted reverse micelle (MARM) and ultrasound assisted reverse micelle (UARM) methods. The products were characterized utilizing XRD, SEM, TGA/DSC, BET, and FT‐IR analyses. Based on the results, the samples synthesized by MARM had uniform size distribution, high thermal stability, and significant surface area. Calculations using DFT/B3LYP indicated that the compounds have a tendency to the polymeric form, which could theoretically confirm the formation of Th‐MOF. Results of analysis of variance (ANOVA) showed that synthesis parameters played a critical role in the manufacturing of products with distinctive properties. Response surface methodology (RSM) predicted the possibility of creating Th‐MOF adsorbents with the surface area of 2579 m²/g, which was a considerable value in comparison with the properties of other adsorbents. Adsorption studies showed that, in the optimum conditions, the Th‐MOF products had high adsorption capacity for CO and CH₄. It is believed that the synthesis protocol developed in the present study and the systematic studies conducted on the samples which lead to products with ideal adsorption properties.     

Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber

Melt blending was employed to prepare thermoplastic elastomer (TPE) of reclaimed rubber (RR) and high density polyethylene (HDPE). Mechanical properties of TPE samples were improved in different methods including dynamic vulcanization and reactive blending (reactive compatibilization) during melt mixing in an internal Haake mixer. The physical and mechanical properties of the TPE blends were investigated by the dynamic mechanical analysis (DMA) and tensile tests. The thermal behavior was characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The phase morphology of the blends was studied by scanning electron microscopy (SEM). Experimental results showed that, both static and dynamic mechanical properties of reactively-compatibilized and dynamically-vulcanized samples improved significantly compared with the virgin samples. The effect of dynamic-vulcanization and reactivecompatibilization on the mechanical properties revealed that the Young’s modulus and storage modulus increased with both improvement methods. SEM results showed that, dynamic-vulcanization and reactivecompatibilization methods improved the distribution of RR particles in HDPE matrix. Although both methods improved the thermal and mechanical properties of the HDPE/RR blends, dynamic-vulcanization was more effective and promising approach due to the higher properties of HDPE/RR blends prepared by this method.     

Recent approaches to the synthesis of thieno[2,3-b]pyridines (microreview)

Chemistry of Heterocyclic Compounds - This microreview describes recent approaches to the synthesis of thieno[2,3-b]pyridine derivatives. Selected works published in 2015–2019 are reviewed.     

Critical point approaches to Gradient-Type systems on the Sierpi\'{n}ski Gasket

We investigate the existence of multiple solutions for parametric quasi-linear systems of the gradient-type on the Sierpi\''{n}ski gasket. We give some new criteria to guarantee that the systems have at least three weak solutions by using a variational method and some critical points theorems due to Ricceri. We extend and improve some recent results. Finally, we give two examples to illustrate the main results.     

Existence of three weak solutions for a perturbed anisotropic discrete Dirichlet problem

In this paper, we study the existence of at least three distinct solutions for a perturbed anisotropic discrete Dirichlet problem. Our approach is based on recent variational methods for smooth functionals defined on reflexive Banach spaces. Some examples are presented to demonstrate the application of our main results.     

Bi(NO3)3 · 5H2O mediated synthesis of 4,4′-diaminotriarylmethane leuco malachite compounds under solvent-free conditions

In this report, we described the synthesis and characterization of a variety of diaminotriarylmethane derivatives with dimethylamino functional groups. These compounds were synthesized by the tandem regio-selective electrophilic aromatic substitution reaction of N,N-dimethylaniline with aryl aldehydes to form the corresponding diaminotriarylmethane compounds. In our strategy, Bi(NO₃)₃ was used as a catalyst under solvent free conditions to afford the desired products in good to excellent yields.      

Proteomic analysis of a spring wheat cultivar in response to prolonged cold stress

Cold represents one of the major abiotic factors influencing plant growth and development worldwide. We analysed the long-term responsiveness of an Iranian spring wheat (cv. Kohdasht) to cold from a proteomic point of view, in order to unravel the molecular mechanisms helping a cold-sensitive cultivar to survive exposure to suboptimal temperatures. Plants were grown at 20 or 4°C until entering the reproductive stage and a cross-comparison on the leaf proteomes was performed. Quantitative analyses on protein alterations occurring upon low-temperature exposure showed a reinforcement in ascorbate recycling (dehydroascorbate reductase, ascorbate peroxidase) and protein processing (proteasome subunit, cysteine proteinase), as well as the accumulation of the enzyme devoted to tetrapyrrole resynthesis (glutamate semialdehyde aminomutase). In contrast, among proteins down-regulated after cold stress, we could identify some key Krebs cycle enzymes (isocitrate dehydrogenase, malate dehydrogenase), together with many photosynthesis-related proteins (oxygen-evolving complex proteins, ATP synthase subunits, ferredoxin NADPH oxidoreductase and some Calvin cycle enzymes). Physiological and biochemical parameters (such as shoot apex dissection, chlorophyll, proline and sugar content determination) sustained proteomics findings allowing the present research to contribute to the current knowledge on these long-term responses, which may be crucial to stress adaptation under field conditions.