A simple,rapid and sensitive method based on modified multiwalled carbon nanotube for preconcentration and determination of lead ions in aqueous media in natural pHs

In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL^?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples.     

Solvent selection in ultrasonic-assisted emulsification microextraction: Comparison between high- and low-density solvents by means of novel type of extraction vessel

There are numerous published reports about dispersive liquid phase microextraction of the wide range of substances, however, till now no broadly accepted systematic and purpose oriented selection of extraction solvent has been proposed. Most works deal with the optimization of available solvents without adequate pre-consideration of properness. In this study, it is tried to compare the performances of low- and high-density solvents at the same conditions by means of novel type of extraction vessel with head and bottom conical shape. Extraction efficiencies of seven basic pharmaceutical compounds using eighteen common organic solvents were studied in this work. It was much easier to work with high-density solvents and they mostly showed better performances. This work shows that although exact predicting the performance of the solvents is multifaceted case but the pre-consideration of initial selection of solvents with attention to the physiochemical properties of the desired analytes is feasible and promising. Finally, the practicality of the method for extraction from urine and plasma samples was investigated.     

Computational Study on the Structural and Electronic Properties of Multi-Nuclear Palladium and Nickel Silyl Complexes via DFT and QTAIM Approaches

In this research, we have concentrated on the survey of ability of density functional methods and also modern semi-empirical approaches to reproduce the crystal structure of a binuclear silyl nickel complex and a trinuclear palladium silyl complex. In the structural analysis of the aforesaid nickel and palladium complexes, we have also interested to investigate the possibility of Si-Si bond formation between SiH₂ and μ-SiH moieties from the structural and electronic viewpoints. Comparison of our calculated structural parameters of aforementioned complexes with the available X-ray crystallographical data reveals that both functionals (B3LYP and M062X) can well reproduce X-ray structure of the complex with a near accuracy while the PM6-D2 semi-empirical calculated values are not in a reliable agreement with the crystallographical data. In the next step, we assessed the nature of interactions between palladium and nickel metal ions with silyl ligands via Quantum Theory of Atoms in Molecule (QTAIM) computations. Furthermore, we have analyzed the possibility of Si-Si bond formation in the aforementioned complexes by means of topological electronic indices. Strictly speaking, QTAIM calculations have been performed to explore the electronic density, its laplacian and electronic energy density at some key bond critical points to interpret the structural features of aforesaid complexes from the electronic point of view.     

Isocyanide-based four-component synthesis of ferrocenyl 1,5-disubstituted tetrazoles

A convenient four-component synthesis of ferrocenyl tetrazoles by the reaction of ferrocenecarboxaldehyde, isocyanides, azidotrimethylsilane and alkyl or aryl amines in CH₂Cl₂ at room temperature is reported.     

Atom-economical isocyanide-based multicomponent synthesis of 2,5-dioxopyrrolidines,spirobenzothiazinechromans and 1,5-benzothiazepines

An efficient synthesis of new pharmaceutically relevant dioxopyrrolidines, spirobenzo thiazine-2,3′-chromans, and benzothiazepines via isocyanide-based multicomponent condensation reactions at room temperature is reported. This synthesis serves as a nice addition to group-assistant-purification (GAP) chemistry in which purification via chromatography and recrystallization can be avoided, and the pure products are obtained simply by washing the crude products with 95% ethanol.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.