Synthesis of a graphene‐based nanocomposite for the dispersive solid‐phase extraction of vancomycin from biological samples

The approach of this work was to study the capability of graphene‐based materials in the field of biological sample preparation. A polypyrrole/graphene composite was synthesized and characterized. The potential of the nanocomposite was investigated as a sorbent in dispersive solid‐phase extraction followed by high‐performance liquid chromatography with UV detection for vancomycin as a model drug. The effect of different parameters influencing extraction efficiency such as sample pH and sample volume, ionic strength, extraction time, type, and volume of desorption solvent and desorption time were investigated. A comparison study was also conducted between polypyrrole/graphene and some different novel and classic sorbents. Under optimized conditions, the calibration curve for vancomycin showed linearity in the range of 0.05–10 μg/mL. In addition, limits of detection, and quantification were 0.003 and 0.01 μg/mL, respectively. The intraday and interday relative standard deviations at a concentration of 0.05 μg/mL (n = 3) were 1.6 and 2.1%, respectively. Furthermore, the proposed method was successfully applied for the determination of vancomycin in plasma and urine samples. The relative recoveries indicated the feasibility of graphene‐based sorbents in biological sample analysis.     

Highly efficient synthesis of dicoumarols and xanthene derivatives in presence of Brønsted–Lewis acidic ionic liquids catalyst

A series of metal chloride-based acidic ionic liquids have been prepared and used as an efficient catalyst in one-pot multicomponent synthesis of biscoumarins and substituted xanthenes derivatives under solvent-free conditions. Among the acidic ionic liquids, N-methylpyrrolidonium zinc chloride (Hnmp/ZnCl₃)-based Brønsted–Lewis acidic ionic liquids were found to be an effective and recyclable catalyst for a one-pot synthesis of biscoumarins through the domino Knoevenagel–Michael reaction of a variety of aldehydes with 4-hydroxycoumarin in short reaction times. The reactions which occur under relatively mild conditions afforded the biscoumarin derivatives employing a very low loading of catalyst in satisfactory isolated yields and high purity after simple work-up. The Brønsted–Lewis acidic ionic liquid catalyst was reused four times without any variation in yield.     

Oligosilanylated Silocanes

A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KO^tBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides. However, the reaction of the 1,1-bis[tris(trimethylsilyl)silylated] silocane with two equivalents of KO^tBu leads to the replacement of one tris(trimethylsilyl)silyl unit with a tert-butoxy substituent followed by silanide formation via KO^tBu attack at one of the SiMe₃ units of remaining tris(trimethylsilyl)silyl group. For none of the silylated silocanes, signs of hypercoordinative interaction between the nitrogen and silicon silocane atoms were detected either in the solid state. by single crystal XRD analysis, nor in solution by ²⁹Si-NMR spectroscopy. This was further confirmed by cyclic voltammetry and a DFT study, which demonstrated that the N-Si distance in silocanes is not only dependent on the energy of a potential N-Si interaction, but also on steric factors and through-space interactions of the neighboring groups at Si and N, imposing the orientation of the p_z(N) orbital relative to the N-Si-X axis.     

Cathodic electrodeposition and characterization of nanostructured Y2O3 from chloride solution Part I: Effect of current density

Nanoparticles, nanospheres and nanorods of Y(OH)₃ and Y₂O₃ were prepared via cathodic electrodeposition from chloride bath through applying different current densities. First, yttrium hydroxide precursors were cathodically grown on the cathode surface at the current densities of 2, 1, 0.5, 0.25 and 0.1 mA cm^?2. Then hydroxide powders were heat-treated at 600°C for 3 h. The composition, crystal structure and morphology of the prepared oxide and hydroxide products were investigated by means of differential scanning calorimetery (DSC), X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM and TEM) and FT-IR spectroscopy. Mechanism of base electrogeneration at the applied conditions, and intercalation of chloride ions in the deposit structure during the electrodeposition were proposed and confirmed by the XRD and TG analyses. The results showed that the structural and morphological properties of the products are directly dictated by the applied current density and it can be recognized as the main factor affecting on the cathodic electrodeposition of Y₂O₃.     

Triphenylphosphine-Catalyzed Simple Synthesis of Dimethyl 1-Aryl-4-ethoxy-5-oxo-4,5-dihydro-1 H -pyrrole-2,3-dicarboxylates

Ethyl 2-arylamino-2-oxo-acetates undergo a complex reaction with dimethyl acetylenedicarboxylate in the presence of triphenylphosphine to produce dimethyl 1-aryl-4-ethoxy-5-oxo-4,5-dihydro-1 H -pyrrole-2,3-dicarboxylates in good yields. Dynamic NMR study of dimethyl 1-(2-methylphenyl)-4-ethoxy-5-oxo-4,5-dihydro-1 H -pyrrole-2,3-dicarboxylate shows a fairly high energy barrier ( j G p = 53.2 kJmol m 1 ) for rotation around the N-aryl single bond, which leads to an observable atropisomerism.     

Preparation of chitosan functionalized end‐capped Ag‐NPs and composited with Fe3O4‐NPs: Controlled release to pH‐responsive delivery of progesterone and antibacterial activity against pseudomonas aeruginosa (PAO‐1)

In this work, functionalized chitosan end‐capped Ag nanoparticles (NPs) and composited with Fe₃O₄‐NPs was prepared as pH‐responsive controlled release carrier for gastric‐specific drug delivery. The structure of prepared material was characterized by FE‐SEM, XRD, EDS and FT‐IR analysis. The loading behavior of the progesterone onto this novel material was studied in aqueous medium at 25°C and their release was followed spectrophotometrically at 37°C in seven different buffer solutions (pH 1.2, 2.2, 3.2, 4.2, 5.2, 6.2 and 7.2) to simulate intestine and gastric media which experimental results reveal more release rate in pH 1.2 (gastric medium) with respect to other buffers. This observation is attributed to dependency of the CS‐IMBDO‐Ag‐Fe₃O₄‐NPs and progesterone structure with buffer pH that candidate this new material as prospective pH‐sensitive carrier for gastric‐targeted drug delivery. On the other hand, the antibacterial properties of this material against gram‐negative bacterium pseudomonas aeruginosa (PAO‐1) in agar plates was studied and accordingly based on broth micro dilution the minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC) with respect to standard CLSI in different concentrations of CS‐IMBDO‐Ag‐Fe₃O₄‐NPs was calculated. The results reveal that MIC and MBC values are 50 and 1250 μg/mL, respectively. In addition, extracts of Portulaca oleracea leaves was prepared and its antibacterial activity in single and binary system with CS‐IMBDO‐Ag‐Fe₃O₄‐NPs as synergies effect against PAO‐1 was tested and results shown that these materials have significant synergistic effect for each other.     

A three-component cyclocondensation reaction for the synthesis of new triazolo[1,5-a]pyrimidine scaffolds using 3-aminotriazole,aldehydes and ketene N,S-acetal

Molecular Diversity - This study describes the use of 3-aminotriazole, different aldehydes and N-methyl-1-(methylthio)-2-nitroethenamine as a ketene N,S-acetal in a three-component condensation for...     

纳米尺度NiLa2O4尖晶石催化NaBH4还原亚胺制仲胺

由溶胶-凝胶法制得的Ni-La化合物经热分解制备了纳米尺度NiLa2O4尖晶石，在750 oC焙烧后形成了结晶良好的尖晶石结构.采用差热分析、X射线衍射、透射电镜、扫描电镜和粒度分布分析等手段表征了该尖晶石的物理化学性质.结果表明，该纳米颗粒有规则的外形和确定的晶面，由平均粒径为40 nm的规整半球晶粒组成.精修的晶胞参数a=3.861205?和c=12.6793?.在NaBH4选择还原亚胺制相应仲胺的反应中，该新型纳米NiLa2O4尖晶石可用作高效多相催化剂，得到了较高的产物产率.所有反应可在室温和相对较短的时间内完成.在优化的反应条件下，均可得到带有不同芳基的，包括带有吸电子和供电子基团的仲胺.该催化剂回收简便，重复使用4次，其催化活性未见明显下降.     

Photometric determination of tetracycline based on surface plasmon resonance of silver nanoparticles

We report on a simple and sensitive method for the determination of tetracycline based on its reducing action on AgNO₃ in alkaline medium containing ammonia and sodium hydroxide at 65°C. As a result of this reaction, silver nanoparticles (AgNPs) are formed. The AgNPs are stabilized in solution by adding poly(vinyl pyrrolidone) as a capping agent. The formed AgNPs were identified by surface plasmon resonance absorption spectrum and transmission electron microscopy image. The plasmon absorption peak at 411 nm is proportional to the concentration of tetracycline. The calibration graph is linear in the concentration range of 0.05–5.0 mg/L with a detection limit of 0.013 mg/L. This method was applied to the determination of tetracycline in pharmaceutical products.