Direct Determination of Pyrethroids in Aqueous Samples by a Metal Organic Framework “MIL-101(Cr)” Sorbent for Solid-Phase Extraction and Thermal Desorption Coupled with GC-FID

Journal of Analytical Chemistry - In this study, an online solid-phase extraction-thermal desorption method coupled with gas chromatography-flame ionization detection was used to extract seven...     

Precursor-Directed Biosynthesis of Aminofulvenes: New Chalanilines from Endophytic Fungus Chalara sp.

The plant endophyte Chalara sp. is able to biotransform the epigenetic modifier vorinostat to form unique, aniline-containing polyketides named chalanilines. Here, we sought to expand the chemical diversity of chalaniline A-type molecules by changing the aniline moiety in the precursor vorinostat. In total, twenty-three different vorinostat analogs were prepared via two-step synthesis, and nineteen were incorporated by the fungus into polyketides. The highest yielding substrates were selected for large-scale precursor-directed biosynthesis and five novel compounds, including two fluorinated chalanilines, were isolated, purified, and structurally characterized. Structure elucidation relied on 1D and 2D NMR techniques and was supported by low- and high-resolution mass spectrometry. All compounds were tested for their bioactivity but were not active in antimicrobial or cell viability assays. Aminofulvene-containing natural products are rare, and this high-yielding, precursor-directed process allows for the diversification of this class of compounds.     

The synthesis of 5-amino-1H-pyrazole-4-carbonitriles by anomeric based oxidative aromatization over [CSPy]ZnCl3 as a new catalyst

Research on Chemical Intermediates - 4-Carboxy-1-sulfopyridin-1-ium monozinc(II) trichloride {[4CSPy]ZnCl3} as a new acidic catalyst was designed and tested on the synthesis of...     

Adsorption properties of OCN radical on (6,0), (8,0), and (10,0) zigzag single-walled carbon nanotubes: a density functional study

Abstract  

The behavior of the OCN radical adsorbed on the external surface of H-capped (6,0), (8,0), and (10,0) zigzag single-walled carbon nanotubes was studied by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 98 suite of programs. We present the nature of the OCN radical–surface interaction in selected sites of the nanotubes. Binding energies corresponding to adsorption of the OCN radical are calculated to be in the range 280–315 kJ mol⁻¹. More efficient binding energies cannot be achieved by increasing the nanotube diameter. We also provide the effects of OCN radical adsorption on the electronic properties of the nanotubes.     

Improving the Performance of Nafion®-Based Fuel Cell Membranes by Introducing Histidine Functionalized Carbon Nanotubes

A new polymer nanocomposite membrane based on Nafion and functionalized carbon nanotubes (CNTs) was developed for proton exchange membrane fuel cell (PEMFC) applications. Histidine, an imidazole-based amino acid, was used for modifying the surface of CNTs. The modification of CNTs was characterized by means of Fourier transform infrared spectroscopy (FTIR) and their Zeta potential. The imidazole groups, due to forming and breaking of hydrogen bonding, can facilitate proton transport across the polymer matrix by the Grotthuss mechanism. The final structure of the Nafion/CNT nanocomposites was investigated by small angle X-ray scattering (SAXS). The results confirm that the transport properties of the fabricated new membranes were significantly improved in comparison with unmodified and conventional Nafion® membranes. The power density of the imidazole-CNT (Im-CNT) Nafion® composite membranes was about three times more than Nafion® membranes. Also, the experimental results showed that the proton conductivity for the conventional Nafion® membranes decreased over 100°C but the conductivity for the Nafion®/Im-CNT remained at a nearly constant value above 100°C up to 120°C. Thus, the nanocomposite based on Nafion/imidazole functionalized CNT can be considered as an anhydrous PEMFC membrane for high-temperature applications.     

Hydrothermal synthesis and physicochemical characterization of CuO/ZnO/Al2O3 nanopowder. Part I: Effect of crystallization time

A hydrothermal method was successfully used for synthesis of CuO/ZnO/Al₂O₃ (CZA) nanopowder with atomic ratio of 6:3:1. The effect of crystallization time (3, 6, 9, and 12 h) on physicochemical properties of nanopowder was investigated. Nanopowders were characterized using XRD, FESEM, EDX, FTIR, TG, and BET techniques. The XRD patterns confirmed metal oxides formation and their good crystallinity with average crystallite size of 20 nm as obtained by the Scherrer equation. Relative crystallinity was shown to increase with increasing crystallization time. In agreement with XRD results, FESEM images also illustrated nanosized particles. EDX mapping indicated homogenous dispersion of elements. BET specific surface area analysis showed acceptable surface area for CZA nanopowder. FTIR spectroscopy confirmed metal oxides formation during hydrothermal and calcination processing. TG results illustrated high thermal stability of the synthesized nanopowders. TG-DTG and FTIR analyses were used to propose a reaction mechanism for nanopowder formation during processing. Physicochemical characterization showed optimal crystallization time to be 6 h.     

Rapid Detection of Antibody in Biological Fluids on a Bioarray Chip

A bioarray chip was developed for the rapid and sensitive detection of the antibody (Ab) in nanoliter volumes of biological fluids. The chip was used to detect the anti-hemagglutinin (anti-HA) Ab from mouse ascites fluids. On the bioarray chip, lanes of antigens (i.e., a 13-amino acid peptide, HA, that is bound by anti-HA Ab) were printed in one dimension on the chip surface. The antigens probed the protein samples (i.e., mouse anti-HA) obtained from biological fluids flowing in channels arranged in the perpendicular dimension. To determine if the detection sensitivity was increased by using different fluorescent labeling methods, two types of labeling reagents were compared, namely AlexaFluor 647-labeled goat anti-mouse Ab (AxIgG), and biotin-labeled anti-mouse Ab (BioIgG) followed by cyanine 5-tagged streptavidin (SA-Cy5). In addition, the assay procedure was shortened by omitting the reduction and blocking steps, while maintaining the sensitivity. In conclusion, a bioarray chip was adopted to detect as low as 10?pM mouse monoclonal antibody (anti-HA) in 500 nL of biological fluids (i.e., corresponding to 5 attomoles of antibody). Our results demonstrate that on-chip detection using this bioarray format is more sensitive and less time-consuming than traditional analyses.     

Catalytic decomposition of Bismarck brown by nanostructured CuS in mild conditions

Two samples of nanostructured CuS were synthesized by two different methods, and were used for degradation of Bismarck Brown, as an azo dye. The first sample consists an assembly of nanosheets, and the second one has prolat-like spheroid structure. It is shown that CuS nanosheets have higher catalytic activity than the second sample for degradation of Bismarck Brown in the presence of H₂O₂. The catalytic activity of the CuS nanosheets was investigated by different variables such as reaction time, solution temperature, volume of H₂O₂, catalyst mass, dye concentration and presence of NaCl. CuS nanosheets have high degradation efficiency under mild conditions and in the dark medium. It was found that the rate of dye degradation by H₂O₂ is fast in the presence of CuS nanosheets, and most of the reactant molecules are degraded within 10?minute. As the main products of dye degradation by the CuS nanosheet, and in presence of H₂O₂ are CO₂ and CO, it is a good catalyst for water purification. Another advantage of this catalyst is its reusability and recyclability, which maintains its stability after several cycles. Finally, the catalytic performance of CuS nanosheets was investigated for degradation of dye mixture (Bismarck Brown and Methyl violet).     

In Vitro Selection of Chromium‐Dependent DNAzymes for Sensing Chromium(III) and Chromium(VI)

Chromium is a very important analyte for environmental monitoring, and developing biosensors for chromium is a long‐standing analytical challenge. In this work, in vitro selection of RNA‐cleaving DNAzymes was carried out in the presence of Cr³⁺. The most active DNAzyme turned out to be the previously reported lanthanide‐dependent Ce13d DNAzyme. Although the Ce13d activity was about 150‐fold lower with Cr³⁺ than that with lanthanides, the activity of lanthanides and other competing metals was masked by using a phosphate buffer; this left Cr³⁺ as the only metal that could activate Ce13d. With 100 μm Cr³⁺, the cleavage rate is 1.6 h^?1 at pH 6. By using a molecular beacon design, Cr³⁺ was measured with a detection limit of 70 nm , which was significantly lower than the United States Environmental Protection Agency (EPA) limit (11 μm ). Cr⁴⁺ was measured after reduction by NaBH₄ to Cr³⁺, and it could be sensed with a similar detection limit of 140 nm Cr⁴⁺; this value was lower than the EPA limit of 300 nm . This sensor was tested for chromium speciation analysis in a real sample, and the results supported its application for environmental monitoring. At the same time, it has enhanced our understanding of the interactions between chromium and DNA.     

An efficient and green synthesis of phthalide-fused pyrazole and pyrimidine derivatives

An efficient and green method for the synthesis of phthalide [isobenzofuran-1(3H)-one] fused pyrazoles via the catalyst-free condensation reaction of 2-formylbenzoic acid, hydrazine hydrate, and acetylenic esters in water is reported. Reaction of 2-formylbenzoic acid with 6-amino-uracils or cyclic 1,3-diketones resulted in the formation of phthalide-fused pyrimidine or cyclic 1,3-diketone derivatives.