A needle trap device packed with MIL-100(Fe) metal organic frameworks for efficient headspace sampling and analysis of urinary BTEXs

The aim of this study was to develop a new method for the determination of benzene, toluene, ethylbenzene and xylene isomers (BTEXs) in urine samples. In this method, MIL-100(Fe)@Fe₃O₄@SiO₂ metal–organic framework was synthesized, characterized and packed inside a needle trap device (NTD) as a sorbent for headspace extraction of unmetabolized BTEXs from urine samples followed by gas chromatography (GC) analysis. The GC device was equipped with a flame ionization detector (FID). The results showed that the optimal extraction time, extraction temperature and salt content were 60 min, 30°C and 5%, respectively. Also, the optimal desorption time and temperature were determined to be 1 min and 250°C, respectively. The limits of detection and quantification of the analytes of interest were in the ranges 0.0001–0.0005 and 0.0003–0.0014 μg ml⁻¹, respectively. The intra- and inter-day repeatability were <7.6%. The accuracy of the measurements in urine samples was in the range 7.1–11.4%. The results also demonstrated that the proposed NTD offered various advantages such as having high sensitivity and being inexpensive, reusable, user friendly, environmentally friendly and compatible for use with the GC device. Therefore, it can be efficiently used as a MIL–NTD for the extraction and analysis of unmetabolized BTEXs from urine samples.     

Preparation,characterization and catalytic application of molybdenum Schiff‐base complex immobilized on silica‐coated Fe3O4 as a reusable catalyst for the synthesis of pyranopyrazole derivatives

A recoverable molybdenum Schiff‐base complex immobilized on silica‐coated Fe₃O₄ nanoparticles was prepared and characterized. This superparamagntic nanocatalyst, which is separable using an external magnet, can be used as an efficient catalyst for the promotion of the synthesis of pyranopyrazole derivatives. A variety of desired products were obtained in high to excellent yields within short times. In comparison with other catalysts employed in the condensation of various aromatic aldehydes, malononitrile and 3‐methyl‐1‐phenyl‐2‐ pyrazoline‐5‐one, the present catalyst showed a much higher activity in terms of mild conditions and short reaction time. The catalyst can be reused for several times without significant loss of activity.     

A new computational method for solving two‐dimensional Stratonovich Volterra integral equation

This paper presents a method for computing numerical solutions of two‐dimensional Stratonovich Volterra integral equations using one‐dimensional modification of hat functions and two‐dimensional modification of hat functions. The problem is transformed to a linear system of algebraic equations using the operational matrix associated with one‐dimensional modification of hat functions and two‐dimensional modification of hat functions. The error analysis of the method is given. The method is computationally attractive, and applications are demonstrated by a numerical example. Copyright © 2017 John Wiley & Sons, Ltd.     

Comparison of volatile constituents, and antioxidant and antibacterial activities of the essential oils of Thymus caucasicus, T. kotschyanus and T. vulgaris

A comparison of the chemical composition, and antioxidant and antibacterial activities of the essential oils obtained from the aerial parts of Thymus caucasicus, T. kotschyanus, and T vulgaris was carried out. The oils, obtained by hydrodistillation, were analyzed by GC and GC/MS. Twenty, 29 and 22 compounds representing 94.8%, 96.6% and 98.2% of the essential oils of T. caucasicus, T. kotschyanus and T. vulgaris, respectively, have been identified. The oil of T. caucasicus was characterized by 1,8-cineol (21.5%), thymol (12.6%), beta-fenchyl alcohol (8.7%), nerolidol (7.8%), terpinolene (7.2%), alpha-pinene (7.0%) and myrcene (6.8%). In the oil of T. kotschyanus, carvacrol (24.4%), beta-caryophyllene (14.5%), gamma-terpinene (12.4%), alpha-phellandrene (10.8%), p-cymene (9.8%) and thymol (6.8%) were the predominant compounds, whereas the main components of T. vulgaris oil were thymol (43.8%), p-cymene (15.2%), germacrene-D (11.7%), terpinolene (3.4%), carvacrol (3.2%), beta-caryophyllene (2.8%) and alpha-thujene (2.2%). In all three plants oil, hydrocarbon monoterpenes predominated over sesquiterpenes. Antioxidant activities were assessed by determining IC50 values in the DPPH radical scavenging assay. Antibacterial activity was determined by measuring minimum inhibitory concentration (MIC) using the broth dilution method. The essential oils of T. caucasicus, T. kotschyanus and T. vulgaris showed free radical scavenging and antibacterial activity.     

Development of a needle trap device packed with titanium‐based metal‐organic framework sorbent for extraction of phenolic derivatives in air

We developed a novel method of needle trap device packed with titanium‐based metal‐organic framework for the extraction of phenolic derivatives in air followed by gas chromatography‐flame ionization detector analysis. The synthetized adsorbent was packed inside a 22‐gauge spinal needle. This method was first tested at laboratory scale, and then was used for field sampling of phenolic derivatives in air. A glass chamber placed on a heater at 60°C was used to provide different concentrations of phenolic derivatives. The desorption conditions and breakthrough volume were optimized using response surface methodology. The limit of detection and limit of quantitation of the proposed method were estimated to be in the range of 0.001–0.12 and 0.003–0.62 ng/mL, respectively, indicating a high sensitivity for the suggested sampler. Storing the packed needle trap device in a refrigerator at 4?C for 60 days did not dramatically affect the storage stability. Our findings indicated that there was a high correlation coefficient (R² = 0.99) between the measurement results of this method and the NIOSH recommended method (XAD‐7 sorbent tube). Therefore, it can be concluded that the needle trap device packed with titanium‐based metal‐organic framework can be used as a efficient method for extraction of phenolic derivatives in air.     

Boron nitride nanocluster as a carrier for lomustine anticancer drug delivery: DFT and thermodynamics studies

Monatshefte für Chemie - Chemical Monthly - Previous reports were shown that boron nitride nanostructures can be biocompatible and nontoxic. Therefore, interaction of lomustine as an...     

Structural Relationships and Theoretical Study of Electron Transfer Properties of 1,3,2-Dithiazolyl Radicals with Fullerenes in Nanostructure [1,3,2-DTA(s)]@Cn Supramolecular Complexes

Various empty carbon fullerenes with different carbon atoms have been obtained and investigated. The dithiazolyl radicals have shown important electron-transfer properties. Topological indices are digital values that are assigned based on chemical composition. These values are purported to correlate chemical structures with various chemical and physical properties. They have been successfully used to construct effective and useful mathematical methods to establish clear relationships between structural data and the physical properties of these materials. In this study, the number of carbon atoms in the fullerenes was used as an index to establish a relationship between the structures of 2,3-naphthalene-1,3,2-dithiazolyl (NDTA), 2,3-quinoxaline-1,3,2-dithiazolyl (QDTA), and 1,2,5-thiazolo[3,4-b]-1,3,2-dithiazolo[3,4-b]pyridazin-2-yl (TDP-DTA), radicals, 1–3 as molecular conductor radicals and fullerenes C_n (n = 60, 70, 76, 82, and 86), which create [1,3,2-DTA(s)]@C_n, A-1 to A-5 (NDTA]@C_n), B-1 to B-5 ([QDTA]@C_n), and C-1 to C-5 ([TDP-DTA]@C_n). The relationship between the number of carbon atoms and the free energies of electron transfer (ΔG_et(1) to ΔG_et(4) ) are assessed using the Rehm–Weller equation for A-1 to A-5, B1 to B-5, and C-1 to C-5 supramolecular [1,3,2-DTA(s)]@C_n complexes. Calculations are presented for the four reduction potentials ( ^Red.E₁ to ^Red.E₄ ) of fullerenes C_n . The results were used to calculate the four free energies of electron transfer (ΔG_et(1) to ΔG_et(4) ) of supramolecular complexes A-1 to A-18, B-1 to B-18, and C-1 to C-18 (5–60) for fullerenes C₆₀ to C₃₀₀.     

A needle trap device packed with a sol–gel derived,multi-walled carbon nanotubes/silica composite for sampling and analysis of volatile organohalogen compounds in air

A needle trap device (NTD) packed with silica composite of multi-walled carbon nanotubes (MWCNTs) prepared based on sol–gel technique was utilized for sampling and analysis of volatile organohalogen compounds (HVOCs) in air. The performance of the NTD packed with MWCNTs/silica composite as sorbent was examined in a variety of sampling conditions and was compared with NTDs packed with PDMS as well as SPME with Carboxen/PDMS-coated fibers. The limit of detection of NTDs for the GC/MS detection system was 0.01–0.05 ng mL⁻¹ and the limit of quantitation was 0.04–0.18 ng mL⁻¹. The RSD were 1.1–7.8% for intra-NTD comparison intended for repeatability of technique. The NTD-MWCNTs/silica composite showed better analytical performances compared to the NTD-PDMS composite and had the same analytical performances when compared to the SPME-Carboxen/PDMS fibers. The results show that NTD-MWCNTs-GC/MS is a powerful technique for active sampling of occupational/environmental pollutants in air.     

The Willgerodt-Kindler Reaction in Water: High Chemoselectivity of Benzaldehydes over Acetophenones

Water has been found for the first time as a useful solvent in the Willgerodt-Kindler (WK) reaction for the synthesis of benzothiomorpholides in high yield at 80°C for 3 h. This novel approach confronts the WK protocol with a new situation in which water not only is not regarded as a serious disadvantage but also is applied in this case as a useful solvent in the reaction. The basis of this finding is the presence of a methylene chain in the carbonyl substrates, which leads to the high reaction selectivity of benzaldehydes over acetophenones.