Liquid-liquid extraction of palladium(II) from hydrobromic acid media by hexadecylpyridinium bromide.

A simple and rapid liquid-liquid extraction of palladium has been studied involving ion-pairing of bromocomplexes of palladium(II) with hexadecylpyridinium bromide (HDPB) dissolved in chloroform. The stoichiometry and distribution of (HDP)2PdBr4 between the aqueous and organic phase was investigated by spectrophotometric mole ratio method. The extraction efficiency of palladium(II) by HDPB was studied as a function of several variables: acid, salt, surfactant concentration and equilibrium time. The results showed that PdBr4(2-) extraction could be explained by assuming the formation of (HDP)2PdBr4 complexes in the aqueous solution and transfer to organic phase. The extraction was fast and the shaking time was only a few min. The average recovery of palladium(II) from an aqueous solution containing 10 microg/ml of analyte was 99% with an RSD% of 0.95. The percentage recovery of 0.2 microg/ml palladium(II) was 96%.     

Magnetic Solid Phase Extraction Coupled with HPLC Towards Removal of Pigments and Impurities from Leaf-derived Paclitaxel Extractions of Taxus baccata and Optimization via Response Surface Methodology

A reusable and cost-effective magnetic graphite oxide (Fe₃O₄NPs@GO) nanocomposite was fabricated and applied for pre-purification of paclitaxel from leaf-derived crude extract of Taxus baccata. Furthermore, the potential roles of three crucial criteria (i.e., adsorbent dosage, sorption temperature and agitation/shaking power) on the two responses [i.e., efficiency of plant pigments removal (EPPR) and efficiency of taxol purity (ETP)] were examined and simultaneously optimized through response surface methodology. The nanocomposite was accurately characterized using TEM, AFM, BET, FT-IR, Raman and VSM. Moreover, for both proposed second-degree polynomial regression models, highly significant correlations were achieved between the experimental and predicted data (p < 0.0001). Meanwhile, the optimum conditions to simultaneously acquire the maximum EPPR (94.0 %) and ETP (11.4 %) were recorded as adsorbent dosage of 37.7 g L⁻¹, sorption temperature of 30.7 °C and agitation power of 153.1 rpm; and the predictive results were confirmed using experimental rechecking survey. Interestingly, upon five consecutive treatments, the nanocomposite still exhibited substantial potency in eliminating large amounts of plant pigments and impurities (up to 90 %), without significant reduction on sorption capacity and magnetism thereof. Our results demonstrated that the current nanocomposite, as SPE sorbent for MSPE, could be a simple, fast and reusable approach for HPLC-based purification studies of paclitaxel, and probably other plant secondary metabolites.

     

Generating and analyzing spatial social networks

In this paper, we propose a class of models for generating spatial versions of three classic networks: Erdös-Rényi (ER), Watts-Strogatz (WS), and Barabási-Albert (BA). We assume that nodes have geographical coordinates, are uniformly distributed over an m × m Cartesian space, and long-distance connections are penalized. Our computational results show higher clustering coefficient, assortativity, and transitivity in all three spatial networks, and imperfect power law degree distribution in the BA network. Furthermore, we analyze a special case with geographically clustered coordinates, resembling real human communities, in which points are clustered over k centers. Comparison between the uniformly and geographically clustered versions of the proposed spatial networks show an increase in values of the clustering coefficient, assortativity, and transitivity, and a lognormal degree distribution for spatially clustered ER, taller degree distribution and higher average path length for spatially clustered WS, and higher clustering coefficient and transitivity for the spatially clustered BA networks.     

Determination of migrated phthalic acid residues into edible oils using a green mode of air-assisted liquid–liquid microextraction followed by high-performance liquid chromatography–diode array detector

In this study, for the first time, an organic solvent-free air-assisted liquid–liquid microextraction method has been reported for the extraction and preconcentration of phthalic acids (o-phthalic acid, m-phthalic acid, and p-phthalic acid) from edible oil samples. The method is based on the repeated aspirating/injection of an alkaline aqueous solution and the oil sample mixture in a conical bottom centrifuge tube to form a cloudy solution. After phase separation by centrifuging, the sedimented phase is directly analyzed by high-performance liquid chromatography–diode array detection. Under the optimum extraction conditions, the method showed low limits of detection and quantification between 0.11–0.29 and 0.28–0.91 ng mL^?1, respectively. Extraction recoveries and enrichment factors were from 81 to 97% and 406 to 489, respectively. The relative standard deviations for the analysis of 5 ng mL^?1 of each analyte were less than 5.9% for intraday (n = 6) and interday (n = 5) precisions. Finally, different oil samples were successfully analyzed using the proposed method and m-phthalic acid, and p-phthalic acid were determined in some of them at ng mL^?1 level.     

Chemoselective Route for Synthesis of N‐Aryl‐3‐oxochromeno[2,3‐c]pyrazole‐2(3H)‐carbothioamide Derivatives

A chemoselective route for the synthesis of chromeno[2,3‐c]pyrazole‐2(3H)‐carbothioamide derivatives by a five‐component reaction of salicylaldehyde, malononitrile, NH₂NH₂?H₂O, aryl isothiocyanate, and H₂O in EtOH/AcOH mixture is reported. This new protocol has the advantages of high yields, short reaction times, ease of operation, and simple purification. All structures were confirmed by IR, ¹H‐ and ¹³C‐NMR, and MS analyses. A plausible mechanism for this type of reaction is proposed (Scheme 2).     

Bilinear optimality constraints for the cone of positive polynomials

For a proper cone \({{\mathcal K}\subset\mathbb{R}^n}\) and its dual cone \({{\mathcal K}^*}\) the complementary slackness condition \({\langle{\rm {\bf x}},{\rm {\bf s}}\rangle=0}\) defines an n-dimensional manifold \({C({\mathcal K})}\) in the space \({{\mathbb R}^{2n}}\) . When \({{\mathcal K}}\) is a symmetric cone, points in \({C({\mathcal K})}\) must satisfy at least n linearly independent bilinear identities. This fact proves to be useful when optimizing over such cones, therefore it is natural to look for similar bilinear relations for non-symmetric cones. In this paper we define the bilinearity rank of a cone, which is the number of linearly independent bilinear identities valid for points in \({C({\mathcal K})}\) . We examine several well-known cones, in particular the cone of positive polynomials \({{\mathcal P}_{2n+1}}\) and its dual, and show that there are exactly four linearly independent bilinear identities which hold for all \({({\rm {\bf x}},{\rm {\bf s}})\in C({\mathcal P}_{2n+1})}\), regardless of the dimension of the cones. For nonnegative polynomials over an interval or half-line there are only two linearly independent bilinear identities. These results are extended to trigonometric and exponential polynomials. We prove similar results for Müntz polynomials.     

A new solid phase micro extraction for simultaneous head space extraction of ultra traces of polar and non-polar compounds

The results of the innovative study on a new stationary phase with high efficiency based on ZnO nano and micro rod coating on fused silica are reported in this paper. ZnO nanorods with a diameter in the range of 70–300 nm and the length of about 500 nm, have been grown on fused silica fibers using a hydrothermal process. The extraction properties of the fiber were investigated using headspace solid-phase microextraction (HS-SPME) mode coupled with gas chromatography–mass spectrometry detection (GC–MS) for 1,4-dichloro-nitrobenzene, biphenyl and acenaphthene. The calibration curves were linear up to 10²–10⁷ ng L⁻¹ (R² > 0.995) with detection limits of 10⁻³ ng L⁻¹ for biphenyl and acenaphthene and 10 ng L⁻¹ for 1,4-dichloro-nitrobenzene. The RSD for single fiber and fiber-to-fiber were less than 7.0 and 11.5%, respectively. The high stability of the ZnO coating is proved at relatively high temperatures (up to 300 °C) with a high extraction capacity and long lifespan (more than 100 times). Promising recoveries (91–102%) were obtained in environmental water samples analysis by applying the proposed technique.