Tosylmethylisocyanide (TosMIC) [3+2] cycloaddition reactions: A facile Van Leusen protocol for the synthesis of the new class of spirooxazolines,spiropyrrolines and Chromeno[3,4-c]pyrrols

The reactivity and chemo-, regio- and diastreo-selectivity of tosylmethyl isocyanides (TosMIC) are investigated in Van Leusen type [3 + 2] cycloaddition reactions with the various activate cyclic ketones and double CC bonds in the synthesis of spirooxazolines, spiropyrrolines and chromeno[3,4-c]pyrrols in good to excellent yields under catalyst-free conditions without any activation at ambient temperature.     

Electrospun Polyethylene Terephthalate/Graphene Nanocomposite as a New Solid-Phase Microextraction Fiber Coating for Enhanced Determination of Organochlorine Compounds

A new unbreakable solid-phase microextraction fiber coating based on polyethylene terephthalate/graphene nanocomposite was developed. The nanocomposite coatings were prepared by an electrospinning technique using a polyethylene terephthalate (PET) polymer solution containing the dispersed graphene on the outer surface of a stainless-steel rod. The applicability of polyethylene terephthalate/graphene nanocomposite coatings was examined by extraction of organochlorine compounds (OCs) including heptachlor epoxide, aldrin, γ-HCH, and β-HCH from aqueous samples in headspace mode. Influential parameters on extraction efficiency such as polymer concentration, the weight ratio of components, the electrospinning time, time and temperature of extraction, the salt concentration, and desorption condition were investigated. Eventually, the developed method was validated by gas chromatography micro electron capture detector (GC-µECD). At the optimum conditions, the intra-day relative standard deviations for the determination of chloro compounds in distilled water spiked at the levels of 400, 800, and 1500 ng L^??1 were 1.9–7.3% (n?=?3), the limit of detection is between 5 and 30 ng L^??1, and the calibration plots cover the 100 to 5000 ng L^??1 range. Inter-day precision values obtained for three replicates measured on different days were in the range of 2.6–9.5% at concentration levels of 400, 800, and 1500 ng L^??1. The method was applied to the analysis of (spiked) water samples and relative recoveries were found to range from 81 to 106%.     

Electrochemical behavior of electrodeposited rutin film on a multi-wall carbon nanotubes modified glassy carbon electrode. Improvement of the electrochemical reversibility and its application as a hydrazine sensor

By immobilizing rutin at the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotubes (MWCNT), a new modified electrode has been fabricated and its electrochemical behavior was investigated by cyclic voltammetry. Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristics. The results show that the reversibility of rutin is significantly improved at a MWCNT modified GCE in comparison with GCE alone. The charge transfer coefficient, α, was calculated to be 0.4, and charge transfer rate constant, k_s, was 46.7 s⁻¹ in pH 8, indicating great facilitation of the electron transfer between rutin and MWCNT deposited on the electrode surface. The rutin MWCNT (RMWCNT) modified GCE showed excellent mediation of hydrazine oxidation: a decrease in the overvoltage of hydrazine electrooxidation was observed as well as a dramatic increase in the peak current compared to that seen at a rutin modified GCE (RMGCE), activated GCE or bare GCE. Hydrazine was determined amperometrically at the surface of RMWCNT modified GCE in pH 8. Under the optimized conditions the calibration curve is linear in the concentration range 2.0–190.0 μM hydrazine. The detection limit and sensitivity are 0.61 μM and 0.0656 μA μM⁻¹, respectively. Finally the kinetic parameters of the electron transfer coefficient, α, the heterogeneous rate constant of dependent to different potentials, k′(E), and the standard heterogeneous rate constant, k⁰, for oxidation of hydrazine at the RMWCNT surface were determined using various electrochemical methods. The advantages of this modified electrode for hydrazine determination are high sensitivity, excellent catalytic activity, short response time, wide linear range, and high exchange current density.     

Fabrication of a nanostructured TiO2/carbon nanotube composite electrode for voltammetric and impedimetric determination of NTO explosive in the water and soil samples

An electrochemical oxidation route was developed for sensitive and selective assay of nitrotriazolone (NTO) explosive in some environmental samples on a multi-walled carbon nanotube (MWCNTs)/TiO₂ nanocomposite paste electrode, for prevention of the analytical interference of conventional reducible energetic compounds. Detailed evaluations were made for the electrochemical behaviour of NTO on the modified electrode by adsorptive stripping voltammetry, electrochemical impedance spectroscopy (EIS) and chronoamperometry techniques in the pH range of 2.0–10.0. Parameters such as diffusion coefficient constant of NTO were calculated, and various experimental conditions were also optimised. Under optimal conditions the calibration curve had two linear dynamic ranges of 130.0–3251.5 μg L^?1 and 6.5–26.0 mg L^?1 with a detection limit of 26.0 μg L^?1 (0.2 μmol L^?1) and precision of <3%. This electrochemical sensor was further applied to determine NTO in real soil and water samples with satisfactory results.     

A review of recent methods for the determination of ranges of feasible solutions resulting from soft modelling analyses of multivariate data

Soft modelling or multivariate curve resolution (MCR) are well-known methodologies for the analysis of multivariate data in many different application fields. Results obtained by soft modelling methods are very likely impaired by rotational and scaling ambiguities, i.e. a full range of feasible solutions can describe the data equally well while fulfilling the constraints of the system. These issues are severely limiting the applicability of these methods and therefore, they can be considered as the most challenging ones. The purpose of the current review is to describe and critically compare the available methods that attempt at determining the range of ambiguity for the case of 3-component systems. Theoretical and practical aspects are discussed, based on a collection of simulated examples containing noise-free and noisy data sets as well as an experimental example.     

Analytical solution and meaning of feasible regions in two-component three-way arrays

Although many efforts have been directed to the development of approximation methods for determining the extent of feasible regions in two- and three-way data sets; analytical determination (i.e. using only finite-step direct calculation(s) instead of the less exact numerical ones) of feasible regions in three-way arrays has remained unexplored. In this contribution, an analytical solution of trilinear decomposition is introduced which can be considered as a new direct method for the resolution of three-way two-component systems. The proposed analytical calculation method is applied to the full rank three-way data array and arrays with rank overlap (a type of rank deficiency) loadings in a mode. Close inspections of the analytically calculated feasible regions of rank deficient cases help us to make clearer the information gathered from multi-way problems frequently emerged in physics, chemistry, biology, agricultural, environmental and clinical sciences, etc. These examinations can also help to answer, e.g., the following practical question: “Is two-component three-way data with proportional loading in a mode actually a three-way data array?” By the aid of the additional information resulted from the investigated feasible regions of two-component three-way data arrays with proportional profile in a mode, reasons for the inadequacy of the seemingly trilinear data treatment methods published in the literature (e.g., U-PLS/RBL-LD that was used for extraction of quantitative and qualitative information reported by Olivieri et al. (Anal. Chem. 82 (2010) 4510–4519)) could be completely understood.     

Application of CdSe–PVK Nanocomposite as a Hole Transport Layer for OLEDs

An organic light‐emitting diode was fabricated using cadmium selenide (CdSe)/poly(N‐vinylcarbazole) nanocomposite as the hole transport layer (HTL). The CdSe nanoparticles (NPs) with a mean crystallite size of 6.2 nm were prepared by high‐energy ball milling. Based on the current–voltage curves, the threshold voltage (V _th) of the composite diode was found to be ~1.3 ± 0.1 V lower than that of the diode without CdSe, with a significant increase in the current density for the composite diode. Moreover, the electroluminescence (EL) properties (luminous flux, emittance, and intensity) of the diode were found to be enhanced by ~16% with respect to those of the diode without CdSe. The decrease of the threshold voltage and the increase of the current density and the EL were due to the CdSe NPs that operate as hole trap centers in the HTL.