Charge‐Assisted Halogen Bonding: Donor–Acceptor Complexes with Variable Ionicity

Charge‐assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge‐transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT‐TTFI₂)₂(TCNQF_n), n=0–2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT‐TTFI₂, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF₂) through highly directional C? I???N≡C halogen‐bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge‐transfer complex is isolated whereas with the more oxidizing TCNQF₂ acceptor, an ionic, highly conducting charge‐transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral–ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the C? I???N≡C halogen‐bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen‐bonding interaction. The neutral–ionic conversion in (EDT‐TTFI₂)₂(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups.     

Applicability of Gd-doped BaZrO3, SrZrO3, BaCeO3 and SrCeO3 proton conducting perovskites as electrolytes for solid oxide fuel cells

Four proton conducting oxides of perovskite structure: BaZrO₃, SrZrO₃, BaCeO₃ and SrCeO₃ doped with 5 mol.% of gadolinium are compared in terms of crystal structure, microstructure, sinterability, water sorption ability, ionic transference number, electrical conductivity and stability towards CO₂. Relations between proton conductivity, structural and chemical parameters: pseudo-cubic unit cell volume, lattice free volume, tolerance factor, crystal symmetry and electronegativity are discussed. The grain boundary resistance is shown to be the limiting factor of total proton-conductivity for the materials examined. The highest proton conductivity was observed for BaCeO₃, however, it turned out to be prone to degradation in CO₂-containing atmosphere and reduction at high temperatures. On the other hand, Ba and Sr zirconates are found to be more chemically stable, but exhibit low electrical conductivity. Electrical conductivity relaxation upon hydration is used to calculate proton diffusion coefficient. Selected materials were tested as electrolytes in solid oxide fuel cells.      

Field-amplified sample injection coupled with pseudo-isotachophoresis technique for sensitive determination of selected psychiatric drugs in human urine samples after dispersive liquid–liquid microextraction

A field-amplified sample injection (FASI) technique was elaborated for fast and sensitive determination of selected central nervous system drugs in human urine samples. Factors affecting the sensitivity enhancement, such as background electrolyte (BGE) and the analytical matrix composition were optimized and discussed. Pseudo-isotachophoresis (p-ITP) mechanism contribution in preconcentration mechanism was discussed. All separations were performed in uncoated fused silica capillaries 50 μm × 57 cm at 22 kV. The optimized analytical matrix was composed of 0.25 mM HCOOH in 90% (v/v) methanol, while BGE contained 45 mM TRIS/HCl (pH 2.20). The head-column injection was performed in 0.25 mM HCOOH water solution (3 s, 3.45 kPa). Sample was introduced into the capillary by electrokinetic injection (70 s, 5 kV) followed by short BGE plug (3 s, 3.45 kPa). Seven psychiatric drugs (olanzapine, prochlorperazine dimaleate, trifluoperazine dihydrochloride, perphenazine, promazine hydrochloride, clomipramine hydrochloride, and chlorprothixene hydrochloride) were separated in about 6 min. The elaborated method was additionally supported with dispersive liquid–liquid microextraction (DLLME) technique which in summary with FASI provided about 8000–13,000-fold sensitivity enhancement in comparison to the capillary zone electrophoresis (CZE) method with standard hydrodynamic injection (5 s, 3.45 kPa).     

Study of Microwave Torch Plasmachemical Synthesis of Iron Oxide Nanoparticles Focused on the Analysis of Phase Composition

This work presents the results obtained on the single-step route towards the synthesis of iron oxide nanoparticles in a microwave plasma torch. The torch is supplied by 660 sccm of Ar mixed with 1 sccm of Fe(CO)₅ and a variable amount of O₂. The influence of oxygen addition on the phase composition of the synthesized powder was studied. Magnetite and maghemite phases could not be distinguished using the standard X-ray diffraction (XRD) analysis. Therefore, a combined XRD and Raman spectra analysis had to be applied, which is based on fitting of selected diffraction peaks and spectral features. According to XRD and Raman spectroscopy, the powder synthesized from Ar/Fe(CO)₅ consisted about 50 % of magnetite, Fe₃O₄, the rest being α-Fe and FeO. An increase in oxygen flow rate led to an increase in γ-Fe₂O₃ percentage, at the expense of α-Fe, FeO and Fe₃O₄. Almost pure γ-Fe₂O₃ was synthesized at oxygen flow rates 25–75× higher than the flow rate of Fe(CO)₅. A further increase in the oxygen flow rate led to α-Fe₂O₃ and ε-Fe₂O₃ production. The distributions of nanoparticles’ (NPs) diameters were obtained using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The mean diameter of the NPs measured by TEM was 13 nm while the DLS measurements led to the mean diameter of 12 nm. About 90 % of all particles had the diameter in the range of 5–21 nm but a few larger particles were observed in TEM micrographs.     

Characterisation of Ni-C films obtained in PVD/CVD process

The work presents the results of the scanning electron microscopy (SEM) and Raman spectrometry studies of carbonaceous nanostructures containing nickel nanocrystallites. The films were obtained using a two-step method. In the first phase the Physical Vapour Deposition (PVD) method was applied, whereas in the second Chemical Vapour Deposition (CVD) method was used. The paper presents results for samples with various Ni content obtained with different parameters of the two-phase technological process. The research confirms that the thin films obtained by PVD method contain Ni nanocrystallites distributed in a carbonaceous matrix. The matrix is composed of various carbon allotropes (amorphous carbon, graphite, fullerene). The thin films made by CVD method make a matrix when multiwalled, carbonaceous nanotubes are obtained. Depending on the technological process parameters of each phase, we obtain multiwall nanotubes with a various degree of defects.     

Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys

CuAl layered double hydroxide (CuAl-LDH) was synthesized by co-precipitation. Sodium phenyl phosphate (SPP) and sodium dodecyl sulfate (SDS) are used to modify CuAl-LDH for preparing CuAl-(SPP)LDH and CuAl-(SDS)LDH, which were incorporated into epoxy resin (EP) to obtain EP/CuAl-(SPP)LDH and EP/CuAl-(SPP)LDH nanocomposites. The results indicate that SPP and SDS are intercalated into the interlayers of CuAl-LDH, and CuAl-(SPP)LDH has larger layer spacing than CuAl-(SDS)LDH. The thermal stability and flame-retardant performances of EP/CuAl-(SPP)LDH nanocomposites were better than those of EP/CuAl-(SDS)LDH composites. Compared with those of EP/4CuAl-(SDS)LDH nanocomposites, the peak heat release rate (PHRR) of EP/4CuAl-(SPP)LDH nanocomposites is reduced 25.8% and 55.6%, and peak smoke production rate (PSPR) value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, respectively. The improved flame retardancy and smoke suppression performances of EP/CuAl-(SPP)LDH nanocomposites were attributed to the combination of copper compounds and SPP, promoting the formation of swollen, continuous and compact char layers on the surface of EP nanocomposites during combustion, eventually restraining the decomposition of EP nanocomposites.

     

Analytical methods for determination of benzodiazepines. A short review

Benzodiazepines (BDZs) are generally commonly used as anxiolytic and/or hypnotic drugs as a ligand of the GABA_A-benzodiazepine receptor. Moreover, some of benzodiazepines are widely used as an anti-depressive and sedative drugs, and also as anti-epileptic drugs and in some cases can be useful as an adjunct treatment in refractory epilepsies or anti-alcoholic therapy. High-performance liquid chromatography (HPLC) methods, thin-layer chromatography (TLC) methods, gas chromatography (GC) methods, capillary electrophoresis (CE) methods and some of spectrophotometric and spectrofluorometric methods were developed and have been extensively applied to the analysis of number of benzodiazepine derivative drugs (BDZs) providing reliable and accurate results. The available chemical methods for the determination of BDZs in biological materials and pharmaceutical formulations are reviewed in this work.      

Preparation of Allylstannanes and Distannanes Using Zinc in Liquid Ammonia

Abstract

Barbier-type reductive coupling of allylic bromides and organotin compounds can be carried out in liquid ammonia (?33°C) using commercial zinc powder. This procedure provide a new simple and environment-friendly method for the synthesis of allylstannanes and distannanes.     

Approach to accuracy assessment of the glass-electrode potentiometric determination of acid-base properties

Thermodynamic data are suitable subject for investigating strategies and concepts for the evaluation of complete measurement uncertainty budgets in situations where the measurand cannot be expressed in a mathematical formula. Some suitable approaches are the various forms of Monte Carlo simulations in combination with computer-intensive statistical methods that are directed to an evaluation of empirical distribution curves for the uncertainty budget. Basis of the analysis is a cause-and-effect diagram. Some experience is available with cause-and-effect analysis of thermodynamic data derived from spectrophotometric data. Another important technique for the evaluation of thermodynamic data is glass-electrode potentiometry. On basis of a newly derived cause-and-effect diagram, a complete measurement uncertainty budget for the determination of the acidity constants of phosphoric acid by glass-electrode potentiometry is derived. A combination of Monte Carlo and bootstrap methods is applied in conjunction with the commercially available code SUPERQUAD. The results suggest that glass-electrode potentiometry may achieve a high within-laboratory precision because major uncertainty contributions become evident via interlaboratory comparisons. This finding is further underscored by analysing available literature data.