Indirect Speciation Analysis of Thallium in Plant Extracts by Anodic Stripping Voltammetry

A sensitive voltammetric method (DPASV) was developed for the determination of Tl(I) and Tl(III) in plant extracts. To limit the influence of the organic matrix on the measurements, UV irradiation and addition of Amberlite XAD‐7 resin was studied. The application of 0.5 g of the resin allowed defining thallium speciation in 10.0 mL of a solution containing 0.20 mL of Sinapis alba extract. The quantification limit of 0.5 ng mL^?1 Tl(I) was found for only 10 min of preconcentration, and is low enough to allow dilution of the sample before thallium determination. The procedure was validated using the recovery study and intermethod comparison with HPLC ICP MS.     

Fouling of nanofiltration membranes used for separation of fermented glycerol solutions

In this study, the glycerol solutions were fermented using Lactobacillus casei bacteria. The broths were pre-treated by microfiltration, followed by a further separation with nanofiltration. The latter process was carried out in two stages, using the NF270 and NF90 membranes, respectively. The concentrates thus obtained were enriched with citric acid (first stage) and then with lactic acid and glycerol (second stage). By means of SEM and AFM microscopy, as well as ATR-FTIR analysis, the intensity of membrane-fouling was studied. The colloidal fouling and bio-fouling caused a more than two-fold decrease in the permeate flux during microfiltration of the broth. This pre-treatment stage was effective, and a permeate turbidity of less than 0.2 NTU was obtained. However, the nanofiltration membranes exhibited a 30 % flux decline over the course of the process, mainly due to the organic fouling.     

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.     

Heterogeneous zirconocene catalyst on magnesium support MgCl2(THF)2 modified by AlEt2Cl for ethylene polymerisation

The heterogeneous bis(cyclopentadienyl)zirconium(IV) dichloride catalyst of the composition MgCl₂(THF)/(AlEt₂Cl)_0.34/(Cp₂ZrCl₂)_0.01 as determined by FTIR, XRD, and AAS analyses was synthesised and, after activation by MAO, applied for ethylene polymerisation. The catalyst turned out to be stable and more active than those magnesium supported catalysts already known from the literature. The polyethylene produced has a relatively high molecular weight (M_w > 200,000 g/mol), a narrow and monomodal molecular weight distribution (MWD = 2.4), a bulk density of about 180 g/dm³, and monomodal particle size distribution. Application of a ternary Al(i-Bu)₃/MAO/B(C₆F₅)₃ activator decreased the amount of MAO needed and increased catalyst activity, but did not change the reaction mechanism.     

Synthesis and reactivity of bis(cycloamidinium-2-yl)alkane bromide tribromides, brominating agents and tectons for molecular engineering

Bis(cycloamidine-2-yl)alkanes easily form bromide tribromide salts in the reduction-oxidation processes with bromine. Bis(tetrahydroimidazolium-2-yl)ethane and bis(hexahydropyrimidinium-2-yl)-ethane bromide tribromides are such new convenient brominating agents for aromatic amides in chemo- and regioselective electrophilic substitutions and α-bromination reactions.     

Sequential homo-coupling Diels-Alder/retro Diels-Alder reaction of 5,5′-bi-1,2,4-triazine-containing thiamacrocycles as a new route to thiacrown ethers incorporating a 2,2′-bipyridine subunit

A new route to thiacrown ethers 5a-d and 6a-d incorporating a 2,2′-bipyridine subunit is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfides 3a-d tethered to poly(ethylene glycol) chains with potassium cyanide and (2) Diels-Alder/retro Diels-Alder reaction with norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps.     

Nanostructured micellar films formed via layer-by-layer deposition of photoactive polymer

Photoactive nanostructured micellar films were prepared from the amphiphilic copolymer poly(sodium styrenesulfonate- stat-2-vinylnaphthalene) (PSSS- stat-VN) and cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) or poly(allylamine hydrochloride) (PAH) on quartz and silicon substrates via layer-by-layer (LbL) electrostatic self-assembly. The macromolecules of this amphiphilic copolymer adopt a coiled micellar conformation in aqueous solution that is preserved in the films as evidenced by atomic force microscopy (AFM) and spectroscopic studies. The hydrophobic domains present in the film can serve as host sites for various organic molecules. The probe molecules reside in those isolated nanosize domains. Their aggregation and quenching of their emission is eliminated. The experiments showed a regular growth of multilayer thickness and the content of solubilized compounds in the films. Thus, a defined amount of the hydrophobic compounds of interest may be introduced into these water-processable polymeric films. Some stratification of the films was induced by the presence of stiff nanoparticle-like micelles. That makes these films an important new material for studies of photoinduced energy and electron transfer.     

(E)-4-alkoxycarbonylalkylthiochalcones: differentiation of isomeric derivatives by electron ionization mass spectrometry

The principal fragmentation pathways of the molecular ions of 18 new (E)-4-alkoxycarbonylalkylthiochalcones have been investigated. It has been shown that the data derived from electron ionization mass spectra (the relative abundance of the fragment ions and values of coefficients micro) can be used to differentiate the isomers. The fragmentation rules deduced here could help in the characterization of other chalcones of these types.     

Thin-layer chromatography-densitometric measurements for determination of N-(hydroxymethyl)nicotinamide in tablets and stability evaluation in solutions

A thin-layer chromatography (TLC)-densitometric method was developed to determine N-(hydroxymethyl)nicotinamide in tablets and basic solutions along with nicotinic acid. Analysis was performed on silica gel F254 plates using chloroform-ethanol (2 + 3, v/v) mobile phase. The densitometric observations were made at 260 nm. The results showed good precision and accuracy; relative standard deviation was 2.37%, and recovery ranged from 97.60 to 100.82%. The limit of detection was 0.1 microg/spot, while the linearity range was from 0.2 to 1.75 microg/spot. Applicability of the newly developed method was tested for determination of N-(hydroxymethyl)nicotinamide in the preparation Cholamid. Densitometric measurements were used to evaluate stability of N-(hydroxymethyl)nicotinamide in basic solutions. It was found that decomposition corresponded to first-order reaction kinetics. The computed kinetic and thermodynamic parameters at 30 degrees C were as follows: k = 0.00675/min, t0,5 = 1.71 h, t0,1 = 0.26 h, and Ea = 44.75 kJ/mol.