Graft copolymers of polycaproamide with polyimide based on fluorene dianiline and 3,3′,4,4′-tetracarboxydiphenyloxide: Microstructure and properties

It is established that graft copolymers of polycaproamide with 3–5 wt % of polyimide exhibit a rubber-like elasticity region above the polycaproamide melting temperature. Polycaproamide modification with polyimide increases the polymer thermal resistance, glass-transition temperature, and impact strength. Scanning electron microscopy revealed that the supramolecular organization of polycaproamide is similar to that of its copolymers with polyimide but differs in the spherulite size.     

Study of factors affecting the results of natural water analyses by total reflection X‐ray fluorescence

The study aims to choose the conditions for the direct analysis of different types of natural water samples by total reflection X‐Ray fluorescence spectrometry (TXRF). The effect of some factors on TXRF results was studied such as the surface density of dried water residue on the sample carrier, the dilution ratio of high‐mineralized samples with ultrapure water and the solution of the detergent Triton X‐100, the salt contents, the internal standard concentration, and repeated pipetting of an aliquot of fresh water. The influence of self‐absorption phenomena on quantification results was demonstrated by using brine samples. The TXRF results for natural waters of varying salinity (brines, fresh waters, and ground waters) and model solutions are presented. For a number of analytes, the data obtained by TXRF were compared to those obtained by ‘wet’ chemistry and inductively coupled plasma mass spectrometry. Copyright © 2013 John Wiley & Sons, Ltd.     

Magnetically soft semiconductor InSb〈Mn,Zn〉 with the curie temperature of 320 K

The magnetic properties of a ferromagnetic semiconductor based on indium antimonide doped with manganese and zinc having the Curie temperature T _c = 320 K are studied. Field dependences of magnetization of InSb??Mn,Zn?? recorded at 4 and 260 K indicate that this material is magnetically soft with the coercive force no higher than 18 Oe at T = 300 K.     

Closely spaced external standard: a universal method of achieving 5 ppm mass accuracy over the entire MALDI plate in axial matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Close deposition of the sample and external standard was used in axial matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) to achieve mass accuracy equivalent to that obtained with an internal standard across the entire MALDI plate. In this work, the sample and external standard were deposited by continuous deposition in separate traces, each approximately 200 micro m wide. The dependence of the mass accuracy on the distance between the sample and standard traces was determined across a MALDI target plate with dimensions of 57.5 mm x 57.0 mm by varying the gap between the traces from 100 micro m to 4 mm. During acquisition, two adjacent traces were alternately irradiated with a 200-Hz laser, such that the peaks in the resulting mass spectra combined the sample and external standard. Ion suppression was not observed even when the peptide concentrations in the two traces differed by more than two orders of magnitude. The five peaks from the external standard trace were used in a four-term mass calibration of the masses of the sample trace. The average accuracy across the whole plate with this method was 5 ppm when peaks of the sample trace had signal-to-noise ratios of at least 30 and the gap between the traces was approximately 100 micro m. This approach was applied to determining peptide masses of a reversed-phase liquid chromatographic (LC) separation of a tryptic digest of beta-galactosidase deposited as a long serpentine trace across the MALDI plate, with accuracy comparable to that obtainable using internal calibration. In addition, the eluent from reversed-phase LC separation of a strong cation-exchange fraction containing tryptic peptides from a yeast lysate along with the closely placed external standard was deposited on the MALDI plate. The data obtained in the MS and MS/MS modes on a MALDI-TOF/TOF mass spectrometer were combined and used in database searching with MASCOT. Since the significant score is a function of mass accuracy in the MS mode, database searching with high mass accuracy reduced the number of false positives and also added peptides which otherwise would have been eliminated at lower mass accuracy (false negatives).     

Anionic polymerization of ε-caprolactam and its copolymerization with ω-dodecanelactam in the presence of aromatic polyimides

The anionic polymerization of ε-caprolactam in the presence of aromatic polyimides as activators has been studied under adiabatic conditions. It has been shown that despite the crosslinked structure the produced graft copolymers of polycaproamide and polyimides contain the crystalline phase and are characterized by better water resistance and thermal stability, a higher content of the gel fraction, and improved mechanical properties as compared to copolymers prepared under the so-called isothermal conditions. It has been demonstrated that the catalytic system MgBr-ε-caprolactam-aromatic polyimide may be used for the anionic copolymerization of ε-caprolactam with ω-dodecanelactam, and experimental conditions providing a copolymer yield of 75% have been developed.     

Effect of synthesis methods on the morphology of nanosized tin dioxide particles

The effect of precursors on the microstructure of nanocrystalline tin dioxide is studied by thermal analysis, IR spectroscopy, electron microscopy, and X-ray powder diffraction. The precursor precipitated in an optimal pH range whose dehydration and crystallization occur over a wide temperature range with low degrees of oxolation yields crystalline tin dioxide with grain sizes on the order of 16 nm upon calcination at 800°C for 2 h.     

Ferromagnetism in dilute magnetic semiconductors and new materials for spintronics

Spintronics materials may be classified under concentrated magnetic semiconductors, semimetals and half-metals, semimagnetic semiconductors, and dilute magnetic semiconductors (DMS). The nature of ferromagnetism, that occurs in p-type DMS with an increase in the transition metal content, is governed by the proposed kinematic exchange involving the kinetic energy gain of the heavy hole carriers caused by their hybridization with 3d electrons of impurities. The synthesis of DMS (In,Mn)Sb is proposed on the basis of hint at its T_C from kinematic mechanism. The effect of the dimensionality-driven T_C increase is derived for spintronics materials such as delta-doped DMS (DDMS) and DMS heterostructures. The state-of-the-art in the field of synthesis and research of “new” DMS with announced “high T_C” is also outlined with particular attention to chalcopyrite-based systems.     

Adsorption of water isotopomers H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O on hypercross-linked polystyrene MN-272

Adsorption of light and heavy water (H₂O and D₂O) on porous hypercross-linked polystyrene MN-272 was studied by gas chromatography. For the estimation of the properties of this polymer surface, n-alkanes (C6—C9), C_{6 6}, and polar compounds (CHCl₃, MeNO₂, MeCN, Me₂CO, EtCOOCH₃, Et₂O) were used as test adsorbates. The contributions of energies of dispersion and specific (donor-acceptor) intermolecular interactions to the total energy of adsorption were determined on the basis of experimental data on the retention of the sorbates. The electron-donor and electron-acceptor characteristics of the hypercross-linked polystyrene MN-272 surface were estimated. Hypercross-linked polystyrene MN-272 was found to be a weakly specific adsorbent with predomination of electron-donating properties. The adsorption isotherms of H₂O and D₂O were measured on this polymer at 50, 60, and 70 °C. The dependences of the isosteric heats of adsorption on the amount adsorbed were determined. The contribution of the energy of specific interactions to the total energy of adsorption for all polar adsorbates (except for acetone, light and heavy water) does not exceed 20%. Adsorption of H₂O on hypercross -linked polystyrene MN-272 is slightly weaker than that of D ₂O.     

Determination of water-soluble vitamins in vitamin premixes,bioacitve dietary supplements,and pharmaceutical preparations using high-efficiency liquid chromatography with gradient elution

The influence of the pH and temperature of the mobile phase on the retention and separation of 14 vitamins and vitameric forms has been studied for four different stationary phases. The chromatographic conditions allowing the separation of 12 water-soluble vitamins and vitameric forms have been proposed. It has been established that the best separation of water-soluble vitamins can be achieved by employing gradient elution. The mobile phase A, (0.6% phosphoric acid) pH 1.5–1.8; mobile phase B, acetonitrile. For the separation of nicotinic and ascorbic acid it is preferable to use stationary phases Luna C18(2) and Gemini C18, while for the separation of riboflavin and riboflavin-5-phosphate the Synergy Hydro RP and Zorbaz SB-C18 stationary phases should be used. The selected conditions have been used for the determination of vitamins in commercial samples of vitamin preparations. The results are in good accordance with the producer data.