SOCl2 and POCl3 as reducing agents for TcO 4 − formation and EPR detection of Tc(VI)-compounds

Pertechnetate, TcO ₄ ^– , is reduced by thionyl chloride and phosphoryl chloride, respectively, to yield semistable Tc(VI) intermediates which can easily be detected by EPR spectroscopy. Spectra are recorded in liquid and frozen solutions. EPR data as well as chemical behaviour suggest the compounds obtained to be oxochloro complexes of technetium(VI).     

Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

Thermomechanical properties of polymers highly depend on their glass transition temperature (T _g). Differential scanning calorimetry (DSC) is commonly used to measure T _g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T _g in such type of polymers. The changes in specific heat capacity (Δc _p) at T _g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc _p from flexible polymer (0.28 J g^?1 K^?1 for polystyrene) to rigid CPs (10^?3 J g^?1 K^?1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc _p at T _g by a factor of 10, confirming that backbone rigidity reduces the Δc _p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc _p. We conclude that the difficulties of determining T _g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1635–1644     

Synthesis and Evaluation of Imidazo[1,2‐a]pyridine Analogues of the ZSTK474 Class of Phosphatidylinositol 3‐Kinase Inhibitors

Using a scaffold‐hopping approach, imidazo[1,2‐a]pyridine analogues of the ZSTK474 (benzimidazole) class of phosphatidylinositol 3‐kinase (PI3K) inhibitors have been synthesized for biological evaluation. Compounds were prepared using a heteroaryl Heck reaction procedure, involving the palladium‐catalysed coupling of 2‐(difluoromethyl)imidazo[1,2‐a]pyridines with chloro, iodo or trifluoromethanesulfonyloxy (trifloxy) substituted 1,3,5‐triazines or pyrimidines, with the iodo intermediates being preferred in terms of higher yields and milder reaction conditions. The new compounds maintain the PI3K isoform selectivity of their benzimidazole analogues, but in general show less potency.     

Determination of trace elements in biological tissues by aluminum block digestion and spike-height flame atomic absorption spectrometry

A method for the determination of cadmium, copper, lead, and zinc in biological tissues using small volumes of digest is described. An aluminium heating block is used to digest samples and elements are determined by spike-height flame atomic absorption spectrometry. Interferences have been assessed and the sample decomposition procedure evaluated.     

Hyperfine structure in the configuration 4f 115d6s 2 of Er I

Hyperfine constants of low lying levels of the configuration 4f ¹¹5d6s ² in Er I have been measured for the only stable odd isotope,¹⁶⁷Er, using high resolution laseratomic-beam spectroscopy. Hyperfine parameters were evaluated from the experimental data using the effective tensor operator formalism. For this purpose eigenfunctions have been determined from an analysis of the fine structure energies of Er I as well as from ab initio multiconfiguration Dirac-Fock calculations. With the latter method also ab initio hyperfine constants for the levels investigated were evaluated. A comparison of calculated fine structure energies, Landég _J -factors and hyperfine constants with the experimental data allowed a test of the reliability of the fine structure and multiconfiguration Dirac-Fock wavefunctions. Effective nuclear electric quadrupole moments for¹⁶⁷Er have been determined from the experimental hyperfine constants using both calculated relativistic electronic radial integrals and hyperfine parameters for the 4f and 5d electrons in the configuration 4f ¹¹5d6s ² in Er I. From a comparison with the nuclear quadrupole moment measured in the mesic atom Sternheimer shielding factors are calculated. Configuration-interaction contributions to the radial integrals 〈r ^?3〉 _nl ⁰¹ of the 4f and 5d electrons have been determined.     

Bifunctional even-electron ions. II. Fragmentation behaviour of aliphatic ω-hydroxy and ω-methoxy methoxonium ions

Bifunctional methoxonium ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} -\mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OH}({\rm b}) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} - \mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OCH}_3 ({\rm c}) $\end{document} (c) show as the main reactions those caused by functional group interaction, as has already been found for the analogous hydroxonium ions (g). Although there are similarities in the fragmentation behaviour of the isomeric ions b and g, their fragmentation pathways are different, proving b and g as distinct species. The dominant primary fragmentation for b and c is loss of CH₃OH. The hydrogen migrations prior to this reaction have been established by deuterium labelling. The findings on the fragmentation behaviour of the bifunctional methoxonium ions have been extended to the general behaviour of hydroxy and alkoxy substituted alkoxonium ions.     

Determination of dopamine and its metabolites in small volumes of rat brain dialysates using small-bore liquid chromatography with electrochemical detection

A miniaturized liquid chromatographic system with electrochemical detection (LC-ED) was developed and applied to the analysis of dopamine and its metabolites in dialysate samples collected from the rat brain in vivo. An existing LC-ED system was down-scaled using a 1 mm I.D. small-bore column operated at a reduced flow-rate and with an injection volume of 1 microliter. With the small-bore system the limit of detection for dopamine of ca. 0.06 pg was almost 50 times less than with the conventional system, which represents a two-fold improvement in concentration sensitivity. Miniaturization was accomplished with negligible loss in resolution by using a conventional commercial amperometric detector with minor modifications. The results indicate that a number of useful advantages could be realized by the combination of this small-bore LC-ED system and the in vivo brain dialysis method.     

Determination of an aldosterone antagonist in urine by high-performance liquid chromatography using automated column switching

An automated high-performance liquid chromatographic assay for the determination of an aldosterone antagonist (I) is described using column switching for direct injection of urine samples. After dilution with buffered internal standard solution, the sample was injected onto a clean-up column (17 X 4.6 mm I.D.), dry-packed with C18 reversed-phase material (particle size 30 micron). Polar urine components were removed by flushing the clean-up column with water. Retained substances, including I and the internal standard, were desorbed by backflush elution onto a 5-micron ODS-silica analytical column (125 X 4 mm I.D.), separated with water-methanol-tetrahydrofuran, and detected at 295 nm. After backflushing the analytical column and re-equilibrating the clean-up column, the system was ready for the next injection. The limit of quantification was ca. 100 ng/ml, using a 100-microliter specimen of diluted urine. The mean inter-assay precision of the method up to 25.6 micrograms/ml was 2%. Practicability and accuracy of the new method were demonstrated by the application to excretion studies performed with human volunteers.     

Derivatized vancomycin stationary phases for LC chiral separations

In this work, synthetic and natural chiral selectors were combined to form two different chiral stationary phases (CSPs). These were made by bonding R- or S-(1-naphthylethyl) carbamate (R-NEC or S-NEC)-derivatized vancomycin molecules to a silica gel support. The two CSPs were evaluated using a set of 60 enantiomeric pairs. The results were compared to the ones obtained with the commercial underivatized vancomycin CSP. Three Chromatographic modes were used: (i) the normal-phase mode using a nonpolar mobile phase with different ratios of hexane and ethanol; (ii) the reversed-phase mode with hydro-organic mobile phases; and (iii) the polar aprotic organic mode with nonaqueous acetonitrile plus small amounts of methanol and an acid and/or base to control retention and selectivity. It is shown that the polarity of the underivatized vancomycin phase is higher than that of the two R- and S-NEC-derivatized CSPs. In the pH range 4-7, there is no ionization change of the chiral selector for the three CSPs. 43% of the studied compounds were resolved by the NEC-derivatized phases when they could not be resolved by the vancomycin CSP. However, the enantiorecognition for 12% of the compounds on the native vancomycin CSP was lost upon NEC derivatization. 45% of the studied compounds were resolved by the NEC-derivatized and native CSPs. The NEC derivatization procedure may block some useful active sites on the vancomycin molecule. Also, the R- and S-NEC moieties are chiral themselves and can contribute additional interaction sites not available on the native vancomycin molecule.     

Zustandsbarogramme — Zustandsdiagramme durch Gesamtdruckmessungen

From phasebarograms it is possible to construct phase diagrams. We show on example of the system Bi/Se/O how follow ternary sections from the total pressure measurements in equilibrium and how we can attribute the barogram of the ternary region Bi₂Se₃/Bi₂O₂Se/Se to the binary system Bi₂Se₃/Se. The knowledge of the ternary system Bi/Se/I and its coexistent pressure courses allow to followT-p-x conditions for the chemical transport of phases from this system.