Polymerization of nitrogen in sodium azide

The high-pressure behavior of nitrogen in NaN(3) was studied to 160 GPa at 120-3300 K using Raman spectroscopy, electrical conductivity, laser heating, and shear deformation methods. Nitrogen in sodium azide is in a molecularlike form; azide ions N(3-) are straight chains of three atoms linked with covalent bonds and weakly interact with each other. By application of high pressures we strongly increased interaction between ions. We found that at pressures above 19 GPa a new phase appeared, indicating a strong coupling between the azide ions. Another transformation occurs at about 50 GPa, accompanied by the appearance of new Raman peaks and a darkening of the sample. With increasing pressure, the sample becomes completely opaque above 120 GPa, and the azide molecular vibron disappears, evidencing completion of the transformation to a nonmolecular nitrogen state with amorphouslike structure which crystallizes after laser heating up to 3300 K. Laser heating and the application of shear stress accelerates the transformation and causes the transformations to occur at lower pressures. These changes can be interpreted in terms of a transformation of the azide ions to larger nitrogen clusters and then polymeric nitrogen net. The polymeric forms can be preserved on decompression in the diamond anvil cell but transform back to the starting azide and other new phases under ambient conditions.     

2‐(4‐Hydroxy­phenyl)‐4,4‐dimethyl‐2‐oxazoline: X‐ray and density functional theory study

In the crystal structure of the title compound, C₁₁H₁₃NO₂, there are strong inter­molecular O—H⋯N hydrogen bonds which, together with weak intra­molecular C—H⋯O hydrogen bonds, lead to the formation of infinite chains of mol­ecules, held together by weak inter­molecular C—H⋯O hydrogen bonds. A theoretical investigation of the hydrogen bonding, based on density functional theory (DFT) employing periodic boundary conditions, is in agreement with the experimental data. The cluster approach shows that the influence of the crystal field and of hydrogen‐bond formation are responsible for the deformation of the 2‐oxazoline ring, which is not planar and adopts a ⁴T₃ (^C3T_C2) conformation.     

Biocompatible hydrogels based on chitosan,cellulose/starch,PVA and PEDOT:PSS with high flexibility and high mechanical strength

Fabricating mechanically strong hydrogels that can withstand the conditions in internal tissues is a challenging task. We have designed hydrogels based on multicomponent systems by combining chitosan, starch/cellulose, PVA, and PEDOT:PSS via one-pot synthesis. The starch-based hydrogels were homogeneous, while the cellulose-based hydrogels showed the presence of cellulose micro- and nanofibers. The cellulose-based hydrogels demonstrated a swelling ratio between 121 and 156%, while the starch-based hydrogels showed higher values, from 234 to 280%. Tensile tests indicated that the presence of starch in the hydrogels provided high flexibility (strain at break?>?300%), while combination with cellulose led to the formation of stiffer hydrogels (elastic moduli 3.9–6.6 MPa). The ultimate tensile strength for both types of hydrogels was similar (2.8–3.9 MPa). The adhesion and growth of human osteoblast-like SAOS-2 cells was higher on hydrogels with cellulose than on hydrogels with starch, and was higher on hydrogels with PEDOT:PSS than on hydrogels without this polymer. The metabolic activity of cells cultivated for 3 days in the hydrogel infusions indicated that no acutely toxic compounds were released. This is promising for further possible applications of these hydrogels in tissue engineering or in wound dressings.

Graphical abstract

     

Photometrische Wismutbestimmung mit Brenzcatechinviolett

Zusammenfassung Es wurden die Bedingungen der photometrischen Wismutbestimmung mit Brenzcatechinviolett bei der WellenlÄnge _max=580 nm ausgearbeitet und der Einflu\ der Fremdionen untersucht. Das Lambert-Beersche Gesetz gilt in den Konzentrationsgrenzen 0,0–6,2 g Bi/ml bei 1,6 cm Schichtdicke.

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Summary A method is given for the photometric determination of bismuth using pyrocatechol violet, at the wave-length of _max=580 nm. Interferences by foreign ions have been examined. Beer's law is obeyed from 0.0 to 6.2 g Bi/ml (1,6 cm cuvettes).

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Als erste Mitteilung dieser Reihe soll die Arbeit: Malát, M.: Naturwissenschaften 48, 569 (1961) betrachtet werden.     

Modelling,optimisation and control of selectivity in the separation of aromatic bases by electrokinetic chromatography using a neutral cyclodextrin as a pseudostationary phase

A simple mathematical model describing the separation of a series of aromatic bases by electrokinetic chromatography using beta-cyclodextrin (beta-CD) as a pseudostationary phase is described. The model takes into account changes in electrolyte pH and the different formation constants between the neutral and charged forms of the analytes with the CD. Constants in the model were obtained within the two-dimensional experimental space defined by pH and [beta-CD] with nonlinear regression using only five experimental points. These constants agreed with expected trends in analyte-CD interactions and predicted much higher formation constants for the neutral analyte-CD complex than for the charged analyte-CD complex. Correlation between predicted and observed mobilities using additional 20 points within the experimental space gave r(2) = 0.995. Optimisation of the pH and [beta-CD] was performed using both the normalised resolution product and minimum resolution product criteria and provided two optimum separations which exhibited different selectivities. Differences between predicted and observed migration times at these optima were less than 2.5 and 5% for the normalised resolution product and the minimum resolution criteria, respectively. In both cases the correct migration order was predicted. The model was also applied successfully to the optimisation of conditions for the separation of a specific mixture of analytes or for conditions under which particular analytes migrated in a desired order.     

On-line coupling of capillary isotachophoresis and zone electrophoresis for the assay of phenolic compounds in plant extracts

The combination of capillary isotachophoresis (ITP) and capillary zone electrophoresis (CZE) in the column coupling configuration was optimized in a mode where the electrolyte for the CZE step is different from the leading and terminating ITP electrolytes. Two colored markers, picric acid and 1-nitroso-2-naphthol, were used for exact timing of the transfer of isotachophoretically stacked analyte zones into the CZE column and for the control of the residual amount of the leading and terminating ITP electrolytes entering the CZE capillary together with the analytes, thus controlling the duration of transient ITP migration in the CZE capillary and ensuring good separation of the analytes and reproducibility of the migration times (relative standard deviations 1%). ITP-CZE was applied to the simultaneous assay of several cinnamic acid derivatives and flavonoids in methanolic extracts of Sambucus flowers and Crataegus leaves and flowers. The preconcentrating and cleansing effect of the ITP step allowed injection of relatively large sample volumes (30 microL). The limits of detection were approximately 20-50 ng x mL(-1) and 100 ng x mL(-1) for the acids and flavonoids, respectively ( thick similar 200-times lower compared to conventional CE) with spectrophotometric detection at 254 nm. The ITP-CZE exhibited satisfactory linearity and precision when using CZE buffer of pseudo "pH" 9.0; 1-nitroso-2-naphthol was employed as the internal standard. The separation took approximately 35 min. The ITP-CZE results for rutin, hyperoside, and vitexin-2-O"-rhamnoside were in good accordance with those obtained previously by high-performance liquid chromatography.     

On the Hahn-Banach Extension Property in Hardy and mixed norm spaces on the unit ball

For a nonempty setE of nonnegative integers letH _E ^{p, q, a} andH _E ^p be the closed linear span of

Structural transformation of molecular nitrogen to a single-bonded atomic state at high pressures

The transformation of molecular nitrogen to a single-bonded atomic nitrogen is of significant interest from a fundamental stand point and because it is the most energetic non-nuclear material predicted. We performed an x-ray diffraction of nitrogen at pressures up to 170 GPa. At 60 GPa, we found a transition from the rhombohedral (R3c) epsilon-N(2) phase to the zeta-N(2) phase, which we identified as orthorhombic with space group P222(1) and with four molecules per unit cell. This transition is accompanied by increasing intramolecular and decreasing intermolecular distances. The major transformation of this diatomic phase into the single-bonded (polymeric) phase, recently determined to have the cubic gauche structure (cg-N), proceeds as a first-order transition with a volume change of 22%.     

Synthesis and thermostability of the binary condensed phosphates

Some condensed phosphates, especially cyclo-tetraphosphates have been synthetized as new binary compounds and their existence has been proved. The synthesis of cyclo-CdMgP₄O₁₂ is shown as an example. The products crystallize in the monoclinic system (C2c group) and are stable to 900°C. The synthesis is based on a thermal procedure making use of the reversible transformation of cyclo-tetraphosphates to higher linear phosphates (the 1.method) and on a calcination of the starting binary dihydrogenphosphate at quasi-isothermal-isobaric conditions (the 2.method).

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Zusammenfassung Einige kondensierte Phosphate, im besonderen Zyklotetraphosphate wurden als neue binäre Verbindungen hergestellt. Als Beispiel wird Zyklo-Cd MgP₄ O₁₂ angeführt. Das Produkt kristallisiert monoklin /Gruppe C2/c/ und ist bis 900°C stabil. Die Synthese basiert auf einem thermischen Verfahren unter Anwendung des reversiblen Überganges von Zyklotetraphosphaten zu höhereren linearen Phosphaten /Verfahren 1/ und auf dem Kalzinieren der binären Ausgangsverbindung Dihydrogenphos phat bei quasi-isothermen-isobaren Bedingungen /Verfahren 2/.

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$ , . - dMgP₄O_I2. $ / 2/ $ 900°. $ $ , — $ - .