Thermal decompositions of kaolinite intercalation compounds

Through a combination of X-ray diffraction and thermal analysis (simultaneous TG-DTG-DTA and quasi-isothermal TG), it was shown that the molar ratio intercalation agent/kaolinite in all intercalation compounds is approximately 1. In a saturated atmosphere of the corresponding intercalation agent, the intercalation compounds are stable up to more than 150 °C.Decomposition of the potassium acetate intercalation compound proceeds simultaneously with the dehydroxylation of kaolinite at an extrapolated onset temperature of 360 °C. The high-temperature reactions (dehydroxylation and transformation) of kaolinite obtained through the decomposition of intercalation compounds with volatile intercalation agents depend on the conditions applied during decomposition.

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Zusammenfassung Mittels Röntgenbeugung und thermischer Analyse (simultane TG-DTG-DTA und quasi-isotherme-quasi-isobare TG) konnte gezeigt werden, daß das molare Verhältnis Einlagerungsmedium/Kaolinit in allen Einlagerungsverbindungen etwa 1 ist. In gesättigter Atmosphäre des jeweiligen Einlagerungsmediums ist die Einlagerungsverbindung stabil bis über 150 °C. Die Zersetzung der Kaliumacetat-Einlagerungsverbindung läuft zusammen mit der Dehydroxylation des Kaolinits bei einer extrapolierten onset-Temperatur von 360 °C ab. Die Hochtemperaturreaktionen (Dehydroxylation, Phasenneubildung) von Kaolinit, der aus der Zersetzung von Einlagerungsverbindungen mit flüchtigen Einlagerungsmedien erhalten würde, werden von den Zersetzungsbedingungen beeinflußt.

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- ( , , ) , - 1. , , 150°. — ** 360°, ** . , , .

     

Translations and rotations are correlated in granular gases

In a granular gas of rough particles the axis of rotation is shown to be correlated with the translational velocity of the particles. The average relative orientation of angular and linear velocities depends on the parameters which characterize the dissipative nature of the collision. We derive a simple theory for these correlations and validate it with numerical simulations for a wide range of coefficients of normal and tangential restitution. The limit of smooth spheres is shown to be singular: even an arbitrarily small roughness of the particles gives rise to orientational correlations.     

Messung der Magnetostriktionskonstanten des Kobalts als Funktion der Temperatur

The single crystal magnetostriction constants of hexagonal cobalt are measured between ?200 °C and 400 °C in magnetic fields up to 26 kOe. The shear constant λ_E=2 λ_D?λ_A/2?λ_C/2 which is of interest in connection with domain structures, as well as the volume constant λ_V=λ_A+ λ_B+ λ_C show a relatively strong temperature dependance, which cannot be explained by present theories.     

The electrical activation of implanted arsenic in silicon

The activation energy for the annealing of arsenic implanted layers in silicon was studied by isothermal and isochronal annealing experiments. Different mechanisms are responsible for the annealing behavior. At low doses and at temperatures below 700°C a doubly charged complex is formed with an activation energy of 0.86 eV which dissociates at higher temperatures with an activation energy of 3.58 eV. At high doses which result in the formation of an amorphous layer a single activation energy of 2.75 eV is measured.     

Electrical and backscattering measurements of arsenic implanted silicon

Measurements of doping concentration and mobility of arsenic implanted silicon at high energies and at low energies with following drive-in diffusion are presented. The electrical measurements are compared with and supported by backscattering measurements. Tails which are present after short time anneals vanish during drive-in diffusion. A temperature of at least 825°C is required to fully activate the arsenic and to obtain the same mobility as in diffused samples. Backscattering data reveal an anomaly in the annealing behavior of the damage. After prolonged annealing As shows some accumulation at the surface. For drive-in diffusions lattice location experiments were performed.     

Photo- and electroluminescence of nitrogen isoelectronic traps in GaAs1–xPx

The variation with temperature of the charge on the surface of NaCl single crystals has been measured directly by means of vibrating capacitor probe. The charge is negative at room temperature, in agreement with theory based on values of the free energy of vacancy formation, decreases with increase of temperature in two stages to a zero value at the isoelectric temperature, and then becomes positive. Values of isoelectric temperature obtained on surfaces are consistent with those obtained by experiments on charged dislocations, which suggests that surfaces could be used to obtain accurate values of the free energy of formation of cation and anion vacancies.     

Protonation‐Driven Membrane Insertion of a pH‐Low Insertion Peptide

The pH‐low insertion peptide (pHLIP) inserts into membranes and forms a transmembrane (TM) α‐helix in response to slight acidity, and has shown great potential for cancer diagnosis and treatment. As a lead, pHLIP is challenging to optimize because the mechanism of its pH‐dependent membrane interactions is not completely understood. Within pHLIP there are multiple D/E residues which could sense the pH change, the particular role played by each of them in the protonation‐driven insertion process is not clear. The precise location of the TM helix within the pHLIP sequence is also unknown. In this work, solid‐state NMR spectroscopy is used to address these central questions. Tracing backbone conformations revealed that the TM helix spans from A10 to D33 with a break at T19 to P20. Residue‐specific pK_a values of D31, D33, D25, and D14 were determined to be 6.5, 6.3, 6.1, and 5.8, respectively, and define the sequence of protonations which lead to insertion. Furthermore, possible intermediate states which disrupt membranes at pH 6.4 were proposed based on tryptophan fluorescence quenching and NMR data.     

Circular dichroism analysis of penicillin G acylase covalently immobilized on silica nanoparticles

Circular dichroism (CD) was used to characterize the secondary structure of penicillin G acylase upon covalent immobilization on silica nanoparticles. Covalent immobilization was achieved by functionalizing the silica nanoparticles with glutardialdehyde and coupling to the free NH(2) groups of the enzyme (lysine and arginine side chains). The loading of the covalently bound enzyme was increased up to saturation, which was reached at 54.6 mg immobilized enzyme per g silica nanobeads. For structural characterization of the commercially available enzyme its exact molecular mass was determined by mass spectrometry in order to enable precise evaluation of the CD data. The fraction of secondary structure elements of the free and immobilized enzyme were estimated from the respective CD spectra using standard algorithms (CONTINLL, CDSSTR, SELCON3). The fractions obtained by the different algorithms for the free enzyme agreed well with one another and also with data from X-ray diffraction described in the literature. Interestingly, the secondary structure fractions found for the immobilized enzyme were very similar to the free enzyme and nearly constant over all experiments. These results indicate that even a loading of up to 55.8 mg/g (enzyme per silica nanoparticles) causes only slight structural changes. However, the specific activity determined by a kinetic assay decreased by around 60%, when increasing the loading from 14.9 to 55.8 mg/g. Because of the fact that we found no major changes in the secondary structure, diffusion limitation seems to be the main reason for the decline of the specific activity.