K

Tetrahedral framework structures with topologies that show close relationships to the feldspar group or to gismondine are formed by the zincoborophosphates A[ZnBP(2)O(8)] (see picture). The compounds are readily accessible under mild hydrothermal conditions (T(max)=170 degrees C) and are thermally remarkably stable (for example, 940 degrees C for A=Cs). Metalloborophosphates are a new class of compounds, which are expected to provide access to zeolite-like microporous systems.     

Structural determinations of single-crystal K β-alumina and cobalt-doped K β-alumina

Single-crystal structural refinements of K β-alumina and Co²⁺-doped K β-alumina show that the distribution of potassium ions in the diffusing planes is very similar to that in the isomorphous compound Na β-alumina but quite different from Ag β-alumina. The Co²⁺ ions selectively fill the underbonded, tetrahedrally coordinated, Al(2) sites in the middle of the spinel block portion of the structure. This tends to support the aluminum vacancy mechanism of charge compensation. The positional parameters of the spinel block are well-determined and appear insensitive to the diffusing plane ions and arrangement.     

K and mixed K+O adlayers on Rh(110)

The evolution of the structure of the adlayers and the substrate during adsorption of K and coadsorption of K and O on Rh(110) is studied by scanning tunneling microscopy and low-energy electron diffraction. The K adsorption at temperature above 450 K leads to consecutive (1x4), (1x3), and (1x2) missing-row reconstructions for coverage up to 0.12 ML, which revert back to (1x3) and (1x4) with increasing coverage up to 0.21 ML. The coadsorption of different oxygen amount at T>450 K and eventually following reduction-reoxidation cycles led to a wealth of coadsorbate structures, all involving substrate missing-row-type reconstructions, some including segmentation of Rh rows along the [110] direction. The presence of K stabilizes the (1x2) missing-row reconstruction, which facilitates the formation of a great variety of very open (10x2)-type reconstructions at high oxygen coverage, not observed in the single adsorbate systems.     

Crystallographic analysis of thermochromic,unsolvated tetramesityldisilene at 173 K and 295 K

X-ray crystal structure determinations of tetramesityldisilene ( 1 ) at 295 K, where it is bright orange, and at 173 K, where it is pale yellow, were experimentally equivalent. The thermochromism of 1 , therefore, is not due to changes in conformation; a vibrational origin is considered. The crystal structure of unsolvated 1 differs substantially from that of the toluene solvate ( 1 ·C₇H₈) because of different crystal packing of the two forms. These two solid-state structures are compared with those of four other disilenes.     

Molar volumes of the KKI and KKCl molten solutions

Molar volumes in molten solutions of KKI at 973 and 1073°K and KKCl at 1073°K in the molar fraction range of 0-0.2, were determined by a gamma ray absorption method. For both systems the excess volumes were equal to zero which is consistent with theoretical considerations by Katz and Rice for alkali metal - molten salt solutions.     

Further evidence for phase transitions in biphenyl near 40 K and 16 K

Phase transitions have been detected in biphenyl at about 42 and 17 K by noting changes in the transmitted light intensity when the crystal is placed at extinction between crossed polaroids and the crystal temperature slowly varied. The phase transition at 42 K is gradual (i.e. it occurs over a range of temperature) while the 17 K transition is abrupt. The effect is observed only for light propagating normal to an a*b section which implies that the atomic displacements at the phase changes are largely restricted to this plane. An analogous behaviour is observed for biphenyl-d₁₀ except that the onset of the gradual transition on cooling is at 38 K and the abrupt transition is at 24 K.     

Radical reactions in malonic acid single crystal between 4 K and 300 K

For three out of the four different radicals which are produced by γ-irradiation in malonic acid single crystals, two stereo-isomers have been observed. The structures and orientations of these radicals were determined. ?H₂COOH proceeds from the cation and is already formed at 4 K; as to H?(COOH)₂, it proceeds from the molecular form of the protonated anion COOHCH₂?(OH)₂.     

Enthalpies de melange du systeme antimoine-tellure a 909,30 K, 911,85 K et 917,95 K

Thermodynamical data on Sb-Te system at 909,30 K, 911,85 K and 917,95 K. The integral molar enthalpies of formation of liquid Sb-Te alloys were measured at three temperatures by drop calorimetry.Partial molar enthalpies of formation of these alloys, referring to the pure liquid constituants, and enthalpie of formation at 298 K of the compound Sb₄₀₅Te₅₉₅ were deduced.

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Zusammenfassung Thermodynamische Daten, des Systemes Sb-Te bei 909,30, 911,85 und 917,95 K. Mittels Drop-Kalorimetrie wurden die integralen molaren Bildungsenthalpien von flüssigen Sb-Te Legierungen bei drei verschiedenen Temperaturen gemessen. Die partiellen molaren Bildungsenthalpien dieser Legierungen, bezogen auf die reinen flüssigen Komponenten sowie die Bildungsenthalpie der Verbindung Sb_0.405Te_0.595 bei 298 K wurden abgeleitet.

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Sb-Te 909,30; 911,85 917,95 . , Sb_0.4050.595 298 .

     

Study of Molecular Interactions in Binary Mixtures of Aniline with Carboxylic Acids at 293.15 K, 303.15 K and 313.15 K

Ultrasonic velocity, density, refractive index and viscosity of binary mixtures of aniline with acetic acid (AA) and propionic acid (PA) have been measured at 293.15, 303.15 and 313.15 K over the entire composition range. Further, the specific heat ratio, heat capacity, effective Debye temperature and pseudo-Gruensisen parameter and non-linearity parameter have been evaluated using ultrasonic absorption data. The deviation in isentropic compressibility, excess molar volume, excess intermolecular free length, deviation in molar refraction, deviation in viscosity, relaxation time, enthalpy, entropy and Gibbs energy of activation have been calculated from the experimental data and fitted with the Redlich-Kister polynomial equation. A comparative study has also been made between experimental and theoretically calculated values of densities using the HBT and Rackett density models. Mixing rules for the prediction of refractive index, e.g. Lorentz-Lorenz (L-L), Eykmen (Eyk), Weiner (W), Heller (H), Gladstone-Dale (G-D), Arago-Biot (A-B) and Newton (N) have been applied to these binary mixtures.     

Separation of capsular polysaccharide K4 and defructosylated K4 by high-performance capillary electrophoresis

A rapid, highly sensitive and reproducible high-performance capillary electrophoresis (HPCE) method (electrokinetic chromatography with sodium dodecyl sulfate) is described for the determination of the polysaccharide from the uropathogenic Escherichia coli K4 bacteria (05:K4:H4) and its defructosylated product. The two polyanions, K4 and defructosylated K4, are separated and readily determined within 30 min on an uncoated fused-silica capillary using normal polarity at 20 kV and detection at 200 nm. A linear relationship was found for the two polysaccharides over a wide range of concentrations, from approximately 30 ng (0.5 microg/microL) to 210 ng (3.5 microg/microL). The described method was used to evaluate the defructosylation process of K4 under drastic acid conditions.     

The crystal structure of 1-p-bromophenylsilatrane at 293 K and 133 K

The crystal structure of 1-p-bromophenylsilatrane was determined at ambient and low temperature. The methylene groups of the silatrane skeleton in the β-position to the nitrogen atom are disordered in the ambient temperature structure. The disorder disappears at 133 K. The Si ← N dative bond length is nearly identical at both temperatures (2.139(3) and 2.132(2) Å). The deviation of the atoms in the silatrane moiety from the ideal three-fold symmetry seems to point to the most dynamically behaving parts of the molecule.     

Gas chromatography and mass spectrometry investigations of phytylubiquinone Vitamin K1, and Vitamin K2

The trimethylsilyl ethers of reduced vitamins K₁, K₂, and of phytylubiquinone were investigated by means of gas chromatography and mass spectrometry.     

Microcalorimetric Investigations of K+- and Mg2+-Induced Polymerization of Actin at Temperatures from 293.15 K to 310.15 K

Microcalorimetric measurements of the polymerization of actin in the presence of 100 mM KCl and 2 mM MgCl₂were carried out with a Calvet MS-80 microcalorimeter at temperatures from 293.15 to 310.15 K. It was observed that the polymerization of actin was endothermic and the enthalpy change for actin polymerization was temperature-dependent. The enthalpy change ΔH^owas fitted to ΔH^o(kJ mol^-1)=434.0-1.16 (T/K) and the change in heat capacity ΔC_p ^ocalculated from ΔH^owas -1.16 kJ (mol K)^-1in the above range of temperatures. The direct calorimetry results showed that the enthalpy and entropy change for actin polymerization could not be obtained from measurements of the critical concentration and the only way to assess the enthalpy change for the polymerization of actin and similar reactions lies in the use of calorimetry. This revised version was published online in July 2006 with corrections to the Cover Date.