Angle resolved ion scattering spectroscopy reveals the local topography around atoms in a liquid surface

Neutral impact collision ion scattering spectroscopy under normal incidence is known to yield the concentration depth profiles of all elements except hydrogen at the surface of liquids and other amorphous material. In the evaluation of the data one tactically has to assume that the top surface layer and the adjacent layers are laterally homogeneous. In the present paper we establish that the angular resolved mode of this spectroscopy is able to test with high accuracy whether the lateral homogeneity is valid and-if this is not the case-in which way the top layer is structured. In particular, it is possible to map out the local environment of selected atoms. We expect that this so far inaccessible information on the local topography at liquid surfaces will have an impact on the understanding of reactions at the gas/liquid interface.     

Short-range order in metallic Co−Zr glasses

For melt-spun metallic Co_xZr_100–x glasses (22x53) the total pair correlation functionG(r) has been derived from X-ray diffraction measurements. In most samples, the first maximum ofG(r) can be resolved into two single maxima belonging to the Co–Zr and Zr–Zr nearest-neighbor distance, respectively. Partial correlation numbers are estimated in the whole concentration range. The density of the samples has been measured with a buoyancy method. It is compared to those of otherM–Zr glasses (M=Fe, Ni, Cu) and to predictions deduced from Miedema's model of alloy formation.     

Evaluation of the solid state dipole moment and pyroelectric coefficient of phosphangulene by multipolar modeling of X-ray structure factors

The electron density distribution of the molecular pyroelectric material phosphangulene has been studied by multipolar modeling of X-ray diffraction data. The "in-crystal" molecular dipole moment has been evaluated to 4.7 D corresponding to a 42% dipole moment enhancement compared with the dipole moment measured in a chloroform solution. It is substantiated that the estimated standard deviation of the dipole moment is about 0.8 D. The standard uncertainty (s.u.) of the derived dipole moment has been derived by splitting the dataset into three independent data-sets. A novel method for obtaining pyroelectric coefficients has been introduced by combining the derived dipole moment with temperature-dependent measurements of the unit cell volume. The derived pyroelectric coefficient of 3.8(7) x 10-6 Cm 2K-1 is in very good agreement with the measured pyroelectric coefficient of p = 3 +/- 1 x 10-6 Cm-2 K-1. This method for obtaining the pyroelectric coefficient uses information from the X-ray diffraction experiment alone and can be applied to much smaller crystals than traditional methods.     

Ag6B10S18: Ein neues Thioborat mit tetraedrischer Koordination des Bors

Ag₆B₁₀S₁₈: A Novel Thioborate with Tetrahedral Coordination of Boron Ag₆B₁₀S₁₈ was prepared as a novel thioborate from the reaction of stoichiometric amounts of Ag₂S, B, and S at 700°C with successive annealing at 580–460°C. The orange-yellow compound crystallizes in the monoclinic space group C2/c with a = 21.663(8), b = 21.639(8), c = 16.572(5) Å, ß = 129.40(4)°, Z = 8, d_x = 2.948 g · cm^?3. According to the complete X-ray crystal structure analysis the anionic part of the Ag₆B₁₀S₁₈ structure contains B₁₀S₂₀ “supertetrahedra” consisting of ten parallel corner-sharing BS₄ tetrahedra; the B₁₀S₂₀ groups are linked through corners to form a layer-like arrangement of (B₁₀S₁₆S_4/2^6?)_n = (B₁₀S₁₈^6?)_n polyantions. The mean B? S bond length is 1.915 Å. The electron densities in the regions of the Ag⁺ ions show a dynamically disordered arrangement which can be described by a distribution of the 6 Ag⁺ ions of the asymmetric unit over 18 partially occupied sites, these structural characteristics making Ag₆B₁₀S₁₈ an Ag⁺ ionic conductor. The i.r. spectrum of the compound shows B? S stretching vibrations at 610, 640, 685, 735, and 760 cm^?1.     

Die Kristallstrukturen von Pb4SeBr6, Pb5S2J6 und Pb7S2Br10

Crystal Structures of Pb₄SeBr₆, Pb₅S₂I₆, and Pb₇S₂Br₁₀. The crystal structures of Pb₄SeBr₆, Pb₅S₂I₆ and Pb₇S₂Br₁₀ have been determined from single crystal X-ray analyses. Unit cell data see “Inhaltsübersicht”. The compounds have common structural features with the pure halides of lead. In Pb₄SeBr₆ all Pb atoms have trigonal prismatic coordination by Br(Se), additional neighbours above the prism faces completing the coordination number to 7, 8 or 9. In Pb₅S₂I₆ some of the Pb atoms are surrounded by 6 I + 1 S or 5 I + 3 S in the same extended trigonal prismatic arrangement, others are in the centers of PbI₆ octahedra. Pb₇S₂Br₁₀ is isostructural with Th₇S₁₂ with statistical occupancy of part of the metal and nonmetal positions.     

Preparation of highly efficient manganese catalase mimics

The series of compounds [Mn(bpia)(mu-OAc)](2)(ClO(4))(2) (1), [Mn(2)(bpia)(2)(muO)(mu-OAc)](ClO(4))(3).CH(3)CN (2), [Mn(bpia)(mu-O)](2)(ClO(4))(2)(PF(6)).2CH(3)CN (3), [Mn(bpia)(Cl)(2)](ClO)(4) (4), and [(Mn(bpia)(Cl))(2)(mu-O)](ClO(4))(2).2CH(3)CN (5) (bpia = bis(picolyl)(N-methylimidazol-2-yl)amine) represents a structural, spectroscopic, and functional model system for manganese catalases. Compounds 3 and 5 have been synthesized from 2 via bulk electrolysis and ligand exchange, respectively. All complexes have been structurally characterized by X-ray crystallography and by UV-vis and EPR spectroscopies. The different bridging ligands including the rare mono-mu-oxo and mono-mu-oxo-mono-mu-carboxylato motifs lead to a variation of the Mn-Mn separation across the four binuclear compounds of 1.50 A (Mn(2)(II,II) = 4.128 A, Mn(2)(III,III) = 3.5326 and 3.2533 A, Mn(2)(III,IV) = 2.624 A). Complexes 1, 2, and 3 are mimics for the Mn(2)(II,II), the Mn(2)(III,III), and the Mn(2)(III,IV) oxidation states of the native enzyme. UV-vis spectra of these compounds show similarities to those of the corresponding oxidation states of manganese catalase from Thermus thermophilus and Lactobacillus plantarum. Compound 2 exhibits a rare example of a Jahn-Teller compression. While complexes 1 and 3 are efficient catalysts for the disproportionation of hydrogen peroxide and contain an N(4)O(2) donor set, 4 and 5 show no catalase activity. These complexes have an N(4)Cl(2) and N(4)OCl donor set, respectively, and serve as mimics for halide inhibited manganese catalases. Cyclovoltammetric data show that the substitution of oxygen donor atoms with chloride causes a shift of redox potentials to more positive values. To our knowledge, complex 1 is the most efficient binuclear functional manganese catalase mimic exhibiting saturation kinetics to date.     

The Regulation of the Calcium Signal by Membrane Pumps

Calcium may have a static, structure‐stabilizing role in biological organs like the bones and the teeth, or may fulfill a dynamic function in cells as a regulator of signal‐transduction pathways. This is made possible by the properties of the Ca²⁺ ion (e.g., high dehydration rate, great flexibility in coordinating ligands, largely irregular geometry of the coordination sphere). Since Ca²⁺ is a universal carrier of signals, the control of its homeostasis is of central importance for the organism. It involves exchanges between the skeleton (which is the major calcium reservoir) and the extracellular and intracellular fluids. It also involves the intestine and the kidney, the organs of Ca absorption and release, respectively. The highly integrated homeostasis process consists of a number of hormonally controlled feedback loops, and an elaborate system of membrane channels, exchangers, and pumps that control the Ca²⁺ flux into and out of cells.