Pressure-Induced Polymerization of Acetylene: Structure-Directed Stereoselectivity and a Possible Route to Graphane

Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis-isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect reaction route has been proposed for this pressure-induced polymerization. Using in situ neutron diffraction and meta-dynamic simulation, we discovered that under high pressure, acetylene molecules react along a specific crystallographic direction that is perpendicular to those previously proposed. Following this route produces a pure cis-isomer and more surprisingly, predicts that graphane is the final product. Experimentally, polycyclic polymers with a layered structure were identified in the recovered product by solid-state nuclear magnetic resonance and neutron pair distribution functions, which indicates the possibility of synthesizing graphane under high pressure.     

Laser-scanning confocal imaging of calcium in spontaneously contracting cardiac cells: nuclear-cytosolic Ca differences

Laser scanning confocal microscopy (LSCM) of Ca²⁺ -sensitive fluorophores was used to investigate Ca²⁺ oscillations in the nuclear environment of spontaneously contracting, isolated, rat cardiac myocytes. LSCM allowed for clear separation of the intranuclear and cytosolic Ca²⁺ changes that resulted from the sponteneous local elevations of Ca²⁺ that propagated in these cells. While we were not able to resolve any clear differences in the timecourse of the elevation of Ca²⁺ in some of these cells, the rate of sequestration of nuclear Ca²⁺ could be seen to clearly lag behind that of the neighboring cytosol. This resulted in distinct images of cells transiently showing significantly higher nuclear than cytosolic Ca²⁺ levels. The enhanced spatial resolution and rejection of out-of-focus information of confocal microscopy, are important features of this technique, that will allow for the detailed analysis of the spatial and temporal second messenger responses of living cells and tissues.     

Synthesis and Structure of the Layered Thorium Telluride CsTh(2)Te(6)

The compound CsTh(2)Te(6) has been synthesized at 800 degrees C by the reaction of Th with a Cs(2)Te(3)/Te melt as a reactive flux. The compound crystallizes in the space group -Cmcm of the orthorhombic system with two formula units in a cell of dimensions a = 4.367(2) ?, b = 25.119(10) ?, c = 6.140(3) ?, and V = 673.5(5) ?(3) at T = 113 K. The structure of CsTh(2)Te(6) has been determined from single-crystal X-ray data. The structure comprises infinite, two-dimensional double layers of ThTe(8)-bicapped trigonal prisms. The structural motif of the trigonal prisms resembles that found in UTe(2). Cs(+) cations, disordered equally over two crystallographically equivalent sites, separate the layers and are coordinated by eight Te atoms at the corners of a rectangular parallelepiped. Short Te-Te distances of 3.052(3) and 3.088(3) ? form linear, infinite, one-dimensional chains within the layers. Simple formalisms describe neither the Te-Te bonding in the chain nor the oxidation state of Th. The compound shows weak semiconducting behavior along the Th/Te layers perpendicular to the Te-Te chain.