Stereoselective Ring Opening of Electronically Excited Cyclohexa-2, 4-dienones: Cause and effect

The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction).     

Three-dimensional visualization of protein expression in mouse brain structures using imaging mass spectrometry

We have developed a method to visualize matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI IMS) data aligned with optically determinable tissue structures in three dimensions. Details of the methodology are exemplified using the 3-D reconstruction of myelin basic protein (MBP) in the corpus callosum of a mouse brain. In this procedure, optical images obtained from serial coronal sections are first aligned to each other to reconstruct a surface of the corpus callosum from segmented contours of the aligned images. The MALDI IMS data are then coregistered to the optical images and superimposed into the surface to create the final 3-D visualization. Correlating proteomic data with anatomical structures provides a more comprehensive understanding of healthy and pathological brain functions, and holds promise to be utilized in more complex anatomical arrangements.     

Lattice defects and its influence on hyperfine interactions on EuS evaporated thin films

In a study of the Mössbauer effect on¹⁵¹Eu in bulk EuS and evaporated thin films the influence of lattice defects on the hyperfine interactions has been investigated by variation of the substrate temperature during evaporation. The changes in the hyperfine and the lattice parameters with lattice defects are similar to the changes in those parameters observed in substances exhibiting an increasing portion of covalency.     

The density and pressure of helium in bubbles in metals

Abstract

The energy shift of the He 1¹S₀?2¹P₁ transition, ΔE(n), can be used to determine the density, n, of He in bubbles in metals. A self-consistent band structure calculation for solid fcc He yields a linear relationship ΔE=C.n with C _th=22 × 10^?3 eV nm³. Systematic electron energy loss spectroscopy and transmission electron microscopy studies of He bubbles in Al for various He doses and temperatures result in C_exp=(24±8).10^?3 eV nm³ in agreement with theory. The analysis is consistent with the assumption that dislocation loop punching is the dominant bubble growth mechanism during high-dose room temperature implantation. The application to He bubbles in Ni indicates a maximum He density of n=0.2 × 10³ nm^?3 for which He should be solid at room temperature.     

Mechanism of copper underpotential deposition at Pt(<Emphasis Type="Italic">hkl</Emphasis>)-electrodes: Quantum-chemical modelling

Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)- or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption.