First-principles study of the water structure on flat and stepped gold surfaces

The geometric structure and electronic properties of flat and stepped gold–water interfaces have been addressed by periodic density functional theory (DFT) calculations. This work was motivated by a recent electron energy loss spectroscopy study [H. Ibach, Surf. Sci. 604 (2010) 377] indicating that the structure of a water layer on stepped Au(511) differs significantly from the one on Au(100). Based on ab initio molecular dynamics simulations, the measured spectra have been reproduced and linked to the geometric arrangement of the water molecules. Furthermore, we find a strong polarization of the water layers which contributes to the water-induced work function change of the substrate.     

Thermoelectric power of CuCrxVySe4 p-type spinel semiconductors

Structural, electrical and magnetic measurements of polycrystalline CuCr_xV_ySe₄ spinels with x=1.79, 1.64 and 1.49 and y=0.08, 0.22 and 0.45, respectively, are presented. The compounds under study crystallize in regular system of a normal spinel type MgAl₂O₄ structure with the space group symmetry Fd3m. The chromium spins are coupled ferromagnetically and show both strong long- and short-range magnetic interactions evidenced by the large values of the Curie (T_C) and Curie–Weiss (θ_CW) temperatures, decreasing from T_C=407 K and θ_CW=415 K for y=0.08, via T_C=349 K and θ_CW=367 K for y=0.22 to T_C=283 K and θ_CW=293 K for y=0.45, respectively. In all the studied spinels a change of the electrical conductivity character from the semiconductive into the metallic one above 230 K was observed. A detailed thermoelectric power analysis showed a domination of diffusion thermopower component, maximum of phonon drag component at 230 K, a decrease of impurity component with increasing V content, as well as the weak magnon excitations at 40 K.     

Copper(I) Photocatalyzed Bromonitroalkylation of Olefins: Evidence for Highly Efficient Inner-Sphere Pathways

We report the visible light-mediated copper-catalyzed vicinal difunctionalization of olefins utilizing bromonitroalkanes as ATRA reagents. This protocol is characterized by high yields and fast reaction times under environmentally benign reaction conditions with exceptional scope, allowing the rapid functionalization of both activated and unactivated olefins. Moreover, late-stage functionnalization of biologically active molecules and upscaling to gram quantities is demonstrated, which offers manifold possibilities for further transformations, e.g. access to nitro- and aminocyclopropanes. Besides the synthetic utility of the title transformation, this study undergirds the exclusive role of copper in photoredox catalysis showing its ability to stabilize and interact with radical intermediates in its coordination sphere. EPR studies suggest that such interactions can even outperform a highly favorable cyclization of transient to persistent radicals contrasting iridium-based photocatalysts.