Generator‐collector Voltammetry at Dual‐plate Gold‐gold Microtrench Electrodes as Diagnostic Tool in Ionic Liquids

Ionic liquids provide high viscosity solvent environments with interesting voltammetric characteristics and new electrochemical mechanisms. Here, a gold‐gold dual‐plate microtrench electrode is employed in generator‐collector mode to enhance viscosity‐limited currents in ionic liquids due to fast feedback within small inter‐electrode gaps (5 μm inter‐electrode gap, 27 μm microtrench depth) and to provide a mechanistic diagnosis tool. Three redox systems in the ionic liquid BMIm⁺BF₄^? are investigated: (i) ferrocene oxidation, (ii) oxygen reduction, and (iii) 2‐phenyl‐naphthyl‐1,4‐dione reduction. Both transient and steady state voltammetric responses are compared. Asymmetric diffusion processes, reaction intermediates, and solubility changes in the ionic liquid are revealed.     

De–excitation of compound nuclei with A around 56: reduction of the emission barriers for protons and alpha particles

This paper contributes to the discussion on the phenomena of the enhanced emission of low–energetic charged particles during compound nuclei decay. The decay of compound nuclei ⁵²Fe, ⁵⁶Ni, and ⁵⁹Cu was studied. Energy spectra and emission angles of evaporated charged particles were measured in coincidence with gamma rays to determine the corresponding evaporation residue nucleus. Additionally, evaporation residue distributions were determined with the Munich rf recoil spectrometer. In this way, detailed channel–specific evaporation data were obtained for theoretical analysis. We extracted evaporation barriers and compared them with corresponding fusion barriers. The main result was revealed to be a lowering of the evaporation barrier for protons and alpha particles relative to the fusion barriers. But the observed effect is not as intensive as reported in recent studies. Received: 15 June 1998 / Revised version: 5 November 1998     

TDPAC studies on the sorption of Hf(IV) onto a silica surface

¹⁸¹Hf-PAC investigations were undertaken as a contribution to the understanding of the aquatic chemistry of the tetravalent elements. In solution, the growth of polymeric species with increasing pH was observed by PAC. For the sorption of Hf on silica surfaces we found a strong dependence of the PAC results on the pH value. The corresponding sites were assigned to surface complexation and surface precipitation, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quadruple Decker [3.3][3.3][3.3]Orthocyclophane Acetal—An Orthocyclophane Ladder

Through clever bridging of orthocyclophanes (in this case by acetalization), molecules such as 1 can be formed with four benzene rings in a stacked face-to-face arrangement. UV/Vis spectroscopic and electrochemical properties of 1 are governed by π–π through-space interactions within the molecule.     

Silica‐Coating of Hematite Nanoparticles Using Reactive Water‐Soluble Polyalkoxysiloxanes

In this article, we report on a new one‐step synthetic route to obtain multi‐functional silica‐coated hematite particles using a water‐based surfactant‐free technology. The synthesis and properties of uniform silica‐coated hematite particles with adjustable size, morphology, and silica shell thickness are discussed in detail. The developed method allows simultaneous formation of the silica shell around hematite core and incorporation of reactive groups on the surface of core–shell nanoparticles. Vinyl groups are introduced to the silica surface at once by pre‐functionalization of a water‐soluble hyperbranched polyalkoxysiloxanes with active double bonds. The reactivity of these surface‐immobilized vinyl groups is demonstrated by covalent attachment of rhodamine B using a thiol‐en click reaction.     

Ruthenium‐Catalyzed Functionalization of Pyrroles and Indoles with Propargyl Alcohols

Several ruthenium‐catalyzed atom‐economic transformations of propargyl alcohols with pyrroles or indoles leading to alkylated, propargylated, or annulated heteroaromatics are reported. The mechanistically distinct reactions are catalyzed by a single ruthenium(0) complex containing a redox‐coupled dienone ligand. The mode of activation regarding the propargyl alcohols determines the reaction pathway and depends on the alcohols’ substitution pattern. Secondary substrates form alkenyl complexes by a 1,2‐hydrogen shift, whereas the transformation of tertiary substrates involves allenylidene intermediates. 1‐Vinyl propargyl alcohols are converted by a cascade allylation/cyclization sequence. The environmentally benign processes are of broad scope and allow the selective synthesis of highly functionalized pyrroles and indoles generating water as the only waste product.     

Chern-Simons expectation values and quantum horizons from loop quantum gravity and the Duflo map

We report on a new approach to the calculation of Chern-Simons theory expectation values, using the mathematical underpinnings of loop quantum gravity, as well as the Duflo map, a quantization map for functions on Lie algebras. These new developments can be used in the quantum theory for certain types of black hole horizons, and they may offer new insights for loop quantum gravity, Chern-Simons theory and the theory of quantum groups.     

Model dependence of the impulse approximation

We investigate the model dependence of the impulse approximation for proton-nucleus elastic scattering stemming from off-shell and non-local effects. A perturbative treatment allows a direct comparison between off-shell and relativistic effects. Off-shell effects are found to be significantly smaller and unable to account in a natural way for the needed repulsive central potential in the nuclear interior region at proton energies between 300 and 800 MeV.     

Temperature dependence of the electric field gradient in HfF4.HF.2H2O

The hyperfine quadrupole interaction in HfF₄.HF.2H₂O was studied using the time differential perturbed angular correlation (TDPAC) technique. The electric field gradient (EFG) and the corresponding asymmetry parameter were measured in the temperature range from 9 to 350 K. The EFG is characterized by a rather strong increase with temperature, whereas the asymmetry parameter reaches its maximum value (η≈1) at aboutT=160 K. At 420 K, the complex is dehydrated and looses HF: The quadrupole parameters determined from subsequent TDPAC measurements are charateristic for HfF₄.