Asymmetric organocatalytic conjugate addition of malonates to enones using a proline tetrazole catalyst

5-Pyrrolidin-2-yltetrazole performs as a useful organocatalyst for the asymmetric addition of malonates to a range of enones, with good to excellent enantioselectivities.     

Target structure induced suppression of the ionization cross section for very low energy antiproton-hydrogen collisions

Low energy antiprotons have been used previously to give benchmark data for theories of atomic collisions. Here we present measurements of the cross section for single, nondissociative ionization of molecular hydrogen for impact of antiprotons with kinetic energies in the range 2-11 keV, i.e., in the velocity interval of 0.3-0.65 a.u. We find a cross section which is proportional to the projectile velocity, which is quite unlike the behavior of corresponding atomic cross sections, and which has never previously been observed experimentally.     

Events Maps in a Stick-Slip System

This paper describes a one-dimensional map generated by a two degree-of-freedom mechanical system that undergoes self-sustained oscillations induced by dry friction. The iterated map allows a much simpler representation and a better understanding of some dynamic features of the system. Some applications of the map are illustrated and its behaviour is simulated by means of an analytically defined one-dimensional map. A method of reconstructing one-dimensional maps from experimental data from the system is introduced. The method uses cubic splines to approximate the iterated mappings. From a sequence of such time series the parameter dependent bifurcation behaviour is analysed by interpolating between the defined mappings. Similarities and differences between the bifurcation behaviour of the exact iterated mapping and the reconstructed mapping are discussed.     

CO-induced embedding of Pt adatoms in a partially reduced FeO(x) film on Pt(111)

The reduction of a single-layer FeO film grown on Pt(111) by CO at elevated pressures and temperatures has been studied through an interplay of scanning tunneling microscopy, ambient-pressure X-ray photoelectron spectroscopy, and density functional theory calculations. Exposure of the FeO thin film to CO at pressures between 1 and 30 Torr and temperatures between 500 and 530 K leads to formation of a honeycomb-structured Fe(3)O(2) film with hollow sites occupied by single Pt atoms extracted from the substrate surface. The formation of these adatoms is driven by an increase in CO adsorption energy. In addition, the structure incorporates undercoordinated Fe centers, which are proposed to have substantial effects on the catalytic properties of the surface.     

Adsorption of L-cysteine on rutile TiO2(110)

We have used X-ray photoelectron spectroscopy to study the adsorption of L-cysteine on a rutile TiO₂(110) surface at room temperature and ? 65 °C. For the molecules in direct contact with the surface our results suggest that the molecules bind dissociatively to the fivefold-coordinated Ti atoms of the surface through their deprotonated carboxylic groups. A second, dissociative interaction occurs between the molecular thiol groups and the surface. It is attributed to a dissociative bond to the bridging oxygen vacancies. Most likely, the thiol groups are deprotonated and a bond is formed between the thiolates and defects. In an alternative scenario, the C–S bond is cleaved and atomic sulfur binds to the defects. With regard to the molecular amino groups, they remain neutral at the lowest investigated coverages (0.3–0.5 ML), but already starting from around 0.7 ML nominal coverage protons are being transferred to them. The fraction of protonated amino groups increases with coverage and becomes dominating in multilayers prepared at room temperature and ? 65 °C. In these multilayers the carboxylic groups are deprotonated.     

Modification of the size of supported clusters by coadsorption of an organic compound: gold and L-cysteine on rutile TiO2(110)

Using X-ray photoelectron spectroscopy we studied the coadsorption of the amino acid L-cysteine and gold on a rutile TiO(2)(110) surface under ultrahigh vacuum conditions. Irrespective of the deposition order, i.e., irrespective of whether L-cysteine or gold is deposited first, the primary interaction between L-cysteine and the gold clusters formed at the surface takes place through the deprotonated thiol group of the molecule. The deposition order, however, has a profound influence on the size of the gold clusters as well as their location on the surface. If L-cysteine is deposited first the clusters are smaller by a factor two to three compared to gold deposited onto the pristine TiO(2)(110) surface and then covered by L-cysteine. Further, in the former case the clusters cover the molecules and thus form the outermost layer of the sample. We also find that above a minimum gold cluster size the gold cluster/L-cysteine bond is stronger than the L-cysteine/surface bridging oxygen vacancy bond, which, in turn, is stronger than the gold cluster/vacancy bond.     

Growth of thin films of TiN on MgO(100) monitored by high-pressure RHEED

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the initial growth of titanium nitride (TiN) thin films on single-crystal (100) MgO substrates by pulsed laser deposition (PLD). This is the first RHEED study where the growth of TiN films is produced by PLD directly from a TiN target. At the initial stage of the growth (average thickness ∼2.4 nm) the formation of islands is observed. During the continuous growth the islands merge into a smooth surface as indicated by the RHEED, atomic force microscopy and field emission scanning electron microscopy. These observations are in good agreement with the three-dimensional Volmer–Weber growth type, by which three-dimensional crystallites are formed and later cause a continuous surface roughening. This leads to an exponential decrease in the intensity of the specular spot in the RHEED pattern as well.     

Comment on "silent research vessels are not quiet" [J. Acoust. Soc. Am. 121, EL145-EL150

The recent paper by Ona et al. [J. Acoust. Soc. Am. 121, EL145-EL150] compared avoidance reactions by herring (Clupea harengus) to a traditional and a "silent" research vessel. Surprisingly, the latter evoked the strongest avoidance, leading to the conclusion that "candidate stimuli for vessel avoidance remain obscure." In this Comment, it is emphasized that the otolith organs in fish are linear acceleration detectors with extreme sensitivity to infrasonic particle acceleration. Near-field particle motions generated by a moving hull are mainly in the infrasonic range, and infrasound is particularly potent in evoking directional avoidance responses in several species of fish. The stimuli initiating vessel avoidance may thus include infrasonic particle acceleration.     

Mössbauer spectroscopic studies of [Fe(H2O)6]3+ in amorphous frozen solutions at weak applied magnetic fields

The ferric hexaquo complex, [Fe(H₂O)₆]³⁺, has been studied by Mössbauer spectroscopy of amorphous aqueous frozen solutions at weak applied magnetic fields. Spectra of well resolved paramagnetic hyperfine structure have been interpreted in terms of a spin Hamiltonian model for the crystal field interaction proposed in a previous work. Reasonable fits could be obtained only by the addition of a random magnetic field of a few Gauss which is attributed partly to the dipolar interaction with neighbouring iron ions, and partly to the ligand hyperfine interaction.