Structures of Neutral Au7, Au19, and Au20 Clusters in the Gas Phase
Philipp Gruene, David M. Rayner, Britta Redlich, Alexander F. G. van der Meer, Jonathan T. Lyon, Gerard Meijer, André Fielicke
"The unique catalytic properties of gold nanoparticles are determined by their electronic and geometric structures. Here the geometries of several small
neutral gold clusters in the gas phase are revealed by means of vibrational spectroscopy between 47 and 220 wavenumbers. A two-dimensional structure for neutral Au7 and a pyramidal structure for neutral Au20 can be unambiguously assigned. The lowering of the symmetry when a corner-atom is cut from the tetrahedral Au20 cluster is directly reflected in the vibrational spectrum of Au19. [...]"
Red-shifted optogenetic excitation: a tool for fast neural control derived from Volvox carteri
Feng Zhang, Matthias Prigge, Florent Beyrière, Satoshi P Tsunoda, Joanna Mattis, Ofer Yizhar, Peter Hegemann & Karl Deisseroth
Nat. Neurosci 2008, 11, 631;
The introduction of two microbial opsin–based tools, channelrhodopsin-2 (ChR2) and halorhodopsin (NpHR), to neuroscience has generated interest in fast, multimodal, cell type–specific neural circuit control. Here we describe a cation-conducting channelrhodopsin (VChR1) from Volvox carteri that can drive spiking at 589 nm, with excitation maximum red-shifted 70 nm compared with ChR2.
These results demonstrate fast photostimulation with yellow light, thereby defining a functionally distinct third category of microbial rhodopsin proteins.
Photosynthetic water oxidation at elevated dioxygen partial pressure monitored by time-resolved X-ray absorption measurements
Michael Haumann, Alexander Grundmeier, Ivelina Zaharieva, and Holger Dau
PNAS 2008, 105, 17384;
The atmospheric dioxygen (O2) is produced at a tetramanganese complex bound to the proteins of photosystem II (PSII). To investigate product inhibition at elevated oxygen partial pressure (pO2 ranging from 0.2 to 16 bar), we monitored specifically the redox reactions of the Mn complex in its catalytic S-state cycle by rapid-scan and time-resolved X-ray absorption near-edge spectroscopy (XANES) at the Mn K-edge.
By using a pressure cell for X-ray measurements after laser-flash excitation of PSII particles, we found a clear pO2 influence on the redox reactions of the Mn complex, with a similar half-effect pressure as determined (2–3 bar). However, XANES spectra and the time courses of the X-ray fluorescence collected with microsecond resolution suggested that the O2 evolution transition itself (S3⇒S0+O2) was not affected. Additional (nonstandard) oxidation of the Mn complex at high pO2 explains our experimental findings more readily. Our results suggest that photosynthesis at ambient conditions is not limited by product inhibition of the O2 formation step.
Activation of Methane by Oligomeric (Al2O3)x+ (x=3,4,5): The Role of Oxygen-Centered Radicals in Thermal Hydrogen-Atom Abstraction
Sandra Feyel, Jens Döbler, Robert Höckendorf, Martin K. Beyer, Joachim Sauer, and Helmut Schwarz
Angew. Chem. Int. Ed. 2008, 47, 1946;
Experimental and theoretical studies show that the cationic polynuclear aluminum oxide clusters, which are oligomeric systems of (Al2O3)x+ (x=3, 4, 5), activate methane at room temperature (see picture). In contrast, clusters with an odd number of aluminum atoms are unreactive.
The Mechanism of Assembly and Cofactor Insertion into Rhodobacter capsulatus Xanthine Dehydrogenase
Silvia Schumann, Miguel Saggu, Nadine Möller, Stefan D. Anker, Friedhelm Lendzian, Peter Hildebrandt, and Silke Leimkühler
J. Biol. Chem., 283, 16602;
Rhodobacter capsulatus xanthine dehydrogenase (XDH) is a molybdo-flavoprotein that is highly homologous to the homodimeric mammalian xanthine oxidoreductase. However, the bacterial enzyme has an (αβ)2 heterotetrameric structure, and the cofactors were identified to be located on two different polypeptides.
We have analyzed the mechanism of cofactor insertion and subunit assembly of R. capsulatus XDH, using engineered subunits with appropriate substitutions in the interfaces.
Counting Electrons Transferred through a Thin Alumina Film into Au Chains
N. Nilius, M.V. Ganduglia-Pirovano, V. Brázdová, M. Kulawik, J. Sauer, and H.-J. Freund
PhysRevLett., 100, 096802(4);
Low-temperature STM measurements combined with density functional theory calculations are employed to study the adsorption of gold on alumina/NiAl(110). The binding of Au monomers involves breaking of an oxide Al-O bond below the adatom and stabilizing the hence undercoordinated O ion by forming a new bond to an Al atom in the NiAl. The adsorption implies negative charging of the adatom.
The linear arrangement of favorable binding sites induces the self-organization of Au atoms into chains. For every ad-chain, the number of transfer electrons from the support is determined by analyzing the node structure of the corresponding highest occupied molecular orbital.
A “Side-on” Superoxonickel Complex [LNi(O2)] with a Square-Planar Tetracoordinate Nickel(II) Center and Its Conversion into [LNi(m-OH)2NiL]
Shenglai Yao, Eckhard Bill, Carsten Milsmann, Karl Wieghardt, and Matthias Driess
Angew. Chem. Int. Ed. 2008, 47, 7110;
Dioxygen activation mediated by transition-metal sites is of importance in numerous stoichiometric and catalytic transformations of organic substrates in biological and industrial processes. Using dioxygen as a primary oxidant (aerobic oxidation) is very attractive because it is cheap and ecologically benign, but it is still difficult to control in a broad range of synthetic systems.
It is of particular interest in synthetic chemistry to develop novel metal–dioxygen compounds that are capable of chemoselective CH bond functionalization without autoxidation and overoxidation of the substrates.
The Effect of Charge on CO Binding in Rhodium Carbonyls: From Bridging to Terminal CO
Ingmar Swart, Frank M. F. de Groot, Bert M. Weckhuysen*, David M. Rayner, Gerard Meijer*, and André Fielicke*
"Changing the electron density of a catalyst can have a profound influence on its selectivity and activity. For this reason, electronic promoter materials are often added to a catalyst to tailor the electron density of the active particle and to obtain optimal performance. Despite the widespread use of electronic promoters, the mechanisms responsible for the observed effect(s) are often poorly understood. For CO oxidation over a Pt catalyst, the activity increases with electron density.
In contrast, the hydrogenation of CO over cobaltand rhodium-based catalysts is found to be more active and more selective upon reducing the electron density of the metal particles. This change in electron density also leads to a decrease in the ratio of bridge to linear-bound CO but the mechanism behind this destabilization of bridge-bound CO is unknown [...]"